Herein, the fabrication of Ir‐CoO/Al2O3 catalysts derived from Ir/CoAl LDH composites is reported for photo‐thermal CO2 methanation, which consist of Ir‐CoO ensembles as active centers that are evenly anchored on amorphous Al2O3 nanosheets. A CH4 production rate of 128.9 mmol gcat⁻1 h⁻1  is achieved at 250 °C under ambient pressure and visible light irradiation, outperforming most reported metal‐based catalysts. Mechanism studies based on density functional theory (DFT) calculations and numerical simulations reveal that the CoO nanoparticles function as photocatalysts to donate electrons for Ir nanoparticles and meanwhile act as “nanoheaters” to effectively elevate the local temperature around Ir active sites, thus promoting the adsorption, activation, and conversion of reactant molecules. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) demonstrates that illumination also efficiently boosts the conversion of formate intermediates. The mechanism of dual functions of photothermal semiconductors as photocatalysts for electron donation and as nano‐heaters for local temperature enhancement provides new insight in the exploration for efficient photo‐thermal catalysts.Photo‐thermal catalytic CO 2O3 catalysts to realize the highly efficient photo‐thermal catalytic CO2 methanation under mild conditions. The CoO nanoparticles function as photocatalysts to donate electrons for Ir nanoparticles and meanwhile act as “nanoheaters” to effectively elevate the local temperature around Ir active sites, thus promoting the adsorption, activation, and conversion of reactant molecules.This work prepares Ir‐CoO/Al Among the reported conversion approaches, reduction of CO2 to CH4 with H2 generated from renewable sources has been intensively explored, as CH4 is a clean fuel with high energy density and can be readily transported via natural gas pipelines. Compared with the solely light‐driven or the conventional thermal catalytic Sabatier reaction approaches, photo‐thermal catalytic processes where external heat and photo energy are coupled, overcome the low activity in sole solar‐driven catalytic processes and the harsh reaction conditions in thermal catalysis, thereby offering new avenues for efficient CO2 conversion under relatively mild conditions. In addition to the activation of reactants by external thermal energy, the photo‐excited charge carriers generated on semiconductor materials or the hot electrons produced on the surface of plasmonic metals could be injected into the antibonding orbitals of the reactants to activate the reactant molecules for redox reactions. It has been demonstrated that hot electrons on surface of Au nanoparticles effectively induced the dissociation of H2, which is a key step in many CO2 reduction reactions. As such, effective utilization of photo‐induced charge carriers is critical for enhancing the photochemical contribution in photo‐thermal catalytic process. To date, most reported photo‐thermal catalysts for gas‐phase heterogeneous catalysis are made of metal oxide‐based semiconductors decorated with metal nanoparticles, with inherent limitations including narrow light absorption spectrum and inferior separation efficiency of photo‐induced charge carriers. To overcome these obstacles, approaches including band gap engineering, introduction of defects, and internal electric field building have been studied to promote charge carrier generation and migration for metal/metal oxide catalysts.Conversion of COon goals.1 Amon Zeng et al. encapsulated Au and Pt nanoparticles into ZIF‐8 to construct Au&Pt@ZIF catalysts, and found that the increased surface temperature of Pt active sites due to the LSPR effect of adjacent Au nanoparticles under light irradiation could enhance the photothermal CO2 hydrogenation for methanol production effectively. However, most of the investigated photothermal materials are noble metals such as Au and Ag, and their high cost and scarcity present obstacles to industrial application. To this end, the exploitation of inexpensive and naturally‐abundant nanomaterials that could replace noble metals as “nanoheaters” is of great significance. Based on these analyses, we believe that the fabrication of composited catalysts with both high charge carrier separation efficiency and photo‐to‐thermal conversion ability could be a promising approach to achieving efficient photo‐thermal conversion of CO2.In addition to the promoted reactants adsorption/activation effect originating from the charge carriers, it is also found that the elevated local temperature around the active sites could dramatically accelerate the reaction kinetics. Recent advances have highlighted that localized photo‐to‐thermal conversion over photothermal materials, triggered via localized surface plasmon resonance (LSPR) or charge carrier relaxation, could dramatically accelerate the catalytic reaction by increasing the temperature of active sites.9 Zeng2 methanation performances over Ir‐CoO/Al2O3 catalysts derived from Ir/CoAl LDH composites, where CoO carriers play dual critical roles in the hybrid by forming the intimate Ir‐CoO interfaces, expediting photo‐induced charge carrier generation and transportation, and functioning as “nanoheaters” to rapidly elevate the local temperature around the active sites, which benefit the adsorption and activation of CO2 molecules. The Al2O3 nanosheets with high thermal stability could effectively prohibit the agglomeration of tiny Ir‐CoO active centers during the reaction and thus assure the long durability of the composited catalysts. Thanks to the aforementioned merits, the optimized catalysts (0.16%Ir‐CoO/Al2O3) achieved an unprecedented CH4 production rate of 128.9 mmol gcat⁻1 h⁻1 with 92% selectivity and exceptional stability. By contrast, Ir/Al2O3 without CoO exhibits much lower catalytic activity under consistent conditions, highlighting the significance of CoO nanoparticles. To reveal the essence of intimate interaction between Ir and CoO, we impregnate Ir nanoparticles on the already prepared CoO/Al2O3 surface, and find that the produced Ir/CoO/Al2O3 catalysts show a CH4 production rate of 32 mmol gcat⁻1 h⁻1, which is much lower than that of Ir‐CoO/Al2O3. In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS) measurements reveals that light irradiation brings no changes to the reaction pathways but efficiently boosts the rate‐determining step. To sum up, under light irradiation, the intimate interaction between Ir and CoO brings efficient charge generation and enhanced photothermal effect, which facilitated the adsorption and activation of reactant molecules and intermediate species and resulted in a higher CH4 production rate.Herein, we report dramatically enhanced photo‐thermal CO22.12/N2 stream for 2 h to produce the Ir‐CoO/Al2O3 catalysts  images manifested that Ir‐CoO/Al2O3 composites inherited the sheet‐like architecture of Ir/CoAl LDH precursors  were first supported on the surface of CoAl layered double hydroxide (LDH) to give the Ir/CoAl LDH composites, which were then calcined in a 5 vol.% Hs Figure 1a. X‐ray  at 533.1 eV and hydroxyl species (Ohyd) at 531.8 eV. Noticeably, two peaks at 530.4 eV and 531.5 eV observed on 0.16% Ir‐CoO/Al2O3 could be ascribed to metal‐oxygen bonds (Co‐O and Al‐O), which was in line with the XRD result and demonstrated the formation of metal oxides. In addition, XPS spectra under light irradiation (visible irradiation provided with Xenon lamp) were further obtained to study the direction of electron transfer in the Ir‐CoO/Al2O3 composites  measurements were carried out to probe the surface chemical properties and the interaction between the constituents of catalysts. In the core‐level Ir 4f spectrum of 0.16% Ir/CoAl LDH Figure 2a, two pic state.12 The2O3, CoO/Al2O3, and Ir‐CoO/Al2O3 catalysts was studied , the surface temperature of the three catalysts  increased rapidly and reached the plateaus after ≈3 min. The peaked surface temperature of 0.16% Ir/Al2O3 and CoO/Al2O3 were 53 and 75 °C, respectively. Notably, the highest surface temperature of 0.16% Ir‐CoO/Al2O3 reached 90 °C, which was 37 and 15 °C higher than that of 0.16% Ir/Al2O3 and CoO/Al2O3, respectively. To gain insight into the enhancement mechanism of photothermal effect of Ir‐CoO/Al2O3, the induced electric field distributions of CoO, Ir nanoparticles and Ir‐CoO in the presence of 420 nm illumination were simulated by COMSOL Multiphysics based on finite element methods. As shown in Figure  Surprisingly, when the Ir nanoparticle were in close contact with CoO, an extremely intense localized electromagnetic field was produced at the interface, resulting in near‐field enhancement due to the LSPR effect near the semiconductor surface . As shown in Figure 2O3 catalyst showed negligible catalytic activity with a CH4 production rate of 6.85 mmol gcat⁻1 h⁻1 at 250 °C under light irradiation, indicating the necessity of catalytically active Ir nanoparticles. Compared with CoO/Al2O3, all the Ir‐CoO/Al2O3 catalysts showed significantly enhanced catalytic activity, and the CH4 production rate displayed a volcano‐like tendency with respect to the Ir content. The highest CH4 production rate of 128.9 mmol gcat⁻1 h⁻1 (80.6 mol gIr⁻1 h⁻1) was obtained at 250 °C under light irradiation , solely light‐driven and photo‐thermal conditions were compared and the results are shown in Figure 4 production rate of 18.8 mmol gcat⁻1 h⁻1 was achieved over 0.16% Ir‐CoO/Al2O3 catalyst and a much lower value of 1.9 mmol gcat⁻1 h⁻1 was obtained in the presence of sole light irradiation, suggesting that the photo‐thermal catalytic CO2 hydrogenation was dominantly a thermal‐driven process. Strikingly, ≈sevenfold enhancement of CH4 production rate (128.9 mmol gcat⁻1 h⁻1) was observed in photo‐thermal process compared with the thermal catalytic process, demonstrating that light irradiation could significantly enhance the thermal catalytic reaction . As shown in Figure 4 production rate under infrared (62.4 mmol gcat⁻1 h⁻1) and UV light (35.7 mmol gcat⁻1 h⁻1) irradiation was much lower than that under visible light (128.9 mmol gcat⁻1 h⁻1) irradiation, indicating that the plasmonic absorption in the visible light region of Ir‐CoO/Al2O3 catalysts greatly contributed to the high activity. To further highlight the significance of light source, the catalytic activity of 0.16% Ir‐CoO/Al2O3 was also evaluated under full spectrum irradiation and a much higher CH4 production rate of 177.9 mmol gcat⁻1 h⁻1 was achieved, far exceeding the performance under visible irradiation. This could be attributed to the greatly increased photo‐induced electrons generated due to the strong absorption across the UV‐Vis‐NIR region of Ir‐CoO/Al2O3 catalysts. These results clearly showed that the external heat and light irradiation synergistically enhanced CO2 hydrogenation performance, achieving a much higher CH4 production rate than the sum under sole light irradiation and sole thermal catalytic condition. However, it is still challenging to quantify the individual contribution from light irradiation and external heating process.To investigate the effect of light on catalytic activity, the CH2O3 catalysts, a 30 h long‐term stability test was conducted at 250 °C under light irradiation in the flow reactor. As shown in Figure 4 production rate was detected during 30 h of catalytic reactions, indicating that the Ir‐CoO/Al2O3 catalysts were highly stable. Besides, the stability of catalysts in dark (250 °C) was also investigated  measurements were carried out. As depicted in Figure 2O3 showed two broad peaks at 594 and 684 °C, which could be attributed to the reduction of CoO to metallic Co and the reduction of cobalt aluminates species, respectively. For 0.16% Ir‐CoO/Al2O3, the peak at 340 °C was assigned to the reduction of the IrO2 species that strongly interacted with CoO and the other two peaks at high temperature regions corresponded to the reduction of CoO and cobalt aluminates species. Notably, the addition of Ir led to the decrease in the reduction temperature of CoO and cobalt aluminates species toward 505 and 623 °C, respectively, which could be ascribed to the efficient dissociation and spillover of H2, elucidating that H2 molecules could be easily dissociated on Ir‐CoO/Al2O3 to participate in the hydrogenation reaction. In addition, the CO2 adsorption properties of CoO/Al2O3 and 0.16% Ir‐CoO/Al2O3 catalysts were studied using CO2 temperature‐programmed desorption (CO2‐TPD) and the results are shown in Figure 2O3 catalyst was related to the chemically adsorbed CO2 molecules. The 0.16% Ir‐CoO/Al2O3 catalyst exhibited three desorption peaks at 233, 360, and 518 °C, which could be assigned to the weakly and strongly adsorbed CO2 molecules on the surface of 0.16% Ir‐CoO/Al2O3 catalyst. Apparently, compared with CoO/Al2O3, the 0.16%Ir‐CoO/Al2O3 catalyst showed stronger CO2 adsorption capacity when the temperature was lower than 400 °C, indicating that the Ir species could promote adsorption of CO2 on the catalyst. Generally, valid CO2 adsorption is one of the prerequisites for high CO2 conversion efficiency. This may be a credit from the formation of Ir‐CoO interface, which promotes the adsorption of CO2.To investigate the reduction behavior of catalysts and the interaction between Ir species and support, Hectively.21 For This result unveils that the CoO close to the interface is positively charged, whereas the Ir near the interface is negatively charged due to the electron transfer from CoO to Ir.To understand the effect of charge transfer between Ir nanoparticles and CoO on the Sabatier reaction kinetics, density functional theory (DFT) calculations were conducted. As revealed by the charge difference distribution of Ir‐CoO in Figure 23 Thi2 adsorption sites on the catalysts surface, the CO2 adsorption behavior on Ir surface and at Ir‐CoO interface is investigated by DFT calculations. The optimized geometries of CO2 adsorbed on Ir surface and at Ir‐CoO interface are exhibited in Figure 2 molecules at the Ir‐CoO interface. Besides, the adsorption energy (Eads) of CO2 on the Ir surface and at Ir‐CoO surface are ‐3.0 and ‐3.11 eV, respectively, suggesting that the CO2 is more easily adsorbed at the Ir‐CoO interface. Therefore, the Ir‐CoO interface is considered as the most active adsorption site of CO2 molecules. In addition, to shed light on the effect of the photo‐induced electrons on the adsorption of reactants, the adsorption behavior of H2 molecules on the surface of Ir nanoparticles was also explored by DFT calculations. We simulated the neutral and negatively charged Ir surface by constructing the geometries of Ir(111) and Ir(111)‐CoO, denoted as [Ir(111)] and [Ir(111)]–, respectively. Figure 2 adsorbed [Ir(111)] and [Ir(111)]– surfaces, and the corresponding bond lengths and adsorption energy are also simulated (Table 2 is more easily adsorbed on the [Ir(111)]– surface. The σ*antibonding orbitals of H2 molecules could then accept electrons from the negatively charged Ir surface, and this process would enable the dissociation of adsorbed H2 into H species, which would readily react with the adsorbed CO2 molecules to initiate the hydrogenation process.To further clarify the COnterface.24 Bes2 methanation process over Ir‐CoO/Al2O3, in situ DRIFTS measurements were carried out. As shown in Figure 2 and H2 were introduced into the reactor at room temperature, several vibrational peaks could be observed at 1385, 1530 and 1628 cm⁻1. The bands at 1385/1628 and 1529 cm⁻1 were ascribed to the formation of bicarbonate (*HCO3) and carbonates (*CO3) species, respectively, indicating that CO2 was first adsorbed and existed in the form of *HCO3 and *CO3. Noticeably, these bands of *HCO3 disappeared as the temperature reached 200 °C, whereas vibrations peaks at 1362 and 1583 cm⁻1 corresponding to the formate species (*HCOO) appeared, suggesting that *HCO3 was transformed into *HCOO. As the temperature further increased to 300 °C, two new peaks were observed at 1341 and 1427 cm⁻1, which were ascribed to *HCO3 species, hinting that high temperature was favorable for CO2 activation  is thermodynamically more favorable than the dissociation of *HCOO to *CO (energy change: 1.09 eV), which is consistent with the fact that the selectivity of CO is relatively low. The generated *H2COO is further hydrogenated to *H2COOH, with an energy change of 0.26 eV. Afterward, the *H2COOH dissociates into *H2CO and *OH via the direct C‐O bond cleavage pathway. Notably, the further dissociation of *H2CO to *CH2 is evidently more favorable than the hydrogenation of *H2CO to *H3CO, and therefore, *CH2 is hydrogenated to CH4. Namely, the *H2CO species favor dissociation energetically rather than hydrogenation, resulting in lower CH3OH selectivity and higher selectivity for the targeted CH4.Furthermore, DFT calculations were carried out based on the models of Ir supported on the CoO (200) slabs to illustrate the reaction pathway, and the change of free energy was indicated for each elementary step Figure . The opt2 methanation on Ir‐CoO/Al2O3 catalysts are proposed  was achieved over 0.16% Ir‐CoO/Al2O3 catalyst at 250 °C under ambient pressure, outperforming most of the reported metal‐based catalysts. This work provides in‐depth understanding on the synergistic effects in photo‐thermal catalytic process and proposes a novel catalyst for the efficient conversion of CO2 under mild conditions.In summary, we have prepared Ir‐CoO/AlThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.


In this work, a facile interface engineering strategy to control the surface structure and energy‐level alignment of perovskite films by tailoring the interface between the FAPbI3 film and hole‐transporting layer using 4‐hydroxypicolinic acid (4HPA) is reported. According to density functional theory studies, 4HPA has prominent electron delocalization distribution properties that enable it to anchor to the perovskite film surface and facilitate charge transfer at the interface. By enabling multiple bonding interactions with the perovskite layer, including hydrogen bonds, Pb—O, and Pb—N dative bonds, 4HPA passivation significantly reduces the trap density and efficiently suppresses nonradiative recombination. The obtained perovskite films exhibit superior optoelectronic properties with improved crystallinity, pure α‐phase FAPbI3, and favorable energy band bending. Following this strategy, 4HPA post‐treatment PeSCs achieve a champion power conversion efficiency of 23.28% in 0.12 cm2 cells and 19.26% in 36 cm2 modules with excellent environmental and thermal stabilities.Perovskite solar cells (PeSCs) using FAPbI 3 perovskite film with multifunctional molecule 4‐hydroxypicolinic acid (4HPA) shows excellent optoelectronic properties with improved crystallinity, pure α‐phase FAPbI3, and favorable energy band bending. The 4HPA post‐treated PeSC achieves a champion power conversion efficiency of 23.28% in 0.12 cm2 cells and 19.26% in 36 cm2 modules, with excellent environmental and thermal stabilities.The surface post‐treatment of FAPbI Indeed, the latest certified PCE for single‐junction PeSCs has now reached 25.7%, exceeding that of top‐level polycrystalline silicon solar cells, making them highly attractive for commercialization. Despite the tremendous advancements made toward improving efficiency, the long‐term stability and restricted scalable fabrication protocols remain major hurdles in their industrialization. Specifically, most PeSC materials use organic formamidinium (FA) or methylammonium (MA) cations in combination with inorganic PbI3 perovskite components. Among them, FAPbI3 is generally preferred over MAPbI3 because of its higher thermal stability, superior charge carrier transport capabilities, and smaller bandgap energy that extends into the near‐infrared range. Nevertheless, at room temperature, the phase transformation of the photovoltaically active black α‐phase of FAPbI3 to the undesirable but more stable yellow δ‐phase, a non‐perovskite material, severely limits practical PeSC applications based on FAPbI3. In addition, the solution‐processed FAPbI3 film inevitably yields a significant number of defects, especially at the surfaces and grain boundaries (GBs), owing to the loss of organic components during thermal annealing and the heterogeneity of polycrystals. These defects act as trap sites in the charge carriers transport and collection process, thereby degrading the efficiency and long‐term operational stability of PeSCs. Moreover, these defects hinder the scalability of PeSCs to modules, ultimately limiting their potential for commercialization.Metal halide perovskite solar cells (PeSCs) have gained considerable attention during the past decade because of their superior advantages such as excellent photovoltaic properties,1 low‐3 materials to address these issues. However, although these diverse approaches have achieved tremendous success, improvements in stability and photoelectric efficiency are often accompanied by unintended consequences. For instance, the alloying reaction of MA and Br in FAPbI3 gives rise to various issues, including low thermal stability due to MA molecules, phase separation due to the presence of mixed halides, and reduced photon absorption, resulting in a low current density due to undesirable widening of the bandgap. Optimization of the growth of FAPbI3 crystals by introducing additives, including Pb(SCN)2, 1‐cyclohexyl‐2‐pyrrolidone, and thiosemicarbazide, is incompatible with low‐cost scalable coating processes such as blade‐coating, which remains a challenge for the scale‐up manufacture of large‐area perovskite films. These negative consequences significantly restrict the large‐scale development of FAPbI3‐based perovskite device applications.Researchers have investigated compositional optimization and additive incorporation of FAPbIe issues.13 How Up to now, achieving efficient and stable PeSCs often involves using surficial post‐treatment with alkylammonium halides, and numerous compounds have been assessed. After treatment with alkylammonium halides, a secondary 2D perovskite layer is typically formed on top of the primary perovskite layer, which improves device stability. Unfortunately, surface 2D perovskite layers often exhibit a tenacious in‐plane orientation and high exciton binding energy, which may limit the impact of passivation and impede charge transfer, especially in the presence of larger spacer cations. This prompted You et al. to eliminate the annealing process after post‐treatment to replace the 2D perovskite layer with a thin phenylethylammonium iodide (PEAI) layer, resulting in more efficient surface passivation. Consequently, they achieved a certified PCE of more than 23% using a combination of π‐conjugated phenyl rings promoting charge transfer, amine coordination reducing Pb2+ interstitials, and iodide ions filling iodine vacancies. However, the PCEs of these devices still decreased at higher working temperatures because of the conversion of PEAI to 2D PEA2PbI4. In addition, long alkyl chains in the modifier can create an unnecessary charge barrier between the hole transfer layer (HTL) and perovskite layer. Therefore, there is a great need for a short chain‐based agent or related new hybrid structure that can withstand higher temperatures without forming 2D perovskite and can effectively passivate the surface defects of perovskite to achieve high‐performance PeSCs and modules.Meanwhile, interface modification has proven to be an effective and straightforward strategy for reducing defect density and improving charge transport without the need for complex fabrication processes.21 Up 3 perovskite and the HTL. There are multiple advantages to using 4HPA to improve the photovoltaic performance of perovskite devices. First, 4HPA exhibits significant electron delocalization properties through its unique conjugated π system, which enhances the effectiveness of charge transfer through the ligand compared to ligands containing alkyl chains. Second, the π‐conjugated aromatic backbone in 4HPA has strong steric hindrance, which allows 4HPA to be anchored to the perovskite surface in a certain orientation, which is beneficial for improving the charge transfer at the interface. Third, the ligand has good rigidity and high thermal stability, contains a carbonyl group (C=O) and hydrogen bonding donors (—OH), which can passivate ionic defects through coordination and hydrogen bonding. To further investigate the correlation between ligand molecular structure and device performance, we also compared the effects of 2‐picolinic acid (PA) and its isomer 5‐hydroxypyridine carboxylic acid (5HPA) on device performance  of 1.15 V, and a fill factor (FF) of 80.11%, outperforming the control device (19.23%). In addition, the devices demonstrated enhanced long‐term stability under ambient conditions and high temperature. Furthermore, a FAPbI3‐based perovskite module with a total area of 36 cm2 exhibited a high efficiency of 19.26%.In this study, we selected a pyridine‐based multifunctional ligand, 4‐hydroxypicolinic acid (4HPA), to tailor the interface between the FAPbI23 perovskite film . Hereinafter, the pristine composition (FAPbI3) and the perovskite coated with 4HPA (FAPbI3/4HPA) are referred to as the control and the target material, respectively. Based on the statistical analysis of PeSC efficiencies treated with various concentrations of 4HPA, we determined that the optimal concentration is 1.0 mg mL−1. We first used density functional theory (DFT) to perform quantum chemical calculations and visualize the frontier orbitals of 4HPA. As illustrated in Figure 2+ in FAPbI3 through coordination between the Lewis acid and base.To test the potential of the 4HPA ligand and assess its role in enhancing the photovoltaic performance of perovskites, a solution of 4HPA in isopropyl alcohol was spin‐coated on top of the annealed FAPbIm Figure 1a. In ad2 solutions. Typically, the formation of coordination bonds between metal ions and organic ligands affects the conjugated structure of chromophores, resulting in shifts in the absorption peaks. When dissolved in an N, N‐dimethyl formamide (DMF) solution, 4HPA displays a broad absorption band in the 250–400 nm range, with two characteristic peaks at 282 and 360 nm, as shown in Figure 2 in the same DMF solution, the resulting mixture exhibits significantly stronger and blueshifted absorption (two peaks at 471 and 353 nm) than the neat 4HPA solution. The observed changes can be attributed to the Lewis base–acid interaction and hydrogen bonding between PbI2 and 4HPA , as well as a weakening of the push‐pull effect of 4HPA. Fourier transform infrared (FTIR) spectra were recorded to further confirm the interaction mechanism to analyze the 4HPA powder and the 4HPA:PbI2 mixture . Conversely, the vibrational signal of the C=O groups shifted by 13 cm−1 to higher wavenumbers, suggesting the presence of significant interactions  between the solid 4HPA and PbI2. The shift of the C=O stretching vibration peak to higher wavenumbers was also observed in the target film  facilitates the coordination of C=O and Pb2+. According to previous reports, we estimated that the —OH groups formed hydrogen bonds with iodide anions, which contributed to the binding of the C=O group to the uncoordinated Pb2+ defects in the FAPbI3 films. In comparison, the vibrational signal of the C=N group insignificantly shifted after 4HPA was mixed with PbI2, indicating weaker interactions between C=N and PbI2.To confirm the formation of Lewis adducts of Pb and O or N, we carried out UV–vis absorption measurements for neat 4HPA and mixed 4HPA:PbIon peaks.27 Whee Figure . The nea2+ ions to form Lewis adducts, and the increased activation energy of ions can reduce ion migration. Computational confirmation of a stable adsorbate structure was achieved through density functional theory (DFT) calculations, which identified a surface binding energy of −0.78 eV  toward a lower binding energy, as shown in Figure  The 4HPA molecule contains an electron‐rich N atom with a coordinated lone pair of electrons. As a result of the electrostatic attraction, the lone pair electrons establish dative covalent bonds with the positive charge on the metal ion and cause the positive charge to become delocalized within the pyridine molecule. A shift in the binding energy is expected due to charge transfer between the perovskite and the Lewis base. As shown in Figure 7/2, Pb 4f5/2) and I  in the target film are moved to lower positions than that of the control film . This shift in binding energies suggests that the interaction between Pb and I is weakened after treatment with 4HPA, likely due to the bonding of 4HPA with Pb and I. Simultaneously, the treatment effectively passivated uncoordinated lead and halogen defects, resulting in an improvement in the crystal quality of the perovskite films.X‐ray photoelectron spectroscopy (XPS) measurements further confirmed the electronic interaction between 4HPA and perovskite. The O 1s peak of the 4HPA molecule is characterized by a binding energy of 532.4 eV Figure . Howeverigration.29 ComV Figure . In this3 films. The two dominant peaks at ≈14° and 28° in the XRD pattern were assigned to the characteristic (100) and (200) crystal planes of the α‐phase FAPbI3. In the control perovskite film, the peaks corresponding to the α‐phase perovskite were dominant, but the δ‐phase FAPbI3 peak at 11.4° was present  decreased significantly after treatment with 4HPA. Furthermore, the diffraction intensities of the (100) and (200) peaks are enhanced. These findings demonstrate that the interaction between 4HPA and PbI2 promotes the reconstruction of the perovskite layer and effectively suppresses the formation of δ‐phase FAPbI3. Moreover, the absence of peaks in the low‐angle area implies that the post‐treatment is unrelated to the 2D perovskite formation. To explore the impact of 4HPA on the morphology of the FAPbI3 films, top‐view scanning electron microscopy (SEM) measurements were conducted. The control film without the 4HPA treatment exhibited obvious GBs on the surface of the FAPbI3 film  measurements were performed to study the effect of 4HPA post‐treatment on the crystallization properties of FAPbIe FAPbI3.10b Inm Figure . A unifom Figure . Simulta3 film, indicating that nonradiative recombination was suppressed because of the effectively reduced surface charge traps. In addition, time‐resolved photoluminescence (TRPL) measurements were performed to elucidate the contribution of the enhanced PL lifetime. As shown in Figure Voc and FF of the devices.To track the enhancement of charge extraction and reduction of charge recombination, the optical properties of the perovskite films were explored. Following the 4HPA treatment, the absorption of the perovskite thin film increased Figure , which wge traps.33 In Figure  Therefore, PeSCs fabricated using 4HPA‐treated films are expected to have a higher Voc. To evaluate this idea, the C−2 versus V characteristics of the corresponding devices were obtained by capacitance–voltage measurements  were estimated as 0.94 and 1.02 V for the control and target devices, respectively. The highest Vbi of the 4HPA treated device is usually related to the highest Voc. Then, the dark space‐charge‐limited currents were measured for the control and 4HPA post‐treated devices. The defect density was calculated on the grounds of the equation of Nd = (2εε0VTFL)/(eL2), where e is the elementary charge, L is the thickness of the perovskite thin film, ε0 is the permittivity in vacuum (8.85 × 1012 F m−1), and ε is the relative dielectric constant of FAPbI3 (46.9). The determined VTFL value of the target device decreased from 0.24 V for the control device to 0.13 V  and the subsequent retardation of ion migration by 4HPA passivation. A lower defect density is advantageous for a steady device output and suppression of hysteresis. Furthermore, because the defects of the perovskite films are mostly concentrated at the GBs, the ligand can effectively cover the surface and penetrate the surface at the GBs during treatment, thereby improving the Voc of the devices.The influence of 4HPA on the electronic properties of perovskites was elucidated using UV photoelectron spectroscopy (UPS). The corresponding UPS spectra of the secondary electron cut‐off region and valence band edge region are shown in Figure 34 Thes Figure . The buiV Figure . Based o2/perovskite/4HPA/Spiro‐OMeTAD/Au planar configuration were fabricated, as depicted in Figure −1. The control device demonstrated an average short‐circuit current density (Jsc) of 23.82 ± 0.43 mA cm−2, average Voc of 1.05 ± 0.04 V, average FF of 74.84 ± 1.83%, and average PCE of 18.72 ± 0.77%. Conversely, the device treated with 4HPA (1.0 mg mL−1) yielded an average Jsc of 25.08 ± 0.22 mA cm−2, an average Voc of 1.15 ± 0.02 V, an average FF of 79.18 ± 1.42%, and an average PCE of 22.85 ± 0.43%, respectively. Evidently, both Voc and FF are greatly enhanced, along with a slight improvement in Jsc, which is attributed to the efficient passivation of the defects at the surfaces and GBs of perovskite films by 4HPA molecules. Figure J–V curves for both the control and 4HPA‐treated devices, and Table Jsc of 24.05 mA cm−2, Voc of 1.06 V, and FF of 75.21%) in the reverse scan and PCE of 18.26%  in the forward scan. For comparison, the target device exhibited a significantly enhanced PCE of 23.28%  in the reverse scan and PCE of 23.15%  in the forward scan, respectively. Moreover, the hysteresis index (HI) for the control device was 5.04%, whereas that for the target PeSC was 0.56%. A small hysteresis factor implies a more efficient relief of trap states and ion migration in the target device.To further assess the effect of 4HPA on the photovoltaic characteristics of PeSCs, devices with FTO/TiOdensity Jsc of 23.−2, respectively, confirming the accuracy of the J–V performance. Particularly noteworthy is that the current density of the control device at the MPP decreased from 23.4 to 21.8 mA cm−2 over time, whereas the target device maintained a current density of 23.5 mA cm−2 and a stabilized output of 22.6%, demonstrating excellent operational stability. The corresponding incident photon‐to‐electron conversion efficiency (IPCE) spectra demonstrated that the calculated integrated Jsc value after 4HPA treatment was 24.19 mA cm−2, higher than that of the control (22.76 mA cm−2), which was consistent with the previous J–V test results  to estimate the extent of trap‐assisted nonradiative recombination and bimolecular radiative recombination. The power law Jsc ∝ αI describes the relationship between Jsc and I, where α is a factor that depends on the degree of bimolecular recombination. As shown in Figure α values that are very close to 1, indicating that bimolecular recombination is negligible owing to the high quality of the perovskites. In addition, according to the following equation, Voc should exhibit a linear correlation with the logarithm of light intensityn is the ideality factor, e is the elementary charge, KB is Boltzmann's constant, and T is the thermodynamic temperature. The deviation of the slope from KBT/e was attributed to trap‐assisted recombination. As shown in Figure KBT/e compared with the 1.46 KBT/e of the control device, further demonstrating that 4HPA could effectively suppress trap‐assisted recombination. The prominence of both suppressed trap‐assisted recombination and bimolecular recombination revealed that 4HPA converges surface defect passivation and expedites interface charge transfer, thereby lowering energy loss and improving the photovoltaic performance of PeSCs.The Rct) than the control device because of the enhanced interfacial charge transfer assisted by the integrated 4HPA, which should account for the improved FF. In addition, treatment with 4HPA significantly increased the recombination resistance (rRce) by suppressing charge recombination, as evidenced by the reduced defect density, potentially leading to a higher Voc. We further applied theoretical calculations to gain deeper insight into the effect of 4HPA on atomic‐scale interface charge transfer. The charge density difference plots are shown in Figure 2+, effectively inhibiting charge recombination.Electrochemical impedance spectroscopy (EIS) is an additional helpful technique for gaining insight into the charge transport and transfer processes. Figure 3 perovskite undergoes a spontaneous phase transition from α‐ to δ‐FAPbI3 under ambient conditions, we tested the environmental stability of different devices. As a result of the passivation of the decomposition sites in FAPbI3 perovskite and the moisture resistance provided by the hydrophobic aromatic rings in 4HPA, the post‐treatment strategy using 4HPA significantly enhances the stability of the α phase of FAPbI3 perovskite. Figure 3 devices was considerably improved, maintaining over 90% of the original efficiency for more than 2000 h at an RH of 25 ± 5%, in contrast to less than 70% for the control devices. Post‐treatment with 4HPA increased the contact angle from 70.6°  was employed to investigate the impact of 4HPA on the phase transformation of perovskites. Specifically, the electron beam (E‐beam) generated by the HRTEM instrument is used as the thermal energy source. The target and control perovskites exhibited FAPbI3 layers with different crystallographic orientations, as shown in Figure 3, as depicted in Figure 3 layer with new diffraction spots at 3.89 nm−1 (2.9 Å) on the FFT. These morphological characteristics indicate that the crystalline perovskite phase was partially transformed into an amorphized phase and that the region had precipitated hexagonal PbI2 grains, consistent with previous studies, which found that the thermal degradation of perovskite can generally be considered the reverse process of perovskite film growth. Therefore, we speculate that 4HPA acts as a molecular lock when interacting with perovskite, increasing the activation energy required for perovskite decomposition, thus preventing its degradation at high temperatures.We further evaluated the thermal stability of the PeSCs without encapsulation at 85 °C in a nitrogen environment Figure . The tarm growth.37 The33 thin films using a post‐treatment approach. Strong interactions between 4HPA and Pb2+ ions increased the stabilized phase‐pure FAPbI3 perovskite by effectively inhibiting the formation of δ‐phase nonperovskite. Moreover, the formation of hydrogen bonds between the 4HPA and I− ions further strengthened the binding and retarded the decomposition of the FAPbI3 perovskite films. Multiple interactions of the 4HPA molecule with the perovskite improved the film quality, reduced the trap state density, and suppressed nonradiative recombination. These superior merits enabled a champion PCE of 23.28% in 0.12 cm2 cells and 19.26% for 36 cm2 modules with excellent environmental and thermal stabilities.In summary, we have successfully demonstrated that the pyridine‐based ligand 4HPA can be used as an efficient chemical passivator for the surface of FAPbIThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.


Formaldehyde (HCHO: FA) is one of the most abundant but hazardous gaseous pollutants. Transition metal oxide (TMO)‐based thermocatalysts have gained much attention in its removal due to their excellent thermal stability and cost‐effectiveness. Herein, a comprehensive review is offered to highlight the current progress in TMO‐based thermocatalysts  in association with the strategies established for catalytic removal of FA. Efforts are hence made to describe the interactive role of key factors  governing the catalytic activity of TMO‐based thermocatalysts against FA. Their performance has been evaluated further between two distinctive operation conditions  based on computational metrics such as reaction rate. Accordingly, the superiority of TMO‐based composite catalysts over mono‐ and bi‐metallic TMO catalysts is evident to reflect the abundant surface oxygen vacancies and enhanced FA adsorptivity of the former group. Finally, the present challenges and future prospects for TMO‐based catalysts are discussed with respect to the catalytic oxidation of FA. This review is expected to offer valuable information to design and build high performance catalysts for the efficient degradation of volatile organic compounds. Formaldehyde is one of the most abundant but hazardous gaseous pollutants. Transition metal oxide (TMO)‐based thermocatalysts have gained much attention in its removal due to their excellent thermal stability and cost‐effectiveness. Herein, the current progress in TMO‐based thermocatalysts is reviewed in association with their preparation/modification strategies, performance evaluation, and the interactive role of key factors governing their catalytic activities. In light of the adverse health effects of FA, the World Health Organization has set its short‐term (30 min) exposure limit in indoor environment at 0.1 mg m−3. There is even more strict technical standard of 0.03 mg m−3 for the emission control in interior decoration systems such as residential buildings in China. As people are spending more of their time indoors, it is critical to control FA levels in indoor air to avoid their adverse effects on human health.Formaldehyde (FA) is represented as one of the simplest forms of volatile organic compounds (VOCs). FA is often regarded as the priority target for treatment because of its ubiquity, abundance, and negative effects on human health.1 Sour2O and CO2) under atmospheric pressure with heat energy. As thermocatalysis can proceed in the absence of a light source, it can be regarded as a superior option over photocatalytic degradation method. Generally, the thermocatalytic degradation of gaseous FA has been achieved using noble  and/or transition metal (TM)  based materials. However, their real‐world applications are often restricted by the combined effects of both low abundance of noble metals and their high costs. As a result, TM‐based catalysts have gained interest as alternative options due to their high stability, good catalytic activity, abundant resource, and cost‐effectiveness. TM catalysts can offer unpaired d electrons or empty d orbitals to efficiently attract target molecules during the catalysis process. As such, the catalytic destruction of pollutants over these TMs can be promoted by forming chemical bonds and/or by lowering the activation energy of the reaction. Moreover, the catalytic activities of TM‐based composites were also reported to be higher than those of their pure forms such as Co3O4, CeO2, and MnO2. Such enhancement was mainly due to the improved oxidation capacity of the composites with higher FA adsorptivity and/or oxygen vacancies.Recently, the thermocatalytic degradation approach is recognized as an effective option to achieve the complete decomposition of gaseous FA into harmless products  to properly evaluate their potential for real‐world applications. Finally, the current challenges and outlook of the research are also discussed. The current review is expected to deliver salient information for the construction of highly active TMO‐based thermocatalysts for the effective removal of gaseous FA.The objectives of this review are to highlight the recent progress in the development of TM‐based thermocatalysts  for the degradation of gaseous FA. The discussion has been extended to cover their structural activity relationship and their FA degradation mechanism. Effective strategies  developed for improving their catalytic activities are also discussed. Moreover, the FA degradation efficiencies of TM‐based thermocatalysts are also evaluated in terms of the key performance metrics  from valence band are excited to the conduction band to leave positive holes (h+) in the valence band even at low temperature . The concentration of e−/h+ in thermocatalysts generally increases at elevated temperature . The thermally generated charge carriers further move to the surface of the catalyst to react with adsorbed oxygen molecules and water for the generation of surface adsorbed oxygen species such as superoxide anions  and hydroxyl radicals . Further, water can also be converted into O2 and ●OH with the assistance of O2−. The target pollutants can thus be catalytically oxidized to CO2 and H2O by these surface adsorbed oxygen species. The production of surface adsorbed oxygen species is also affected by the amount of oxygen vacancies (OVs) of the thermocatalysts . The surface oxygen vacancies possess localized electrons that can easily charge adsorbed oxygen  via the molecular oxygen activation channel. Hence, the O2 molecules can accept delocalized electrons from oxygen vacancies  to be converted into active species.A better knowledge of the catalytic oxidation mechanism of FA by TM‐based thermocatalysts can help in the design of highly active, stabile, and efficient thermocatalysts. As thermocatalysts are exposed to the external heat energy, electrons (eerature).12 The In addition, higher concentrations of oxygen vacancies in the thermocatalysts can narrow the band gap to enhance the catalytic activity against VOC degradation. The lattice oxygen species were also found to enhance the formation of surface adsorbed oxygen species through its complex interaction with oxygen vacancy and molecularly oxygen. As such, the FA catalytic activity of catalysts was enhanced. For instance, the FA catalytic activity for four MnO2 catalysts  was in line with their amount of lattice oxygen with the following relative order: δ‐MnO2 > α‐MnO2 > β‐MnO2 > γ‐MnO2.The creation of surface defects  over the thermocatalysts is also recognized as an effective way to achieve abundant oxygen vacancies.16 In  In such a mechanism, pollutants are initially oxidized by the surface adsorbed oxygen species to lead to the reduction of metal sites  has been proposed , respectively. The oxygen molecules are dissociated and activated into surface adsorbed oxygen species  by oxygen vacancies at low/high temperature . Then, the adsorbed FA molecules rapidly react with surface adsorbed oxygen species to be converted into dioxymethylene intermediates and further into formate species so as to form hydrocarbonates. These hydrocarbonate species are to be ultimately oxidized into H2O and CO2. Similar oxidation pathways were also found when pure/surface defected manganese and cobalt catalyst were used for the thermal oxidation of FA. In addition, thermocatalytic degradation of FA over noble metal catalysts  can also be explained by a similar Mars‐van Krevelen mechanism. More specifically, the FA molecules were adsorbed on the surface of catalysts and then directly oxidized into formate species by surface adsorbed oxygen species. The formate species were subsequently decomposed into H2O and CO which was further oxidized into CO2. Interestingly, as the existence of strong metal‐support interactions in Pt/TiO2 catalysts can cause the partial reduction of the Ti4+ species into Ti3+, it can favorably enhance the FA catalytic activity through the generation of OVs. If the surface of the thermocatalysts possesses abundant surface hydroxyl (—OH) groups, the adsorption of FA on the thermocatalyst's surface can be enhanced to induce its subsequent degradation with the assistance of surface —OH. In addition, the formate intermediate species might be directly oxidized to CO2 and H2O by surface —OH groups (HCOO− + —OH → CO2 + H2O) during the FA oxidation process. Therefore, the surface —OH groups are considered the main factor for determining the rate of FA oxidation.The thermocatalytic oxidation of FA over transition‐metal based catalysts  was found to follow a Mars‐van Krevelen mechanism in which OVs can play a vital role during the degradation process.20 In 3The TM‐based thermocatalysts can be classified based on their composition (such as mono‐TM oxides (mono‐TMO), bi‐TMO, and composite transition metal oxide (TMO)‐based thermocatalysts) with regard to FA oxidation.3.1 Such thermocatalysts possess favorable pore structure, high surface area, good catalytic activity, high stability, and low cost, and they can be used for environmental remediation, Many approaches have been proposed for developing TM‐based catalysts such as sol‐gel, hydrothermal, precipitation, and template methods. As the preparation of TM‐based thermocatalysts has been discussed previously, interested readers may refer to the synthesis methods described elsewhere.A plethora of mono TMO‐based thermocatalysts  have been developed for the degradation of FA.27 Suc In particular, manganese oxide can exist in many different forms of crystals , which consist of [MnO6] octahedra to share corners and edges in their structure  to amplify the thermocatalytic activity. Water molecules can also help generate the consumed surface —OH groups (during the FA oxidation) through the reaction with surface active oxygen species .Monometallic TMO‐based thermocatalysts can exist in several crystallographic structures.19 In  For instance, the CeO2 spherical‐like aggregate of nanoplates exhibited excellent FA oxidation activity  with the aid of the abundant surface hydroxyl and oxygen groups  with a 2D sheet‐like morphology and high concentration of OVs was also observed to completely degrade 50 ppm FA at 310 °C. In another study, a 3D MnO2 structure with an interconnected network structure was developed through a freeze‐drying method. The 3D monolith network facilitated the diffusion of reactants onto the active sites of the catalyst. As such, the 3D MnO2 was able to fully destruct FA (100 ppm) at 80 °C under a gas hourly space velocity (GHSV) of 180 L g−1 h−1. In addition, Co3O4 nano‐rods were built to have a large surface area and a high content of surface Co3+. Such characteristics offered large numbers of oxygen anionic sites to promote the adsorption of H2O molecules. The adsorbed water molecules can further be dissociated to form ●OH active species for the oxidation of FA.The monometallic TMO‐based thermocatalysts can also be designed into various morphologies .33 ForTable2 activation and limited oxygen vacancies) that affect their FA degradation efficiency. For example, high temperature (>90 °C)  is often required to achieve complete FA oxidation  is due to their high surface oxygen mobility and OVs, which help promote the transportation of charges during redox cycles. In this regard, mono‐TMO‐based thermocatalysts such as cerium oxides are frequently bound with other TMOs . In such a case, the combination of two metal oxides helps synergize the overall thermocatalytic degradation capabilities of FA. For instance, cerium oxides in CeO2‐Co3O4 thermocatalysts offer high oxygen storage capacity, good redox performance, and high lattice oxygen activity, while Co3O4 provides strong oxidation activity with good electron transfer properties  can be achieved by the synergy between manganese and cobalt oxides in CoxMn3‐xO4 catalysts compared to each of their pristine forms, that is, MnOx (170 °C) or CoOx (180 °C). The synergy was obtained through a series of redox cycles including Mn4+/Mn3+ and Co3+/Co2+ involving the activation of oxygen molecule by Co and its transfer to Mn. Generally, the FA oxidation reaction over bi‐TMO‐based thermocatalyst  follows the formate decomposition route .Bi‐TMO‐based catalysts have been reported to exhibit superior catalytic activities for FA compared to their mono metallic counterparts.36 Bi‐] Table . Similar For instance, Ni0.8Co2.2 oxides synthesized by co‐precipitation method at 300 °C (Ni0.8Co2.2‐CP‐300) had the best FA catalytic activity  among all NixCo3‐x‐CP‐300 (x = 0–1) catalysts  spectrum  was found for a Co/(Co + Ce) atomic ratio of 0.95. Moreover, according to O2‐temperature‐programmed desorption (TPD) analysis, the large desorption peak of O2 in CeO2‐Co3O4 (ratio of 0.95) thermocatalyst also indicated an increased O2 adsorption capacity, which helped produce surface active oxygen. In contrast, the pure Co3O4 (containing no Ce) showed only 35% FA removal under the same temperature (80 °C). Such a difference could be attributed to the increase of surface adsorbed oxygen species as evidenced by H2‐ temperature programmed reduction analysis. However, at higher Co/(Co + Ce) atomic rations (>0.95) the phase separation resulted in lower FA catalytic activities for the catalyst. Likewise, when the ratio of Co:Mn was 3:1, MnxCo3‐xO4 possessed the highest amount of surface oxygen and exhibited the best catalytic activity against FA relative to other Co:Mn ratios . As such, MnxCo3‐xO4 exhibited the best catalytic performance to achieve 100% oxidation of 80 ppm FA at a lower temperature (75 °C) than that of its pure counterparts  and Co3O4 (105 °C)).The ratio of TMs in bi‐TMO‐based catalysts can significantly influence their catalytic activities against FA.39 Form Figure .[40]3.3 In addition, as other TMO forms  tend to agglomerate, their catalytic performance can be degraded. Therefore, various nanomaterials  with advanced properties  have been coupled with TMOs to fabricate TMO‐based composites. In addition, the utilization of various nanomaterials as matrix/substrate has also been recognized as an effective route to increase the FA oxidation performance over TMO‐based catalysts by imparting abundant surface oxygen vacancies.Despite the good performance of pure TMO‐based thermocatalysts , their application in powder or particle forms often gives rise to dust contamination, which complicates the process.41 In  To prepare the MnO2 modified activated carbon (MnO2/AC) spheres, the AC spheres were impregnated with Mn(NO3)2·4H2O solution and then dried at 105 °C for 24 h. The final product was obtained through a calcination process at 300 °C for 3.5 h under a nitrogen atmosphere. For the in situ approach, the TMOs can be synthesized in the presence of the matrix for the generation of stable composites. The synthesis approach has also influenced the thermocatalytic properties of TMO‐based composites. For example, the crystallinity of Co3O4 was lowered after the in situ growth of Co3O4 nanowires on the Ni foam surface. This approach helped introduce more oxygen vacancies for oxidation of FA. Accordingly, the reduced (r)‐Co3O4 NW@Ni foam composites possessed more active oxygen species with high mobility and reactivity with the aid of increased surface OVs. Such abundant surface OVs could lower O2 adsorption energy to make r‐Co3O4 NW@Ni foam composites easily adsorb and store more active oxygen species. As such, r‐Co3O4 NW@Ni foam composites exhibited the best FA oxidation performance with a much reduced T10  of 75 °C compared to the pristine Co3O4 (132 °C).The TMO‐based composite catalysts are generally formulated through solution mixing, calcination, and in situ approaches.45 To  As an example, CeO2 was anchored on the 3D hierarchical nitrogen‐doped porous carbon (3D‐CeO2@CN) and used for FA oxidation. In this case, CeO2 provided a high number of oxygen vacancies, abundant active surface oxygen, and high reducibility. Electron transfer from the N atoms of the surface CN further resulted in more oxygen defects and surface oxygen on CeO2 compared to pure CeO2. The 3D hierarchical structure of CN helped stabilize CeO2, facilitating the mass transfer of FA molecules. As such, the prepared 3D‐CeO2@CN was able to completely oxidize 90 ppm FA at 170 °C, which was about 130 °C lower than that of pure CeO2 catalysts at a GSHV of 100 L g−1 h−1. The surface functionalization of the matrix is regarded as an effective approach to enhance the compatibility of TMOs with nanomaterial matrices. For example, the carboxyl and hydroxyl functionalization of a polyethylene terephthalate (PET) surface  helped form a firmly attached thin MnOx layer on the surface of PET fibers. The synthesized MnOx/PET composite showed no agglomeration of powder MnOx catalysts with the reduced air pressure drop. In addition, the formulated composite was capable of degrading ≈94% of FA (0.6 mg m−3) at room temperature.Matrices including carbonaceous materials , polyester fibers, and cellulose fibers, generally show improved surface area and porosity in the synthesis of TMO‐based composite catalysts.46 As  In comparison to the pure MnO2, the 2D structure of graphene can facilitate the adsorption of FA and O2 molecules to expose more active sites for catalysis. Hybridized areas of graphene‐MnO2 provide important interfaces where the conducting graphene greatly accelerated the charge transfer between Mn4+ and Mn3+ species. As such, the catalytic performance of MnO2/graphene hybrids achieved completed conversion of FA (100 ppm) at 65 °C, which lasted up to 70 h. Likewise, the heterostructure of nanosheet MnO2 encapsulating N‐doped graphene spheres (GS) was deposited in a network‐like sponge (acting as support) to prepare 3D structure MnO2‐GS sponge composites for FA oxidation , which was far better than that of the pristine MnO2 nanosheets (95.3% conversion at 40 °C)  have also received interest because of their large surface reactive sites suitable for high catalytic efficiency. For instance, NCNT increased the number of structural defects with increases in electron transfer at the interfaces between NCNT and MnO2 of MnO2/NCNT composites. In addition, oxygen molecules were readily activated on NCNT through the formation of active superoxide species to promote the regeneration of MnO2. As such, the prepared MnO2/NCNT composites showed good activity and selectivity for FA oxidation.Graphene has also been employed to couple with TMOs for accelerating charge transport during redox processes against FA using its exceptional electron conductivity.26a Ins Figure .) Figure . The exc3O4 with sufficient Co3+ was also found to be the most effective plane for FA oxidation relative to other facets ). This is because Co3+ of Co3O4 (1 1 0) facets exhibited strong ability to dissociate FA (Co3+ + HCHO→ Co2+ + ●CHO + H+) with good affinity toward FA and O2 molecules. Moreover, the adsorbed O2 could also be readily converted into active oxygen species  on the Co3O4 (1 1 0) facets to increase FA catalytic activity.In another study, the (1 1 0) facet of Co(2 2 0)).13a Th4.2 As such, the modification of TMO‐based thermocatalysts with metal‐like alkali metal  and nitrogen is an effective option to enhance the formation of abundant OVs, to facilitate adsorbed O2 activation, and to promote the adsorption of FA molecules for the effective thermocatalysis of FA. For instance, the introduction of K+ ions over Co3O4 catalysts both increased the proportion of Co3+/Co2+ (0.42) relative to pure Co3O4 (0.30) and improved the number of OVs on the surface of modified Co3O4. This further boosted the oxidation ability of the modified thermocatalysts toward FA molecules. As a result, the K+ modified Co3O4 was able to completely convert 100 ppm FA to CO2 at a lower temperature  than the pure Co3O4 (120 °C). Interestingly, the isolated and localized K+ modification of layered MnO2 exhibited a distinct effect on FA removal for the generated thermocatalyst. As the isolated K+ was dissociated between layers via weak chemical bonds, the desorption of H2O molecules was restricted to hinder the FA catalytic process. In contrast, the coordination of localized K+ with oxygen atoms at the vacancy sites was a useful option to activate O2 with poor adsorption of H2O molecules. As such, the FA catalytic activity of the resulting thermocatalyst was enhanced in a localized K+ modified layer MnO2. Similar alkali‐promoted effects were also observed for noble metal supported catalysts . Recently, the nitrogen modified α‐MnO2 was reported to enhance the thermocatalytic decomposition of FA by achieving complete oxidation of 60 ppm FA under a GHSV of 90 L g−1 h−1 at 90 °C. In this respect, the interstitial sites of thermocatalysts (Mn‐N‐O or Mn‐O‐N) were found to be the most suitable sites for introducing non‐metal nitrogen on α‐MnO2. This was due to the potential of such interstitial sites for OV formation as well as FA/O2 adsorption/activation, which are beneficial for FA oxidation.The introduction of alkali metal/nitrogen has been reported for enhancing the catalytic activity of oxides materials by imparting abundant OVs and enhancing FA adsorption.53 As 4.3 The utilization of bases during the synthesis of TMO‐based catalysts promoted their FA catalytic oxidation properties through increases in their OH− content and surface area. As such, the effect of alkali precipitants  was investigated with regard to the thermal catalytic activity of Co3O4 catalysts toward gaseous FA. The Co3O4 synthesized using KHCO3 possessed abundant hydroxyl groups with a high ratio of Co3+/Co2+, exhibiting high catalytic activity against gaseous FA. Moreover, the BET specific areas and pore volumes of KHCO3 derived Co3O4 (97.9 m2 g−1/0.411 cm3 g−1) were higher than that of Co3O4 prepared by NH3·H2O (67.7 m2 g−1/0.135 cm3 g−1), KOH (54.8 m2 g−1/0.105 cm3 g−1), NH4HCO3 (95.4 m2 g−1/0.393 cm3 g−1), and K2CO3 (78.7 m2 g−1/0.337 cm3 g−1). Such larger specific areas and pore volumes of KHCO3 derived Co3O4 can also facile the FA transportation onto active sites for oxidation, thereby enhancing the FA oxidation process. The role of manganese ions as precursors on the crystal forms of palygorskite (PG)‐supported manganese oxides (MnOx/PG) was investigated in another study. Accordingly, the utilization of manganese acetate (MA) resulted in the formation of amorphous Mn2O3 and a crystalline Mn3O4 mixture. The utilization of manganese nitrate (MN) yielded β‐MnO2, while manganese sulfate (MS) formed a mixture of Mn3O4 and low crystalline γ‐MnO2. In contrast, low crystalline δ‐MnO2 was obtained when potassium permanganese (PP) was used as a manganese ionic source , high content of Mn4+ species, and increased lattice oxygen content. Consequently, the MnOx/PG‐PP exhibited the best catalytic activity  even after 600 min among all other MnOx/PG‐ catalysts (below 30% after 600 min)  Figure .[56c4.4 For instance, the post alkali (NaOH) treatment of NiCo2O4 endowed it with more hydroxyl groups and Co3+/Ni2+ content compared to the untreated NiCo2O4. In another study, birnessite‐type MnO2 treated by tetrabutylammonium hydroxide exhibited a lower apparent activation energy for FA oxidation than the pristine MnO2. This is because tetrabutylammonium hydroxide helped generate irregular surface pits on MnO2, which both provided larger specific surface areas and led to the formation of more high valent manganese species  and surface oxygen. As a result, the FA adsorption and oxidation properties of MnO2 were enhanced considerably. Likewise, ammonia was also utilized to control the OV formation onto δ‐MnOx supported by AC (δ‐MnOx/AC) for the enhancement of FA catalytic removal. Accordingly, the δ‐MnOx/AC‐N2 (ammonia used at 0.07 mol) had recorded higher ratio values for adsorbed oxygen (Oads)/lattice oxygen (Olatt) (0.71) and Mn3+/Mn4+ (1.25) than those of pristine δ‐MnOx/AC   was evident in electron paramagnetic resonance (EPR) spectra .Alkali/acid treatments can be used to improve the FA catalytic performance of TMO‐based catalysts through the introduction of —OH groups, defect sites, and OVs.58 Fora Figure . The abu In particular, the H2SO4 treatment of MnOx‐CeO2 catalysts showed higher surface area (310%) and stronger redox properties than their untreated counterparts. It was observed that the textural and redox properties of MnOx‐CeO2 samples were altered considerably when the Mn content was above 50%. The higher surface area of acid treated thermocatalysts may reflect the dissolution of Mn2+ ions by H2SO4 acid. In addition, acid treatment oxidized the manganese species to a higher oxidation state via Mn dismutation reaction (Mn3O4 + 4H+ = MnO2 + 2Mn2+ + 2H2O) improving the redox properties of catalysts. The extension of acid treatment time can also improve textual properties  of the ε‐MnO2 catalyst while developing interconnected macro‐mesoporous networks  as summarized in Tables 90 value is the temperature corresponding to 90% removal efficiency of FA gas over TMO‐based catalysts. The kinetic reaction rate  values at room temperature (RT) and at high temperature  are utilized to compare their catalytic performances.Quantitative evaluation of thermocatalytic performance of TMO‐based catalysts is important to properly assess their practical feasibility toward FA oxidation. In this regard, the catalytic performances of different types of TMO‐based catalysts were compared in terms of the key metrics  (r: 2.39E‐02 mmol mg−1 h−1) > C@MnO (r: 1.47E‐02 mmol mg−1 h−1) > birnessite manganese oxide catalysts (r: 1.25E‐02 mmol mg−1 h−1) > carbon sphere/MnO2 (r: 4.91E‐03 mmol mg−1 h−1) > MnO2/PEG (r: 4.75E‐02 mmol mg−1 h−1) (Table δ‐MnOx/AC‐N) is attributed to the following reasons. i) δ‐MnOx‐supported AC possessed a large content of oxygen vacancies for FA degradation. ii) The ammonia modification of δ‐MnOx/AC provided more basic sites for the adsorption of FA onto surface of δ‐MnOx/AC. iii) The surface oxygen vacancies (OVs) of δ‐MnOx can promote the adsorption and activation of O2 for forming active O, which makes FA oxidation more thermodynamically favorable.The TMO‐based catalyst systems showed high FA degradation rates at low temperature. For instance, the top five thermocatalysts performers, if sorted out in terms of r value, were ammonia modified 2/cellulose (r: 1.60E‐01 mmol mg−1 h−1) > graphene/MnO2 (r: 9.82E‐02 mmol mg−1 h−1) = alkali treated birnessite MnO2 (r: 9.82E‐02 mmol mg−1 h−1) > K modified MnO2 (r: 9.23E‐02 mmol mg−1 h−1) > 3D‐MnO2 (r: 7.36E‐02 mmol mg−1 h−1) > MnOx‐CeO2 (r: 7.12E‐02 mmol mg−1 h−1)  was approximately seven times larger than that of low temperature TMO‐based composites thermocatalysts . Such results might suggest that the high temperature was beneficial for maximizing e−/h+ in the TMO‐based composite thermocatalysts to promote the FA degradation through the generation of reactive oxygen species . In light of the above comparison, the FA catalytic performance of TMO‐based composite catalysts outperformed the other types TMO‐based catalysts  in terms of r values for both low/high temperature conditions as defined above.The high degradation efficiency of TMO‐based composites over other performers was also confirmed when FA degradation performance was evaluated for different TMO‐based thermocatalysts at high reaction temperature Table . The top62, and enhancement of FA adsorption. Finally, the quantitative performance evaluation of diverse applied TMO‐based catalysts was carried out based on their kinetic reaction rate values. The FA catalytic performance of the TMO‐based catalysts was evaluated using kinetic reaction rate as the suitable metric under both low and high reaction temperature conditions. Based on this evaluation, TMO‐based composites catalysts outperformed other types of TMO‐based catalysts  under all temperature conditions. As such, the TMO‐based composites catalysts appeared to be the more feasible option than mono‐ and bi‐TMO based catalysts for FA degradation. These observations may offer clear guidance for better design strategies for developing an effective thermocatalytic reactor for large scale applications.The present review was organized to report the recent scientific developments of TMO‐based thermocatalysts used for the degradation of gaseous FA. TMO‐based catalysts have drawn great attention because of their availability, thermal stabilities, abundance, and cost‐effectiveness. The mechanisms of FA removal over the TMO‐based catalysts have also been discussed. To provide an in‐depth discussion on applied TMO‐based catalysts for thermal degradation of gaseous FA, monometallic, bimetallic, and composite‐based TMO thermocatalysts were compared. Accordingly, the FA catalytic performance of the TMO‐based catalysts was significantly affected by a number of factors  that influence the generation of abundant TM cations, provide a high content of oxygen vacancies, activation of adsorbed OIt was observed that TMO composite thermocatalysts possessing functional matrices  exhibited superior FA degradation performance compared to pristine TMO catalysts. Therefore, we recommend investigating the effect of other advanced materials like metal organic frameworks  as matrices to further improve the catalytic performances of pure TMO‐based thermocatalysts.An ample understanding of the interactions between pollutants and TMO‐based catalysts may help researchers develop efficient catalysts. For this purpose, the use of computational simulations such as density function theory and molecular dynamic simulations may have to be considered.As most TMO‐based thermocatalysts are commonly prepared with a batch synthesis mode, they may suffer from some drawbacks . For the upscaled application of TMO‐baed thermocatalysts, the novel synthesis routes are to be developed with the proper control of properties .In most of the lab‐scale studies, thermocatalytic removal of FA on TMO‐based catalysts has been assessed under highly favorable reaction conditions , and large catalysts mass). However, FA is frequently present in the sub‐ppm or ppb level in the real indoor environment. To obtain more practical information for the removal of FA under real‐world conditions, the performances of TMO‐based catalysts should be evaluated properly to reflect the real‐world conditions .Based on the performance evaluation, the TMO‐based composite catalysts are found to have superior degradation efficiencies at elevated temperature. Hence, in the pursuit of the cost‐effective TMO‐based catalysts, it is desirable to develop some strategies  for their practical operation under low temperature  conditions.Despite the great potential of TMO‐based thermocatalysts for FA removal, more efforts are needed to expand their real‐word applications as explained below.The authors declare no conflict of interest.


Other transition metal ions also show the same rapid gelation, but not basic metal ions. Interestingly, although type I to IV collagen molecules show rapid gelation, other extracellular matrices  do not exhibit this phenomenon. Live imaging of colon cancer organoids in 3D culture indicates a collective migration property with modulating high elastic modulus, suggesting activation for metastasis progress. This technology will be useful as a new class of 3D culture for cells and organoids due to its facility for deep‐live observation and mechanical stiffness adjustment.Collagen is the most abundant protein in the human body and one of the main components of stromal tissues in tumors which have a high elastic modulus of over 50 kPa. Although collagen has been widely used as a cell culture scaffold for cancer cells, there have been limitations when attempting to fabricate a tough collagen gel with cells like a cancer stroma. Here, rapid gelation of a collagen solution within a few minutes by transition metal complexation is demonstrated. Type I collagen solution at neutral pH shows rapid gelation with a transparency of 81% and a high modulus of 1,781 kPa by mixing with K Specific gelation of collagen molecules for construction of transparent gels with controlling elastic modulus from tens to over mega pascals by transition metal complexation within a couple of minute is discovered for the first time. This technology has a great potential for 3D culture of cancer cells and organoids due to its deep‐live observation and easy adjusting of elastic modulus functions. Col is a main ECM component of connective  tissues including tumors. Recently, increase in ECM stiffness caused by increasing the secreted amount of Col has been found to be one of the strongest risk factors for cancer progression. For example, although normal breast has a stiffness of only 0.8 kPa, nodal metastasis rates of 396 breast cancer patients ranged from 7% for tumors with a mean stiffness of < 50 kPa to 41% for tumors with a mean stiffness of > 150 kPa. Moreover, increased the elastic modulus of colorectal cancer tissues of 106 patients showed a strong correlation with T stage, denoting the size and extent of the main tumor, and the median values of the elastic moduli at T1 and T4 stages were 2.81 (max. 3.96) and 13.8 (max. 68.0) kPa, respectively. The reason for these stiffness increases depending on cancer progression has been clarified as increasing Col secretion. Accordingly, cytocompatible control of the elastic modulus of Col hydrogels for the 3D culture of cancer cells has been keenly sought after.Extracellular matrices (ECMs) contain/possess/are made of key components for regulating the cell microenvironment, controlling cell functions such as adhesion, migration, growth, differentiation, cell‐cell interaction, protein secretion, and metabolism.1, 2 or 1‐ethyl‐1‐3‐(3‐dimethylaminopropyl) carbodiimide hydrochloride (EDC)‐N‐hydroxysuccinimide (NHS), an enzyme such as transglutaminase or peroxidase, and UV irradiation. However, the elastic modulus of the obtained gels is not high and the crosslinkers show cytotoxicity. Genipin has been reported as a cytocompatible crosslinker, but the obtained gel is stained blue by the reacted genipin derivatives. There have been a few reports on physical crosslinkers, but the elastic moduli of the obtained gels were low. To avoid the cytotoxicity issue of crosslinkers, a physical crosslinking method by neutralization and heating of a collagen acidic solution has been used as a standard method of 3D‐cell culture. Recently, Lama and co‐workers reported the fabrication of tough collagen gels by a method of concentrating collagen microparticles. Salameh et al. discovered transparent tough collagen materials by finding a narrow range of collagen concentration that inhibited light scattering. Although these reports are promising, their application in 3D‐cell culture is challenging. Tough Col hydrogels for 3D‐cell culture with over tens kPa modulus have generally not been constructed because of the low dissolving property of Col molecules into an aqueous solution at neutral pH condition for cell culture. Accordingly, Col hydrogels below 1.0 wt% concentration are commonly used for 3D culture of cancer cells so their elastic modulus is lower than 1.0 kPa. We recently reported a unique approach, “sedimentary culture”, using a collagen microfiber (CMF) to fabricate large‐scale engineered tissues. The millimeter‐sized tissues with high ECM density were easily obtained by centrifugation of cells and CMFs, but the maximum elastic modulus of the obtained tissues was ≈10 kPa, much lower than that of cancer at the late stage.To prepare Col hydrogels, covalent bond formation has been generally formed by using a chemical crosslinker such as glutaraldehyde (GA)9 or 1 3D‐cell culture in the transparent gels has yet to be achieved. Live observation at great depth is still a major challenge in Col gel culture.Another limitation of Col gel culture is observation because, although it is a standard method of 3D‐cell culture, the gels cannot be observed clearly at great depth even by confocal laser scanning microscopy (CLSM) due to their opaque color. Although transparent collagen gels have been reported in the field of cornea,23 3D‐cis‐diamminedichloroplatinum (II) (cisplatin), which is a well‐known anticancer agent, and a Col model peptide has been reported, there are no reports on crosslinking of natural Col fibers to rapidly form a gel by complexation with transition metal ions. The elastic modulus of the obtained transparent Col gels is widely controllable by varying the metal ion concentration up to 1.8 MPa. Furthermore, we found that live imaging of a patient‐derived colon cancer organoid showed activated morphology of the collective migration at 162 kPa, which is a higher modulus range than that of a colon cancer at the T4 stage. This rapid‐gelation technology for modulus‐controllable and transparent Col gels will provide a new class of 3D‐cell cultures for drug assessment and basic cancer biology.In this study, we demonstrate for the first time the rapid gelation of Col solutions by transition metal complexation. Transition metal ions form a complex between a nitrogen or oxygen atom of inter/intra Col molecules, whereas basic metal ions do not. Although interaction between reported,24 the2 which undergo a reversible sol‐gel transition from 4 °C to 37 °C under neutral pH conditions were used in this study to avoid the influence of pH on gelation because conventional type I collagen needs to be dissolved in an acidic solution at 4 °C and then both neutralization and heating are necessary for its gelation. When K2Pt(II)Cl4 solution was added to the CNF solution under a stirring condition, the solution quickly solidified (within 3 min) and the stirring bar was completely stopped Cl4 The obtained gels were completely transparent and stably maintained even after flipping the bottle. The elastic modulus of the obtained gels increased with increasing K2Pt(II)Cl4 and CNF concentrations and reached a plateau at 0.1 mM, independent of CNF concentration Cl4 condition. Even the lowest 0.2 wt% CNF condition yielded 162 kPa at 0.5 mM K2Pt(II)Cl4, a much higher value than that of the conventional 1.0 wt% Col hydrogels with a 1.0 kPa modulus prepared by neutralization and heating.Type I collagen nanofibers (CNFs)25 whiInterestingly, almost all water‐soluble transition metal ions such as group 10 (Ni(II), Pd(II), and Pt(II)/(IV)), group 11 (Cu(II) and Au(III)), and group 12 (Zn(II)) showed rapid gelation with a high elastic modulus Cl4 and CNF concentrations Cl4 also indicated the same triple‐helix CD spectra  spectra of the gels using HAu(III)Cla Figure 3a, the c2Pt(II)Cl4 in the same way as for Col I (Table 10) had a collagen triple‐helix structure with a positive peak at 225 nm in the CD spectra but did not show gelation probably due to its much lower molecular weight. DNA has a double‐helix structure but yielded the same results. Laminin and fibronectin are well known cell adhesive ECMs with the same high molecular weight as collagen, however gelation was not observed. Natural polysaccharides, heparin and alginate, and the synthetic polymer polyacrylate were also used because of their abundance of oxygen atoms that can be expected to form coordinate bonds with Pt ions. However, none of the molecules exhibited gelation in the same manner as collagen molecules. These results strongly suggest that this method reveals huge and rigid molecule selectivity of the collagen triple helix. The difference between DNA and the collagen triple helix is interesting because both have a rigid helical structure and DNA is well known for its ability to make coordinate bonds with cisplatin Pt(II). The triple helix of collagen is a more linear and packed molecule than DNA because it self‐assembles to form collagen fibrils. Thus, dense packing of the huge molecules is considered to be important.To understand the role of Col gelation, other commercially available types of collagen molecules such as type II, III, and IV from different animal species were mixed with Kn Pt(II).28 The2Pt(II)Cl4 were used as shown in Table 2PtCl4 solution, probably due to partially formed triple helical structure packing. To understand molecular entanglement, the viscoelasticity of both Col I and gelatin were measured at different concentrations  was performed. Col‐Pt gel prepared from K2Pt(II)Cl4 was incubated for 1 week at 4 °C to form the tough gel, and XAS experiments were conducted with fluorescent method. Focusing on the X‐ray absorption near edge structure (XANES) region, the absorption edge of the Col‐Pt gel appeared at 11 565 eV, which is ≈1 eV higher than that of K2Pt(II)Cl4 in PBS Cl4, and lower than that of K2Pt(IV)Cl6, indicating that the platinum atom in Col‐Pt gel possesses a square‐planer geometry which is typical for Pt(II) complexes. The extended X‐ray absorption fine structure (EXAFS) of Col‐Pt gel, K2Pt(II)Cl4, and K2Pt(IV)Cl6 were shown in Figure 2Pt(II)Cl4 and K2Pt(IV)Cl6, a peak was observed at 1.9 Å which corresponds the Pt–Cl scattering. Meanwhile, the peak was shifted to 1.6 Å after gel formation. This result indicates that the nearest elements of platinum were replaced by light elements, such as oxygen and nitrogen, showing a good agreement with the result of XANES data. To sum up, the platinum in the Col‐Pt gels has a square planar structure and is found to bind to nitrogen and oxygen atoms present in collagen. Hence, it is thought that the platinum plays a role in connecting the collagen fibers having triple‐helix structure to form a cross‐linked network as shown in Figure To confirm the local geometry around platinum atom in Col‐Pt gels, Pt LS Figure . Since t7/2 core level was used to evaluate the electric state. Although the peak for K2Pt(II)Cl4 powder was a single peak at 72.8 eV which was the same as in a previous report, two peaks at 71.8 and 73.0 eV were estimated by curve fitting, suggesting the exchange of ligands from Cl atoms to the other atoms . The peak splitting was also observed on N 1s XPS in CNF gels  and N or O atoms in collagen molecules, the X‐ray photoelectron spectroscopy (XPS) analysis was conducted Figures . The 4f ic state.29 Alts Figure . The peas Figure . The peas Figure . The res2Pt(II)Cl4 was calculated as 2.4 × 10−7 by the 12 µg of Pt(II) ions because Pt(II) ions form tetragonal coordinate bonds. Amino acids that could possibly be crosslinked in collagen molecules by Pt(II) ions are expected to be hydroxyproline, serine, tyrosine, threonine, histidine, lysine, hydroxylysine, asparagine, aspartic acid, glutamine, glutamic acid, methionine, and cysteine based on the results of XPS spectra indicating Pt–N and Pt–O formation  ions used for crosslinking to form the Col‐TM gels, inductively coupled plasma (ICP) spectroscopy was conducted Cl4 and 1.0 wt% CNF at the cleavage interfaces and the gels were then incubated at r.t. for 1 h Cl4, the adhesive phenomenon was not observed at all. However, in the solution with CNF, adhesion of the cleavage surfaces was clearly observed within 10 min, which might have been due to excess Pt(II) ions, as shown in Figure For the application of the Col‐TM gels, the self‐healing property at the cleavage surface was expected because of the noncovalent nature of the coordinate bond as previously reported.33 Unf2Pt(II)Cl4 or glutal aldehyde (GA) at varied concentration for 3 days, and then half maximal inhibitory concentration (IC50) of Pt(II) ions and GA was estimated  ions to JC‐011 and NHDFs were 680 and 310 µM respectively and these were 8.2 and 3.4‐fold lower cytotoxicities than those of GA, suggesting the potential of the Col‐TM gels for 3D cell cultures at high elastic modulus. To understand the effect of Pt(II) ions to cell growth, cell proliferation profiles of NHDFs were evaluated for 4 days in DMEM containing 10% FBS with 0.1 mM NaCl, K2Pt(II)Cl4 or GA, respectively  and normal human dermal fibroblasts (NHDFs) were cultured in dulbecco's modified eagle medium (DMEM) containing 10% fetal bovine serum (FBS) and Ky Figure . Pt(II)  The organoids prepared by CTOS method is useful for drug screening and personalized therapy because it retains the properties of cancer cells in the patient's original tumor. When CRC organoids were cultured in control soft collagen gels at 1 kPa, no morphological changes were observed and the cancer cells remained uniformly aligned. However, the 162 kPa Col‐TM gels clearly indicated a marked spike and cell migration toward the outer boundary, suggesting morphology of collective migration that is the process by which a group of cells moves together, without completely disrupting their cell‐cell contacts. To understand the stiffness effect in detail, the concentration of CNF and K2Pt(II)Cl4 solutions was varied for 3D culture of the organoids and the ratio of collective migration was estimated from the organoid morphology Cl4 solutions was adjusted to <1.0 mM to avoid cytotoxicity. When concentration of K2Pt(II)Cl4 solutions was increased, the ratio of the collective migration clearly increased regardless of Col concentration. This suggests that collective migration may be induced by the stiffening of the ECM scaffolds in 3D culture. The collective migration is important during morphogenesis, and in pathological processes such as wound healing and cancer cell invasion. While the molecular mechanisms of collective migration are becoming clear, analysis of the underlying mechanisms of collective migration in cancer is still at an early stage. The importance of mechanical cues in the collective migration has recently been studied, and in vivo experiments have revealed that tissue stiffening initiates the epithelial‐to‐mesenchymal transition that triggers collective migration. Although biomechanical methods such as 2D culture, micro‐patterning, 3D‐tube migration, and computational simulation have been reported extensively, there are no reports of collective migration initiated by stiffening the ECM scaffolds in 3D culture. The 3D culture in the Col‐TM gels with controllable environmental ECM stiffness has the potential to accelerate in vitro analysis of the underlying mechanism of collective migration in cancer.To understand the stiffness effect of the collagen‐gel matrix to the phenotype of cancer cells, patient‐derived colorectal cancer (CRC) organoids were sandwich‐cultured by the Col‐TM gels at a stiff (162 kPa) elastic modulus for 7 days and observed by CLSM in live conditions Figure . We prev34 The3 This study reveals the historical mechanism of complexation of transition metal ions with collagen fibers and shows a new application of collagen transparent gelation in the biomedical field. This stiffness‐controllable, rapid, and transparent gelation technique may be useful for a new class of biomaterials for tissue engineering and basic biology.We reported the rapid gelation of Col solutions by transition metal complexation with nitrogen or oxygen atoms of inter/intra Col molecules. It has been reported that chrome treatment improves the heat resistance of tanned leather, and the complexation of collagen fibrils and chromium was proposed as the mechanism, but the details remained unclear.40 Thi4Pepsin‐treated Type I collagen (Col I) sponge were kindly donated by NH Foods Ltd . The 50 mg of type I collagen sponge and 5 ml of PBS  were added into a 15 ml centrifuge tube . A φ8 mm blade was set in a homogenizer  and homogenized collagen sponge at a speed of 6  for 6 min. After homogenization, the collagen suspension was incubated at 4 °C for 1 day to dissolve collagen microfibers. After incubation, the solution was centrifuged  at 25 °C and 10 000 rpm for 3 min to remove bubbles and CNF solution. Other concentrations were prepared in the same manner by changing the amount of collagen sponge or adjusting the concentration after resuspension.2PtCl4: 206075‐1G, Sigma‐Aldrich, St. Louis, USA) in PBS to the sample tube . Then, they were mixed using a pipetter  for high viscous solution, 0.5 mM Pt(II)−0.5 wt% CNF gel was prepared at 4 °C for 1 day. For the following metal species, gels were prepared in the same manner and the concentration of each metal was adjusted by the amount of metal solution. Magnesium chloride , Calcium chloride , Barium (II) chloride , Iron (III) chloride , Cobalt (II) chloride , Iridium (IV) chloride , Nickel (II) chloride , Palladium (II) chloride , Cis‐diamine dichloroplatinum (II) (Pt(NH2)Cl2: 039–20093, WAKO, Osaka, Japan), Potassium hexachloroplatinum (IV) , Copper (II) chloride , Silver (I) nitrate , Gold nanoparticles , Gold (III) acid tetrahydrate , and Zinc (II) chloride .Five hundred µl of 0.5 wt% CNF solution and 20 µl of 12.5 mM potassium tetrachloroplatinum (II) acid  and then the elastic moduli of the obtained gels were measured after 1 day of incubation at 37 °C.Colorectal cancer surgical specimens were collected from patients who underwent surgery of primary and metastasized colorectal tumor. The patients submitted written informed consent for genetic and biological analyses, which were performed in accordance with the protocols approved by the institutional review board (IRB) of Japanese Foundation for Cancer Research (#2013‐1093).XAS measurements were performed at the BL‐9A of KEK under the approval of the Photon Factory Program Advisory Committee .The authors declare no conflict of interest.Supporting InformationClick here for additional data file.Supplementary Video S1Click here for additional data file.Supplementary Video S2Click here for additional data file.Supplementary Video S3Click here for additional data file.Supplementary Video S4Click here for additional data file.


Previous studies have demonstrated that mitogen‐activated protein kinase 11 (MAPK11) functions as an important point of integration in signalling transduction pathways and controlling endocellular processes, including viability of cells, differentiation, proliferation and apoptosis, through the sequence phosphorylation of the substrate protein Ser/Thr kinase protein cascade. Though MAPK 11 plays an important role in various tumours, especially in the invasive and metastatic processes, its expression and molecular mechanism in clear cell renal cell carcinoma (ccRCC) remain unclear. Runt‐associated transcription factor 2 (RUNX2), a main transcription factor for osteoblast differentiation and chondrocyte maturation, has high expression in a number of tumours. In this study, the mRNA and protein levels of targeted genes in ccRCC tissues and adjacent tissues are analysed using the Cancer Genome Atlas (TCGA) database and western blotting. The ccRCC cell proliferation was measured with colony formation and EdU assay, and cell migration was examined through transwell assay. The interactive behaviour between proteins was detected with immunoprecipitation. Half‐life period of RUNX2 protein was measured with cycloheximide chase assay. The results of the study indicated overexpression of MAPK11 and RUNX2 in ccRCC tissues and cell lines. MAPK11 and RUNX2 promoted the ccRCC cell proliferation and migration. Additionally, physical interaction took place between RUNX2 and P‐MAPK11, which functioned to sustain the stability of RUNX2 protein. The high expression of RUNX2 could neutralize the functional degradation in MAPK11. And the outcomes of the study suggest that the P‐MAPK11/RUNX2 axis may be used as a potential therapeutic target of ccRCC. The tri‐tiered activation structure is composed of MAPK Kinase Kinase (MAP3K), phosphorylation of a MAPK Kinase, dual phosphorylation of MAPK proteins.RUNX2 is a key transcription factor in osteogenesis, performs an important function in osteoblast differentiation.Studies indicate p38β is also related to a few transcription factors.Phosphorylation of MEF2A and MEF2C by p38β occurs in the transcriptional activation domain of MEF2 and stimulates the transcriptional activity in vivo.The results of this study showed that P‐MAPK11 and RUNX2 were overly expressed in ccRCC, and P‐MAPK11 could have physical interaction with RUNX2. In addition, P‐MAPK11 helps keep RUNX2 protein stable by blocking its pathway of ubiquitination degradation.22.1http://gepia.cancer‐pku.cn.The Cancer Genome Atlas (TCGA) was used for the analysis of the mRNA expression levels of particular genes in ccRCC tissues. Relevant information to TCGA is available on this website: 2.2The tissue samples were derived from 32 patients hospitalized at the First Hospital of China Medical University from November 2021 to February 2022. All tissues were histologically examined and diagnosed as ccRCC. The study won approval from the hospital and all patients signed a consent form.2.3All cells were incubated in strict accordance with the manufacturer's protocol. Different types of cells were cultivated in different culture mediums: RPMI‐1640 medium for human ccRCC cell lines, McCoy's 5A medium for CAKI‐1 cells, MEM medium for ACHN cells and DMEM/F12 medium for HK‐2 cells. Fetal bovine serum  was added to the mediums. All cell lines were obtained from Shanghai‐based Chinese Academy of Sciences and humidified incubated at 37°C in the required environment (95% air and 5% CO2). The cells at 80% confluence were treated with 1× PBS and trypsinized at 37°C for a requested duration to facilitate cell passage cultivation.Losmapimod (GW856553X) and cycloheximide (CHX) were bought from MCE (MedChemExpress). The cells were cultivated with Losmapimod (GW856553X) (20 nmol/L) for at least 24 h and then the protein extraction was performed. Following the treatment of cells with CHX (100 μg/mL), cellular protein was collected for immunoblotting analysis to judge the half‐life period of RUNX2.2.4RIPA buffer combined with protease inhibitor cocktail were applied to lysed tissues and cells, and a BCA protein assay kit was utilized for protein concentration detection. SDS‐PAGE  was employed for the separation of protein fractions. A Mini Transblot Cell device was selected to transfer resolved protein (350 mA) to PVDF membranes (0.2 μm). The membranes were blocked in a capsule with fat‐free milk (5%) at 37°C for 60 minutes and cultured at 4°C overnight with antibodies. The antibodies included anti‐RUNX2  and anti‐β‐tubulin  from Cell Signalling Technology, anti‐MAPK11  and anti‐P‐MAPK11  from Abmart. The membranes were afterwards cultured with the anti‐rabbit secondary antibody for 60 min at 37°C. Quantification of the immunoblots was performed using ImageJ software (version 1.51).2.5The separation of aggregate RNA was via TRIzol reagent and PrimeScriptTM RT reagent Kit from Takara Biotechnology Dalian and Takara in Japan. Reverse transcription process strictly followed the manufacturer's protocol. Quantitative PCR in real‐time was evaluated with the Swiss system of LightCycler™480 II Relative quantification was conducted using. The forward and reverse primers were as such: MAPK11 (5′‐ GGAGAACTGGTCGCCATCAAG ‐3′ and 5′‐ ACATTGGGTTCTCCTCGGACC ‐3′); RUNX2 (5’‐GCGCATTCCTCATCCCAGTA‐3′ and 5’‐GGCTCAGGTAGGAGGGGTAA‐3′); GAPDH (5’‐GGAGCGAGATCCCTCCAAAAT‐3′ and 5’‐GGCTGTTGTCATACTTCTCATGG‐3′).2.6Lentiviral‐based plasmids for MAPK11 knockdown and those for the overexpression of RUNX2 were synthesized by and purchased from Shanghai‐based GeneChem. MAPK11 knockdown stable cell lines were produced with the lentivirus vector containing short hairpin (sh) RNAs targeting MAPK11 (shRNA‐MAPK11) and negative control vector (shRNA‐Ctrl). Virosome that contains RUNX2 fragment in full length were deployed to produce LV‐RUNX2. The negative control vectors (LV‐Ctrl) were produced as well. Lentivirus infection technology was used to make stable cell lines and the infected cells were selected after treatment of the growth medium with 10 μg/mL puromycin (for no less than four passages).2.7g) for 20 min at 4°C for immunoprecipitation. Subsequently, the cell lysate was cultured with a mixture of antibodies composed of anti‐P‐MAPK11, anti‐RUNX2 and anti‐IgG overnight at 4°C in rotation. The antibodies were obtained from Abmart or Cell Signalling Technology, respectively. The pyrolysis solution underwent rotation for 4 h with magnetic beads in. After the beads were taken out with a magnetic rack, protein loading buffer (5×) was added and denatured at 100°C for 10 min. Western blotting was carried out subsequently.RIPA buffer combined with protease inhibitor cocktail were employed to lysed cells and centrifugation was performed with the cells . Then, cells treated with serum‐free medium (200‐μL) were cultured on the upper layer of the 24‐well plates, and the solution was  was infused into the lower layer. After 12‐h incubation in dark environment, crystal violet staining was performed for 10 min to the chamber. Cells in the upper layer were collected with buccal swabbing technique and observed for migrating effects using ImageJ.Serum starvation was performed for 24 h and the cells were then seeded in transwell inserts  for labelling. Culture medium was taken away followed by EdU staining after being labelled, the cells were treated for half an hour with click reaction cocktail in dark environment at normal room temperature in conformity with the manufacturer's guidelines. A fluorescent microscope (Olympus Corporation) was used for imaging.2.11p < 0.05 is statistically significant.Data analysis was performed with SPSS 21.0 software and GraphPad Prism version 9.0 . All the statistics were expressed as mean ± SD. The difference with 33.1The transcription levels of MAPK11 and RUNX2 in ccRCC from TCGA database were analysed drawing upon the Gene Expression Profiling Interactive Analysis. And it was revealed that the transcription level of MAPK11 and RUNX2 was upregulated in ccRCC Figure . P‐MAPK13.2MAPK11 is a gene that plays a vital part in tumour cell proliferation and migration.3.3Previous studies have been shown that MAPK14 depletion could result in a decline in RUNX2 protein level.3.4To determine whether the decline of RUNX2 protein was a consequence of that of P‐MAPK11, the study selected the inhibitor Losmapimod (GW856553X) of P‐MAPK11, which could downgrade the phosphorylation level of MAPK11 while maintaining the protein level in MAPK11.3.5In order to explore the role RUNX2 played in MAPK11/P‐MAPK11‐mediated cellular proliferating, migrating and invasive behaviour of ccRCC, the MAPK11 knockdown cells were transfected with virosome that contains RUNX2 in full length (shRNA‐MAPK11/LV‐RUNX2). As shown by migration assay Figure , the ove4This study found no increase in the level of transcription and translation of MAPK11 in ccRCC. Protein expression in P‐MAPK11 and RUNX2 were markedly elevated in ccRCC cell lines and tissues. Apart from that, the overexpression of P‐MAPK11 and RUNX2 in protein levels correlated with the Fuhrman grade of ccRCC tissues. The expression of P‐MAPK11 was closely linked to protein expression of RUNX2 in diseased tissues. This study indicated that MAPK11 and RUNX2 could be a biomarker and targeted therapy for ccRCC in clinical practice. P‐MAPK11 could have physical interaction with RUNX2, and hence promote cell proliferation and migration in the cancer in question. P‐MAPK11 demonstrated a regulatory function in the protein expression of RUNX2 and a stabilizing role in RUNX2 protein via ubiquitination degradation pathway.It has been reported that a variety of proteins and substrates could be phosphorylated by P38 MAPK including many transcription factors.RUNX2 could push osteoblast phenotype to change from immaturity to maturity and hence promote skeletal developmentIn conclusion, P‐MAPK11 could intermodulate with RUNX2 to facilitate the progress of ccRCC. Our research outcomes reveal that RUNX2 is a substrate of P‐MAPK11, and P‐MAPK11 could play a preventative role through binding. As a consequence, it is in need of exploring the regulatory mechanism of P‐MAPK11 in the ubiquitination pathway degradation of RUNX2.Xiandong Song: Conceptualization (lead); data curation (lead); formal analysis (lead); funding acquisition (lead); investigation (lead); methodology (lead); project administration (lead); resources ; software ; writing – original draft (lead); writing – review and editing (lead). Changming Dong: Supervision . Xiaojun Man: Validation ; visualization .No funding from any individual or organization is involved in this study.We declare that our work involves no conflict of interest of any nature with any individual or professional organization.