In this work, polyacrylonitrile (PAN) based carbon nanofibers (CNFs) were investigated for their CO2 separation capabilities using dynamic gas adsorption. The CNFs were prepared by electrospinning and subsequent carbonization at various temperatures ranging from 600 to 1000 °C. A thorough investigation of the CO2/N2 selectivity resulted in measured values of 53–106 at 1 bar and 25 °C on CNFs carbonized at 600, 700, or 800 °C. Moreover, the selectivity increased with lower measurement temperatures and lower CO2 partial pressures, reaching values up to 194. Further analysis revealed high long‐term stability with no degradation over 300 cycles and fast adsorption kinetics for CNFs carbonized at 600 or 700 °C. These excellent properties make PAN‐based CNFs carbonized at 600 or 700 °C promising candidates for the capture of CO2.The development of highly selective adsorbents for CO 2 separationCO: Dynamic gas adsorption makes it possible to study the adsorption of gas mixtures and analyze the separation of gases under conditions close to application. With this method, polyacrylonitrile‐based carbon nanofibers are assessed as adsorbent for carbon capture. Unlike other carbon materials, they exhibit an excellent CO2/N2 selectivity while featuring high stability as well as a simple and scalable synthesis procedure. The latter can include CO2 separation from either flue gas or ambient air . However, in comparison to air (>400 ppm),2 content in typical flue gases (3–15 % CO2)2 separation from flue gas seems more practical.The emission of CO2 from various gas streams.Currently, amine scrubbing is the only process applied on an industrial scale to remove CO2 from flue gas by adsorption processes is considered as an interesting alternative.[2 is only weakly bound via physi‐ rather than chemisorption, leading to a reduced energy demand for sorbent regeneration as compared to amine scrubbing.Among other technologies, the separation of COernative.8, 9 P2 separation should feature a high working capacity, fast sorption kinetics and mass transfer, an energy‐efficient regeneration procedure, and low production costs.2 is a crucial parameter as it has a significant impact on the process costs.2/N2 selectivity is most important as N2 is the main component in air and in flue gas.For an efficient process the sorbent for CO2 separation like zeolites,Until now, no sorbent was able to sufficiently incorporate all the material properties mentioned above. The adsorbents that are commonly investigated for CO2/N2 selectivity as predicted by calculations based on the ideal adsorbed solution theory (IAST) are as follows: Abdelmoaty et al. showed that porous carbon synthesized from a mixture of pyrazole and KOH may feature an IAST selectivity of up to 128 .2, 323 K) for hierarchical N‐doped carbon based on a polypyrrole precursor.2, 323 K).Most recent reports regarding modified carbon materials that exhibit high CO2/N2‐IAST selectivity of up to 350 .In a recent study of ours, it was shown that non‐modified electrospun PAN‐based carbon nanofibers (CNFs) may exhibit a CO2/N2 selectivity, often only IAST values are reported. This simple method calculates the adsorption data of gas mixtures from the corresponding and often readily available pure‐component adsorption isotherms fitted with a suitable isotherm model.[As described above, with respect to the COrm model.26, 27Therefore, measured selectivity values are more reliable and can be obtained by dynamic gas adsorption. For this technique, the gas mixture is directly applied on the adsorbent by streaming a constant gas flow over the adsorbent in a fixed bed column. From the breakthrough curve of each adsorptive the adsorbed amount, the selectivity and various other parameters can be deduced, highlighting the advantages of this method.28, 292/N2 gas mixtures. For this purpose, the selectivity at 0 °C was measured and compared to the IAST calculations. To investigate the separation capabilities of the material at conditions more typical for flue gas, the selectivity was thoroughly measured at additional temperatures as well as different pressures and gas compositions. In addition, the breakthrough and desorption curves are analyzed with regard to the sorption kinetics since fast mass transfer and adsorption kinetics are vital for an efficient separation process. For a comparison with N2 and CO2 isotherms obtained by static gas adsorption, N2 and CO2 isotherms were acquired by dynamic adsorption as well. Additionally, the isotherm data were complemented by high‐pressure isotherms up to a partial pressure of 18 bar.With this work, we seek to elucidate the agreement of the IAST results previously reported for PAN‐based CNFs2/N2 separation potential of PAN‐based carbon nanofibers (CNFs) carbonized at temperatures ranging from 600 to 1000 °C, at first, pure component sorption isotherms of CO2 and N2 are discussed. The sorption isotherms of CO2 and N2 are shown in Figure To study the CO2 adsorption, the CNFs carbonized in a temperature range from 600 to 800 °C exhibit concave isotherms with a high CO2 adsorption capacity of up to 2.3 mmol g−1 adsorbed CO2 at 1.0 bar. The CO2 uptake is already high at low pressures, which is attributed to a large amount of ultramicropores.2 adsorption capacity of CNFs carbonized at 900 and 1000 °C is drastically reduced, which was explained previously by a size reduction of the ultramicropores due to an increasing carbonization temperature. As a consequence, the ultramicropores become partially inaccessible for CO2 at 900 °C and completely inaccessible at 1000 °C. A correlation with the amount of surface functional groups was not apparent.Briefly summarizing the results of the static CO2 isotherms acquired using the dynamic gas adsorption technique are shown. Again, the samples carbonized at 600, 700, and 800 °C exhibit concave isotherms with a high CO2 adsorption capacity of up to 2.1 mmol g−1 at 1 bar. In contrast, the sample carbonized at 900 °C exhibits a significantly lower CO2 adsorption capacity of 0.84 mmol g−1 at 1 bar, and the sample carbonized at 1000 °C yields a linear isotherm with an even lower CO2 adsorption capacity of 0.07 mmol g−1 at 1 bar.In Figure 2 isotherms in Figure 2 adsorption capacity of the samples carbonized at 800 °C or below is in good agreement with each other as the deviations between both methods amount to less than 10 % and are within experimental deviation. However, CNFs prepared at higher carbonization temperature exhibit a reduced adsorption capacity under dynamic flow conditions. For the sample carbonized at 900 °C, the deviation in capacity between the dynamic and static measurement equals 35 % at 1.0 bar and increases for the sample carbonized at 1000 °C to 75 %. A deviation from the statically measured loading usually indicates slow adsorption kinetics or diffusion, because the equilibrium is not attained within the breakthrough time.A comparison of the static and dynamic CO2 adsorption in Figure 2 adsorption capacities at 1 bar of samples carbonized below 900 °C reach about 0.35 to 0.40 mmol g−1, the adsorption capacity is only 0.16 and 0.008 mmol g−1 for the CNFs carbonized at 900 and 1000 °C, respectively.Summarizing the results for the static N2 adsorption, the reduction of the ultramicropore size might explain the significant drop of the N2 adsorption capacity for CNFs carbonized at 900 and 1000 °C as compared to the CNFs carbonized at 800 °C, since CO2 and N2 are of similar size according to Breck2 the affinity of the fibers towards N2 appears to be much lower than towards CO2, which might stem from the reduced polarizability and quadrupole moment of N2 compared to CO22 compared to CO2 as their evaporation temperatures deviate significantly  are relevant as well. Therefore, high‐pressure adsorption isotherms up to a partial pressure of 18 bar were recorded using dynamic gas adsorption. Figure  bar are 2 above 1 bar has nearly no beneficial influence on the working capacity. Thus, depending on the CO2 content in the gas mixture, this material might be most interesting for VSA or VPSA applications.For the application in a PSA process this means increasing the partial pressure of CO2 on the CNFs, since the shape of a breakthrough contains information about the adsorption and diffusion processes taking place in a fixed bed column.2 in He at 0 °C and 5 bar. The shape of the breakthrough curves and their corresponding desorption curves are discussed qualitatively. For a quantitative assessment, the breakthrough curves were modeled with the linear driving force approach using the commercial software 3PSim.kLDF that is a measure for the rate of adsorption on the corresponding material. To obtain the mass transfer coefficient kLDF for each sample, the modeled breakthrough curve was fitted to the experimental breakthrough curve by varying kLDF. For the modeling the following assumptions are made:In this section, breakthrough curves are analyzed to obtain insight into the sorption kinetics of CO    Heat effects are neglected .The gas phase obeys the ideal gas law.There is no pressure drop along the column.The flow behavior can be described as a dispersed plug flow.The radial dispersion is negligible.The column is uniformly packed.   A description of the applied formula is given in the Supporting Information. In addition, Table C/C0 versus time plots. For all samples a good agreement of the model with the experimental shape of the breakthrough curve is observed. A qualitative comparison of the shape between the individual samples reveals a clear difference. For CNFs carbonized at 600, 700, and 800 °C steep and focused breakthrough curves are found, whereas a further increase of the carbonization temperature to 900 °C results in a disperse and asymmetric curve as shown in Figure 2 isotherms of the CNFs carbonized between 600 and 900 °C all have concave isotherms  to 900 °C (0.55 min−1) as the mass transfer coefficient decreases almost one order of magnitude, highlighting the strong kinetic limitations of this sample and resulting in the disperse breakthrough curve in Figure 2 isotherm in Figure 2 uptake at lower flowrates, illustrating the slow kinetics of this sample.The mass transfer coefficient 2 adsorption measurements were fitted using a pseudo‐first‐order (PFO) kinetic model that is similar to the linear driving force approach in this work. The mass transfer coefficient kPFO obtained from that work  is shown in Figure kLDF from this work . As observed for kLDF, kPFO decreases with increasing carbonization temperature and exhibits a significant decline from 800 (3.24 min−1) to 900 °C (0.542 min−1) by six times. In addition, the values of both methods match each other reasonably well considering the different experimental origins, thus yielding a good agreement of both approaches.In our previous work, the equilibration curves of static COAll in all, the findings are consistent with the pore model for the investigated CNFs.2 as compared to most of the other samples. During the long‐term testing more than 300 cycles of CO2 adsorption and desorption were performed, which is shown in Figure 2 in N2 at 25 °C and 10 bar, whereas the desorption was carried out at 1.0 bar with 100 % N2. As a result of this investigation, it can be seen that the adsorption capacity is largely stable and as high as 1.14±0.03 mmol g−1 during almost the whole experiment. Only the first cycle exhibits a slightly higher adsorption capacity (1.29 mmol g−1), prior to which the sample was degassed at 250 °C, indicating that 0.15 mmol g−1 of CO2 do not desorb during the following regeneration steps with N2 at 25 °C.Beyond fundamental investigations, the long‐term stability of the analyzed CNFs was investigated, too Figure . For theAll in all, the stable adsorption capacity over a long period indicates a high stability of the material itself, which is a significant advantage of carbon materials reported in literature.9, 42 2/N2 selectivity of the investigated CNFs, breakthrough experiments with CO2 and N2 as adsorptives and helium as non‐adsorbing carrier gas were performed. The breakthrough curves are shown exemplarily in Figure 2 and 45 % N2 in helium on CNFs carbonized at 700 °C . In the diagram, the amount of adsorbed gas is proportional to the integral between the breakthrough curve of the sample and the blank run. For CO2, there is one large integral up to 8 min corresponding to the adsorption of CO2 . For N2, two different integrals are apparent : The first integral from 0.3 to 1.0 min corresponds to the initial adsorption of N2, whereas the second integral from 1.0 to 7.5 min is attributed to a roll‐up effect, where the N2 concentration rises over the inlet N2 concentration. This roll‐up of N2 is attributed to the absence of CO2 at the outlet as well as the desorption of N2 caused by the displacement by CO2.When discussing the separation capabilities of a material, the selectivity is one of the most crucial properties.2 and CO2 sorption in Figure 2 is adsorbed in significantly higher quantities than N2, although its partial pressure is nine times lower than the partial pressure of N2. This already indicates a high selectivity of the CNFs towards CO2. However, the high selectivity towards CO2 and the corresponding low N2 uptake can induce some challenges in order to precisely quantify the amount of the light component, here N2, as reported by Wilkins et al.[2 (7.5 min) and N2 (1.0 min) the displaced amount of N2 is eluted over a relatively long period of time (6.5 min) and, therefore, results in a high inaccuracy. A more reliable method to quantify the amount of adsorbed N2 as proposed by Wilkins et al.[2 by integration of the desorption curve. From the amount of adsorbed CO2 obtained from the adsorption and the amount of adsorbed N2 quantified from the desorption curve, the selectivity S can be calculated according to Equation A qualitative comparison of the integrals corresponding to the Nns et al.43, 44 al.[2 7. min and ) and N2 .0 min thiq denotes the adsorbed amount of component i, and iy denotes the volume fraction of component i in the gas phase. The results for the corresponding analysis are shown in Figure 2 and N2 partial pressure. In addition, Figure 2/N2 ratio on the selectivity. The two rows in Figure 2/N2 ratios in the gas phase, 5 : 95 on the top  and 10 : 90 on the bottom , while each column was obtained at different temperatures, 0 °C on the left , 25 °C in the middle , and 50 °C on the right  .Here, A look at the results in Figure 2/N2 shows only insignificant differences. Curve shapes and the selectivity values resemble each other at the same conditions. However, a closer look reveals that a smaller CO2 fraction slightly enhances the selectivity at an adsorptive pressure of 0.25 bar as depicted in Figure S8. For example, the selectivity at 25 °C and 0.25 bar increases from around 115 at 10 % CO2 .In addition, in Figure 2 and N2 isotherms of the samples carbonized at 600, 700, and 800 °C. A comparison of the amount of CO2 and N2 adsorbed on these samples shown in Figures 2. Among these three samples, the sample prepared at 600 °C adsorbs the least N2, whereas the sample prepared at 800 °C adsorbs the most N2. In consideration of the almost identical pure component N2 isotherms of these samples . Thus, the predicted selectivity gradually decreases with increasing carbonization temperature as well. As discussed above, the higher initial slope is likely to be a result of the higher nitrogen content in the CNFs.A common method to predict selectivity values from pure component isotherms are IAST calculations. The result of IAST calculations based on the isotherms shown in Figure 2 uptake as well as a lower N2 uptake predicted by the IAST compared to the dynamic gas adsorption measurement. This is a known issue of IAST in literature.[2 isotherms.A quantitative analysis reveals that, although the values obtained from the measurements and the IAST calculations are in the same order of magnitude, the prediction by IAST overestimates the selectivity values by a factor of 1.5 to 2.2 for the CNFs carbonized at 600, 700, and 800 °C. As illustrated in Figures S11 and S12, this can be attributed to a higher COterature.19, 482/N2 selectivity values of several carbonaceous materials reported in literature for comparison. Usually measurements at 1.0 bar and 25 °C with CO2 fractions from 10 to 16.7 %, which are close to the CO2 fraction in flue gas, are reported,[2/N2 selectivity of 4 to 10.[Table reported,49, 502) increasing the selectivity by one order of magnitude compared to the untreated carbon materials. At lower overall pressures, the selectivity for this sample is determined to be even higher and can be as high as 194, outperforming the reported carbon materials. Only carbon materials that have been intensely modified, such as the activated carbon Laponite® composite (114.3),The sample prepared at 600 °C even reaches a selectivity of 106 under these conditions  were prepared at different carbonization temperatures ranging from 600 to 1000 °C, and the resulting fibers were analyzed with respect to CO2 breakthrough curves was observed, indicating a slow adsorption rate due to kinetic limitations, which was confirmed by modeling of the breakthrough curves. In contrast, the samples carbonized at lower temperatures do not exhibit kinetic limitations due to a better accessibility of the ultramicropores. Thus, the samples carbonized at 600 and 700 °C are preferable for practical applications such as CO2 removal from flue gas due to their fast adsorption and excellent selectivity. Moreover, the CNFs carbonized at 700 °C were tested in a long‐term experiment of more than 300 adsorption and desorption cycles and did not show any degradation, practically indicating the excellent stability of the material.For the samples carbonized at 900 °C a flattening of the CO−1, BOC Science, USA) was dissolved in N,N‐dimethylformamide  by stirring for two days at room temperature. Afterwards, the solution was electrospun using an electrospinning device equipped with a rotating drum collector and a climate chamber . The tip‐collector distance was 15 cm, the applied voltage was 25 kV, and the flowrate of the polymer solution was set to 40 μL min−1. The drum collector had a diameter of 6 cm and rotated at a speed of 1500 rpm. The nozzle with a diameter of 0.8 mm moved laterally with respect to the drum collector in a range of ±60 mm from the central position at a speed of 20 mm s−1 and a turn delay of 500 ms. The atmosphere was kept constant at 25 °C and 30 % relative humidity. After 6 h of continuous electrospinning, a PAN‐nanofiber mat was obtained and the polymer chains within the PAN‐nanofibers were crosslinked at 250 °C in air for 12 h in a drying furnace. Subsequently, carbonization was carried out in a tube furnace at various temperatures ranging from 600 to 1000 °C under argon atmosphere. Each sample was heated with 300 K h−1 to the desired temperature, which was held for 3 h. To densify the material, about 2 g of the fiber mats was pressed to obtain a pellet of carbon powder using a hydraulic press . Afterwards, the pellet was chopped into 1–2 mm large pieces that were used for the gas adsorption experiments.All chemicals were used as received without further purification. To obtain PAN‐based CNFs, 10 wt% of PAN  and N2  were measured on a 3P micro 300 . 0.3–0.6 g of the pressed CNFs was filled into the measurement cell and degassed for 24 h under vacuum at 150 °C. After degassing the sample mass was quantified again. The isotherms were measured at 273 K.Static isotherms of CO2 and N2 with the ratios of 5 : 95 and 10 : 90 were performed with the commercial software 3PSim . As input for the calculations Tóth fits of the static CO2 and N2 isotherms . Details on the setup can be found in Figure S13. Binary gas mixtures were analyzed with a thermal conductivity detector. Ternary gas mixtures were analyzed using a mass spectrometer . About 1.3–1.5 g of CNFs was filled into the measurement column  until a fill level of 8–10 cm was reached. Afterwards, the sample was pre‐treated at 300 °C under 20 mL mincin=cout) was observed. For the evaluation of all measurements, the variation of the outlet gas stream due to adsorption was accounted for using helium as an internal standard. More details on this procedure are given in the Supporting Information. The adsorption capacity for all measurements was obtained subtracting the integrated value of a blank run from the integrated value of the sample run. A visualization of the evaluation procedure is shown in Figure S14. The blank run was performed using glass beads  with a diameter of 0.4 to 0.6 mm as a filling material to match the void volume of the blank run with the void volume of the sample run. The result of the blank run was averaged over three measurements.The analysis of the breakthrough was done using the mixSorb Manager . Further information on the analysis is provided in the Supporting Information. Each breakthrough curve was integrated from the start of the experiment until no further change in the gas composition  were measured with helium  as a carrier gas at 273 K and 10.0 bar. The total flow rate was set to 50 mL min−1. For the first breakthrough curve the adsorptive fraction (v/v) equaled 1 %. After saturation was reached, an additional isotherm point was recorded by increasing the CO2 fraction by 1 %. This procedure was performed for subsequent isotherm points until a fraction of 10 % was reached. High‐pressure isotherms of CO2 and N2  were recorded in a similar manner. Unlike before, these measurements were performed at a total pressure of 45 bar and the adsorptive fraction was increased in 5 % steps up to 40 % resulting in a CO2 partial pressure ranging from 2.25 to 18 bar. Dynamic isotherms of N2 up to 1 bar were acquired measuring five separate breakthrough curves from 0 % to 4, 8, 12, 16, and 20 % N2 in He, respectively. Between each breakthrough experiment, the sample was regenerated by 20 mL min−1 He and vacuum at 273 K for 60 min. The breakthrough curves of these measurements are shown in Figures S15 to S18.Dynamic isotherms of COModeling of the breakthrough curves was carried out using the commercial software 3P Sim (3P Instruments GmbH). Details on the applied formulas can be found in the Supporting Information.2/N2 adsorption was measured at 5 bar and a flow rate of 100 mL min−1 with helium as the carrier gas. The investigated gas compositions are given in Table S3. After each breakthrough experiment, the desorption curve was recorded under the same conditions but with CO2 and N2 turned off. The desorption curves were measured and integrated over 120 min. Afterwards, the sample was further regenerated applying vacuum and 20 mL min−1 He for 30 min. The breakthrough curves are shown in the Supporting Information.The selectivity of the CO2 in N2 at 25 °C and a total pressure of 10 bar were used for adsorption, whereas desorption was carried out at a pressure of 1 bar with pure N2. In both cases, the flow rate was 50 mL min−1. A complete list of the conditions of the dynamic measurements is given in the Supporting Information in Tables S3 and S4.The long‐term sorption performance was tested for CNFs carbonized at 700 °C (0.3 g) by consecutive ad‐ and desorption steps. For this, over 300 cycles of adsorption and desorption were performed. 5 % COThe authors have patent #WO2020249441A1 issued to Forschungszentrum Jülich.1As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.Supporting InformationClick here for additional data file.


The nano‐ring is formed via self‐assembly from metal precursors in aqueous acidic medium. The compound (NH4)16[(BiPMo11O39)4] ⋅ 22 H2O; 4Bi4Mo44), Raman spectroscopy, matrix‐assisted laser desorption/ionisation‐time of flight mass spectrometry (MALDI‐TOF), and thermogravimetry/differential scanning calorimetry mass spectrometry (TG‐DSC‐MS). The formation of the nano‐ring in solution was studied by time‐resolved in situ small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo−K and the Bi−L3 edge indicating a two‐step process consisting of condensation of Mo‐anions and formation of Bi−Mo‐units followed by a rapid self‐assembly to yield the final tetrameric ring structure.A new hetero‐bimetallic polyoxometalate (POM) nano‐ring was synthesized in a one‐pot procedure. The structure consists of tetrameric units containing four bismuth‐substituted monolacunary Keggin anions including distorted [BiO Formation of a tetrameric heteropolyoxometalate ring of bismuth‐containing lacunary phosphomolybdate clusters. During addition of the bismuth nitrate solution to an AHM solution, a white precipitate was immediately formed. After addition of phosphoric acid, the colour of the slurry changed gradually from bright yellow to orange. The precipitate was subsequently filtered and washed in water. From this solution suitable crystals were derived upon evaporation of the solvent in air.The heteropolyoxometalate  of the product are in good agreement with the simulated powder pattern calculated from the crystal structure.1 is assembled by four monolacunary Keggin anions [PMo11O39]7− connected via four Bi3+ cations. The bismuth atoms substitute one Mo position in an ideal α‐Keggin anion ([α‐PMo11O39Bi]4−) and connect to four MoO6 octahedra of an adjacent Keggin ion. Each Bi3+ is coordinated in an 8‐fold coordination with square‐antiprismatic geometry. The resulting ring structure adopts a Ch2 symmetry and consists of a ring with a size of 2.3×2.3×1.4 nm3. This ring structure is surrounded by water and ammonium molecules  appears at 963 cm−1 indicating the increased condensation degree of the molybdate ions. Additionally, the following bands are observed: 946, 907, 836, and 360 cm−1 which allow an assignment to [Mo8O26]4− anions  cannot be completely excluded.−1, which is in agreement with the formation of β‐[Mo8O26]4−.−1.While the most prominent band at 963 cmThe formation mechanism of the Keggin ring in solution was followed using a TRIS approach which comprises EXAFS and SAXS/WAXS experiments.3 edge (13 419 eV) were performed in a custom‐made in situ cell allowing monitoring of typical beaker chemistry synthesis under heating with continuous stirring  oxidation state.3‐edge measurements (bismuth nitrate solution). The EXAFS curves of the initial Mo‐containing solution can be fitted with the structure of ammonium heptamolybdate (NH4)64(NO3) ⋅ 6 H2O.3+ ions are only coordinated by oxygen in a (6+1) coordination sphere.EXAFS measurements at the Mo−K edge (20 000 eV) and the Bi−L8O26]4− polyoxomolybdate anions, whereby each [Mo8O26]4− anion coordinates to Bi3 after adding the H3PO4 solution and upon heating (to 50 °C). the precipitate becomes more homogeneous. In this period a significant change in the Mo coordination is observed. The EXAFS spectra change to the characteristic spectrum of the final ring structure. EXAFS data collected from the final product in solution and in solid‐state can be both fitted with the measured single‐crystal structure.After addition of the Bi‐solution a white, cloudy precipitate consisting of large inhomogeneous flakes is obtained and a change in the Mo‐spectrum is observed. The decrease in the pH value (pH=2.3) leads to a condensation of the molybdate anions to 6− present in the solution. After injection of the bismuth nitrate solution the SAXS signal changes within a single data frame of 10 s. The form factor changes and in addition a 100‐fold increase in intensity at low‐q is observed 16)(H2O)37, PDF 73‐2295, in our case NH4+ is the counter ion) and Bi6O5(OH)3(NO3)5(H2O)3 (PDF 70‐1226). After the injection of H3PO4, the process is highly exothermic according to the T‐profile. During the reaction of the H3PO4, the crystalline phase gradually dissolves up to approx. 4500 s exist in equilibrium in solution depending on the pH value (P is in accordance with the ex situ and in situ data: i) Formation of the lacunary Keggin ion via bismuth insertion and ii) ring closure of the tetrameric ring linking four [α‐PBiMo11O39]4− together in a final self‐assembly step. Most probably, the substitution of a Mo6+ cation by the lower valent Bi3+ cation leads to an increase in the basicity of the lacunary Keggin ions and thus a tendency to oligomerize through intermolecular Bi−O…O−Mo contacts). MALDI‐TOF data  indicate that dimeric structures are formed in between.The following mechanism of formation of 2SiW10O39}4]24−.4Bi4Mo44) analysis and temperature‐resolved XRD . The lacunary anion complex is destroyed above 250 °C forming a crystalline cubic phase containing intact Keggin ions ((NH4)3PO4(MoO3)12 ⋅ 4 H2O). This phase decomposes above 450 °C under formation of BiPO4 and MoO3.Alternatively a dimer of dimers mechanism could also lead to a tetrameric structure. However, the final step is difficult to access as can be assumed from both Raman and EXAFS data indicating that the annealed samples already greatly resemble the final structure. Similar conclusions have been drawn by Kortz et al. for tetrameric ring structure [{β‐Ti3+‐substituted polyoxomolybdates are prone to form larger cyclic entities. More broadly, our study shows that the incorporation of Bi can offer access to larger ring structures.In summary, we report on the synthesis, structural characterization, and formation mechanism of a new polyoxometalate ring structure composed of lacunary Keggin ions connected via Bi cations. The structure represents the first example of a tetrameric bismuth‐molybdate nano‐ring. We investigated the formation process using time‐resolved in situ EXAFS and in situ SAXS/WAXS complemented by Raman spectroscopy and MALDI‐TOF spectroscopy. The formation of the tetrameric anion under mild conditions indicates that BiSee Supporting Information for full details of synthesis, characterisation methods and physical measurements.P4Bi4Mo44)Deposition Number(s) 2124803 (for  contain(s) the supplementary crystallographic data for this paper. These data are provided free of charge by the joint Cambridge Crystallographic Data Centre and Fachinformationszentrum Karlsruhe Access Structures service www.ccdc.cam.ac.uk/structures.The authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.Supporting InformationClick here for additional data file.


We thank Tung and Ma for their interest in our recently published paper presenting correlations between 4β-hydroxycholesterol (4βOHC) concentrations and three other CYP3A metrics, including intestinal and hepatic CYP3A4 protein concentrations and microsomal activity, and in vivo midazolam pharmacokinetics in primarily a population with obesity, to assess 4βOHC’s potential as an endogenous CYP3A4 biomarker . In the First, we agree that correlation coefficients have certain limitations and that predictive performance via assessment of bias and precision should be included in the validation of phenotyping biomarkers and/or probe drugs. However, the nature of our study was exploratory, and as such, correlations analyses were performed, which are useful to assess associations between variables. One of the major strengths of our study was the ability to investigate the relationship between 4βOHC concentrations and both CYP3A4 protein expression and microsomal activity in paired liver and jejunum samples. This provides novel information, which is lacking in the literature and is actually suggested to be one of several validation criteria for phenotyping metrics .Indeed, we do not believe that the results presented in our study may lead to inappropriate use of 4βOHC as a biomarker, but rather provide increased knowledge on when or how 4βOHC may be utilized as a CYP3A4 biomarker. Tung and Ma claim that there have been concerns regarding the utility of 4βOHC as a CYP3A4 biomarker, e.g., due to the uncertainty with regard to the intestinal contribution in 4βOHC formation and systemic level [Tung and Ma comment on the lack of correlation between 4βOHC and systemic midazolam clearance as an argument against the value of 4βOHC as CYP3A4 biomarker. While midazolam is considered to be the gold standard CYP3A probe drug, it is reported to have a highly variable extraction ratio in the literature , and henTo date, the perfect CYP3A4 biomarker does not exist and any information obtained by the use of such metrics should be interpreted with care. However, our study suggests that 4βOHC may serve as a valuable measure to obtain information on hepatic CYP3A4 activity in clinical studies.


In silico conformational analysis and pKa calculations suggest a plausible mechanism for the superior efficacy of the advanced SI spacer compared to state‐of‐art analogues.Amine‐carbamate self‐immolative (SI) spacers represent practical and versatile tools in targeted prodrugs, but their slow degradation mechanism limits drug activation at the site of disease. We engineered a pyrrolidine‐carbamate SI spacer with a tertiary amine handle which strongly accelerates the spacer cyclization to give a bicyclic urea and the free hydroxy groups of either cytotoxic (Camptothecin) or immunostimulatory (Resiquimod) drugs.  The functionalization of a pyrrolidine‐carbamate self‐immolative spacer with a tertiary amine handle leads to a highly reactive construct, showing fast carbamate cleavage and release of OH‐bearing drugs. Sp1, Figure The selective delivery of drugs to the site of disease represents a widely pursued research goal, aimed at improving the efficacy and tolerability of pharmacological interventions. In this context, the covalent conjugation of pharmaceutical ingredients to antibodies  represents one of the most validated technologies.Sp1. In 2020, we reported that the pyrrolidine‐carbamate SI spacer Sp2  and cyclic urea 2 at higher rates than Sp1. The incorporation of Sp1 and Sp2 into protease‐activable anticancer prodrugs provided experimental evidence that a fast SI spacer degradation augments the anticancer effects in vitro.in vivo. Indeed, even if the trigger activation  for a faster hydroxy cargo release. The molecular structures of the synthesized SI spacers are reported in Figure Sp2 pyrrolidine ring was replaced by either a piperidine (in Sp4) or an isoxazolidine (in Sp5) cycle. In particular, Sp4 was designed to assess the impact of the cyclic amine ring size on the SI spacer degradation.Sp5 aimed at evaluating the contribution of the “α‐effect” to the spacer reactivity.Sp4 was prepared starting from racemic 2‐piperidinecarbaldehyde, the synthesis of Sp5 was inspired by Bode's route to 5‐oxaproline.Ka value and increasing its nucleophilic character.Sp3 and Sp6/8 were endowed with a tertiary amine handle connected either at the carbamate N atom (in Sp3 and Sp7) or at the pyrrolidine ring (in Sp6 and Sp8). While the former spacers were rapidly obtained by reductive amination of Boc‐l‐prolinal, the latter were prepared by multistep synthesis, starting from oxygenated proline derivatives, such as 4‐oxo‐l‐proline and hydroxyproline. Firstly, the exocyclic secondary amine of SI spacers Sp3/8 was conjugated to the tertiary hydroxy group of the anticancer drug Camptothecin (CPT) via carbamate bond. As described recently,[Sp3/8‐CPT . The results of this first screening are summarized in Figure We undertook the structural optimization of the pyrrolidine‐carbamate SI spacer lf‐life t1/2 for alf‐life t1/2 for alf‐life t1/2 for alf‐life t1/2 for alf‐life t1/2 for alf‐life t1/2 for alf‐life t1/2 for aSp4) and an isoxazolidine (Sp5) led to a complete inhibition of the cyclative carbamate cleavage.Sp6‐CPT released CPT with lower rates than reference Sp2‐CPT , while the reactivity of SI spacers Sp7 (t1/2=3.3 h) and Sp8 (t1/2=3.2 h) was slightly improved, but very similar to the one of native Sp2. To our delight, carbamate Sp3‐CPT showed a half‐life of 0.9 h, i. e. four times shorter than reference compound Sp2‐CPT.Sp6 and Sp8) showed no significant impact on the CPT release rates compared to reference Sp2. The importance of the amine handle proximity is even more evident by considering the better CPT release performance of Sp3  compared to Sp7 .Notably, replacement of the native pyrrolidine ring with a piperidine . This imidazoquinoline (IMD) is a potent agonist of Toll‐like receptors (TLR) 7 and 8, intracellular proteins expressed by several types of immune cells and involved in the host defence from viral infections.With the aim at confirming the superior efficacy of the new SI spacer Sp1, Sp2 and Sp3 were connected to the tertiary hydroxy group of R848 via carbamate bond. The resulting Sp1/3‐R848 adducts were dissolved in a DMSO/phosphate buffer (pH 7.5) mixture and incubated at 37 °C, following drug release analysis as described above. As shown by the HPLC traces and the chart in Figure Sp2 showed a very slow carbamate cleavage, with a half‐life of 40 h calculated for the Sp2‐R848 construct. As expected, the drug release activity shown by Sp2 was superior than the benchmark ethylenediamine‐carbamate spacer Sp1, which released only traces of drug after eight‐hour incubation. As observed with the CPT adducts, the tertiary amine‐bearing spacer Sp3 showed the highest drug release activity of the series, as the half‐life of Sp3‐R848 carbamate (t1/2=7.6 h) resulted approximately five times shorter than that of the Sp2‐bearing analogue. In this experiment, LC‐MS analysis of the Sp3‐R848 adduct upon eight‐hour incubation confirmed the formation of bicyclic urea 2 during Sp3 degradation . These CPT and R848 release data confirmed the superior performance of the advanced Sp3 spacer compared to both Sp2 and, even more dramatically, Sp1 references.By mimicking single‐strand RNA fragments, IMDs induce TLR homodimerization and activate downstream pro‐inflammatory pathways. Due to these pharmaceutical effects, tumour‐targeted IMD prodrugs are being increasingly investigated to selectively activate the immune system at the site of disease, thus improving the outcomes of immunotherapy regimens.4, 28 Sp3 spacer exceptional reactivity, we performed conformational analyses by computational methods of both Sp2 and Sp3 structures, connected to a generic alcohol  through a carbamate bond. In particular, Monte Carlo/Energy Minimization (MC/EM) conformational searchestBuSp2‐ and tBuSp3‐ in their main ionization state at pH 7.5, corresponding to positively‐charged amino groups . Representative minimum‐energy conformations selected from the molecular mechanics calculations were optimized at the DFT B3LYP/6‐31G* level of theory.Ka values of the protonated species were calculated on DFT minimum energy structures displaying the lowest solution phase energies. According to these calculations, carbamate tBuSp2‐ adopts a preferential conformation , which can individually engage either O atoms . Interestingly, the two pyrrolidinium protons in the “Sp3‐tBu syn” conformation proved more acidic  than the trialkyl ammonium species (pKa=11.0).“s Figure A. In conin silico data suggest a possible explanation for the observed SI spacer reactivity. Firstly, at the onset of SI spacer degradation, it is reasonable to assume that the nucleophilic attack of the uncharged pyrrolidine N atom to the carbonyl group occurs with a N−C−O bond angle >90°, following the well‐known Bürgi‐Dunitz trajectory.syn rotamers. Secondly, considering the perturbed pKa of the pyrrolidinium ion in the “Sp3‐tBu syn” structure, it is possible that the pyrrolidine nucleophilic attack in Sp3 is also facilitated by a preferential proton dissociation in aqueous medium.These 2‐hybridized O atom in intermediate I may facilitate the pyrrolidine cyclization (Step 2) to give the tetrahedral intermediate II. Here, the basicity of the tertiary amine may favor the restoration of the sp2‐hybridized C center (bicyclic urea formation) and the liberation of the hydroxy group (Step 3). This impact of neighbouring groups on bond cleavage kinetics is reminiscent of “catalytic triads” in the active site of hydrolytic enzymes,In summary, the tertiary amine proximity to the carbamate group may facilitate the SI spacer degradation at different stages of the cyclization reaction, following the mechanism proposed in Figure Sp3) in which a superfast carbamate cyclative cleavage is induced by the presence of a tertiary amine handle in close proximity to the carbamate bond. This advanced spacer showed better performance than Sp2 in the release of both the cytotoxic agent CPT and immunostimulatory drug R848. In silico conformational analysis and pKa calculations allowed us to propose a plausible rationale for the superior efficacy of the advanced SI spacer compared to reference Sp2. Considering the very slow R848 release observed with state‐of‐art SI spacers Sp1 and Sp2, the new spacer Sp3 may be pivotal for the design of cleavable R848 conjugates, alternative to previous strategies for IMD derivatization.Sp2 reference,[Sp3 module can be easily installed into functional drug delivery systems. For instance, the Sp3 connection to a para‐aminobenzyl carbamate (PABC) spacer will access to protease‐activable prodrugs, which represent the backbone of drug delivery technologies, including marketed ADCs.Sp3 application in different types of stimuli‐responsive materials can be envisioned as a valid alternative to current strategies for hydroxyl cargo delivery.[The present work describes a highly reactive pyrrolidine‐carbamate SI spacer  should be addressed to the authors.Supporting InformationClick here for additional data file.


IV and PdII chloride salts from the organic phase into a 6 m HCl aqueous phase facilitated their separation by precipitation of PtIV using a simple diamide ligand. In contrast, the retention of AuIII chloridometalate in the organic phase allowed its selective separation from Ni and Cu from a leachate solution obtained from electronic CPUs. This new approach has potential application in the hydrometallurgical leaching and purification of NMs from ores, spent catalysts, and electronic and nano‐wastes.The dissolution of elemental noble metals (NMs) such as gold, platinum, palladium, and copper is necessary for their recycling but carries a high environmental burden due to the use of strong acids and toxic reagents. Herein, a new approach was developed for the rapid dissolution of elemental NMs in organic solvents using mixtures of triphenylphosphine dichloride or oxalyl chloride and hydrogen peroxide, forming metal chloride salts directly. Almost quantitative dissolution of metallic Au, Pd, and Cu was observed within minutes at room temperature. For Pt, dissolution was achieved, albeit more slowly, using the chlorinating oxidant alone but was inhibited on addition of hydrogen peroxide. After leaching, transfer of Pt Leaching: Noble metals such as Au, Pd, Pt, and Cu are leached rapidly in organic solvents using the cheap and recyclable chemicals triphenylphosphinedichloride/oxalyl chloride, and the green oxidant hydrogen peroxide. This procedure could replace classical and highly toxic leaching methods for e‐waste recycling. Noble metals (NMs) such as gold (Au), palladium (Pd), platinum (Pt) are well‐known for their uses in jewellery, investment, modern electronics, medicine, and chemical catalysis. They are extracted from ores with very low abundance and, as such, the “mining” of secondary resources such as electronic waste (e‐waste) has become an increasingly attractive proposition due to the higher abundance of NMs in these materials compared with mining deposits.1, 2 T4−, AuCl4−, and PdCl42−.Hydrometallurgical refining and recycling processes generally comprise leaching of metals from the ore or secondary source, separation of the selected metal ions from the mixed‐metal leachate, and isolation/reduction of the separated metal ions as the elemental metal or metal compound. However, the individual steps within these processes are often associated with high energy consumption and environmental burden due to the nature of the chemical reagents employed. As such, many new approaches have been recognized, particularly those that improve the metal separation step. For example, Stoddart and co‐workers exploited host–guest supramolecular strategies to precipitate selectively NMs such as gold and platinum using α‐cyclodextrins and cucurbiturils.4, 5 Y2, and the leaching of gold from e‐waste requires strongly oxidizing acids such as aqua regia. However, new methods for the dissolution of NMs are being developed. For example, the dissolution of silver using glucose solution has been studied by Pradeep and co‐workers, although in this process, only 0.7 ppm of silver was leached using a 27.8 mm glucose solution after 7 days.2), which showed high selectivity towards Pt/Au/Pd and Au/Pd mixtures.0 to AuIII and effect its dissolution.2O2 in ethanol solutions to dissolve gold.N‐bromosuccinimide as an oxidant in pyridine to dissolve gold in water at pH 8.2 and ZnO photocatalysts.While new processes that facilitate the separation of individual NMs from mixed‐metal leach solutions are being increasingly realized, environmentally benign methods for the leaching of NMs are less established. Industrial gold leaching still involves the extensive use of cyanide to form the soluble coordination complex NaAu(CN)3PCl2) and hydrogen peroxide. Similarly, rapid dissolution of Au and Cu is seen using mixtures of another chlorinating agent, oxalyl chloride, and H2O2 in organic solvents. Regeneration of the spent triphenyldichlorophosphorane (as phosphine oxide) is achieved using oxalyl chloride. The selective transport and precipitation of NMs were achieved using biphasic mixtures, allowing for the facile separation of Au, Pt, and Pd.Herein, we report the very rapid dissolution of elemental Au, Pd, and Cu as their chloridometalates in various organic solvents using a mixture of triphenyldichlorophosphorane (Ph3PCl2 (0.450 mmol) in acetonitrile at room temperature (RT) results in 25 % gold dissolution over 24 h  to this reaction mixture causes a significant acceleration of gold dissolution; in this latter case, 100 % dissolution is achieved in just 3 min at RT , whereas a much slower dissolution rate is seen using 2‐methyltetrahydrofuran (Me‐THF); polar protic solvents resulted in either a slow dissolution rate (1‐octanol) or poor yields (ethanol). A time‐dependent study of Au leaching was undertaken using Ph3PCl2 (0.450 mmol) and H2O2 (50 μL) in acetonitrile  and shows 55 % dissolution after 30 s. This overall dissolution rate (100 mg h−1) is significantly faster than the previous examples using 2‐mercaptobenzimidazole as a ligand in the presence of catalytic quantities of iodine (0.15 mg h−1)2O2 (12.9 mg h−1).The investigation was initiated with Au dissolution experiments. The reaction between fine Au powder (0.025 mmol) and Ph h Table , entry 13PCl2/H2O2 was recorded. In the negative ion mode, the sole formation of AuCl4− is observed 2H+ and (PPh3O)H+ . This speciation in solution is supported by the UV/Vis spectrum of the same solution, in which the presence of AuCl4− is confirmed by a peak at 323 nm  along with absorption due to Ph3PO in the range of 260–280 nm. This is further evidenced by a 31P{1H} nuclear magnetic resonance (NMR) spectrum that shows a resonance at 40.1 ppm  attributed to the formation of (PPh3O)2H+.0 to form the AuIII complex AuCl4−. An overall reaction equation is presented in Figure S4.To understand which gold complexes are formed during the dissolution process, electro‐spray ionization mass spectrometry (ESI‐MS) of the acetonitrile solution after Au dissolution by Ph3PCl2 (0.450 mmol) and H2O2 (50 μL) in acetonitrile  and shows around 68 % dissolution after 30 s, which is faster than Au dissolution (55 % after 30 s) under similar conditions; however, the time taken for complete dissolution generates a rate of 100 mg h−1, which is similar to that for Au dissolution. The dissolution rate of Pt  is slower, taking 6 h to dissolve 100 % of the Pt in acetonitrile in the absence of H2O2 . The inclusion of H2O2 into the leachate decreases the rate of dissolution, with only 87 % of Pt dissolved after 24 h . This may be due to the peroxide being oxidized by PtIV halides, thereby limiting overall dissolution. This observation may deliver an unexpected advantage by presenting a route for the kinetic separation of Pd and Pt.The dissolution of Pd  was studied using the same protocol and complete dissolution is observed after 3 min in either acetonitrile or dichloromethane . A time‐dependent dissolution study was performed using Phm HCl results in the phase‐transport of Pd [99.5 % by inductively coupled plasma optical emission spectroscopy (ICP‐OES)] and Pt (99.2 % by ICP‐OES) into the aqueous phase  and the retention of Ph3PO in the organic phase. The UV/Vis spectra of these complexes are similar to those of PdCl42− and PtCl62− in 6 m HCl , supporting the formation of PdII and PtIV chloridometalates. The 31P{1H} NMR spectrum of the organic layer shows that Ph3PO remains in the organic layer . The formation of Pd and Pt chloridometalates and their phase transport into 6 m HCl allows their separation to be undertaken using our previously described precipitation method.2CH2)NMeC(O)Ph (L) results in the complete precipitation of [HL]2PtCl6 . It is therefore evident that the combination of this new leaching protocol with our previously reported selective precipitation method could result in a more sustainable and selective recovery of NMs.To characterize the complexes formed, ESI‐MS for the Pd and Pt leached solutions were studied in the negative mode in acetonitrile from which a range of chloridometalate ions are detected . Evaporation of these leach solutions, dissolution in chloroform, and contacting with 6 3PCl2/H2O2/acetonitrile) which results in its complete dissolution after 2 min at RT . As with the above, the organic leach solution was contacted with 2 m HCl to transport the metal complex into the aqueous phase. The UV/Vis spectrum of this aqueous phase is analogous to that of CuCl42− in 2 m HCl .Lastly, the leaching of elemental copper was also undertaken using the same protocol . Subsequent addition of dichloromethane and 2 m HCl causes a distinct phase separation in which [(Ph3PO)2H][AuCl4]  remains in the organic phase while CuCl42− is transported into the aqueous phase . Given the straightforward nature of this model Cu/Au separation, the leaching and separation protocol was applied to e‐waste central processing units (CPU). Soaking a CPU in an acetonitrile solution of Ph3PCl2/H2O2 results in metal dissolution from the surface  mixture with Ph3PCl2 and H2O2 in acetonitrile at RT rapidly and completely leaches the simulated nano‐waste , thus demonstrating that this procedure can be exploited to replace classical leaching methods for this growing waste stream.The increased growth in high‐efficiency compact storage devices, medical diagnostics, photovoltaics, imaging, and other gold‐based nanotechnology24, 253PO)2H][AuCl4] produced to isolate metallic gold and to regenerate the triphenyldichlorophosphorane oxidant Ph3PCl2 from the oxide Ph3PO. In the first instance, NaBH4 was added to the Au‐containing leach solution which results in the rapid reduction and precipitation of metallic gold (99 %) . Triphenylphosphine oxide remains in the organic solution after reduction, as confirmed by a resonance at 27.5 ppm in the 31P{1H} NMR spectrum .After the dissolution of Au and its separation from other metals, it is necessary to reduce the [ with Ph3PO (0.90 mmol) in acetonitrile, after which the solution was purged with nitrogen gas to remove any carbon monoxide released by oxalyl chloride decomposition. The addition of 50 mg of Pd/C and 50 μL H2O2 to this reaction mixture  in organic solvents in the absence of Ph3PCl2 (Table S3), with 100 % dissolution of gold occurring in 3 min at RT. A time‐dependent dissolution study  revealed around 58 % dissolution is achieved after 30 s, which is similar to that seen using PPh3Cl2/H2O2 mixtures (55 %). Formation of HAuCl4 is confirmed by analysis of the ESI‐MS and UV/Vis spectra of the leached solution in acetonitrile . Formation of HAuCl4 is again supported by UV/Vis spectra after evaporating the acetonitrile leach solution and redissolving in 2 m HCl . The quantitative precipitation of HAuCl4 was also achieved using PhC(O)NMe(CH2CH2)NMeC(O)Ph (L) .3Cl2 and H2O2 (method I) and oxalyl chloride and H2O2 (method II) is shown in Scheme S1.The recycling of the oxidant Phloride 0.5 mmol wi3PCl2, taking 6 h to dissolve 88 % of the Pt in acetonitrile . As with Ph3PCl2, the addition of H2O2 hinders dissolution rates, with only 83 % of Pt leached after 24 h . Formation of the PtIV chloride complex is confirmed by UV/Vis spectra after evaporating the leach solution and redissolving in 6 m HCl . Lastly, copper (5 mg) is also dissolved rapidly (2 min) using oxalyl chloride (0.45 mmol) and H2O2 (50 μL) in acetonitrile (Table S4). Formation of a CuII chloride complex was confirmed by UV/Vis spectra after evaporating the leach solution and redissolving in 2 m HCl .Oxalyl chloride is also found to leach Pd from carbon over 24 h, but in this case, the resulting mixture is reduced to Pd black due to the presence of CO .29, 303PCl2/H2O2 or (COCl)2/H2O2 in organic solvents such as acetonitrile. Both processes dissolve noble metals (NMs) quantitatively to produce organic‐soluble chloridometalate complexes and are extremely rapid (except for Pt), with complete dissolution of the metals occurring in minutes. Significantly, simple phase‐transfer operations allow for the separation of Au from other metals. The regeneration of the triphenyldichlorophosphorane and the recycling of the organic solvent results only in the consumption of the relatively inexpensive hydrogen peroxide and oxalyl chloride, although the latter could, in principle, be replaced by chlorine gas. Similar dissolution of other platinum group metals such as Ir and Rh is likely using this procedure. These findings suggest that this leaching protocol has the potential to be exploited in the sustainable purification of NMs from ores, spent catalysts, and electronic and nano‐wastes.We have demonstrated new methods for the dissolution of Au, Pd, Pt, and Cu using mixtures of Ph3PCl2  and H2O2  in acetonitrile (3 mL) at room temperature while stirring (900 rpm). Pd and Cu were treated by the same protocol. Oxalyl chloride (0.45 mmol) could be used in place of Ph3PCl2 using the same protocol. Pt was dissolved using two protocols: (a) 100 mg of fine Pt/C powder (5 wt % Pt) , Ph3PCl2 , and (b) 100 mg of fine Pt/C powder (5 wt % Pt) , Ph3PCl2  and H2O2  in acetonitrile (3 mL). Note that any H2O2 remaining on completion of the dissolution experiments was destroyed prior to disposal of the mixtures.In a typical dissolution process, 5 mg of gold (0.025 mmol) was added to a mixture of Ph3PCl2  and H2O2  in acetonitrile (6 mL) for 4 h at room temperature. After this period, the solution was decanted and the CPU was soaked for a second time for 4 h in a fresh Ph3PCl2/H2O2/acetonitrile solution. The leach solutions were combined and analyzed by ICP‐OES to determine the extent of metal dissolution from the CPU.The metals present in the CPU were dissolved using a modification of the typical procedure described above. The CPU was soaked in a mixture of PhThe authors declare no conflicts of interest.1As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.Supporting InformationClick here for additional data file.


The purpose of the study aims to understand the regeneration process and its cytology mechanism in economic echinoderms.Apostichopus japonicus was investigated by immunohistochemistry and the cell proliferation was detected by immunofluorescence and flow cytometry. Fibroblast growth factor 4 of A. japonicus (AjFGF4) was screened by RNA‐seq analysis and validated to regulate cell proliferation by siAjFGF4 and recombinant‐AjFGF4 treatment. The binding and co‐localization of AjFGF4 and AjFGFR2 were verified by Co‐IP, GST‐pull down, and immunofluorescence. Then, the AjFGF4‐AjFGFR2‐ERK‐cell cycle axis was examined by western blot, immunofluorescence, and flow cytometry techniques.The intestine regeneration process of The mesentery was served as the epicenter of intestinal regeneration via activating cell proliferation and other cellular events. Mechanically, AjFGF4‐mediated cell proliferation was dependent on the binding to its receptor AjFGFR2, and then triggered the conserved ERK–MAPK pathway but not JNK and p38 pathway. The activated ERK–MAPK subsequently mediated the expression of cell cycle regulatory proteins of CDK2, Cyclin A, and Cyclin B to promote cell proliferation.We provide the first functional evidence that AjFGF4‐AjFGFR2‐ERK‐cell cycle axis mediated cell proliferation was the engine for mesentery‐derived intestine regeneration in echinoderms. Mesentery served as the epicenter of intestinal regeneration to form a new intestine mainly via cell proliferation. Fibroblast growth factor 4 (AjFGF4) was found to regulate cell proliferation by specifically binding to AjFGFR2, and then triggered the conserved ERK–MAPK pathway but not JNK and p38 pathway. The activated ERK–MAPK subsequently mediated the expression of cell cycle regulatory proteins of CDK2, Cyclin A, and Cyclin B to promote cell proliferation. However, the intestine regeneration ability varies from species to species. For example, in widely studied mammals, the epithelial lining of the intestine is renewed continuously to repair local damage.Apostichopus japonicus) is an essential commercial Holothuroidea species in Asia aquaculture, and its annual worldwide trade has exceeded 15 billion US dollars. Like many other holothurians, A. japonicus has the capability to regenerate its lost digestive tract under suitable breeding conditions. However, such a spontaneous intestine remodeling process is an additional energy expenditure that diverts nutrients from growth and development, negatively affects body weight and reproduction, and sometimes even affects the function of the defense system, which is a bottleneck for the development of its commercial and subsistence fisheries.A. japonicus have focused on the morphological formation of the new intestine post‐self‐evisceration, while little is known about the cellular characteristics and molecular signaling mechanisms in the process of intestinal regeneration.A. japonicus. Impressively, we observed that the thickening of the free end of the mesentery was crucial to the formation of the intestine and such a process was always accompanied by a massive cell proliferation, which might supply additional cells necessary for the formation of new tissue. Then, RNA‐seq technology was conducted to identify the potential molecules for cell proliferation regulation in the process of intestinal regeneration, and a possible candidate gene fibroblast growth factor 4 (AjFGF4) was found significantly enriched during all the regeneration stages. Further assays confirmed that the AjFGF4‐mediated cell proliferation was facilitated by binding its receptor AjFGFR2, specifically activating the ERK–MAPK pathway and promoting the expression of cell cycle‐related protein  during intestine regeneration. Taken together, our work not only emphasized the importance of mesentery in intestinal regeneration and uncovered a previously unrecognized mechanism of the mesentery AjFGF4–AjFGFR2–ERK pathway modulates intestinal regeneration via targeting cell cycle in echinoderms, but also provides a reference for the exploration of internal organ regeneration in humans.Sea cucumber (22.1A. japonicus (average weight: 100 ± 5 g) were collected from a farm in Dalian, Liaoning province, China. They were quarantined in oxygen‐supplying natural seawater , and fed daily with mixed feed for 1 week before treatment. After acclimation, these organisms were treated to induce evisceration by intra‐coelomic injection of 0.35 M KCl (3–5 ml) and left in seawater aquaria to undergo intestinal regeneration.Healthy sea cucumbers 2.2The regeneration tissues including mesentery and/or intestinal rudiment were sampled at 2, 7, 12, 20, and 28 days postevisceration (dpe) treatment. The regeneration tissues of healthy sea cucumbers without any treatment were also sampled and served as the control. These sampled tissues were fixed in Bouin's fluid for 24 h and dehydrated in a graded series of alcohol (70%–l00%), cleared in xylene, and infiltrated in molten paraffin. Subsequently, transverse tissue sections (5–6 μm) were prepared using a rotary microtome , stained by hematoxylin and eosin, and examined using light microscopy. The digital images were then taken by an Axio Vert A1 microscope (ZEISS).2.3http://rsbweb.nih.gov/ij/). At least three non‐consecutive tissue sections were evaluated to obtain the average of intestine rudiment area per animal. For flow cytometry assay, the single‐cell suspensions of each regenerated stage's tissues were harvested by digestion with collagenase type iv and trypsin (Gibco). These cell suspensions were then pelleted by centrifugation for 5 min at 800g and resuspended in 4% formaldehyde for 10 min. After three washes with PBST, these cells were incubated with EdU click reaction solution (Beyotime) for 30 min at room temperature in dark. After the last wash in a triple, the percentage of proliferation activity of these cells (105 cells) was measured by a flow cytometer (Miltenyi Biotec). The data were analyzed using FlowJo software v10.6.1 (BD Biosciences).5‐Ethynyl‐2′‐deoxyuridine (EdU)‐based immunohistochemistry and flow cytometry methods were performed to detect the tissue distribution characteristics and quantitative dynamic trend of cell proliferation during intestinal regeneration. EdU was injected intraperitoneally 24 h in advance at each sampling time point of intestinal regeneration. For immunohistochemistry, a dorsal incision of sea cucumber was made to expose its internal cavity and facilitates the separation of the mesentery from the body wall and intestine. In the case of non‐eviscerated sea cucumbers, the mesentery attached to the intestine and body wall was stripped away using small surgical scissors. The full length of mesentery from the anterior end (next to the esophagus) to the posterior end (next to the cloaca) of sea cucumbers were sampled and embedded in the frozen section compound  and stored at −80°C. Then, continuous 6‐μm thick frozen sections of these tissues were performed using a Leica CM1900 cryostat at −20°Cand immersed with pre‐cooled (4°C) acetone for 15 min. Following washed in PBST (PBS containing 0.5% Tween 20) for 10 min, the sections were permeabilized with a harsh detergent like Triton X‐100 (0.5 and 0.05%) for 30 min. After being washed again, the sections were thereafter incubated with EdU click reaction solution for 30 min at room temperature in dark. Finally, the sections were stained with Hoechst 33342 to visualize the nucleus for 10 min at room temperature and observed by a fluorescence microscope (ZEISS). The size of the regenerative tissues was calculated by the ImageJ software (2.4A. japonicus genome (MRZV00000000.1) using HISAT2. Potential novel transcripts were evaluated by StringTie and CPC2 v1.0.1.p < 0.05 and FoldChange >2).The regeneration tissues from nine individuals were respectively sampled at each sampling time point as described above and combined as one specimen for transcription sequencing. Total mRNA was performed following the protocol described by Sun et al.2.5A. japonicus  were inserted into the expression vector pGEX‐4 T‐2 (Novagen) and then were transformed and induced in Escherichia coli Rosetta (DE3) by 0.5 mM isopropyl‐β‐D‐thiogalactopyranoside at 18°C overnight. The gene‐specific primers were listed in Table Fibroblast growth factor 4 sequences of The antibodies used in this study were all listed in Table 2.6g for 20 min at 4°C, the supernatants of the cell lysates were immunoprecipitated using Protein A/G magnetic beads  which were bound with anti‐flag  or anti‐GFP antibodies  and rotated slowly at 4°C overnight. The precipitates were washed 10 times with lysis buffer and then eluted by boiling the pellets with 5 × SDS PAGE loading buffer. Finally, the eluted samples were analyzed by immunoblotting with the indicated antibodies.The full‐length open reading frame of FGF4 1–352 aa) and the IG2 and IG3 domain regions (81–431 aa) of FGFR2 were respectively cloned and inserted into the pcDNA3.1‐EGFP and pcDNA3.1–3 × flag expression vector (Invitrogen) to construct the following plasmids: pcDNA‐flag‐FGF4, pcDNA‐flag‐FGFR2, and pcDNA‐EGFP‐FGFR2. The primers used to amplify the gene fragments were listed in Table –352 aa a2.7E. coli Rosseta cells harboring induced expression of GST‐tag labeled AjFGF4 or GST‐tag were pelleted by centrifugation and lysed in lysis buffer via ultrasonication. After centrifugation at 13,000g at 4°C for 15 min, the GST‐tag and GST‐tag‐labeled AjFGF4 protein was purified by anti‐GST magnetic beads  and used for pull‐down assays. Subsequently, the GST magnetic beads were washed five times with lysis buffer to remove unbound proteins and were then used to incubate with HEK‐293T cell lysate overnight which was transfected with pcDNA‐flag‐FGFR2 plasmids. Finally, the beads were washed five times with 10 resin‐bed volumes of RIPA buffer for 10 min and then analyzed via immunoblot analysis to detect the flag‐FGFR2 proteins using an anti‐flag antibody .To further explore the direct combination relationship of AjFGF4 and AjFGFR2, the pull‐down assay was performed as previously reported with minor modifications.2.86 cells in each group) and fixed in 4% paraformaldehyde for 15 min. After washing three times with PBS, the fixed cells were then pre‐incubated with 0.5% Triton‐X‐100 in PBS for 10 min, then blocked with 5% bovine serum albumin (BSA) in PBS for 90 min at room temperature. Next, the four groups of cells were respectively incubated with the pre‐immune mouse sera (1:200 dilution), and the pre‐immune rabbit sera (1:200 dilution), the mouse anti‐FGFR2 antibody (1:200 dilution) and the pre‐immune rabbit sera (1:200 dilution), the rabbit anti‐FGF4 antibody (1:200 dilution), and the pre‐immune mouse sera (1:200 dilution), and the mouse anti‐FGFR2 antibody (1:200 dilution) and rabbit anti‐FGF4 antibody (1:200 dilution) as the primary antibodies in a moisture chamber at 37°C for 90 min. After washing three times with PBST, the cells were first incubated with FITC‐conjugated goat anti‐mouse IgG  as the secondary antibodies at 37°C for 90 min. After another three washes with PBST, Cy3‐conjugated goat anti‐rabbit IgG (H1L)  was then incubated with the cells at 37°C for 90 min. Then, the nuclei were stained in DAPI  for 10 min at room temperature. Images were captured using a laser scanning spectral confocal microscope (ZEISS).The immunofluorescence analysis was performed to detect the subcellular localization of AjFGF4 and AjFGFR2 in sea cucumber coelomocytes. The single‐cell suspensions of regenerating tissues at 12 dpe were prepared by digestion with collagenase type iv and trypsin (Gibico) for 1 h at 4°C. Cells were divided into four groups , cells were resuspended in Leiboviz's L‐15 cell culture medium (Invitrogen) containing penicillin (100 U/ml) and streptomycin sulfate (100 mg/ml). Next, for RNA interference, siAjFGF4, siAjFGFR2, or siRNA‐NC transfected with Lipofectamine 6000 (Beyotime) according to the manufacturer's recommended conditions. At 48 and 72 h post‐interference, the cells were collected and used to analyze the protein and phosphorylation levels of p38, JNK, and ERK.The specific interference oligonucleotides targeting AjFGF4 (siAjFGF4‐1 and siAjFGF4‐2), AjFGFR2 (siAjFGFR2‐1 and siAjFGFR2‐2), and its negative control siRNA (siNC) were designed and synthesized by the GenePharma Company  is a type of ERK inhibitor, which inhibited the kinase activity of ERK1 and ERK2, with Ki values of 0.31 and 0.14 μM, respectively.2.11A. japonicus through AjFGFR2, the eviscerated‐sea cucumbers were transfected with siAjFGFR2 for six times in every 2 days and supplemented it with 5 μg rAjFGF4 or BSA at 24 h post‐siAjFGFR2 transfection, and the cell proliferation levels and the size of regenerative tissues were detected. For exploring whether AjFGF4/AjFGFR2‐mediated cell proliferation through the ERK–MAPK pathway during intestinal regeneration, the single‐cell suspension of the mesentery at the stage of 12 dpe was cultured, treated with specific inhibitor FR180204 for ERK and its control DMSO for 24 h, and further supplemented it with 500 ng rAjFGF4 to detect the cell proliferation levels by the EdU staining assay. To address whether the cell proliferation could be regulated by the AjFGF4/AjFGFR2‐ERK axis through the expression of cell cycle‐related proteins, the eviscerated‐sea cucumbers were transfected with FR180204 for six times in every 2 days and supplemented with the 5 μg rAjFGF4 or BSA at 24 h post‐siAjFGFR2 transfection, and the cell proliferation levels and the protein expression level of CDK2, Cyclin A, and Cyclin B were detected.The purified and refolded rAjFGF4 were prepared as described above. For verifying whether AjFGF4 mediates the intestinal regeneration in 2.12p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.All statistical analyses were performed using GraphPad Prism program . One‐way analysis of variance (ANOVA) was applied to discern significant differences between the control and experimental groups for the percentage of EDU‐positive cell population. These results were representative of at least three independent experiments and were presented as mean ± standard deviation (SD) and significance levels were defined as *33.1A. japonicus following spontaneous evisceration, the morphological changes of internal organs during the period of self‐evisceration and regeneration were observed for 28 days. Our result showed that only a part of the esophagus, cloaca, and a continuous mesentery remained in the body cavity left after evisceration . More interesting was that the muscle layer disappeared from the growth along the mesentery up to its tip , which might involve a fate transition of cell dedifferentiation. Subsequently, the first indication of swelling of the distal mesentery was observed at the stage of 7 dpe . The muscle layer gradually disappeared from the free end of the mesentery, and only a little was observed near the end of the body cavity wall . In the following days (12 dpe), there was significant growth in the size of the thickening that would form the intestinal rudiment. This rudiment acquired an elongated oval morphology composed of a large number of cells within an inner connective tissue and starts, although in some cases or sections the growth could be somewhat irregular . In the late stage of regeneration (28 dpe), the intestinal rudiment continued to grow and acquired a digestive tract shape . As noted above, our results confirmed that the mesentery played an important role in the process of intestinal regeneration and the new intestinal rudiment was a swelling developed at the free edge of the mesentery in A. japonicus, which might involve a series of cellular events .To investigate the intestine regeneration process of n Figure . Notablye Figure , and inge Figure 1. The mr Figure . At the r Figure , and ther Figure 1. In the Figure . The inte Figure 1. As no3.21–3–f1–3) were sampled as shown in Figure 1–b3). Then, at the stage of 7 dpe, the number of EdU‐labeled cells increased in all areas of the intestinal rudiment, especially at the free end of the mesentery, which correlated with an increase in its size . From the 12 dpe, the cell masses were observed in all samples in the form of thickenings at the free end of the mesentery. At this time, a very narrow cavity was found in the anterior regenerated primordium, which was near the end of the esophagus. The distribution of EdU‐labeled dividing cells was somewhat heterogeneous with more labeled cells found in the mesothelial layer and luminal epithelium of the distal mesenterial area. However, during this period, the regeneration primordia of the medial and posterior sides were smaller than that of the anterior side, and no cavity formation was observed. The proliferating cells of the mesentery were distributed in the mesothelial layer at the end of the mesentery . At the stage of 20 dpe, except for the regenerated primordia in the middle, cavities were formed in both the front and rear ends, and proliferating cells exploded in large numbers, and were distributed in the cavities of the terminal enlargement, which seemed to prepare for the formation of intestinal epithelial cells . Afterward, in the later stages of intestinal regeneration (28 dpe), the entire intestinal rudiment including the anterior, middle, and posterior had formed a cavity, and EdU‐labeled dividing cells were mainly distributed in the mesothelial layer and the epithelial layer that has formed folds .According to our histochemical results described in Figure e Figure , c1–c3. y Figure , d1–d3. s Figure , e1–e3. s Figure , f1–f3.We also performed EdU‐based flow cytometry to detect the changes in cell proliferation during intestinal regeneration under the same conditions. As shown in Figure 3.3p < 0.05) at the stage of 2‐, 7‐, 12‐, 20, and 28 dpe, respectively. In view of the fact that the cell proliferation of 2 dpe is not obvious in the results  were used to investigate the underlying molecular pathways involved in cell proliferation during intestine regeneration. The raw data has been uploaded to NCBI Sequence Research Archive under accession number SAMN29388289. The result showed that 14,763, 13,037, 13,990, 12,856, and 11,516 DEGs were detected , a total of four FGFR candidates were found, including AjFGFR1 , AjFGFR2 , AjFGFR3 , and AjFGFR4 . First, the AphaFold2 was used to predict the protein structure prediction.https://zdock.umassmed.edu/) was performed to identify the possible binding partners of these four AjFGFR candidates to AjFGF4.In higher vertebrates, FGFs function by interacting with their specific receptors (FGFRs) to activate different signals in various cells.3.5A. japonicus.To further explore whether AjFGF4 mediated intestinal regeneration by recognizing AjFGFR2, we investigated the changes in the levels of cell proliferation during intestinal regeneration post‐siAjFGFR2‐1/ siAjFGFR2‐2 or siRNA‐NC treatment. As shown in Figures A. japonicus through AjFGFR2, we transfected siAjFGFR2 in eviscerated‐sea cucumbers six times every 2 days and then supplemented it with the same dose of rAjFGF4 or BSA at 24 h post‐siAjFGFR2 transfection. As shown in Figure To further verify that AjFGF4 mediated the intestinal regeneration in 3.6The MAPK signaling pathway was reported to be closely associated with cell survival, proliferation, and differentiation during regeneration in several animals, such as hydra and zebrafish.3.7In mammals, the complex of cyclins and CDKs could drive cell from one stage to another during cell proliferation.4A. japonicus).A. japonicus. Notably, an increase in cellular proliferation was also observed closely with the size of the initial intestinal rudiment on the edge of the mesentery. Mechanically, we reported mesentery AjFGF4‐AjFGFR2‐ERK axis was involved in regulating intestinal regeneration via targeting cell cycle proteins in echinoderms. We found that AjFGF4 regulated A. japonicus cell proliferation depending on the recognition of AjFGFR2 during intestinal regeneration. Moreover, AjFGF4/AjFGFR2 modulated intestinal regeneration by promoting the expression of the cell cycle‐related proteins  by specifically activating the ERK–MAPK pathway, but not the JNK and the p38 pathway , Natural Science Foundation of Zhejiang Province (LZ19C190001), Research and Innovation Fund of Ningbo University (IF2022151) and the K.C.Wong Magna Fund in Ningbo University to Chenghua Li. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.The authors declare no conflict of interest.Data S1 Supporting informationClick here for additional data file.


However, the catalytic mechanism remains ambiguous, especially that under light irradiation. Here we systematically investigate the heterogeneous conversion of SO2 on diesel soot or black carbon (DBC) under light irradiation. The experimental results show that the presence of DBC under light irradiation can significantly promote the heterogeneous conversion of SO2 to H2SO4, mainly through the heterogeneous reaction between SO2 and photo-induced OH radicals. The detected photo-chemical behaviors on DBC suggest that OH radical formation is closely related to the abstraction and transfer of electrons in DBC and the formation of reactive superoxide radical (•O2−) as an intermediate. Our results extend the known sources of atmospheric H2SO4 and provide insight into the internal photochemical oxidation mechanism of SO2 on DBC.Both field observation and experimental simulation have implied that black carbon or soot plays a remarkable role in the catalytic oxidation of SO 2SO4 remains unclear in the atmosphere. This work first demonstrates that the formation of photoinduced •OH radical can directly promote the heterogeneous conversion of SO2 to H2SO4 on real diesel soot under light irradiation, extending the known sources of atmospheric H2SO4.Potential source of H BC particles in vehicle exhaust are mainly formed by incomplete combustion of hydrocarbon fuels7. In particular, in northern China, BC mass concentrations of up to 20 μg m−3  have been observed during haze episodes8. High loading of BC can increase atmospheric stability through the formation of a temperature inversion, which will feed back to the development of extreme haze via suppressing air pollutant dispersion9. Moreover, BC aerosol can influence climate by directly absorbing solar radiation and affecting cloud formation and surface albedo through deposition on snow and ice15.The rapid increase in vehicle numbers has resulted in the emission of large quantities of black carbon (BC) into the lower atmosphere17. For instance, gaseous nitrous acid (HONO) is an important precursor of hydroxyl radical (OH) in the troposphere. Numerous studies have shown that the heterogeneous reduction of NO2 on the BC surface is an important HONO source22. Moreover, sulfate is the fastest-forming species and rapidly becomes the main component of secondary aerosols during the evolution of haze28. Recent laboratory simulation and theoretical calculation works have indicated that soot can act as a catalyst to promote the heterogeneous oxidation of SO2 to sulfate under dark conditions31. Chamber experiments also proved that the catalytic role of soot in sulfate formation can be further amplified by reducing NO2 to HONO in the presence of both NO2 and NH3 under dark conditions32. A recent field measurement in urban Beijing conducted by Yao et al. indicated that the catalytic oxidation of SO2 on traffic-related soot can induce the formation of gas-phase SO3 in the early morning33. Therefore, the heterogeneous chemistry involving soot has recently attracted increasing attention in the field of atmospheric chemistry.Recent works proved that the interactions between BC and other inorganic species can enhance the atmospheric oxidation capacity and contribute to the formation of complex air pollution37. The EC-initiated photooxidation of OC was found to proceed through radical reactions initiated by electron transfer, and the absorption of light by OC-induced direct photoaging by energy transfer. Recent observational evidence suggested that photochemical reactions on soot particles may contribute to the production of atmospheric sulfate during the daytime38. However, the intrinsic reaction mechanism of SO2 on BC remains poorly resolved. Moreover, whether photoinduced radical chemistry can contribute to the heterogeneous conversion of SO2 remains unclear.Relative to its role under dark conditions, some recent studies reported that both elemental carbon (EC) and organic carbon (OC) in BC exhibited conspicuous photo-reactivity due to their strong light absorption capability under illumination2 oxidation mechanism on soot particles emitted from diesel vehicles (DBC) under light irradiation. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements and thermogravimetric analysis mass (TGA–MS) analysis are applied to characterize the formation of surface H2SO4 on DBC under light irradiation. Combined with the reactive oxygen species (ROS) analysis from electron spin resonance (ESR), it is found that OH radical resulting from the conversion of superoxide radicals is the crucial oxidant during the heterogeneous conversion of SO2 to H2SO4. These results help in understanding the sources of atmospheric oxidation capacity and particulate H2SO4.In this work, a series of laboratory experiments are conducted to explore the underlying SOThe composition and structure of DBC were firstly analyzed and characterized using in-situ DRIFTS, XPS, and XRD methods. The detailed characterization results for DBC are shown in Fig. 2 on the DBC surface was systematically investigated using in-situ DRIFTS. The main peak at 1100 cm−1 represents the characteristic vibrations of S=O bonds in sulfur-containing products .Heterogeneous conversion of SOcts Fig. 39. The s2 are at the ppb level  on the DBC surface was carried out in a tube plug flow reactor  on DBC/SiO2 mixtures is much greater than that on SiO2. Moreover, the uptake of 10 ppb SO2 on DBC is also observed to last more than 10 h under light irradiation. These results indicate that the heterogeneous uptake of SO2 on DBC is significant even under conditions close to the real atmosphere. The comparison of extracted SO42− ions from different samples  on DBC of different masses were also carried out 32. This is comparable with the reported formation rate of gaseous H2SO4 (∼0.001–0.1 μg m−3 h−1) from the OH reaction pathway27. These results suggest that the photooxidation of SO2 on BC could be an important source of sulfate in areas with high BC loading.Considering that typical atmospheric concentrations of SOvel Fig. , the hettor Fig. . Figure les Fig.  further out Fig. . The meah−1 Fig. . On thisX selective catalytic reduction catalyst in diesel after-treatment systems and be emitted along with DBC, we investigated the elemental composition of DBC by XPS. From the survey XPS spectrum of DBC shown in Fig. 2 on DBC mainly produces H2SO4 or sulfur-containing organics rather than metal sulfate complexes.To further reveal the form of sulfur species on the DBC surface, several characterization techniques were employed. Given that trace amounts of metal elements that can act as catalysts may break off from the NO2−aged DBC (∼2.68) was apparently lower than that of fresh DBC (∼3.74), which suggested that H2SO4 was formed in the photooxidation reaction on DBC. To confirm the formation of particulate H2SO4, TGA–MS was employed to characterize H2SO4 on aged-DBC42. From the TGA–MS of aged-DBC, a saddle-like change in SO2 (H2SO4)2)n). Previous studies proved that the pyrolysis of H2SO4–GIC could produce SO2 fragments in the range 400–600 °C44. Furthermore, the similar formation and evolution of sulfur-containing fragments in TGA–MS of a H2SO4–DBC mixture (30 μL H2SO4 and 15 mg DBC) further support the supposition that the interaction between DBC and H2SO4 can produce some other sulfur-containing species  after 24 h reaction under light irradiation was greater than that (0.7 ± 0.1 μg ml−1) under dark conditions. This further provided convincing evidence for the formation of gaseous H2SO4. The condensation of gaseous H2SO4 could be a source of surface H2SO4.Recent work reported that the soot surfaces upon irradiation can give rise to gaseous OH radicalsank Fig.  were cap34. To shed light on the mechanism of DBC photocatalysis in SO2 oxidation, we also examined the generation of photo-induced electrons and reactive oxygen radicals during DBC photooxidation by the spin-trapping EPR technique. TEMPO was used as the spin-trapping agent for photo-induced electrons. As shown in Fig. 47. The conversion of TEMPO to TEMPOH indirectly indicated that DBC photooxidation can indeed induce the generation and transfer of electrons.A recent work by Li et al. proved that the EC-initiated photooxidation of soot mainly involves electron transfer and the formation of reactive oxygen species34. To verify this, the OC in DBC was extracted and further analyzed by GC-MS. The results of GC–MS  on excited EC may abstract electrons from OC and subsequently donate electrons to other available acceptors such as adsorbed O2 , we chose two spin traps, DMPO and BMPO, to capture •O2− and OH radical, respectively. As shown in Fig. 2− adducts were observed in a DBC suspension in methanol under light irradiation, while no signal was observed under dark conditions54. This demonstrated that electrons were transferred to the dissolved O2 in the DBC suspension, resulting in the formation of •O2− radical  to form a series of sulfur-containing radicals 57. The free radical chain reaction dominated by sulfur-containing radicals would eventually result in sulfate formation. However, it should be noted that these sulfur-containing radicals are scarcely detected in the BMPO spin-trapping ESR spectra of SO2-aged DBC . PrevioDBC Fig.  accordin2− radical is also the key intermediate species in OH radical production during photo-induced interfacial reactions; thus, OH radicals in DBC suspension were further measured via the spin trapping EPR technique60. As shown in Fig. 2. Almost no BMPO–OH adduct signals were observed in DBC under dark conditions or in ultrapure water under light . From the results of in-situ DRIFTS experiments shown in Fig. 2SO4 on DBC. Moreover, the results of experiments in a coated-wall quartz flow tube reactor also showed that the presence of DBC indeed can promote the conversion of NO to HONO under light irradiation relative to the control experiment. Furthermore, the addition of SO2 can also in turn hamper the heterogeneous conversion of NO to HONO , an, an2− raDBC Fig. . This imO4 (Eqs.  and 8)))2− radicONO Fig. . These r2 to HONO and hence elevate the atmospheric oxidation capacity in the atmosphere22. In this work, our experimental results indicated that DBC under light irradiation can act as an oxidation medium to directly promote the heterogeneous oxidation of SO2 to H2SO4. Moreover, it was also proven that the promoting role of DBC photochemistry on the rapid conversion of SO2 is linked to the photo-induced formation of OH radicals. As for the source of OH radicals on soot under light irradiation, He et al. proposed that these OH radicals mainly derive from the reaction of photoinduced singlet oxygen (1O) and H2O on soot based on the density functional theory (DFT) results45. In this study, we found that the formation of OH radical is also closely related to the formation and conversion of the intermediate reactive superoxide radical (•O2−) triggered by the abstraction and transfer of photoinduced electrons. Thus, our work further complements or improves the production mechanism of OH radicals on DBC under light irradiation, which provides insight into the photochemical reaction process on DBC.The conventional view recognizes BC particles as a reducing agent in the atmosphere. For example, BC was found to initiate the heterogeneous reduction of NO2SO4 in the atmosphere mainly comes from the reaction of SO3 and H2O, which is the critical precursor causing the rapid nucleation and growth of ultra-fine particle62. Thus, exploring the unknown sources of SO3 and H2SO4 is crucial for understanding the formation and growth of new particles. Recently, both DFT calculation and field observation indicated that the formation of gaseous SO3 during the early morning is closely related to the catalytic oxidation of SO2 on the surface of soot33. Another field observation by Zhang et al. found that the photooxidation of BC-containing particles can further enhance the formation of sulfate38. Here, our experimental results provide reliable experimental evidence for these recent observations and DFT calculation results, especially under light irradiation. Hence, the heterogeneous oxidation of SO2 to H2SO4 driven by the photochemical process on DBC may very directly contribute to the rapid formation and growth of new particles in the atmosphere via inducing the formation of gaseous and particulate H2SO4. Our study highlights the photooxidation role of DBC in the heterogeneous formation of H2SO4, which has important atmospheric implications for understanding new particle formation and the source of atmospheric sulfate. It was worth noting that further model simulation and field observation in future studies should be effectively combined to quantitatively evaluate the contribution of this new pathway to H2SO4 formation in the atmosphere.H65. In particular, the internal mixing between BC and other aerosol components through processes such as gas condensation and coagulation can remarkably affect light absorption by BC67. This work proved that the photooxidation of DBC could directly promote the heterogeneous conversion of SO2 to H2SO4. Thus, an in-depth study of the optical properties of BC aerosol internally mixed with sulfuric acid in the future will help to evaluate the effect of variation of the mixing state on direct radiative forcing and climate.Additionally, black carbon has strong effects on regional and global climate due to the remarkable positive (warming) radiative forcing in the atmosphere2 or SO2/NO on diesel soot particles were measured by in-situ DRIFTS , equipped with a diffuse reflection chamber and a high-sensitivity mercury cadmium telluride (MCT) detector. The MCT was cooled by liquid N2 prior to the measurement. The infrared spectra were collected by means of a computer using OMNIC 6.0 software . All spectra reported here were recorded at a resolution of 4 cm−1 for 100 scans in the spectral range 4000−650 cm−1. The spectra are presented in the Kubelka−Munk (K−M) scale, which can provide a better linear relation with concentration via reducing or eliminating the mirror effect. To simulate solar irradiation, a high uniformity integrated xenon lamp  was used as the light source34. Its visible spectrum ranges from 330 to 850 nm  of a China VI heavy-duty diesel engine (ISUZU from China). A diesel engine bench test was run under the conditions of the World Harmonized Transient Cycle (WHTC). China VI fuels were used in this study, meeting the GB T32859-2016 standard. The heterogeneous reactions of SO nm Fig. . The lig69. The coated tube with the deposited DBC sample was horizontally placed in the main reactor. Synthetic air, as the carrier gas, introduced NO and SO2 into the coated flow tube at a total flow rate of 2 L min−1. Inorganic gases (SO2 and NO) were introduced into the flow tube through a movable injector with 0.3 cm radius. HONO was measured by a long-path absorption photometer , while the reactant gas SO2 in the coated flow tube was measured by a Thermo Scientific analyzer . To better simulate the heterogeneous conversion of SO2 on DBC under close-to-atmosphere conditions, heterogeneous experimental tests with low SO2 concentrations (∼60 and 10 ppb) were further carried out in a quartz tube plug flow reactor  at 37% RH. Before loading the sample into the plug flow reactor, ∼2 mg DBC needed to be diluted using ∼1 g silica sand  to ensure the reaction gas could flow fluently through the DBC. To further verify that DBC photooxidation in the presence of SO2 could also promote the formation of gaseous H2SO4, the heterogeneous reaction of SO2 (∼60 ppb) on DBC (∼0.25 g) powder alone was carried out in a quartz photoreaction tank at 50% RH. Prior to the reaction, 0.25 g DBC power was uniformly dispersed into a shallow quartz vessel (7 cm in diameter and 0.4 cm in depth) and then placed into the photoreaction tank. The outlet of the quartz photoreaction tank was connected with a quartz trap bottle (2 cm in diameter and 7 cm in depth) with 4 ml formaldehyde solution (20% v/v). Gaseous H2SO4 from the interaction between SO2 and DBC was captured using ultrapure water in the quartz trap. The captured H2SO4 was analyzed using IC. The designed RH in the DRIFTS chamber or in the flow tube was obtained by varying the ratio of dry zero air to wet zero air. A flow of humid vapor was generated by bubbling zero air through ultrapure water. A Vaisala HMP110 probe was used to monitor the changes in RH online.The experiments on HONO detection were conducted in a coated-wall quartz flow tube reactor λ = 0.15406 nm) operated at 40 kV and 40 Ma was used to characterize the crystalline form and interlayer spacings of the DBC power. The patterns were measured over the 2θ range from 10° to 80° with a scanning step size of 0.02°. The OC in DBC was analyzed and identified via gas chromatography coupled with mass spectrometry . DBC was first ultrasonically extracted for 10 min using 20 ml of dichloromethane (CH2Cl2), which was filtered through a quartz sand filter. The obtained supernatant liquid was subsequently concentrated using the N2 blowing method for final analysis. The gas chromatograph was equipped with a DB-5MS 30 m × 0.25 mm × 0.25 mm capillary column and the mass spectrometer employed a quadrupole mass filter with a 70 eV electron impact ionizer. The temperature of the programmed temperature vaporizer was held at 270 °C. The initial oven temperature was set at 40 °C for 2 min, then increased step-by-step to 150 °C (by 5 °C min−1) for 5 min, 280 °C (by 10 °C min−1) for 10 min, and 320 °C (by 10 °C min−1) for 5 min. A pH meter  was used to measure the acidity change of DBC after the reaction. The UV–vis spectra of residual EC and extracted OC were measured using the UV–vis spectroscopy (Perkin Elmer LAMBDA 650).Surface chemical states were analyzed by X-ray photoelectron spectrometry (XPS) . An X-ray powder diffractometer (Bruker D8 ADVANCE 28 diffractometer) with Cu Kα radiation . Afterward, the sample was weighed and placed in the sample container. The pure DBC (15 mg), SO2-aged DBC (15 mg), pure H2SO4 solution (60 μL), and an H2SO4–DBC mixture (30 μL H2SO4 (1.8 mol/L) and 15 mg DBC) were placed in sequence in an alumina crucible of 70 µL. The mass spectra of m/z 98, 80, 64, and 48, which correspond to the main fragment components of H2SO4 , were chosen to further verify H2SO4 formation.The sulfur-containing species produced during diesel soot photooxidation were investigated using a combined method of thermogravimetry–mass spectrometry (TGA–MS). In brief, a Mettler-Toledo thermogravimetry system  was coupled with a quadrupole mass spectrometer  by a silica capillary at a temperature of 250 °C. The MS system was equipped with an electron ionization source with the voltage at 70 eV and provided the mass spectra up to 2−). 2,2,6,6−tetramethylpiperidine-1-oxyl (TEMPO) was used to capture the photo-induced electrons in the DBC suspension. DBC suspensions loaded in a quartz capillary tube (1 mm Ø and 10 cm length) were continuously irradiated with the Xenon lamp during the monitoring of radical signals in the ESR spectrometer. The typical parameters for ESR measurement were as follows: the sweep width was 100 G, the modulation amplitude was 1.00 G, and the sweep time was 81.92 ms.An electron spin resonance spectrometer  with a modulation frequency of 100 kHz and a microwave frequency of 9.5 GHz was used to capture reactive radical signals. 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO) added to a freshly prepared 0.1 M solution in deionized water was used for capturing OH radicals in aqueous solutions. 5,5-dimethylpyrroline-N-oxide (DMPO) was used to capture superoxide  was employed to analyze the changes in the concentrations of water-soluble ions (such as SO42− and NO3−). A certain amount of SO42− may be contained in the primordial DBC samples due to the combustion of sulfur-containing species in fuel. Thus, DBC samples were ultrasonically extracted using ultrapure water at least 10 times to exclude interference from these preexisting SO42− ions in the measurement of newly produced SO42− ions during IC analysis. After the reaction finished, DBC samples (25 mg) obtained under different experimental conditions were first dispersed in 20 mL of ultrapure water and sonicated for 10 min, and subsequently filtered using a syringe filter . The filtered liquid was split in half. Half of the samples were directly analyzed by IC.To quantitively the HSupplementary InformationPeer Review File