In this study, the relationship between photocurrent and the charge balance of electrons and holes in van der Waals heterojunctions is investigated. To observe this phenomenon, a p‐WSe2/n‐WS2/n‐MoS2 heterojunction device with both p–n and n–n junctions is fabricated. The device can modulate the charge carrier balance between heterojunction layers to generate photocurrent upon illumination by selectively applying electrostatic doping to a specific layer. Using photocurrent mapping, the operating transition zones for the device is demonstrated, allowing to accurately identify the locations where photocurrent generates. Finally, the origins of flicker and shot noise at the different semiconductor interfaces are analyzed to understand their effect on the photoresponsivity and detectivity of unit active area  in the p‐WSe2/n‐WS2/n‐MoS2 heterojunction device.Heterojunction structures using 2D materials are promising building blocks for electronic and optoelectronic devices. The limitations of conventional silicon photodetectors and energy devices are able to be overcome by exploiting quantum tunneling and adjusting charge balance in 2D p–n and n–n junctions. Enhanced photoresponsivity in 2D heterojunction devices can be obtained with WSe 2/n‐WS2/n‐MoS2 heterojunction device with both p–n and n–n junctions can modulate the charge carrier balance between heterojunction layers to generate photocurrent upon illumination. The relationship between photocurrent and the charge balance of electrons and holes in van der Waals heterojunctions is investigated. By selectively applying electrostatic doping to a specific channel layer, a p‐WSe Furthermore, single‐layer TMDCs have a direct bandgap and possess excellent absorption characteristics. To achieve high‐efficiency TMDC‐based optoelectronic devices, the photocurrent generation and charge balance must be optimized. High responsivity and high detectivity TMDC phototransistors require ideal charge depletion conditions to produce low dark currents. However, photocurrent generation in TMDCs is limited because there is not enough energy to split the excitons due to their high exciton binding energy (≈0.897 eV). To solve such inherent challenges, a method for forming a built‐in potential (Vbi) by the creation of a heterojunction structure in the device channel was introduced. Heterojunction structures typically consist of junctions of different n‐type and p‐type semiconductors. For optimal photocurrent generation in a van der Waals heterojunction, forming an optimal Vbi in the device is crucial. The Vbi can be created by controlling the balance of electron and hole concentrations and the proper doping of 2D materials. However, chemical doping of the 2D materials remains difficult because of self‐purification in low‐dimensional systems. Also, it is important to systematically determine the origins of photocurrent and noise in van der Waals heterojunction devices to maximize the critical photodetector figure of merit such as responsivity (A W−1), and detectivity . However, the effect of the Vbi in the van der Waals heterojunction to photocurrent generation efficiency as well as the effect of flick noise and shot noise on the responsivity and detectivity have not yet been elucidated.2D transition metal dichalcogenides (TMDC) have attracted great attention as ideal building blocks for electronic and optoelectronic applications.7, 82/n‐WS2/n‐MoS2 structure. Both p–n and n–n junctions in the heterojunction phototransistor were designed to control the major charge carriers by applying the gate bias to the WS2 layer only. We used a thin hexagonal‐BN (h‐BN) layer as a dielectric material to minimize dielectric traps and the operation gate voltage. In these devices, we analyzed the density of charge carriers precisely and the exact position of photocurrent generation as a function of gate bias using scanning photocurrent mapping system (beam size: 898 nm). We also identified the origins of flicker noise and shot noise according to the charge balance between electrons and holes. When the optimum charge concentration  was attained, the device exhibited fast time‐resolved photocurrent response (<10 ms), high responsivity (≈106 A W−1), and high D* (≈1015 cm Hz1/2 W−1) in a unit of acitve area .To identify the origins of photocurrent generation and noise in van der Waals heterojunctions, we fabricated a multifunctional 2D heterojunction phototransistor with a lateral p‐WSe voltage.26 In 22 layer. The p–n–n device demonstrates the origin of photocurrent generation and noise for the different junction types (p–n and n–n junctions) by tuning the Fermi level of the intrinsic WS2 layer. The p–n–n device is composed of prepatterned electrodes formed on silicon substrate with a 300 nm  thick SiO2 dielectric layer applying a global gate voltage, and the main structure formed by stacking thin h‐BN layers as a dielectric on the gate electrode. By using of h‐BN the layered structure is formed with no mutual coupling with the other 2D materials, reducing interface and vacancy trap effects and maximizing gate efficiency (Ch‐BN = 1.20 × 10−3 F m−2). A thin WS2 layer exfoliated from bulk flakes is then stacked over the h‐BN dielectric layer. WSe2 as p‐type semiconductor and MoS2 as n‐type semiconductor are stacked on both ends of the WS2 sheet to form the p–n–n junction as shown in Section S1 (Supporting Information). Finally, as shown in Figure 2 and MoS2 stacked on WS2, respectively, using PMMA‐masked electron beam lithography (EBL). Figure To control the major charge concentration of the 2D materials, we designed a p–n–n heterojunction device with cascade band alignment and applied the gate bias on only the WS12g) and out‐of‐plane (A1g) vibration modes for each materials using Raman spectroscopy, we were able to identify the WSe2, WS2, MoS2, and h‐BN layers . The device, measured from −1.5 to 0.5 VG region under dark conditions, shows an ideal diode behavior with two different directions as shown in Figure G in the reverse‐cool zone and the forward‐hot zone according to the applied gate voltage and drain voltage. Notably, the threshold voltage (VTh) as indicated by the black dash line shows two different diode directions due to proportion to the threshold barrier of qVbi = ϕp−ϕn at the relative p–n junction, where q is electron charge and ϕ is work function. As a function of the gate bias, shifting the Fermi level of WS2 leads to a change in the threshold barriers in the WSe2 and MoS2 junctions. The bulk bandgap (Eg) of TMDCs is around ≈1.3 eV, and the Vbi in the junction according to the Fermi level alignment can be estimated using the following p–n junction formulaNC is the effective concentration of electrons in the conduction band, NV is the effective concentration of holes in the valence band, and N′D and N′A are the net donor and acceptor concentrations, respectively.To demonstrate the optoelectronic properties of the p–n–n cascade phototransistor, we first measured the transfer curves for WSermation).33 The2 (NC/N′D) can be tuned as a function of the gate bias, NV/N′A can be considered as a constant. Therefore, the change in VTh depends on the change in qVbi according to the applied gate bias to WS2. When white light (52 µW cm−2) illuminated the device, the photovoltaic effect was observed as shown in Figure −12 to 10−9 A by photocurrent generation. In the specific gate range −1.5 to −0.5 VG, we observed a typical photovoltaic effect, and it gradually disappeared above the −0.5 VG region. The open‐circuit voltage (VOC) measured in the range of −0.9 to −0.7 VG is 0.42 V, which is higher than the 0.33 V  observed in the previously reported BP/WS2 heterojunction devices. The VOC as a function of the applied gate bias was changed as marked by the blue line in zero current line. To understand the mechanism for the photovoltaic effect as a function of gate bias in detail, the photocurrent map was divided into three different transition zones: Zone‐I is the p–n junction, where VOC is maintained; Zone‐II is a transient region, where VOC is shrinking; and Zone‐III involves the n–n junction, where VOC has vanished. The photovoltaic effect can be understood by using the band diagram shown in Figure 2 layer (capacitor symbol), only the WS2 layer in the heterojunction band diagram shows a Fermi level shift. We clearly confirmed the Fermi level shift of WS2 as a function of the applied gate bias through Kelvin probe force microscope measurement (KPFM) in Section S2 (Supporting Information). The Zone‐I transition (VG < VTh) shows the primary cascade p–n–n band alignment which has a sufficient band offset between the valence band of WSe2 and the conduction band of WS2 upon illumination with white light (52 µW cm−2), exhibiting the photovoltaic effect with VOC. The Zone‐II transient state (VG ∼ VTh) shows that the band offset of WSe2 and WS2 are smaller than in Zone‐I and as a result, VOC almost disappears. In the Zone‐III transient state (VG > VTh), as the potential barrier between the conduction band of WS2 and WSe2 narrows further, the transport between WSe2 and WS2 involves direct tunneling, which is similar to previous reports. Therefore, the n–n junction between WS2 and MoS2 is preferentially created as shown in the Zone‐III transition state in Figure Since only the Fermi level of WS2 NC/N′D can2 NC/N′D canG as described in Section S6 (Supporting Information). The position of photocurrent generation varied depending on the transition zone. The photocurrent map was generated by applying −0.5, 0, and 0.5 VD at constant −0.3 VG to investigate the exact positions of photocurrent generation by the device at forward and reverse bias.To identify the precise positions of photocurrent generation in the three different zones, the scanning photocurrent mapping with a 405 nm  laser with a divergence of 0.5 mrad was performed as detailed in Section S5 (Supporting Information). The transient zones have a unique output curve where different built‐in barriers are found along the drain voltage direction at −0.3 VFigure 2 and WSe2, not in the overlapping junction area. The direction of photocurrent generation tends to extend from the contact line to the center of the WS2 sheet. Because the MoS2 layer is grounded and the drain bias is only applied on the WSe2 layer, the contact line with a low potential barrier in the reverse bias direction shows active photocurrent generation. As shown in Figure D generates the photocurrent only at the WS2 and MoS2 contact line. These results imply that the external VD changes the thickness and the position of the depletion layer. The thickness of the depletion layer can be verified by w≈Vbi±VD as a function of the external VD. Therefore, as shown in Figure D generated photocurrents in different directions and gradually disappeared from the center of WS2 layer. The depletion layer thickness and the depletion layer ratio in the heterojunction structure can be determined from wTotal≈(1NA′+1ND′) and wnwp=NA′ND′ considering the equilibrium state of the junction, respectively. The N′A of WSe2 (N′D of MoS2) is fixed and the N′D of WS2 can be controlled by electrostatic doping as detailed in Section S7 (Supporting Information). As the value of N′D increases, the thickness wn of the depletion layer becomes insufficient due to the decrease of wTotal, so that the photocurrent generated by the drain bias in the WS2 layer increases more than the photocurrent generated by the built‐in barrier. This phenomenon is consistent with the photocurrent distribution formed in a single 2D material‐based phototransistor. We also performed the photocurrent mapping as a function of gate voltage under the two different diode directions as p–n junction and n–n junction. As shown in Figure G and −1 VD and the second diode condition requires −0.5 VG and 1 VD. In Figure 2 layer. On the other hand, the n–n junction in Figure G conditions in Figure 9 Ω) rather than by the rectification behavior (≈1012 Ω). When the Fermi level of WS2 is close enough to the conduction band, the MoS2 contact region forms the second diode barrier. As shown in Figure 2 in the conduction band causes photocurrent diffusion from the contact line as detailed in Section S8 (Supporting Information). Furthermore, the initial pinch‐off effect (<0.5 VD) at the p–n++–n+ transistor of WSe2–WS2–MoS2 (relative quasi p–n–p) allows us to observe the sufficient n‐type degeneration of WS2 as described in Section S9 (Supporting Information).Vbi is large enough to overcome the exciton coupling energy, sufficient photocurrent generation is possible without an external bias. However, when the Vbi is low, photocurrent generation needs to be assisted by an external applied bias.Thus, we have demonstrated that the main photocurrent in the 2D heterojunction can be controlled by the applied gate voltage. If the D* is a very important figure of merit for photodetectors. To derive D*, the noise equivalent power (NEP) of the photodetector should be considered. In the case of phototransistors, however, the accurate measurement of noise current is very difficult due to the measurement limits. The noise current in photodetectors can be estimated from the sum of Johnson noise , shot noise (bias) and flicker noise (bias and frequency) as detailed in Section S10 (Supporting Information). We can convert the dark current as a function of gate bias into shot noise and flicker noise. Generally, shot noise tend to increase with increasing dark current. Shot noise current iSN can be extracted from the dark current using the following equation, iSN=2·q·Idarkwhere Idark is the dark current of the device. We can also extract the flicker noise current through fitting following the relationship (1/f)α in noise power density (A2 Hz−1). However, to date, there is no optimal method for measuring the exact flicker noise current in a 2D‐based phototransistor. Generally, the reported 2D‐based phototransistors have been used the shot noise current estimated from the dark current to calculate the D* using the equation, D* = (R · A1/2) /(2 · q · Idark)1/2, where A is the active area of the device and q is the electron charge. However, when using the shot noise current to estimate D*, it is possible that it can be overestimated by several orders of magnitude compared to flicker noise current. To eliminate this problem, we verified the origin of phototransistor flicker noise current as a function of gate voltage.Figure 2–WS2 junction diode and the n–n WS2–MoS2 junction diode, respectively. Figure G) and reverse (−1 VG) bias under dark condition. The dark current as a function of gate bias can be converted into the shot noise and flicker noise currents. In Figure −10 A at −0.7 VG has a noise floor behavior around 10−26 A2 Hz−1.−9 A at −0.6 VG begins to show the flicker noise current from the sub‐log‐linear fit (1/f)α. Figure −10 A. As the dark current increases, the flicker noise current gradually increases to 1000 times more than the shot noise. On the other hands, the dark current (6 × 10−11 A) of the n–n junction diode is much higher than the dark current (2 × 10−12 A) of the p–n junction diode as shown in Figure A current level of 10t (1/f)α.46 FigG, as shown in Figure Interestingly, the flicker noise current measured at 0.2 VG; diode 2: 0 VG) with a 1 Hz  chopped 405 nm  laser (beam size: 0.5 µm) as a function of incident light power to obtain the responsivity (detailed in Section S12 in the Supporting Information). The responsivity and TRPR measured under reverse bias conditions of the first diode were 3.82 × 106A W−1and 9 ms. Additionally, the D* can be calculated using the following formula, D∗=RA·B/iFN=A·B/NEP, where R is the responsivity, A is the active area of detector, B is the bandwidth, iFN is the flicker noise current, and NEP is iFN/R. The calculated D* is 5.98 × 1015 cm Hz1/2 W−1, which is much higher than the value reported for previous 2D heterojunction devices.We also measured the time‐resolved photocurrent response (TRPR) at each optimized diode condition  was also achieved. The results demonstrate that the charge balance in van der Waals heterojunction is very important for optoelectronic applications. This study reveals that even if the charge densities of the active materials of the layered structures are not perfectly matched, it is still possible to create an optoelectronic device having excellent characteristics by tuning the charge balance through the gate voltage.In summary, we have demonstrated a multifunctional 2D heterojunction p–n–n phototransistor where the charge balance can be controlled via electrostatic doping to pinpoint the origin of photocurrent and noise current in various heterojunction devices. Through photocurrent mapping, we identified two kinds of photocurrent generation mechanisms. First, the drain bias applied to the WSThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.


The fluid history of subducted rocks lies at the heart of this debate: rocks that experience significant infiltration by a water-bearing fluid may release orders of magnitude more CO2 than rocks that are metamorphosed in a closed chemical system. Numerical models make a wide range of predictions regarding water mobility, and further progress has been limited by a lack of direct observations. Here we present a comprehensive field-based study of decarbonation efficiency in a subducting slab , and show that ~40% to ~65% of the CO2 in subducting crust is released via metamorphic decarbonation reactions at forearc depths. This result precludes extensive deep subduction of most CO2 and suggests that the mantle has become more depleted in carbon over geologic time.The fate of subducted CO 2 remains debated, with estimates mainly from numerical predictions varying from wholesale decarbonation of the shallow subducting slab to massive deep subduction of CO2. Here, the authors present field-based data and show that ~40% to ~65% of the CO2 in subducting crust is released via metamorphic decarbonation reactions at forearc depths.The fate of subducted CO There is, however, a long-standing debate surrounding the fate of subducted CO2. Recent papers have argued that the vast majority of oceanic carbon is deeply subducted4 or that the vast majority is released by subarc depths2.Subduction of oceanic lithosphere is arguably the most important process in global geochemical cycling. Subduction delivers material from Earth’s surface into the deep mantle, but chemical reactions in the subducting slab can also release volatiles which ultimately return to the atmosphere5. A model reaction is 2 Quartz + 3 Dolomite + 2 Albite + H2O = 3 Aragonite + Glaucophane + 3 CO2. For decades, thermodynamic models of subducted rocks have been used to estimate the degree of carbon loss10. However, the modeling results vary widely, due mostly to uncertainties on the nature of aqueous fluid infiltration into subducting rocks. Closed-system models predict evolution under relatively water-poor conditions7, whereas models that consider open-system fluid infiltration allow for more water-rich environments10. The presence of a water-bearing fluid has a profound effect on carbonate stability, decreasing reaction temperatures by as much as hundreds of Kelvin11. Thus, it is essential to constrain the nature and extent of fluid infiltration to estimate the resultant CO2 release.Carbon dioxide is released during metamorphism when a carbonate mineral such as aragonite or dolomite breaks down via prograde decarbonation reactions2. These large uncertainties in our current understanding of CO2 subduction leave basic questions about global geochemical cycling unanswered. For example, has the deep Earth become depleted or enriched in carbon over geologic time? To what extent might enhanced carbonate subduction add CO2 to Earth’s atmosphere? Providing answers to such questions requires a new constraint on the fate of subducted CO2.Given a lack of observational constraints, models predict that anywhere from ~0.0001 to 52 Megatons of oceanic carbon will be deeply subducted annually2 in the typical subducting oceanic crust is released at forearc depths by decarbonation reactions. Other processes, such as stoichiometric carbonate dissolution4, would add to the total. Whether the released carbon is ultimately stored in the overriding lithosphere or delivered to Earth’s atmosphere, much of it is not returned to the deep mantle, which, as a consequence, has likely become more depleted in carbon over geologic time.Here, we provide an extensive field-based record of decarbonation efficiency in a subducted slab. We combine detailed observations, stable isotope measurements, and bulk chemical analysis with thermodynamic modeling to show that subducted rocks from the Cycladic Blueschist Unit in Greece underwent major fluid infiltration and decarbonation. Our results show that at least ~40%, and more likely ~65%, of the CO14. Rocks reached peak temperatures (T) of ~500 to ~550 °C and peak pressures (P) of ~1.5 to 2.0 GPa18. Preservation of subduction-related features in the CBU is superlative—Syros Island in particular is home to one of the best-preserved and most thoroughly studied subduction complexes on Earth. Apart from its exceptional preservation, the CBU represents a normal subduction complex, with multiple studies using observations of the CBU for inferences about subduction in general23.The Cycladic Blueschist Unit (CBU) in Greece is an ideal field area to test existing models of subduction zone decarbonation. It was metamorphosed in the Eocene when the African plate subducted northward beneath EurasiaWe collected more than 600 hand samples of carbonate-bearing rocks from the islands of Syros and Tinos , we compare its modern CO2 content to its composition before major metamorphic devolatilization began. The modern CO2 content is easily measured (see “Methods”), but the initial volatile content is not directly preserved. Thus we need a technique to determine how much CO2 was in each rock prior to metamorphic decarbonation.Samples preserve their mineralogy, and therefore mineral-bound CO2-bearing fluid present in excess at lower grade P–T conditions (310 °C and 0.8–1.0 GPa) consistent with estimates of the prograde P–T path on Syros16 and warm subduction in general25. The initial back-projected composition is then taken as the composition of the solid minerals at these lower P–T conditions. In most samples, the modeled CO2 content is insensitive to changes in P, T, or fluid mole fraction of CO2  Rocks that contained carbonate at peak P–T contained an equal or greater mass of carbonate prior to metamorphism. (3) Rocks did not undergo major element metasomatism other than volatile loss. The most likely metasomatic process is stoichiometric carbonate dissolution26 which would add to the total CO2 released. Thus, once again, our estimates for ∆CO2 are conservative.The back-projection method requires only three assumptions. (1) Rocks were in equilibrium with a CO7 and (2) a system open to fluid infiltration, approximated with a fixed-27 (see “Methods”). Fully closed-system models are run at peak P–T conditions (525 °C and 1.5 GPa) to estimate the resulting rock and fluid compositions. Fluid-infiltrated models use observations of the mineral assemblage in each sample  a fully closed system a fully 2 loss for each sample. The mineral assemblage is calculated at peak conditions with a very water-rich  ∆CO2 of each sample.Furthermore, we estimate the maximum plausible COP–T values of 550 °C and 2.0 GPa does not impact our conclusions (see below).Using higher 2  conditions 28, most (>70%) record significantly lighter C and O isotope signatures.Carbon and oxygen isotope data show a wide range of values from δ8 ‰ Fig. . While m18O may result from the prograde exchange with local silicates29, but very low δ18O must be attributed to external fluid infiltration26, perhaps up-temperature fluid flow in particular30. Low δ13C values may indicate the presence of reduced carbon, isotope fractionation as a result of high degrees of decarbonation31, or infiltration by a low δ13C fluid.Some of the variations in δ33; we conclude that this is the most likely source of the water-bearing fluid which eventually traveled into the carbonate rocks, perhaps as part of a channelized flow system34, altering isotopic compositions and phase equilibria.Dewatering of subducted serpentinite or other hydrated lithologies  is expected to release substantial water2) values, ranging from 0 to 91% CO2 loss by mass . This allows us to calculate (1) the P–T conditions at which decarbonation occurred, (2) the rate of CO2 release, and (3) how decarbonation may have proceeded if the rocks had continued to subduct. Using the same global average crustal stack, we generate curves showing the percentage of the initial CO2 released at each P–T step with a 20 °C moving mean  altered oceanic crust. Assuming a crustal stack with 250 m of limestone (a rough approximation of the sediments recorded at DSDP site 495)35, and 100 m of lightly altered oceanic crust, we predict only ~6% CO2 loss by 550 °C, much less than the global average of ~40%. Tonga represents the other extreme, with essentially no carbonate-bearing sediments, and nearly all subducted CO2 hosted in lightly altered oceanic crust36. We would, therefore, predict that metamorphic reactions would release ~45% of the rock’s CO2 at comparable conditions. The differences become even more pronounced in the projection to 650 °C, where Central American and Tongan subducted lithologies are predicted to have undergone ~10% and ~95% decarbonation, respectively. These results are fully consistent with those predicted on a conceptual basis by ref. 3.Because the proportion of CO2 loss ranges considerably, but systematically, across rocks of different compositions. Assuming lithologic proportions representing average oceanic crust and sediments, these rocks record that ~40% of subducted CO2 was released. Forward modeling predicts an additional ~25% CO2 loss into the forearc, with most decarbonation concentrated in a sharp peak.Rocks of the CBU record a robust and consistent record of substantial aqueous fluid infiltration which drove metamorphic decarbonation. The CO2 in the slab to travel to subarc depths and, perhaps, beyond  was corrected for ferric iron with Fe2 and H2O with results from point-counting of representative thin sections. Samples were point-counted in detail to constrain wt% H2O, and the remaining LOI was assumed to be CO2 . For heavily altered volcanics and lightly altered oceanic crust (samples with relatively low LOI where wt% H2O might have a large effect), every sample was point-counted. For carbonate-bearing siliciclastics and limestones, three representative samples of each type were point-counted. These results were extrapolated to the remaining samples of that type assuming a linear relationship between wt% H2O and wt% LOI within each sample group such that:This corrected LOI was then converted to weight percent COslimestone = −0.0319 ± 0.0044, blimestone = 1.41 ± 0.17, sclastic = −0.1159 ± 0.1171, and bclastic = 3.39 ± 1.85 .where 2O) compared to wt% CO2 (1.5–43.8)  and field context, with visible continuous compositional layering in a cohesive section indicating metasedimentary origin. Heavily altered volcanics were differentiated from lightly altered basaltic crust based on the degree of observed and back-projected carbonation, with lightly altered samples having initial CO2 < 10 wt%.Rocks were sorted into four categories based on their protolith: heavily altered volcanics, lightly altered oceanic crust, carbonate-bearing siliciclastics, and limestones. Samples with SiOCarbon and oxygen stable isotopes were analyzed in the Yale Analytical and Stable Isotope Center on either a Thermo MAT 253 KIEL IV with carbonate device or Thermo DeltaPlus XP Stable Isotope Ratio mass spectrometer with a Thermo Gasbench II interface. Consistency between the two methods was ensured via analysis of in-house standards and repeat analysis of a subset of samples. Precision is better than ± 0.1 per mille (1σ).Carbon and oxygen isotope values are reported in δ notation relative to Vienna Pee Dee Belemnite (V-PDB) and Vienna Standard Mean Ocean Water (V-SMOW), respectively. Fig. . IsotopeP–T pseudosections) were performed in the system Na2O–CaO–K2O–FeO–Fe2O3–MgO–MnO–Al2O3–SiO2–CO2–H2O–TiO2 using the Theriak-Domino software package52 with code as in ref. 53 and the database of ref. 54. Mineral and fluid activity models59 are given in Supplementary Table 2O and CO2 are from ref. 60, while remaining fluid endmembers are from ref. 61. Additions to the default database file for full COH fluid mixing are also given in Supplementary Data Thermodynamic calculations 2, would have 30 moles CO2. Note that the proportions of nonvolatile species  are fixed to match the modern bulk composition, and only volatile components (CO2 and H2O) are variable.We calculate the stable minerals in each sample at this lower 2 content forms a flat or stepped function with broad plateaus as a function of 2 content is nearly constant across the entire range of conditions, insensitive to changes in P, T, or 2 content, and therefore, minimum ∆CO2  such thatmi is the mass of a species, Ci is the concentration of a species, and ′ and o denote the final and initial rock compositions, respectively26. The ΔCO2observed is calculated with C′i from modern measured samples, whereas ΔCO2potential is calculated with C′i from rock compositions resulting from forward modeling as described in the main text.Carbon dioxide loss is calculated through a comparison of the initial and final wt% CO2 loss of each lithology type is taken as the average CO2 loss of the corresponding type in our dataset , as is the initial weight fraction of CO2 for each rock type . The total input flux into subduction zones is calculated using these thicknesses and densities in combination with global subduction length (L = 4.45 × 107 m)36 and average convergence rate (R = 0.05 m yr−1)36 to find Eq. We construct a model crustal stack approximately representative of the global average subducted sediments + crust. The CO2 loss fraction, this gives a flux off the slab of 2.06 Tmol CO2 yr−1.Multiplied by the total COThe decarbonation proportions of Central American and Tongan crustal stacks are calculated via an analogous procedure, changing only the thickness of each lithologic unit as specified in the main text. Note that we do not take into account the specific thermal structure of these end-member subduction zones, but this does not have a substantial effect on the total decarbonation predicted by our model (see main text).2 loss of average subducting crust is calculated along two linear prograde P–T paths. Both paths begin at 310 °C and 1.0 GPa; the hotter path, path A, passes through ‘peak field conditions’ of 525 °C and 1.5 GPa and proceeds up to 650 °C and 1.8 GPa. Path B passes through peak field conditions at 550 °C and 2.0 GPa, proceeding up to 650 °C and 2.4 GPa. Note that the pressures reached at 650 °C are prescribed by the assumption of a path that is linear in P–T space.The CO2 content of each rock is determined at steps of 1 °C along the prograde P–T paths, passing through the peak field conditions, and continuing up to 650 °C.Beginning with the back-projected composition, each sample is forward modeled in a system with a fluid of a prescribed 2 compositions to be conservative. However, the observed mineralogy and final volatile content of these rocks require P and T increase from starting to peak conditions. The other nine samples can achieve the most conservative back-projected CO2 content and the observed modern mineralogy and CO2 content at the same Recall that we model 12 representative samples (three from each lithologic group). In nine samples, the fluid composition is fixed at a given P–T paths (A and B) in order to match our observations. That is, the system is underdetermined: given our observations of mineralogy and volatile content and two of the set {P, T, Note that each of the 12 samples requires a slightly different fluid composition for the differing 2 content of each selected rock is calculated at steps of 1 °C along both P–T paths. The incremental CO2 released at each P–T step is calculated by difference with the preceding steps. The average mass change of CO2 of each lithologic type is combined with the same unit thicknesses and densities from the global flux calculation to arrive at a weighted average degree of decarbonation for the stack.The CO2 loss fraction of the three representative metamorphosed limestones, multiplying by ~0.7 to correct from 4.5% CO2 loss to the total group average of 3.2%. In this way, the total decarbonation of the crustal section is forced to equal 41% at peak P–T conditions. The same factor is used in the forward modeling to higher P–T conditions: for example, the three metamorphosed limestones average 6.5% decarbonation at 650 °C, which is multiplied by 0.7 to arrive at 4.5% decarbonation for the whole suite of metamorphosed limestones. The correction factors for the three remaining lithologic types are all between 0.95 and 1.05 for both P–T paths. Similarly, the initial average wt% CO2 of each lithologic group is set to match the entire dataset. Supplementary Fig. P–T path and the adjusted average mass change for each lithologic group.The three samples representing each lithology were forced to match the average decarbonation of their whole lithologic group by multiplying by some constant value. These are small corrections, the largest being an adjustment of the COSupplementary InformationDescription of Additional Supplementary FilesSupplementary Data 1Supplementary Data 2Supplementary Data 3


Ligand 10 showed an efficient, selective and rapid separation of AmIII and CmIII from nitric acid. The speciation of the ligands with trivalent f‐block metal ions was probed using NMR titrations and competition experiments, time‐resolved laser fluorescence spectroscopy and X‐ray crystallography. While the tetradentate ligands 8 and 10 formed LnIII complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3, significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10. The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with YIII, LuIII and PrIII are very similar to those formed by 2 and 3 with LnIII. Ligand 10 forms CmIII and EuIII 1:2 complexes that are thermodynamically less stable than those formed by ligand 3, suggesting that less hydrophobic ligands form less stable AnIII complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity.The synthesis and evaluation of three novel bis‐1,2,4‐triazine ligands containing five‐membered aliphatic rings are reported. Compared to the more hydrophobic ligands  Calling all actinides! Bis‐1,2,4‐triazine ligands bearing five‐membered rings were synthesized and evaluated as actinide‐selective extractants. Tuning the size of the aliphatic ring leads to subtle changes in actinide‐extraction properties. The origins of these changes were elucidated at the molecular level, paving the way for the rational design of improved actinide‐selective extractants for reprocessing of spent nuclear fuel., However, the spent fuel that is produced in nuclear fission reactors is long‐lived and highly radiotoxic.f orbitals of the actinides and ligand lone pairs is thought to be the basis for this separation.1–3 , and we show that this small but subtle modification to the ligand structure can have unexpected effects on the extraction properties and metal ion speciation of these ligands.Numerous soft N‐ and S‐donor ligands have been evaluated to accomplish the challenging separation of the minor actinides from the lanthanides in a future solvent extraction process.6, 8 and 10 were synthesized in moderate to high yields as shown in Scheme 5 was synthesized by the oxidation of 2,2,4,4‐tetramethylcyclopentanone with selenium(IV) oxide as previously described.5 with the known bis‐amidrazone 4] increases. With ligand 8, a more efficient and selective extraction of AmIII was observed at high nitric acid concentrations than with ligand 6. The selectivity of 8 for AmIII over EuIII was significantly higher than that of ligand 6, and the average separation factor was approx. 100 between 0.1 m and 3 m HNO3. Once again, no significant selectivity for AmIII over CmIII was observed with 8 (see Supporting Information section 4.2). Interestingly, the D values for AmIII and EuIII for 8 were approximately an order of magnitude lower than those previously reported for the more hydrophobic ligand 2 under similar conditions.N,N′‐dimethyl‐N,N′‐dioctyl‐2‐hexyloxyethyl malonamide 11, was used in the case of 2. To allow a direct comparison with 2, we carried out extraction experiments for 8 in 1‐octanol in the presence of 0.25 m11 (see Supporting Information section 4.2). This led to a slight increase in the D values for AmIII at ≥1 m HNO3, but a marked decrease in the selectivity for AmIII over EuIII (SFAm/Eu≤57 at 1–4 m HNO3) compared to the results in the absence of 11. This is due to the competing non‐selective co‐extraction of AmIII and EuIII by 11, which lowers the separation factor. However, the distribution ratios for AmIII and EuIII were still significantly lower with 8 than with 2.Results for the extraction of AmIII and EuIII by tetradentate ligand 10 at different nitric acid concentrations are presented in Figure III over EuIII was observed across a range of nitric acid concentrations. The D values for AmIII reached a maximum value of 112 at 1 m HNO3. A maximum selectivity for AmIII over EuIII was also observed at 1 m HNO3 (SFAm/Eu=237). The selectivity for AmIII over EuIII shown by ligand 10 was similar to that shown by the analogous, more hydrophobic ligand 3.D values for both AmIII and EuIII were approximately an order of magnitude lower with ligand 10 at high acidity than with ligand 3 . This could allow for easier back‐extraction (stripping) of the metals from the loaded organic phase after the extraction stages have been carried out. Ligand 10 did not show any significant selectivity for AmIII over CmIII , in contrast to ligand 3.Results for the extraction of AmIII and EuIII by ligand 10 as a function of contact time is presented in Figure III extraction equilibrium was reached within 10 minutes of phase mixing, while EuIII extraction equilibrium was reached after a mixing time of 20 minutes. Thus, the rates of metal extraction were slightly faster for the less hydrophobic ligand 10 than for its more hydrophobic analogue 3 under the same conditions (15 minutes for DAm and ≥60 minutes for DEu to reach equilibrium for 3).The extraction of AmIII and light trivalent lanthanides, which must be separated from the minor actinides. We therefore measured the distribution ratios for YIII and all lanthanides (except PmIII) as well as the trivalent actinides. For all three ligands 6, 8 and 10, the D values for the lanthanides showed an extraction profile across the lanthanide series of first increasing, then decreasing D values, in agreement with previous results for ligands 2 and 3.m HNO3, HoIII exhibited the highest D values for ligands 8 and 10 , while DyIII exhibited the highest D value for ligand 6 (DDy=0.08). Thus a practical separation of AmIII and CmIII from all the lanthanides could be feasible with ligands 6 and 8 (DLn<1). Although the later lanthanides TbIII–YbIII are somewhat extracted by ligand 10 at high nitric acid concentrations, a highly selective separation of AmIII and CmIII from all the lanthanides is feasible since selective lanthanide back‐extraction can be carried out at lower nitric acid concentrations . Furthermore, the later lanthanides are not present in spent fuel solutions, so their extraction is less relevant than that of the early lanthanides.Spent nuclear fuel solutions contain large amounts of Y1H NMR titrations of the ligands with YIII and the diamagnetic lanthanides LaIII and LuIII. We have previously employed this method to investigate the solution speciation of the analogous ligands 2 and 3, and related tetradentate ligands with trivalent lanthanides.2 and 3.To gain further insight into the solution speciation of these ligands with metal ions and to rationalise the extraction results, we carried out some 8, both 1:1 and 1:2 m:L species were observed during the 1H NMR titration with Y(NO3)3 in deuterated acetonitrile. A single species was observed initially during the titration, and the disappearance of the free ligand resonances at a metal:ligand ratio of 0.5 indicates this was the 1:2 species [Y(8)2(NO3)]2+. Small amounts of the charge neutral 1:1 complex [Y(8)(NO3)3] were observed at higher metal:ligand ratios, reaching a maximum of 14 %. This complex is formed by partial dissociation of the 1:2 complex. The species distribution curve for the titration of ligand 8 with Y(NO3)3 is shown in Figure For tetradentate ligand 1H NMR titrations of ligand 10 with LaIII, LuIII and YIII (see Supporting Information section 5.3). Both 1:1 and 1:2 m:L species were observed during the 1H NMR titration of 10 with La(NO3)3 in deuterated acetonitrile. The 1:2 complexes [M(10)2(NO3)]2+  were observed initially and small amounts of the charge neutral 1:1 complexes [M(10)(NO3)3] were observed at higher metal:ligand ratios, reaching a maximum of 35, 30 and 18 % for LaIII, LuIII and YIII, respectively. Although these results are broadly in agreement with those reported previously for tetradentate ligands 2 and 3,8 and 10, the percentage of the 1:1 complex [M(L)(NO3)3] for a given metal ion is significantly higher than that observed for ligands 2 and 3 . Since it is known that the extracted species is the more hydrophobic 1:2 complex [M(L)2(NO3)]2+ (L=ligand), this could suggest that the lower distribution ratios observed above for ligands 8 and 10 in comparison to the analogous ligands 2 and 3 could be due to the lower percentage of 1:2 complexes being formed by these ligands under extraction conditions.Similar results were observed for the 1H NMR titration of terdentate ligand 6 with Y(NO3)3 in deuterated acetonitrile, a single complex species was observed initially (see Supporting Information section 5.1). The complete disappearance of the free ligand resonances at a metal:ligand ratio of between 0.3 and 0.4 suggests that this is the expected 1:3 m:L complex [Y(6)3]3+. These 1:3 complexes are the major solution species formed by terdentate bis‐1,2,4‐triazine ligands with trivalent lanthanides.During the 1H NMR competition experiments were then carried out to determine if phenanthroline‐derived ligand 10 formed thermodynamically more stable complexes with the lanthanides than bipyridine‐derived ligand 8, as implied by the higher distribution ratios observed in the extraction experiments for 10. The aliphatic region of the 1H NMR spectrum of a 1:1:1 mixture of 8, 10 and La(NO3)3 in deuterated acetonitrile is presented in Figure 8, the 1:2 bis‐complex of 10, and an additional set of resonances  which were assigned to the heteroleptic 1:2 bis‐complex [La(8)(10)(NO3)]2+. The heteroleptic complex showed one singlet, one triplet, two doublets and a multiplet in the aromatic region (see Supporting Information section 5.4). These resonances were not previously observed in the 1H NMR titration of 10 with La(NO3)3. The ratio of bis‐8 complex/bis‐10 complex/heteroleptic bis‐complex was 1:1:2, indicating that a statistical mixture of the three 1:2 bis‐complexes had been formed, in agreement with previous work on ligands 2 and 3.A series of 8 and 10 was able to displace the other from its lanthanide 1:2 bis‐complexes. Addition of a solution of ligand 10  to a solution of the 1:2 bis‐complex of ligand 8 with La(NO3)3  gave rise to a mixture of the 1:2 bis‐complex of 10, the heteroleptic 1:2 bis‐complex and free uncomplexed 8 (see Supporting Information section 5.4). The major species present was the 1:2 bis‐complex of 10, and no traces of the 1:2 bis‐complex of 8 were observed. Thus ligand 10 displaces ligand 8 from its LaIII complex and forms the thermodynamically more stable complex with LaIII than 8.NMR experiments were then carried out to determine if each of the ligands 8  was added to a solution of the 1:2 bis‐complex of ligand 10 with La(NO3)3 , a mixture almost identical in composition to that observed above was obtained (see Supporting Information section 5.4). The 1:2 bis‐complex of 10 was again the major species formed, and no traces of either the 1:2 bis‐complex of 8, or free uncomplexed 10 were observed. Thus ligand 8 is at best able to displace one of ligand 10 from its 1:2 bis‐complexes but is never able to displace both. We have previously observed the same phenomenon with ligands 2 and 3.When a solution of ligand 8, 10 and Y(NO3)3 in deuterated acetonitrile led again to the expected statistical mixture of the three 1:2 bis complexes  in a ratio of 1:1:2 (see Supporting Information section 5.4). However, in contrast to LaIII, only partial ligand displacement reactions were observed when either 8 or 10 was added to a solution of the YIII bis‐complex of the other ligand. Addition of 10 to the 1:2 bis‐complex of 8 with YIII led to a mixture containing mostly the bis‐complex of 8 and free uncomplexed ligand 10, as well as traces of the heteroleptic 1:2 bis‐complex [Y(8)(10)(NO3)]2+. Addition of 8 to the 1:2 bis‐complex of 10 with YIII led to a mixture of primarily the bis‐complex of 10 and uncomplexed 8, as well as traces of the heteroleptic 1:2 bis‐complex. The partial ligand displacement reactions observed here for YIII are likely due to its higher kinetic inertness towards ligand substitution compared to LaIII, in agreement with the lower ligand exchange rate constant observed for the YIII aqua complex.Similarly, a 1:1:1 mixture of ligands 10 with Y(NO3)3 or Lu(NO3)3 were of the minor 1:1 neutral complexes [Y(10)(NO3)3] and [Lu(10)(NO3)3]. The structure of the LuIII complex is shown in Figure To further characterise the various species produced upon complexation, single crystal X‐ray crystallography experiments were performed. Perhaps surprisingly, the crystals grown from solutions of 10)(NO3)3] (see Supporting Information section 3.2), all three nitrate ligands are bidentate with Ln−O distances in the 2.47–2.56 Å range for those in axial positions and around 2.37 Å for the nitrate ligand in the equatorial position which lies in roughly the same plane as the ligand. The structure is very similar to that of the 10‐coordinate [Y(3)(NO3)3] complex published previously.10)(NO3)3] are bidentate, one in an axial and the other in an equatorial position (NO3)3] lying in the ca. 2.41–2.44 Å range for the axial positions and around 2.33 Å for the equatorial position. The third nitrate ligand is monodentate with a bond distance of 2.288(2) Å, giving a nine‐coordinate complex overall. This phenomenon has been observed previously in complexes of LuIII with tetradentate bis‐1,2,4‐triazine ligands, where a water molecule displaced one of the nitrate ligands to the outer coordination sphere.Both structures crystallised as acetonitrile disolvates and were essentially isomorphous, sharing similar unit cell parameters, space groups and packing. The two structures are distinguishable, however, by the coordination of the three nitrate ligands about the lanthanide ion. In the structure of [Y(NO3)3]. A quantitative measure of this is the N3‐Ln1‐N6 bond angle, which demonstrates the effect of this twist on the coordination of the ligand about Ln1. For [Y(10)(NO3)3] this angle is 165.91(5)° whereas the more pronounced twist observed in [Lu(10)(NO3)3] gives rise to an angle of 161.02(7)°. This very slight deviation is enough to reduce the space available to the monodentate nitrate and prevent it binding in a bidentate fashion while also providing greater access to the metal ion to the nitrate trans to it allowing it to bind more strongly and with shorter contacts than the axial nitrate ligands in [Y(10)(NO3)3].This discrepancy in coordination geometry can be rationalised by considering the ionic radii of the lanthanides in question. With an ionic radius of 86 pm, LuIII complex with ligand 8, [Pr(8)2(NO3)][Pr(NO3)5], were grown providing a representative structure of one of these 1:2 bis‐complexes , one of each of the Δ and Λ optical isomers. In terms of their coordination, the structure is very similar to those of 2 with EuIII[24] and 3 with PuIII.Attempts to obtain the structures of any of the 1:2 bis‐complex species observed in the course of the NMR titrations proved unsuccessful. However, good quality single crystals of a Prs Figure . The asy8 (see Supporting Information section 3.2) shows that the ligand adopts the non‐chelating trans conformation in the solid state with respect to the C−C torsion between the central pyridine rings. This was also observed in the structure of the analogous ligand 2,cis conformer.The X‐ray crystal structure of free ligand III and EuIII with ligand 10 was studied by time‐resolved laser fluorescence spectroscopy. This technique allows the study of the coordination chemistry of fluorescent metal ions.III and EuIII represent trivalent actinides and lanthanides, respectively with excellent fluorescence properties.To gain further insight on the speciation in solution and support the NMR and X‐ray crystallography findings, the complexation of Cm3 show relatively slow complexation kinetics.III at a given ligand concentration was measured as a function of time after addition of 10. CmIII fluorescence spectra resulting from the 6D7/2→8S7/2 transition are shown in Figure 10 the CmIII solvent spectrum at 599.1 nm was observed with a shoulder at 595.4 nm. Upon addition of 10 the emission band at 599.1 nm decreased and new emission bands at 606.4 nm and 618.7 nm occurred. With time the emission band at 618.7 nm became dominant. No further changes of the CmIII fluorescence spectrum were observed after 23 h, indicating that the system was at equilibrium.Tetradentate bis‐1,2,4‐triazine derivatives such as III, the fluorescence emission bands of the 5D0→7Fn  transitions were studied as a function of time after addition of 10 (see Supporting Information section 6.1). Without 10 an emission band at 578.9 nm for the 5D0→7F0 transition of the EuIII solvent species was observed. Upon addition of 10 two new emission bands at 579.5 nm and 581.1 nm occurred. The 5D0→7F1 and 5D0→7F2 transitions exhibited a change of shape and splitting of the emission bands due to complexation of EuIII with 10. No further changes of the EuIII fluorescence emission spectra were observed after 4.5 h, confirming chemical equilibrium.In the case of EuIII and EuIII with 10, the evolution of the fluorescence spectra of CmIII and EuIII as a function of the concentration of 10 was studied in nitrate free media. Batch samples containing increasing concentrations of 10 were equilibrated for 24 h before being measured. The normalized CmIII fluorescence spectra are shown in Figure III solvent species and both complex species are shown in the Supporting Information (section 6.2).To determine thermodynamic data for the complexation of Cm−9 m of free 10 and becomes dominant at 2.8×10−7 m. The relative ratio of species 1 is irrelevant (<3 %) under the applied conditions and is therefore not shown in Figure The fluorescence intensity factor (FI) describes the fluorescence intensity of a species relative to a reference. Due to the high FI of species 2 (FI=56±6), the speciation was determined from the overall fluorescence intensity. The speciation is shown in Figure 10)2]3+ (see Supporting Information section 6.2). The conditional stability constant for the formation of the 1:2 complex according to Equation β′2=13.1±0.2.The slope of the linear correlation indicates the number of coordinated ligand molecules. A slope of 2.11±0.17 was obtained, showing that species 2 is the 1:2 complex 3+. The conditional stability constant for this complex is log β′2=10.3±0.4.The Eu10 and 3 under the same conditions, it is evident that 3 is a stronger ligand than 10. The stability constants for both the CmIII and the EuIII 1:2 complexes are approximately one order of magnitude lower in the case of 10 ]2+ complexes containing one inner‐sphere nitrate anion (L=2 or 3).10 was studied in a similar manner by extracting CmIII or EuIII from solutions containing 0.1 m nitric acid and 1.9 m NH4NO3 into solutions of 10 mm10 in 1‐octanol. After phase separation, the organic phases were studied by time‐resolved laser fluorescence spectroscopy.Tetradentate bis‐1,2,4‐triazine ligands extract trivalent actinide and lanthanide ions from nitric acid or nitrate solutions as 1:2 complexes.III (top) and EuIII (bottom) spectra of the 1:2 complexes of 10 in methanol with those from the solvent extraction experiments. The emission spectrum of the extracted CmIII complex shows an emission band at 620.1 nm, which is bathochromically shifted by 1.4 nm with respect to the emission band of the [Cm(10)2]3+ complex (618.7 nm). In the case of EuIII, the emission band of the 5D0→7F1 and 5D0→7F2 transitions of the [Eu(10)2]3+complex and the complex in the organic phase of the extraction experiment differ in shape and position. The emission band (5D0→7F2 transition) of the complex formed during the extraction experiment displays a peak maximum at 613.3 nm while the emission band of the [Eu(10)2]3+ complex exhibits a peak maximum at 615.7 nm. Similar shifts and changes in position and shape of the emission bands were observed for 2 and 3 and were assigned to the additional complexation of a nitrate ion in the inner coordination sphere of CmIII.Figure 10)2]3+ complex resulted in a comparable bathochromic shift of the emission band from initially 618.7 nm (no nitrate added) to 619.2 nm (9.97×10−2 m of nitrate added), as shown in the Supporting Information (section 6.3).Adding ammonium nitrate to a solution containing the 2+ complexes, as was previously observed for 2 and 3.In the case of EuIII complexes of ligand 10 are less stable than those of ligand 3, DFT calculations were carried out on free ligands 3 and 10 and their respective [AmL2(NO3)]2+ complexes (L=3 or 10) using a level of theory successfully used in previous studies of actinide complexes.3 when forming [Am(3)2(NO3)]2+ was 1.76 kJ mol−1 less favorable than the binding of 10 when forming [Am(10)2(NO3)]2+ in an acetonitrile solvent field (see Supporting Information section 7). Similar values were obtained from calculations in the gas phase and in a 1‐octanol solvent field. This suggests that the 1:2 complex of 10 is marginally more stable than that of 3, but that neither has a significantly greater binding energy than the other. This may indicate that there is little difference between the inherent metal binding energies of the ligands 3 and 10, and that the differences in extraction properties observed above arise instead from specific solvent interactions.In an attempt to gain further insight into why Anf‐block metal ions, the thermodynamic stabilities of the formed metal complexes, and the trivalent actinide extraction affinities of the ligands. We propose that this insight could enable a more rational design of actinide‐selective ligands with tailored solvent extraction properties suitable for future spent nuclear fuel reprocessing to close the nuclear fuel cycle.We report on three novel bis‐1,2,4‐triazine ligands derived from a five‐membered ring diketone, and we show for the first time how tuning the aliphatic ring size of bis‐1,2,4‐triazine ligands leads to subtle changes in the speciation of the ligands with trivalent 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.SupplementaryClick here for additional data file.


Nanointegration of NIR CDs and peroxalate (P‐CDs) through the bridging effect of amphiphilic triblock copolymer can serve as turn‐on probes for the detection and imaging of hydrogen peroxide (H2O2). Considering high efficiency and large penetration depth of NIR photons, the P‐CDs are employed in bioimaging H2O2 in vitro and in vivo, and the detection limit can reach 5 × 10−9m, among the best reported of CDs‐based sensors. Moreover, imaging of inflammatory H2O2 in a mouse model of peritonitis is achieved by employing the P‐CDs as sensors. The results may provide a clue for the diagnosis and treatment of inflammation or cancers employing CL CDs as sensors.Reactive oxygen species (ROS) are generated in the body and related to many pathophysiological processes. Hence, detection of ROS is indispensable in understanding, diagnosis, and treatment of many diseases. Here, near‐infrared (NIR) chemiluminescent (CL) carbon nanodots (CDs) are fabricated for the first time and their CL quantum yield can reach 9.98 × 10 2O2 in vitro and in vivo with the detection limit is 5 × 10−9m. Bioimaging inflammatory H2O2 in a mouse model of peritonitis is achieved.NIR carbon nanodots (CDs) with efficient chemiluminescence are developed. Nanointegration of NIR CDs and peroxalate can serve as turn‐on probes for bioimaging of exogenous and endogenous H Thus it is of great importance in monitoring the concentration of H2O2 in living specimens. To this end, a number of mapping tools including “dark” biological processes and radiative recombination mechanism have been developed. Chemiluminescence (CL), a kind of light emission induced by energy transfer from chemical reactions, has evoked considerable interest as one ultrasensitive chemical analysis method with quantification and localization. Without auto‐fluorescent interference and phototoxicity from high‐energy excitation light, CL shows high signal‐to‐noise ratio and low perturbation in sensing H2O2 in vivo compared to photoluminescence (PL) method. Moreover, unlike the bioluminescence probe requiring the activation of bioactive enzyme, CL imaging of H2O2 is a process of nonenzymatic reaction employing a H2O2‐responsive peroxalate that can transfer chemical energy to the CL emitter. Nevertheless, current CL reporters on H2O2 concentrate mainly on small‐molecular dyes, semiconducting polymer, and aggregation induced emission nanoparticles, which suffer from low efficiency, short emission wavelength, and low chemical stability in highly oxidative ROS. Thereby, it is meaningful to develop new class of CL nanosensors for the imaging and detecting ROS in vitro and in vivo.Reactive oxygen species (ROS), as significant reactive and signaling molecules in the process of intravital metabolism, play a great role in many biological processes.3, 4 Recently, the CL properties of CDs in peroxlate–H2O2 system have been investigated, and it has been found that multicolor bright and persistent CL can be obtained from CDs. Therefore, it is practicable to develop versatile CL probes based on CDs to detect ROS via in vivo or in vitro imaging. In general, there are several advantages for CDs as the CL imaging probes: (i) CDs exhibit excellent light emission ability and the luminescence property can be tuned by different methods; (ii) CDs with emission wavelength at near‐infrared (NIR) region (beyond 650 nm) can be synthesized, which is particularly important for bioimaging due to the deep tissue penetration; (iii) the energy level of CDs can be modulated to reduce the energy interval with the energetic intermediate‐1,2‐dioxetanedione, which is beneficial to the electron transfer in the process of H2O2‐activated luminescence and further enhances the CL quantum efficiency (QY) of CDs; (iv) the abundant surface radicals endow CDs with the good ability of drug carriers; (v) benign biocompatibility and high photostability of CDs make them promising application in CL bioimaging. Hence, it is significant to develop CD‐based CL probes to generate luminescent signals in response to H2O2 and further provides a category of bioimaging for ROS.Carbon nanodots (CDs), which are considered as discrete quasi‐spherical nanoparticles with sizes less than 10 nm, are one kind of promising nanomaterials in bioimaging, photocatalysis, optoelectronics, and sensing owing to its unique properties such as high emission efficiency, good biocompatibility, high photo‐stability, and tunable luminescence.28 RecN,N‐diethylformamide (DEF). The CDs exhibit an QY of 9.98 × 10−3 einstein mol−1 in bis oxalate (CPPO) and H2O2 solution, which is the highest value ever reported for the CL from CDs. In addition, P‐CDs are transformed from NIR CDs and CPPO through the nanoscopic coaggregation process in the existence of amphiphilic polymeric conjugate (PEG‐b‐PPG‐b‐PEG). By virtue of the high efficiency and deep penetration of NIR emission, the P‐CDs have been employed to bioimaging H2O2 in vitro and in vivo. Moreover, imaging of inflammatory H2O2 in a mouse model of peritonitis has been achieved by employing the P‐CD as a sensor. The present work exhibits considerable potential for CDs as new class of CL probes for in vivo imaging applications in the diagnosis and treatment of inflammation or cancers.Here, CDs with NIR CL have been synthesized with solvothermal method employing citric acid and urea as precursors in 22‐domains, implying that it is promising to excavate the application of CDs as novel probes for ROS sensing. However, a high CL QY and NIR emission of CD based probes are still urgent to be developed.In our previous report, it is found that multicolor PL and CL can be obtained from CDs by changing the degree of graphitization of the conjugated sp sensing.29 How[–42] Transmission electron microscopy (TEM) has been used to characterize the morphology of the CDs, as shown in Figure−1) and D band (1350 cm−1) of about 0.99 . In addition, the deconvoluted high‐resolution X‐ray photoelectron spectra (XPS) for C1s, N1s, and O1s reveal that there are O‐ and N‐containing functional groups on the surface of the CDs, which facilitates the surface modification for the CDs . The PL and CL properties of the CDs are illustrated in Figure 2 C, n−π* transition of conjugated C=O and Mie scattering due to the extended conjugation in the CD structure, respectively. The PL lifetime of 5.9 ns for the CDs can be calculated and obtained with a single exponential function . Moreover, the CL emission spectra (≈647 nm) after adding CDs into CPPO and H2O2 solution present consistent spectra with the PL spectra, implying that the CD‐based CL is originated from direct radiative recombination of the CDs under the chemical excitation  than that in the presence of other ROS, verifying that the CL system based on the CDs has a high selectivity to H2O2  and urea (2 g) in 10 mL DEF by one‐step solvothermal strategy (160 °C for 8 h). DEF, as polar aprotic solvents, can exacerbate dehydration reaction and increase the conjugation degree of CDs due to effective dehydration reaction happened between citric acid and intramolecules with longer carbon chains (ethyl group from DEF).40–42  g and ur2 Figure . AdditioFigure2 in dimethylformamide (DMF) as illustrated in Experimental Section. With dichloromethane (CH2Cl2) as eluent, the hydrophobic M‐CDs can be extracted from DMF with massive water and kept in dichloromethane (CH2Cl2) solution. As illustrated in the TEM images, the as‐prepared M‐CDs are spherical nanoparticles with an average diameter of around 5 nm, which is similar to the CDs shown in Figure 1H nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) have been employed to characterize the modification for the surface functional groups of the CDs and M‐CDs  and hydrophilic CDs to form nanointegrated CDs (P‐CDs), we have first developed one facile method to modulate CDs with lipophilic long chain . As shown in s Figure . The intFigure−3 einstein mol−1, which is 7.6 times higher than those loaded with 2 mg water‐soluble CDs  have been prepared through the nanoprecipitation of oil‐soluble M‐CDs, CPPO, and amphiphilic PEG‐b‐PPG‐b‐PEG, as illustrated in 2O2 in vitro and in vivo. Figurea illustrates the scheme of in vitro and in vivo CL imaging generated from P‐CDs with the existence of H2O2 from exogenous environment or endogenous disease. The practicability of P‐CDs for in vitro imaging of exogenous H2O2 in aqueous has been first assessed by the PL and CL imaging with the IVIS imaging system. The PL and CL images are captured after adding P‐CDs into different concentrations of H2O2 aqueous solution. As shown in Figure 2O2 is at a high concentration of 5 × 10−6m, implying the PL imaging with P‐CDs is not applicable to the detection of H2O2. In contrast, the CL intensity of the P‐CDs presents a significant increase with increasing the H2O2 concentrations, as indicated in Figure −9m with a detection limit of 5 × 10−9m . The detection limit (5 × 10−9m) is much smaller than the usual concentration of H2O2 (≈100 × 10−9m) in living bodies, which is the best value ever reported for CDs based probes . To evaluate the ability of in vivo sensing the exogenous H2O2 for the P‐CDs, the images of PL and CL intensity are also recorded when the anaesthetized nude mice are subcutaneously injected into the dorsal area with the P‐CDs solution and different concentrations of H2O2. As shown in Figure 2O2 concentration. Nevertheless, the CL intensity increases linearly with the increase of H2O2 concentration from 0 × 10−9 to 100 × 10−9m. Meanwhile, the CL intensity of the P‐CDs with the existence of 5 × 10−9m H2O2 is about 1.5‐fold higher than that of the P‐CDs alone.With the merit of low toxicity, long persistent glowing, and deep penetration of NIR emission, the P‐CDs can be employed as bioimaging probes to detect H2O2 due to the abnormal variation in the body of living mice. Endogenous H2O2 is the significant metabolite when the body suffers from inflammation or cancers. Hence, the early diagnostics and treatment of these diseases can be achieved through monitoring the low concentration endogenous H2O2. As a proof‐of‐concept, the inflammatory mouse models have been established through intraperitoneal injection of lipopolysaccharide (LPS), which can be used to induce the mouse model of peritonitis and further result in the generation of excessive H2O2. The deep images of mouse models are captured for 3 min after the injection of P‐CDs  at an early stage of peritonitis (4 h after LPS injection). As shown in FigureAlong with the high sensitivity, good biocompatibility, and potential deep tissue penetration, P‐CDs are beneficial for detecting the endogenous H32O2. With further modification, the CDs can be modified from hydrophilic to hydrophobic. P‐CDs can be produced by combining the CDs, CPPO, and PEG‐b‐PPG‐b‐PEG through the nanoscopic coaggregation. The NIR P‐CDs generate good in vitro and in vivo CL signals in response to H2O2 with a linear range from 0 to 100 × 10−9m and a low detection limit of 5 × 10−9m. Furthermore, the P‐CDs are proved to be a potential CL probe for bioimaging H2O2 in the inflammation‐related diseases in living mice. The results reported in this paper may provide a clue for the diagnosis and treatment of inflammation or cancers employing CL CDs as sensors.In summary, we have demonstrated efficient NIR emissive CDs‐based CL system via energy transfer from the chemical reaction of peroxalate and H4An amount of 1 g citric acid and 2 g urea were dispersed in 10 mL of DEF. The mixtures were added into Teflon‐lined stainless autoclave (20 mL). Then the sealed autoclave vessels were placed into an electric oven, which was set at 160 °C and hold for 8 h. The resulting solvents were purified via silica column chromatography using DMF as the eluent, and then the as‐prepared CDs were precipitated with absolute ethyl alcohol and collected by vacuum drying at 60 °C for 1 day. The final products were collected for characterizations and further used.2 were dispersed into 50 mL DMF, where the octadecylamine was used to switch the water−oil soluble of the CDs and mPEG‐NH2 was used to increase the cross‐linking of CDs and octadecylamine. After stirring with air flow for 12 h under 60 °C, 10 mL mixture was dispersed in 20 mL CH2Cl2. With dichloromethane CH2Cl2 as eluent, the hydrophobic M‐CDs can be extracted from DMF with massive water and kept in CH2Cl2 solution. The as‐prepared M‐CDs were collected by vacuum drying at 60 °C for 1 day. The final products were collected for characterizations and further used.An amount of 0.2 g CDs powder, 0.8 g octadecylamine, and 0.1 g mPEG‐NH2Cl2 (5.0 mL) solution. After CH2Cl2 was evaporated with air flow, the powder was redispersed into 2 mL deionized water and filtered through a 0.22 µm PVDF syringe driven filter (Millipore). The formed P‐CDs suspension was finally concentrated to different concentrations by ultrafiltration and used immediately for experiments.PEG‐b‐PPG‐b‐PEG (40 mg), CPPO (4 mg), and different mass of M‐CDs  were dispersed into CH2O2 as oxidant with a known QY of 8.3 × 10−3 einstein mol−1 at pH 11 according to the previous literatures. According to the CL spectra and kinetic curves, the CL QYs were calculated according to the following equations:CL is the CL QYs of CDs and P‐CDs, Q is the total light emission obtained by integration of emission intensity under time curves. fluc is obtained by measuring the emission kinetics of lucigenin reaction performed in standard conditions. fphoto is obtained from the sensitivity at the emission wavelength (λmax = 475 nm) of the lucigenin standard, f(λluc), and the emission of the CDs and P‐CDs, f(λs). n is the number of moles of lucigenin (nluc) or the number of moles of CPPO.The CL QYs of the CDs and P‐CDs were measured using lucigenin with Heratures.29 Acc−1, 1 mL) were placed in EP tubes. After addition of different concentrations  of H2O2, both PL and CL imaging were performed using an IVIS spectrum imaging system. CL images were acquired for 30 s with open filter or emission at 640 ± 10 nm, and fluorescence images were acquired for 0.1 s with excitation of 550 ± 10 nm, and emission at 640 ± 10 nm. The media pH 7.4 was controlled using phosphate buffer saline (PBS) buffer solution.For the quantitative analysis, P‐CDs (10 mg mL−1) of P‐CDs was used for incubating the Hela cells for 24 h at 37 °C. Then, the cell viability of Hela cell was tested using standard MTT method for assessing the cytotoxicity of the P‐CDs.The PBS solution with different concentrations  were mixed with different concentrations  of H2O2, and the P‐CD suspension (0.1 mL) was injected subcutaneous into the dorsal of anaesthetized mice (2% isoflurane in oxygen). The media pH 7.4 was controlled using PBS buffer solution. CL images were obtained with a 3 min acquisition time with open filter or emission at 640 ± 10 nm, and fluorescence images were acquired for 30 s with excitation of 550 ± 10 nm, and emission at 640 ± 10 nm.All animal studies were performed in compliance with the Guide Care and Use of Laboratory Animals proposed by the National Institutes of Health. All procedures and protocols were approved by the Animal Ethics Committee at Zhengzhou University . For in vivo bioimaging exogenous H2O2 in the mouse model of peritonitis, mice (6−8 weeks old) were injected intraperitoneally with LPS (8 mg kg−1). For the inhibitor study, mice were treated intraperitoneally 5 min before LPS treatment using 200 mg kg−1 GSH. The control mice were treated only using 200 mg kg−1 saline. After 4 h, anesthetized mice (2% isoflurane in oxygen) were treated with intraperitoneal injection of P‐CDs . CL images were captured with a 3 min acquisition time with open filter using the IVIS spectrum imaging system. Fluorescence images were captured with a 0.1 s acquisition time with excitation of 550 ± 10 nm, and emission at 640 ± 10 nm using the IVIS spectrum imaging system.To image endogenous HMore details about the characterization of material and data are demonstrated in Supporting Information.The authors declare no conflict of interest.Supporting InformationClick here for additional data file.


The authors wish to make the following correction to this paper :We found that one sentence is repeatedly printed in the results Section 3.4, lines 2–5. The sentence should read: “In particular, the estimated first generation of newly-invaded FAW emerged on 20–30 May for A1, on 1–10 June for B1, on 11–20 June for C1, and on 21–30 June for D1, whereas the peak adult emergence of the second generation was suggested to occur on 10–20 July for A2, 1–10 July for B2, 11–20 July for C2, and 21–30 July for D2, respectively.”The authors would like to apologize for any inconvenience caused to the readers by these changes.


Deprotonation of the ligand precursor with lithium bases to the respective dilithio carbenaporphyrin complex and transmetallation to scandium lead to complexes that exhibit orange fluorescence. Optical property combined with TD‐DFT studies verify an aromatic character for each heterocyclic moiety rather than an antiaromatic macrocycle in the ligand precursor as well as in the complexes. While the geometric features of the carbenaporphyrin ligand strongly resemble those of porphyrin, DFT calculations reveal a stronger electron‐donating ability of the new ligand.The synthesis of an NHC‐containing porphyrinoid ligand is presented. The formally antiaromatic 20 πe + and Sc3+ complexes the ligand reveals striking geometric similarity to porphyrins, but is a stronger electron donor.The synthesis of a carbenaporphyrin ligand based on carbazole and triazolylidene is reported. Instead of a macrocyclic aromatic or antiaromatic character, the aromaticity of each heterocyclic moiety is preserved, which results in optical properties different from porphyrins, for example, fluorescence. In Li The synthesis of 1 and the investigation of its special properties are the objectives of this work.N‐heterocyclic carbene ligands (NHCs) are stable (“bottleable”) singlet carbenes3 and azide 4 are literature‐known compounds and can be obtained from carbazole 2.THF) shows five aromatic signals of equal ratio , two broad N−H signals (10.19 (Carb‐N) and 9.43 ppm (Carb‐C)) and two singlets for the tert‐butyl groups (1.54 and 1.56 ppm). X‐ray structure analysis of a colorless single crystal—obtained from slow evaporation of a solution in tetrahydrofuran—confirms the identity of 5  and a larger of the triazole planes (72.3°) into the opposite direction (tilting of the triazole plane against the carbazole plane 36° (mean)), so that the C−H and N−H groups are pointing away from each other. It is enhanced by N−H hydrogen bonds to one molecule of tetrahydrofuran. This coordination provides an explanation for the broadened N−H signals in the 1H NMR spectrum.The 5 to form the triazolium moieties in 6 did not proceed with methyl iodide but required the stronger Meerwein's salt (trimethyloxonium tetrafluoridoborate). The dicationic macrocycle 6 was obtained quantitatively as a colorless crystalline material. In the 1H NMR spectrum product 6 is identified by the signal of the methyl groups at 4.55 ppm. Although the N−H groups are chemically inequivalent, only one (broad) signal (2 H) at 9.40 ppm is observed, possibly due to fast exchange. The downfield‐shifted signal of the triazolium C−H moiety at 9.92 ppm, which indicates a higher acidic character of the hydrogen atom than in 5, and its carbon chemical shift at δ(13C)=132.2 ppm compared to 124.8 ppm in 5 are very characteristic features.The alkylation of 6.The X‐ray structure analysis of single crystals obtained from slow evaporation of a solution in tetrahydrofuran confirms the successful formation of the triazolium macrocycle 5, hydrogen bonding to the acidic hydrogen atoms is observed, which in the case of 6 also includes the triazolium hydrogen atoms. They have short contacts to the tetrahydrofuran oxygen, while the carbazole N−H atoms are hydrogen‐bonded to the fluorine atom of one of the BF4− counterions . The triazolium planes are inclined by 87.1° and are tilted by an average of 44.1° against the carbazole planes .Similar to macrocycle s Figure . As alre5 the CTP precursor 6 is a colorless compound, (porphin is dark red), which indicates that 6 lacks antiaromatic character . Instead, it resembles other carbazole porphyrinoids regarding this feature. (217.8 ppm) is no longer observed.Transmetallation of 8 Scheme  that exh8 by removal of the solvent resulted in decomposition of this highly moisture sensitive complex. However, from a supersaturated solution of 8 in tetrahydrofuran, orange single crystals were obtained and subjected to X‐ray structure analysis.4‐coordination mode of the CTP ligand to scandium by substitution of two chlorido and two tetrahydrofuran ligands. The CTP ligand takes in a basal coordination, so that the scandium is located 0.99 Å above the plane spanned by the coordinating atoms N9‐C5′‐N19‐C10′. This coordination is typically found in porphyrin lanthanoid complexes, which leads to cis coordination of additional ligands.8 the additional tetrahydrofuran ligand leads to a coordination number of 6 in a distorted prismatic arrangement. The carbazole planes are almost coplanar (4.0°) and the inclination of the triazole planes is reduced to only 44.1°. They are tilted against the carbazole planes by 22° (mean). The angles at the carbene atoms  are reduced (by 3°) compared to the carbene precursor 6 as it is typically found for NHC ligands and their respective azolium precursors.All attempts to isolate complex 8 and the porphyrin Sc complex TTPScClWhile the geometric features of the CTP coordination to Sc are similar to that of the porphyrin ligand, the electronic properties of the carbene moiety should impart a stronger electron‐donating character to the CTP ligand. Therefore, we calculated the Mulliken charge of complex δ(1H)=1.68 ppm). To probe a potential ring current in our CTP ligand, we added CpLi to a solution of complex 8 in [D8]THF =5.21 ppm (LiCp: δ(1H)=5.69 ppm), which is comparable to other CpSc complexes.9 can also be synthesized in a one‐pot procedure starting from the ligand precursor 6 in 80 % isolated yield as an orange solid. The color results from a weak absorption with a maximum at 485 nm and a stronger one with a maximum at 408 nm in THF. The complex shows orange fluorescence in the solid state  and yellow fluorescence in solution ) (Supporting Information).It is known from the mixed Cp‐porphyrin sandwich complex [ScCp(OEP)] (OEP=octaethylporphyrin)F Scheme . The for1 (CTP) and its lithium and scandium complexes. A potential aromatic or antiaromatic character of an 18 or 20 πe− macrocycle in the carbene precursor 6 or in the complexes 7–9 can be excluded. Instead, the heterocyclic moieties keep their individual aromaticity, but provide the geometric features of porphyrins upon complexation with lithium and scandium. Thus, a porphyrinoid character can be attributed to ligand 1, and in addition it features stronger electron‐donor properties than porphyrins owing to its mesoionic NHC moieties. The influence of the electronic properties on the reactivity of these complexes and on those with redox‐active metal centers is subject of our current research.To conclude, we have synthesized and investigated the properties of the carbenaporphyrin ligand 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.SupplementaryClick here for additional data file.


Mediators of Inflammation has retracted the article titled “Neuropilin-1highCD4+CD25+ Regulatory T Cells Exhibit Primary Negative Immunoregulation in Sepsis” [Figure duplication concerns were raised to our attention and then noted on PubPeer . A reassPanel 4 in Figure 1(e) is the same as panel 10 in Figure 2(c).Panel 1 in Figure 1(f) is the same as panel 5 in Figure 1(f).Duplications were also identified within the article :Panel 4The authors did not provide a satisfactory response and the article is therefore being retracted with the agreement of the Chief Editor. The authors do not agree to the retraction.