Efficient Visible-Light-Driven CO2 Reduction Mediated by Defect-Engineered BiOBr Atomic Layers

Indium oxide with oxygen vacancies boosts O2 adsorption and activation for electrocatalytic H2O2 production

Oxygen reduction reaction via the two-electron pathway (2e- ORR) offers a sustainable opportunity for hydrogen peroxide (H2O2) production, but suffers from low selectivity. In this work, indium oxide with oxygen vacancies (In2O3-x) exhibits a H2O2 selectivity close to 98% at 0.6 V vs. RHE. Further, a Faradaic efficiency (FE) of around 95% at 0.4-0.6 V vs. RHE and a H2O2 productivity of 3.7 mol gcatalyst-1 h-1 are reached in a flow cell. In situ Raman spectra indicate that In2O3-x promotes the adsorption and activation of O2 and stabilizes oxygen intermediates. This work provides an insight into improving H2O2 selectivity for 2e- ORR catalysts.

S‑scheme heterojunction of thin-layer O-modified graphitic carbon nitride/cobalt porphyrin to promote photocatalytic CO2 conversion

The emissions of CO2 are increasing year by year, which have led to serious environmental problems. Converting CO2 into valuable fuels through photocatalysis is a promising strategy. In this research, oxygen atoms were successfully innovated into graphitic carbon nitride (CN). Additionally, cobalt porphyrin (CoTPP) was successfully loaded onto the modified carbon nitride (Co/CN). The generation of interfacial electric fields and bending bands between CN and CoTPP was demonstrated experimentally. The electrons in the CN and the holes in the CoTPP were combined to form a unique S-scheme heterojunction structure, and efficient separation of carriers was promoted. As a result, the CO conversion under visible light irradiation reached an impressive 100.70 μmol g-1 h-1. By integrating theoretical and experimental findings, this study underscores the critical role of catalyst design in enabling efficient photocatalytic CO2 reduction.

Three-layered nanoplates and amorphous/crystalline interface synergism boost CO2 photoreduction on bismuth oxychloride nanospheres

Structural features like 3D nano-size, ultrathin thickness and amorphous/crystalline interfaces play crucial roles in regulating charge separation and active sites of photocatalysts. However, their co-occurrence in a single catalyst and exploitation in photocatalytic CO2 reduction (PCR) remains challenging. Herein, nano-sized bismuth oxychloride spheres (BiOCl-NS) confining three-layered nanoplates (∼2.2 nm ultrathin) and an amorphous/crystalline interface are exclusively developed via intrinsic engineering for an enhanced sacrificial-reagent-free PCR system. The results uncover a unique synergism wherein the three-layered nanoplates accelerate electron-hole separation, and the amorphous/crystalline interface exposes electron-localized active sites (Bi-Ovac-Bi). Consequently, BiOCl-NS exhibit efficient CO2 adsorption and activation with the lowering of rate-determining-step energy barriers, leading to remarkable CO production (102.72 μmol g-1 h-1) with high selectivity (>99%), stability (>30 h), and apparent quantum efficiency (0.51%), outperforming conventional counterparts. Our work provides a facile structural engineering approach for boosting PCR and offers distinct synergism for advancing diverse materials.

WO3/BiOBr S-Scheme Heterojunction Photocatalyst for Enhanced Photocatalytic CO2 Reduction

The photocatalytic CO2 reduction strategy driven by visible light is a practical way to solve the energy crisis. However, limited by the fast recombination of photogenerated electrons and holes in photocatalysts, photocatalytic efficiency is still low. Herein, a WO3/BiOBr S-scheme heterojunction was formed by combining WO3 with BiOBr, which facilitated the transfer and separation of photoinduced electrons and holes and enhanced the photocatalytic CO2 reaction. The optimized WO3/BiOBr heterostructures exhibited best activity for photocatalytic CO2 reduction without any sacrificial reagents, and the CO yield reached 17.14 μmol g-1 after reaction for 4 h, which was 1.56 times greater than that of BiOBr. The photocatalytic stability of WO3/BiOBr was also improved.

Bipolaronic Motifs Induced Spatially Separated Catalytic Sites for Tunable Syngas Photosynthesis From CO2

Photocatalytic reduction of CO2 into syngas is a promising way to tackle the energy and environmental challenges; however, it remains a challenge to achieve reaction decoupling of CO2 reduction and water splitting. Therefore, efficient production of syngas with a suitable CO/H2 ratio for Fischer-Tropsch synthesis can hardly be achieved. Herein, bipolaronic motifs including Co(II)-pyridine N motifs and Co(II)-imine N motifs are rationally designed into a crystalline imine-linked 1,10-phenanthroline-5,6-dione-based covalent organic framework (bp-Co-COF) with a triazine core. These featured structures with spatially separated active sites exhibit efficient photocatalytic performance toward CO2-to-syngas conversion with a suitable CO/H2 ratio (1:1-1:3). The bipolaronic motifs enable a highly separated electron-hole state, whereby the Co(II)-pyridine N motifs tend to be the active sites for CO2 activation and accelerate the hydrogenation to form *COOH intermediates; whilst, the Co(II)-imine N motifs increase surface hydrophilicity for H2 evolution. The photocatalytic reductions of CO2 and H2O thus decouple and proceed via a concerted way on the bipolaronic motifs of bp-Co-COF. The optimal bp-Co-COF photocatalyst achieves a high syngas evolution rate of 15.8 mmol g-1 h-1 with CO/H2 ratio of 1:2, outperforming previously reported COF-based photocatalysts.

Surface-Integrating Oxygen Vacancy and CuxO Nanodots Enabling Synergistic Electric Field and Dual Catalytic Sites Boosting CO2 Photoreduction

High carrier separation efficiency and rapid surface catalytic reaction are crucial for enhancing catalytic CO2 photoreduction reaction. Herein, integrated surface decoration strategy with oxygen vacancies (Ov) and anchoring CuxO (1 < x < 2) nanodots below 10 nm is realized on Bi2MoO6 for promoting CO2 photoreduction performance. The charge interaction between Ov and anchored CuxO enables the formation of enhanced internal electric field, which provides a strong driving force for accelerating the separation of photocharge carriers on the surface of Bi2MoO6 (ηsurf ≈71%). They can also cooperatively reduce the surface work function of Bi2MoO6, facilitating the migration of carrier to the surface. Meanwhile, surface-integrated Ov and CuxO nanodots allowing dual catalytic sites strengthens the adsorption and activation CO2 into *CO2 over Bi2MoO6, considerably boosting the progression of CO2 conversion process. In the absence of co-catalyst or sacrificial agent, Bi2MoO6 with Ov and CuxO nanodots achieves a photocatalytic CO generation rate of 12.75 µmol g-1 h-1, a remarkable increase of over ≈15 times that of the original counterpart. This work provides a new idea for governing charge movement behaviors and catalytic reaction thermodynamics on the basis of synergistic improvement of electric field and active sites by coupling of the internal defects and external species.

Elucidating Structural Disorder in Ultra-Thin Bi-Rich Bismuth Oxyhalide Photocatalysts

Advancing the field of photocatalysis requires the elucidation of structural properties that underpin the photocatalytic properties of promising materials. The focus of the present study is layered, Bi-rich bismuth oxyhalides, which are widely studied for photocatalytic applications yet poorly structurally understood, due to high levels of disorder, nano-sized domains, and the large number of structurally similar compounds. By connecting insights from multiple scattering techniques, utilizing electron-, X-ray- and neutron probes, the crystal phase of the synthesized materials is allocated as layered Bi24O31X10 (X = Cl, Br), albeit with significant deviation from the reported 3D crystalline model. The materials comprise anisotropic platelet-shaped crystalline domains, exhibiting significant in-plane ordering in two dimensions but disorder and an ultra-thin morphology in the layer stacking direction. Increased synthesis pH tailored larger, more ordered crystalline domains, leading to longer excited state lifetimes determined via femtosecond transient absorption spectroscopy (fs-TAS). Although this likely contributes to improved photocatalytic properties, assessed via the photooxidation of benzylamine, increasing the overall surface area facilitated the most significant improvement in photocatalytic performance. This study, therefore, enabled both phase allocation and a nuanced discussion of the structure-property relationship for complicated, ultra-thin photocatalysts.

Preparation of core-shell structure Ag@TiO2 plasma photocatalysts and reduction of Cr(VI): Size dependent and LSPR effect

The poor light absorption and low carrier separation efficiency of Titanium dioxide (TiO2) limit its further application. The introduction of plasma metal Ag have the potential to solve these drawbacks owing to its plasma resonance effect. Thus core-shell structure Ag@TiO2 plasma photocatalysts was prepared by using facile reduction method in this work. More specifically, Ag@TiO2 composite catalysts with different Ag loading amounts were prepared in the presence of surfactant PVP. Ag@TiO2 demonstrates excellent light absorption performance and photoelectric separation efficiency compared with pure TiO2. As a result, it displays excellent performance of Cr(VI) reduction under visible light. The optimal composite catalysts Ag@TiO2-5P achieves exceptional visible-light-driven photocatalytic Cr(VI) reduction efficiency of 0.01416 min-1 that is 2.29 times greater than pure TiO2. To investigate the role of PVP, we also synthesized Ag@TiO2-5 without PVP. The experimental results show that although Ag@TiO2-5 Cr(VI) reduction performance is superior to pure TiO2, it significantly decreases compared with Ag@TiO2-5P. The results of TEM and optoelectronic testing show that agglomeration of Ag particles leads to a decrease in the photoelectric separation efficiency of Ag@TiO2-5. The smaller Ag particles provide more active sites and demonstrating a stronger overall local surface plasmon resonance (LSPR) effect. DMPO spin-trapping ESR spectra testing indicates that ∙O2- and ∙OH are the main reactive species. This research provides a potential strategy to prepare Ag-based plasma photocatalysts for environment protection.

Ligand-mediated exciton dissociation and interparticle energy transfer on CsPbBr3 perovskite quantum dots for efficient CO2-to-CO photoreduction

Perovskite quantum dots (PQDs) hold immense potential as photocatalysts for CO2 reduction due to their remarkable quantum properties, which facilitates the generation of multiple excitons, providing the necessary high-energy electrons for CO2 photoreduction. However, harnessing multi-excitons in PQDs for superior photocatalysis remains challenging, as achieving the concurrent dissociation of excitons and interparticle energy transfer proves elusive. This study introduces a ligand density-controlled strategy to enhance both exciton dissociation and interparticle energy transfer in CsPbBr3 PQDs. Optimized CsPbBr3 PQDs with the regulated ligand density exhibit efficient photocatalytic conversion of CO2 to CO, achieving a 2.26-fold improvement over unoptimized counterparts while maintaining chemical integrity. Multiple analytical techniques, including Kelvin probe force microscopy, temperature-dependent photoluminescence, femtosecond transient absorption spectroscopy, and density functional theory calculations, collectively affirm that the proper ligand termination promotes the charge separation and the interparticle transfer through ligand-mediated interfacial electron coupling and electronic interactions. This work reveals ligand density-dependent variations in the gas-solid photocatalytic CO2 reduction performance of CsPbBr3 PQDs, underscoring the importance of ligand engineering for enhancing quantum dot photocatalysis.

Enhanced photocatalytic performance of Bi2O2CO3/Bi4O5Br2/reduced graphene oxide Z-schemehe terojunction via a one-pot room-temperature synthesis

Bi2O2CO3(BOC)/Bi4O5Br2(BOB)/reduced graphene oxide (rGO) Z-scheme heterojunction with promising photocatalytic properties was synthesized via a facile one-pot room-temperature method. Ultra-thin nanosheets of BOC and BOB were grown in situ on rGO. The formed 2D/2D direct Z-scheme heterojunction of BOC/BOB with oxygen vacancies (OVs) effectively leads to lower negative electron reduction potential of BOB as well as higher positive hole oxidation potential of BOC, showing improved reduction/oxidation ability. Particularly, rGO is an acceptor of the electrons from the conduction band of BOC. Its dual roles significantly improve the transfer performance of photo-induced charge carriers and accelerate their separation. With layered nanosheet structure, rich OVs, high specific surface area, and increased utilization efficiency of visible light, the multiple synergistic effects of BOC/BOB/rGO can achieve effective generation and separation of the electron-holes, thereby generating more •O2- and h+. The photocatalytic reduction efficiency of CO2 to CO (12.91 µmol/(g·hr)) is three times higher than that of BOC (4.18 µmol/(g·hr)). Moreover, it also achieved almost 100% removal of Rhodamine B and cyanobacterial cells within 2 hours.

Disclosing Support-Size-Dependent Effect on Ambient Light-Driven Photothermal CO2 Hydrogenation over Nickel/Titanium Dioxide

The size of support in heterogeneous catalysts can strongly affect the catalytic property but is rarely explored in light-driven catalysis. Herein, we demonstrate the size of TiO2 support governs the selectivity in photothermal CO2 hydrogenation by tuning the metal-support interactions (MSI). Small-size TiO2 loading nickel (Ni/TiO2 -25) with enhanced MSI promotes photo-induced electrons of TiO2 migrating to Ni nanoparticles, thus favoring the H2 cleavage and accelerating the CH4 formation (227.7 mmol g-1  h-1 ) under xenon light-induced temperature of 360 °C. Conversely, Ni/TiO2 -100 with large TiO2 prefers yielding CO (94.2 mmol g-1  h-1 ) due to weak MSI, inefficient charge separation, and inadequate supply of activated hydrogen. Under ambient solar irradiation, Ni/TiO2 -25 achieves the optimized CH4 rate (63.0 mmol g-1  h-1 ) with selectivity of 99.8 %, while Ni/TiO2 -100 exhibits the CO selectivity of 90.0 % with rate of 30.0 mmol g-1  h-1 . This work offers a novel approach to tailoring light-driven catalytic properties by support size effect.

A Comprehensive Review on the Boosted Effects of Anion Vacancy in the Heterogeneous Photocatalytic Degradation, Part II: Focus on Oxygen Vacancy

Environmental problems, including the increasingly polluted water and the energy crisis, have led to a need to propose novel strategies/methodologies to contribute to sustainable progress and enhance human well-being. For these goals, heterogeneous semiconducting-based photocatalysis is introduced as a green, eco-friendly, cost-effective, and effective strategy. The introduction of anion vacancies in semiconductors has been well-known as an effective strategy for considerably enhancing the photocatalytic activity of such photocatalytic systems, giving them the advantages of promoting light harvesting, facilitating photogenerated electron-hole pair separation, optimizing the electronic structure, and enhancing the yield of reactive radicals. This Review will introduce the effects of anion vacancy-dominated photodegradation systems. Then, their mechanism will illustrate how an anion vacancy changes the photodegradation pathway to enhance the degradation efficiency toward pollutants and the overall photocatalytic performance. Specifically, the vacancy defect types and the methods of tailoring vacancies will be briefly illustrated, and this part of the Review will focus on the oxygen vacancy (OV) and its recent advances. The challenges and development issues for engineered vacancy defects in photocatalysts will also be discussed for practical applications and to provide a promising research direction. Finally, some prospects for this emerging field will be proposed and suggested. All permission numbers for adopted figures from the literature are summarized in a separate file for the Editor.

Copper Modulated Lead-Free Cs4 MnSb2 Cl12 Double Perovskite Microcrystals for Photocatalytic Reduction of CO2

In order to deal with the global energy crisis and environmental problems, reducing carbon dioxide through artificial photosynthesis has become a hot topic. Lead halide perovskite is attracted people's attention because of its excellent photoelectric properties, but the toxicity and long-term instability prompt people to search for new photocatalysts. Herein, a series of <111> inorganic double perovskites Cs4 Mn1-x Cux Sb2 Cl12 microcrystals (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) are synthesized and characterized. Among them, Cs4 Mn0.7 Cu0.3 Sb2 Cl12 microcrystals have the best photocatalytic performance, and the yields of CO and CH4 are 503.86 and 68.35 µmol g-1 , respectively, after 3 h irradiation, which are the highest among pure phase perovskites reported so far. In addition, in situ Fourier transform infrared (FT-IR) spectroscopy and electron spin resonance (ESR) spectroscopy are used to explore the mechanism of the photocatalytic reaction. The results highlight the potential of this class of materials for photocatalytic reduction reactions.

Solar-driven CO2-to-ethanol conversion enabled by continuous CO2 transport via a superhydrophobic Cu2O nano fence

The overall photocatalytic CO2 reduction reaction presents an eco-friendly approach for generating high-value products, specifically ethanol. However, ethanol production still faces efficiency issues (typically formation rates <605 μmol g-1 h-1). One significant challenge arises from the difficulty of continuously transporting CO2 to the catalyst surface, leading to inadequate gas reactant concentration at reactive sites. Here, we develop a mesoporous superhydrophobic Cu2O hollow structure (O-CHS) for efficient gas transport. O-CHS is designed to float on an aqueous solution and act as a nano fence, effectively impeding water infiltration into its inner space and enabling CO2 accumulation within. As CO2 is consumed at reactive sites, O-CHS serves as a gas transport channel and diffuser, continuously and promptly conveying CO2 from the gas phase to the reactive sites. This ensures a stable high CO2 concentration at reactive sites. Consequently, O-CHS achieves the highest recorded ethanol formation rate (996.18 μmol g-1 h-1) to the best of our knowledge. This strategy combines surface engineering with geometric modulation, providing a promising pathway for multi-carbon production.

Selective Photoreduction of CO2 to CH4 Triggered by Metal-Vacancy Pair Sites

Selectively achieving the photoreduction of carbon dioxide (CO2) to methane (CH4) remains a significant challenge, which primarily arises from the complexity of the protonation process. In this work, we designed metal-vacancy pair sites in defective metal oxide semiconductors, which anchor the reactive intermediates with a bridged linkage for the selective protonation to produce CH4. As an example, oxygen-deficient Nb2O5 nanosheets are synthesized, in which the niobium-oxygen vacancy pair sites are demonstrated by X-ray photoelectron spectroscopy and electron paramagnetic resonance spectra. In situ Fourier transform infrared spectroscopy monitors the *CH3O intermediate, a key intermediate for CH4 production, during the CO2 photoreduction in oxygen-deficient Nb2O5 nanosheets. Importantly, the built metal-vacancy pair sites regulate the *CH3O formation step as a spontaneous process, making the reduction of CO2 to CH4 the preferred method. Therefore, the oxygen-deficient Nb2O5 nanosheets exhibit a CH4 formation rate of 19.14 μmol g-1 h-1, with an electron selectivity of ∼94.1%.

Stabilizing Undercoordinated Zn Active Sites through Confinement in CeO2 Nanotubes for Efficient Electrochemical CO2 Reduction

Zn-based catalysts hold great potential to replace the noble metal-based ones for CO2 reduction reaction (CO2 RR). Undercoordinated Zn (Znδ+ ) sites may serve as the active sites for enhanced CO production by optimizing the binding energy of *COOH intermediates. However, there is relatively less exploration into the dynamic evolution and stability of Znδ+ sites during CO2 reduction process. Herein, we present ZnO, Znδ+ /ZnO and Zn as catalysts by varying the applied reduction potential. Theoretical studies reveal that Znδ+ sites could suppress HER and HCOOH production to induce CO generation. And Znδ+ /ZnO presents the highest CO selectivity (FECO 70.9 % at -1.48 V vs. RHE) compared to Zn and ZnO. Furthermore, we propose a CeO2 nanotube with confinement effect and Ce3+ /Ce4+ redox to stabilize Znδ+ species. The hollow core-shell structure of the Znδ+ /ZnO/CeO2 catalyst enables to extremely expose electrochemically active area while maintaining the Znδ+ sites with long-time stability. Certainly, the target catalyst affords a FECO of 76.9 % at -1.08 V vs. RHE and no significant decay of CO selectivity in excess of 18 h.

Mechanism insights into photo-assisted peroxymonosulfate activation on oxygen vacancy-enriched nolanites via an electron transfer regime

The utilization of photo-assisted persulfate activation for the removal of organic contaminants in water has garnered significant research interest in recent times. However, there remains a lack of clarity regarding specific contributions of light irradiation and catalyst structure in this process. Herein, a photo-assisted peroxymonosulfate (PMS) activation system is designed for the highly efficient degradation of organic contaminants on oxygen vacancy-enriched nolanites (Vo-FVO). Results suggest that the degradation of bisphenol A (BPA) in this system is a nonradical-dominated process via an electron transfer regime, in which VO improves the local electron density and thus facilitates the electron shuttling between BPA and PMS. During BPA degradation, PMS adsorbed at the surface of FVO-180 withdraws electrons near VO and forms FVO-PMS* complexes. Upon light irradiation, photoelectrons effectively restore the electron density around VO, thereby enabling a sustainable electron transfer for the highly efficient degradation of BPA. Overall, this work provides new insights into the mechanism of persulfate activation based on defects engineering in nolanite minerals.

Supramolecular self-assemble deficient carbon nitride nanotubes for efficient photocatalytic CO2 reduction

Carbon nitride is an attractive non-metallic photocatalyst due to its small surface area, rapid electron-hole recombination, and low absorption of visible light. In this study, one-dimensional carbon nitride nanotubes were successfully synthesized by supramolecular self-assembly method for photocatalytic reduction of CO2 under mild conditions. The material demonstrates significantly improved CO2-to-CO activity compared to bulk carbon nitride under visible light irradiation, with a rate of 12.58 μmol g-1h-1, which is 3.37 times higher than that of pristine carbon nitride. This enhanced activity can be attributed to the abundant oxygen defects and nitrogen vacancies in the unique tubular carbon nitride structure, which results in the generation of more active sites and the efficient acceleration of the migration of photogenerated electron-hole pairs. Various characterizations collectively support the presence of these defects and vacancies. Moreover, in situ DRIFTS spectroscopy supported the proposed reaction mechanism for the photoreduction of CO2. This eco-friendly design approach provides novel insights into utilizing solar energy for the production of value-added products.

Piezo-photocatalysis for efficient charge separation to promote CO2 photoreduction in nanoclusters

The substantial emissions of CO2 greenhouse gases have resulted in severe environmental problems, and research on the implementation of semiconductor materials to minimize CO2 is currently a highly discussed subject. Effective separation of interface charges is a major challenge for efficient piezo-photocatalytic systems. Meanwhile, the ultrasmall-sized metal nanoclusters can shorten the distance of electron transport. Herein, we synthesized Au25(p-MBA)18 nanoclusters (Au25 NCs) modified red graphitic carbon nitride (RCN) nanocatalysts with highly exposed Au active sites by in-situ seed growth method. The loading of Au25 NCs on the RCN surface provides more active sites and creates a long-range ordered electric field. It allows for the direct utilization of the piezoelectric field to separate photogenerated carriers during photo-piezoelectric excitation. Based on the above advantages, the rate of CO2 reduction to CO over Au25 NCs/RCN (111.95 μmol g-1 h-1) was more than triple compared to that of pristine RCN. This paper has positive implication for further application of metal clusters loaded semiconductor for piezo-photocatalytic CO2 reduction.

Getting the Most Out of Fluorogenic Probes: Challenges and Opportunities in Using Single-Molecule Fluorescence to Image Electro- and Photocatalysis

Single-molecule fluorescence microscopy enables the direct observation of individual reaction events at the surface of a catalyst. It has become a powerful tool to image in real time both intra- and interparticle heterogeneity among different nanoscale catalyst particles. Single-molecule fluorescence microscopy of heterogeneous catalysts relies on the detection of chemically activated fluorogenic probes that are converted from a nonfluorescent state into a highly fluorescent state through a reaction mediated at the catalyst surface. This review article describes challenges and opportunities in using such fluorogenic probes as proxies to develop structure-activity relationships in nanoscale electrocatalysts and photocatalysts. We compare single-molecule fluorescence microscopy to other microscopies for imaging catalysis in situ to highlight the distinct advantages and limitations of this technique. We describe correlative imaging between super-resolution activity maps obtained from multiple fluorogenic probes to understand the chemical origins behind spatial variations in activity that are frequently observed for nanoscale catalysts. Fluorogenic probes, originally developed for biological imaging, are introduced that can detect products such as carbon monoxide, nitrite, and ammonia, which are generated by electro- and photocatalysts for fuel production and environmental remediation. We conclude by describing how single-molecule imaging can provide mechanistic insights for a broader scope of catalytic systems, such as single-atom catalysts.

Boosted C-C coupling with Cu-Ag alloy sub-nanoclusters for CO2-to-C2H4 photosynthesis

The selective photocatalytic conversion of CO2 and H2O to high value-added C2H4 remains a great challenge, mainly attributed to the difficulties in C-C coupling of reaction intermediates and desorption of C2H4* intermediates from the catalyst surface. These two key issues can be simultaneously overcome by alloying Ag with Cu which gives enhanced activity to both reactions. Herein, we developed a facile stepwise photodeposition strategy to load Cu-Ag alloy sub-nanoclusters (ASNCs) on TiO2 for CO2 photoreduction to produce C2H4. The optimized catalyst exhibits a record-high C2H4 formation rate (1110.6 ± 82.5 μmol g-1 h-1) with selectivity of 49.1 ± 1.9%, which is an order-of-magnitude enhancement relative to current work for C2H4 photosynthesis. The in situ FT-IR spectra combined with DFT calculations reveal the synergistic effect of Cu and Ag in Cu-Ag ASNCs, which enable an excellent C-C coupling capability like Ag and promoted C2H4* desorption property like Cu, thus advancing the selective and efficient production of C2H4. The present work provides a deeper understanding on cluster chemistry and C-C coupling mechanism for CO2 reduction on ASNCs and develops a feasible strategy for photoreduction CO2 to C2 fuels or industrial feedstocks.

Triangle Cl-Ag1 -Cl Sites for Superior Photocatalytic Molecular Oxygen Activation and NO Oxidation of BiOCl

BiOCl photocatalysis shows great promise for molecular oxygen activation and NO oxidation, but its selective transformation of NO to immobilized nitrate without toxic NO2 emission is still a great challenge, because of uncontrollable reaction intermediates and pathways. In this study, we demonstrate that the introduction of triangle Cl-Ag1 -Cl sites on a Cl-terminated, (001) facet-exposed BiOCl can selectively promote one-electron activation of reactant molecular oxygen to intermediate superoxide radicals (⋅O2 - ), and also shift the adsorption configuration of product NO3 - from the weak monodentate binding mode to a strong bidentate mode to avoid unfavorable photolysis. By simultaneously tuning intermediates and products, the Cl-Ag1 -Cl-landen BiOCl achieved >90 % NO conversion to favorable NO3 - of high selectivity (>97 %) in 10 min under visible light, with the undesired NO2 concentration below 20 ppb. Both the activity and the selectivity of Cl-Ag1 -Cl sites surpass those of BiOCl surface sites (38 % NO conversion, 67 % NO3 - selectivity) or control O-Ag1 -O sites on a benchmark photocatalyst P25 (67 % NO conversion and 87 % NO3 - selectivity). This study develops new single-atom sites for the performance enhancement of semiconductor photocatalysts, and also provides a facile pathway to manipulate the reactive oxygen species production for efficient pollutant removal.

Target-Induced Photocurrent-Polarity-Switching PEC Sensing Platform Based on In Situ Generation of Oxygen Vacancy-Modulated Energy Band Structures

The polarity of the photocurrent can be modulated by tunable bipolar photoelectrochemical (PEC) behavior, which is anticipated to address the issues of high background signal caused by traditional unidirectional increasing/decreasing response and false-positive/false-negative problems. Here, a new approach is suggested for the first time, which employs a target-induced enzyme-catalyzed reaction and in situ oxygen vacancy (OV) generation to achieve heterojunction photocurrent switching for highly sensitive detection of alkaline phosphatase (ALP). Among them, the ALP can catalyze the decomposition of ascorbic acid phosphate to produce ascorbic acid, which not only acts as an electron donor to change the redox environment but also acts as a reducing agent to introduce OVs into BiOBr semiconductors in cooperation with illumination. The introduction of vacancies can effectively modulate the energy band structure of BiOBr, while with the change of redox conditions, the transfer path of photogenerated carriers is changed, thus realizing the switching of photocurrents, which leads to its use in the construction of a negative-background anti-interference PEC sensing platform, achieving a wide linear range from 0.005 to 500 U·L-1 with a low detection limit of 0.0017 U·L-1. In conclusion, the photocurrent switching operation of this system is jointly regulated by chemistry, optics, and carrier motion, which provides a new idea for the construction of a PEC sensing platform based on photocurrent polarity switching.

Rapid Energy Exchange between In Situ Formed Bromine Vacancies and CO2 Molecules Enhances CO2 Photoreduction

Photocatalytic reduction of CO2 into fuels provides a prospective tactic for regulating the global carbon balance utilizing renewable solar energy. However, CO2 molecules are difficult to activate and reduce due to the thermodynamic stability and chemical inertness. In this work, we develop a novel strategy to promote the adsorption and activation of CO2 molecules via the rapid energy exchange between the photoinduced Br vacancies and CO2 molecules. Combining in situ continuous wave-electron paramagnetic resonance (cw-EPR) and pulsed EPR technologies, we observe that the spin-spin relaxation time (T2) of BiOBr is decreased by 198 ns during the CO2 photoreduction reaction, which is further confirmed by the broadened EPR linewidth. This result reveals that there is an energy exchange interaction between in situ formed Br vacancies and CO2 molecules, which promotes the formation of high-energy CO2 molecules to facilitate the subsequent reduction reaction. In addition, theoretical calculations indicate that the bended CO2 adsorption configuration on the surface of BiOBr with Br vacancies caused the decrease of the lowest unoccupied molecular orbital of the CO2 molecule, which makes it easier for CO2 molecules to acquire electrons and get activated. In situ diffuse reflectance infrared Fourier transform spectroscopy further shows that the activated CO2 molecules are favorably converted to key intermediates of COOH*, resulting in a CO generation rate of 9.1 μmol g-1 h-1 and a selectivity of 100%. This study elucidates the underlying mechanism of CO2 activation at active sites and deepens the understanding of CO2 photoreduction reaction.

Integrating Enrichment, Reduction, and Oxidation Sites in One System for Artificial Photosynthetic Diluted CO2 Reduction

Artificial photosynthetic diluted CO2 reduction directly driven by natural sunlight is a challenging, but promising way to realize carbon-resources recycling utilization. Herein, a three-in-one photocatalytic system of CO2 enrichment, CO2 reduction and H2 O oxidation sites is designed for diluted CO2 reduction. A Zn-Salen-based covalent organic framework (Zn-S-COF) with oxidation and reductive sites is synthesized; then, ionic liquids (ILs) are loaded into the pores. As a result, [Emim]BF4 @Zn-S-COF shows a visible-light-driven CO2 -to-CO conversion rate of 105.88 µmol g-1 h-1 under diluted CO2 (15%) atmosphere, even superior than most photocatalysts in high concentrations CO2 . Moreover, natural sunlight driven diluted CO2 reduction rate also reaches 126.51 µmol g-1 in 5 h. Further experiments and theoretical calculations reveal that the triazine ring in the Zn-S-COF promotes the activity of H2 O oxidation and CO2 reduction sites, and the loaded ILs provide an enriched CO2 atmosphere, realizing the efficient photocatalytic activity in diluted CO2 reduction.

Reconfigurable Manipulation of Oxygen Content on Metal Oxide Surfaces and Applications to Gas Sensing

Oxygen vacancies and adsorbed oxygen species on metal oxide surfaces play important roles in various fields. However, existing methods for manipulating surface oxygen require severe settings and are ineffective for repetitive manipulation. We present a method to manipulate the amount of surface oxygen by modifying the oxygen adsorption energy by electrically controlling the electron concentration of the metal oxide. The surface oxygen control ability of the method is verified using first-principles calculations based on density functional theory (DFT), X-ray photoelectron spectroscopy (XPS), and electrical resistance analysis. The presented method is implemented by fabricating oxide thin film transistors with embedded microheaters. The method can reconfigure the oxygen vacancies on the In2O3, SnO2, and IGZO surfaces so that specific chemisorption dominates. The method can selectively increase oxidizing (e.g., NO and NO) and reducing gas (e.g., H2S, NH3, and CO) reactions by electrically controlling the metal oxide surface to be oxygen vacancy-rich or adsorbed oxygen species-rich. The proposed method is applied to gas sensors and overcomes their existing limitations. The method makes the sensor insensitive to one gas (e.g., H2S) in mixed-gas environments (e.g., NO2+H2S) and provides a linear response (R2 = 0.998) to the target gas (e.g., NO2) concentration within 3 s. We believe that the proposed method is applicable to applications utilizing metal oxide surfaces.

A Fully Conjugated Covalent Organic Framework with Oxidative and Reductive Sites for Photocatalytic Carbon Dioxide Reduction with Water

Constructing a powerful photocatalytic system that can achieve the carbon dioxide (CO2 ) reduction half-reaction and the water (H2 O) oxidation half-reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with a crystalline topological network, named viCOF-bpy-Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust -C=C- bond linkages. The charge-separation ability of viCOF-bpy-Re is promoted by low polarized π-bridges between rhenium complexes and triazine ring units, and the efficient charge-separation enables the photogenerated electron-hole pairs, followed by an intramolecular charge-transfer process, to form photogenerated electrons involved in CO2 reduction and photogenerated holes that participate in H2 O oxidation simultaneously. The viCOF-bpy-Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate (190.6 μmol g-1  h-1 with about 100 % selectivity) and oxygen (O2 ) evolution (90.2 μmol g-1 h-1 ) among all the porous catalysts in CO2 reduction with H2 O as sacrificial agents. Therefore, a powerful photocatalytic system was successfully achieved, and this catalytic system exhibited excellent stability in the catalysis process for 50 hours. The structure-function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.

Enhanced photocatalytic activity and mechanism insight of copper-modulated lead-free Cs2AgSbCl6 double perovskite microcrystals

Lead halide perovskites are prospective candidates for CO₂ photoconversion. Herein, we report copper-doped lead-free Cs₂AgSbCl₆ double perovskite microcrystals (MCs) for gas-solid phase photocatalytic CO₂ reduction. The 0.2Cu@Cs₂AgSbCl₆ double perovskite MCs display unprecedented CO₂ photoreduction capability with CO and CH₄ yields of 412 and 128 μmol g^-1, respectively. The ultrafast transient absorption spectroscopy reveals the enhanced separation of photoexcited carriers in copper-doped Cs₂AgSbCl₆ MCs. The active sites and reaction intermediates on the surface of the doped Cs₂AgSbCl₆ are dynamically monitored and precisely unraveled based on the in-situ Fourier transform infrared spectroscopy investigation. In combination with density functional theory calculations, it is revealed that the copper-doped Cs₂AgSbCl₆ MCs facilitate sturdy CO₂ adsorption and activation and strikingly enhance the photocatalytic performance. This work offers an in-depth interpretation of the photocatalytic mechanism of Cs₂AgSbCl₆ doped with copper, which may provide guidance for future design of high-performance photocatalysts for solar fuel production.

Nanoscale Janus Z-Scheme Heterojunction for Boosting Artificial Photosynthesis

Artificial photosynthesis for CO2 reduction coupled with water oxidation currently suffers from low efficiency due to inadequate interfacial charge separation of conventional Z-scheme heterojunctions. Herein, an unprecedented nanoscale Janus Z-scheme heterojunction of CsPbBr3 /TiOx is constructed for photocatalytic CO2 reduction. Benefitting from the short carrier transport distance and direct contact interface, CsPbBr3 /TiOx exhibits significantly accelerated interfacial charge transfer between CsPbBr3 and TiOx (8.90 × 108 s-1 ) compared with CsPbBr3 :TiOx counterpart (4.87 × 107 s-1 ) prepared by traditional electrostatic self-assembling. The electron consumption rate of cobalt doped CsPbBr3 /TiOx can reach as high as 405.2 ± 5.6 µmol g-1 h-1 for photocatalytic CO2 reduction to CO coupled with H2 O oxidation to O2 under AM1.5 sunlight (100 mW cm-2 ), over 11-fold higher than that of CsPbBr3 :TiOx , and surpassing the reported halide-perovskite-based photocatalysts under similar conditions. This work provides a novel strategy to boost charge transfer of photocatalysts for enhancing the performance of artificial photosynthesis.

Recent Advances of Constructing Metal/Semiconductor Catalysts Designing for Photocatalytic CO2 Hydrogenation

With the development of the world economy and the rapid advancement of global industrialization, the demand for energy continues to grow. The significant consumption of fossil fuels, such as oil, coal, and natural gas, has led to excessive carbon dioxide emissions, causing global ecological problems. CO2 hydrogenation technology can convert CO2 into high-value chemicals and is considered one of the potential ways to solve the problem of CO2 emissions. Metal/semiconductor catalysts have shown good activity in carbon dioxide hydrogenation reactions and have attracted widespread attention. Therefore, we summarize the recent research on metal/semiconductor catalysts for photocatalytic CO2 hydrogenation from the design of catalysts to the structure of active sites and mechanistic investigations, and the internal mechanism of the enhanced activity is elaborated to give guidance for the design of highly active catalysts. Finally, based on a good understanding of the above issues, this review looks forward to the development of future CO2 hydrogenation catalysts.

A conductive catecholate-based framework coordinated with unsaturated bismuth boosts CO2 electroreduction to formate

Bismuth-based metal-organic frameworks (Bi-MOFs) have received attention in electrochemical CO₂-to-formate conversion. However, the low conductivity and saturated coordination of Bi-MOFs usually lead to poor performance, which severely limits their widespread application. Herein, a conductive catecholate-based framework with Bi-enriched sites (HHTP, 2,3,6,7,10,11-hexahydroxytriphenylene) is constructed and the zigzagging corrugated topology of Bi-HHTP is first unraveled via single-crystal X-ray diffraction. Bi-HHTP possesses excellent electrical conductivity (1.65 S m^-1) and unsaturated coordination Bi sites are confirmed by electron paramagnetic resonance spectroscopy. Bi-HHTP exhibited an outstanding performance for selective formate production of 95% with a maximum turnover frequency of 576 h^-1 in a flow cell, which surpassed most of the previously reported Bi-MOFs. Significantly, the structure of Bi-HHTP could be well maintained after catalysis. In situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirms that the key intermediate is *COOH species. Density functional theory (DFT) calculations reveal that the rate-determining step is *COOH species generation, which is consistent with the in situ ATR-FTIR results. DFT calculations confirmed that the unsaturated coordination Bi sites acted as active sites for electrochemical CO₂-to-formate conversion. This work provides new insights into the rational design of conductive, stable, and active Bi-MOFs to improve their performance towards electrochemical CO₂ reduction.

Indium Cyanamide for Industrial-Grade CO2 Electroreduction to Formic Acid

Developing industrial-grade electroreduction of CO2 to produce formate (HCOO-)/formic acid (HCOOH) depends on highly active electrocatalysts. However, structural changes due to the inevitable self-reduction of catalysts result in severe long-term stability issues at industrial-grade current density. Herein, linear cyanamide anion ([NCN]2-)-constructed indium cyanamide nanoparticles (InNCN) were investigated for CO2 reduction to HCOO- with a Faradaic efficiency of up to 96% under a partial current density (jformate) of 250 mA cm-2. Bulk electrolysis at a jformate of 400 mA cm-2 requires only -0.72 VRHE applied potential with iR correction. It also achieves continuous production of pure HCOOH at ∼125 mA cm-2 for 160 h. The excellent activity and stability of InNCN are attributed to its unique structural features, including strongly σ-donating [NCN]2- ligands, the potential structural transformation of [N═C═N]2- and [N≡C-N]2-, and the open framework structure. This study affirms metal cyanamides as promising novel materials for electrocatalytic CO2 reduction, broadening the variety of CO2 reduction catalysts and the understanding of structure-activity relationships.

Degradation pathways of atrazine by electrochemical oxidation at different current densities: Identifications from compound-specific isotope analysis and DFT calculation

Current density was the key factor that impacted pollutant degradation by electrochemical oxidation, and reaction contributions at various current densities were non-negligible for the cost-effective treatments of organic pollutants. This research introduced compound specific isotope analysis (CSIA) into atrazine (ATZ) degradation by boron doped diamond (BDD) with current density of 2.5-20 mA/cm², in order to provide "in-situ" and "fingerprint" analysis of reaction contributions with changed current densities. As results, the increased current density displayed a positive impact on ATZ removal. The Ʌ_C/H values (correlations of Δδ¹³C and Δδ²H) were 24.58, 9.18 and 8.74 when current densities were 20, 4, and 2.5 mA/cm², with ·OH contribution of 93.5%, 77.2% and 80.35%, respectively. While DET process favored lower current density with contribution rates up to ∼20%. What's more interesting, though the carbon and hydrogen isotope enrichment factors (ε_C and ε_H) were fluctuate, the Ʌ_C/H linearly increased accompanied with applied current densities. Therefore, increasing current density was effective due to the larger ·OH contribution even though side reactions may occur. DFT calculations proved the increase of C-Cl bond length and the delocalization of Cl atom, confirming dechlorination reaction mainly occurred in the direct electron transfer process. While ·OH radical mainly attack the C-N bond on the side chain, which was more benefit to the fast decomposition of ATZ molecule and intermediates. It was forceful to discuss pollutant degradation mechanism by combining CSIA and DFT calculations. Target bond cleavage (i.e., dehalogenation reaction) can be conducted by changing reaction conditions like current density due to the significantly different isotope fractionation and bond cleavage.

Applications of BiOX in the Photocatalytic Reactions

BiOX (X = Cl, Br, I) families are a kind of new type of photocatalysts, which have attracted the attention of more and more researchers. The suitable band gaps and their convenient tunability via the change of X elements enable BiOX to adapt to many photocatalytic reactions. In addition, because of their characteristics of the unique layered structure and indirect bandgap semiconductor, BiOX exhibits excellent separation efficiency of photogenerated electrons and holes. Therefore, BiOX could usually demonstrate fine activity in many photocatalytic reactions. In this review, we will present the various applications and modification strategies of BiOX in photocatalytic reactions. Finally, based on a good understanding of the above issues, we will propose the future directions and feasibilities of the reasonable design of modification strategies of BiOX to obtain better photocatalytic activity toward various photocatalytic applications.

In Situ Growth of Lead-Free Cs2CuBr4 Perovskite Quantum Dots in KIT-6 Mesoporous Molecular Sieve for CO2 Adsorption, Activation, and Reduction

Metal halide perovskites (MHPs) are emerging as promising candidates for photocatalytic CO₂ conversion. However, their practical application is still restricted by the poor intrinsic stability and weak adsorption/activation toward CO₂ molecules. The rational design of MHPs-based heterostructures with high stability and abundant active sites is a potential solution to this obstacle. Herein, we report the in situ growth of lead-free Cs₂CuBr₄ perovskite quantum dots (PQDs) in KIT-6 mesoporous molecular sieve, obtaining remarkable photocatalytic CO₂ reduction activity and durable stability. The optimized Cs₂CuBr₄@KIT-6 heterostructure exhibits the photocatalytic CO and CH₄ evolution rates of 51.6 and 17.2 μmol g^-1 h^-1, respectively, far exceeding those of pristine Cs₂CuBr₄. On the basis of in situ diffuse reflectance infrared Fourier transform spectra and theoretical investigations, the detailed CO₂ photoreduction pathway is systematically revealed. This work provides a new route for the rational construction of perovskite-based heterostructures with strong CO₂ adsorption/activation and good stability for photocatalytic CO₂ reduction.

Light Control-Induced Oxygen Vacancy Generation and In Situ Surface Heterojunction Reconstruction for Boosting CO2 Reduction

The weak adsorption of CO₂ and the fast recombination of photogenerated charges harshly restrain the photocatalytic CO₂ reduction efficiency. The simultaneous catalyst design with strong CO₂ capture ability and fast charge separation efficiency is challenging. Herein, taking advantage of the metastable characteristic of oxygen vacancy, amorphous defect Bi₂O₂CO₃ (named BO_vC) was built on the surface of defect-rich BiOBr (named BO_vB) through an in situ surface reconstruction progress, in which the CO₃^2- in solution reacted with the generated Bi^(3-x)+ around the oxygen vacancies. The in situ formed BO_vC is tightly in contact with the BO_vB and can prevent the further destruction of the oxygen vacancy sites essential for CO₂ adsorption and visible light utilization. Additionally, the superficial BO_vC associated with the internal BO_vB forms a typical heterojunction promoting the interface carriers' separation. Finally, the in situ formation of BO_vC boosted the BOvB and showed better activity in the photocatalytic reduction of CO₂ into CO (three times compared to that of pristine BiOBr). This work provides a comprehensive solution for governing defects chemistry and heterojunction design, as well as gives an in-depth understanding of the function of vacancies in CO₂ reduction.

Photocatalytic CO2 reduction using La-Ni bimetallic sites within a covalent organic framework

The precise construction of photocatalysts with diatomic sites that simultaneously foster light absorption and catalytic activity is a formidable challenge, as both processes follow distinct pathways. Herein, an electrostatically driven self-assembly approach is used, where phenanthroline is used to synthesize bifunctional LaNi sites within covalent organic framework. The La and Ni site acts as optically and catalytically active center for photocarriers generation and highly selective CO₂-to-CO reduction, respectively. Theory calculations and in-situ characterization reveal the directional charge transfer between La-Ni double-atomic sites, leading to decreased reaction energy barriers of *COOH intermediate and enhanced CO₂-to-CO conversion. As a result, without any additional photosensitizers, a 15.2 times enhancement of the CO₂ reduction rate (605.8 μmol·g^-1·h^-1) over that of a benchmark covalent organic framework colloid (39.9 μmol·g^-1·h^-1) and improved CO selectivity (98.2%) are achieved. This work presents a potential strategy for integrating optically and catalytically active centers to enhance photocatalytic CO₂ reduction.

Regulating π-Conjugation in sp2 -Carbon-Linked Covalent Organic Frameworks for Efficient Metal-Free CO2 Photoreduction with H2 O

The development of sp² -carbon-linked covalent organic frameworks (sp² c-COFs) as artificial photocatalysts for solar-driven conversion of CO₂ into chemical feedstock has captured growing attention, but catalytic performance has been significantly limited by their intrinsic organic linkages. Here, a simple, yet efficient approach is reported to improve the CO₂ photoreduction on metal-free sp² c-COFs by rationally regulating their intrinsic π-conjugation. The incorporation of ethynyl groups into conjugated skeletons affords a significant improvement in π-conjugation and facilitates the photogenerated charge separation and transfer, thereby boosting the CO₂ photoreduction in a solid-gas mode with only water vapor and CO₂ . The resultant CO production rate reaches as high as 382.0 µmol g^-1  h^-1 , ranking at the top among all additive-free CO₂ photoreduction catalysts. The simple modulation approach not only enables to achieve enhanced CO₂ reduction performance but also simultaneously gives a rise to extend the understanding of structure-property relationship and offer new possibilities for the development of new π-conjugated COF-based artificial photocatalysts.

Potential utility of BiOX photocatalysts and their design/modification strategies for the optimum reduction of CO2

As an effective means to efficiently control the emissions of carbon dioxide (CO₂), photo-conversion of CO₂ into solar fuels (or their precursors) is meaningful both as an option to generate cleaner energy and to alleviate global warming. In this regard, bismuth oxyhalide (BiOX, where X = Cl, Br, and I) semiconductors have sparked considerable interest due to their multiple merits (e.g., visible light-harvesting, efficient charge carriers separation, and excellent chemical stability). In this review, the fundamental aspects of BiOX-based photocatalysts are discussed in relation to their modification strategies and associated reduction mechanisms of CO₂ to help expand their applicabilities. In this context, their performance is also evaluated in terms of the key performance metrics (e.g., quantum efficiency (QE), space-time yield (STY), and figure of merit (FoM)). Accordingly, the morphology design of BiOX materials is turned out as one of the most efficient strategies for the maximum yield of CO while the introduction of heterojunctions into BiOX materials was more suitable for CH₄ formation. As such, the adoption of the proper modification approach is recommended for efficient conversion of CO₂.

Poly(ionic liquid)s for Photo-Driven CO2 Cycloaddition: Electron Donor-Acceptor Segments Matter

CO₂ cycloaddition with epoxides is a key catalytic procedure for CO₂ utilization. Several metal-based catalysts with cocatalysts are developed for photo-driven CO₂ cycloaddition, while facing difficulties in product purification and continuous reaction. Here, poly(ionic liquid)s are proposed as metal-free catalysts for photo-driven CO₂ cycloaddition without cocatalysts. A series of poly(ionic liquid)s with donor-acceptor segments are fabricated and their photo-driven catalytic performance (conversion rate of 83.5% for glycidyl phenyl ether) outstrips (≈4.9 times) their thermal-driven catalytic performance (17.2%) at the same temperature. Mechanism studies confirm that photo-induced charge separation is promoted by the donor-acceptor segments and can accelerate the CO₂ cycloaddition reaction. This work paves the way for the further use of poly(ionic liquid)s as catalysts in photo-driven CO₂ cycloaddition.

Understanding the intermediates and carbon dioxide adsorption of potassium chloride-incorporated graphitic carbon nitride with tailoring melamine and urea as precursors

In this study, we demonstrated the synthesis of potassium chloride (KCl)-incorporated graphitic carbon nitride, (g-C₃N₄, CN) with varying amounts of N-vacancies and pyridinic-N as well as enhanced Lewis basicity, via a single-step thermal polymerization by tailoring the precursors of melamine and urea for carbon oxide (CO₂) capture. Melamine, as a precursor, undergoes a phase transformation into melam and triazine-rich g-C₃N₄, whereas the addition of urea polymerizes the mixture to form melem and heptazine-rich g-C₃N₄ (CN11). Owing to the abundance of pyridinic-N and the high surface area, CN11 adsorbed higher amounts of CO₂ (44.52 μmol m^-2 at 25 °C and 1 bar of CO₂) than those reported for other template-free carbon materials. Spectroscopic analysis revealed that the enhanced CO₂ adsorption is due to the presence of pyridinic-N and Lewis basic sites on the surface. The intermediates of CO₂adsorption, including carbonate and bicarbonate species, attached to the CN samples were identified using in-situ Fourier-transform infrared spectroscopy (FTIR). This work provides insights into the mechanism of CO₂ adsorption by comparing the structural features of the synthesized KCl-incorporated g-C₃N₄ samples_. CN11, with an excellent CO₂ uptake capacity, is viewed as a promising candidate for CO₂ capture and storage.

Review on Electrocatalytic Coreduction of Carbon Dioxide and Nitrogenous Species for Urea Synthesis

The electrochemical coreduction of carbon dioxide (CO₂) and nitrogenous species (such as NO₃^-, NO₂^-, N₂, and NO) for urea synthesis under ambient conditions provides a promising solution to realize carbon/nitrogen neutrality and mitigate environmental pollution. Although an increasing number of studies have made some breakthroughs in electrochemical urea synthesis, the unsatisfactory Faradaic efficiency, low urea yield rate, and ambiguous C-N coupling reaction mechanisms remain the major obstacles to its large-scale applications. In this review, we present the recent progress on electrochemical urea synthesis based on CO₂ and nitrogenous species in aqueous solutions under ambient conditions, providing useful guidance and discussion on the rational design of metal nanocatalyst, the understanding of the C-N coupling reaction mechanism, and existing challenges and prospects for electrochemical urea synthesis. We hope that this review can stimulate more insights and inspiration toward the development of electrocatalytic urea synthesis technology.

Defective Metal Oxides: Lessons from CO2 RR and Applications in NOx RR

Sluggish reaction kinetics and the undesired side reactions (hydrogen evolution reaction and self-reduction) are the main bottlenecks of electrochemical conversion reactions, such as the carbon dioxide and nitrate reduction reactions (CO₂ RR and NO₃ RR). To date, conventional strategies to overcome these challenges involve electronic structure modification and modulation of the charge-transfer behavior. Nonetheless, key aspects of surface modification, focused on boosting the intrinsic activity of active sites on the catalyst surface, are yet to be fully understood. Engingeering of oxygen vacancies (OVs) can tune surface/bulk electronic structure and improve surface active sites of electrocatalysts. The continuous breakthroughs and significant progress in the last decade position engineering of OVs as a potential technique for advancing electrocatalysis. Motivated by this, the state-of-the-art findings of the roles of OVs in both the CO₂ RR and the NO₃ RR are presented. The review starts with a description of approaches to constructing and techniques for characterizing OVs. This is followed by an overview of the mechanistic understanding of the CO₂ RR and a detailed discussion on the roles of OVs in the CO₂ RR. Then, insights into the NO₃ RR mechanism and the potential of OVs on NO₃ RR based on early findings are highlighted. Finally, the challenges in designing CO₂ RR/NO₃ RR electrocatalysts and perspectives in studying OV engineering are provided.

Identification of the Active Sites on Metallic MoO2-x Nano-Sea-Urchin for Atmospheric CO2 Photoreduction Under UV, Visible, and Near-Infrared Light Illumination

We report an oxygen vacancy (V_o )-rich metallic MoO_2-x nano-sea-urchin with partially occupied band, which exhibits super CO₂ (even directly from the air) photoreduction performance under UV, visible and near-infrared (NIR) light illumination. The V_o -rich MoO_2-x nano-sea-urchin displays a CH₄ evolution rate of 12.2 and 5.8 μmol g_catalyst ^-1  h^-1 under full spectrum and NIR light illumination in concentrated CO₂ , which is ca. 7- and 10-fold higher than the V_o -poor MoO_2-x , respectively. More interestingly, the as-developed V_o -rich MoO_2-x nano-sea-urchin can even reduce CO₂ directly from the air with a CO evolution rate of 6.5 μmol g_catalyst ^-1  h^-1 under NIR light illumination. Experiments together with theoretical calculations demonstrate that the oxygen vacancy in MoO_2-x can facilitate CO₂ adsorption/activation to generate *COOH as well as the subsequent protonation of *CO towards the formation of CH₄ because of the formation of a highly stable Mo-C-O-Mo intermediate.