Efficiency Of Photocatalytic CO2 Reduction Research Articles

One-Step Fabricated Sn0 Particle on S-Vacancies SnS2 to Accelerate Photoelectron Transfer for Sterling Photocatalytic CO2 Reduction in Pure Water Vapor Environment.

Promoting the proton-coupled electron transfer process in order to solve the sluggish carrier migration dynamics is an efficient way to accelerate the photocatalytic CO2 reduction (PCR) process. Herein, through the reduction of Sn4+ by amino and sulfhydryl groups, Sn0 particles are lodged in S-vacancies SnS2 nanosheets. The high conductance of Sn0 particles expedites the collection and transport of photogenerated electrons, activating the surrounding surface of unsaturated sulfur (Sx 2- ) and thus lowering the energy barrier for generation of *COOH. Meanwhile, S-vacancies boost H2 O adsorption while Sx 2- increases CO2 adsorption, as demonstrated by density functional theory (DFT), obtaining a selectivity of 97.88% CO and yield of 295.06 µmol g-1 h-1 without the addition of co-catalysts and sacrificial agents. This work provides a new approach to building a fast electron transfer interface between metal particles and semiconductors, which works in tandem with S-vacancies and Sx 2- to boost the efficiency of photocatalytic CO2 reduction to CO in pure water vapor environment.

Facile synthesis of a Z-scheme CeO2/C3N4 heterojunction with enhanced charge transfer for CO2 photoreduction

Using solar energy to convert CO2 into value-added fuel is crucial for the goal of global carbon neutrality. Effective separation of photogenerated charges is important for improving photocatalytic CO2 reduction efficiency. Herein, we report a facile in situ exfoliation and conversion strategy to synthesize a novel CeO2/C3N4 heterostructure by uniformly distributing CeO2 nanoparticles onto ultrathin porous C3N4 nanosheets. The ultrathin porous structure of C3N4 not only increases the specific surface area to provide more active sites but also effectively shortens the migration distance of photogenerated electron holes to avoid their recombination. In addition, the well-dispersed CeO2 on C3N4 shows an intimate interface contact, which allows more charges to be transferred through the increased interface surface area. The as-synthesized CeO2/C3N4 heterojunction with well-matched band gaps and a Z-scheme structure prolongs the lifetime of photo-induced charge carriers and maximizes the redox ability of the photocatalyst. Without a noble metal cocatalyst or a sacrificial agent, the CO2 photoreduction performance of the CeO2/C3N4 heterojunction is approximately 5-fold enhanced compared with that of bulk C3N4. This study provides a facile strategy for the design and practical application of direct Z-scheme pho-tocatalysts for sustainable energy conversion.

Significant Acceleration of Photocatalytic CO2 Reduction at the Gas-Liquid Interface of Microdroplets.

Solar-driven CO2 reduction reaction (CO2RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalytic CO2RR efficiency at the abundant gas-liquid interface provided by microdroplets is two orders of magnitude higher than that of the corresponding bulk phase reaction. Even in the absence of sacrificial agents, the production rates of HCOOH over WO3·0.33H2O mediated by microdroplets reaches 2536 μmol h-1g-1 (vs. 13 μmol h-1g-1 in bulk phase), which is significantly superior to the previously reported photocatalytic CO2RR in bulk phase reaction condition. Beyond the efficient delivery of CO2 to photocatalyst surfaces within microdroplets, we reveal that the strong electric field at the gas-liquid interface of microdroplets essentially promotes the separation of photogenerated electron-hole pairs. This study provides a deep understanding of ultrafast reaction kinetics promoted by the gas-liquid interface of microdroplets and a novel way of addressing the low efficiency of photocatalytic CO2 reduction to fuel.

Significant Acceleration of Photocatalytic CO2 Reduction at the Gas‐Liquid Interface of Microdroplets**

AbstractSolar‐driven CO2 reduction reaction (CO2RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalytic CO2RR efficiency at the abundant gas‐liquid interface provided by microdroplets is two orders of magnitude higher than that of the corresponding bulk phase reaction. Even in the absence of sacrificial agents, the production rates of HCOOH over WO3 ⋅ 0.33H2O mediated by microdroplets reaches 2536 μmol h−1 g−1 (vs. 13 μmol h−1 g−1 in bulk phase), which is significantly superior to the previously reported photocatalytic CO2RR in bulk phase reaction condition. Beyond the efficient delivery of CO2 to photocatalyst surfaces within microdroplets, we reveal that the strong electric field at the gas‐liquid interface of microdroplets essentially promotes the separation of photogenerated electron‐hole pairs. This study provides a deep understanding of ultrafast reaction kinetics promoted by the gas‐liquid interface of microdroplets and a novel way of addressing the low efficiency of photocatalytic CO2 reduction to fuel.

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 BOvC) was built on the surface of defect-rich BiOBr (named BOvB) through an in situ surface reconstruction progress, in which the CO32- in solution reacted with the generated Bi(3-x)+ around the oxygen vacancies. The in situ formed BOvC is tightly in contact with the BOvB and can prevent the further destruction of the oxygen vacancy sites essential for CO2 adsorption and visible light utilization. Additionally, the superficial BOvC associated with the internal BOvB forms a typical heterojunction promoting the interface carriers' separation. Finally, the in situ formation of BOvC 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.

Atomic Interface Engineering of Single-Atom Pt/TiO2 -Ti3 C2 for Boosting Photocatalytic CO2 Reduction.

Solar-driven CO2 conversion into valuable fuels is a promising strategy to alleviate the energy and environmental issues. However, inefficient charge separation and transfer greatly limits the photocatalytic CO2 reduction efficiency. Herein, single-atom Pt anchored on 3D hierarchical TiO2 -Ti3 C2 with atomic-scale interface engineering is successfully synthesized through an in situ transformation and photoreduction method. The in situ growth of TiO2 on Ti3 C2 nanosheets can not only provide interfacial driving force for the charge transport, but also create an atomic-level charge transfer channel for directional electron migration. Moreover, the single-atom Pt anchored on TiO2 or Ti3 C2 can effectively capture the photogenerated electrons through the atomic interfacial PtO bond with shortened charge migration distance, and simultaneously serve as active sites for CO2 adsorption and activation. Benefiting from the synergistic effect of the atomic interface engineering of single-atom Pt and interfacial TiOTi, the optimized photocatalyst exhibits excellent CO2 -to-CO conversion activity of 20.5µmol g-1 h-1 with a selectivity of 96%, which is five times that of commercial TiO2 (P25). This work sheds new light on designing ideal atomic-scale interface and single-atom catalysts for efficient solar fuel conversation.

Efficient visible-light-driven CO2 reduction mediated by novel Au-doped BiOBr nanosheets

Photocatalytic reduction of CO2 into valuable resources presents an efficient solution to mitigate the energy crisis and effects of climate change. However, the low efficiency of photocatalytic CO2 reduction of photocatalysts under visible light irradiation limits their industrial applications. Bismuth oxybromide (BiOBr) is a typical visible-light-driven photocatalyst with an appropriate band gap, but the charge separation efficiency still needs to be improved. In this work, the Au-doped BiOBr nanosheets with enhanced electrochemical characteristics were successfully synthesized through a simple one-step hydrothermal procedure. After Au-doping modification, the charge separation efficiency of BOB-Au-I sample were measured as 2.5 times than that of BiOBr nanosheets. And the BOB-Au-I samples exhibited an outstanding photocatalytic capacity for converting CO2 to CO with a yield rate of approximately four times higher than that of BOB nanosheets under visible light irradiation. Furthermore, the mechanism of CO2 reduction was elucidated through in situ Fourier-transform infrared spectroscopy. This study provides a facile method for achieving Au-doping modification of BiOBr nanosheets for efficient reduction of CO2.

Studying the role of dual vacancies over g-C3N4/Zn0.3Cd0.7S for photocatalytic CO2 reduction

Defect engineering as an important surface regulation method, is closely related to the adsorption, activation and transformation of reactant molecules. To improve the efficiency of photocatalytic CO2 reduction from the interfacial perspective, g-C3N4/Zn0.3Cd0.7S (CN/ZCS) heterojunction with dual vacancies were successfully synthesized. The production of CO for the optimal sample (3% CN/ZCS) is significantly improved, about 3.5 times of ZCS and 309.8 times of CN, respectively. Meanwhile, the CO2 adsorption and transformation process are deduced and revealed by monitoring the intermediate and final products on the in-situ FTIR. The underlying enhanced reason can be elucidated by the defective sites and Z-scheme transfer model, which increase the carrier density, active sites and the utilization of photogenerated charge carriers (PCCs). This study provides a new and powerful example in designing novel heterojunction photocatalysts by defect engineering, and helps us to enhance the photocatalytic activity from the interfacial perspective.

Cobalt-Doped MoS2-Integrated Hollow Structured Covalent Organic Framework Nanospheres for the Effective Photoreduction of CO2 under Visible Light

Photocatalytic conversion of CO2 into beneficial raw chemicals has gained a great deal of attention for well over the recent decade due to its prospect for alleviating energy scarcity and global warming. Even though photocatalytic CO2 reduction technique has shown great promise, the successful conversion of CO2 to the intended outputs has remained a key barrier. Here, we present the design synthesis of a hollow nanospherical keto-enamine TpPa-1 covalent organic framework (COF) integrated single-atom Co-1T-MoS2 (TpPa-1/Co-1T-MoS2) composite with the appropriate band edge potential and an enhanced charge separation to improve its CO2 photoreduction efficiency under visible light irradiation. With a selectivity of 93%, the developed TpPa-1/Co-1T-MoS2 nanocomposite exhibits impressive photocatalytic CO2 reduction efficiency of up to ∼196 μmol g–1 h–1 of CO. Bare TpPa-1 and Co-1T-MoS2 both had around 1.23 and 1.6 times lower CO than TpPa-1/Co-1T-MoS2. Parametric analyses show that the TpPa-1 and Co-1T-MoS2 counterparts have a remarkable cumulative influence on the specificity and efficacy of photoreduction of CO2 to CO. TpPa-1/Co-1T-MoS2 composite is one of the handful of notable values cited in the literature, with an apparent quantum yield of 0.7% at 420 nm under ideal conditions. 13C labeling confirms that the selective conversion of CO2 to CO was facilitated by couplings between TpPa-1 and Co-1T-MoS2, which enhanced charge separation and migration to the surface. The findings show that COFs and their single-atom-based composites can be developed for next-generation photocatalytic systems and that this technology may also be interesting for other energy conversion applications.

In-depth insight into the mechanism on photocatalytic selective CO2 reduction coupled with tetracycline oxidation over BiO1-xBr/g-C3N4

To effectively alleviate environmental pollution and energy shortage and simultaneously utilize the photo-induced electrons and holes in one system. Herein, a dual-purpose reaction system is structured by coupling CO2 reduction with tetracycline (TC) mineralization, which is realized using model BiOBr/g-C3N4 photocatalyst with rich oxygen vacancies (OVs) (donated as BiO1-xBr/g-C3N4). Compared to two half-reactions of the individual CO2 photoreduction and independent TC oxidation under Ar atmosphere, such designed coupled reaction system presents much superior catalytic performance than those of two half-reactions. Another crucial finding is that the concentration and molecular structure of TC directly affect the selectivity and synergistic efficiency of photocatalytic CO2 reduction to CO. The mechanism of cooperative effect is discussed deeply according to theoretical calculation and experiments. Besides, the intermediates and pathway of TC degradation are extremely inquired by LC-MS. The work is expected to provide beneficial guidance on reasonably devising the bifunctional catalysts with efficacious integrating reaction systems for coupling CO2 reduction with antibiotic removal.

Tailored Persistent Radical‐containing Heterotrimetal‐Organic Framework for Boosting Efficiency of Visible/NIR Light‐driven Photocatalytic CO2 Reduction

AbstractPromoting light absorption range of photocatalysts is of great significance to improve solar light‐driven photocatalytic CO2 reduction efficiency. Herein, a new viologen‐based multicomponent heterotrimetallic metal–organic framework (MOF) [Cu3Th6(µ3‐O)4(µ3‐OH)4(cpb)12][FeIII(CN)6]6 (IHEP‐14) with an unprecedented (6, 18)‐connected she‐d topology is presented. Upon UV irradiation, this MOF undergoes ligand and iron photoreduction, and a single‐crystal‐to‐single‐crystal transformation to generate persistent radical‐containing MOF [Cu3Th6(µ3‐O)4(µ3‐OH)4(cpb•)12][FeII(CN)6]6 (IHEP‐15). This radical‐containing MOF shows excellent stability without fading after at least 2 months in air. Besides extending the photoabsorption to a wider wavelength range covering from 200 to 2,500 nm, the generation of persistent radical in IHEP‐15 also largely enhances its CO2 adsorption capacity by a factor of three due to the strong affinity between π orbital of the radical and the π system of CO2. These attributes endow IHEP‐15 with excellent visible/NIR light‐driven CO2 photoreduction activity, with CO production rates under visible and NIR irradiation of 570.3 and 209.3 µmol h−1 g−1, respectively. Notably, the latter is a record high for NIR‐induced CO production among all MOFs reported so far.

Vacancy Pair-Induced Charge Rebalancing with Surface and Interfacial Dual Polarization for CO2 Photoreduction

Poor charge kinetics greatly reduce the efficiency of photocatalytic CO2 reduction. Herein, a synchronous surface and interfacial dual polarization strategy was developed to promote charge separation. Bi–O vacancy pairs in Bi24O31Br10 atomic layers can trigger strong coupling between black phosphorus (BP) and Bi24O31Br10, forming a restructured closely contacted BP–Bi24O31Br10 configuration with a charge-redistributed interface via electronegativity-induced charge rebalancing. The Bi–O vacancy pairs on the surface of Bi24O31Br10 and restructured BP/Bi24O31Br10 interface enable synchronous surface and interfacial dual polarization, creating an electronic bridge from the interior of Bi24O31Br10 to the BP surface, as proven by ultrafast transient absorption spectroscopy. This configuration favors a low CO2 activation energy barrier, effectively stabilizes COOH* intermediates, and decreases the rate-determining step energy barrier. Benefiting from these features, the stable CO generation rate of optimized BP–Bi24O31Br10 reaches up to 39.8 μmol g–1 h–1 via CO2 photoreduction in water, which is 2.4 and 46.8 times higher than those of defective Bi24O31Br10 atomic layers and defect-poor Bi24O31Br10, respectively. This study provides insights into the synchronous design of surface defects and restructured interfaces for dual polarization.

A template co-pyrolysis strategy towards the increase of amino/imino content within g-C3N4 for efficient CO2 photoreduction

Photocatalytic CO2 reduction reaction (CO2RR) is an effective mean to address the current environmental and energy issues. As a kind of typical photocatalyst, g-C3N4 possesses lots of advantages (i.e., facile synthesis, visible-light response, and high stability) in CO2 reduction. However, the poor capacity of CO2 capture and rapid recombination of photo-generated electron and hole, both hinder the further development of g-C3N4 for CO2RR. Herein, we developed a template co-pyrolysis strategy to prepare C–NHx-rich (x = 1 or 2) g-C3N4, to increase the CO2 binding and the subsequent photocatalytic CO2 reduction efficiency. Specifically, organic molecules with multiple imino groups were used as additives to co-pyrolyze with urea. These additives can act as templates to facilitate the formation of g-C3N4 with abundant C–NHx groups, which effectively improved the capacity of CO2 capture. Meanwhile, the capacity of light absorption and the separation of photo-generated electron and hole were also optimized. As a result, the obtained C–NHx-rich g-C3N4 showed greatly enhanced photocatalytic activity for CO2RR, over 74-fold higher than that of g-C3N4 conventionally prepared. This work provides a new avenue for optimizing the g-C3N4-based photocatalysts for CO2RR.

Surface-iodination-induced efficient charge separation in bismuth oxysulfide crystals for enhanced photocatalytic CO2 conversion

Solar-energy-driven CO2 conversion to green fuels has great potential to alleviate energy crises and environmental issues. However, the low separation efficiency of charge carriers and the weak adsorption ability towards CO2 still hamper the efficiency of photocatalytic CO2 reduction. Herein, surface iodinated Bi2O2S materials (IBOS) were demonstrated to be efficient [Bi2O2]2+-containing photocatalysts, which could be prepared through facile hydrothermal process. The surface iodide ions are grafted onto the Bi atoms of Bi2O2S by replacing surface adsorbed OH, which slightly changes the electronic structure and then facilitates the separation of photo-generated electrons and holes in IBOS. Meanwhile, surface iodination also exhibits an enhanced adsorption and activation ability towards CO2, which contributes to photocatalytic CO2 conversion to CH4. The vital role of surface iodination was evidenced by the experimental analyses and theoretical calculations in detail. The optimized 2.0%IBOS shows marked photocatalytic CO2 reduction performance with a CH4 yield of 80.03 μmol g−1 under 90 min of visible light irradiation, which is ∼25-folds higher than pristine Bi2O2S. The mechanism of green transformation of CO2 to CH4 on 2.0%IBOS was finally proposed by the analyses of in situ FT-IR patterns. This work offers inspiration in designing and modifying [Bi2O2]2+-containing photocatalysts for highly efficient photocatalytic CO2 conversion.

Construction of Zn0.2Cd0.8S/g-C3N4 nanosheet array heterojunctions toward enhanced photocatalytic reduction of CO2 in visible light

The efficiency of photocatalytic CO2 reduction is severely limited by slow surface reaction kinetics and poor structural stability. In this study, a three-dimensional Zn0.2Cd0.8S/g-C3N4 (ZnCdS/CN) nanosheet array with type Ⅱ-scheme heterojunction structures was prepared using a mild in situ method. This heterojunction structure exhibited greatly improved carrier separation and specific surface area (45 m2 g−1), excellent stability, and broad-spectrum visible-light sensitivity. Without the use of any sacrificial agent, ZnCdS/CN20% demonstrated the highest photocatalytic efficiency of all the samples, with a CH3OH yield of 700.5 μmol·g−1·h−1. The type-Ⅱ-scheme heterojunction structure was responsible for the remarkable activity and stability because the photogenerated holes were transmitted to g-C3N4 across the heterojunction interface for the oxidation reaction, while the photogenerated electrons accumulated on Zn0.2Cd0.8S for the reduction reaction. This structure prevented oxidative corrosion on Zn0.2Cd0.8S and significantly improved the photogenerated electron–hole separation. This synthetic strategy provides new perspectives on the design and construction of efficient heterojunction photocatalysts for the solar-driven catalytic conversion of CO2.

Creation of SnxNb1−xO2 solid solution through heavy Nb-doping in SnO2 to boost its photocatalytic CO2 reduction to C2+ products under simulated solar illumination

Photocatalytic CO2 reduction driven by green solar energy could be a promising approach for the carbon neutral practice. In this work, a novel defect engineering approach was developed to form the SnxNb1−xO2 solid solution by the heavy substitutional Nb-doping of SnO2 through a robust hydrothermal process. The detailed analysis demonstrated that the heavy substitution of Sn4+ by a higher valence Nb5+ created a more suitable band structure, a better photogenerated charge carrier separation and transfer, and stronger CO2 adsorption due to the presence of abundant acid centers and excess electrons on its surface. Thus, the SnxNb1−xO2 solid solution sample demonstrated a much better photocatalytic CO2 reduction performance compared to the pristine SnO2 sample without the need for sacrificial agent. Its photocatalytic CO2 reduction efficiency reached ∼292.47 µmol/(g·h), which was 19 times that of the pristine SnO2 sample. Furthermore, its main photocatalytic CO2 reduction product was a more preferred multi-carbon (C2+) compound of C2H5OH, while that of the pristine SnO2 sample was a one-carbon (C1) compound of CH3OH. This work demonstrated that, the heavy doping of high valence cations in metal oxides to form solid solution may enhance the photocatalytic CO2 reduction and modulate its reduction process, to produce more C2+ products. This material design strategy could be readily applied to various material systems for the exploration of high-performance photocatalysts for the solar-driven CO2 reduction.

Bioinspired Self‐Supporting Phthalocyanine@ZnIn2S4 Foam for Photocatalytic CO2 Reduction Under Visible Light Irradiation

Molecular catalysis for photocatalytic CO2 reduction (PCR) has recently attracted much attention, whereas its scaled practical application is usually limited by the difficulty of recycling and its photochemical instability in homogeneous solutions. Immobilization of molecular catalysts on solid matrices, that is, covalent bonds or noncovalent interactions, provides a great blueprint to tackle this issue. Herein, a bioinspired self‐supporting phthalocyanine@ZnIn2S4 (Pc@ZnIn2S4) foam by growing ZnIn2S4 nanosheets on the commercialized polyurethane foam (PF) followed by loading amino‐modified cobalt phthalocyanine (CoPc–NH2) is developed. The self‐supporting Pc@ZnIn2S4 PF carrier can be directly taken out of the reaction system for the next reaction cycle without any other procedures. The optimized Pc@ZnIn2S4 PF demonstrates superior PCR efficiency under visible light (λ = 420 nm), achieving 474.65 μmol CO g−1 catalyst after 8 h. The superior PCR performance is attributed to the elevated light‐harvesting ability induced by the porous foam structure and the enhanced charge separation efficiency facilitated by the dimension‐matched interface between ZnIn2S4 and Pc. The special design of the immobilization molecular catalyst on solid supporters presented herein develops an efficient strategy for solar‐driven energy conversion.

Bioinspired spike-like double yolk–shell structured TiO2@ZnIn2S4 for efficient photocatalytic CO2 reduction

A spike-like double yolk–shell structured TiO2@ZnIn2S4 (D-Y-TiO2@ZnIn2S4) photocatalyst was designed, which possesses superior photocatalytic CO2 reduction efficiency.

Reduced graphene oxide-modified Z-scheme g-C3N4/CdS photocatalyst with a staggered structure for the enhanced photoreduction of CO2

The prepared Z-scheme CN/CdS@rGO photocatalyst formed a 2D/2D staggered structure: CN/CdS, CdS/rGO and CN/rGO, which provided more paths for electron transport and greatly improved the photocatalytic CO2 reduction efficiency.

Surface-amino-induced boosting solar conversion of CO2 to CO over natural metal-free catalyst

Design and construction of visible-light-responsive and low-cost catalyst to improve photocatalytic CO2 reduction efficiency are highly urgent due to rapid increment of CO2 emission. Herein, a facile but effective strategy is proposed to synthesize heteroatoms-doped porous treated rape pollen (TRP) and NH2-functionalized TRP for CO2 reduction. Heteroatoms doping can accelerate photoinduced charge transfer between neighboring carbon atom. The introduction of NH2- group offers effective sites to boost CO2 adsorption, which is beneficial to facilitate CO2-to-CO conversion. The experimental results indicate that TRP-NH2 exhibits visible-light-driven CO formation rate of 1165.3 μmol h−1 g−1 in the gas-solid reaction system without co-catalysts or sacrificial agents, which is 2.4 and 70.1 times than those of TRP (488.4 μmol h-1 g-1) and g-C3N4 (16.6 μmol h-1 g-1), and exceeds reported state-of-the-art carbon-based photocatalysts. The theoretical investigation shows that the incorporation of NH2- group can improve its charge density and converge more electrons to adsorb CO2 molecules. In situ Fourier transform infrared (FT-IR) spectroscopy spectra disclose that the COOH* radical is the main intermediate. The findings reveal the correlation between surface NH2- group and photocatalytic CO2 reduction performance and can be extended to other sustainable metal-free based catalysts for solar-driven CO2 reduction.