Photocatalytic CO2 Reduction Research Articles

Self-standing Z-scheme structured heterogeneous nanosheet arrays of ZnIn2S4/cobalt porphyrin sulfonate for bifunctional photocatalytic carbon dioxide reduction and antibacterial

Photocatalytic CO2 reduction for solar fuel generation and photocatalytic sterilization are highly desired green routes for sustainable environmental purification. Herein, a bifunctional self-standing nanosheet array of Z-scheme structured inorganic–organic heterojunction is synthesized via in-situ growth of ZnIn2S4 (ZIS) on carbon cloth (CC) followed by self-assembly with cobalt porphyrin (meso-tetra(4-sulfonatophenyl) porphyrin, CoTPPS). The obtained CC-ZIS-CoTPPS performed well in the photocatalytic CO2 reduction and antibacterial processes simultaneously in a portable photocatalytic system with a negligible amount of solution. Specifically, the optimized CC-ZIS-CoTPPS demonstrates more than 140 times enhanced CO evolution than pristine CoTPPS. Experimental and theoretical results imply that the enhanced photocatalytic CO2 reduction is associated with elevated light absorption, promoted charge separation, and improved CO2 activation in the inorganic–organic Z-scheme heterojunction. In addition, the self-standing nanosheet array possesses a mechanical cutting effect, which can kill bacteria adhering to the surface even in dark conditions. Moreover, CC-ZIS-CoTPPS achieved a 100 % killing rate under visible light irradiation by synergistically chemical and mechanical sterilization. Furthermore, CC-ZIS-CoTPPS exhibits efficient bifunctional photocatalytic photocatalytic CO2 reduction coupled with in-situ sterilization. This work presents an atomic perspective for developing innovative bifunctional photocatalysts, which hold great potential in portable devices to alleviate energy and environmental crises.

In-situ preparation of BiOBr/Bi-doped CsPbBr3 S-scheme heterojunction for efficient photocatalytic CO2 reduction

Metal halide perovskite nanocrystals have garnered significant attention in the realm of photocatalytic CO2 reduction in recent years owing to their remarkable reducing properties and high selectivity. However, the issue of low photocatalytic activity due to severe carrier recombination phenomena in perovskite has posed a significant challenge. To address this, a one-pot in-situ preparation strategy was employed to create a BiOBr/Bi-doped perovskite nanocrystal S-scheme heterojunction, resulting in a significant improvement in the CO2 photoreduction performance. The heterojunction material exhibited a CO yield of 151.56 μmolg-1h−1, with a selectivity for CO of 93.6 %. The molar ratio of the components was modulated using an in-situ water aging strategy, yielding a photocatalyst performance that exceeded that of pure BiOBr. The synthesis strategy of one-step in-situ preparation of heterojunctions overcomes the problem of insufficient bonding caused by two-step methods. And various characterizations and DFT calculations strongly support the S-scheme mechanism of the photocatalyst. The active site effectively reduces the energy barrier for the transition from *COOH to *CO intermediate, thereby significantly improving photocatalytic activity.

Enabling Interfacial Lattice Matching by Selective Epitaxial Growth of CuS Crystals on Bi2WO6 Nanosheets for Efficient CO2 Photoreduction into Solar Fuels

Photocatalytic CO2 reduction serves as an important technology for value‐added solar fuel production; however, it is generally limited by interfacial charge transport. To address this limitation, a two‐dimensional/two‐dimensional (2D/2D) p‐n heterojunction CuS‐Bi2WO6 (CS‐BWO) with highly connected and matched interfacial lattices was designed via a two‐step hydrothermal tandem synthesis strategy. The integration of CuS with BWO created a robust interface electric field and provided fast charge transfer channels due to the work function difference, as well as highly connected and matched interfacial lattices. The p‐n heterojunction promoted electron transfer from the Cu to Bi sites, leading to coordination of Bi sites with high electronic density and low oxidation state. The Bi sites in BWO nanosheets facilitated the adsorption and activation of CO2, and generation of high‐coverage key intermediate b‐CO32‐, while broad light‐harvesting CuS (CS) provide abundant photoinduced electrons that were injected into the conduction band of BWO for CO2 photoreduction reaction. Remarkably, the p‐n heterojunction CS‐BWO exhibited CO and CH4 yields of 135.7 and 62.5 µmol g‐1, respectively, which were significantly higher than those of CS, BWO, and physical mixture CS‐BWO nanosheets. This work provided an innovative design strategy for developing high‐activity heterojunction photocatalyst for converting CO2 into value‐added solar fuels.

Enabling Interfacial Lattice Matching by Selective Epitaxial Growth of CuS Crystals on Bi2WO6 Nanosheets for Efficient CO2 Photoreduction into Solar Fuels.

Photocatalytic CO2 reduction serves as an important technology for value-added solar fuel production; however, it is generally limited by interfacial charge transport. To address this limitation, a two-dimensional/two-dimensional (2D/2D) p-n heterojunction CuS-Bi2WO6 (CS-BWO) with highly connected and matched interfacial lattices was designed via a two-step hydrothermal tandem synthesis strategy. The integration of CuS with BWO created a robust interface electric field and provided fast charge transfer channels due to the work function difference, as well as highly connected and matched interfacial lattices. The p-n heterojunctionpromotedelectron transfer from the Cu to Bi sites, leading to coordination of Bi sites with high electronic density and low oxidation state. The Bi sites in BWO nanosheets facilitated the adsorption and activation of CO2, and generation of high-coverage key intermediate b-CO32-, while broad light-harvesting CuS (CS)provide abundant photoinduced electrons that were injected into the conduction band of BWO for CO2 photoreduction reaction. Remarkably, the p-n heterojunction CS-BWO exhibited CO and CH4 yields of 135.7 and 62.5 µmol g-1, respectively, which were significantly higher than those of CS, BWO, and physical mixture CS-BWO nanosheets. This work provided an innovative design strategy for developing high-activity heterojunction photocatalyst for converting CO2into value-added solar fuels.

Ag–Pt Alloy Nanoparticles Modified Zn‐Based Nanosheets for Highly Selective CO2 Photoreduction to CH4

AbstractMulti‐electron involved photoreduction of CO2 to hydrocarbon fuels is a long‐standing challenge, particularly in manipulating the selectivity of the target products. Here, a novel Ag–Pt bimetallic alloy on Zn‐based supports by photo‐deposition is designed for photocatalytic CO2 reduction to CH4 without any additives. This photocatalyst exhibits ≈ 98.9% selectivity for CH4. Experimental and theoretical calculations demonstrated that the excellent performance of the photocatalyst can be attributed to the localized surface plasmon resonance effect of metals, as well as the synergistic effects of the bimetallic sites. These factors are found to be beneficial not only for capturing solar radiation and facilitating electron migration but also for promoting the adsorption and activation of CO2 and the protonation of *CO. As a result, the photocatalyst achieved high selectivity and activity of photoreduction of CO2 to CH4. This work provides insights into the design of photocatalysts with highly selective target products for CO2 reduction.

Facts and Fictions About Photocatalytic CO2 Reduction to C2+ Products.

In response to carbon neutrality, photocatalytic reduction of CO2 has been the subject of growing interest for researchers over the past few years. Multi-carbon products (C2+) with higher energy density and larger market value produced from photocatalytic reduction of CO2 are still very limited owing to the low photocatalytic productivity and poor selectivity of products. This review focuses on the recent progress on photocatalytic reduction of CO2 towards C2+ products from the perspective of performance evaluation and mechanistic understanding. We first provide a systematic description of the entire fundamental procedures of photocatalytic reduction of CO2. An in-depth strategy analysis for improving the selectivity of photocatalytic reduction of CO2 to C2+ products is then addressed. Then the focus was on summarizing the ways to improve C2+ selectivity. The intrinsic mechanisms of photocatalytic reduction of CO2 to C2+ products are summarized in the final. Combining the foundation of photocatalysis with promising catalyst strategies, this review will offer valuable guidance for the development of efficient photocatalytic systems for the synthesis of C2+ products.

Effective Near-Infrared Light-Driven Photocatalytic Reduction of CO2 by Dual-Site Doped Carbon Nitrides

Effective Near-Infrared Light-Driven Photocatalytic Reduction of CO₂ by Dual-Site Doped Carbon Nitrides

Unraveling the roles of atomically-dispersed Au in boosting photocatalytic CO2 reduction and aryl alcohol oxidation

Atomically-dispersed metal-based materials represent an emerging class of photocatalysts attributed to their high catalytic activity, abundant surface active sites, and efficient charge separation. Nevertheless, the roles of different forms of atomically-dispersed metals (i.e., single-atoms and atomic clusters) in photocatalytic reactions remain ambiguous. Herein, we developed an ethylenediamine (EDA)-assisted reduction method to controllably synthesize atomically dispersed Au in the forms of Au single atoms (AuSA), Au clusters (AuC), and a mixed-phase of AuSA and AuC (AuSA+C) on CdS. In addition, we elucidate the synergistic effect of AuSA and AuC in enhancing the photocatalytic performance of CdS substrates for simultaneous CO2 reduction and aryl alcohol oxidation. Specifically, AuSA can effectively lower the energy barrier for the CO2→*COOH conversion, while AuC can enhance the adsorption of alcohols and reduce the energy barrier for dehydrogenation. As a result, the AuSA and AuC co-loaded CdS show impressive overall photocatalytic CO2 conversion performance, achieving remarkable CO and BAD production rates of 4.43 and 4.71 mmol g−1 h−1, with the selectivities of 93% and 99%, respectively. More importantly, the solar-to-chemical conversion efficiency of AuSA+C/CdS reaches 0.57%, which is over fivefold higher than the typical solar-to-biomass conversion efficiency found in nature (ca. 0.1%). This study comprehensively describes the roles of different forms of atomically-dispersed metals and their synergistic effects in photocatalytic reactions, which is anticipated to pave a new avenue in energy and environmental applications.

MPS@BWO with High Adsorption Capacity for Efficient Photocatalytic Reduction of CO2

Photocatalysis can reduce CO2 to available energy by means of light energy, which is considered to be an effective solution to alleviate energy and environmental problems. In this paper, an MPS@Bi2WO6 composite photocatalyst was prepared by in situ hydrothermal method. BWO grew on the surface of MPS, which increased the CO2 absorption capacity of the photocatalyst and improved the microstructure. Under the synergistic effect of the two aspects, BWS achieves the enhancement of light energy absorption capacity and can effectively excite electron-hole pairs. The transition electrons with high reduction ability migrate to the surface and contact with high concentrations of CO2, achieving efficient CO2 reduction under visible light. Among the photocatalysts in this paper, BWS-1 (BWO: MPS = 1:1) has efficient CO2 gas phase reduction ability under visible light, and the CO yield reaches 29.51 μmol/g. The MPS@BWO photocatalyst is a low-cost and efficient CO2 photoreduction catalyst with broad application prospects.

Copper porphyrin modified BiOBr/Bi19S27Br3 for efficient CO2 photoreduction

The insufficient solar light response ability of the photocatalyst, rapid recombination of interface charges, and lack of active sites significantly inhibit the efficiency of photocatalytic CO2 reduction. Addressing these challenges simultaneously is a very challenging task. Herein, an interface engineering coupled surface polarization strategy is proposed to optimize the CO2 photoreduction performance. The copper tetracarboxyphenylporphyrin (CuTCPP) modified BiOBr/Bi19S27Br3 (BBS) heterostructure was developed. The built-in electric field formed between BiOBr and Bi19S27Br3 interfaces induces the effective interfacial charge separation, while the surface polarization of CuTCPP induces the transfer of electrons from the conduction band (CB) of BBS to the CB of CuTCPP. Benefiting from this unique configuration and abundant active sites in CuTCPP, greatly improved photocatalytic CO2 reduction performance can be realized. Without adding cocatalysts and sacrificial agents, the optimized CO generation performance of CuTCPP-BiOBr/Bi19S27Br3 (BBS-CT) is 3.5 times higher than that of BBS. This work provides valuable insights of interface engineering coupled surface polarization strategy for collaborative improve the photocatalytic CO2 reduction performance.

Electronic Effects in Cobalt Phthalocyanine Catalysts Towards Noble-Metal-Free, Photocatalytic CO2-to-CO Reduction

Noble-metal-free CO2 reduction systems based on cobalt phthalocyanine (CoPc) and its derivatives have demonstrated remarkable photocatalytic performances; however, their structure-activity relationship with electronic tuning remains unexplored. Herein, we now provide a systematic study to investigate the electron effects of substituents on the CoPc family in photocatalytic CO2 reduction, where a Cu(I) heteroleptic photosensitizer is utilized. The highest performance can be achieved using cobalt tetracarboxylphthalocyanine in light-driven CO2-to-CO reduction, with a maximum turnover number of 2950 at 450 nm and an outstanding apparent quantum yield of 63.5% at 425 nm, over ten times the activity with the tetra-dimethylamino-substituted CoPc derivative. The favorable electron-withdrawing effects have been further verified by DFT calculations and cyclic voltammetry, which reduces the overpotential required for CO2 reduction and decreases the Gibbs free energy of the catalyst active intermediates, particularly the CO-desorption energetics.

Rape straw biochar-assisted preparation of flower-like BiOCl with enriched oxygen vacancies for efficient photocatalytic CO2 reduction and pollutants degradation

Utilizing photocatalytic technology to transform CO2 into high added value chemical products has represented an effective strategy for alleviating the climate problems that have arisen due to excessive CO2 emissions. As a typical bismuth-based photocatalyst, BiOCl has garnered widespread attention due to its unique layered structure and low toxicity. However, the low light utilization efficiency and the rapid recombination of e−/h+ pairs severely hinder the practical application of BiOCl. Introducing oxygen vacancies (OVs) into BiOCl has been demonstrated to be one of the effective strategies for enhancing the photocatalytic performance of BiOCl. However, introduction of OVs through a mild and cost-effective approach remains a significant challenge. In this work, we developed a strategy for introducing OVs on BiOCl, which indues the growth of BiOCl into flower-like spherical structures and introduction of abundant OVs through addition of rape straw biochar (RC) under hydrothermal conditions. The synergistic interaction of RC and OVs endows with BiOCl more active sites as well as higher photogenerated carriers (e−/h+) separation efficiency. When the mass ratio of RC to BiOCl is 0.5 % (RC-0.5), the sample demonstrates the best performance, conversion of CO2 to CO on the sample is 4.0 μmol g−1 h−1, which is 3.08 times higher than that on the reference BiOCl. Additionally, versatility of the photocatalysts was further evaluated through photocatalytic degradation of rhodamine B (RhB) and perfluorooctanoic acid (PFOA). The degradation rate constant of RhB and PFOA on the RC-0.5 sample is 0.0642 min−1 and 0.00566 min−1, respectively, which is 2.26 times and 0.43 times higher than that on the reference BiOCl. Total organic carbon (TOC) experiments demonstrate that RhB can be effectively mineralized into CO2, H2O and small molecules on the photocatalyst. The main reactive species involved in the photocatalytic degradation process were investigated through active free radical trapping experiments and electron paramagnetic resonance (EPR). This work provides a viable strategy for the development of high-performance BiOCl photocatalysts for environmental applications.

Reducing Dielectric Confinement Effect Enhances Carrier Separation in Two-Dimensional Hybrid Perovskite Photocatalysts.

Two-dimensional organic-inorganic hybrid perovskites (OIHPs) with alternating structure of the organic and inorganic layers have a natural quantum well structure. The difference of dielectric constants between organic and inorganic layers in this structure results in the enhancement of dielectric confinement effect, which exhibits a large exciton binding energy and hinders the separation of electron-hole pairs. Herein, a strategy to reduce the dielectric confinement effect by narrowing the dielectric difference between organic amine molecule and [PbBr6]4- octahedron is put forward. The Ethanolamine (EOA) contains hydroxyl groups, resulting in the positive and negative charge centers of O and H non-overlapping, which generated a larger polarity and dielectric constant. The reduced dielectric constant produces a smaller exciton binding energy (71.03 meV) of (C2H7NO)2PbBr4 ((EOA)2PbBr4) than (C8H11N)2PbBr4 ((PEA)2PbBr4 (156.07 meV), and promotes the dissociation of electrons and holes. The increasing of lifetime of photogenerated carrier in (EOA)2PbBr4 are proved by femtosecond transient absorption spectra. Density functional theory (DFT) calculations have also indicated that the small energy shift of the total density of states (DOS) between the C/H/N and the Pb/Br in (EOA)2PbBr4 favors the separation of electrons and holes. In addition, this work demonstrates the application of (PEA)2PbBr4 and (EOA)2PbBr4 in the field of photocatalytic CO2 reduction.

Ni-Metalized Covalent Organic Cage as a Photocatalyst for Selective Photoreduction of CO2 to CO.

Metal complex-based photocatalysts are promising for CO2 reduction. Their catalytic performances greatly rely on the synergy of ligands and metal ions. Here, we demonstrate an assembly of covalent organic cage (COC) and metal ions for photocatalytic CO2 reduction. The coordinated metal serves as catalytically active site for CO2 reduction, while the cage not only chelates the metal site, but also enhances the local concentration of CO2 around metal site, and decreases the key intermediate reaction energy barrier, thereby promoting the CO2 reduction reaction kinetically and thermodynamically. Accordingly, a Ni metalized COC exhibited outstanding photocatalytic performance in CO2-to-CO conversion under visible light irradiation. This study highlights the feasibility and advantage of organic cages for the construction of photocatalysts for artificial photosynthesis.

An Electron Bridge of Shared Atoms Mediated Cs3Bi2Br9/Bi2WO6 Z‐Scheme Heterojunction for Photocatalytic CO2 Reduction

AbstractConverting clean solar energy into chemical energy through artificial photosynthesis is an effective solution to solve the energy and environmental issues. Here, we report a Cs3Bi2Br9/Bi2WO6 (CBB/BWO) Z‐scheme heterojunction constructed via electrostatic self‐assembly, which facilitates efficient separation of photogenerated carriers and ensures the corresponding redox capacity of both components. By sharing Bi atoms, a Br−Bi−O bond is established between CBB and BWO, serving as an “electron bridge”. The electrons generated by BWO are efficiently channeled to CBB through the heterojunction‐formed “electron bridge”, thereby achieving effective photocatalytic CO2 reduction. Under simulated sunlight conditions, it exhibits the highest CO yield of 72.52 μmol g−1 (without the addition of any precious metal, photosensitizers or sacrifices), which is approximately 7‐fold and 18‐fold greater than that of pure CBB and BWO, respectively. This work provides a more profound comprehension of the regulation of electron transfer through interfacial chemical bonds, thereby proposing a promising strategy for the development of efficient heterojunction photocatalysts for CO2 photoreduction.

Dual-active-group co-modification of BiOBr for boosting photocatalytic CO2 reduction coupled with ciprofloxacin oxidation

Coupling CO2 photoreduction with ciprofloxacin (CIP) oxidation presents a promising strategy for achieving not only the complete utilization of photoexcited carriers but also the win–win goals of energy conversion and environmental remediation. In this study, we utilized an aminated BiOBr catalyst with surface hydroxyl groups (NH2/BOB–OH) for efficient photocatalytic CO2 reduction coupled with CIP oxidation. In this process, hydroxyl (OH) and amino groups (NH2) adsorbed and activated CIP (an organic pollutant) and CO2 molecules, respectively, promoting the overall photocatalytic redox activity. Remarkably, 0.5NH2/BOB–OH exhibited excellent photocatalytic redox performance for CO2 reduction coupled with CIP oxidation, with the CO yield and CIP degradation efficiency being 6.85 and 1.08 times higher, respectively, than those achieved using BiOBr without any active groups. Moreover, a series of in situ experimental characterizations and theoretical simulations revealed that these two opposing active groups not only accelerated carrier separation but also boosted the surface reactivity of the catalyst. These findings provide helpful insights into the dual-active-group functionalization of semiconductors, leading to their high photoredox activity for energy conversion along with environmental remediation.

Fabrication of rGO-Bridged TiO2/g-C3N4 Z-Scheme Nanocomposites via Pulsed Laser Ablation for Efficient Photocatalytic CO2 Reduction.

Highly efficient photocatalysts can be fabricated using favorable charge transfer nanocomposite channel structures. This study adopted pulsed laser ablation in liquid (PLAL) to obtain rGO-bridged TiO2/g-C3N4 (rGO-TiO2/g-C3N4) photocatalytic Z-scheme without the need for noble metals. In addition to evaluating the resulting nanocomposite (comprising rGO nanosheets, TiO2 nanotubes, and g-C3N4 nanosheets) CO2 reduction effectiveness, its chemical, morphological, structural, and optical characteristics were examined using various analytical techniques. The findings revealed a synergistic interaction between g-C3N4 and TiO2, suggesting the presence of unique interfacial bonding, as well as enhanced visible light absorption. Notably, the ternary rGO-TiO2/g-C3N4 Z-scheme exhibits an excellent photocatalytic performance by photocatalytically converting CO2 into CO and CH4, with 81 % selectivity towards the CO and 1.91 % apparent quantum efficiency at 420 nm. Thus, the findings can pave the way for various Z-scheme systems in wide photocatalytic applications.

Hydrogen- assisted synthesis of defective triazine/heptazine homostructured nanosheets for efficient CO2photoreduction.

Homostructure construction has been demonstrated to be an effective way for boosting the photocatalytic activity of polymeric carbon nitride. However, the contribution of the intrinsic activity of molecular fragments in the catalytic performance of homostructured carbon nitride is yet to be explored. In this paper, a facile hydrogen-assisted strategy was used to synthesize triazine/heptazine intermolecular homojunctions (g-C3N4(MU-H)) with an ultrathin and defective structure, via the co-pyrolysis of melamine and urea precursors. Experimental characterizations and theoretical calculations revealed the copolymerization of triazine- and heptazine-based carbon nitride generated a homostructured interface with a large build-in electric field for efficient separation of photogenerated carriers. Due to the synergestic effect between the homostructured interface and nitrogen vacancies, as-synethesized g-C3N4(MU-H) exhibited an outstanding activity for photocatalytic CO2 reduction, with a CO yield rate of 14.45 μmol h-1, which was 23.5 and 3.64 times higher than those of bulk g-C3N4 and g-C3N4(M-H) synthesized from a single precursor, respectively. This study provides a new avenue for optimizing the charge separation efficiency of CO2 photoreduction catalysts by constructing intramolecular homojunction.

Strategy in Promoting Visible Light Absorption, Charge Separation, CO2 Adsorption and Proton Production for Efficient Photocatalytic CO2 Reduction with H2O.

Solar-energy-driven photocatalytic CO2 reduction by H2O to high-valuable carbon-containing chemicals has become one of the greatest concerns in both scientific and industrial communities, due to its potential in solving energy and environmental problems. However, efficiency of photocatalytic CO2 reduction by H2O is still far below the needs of large-scale applications. The reduction efficiency is closely related to ability of photocatalysts in absorbing visible light which is the main part of sunlight (44 %), separating photogenerated electron-hole pairs, adsorbing CO2 and producing protons for reducing CO2. Thus, photocatalysts with enhanced visible light absorption, electron-hole separation, CO2 adsorption and proton production are highly desired. Herein, we aim to provide a picture of recent progresses in improving ability of photocatalysts in visible light absorption, electron-hole separation, CO2 adsorption and proton production, and give an outlook for future researches associated with photocatalytic CO2 reduction by H2O.

Tannic Acid Selective Modulation Defects to Enhance the Photocatalytic CO2 Reduction Activity of Layered Double Hydroxides.

Recently, layered double hydroxides (LDH) have shown great potential in photoreduction of CO2 owing to its flexible structural adjustability. In this study, the mild acidic property of tannic acid (TA) is exploited to etch the bimetal LDH to create abundant vacancies to gain the coordination unsaturated active centers. Based on the different chelating abilities of TA to various metal ions, the active metals are remained by selective chelation while the inert metals are removed during the etching process of bimetal LDH. Furthermore, selective chelating with metal ions not only increases the percentage of highly active metals but also compensates for the structural damage caused by the etch, which achieves a scalpel-like selective construction of vacancies. The NiAl-LDH etched and functionalized by TA for 3h exhibits superior photo-reduction of CO2 performance without co-catalysts and photo-sensitizers, which is 14 times that of the pristine NiAl-LDH. The fact that many bimetal LDHs can be functionalized by TA and exhibit significantly improved photocatalytic efficiency is confirmed, suggesting this strategy is generalized to functionalize double- or multi-metal LDH. The method provided in this work opens the door for polyphenol-functionalized LDHs to enhance their ability for light-driven chemical transformations.