Coupling Benzylamine Oxidation with CO2 Photoconversion to Ethanol over a Black Phosphorus and Bismuth Tungstate S-Scheme Heterojunction

Photoconversion of CO₂ and H₂O into ethanol is an ideal strategy to achieve carbon neutrality. However, the production of ethanol with high activity and selectivity is challenging owing to the less efficient reduction half-reaction involving multi-step proton-coupled electron transfer (PCET), a slow C−C coupling process, and sluggish water oxidation half-reaction. Herein, a two-dimensional/two-dimensional (2D/2D) S-scheme heterojunction consisting of black phosphorus and Bi₂WO₆ (BP/BWO) was constructed for photocatalytic CO₂ reduction coupling with benzylamine (BA) oxidation. The as-prepared BP/BWO catalyst exhibits a superior photocatalytic performance toward CO₂ reduction, with a yield of 61.3 μmol g⁻¹ h⁻¹ for ethanol (selectivity of 91 %).In situ spectroscopic studies and theoretical calculations reveal that S-scheme heterojunction can effectively promote photogenerated carrier separation via the Bi−O−P bridge to accelerate the PCET process. Meanwhile, electron-rich BP acts as the active site and plays a vital role in the process of C−C coupling. In addition, the substitution of BA oxidation for H₂O oxidation can further enhance the photocatalytic performance of CO₂ reduction to C₂H₅OH. This work opens a new horizon for exploring novel heterogeneous photocatalysts in CO₂ photoconversion to C₂H₅OH based on cooperative photoredox systems.     

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⁻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.     

Non-Interacting Ni and Fe Dual-Atom Pair Sites in N-Doped Carbon Catalysts for Efficient Concentrating Solar-Driven Photothermal CO2 Reduction

Solar-to-chemical energy conversion under weak solar irradiation is generally difficult to meet the heat demand of CO₂ reduction. Herein, a new concentrated solar-driven photothermal system coupling a dual-metal single-atom catalyst (DSAC) with adjacent Ni−N₄ and Fe−N₄ pair sites is designed for boosting gas-solid CO₂ reduction with H₂O under simulated solar irradiation, even under ambient sunlight. As expected, the (Ni, Fe)−N−C DSAC exhibits a superior photothermal catalytic performance for CO₂ reduction to CO (86.16 μmol g⁻¹ h⁻¹), CH₄ (135.35 μmol g⁻¹ h⁻¹) and CH₃OH (59.81 μmol g⁻¹ h⁻¹), which are equivalent to 1.70-fold, 1.27-fold and 1.23-fold higher than those of the Fe−N−C catalyst, respectively. Based on theoretical simulations, the Fermi level and d-band center of Fe atom is efficiently regulated in non-interacting Ni and Fe dual-atom pair sites with electronic interaction through electron orbital hybridization on (Ni, Fe)−N−C DSAC. Crucially, the distance between adjacent Ni and Fe atoms of the Ni−N−N−Fe configuration means that the additional Ni atom as a new active site contributes to the main *COOH and *HCO₃ dissociation to optimize the corresponding energy barriers in the reaction process, leading to specific dual reaction pathways (COOH and HCO₃ pathways) for solar-driven photothermal CO₂ reduction to initial CO production.     

Tweaking Photo CO2 Reduction by Altering Lewis Acidic Sites in Metalated-Porous Organic Polymer for Adjustable H2/CO Ratio in Syngas Production

Herein, we have specifically designed two metalated porous organic polymers ( Zn-POP and Co-POP ) for syngas (CO+H₂) production from gaseous CO₂. The variable H₂/CO ratio of syngas with the highest efficiency was produced in water medium (without an organic hole scavenger and photosensitizer) by utilizing the basic principle of Lewis acid/base chemistry. Also, we observed the formation of entirely different major products during photocatalytic CO₂ reduction and water splitting with the help of the two catalysts, where CO (145.65 μmol g⁻¹ h⁻¹) and H₂ (434.7 μmol g⁻¹ h⁻¹) production were preferentially obtained over Co-POP & Zn-POP , respectively. The higher electron density/better Lewis basic nature of Co-POP was investigated further using XPS, XANES, and NH₃-TPD studies, which considerably improve CO₂ activation capacity. Moreover, the structure–activity relationship was confirmed via in situ DRIFTS and DFT studies, which demonstrated the formation of COOH* intermediate along with the thermodynamic feasibility of CO₂ reduction over Co-POP while water splitting occurred preferentially over Zn-POP .     

Synergistic Metal-Nonmetal Active Sites in a Metal-Organic Cage for Efficient Photocatalytic Synthesis of Hydrogen Peroxide in Pure Water

Photocatalytic synthesis of hydrogen peroxide (H₂O₂) is a potential clean method, but the long distance between the oxidation and reduction sites in photocatalysts hinders the rapid transfer of photogenerated charges, limiting the improvement of its performance. Here, a metal-organic cage photocatalyst, Co₁₄(L−CH₃)₂₄ , is constructed by directly coordinating metal sites (Co sites) used for the O₂ reduction reaction (ORR) with non-metallic sites (imidazole sites of ligands) used for the H₂O oxidation reaction (WOR), which shortens the transport path of photogenerated electrons and holes, and improves the transport efficiency of charges and activity of the photocatalyst. Therefore, it can be used as an efficient photocatalyst with a rate of as high as 146.6 μmol g⁻¹ h⁻¹ for H₂O₂ production under O₂-saturated pure water without sacrificial agents. Significantly, the combination of photocatalytic experiments and theoretical calculations proves that the functionalized modification of ligands is more conducive to adsorbing key intermediates (*OH for WOR and *HOOH for ORR), resulting in better performance. This work proposed a new catalytic strategy for the first time; i.e., to build a synergistic metal-nonmetal active site in the crystalline catalyst and use the host–guest chemistry inherent in the metal-organic cage (MOC)to increase the contact between the substrate and the catalytically active site, and finally achieve efficient photocatalytic H₂O₂ synthesis.     

Strong-Base-Assisted Synthesis of a Crystalline Covalent Triazine Framework with High Hydrophilicity via Benzylamine Monomer for Photocatalytic Water Splitting

Methods to synthesize crystalline covalent triazine frameworks (CTFs) are limited and little attention has been paid to development of hydrophilic CTFs and photocatalytic overall water splitting. A route to synthesize crystalline and hydrophilic CTF-HUST-A1 with a benzylamine-functionalized monomer is presented. The base reagent used plays an important role in the enhancement of crystallinity and hydrophilicity. CTF-HUST-A1 exhibits good crystallinity, excellent hydrophilicity, and excellent photocatalytic activity in sacrificial photocatalytic hydrogen evolution (hydrogen evolution rate up to 9200 μmol g⁻¹ h⁻¹). Photocatalytic overall water splitting is achieved by depositing dual co-catalysts in CTF-HUST-A1, with H₂ evolution and O₂ evolution rates of 25.4 μmol g⁻¹ h⁻¹ and 12.9 μmol g⁻¹ h⁻¹ in pure water without using sacrificial agent.     

Aqueous Processable Two-Dimensional Triazine Polymers with Superior Photocatalytic Properties

Efficient and scalable production of high-quality and processable two-dimensional (2D) polymers are highly desired but have not yet been reported. Herein, we demonstrate a convenient noncovalent functionalization strategy for producing highly uniform, aqueous processable and semiconducting 2D triazine polymers. Experimental and theoretical analysis reveal that the aromatic amphiphilic 1-pyrenebutyrate can adsorb and intercalate into the interlayer of bulk crystalline covalent triazine framework (CTF) through noncovalent π-π stacking interaction between the pyrene moiety and the porous basal plane of 2D triazine polymer layer, which greatly facilitate the exfoliation of CTF in water in large scale. The as-prepared highly water-dispersible single-layer/few-layer 2D triazine polymer nanosheets can be easily processed into ultralight aerogels with a density of 5–15 mg cm⁻³, which can be further shaped into mechanically strong films upon simple compression. This noncovalent functionalization not only improve the dispersibility and processability of 2D triazine polymer, but also optimize its band structure and promote the photogenerated carrier separation via an interesting surface molecule doping effect, thus resulting in a remarkable photocatalytic hydrogen evolution rate of 1249 μmol h⁻¹ (24980 μmol g⁻¹ h⁻¹) and apparent quantum efficiency up to 27.2 % at 420 nm for the 2D triazine polymer, outperforming most metal-free photocatalysts ever reported.     

Photocatalytic Oxidative Coupling of Methane over Au1Ag Single-Atom Alloy Modified ZnO with Oxygen and Water Vapor: Synergy of Gold and Silver

C−H dissociation and C−C coupling are two key steps in converting CH₄ into multi-carbon compounds. Here we report a synergy of Au and Ag to greatly promote C₂H₆ formation over Au₁Ag single-atom alloy nanoparticles (Au₁Ag NPs)-modified ZnO catalyst via photocatalytic oxidative coupling of methane (POCM) with O₂ and H₂O. Atomically dispersed Au in Au₁Ag NPs effectively promotes the dissociation of O₂ and H₂O into *OOH, promoting C−H activation of CH₄ on the photogenerated O⁻ to form *CH₃. Electron-deficient Au single atoms, as hopping ladders, also facilitate the migration of electron donor *CH₃ from ZnO to Au₁Ag NPs. Finally, *CH₃ coupling can readily occur on Ag atoms of Au₁Ag NPs. An excellent C₂H₆ yield of 14.0 mmol g⁻¹ h⁻¹ with a selectivity of 79 % and an apparent quantum yield of 14.6 % at 350 nm is obtained via POCM with O₂ and H₂O, which is at least two times that of the photocatalytic system. The bimetallic synergistic strategy offers guidance for future catalyst design for POCM with O₂ and H₂O.     

Eosin Y‐Functionalized Conjugated Organic Polymers for Visible‐Light‐Driven CO2 Reduction with H2O to CO with High Efficiency

Visible‐light‐driven photoreduction of CO₂ to energy‐rich chemicals in the presence of H₂O without any sacrifice reagent is of significance, but challenging. Herein, Eosin Y‐functionalized porous polymers (PEosinY‐N, N=1–3), with high surface areas up to 610 m² g^?1, are reported. They exhibit high activity for the photocatalytic reduction of CO₂ to CO in the presence of gaseous H₂O, without any photosensitizer or sacrifice reagent, and under visible‐light irradiation. Especially, PEosinY‐1 derived from coupling of Eosin Y with 1,4‐diethynylbenzene shows the best performance for the CO₂ photoreduction, affording CO as the sole carbonaceous product with a production rate of 33 μmol g^?1 h^?1 and a selectivity of 92 %. This work provides new insight for designing and fabricating photocatalytically active polymers with high efficiency for solar‐energy conversion.     

CO2 Laser-Induced Graphene with an Appropriate Oxygen Species as an Efficient Electrocatalyst for Hydrogen Peroxide Synthesis

Oxygen species functionalized graphene (O−G) is an effective electrocatalyst for electrochemically synthesizing hydrogen peroxide (H₂O₂) by a 2 e⁻ oxygen reduction reaction (ORR). The type of oxygen species and degree of carbon crystallinity in O−G are two key factors for the high catalytic performance of the 2 e⁻ ORR. However, the general preparing method of O−G by the precursor of graphite has the disadvantages of consuming massive strong oxidant and washing water. Herein, the biomass-based graphene with tunable oxygen species is rapidly fabricated by a CO₂ laser. In a flow cell setup, the laser-induced graphene (LIG) with abundant active oxygen species and graphene structure shows high catalytic performance including high Faraday efficiency (over 78 %) and high mass activity (814 mmolg_catalyst⁻¹ h⁻¹), superior to most of the reported carbon-based electrocatalysts. Density function theory demonstrates the meta-C atoms at nearby C−O, O−C=O species are the key catalytic sites. Therefore, we develop one facile method to rapidly convert biomass to graphene electrocatalyst used for H₂O₂ synthesis.     

Thiophene-Containing Covalent Organic Frameworks for Overall Photocatalytic H2O2 Synthesis in Water and Seawater

H₂O₂ is a significant chemical widely utilized in the environmental and industrial fields, with growing global demand. Without sacrificial agents, simultaneous photocatalyzed H₂O₂ synthesis through the oxygen reduction reaction (ORR) and water oxidation reaction (WOR) dual channels from seawater is green and sustainable but still challenging. Herein, two novel thiophene-containing covalent organic frameworks (TD-COF and TT-COF) were first constructed and served as catalysts for H₂O₂ synthesis via indirect 2e⁻ ORR and direct 2e⁻ WOR channels. The photocatalytic H₂O₂ production performance can be regulated by adjusting the N-heterocycle modules (pyridine and triazine) in COFs. Notably, with no sacrificial agents, just using air and water as raw materials, TD-COF exhibited high H₂O₂ production yields of 4060 μmol h⁻¹ g⁻¹ and 3364 μmol h⁻¹ g⁻¹ in deionized water and natural seawater, respectively. Further computational mechanism studies revealed that the thiophene was the primary photoreduction unit for ORR, while the benzene ring (linked to the thiophene by the imine bond) was the central photooxidation unit for WOR. The current work exploits thiophene-containing COFs for overall photocatalytic H₂O₂ synthesis via ORR and WOR dual channels and provides fresh insight into creating innovative catalysts for photocatalyzing H₂O₂ synthesis.     

Photo-thermal Cooperative Carbonylation of Ethanol with CO2 on Cu2O-SrTiCuO3-x

Carbonylation of ethanol with CO₂ as carbonyl source into value-added esters is of considerable significance and interest, while remains of great challenge due to the harsh conditions for activation of inert CO₂ in that the harsh conditions result in undesired activation of α-C−H and even cleavage of C−C bond in ethanol to deteriorate the specific activation of O−H bond. Herein, we propose a photo-thermal cooperative strategy for carbonylation of ethanol with CO₂, in which CO₂ is activated to reactive CO via photo-catalysis with the assistance of *H from thermally-catalyzed dissociation of alcoholic O−H bond. To achieve this proposal, an interfacial site and oxygen vacancy both abundant SrTiCuO_3-x supported Cu₂O (Cu₂O-SrTiCuO_3-x) has been designed. A production of up to 320 μmol g⁻¹ h⁻¹ for ethyl formate with a selectivity of 85.6 % to targeted alcoholic O−H activation has been afforded in photo-thermal assisted gas-solid process under 3.29 W cm⁻¹ of UV/Vis light irradiation (144 °C) and 0.2 MPa CO₂. In the photo-driven activation of CO₂ and following carbonylation, CO₂ activation energy decreases to 12.6 kJ mol⁻¹, and the cleavage of alcoholic α-C−H bond has been suppressed.     

Engineering a Copper Single-Atom Electron Bridge to Achieve Efficient Photocatalytic CO2 Conversion

Developing highly efficient and stable photocatalysts for the CO₂ reduction reaction (CO₂RR) remains a great challenge. We designed a Z-Scheme photocatalyst with N−Cu₁−S single-atom electron bridge (denoted as Cu-SAEB), which was used to mediate the CO₂RR. The production of CO and O₂ over Cu-SAEB is as high as 236.0 and 120.1 μmol g⁻¹ h⁻¹ in the absence of sacrificial agents, respectively, outperforming most previously reported photocatalysts. Notably, the as-designed Cu-SAEB is highly stable throughout 30 reaction cycles, totaling 300 h, owing to the strengthened contact interface of Cu-SAEB, and mediated by the N−Cu₁−S atomic structure. Experimental and theoretical calculations indicated that the SAEB greatly promoted the Z-scheme interfacial charge-transport process, thus leading to great enhancement of the photocatalytic CO₂RR of Cu-SAEB. This work represents a promising platform for the development of highly efficient and stable photocatalysts that have potential in CO₂ conversion applications.     

Designing Heteroatom-Codoped Iron Metal–Organic Framework for Promotional Photoreduction of Carbon Dioxide to Ethylene

Rational engineering active sites and vantage defects of catalysts are promising but grand challenging task to enhance photoreduction CO₂ to high value-added C2 products. In this study, we designed an N,S-codoped Fe-based MIL-88B catalyst with well-defined bipyramidal hexagonal prism morphology via a facile and effective process, which was synthesized by addition of appropriate 1,2-benzisothiazolin-3-one (BIT) and acetic acid to the reaction solution. Under simulated solar irradiation, the designed catalyst exhibits high C₂H₄ evolution yield of 17.7 μmol g⁻¹⋅h, which has been rarely achieved in photocatalytic CO₂ reduction process. The synergistic effect of Fe-N coordinated sites and reasonable defects in the N,S-codoped photocatalyst can accelerate the migration of photogenerated carriers, resulting in high electron density, and this in turn helps to facilitate the formation and dimerization of C−C coupling intermediates for C₂H₄ effectively.     

Designed Construction of SrTiO3/SrSO4/Pt Heterojunctions with Boosted Photocatalytic H2 Evolution Activity

Efficient separation of photogenerated electron–hole pairs is a crucial factor for high-performance photocatalysts. Effective electron–hole separation and migration could be achieved by heterojunctions with suitable band structures. Herein, a porous SrTiO₃/SrSO₄ heterojunction is prepared by a sol-gel method at room temperature followed by an annealing process. XRD characterization suggests high crystallinity of the heterostructure. A well-defined interface between the two phases is confirmed by high-resolution (HR)TEM. The photocatalytic H₂ evolution productivity of the SrTiO₃/SrSO₄ heterojunction with Pt as co-catalyst reaches 396.82 μmol g⁻¹ h⁻¹, which is 16 times higher than that of SrTiO₃/Pt. The boosted photocatalytic activity of SrTiO₃/SrSO₄/Pt can be ascribed to the presence of SrSO₄, which promotes the transfer and migration of photogenerated carriers by forming the heterojunction and porous structure, which provides a large amount of active sites. This novel porous heterostructure brings new ideas for the development of high-efficiency photocatalysts for H₂ release.     

Promoting near-infrared photocatalytic activity of carbon-doped carbon nitride via solid alkali activation

Ultrabroad spectral absorption is required for semiconductor photocatalysts utilized for solar-to-chemical energy conversion. The light response range can be extended by element doping, but the photocatalytic performance is generally not enhanced correspondingly. Here we present a solid alkali activation strategy to synthesize near-infrared (NIR) light-activated carbon-doped polymeric carbon nitride (A-cPCN) by combining the copolymerization of melamine and 1,3,5-trimesic acid. The prepared A-cPCN is highly crystalline with a narrowed bandgap and enhanced efficiency in the separation of photogenerated electrons and holes. Under irradiation with NIR light (780 nm ≥ λ ≥ 700 nm), A-cPCN shows an excellent photocatalytic activity for H₂ generation from water with rate of 165 µmol g⁻¹ h⁻¹, and the photo-redox activity for H₂O₂ production (109 µmol g⁻¹ h⁻¹) from H₂O and O₂, whereas no observed photocatalytic activity over pure PCN. The NIR photocatalytic activity is due to carbon doping, which leads to the formation of an interband level, and the alkali activation that achieved shrinking the transfer distance of photocarriers. The current synergistic strategy may open insights to fabricate other carbon-nitrogen-based photocatalysts for enhanced solar energy capture and conversion.     

Semiconductor/Covalent-Organic-Framework Z-Scheme Heterojunctions for Artificial Photosynthesis

A strategy to covalently connect crystalline covalent organic frameworks (COFs) with semiconductors to create stable organic–inorganic Z-scheme heterojunctions for artificial photosynthesis is presented. A series of COF–semiconductor Z-scheme photocatalysts combining water-oxidation semiconductors (TiO₂, Bi₂WO₆, and α-Fe₂O₃) with CO₂ reduction COFs (COF-316/318) was synthesized and exhibited high photocatalytic CO₂-to-CO conversion efficiencies (up to 69.67 μmol g⁻¹ h⁻¹), with H₂O as the electron donor in the gas–solid CO₂ reduction, without additional photosensitizers and sacrificial agents. This is the first report of covalently bonded COF/inorganic-semiconductor systems utilizing the Z-scheme applied for artificial photosynthesis. Experiments and calculations confirmed efficient semiconductor-to-COF electron transfer by covalent coupling, resulting in electron accumulation in the cyano/pyridine moieties of the COF for CO₂ reduction and holes in the semiconductor for H₂O oxidation, thus mimicking natural photosynthesis.     

Graphene Oxide-Assisted Covalent Triazine Framework for Boosting Photocatalytic H2 Evolution

Covalent triazine frameworks (CTFs) with two-dimensional structures have exhibited promising visible-light-induced H₂ evolution performance. However, it is still a challenge to improve their activity. Herein, we report π-conjugation-linked CTF-1/GO for boosting photocatalytic H₂ evolution. The CTF-1/GO hybrid material was obtained by a facile low-temperature condensation of 1,4-dicyanobenzene in the presence of GO. The results of photocatalytic H₂ evolution indicate that the optimum hybrid, CTF-1/GO-3.0, exhibited an H₂ evolution rate of 2262.4 μmol ⋅ g⁻¹ ⋅ h⁻¹ under visible light irradiation, which was 9 times that of pure CTF-1. The enhanced photocatalytic performance could be attributed to the fact that GO in CTF-1/GO hybrids not only acts as an electron collector and transporter like a “bridge” to facilitate the separation and transfer of photogenerated charges but also shortens the electron migration path due to its thin sheet layer uniformly distribution over CTF-1. This work could help future development of novel conjugated CTF-based composite materials as high-efficiency photocatalyst for photocatalysis.     

Wurtzite CuGaS2 with an In-Situ-Formed CuO Layer Photocatalyzes CO2 Conversion to Ethylene with High Selectivity

We present surface reconstruction-induced C−C coupling whereby CO₂ is converted into ethylene. The wurtzite phase of CuGaS_2. undergoes in situ surface reconstruction, leading to the formation of a thin CuO layer over the pristine catalyst, which facilitates selective conversion of CO₂ to ethylene (C₂H₄). Upon illumination, the catalyst efficiently converts CO₂ to C₂H₄ with 75.1 % selectivity (92.7 % selectivity in terms of R_electron) and a 20.6 μmol g⁻¹ h⁻¹ evolution rate. Subsequent spectroscopic and microscopic studies supported by theoretical analysis revealed operando-generated Cu²⁺, with the assistance of existing Cu⁺, functioning as an anchor for the generated *CO and thereby facilitating C−C coupling. This study demonstrates strain-induced in situ surface reconstruction leading to heterojunction formation, which finetunes the oxidation state of Cu and modulates the CO₂ reduction reaction pathway to selective formation of ethylene.     

Solar-Driven CO2 Conversion via Optimized Photothermal Catalysis in a Lotus Pod Structure

Photothermal CO₂ reduction is one of the most promising routes to efficiently utilize solar energy for fuel production at high rates. However, this reaction is currently limited by underdeveloped catalysts with low photothermal conversion efficiency, insufficient exposure of active sites, low active material loading, and high material cost. Herein, we report a potassium-modified carbon-supported cobalt (K⁺−Co−C) catalyst mimicking the structure of a lotus pod that addresses these challenges. As a result of the designed lotus-pod structure which features an efficient photothermal C substrate with hierarchical pores, an intimate Co/C interface with covalent bonding, and exposed Co catalytic sites with optimized CO binding strength, the K⁺−Co−C catalyst shows a record-high photothermal CO₂ hydrogenation rate of 758 mmol g_cat⁻¹ h⁻¹ (2871 mmol g_Co⁻¹ h⁻¹) with a 99.8 % selectivity for CO, three orders of magnitude higher than typical photochemical CO₂ reduction reactions. We further demonstrate with this catalyst effective CO₂ conversion under natural sunlight one hour before sunset during the winter season, putting forward an important step towards practical solar fuel production.