Asymmetric Triple-Atom Sites Confined in Ternary Oxide Enabling Selective CO2 Photothermal Reduction to Acetate

Covalently connected core-shell NH2-MIL-125@COFs-OH hybrid materials for visible-light-driven CO2 reduction

Herein, the covalently connected core-shell metal-organic frameworks (MOFs)@covalent-organic frameworks (COFs) hybrid materials were successfully constructed by coating the stable COF-OH shell on the NH₂-MIL-125 core. The introduction of the NH₂-MIL-125 core endowed the hybrid materials with high Brunauer-Emmett-Teller (BET) surface area (S_BET) and abundant unsaturated metal sites. And the coating of COF-OH shell endowed the hybrid materials outstanding physicochemical stability and visible-light response, and suitable band gaps. Moreover, the thickness of the COF-OH shell was carefully adjusted according to the feeding amount of NH₂-MIL-125. Impressively, the electron transfer pathway in the formed heterostructure was clarified and it was proven that a type-II heterojunction was generated between the MOFs and the COFs. The formed stable CN covalent bonds in the interfacial layer was beneficial to the photogenerated electron transfer and the electron-hole pairs separation, which greatly enhanced the CO₂ photocatalytic reduction. The product NH₂-MIL-125@COF-3 exhibited the highest CO yield of 22.93 μmol·g^-1·h^-1, about 2 times higher than NH₂-MIL-125 (11.82 μmol·g^-1·h^-1) and 3 times greater than COF-OH (7.26 μmol·g^-1·h^-1). This work can provide helpful ideas for the careful design of the novel MOFs@COFs hybrid materials as well as useful exploration for the CO₂ photocatalytic reduction.

Chelated Ion-Exchange Strategy toward BiOCl Mesoporous Single-Crystalline Nanosheets for Boosting Photocatalytic Selective Aromatic Alcohols Oxidation

The photoresponse and photocatalytic efficiency of bismuth oxychloride (BiOCl) are greatly limited by rapid recombination of photogenerated carriers. The construction of porous single-crystal BiOCl photocatalyst can effectively alleviate this issue and provide accessible active sites. Herein, a facile chelated ion-exchange strategy is developed to synthesize BiOCl mesoporous single-crystalline nanosheets (BiOCl MSCN) using acetic acid and ammonia solution respectively as chelating agent and ionization promoter. The strong chelation between acetate ions and Bi³⁺ ions introduces acetate ions into the precipitated product to exchange with Cl^- ions, resulting in large lattice mismatch, strain release, and formation of void-like mesopores. The prepared BiOCl MSCN photocatalyst exhibits excellent catalytic performance with 99% conversion and 98% selectivity for oxidation of benzyl alcohol to benzaldehyde and superior general adaptability for various aromatic alcohols. The theoretical calculations and characterizations confirm that the superior performance is mainly attributed to the abundant oxygen vacancies, plenty of accessible adsorption/active sites and fast charge transport path without grain boundaries.

Selective CO2 Photoreduction to Acetate at Asymmetric Ternary Bridging Sites

Photoreduction of CO₂ is a promising strategy to synthesize value-added fuels or chemicals and realize carbon neutralization. Noncopper catalysts are seldom reported to generate C₂ products, and the selectivity over these catalysts is low. Here, we design rich-interface, heterostructured In₂O₃/InP (r-In₂O₃/InP) for highly competitive photocatalytic CO₂-to-CH₃COOH conversion with a productivity of 96.7 μmol g^-1 and selectivity > 96% along with water oxidation to O₂ in pure water (no sacrificial agent) under visible light irradiation. The hard X-ray absorption near-edge structure (XANES) shows that the formation of r-In₂O₃/InP with the isogenesis cation adjusts the coordination environment via interface engineering and forms O-In-P polarized sites at the interface. In situ FT-IR and Raman spectra identify the key intermediates of OCCO* for acetate production with high selectivity. Density functional theory (DFT) calculations reveal that r-In₂O₃/InP with rich O-In-P polarized sites promotes C-C coupling to form C₂ products because of the imbalanced adsorption energies of two carbon atoms. This work reports an interesting indium-based photocatalyst for selective CO₂ photoreduction to acetate under strict solution and irradiation conditions and provides significant insights into fabricating interfacial polarization sites to promote the process.

Electron-Rich Bi Nanosheets Promote CO2 ⋅- Formation for High-Performance and pH-Universal Electrocatalytic CO2 Reduction

Electrochemical CO₂ reduction reaction (CO₂ RR) to chemical fuels such as formate offers a promising pathway to carbon-neutral future, but its practical application is largely inhibited by the lack of effective activation of CO₂ molecules and pH-universal feasibility. Here, we report an electronic structure manipulation strategy to electron-rich Bi nanosheets, where electrons transfer from Cu donor to Bi acceptor in bimetallic Cu-Bi, enabling CO₂ RR towards formate with concurrent high activity, selectivity and stability in pH-universal (acidic, neutral and alkaline) electrolytes. Combined in situ Raman spectra and computational calculations unravel that electron-rich Bi promotes CO₂ ⋅^- formation to activate CO₂ molecules, and enhance the adsorption strength of *OCHO intermediate with an up-shifted p-band center, thus leading to its superior activity and selectivity of formate. Further integration of the robust electron-rich Bi nanosheets into III-V-based photovoltaic solar cell results in an unassisted artificial leaf with a high solar-to-formate (STF) efficiency of 13.7 %.

Enhanced Interfacial Electron Transfer by Asymmetric Cu-Ov -In Sites on In2 O3 for Efficient Peroxymonosulfate Activation

Enhancing the peroxymonosulfate (PMS) activation efficiency to generate more radicals is vital to promote the Fenton-like reaction activity, however, how to promote the PMS adsorption and accelerate the interfacial electron transfer to boost its activation kinetics remains a great challenge. Herein, we prepared Cu-doped defect-rich In₂ O₃ (Cu-In₂ O₃ /O_v ) catalysts containing asymmetric Cu-O_v -In sites for PMS activation in water purification. The intrinsic catalytic activity is that the side-on adsorption configuration of the O-O bond (Cu-O-O-In) at the Cu-O_v -In sites significantly stretches the O-O bond length. Meanwhile, the Cu-O_v -In sites increase the electron density near the Fermi energy level, promoting more and faster electron transfer to the O-O bond for generating more SO₄ ⋅^- and ⋅OH. The degradation rate constant of tetracycline achieved by Cu-In₂ O₃ /O_v is 31.8 times faster than In₂ O₃ /O_v , and it shows the possibility of membrane reactor for practical wastewater treatment.

Room-temperature photosynthesis of propane from CO2 with Cu single atoms on vacancy-rich TiO2

Photochemical conversion of CO₂ into high-value C₂₊ products is difficult to achieve due to the energetic and mechanistic challenges in forming multiple C-C bonds. Herein, an efficient photocatalyst for the conversion of CO₂ into C₃H₈ is prepared by implanting Cu single atoms on Ti_0.91O₂ atomically-thin single layers. Cu single atoms promote the formation of neighbouring oxygen vacancies (V_Os) in Ti_0.91O₂ matrix. These oxygen vacancies modulate the electronic coupling interaction between Cu atoms and adjacent Ti atoms to form a unique Cu-Ti-V_O unit in Ti_0.91O₂ matrix. A high electron-based selectivity of 64.8% for C₃H₈ (product-based selectivity of 32.4%), and 86.2% for total C₂₊ hydrocarbons (product-based selectivity of 50.2%) are achieved. Theoretical calculations suggest that Cu-Ti-V_O unit may stabilize the key *CHOCO and *CH₂OCOCO intermediates and reduce their energy levels, tuning both C₁-C₁ and C₁-C₂ couplings into thermodynamically-favourable exothermal processes. Tandem catalysis mechanism and potential reaction pathway are tentatively proposed for C₃H₈ formation, involving an overall (20e^- - 20H⁺) reduction and coupling of three CO₂ molecules at room temperature.

Nanostructured Materials for Photothermal Carbon Dioxide Hydrogenation: Regulating Solar Utilization and Catalytic Performance

Converting carbon dioxide (CO₂) into value-added fuels or chemicals through photothermal catalytic CO₂ hydrogenation is a promising approach to alleviate the energy shortage and global warming. Understanding the nanostructured material strategies in the photothermal catalytic CO₂ hydrogenation process is vital for designing photothermal devices and catalysts and maximizing the photothermal CO₂ hydrogenation performance. In this Perspective, we first describe several essential nanomaterial design concepts to enhance sunlight absorption and utilization in photothermal CO₂ hydrogenation. Subsequently, we review the latest progress in photothermal CO₂ hydrogenation into C₁ (e.g., CO, CH₄, and CH₃OH) and multicarbon hydrocarbon (C₂₊) products. Finally, the relevant challenges and opportunities in this exciting research realm are discussed. This perspective provides a comprehensive understanding for the light-heat synergy over nanomaterials and instruction for rational photothermal catalyst design for CO₂ utilization.

Multifunctional Au/Hydroxide Interface toward Enhanced C-C Coupling for Solar-Driven CO2 Reduction into C2H6

The high-grade C₂₊ products from CO₂ photoreduction are limited by the kinetic bottleneck. Herein, a multifunctional Au/hydroxide interface was put forward to improve the C-C coupling. As a prototype, the synthesized Au/ZnSn(OH)₆ tuned the CO generation and afforded about 50% electrons toward C₂H₆ selectivity. The prominent enhancement resulted from the following effects: (1) strong metal-support electronic interactions built an electric field at the interface of ZnSn(OH)₆ nearby the Au nanoparticles, leading to fast transfer of electrons for the C-H and C-C bonding reactions. (2) The surface solid-state Sn-OH and Zn-OH lattice hydroxyls served as donors to feed rich H⁺ and oxygen vacancies (OVs) via hole-induced oxidation for the boosted C₂H₆ formation. (3) The synergetic OVs and Au sites allowed efficient e^-/H⁺ to boost *CO hydrogenation toward *CH₃ and *CH₃*CH₃ formation into the C₂H₆ product.

Correlating Oxidation State and Surface Ligand Motifs with the Selectivity of CO2 Photoreduction to C2 Products

The design for non-Cu-based catalysts with the function of producing C₂₊ products requires systematic knowledge of the intrinsic connection between the surface state as well as the catalytic activity and selectivity. In this work, photochemical in situ spectral surface characterization techniques combined with the first principle calculations (DFT) were applied to investigate the relationships between the composition of surface states, coordinated motifs, and catalytic selectivity of a titanium oxynitride catalyst. When the catalyst mediates CO₂ photoreduction, C₂ product selectivity is positively correlated with the surface Ti²⁺ /Ti³⁺ ratio and the surface oxidation state is regulated and controlled by coordinated motifs of N-Ti-O/V[O], which can reduce the potential dimerization energy barriers of *CO-CO* and promote spontaneous formation of the subsequent *CO-CH₂ * intermediate. This phenomenon provides a new perspective for the design of heterogeneous catalysts for photoreduction of CO₂ into useful products.

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.

Direct Polyethylene Photoreforming into Exclusive Liquid Fuel over Charge-Asymmetrical Dual Sites under Mild Conditions

Direct polyethylene photoreforming to high-energy-density C₂ fuels under mild conditions is of great significance and still faces a huge challenge, which is partly attributed to the extreme instability of *CH₂CH₂ adsorbed on the traditional catalysts with single catalytic sites. Herein, charge-asymmetrical dual sites are designed to boost the adsorption of *CH₂CH₂ for direct polyethylene photoreforming into C₂ fuels under normal temperature and pressure. As a prototype, the synthetic Zr-doped CoFe₂O₄ quantum dots with charge-asymmetrical dual metal sites realize direct polyethylene photoreforming into acetic acid, with 100% selectivity of liquid fuel and the evolution rate of 1.10 mmol g^-1 h^-1, outperforming those of most previously reported photocatalysts under similar conditions. In situ X-ray photoelectron spectra, density-functional-theory calculations, and control experiments reveal the charge-asymmetrical Zr-Fe dual sites may act as the predominate catalytic sites, which can simultaneously bond with the *CH₂CH₂ intermediates for the following stepwise oxidation to form C₂ products.

Progress and perspectives on 1D nanostructured catalysts applied in photo(electro)catalytic reduction of CO2

Reducing CO₂ into value-added chemicals and fuels by artificial photosynthesis (photocatalysis and photoelectrocatalysis) is one of the considerable solutions to global environmental and energy issues. One-dimensional (1D) nanostructured catalysts (nanowires, nanorods, nanotubes and so on.) have attracted extensive attention due to their superior light-harvesting ability, co-catalyst loading capacity, and high carrier separation rate. This review analyzed the basic principle of the photo(electro)catalytic CO₂ reduction reaction (CO₂ RR) briefly. The preparation methods and properties of 1D nanostructured catalysts are introduced. Next, the applications of 1D nanostructured catalysts in the field of photo(electro)catalytic CO₂ RR are introduced in detail. In particular, we introduced the design of composite catalysts with 1D nanostructures, for example loading 0D, 1D, 2D, and 3D materials on a 1D nanostructured semiconductor to construct a heterojunction to optimize the photo-response range, carrier separation and transport efficiency, CO₂ adsorption and activation capacity, and stability of the catalyst. Finally, the development prospects of 1D nanostructured catalysts are discussed and summarized. This review can provide guidance for the rational design of advanced catalysts for photo(electro)catalytic CO₂ RR.

Engineering Single-Atom Active Sites on Covalent Organic Frameworks for Boosting CO2 Photoreduction

Solar carbon dioxide (CO₂) conversion is an emerging solution to meet the challenges of sustainable energy systems and environmental/climate concerns. However, the construction of isolated active sites not only influences catalytic activity but also limits the understanding of the structure-catalyst relationship of CO₂ reduction. Herein, we develop a universal synthetic protocol to fabricate different single-atom metal sites (e.g., Fe, Co, Ni, Zn, Cu, Mn, and Ru) anchored on the triazine-based covalent organic framework (SAS/Tr-COF) backbone with the bridging structure of metal-nitrogen-chlorine for high-performance catalytic CO₂ reduction. Remarkably, the as-synthesized Fe SAS/Tr-COF as a representative catalyst achieved an impressive CO generation rate as high as 980.3 μmol g^-1 h^-1 and a selectivity of 96.4%, over approximately 26 times higher than that of the pristine Tr-COF under visible light irradiation. From X-ray absorption fine structure analysis and density functional theory calculations, the superior photocatalytic performance is attributed to the synergic effect of atomically dispersed metal sites and Tr-COF host, decreasing the reaction energy barriers for the formation of *COOH intermediates and promoting CO₂ adsorption and activation as well as CO desorption. This work not only affords rational design of state-of-the-art catalysts at the molecular level but also provides in-depth insights for efficient CO₂ conversion.

Polarized Cu-Bi Site Pairs for Non-Covalent to Covalent Interaction Tuning toward N2 Photoreduction

A universal atomic layer confined doping strategy is developed to prepare Bi₂₄ O₃₁ Br₁₀ materials incorporating isolated Cu atoms. The local polarization can be created along the CuOBi atomic interface, which enables better electron delocalization for effective N₂ activation. The optimized Cu-Bi₂₄ O₃₁ Br₁₀ atomic layers show 5.3× and 88.2× improved photocatalytic nitrogen fixation activity than Bi₂₄ O₃₁ Br₁₀ atomic layer and bulk Bi₂₄ O₃₁ Br₁₀ , respectively, with the NH₃ generation rate reaching 291.1 µmol g^-1 h^-1 in pure water. The polarized Cu-Bi site pairs can increase the non-covalent interaction between the catalyst's surface and N₂ molecules, then further weaken the covalent bond order in NN. As a result, the hydrogenation pathways can be altered from the associative distal pathway for Bi₂₄ O₃₁ Br₁₀ to the alternating pathway for Cu-Bi₂₄ O₃₁ Br₁₀ . This strategy provides an accessible pathway for designing polarized metal site pairs or tuning the non-covalent interaction and covalent bond order.

Photocatalytic CO2 conversion: from C1 products to multi-carbon oxygenates

Photocatalytic CO₂ conversion into high-value chemicals has been emerging as an attractive research direction in achieving carbon resource sustainability. The chemical products can be categorized into C1 and multi-carbon (C₂₊) products. In this review, we describe the recent research progress in photocatalytic CO₂ conversion systems from C1 products to multi-carbon oxygenates, and analyze the reasons related to their catalytic mechanisms, as the production of multi-carbon oxygenates is generally more difficult than that of C1 products. Then we discuss several examples in promoting the photoconversion of CO₂ to value-added multi-carbon products in the aspects of photocatalyst design, mass transfer control, determination of active sites, and intermediate regulation. Finally, we summarize perspectives on the challenges and propose potential directions in this fast-developing field, such as the prospect of CO₂ transformation to long-chain hydrocarbons like salicylic acid or even plastics.

Carbon Nitride Photocatalysts with Integrated Oxidation and Reduction Atomic Active Centers for Improved CO2 Conversion

Single-atom active-site catalysts have attracted significant attention in the field of photocatalytic CO₂ conversion. However, designing active sites for CO₂ reduction and H₂ O oxidation simultaneously on a photocatalyst and combining the corresponding half-reaction in a photocatalytic system is still difficult. Here, we synthesized a bimetallic single-atom active-site photocatalyst with two compatible active centers of Mn and Co on carbon nitride (Mn₁ Co₁ /CN). Our experimental results and density functional theory calculations showed that the active center of Mn promotes H₂ O oxidation by accumulating photogenerated holes. In addition, the active center of Co promotes CO₂ activation by increasing the bond length and bond angle of CO₂ molecules. Benefiting from the synergistic effect of the atomic active centers, the synthesized Mn₁ Co₁ /CN exhibited a CO production rate of 47 μmol g^-1  h^-1 , which is significantly higher than that of the corresponding single-metal active-site photocatalyst.

Direct Conversion of CO2 into Hydrocarbon Solar Fuels by a Synergistic Photothermal Catalysis

Photothermal coupling catalysis technology has been widely studied in recent years and may be a promising method for CO2 reduction. Photothermal coupling catalysis can improve chemical reaction rates and realize the controllability of reaction pathways and products, even in a relatively moderate reaction condition. It has inestimable value in the current energy and global environmental crisis. This review describes the application of photothermal catalysis in CO2 reduction from different aspects. Firstly, the definition and advantages of photothermal catalysis are briefly described. Then, different photothermal catalytic reductions of CO2 products and catalysts are introduced. Finally, several strategies to improve the activity of photothermal catalytic reduction of CO2 are described and we present our views on the future development and challenges of photothermal coupling. Ultimately, the purpose of this review is to bring more researchers’ attention to this promising technology and promote this technology in solar fuels and chemicals production, to realize the value of the technology and provide a better path for its development.

Synthetic strategies for MOF-based single-atom catalysts for photo- and electro-catalytic CO2 reduction

The excessive CO₂ emission has resulted in climate changes, which has threatened human existence. Photocatalytic and electrocatalytic CO₂ reduction, driven by wind electricity and solar energy, are feasible ways of tackling carbon dioxide emission, as both energies are clean and renewable. Single-atom catalyst (SAC) is a candidate owing to excellent electrocatalytic and photocatalytic performance. Methods for preparing an SAC by using metal-organic frameworks (MOFs) as support or precursors are summarized. Also, applications in energy conversion are exhibited. However, the real challenge is to improve the selectivity of catalytic reactions to yield higher value products, which is to be discussed.

Selective photocatalytic CO2 reduction in aerobic environment by microporous Pd-porphyrin-based polymers coated hollow TiO2

Direct photocatalytic CO2 reduction from primary sources, such as flue gas and air, into fuels, is highly desired, but the thermodynamically favored O2 reduction almost completely impedes this process. Herein, we report on the efficacy of a composite photocatalyst prepared by hyper-crosslinking porphyrin-based polymers on hollow TiO2 surface and subsequent coordinating with Pd(II). Such composite exhibits high resistance against O2 inhibition, leading to 12% conversion yield of CO2 from air after 2-h UV-visible light irradiation. In contrast, the CO2 reduction over Pd/TiO2 without the polymer is severely inhibited by the presence of O2 ( ≥ 0.2 %). This study presents a feasible strategy, building Pd(II) sites into CO2-adsorptive polymers on hollow TiO2 surface, for realizing CO2 reduction with H2O in an aerobic environment by the high CO2/O2 adsorption selectivity of polymers and efficient charge separation for CO2 reduction and H2O oxidation on Pd(II) sites and hollow TiO2, respectively.

Engineering Catalytic Interfaces in Cuδ+/CeO2-TiO2 Photocatalysts for Synergistically Boosting CO2 Reduction to Ethylene

Photocatalytic CO₂ conversion into a high-value-added C₂ product is a highly challenging task because of insufficient electron deliverability and sluggish C-C coupling kinetics. Engineering catalytic interfaces in photocatalysts provides a promising approach to manipulate photoinduced charge carriers and create multiple catalytic sites for boosting the generation of C₂ product from CO₂ reduction. Herein, a Cu^δ+/CeO₂-TiO₂ photocatalyst that contains atomically dispersed Cu^δ+ sites anchored on the CeO₂-TiO₂ heterostructures consisting of highly dispersed CeO₂ nanoparticles on porous TiO₂ is designedly constructed by the pyrolytic transformation of a Cu²⁺-Ce³⁺/MIL-125-NH₂ precursor. In the designed photocatalyst, TiO₂ acts as a light-harvesting material for generating electron-hole pairs that are efficiently separated by CeO₂-TiO₂ interfaces, and the Cu-Ce dual active sites synergistically facilitate the generation and dimerization of *CO intermediates, thus lowering the energy barrier of C-C coupling. As a consequence, the Cu^δ+/CeO₂-TiO₂ photocatalyst exhibits a production rate of 4.51 μmol^-1·g_cat^-1·h^-1 and 73.9% selectivity in terms of electron utilization for CO₂ to C₂H₄ conversion under simulated sunlight, with H₂O as hydrogen source and hole scavenger. The photocatalytic mechanism is revealed by operando spectroscopic methods as well as theoretical calculations. This study displays the rational construction of heterogeneous photocatalysts for boosting CO₂ conversion and emphasizes the synergistic effect of multiple active sites in enhancing the selectivity of C₂ product.

State-of-the-Art Advancements of Atomically Thin Two-Dimensional Photocatalysts for Energy Conversion

Excessive use of fossil fuels leads to energy shortages and environmental pollution, threatening human health and social development. As a clean, green, and sustainable technology, generation of renewable energy from...