Implanting CoOx Clusters on Ordered Macroporous ZnO Nanoreactors for Efficient CO2 Photoreduction

A Review of Metal-Organic Frameworks Derived Hollow-Structured Photocatalysts: Synthesis and Applications

Photocatalysis is a most important approach to addressing global energy shortages and environmental issues due to its environmentally friendly and sustainable properties. The key to realizing efficient photocatalysis relies on developing appropriate catalysts with high efficiency and chemical stability. Among various photocatalysts, Metal-organic frameworks (MOFs)-derived hollow-structured materials have drawn increased attention in photocatalysis based on advantages like more active sites, strong light absorption, efficient transfer of pho-induced charges, excellent stability, high electrical conductivity, and better biocompatibility. Specifically, MOFs-derived hollow-structured materials are widely utilized in photocatalytic CO2 reduction (CO2RR), hydrogen evolution (HER), nitrogen fixation (NRR), degradation, and other reactions. This review starts with the development story of MOFs, the commonly adopted synthesis strategies of MOFs-derived hollow materials, and the latest research progress in various photocatalytic applications are also introduced in detail. Ultimately, the challenges of MOFs-derived hollow-structured materials in practical photocatalytic applications are also prospected. This review holds great potential for developing more applicable and efficient MOFs-derived hollow-structured photocatalysts.

Photocatalytic CO2 Reduction to Ethanol by ZnCo2O4/ZnO Janus Hollow Nanofibers

Photocatalytic carbon dioxide (CO2) reduction for high-value hydrocarbon fuel production is a promising strategy to tackle global energy demand and climate change. However, this technology faces formidable challenges, primarily stemming from low yield and poor selectivity of C2 products of the desired hydrocarbon fuels. This study reported ZnO/ZnCo2O4 Janus hollow nanofibers (ZnO/ZCO JHNFs) prepared by electrospinning and atomic layer deposition. Photocatalytic tests revealed an ethanol yield of 4.99 μmol g-1 h-1 for ZnO/ZnCo2O4 JHNFs, surpassing mixed ZnO/ZnCo2O4 nanofibers (ZnO/ZCO NFs) by 4.35 times and pure ZnO by 12.7 times. The selectivity of 58.8% is 2.38 and 4.49 times higher than those of ZnO/ZnCo2O4 NFs and ZnO, respectively. These enhancements are attributed to efficient carrier separation facilitated by the ordered internal electric field of the Z-scheme heterojunction interface, validated by the energy band evaluations from experimentation and density functional theory (DFT) simulations and charge separation characterizations of photocurrent, impedance, and photoluminescence spectra. The Janus structure also effectively exposes the surface of ZnCo2O4 to CO2 molecules, increasing the active site availability, as confirmed by BET nitrogen adsorption/desorption, temperature-programmed desorption tests, and DFT adsorption energy calculations. This study proposes a novel approach for efficient photocatalytic hydrocarbon fuel production, with potential applications in energy and climate crisis mitigation.

A Novel Perspective on Enhancing Photocatalytic Performance through the Synergistic Effect of Nd Single Atoms and Heterostructures

There are few reports on lanthanide single atom modified catalysts, as the role of the 4f levels in photocatalysis is difficult to explain clearly. Here, the synergistic effect of 4f levels of Nd and heterostructures is studied by combining steady-state, transient, and ultrafast spectral analysis techniques with DFT theoretical calculations based on the construction of Nd single atom modified black phosphorus/g-C3N4 (BP/CN) heterojunctions. As expected, the generation rates of CO and CH4 of the optimized heterostructure are 7.44 and 6.85 times higher than those of CN, and 8.43 and 9.65 times higher than those of BP, respectively. The Nd single atoms can not only cause surface reconstruction and regulate the active sites of BP, but also accelerate charge separation and transfer, further suppressing the recombination of electron-hole pairs. The electrons can transfer from g-C3N4:Nd to BP:Nd, with a transfer time of ≈11.4 ps, while the radiation recombination time of electron-hole pairs of g-C3N4 is ≈26.13 µs, indicating that the construction of heterojunctions promotes charge transfer. The 2P1/2/2G9/2/4G7/2/2H11/2/4F7/2→4I9/2 emissions from Nd3+ can also be absorbed by heterostructures, which improves the utilization of light. The energy change of the key rate measurement step CO2 *→COOH* decreases through Nd single atom modification.

Efficient Holes Abstraction by Precisely Decorating Ruthenium Single Atoms and RuOx Clusters on ZnIn2S4 for Photocatalytic Pure Water Splitting

Developing efficient photocatalysts for two-electron water splitting with simultaneous H2O2 and H2 generation shows great promise for practical application. Currently, the efficiency of two-electron water splitting is still restricted by the low utilization of photogenerated charges, especially holes, of which the transfer rate is much slower than that of electrons. Herein, Ru single atoms and RuOx clusters are co-decorated on ZnIn2S4 (RuOx/Ru-ZIS) to employ as multifunctional sites for efficient photocatalytic pure water splitting. Doping of Ru single atoms in the ZIS basal plane enhances holes abstraction from bulk ZIS by regulating the electronic structure, and RuOx clusters offer a strong interfacial electric field to remarkably promote the out-of-plane migration of holes from ZIS. Moreover, Ru single atoms and RuOx clusters also serve as active sites for boosting surface water oxidation. As a result, an excellent H2 and H2O2 evolution rates of 581.9 µmol g-1 h-1 and 464.4 µmol g-1 h-1 is achieved over RuOx/Ru-ZIS under visible light irradiation, respectively, with an apparent quantum efficiency (AQE) of 4.36% at 400 nm. This work paves a new way to increase charge utilization by manipulating photocatalyst using single atom and clusters.

Asymmetric Atomic Dual-Sites for Photocatalytic CO2 Reduction

Atomically dispersed active sites in a photocatalyst offer unique advantages such as locally tuned electronic structures, quantum size effects, and maximum utilization of atomic species. Among these, asymmetric atomic dual-sites are of particular interest because their asymmetric charge distribution generates a local built-in electric potential to enhance charge separation and transfer. Moreover, the dual sites provide flexibility for tuning complex multielectron and multireaction pathways, such as CO2 reduction reactions. The coordination of dual sites opens new possibilities for engineering the structure-activity-selectivity relationship. This comprehensive overview discusses efficient and sustainable photocatalysis processes in photocatalytic CO2 reduction, focusing on strategic active-site design and future challenges. It serves as a timely reference for the design and development of photocatalytic conversion processes, specifically exploring the utilization of asymmetric atomic dual-sites for complex photocatalytic conversion pathways, here exemplified by the conversion of CO2 into valuable chemicals.

Dual-Atom P-Co-Dy Charge-Transfer Bridge on Black Phosphorus for Enhanced Photocatalytic CO2 Reduction

The synergistic effect of rare earth single-atoms and transition metal single-atoms may enable us to achieve some unprecedented performance and characteristics. Here, Co-Dy dual-atoms on black phosphorus with a P-Co-Dy charge-transfer bridge are designed and fabricated as the active center for the CO2 photoreduction reaction. The synergistic effect of Co-Dy on the performance of black phosphorus is studied by combining X-ray absorption spectroscopy, ultrafast spectral analysis, and in situ technology with DFT calculations. The results show that the Co and Dy bimetallic active site can promote charge transfer by the charge transfer bridge from P to Dy, and then to Co, thereby improving the photocatalytic activity of black phosphorus. The performance of catalysts excited at different wavelength light indicates that the 4G11/2/2I15/2/4F9/2→6H15/2 and 4F9/2→6H13/2 emissions of Dy can be absorbed by black phosphorus to improve the utilization of sunlight. The in situ DRIFTS and density functional theory (DFT) calculations are used to investigate the CO2 photoreduction pathway. This work provides an depth insight into the mechanism of dual-atom catalysts with enhanced photocatalytic performance, which helps to design novel atomic photocatalysts with excellent activity for CO2 reduction reactions.

Hierarchically Ordered Pore Engineering of Metal-Organic Framework-Based Materials for Electrocatalysis

Ordered pore engineering that embeds uniform pores with periodic alignment in electrocatalysts opens up a new avenue for achieving further performance promotion. Hierarchically ordered porous metal-organic frameworks (HOP-MOFs) possessing multilevel pores with ordered distribution are the promising precursors for the exploration of ordered porous electrocatalysts, while the scalable acquisition of HOP-MOFs with editable components and adjustable pore size regimes is critical. This review presents recent progress on hierarchically ordered pore engineering of MOF-based materials for enhanced electrocatalysis. The synthetic strategies of HOP-MOFs with different pore size regimes, including the self-assembly guided by reticular chemistry, surfactant, nanoemulsion, and nanocasting, are first introduced. Then the applications of HOP-MOFs as the precursors for exploring hierarchically ordered porous electrocatalysts are summarized, selecting representatives to highlight the boosted performance. Especially, the intensification of molecule and ion transport integrated with optimized electron transfer and site exposure over the hierarchically ordered porous derivatives are emphasized to clarify the directional transfer and integration effect endowed by ordered pore engineering. Finally, the remaining scientific challenges and an outlook of this field are proposed. It is hoped that this review will guide the hierarchically ordered pore engineering of nanocatalysts for boosting the catalytic performance and promoting the practical applications.

Sub-Nanometer Mono-Layered Metal-Organic Frameworks Nanosheets for Simulated Flue Gas Photoreduction

The dilemma between the thickness and accessible active site triggers the design of porous crystalline materials with mono-layered structure for advanced photo-catalysis applications. Here, a kind of sub-nanometer mono-layered nanosheets (Co-MOF MNSs) through the exfoliation of specifically designed Co3 cluster-based metal-organic frameworks (MOFs) is reported. The sub-nanometer thickness and inherent light-sensitivity endow Co-MOF MNSs with fully exposed Janus Co3 sites that can selectively photo-reduce CO2 into formic acid under simulated flue gas. Notably, the production efficiency of formic acid by Co-MOF MNSs (0.85 mmol g-1 h-1) is ≈13 times higher than that of the bulk counterpart (0.065 mmol g-1 h-1) under a simulated flue gas atmosphere, which is the highest in reported works up to date. Theoretical calculations prove that the exposed Janus Co3 sites with simultaneously available sites possess higher activity when compared with single Co site, validating the importance of mono-layered nanosheet morphology. These results may facilitate the development of functional nanosheet materials for CO2 photo-reduction in potential flue gas treatment.

Interconnected Periodic Macroporous NaNbO3 for High-Efficiency Solar-Driven Photocatalytic Hydrogen Evolution

Highly ordered periodic macroporous structures have been extensively utilized to significantly enhance the photocatalytic activity. However, constructing 3D interconnected ordered porous ternary nanostructures with highly crystalline frameworks remains a formidable challenge. Here, we introduce the design and fabrication of 3D interconnected periodic macroporous NaNbO3 (PM NaNbO3) to effectively increase the density of surface-active sites and optimize the photogenerated carrier-transfer efficiency. By incorporating Pt as a cocatalyst, PM NaNbO3 exhibits an exceptional photocatalytic hydrogen generation rate of 10.04 mmol h-1 g-1, which is approximately six and five times higher than those of calcined NaNbO3 (C-NaNbO3) and hydrothermal NaNbO3 (H-NaNbO3), respectively. This outstanding performance can be attributed to the synergistic effects arising from its well-interconnected pore architecture, large surface area, enhanced light absorption capability, and improved charge carrier separation and transport efficiency. The findings presented in this study demonstrate an innovative approach toward designing hierarchically periodic macroporous materials for solar-driven hydrogen production.

Advances in zeolitic-imidazolate-framework-based catalysts for photo-/electrocatalytic water splitting, CO2 reduction and N2 reduction applications

Harnessing electrical or solar energy for the renewable production of value-added fuels and chemicals through catalytic processes (such as photocatalysis and electrocatalysis) is promising to achieve the goal of carbon neutrality. Owing to the large number of highly accessible active sites, highly porous structure, and charge separation/transfer ability, as well as excellent stability against chemical and electrochemical corrosion, zeolite imidazolate framework (ZIF)-based catalysts have attracted significant attention. Strategic construction of heterojunctions, and alteration of the metal node and the organic ligand of the ZIFs effectively regulate the binding energy of intermediates and the reaction energy barriers that allow tunable catalytic activity and selectivity of a product during reaction. Focusing on the currently existing critical issues of insufficient kinetics for electron transport and selective generation of ideal products, this review starts from the characteristics and physiochemical advantages of ZIFs in catalytic applications, then introduces promising regulatory approaches for advancing the kinetic process in emerging CO2 reduction, water splitting and N2 reduction applications, before proposing perspective modification directions.

Pyrolysis Free Out-of-Plane Co-Single Atomic Sites in Porous Organic Photopolymer Stimulates Solar-Powered CO2 Fixation

Herein, a facile strategy is illustrated to develop pyrolysis-free out-of-plane coordinated single atomic sites-based M-POP via a one-pot Friedel Craft acylation route followed by a post-synthetic metalation. The optimized geometry of the Co@BiPy-POP clearly reveals the presence of out-of-plane Co-single atomic sites in the porous backbone. This novel photopolymer Co@BiPy-POP shows extensive π-conjugations followed by impressive light harvesting ability and is utilized for photochemical CO2 fixation to value-added chemicals. A remarkable conversion of styrene epoxide (STE) to styrene carbonate (STC) (≈98%) is obtained under optimized photocatalytic conditions in the existence of promoter tert-butyl ammonium bromide (TBAB). Synchrotron-based X-ray adsorption spectroscopy (XAS) analysis reveals the single atom coordination sites along with the metal (Co) oxidation number of +2.16 in the porous network. Moreover, in situ diffuse reflectance spectroscopy (DRIFTS) and electron paramagnetic resonance (EPR) investigations provide valuable information on the evolution of key reaction intermediates. Comprehensivecomputational analysis also helps to understand the overall mechanistic pathway along with the interaction between the photocatalyst and reactants. Overall, this study presents a new concept of fabricating porous photopolymers based on a pyrolysis-free out-of-plane-coordination strategy and further explores the role of single atomic sites in carrying out feasible CO2 fixation reactions.

Low-Temperature Synthesis of Mesoporous Half-Metallic High-Entropy Spinel Oxide Nanofibers for Photocatalytic CO2 Reduction

High-entropy oxides (HEOs) exhibit great prospects owing to their varied composition, chemical adaptability, adjustable light-absorption ability, and strong stability. In this study, we report a strategy to synthesize a series of porous high-entropy spinel oxide (HESO) nanofibers (NFs) at a low temperature of 400 °C by a sol-gel electrospinning technique. The key lies in selecting six acetylacetonate salt precursors with similar coordination abilities, maintaining a high-entropy disordered state during the transformation from stable sols to gel NFs. The as-synthesized HESO NFs of (NiCuMnCoZnFe)3O4 show a high specific surface area of 66.48 m2/g, a diverse elemental composition, a dual bandgap, half-metallicity property, and abundant defects. The diverse elements provide various synergistic catalytic sites, and oxygen vacancies act as active sites for electron-hole separation, while the half-metallicity and dual-bandgap structure offer excellent light absorption ability, thus expanding its applicability to a wide range of photocatalytic processes. As a result, the HESO NFs can efficiently convert CO2 into CH4 and CO with high yields of 8.03 and 15.89 μmol g-1 h-1, respectively, without using photosensitizers or sacrificial agents.

Activating two-dimensional semiconductors for photocatalysis: a cross-dimensional strategy

The emerging two-dimensional (2D) semiconductors substantially extend materials bases for versatile applications such as semiconductor photocatalysis demanding semiconductive matrices and large surface areas. The dimensionality, while endowing 2D semiconductors the unique properties to host photocatalytic functionality of pollutant removal and hydrogen evolution, hurdles the activation paths to form heterogenous photocatalysts where the photochemical processes are normally superior over these on the mono-compositional counterparts. In this perspective, we present a cross-dimensional strategy to employ thenD (n= 0-2) clusters or nanomaterials as activation partners to boost the photocatalytic activities of the 2D semiconductors. The formation principles of heterogenous photocatalysts are illustrated specifically for the 2D matrices, followed by selection criteria of them among the vast 2D database. The computer investigations are illustrated in the density functional theory route and machine learning benefitted from the vast samples in the 2D library. Synthetic realizations and characterizations of the 2D heterogenous systems are introduced with an emphasis on chemical methods and advanced techniques to understand materials and mechanistic studies. The perspective outlooks cross-dimensional activation strategies of the 2D materials for other applications such as CO2removal, and materials matrices in other dimensions which may inspire incoming research within these fields.

Localized Phase Transformation Triggering Lattice Matching of Metal Oxide and Carbonate Hydroxide for Efficient CO2 Photoreduction

Orderly heterostructured catalysts, which integrate nanomaterials of complementary structures and dimensions into single-entity structures, have hold great promise for sustainability applications. In this work, it is showcased that air as green reagent can trigger in situ localized phase transformation and transform the metal carbonate hydroxide nanowires into ordered heterostructured catalyst. In single-crystal nanowire heterostructure, the in situ generated and nanosized Co3 O4 will be anchored in single-crystal Co6 (CO3 )2 (OH)8 nanowires spontaneously, triggered by the lattice matching between the (220) plane of Co3 O4 and the (001) plane of Co6 (CO3 )2 (OH)8 . The lattice matching allows intimate contact at heterointerface with well-defined orientation and strong interfacial coupling, and thus significantly expedites the transfer of photogenerated electrons from tiny Co3 O4 to catalytically active Co6 (CO3 )2 (OH)8 in single-crystal nanowire, which elevates the catalytic efficiency of metal carbonate catalyst in the CO2 reduction reaction (VCO = 19.46 mmol g-1 h-1 and VH2 = 11.53 mmol g-1 h-1 ). The present findings add to the growing body of knowledge on exploiting Earth-abundant metal-carbonate catalysts, and demonstrate the utility of localized phase transformation in constructing advanced catalysts for energy and environmental sustainability applications.

Modulating the Reaction Configuration by Breaking the Structural Symmetry of Active Sites for Efficient Photocatalytic Reduction of Low-concentration CO2

Photocatalytic conversion of low-concentration CO2 is considered as a promising way to simultaneously mitigate the environmental and energy issues. However, the weak CO2 adsorption and tough CO2 activation process seriously compromise the CO production, due to the chemical inertness of CO2 molecule and the formed fragile metal-C/O bond. Herein, we designed and fabricated oxygen vacancy contained Co3 O4 hollow nanoparticles on ordered macroporous N-doped carbon framework (Vo-HCo3 O4 /OMNC) towards photoreduction of low-concentration CO2 . In situ spectra and ab initio molecular dynamics simulations reveal that the constructed oxygen vacancy is able to break the local structural symmetry of Co-O-Co sites. The formation of asymmetric active site switches the CO2 configuration from a single-site linear model to a multiple-sites bending one with a highly stable configuration, enhancing the binding and structural polarization of CO2 molecules. As a result, Vo-HCo3 O4 /OMNC shows unprecedent activity in the photocatalytic conversion of low-concentration CO2 (10 % CO2 /Ar) under laboratory light source or even natural sunlight, affording a syngas yield of 337.8 or 95.2 mmol g-1  h-1 , respectively, with an apparent quantum yield up to 4.2 %.

Synergistic Trimetallic Nanocomposites as Visible-NIR-Sunlight-Driven Photocatalysts for Efficient Artificial Photosynthesis

Here, we report monodispersed tricomponent MnNSs-SnO2@Pt and MnNFs-SnO2@Pt nanocomposites prepared by simultaneous SnO2 and Pt nanodot coating on Mn nanospheres (MnNSs) and Mn nanoflowers (MnNFs) for highly efficient CO2 photoreduction in visible-NIR-sunlight irradiation. MnNFs-SnO2@Pt showed higher efficiency with a quantum yield of 3.21% and a chemical yield of 5.45% for CO2 conversion under visible light irradiation for HCOOH formation with 94% selectivity. Similarly, MnNFs-SnO2@Pt displayed significant photocatalytic efficiency in NIR and sunlight irradiation for HCOOH yield. MnNFs-SnO2@Pt nanocomposites also showed robust morphology and sustained structural stability with shelf-life for at least 1 year and were utilized for at least 10 reaction cycles without losing significant photocatalytic efficiency. The high surface area (94.98 m2/g), efficient electron-hole separation, and Pt-nanodot support in MnNFs--SnO2@Pt contributed to a higher photocatalytic efficacy toward CO2 reduction.

Nanoreactor Engineering Can Unlock New Possibilities for CO2 Tandem Catalytic Conversion to C-C Coupled Products

Climate change is becoming increasingly more pronounced every day while the amount of greenhouse gases in the atmosphere continues to rise. CO₂ reduction to valuable chemicals is an approach that has gathered substantial attention as a means to recycle these gases. Herein, some of the tandem catalysis approaches that can be used to achieve the transformation of CO₂ to C-C coupled products are explored, focusing especially on tandem catalytic schemes where there is a big opportunity to improve performance by designing effective catalytic nanoreactors. Recent reviews have highlighted the technical challenges and opportunities for advancing tandem catalysis, especially highlighting the need for elucidating structure-activity relationships and mechanisms of reaction through theoretical and in situ/operando characterization techniques. In this review, the focus is on nanoreactor synthesis strategies as a critical research direction, and discusses these in the context of two main tandem pathways (CO-mediated pathway and Methanol-mediated pathway) to C-C coupled products.

An elegant 3D-ordered hierarchically porous framework to anchor Pt nanocrystals for durable oxygen reduction reaction

While Platinum (Pt)-based electrocatalysts have been extensively studied for the oxygen reduction reaction (ORR), improving their durability remains a challenge. One promising approach is to design structure-defined carbon supports that can uniformly immobilize Pt nanocrystals (NCs). In this study, we present an innovative strategy for constructing three-dimensional ordered, hierarchically porous carbon polyhedrons (3D-OHPCs) as an efficient support for immobilizing Pt NCs. We achieved this by template-confined pyrolysis of a zinc-based zeolite imidazolate framework (ZIF-8) grown within the voids of polystyrene templates, followed by carbonizing the native oleylamine ligands on Pt NCs to produce graphitic carbon shells. This hierarchical structure enables the uniform anchorage of Pt NCs, while enhancing facile mass transfer and local accessibility of active sites. The optimal material with graphitic carbon armor shells on the surface of Pt NCs (CA-Pt), named CA-Pt@3D-OHPCs-1600, shows comparable activities to commercial Pt/C catalysts. Furthermore, it can withstand over 30,000 cycles of accelerated durability tests, owing to the protective carbon shells and hierarchically ordered porous carbon supports. Our study presents a promising approach for designing highly efficient and durable electrocatalysts for energy-based applications and beyond.

Recent Advances in Carbon Nitride-Based S-scheme Photocatalysts for Solar Energy Conversion

Energy shortages are a major challenge to the sustainable development of human society, and photocatalytic solar energy conversion is a potential way to alleviate energy problems. As a two-dimensional organic polymer semiconductor, carbon nitride is considered to be the most promising photocatalyst due to its stable properties, low cost, and suitable band structure. Unfortunately, pristine carbon nitride has low spectral utilization, easy recombination of electron holes, and insufficient hole oxidation ability. The S-scheme strategy has developed in recent years, providing a new perspective for effectively solving the above problems of carbon nitride. Therefore, this review summarizes the latest progress in enhancing the photocatalytic performance of carbon nitride via the S-scheme strategy, including the design principles, preparation methods, characterization techniques, and photocatalytic mechanisms of the carbon nitride-based S-scheme photocatalyst. In addition, the latest research progress of the S-scheme strategy based on carbon nitride in photocatalytic H₂ evolution and CO₂ reduction is also reviewed. Finally, some concluding remarks and perspectives on the challenges and opportunities for exploring advanced nitride-based S-scheme photocatalysts are presented. This review brings the research of carbon nitride-based S-scheme strategy to the forefront and is expected to guide the development of the next-generation carbon nitride-based S-scheme photocatalysts for efficient energy conversion.

Topologically Porous Heterostructures for Photo/Photothermal Catalysis of Clean Energy Conversion

As a straightforward way to fix solar energy, photo/photothermal catalysis with semiconductor provides a promising way to settle the energy shortage and environmental crisis in many fields, especially in clean energy conversion. Topologically porous heterostructures (TPHs), featured with well-defined pores and mainly composed by the derivatives of some precursors with specific morphology, are a major part of hierarchical materials in photo/photothermal catalysis and provide a versatile platform to construct efficient photocatalysts for their enhanced light absorption, accelerated charges transfer, improved stability, and promoted mass transportation. Therefore, a comprehensive and timely review on the advantages and recent applications of the TPHs is of great importance to forecast the potential applications and research trend in the future. This review initially demonstrates the advantages of TPHs in photo/photothermal catalysis. Then the universal classifications and design strategies of TPHs are emphasized. Besides, the applications and mechanisms of photo/photothermal catalysis in hydrogen evolution from water splitting and CO_x hydrogenation over TPHs are carefully reviewed and highlighted. Finally, the challenges and perspectives of TPHs in photo/photothermal catalysis are also critically discussed.

Scalable Synthesis of Holey Deficient 2D Co/NiO Single-Crystal Nanomeshes via Topological Transformation for Efficient Photocatalytic CO2 Reduction

Preparation of holey, single-crystal, 2D nanomaterials containing in-plane nanosized pores is very appealing for the environment and energy-related applications. Herein, an in situ topological transformation is showcased of 2D layered double hydroxides (LDHs) allows scalable synthesis of holey, single-crystal 2D transition metal oxides (TMOs) nanomesh of ultrathin thickness. As-synthesized 2D Co/NiO-2 nanomesh delivers superior photocatalytic CO₂ -syngas conversion efficiency (i.e., V_CO of 32460 µmol h^-1 g^-1 CO and V H 2 ${V_{{{\rm{H}}_2}}}$ of 17840 µmol h^-1 g^-1 H₂ ), with V_CO about 7.08 and 2.53 times that of NiO and 2D Co/NiO-1 nanomesh containing larger pore size, respectively. As revealed in high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), the high performance of Co/NiO-2 nanomesh primarily originates from the edge sites of nanopores, which carry more defect structures (e.g., atomic steps or vacancies) than basal plane for CO₂ adsorption, and from its single-crystal structure adept at charge transport. Theoretical calculation shows the topological transformation from 2D hydroxide to holey 2D oxide can be achieved, probably since the trace Co dopant induces a lattice distortion and thus a sharp decrease of the dehydration energy of hydroxide precursor. The findings can advance the design of intriguing holey 2D materials with well-defined geometric and electronic properties.

Recent Progress in Metal Oxide-Based Photocatalysts for CO2 Reduction to Solar Fuels: A Review

One of the challenges in developing practical CO₂ photoconversion catalysts is the design of materials with a low cost, high activity and good stability. In this paper, excellent photocatalysts based on TiO₂, WO₃, ZnO, Cu₂O and CeO₂ metal oxide materials, which are cost-effective, long-lasting, and easy to fabricate, are evaluated. The characteristics of the nanohybrid catalysts depend greatly on their architecture and design. Thus, we focus on outstanding materials that offer effective and practical solutions. Strategies to improve CO₂ conversion efficiency are summarized, including heterojunction, ion doping, defects, sensitization and morphology control, which can inspire the future improvement in photochemistry. The capacity of CO₂ adsorption is also pivotal, which varies with the morphological and electronic structures. Forms of 0D, 1D, 2D and 3DOM (zero/one/two-dimensional- and three-dimensional-ordered macroporous, respectively) are involved. Particularly, the several advantages of the 3DOM material make it an excellent candidate material for CO₂ conversion. Hence, we explain its preparation method. Based on the discussion, new insights and prospects for designing high-efficient metallic oxide photocatalysts to reduce CO₂ emissions are presented.

Functionalized MOF-Based Photocatalysts for CO2 Reduction

Metal-organic frameworks (MOFs) materials have become a research forefront in the field of photocatalytic CO₂ reduction attributed to their ultra-high specific surface area, adjustable structure, and abundant catalytic active sites. Particularly, MOFs can be facilely tuned to match CO₂ photoreduction by utilizing post-modification of metal nodes, functionalization of organic linkers, and combination with other active materials. Herein, the recent advances in the construction strategy of MOF-based photocatalysts materials for CO₂ reduction are highlighted. Some systematic modification strategies on MOF-based photocatalysts are also discussed, such as modification of metal sites and organic ligands, construction of heterojunction, introduction of single/dual-atom, and strain engineering. Finally, the future development directions of MOF-based photocatalysts in the field of CO₂ reduction are presented.