Ultrathin Nanosheet Assembled Multishelled Superstructures for Photocatalytic CO2 Reduction

Ruthenium Single Atomic Sites Surrounding the Support Pit with Exceptional Photocatalytic Activity

Single-metal atomic sites and vacancies can accelerate the transfer of photogenerated electrons and enhance photocatalytic performance in photocatalysis. In this study, a series of nickel hydroxide nanoboards (Ni(OH)x NBs) with different loadings of single-atomic Ru sites (w-SA-Ru/Ni(OH)x) were synthesized via a photoreduction strategy. In such catalysts, single-atomic Ru sites are anchored to the vacancies surrounding the pits. Notably, the SA-Ru/Ni(OH)x with 0.60 wt % Ru loading (0.60-SA-Ru/Ni(OH)x) exhibits the highest catalytic performance (27.6 mmol g-1 h-1) during the photocatalytic reduction of CO2 (CO2RR). Either superfluous (0.64 wt %, 18.9 mmol g-1 h-1; 3.35 wt %, 9.4 mmol-1 h-1) or scarce (0.06 wt %, 15.8 mmol g-1 h-1; 0.29 wt %, 21.95 mmol g-1 h-1; 0.58 wt %, 23.4 mmol g-1 h-1) of Ru sites have negative effect on its catalytic properties. Density functional theory (DFT) calculations combined with experimental results revealed that CO2 can be adsorbed in the pits; single-atomic Ru sites can help with the conversion of as-adsorbed CO2 and lower the energy of *COOH formation accelerating the reaction; the excessive single-atomic Ru sites occupy vacancies that retard the completion of CO2RR.

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.

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 %.

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.

A General Strategy for Synthesis of Binary Transition Metal Phosphides Hollow Sandwich Heterostructures

The hollow sandwich core-shell micro-nanomaterials are widely used in materials, chemistry, and medicine, but their fabrication, particularly for transition metal phosphides (TMPs), remains a great challenge. Herein, a general synthesis strategy is presented for binary TMPs hollow sandwich heterostructures with vertically interconnected nanosheets on the inside and outside surfaces of polyhedron FeCoP_x /C, demonstrated by a variety of transition metals (including Co, Fe, Cd, Mn, Cu, Cr, and Ni). Density functional theory (DFT) calculation reveals the process and universal mechanism of layered double hydroxide (LDH) growth on Prussian blue analog (PBA) surface in detail for the first time, which provides the theoretical foundations for feasibility and rationality of the synthesis strategy. This unique structure exhibits a vertical nanosheet-shell-vertical nanosheet configuration combining the advantages of sandwich, hollow and vertical heterostructures, effectively achieving their synergistic effect. As a proof-of-concept of their applications, the CoNiP_x @FeCoP_x /C@CoNiP_x hollow sandwich polyhedron architectures (representative samples) show excellent catalytic performance for the oxygen evolution reaction (OER) in alkaline electrolytes. This work provides a general method for constructing hollow-sandwich micro-nanostructures, which provides more ideas and directions for design of micro-nano materials with special geometric topology.

Recent Advances and Perspectives of Core-Shell Nanostructured Materials for Photocatalytic CO2 Reduction

Photocatalytic CO₂ conversion into solar fuels is a promising technology to alleviate CO₂ emissions and energy crises. The development of core-shell structured photocatalysts brings many benefits to the photocatalytic CO₂ reduction process, such as high conversion efficiency, sufficient product selectivity, and endurable catalyst stability. Core-shell nanostructured materials with excellent physicochemical features take an irreplaceable position in the field of photocatalytic CO₂ reduction. In this review, the recent development of core-shell materials applied for photocatalytic reduction of CO_{2 is introduced} . First, the basic principle of photocatalytic CO₂ reduction is introduced. In detail, the classification and synthesis techniques of core-shell catalysts are discussed. Furthermore, it is also emphasized that the excellent properties of the core-shell structure can greatly improve the activity, selectivity, and stability in the process of photocatalytic CO₂ reduction. Hopefully, this paper can provide a favorable reference for the preparation of efficient photocatalysts for CO₂ reduction.

Intrinsic Charge Polarization in Bi19 S27 Cl3 Nanorods Promotes Selective CC Coupling Reaction during Photoreduction of CO2 to Ethanol

Obtaining multi-carbon products via CO₂  photoreduction is a major catalytic challenge involving multielectron-mediated CC bond formation. Complex design of multicomponent interfaces that are exploited to achieve this chemical transformation, often leads to untraceable deleterious changes in the interfacial chemical environment affecting CO₂  conversion efficiency and product selectivity. Alternatively, robust metal centers having asymmetric charge distribution can effectuate CC coupling reaction through the stabilization of intermediates, for desired product selectivity. However, generating inherent charge distribution in a single component catalyst is a difficult material design challenge. Here, a novel photocatalyst, Bi₁₉ S₂₇ Cl₃ , is presented which selectively converts CO₂  to a C₂  product, ethanol, in high yield under visible light irradiation. Structural analysis through transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy reveals the presence of charge polarized bismuth centers in Bi₁₉ S₂₇ Cl₃ . The intrinsic electric field induced by charge polarized bismuth centers renders better separation efficiency of photogenerated electron-hole pair. Furthermore, charge polarized centers yield better adsorption of CO* intermediate and accelerate the rate determining CC coupling step through the formation of OCCOH intermediate. Formation of these intermediates is experimentally mapped by in situ Fourier-transform infrared spectroscopy and further confirmed by theoretical calculation.

Modular Construction of an MIL-101(Fe)@MIL-100(Fe) Dual-Compartment Nanoreactor and Its Boosted Photocatalytic Activity toward Tetracycline

Iron-based metal-organic frameworks (MOFs) have aroused extensive concern as prospective photocatalysts for antibiotic (e.g., tetracycline, TC) degradation. However, efficiencies of single and simple Fe-based MOFs still undergo restricted light absorption and weak charge separation. Assembly of different iron-based MOF building blocks into a hybrid MOF@MOF heterostructure reactor could be an encouraging strategy for the effective capture of antibiotics from the aqueous phase. This paper reports a new-style MIL-101(Fe)@MIL-100(Fe) photocatalyst, which was groundbreakingly constructed to realize a double win for boosting the performances of adsorption and photocatalysis. The optical response range, surface open sites, and charge separation efficiency of MIL-101(Fe)@MIL-100(Fe) can be regulated through accurate design and alteration. Attributed to the synergistic effects of double iron-based MOFs, MIL-101(Fe)@MIL-100(Fe) exhibits an excellent photocatalytic activity toward TC degradability compared to MIL-101(Fe) and MIL-100(Fe), which is even superior to those reported previously in the literature. Furthermore, the main active species of •O₂^- and h⁺ were proved through trapping tests of the photocatalytic process. Additionally, MIL-101(Fe)@MIL-100(Fe) possesses remarkable stability, maintaining more than 90% initial photocatalytic activity after the fifth cycle. In brief, MIL-101(Fe)@MIL-100(Fe) was highly efficient for TC degradation. Our work offers a new strategy for visible-light photodegradation of TC by exploring the double Fe-based MOF composite.

A Hexagonal Nut-Like Metal-Organic Framework and Its Conformal Transformation

Hollow structured metal-organic frameworks (MOFs) and their derivatives are desired in catalysis, energy storage, etc. However, fabrication of novel hollow MOFs and revelation of their formation mechanisms remain challenging. Herein, open hollow 2D MOFs in the form of hexagonal nut are prepared through self-template method, which can be readily scaled up at gram scale in a one-pot preparation. The evolution from the initial superstructure to the final stable MOFs is tracked by wide-angle X-ray scattering, transforming from solid hexagon to open hollow hexagon. More importantly, this protocol can be extended to synthesizing a series of open hollow structured MOFs with sizes ranging from ≈120 to ≈1200 nm. Further, open hollow structured cobalt/N-doped porous carbon composites are realized through conformal transformation of the as-prepared MOFs, which demonstrates promising applications in sustainable energy conversion technologies. This study sheds light on the kinetically controlled synthesis of novel 2D MOFs for their extended utilizations.

Ni-Co Bimetallic Hydroxide Nanosheet Arrays Anchored on Graphene for Adsorption-Induced Enhanced Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction can be implemented to use CO₂ , a greenhouse gas, as a resource in an energy-saving and environmentally friendly way, in which suitable catalytic materials are required to achieve high-efficiency catalysis. Insufficient accessible active sites on the catalyst surface and inhibited electron transfer severely limit the photocatalytic performance. Therefore, porous aerogels are constructed from composites comprising different ratios of Ni-Co bimetallic hydroxide (Ni_x Co_y ) grown on reduced graphene oxide (GR) into a hierarchical nanosheet-array structure using a facile in situ growth method. Detailed characterization shows that this structure exposes numerous active sites for enhanced adsorption-induced photocatalytic CO₂ reduction. Moreover, under the synergistic effect of Ni-Co bimetallic hydroxide, the CO₂ adsorption capacity as well as charge-carrier separation and transfer are excellent. As a result, the Ni₇ Co₃ -GR catalyst exhibits highly improved catalytic performance when compared with recently reported values, with a high CO release rate of 941.5 µmol h^-1  g^-1 and a selectivity of 96.3% during the photocatalytic reduction of CO₂ . This work demonstrates a new strategy for designing nanocomposites with abundant active sites structures.