Ru Single Atom Dispersed Cu Nanoparticle with Dual Sites Enables Outstanding Photocatalytic CO2 Reduction.

Cu-based catalysts are promising candidates for CO2 reduction owing to the favorable energetics of Cu sites for CO2 adsorption and transformation. However, CO2 reduction involving insurmountable activation barriers and various byproducts remains a significant challenge to achieve high activity and selectivity. Herein, a photocatalyst constructed with single-Ru-site-on-Cu-nanoparticle on Bi4Ti3O12 exhibits exceptional activity and selectivity for CO2 conversion to CO. The experimental and theoretical results consistently reveal that the Ru-Cu dual sites allow the rapid transfer of photogenerated carriers for closely interacting with CO2 molecules. Importantly, the Ru-Cu dual sites exhibit extremely strong CO2 adsorption ability, and the Gibbs free energy of the rate-determining step (*CO2 to *COOH) has been significantly reduced, synergistically enhancing the entire CO2 conversion process. The optimal BTOCu2Ru0.5 photocatalyst manifests a high performance for selective reduction of CO2 to CO, yielding 10.84 µmol over 15 mg of photocatalyst in 4 h (180.67 µmol·g-1·h-1) under a 300 W Xe lamp without any photosensitizer and sacrificial reagent, outperforming all bismuth-based materials and being one of the best photocatalysts ever reported under similar reaction conditions. This work presents a strategy for the rational design of multiple metal sites toward efficient photocatalytic reduction of CO2.

MXene Synthesis and Carbon Capture Applications: Mini-Review.

MXenes, a class of two-dimensional transition metal carbides, nitrides, and carbonitrides, have garnered significant attention due to their remarkable potential for energy storage, electrocatalysis, and gas separation applications. The fabrication processes of MXene involve building up the MXene structure from constituent elements and the selective elimination of M-A bonds from the precursor MAX. However, considerable efforts are still required to design and develop efficient MXene-based technologies. This review article aims to briefly analyse the synthesis methods employed for MXene production, ranging from direct synthesis and conventional chemical wet etching approach to the more recent molten salt etching technique. The review highlights the advancements made in achieving precise control over the terminal groups, which is paramount for tailoring the properties of MXenes for specific applications. Furthermore, the potential of MXene-based materials for carbon capture applications, particularly in developing advanced adsorbents, is emphasized. The in-depth examination of MXene synthesis techniques and their implications for carbon capture applications provides a solid foundation for developing and optimizing these promising materials.

Wettability Engineering of Solar Methanol Synthesis.

Engineering the wettability of surfaces with hydrophobic organics has myriad applications in heterogeneous catalysis and the large-scale chemical industry; however, the mechanisms behind may surpass the proverbial hydrophobic kinetic benefits. Herein, the well-studied In2O3 methanol synthesis photocatalyst has been used as an archetype platform for a hydrophobic treatment to enhance its performance. With this strategy, the modified samples facilitated the tuning of a wide range of methanol production rates and selectivity, which were optimized at 1436 µmol gcat-1 h-1 and 61%, respectively. Based on in situ DRIFTS and temperature-programmed desorption-mass spectrometry, the surface-decorated alkylsilane coating on In2O3 not only kinetically enhanced the methanol synthesis by repelling the produced polar molecules but also donated surface active H to facilitate the subsequent hydrogenation reaction. Such a wettability design strategy seems to have universal applicability, judged by its success with other CO2 hydrogenation catalysts, including Fe2O3, CeO2, ZrO2, and Co3O4. Based on the discovered kinetic and mechanistic benefits, the enhanced hydrogenation ability enabled by hydrophobic alkyl groups unleashes the potential of the surface organic chemistry modification strategy for other important catalytic hydrogenation reactions.

New black indium oxide-tandem photothermal CO2-H2 methanol selective catalyst.

It has long been known that the thermal catalyst Cu/ZnO/Al2O3(CZA) can enable remarkable catalytic performance towards CO2 hydrogenation for the reverse water-gas shift (RWGS) and methanol synthesis reactions. However, owing to the direct competition between these reactions, high pressure and high hydrogen concentration (≥75%) are required to shift the thermodynamic equilibrium towards methanol synthesis. Herein, a new black indium oxide with photothermal catalytic activity is successfully prepared, and it facilitates a tandem synthesis of methanol at a low hydrogen concentration (50%) and ambient pressure by directly using by-product CO as feedstock. The methanol selectivities achieve 33.24% and 49.23% at low and high hydrogen concentrations, respectively.

Host/Guest Nanostructured Photoanodes Integrated with Targeted Enhancement Strategies for Photoelectrochemical Water Splitting.

Photoelectrochemical (PEC) hydrogen production from water splitting is a green technology that can solve the environmental and energy problems through converting solar energy into renewable hydrogen fuel. The construction of host/guest architecture in semiconductor photoanodes has proven to be an effective strategy to improve solar-to-fuel conversion efficiency dramatically. In host/guest photoanodes, the absorber layer is deposited onto a high-surface-area electron collector, resulting in a significant enhancements in light-harvesting as well as charge collection and separation efficiency. The present review aims to summarize and highlight recent state-of-the-art progresses in the architecture designing of host/guest photoanodes with integrated enhancement strategies, including i) light trapping effect; ii) optimization of conductive host scaffolds; iii) hierarchical structure engineering. The challenges and prospects for the future development of host/guest nanostructured photoanodes are also presented.

In Situ Determination of Polaron-Mediated Ultrafast Electron Trapping in Rutile TiO2 Nanorod Photoanodes.

Mechanistic understanding of the photogenerated charge carrier dynamics in modified semiconductor photoanodes is vital for the efficient enhancement of photoelectrochemical (PEC) water splitting. Here, an in situ femtosecond (fs)-transient absorption spectroscopy (TAS) assisted spectroelectrochemistry technique is used to probe the behavior of charge carriers in rutile TiO2 nanorod photoanodes under the different applied potentials and different density of surface polaron states that can be tuned via direct electrochemical protonation. We interpreted the background absorption with long-time decay in terms of polaron-mediated ultrafast electron trapping. The depleted surface polaron states on rutile TiO2 nanorods can trap photogenerated electrons and endow them with a long lifetime; thus, increasing the polaron state density can enhance the charge separation efficiency and the photocurrent density of the TiO2 nanorod electrode.

Hollow InVO4 Nanocuboid Assemblies toward Promoting Photocatalytic N2 Conversion Performance.

The unique InVO4 mesocrystal superstructure, particularly with cubical skeleton and hollow interior, which consists of numerous nanocube building blocks, closely stacking by stacking, aligning by aligning, and sharing the same crystallographic orientations, is successfully fabricated. The synergy of a reaction-limited aggregation and an Ostwald ripening process is reasonably proposed for the growth of this unique superstructure. Both single-particle surface photovoltage and confocal fluorescence spectroscopy measurements demonstrate that the long-range ordered mesocrystal superstructures can significantly retard the recombination of electron-hole pairs through the creation of a new pathway for anisotropic electron flow along the inter-nanocubes. This promising charge mobility feature of the superstructure greatly contributes to the pronounced photocatalytic performance of the InVO4 mesocrystal toward fixation of N2 into NH3 with the quantum yield of 0.50% at wavelength of 385 nm.

Raw biomass electroreforming coupled to green hydrogen generation.

Despite the tremendous progress of coupling organic electrooxidation with hydrogen generation in a hybrid electrolysis, electroreforming of raw biomass coupled to green hydrogen generation has not been reported yet due to the rigid polymeric structures of raw biomass. Herein, we electrooxidize the most abundant natural amino biopolymer chitin to acetate with over 90% yield in hybrid electrolysis. The overall energy consumption of electrolysis can be reduced by 15% due to the thermodynamically and kinetically more favorable chitin oxidation over water oxidation. In obvious contrast to small organics as the anodic reactant, the abundance of chitin endows the new oxidation reaction excellent scalability. A solar-driven electroreforming of chitin and chitin-containing shrimp shell waste is coupled to safe green hydrogen production thanks to the liquid anodic product and suppression of oxygen evolution. Our work thus demonstrates a scalable and safe process for resource upcycling and green hydrogen production for a sustainable energy future.

Rational Synthesis of Amorphous Iron-Nickel Phosphonates for Highly Efficient Photocatalytic Water Oxidation with Almost 100 % Yield.

A simple solvent ligation effect was successfully used to disrupt the growth of a model compound, Fe[(OH)(O3 P(CH2 )2 CO2 H)]⋅H2 O (MIL-37), into an extended 2D structure by replacing water with dimethylformamide (DMF) as the solvent during the synthesis. Owing to the lack of -OH group, which provides the corner-sharing (binding) oxygen atoms for the octahedra, an amorphous and porous structure is formed. When Fe3+ is partially replaced by Ni2+ , the amorphous structure remains and the resultant binary metal catalyst displays excellent photocatalytic oxygen evolution activity with almost 100 % yield achieved under visible light irradiation using [Ru(bpy)3 ]2+ as the photosensitizer. This study opens up new possibilities of using the simple solvent effect to synthesize high surface area metal phosphonates for catalytic and other applications.

Isolated Square-Planar Copper Center in Boron Imidazolate Nanocages for Photocatalytic Reduction of CO2 to CO.

Photocatalytic reduction of CO2 to value-added fuel has been considered to be a promising strategy to reduce global warming and shortage of energy. Rational design and synthesis of catalysts to maximumly expose the active sites is the key to activate CO2 molecules and determine the reaction selectivity. Herein, we synthesize a well-defined copper-based boron imidazolate cage (BIF-29) with six exposed mononuclear copper centers for the photocatalytic reduction of CO2 . Theoretical calculations show a single Cu site including weak coordinated water delivers a new state in the conduction band near the Fermi level and stabilizes the *COOH intermediate. Steady-state and time-resolved fluorescence spectra show these Cu sites promote the separation of electron-hole pairs and electron transfer. As a result, the cage achieves solar-driven reduction of CO2 to CO with an evolution rate of 3334 µmol g-1 h-1 and a high selectivity of 82.6 %.

Anchoring Active Pt2+ /Pt0 Hybrid Nanodots on g-C3 N4 Nitrogen Vacancies for Photocatalytic H2 Evolution.

A Pt2+ /Pt0 hybrid nanodot-modified graphitic carbon nitride (CN) photocatalyst (CNV-P) was fabricated for the first time using a chemical reduction method, during which nitrogen vacancies in g-C3 N4 assist to stabilize Pt2+ species. It is elucidated that the coexistence of metallic Pt0 and Pt2+ species in the Pt nanodots loaded on g-C3 N4 results in superior photocatalytic H2 evolution performance with very low Pt loadings. The turnover frequencies (TOFs) are 265.91 and 116.38 h-1 for CNV-P-0.1 (0.1 wt % Pt) and CNV-P-0.5 (0.5 wt % Pt), respectively, which are much higher than for other g-C3 N4 -based photocatalysts with Pt co-catalyst reported previously. The excellent photocatalytic H2 evolution performance is a result of i) metallic Pt0 facilitating the electron transport and separation and Pt2+ species preventing the undesirable H2 backward reaction, ii) the strong interfacial contact between Pt2+ /Pt0 hybrid nanodots and nitrogen vacancies of CNV facilitating the interfacial electron transfer, and iii) the highly dispersed Pt2+ /Pt0 hybrid nanodots exposing more active sites for photocatalytic H2 evolution. Our findings are useful for the design of highly active semiconductor-based photocatalysts with extremely low precious metal content to reduce the catalyst cost while achieving good activity.

Amino-Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g-C3 N4 for Enhanced Photocatalytic CO2 Reduction.

Halide perovskite quantum dots (QDs) have great potential in photocatalytic applications if their low charge transportation efficiency and chemical instability can be overcome. To circumvent these obstacles, we anchored CsPbBr3 QDs (CPB) on NHx -rich porous g-C3 N4 nanosheets (PCN) to construct the composite photocatalysts via N-Br chemical bonding. The 20 CPB-PCN (20 wt % of QDs) photocatalyst exhibits good stability and an outstanding yield of 149 µmol h-1 g-1 in acetonitrile/water for photocatalytic reduction of CO2 to CO under visible light irradiation, which is around 15 times higher than that of CsPbBr3 QDs. This study opens up new possibilities of using halide perovskite QDs for photocatalytic application.

Visible-light-driven removal of tetracycline antibiotics and reclamation of hydrogen energy from natural water matrices and wastewater by polymeric carbon nitride foam.

Water and energy are key sustainability issues that need to be addressed. Photocatalysis represents an attractive means to not only remediate polluted waters, but also harness solar energy. Unfortunately, the employment of photocatalysts remains a practical challenge in terms of high cost, low efficiency, secondary pollution and unexploited water matrices influence. This study investigated the feasibility of photocatalysis to both treat water and produce hydrogen with practical water systems. Polymeric carbon nitride foam (CNF) with large surface area and mesoporous structure was successfully prepared via the bubble-template effect of ammonium chloride decomposition during thermal condensation. The reaction kinetics, mechanisms, and effect of natural water matrices and wastewater on CNF-based photocatalytic removal of tetracycline hydrochloride (TC-HCl) were systematically investigated. Furthermore, the efficiency of clean hydrogen energy from natural water matrices and wastewater was also evaluated. It was found that the photocatalytic performance of CNF for TC-HCl removal was principally affected by calcination temperature in the presence of NH4Cl. The degradation rates of CNF-4 (calcined at 550 °C) were approximately 1.84, 2.49 and 7.47 times than that of the CNF-2 (calcined at 600 °C), CNF-1 (calcined at 500 °C) and GCN (without NH4Cl), respectively. Results indicate that the improved photocatalytic performance was predominantly ascribed to the large specific surface area, increased availability of exposed active sites, and enhanced transport and separation efficiency of the photogenerated carrier. Based on electron spin resonance, chemical trapping experiment and density functional theory calculation, photoinduced oxidizing species (·O2- and holes) initially attacked the C-N-C fragment of TC molecules, which were finally mineralized to CO2, water and inorganic matters. Under the synergistic influence of water constituents (including acidity and alkalinity, ion species and dissolved organic substances), various water matrices greatly affected the degradation rate of TC-HCl, with the highest removal efficiency of 78.9% in natural seawater, followed by reservoir water (75.0%), tap water (62.3%), deionized water (49.8%), reverse osmosis concentrate (32.7%) and pharmaceutical wastewater (18.9%). Interestingly, low amounts of the emerging microplastics slightly improved TC-HCl removal, whereas high amounts (1.428 × 107 P/cm3) restricted removal due to light absorption and the intrinsic adsorption interaction. Moreover, the photocatalysts were able over repeated usage. Notably, the hydrogen yields rates of polymeric carbon nitride foam were 352.2, 299.8, 184.9 and 94.3 µmol/g/h in natural seawater, pharmaceutical wastewater, water from reservoir and tap water, respectively. This study proves the potential of novel nonmetal porous photocatalyst to simultaneously treat wastewater while converting solar energy into clean hydrogen energy.

Rational Design of Catalytic Centers in Crystalline Frameworks.

Crystalline frameworks including primarily metal organic frameworks (MOF) and covalent organic frameworks (COF) have received much attention in the field of heterogeneous catalysts recently. Beyond providing large surface area and spatial confinement, these crystalline frameworks can be designed to either directly act as or influence the catalytic sites at molecular level. This approach offers a unique advantage to gain deeper insights of structure-activity correlations in solid materials, leading to new guiding principles for rational design of advanced solid catalysts for potential important applications related to energy and fine chemical synthesis. In this review, recent key progress achieved in designing MOF- and COF-based molecular solid catalysts and the mechanistic understanding of the catalytic centers and associated reaction pathways are summarized. The state-of-the-art rational design of MOF- and COF-based solid catalysts in this review is grouped into seven different areas: (i) metalated linkers, (ii) metalated moieties anchored on linkers, (iii) organic moieties anchored on linkers, (iv) encapsulated single sites in pores, and (v) metal-mode-based active sites in MOFs. Along with this, some attention is paid to theoretical studies about the reaction mechanisms. Finally, technical challenges and possible solutions in applying these catalysts for practical applications are also presented.

Quasi-polymeric construction of stable perovskite-type LaFeO3/g-C3N4 heterostructured photocatalyst for improved Z-scheme photocatalytic activity via solid p-n heterojunction interfacial effect.

Materials of perovskite-type structure have attracted considerable attention for their applications in photocatalysis. In this study, a novel composite of p-type LaFeO3 microsphere coated with n-type nanosized graphitic carbon nitride nanosheets was constructed by the quasi-polymeric calcination method with the aid of electrostatic self-assembly interaction. Results indicate that the LaFeO3/g-C3N4p-n heterostructured photocatalyst obtained, in contrast to the pure constituents, enabled improved visible-light absorption, and more efficient separation and migration of charge carriers via solid p-n heterojunction interfacial effect. Correspondingly, the LaFeO3/g-C3N4 composite allowed for higher visible-light-responsive photocatalytic activity for the degradation of Brilliant Blue, which was 16.9 and 7.8 times that of pristine g-C3N4 and LaFeO3, respectively. The photocatalytic degradation of Brilliant Blue was ascribed to the combined contributions of the photogenerated holes (h+), superoxide radicals (O2-) and hydroxyl radicals (OH). Based on solid p-n heterojunction interfacial interaction, a Z-scheme charge carrier transfer pathway integrated with the dye-sensitization effect is proposed as the underlying mechanism of the photocatalytic reaction process. Therefore, we believe that the perovskite-type LaFeO3/g-C3N4 Z-scheme photcatalyst promotes the development of photocatalysis and holds much promise for environmental remediation.

A Highly Efficient Oxygen Evolution Catalyst Consisting of Interconnected Nickel-Iron-Layered Double Hydroxide and Carbon Nanodomains.

In this work, a one-pot solution method for direct synthesis of interconnected ultrafine amorphous NiFe-layered double hydroxide (NiFe-LDH) (<5 nm) and nanocarbon using the molecular precursor of metal and carbon sources is presented for the first time. During the solvothermal synthesis of NiFe-LDH, the organic ligand decomposes and transforms to amorphous carbon with graphitic nanodomains by catalytic effect of Fe. The confined growth of both NiFe-LDH and carbon in one single sheet results in fully integrated amorphous NiFe-LDH/C nanohybrid, allowing the harness of the high intrinsic activity of NiFe-LDH due to (i) amorphous and distorted LDH structure, (ii) enhanced active surface area, and (iii) strong coupling between the active phase and carbon. As such, the resultant NiFe-LDH/C exhibits superior activity and stability. Different from postdeposition or electrostatic self-assembly process for the formation of LDH/C composite, this method offers one new opportunity to fabricate high-performance oxygen evolution reaction and possibly other catalysts.

Construction of unique two-dimensional MoS2-TiO2 hybrid nanojunctions: MoS2 as a promising cost-effective cocatalyst toward improved photocatalytic reduction of CO2 to methanol.

Two-dimensional MoS2 nanosheets were in situ grown on TiO2 nanosheets to form two-dimensional (2D) hybrid nanojunctions, with which MoS2 nanosheets compactly contact with TiO2 to increase the interfacial area. MoS2 was identified as a promising cost-effective substitute for noble metal cocatalysts such as Pt, Au, and Ag, and shows superior activity and selectivity for reducing CO2 to CH3OH in aqueous solution to these metal cocatalysts under UV-vis light irradiation. The photo-luminescence (PL) spectra and transient time-resolved PL decay measurements reveal that the fast electron transfer from TiO2 to MoS2 can minimize charge recombination losses to improve the conversion efficiency of photoreduction. It reveals that Mo-terminated edges of MoS2 nanosheets possess the metallic character and a high d-electron density, and the Mo cation sites may benefit the stabilization of CHxOy intermediates via electrostatic attraction to enhance the CH3OH formation from the reduction of CO2 in aqueous solution.

Self-template synthesis of CdS/NiSx heterostructured nanohybrids for efficient photocatalytic hydrogen evolution.

Photocatalytic hydrogen (H2) evolution from water splitting is attracting enormous interest due to the possibility of converting solar energy into green chemical energy. The construction of highly efficient and stable photocatalysts is of importance and necessary for the development of photocatalytic water splitting technology. In this study, we have developed a self-template synthetic strategy for the preparation of heterostructured nanohybrids composed of ultrasmall CdS and NiSx nanoparticles by using Cd(ii)-Ni(ii)-(4,4'-bipyridine) coordination polymers as the precursor and template. The CdS/NiSx nanohybrids are comprised of integrated CdS and NiSx nanoclusters in a heterostructure which function as highly efficient visible-light-driven H2 evolution photocatalysts. The enhanced photocatalytic performance could be attributed to the formation of hetero-junctions between CdS and NiSx nanoparticles inside the nanohybrids which could effectively improve the separation efficiency of photogenerated electrons and holes, and thus enhance the photocatalytic activity. This work can provide a new insight into the design and fabrication of other heterostructured photocatalysts for solar-driven water splitting or other photocatalytic applications.

Nickel Nanoparticles Encapsulated in Few-Layer Nitrogen-Doped Graphene Derived from Metal-Organic Frameworks as Efficient Bifunctional Electrocatalysts for Overall Water Splitting.

Nickel nanoparticles encapsulated in few-layer nitrogen-doped graphene (Ni@NC) are synthesized by using a Ni-based metal-organic framework as the precursor for high-temperature annealing treatment. The resulting Ni@NC materials exhibit highly efficient and ultrastable electrocatalytic activity toward the hydrogen evolution reaction and the oxygen evolution reaction as well as overall water splitting in alkaline environment.

Z-Scheme Photocatalytic Systems for Promoting Photocatalytic Performance: Recent Progress and Future Challenges.

Semiconductor photocatalysts have attracted increased attention due to their great potential for solving energy and environmental problems. The formation of Z-scheme photocatalytic systems that mimic natural photosynthesis is a promising strategy to improve photocatalytic activity that is superior to single component photocatalysts. The connection between photosystem I (PS I) and photosystem II (PS II) are crucial for constructing efficient Z-scheme photocatalytic systems using two photocatalysts (PS I and PS II). The present review concisely summarizes and highlights recent state-of-the-art accomplishments of Z-scheme photocatalytic systems with diverse connection modes, including i) with shuttle redox mediators, ii) without electron mediators, and iii) with solid-state electron mediators, which effectively increase visible-light absorption, promote the separation and transportation of photoinduced charge carriers, and thus enhance the photocatalytic efficiency. The challenges and prospects for future development of Z-scheme photocatalytic systems are also presented.