Combined Analyses on Electronic Structure and Molecular Orbitals of d10 Bimetal Oxide In2Ge2O7 and Photocatalytic Performances for Overall Water Splitting and CO2 Reduction

Semiconducting photocatalytic overall water splitting and CO2 reduction are possible solutions to the emerging worldwide challenges of oil shortage and continual temperature increase, and the key is to develop an efficient photocatalyst. Most photocatalysts contain the d0, d10 or d10ns2 metals, and a guiding principle is desired to help to distinguish outstanding semiconductors. Here, the d10 bimetal oxide In2Ge2O7 was selected as the target. First, density functional theory (DFT) calculations point out that the nonbonding O 2p orbitals dominate the valence band maximum (VBM), and In 5s-O 2s and Ge 4s-O 2s antibonding orbitals are the major components of conduction band minimum (CBM). Moreover, the molecular orbitals were analyzed to consolidate the DFT calculations and make it more understandable for chemists. Due to the very small specific surface area (0.51 m2/g) and wide band gap (4.14 eV), as-prepared In2Ge2O7 did not exhibit any overall water splitting activity; nevertheless, when loading with 1 wt% cocatalyst (i.e., Pt, Pd), the surficial charge recombination can be greatly eliminated and the overall water splitting activity is significantly improved to 33.0(4) and 17.2(7) μmol/h for H2 and O2 generation, respectively. The apparent quantum yield (AQY) at 254 nm is 8.28%. This observation is proof that the inherent electronic structure of In2Ge2O7 is beneficial for the charge migration in bulk. Moreover, this catalyst also exhibits an observable CO2 reduction activity in pure water, which is a competition reaction with water splitting, anyway, the CH4 selectivity can be enhanced by loading Pd. This is a successful attempt to unravel the structure-property relationship by combining the analyses on electronic structure and molecular orbitals and is enlightening to further discover good candidates to photocatalysts.

Optimized full CO2 photoreduction process by defective spinel atomic layers

The impact of defects on the carbon dioxide (CO2) photoreduction property is sometimes contradictory. Herein, we employ two-dimensional materials, possessing high-density and high-uniformity active sites, as ideal models to thoroughly investigate the influence of defects on three main processes during CO2 photoreduction. As an example, oxygen-deficient ZnGa2O4 atomic layers are successfully fabricated, verified by the electron spin resonance spectra, X-ray photoelectron spectroscopy spectra and X-ray absorption near edge structure spectra. UV-vis diffuse reflectance spectra, photoluminescence spectra, surface photovoltage spectroscopy, N2 adsorption-desorption isotherm plots and density functional theory calculations indicate that the presence of oxygen defects helps to expand the photoabsorption, accelerate the carrier separation, and enhance the CO2 adsorption and protonation process. As a result, the carbon monoxide evolution rate of the defective ZnGa2O4 atomic layers was approximately 88 times higher than that of the ZnGa2O4 atomic layers under visible light irradiation. In other words, this work discloses that the introduction of defects on photocatalysts allows the optimization of the three primary processes, thus obtaining boosted CO2 photoreduction performance.

Oxygen Vacancy Induced Atom-Level Interface in Z-Scheme SnO2/SnNb2O6 Heterojunctions for Robust Solar-Driven CO2 Conversion

The modulation of Z-scheme charge transfer is essential for efficient heterostructure toward photocatalytic CO₂ reduction. However, constructing a compact hetero-interface favoring the Z-scheme charge transfer remains a great challenge. In this work, an interfacial Nb-O-Sn bond and built-in electric field-modulated Z-scheme O_v-SnO₂/SnNb₂O₆ heterojunction was prepared for efficient photocatalytic CO₂ conversion. Systematic investigations reveal that an atomic-level interface is constructed in the O_v-SnO₂/SnNb₂O₆ heterojunction. Under simulated sunlight irradiation, the obtained O_v-SnO₂/SnNb₂O₆ photocatalyst exhibits a high CO evolution rate of 147.4 μmol h^-1 g^-1 from CO₂ reduction, which is around 3-fold and 3.3-fold of SnO₂/SnNb₂O₆ composite and pristine SnNb₂O₆, respectively, and favorable cyclability by retaining 95.8% rate retention after five consecutive tests. As determined by electron paramagnetic resonance spectra, in situ Fourier transform infrared spectra, and density functional theory calculations, Nb-O-Sn bonds and built-in electric field induced by the addition of oxygen vacancies jointly accelerate the Z-scheme charge transfer for enhanced photocatalytic performance. This work provides a promising route for consciously modulating Z-scheme charge transfer by atomic-level interface engineering to boost photocatalytic performance.

Photoactive p-Type Spinel CuGa2O4 Nanocrystals

Herein we report the synthesis and characterization of spinel copper gallate (CuGa₂O₄) nanocrystals (NCs) with an average size of 3.7 nm via a heat-up colloidal reaction. CuGa₂O₄ NCs have a band gap of ∼2.5 eV and marked p-type character, in agreement with ab initio simulations. These novel NCs are demonstrated to be photoactive, generating a clear and reproducible photocurrent under blue light irradiation when deposited as thin films. Crucially, the ability to adjust the Cu/Ga ratio within the NCs, and the effect of this on the optical and electronic properties of the NCs, was also demonstrated. These results position CuGa₂O₄ NCs as a novel material for optoelectronic applications, including hole transport and light harvesting.

Electrochemical generation of hydrogen peroxide from a zinc gallium oxide anode with dual active sites

Electrochemical water oxidation enables the conversion of H₂O to H₂O₂. It holds distinct advantages to the O₂ reduction reaction, which is restricted by the inefficient mass transfer and limited solubility of O₂ in aqueous media. Nonetheless, most reported anodes suffer from high overpotentials (usually >1000 mV) and low selectivity. Electrolysis at high overpotentials often causes serious decomposition of peroxides and leads to declined selectivity. Herein, we report a ZnGa₂O₄ anode with dual active sites to improve the selectivity and resist the decomposition of peroxides. Its faradaic efficiency reaches 82% at 2.3 V versus RHE for H₂O₂ generation through both direct (via OH^-) and indirect (via HCO₃^-) pathways. The percarbonate is the critical species generated through the conversion of bicarbonate at Ga-Ga dual sites. The peroxy bond is stable on the surface of the ZnGa₂O₄ anode, significantly improving faradaic efficiency.

Promoting Photocatalytic Carbon Dioxide Reduction by Tuning the Properties of Cocatalysts

Suppressing the amount of carbon dioxide in the atmosphere is an essential measure toward addressing global warming. Specifically, the photocatalytic CO₂ reduction reaction (CRR) is an effective strategy because it affords the conversion of CO₂ into useful carbon feedstocks by using sunlight and water. However, the practical application of photocatalyst-promoting CRR (CRR photocatalysts) requires significant improvement of their conversion efficiency. Accordingly, extensive research is being conducted toward improving semiconductor photocatalysts, as well as cocatalysts that are loaded as active sites on the photocatalysts. In this review, we summarize recent research and development trends in the improvement of cocatalysts, which have a significant impact on the catalytic activity and selectivity of photocatalytic CRR. We expect that the advanced knowledge provided on the improvement of cocatalysts for CRR in this review will serve as a general guideline to accelerate the development of highly efficient CRR photocatalysts.

Impacts of the Catalyst Structures on CO2 Activation on Catalyst Surfaces

Utilizing CO2 as a sustainable carbon source to form valuable products requires activating it by active sites on catalyst surfaces. These active sites are usually in or below the nanometer scale. Some metals and metal oxides can catalyze the CO2 transformation reactions. On metal oxide-based catalysts, CO2 transformations are promoted significantly in the presence of surface oxygen vacancies or surface defect sites. Electrons transferable to the neutral CO2 molecule can be enriched on oxygen vacancies, which can also act as CO2 adsorption sites. CO2 activation is also possible without necessarily transferring electrons by tailoring catalytic sites that promote interactions at an appropriate energy level alignment of the catalyst and CO2 molecule. This review discusses CO2 activation on various catalysts, particularly the impacts of various structural factors, such as oxygen vacancies, on CO2 activation.

Extraterrestrial artificial photosynthetic materials for in-situ resource utilization

Aerospace milestones in human history, including returning to the moon and manned Martian missions, have been implemented in recent years. Space exploration has become one of the global common goals, and to ensure the survival and development of human beings in the extraterrestrial extreme environment has been becoming the basic ability and technology of manned space exploration. For the purpose of fulfilling the goal of extraterrestrial survival, researchers in Nanjing University and the China Academy of Space Technology proposed extraterrestrial artificial photosynthesis (EAP) technology. By simulating the natural photosynthesis of green plants on the Earth, EAP converts CO2/H2O into fuel and O2 in an in-situ, accelerated and controllable manner by using waste CO2 in the confined space of spacecraft, or abundant CO2 resources in extraterrestrial celestial environments, e.g. Mars. Thus, the material loading of manned spacecraft can be greatly reduced to support affordable and sustainable deep space exploration. In this paper, EAP technology is compared with existing methods of converting CO2/H2O into fuel and O2 in the aerospace field, especially the Sabatier method and Bosch reduction method. The research progress of possible EAP materials for in-situ utilization of extraterrestrial resources are also discussed in depth. Finally, this review lists the challenges that the EAP process may encounter, which need to be focused on for future implementation and application. We expect to deepen the understanding of artificial photosynthetic materials and technologies, and aim to strongly support the development of manned spaceflight.

Noble-Metal-Free Multicomponent Nanointegration for Sustainable Energy Conversion

Global energy and environmental crises are among the most pressing challenges facing humankind. To overcome these challenges, recent years have seen an upsurge of interest in the development and production of renewable chemical fuels as alternatives to the nonrenewable and high-polluting fossil fuels. Photocatalysis, photoelectrocatalysis, and electrocatalysis provide promising avenues for sustainable energy conversion. Single- and dual-component catalytic systems based on nanomaterials have been intensively studied for decades, but their intrinsic weaknesses hamper their practical applications. Multicomponent nanomaterial-based systems, consisting of three or more components with at least one component in the nanoscale, have recently emerged. The multiple components are integrated together to create synergistic effects and hence overcome the limitation for outperformance. Such higher-efficiency systems based on nanomaterials will potentially bring an additional benefit in balance-of-system costs if they exclude the use of noble metals, considering the expense and sustainability. It is therefore timely to review the research in this field, providing guidance in the development of noble-metal-free multicomponent nanointegration for sustainable energy conversion. In this work, we first recall the fundamentals of catalysis by nanomaterials, multicomponent nanointegration, and reactor configuration for water splitting, CO₂ reduction, and N₂ reduction. We then systematically review and discuss recent advances in multicomponent-based photocatalytic, photoelectrochemical, and electrochemical systems based on nanomaterials. On the basis of these systems, we further laterally evaluate different multicomponent integration strategies and highlight their impacts on catalytic activity, performance stability, and product selectivity. Finally, we provide conclusions and future prospects for multicomponent nanointegration. This work offers comprehensive insights into the development of cost-competitive multicomponent nanomaterial-based systems for sustainable energy-conversion technologies and assists researchers working toward addressing the global challenges in energy and the environment.

Enhancing Rechargeable Persistent Luminescence via Organic Dye Sensitization

Owing to their unique afterglow ability, long-wavelength light activatable persistent luminescence (PersL) nanoparticles (PLNPs) have been emerging as an important category of imaging probes. Long-wavelength LED light has been shown to be effective in recharging these nanoparticles. However, finding a simple and effective method to amplify such renewable PersL signals under long-wavelength light is still a key challenge. Herein, we discovered that a dye-sensitization strategy was able to effectively boost the renewable PersL signals of the NIR emitting ZnGa₂ O₄ :Cr³⁺ (ZGC)) under long-wavelength LED light. Moreover, as a proof-of-principle tumorectomy demonstration, this new class of dye sensitized ZGC enabled simultaneous intraoperative anatomic tumor navigation and effective microscopic detection of tumor cells in pathological diagnosis.

An Anthracene-Based Metal-Organic Framework for Selective Photo-Reduction of Carbon Dioxide to Formic Acid Coupled with Water Oxidation

A Zr-based metal-organic framework has been synthesized and employed as a catalyst for photochemical carbon dioxide reduction coupled with water oxidation. The catalyst shows significant carbon dioxide reduction property with concomitant water oxidation. The catalyst has broad visible light as well as UV light absorption property, which is further confirmed from electronic absorption spectroscopy. Formic acid was the only reduced product from carbon dioxide with a turn-over frequency (TOF) of 0.69 h^-1 in addition to oxygen, which was produced with a TOF of 0.54 h^-1 . No external photosensitizer is used and the ligand itself acts as the light harvester. The efficient and selective photochemical carbon dioxide reduction to formic acid with concomitant water oxidation using Zr-based MOF as catalyst is thus demonstrated here.

Enhanced CO2 Photocatalysis by Indium Oxide Hydroxide Supported on TiN@TiO2 Nanotubes

Herein is developed a ternary heterostructured catalyst, based on a periodic array of 1D TiN nanotubes, with a TiO₂ nanoparticulate intermediate layer and a In₂O_3-x(OH)_y nanoparticulate shell for improved performance in the photocatalytic reverse water gas shift reaction. It is demonstrated that the ordering of the three components in the heterostructure sensitively determine its activity in CO₂ photocatalysis. Specifically, TiN nanotubes not only provide a photothermal driving force for the photocatalytic reaction, owing to their strong optical absorption properties, but they also serve as a crucial scaffold for minimizing the required quantity of In₂O_3-x(OH)_y nanoparticles, leading to an enhanced CO production rate. Simultaneously, the TiO₂ nanoparticle layer supplies photogenerated electrons and holes that are transferred to active sites on In₂O_3-x(OH)_y nanoparticles and participate in the reactions occurring at the catalyst surface.

Thermocatalytic hydrogen peroxide generation and environmental disinfection by Bi2Te3 nanoplates

The highly reactive nature of reactive oxygen species (ROS) is the basis for widespread use in environmental and health-related fields. Conventionally, there are only two kinds of catalysts used for ROS generation: photocatalysts and piezocatalysts. However, their usage has been limited due to various environmental and physical factors. To address this problem, herein, we report thermoelectric materials, such as Bi₂Te₃, Sb₂Te₃, and PbTe, as thermocatalysts which can produce hydrogen peroxide (H₂O₂) under a small surrounding temperature difference. Being the most prevalent environmental factors in daily life, temperature and related thermal effects have tremendous potential for practical applications. To increase the practicality in everyday life, bismuth telluride nanoplates (Bi₂Te₃ NPs), serving as an efficient thermocatalyst, are coated on a carbon fiber fabric (Bi₂Te₃@CFF) to develop a thermocatalytic filter with antibacterial function. Temperature difference induced H₂O₂ generation by thermocatalysts results in the oxidative damage of bacteria, which makes thermocatalysts highly promising for disinfection applications. Antibacterial activity as high as 95% is achieved only by the treatment of low-temperature difference cycles. The current work highlights the horizon-shifting impacts of thermoelectric materials for real-time purification and antibacterial applications.

Recent advances in hydrogenation of CO2 into hydrocarbons via methanol intermediate over heterogeneous catalysts

This review provides recent advances in the conversion of CO₂ to methanol, methanol to hydrocarbons, and direct conversion of CO₂ to hydrocarbons via methanol intermediate over various monofunctional and bifunctional solid catalysts.

Solid Nanoporosity Governs Catalytic CO2 and N2 Reduction

Global demand for green and clean energy is increasing day by day owing to ongoing developments by the human race that are changing the face of the earth at a rate faster than ever. Exploring alternative sources of energy to replace fossil fuel consumption has become even more vital to control the growing concentration of CO₂, and reduction of CO₂ into CO or other useful hydrocarbons (e.g., C₁ and C_≥2 products), as well as reduction of N₂ into ammonia, can greatly help in this regard. Various materials have been developed for the reduction of CO₂ and N₂. The introduction of pores in these materials by porosity engineering has been demonstrated to be highly effective in increasing the efficiency of the involved redox reactions, over 40% increment for CO₂ reduction to date, by providing an increased number of exposed facets, kinks, edges, and catalytically active sites of catalysts. By shaping the surface porous structure, the selectivity of the redox reaction can also be enhanced. In order to better understand this area benefiting rational design for future solutions, this review systematically summarizes and constructively discusses the porosity engineering in catalytic materials, including various synthesis methods, characterization of porous materials, and the effects of porosity on performance of CO₂ reduction and N₂ reduction.

Atomic-scale synthesis of nanoporous gallium-zinc oxynitride-reduced graphene oxide photocatalyst with tailored carrier transport mechanism

Surface modified gallium-zinc oxynitride solid solution exhibited outstanding stability and visible-light activity for water splitting. However, the considerable rate of photo-induced charge recombination and the low surface area of the bulk photocatalyst limited its performance. Here, an efficient technique is proposed for the synthesis of a nanoporous oxynitride photocatalyst and its graphene-hybridized material. The nanoporous oxynitride photocatalyst was prepared via a nanoscale solid-state route, using microwave irradiation as an intermolecular-state activation method, Ga3+/Zn2+ layered double hydroxide as an atomic-level uniform mixed-metal precursor, and urea as a non-toxic ammonolysis soft-template. The graphene-hybridized photocatalyst was fabricated using a facile electrostatic self-assembly technique. The photocatalytic activity of the synthesized graphene hybridized nanoporous oxynitride photocatalyst was systematically improved through shortening the majority-carrier diffusion length and enhancing the density of active hydrogen evolution sites within the quasi-three-dimensional nanostructure, reaching 7.5-fold sacrificial photocatalytic hydrogen evolution, compared to the conventional 1 wt% Rh-loaded oxynitride photocatalyst.

Imparting CO2 reduction selectivity to ZnGa2O4 photocatalysts by crystallization from hetero nano assembly of amorphous-like metal hydroxides

Imparting an enhanced CO₂ reduction selectivity to ZnGa₂O₄ photocatalysts has been demonstrated by controlled crystallization from interdispersed nanoparticles of zinc and gallium hydroxides. The hydroxide precursor in which Zn(ii) and Ga(iii) are homogeneously interdispersed was prepared through an epoxide-driven sol-gel reaction. ZnGa₂O₄ obtained by a heat-treatment exhibits a higher surface basicity and an enhanced affinity for CO₂ molecules than previously-reported standard ZnGa₂O₄. The enhanced affinity for CO₂ molecules of the resultant ZnGa₂O₄ leads to highly-selective CO evolution in CO₂ photo-reduction with H₂O reductants. The present scheme is promising to achieve desirable surface chemistry on metal oxide photocatalysts.

The Improvement of Coralline-Like ZnGa2O4 by Cocatalysts for the Photocatalytic Degradation of Rhodamine B

To date, various methods have been used to synthesize ZnGa2O4 material to promote photodegradation performance. However, cocatalysts, which usually play a crucial role in the photocatalyst system, have not been studied extensively in photocatalytic degradation reactions. In this paper, ZnGa2O4 semiconducting material was synthesized by a traditional high-temperature solid-state reaction. The as-prepared powder was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet–visible diffused reflectance spectroscopy. The results indicate that the as-prepared sample is a highly crystallized granular sample with a bandgap of 4.44 eV and a uniform particle size distribution. Density functional theory (DFT) was utilized to calculate the electronic structure of ZnGa2O4. The valence bands and conduction bands were chiefly composed of O 2p atomic orbitals and the hybridization orbitals of Ga 4s4p and Zn4s4p, respectively. The photocatalytic performance was tested via the decomposition of rhodamine B (RhB) under the irradiation of ultraviolet light. Cu, Ag, Au, Ni, Pt, and Pd cocatalysts were loaded on the ZnGa2O4 photocatalyst by a photodeposition method. The relatively optimal cocatalyst of ZnGa2O4 in the photocatalytic degradation reaction is Au. Thereafter, the effect of loading different usage amounts of the Au cocatalyst for the photodegradation of the ZnGa2O4 photocatalyst was studied in detail. The experimental results displayed that the optimum photodegradation activity was confirmed with the 3 wt% Au/ZnGa2O4 sample, which was 14.1 times more than the unloaded photocatalyst. The maximum photocatalytic degradation ratio of RhB was 96.7%, with 180 min under ultraviolet light.

Highly selective conversion of CO2 to C2H6 on graphene modified chlorophyll Cu through multi-electron process for artificial photosynthesis

Artificial photosynthesis is a promising strategy for converting carbon dioxide into hydrocarbon fuels through solar energy as it is clean, economical and environmentally friendly. Herein, we developed a selective and stable photocatalyst for CO₂ photocatalytic reduction into C₂H₆ through a multi-electron transfer pathway without the external sacrificial regents. The core component of this composite catalyst was extracted from a silkworm excrement and modified to make chlorophyll Cu (Chl-Cu), which contained a porphyrin structure as an antenna for light absorption and a Cu cation as an active centre. We found that C₂ hydrocarbons such as C₂H₂, C₂H₄, and C₂H₆ tended to generate on chlorophyll-a/graphene. After substituting Mg²⁺ with Cu²⁺ cations in the centre of the porphyrin and modifying with graphene, only C₂H₆ was detected in the 18 hours reaction. This photocatalyst presented an outstanding activity and selectivity for the photocatalytic CO₂ reduction (CO₂RR) with a C₂H₆ yield rate at 68.23 μmol m^-2 h^-1 under visible light irradiation and an apparent quantum efficiency of 1.26% at 420 nm. In this system, the porphyrin rings were excited to produce electron-hole pairs by light. The photo-induced holes oxidized water to produce oxygen while graphene worked as an adsorption centre and electron acceptor for the CO₂ reduction.

A stable covalent organic framework for photocatalytic carbon dioxide reduction

A metal-decorated alkene-linked covalent organic framework is a robust, selective photocatalyst for CO₂ reduction.

Photocatalytic conversion of CO₂ into fuels is an important challenge for clean energy research and has attracted considerable interest. Here we show that tethering molecular catalysts—a rhenium complex, [Re(bpy)(CO)₃Cl]—together in the form of a crystalline covalent organic framework (COF) affords a heterogeneous photocatalyst with a strong visible light absorption, a high CO₂ binding affinity, and ultimately an improved catalytic performance over its homogeneous Re counterpart. The COF incorporates bipyridine sites, allowing for ligation of the Re complex, into a fully π-conjugated backbone that is chemically robust and promotes light-harvesting. A maximum rate of 1040 μmol g^–1 h^–1 for CO production with 81% selectivity was measured. CO production rates were further increased up to 1400 μmol g^–1 h^–1, with an improved selectivity of 86%, when a photosensitizer was added. Addition of platinum resulted in production of syngas, hence, the co-formation of H₂ and CO, the chemical composition of which could be adjusted by varying the ratio of COF to platinum. An amorphous analog of the COF showed significantly lower CO production rates, suggesting that crystallinity of the COF is beneficial to its photocatalytic performance in CO₂ reduction.

Design of core-shell titania-heteropolyacid-metal nanocomposites for photocatalytic reduction of CO2 to CO at ambient temperature

The photocatalytic conversion of CO₂ not only reduces the greenhouse effect, but also provides value-added solar fuels and chemicals. Herein, we report the design of new efficient core-shell nanocomposites for selective photocatalytic CO₂ to CO conversion, which occurs at ambient temperature. A combination of characterization techniques (TEM, STEM-EDX, XPS, XRD, FTIR photoluminescence) indicates that the CO₂ reduction occurs over zinc species highly dispersed on the heteropolyacid/titania core-shell nanocomposites. These core-shell structures create a semiconductor heterojunction, which increases charge separation and the lifetime of charge carriers' and leads to higher electron flux. In situ FTIR investigation of the reaction mechanism revealed that the reaction involved surface zinc bicarbonates as key reaction intermediates. In a series of catalysts containing noble and transition metals, zinc phosphotungstic acid-titania nanocomposites exhibit high activity reaching 50 μmol CO g^-1 h^-1 and selectivity (73%) in the CO₂ photocatalytic reduction to CO at ambient temperature. The competitive water splitting reaction has been significantly suppressed over the Zn sites in the presence of CO₂.

Important Role of Strontium Atom on the Surface of Sr2KTa5O15 with a Tetragonal Tungsten Bronze Structure to Improve Adsorption of CO2 for Photocatalytic Conversion of CO2 by H2O

Sr_1.6K_0.37Na_1.43Ta₅O₁₅, which belongs to the Na-substituted Sr₂KTa₅O₁₅ series of compounds with a tetragonal tungsten bronze structure, was fabricated using a flux mixture of KCl and NaCl (KCl/NaCl molar ratio = 55:45). It exhibited higher CO formation rate (94.6 μmol h^-1), better selectivity for CO evolution (85.5%), and better stability of the photocatalytic activity than those of bare Sr₂KTa₅O₁₅ and other Na-substituted Sr₂KTa₅O₁₅ samples synthesized from flux mixtures with different KCl/NaCl ratios. X-ray photoelectron spectroscopic studies revealed that the surface atomic Sr/Ta ratio of Sr_1.6K_0.37Na_1.43Ta₅O₁₅ was larger than that of Sr₂KTa₅O₁₅. To clarify the factor responsible for the improvement in the photocatalytic activity facilitated by Na substitution, as well as to elucidate the reaction mechanism, the surface species were characterized by in situ Fourier transform infrared spectroscopy. It was observed that the bicarbonate species (HCO₃^-) adsorbed on the active Sr sites of Sr_1.6K_0.37Na_1.43Ta₅O₁₅ was reduced to CO via the formate species during photoirradiation. The plot of the CO formation rate vs. the surface atomic Sr/Ta ratio for tetragonal tungsten bronze-type Sr-K-Ta-O complex oxides had the summit, indicating that Sr atoms on the surface enhance the photocatalytic activity, while an excessive amount of Sr on the surface leads to the decrease in the photocatalytic activity. Hence, it can be concluded that while the presence of Sr on the surface has a determining effect on the adsorption of CO₂ and eventually on the photocatalytic activity, excess Sr on the surface that exists as SrCO₃ or Sr₂Ta₂O₇ suppresses the photocatalytic activity. Thus, Sr_1.6K_0.37Na_1.43Ta₅O₁₅ showed higher CO formation rate than Sr₂KTa₅O₁₅ did.

A Critical Review on Energy Conversion and Environmental Remediation of Photocatalysts with Remodeling Crystal Lattice, Surface, and Interface

Solar energy is a renewable resource that can supply our energy needs in the long term. A semiconductor photocatalysis that is capable of utilizing solar energy has appealed to considerable interests for recent decades, owing to the ability to aim at environmental problems and produce renewal energy. Much effort has been put into the synthesis of a highly efficient semiconductor photocatalyst to promote its real application potential. Hence, we reviewed the most advanced methods and strategies in terms of (i) broadening the light absorption wavelengths, (ii) design of active reaction sites, and (iii) control of the electron-hole (e^--h⁺) recombination, while these three processes could be influenced by remodeling the crystal lattice, surface, and interface. Additionally, we individually examined their current applications in energy conversion (i.e., hydrogen evolution, CO₂ reduction, nitrogen fixation, and oriented synthesis) and environmental remediation (i.e., air purification and wastewater treatment). Overall, in this review, we particularly focused on advanced photocatalytic activity with simultaneous wastewater decontamination and energy conversion and further enriched the mechanism by proposing the electron flow and substance conversion. Finally, this review offers the prospects of semiconductor photocatalysts in the following three vital (distinct) aspects: (i) the large-scale preparation of highly efficient photocatalysts, (ii) the development of sustainable photocatalysis systems, and (iii) the optimization of the photocatalytic process for practical application.

Recent Advances in MOF-based Nanocatalysts for Photo-Promoted CO2 Reduction Applications

The conversion of CO2 to valuable substances (methane, methanol, formic acid, etc.) by photocatalytic reduction has important significance for both the sustainable energy supply and clean environment technologies. This review systematically summarized recent progress in this field and pointed out the current challenges of photocatalytic CO2 reduction while using metal-organic frameworks (MOFs)-based materials. Firstly, we described the unique advantages of MOFs based materials for photocatalytic reduction of CO2 and its capacity to solve the existing problems. Subsequently, the latest research progress in photocatalytic CO2 reduction has been documented in detail. The catalytic reaction process, conversion efficiency, as well as the product selectivity of photocatalytic CO2 reduction while using MOFs based materials are thoroughly discussed. Specifically, in this review paper, we provide the catalytic mechanism of CO2 reduction with the aid of electronic structure investigations. Finally, the future development trend and prospect of photocatalytic CO2 reduction are anticipated.

Encapsulating a Ni(II) molecular catalyst in photoactive metal-organic framework for highly efficient photoreduction of CO2

Photocatalytic reduction of CO₂ to CO is a promising strategy for reducing atmospheric CO₂ levels and storing solar radiation as chemical energy. Here, we demonstrate that a molecular catalyst [Ni^II(bpet)(H₂O)₂] successfully encapsulated into a highly robust and visible-light responsive metal-organic framework (Ru-UiO-67) to fabricate composite catalysts for photocatalytic CO₂ reduction. The composite Ni@Ru-UiO-67 photocatalysts show efficient visible-light-driven CO₂ reduction to CO with a TON of 581 and a selectivity of 99% after 20-h illumination, because of the facile electron transfer from Ru-photosensitizer to Ni(II) active sites in Ni@Ru-UiO-67 system. The mechanistic insights into photoreduction of CO₂ have been studied based on thermodynamical, electrochemical, and spectroscopic investigation, together with density functional theory (DFT) calculations. This work shows that encapsulating molecular catalyst into photoactive MOF highlights opportunities for designing efficient, stable and recyclable photocatalysts.

Sunlight-Fueled, Low-Temperature Ru-Catalyzed Conversion of CO2 and H2 to CH4 with a High Photon-to-Methane Efficiency

Methane, which has a high energy storage density and is safely stored and transported in our existing infrastructure, can be produced through conversion of the undesired energy carrier H2 with CO2. Methane production with standard transition-metal catalysts requires high-temperature activation (300-500 °C). Alternatively, semiconductor metal oxide photocatalysts can be used, but they require high-intensity UV light. Here, we report a Ru metal catalyst that facilitates methanation below 250 °C using sunlight as an energy source. Although at low solar intensity (1 sun) the activity of the Ru catalyst is mainly attributed to thermal effects, we identified a large nonthermal contribution at slightly elevated intensities (5.7 and 8.5 sun) resulting in a high photon-to-methane efficiency of up to 55% over the whole solar spectrum. We attribute the excellent sunlight-harvesting ability of the catalyst and the high photon-to-methane efficiency to its UV-vis-NIR plasmonic absorption. Our highly efficient conversion of H2 to methane is a promising technology to simultaneously accelerate the energy transition and reduce CO2 emissions.

Hydrothermal Approach to Spinel-Type 2D Metal Oxide Nanosheets

The peculiar physical and chemical properties of 2D nanostructures have aroused global research interest in developing new members, synthetic technology, and exploring their potential applications in functional nanodevices. However, it is extremely challenging to directly obtain the 2D nanosheets for these extrinsic layered structures using conventional routines. In this work, we demonstrate the facile and general synthesis of 2D spinel-type metal oxides nanosheets through a simple hydrothermal reaction. Using this method, cubic γ-Ga₂O₃, ZnGa₂O₄ and MnGa₂O₄ nanosheets with triangular/hexagonal configuration and ultrathin thickness have been synthesized, and all these nanosheets show preferential growth along (111) plane with the minimum formation energy. Microstructural and composition analyses using HRTEM, EDS, XPS, and so on reveal that the as-synthesized 2D nanosheets are well-crystallized in cubic fcc-phase and show high purity in composition, and the formation process of MGa₂O₄ nanosheets can be regarded as the competition of M²⁺ and Ga³⁺ in tetrahedral site. Spatially resolved cathodoluminescence measurement of individual 2D nanosheet shows that the γ-Ga₂O₃, ZnGa₂O₄, and MnGa₂O₄ nanosheets exhibit distinct luminescence behavior, and ZnGa₂O₄ nanosheets show the strongest emission in visible region. It is expected that the facile synthesis of spinel-type metal oxides of γ-Ga₂O₃, ZnGa₂O₄, and MnGa₂O₄ nanosheets will further promote the exploration of a variety of semiconductor nanostructures that could not be achieved using conventional technology suitable for layered structures and will also open up some opportunities for the integration of advanced functional nanodevices such as photodetectors, phosphors on the basis of them.

New horizon in C1 chemistry: breaking the selectivity limitation in transformation of syngas and hydrogenation of CO2 into hydrocarbon chemicals and fuels

Recent advances in bifunctional catalysis for conversion of syngas and hydrogenation of CO₂ into chemicals and fuels have been highlighted.

Schottky junction effect enhanced plasmonic photocatalysis by TaON@Ni NP heterostructures

The localized surface plasmon resonance and Schottky junction in the TaON@Ni hybrid photocatalyst improve the light harvesting and promote the electron–hole separation and transport of TaON.

From CO2methanation to ambitious long-chain hydrocarbons: alternative fuels paving the path to sustainability

Comprehensive insight into the thermochemical, photochemical and electrochemical reduction of CO₂to methane and long-chain hydrocarbons as alternative fuels.

Dual-functional persistent luminescent nanoparticles with enhanced persistent luminescence and photocatalytic activity

NIR persistent luminescence and photocatalytic activity of the PLNPs were significantly and simultaneously improved via additional doping of Bi³⁺.

Multi-wavelength tailoring of a ZnGa2O4 nanosheet phosphor via defect engineering

The multi-wavelength luminescence tailoring of an individual phosphor free of external dopants is of great interest and technologically important for practical applications. Using ZnGa2O4 nanosheets as a target phosphor, we demonstrate how to artificially control the luminescence wavelength centers and their emission intensities to simultaneously emit ultraviolet/blue, green and red light via a feasible defect engineering strategy. Simple high-temperature annealing of hydrothermally synthesized ZnGa2O4 nanosheets leads to the effective tunability of their emission process to present multi-wavelength luminescence due to the structural distortion and the formation of oxygen vacancies. Controlling the annealing temperature and time can further precisely modulate the wavelengths and their corresponding intensities. It is speculated that the migration of Ga into the [GaO4] tetrahedron and the O vacancy are responsible for the multi-wavelength luminescence of the ZnGa2O4 nanosheet phosphor. Finally, the tentative multi-wavelength luminescence behavior of the ZnGa2O4 nanosheet phosphor via defect engineering is discussed based on a series of evidenced experimental observations of XRD, XPS, HRTEM and CL.

Lattice Engineering on Metal Cocatalysts for Enhanced Photocatalytic Reduction of CO2 into CH4

Photocatalytic conversion of CO₂ into CH₄ represents an appealing approach to alleviate the world's continued reliance on fossil fuels and global warming resulting from increasing CO₂ concentrations in the atmosphere. However, its practical application is greatly limited by serious electron-hole recombination in the photocatalysts and the production of CO and H₂ as side reactions. Herein, for the first time, it is demonstrated that the photocatalytic reduction of CO₂ to CH₄ can be significantly improved through the simultaneous alloying and hydriding of metal cocatalysts. The isolation of Cu and H atoms in Pd lattices play three roles in the enhancement of CO₂ to CH₄ conversion: 1) Cu atoms provide catalytic sites to reduce CO₂ into CO and then to CH₄ to suppress H₂ evolution; 2) H atoms improve the electron-trapping ability of cocatalysts; and 3) H atoms accelerate the reduction of CO to CH₄ , which is the rate-limiting procedure in the conversion of CO₂ into CH₄ . Arising from the synergistic interplay between Pd-H and Cu-CO sites, C₃ N₄ -Pd₉ Cu₁ H_x (15 mg) achieves 100 % selectivity for CH₄ production with an average rate of 0.018 μmol h^-1 under visible-light irradiation. This work provides insights into the design of a cocatalyst for highly selective CO₂ conversion through lattice engineering at atomic precision.

Photo-generated dinuclear {Eu(II)}2 active sites for selective CO2 reduction in a photosensitizing metal-organic framework

Photocatalytic reduction of CO2 is a promising approach to achieve solar-to-chemical energy conversion. However, traditional catalysts usually suffer from low efficiency, poor stability, and selectivity. Here we demonstrate that a large porous and stable metal-organic framework featuring dinuclear Eu(III)2 clusters as connecting nodes and Ru(phen)3-derived ligands as linkers is constructed to catalyze visible-light-driven CO2 reduction. Photo-excitation of the metalloligands initiates electron injection into the nodes to generate dinuclear {Eu(II)}2 active sites, which can selectively reduce CO2 to formate in a two-electron process with a remarkable rate of 321.9 μmol h-1 mmolMOF-1. The electron transfer from Ru metalloligands to Eu(III)2 catalytic centers are studied via transient absorption and theoretical calculations, shedding light on the photocatalytic mechanism. This work highlights opportunities in photo-generation of highly active lanthanide clusters stabilized in MOFs, which not only enables efficient photocatalysis but also facilitates mechanistic investigation of photo-driven charge separation processes.