Facet-Engineered Surface and Interface Design of Monoclinic Scheelite Bismuth Vanadate for Enhanced Photocatalytic Performance

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.

Nanometer-Resolved Operando Photo-Response of Faceted BiVO4 Semiconductor Nanoparticles

Photo(electro)catalysis with semiconducting nanoparticles (NPs) is an attractive approach to convert abundant but intermittent renewable electricity into stable chemical fuels. However, our understanding of the microscopic processes governing the performance of the materials has been hampered by the lack of operando characterization techniques with sufficient lateral resolution. Here, we demonstrate that the local surface potentials of NPs of bismuth vanadate (BiVO4) and their response to illumination differ between adjacent facets and depend strongly on the pH of the ambient electrolyte. The isoelectric points of the dominant {010} basal plane and the adjacent {110} side facets differ by 1.5 pH units. Upon illumination, both facets accumulate positive charges and display a maximum surface photoresponse of +55 mV, much stronger than reported in the literature for the surface photo voltage of BiVO4 NPs in air. High resolution images reveal the presence of numerous surface defects ranging from vacancies of a few atoms, to single unit cell steps, to microfacets of variable orientation and degree of disorder. These defects typically carry a highly localized negative surface charge density and display an opposite photoresponse compared to the adjacent facets. Strategies to model and optimize the performance of photocatalyst NPs, therefore, require an understanding of the distribution of surface defects, including the interaction with ambient electrolyte.

Photocatalytic Conversion of Methane: Current State of the Art, Challenges, and Future Perspectives

With 28-34 times the greenhouse effect of CO2 over a 100-year period, methane is regarded as the second largest contributor to global warming. Reducing methane emissions is a necessary measure to limit global warming to below 1.5 °C. Photocatalytic conversion of methane is a promising approach to alleviate the atmospheric methane concentrations due to its low energy consumption and environmentally friendly characteristics. Meanwhile, this conversion process can produce valuable chemicals and liquid fuels such as CH3OH, CH3CH2OH, C2H6, and C2H4, cutting down the dependence of chemical production on crude oil. However, the development of photocatalysts with a high methane conversion efficiency and product selectivity remains challenging. In this review, we overview recent advances in semiconductor-based photocatalysts for methane conversion and present catalyst design strategies, including morphology control, heteroatom doping, facet engineering, and cocatalysts modification. To gain a comprehensive understanding of photocatalytic methane conversion, the conversion pathways and mechanisms in these systems are analyzed in detail. Moreover, the role of electron scavengers in methane conversion performance is briefly discussed. Subsequently, we summarize the anthropogenic methane emission scenarios on earth and discuss the application potential of photocatalytic methane conversion. Finally, challenges and future directions for photocatalytic methane conversion are presented.

Nanoarchitectonics on Z-scheme and Mott-Schottky heterostructure for photocatalytic water oxidation via dual-cascade charge-transfer pathways

The bottleneck for water splitting to generate hydrogen fuel is the sluggish oxidation of water. Even though the monoclinic-BiVO₄ (m-BiVO₄)-based heterostructure has been widely applied for water oxidation, carrier recombination on dual surfaces of the m-BiVO₄ component have not been fully resolved by a single heterojunction. Inspired by natural photosynthesis, we established an m-BiVO₄/carbon nitride (C₃N₄) Z-scheme heterostructure based on the m-BiVO₄/reduced graphene oxide (rGO) Mott-Schottky heterostructure, constructing the face-contact C₃N₄/m-BiVO₄/rGO (CNBG) ternary composite to remove excessive surface recombination during water oxidation. The rGO can accumulate photogenerated electrons from m-BiVO₄ through a high conductivity region over the heterointerface, with the electrons then prone to diffuse along a highly conductive carbon network. In an internal electric field at the heterointerface of m-BiVO₄/C₃N₄, the low-energy electrons and holes are rapidly consumed under irradiation. Therefore, spatial separation of electron-hole pairs occurs, and strong redox potentials are maintained by the Z-scheme electron transfer. These advantages endow the CNBG ternary composite with over 193% growth in O₂ yield, and a remarkable rise in ·OH and ·O₂^- radicals, compared to the m-BiVO₄/rGO binary composite. This work shows a novel perspective for rationally integrating Z-scheme and Mott-Schottky heterostructures in the water oxidation reaction.

Photochemical and electrochemical co-regulation of the BiVO4 photoanode for water splitting

A novel pretreatment strategy that can regulate the amount of oxygen vacancies (O_vac) across the wormlike-BiVO₄ photoanode by photochemical and electrochemical co-processing. Upon decorating NiFeO_x as an oxygen evolution cocatalyst for promoting the surface oxidation kinetics, a record-high photocurrent density of 6.42 mA cm^-2 is obtained at 1.23 vs. RHE (100 mW cm^-2).

A BiVO4 Photoanode with a VOx Layer Bearing Oxygen Vacancies Offers Improved Charge Transfer and Oxygen Evolution Kinetics in Photoelectrochemical Water Splitting

Sluggish oxygen evolution kinetics are one of the key limitations of bismuth vanadate (BiVO₄ ) photoanodes for efficient photoelectrochemical (PEC) water splitting. To address this issue, we report a vanadium oxide (VO_x ) with enriched oxygen vacancies conformally grown on BiVO₄ photoanodes by a simple photo-assisted electrodeposition process. The optimized BiVO₄ /VO_x photoanode exhibits a photocurrent density of 6.29 mA cm^-2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination, which is ca. 385 % as high as that of its pristine counterpart. A high charge-transfer efficiency of 96 % is achieved and stable PEC water splitting is realized, with a photocurrent retention rate of 88.3 % upon 40 h of testing. The excellent PEC performance is attributed to the presence of oxygen vacancies in VO_x that forms undercoordinated sites, which strengthen the adsorption of water molecules onto the active sites and promote charge transfer during the oxygen evolution reaction. This work demonstrates the potential of vanadium-based catalysts for PEC water oxidation.

Photochemically Etching BiVO4 to Construct Asymmetric Heterojunction of BiVO4 /BiOx Showing Efficient Photoelectrochemical Water Splitting

BiVO₄ as a promising semiconductor candidate of the photoanode for solar driven water oxidation always suffers from poor charge carrier transport property and photo-induced self-corrosion. Herein, by intentionally taking advantage of the photo-induced self-corrosion process, a controllable photochemical etching method is developed to rationally construct a photoanode of BiVO₄ /BiO_x asymmetric heterojunction from faceted BiVO₄ crystal arrays. Compared with the BiVO₄ photoanode, the resulting BiVO₄ /BiO_x photoanode gains over three times enhancement in short-circuit photocurrent density (≈3.2 mA cm^-2 ) and ≈75 mV negative shift of photocurrent onset potential. This is due to the formation of the strong interacted homologous heterojunction, which promotes photo-carrier separation and enlarges photovoltage across the interface. Remarkably, the photocurrent density can remain at ≈2.0 mA cm^-2 even after 12 h consecutive operation, while only ≈0.1 mA cm^-2 is left for the control photoanode of BiVO₄ . Moreover, the Faraday efficiency for water splitting is determined to be nearly 100% for the BiVO₄ /BiO_x photoanode. The controllable photochemical etching process may shed light on the construction of homologous heterojunction on other photoelectrode materials that have similar properties to BiVO₄ .

Insight into the Crystal Facet Effect of {101} and {100} Facets of CeVO4 in the Photochemical Property and Photocatalysis

To investigate the photochemical property of specific crystal facets, two well-defined CeVO₄ dodecahedrons with exposed {101} and {100} facets are prepared, which have distinguishing appearances and unequal {101}/{100} area ratios (A_{101}/A_{100}), i.e., compressed dodecahedra (CeVO₄ CD, A_{101}/A_{100} ≈ 1) and elongated dodecahedra (CeVO₄ ED, A_{101}/A_{100} ≈ 0.3). During the visible-light-irradiated process, the {101} and {100} facets are certified to selectively deposit photogenerated holes (h⁺) and electrons (e^-), thus exhibiting the photooxidability and photoreducibility, respectively. Meanwhile, a surface heterojunction could form at the adjacent facet interface and facilitate the spatial separation of carriers. Benefiting from the large exposure extent of the {101} facet and the rational A_{101}/A_{100} (∼1), the CeVO₄ CD shows a superior photocatalytic performance for the degradation of tetracycline to the CeVO₄ ED. Finally, simulation calculations reveal that the energy deviations of the valence band (VB) and conduction band (CB) between CeVO₄{101} and CeVO₄{100} impel the photogenerated h⁺ and e^- to transfer in opposite directions, resulting in the facet-dependent photoactivity of the CeVO₄ dodecahedron.

The role of crystal facets and disorder on photo-electrosynthesis

Photoelectrochemistry has the potential to play a crucial role in the storage of solar energy and the realisation of a circular economy. From a chemical viewpoint, achieving high conversion efficiencies requires subtle control of the catalyst surface and its interaction with the electrolyte. Traditionally, such control has been hard to achieve in the complex multinary oxides used in PEC devices and consequently the mechanisms by which surface exposed facets influence light-driven catalysts are poorly understood. Yet, this understanding is critical to further improve conversion yields and fine-tune reaction selectivities. Here, we review the impact that crystal facets and disorder have on photoelectrochemical reactivity. In particular, we discuss how the crystal orientation influences the energetics of the surface, the existence of defects and the transport of reactive charges, ultimately dictating the PEC activity. Moreover, we evaluate how facet stability dictates the tendency of the solid to undergo reconstructions during catalytic processes and highlight the experimental and computational challenges that must be overcome to characterise the role of the exposed facets and disorder in catalytic performance.

Photocatalytic Degradation of Tetracycline under Visible Light Irradiation on BiVO4 Microballs Modified with Noble Metals

Monoclinic scheelite bismuth vanadate (BVO) microballs were prepared by a facile hydrothermal method and subsequently modified with 2 wt% of noble metals (NM = Au, Ag, Cu, Pt and Pd) by a photodeposition route. All materials were characterized by diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The photocatalytic performance was investigated by degradation of tetracycline antibiotic under visible light irradiation. Moreover, photocurrent generation under UV/vis was also examined. It was found that BVO modification with all tested NMs resulted in a significant improvement in photocatalytic performance. The highest activity was obtained for Cu/BVO with mainly oxidized forms of copper. Based on scavenger tests (∙O2− and ∙OH as the main responsible species for TC degradation) and redox properties, it was proposed that the Z-scheme mechanism between copper oxides and BVO was responsible for enhanced photocatalytic activity. However, the co-participation of zero-valent forms of NMs should also be considered, either as electron scavengers, plasmonic sensitizers or conductors. Presented data reveal that porous microballs, highly attractive for practical applications due to micro-sized diameter and efficient light harvesting inside the structure, could be efficiently used for environmental and energy purposes under solar radiation.

Surface Modification of 2D Photocatalysts for Solar Energy Conversion

2D materials show many particular properties, such as high surface-to-volume ratio, high anisotropic degree, and adjustable chemical functionality. These unique properties in 2D materials have sparked immense interest due to their applications in photocatalytic systems, resulting in significantly enhanced light capture, charge-transfer kinetics, and surface reaction. Herein, the research progress in 2D photocatalysts based on varied compositions and functions, followed by specific surface modification strategies, is introduced. Fundamental principles focusing on light harvesting, charge separation, and molecular adsorption/activation in the 2D-material-based photocatalytic system are systemically explored. The examples described here detail the use of 2D materials in various photocatalytic energy-conversion systems, including water splitting, carbon dioxide reduction, nitrogen fixation, hydrogen peroxide production, and organic synthesis. Finally, by elaborating the challenges and possible solutions for developing these 2D materials, the review is expected to provide some inspiration for the future research of 2D materials used on efficient photocatalytic energy conversions.

Synergetic Nanoarchitectonics of Defects and Cocatalysts in Oxygen-Vacancy-Rich BiVO4/reduced graphene oxide Mott-Schottky Heterostructures for Photocatalytic Water Oxidation

Water oxidation process is a pivotal step of photosynthesis and stimulates the progress of high-performance catalysts for renewable fuel production. Despite the performance benefit of cocatalysts, defect engineering holds promise to settle inherent limitations of semiconductors aiming at sluggish water oxidation. Here, we modify the in situ growth pathway of monoclinic BiVO₄ (m-BiVO₄) on reduced graphene oxide (rGO), constructing abundant surface oxygen vacancies (O_V)-incorporated m-BiVO₄/rGO heterostructure toward water oxidation reaction under visible light. Owing to the O_V in the m-BiVO₄ component, a vacancy-related defect level allows more electrons to be photoexcited by low-energy photons to cause the electron transition, boosting photoabsorption as well as photoexcitation. Besides, the O_V can reinforce surface adsorption and reduce the dissociation energy of water molecules. Particularly because of the synergy of O_V and cocatalyst rGO, the O_V functions as electron-trapped sites to facilitate the carrier separation; the rGO not only receives electrons from m-BiVO₄ promoted by internal electric field over Mott-Schottky heterostructures but also spurs further electron diffusion along a highly conductive carbon network. These merits enable the O_V-incorporated m-BiVO₄/rGO heterostructure with an over 209% growth in O₂ yield relative to the counterpart. The increased performance is also validated by the significant rise of ^•OH radicals and ^•O₂^- radicals. The current work paves a novel avenue for the integration of defect engineering and cocatalyst coupling in artificial photosynthesis.

Recent Progress in the Synthesis and Applications of Composite Photocatalysts: A Critical Review

Photocatalysis is an advanced technique that transforms solar energy into sustainable fuels and oxidizes pollutants via the aid of semiconductor photocatalysts. The main scientific and technological challenges for effective photocatalysis are the stability, robustness, and efficiency of semiconductor photocatalysts. For practical applications, researchers are trying to develop highly efficient and stable photocatalysts. Since the literature is highly scattered, it is urgent to write a critical review that summarizes the state-of-the-art progress in the design of a variety of semiconductor composite photocatalysts for energy and environmental applications. Herein, a comprehensive review is presented that summarizes an overview, history, mechanism, advantages, and challenges of semiconductor photocatalysis. Further, the recent advancements in the design of heterostructure photocatalysts including alloy quantum dots based composites, carbon based composites including carbon nanotubes, carbon quantum dots, graphitic carbon nitride, and graphene, covalent-organic frameworks based composites, metal based composites including metal carbides, metal halide perovskites, metal nitrides, metal oxides, metal phosphides, and metal sulfides, metal-organic frameworks based composites, plasmonic materials based composites and single atom based composites for CO₂ conversion, H₂ evolution, and pollutants oxidation are discussed elaborately. Finally, perspectives for further improvement in the design of composite materials for efficient photocatalysis are provided.

Combined Schottky junction and doping effect in CdxZn1-xS@Au/BiVO4 Z-Scheme photocatalyst with boosted carriers charge separation for CO2 reduction by H2O

A Z-scheme photosystems combining Schottky junction and loading of applicable bandgap semiconductor is beneficial for enhancing the charge carriers' separation/transfer as well as maintain their excellent redox ability. Here, Cd_xZn_1-xS@Au was in-situ deposited on the (010) facets of BiVO₄ taking Au as a bridge for constructing a sandwich structure Cd_xZn_1-xS@Au/BiVO₄ Z-scheme photocatalyst. The electrons in BiVO₄ (010) migrate unidirectionally to Au nanoparticles across the Schottky junction and effectively suppress opposite electrons flow, then be captured by the excited holes in Cd_xZn_1-xS. Furthermore, Zn-doping also contributes to an appropriate redox ability and charge carriers separation. Benefiting from the dual-facilitated effects, the ternary Cd_xZn_1-xS@Au/BiVO₄ exhibited superior photocatalytic activity for CO₂ reduction under visible light irradiation using H₂O as a reducing agent, as compared with CdS and CdS@Au/BiVO₄. Furthermore, the intermediate product HCOO* fixed on the surface of Cd_xZn_1-xS@Au/BiVO₄ is identified by in-situ FT-IR, playing a key role in the conversion of CO₂ to CO and then improve photocatalytic selectivity.

Thin p-type NiO nanosheet modified peanut-shaped monoclinic BiVO4 for enhanced charge separation and photocatalytic activities

Typical NiO nanosheet coated BVO type-II composite heterostructure can effectively promote the space separation of charge and improve the photocatalytic performance.

Enhanced HClO production from chloride by dual cocatalyst loaded WO3 under visible light

Photocatalytic production of HClO was improved more than twice by co-loading of Mn compared to the standard Pt/WO3.

Temperature Effect on Photoelectrochemical Water Splitting: A Model Study Based on BiVO4 Photoanodes

Photoelectrochemical (PEC) water splitting is typically studied at room temperature. In this work, the temperature effect on PEC water splitting is studied using crystalline BiVO₄ thin film photoanode as a model system. Systematic temperature-dependent electrochemical study demonstrates that the PEC activity is boosted at elevated electrolyte temperatures and indicates that thermal energy plays a main role in improving charge carrier transport in the bulk of BiVO₄. Irreversible surface reconstruction is observed after PEC reactions at elevated temperature in the presence of hole scavengers, with regularly spaced stripes emerging on BiVO₄ grains. The surface-reconstructed photoanode exhibits up to 40% improvement in photocurrent densities and ∼ 0.25 V shift of photocurrent onset to favorable direction. Detailed investigation shows the formation of an amorphous layer without stoichiometric change at the reconstructed surface. This work provides insights of the temperature effect on the photoelectrode in solar water splitting and reveals the non-negligible effect of hole scavengers in photoelectrochemical measurement.

Vacancy defect engineering of BiVO4 photoanodes for photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting has been regarded as a promising technology for sustainable hydrogen production. The development of efficient photoelectrode materials is the key to improve the solar-to-hydrogen (STH) conversion efficiency towards practical application. Bismuth vanadate (BiVO₄) is one of the most promising photoanode materials with the advantages of visible light absorption, good chemical stability, nontoxic feature, and low cost. However, the PEC performance of BiVO₄ photoanodes is limited by the relatively short hole diffusion length and poor electron transport properties. The recent rapid development of vacancy defect engineering has significantly improved the PEC performance of BiVO₄. In this review article, the fundamental properties of BiVO₄ are presented, followed by an overview of the methods for creating different kinds of vacancy defects in BiVO₄ photoanodes. Then, the roles of vacancy defects in tuning the electronic structure, promoting charge separation, and increasing surface photoreaction kinetics of BiVO₄ photoanodes are critically discussed. Finally, the major challenges and some encouraging perspectives for future research on vacancy defect engineering of BiVO₄ photoanodes are presented, providing guidelines for the design of efficient BiVO₄ photoanodes for solar fuel production.

Morphology Engineering of BiVO4 with CoOx Derived from Cobalt-containing Polyoxometalate as Co-catalyst for Oxygen Evolution

Bismuth vanadate (BiVO₄ ) as a metal oxidation semiconductor has stimulated extensive attention in the photocatalytic water splitting field. However, the poor transport ability and easy recombination of charge carriers limit photocatalytic water oxidation activity of pure BiVO₄ . Herein, the photocatalytic activity of BiVO₄ is enhanced via adjusting its morphology and combination co-catalyst. First, the Cu-BiVO₄ was synthesized by copper doping to control the growth of {110} facet of BiVO₄ , which is regarded for the separation of photo-generated charge carriers. Then the CoO_x in-situ generated from K₆ [SiCo^II (H₂ O)W₁₁ O₃₉ ] ⋅ 16H₂ O was photo-deposited on Cu-BiVO₄ surface as co-catalyst to speed up reaction kinetics. Cu-BiVO₄ @CoO_x hybrid catalyst shows highest photocatalytic activity and best stability among all the prepared catalysts. Oxygen evolution is about 34.6 μmol in pH 4 acetic acid buffer under 420 nm LED irradiation, which is nearly 20 times higher than that of pure BiVO₄ . Apparent quantum efficiency (AQE) in 1 h and O₂ yield are 1.83% and 23.1%, respectively. O₂ evolution amount nearly maintains the original value even after 5 cycles.

Construction of quantum dots self-decorated BiVO4/reduced graphene hydrogel composite photocatalyst with improved photocatalytic performance for antibiotics degradation

In this study, we report the construction of a novel composite photocatalyst (BiVO₄/rGH) composed of quantum dots (QDs) self-decorated BiVO₄-nanoparticels (NPs) and reduced graphene hydrogel (rGH). The composite structures were prepared using an in-situ growth method. The BiVO₄/rGH composite photocatalysts exhibited excellent photocatalytic efficiency for the degradation of tetracycline hydrochloride (TCHCl). The promoted photocatalytic activity of the BiVO₄/rGH is attributed to the synergetic effects of the unique structure involving QDs self-decorated BiVO₄ NPs and a 3D network structure of rGH, which resulted in higher number of photogenerated charge carriers, surplus active sites, and enhanced charge separation. In addition, trapping measurements showed that ·O₂^- and h⁺, as the main active species, play a crucial role in the degradation of TCHCl over the composite photocatalyst. This study facilitates the design and construction of high efficiency hybrid photocatalysts with multifunctional materials for the removal of water pollutants.

The Thermodynamic Stability, Electronic and Photocatalytic Properties of the ZnWO4(100) Surface as Predicted by Screened Hybrid Density Functional Theory

Zinc tungstate (ZnWO₄) is an outstanding photocatalyst for water splitting and organic contaminant degradation under visible light irradiation. Surface termination stabilities are significant for understanding the photochemical oxidation and reactions on the ZnWO₄ surface. Based on density functional theory, we calculated the thermodynamic stability of possible surface terminations for ZnWO₄(100). The surface stability phase diagrams show that the Zn₂O₄-Zn₈W₆O₂₈, W₂O₄-Zn₈W₁₀O₃₆, and Zn₂-Zn₈W₆O₂₄ terminations of ZnWO₄(100) can be stabilized under certain thermodynamic equilibrium conditions. The electronic structures for these three possible stability surface terminations are calculated based on the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional to give dependable theoretical band gap values. It is found that the surface states of W₂O₄-Zn₈W₁₀O₃₆ termination are in the band gap, which shows a delocalized performance. The calculated absorption coefficients of W₂O₄-Zn₈W₁₀O₃₆ termination show stronger absorption than bulk ZnWO₄ in the visible-light region. The band edge calculation shows that the valence band maximum and conduction band minimum of the W₂O₄-Zn₈W₁₀O₃₆ termination can fulfill the hydrogen evolution reaction and oxygen evolution reaction requirements at the same time. Furthermore, work functions are extraordinarily distinct for various surface terminations. This result suggests that the ZnWO₄-based direct Z-scheme heterostructure can be controlled by obtaining the thermodynamically preferred surface termination under suitable conditions. Our results can predict ZnWO₄(100) surface structures and properties under the entire range of accessible environmental conditions.

Highly efficient BiVO4single-crystal nanosheets with dual modification: phosphorus doping and selective Ag modification

BiVO₄, a visible-light response photocatalyst, has shown tremendous potential because of abundant raw material sources, good stability and low cost. There exist some limitations for further applicaitions due to poor capability to separate electron-hole pairs. In fact, a single-component modification strategy is barely adequate to obtain highly efficient photocatalytic performance. In this work, P substituted some of the V atoms from VO₄oxoanions, namely P was doped into the V sites in the host lattice of BiVO₄by a hydrothermal route. Meanwhile, Ag as an attractive and efficient electron-cocatalyst was selectively modified on the (010) facet of BiVO₄nanosheets via facile photo-deposition. As a result, the obtained dually modified BiVO₄sheets exhibited enhanced photocatalytic degradation property of methylene blue (MB). In detail, photocatalytic rate constant (k) was 2.285 min^-1g^-1, which was 2.78 times higher than pristine BiVO₄nanosheets. Actually, P-doping favored the formation of O vacancies, led to more charge carriers, and facilitated photocatalytic reaction. On the other hand, metallic Ag loaded on (010) facet effectively transferred photogenerated electrons, which consequently helped electron-hole pairs separation. The present work may enlighten new thoughts for smart design and controllable synthesis of highly efficient photocatalytic materials.

Surface defects induced charge imbalance for boosting charge separation and solar-driven photocatalytic hydrogen evolution

Low charge separation efficiency of semiconductor materials is the main obstacle for high-performance photocatalyst. Herein, we report surface defects engineered uniform mesoporous TiO₂ nanospheres (DMTNSs) through surfactant-mediated self-assembly solvothermal approach combined with hydrogenation strategy to promote charge separation. The surface defects induced charge imbalance result in the formation of built-in field, which can promote photogenerated charge separation efficiently and be confirmed by experimental and density functional theory (DFT) calculations. Under AM 1.5G irradiation, the photocatalytic hydrogen evolution of DMTNSs is ~3.34 mmol h^-1 g^-1, almost 3.5 times higher than that of pristine non-defective TiO₂ nanospheres (0.97 mmol h^-1 g^-1), due to the engineered surface defects narrowing the bandgap (~3.01 eV) and inducing charge imbalance to boost spatial charge separation and extend visible-light response. The defect induced charge imbalance strategy opens a new valuable perspective for fabricating other high-efficient oxide photocatalysts.

Facet-selective charge separation in two-dimensional bismuth-based photocatalysts

In this review, we summarize recent advances in the facet design of bismuth-based single-crystal plates based on facet-dependent charge separation for photocatalytic reactions, and the manipulation of the spatial charge separation is highlighted.

Self-induced synthesis under neutral conditions and novel visible light photocatalytic activity of Ag4V2O7 polyoxometalate

Ag₄V₂O₇ POM with a nanorod-bundle structure was designed under neutral conditions, which showed good visible photodegradation performance against chloramphenicol.

Crystal Facet-Dependent CO2 Photoreduction over Porous ZnO Nanocatalysts

Crystal facet engineering provides a promising approach to tailor the performance of catalysts because of the close relationship between the photocatalytic activity and the surface atomic and electronic structures. An in-depth understanding mechanism of crystal facet-dependent CO₂ photoreduction is still an open question. Herein, two different types of porous ZnO nanocatalysts are used as model photocatalysts for the investigation, which are, respectively, with exposed {110} and {001} facets. The porous ZnO with an exposed {110} facet exhibits superior photocatalytic activity to the one with the {001} facet. Various influencing factors have been thoroughly studied both theoretically and/or experimentally, including light harvesting (i.e., band gap), reduction capability (potential of conduction band), crystallinity, CO₂ adsorption ability, CO₂ activation, and charge separation. The major influencing factors are eventually figured out based on the experimental and calculation results. The product selectivity and the influence of the hole scavenger can be explained too. Our work may pave a way for directing the future rational design of efficient photocatalysts for CO₂ reduction.

Functional facet isotype junction and semiconductor/r-GO minor Schottky barrier tailored In2S3@r-GO@(040/110)-BiVO4 ternary hybrid

Efficient interfacial exciton transfer and separation have been regarded as the foremost confront of semiconductor oriented photocatalysis. The simultaneous discovery of crystal facet isotype heterojunction across the (040)-reduction and (110)-oxidation facet of monoclinic scheelite BiVO₄ crystal; and Schottky junction at the interfacial region of BiVO₄ crystal with well-exposed functional (040) facet and r-GO sheets has been reflected as an efficient electron injection route. In this context lucrative architecture of a high productive all-solid-state Z-scheme charge transfer dynamics In₂S₃@r-GO@(040/110)-BiVO₄ isotype ternary hybrid photocatalyst was carried out and well-validated by FESEM and HRTEM analyses. Photoelectrochemical measurements have revealed that the accumulated photo-electrons over the exposed (040)-crystal facet of BiVO₄ truncated bipyramid easily cross the minor Schottky junction to expedite the unidirectional injection to the π-π conjugated two-dimensional planar r-GO structure. Besides, subsequent trapping of the injected electrons by the photoinduced holes of In₂S₃ leading to a superior charge carrier separation in the material, validated by PL, EIS, Mott-Schottky, and transient photocurrent analysis. Perceptibly, this intimate interfacial interacted crystal facet dependent electron shuttle provided a longer life span electrons and holes to settle in the conduction band of In₂S₃ and valence band of (110)-BiVO₄, respectively, for elevated photo-activity efficiency. The In₂S₃@r-GO@(040/110)-BiVO₄ ternary hybrid contributes 89.7% of Ciprofloxacin (CIP) detoxification in 150 min and 885.43 µmol of O₂ evolution in 120 min. More in, the constructive interrelations of resultant Physico-chemical, photoelectrochemical, and augmented photocatalytic redox efficiency were well-illustrated. This unique association semiconductor ternary hybrid photocatalyst via metal-free mediating agent crystal-facet sandwich structure will provide a scientific innovative basis for rational design and realization of advanced Z-scheme photocatalytic system for energy and environment application.

In Situ Grown Single-Atom Cobalt on Polymeric Carbon Nitride with Bidentate Ligand for Efficient Photocatalytic Degradation of Refractory Antibiotics

Semiconductor photocatalysis is a promising technology to tackle refractory antibiotics contamination in water. Herein, a facile in situ growth strategy is developed to implant single-atom cobalt in polymeric carbon nitride (pCN) via the bidentate ligand for efficient photocatalytic degradation of oxytetracycline (OTC). The atomic characterizations indicate that single-atom cobalt is successfully anchored on pCN by covalently forming the CoO bond and CoN bond, which will strengthen the interaction between single-atom cobalt and pCN. This single-atom cobalt can efficiently expand optical absorption, increase electron density, facilitate charge separation and transfer, and promote OTC degradation. As the optimal sample, Co(1.28%)pCN presents an outstanding apparent rate constant for OTC degradation (0.038 min^-1 ) under visible light irradiation, which is about 3.7 times than that of the pristine pCN. The electron spin resonance (ESR) tests and reactive species trapping experiments demonstrate that the ¹ O₂ , h⁺ , •O₂^- , and •OH are responsible for OTC degradation. This work develops a new way to construct single-atom-modified pCN and provides a green and highly efficient strategy for refractory antibiotics removal.

Photocatalytic Oxygen Evolution from Water Splitting

Photocatalytic water splitting has attracted a lot of attention in recent years, and O2 evolution is the decisive step owing to the complex four-electrons reaction process. Though many studies have been conducted, it is necessary to systematically summarize and introduce the research on photocatalytic O2 evolution, and thus a systematic review is needed. First, the corresponding principles about O2 evolution and some urgently encountered issues based on the fundamentals of photocatalytic water splitting are introduced. Then, several types of classical water oxidation photocatalysts, including TiO2, BiVO4, WO3, α-Fe2O3, and some newly developed ones, such as Sillén-Aurivillius perovskites, porphyrins, metal-organic frameworks, etc., are highlighted in detail, in terms of their crystal structures, synthetic approaches, and morphologies. Third, diverse strategies for O2 evolution activity improvement via enhancing photoabsorption and charge separation are presented, including the cocatalysts loading, heterojunction construction, doping and vacancy formation, and other strategies. Finally, the key challenges and future prospects with regard to photocatalytic O2 evolution are proposed. The purpose of this review is to provide a timely summary and guideline for the future research works for O2 evolution.