Photocatalytic water splitting by N-TiO2 on MgO (111) with exceptional quantum efficiencies at elevated temperatures

TiN/anatase/rutile phase junction obtained by in-situ thermal transformation for efficient photothermal-assisted photocatalytic hydrogen generation

Phase junctions exhibit great potential in photocatalytic energy conversion, yet the narrow light response region and inefficient charge transfer limit their photocatalytic performance. Herein, an anatase/rutile phase junction modified by plasmonic TiN and oxygen vacancies (TiN/(A-R-TiO2-Ov)) is prepared through an in-situ thermal transformation from TiN for efficient photothermal-assisted photocatalytic hydrogen production for the first time. The content of TiN, oxygen vacancies, and phase components in TiN/(A-R-TiO2-Ov) hybrids can be well-adjusted by tuning the heating time. The as-prepared photocatalysts display a large specific area and wide light absorption due to the synergistic effect of plasmonic excitation, oxygen vacancies, and bandgap excitations. Meanwhile, the multi-interfaces between TiN, anatase, and rutile provide built-in electric fields for efficient separation of photoinduced carriers and hot electron injection via ohmic contact and type-Ⅱ band arrangement. As a result, the TiN/(A-R-TiO2-Ov) photocatalyst shows an excellent photocatalytic hydrogen generation rate of 15.07 mmol/g/h, which is 20.6 times higher than that of titanium dioxide P25. Moreover, temperature-dependent photocatalytic tests reveal that the excellent photothermal conversion caused by plasmonic heating and crystal lattice vibrations in TiN/(A-R-TiO2-Ov) has about 25 % enhancement in photocatalysis (18.84 mmol/g/h). This work provides new inspiration for developing high-performance photocatalysts by optimizing charge transfer and photothermal conversion.

Intramolecular Quaternary Carbon Nitride Homojunction for Enhanced Visible Light Hydrogen Production

In this work, an intramolecular carbon nitride (CN)-based quaternary homojunction functionalized with pyridine rings is prepared via an in situ alkali-assisted copolymerization strategy of bulk CN and 2-aminopyridine for efficient visible light hydrogen generation. In the obtained structure, triazine-based CN (TCN), heptazine-based CN (HCN), pyridine unit incorporated TCN, and pyridine ring inserted HCN constitute a special multicomponent system and form a built-in electric field between the crystalline semiconductors by the arrangement of energy band levels. The electron-withdrawing function of the conjugated heterocycle can trigger the skeleton delocalization and edge induction effect. Highly accelerated photoelectron-hole transfer rates via multi-stepwise charge migration pathways are achieved by the synergistic effect of the functional group modification and molecular quaternary homojunction. Under the addition of 5 mg 2-aminopyridine, the resulting homojunction framework exhibits a significantly improved hydrogen evolution rate of 6.64 mmol g-1 h-1 with an apparent quantum efficiency of 12.27% at 420 nm. Further, the catalyst verifies its potential commercial value since it can produce hydrogen from various real water environments. This study provides a reliable way for the rational design and fabrication of intramolecular multi-homojunction to obtain high-efficient photocatalytic reactions.

Stability and degradation of (oxy)nitride photocatalysts for solar water splitting

Advancing towards alternative technologies for the sustainable production of hydrogen is a necessity for the successful integration of this potentially green fuel in the future. Photocatalytic and photoelectrochemical water splitting are promising concepts in this context. Over the past decades, researchers have successfully explored several materials classes, such as oxides, nitrides, and oxynitrides, in their quest for suitable photocatalysts with a focus on reaching higher efficiencies. However, to pave the way towards practicability, understanding degradation processes and reaching stability is essential, a domain where research has been scarcer. This perspective aims at providing an overview on recent progress concerning stability and degradation with a focus on (oxy)nitride photocatalysts and at providing insights into the opportunities and challenges coming along with the investigation of degradation processes and the attempts to improve the stability of photocatalysts.

An MgO passivation layer and hydrotalcite derived spinel Co2AlO4 synergically promote photoelectrochemical water oxidation conducted using BiVO4-based photoanodes

MxCo3-xO4 co-catalysed photoanodes with high potential for improvement in PEC water-oxidizing properties are reported. However, it is difficult to control the recombination of photogenerated carriers at the interface between the catalyst and cocatalyst. Here, an ultra-thin MgO passivation layer was introduced into the MxCo3-xO4/BiVO4 coupling system to construct a ternary composite photoanode Co2AlO4/MgO/BiVO4. The photocurrent density of the electrode is 3.52 mA cm-2, which is 3.2 times that of BiVO4 (at 1.23 V vs. RHE). The photocurrent is practically increased by 0.86 mA cm-2 and 1.56 mA cm-2 in comparison with that of Co2AlO4/BiVO4 and MgO/BiVO4 electrodes, respectively. Meanwhile, the Co2AlO4/MgO/BiVO4 electrode has the highest charge separation efficiency, the lowest charge transfer resistance (Rct) and best stability. The excellent PEC performance could be attributed to the inhibitive effect provided by the MgO passivation layer that efficaciously suppresses the electron-hole recombination at the interface and drives the hole transfer outward, which is induced by Co2AlO4 to capture the electrode/electrolyte interface for efficient water oxidation reaction. In order to understand the origin of this improvement, first-principles calculations with density functional theory (DFT) were performed. The theoretical investigation converges to our experimental results. This work proposes a novel idea for restraining the recombination of photogenerated carriers between interfaces and the rational design of efficient photoanodes.

Catalyzing Artificial Photosynthesis with TiO2 Heterostructures and Hybrids: Emerging Trends in a Classical yet Contemporary Photocatalyst

Titanium dioxide (TiO2) stands out as a versatile transition-metal oxide with applications ranging from energy conversion/storage and environmental remediation to sensors and optoelectronics. While extensively researched for these emerging applications, TiO2 has also achieved commercial success in various fields including paints, inks, pharmaceuticals, food additives, and advanced medicine. Thanks to the tunability of their structural, morphological, optical, and electronic characteristics, TiO2 nanomaterials are among the most researched engineering materials. Besides these inherent advantages, the low cost, low toxicity, and biocompatibility of TiO2 nanomaterials position them as a sustainable choice of functional materials for energy conversion. Although TiO2 is a classical photocatalyst well-known for its structural stability and high surface activity, TiO2-based photocatalysis is still an active area of research particularly in the context of catalyzing artificial photosynthesis. This review provides a comprehensive overview of the latest developments and emerging trends in TiO2 heterostructures and hybrids for artificial photosynthesis. It begins by discussing the common synthesis methods for TiO2 nanomaterials, including hydrothermal synthesis and sol-gel synthesis. It then delves into TiO2 nanomaterials and their photocatalytic mechanisms, highlighting the key advancements that have been made in recent years. The strategies to enhance the photocatalytic efficiency of TiO2, including surface modification, doping modulation, heterojunction construction, and synergy of composite materials, with a specific emphasis on their applications in artificial photosynthesis, are discussed. TiO2-based heterostructures and hybrids present exciting opportunities for catalyzing solar fuel production, organic degradation, and CO2 reduction via artificial photosynthesis. This review offers an overview of the latest trends and advancements, while also highlighting the ongoing challenges and prospects for future developments in this classical yet rapidly evolving field.

TiO2 nanotube arrays-based photoelectrocatalyst: Tri-Doping engineering and carbon coating engineering boosting visible activity, and stable hydrogen evolution

The integration of non-metallic doping and carbon coating for TiO2-based photoelectrocatalysts can be recognized as a promising strategy to enhance their hydrogen production performance. To this end, this study explored the carbon coating engineering to induce stable multi-element doping with an aim to develop high-performance TiO2 nanotube array-based photoelectrocatalysts. The resulting structures consisted of carbon-nitrogen-sulfur-tri-doped TiO2 nanotube arrays with a nitrogen-sulfur-codoped carbon coating (CNS-TNTA/NSC). The fabrication process involved a one-step, low-cost strategy of the carbon-coated tridoped reaction confined in vacuum space, utilizing polymer thiourea sealed in a controlled environment. Compared the photocurrent density of CNS-TNTA/NSC with pristine TNTA, the photocurrent enhancement of approximately 18.3-fold under simulated sunlight and a remarkable increase of 32.8-fold under simulated visible light conditions. The enhanced photocatalytic activity under visible light was ascribed to two factors: First, C, N, and S tri-doping and Ti3+ created a diverse array of impurity energy levels within the band gap, which synergistically narrowed the band gap and further enhanced response to the visible light range. Second, the presence of a carbon coating shell doped with N and S can greatly promote electron transfer and efficient electron-hole pair separation. This study could provide significant insights concerning the design of sophisticated photoanodes.

Artificial Photosynthetic System with Spatial Dual Reduction Site Enabling Enhanced Solar Hydrogen Production

Although S-scheme artificial photosynthesis shows promise for photocatalytic hydrogen production, traditional methods often overly concentrate on a single reduction site. This limitation results in inadequate redox capability and inefficient charge separation, which hampers the efficiency of the photocatalytic hydrogen evolution reaction. To overcome this limitation, a double S-scheme system is proposed that leverages dual reduction sites, thereby preserving energetic photo-electrons and holes to enhance apparent quantum efficiency. The design features a double S-scheme junction consisting of CdS nanospheres decorated with anatase TiO2 nanoparticles coupled with graphitic C3 N4 . The as-prepared catalyst exhibits a hydrogen evolution rate of 26.84 mmol g-1  h-1 and an apparent quantum efficiency of 40.2% at 365 nm. This enhanced photocatalytic hydrogen evolution is ascribed to the efficient charge separation and transport induced by the double S-scheme. Both theoretical calculations and comprehensive spectroscopy tests (both in situ and ex situ) affirm the efficient charge transport across the catalyst interface. Moreover, substituting the reduction-type catalyst CdS with other similar sulfides like ZnIn2 S4 , ZnS, MoS2 and In2 S3 further confirms the feasibility of the proposed double S-scheme configuration. The findings provide a pathway to designing more effective double S-scheme artificial photosynthetic systems, opening up fresh perspectives in enhancing photocatalytic hydrogen evolution performance.

Recent developments, advances and strategies in heterogeneous photocatalysts for water splitting

Photocatalytic water splitting (PWS) is an up-and-coming technology for generating sustainable fuel using light energy. Significant progress has been made in the developing of PWS innovations over recent years. In addition to various water-splitting (WS) systems, the focus has primarily been on one- and two-steps-excitation WS systems. These systems utilize singular or composite photocatalysts for WS, which is a simple, feasible, and cost-effective method for efficiently converting prevalent green energy into sustainable H2 energy on a large commercial scale. The proposed principle of charge confinement and transformation should be implemented dynamically by conjugating and stimulating the photocatalytic process while ensuring no unintentional connection at the interface. This study focuses on overall water splitting (OWS) using one/two-steps excitation and various techniques. It also discusses the current advancements in the development of new light-absorbing materials and provides perspectives and approaches for isolating photoinduced charges. This article explores multiple aspects of advancement, encompassing both chemical and physical changes, environmental factors, different photocatalyst types, and distinct parameters affecting PWS. Significant factors for achieving an efficient photocatalytic process under detrimental conditions, (e.g., strong light absorption, and synthesis of structures with a nanometer scale. Future research will focus on developing novel materials, investigating potential synthesis techniques, and improving existing high-energy raw materials. The endeavors aim is to enhance the efficiency of energy conversion, the absorption of radiation, and the coherence of physiochemical processes.

Photothermally driven decoupling of gas evolution at the solid-liquid interface for boosted photocatalytic hydrogen production

The slow mass transfer, especially the gas evolution process at the solid-liquid interface in photocatalytic water splitting, restricts the overall efficiency of the hydrogen evolution reaction. Here, we report a novel gas-solid photocatalytic reaction system by decoupling hydrogen generation from a traditional solid-liquid interface. The success relies on annealing commercial melamine sponge (AMS) for effective photothermal conversion that leads to rapid water evaporation. The vapor flows towards the photocatalyst covering the surface of the AMS and is split by the catalyst therein. This liquid-gas/gas-solid coupling system avoids the formation of photocatalytic bubbles at the solid-liquid interface, leading to significantly improved mass transfer and conversion. Utilizing CdS nanorods anchored by highly dispersed nickel atoms/clusters as a model photocatalyst, the highest hydrogen evolution rate from water splitting reaches 686.39 μmol h-1, which is 5.31 times that of the traditional solid-liquid-gas triphase system. The solar-to-hydrogen (STH) efficiency can be up to 2.06%. This study provides a new idea for the design and construction of efficient practical photocatalytic systems.

Pauling-Type Adsorption of O2 Induced by Heteroatom Doped ZnIn2 S4 for Boosted Solar-Driven H2 O2 Production

Breaking the trade-off between activity and selectivity has perennially been a formidable endeavor in the field of hydrogen peroxide (H2 O2 ) photosynthesis, especially the side-on configuration of oxygen (O2 ) on the catalyst surface will cause the cleavage of O-O bonds, which drastically hinders the H2 O2 production performance. Herein, we present an atomically heteroatom P doped ZnIn2 S4 catalyst with tunable oxygen adsorption configuration to accelerate the ORR kinetics essential for solar-driven H2 O2 production. Indeed, the spectroscopy characterizations (such as EXAFS and in situ FTIR) and DFT calculations reveal that heteroatom P doped ZnIn2 S4 at substitutional and interstitial sites, which not only optimizes the coordination environment of Zn active sites, but also facilitates electron transfer to the Zn sites and improves charge density, avoiding the breakage of O-O bonds and reducing the energy barriers to H2 O2 production. As a result, the oxygen adsorption configuration is regulated from side-on (Yeager-type) to end-on (Pauling-type), resulting in the accelerated ORR kinetics from 874.94 to 2107.66 μmol g-1  h-1 . This finding offers a new avenue toward strategic tailoring oxygen adsorption configuration by the rational design of doped photocatalyst.

Nanosized core-shell (NiFe2O4/TiO2) heterostructure for enhanced photodegradation against polycyclic aromatic hydrocarbons

The global level of attention has been raised for photocatalytic pollutant removal technologies for degrading organic pollutants because of rising concerns about their toxicity. In this study, NiFe2O4/TiO2 core shells and pure samples of NiFe2O4 and TiO2 were synthesized using the sol-gel process and used to degrade naphthalene which is one among the polycyclic aromatic hydrocarbons (PAHs) pollutant. The synthesized materials were evaluated using a variety of analytical techniques, and the typical NiFe2O4/TiO2 core-shell results showed good purity and a lack of other impurity structures. Through morphological characterization, the core-shell structure of NiFe2O4/TiO2 has been established. However, the activity of visible light degradation was boosted by the generation of hydroxyl radicals after the electron-hole pair was delayed. Additionally, a lower band gap in NiFe2O4/TiO2 than in pure materials promotes photocatalytic activity. Similarly, photocatalytic naphthalene elimination by the core-shell achieved 67% efficiency after 150 min of visible light exposure. Furthermore, the produced core-shell has a high magnetic property, making separation from the photo-irradiated solutions easier; as a result, recycling was likely successful up to three cycles. The photocatalytic mechanism of the NiFe2O4/TiO2 composite was proposed. This research could also be applied to the degradation of other polycyclic aromatic hydrocarbon contaminants.

Enhanced photocatalytic degradation of organic dye by CeO2/CNT/GO hybrid nanocomposites under UV light for wastewater treatment

Development of nanocomposites as efficient photocatalysts for the removal of hazardous organic pollutants is always in dire demand due to increase in water pollution. In this article, a facile sol-gel method has been used to synthesize cerium oxide (CeO2) nanoparticles followed by their decoration over multi-walled carbon nanotubes (CNTs) and graphene oxide (GO) to construct binary as well ternary hybrid nanocomposites using ultrasonic treatment. The oxygen vacancy defects have been depicted using X-ray photoelectron spectroscopy (XPS) that may result into improved photocatalytic efficiency. The ternary hybrid nanocomposites (CeO2/CNT/GO) showed excellent photocatalytic efficiency towards degradation of rose bengal (RB) dye up to 96.9% in 50 min. CNTs and GO provide the interfacial charge transfer which inhibits the electron-hole pair recombination. The results obtained here indicate that these composites can be effectively utilized as promising materials for the degradation of harmful organic pollutants for wastewater treatment.

Unravelling the interfacial water structure at the photocatalyst strontium titanate by sum frequency generation spectroscopy

The direct conversion of solar energy to hydrogen is considered as a possible method to produce carbon neutral hydrogen fuel. The mechanism of photocatalytic water splitting involves the chemical breakdown of water and re-assembly into hydrogen and oxygen at the interface of a photocatalyst. The selection rules of a suitable material are well established, but the fundamental understanding of the mechanisms, occurring at the interface between the catalyst and the water, remains missing. Using surface specific sum frequency generation spectroscopy, we present here characterisation of the interface between water and the photocatalyst strontium titanate (SrTiO3). We monitor the OH-stretching vibrations present at the interface. Their variations of intensities and frequencies as functions of isotopic dilution, pH and salt concentration provide information about the nature of the hydrogen bonding environment. We observe the presence of water molecules that flip their orientation at pH 5 indicating the point of zero charge of the SrTiO3 layer. These water molecules are oriented with their hydrogen away from the surface when the pH of the solutions is below 5 and pointing towards the surface when the pH is higher than 5. Besides, water molecules donating a H-bond to probably surface TiOH groups are observed at all pH.

Non-Lignin Constructing the Gas-Solid Interface for Enhancing the Photothermal Catalytic Water Vapor Splitting

The progress of solar-driven water-splitting technology has been impeded by the limited light response capability of semiconductor materials. Despite attempts to leverage nearly 50% of infrared radiation for photothermal synergy and catalytic reaction enhancement, heat loss during liquid phase reactions results in low energy conversion efficiency. Here, the photothermally driven catalytic water-splitting system, which designs K-SrTiO3 -loaded TiN silica wool at the water-air interface. Photocatalytic tests and density functional theory calculations demonstrate that the thermal effect transforms liquid water into water vapor, thereby reducing the reaction free energy of catalysts and improving the transmission rate of catalytic products. Hence, the hydrogen evolution rate reaches 275.46 mmol m-2  h-1 , and the solar-to-hydrogen (STH) efficiency is 1.81% under 1 sun irradiation in this gas-solid system, which is more than twice that of liquid water splitting. This novel photothermal catalytic pathway, which involves a coupled reaction of water evaporation and water splitting, is anticipated to broaden the utilization range of the solar spectrum and significantly enhance the conversion efficiency of STH.

Enhancing Photocatalytic Hydrogen Evolution by Synergistic Benefits of MXene Cocatalysis and Homo-Interface Engineering

Photocatalytic water splitting holds great promise as a sustainable and cost-effectiveness alternative for the production of hydrogen. Nevertheless, the practical implementation of this strategy is hindered by suboptimal visible light utilization and sluggish charge carrier dynamics, leading to low yield. MXene is a promising cocatalyst due to its high conductivity, abundance of active sites, tunable terminal functional groups, and great specific surface area. Homo-interface has perfect lattice matching and uniform composition, which are more conducive to photogenerated carriers' separation and migration. In this study, a novel ternary heterogeneous photocatalyst, a-TiO2 /H-TiO2 /Ti3 C2 MXene (MXTi), is presented using an electrostatic self-assembly method. Compared to commercial P25, pristine anatase, and rutile TiO2 , as-prepared MXTi exhibit exceptional photocatalytic hydrogen evolution performance, achieving a rate of 0.387 mmol h-1 . The significant improvement is attributable to the synergistic effect of homo-interface engineering and Ti3 C2 MXene, which leads to widened light absorption and efficient carrier transportation. The findings highlight the potential of interface engineering and MXene cocatalyst loading as a proactive approach to enhance the performance of photocatalytic water splitting, paving the way for more sustainable and efficient hydrogen production.

Observation of inherited plasmonic properties of TiN in titanium oxynitride (TiOxNy) for solar-drive photocatalytic applications

This study demonstrates the synthesis of titanium oxynitride (TiOxNy) via a controlled step-annealing of commercial titanium nitride (TiN) powders under normal ambience. The structure of the formed TiOxNy system is confirmed via XRD, Rietveld refinements, XPS, Raman, and HRTEM analysis. A distinct plasmonic band corresponding to TiN is observed in the absorption spectrum of TiOxNy, indicating that the surface plasmonic resonance (SPR) property of TiN is being inherited in the resulting TiOxNy system. The prerequisites such as reduced band gap energy, suitable band edge positions, reduced recombination, and enhanced carrier-lifetime manifested by the TiOxNy system are investigated using Mott-Schottky, XPS, time-resolved and steady-state PL spectroscopy techniques. The obtained TiOxNy photocatalyst is found to degrade around 98% of 10 ppm rhodamine B dye in 120 min and produce H2 at a rate of ∼1546 μmolg-1h-1 under solar light irradiation along with consistent recycle abilities. The results of cyclic voltammetry, linear sweep voltammetry, electrochemical impedance and photocurrent studies suggest that this evolved TiOxNy system could be functioning via plasmonic Ohmic interface rather than the typical plasmonic Schottky interface due to their amalgamated band structures in the oxynitride phase.

Efficient Photo-Assisted Thermal Selective Oxidation of Toluene Using N-Doped TiO2

Selective oxidation of toluene is a key reaction to produce high value-added products but remains a big challenge. In this study, we introduce a nitrogen-doped TiO₂ (N-TiO₂) catalyst to create more Ti³⁺ and oxygen vacancy (O_V), which act as active sites for selective oxidation of toluene via activating O₂ to superoxide radical (•O₂^-). Interestingly, the resulting N-TiO₂-2 exhibited an outstanding photo-assisted thermal performance with a product yield of 209.6 mmol·g_cat^-1 and a toluene conversion of 10960.0 μmol·g_cat^-1·h^-1, which are 1.6 and 1.8 times greater than those obtained under thermal catalysis. We showed that the enhanced performance under photo-assisted thermal catalysis was attributed to more active species generation by making full use of photogenerated carriers. Our work suggests a viewpoint to apply a noble-metal-free TiO₂ system in the selective oxidation of toluene under solvent-free conditions.

Unconventional rate law of water photooxidation at TiO2 electrodes

Photoelectrochemical oxidation of water over semiconductors is a promising route for the production of sustainable solar fuels. TiO₂ water photooxidation has been intensively studied over the past 50 years, but its rate law and mechanism are still undetermined. The main challenges are that there is no appropriate reaction kinetic model currently, and that both the reaction rate constant and reactant photohole concentration/density are not readily quantified with respect to conventional chemical reactions. Here we report that the rate law and photohole transfer mechanism could be determined by a combination of multiple (photo-) electrochemical techniques. We demonstrate that the kinetics of TiO₂ water oxidation by photogenerated holes can be well-described by a model of surface state mediating charge transfer and recombination. The rate law, in terms of steady-state photocurrent, is the product of the surface hole density exponential dependent rate constant and the surface hole density, with first order for all the surface hole densities studied. This reactant concentration dependent rate constant is conceptually unexpected for an elementary step in conventional chemical reactions. In addition, we find that hydroxyl ions in bulk solutions are involved in the reaction as indicated by observation of the solution pH dependent apparent rate constant. This study may thus lead to key insights both for strategies to evaluate and/or enhance photoelectrochemical performances and for understanding reaction mechanisms.

Plasmonic Cu Nanoparticles for the Low-temperature Photo-driven Water-gas Shift Reaction

The activation of water molecules in thermal catalysis typically requires high temperatures, representing an obstacle to catalyst development for the low-temperature water-gas shift reaction (WGSR). Plasmonic photocatalysis allows activation of water at low temperatures through the generation of light-induced hot electrons. Herein, we report a layered double hydroxide-derived copper catalyst (LD-Cu) with outstanding performance for the low-temperature photo-driven WGSR. LD-Cu offered a lower activation energy for WGSR to H₂ under UV/Vis irradiation (1.4 W cm^-2 ) compared to under dark conditions. Detailed experimental studies revealed that highly dispersed Cu nanoparticles created an abundance of hot electrons during light absorption, which promoted *H₂ O dissociation and *H combination via a carboxyl pathway, leading to the efficient production of H₂ . Results demonstrate the benefits of exploiting plasmonic phenomena in the development of photo-driven low-temperature WGSR catalysts.

Selective adsorption of cysteamine molecules on Au/TiO2 boosts visible light-driven photocatalytic hydrogen evolution

Photocatalytic evolution of hydrogen is becoming a research hotspot because it can help to produce clean energy and reduce environmental pollution. Titanium dioxide (TiO₂) and its composites are photocatalysts that are widely used in hydrogen evolution because of their high abundance in nature, low price, and high photo/chemical stability. However, their catalytic performances still need to be further improved, particularly in the visible light spectrum. Herein, visible light-driven photocatalytic evolution of hydrogen on Au/TiO₂ nanocomposite is enhanced ∼ 10 folds by selectively functionalizing the nanocomposite with cysteamine molecules. It is revealed that the amine group (-NH₂) in cysteamine favors the transfer and separation of photo-generated hot carriers. The rate of hydrogen produced can be further tuned by varying the ionization of the functionalized molecules at different pH values. This work provides a simple, convenient, and effective method that can be used to improve the photocatalytic evolution of hydrogen. This method can also be used for many other nanocatalysts (e.g., Au-MoS₂, Au-BiVO₄) and catalytic reactions (e.g., carbon dioxide reduction, nitrogen reduction).

A Twin S-Scheme Artificial Photosynthetic System with Self-Assembled Heterojunctions Yields Superior Photocatalytic Hydrogen Evolution Rate

Designing heterojunction photocatalysts imitating natural photosynthetic systems has been a promising approach for photocatalytic hydrogen generation. However, in the traditional Z-Scheme artificial photosynthetic systems, the poor charge separation, and rapid recombination of photogenerated carriers remain a huge bottleneck. To rationally design S-Scheme (i.e., Step scheme) heterojunctions by avoiding the futile charge transport routes is therefore seen as an attractive approach to achieving high hydrogen evolution rates. Herein, a twin S-scheme heterojunction is proposed involving graphitic C₃ N₄ nanosheets self-assembled with hydrogen-doped rutile TiO₂ nanorods and anatase TiO₂ nanoparticles. This catalyst shows an excellent photocatalytic hydrogen evolution rate of 62.37 mmol g^-1 h^-1 and high apparent quantum efficiency of 45.9% at 365 nm. The significant enhancement of photocatalytic performance is attributed to the efficient charge separation and transfer induced by the unique twin S-scheme structure. The charge transfer route in the twin S-scheme is confirmed by in situ X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) spin-trapping tests. Femtosecond transient absorption (fs-TA) spectroscopy, transient-state surface photovoltage (TPV), and other ex situ characterizations further corroborate the efficient charge transport across the catalyst interface. This work offers a new perspective on constructing artificial photosynthetic systems with S-scheme heterojunctions to enhance photocatalytic performance.

Critical role of tetracycline's self-promotion effects in its visible-light driven photocatalytic degradation over ZnO nanorods

Zinc oxide (ZnO), which is widely applied for ultraviolet-light driven photocatalysis, has no activity in visible-light photocatalytic process due to its large band gap of ∼3.2 eV. Herein, however, we demonstrated the multiple self-promotion effects of tetracycline as band adjuster, photo-sensitizer, and charge transfer promoter for ZnO nanorods, realizing its visible-light photocatalytic degradation with an excellent removal efficiency up to 91.1% within only 2 h. Besides, the influence of complex realistic factors on this unique process was evaluated together with tests with realistic water matrices. Furthermore, the active species and degradation products were identified. Both acute and developmental toxicities were found to be reduced as the degradation proceeds. These results pave the path for the brand-new self-driven visible-light photocatalysis.

Efficient Near-Infrared Response Antibacterial Ceramics Based on the Method of Facile In Situ Etching Upconversion Glass-Ceramics

As the world is faced with the coronavirus disease 2019 (COVID-19) pandemic, photocatalytic antibacterial ceramics can reduce the consumption of disinfectants and improve the safety of the public health environment. However, these antibacterial ceramics are often limited by poor stability and low light utilization efficiency. Herein, an antibacterial ceramic was developed via the method of facile in situ etching of upconversion glass-ceramics (UGC) (FIEG) with HCl, in which the BiOCl nanosheets were in situ grown on the surface of GC to improve its stability and antibacterial activity. The results suggest that the upconversion antibacterial ceramics can harvest and utilize near-infrared (NIR) photons efficiently, which display notable antibacterial activity for Escherichia coli (E. coli) under NIR (≥780 nm) and visible light (420-780 nm) irradiation, with a maximum inactivation rate of 7.5 log in 30 min. Meanwhile, in the cycle experiment, more than 6 log inactivation of E. coli was achieved using an antibacterial ceramic sheet after 2-h NIR light irradiation, and the stability of the antibacterial ceramic was discussed. Furthermore, the reactive species, fluorescence-based live/dead cells, and cell structure of bacteria were analyzed to verify the antibacterial mechanism. This study provides a promising strategy for the construction of efficient and stable antibacterial ceramics.

Janus (Mo/β-Mo2C)@C heterostructure as an efficient electrocatalyst for the hydrogen evolution reaction in acidic and alkaline media

To explore low-cost, high-efficiency, and noble-metal-free catalysts for electrocatalytic water splitting in both acidic and alkaline media, the metal-metal carbide Janus hierarchical structure comprising Mo andβ-Mo₂C embedded on a carbon layer (Mo/β-Mo₂C)@C is synthesized by a hydrothermal reaction and subsequent low-temperature magnesium thermic process. Systematic characterization by XRD, XPS, Raman scattering, and SEM/TEM reveals the successful formation of metallic Mo andβ-Mo₂C nanoparticles. The synthesized (Mo/β-Mo₂C)@C has a large specific surface area and boasts highly efficient hydrogen evolution reaction activity including low overpotentials of 152 and 171 mV at a current density of 10 mA cm^-2and small Tafel slopes of 51.7 and 63.5 mV dec^-1in acidic and alkaline media, respectively. In addition, the catalyst shows outstanding stability for 48 h in both acidic and alkaline media. The excellent catalytic activity originates from more active sites and greater electron conductivity bestowed by the carbon layer, which also improves the long-term stability in both acidic and alkaline solutions.

Unpaired Electron Engineering Enables Efficient and Selective Photocatalytic CO2 Reduction to CH4

The photocatalytic CO₂ reduction to CH₄ reaction is a long process of proton-coupled charge transfer accompanied by various reaction intermediates. Achieving high CH₄ selectivity with satisfactory conversion efficiency therefore remains rather challenging. Herein, we propose a novel strategy of unpaired electron engineering to break through such a demanding bottleneck. By taking TiO₂ as a photocatalyst prototype, we prove that unpaired electrons stabilize the key intermediate of CH₄ production, i.e., CHO*, via chemical bonding, which converts the endothermic step of CHO* formation to an exothermic process, thereby altering the reaction pathway to selectively produce CH₄. Meanwhile, these unpaired electrons generate midgap states to restrict charge recombination by trapping free electrons. As an outcome, such an unpaired electron-engineered TiO₂ achieves an electron-consumption rate as high as 28.3 μmol·g^-1·h^-1 (15.7-fold with respect to normal TiO₂) with a 97% CH₄ selectivity. This work demonstrates that electron regulation holds great promise in attaining efficient and selective heterogeneous photocatalytic conversion.

Simple preparation of a CuO@γ-Al2O3 Fenton-like catalyst and its photocatalytic degradation function

We designed a photocatalyst and developed sustainable wastewater purification technology, which have significant advantages in effectively solving the global problem of drinking water shortage. In this study, a new nanocomposite was reported and shown to be a catalyst with excellent performance; CuO was coated successively onto functionalized nano γ-Al₂O₃, and this novel structure could provide abundant active sites. We evaluated the performance of the CuO@γ-Al₂O₃ nanocomposite catalyst for polyvinyl alcohol (PVA) degradation under visible light irradiation. Under optimized conditions (calcination temperature, 450 °C; mass ratio of γ-Al₂O₃:Cu(NO₃)₂·3H₂O, 1:15; pH value, 7; catalyst dosage, 2.6 g/L; reaction temperature, 20 °C; and H₂O₂ dosage, 0.2 g/mL), the CuO@γ-Al₂O₃ nanocomposite catalyst presented an excellent PVA removal rate of 99.21%. After ten consecutive degradation experiments, the catalyst could still maintain a PVA removal rate of 97.58%, thus demonstrating excellent reusability. This study provides an efficient and easy-to-prepare photocatalyst and proposes a mechanism for the synergistic effect of the photocatalytic reaction and the Fenton-like reaction.

Pyro-catalysis for tooth whitening via oral temperature fluctuation

Tooth whitening has recently become one of the most popular aesthetic dentistry procedures. Beyond classic hydrogen peroxide-based whitening agents, photo-catalysts and piezo-catalysts have been demonstrated for non-destructive on-demand tooth whitening. However, their usage has been challenged due to the relatively limited physical stimuli of light irradiation and ultrasonic mechanical vibration. To address this challenge, we report here a non-destructive and convenient tooth whitening strategy based on the pyro-catalysis effect, realized via ubiquitous oral motion-induced temperature fluctuations. Degradation of organic dyes via pyro-catalysis is performed under cooling/heating cycling to simulate natural temperature fluctuations associated with intake and speech. Teeth stained by habitual beverages and flavorings can be whitened by the pyroelectric particles-embedded hydrogel under a small surrounding temperature fluctuation. Furthermore, the pyro-catalysis-based tooth whitening procedure exhibits a therapeutic biosafety and sustainability. In view of the exemplary demonstration, the most prevalent oral temperature fluctuation will enable the pyro-catalysis-based tooth whitening strategy to have tremendous potential for practical applications.

Photo-oxygenation of water media using photoactive plasmonic nanocomposites

Plasmonic nanocomposites ZnO–Ag and ZnO–SnO2–Ag(AgCl) were prepared by the polymer–salt method, and their structure and morphology were studied using XRD and SEM analyses. It was found that the addition of photoactive inorganic nanocomposites ZnO–Ag and ZnO–SnO2–Ag(AgCl) in pure water significantly enhances the effectiveness of its disinfection and purification during UV treatment and provides the effective water oxygenation. Oxygen photogeneration under blue light (λex. = 405 nm) can be related to the plasmon-excitation processes in ZnO–SnO2–Ag(AgCl) composites. Prepared composites demonstrate antibacterial activity against both Gram-positive and Gram-negative bacteria. The increase of Ag content in ZnO–Ag and ZnO–SnO2–Ag(AgCl) composites significantly enhances their antibacterial activity.

N-Rich Doped Anatase TiO2 with Smart Defect Engineering as Efficient Photocatalysts for Acetaldehyde Degradation

Nitrogen (N) doping is an effective strategy for improving the solar-driven photocatalytic performance of anatase TiO2, but controllable methods for nitrogen-rich doping and associated defect engineering are highly desired. In this work, N-rich doped anatase TiO2 nanoparticles (4.2 at%) were successfully prepared via high-temperature nitridation based on thermally stable H3PO4-modified TiO2. Subsequently, the associated deep-energy-level defects such as oxygen vacancies and Ti3+ were successfully healed by smart photo-Fenton oxidation treatment. Under visible-light irradiation, the healed N-doped TiO2 exhibited a ~2-times higher activity of gas-phase acetaldehyde degradation than the non-treated one and even better than standard P25 TiO2 under UV-visible-light irradiation. The exceptional performance is attributed to the extended spectral response range from N-rich doping, the enhanced charge separation from hole capturing by N-doped species, and the healed defect levels with the proper thermodynamic ability for facilitating O2 reduction, depending on the results of ∙O2− radicals and defect measurement by electron spin resonance, X-ray photoelectron spectroscopy, atmosphere-controlled surface photovoltage spectra, etc. This work provides an easy and efficient strategy for the preparation of high-performance solar-driven TiO2 photocatalysts.

An effective strategy for improving charge separation efficiency and photocatalytic degradation performance using a facilely synthesized oxidative TiO2 catalyst

Titanium dioxide (TiO₂) has attracted enormous interest in abundant photocatalytic reactions, but its photocatalytic efficiency is limited by its wide bandgap and the rapid recombination of electron-hole pairs. To overcome the disadvantages of its rapid electron-hole recombination rate, herein, oxidative TiO₂ was one-step fabricated using potassium permanganate (KMnO₄), exhibiting improved charge separation efficiency and photocatalytic degradation performance towards methyl orange (MO). Remarkably, the first-order photodegradation rate of oxidative TiO₂ is 3.68 times higher than that of pristine TiO₂ under the irradiation of simulated sunlight and 2.15 times higher under ultraviolet light. This exceptional photocatalytic activity is attributed to the additional oxygen doped into the interstices of the TiO₂ lattice, creating impurity states in the bandgap acting as trapping sites, thus facilitating charge separation. This work provides a promising strategy for the insertion of O atoms into the TiO₂ lattice and expands the photocatalytic application of the related materials.

Thermo-photo catalysis: a whole greater than the sum of its parts

Thermo-photo catalysis, which is the catalysis with the participation of both thermal and photo energies, not only reduces the large energy consumption of thermal catalysis but also addresses the low efficiency of photocatalysis. As a whole greater than the sum of its parts, thermo-photo catalysis has been proven as an effective and promising technology to drive chemical reactions. In this review, we first clarify the definition (beyond photo-thermal catalysis and plasmonic catalysis), classification, and principles of thermo-photo catalysis and then reveal its superiority over individual thermal catalysis and photocatalysis. After elucidating the design principles and strategies toward highly efficient thermo-photo catalytic systems, an ample discussion on the synergetic effects of thermal and photo energies is provided from two perspectives, namely, the promotion of photocatalysis by thermal energy and the promotion of thermal catalysis by photo energy. Subsequently, state-of-the-art techniques applied to explore thermo-photo catalytic mechanisms are reviewed, followed by a summary on the broad applications of thermo-photo catalysis and its energy management toward industrialization. In the end, current challenges and potential research directions related to thermo-photo catalysis are outlined.

Tabrizi B, D’Elia V, Del Gobbo S, Jabbour GE. Microwave-Assisted Non-aqueous and Low-Temperature Synthesis of Titania and Niobium-Doped Titania Nanocrystals and Their Application in Halide Perovskite Solar Cells as Electron Transport Layers

Undoped and Nb-doped TiO2 nanocrystals are prepared by a microwave-assisted non-aqueous sol-gel method based on a slow alkyl chloride elimination reaction between metal chlorides and benzyl alcohol. Sub-4 nm nanoparticles are grown under microwave irradiation at 80 °C in only 3 h with precise control of growth parameters and yield. The obtained nanocrystals could be conveniently used to cast compact TiO2 or Nb-doped TiO2 electron transport layers for application in formamidinium lead iodide-based photovoltaic devices. Niobium doping is found to improve the cell performance by increasing the conductivity and mobility of the electron transport layer. At the same time, a measurable decrease in parasitic light absorption in the low wavelength portion of the spectrum was observed.

Photothermal Chemistry Based on Solar Energy: From Synergistic Effects to Practical Applications

With the development of society, energy shortage and environmental problems have become more and more outstanding. Solar energy is a clean and sustainable energy resource, potentially driving energy conversion and environmental remediation reactions. Thus, solar-driven chemistry is an attractive way to solve the two problems. Photothermal chemistry (PTC) is developed to achieve full-spectral utilization of the solar radiation and drive chemical reactions more efficiently under relatively mild conditions. In this review, the mechanisms of PTC are summarized from the aspects of thermal and non-thermal effects, and then the interaction and synergy between these two effects are sorted out. In this paper, distinguishing and quantifying these two effects is discussed to understand PTC processes better and to design PTC catalysts more methodically. However, PTC is still a little far away from practical. Herein, several key points, which must be considered when pushing ahead with the engineering application of PTC, are proposed, along with some workable suggestions on the practical application. This review provides a unique perspective on PTC, focusing on the synergistic effects and pointing out a possible direction for practical application.

Effect of Defects on Optical, Electronic, and Interface Properties of NiO/SnO2 Heterostructures: Dual-Functional Solar Photocatalytic H2 Production and RhB Degradation

Photocatalytic H₂ evolution and organic pollutant oxidation have witnessed a radical surge in recent times. However, this integration demands spatial charge separation and unique interface properties for a trade-off between oxidation and reduction reactions. In the current work, defect engineering of NiO/SnO₂ nanoparticles aided in altering the optoelectronics and interface properties and enhanced photocatalytic activity. After annealing the catalysts in a N₂ atmosphere, the hydroxyl groups were replaced by water molecules through surface modification. The photoexcited holes accumulated on SnO₂ break the water molecules and facilitate the reduction of protons on NiO; this is known as spatial separation. Meanwhile, direct hole oxidation, an oxygen reduction reaction, ensures the degradation activity in this 2-fold system. By defect engineering, the limitations of SnO₂ such as higher H₂O adsorption, wide bandgap (reduced from 3.02 to 1.88 eV), and electronic properties were addressed. The H₂ production in the current work has attained a value of 3732 μmol/(g h), which is 2.9 times that of the previous best reported under sunlight. Recyclability tests confirmed the stability of vacancies by promoting the reoxidation of defect states during photocatalytic activity. Additionally, efforts were made to study the effect of defect density on the photocurrent, the electrical resistance, and the mechanism of photocatalytic reactions. Electrochemical characterizations, UPS, XPS, UV-DRS, and PL were employed to understand the influence of defects on the bandgap, charge recombination, charge transport, charge carrier lifetime, and the interface properties that are responsible for photocatalytic activity. In this regard, it was understood that maintaining the optimal defect concentration is important for higher photocatalytic efficiencies, as the defect optimality preserves key photocatalytic properties. Apart from characterizations, the photocatalytic results suggest that excess defect density triggers the undesired thermodynamically favored back reactions, which greatly hampered the H₂ yield of the process.

Defective Grey TiO2 with Minuscule Anatase–Rutile Heterophase Junctions for Hydroxyl Radicals Formation in a Visible Light-Triggered Photocatalysis

The novelty of this work was to prepare a series of defect-rich colored TiO2 nanostructures, using a peroxo solvothermal-assisted, high-pressure nitrogenation method. Among these solids, certain TiO2 materials possessed a trace quantity of anatase–rutile heterojunctions, which are beneficial in obtaining high reaction rates in photocatalytic reactions. In addition, high surface area (above 100 m2/g), even when utilizing a high calcination temperature (500 °C), and absorption of light at higher wavelengths, due to the grey color of the synthesized titania, were observed as an added advantage for photocatalytic hydroxyl radical formation. In this work, we adopted a photoluminescent probe method to monitor the temporal evolution of hydroxyl radicals. As a result, promising hydroxyl radical formations were observed for all the colored samples synthesized at 400 and 500 °C, irrespective of the duration of calcination.

Investigating and correlating photoelectrochemical, photocatalytic, and antimicrobial properties of [Formula: see text] nanolayers

Semiconducting transition metal oxides such as [Formula: see text] are promising photo(electro)catalysts for solar water splitting and photoreduction of [Formula: see text] as well as for antibacterial, self-, water and air-cleaning coatings and admixtures in paints, building materials, on window glass or medical devices. In photoelectrocatalytic applications [Formula: see text] is usually used as photoanode only catalyzing the oxidation reaction. In coatings and admixtures [Formula: see text] works as heterogeneous catalyst and has to catalyze a complete redox cycle. While photoelectrochemical charge transport parameters are usually quite well accessible by electrochemical measurements, the quantitative description of photocatalytic properties is more challenging. Here, we present a systematic structural, photoelectrocatalytic, photocatalytic and antimicrobial study to understand if and how photoelectrochemical parameters can be used to predict the photocatalytic activity of [Formula: see text]. For this purpose [Formula: see text] thin films on flourine-doped tin oxide substrates were prepared and annealed at temperatures between 200 and 600 [Formula: see text]. The film morphologies and thicknesses were studied by GIXRD, FESEM, and EDX. Photoelectrochemical properties were measured by linear sweep voltammetry, photoelectrochemical impedance spectroscopy, chopped light chronoamperometry, and intensity modulated photocurrent/ photovoltage spectroscopy. For comparison, photocatalytic rate constants were determined by methylene blue degradation and Escherichea coli inactivation and correlated with the deduced photoelectrocatalytic parameters. We found that the respective photoactivities of amorphous and crystalline [Formula: see text] nanolayers can be best correlated, if the extracted photoelectrochemical parameters such as charge transfer and recombination rates, charge transfer efficiencies and resistances are measured close to the open circuit potential (OCP). Hence, the interfacial charge transport parameters at the OCP can be indeed used as descriptors for predicting and understanding the photocatalytic activity of [Formula: see text] coatings.

Light-driven oxygen evolution from water oxidation with immobilised TiO2 engineered for high performance

Calcination treatments in the range of 500–900 °C of TiO₂ synthesised by the sol–gel resulted in materials with variable physicochemical (i.e., optical, specific surface area, crystallite size and crystalline phase) and morphological properties. The photocatalytic performance of the prepared materials was evaluated in the oxygen evolution reaction (OER) following UV-LED irradiation of aqueous solutions containing iron ions as sacrificial electron acceptors. The highest activity for water oxidation was obtained with the photocatalyst thermally treated at 700 °C (TiO₂-700). Photocatalysts with larger anatase to rutile ratio of the crystalline phases and higher surface density of oxygen vacancies (defects) displayed the best performance in OER. The oxygen defects at the photocatalyst surface have proven to be responsible for the enhanced photoactivity, acting as important active adsorption sites for water oxidation. Seeking technological application, water oxidation was accomplished by immobilising the photocatalyst with the highest OER rate measured under the established batch conditions (TiO₂-700). Experiments operating under continuous mode revealed a remarkable efficiency for oxygen production, exceeding 12% of the apparent quantum efficiency (AQE) at 384 nm (UV-LED system) compared to the batch operation mode.

Ultrasound-Assisted Synthesis of Nonmetal-Doped Titanium Dioxide Photocatalysts for Simultaneous H2 Production and Chemical Oxygen Demand Removal from Industrial Wastewater

A series of nonmetal-doped titanium dioxide (Nm _x /TiO₂, where x is the weight fraction of nonmetal elements) photocatalysts was prepared via ultrasonic-assisted impregnation for simultaneous hydrogen (H₂) production and chemical oxygen demand (COD) removal from industrial wastewater. Three types of Nm elements, carbon (C), silicon (Si), and phosphorus (P), were explored. The P₁/TiO₂ exhibited a higher photocatalytic activity for H₂ production and COD removal than the C₁/TiO₂ and Si₁/TiO₂ photocatalysts. Approximately 6.43 mmol/g photocatalyst of H₂ was produced, and around 26% COD removal was achieved at a P₁/TiO₂ loading of 4.0 g/L, a light intensity of 5.93 mW/cm², and a radiation time of 4 h. This is because the P₁/TiO₂ photocatalyst exhibited lower point of zero charge values and a more appropriate band position compared with other Nm _x /TiO₂ photocatalysts to produce H⁺, which can consequently form H₂, and reactive oxygen species (HO^· and O₂ ^{· -}), which serve as oxidizing agents to degrade the organic pollutants. Increasing the content of the P element doped into the TiO₂-based material up to 7.0% by weight enhanced the H₂ production and COD removal up to 8.34 mmol/g photocatalyst and 50.6%, respectively. This is attributed to the combined effect of the point of zero charge value and the S _BET of the prepared photocatalysts. The photocatalytic activity of the P₇/TiO₂ photocatalyst was still higher than the TiO₂-based material after the fourth use.

Enhanced photocatalytic degradation of 4-chlorophenol under visible light over carbon nitride nanosheets with carbon vacancies

Two-dimensional graphitic carbon nitride (g-C₃N₄, GCN) is considered as one of the promising visible light-responsive photocatalysts for energy storage and environmental remediation. However, the photocatalytic performance of pristine GCN is restricted by the inherent shortcomings of rapid charge carrier recombination and limited absorption of visible light. Vacancy engineering is widely accepted as the auspicious approach for boosting the photocatalytic activity of GCN-based photocatalysts. Herein, a magnesium thermal calcination method has been developed to reconstruct GCN, in which magnesium serves as a carbon etcher for introducing carbon vacancies and pores into GCN (V_c-GCN). The fabricated V_c-GCN demonstrates excellent photocatalytic performances of degrading hazardous 4-chlorophenol under visible light irradiation benefiting from the improved carrier separating and light absorption ability as well as rich reactive sites. The optimal V_c-GCN sample delivers 2.3-fold enhancement from the pristine GCN. The work provides a tactic to prepare GCN photocatalysts with controllable carbon vacancies and for a candidate for the degradation of organic pollutants from the environment.

The Position of Ammonia in Decarbonising Maritime Industry: An Overview and Perspectives: Part I : Technological advantages and the momentum towards ammonia-propelled shipping

Shipping, which accounts for 2.6% of global carbon dioxide emissions, is urged to find clean energy solutions to decarbonise the industry and achieve the International Maritime Organization (IMO)’s greenhouse gas (GHG) emission targets by 2050. It is generally believed that hydrogen will play a vital role in enabling the use of renewable energy sources. However, issues related with hydrogen storage and distribution currently obstruct its implementation. Alternatively, an energy-carrier such as ammonia with its carbon neutral chemical formula, high energy density and established production, transportation and storage infrastructure could provide a practical short-term next generation power solution for maritime industry. This paper presents an overview of the state-of-the-art and emerging technologies for decarbonising shipping using ammonia as a fuel, covering general properties of ammonia, the current production technologies with an emphasis on green synthesis methods, onboard storage and ways to generate power from it.

Intensification of Heterogeneous Photocatalytic Reactions Without Efficiency Losses: The Importance of Surface Catalysis

Advances in LED and photoreactor technology have brought semiconductor photocatalysis to the verge of feasibility of industrial application for the synthesis of value-added chemicals. However, the often observed efficiency losses under intensified illumination conditions still present a great challenge. This perspective discusses the origin of these efficiency losses and what needs to be done to prevent or counteract it and pave the way for efficient, intensified heterogeneous photocatalytic processes. The role of surface catalysis is particularly highlighted as one of the rate-limiting steps.

Graphic Abstract

Sequential cocatalyst decoration on BaTaO2N towards highly-active Z-scheme water splitting

Oxynitride photocatalysts hold promise for renewable solar hydrogen production via water splitting owing to their intense visible light absorption. Cocatalyst loading is essential for activation of such oxynitride photocatalysts. However, cocatalyst nanoparticles form aggregates and exhibit weak interaction with photocatalysts, which prevents eliciting their intrinsic photocatalytic performance. Here, we demonstrate efficient utilization of photoexcited electrons in a single-crystalline particulate BaTaO₂N photocatalyst prepared with the assistance of RbCl flux for H₂ evolution reactions via sequential decoration of Pt cocatalyst by impregnation-reduction followed by site-selective photodeposition. The Pt-loaded BaTaO₂N photocatalyst evolves H₂ over 100 times more efficiently than before, with an apparent quantum yield of 6.8% at the wavelength of 420 nm, from a methanol aqueous solution, and a solar-to-hydrogen energy conversion efficiency of 0.24% in Z-scheme water splitting. Enabling uniform dispersion and intimate contact of cocatalyst nanoparticles on single-crystalline narrow-bandgap particulate photocatalysts is a key to efficient solar-to-chemical energy conversion.