Fundamentals of TiO2 Photocatalysis: Concepts, Mechanisms, and Challenges

Photo-assisted thermal catalytic CO2 reduction over Ru-TiO2 catalysts

Photothermal catalysis is a promising technology to convert CO2 into high value-added products. Here, we show that loading Ru NPs on TiO2 achieved a remarkable photothermal synergistic effect and the Ru-TiO2 demonstrated a high efficiency for the photothermal conversion of low CO2 concentration to CH4 at the gas-solid interface. The photothermal activity of the Ru-TiO2 (217.9 µmol/(g·h)) was nearly 6 times higher than pure thermal activity (38.08 µmol/(g·h)), and nearly 20 times than the photocatalytic activity (10.9 µmol/(g·h)). We revealed that the light excitation could drive the generated electrons from TiO2 to Ru particles, beneficial to CO2 reduction, while external heating showed no influence on the charge separation of the Ru-TiO2. Hence, the photothermal synergy is not a heat-assisted photocatalytic process, but a photo-assisted thermal catalytic process. We finally demonstrated that the CO2 was firstly converted to CO, and the CO was further hydrogenated to CH4. The introduction of light could promote the activation of intermediate CO species at the Ru-Ti interface sites, thus greatly accelerating CO hydrogenation to CH4. This work contributes to further understanding of the mechanism of photothermal catalytic CO2 reduction.

Lignin and Nanolignin: Next-Generation Sustainable Materials for Water Treatment

Water scarcity, contamination, and lack of sanitation are global issues that require innovations in chemistry, engineering, and materials science. To tackle the challenge of providing high-quality drinking water for a growing population, we need to develop high-performance and multifunctional materials to treat water on both small and large scales. As modern society and science prioritize more sustainable engineering practices, water treatment processes will need to use materials produced from sustainable resources via green chemical routes, combining multiple advanced properties such as high surface area and great affinity for contaminants. Lignin, one of the major components of plants and an abundant byproduct of the cellulose and bioethanol industries, offers a cost-effective and scalable platform for developing such materials, with a wide range of physicochemical properties that can be tailored to improve their performance for target water treatment applications. This review aims to bridge the current gap in the literature by exploring the use of lignin, both as solid bulk or solubilized macromolecules and nanolignin as multifunctional (nano)materials for sustainable water treatment processes. We address the application of lignin-based macro-, micro-, and nanostructured materials in adsorption, catalysis, flocculation, membrane filtration processes, and antimicrobial coatings and composites. Throughout the exploration of recent progress and trends in this field, we emphasize the importance of integrating principles of green chemistry and materials sustainability to advance sustainable water treatment technologies.

Development of a UPLC-MS/MS method for pesticide analysis in paddy water and evaluation of anodic TiO2 nanostructured films for pesticide photodegradation and antimicrobial applications

Pesticide contamination in agricultural water poses serious environmental and public health risks, particularly due to the accumulation of harmful residues that threaten aquatic ecosystems and human health. This study investigated the levels of five pesticides-carbaryl (CBR), methiocarb (MTC), diazinon (DZN), chlorpyrifos (CLO), and cypermethrin (CYPER)-in agricultural water samples from Can Tho City and Hau Giang Province, Vietnam. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was employed for their detection and quantification. Chlorpyrifos was the most frequently detected pesticide (32.5%), with concentrations ranging from 1.7 to 10.9 ng mL-1. The concentrations of cypermethrin, carbaryl, methiocarb, and diazinon were 2.6-9.4 ng mL-1, 1.3-14.3 ng mL-1, 4.1-7.7 ng mL-1, and 2.8-10.5 ng mL-1, respectively. The persistence of pesticide residues in the water samples highlights the significant contamination concerns in the region. To address this issue, two types of TiO2 nanophotocatalysts-TiO2 nanotube arrays (TNAs) and TiO2 nanowires on nanotube arrays (TNWs/TNAs)-were synthesized for the photocatalytic degradation of the identified pesticides. Under UV-vis irradiation (∼96 mW cm-2), both nanostructures achieved rapid pesticide degradation, with removal efficiencies of up to 99% within 25 minutes. TNWs/TNAs exhibited superior photocatalytic performance, attributed to their increased surface area compared to TNAs. In addition to pesticide degradation, their antibacterial activity was assessed. Under weak UV-vis light (6.3 mW cm-2), both TNAs and TNWs/TNAs achieved 100% antibacterial efficacy against Escherichia coli, significantly higher than the 68% efficacy of UV light treatment alone. Even under dark conditions, TNWs/TNAs demonstrated enhanced antibacterial activity, achieving 63% efficacy compared to 12% for TNAs. These results underscore the dual functionality of TNWs/TNAs as effective photocatalysts for both pesticide degradation and bacterial inactivation, presenting a promising approach for agricultural water treatment.

Unlocking Low-Temperature Ammonia Decomposition via an Iron Metal-Organic Framework-Derived Catalyst Under Photo-Thermal Conditions

Photo-thermal catalysis, leveraging both thermal and non-thermal solar contributions, emerges as a sustainable approach for fuel and chemical synthesis. In this study, an Fe-based catalyst derived from a metal-organic framework is presented for efficient photo-thermal ammonia (NH3) decomposition. Optimal conditions, under light irradiation without external heating, result in a notable 55% NH3 conversion. Mechanistic investigations reveal that the enhanced catalytic activity arises from the synergistic interplay between light-induced hot carriers and elevated temperatures during irradiation. Supported by density functional theory calculations, the findings elucidate the dual role of the catalyst. At lower temperatures, photo-generated electrons in the Fe3O4 phase serve to raise the energies of reaction intermediates, preventing the formation of a thermodynamic sink. Conversely, at higher temperatures, metallic Fe emerges as the predominant active phase, with thermal contributions prevailing. Overall, this work advances the understanding of the cooperative effects between light and heat in photo-thermal systems, paving the way for innovative applications in sustainable energy conversion.

Light driven water oxidation on silica supported NiO-TiO2 heteronanocrystals yields hydrogen peroxide

Decomposition of nickel nitrate hexahydrate in the presence of rod-shape anatase TiO2 nanocrystals led to the formation of NiO-TiO2 heteronanocrystals confirmed with powder X-ray diffraction and electron microscopy. The heteronanocrystals were supported on amorphous fumed silica to provide a heterogeneous photocatalyst material SiO2/NiO-TiO2. The aqueous suspension of the catalyst, under argon atmosphere, irradiated with a Xe arc lamp led to the formation of H2O2 with trace gaseous product formation. We observed an initial rate of formation of H2O2 of 1.8 μmol g-1 min-1 that decays toward a steady-state concentration of 52 μM. Addition of AgNO3 to the aqueous suspension gave fast reduction of silver ion, and higher initial rates of formation and steady state concentrations of H2O2. We report the concentration dependence of water oxidation versus [AgNO3] with the fastest initial rate of formation of H2O2 as 9.1 μmol g-1 min-1 and a steady-state concentration of 174 μM.

Ultrathin Ti-Deficient TiO2 Nanosheets with Pt Single Atoms Enable Efficient Photocatalytic Nitrate Reduction to Ammonia

Ti-deficient TiO2 nanosheets derived from lepidocrocite-type titanate delamination show a p-type conductivity with a band gap widened by the quantum confinement effect to 3.7 eV. This shift in the extended band positions─and thus in the electron transfer level─allows a direct photocatalytic nitrate reduction to ammonia without the use of any hole scavengers; this in contrast to classic TiO2. The deposition of Pt single atoms as cocatalysts onto the nanosheets significantly enhances the activity and selectivity toward ammonia, which outperforms classic Pt nanoparticles used as cocatalyst. The present study therefore reports not only on the unique photocatalytic properties of these Ti-deficient TiO2 nanosheets but also on the beneficial use of the modified electronic properties that enable entirely novel applications, such as the technologically highly important reduction of nitrate to ammonia.

Synthesis and Characterization of Se4+@TiO2/PET Composite Photocatalysts with Enhanced Photocatalytic Activity by Simulated Solar Irradiation and Antibacterial Properties

To fabricate recyclable catalytic materials with high catalytic activity, Se4+@TiO2 photocatalytic materials were synthesized by the sol-gel method. By introducing free radicals on the surface of polyester (PET) fabrics through plasma technology, Se4+@TiO2/PET composite photocatalytic materials with high photocatalytic activity were prepared. The surface morphology, crystal structure, chemical composition, and photocatalytic performance were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible absorption spectroscopy (UV-Vis), and photoluminescence spectroscopy (PL), respectively. The photocatalytic degradation performance was determined by assessing the degradation of azo dye methyl orange under simulated solar irradiation. The results demonstrated that Se4+@TiO2/PET exhibited a superior degradation rate of methyl orange, reaching up to 81% under simulated sunlight. The PL spectra indicated that the electron-hole pair separation rate of Se4+@TiO2/PET was higher than that of TiO2/PET. Furthermore, UV-Vis spectroscopy demonstrated that the relative forbidden band gap of Se4+@TiO2/PET was determined to be 2.9 eV. The band gap of Se4+@TiO2/PET was narrower, and the absorption threshold shifted toward the visible region, indicating a possible increase in its catalytic activity in simulated solar irradiation. In addition, the antibacterial properties of Se4+@TiO2/PET were subsequently investigated, achieving 99.99% and 98.47% inhibition against S. aureus and E. coli, respectively.

Synergistic Mechanism of Hydroxyl Regulation and a Polyvinylpyrrolidone Surfactant in Enhancing the Catalytic Oxidation Abilities of BiOBr

The rational design of BiOBr photocatalysts with optimized surface properties and enhanced photooxidative capacities is crucial. This study proposes a synergistic strategy combining hydroxyl-rich solvents with polyvinylpyrrolidone (PVP) surfactants to modulate the structural and electronic properties of BiOBr through a solvothermal approach. The resulting self-assembled microspheres demonstrated exceptional efficiency in degrading ciprofloxacin (CIP), methyl orange (MO), and rhodamine B (RhB). Among the synthesized variants, BiOBr-EG-PVP (fabricated with ethylene glycol and PVP) exhibited the highest photocatalytic activity, achieving near-complete removal of 20 mg/L CIP and RhB within 10 min under visible light irradiation, with degradation rates 60.12-101.73 times higher than pristine BiOBr. The structural characterization revealed that ethylene glycol (EG) not only induced the formation of self-assembled microspheres but also introduced abundant surface hydroxyl groups, which simultaneously enhanced the hole-mediated oxidation capabilities. The incorporation of PVP further promoted the development of hierarchical honeycomb-like microspheres and synergistically enhanced both the hydroxyl group density and photooxidative potential through interfacial engineering. Density functional theory (DFT) calculations confirmed that the enhanced photooxidative performance originated from an increased surface oxygen content. This work elucidates the synergistic effects of hydroxyl-rich solvents and surfactant modification in the fabrication of advanced BiOBr-based photocatalysts, providing new insights for high-performance photocatalysis for environmental remediation.

Mechanistic insights into the enhanced photocatalytic efficiency of MoS2-tuned DyFeO3 heterojunction nanocomposites for pollutant degradation

In this study, DyFeO3-MoS2 heterojunction nanocomposites were synthesized by integrating porous DyFeO3 nanoparticles (an n-type semiconductor) with MoS2 nanosheets (a p-type semiconductor). The resulting p-n heterojunction substantially improved the photocatalytic efficiency for degrading methylene blue (MB) and levofloxacin (LFX). This design introduces a built-in electric field at the interface, promoting efficient charge separation and suppressing electron-hole recombination, thereby significantly enhancing photocatalytic performance under solar irradiation compared to DyFeO3 alone. Characterization studies, including XRD, FESEM, TEM, XPS, UV-visible absorbance, photoluminescence, and Mott-Schottky analysis, confirmed the nanocomposites' crystalline structure, well-dispersed MoS2 nanosheets, oxygen vacancies, enhanced visible light absorption, and favorable band positions. The incorporation of MoS2 increased light absorption, enhanced charge separation, and improved surface area by mitigating DyFeO3 aggregation, leading to significantly higher photocatalytic degradation rates. Among the tested compositions, the DyFeO3-MoS2 (80 : 20) nanocomposite, containing 20 wt% MoS2, exhibited the highest efficiencies, with 96.5% degradation for MB and 88.7% for LFX. Further analyses, including activation energy determination, quantum yield measurement, scavenger tests, and reusability assessments, confirmed the optimized nanocomposite's performance and durability. The reduced activation energies and high quantum yields (35.5% for MB, 25.8% for LFX) indicate efficient photon conversion and radical generation, with superoxide radicals (˙O2-) identified as the primary reactive species. Stability tests revealed over 85% retention of activity after four cycles, underscoring the composite's robustness. Moreover, the photocatalytic mechanism revealed key insights into the degradation pathways of pollutants. This investigation demonstrates a viable solar-driven solution for efficient pollutant degradation in wastewater treatment by incorporating MoS2 into porous DyFeO3 nanostructures.

Photodriven PtPdCo-TiO2 heterostructure modified with hyaluronic acid and folic acid enhances antioxidative stress through efficient hydrogen/oxygen delivery and thermal effects in rheumatoid arthritis therapy

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic synovitis and progressive joint damage, primarily caused by oxidative injury from reactive oxygen species (ROS) and hypoxia in immune cells. Hydrogen (H2) has demonstrated potential in scavenging excess ROS and correcting redox imbalances, while oxygen supplementation can alleviate hypoxia, promoting inflammatory remission. This study introduces a novel FA-HA-PtPdCo-TiO2 (F-HPPCT) nano-system for targeted RA therapy. Comprising TiO2 quantum dots on PtPdCo polyhedra, decorated with folate-hyaluronic acid (FA-HA), F-HPPCT selectively targets inflammatory cells. Its metal-semiconductor heterostructure forms Schottky junctions that enhance electron transfer, enabling efficient hydrogen evolution and a photothermal effect under near-infrared light. Additionally, F-HPPCT mimics catalase activity, decomposing overexpressed H2O2 to relieve hypoxia and oxidative stress. The system synergistically scavenges ROS and replenishes oxygen, effectively reducing inflammation and oxidative damage. Both in vitro and in vivo experiments in arthritis models confirmed its efficacy, highlighting F-HPPCT's potential as a groundbreaking nanocatalyst for gas therapy in RA treatment.

A Z-Scheme Heterojunction g-C3N4/WO3 for Efficient Photodegradation of Tetracycline Hydrochloride and Rhodamine B

The construction of heterojunctions can effectively inhibit the rapid recombination of photogenerated electrons and holes in photocatalysts and offers great potential for pollutant degradation. In this study, a Z-scheme heterojunction g-C3N4/WO3 photocatalyst was synthesized using a combination of hydrothermal and calcination methods. The photocatalytic degradation performance was tested under visible light; the degradation efficiency of Rh B reached 97.9% within 15 min and that of TC-HCl reached 93.3% within 180 min. The excellent photocatalytic performance of g-C3N4/WO3 composites can be attributed to the improved absorption of visible light, the increase in surface area, and the effective separation of photogenerated electron-hole pairs. In addition, after four cycles of experiments, the photocatalytic performance of g-C3N4/WO3 did not decrease obviously, remaining at 97.8%, which proved that the g-C3N4/WO3 heterojunction had high stability and reusability. The active radical capture experiment confirmed that h+ and ·O2- played a leading role in the photocatalytic degradation. The Z-scheme heterojunction g-C3N4/WO3 designed and synthesized in this study is expected to become an efficient photocatalyst suitable for environmental pollution control.

Highly Efficient UV-Activated TiO2/SnO2 Surface Nano-matrix Gas Sensor: Enhancing Stability for ppb-Level NOx Detection at Room Temperature

This study presents a new nanoporous TiO2/SnO2 heterojunction for NOx gas detection by using a two-step sol-gel process. The unique TiO2 and SnO2 nanoheterojunction matrix right on the film surface enables the TiO2 photocatalyst to absorb minimal UV power (3 μW/cm2) and effectively transfer electrons to the SnO2 conduction band. The sensor detects NO and NO2 gases down to 4 ppb (response of 0.6%) and 10 ppb (response of 1.3%) at 1 V at room temperature. It also exhibits a fast recovery time (100 ± 40 s at 500 ppb NOx), an improved response over a wide relative humidity range (10-60%), and a long lifetime over 30 days. The ultralow UV power required can be easily harvested from sunlight, eliminating the need for UV LEDs. XPS and SEM analyses indicated that the unique nanoporous TiO2/SnO2 structure improves sensing performance, with oxygen vacancies playing a critical role in the NOx gas sensing mechanism. This work demonstrated the highly efficient UV catalyst effect in sensors with the surface heterojunction matrix. The low-power ppb-level NOx detection is suitable for environmental monitoring and respiratory disease detection.

Optimizing photocatalysis via electron spin control

Solar-driven photocatalytic technology holds significant potential for addressing energy crisis and mitigating global warming, yet is limited by light absorption, charge separation, and surface reaction kinetics. The past several years has witnessed remarkable progress in optimizing photocatalysis via electron spin control. This approach enhances light absorption through energy band tuning, promotes charge separation by spin polarization, and improves surface reaction kinetics via strengthening surface interaction and increasing product selectivity. Nevertheless, the lack of a comprehensive and critical review on this topic is noteworthy. Herein, we provide a summary of the fundamentals of electron spin control and the techniques employed to scrutinize the electron spin state of active sites in photocatalysts. Subsequently, we highlight advanced strategies for manipulating electron spin, including doping design, defect engineering, magnetic field regulation, metal coordination modulation, chiral-induced spin selectivity, and combined strategies. Additionally, we review electron spin control-optimized photocatalytic processes, including photocatalytic water splitting, CO2 reduction, pollutant degradation, and N2 fixation, providing specific examples and detailed discussion on underlying mechanisms. Finally, we outline perspectives on further enhancing photocatalytic activity through electron spin manipulation. This review seeks to offer valuable insights to guide future research on electron spin control for improving photocatalytic applications.

Platinum Single Atoms Strongly Promote Superoxide Formation in Titania-Based Photocatalysis - Platinum Nanoparticles Don't

The selective reduction of molecular oxygen to superoxide is one of the key reactions in electrochemistry and photocatalysis. Here the effect of Pt co-catalysts, dispersed on titania, either as single atoms or as nanoparticles, on the photocatalytic superoxide (•O2 -) formation in O2 containing solutions is investigated. The •O2 - formation is traced by nitroblue tetrazolium (NBT) assays and in detail by EPR measurements using TEMPO as •O2 - radical scavenger. The results show that the photocatalytic formation rate of •O2 - on titania can strongly be enhanced by using Pt single atoms as a co-catalyst, whereas Pt nanoparticles hardly exhibit any accelerating effect. This finding is of considerable significance regarding photocatalytic degradation and photocatalytic oxidative synthesis processes.

Dual Regulation of Sensitizers and Cluster Catalysts in Metal-Organic Frameworks to Boost H2 Evolution

Photocatalytic efficiency is closely correlated to visible-light absorption ability, electron transfer efficiency and catalytic center activity of photocatalysts, nevertheless, the concurrent management of these factors to improve photocatalytic efficiency remains underexplored. Herein, we proposed a sensitizer/catalyst dual regulation strategy on the polyoxometalate@Metal-Organic Framework (POM@MOF) molecular platform to construct highly efficient photocatalysts. Impressively, Ni-Sb9@UiO-Ir-C6, obtained by coupling strong sensitizing [Ir(coumarin 6)2(bpy)]+ with Ni-Sb9 POM with extremely exposed nickel site [NiO3(H2O)3], can drive H2 evolution with a turnover number of 326923, representing a record value among all the POM@MOF composite photocatalysts. This performance is over 34 times higher than that of the typical Ni4P2@UiO-Ir constructed from [Ir(ppy)2(bpy)]+ and Ni4P2 POM. Systematical investigations revealed that dual regulation of sensitizing and catalytic centers endowed Ni-Sb9@UiO-Ir-C6 with strong visible-light absorption, efficient inter-component electron transfer and high catalytic activity to concurrently promote H2 evolution. This work opens up a new avenue to develop highly active POM@MOF photocatalysts by dual regulation of sensitizing/catalytic centers at the molecular level.

Polydopamine functionalized TiO2 with N doping, oxygen vacancies, and carbon layers for enhanced photoelectrocatalytic performance

The development of a photoelectrode featuring both excellent reusability and a simple preparation process remains exceptionally challenging for TiO2-based photoelectrocatalytic technology. Herein, a three-dimensional photoelectrode with N doping, oxygen vacancies (Ovs), and carbon layers (NTC) was prepared via the "carbothermal reduction-pressing-calcination" method. The photoelectrode degraded 97.94% of tetracycline (TC) within 60 min. The first-order kinetic constant for this degradation was 27.3 times higher than that of TiO2-x, and the photoelectric synergy factor reached as high as 13.9. The photoelectrode also demonstrated outstanding anti-interference capability for pH, electrolyte concentration, anions, etc., and was suitable for different water matrixes and various antibiotics removal. In particular, the degradation efficiency of TC decreased by only 1.33% after 20 cycles, demonstrating the excellent reusability of NTC. Furthermore, photoexcited holes (h+) were the dominant active species, and singlet oxygen (1O2) and superoxide radicals (•O2-) played an auxiliary role in removing TC. Finally, possible degradation pathways for TC were proposed and demonstrated to be effective in reducing the toxicity of the pollutant by the Toxicity Evaluation Software Tool (T.E.S.T) and phytotoxicity experiments. This progress might bring new insights into the design and construction of TiO2-based photoelectrodes.

Recent advances in synthesis and application of Magnéli phase titanium oxides for energy storage and environmental remediation

High-temperature reduction of TiO2 causes the gradual formation of structural defects, leading to oxygen vacancy planar defects and giving rise to Magnéli phases, which are substoichiometric titanium oxides that follow the formula Ti n O2n-1, with 4 ≤ n ≤ 9. A high concentration of defects provides several possible configurations for Ti4+ and Ti3+ within the crystal, with the variation in charge ordered states changing the electronic structure of the material. The changes in crystal and electronic structures of Magnéli phases introduce unique properties absent in TiO2, facilitating their diverse applications. Their exceptional electrical conductivity, stability in harsh chemical environments and capability to generate hydroxyl radicals make them highly valuable in electrochemical applications. Additionally, their high specific capacity and corrosion resistance make them ideal for energy storage facilities. These properties, combined with excellent solar light absorption, have led to their widespread use in electrochemical, photochemical, photothermal, catalytic and energy storage applications. To provide a complete overview of the formation, properties, and environmental- and energy-related applications of Magnéli phase titanium suboxides, this review initially highlights the crystal structure and the physical, thermoelectrical and optical properties of these materials. The conventional and novel strategies developed to synthesise these materials are then discussed, along with potential approaches to overcome challenges associated with current issues and future low-energy fabrication methods. Finally, we provide a comprehensive overview of their applications across various fields, including environmental remediation, energy storage, and thermoelectric and optoelectronic technologies. We also discuss promising new directions for the use of Magnéli phase titanium suboxides and solutions to challenges in energy and environment-related applications, and provide guidance on how these materials can be developed and utilised to meet diverse research application needs. By making use of control measures to mitigate the potential hazards associated with their nanoparticles, Magnéli phases can be considered as versatile materials with potential for next generation energy needs.

Applications of Antimony in Catalysis

Antimony is a fifth-period element in the nitrogen family, a silver-white metalloid with weak conductivity and thermal conductivity. It is stable at room temperature and does not react easily with oxygen and water in the air. Natural minerals are found in the form of sulfides. Current research and applications are mostly concentrated on material modification, utilizing the properties of antimony in traditional chemical industries, helping alloys improve their flame retardancy, stability, increasing semiconductor performance, etc. For example, to enhance the electronic conductivity, after coating or embedding antimony or its derivatives in thin layers in photonic nanomaterials, the performance of the original material in photoelectrochemical catalysis can be effectively increased, thereby expanding the efficiency of oxidation-reduction reactions accounting for the degradation of organic matter in wastewater. However, the catalytic reaction between the derivatives of antimony and organic compounds beside the material is less studied, and the mechanism of the studies in organic synthesis is relatively unclear. The reported organic synthesis related to antimony is mainly in the form of Lewis acid catalysts or dual-metal catalytic systems combined with other metals. This Review will focus on the application of antimony in photocatalysis, electrocatalysis, and other organic syntheses in the past 10 years.

Construction of ternary TiO2/CdS/IrO2 heterostructure photoanodes for efficient glycerol oxidation coupled with hydrogen evolution

A TiO2/CdS heterostructure has been widely investigated as a potential photoanode for photoelectrochemical (PEC) water splitting for hydrogen evolution. However, the efficiency and stability still remain challenging due to the sluggish reaction dynamics for water oxidation and easy photocorrosion of CdS. Here we report a ternary TiO2/CdS/IrO2 heterostructure with IrO2 as a hole transport layer for PEC glycerol oxidation coupled with hydrogen evolution. The photocurrent density of the optimized TiO2/CdS photoanode is 18.8 mA cm-2 (1.23 V vs. RHE), which is about 10.6 times higher than that of the pristine TiO2. It is found that most of the glycerol was converted to formic acid (FA) on the TiO2/CdS surface with a production rate of ∼603.0 mmol m-2 h-1. The average H2 production rate reaches 1574.5 mmol m-2 h-1. After loading IrO2 nanoparticles, the products for glycerol oxidation remain unchanged with the production rate of FA reaching 863.4 mmol m-2 h-1, while the hydrogen production rate is increased to 2345.2 mmol m-2 h-1 due to the improved stability. The results show that the obtained TiO2/CdS/IrO2 heterostructure can effectively oxidize glycerol to value-added chemicals. The enhanced PEC performance and stability of the TiO2/CdS/IrO2 photoanode can be ascribed to the greatly enhanced electrode/electrolyte interfacial carrier injection efficiency, caused by the fast glycerol oxidation dynamics and intimate contact. This work provides novel ideas to construct high-efficiency PEC systems for both clean energy production and high-value chemicals.

Isomer-Effects of Aminophenol Decorated Gold Nanoclusters for H2O2 Photoproduction via Two-Step One-Electron Oxygen Reduction Reaction

Gold (Au) nanoclustersare promising photocatalysts for biomedicine, sensing, and environmental remediation. However, the short carrier lifetime, inherent instability, and unclear charge transfer mechanism hinder their application. Herein, the Au nanoclusters decorated with three different isomers of o-Aminophenol, m-Aminophenol, and p-Aminophenol are synthesized, namely o-Au, m-Au, and p-Au, which achieve efficient hydrogen peroxide (H2O2) photoproduction through two-step one-electron oxygen reduction reaction (ORR). The interfacial kinetics for the photocatalytic process in this system are investigated in detail, in which, the isomer-effects of aminophenol decorated in Au nanoclusters are definitely elucidated by combining transient photovoltage (TPV), transient potential scanning (TPS), and photo-induced current (TPC) tests. The reaction pathway of o-Au, m-Au, and p-Au is confirmed to be the same through TPC. Although the conduction band values of o-Au, m-Au, and p-Au are essentially the same under working conditions, the values of surface effective charges (ne) for both m-Au and p-Au are higher than that of o-Au. In addition, m-Au has a stronger adsorption capacity for O2 and a faster ORR rate. Thus, the m-Au manifests the highest photocatalytic activity for the H2O2 photoproduction. This work shows a new way for the in-situ study on charge distribution and transfer on photocatalysts.

Transient Absorption Microscopy Maps Spatial Heterogeneity and Distinct Chemical Environments in Photocatalytic Carbon Nitride Particles

Limitations in solar energy conversion by photocatalysis typically stem from poor underlying charge carrier properties. Transient Absorption (TA) reveals insights on key photocatalytic properties such as charge carrier lifetimes and trapping. However, on the microsecond timescale, these measurements use relatively large probe sizes ranging in millimetres to centimetres which averages the effect of spatial heterogeneity at smaller length scales. A home-built Transient Absorption Microscopy (TAM) setup is reported and used to study single particles of carbon nitride (CNx), an emerging photocatalyst. For the first time, to the best of the authors' knowledge, µs-s timescales are explored within individual particles to gain a more complete understanding of their photophysics. The dynamics of trapped charges are monitored, enabling measurement and quantification of heterogeneity in the transient absorptance signal of individual CNx particles and within them. Particle-to-particle heterogeneity in the trapped charge density is observed, while spatial heterogeneity in lifetimes within a particle is revealed using a smaller probe beam with a ≈5 µm diameter. Overall, the observations suggest that contributions from different local environments independently influence charge trapping at different timescales. TAM on the micron and microsecond spatiotemporal resolution will aid in tackling design questions about optimal chemical environments for the promotion of photoactivity.

Indium-Iron Oxide Nanosized Solid Solutions as Photocatalysts for the Degradation of Pollutants under Visible Radiation

A series of solid solutions of indium and iron oxides with different In/Fe ratios (InxFeyO3, with x + y = 2) were synthesized in the form of nanoparticles (diameter of ca. 30-40 nm) with the purpose of generating enhanced photocatalysts with an intermediate band gap compared to those of the monometallic oxides, In2O3 and Fe2O3. The materials were prepared by co-precipitation from an aqueous solution of iron and indium nitrates and extensively characterized with a combination of techniques. XRD analysis proved the formation of the desired InxFeyO3 solid solutions for Fe content in the range 5-25 mol%. UV-Vis absorption analysis showed that the substitution of In with Fe in the crystalline structure led to the anticipated gradual decrease of the band gap values compared to In2O3. The obtained semiconductors were tested as photocatalysts for the degradation of model organic pollutants (phenol and methylene blue) in water. Among the InxFeyO3 solid solutions, In1.7Fe0.3O3 displayed the highest photocatalytic activity in the degradation of the selected probe molecules under UV and visible radiation. Remarkably, In1.7Fe0.3O3 showed a significantly enhanced activity under visible light compared to monometallic indium oxide and iron oxide, and to the benchmark TiO2 P25. This demonstrates that our strategy consisting in engineering the band gap by tuning the composition of InxFeyO3 solid solutions was successful in improving the photocatalytic performance under visible light. Additionally, In1.7Fe0.3O3 fully retained its photocatalytic activity upon reuse in four consecutive cycles.

Photodegradation of aqueous tetracycline using CuS@TiO₂ composite under solar-simulated light: Complete mineralization, catalyst efficiency, and reusability

While CuS/TiO₂ has been previously synthesized and employed in a limited number of photodegradation studies, the current study investigated its effectiveness for TC degradation under UV-visible light irradiation. CuS is known to be a nontoxic, environmentally friendly material; hence, it has great potential as an alternative to CdS and CdSe, which are used conventionally as sensitizers. In this work, the CuS/TiO₂ photocatalysts achieved a maximum 95 % removal of TC at an initial concentration of 20 ppm, confirming the good utilization of active sites. Even though the efficiency decreased for higher TC concentrations due to the saturation of the active sites, the values of the quantum yield showed that photon utilization was still effective. Consequently, the photocatalyst showed an optimum yield at 0.20 g, and its further addition increased the efficiency rather insignificantly. In addition to the near-complete mineralization of TC by the CuS/TiO₂ composite with few byproducts, its reusability was excellent because it showed almost consistent performance in successive cycles. These results further confirm the continuous relevance and potential of CuS/TiO₂ as a practical, sustainable solution for organic pollutant degradation, reinforcing its value in environmental remediation applications.

The Stability of TiO2 Phases Studied Using r2SCAN in the Hubbard-Corrected Density Functional Theory

Titanium dioxide is a quintessential transition metal oxide with many technologically important applications. With its richness in phases, it has also been a testing ground for numerous theoretical studies including density functional theory. We investigated several phases of TiO2 using the all-electron density functional theory with a regularized-restored strongly constrained appropriately normed (r2SCAN) exchange-correlation functional, a popular choice of meta-generalized gradient approximation (meta-GGA). Specifically, the equilibrium lattice parameters were more accurate than those predicted by GGA and agreed well overall with the experimental data. With increasing pressure, the order of stability was determined as anatase < columbite < rutile < baddeleyite < orthorhombic I < cotunnite, as in the calculations using GGA. Including the Hubbard correction term, the correct ordering between rutile, anatase, and columbite can be achieved, consistent with experimental observations. The necessary U value using r2SCAN is much smaller than that using GGA+U. In addition, the Hubbard correction method using r2SCAN is substantially less sensitive to the size of the local projection space compared to the GGA+U study reported recently. We attribute these significantly improved results to the reduced self-interaction error in the r2SCAN functional.

Recent advances in the design and preparation of graphitic carbon nitride for photocatalysis

Graphitic carbon nitride (g-C3N4) has recently gained tremendous attention as a promising photocatalyst for environmental and energy-related applications owing to its high thermal and physicochemical stability as well as its suitable band structure. However, bulk g-C3N4, typically synthesized by directly heating N-rich small molecules, often suffers from severe aggregation, a low specific surface area for light harvesting and rapid recombination of photogenerated electron-hole pairs. These factors significantly hinder its photocatalytic efficiency. Consequently, considerable efforts have been devoted to the rational design and synthesis of g-C3N4 with tailored morphologies and controllable electronic and band structures, utilizing both top-down and bottom-up approaches. Thus far, in addition to the conventional and commonly used methods for carbon nitride preparation, new techniques and precursor families are continuously being developed. This review discusses the latest advancements in synthetic approaches for g-C3N4-based materials and provides valuable insights into utilizing these methods to enhance their photocatalytic performance. Finally, the review concludes by presenting an outlook on the future directions and challenges in the development of CN materials for photocatalysis.

The photo-electrocatalytic property of hollow mesoporous graphene oxide/tungsten trioxide/titanium dioxide membrane photo-anode

Titania (TiO2) is one of promising photo catalysts for its high ability to resistant photo corrosion and environmental friendliness, but its photocatalytic activity is too low to be used in industry. To find an approach to solve this problem, graphene oxide (GO), tungsten trioxide (WO3) and TiO2 composite with hollow mesoporous structure was prepared by a two-step spray drying method. The composite was used as raw material to constitute a membrane onto ITO glass to form a membrane photo-anode. In this way, its photo-electrocatalytic property was tested. The morphology, crystal phase, microstructure and specific surface area of the composite were characterized by SEM, XRD, TEM and BET, respectively. The surface potential distribution and optical property of the anode were measured by a Kelvin Probe Force Microscopy and a Fs-5 Steady-State Fluorescence Spectrometer, respectively. The forbidden bandwidth of the GO-WO3/TiO2 composite is 2.30 eV, which is much lower than that of the WO3/TiO2 composite, 2.92 eV. When the content of GO in the anode is around 1 wt%, its light absorption ability is the best among all the anodes with different contents of GO, and its photocatalytic ability to degrade methyl orange is the strongest as our experiments concerned. These findings indicate that the addition of GO into the WO3/TiO2 composite can improve its photo-electrocatalytic property. The construction of membrane photo-anode is an efficient approach to solve the problem of the recovery and secondary utilization of nanoscale powder in water treatment.

Optical Properties of Thick TiO2-P25 Films

In this study, TiO2-P25 films on FTO substrates were synthesized using the sol-gel process and studied using Variable Angle Spectroscopy Ellipsometry (VASE) to determine their optical constants and thickness. The measurements were carried out at room temperature in the wavelength range of (300-900) nm at incident angles varying from 55° to 70°. The resulting thicknesses were found to be around 1000 nm. A graded layer model, which allowed for accurate representation of the depth-dependent optical variations, was employed to model the properties of these TiO2-P25 films. This modeling approach provided deeper insights into the internal structure of the films, particularly how the graded structural characteristics impact the overall optical behavior. Understanding these depth-dependent variations is essential for optimizing the use of TiO2-P25 films in technologies such as solar cells and optical devices.

Cluster Engineering in Water Catalytic Reactions: Synthesis, Structure-Activity Relationship and Mechanism

Four fundamental reactions are essential to harnessing energy from water sustainably: oxidation reduction reaction (ORR), oxygen reduction reaction (OER), hydrogen oxidation reaction (HOR), and hydrogen evolution reaction (HER). This review summarizes the research advancements in the electrocatalytic reaction of metal nanoclusters for water splitting. It covers various types of nanoclusters, particularly those at the size level, that enhance these catalytic reactions. The synthesis of cluster-based catalysts and the elucidation of the structure-activity relationships and reaction mechanisms are discussed. Emphasis is placed on utilizing atomically precise cluster materials and the interplay between the carrier and cluster in water catalysis, especially for applying catalytic engineering principles (such as synergy, coordination, heterointerface, and lattice strain engineering) to understand structure-activity relationships and catalytic mechanisms for cluster-based catalysts. Finally, the field of cluster water catalysis is summarized and prospected. We believe that developing cluster-based catalysts with high activity, excellent stability, and high selectivity will significantly promote the development of renewable energy conversion reactions.

Exfoliated MoS2 nanosheets immobilized in porous microbeads as recoverable photocatalysts

Molybdenum disulfide (MoS2) is a highly effective visible light photocatalyst when used as well-exfoliated 2D nanosheets. The ability to make effective use of these properties is significantly compromised by the challenge of preventing nanosheet aggregation or restacking in fluid suspensions. We report a strategy for immobilizing chemically exfoliated MoS2 as single- and few-layer nanosheets in porous crosslinked polymers prepared as microbeads. The polymeric support prevents aggregation of the nanosheets while allowing access to the nanomaterial for model organic compounds present in the surrounding fluid. Exposure to visible light results in high degradation yields (>99%) of these organic species in aqueous media, and the MoS2 nanosheets maintain their photocatalytic efficacy through multiple cycles of use. The recoverability of the porous beads and the persistent photocatalytic activity of the polymer-supported MoS2 offer the potential of realizing an effective, environmentally sustainable platform for photocatalytic degradation of dissolved solutes.

Highly stable 3D cellulose micro-rolls support TiO2 for efficient photocatalysis degradation experiment under weak light conditions

Immobilization of nanometer-scale photocatalysts on a 3D polymeric substrate could play several complementary roles in photocatalysis, such as providing mechanical stability, facilitating easy recycling after usage, enhancing adsorption capability, and improving light harvesting properties through multiple reflections. To achieve stable and efficient photocatalysis under weak light conditions, 3D cellulose micro-rolls were introduced into the photocatalytic composites. Here, the formation of micro-rolls is attributed to the presence of titania nanoparticles, which generate uneven shrinkage stress in cellulose during the freeze-drying process, thereby inducing the cellulose to curl up. The dramatic structural transformation of the 3D micro-rolls increased the Brunauer-Emmett-Teller (BET) surface area of the sample. The 3D micro-roll structure is more favorable for photocatalysis due to its efficient mass transfer and exposed reactive sites, laying the foundation for enhanced adsorption capacity and photocatalytic reactions. The adsorption experiments suggested that the inner space of the micro-rolls provides a sufficient reaction zone, enabling fast mass transfer of molecules and easy access to the active sites. The samples could stand a high strain of 80 % and retain 96 % of the original maximum stress after 200 cyclic compressions, indicating excellent long-term stability. In addition, the photocatalytic tests show that with the help of micro-rolls, TiO2 can convert and utilize weak light that would otherwise be unused, and the catalysate exhibits almost no toxicity towards Escherichia coli.

Au@TiO2 Core-Shell Nanoparticles with Nanometer-Controlled Shell Thickness for Balancing Stability and Field Enhancement in Plasmon-Enhanced Photocatalysis

Plasmonic core-shell nanostructures can make photocatalysis more efficient for several reasons. The shell imparts stability to the nanoparticles, light absorption is expanded, and electron-hole pairs can be separated more effectively, thus reducing recombination losses. The synthesis of metal@TiO2 core-shell nanoparticles with nanometer control over the shell thickness and understanding its effect on the resulting photocatalytic efficiency still remains challenging. In the present study, a synthesis method is presented for preparing Au@TiO2 core-shell nanoparticles with ultrathin shells that can be accurately tuned in the range of 2-12 nm, based on the controlled slow hydrolysis of a titanium precursor. Electromagnetic simulations combined with comprehensive characterization of the opto-physical bulk properties, as well as energy electron loss spectroscopy and electron tomography reconstructions at the nanoscale, aid in understanding the crucial role of the shell in improving both the activity as well as the stability in a photocatalytic reaction. Ultrathin shells in the order of 2 nm do not suffice to prevent sintering of the nanoparticles upon annealing, with a consequent loss of plasmonic properties. After reaching an optimum for a shell of 4 nm, further increasing the shell thickness again reduces the plasmonic properties by a weakened plasmonic coupling. This trend is confirmed by photocatalytic hydrogen evolution experiments, as well as stearic acid degradation tests. With this study, we prove and emphasize the crucial importance of carefully controlling the shell thickness in plasmonic core-shell structures, so their maximum application potential may be unlocked.

TiO2-based photocatalysts from type-II to S-scheme heterojunction and their applications

Photocatalysis is a promising sustainable technology to remove organic pollution and convert solar energy into chemical energy. Titanium dioxide has drawn extensive attention in this field owing to its high activity under UV light, good chemical stability, large availability, low price and low toxicity. However, the poor quantum efficiency derived from fast electron/hole recombination, the limited utilization of sunlight, and a weak reducing ability still hinder its practical application. Among the modification strategies of TiO2 to enhance its performance, the construction of heterojunctions with other semiconductors is a powerful and versatile way to maximise the separation of photogenerated charge carriers and steer their transport toward enhanced efficiency and selectivity. Here, the research progress and current status of TiO2 modification are reviewed, focusing on heterojunctions. A rapid evolution of the understanding of the different charge transfer mechanisms is witnessed from traditional type II to the recently conceptualised S-scheme. Particular attention is paid to different synthetic approaches and interface engineering methods designed to improve and control the interfacial charge transfer, and several cases of TiO2 heterostructures with metal oxides, metal sulfides and carbon nitride are discussed. The application hotspots of TiO2-based photocatalysts are summarized, including hydrogen generation by water splitting, solar fuel production by CO2 conversion, and the degradation of organic water pollutants. Hints about less studied and emerging processes are also provided. Finally, the main issues and challenges related to the sustainability and scalability of photocatalytic technologies in view of their commercialization are highlighted, outlining future directions of development.

A MOF-derived CuO/TiO2 photocatalyst for methanol production from CO2 reduction in an AI-assisted continuous flow reactor

A CuO/TiO2 hybrid heterostructure was successfully engineered from copper metal-organic frameworks (MOFs) using a two-step process involving solvothermal synthesis and calcination. By precisely controlling the CuO loading, this synergistic composite exhibited exceptional performance in photocatalytic CO2 reduction. Notably, AI-assisted continuous flow experimentation achieved a record-breaking methanol production rate of 2.3 mol g-1 h-1 without the need for sacrificial agents.

Molecular-scale insights into the electrical double layer at oxide-electrolyte interfaces

The electrical double layer (EDL) at metal oxide-electrolyte interfaces critically affects fundamental processes in water splitting, batteries, and corrosion. However, limitations in the microscopic-level understanding of the EDL have been a major bottleneck in controlling these interfacial processes. Herein, we use ab initio-based machine learning potential simulations incorporating long-range electrostatics to unravel the molecular-scale picture of the EDL at the prototypical anatase TiO2-electrolyte interface under various pH conditions. Our large-scale simulations, capable of capturing interfacial water dissociation/recombination reactions and electrolytic proton transport, provide unprecedented insights into the detailed structure of the EDL. Moreover, the larger capacitance of the EDL under basic relative to acidic conditions, originating from the higher affinity of the cations for the oxide surface, is found to give rise to distinct charging mechanisms on negative and positive surfaces. Our results are validated by the agreement between the computed EDL capacitance and experimental data.

Manipulating the H2O2 Reactivity on Pristine Anatase TiO2 with Various Surface Features and Implications in Oxidation Reactions

Anatase TiO2 is commonly used as a catalyst/support in reactions involving H2O2, yet the understanding of interactions between common TiO2 surfaces and H2O2 remains limited. Herein, we synthesized well-defined TiO2 crystallites with (101), (001), and fluorine-modified (001) [F-(001)] surfaces to examine how surface features, including the arrangement of five-coordinated Ti (Ti5c) sites and the presence of fluorine, influence H2O2 activation. Our findings reveal that these surface features significantly affect the physiochemical properties of adsorbed H2O2. Specifically, fluorine on the F-(001) surface introduces an additional hydrogen bond to the Ti5c-peroxo species, altering the electronic structure of H2O2 compared to those with the (101) and (001) surfaces. Using cyclohexene as a probe substrate, we successfully distinguished the reactivities of the Ti5c-peroxo species. The activity of those on the F-(001) surface was significantly higher than the activity of those on the (001) surface, while the (101) surface showed negligible oxidation activity. These insights can guide the design of TiO2-based catalysts for H2O2-related reactions.

Cross-Coupling of 1,2,3,4-Tetrachlororodibenzo-p-dioxin with Six Coexisting Polycyclic Aromatic Hydrocarbons during Photodegradation on a Fly Ash Surface

The adverse conditions of the garbage incineration process can lead to the generation of dioxins and polycyclic aromatic hydrocarbons (PAHs). This study aimed to investigate the removal efficiency and possible cross-coupling effect of 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) and six coexisting low-molecular-weight PAHs during photodegradation on the fly ash surface. Due to their higher photoreactivity and light-shielding effect, the six PAHs exhibited inhibitory effects on the photodegradation of 1,2,3,4-TCDD, causing a reduction of 4.1%-21.2% in the removal efficiency. Common degradation products of 1,2,3,4-TCDD and PAHs were identified by LC-MS and GC-MS, and the formation of primary products was verified by theoretical calculations of bond dissociate energies, excitation energy, frontier electron densities, and transition states. In addition, high-molecular-weight coupling products of 1,2,3,4-TCDD and its interaction products with PAHs were observed in the mixed irradiation samples, and two coupling elimination mechanisms were proposed to illustrate their formation through C-O-C bonding and -COO- bonding, respectively. According to toxicity prediction analysis, the developmental toxicity and mutagenicity of most interaction products were higher than 1,2,3,4-TCDD. This study provided some new insights into the transformation, interaction, and related ecological risks of dioxins and PAHs coexisting on the surface of fly ash during the waste incineration process.

Ti3+ Self-Doping of TiO2 Boosts Its Photocatalytic Performance: A Synergistic Mechanism

Pollution remains one of the most significant global challenges. Photocatalysis consists of a new organic pollutant removal technology, with TiO2 widely studied as a photocatalyst in the photocatalytic removal of water pollution. However, intrinsic TiO2 has the disadvantages of weak visible light absorption, low electron separation, and transmission efficiency, as well as few active sites. In this study, anatase-phase Ti3+ self-doped TiO2 (B-TiO2) with a core-shell structure was successfully prepared by forming an amorphous layer rich in oxygen vacancies (OVs) and Ti3+ defects on the TiO2 surface under a nitrogen atmosphere using NaBH4 as a chemical-reducing agent. The visible light absorption performance of the catalyst was notably improved when exposed to light irradiation. The bending of surface energy bands facilitated the separation of photogenerated electron-hole pairs, and the core-shell structure allowed the electron-hole pairs to be transported to the surface of the catalyst and participate in the reaction faster. We observed that 92.86% of Rhodamine B (RhB) was degraded in only 5 min, an increase of 2.73 times that of the degradation rate observed in commercial P25. With extraordinary stability, the photocatalytic efficiency of the catalyst remained at 96.2% after five degradation cycles.

Adsorption Structure-Activity Correlation in the Photocatalytic Chemistry of Methanol and Water on TiO2(110)

ConspectusPhotocatalysis, a process involving light absorption (band gap excitation), charge separation, interfacial charge transfer, and surface redox reactions, has attracted intensive attention because of the potential applications in solar to fuel conversion. Despite the great efforts devoted to the design of materials and optimization of charge separation and overall efficiency, the molecular mechanism of photocatalytic reactions, for example, water oxidation, is still unclear, mainly because of the complexity of powder catalysts and the aqueous environment which prevent the direct experimental detection of adsorption sites, surface species, and charge/energy transfer dynamics. Without direct evidence, the charge transfer and elementary reaction steps remain elusive, and misleading conclusions are sometimes drawn. For instance, the positively charged 5-fold coordinated Ti sites (Ti5cs) on TiO2 surfaces are argued to propel holes and therefore cannot be active sites for oxidative reactions, regardless of the demonstration by scanning tunneling microscopy (STM). Direct site-specific measurements are thus highly demanded. Surface science studies, which rely on well-defined single crystals and ultrahigh vacuum based techniques, can identify the active sites and active species at the catalyst surfaces and measure the interfacial electronic structure and energy of desorbing species for charge transfer analysis, providing direct evidence for investigating the photocatalytic reaction mechanism at the molecular level.In this Account, the elementary photocatalytic chemistry of methanol and water on TiO2, which are investigated by surface science techniques such as atom-resolved STM, ensemble-averaged mass spectrometer based temperature-programmed desorption/time-of-flight spectroscopy, and photoelectron spectroscopy in combination with theoretical calculations, will be described. Both methanol and water can be photocatalytically oxidized at Ti5cs, producing adsorbed formaldehyde and gaseous •OH radicals, respectively, under ultraviolet (UV) light irradiation. The photocatalytic activity shows salient adsorption structure including adsorption site (terminal/bridging), adsorption state (molecular/dissociative) and adsorption configuration (monomer/cluster) dependence, which comes from the ability to generate terminal anions which are capable of capturing photogenerated holes and exhibit superior photocatalytic activity over their parent molecules. These studies reveal the origin of the correlation between photocatalytic activity and adsorption structure of CH3OH and H2O on TiO2 surfaces and suggest that the simple criteria widely used to analyze the feasibility of charge transfer, i.e., the relative position of the band edges and the molecular orbitals of adsorbates, should be replaced by the change of Gibbs free energy of the charge trapping reaction from the thermodynamic point of view. These results contribute to the fundamental understanding of photocatalysis. Based on our research, future state-resolved and time-resolved studies can provide deeper insight into the charge and energy transfer and transient intermediate species, which will benefit the depiction of the overall photocatalytic reactions, for example, the photocatalyzed oxygen evolution reaction from water.

Hyaluronic acid modified prussian blue analogs/TiO₂ janus nanostructures through efficient charge separation to enhance photocatalytic-driven dual gas for achieve multimodal treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by the abnormal proliferation of fibroblast-like synoviocytes and changes in the joint synovium, including elevated reactive oxygen species, decreased pH, and reduced oxygen content. In this study, we synthesized a novel nanocomposite material, namely HA-PBA-TiO2 Janus nanocomposite, by in situ etching in prussian blue analogs doped with Co and Ni, followed by the growth of TiO2 nano-flowers and encapsulation in hyaluronic acid. When these janus nanoparticles diffused to the inflammatory sites of RA, they exhibited outstanding photocatalytic water-splitting ability under 660 nm laser irradiation, generating H2 and O2. This capability helps ameliorate the hypoxic microenvironment at RA inflammatory sites by eliminating reactive oxygen species (ROS) and enhancing antioxidation and oxygenation. Furthermore, owing to the doping of Co and Ni, HA-PBA-TiO2 exhibits photothermal conversion capability, which significant damage to FLS upon exposure to 660 nm laser irradiation, thereby controlling their aberrant proliferation. Through a series of in vitro and in vivo experiments, we validated the significant therapeutic efficacy of HA-PBA-TiO2 in treating RA, highlighting its broad prospects for application.

NOx precipitation and valorization driven by photocatalysis and adsorption over red soil

Nitrogen oxides (NOx) emissions can cause air pollution that is harmful to human health, even producing serious ecological problems. Whether it is diluted in the air or not, the management and valorization of NOx from industrial emissions have been constrained by technology and finance. This study shows that red soil can be used as a photocatalyst to convert NOx into soil nitrate nitrogen (NO3--N) in the soil. The addition of zinc oxide (ZnO) and titanium dioxide (TiO2) onto the soil surface improves the photocatalytic precipitation efficiency of 1 ppm NO, approaching a removal efficiency of 77 % under ultraviolet (UV) light. The efficiency of red soil in precipitating NOx through adsorption exceeded that of photocatalysis at 100 ppm NOx (e.g. 16.02 % versus 7.70 % in 0.1-mm soil). Pot experiment reveals that the precipitated NO3--N promoted biomass of water spinach (Ipomoea aquatica Forsk). Additionally, adding ZnO or TiO2 also affects mineral nutrition. This demonstration of converting air pollutants into available nitrogen (N) for plant growth not only provides a new perspective on treatment and valorization for NOx but also sheds light on the transport of N in the air-soil-plant path.

Sustainable and facile fabrication of chitosan-coated silver-doped zinc oxide nanocomposites exploiting Bergera koenigii foliage for enhanced photocatalysis and antibacterial activity

Industrial and academic chemical pollutants such as Eriochrome Black-T (EBT) and murexide dyes are widely used in academic institution as well as industries, when eluted into rivers, delineate the ill effect on human and aquatic life. Herein, green and ecofriendly synthesis of silver doped-Zinc oxide nanoparticles (Ag/ZnO NPs) and chitosan coated Ag/ZnO nanoparticles (CS/Ag/ZnO NPs) using Bergera koenigii extract to solve environmental issues have been reported for the first time. Spherical and agglomerated particles with crystalline flakes like morphology of Ag/ZnO NPs and CS/Ag/ZnO NPs respectively have been ascertained by Scanning electron morphology (SEM) analyses and XRD. XRD analysis revealed the average crystallite size of 42.16 nm and 48.45 nm for Ag/ZnO NPs with 5 % and 10 % Ag concentration respectively, lesser than crystallite size of 47.394 nm and 52.38 nm for CS-5 % Ag/ZnO NC and CS-10 % Ag/ZnO NC respectively. All the synthesized NPs and NC demonstrated remarkable antibacterial potential against both gram +ve and gram -ve bacteria. Additionally, all the materials showed very high time-dependent photocatalytic degradation activity (>98 %) of EBT and murexide in 12 min. Remarkably, all active nano-catalysts exhibit high durability, and displayed recyclability for >8 cycles. In nutshell, chitosan coated nano-catalyst showed drastic improvement in photocatalytic and antibacterial activities.

High efficiency azo dye removal via a combination of adsorption and photocatalytic processes using heterojunction Titanium dioxide nanoparticles on hierarchical porous carbon

Amidst the rapid development of the textile industry, wastewater problems also arise. High-performance materials for reactive black 5 (RB5) dye treatment by adsorption and photocatalysis were evolved using Titanium dioxide (TiO2) nanoparticles on carbon media. Herein, the synthesis of spherical carbon via the water-in-oil emulsion method alongside a sol-gel process and the production of TiO2 nanoparticles using the precipitation procedure of Titanium isopropoxide and carbonization at 700-900 °C for 2 h are a novel approach in this work. The characterization of these materials indicates that different temperatures result in distinct properties, for instance, raised pores on the surface of the media and changes in the crystal structure of TiO2. The results show that the as-synthesized material carbonized at 900 °C had distinguished dye adsorption, up to 430 ppm in 1 h, due to their high surface area and pore volume. On the contrary, the calcined 700 °C condition had the prominent photocatalytic efficiency on account of the heterojunction band gap between anatase and rutile crystal structure. A mixed phase minimizes the charge recombination, subsequently increasing the photocatalytic capability.

Synthesis and Photochemical Properties of Heterometallic Ti-Cu Ring Clusters Constructed from Myo-Inositol Ligand

Incorporating heterometals into titanium-oxygen clusters represents an effective approach to adjusting the band gap and absorption properties. Herein, a family of heterometallic Ti-Cu clusters was synthesized under solvothermal conditions. The unique structural feature of these clusters is the formation of ring clusters with myo-inositol ligands serving as structure-directing ligands. The myo-inositol ligand, as a typical polyol ligand, demonstrates flexible and distinctive coordination modes capable of chelating up to eight transition metal ions simultaneously. Compounds 4 and 5 show significant absorption in the visible region, indicating that the incorporation of Cu ions can efficiently tune the band gap of titanium-oxygen clusters.

Cerium-Doped Nickel Sulfide Nanospheres as Efficient Catalysts for Overall Water Splitting

The development of non-precious metal electrocatalysts with excellent activity and durability for electrochemical water splitting has always been a goal. Transition metal sulfides are attractive electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this article, we designed and constructed efficient catalysts with multiple synergistic interactions and synthesized Ce-NiS2@NF nanosphere using a solvothermal method. Ce-NiS2@NF exhibits excellent HER performance, OER performance, and overall water splitting capability in alkaline electrolytes, demonstrating good stability. The addition of Ce influences the activity of the catalysts, attributed to the synergistic interactions creating more active sites and higher intrinsic activity through the introduction of Ce heteroatoms. Additionally, the self-supported conductive substrate promotes electron transfer, enhancing the intrinsic activity and active site density of the catalyst. This study provides an in-depth investigation into structural design and performance enhancement, offering ideas for designing efficient catalysts for overall water electrolysis. This work provides an in-depth study in terms of structural design performance enhancement and provides ideas for designing efficient alkaline bifunctional catalysts. Valuable insights have been provided in elucidating the intrinsic mechanism of the catalytic activity of cerium-doped nickel sulfide nanospheres, thus providing new guidance in the field of energy conversion technology.

Photocatalysis of Adsorbed Catechol on Degussa P25 TiO2 at the Air-Solid Interface

Semiconductor photocatalysis with commercial TiO2 (Degussa P25) has shown significant potential in water treatment of organic pollutants. However, the photoinduced reactions of adsorbed catechol, a phenolic air pollutant from biomass burning and combustion emissions, at the air-solid interface of TiO2 remain unexplored. Herein we examine the photocatalytic decay of catechol in the presence of water vapor, which acts as an electron acceptor. Experiments under variable cut-off wavelengths of irradiation (λcut-off ≥ 320, 400, and 515 nm) distinguish the mechanistic contribution of a ligand-to-metal charge-transfer (LMCT) complex of surface chemisorbed catechol on TiO2. The LMCT complex injects electrons into the conduction band of TiO2 from the highest occupied molecular orbital of catechol by visible light (≥2.11 eV) excitation. The deconvolution of diffuse reflectance UV-visible spectral bands from LMCT complexes of TiO2 with catechol, o-semiquinone radical, and quinone and the quantification of the evolving gaseous products follow a consecutive kinetic model. CO2(g) and CO(g) final oxidation products are monitored by gas chromatography and Fourier-transform infrared spectroscopy. The apparent quantum efficiency at variable λcut-off are determined for reactant loss (Φ- TiO2/catechol = 0.79 ± 0.19) and product growth ΦCO2 = 0.76 ± 0.08). Spectroscopic and electrochemical measurements reveal the energy band diagram for the LMCT of TiO2/catechol. Two photocatalytic mechanisms are analyzed based on chemical transformations and environmental relevance.

Unveiling efficient S-scheme charge carrier transfer in hierarchical BiOBr/TiO2 heterojunction photocatalysts

The construction of a potential heterojunction catalyst with proper interface alignment has become a hot topic in the scientific community to effectively utilize solar energy. In this work, a one-dimensional TiO2 nanofiber/BiOBr S-scheme heterojunction was synthesized, and charge carrier dynamics within the interface channel were explored. In addition, we incorporated mixed phase TiO2 with point defects and oxygen vacancies, which greatly promoted the initial band edge shift from the UV region. Upon the addition of BiOBr, absorption in the visible light region of the electromagnetic (EM) spectrum was observed with a decrease in the optical band gap value. The optimized BiOBr heterojunction (BTNF1.5) revealed a higher photocatalytic RhB dye degradation efficiency due to the efficient generation and separation of charge carriers upon light irradiation. The optimum sample BTNF1.5 showed a high degradation efficiency of 98.4% with a rate constant of 47.1 min-1 at 8 min of visible light irradiation, which is double than that of the pure TiO2. Electrochemical analysis, time-resolved photoluminescence and Kelvin probe measurement revealed an S-scheme charge-transfer mechanism within the BiOBr/TiO2 system. This work provides a strategy for the facile synthesis of heterojunction photocatalysts exhibiting exceptional catalytic performance.

A machine learning-assisted study of the formation of oxygen vacancies in anatase titanium dioxide

Defect engineering of semiconductor photocatalysts is critical in reducing the reaction barriers. The generation of surface oxygen vacancies allows substantial tuning of the electronic structure of anatase titanium dioxide (TiO2), but disclosing the vacancy formation at the atomic level remains complex or time-consuming. Herein, we combine density functional theory calculations with machine learning to identify the main factors affecting the formation of oxygen defects and accelerate the prediction of vacancy formation. The results show that the first two-layer oxygen atoms on the typical surfaces of TiO2, including (100), (110), and (211) facets, are more likely to be activated when the gas is more reduced, the pressure is higher, and the reduction temperature is increased. Through machine learning, we can conveniently predict the formation of oxygen defects with high accuracy. Furthermore, we present an equation with acceptable accuracy for quantitatively describing the formation of oxygen vacancies in different chemical environments. Our work provides a fast and efficient strategy for characterizing the surface structure with atomic defects.

Clay Minerals/TiO2 Composites-Characterization and Application in Photocatalytic Degradation of Water Pollutants

TiO2 used for photocatalytic water purification is most active in the form of nanoparticles (NP), but their use is fraught with difficulties in separation from solution or/and a tendency to agglomerate. The novel materials designed in this work circumvent these problems by immobilizing TiO2 NPs on the surface of exfoliated clay minerals. A series of TiO2/clay mineral composites were obtained using five different clay components: the Na-, CTA-, or H-form of montmorillonite (Mt) and Na- or CTA-form of laponite (Lap). The TiO2 component was prepared using the inverse microemulsion method. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopy/energy dispersive X-ray spectroscopy, FTIR spectroscopy, thermal analysis, and N2 adsorption-desorption isotherms. It was shown that upon composite synthesis, the Mt interlayer became filled by a mixture of CTA+ and hydronium ions, regardless of the nature of the parent clay, while the structure of Lap underwent partial destruction. The composites displayed high specific surface area and uniform mesoporosity determined by the size of the TiO2 nanoparticles. The best textural parameters were shown by composites containing clay components whose structure was partially destroyed; for instance, Ti/CTA-Lap had a specific surface area of 420 m2g-1 and a pore volume of 0.653 cm3g-1. The materials were tested in the photodegradation of methyl orange and humic acid upon UV irradiation. The photocatalytic activity could be correlated with the development of textural properties. In both reactions, the performance of the most photoactive composites surpassed that of the reference commercial P25 titania.

Magnetic Chitosan/ZrO2 Composites for Vanadium(V) Adsorption while Concurrently being Transformed to a Dual Functional Catalyst

Spent adsorbents for recycling as catalysts have drawn considerable attention due to their environmentally benign chemistry properties. However, traditional thermocatalytic strategies limit their applications. Here, we developed an enhanced photocatalytic strategy to expand the range of their applications. A magnetic chitosan/ZrO2 composites (MZT) for V(V) adsorption, which were prepared using chitosan, ZrO2 and Fe3O4 by one-pot synthesis. The spent MZT as a catalyst was used to synthesize 2-phenyl-1H-benzo[d]imidazole, yielding up to 89.7 %. It also was implemented to photocatalysis reactions for recycle. The discolored rates of rhodamine B (RhB) were 72.3 % and 97.4 % by new and spent MZT, respectively. The new and spent MZT showed the forbidden bands were 251 nm and 561 nm, respectively. The result displayed spent MZT red shifted to the cyan light region. The mechanism of catalysis also has been studied in detail.

Theoretical investigations of optoelectronic properties, photocatalytic performance as a water splitting photocatalyst and band gap engineering with transition metals (TM = Fe and Co) of K3VO4, Na3VO4 and Zn3V2O8: a first-principles study

First-principles density functional investigations of the structural, electronic, optical and thermodynamic properties of K3VO4, Na3VO4 and Zn3V2O8 were performed using generalized gradient approximation (GGA) via ultrasoft pseudopotential and density functional theory (DFT). Their electronic structure was analyzed with a focus on the nature of electronic states near band edges. The electronic band structure revealed that between 6% Fe and 6% Co, 6% Co significantly tuned the band gap with the emergence of new states at the gamma point. Notable variations were highlighted in the electronic properties of Na3V(1-x)Fe x O4, Na3V(1-x)Co x O4, K3V(1-x)Fe x O4, K3V(1-x)Co x O4, Zn3(1-x)V2(1-x)Co x O8 and Zn3(1-x)V2(1-x)Fe x O8 (where x = 0.06) due to the different natures of the unoccupied 3d states of Fe and Co. Density of states analysis as well as α (spin up) and β (spin down) magnetic moments showed that cobalt can reduce the band gap by positioning the valence band higher than O 2p orbitals and the conduction band lower than V 3d orbitals. Mulliken charge distribution revealed the presence of the 6s2 lone pair on Zn, greater population and short bond length in V-O bonds. Hence, the hardness and covalent character develops owing to the V-O bond. Elastic properties, including bulk modulus, shear modulus, Pugh ratio and Poisson ratio, were computed and showed Zn3V2O8 to be mechanically more stable than Na3VO4 and K3VO4. Optimal values of optical properties, such as absorption, reflectivity, dielectric function, refractive index and loss functions, demonstrated Zn3V2O8 as an efficient photocatalytic compound. The optimum trend within finite temperature ranges utilizing quasi-harmonic technique is illustrated by calculating thermodynamic parameters. Theoretical investigations presented here will open up a new line of exploration of the photocatalytic characteristics of orthovanadates.