Synthesis of uniform ordered mesoporous TiO2 microspheres with controllable phase junctions for efficient solar water splitting

Oxygen vacancy-rich high-pressure rocksalt phase of zinc oxide for enhanced photocatalytic hydrogen evolution

The generation of hydrogen as a clean energy carrier by photocatalysis, as a zero-emission technology, is of significant scientific and industrial interest. However, the main drawback of photocatalytic hydrogen generation from water splitting is its low efficiency compared to traditional chemical or electrochemical methods. Zinc oxide (ZnO) with the wurtzite phase is one of the most investigated photocatalysts for hydrogen production, but its activity still needs to be improved. In this study, an oxygen-deficient high-pressure ZnO rocksalt phase is stabilized using a high-pressure torsion (HPT) method, and the product is used for photocatalysis under ambient pressure. The simultaneous introduction of oxygen vacancies and the rocksalt phase effectively improved photocatalytic hydrogen production to levels comparable to benchmark P25 TiO2, due to improving light absorbance and providing active sites for photocatalysis without any negative effect on electron-hole recombination. These results confirm the high potential of high-pressure phases for photocatalytic hydrogen generation.

Spatial interfacial heterojunctions of TiO2 for photocatalytic degradation of toluene: Effects of interface amorphous region and oxygen vacancy

The catalytic activity of TiO2 is contingent upon its crystal structure and the optoelectronic properties associated with defects. In this study, a one-step method was used to synthesize TiO2 with a spatial interface of rutile/anatase phases, and a simple thermal annealing process was applied to optimize the amorphous regions and oxygen vacancies at the interface between the rutile and anatase phases of TiO2. High-resolution transmission electron microscopy (HRTEM) elucidates the evolution process of the amorphous domain at the interface, skillfully introducing oxygen vacancies at the heterojunction interface by modulating the amorphous domain. The obtained photocatalyst (TiO2-350 °C) after annealing exhibits an optimal interface structure, with its photocatalytic activity and stability in degrading toluene far superior to P25. Photocurrent and photoluminescence (PL) measurements affirm that the existence of interfacial oxygen vacancies heightens the efficiency of electron transfer at the interface, while surface oxygen vacancies significantly enhance the stability and mineralization rate of toluene degradation. The improved photocatalytic properties were attributed to the combined effects of surface/interface oxygen vacancies and spatial interface heterojunctions. The one-step synthesis method developed in this work provides a novel perspective on combining spatially interfaced anatase/rutile phases with surface/interfacial oxygen vacancies.

Defective Nb2C MXene Cocatalyst on TiO2 Microsphere for Enhanced Photocatalytic CO2 Conversion to Methane

Sustainable and scalable solar-energy-driven CO2 conversion into fuels requires earth-abundant and stable photocatalysts. In this work, a defective Nb2C MXene as a cocatalyst and TiO2 microspheres as photo-absorbers, constructed via a coulombic force-driven self-assembly, is synthesized. Such photocatalyst, at an optimized loading of defective Nb2C MXene (5% def-Nb2C/TiO2), exhibits a CH4 production rate of 7.23 µmol g-1 h-1, which is 3.8 times higher than that of TiO2. The Schottky junction at the interface improves charge transfer from TiO2 to defective Nb2C MXene and the electron-rich feature (nearly free electron states) enables multielectron reaction of CO2, which apparently leads to high activity and selectivity to CH4 (sel. 99.5%) production. Moreover, DFT calculation demonstrates that the Fermi level (EF) of defective Nb2C MXene (-0.3 V vs NHE) is more positive than that of Nb2C MXene (-1.0 V vs NHE), implying a strong capacity to accept photogenerated electrons and enhance carrier lifetime. This work gives a direction to modify the earth-abundant MXene family as cocatalysts to build high-performance photocatalysts for energy production.

In situ reaction enabled surface segregation toward dual-heterogeneous antifouling membranes for oil-water separation

Fabricating membranes with superior antifouling property and long-term high performance is in great demand for efficient oil-water separation. Herein, we reported a reaction enabled surface segregation method for antifouling membrane fabrication, in which the pre-synthesized fluorinated ternary copolymer Pluronic F127 was coordinated with Ti4+ as segregation additive in the membrane casting bath. Additionally, tannic acid was utilized to enhance the self-assembly of the copolymer in the coagulation bath, and freshly-biomineralized TiO2 was anchored into the membrane surface through hydrogen bond. A hydrogel layer was constructed onto the membrane surface with synergistically tailored heterogeneous chemical composition and heterogeneous geometrical roughness. The dual-heterogeneous membrane exhibited hydrophilic and underwater superoleophobic features, resulting in high water flux (621.7 L m-2 h-1) at low operation pressure of 0.05 MPa and an excellent antifouling property (only 4.8% flux decline during 24-hour filtration). In situ reaction enabled surface segregation method will accelerate the development of antifouling membranes for oil-in-water emulsion separation.

A review of the photocatalytic degradation of organic pollutants in water by modified TiO2

Organic pollutants in water bodies pose a serious environmental problem, and photocatalytic technology is an efficient and environmentally friendly water treatment method. Titanium dioxide (TiO2) is a widely used photocatalyst, but it suffers from some drawbacks such as a narrow light response range, fast charge recombination, and low photocatalytic activity. To improve the photocatalytic performance of TiO2, this article reviews the preparation methods, performance evaluation, and applications of modified TiO2 photocatalysts. Firstly, the article introduces the effects of doping modification, semiconductor composite modification, and other modification methods on the structure and properties of TiO2 photocatalysts, as well as the common characterization techniques and activity test methods of photocatalysts. Secondly, the article discusses the effects and mechanisms of modified TiO2 photocatalysts on degrading dye, pesticide, and other organic pollutants in water bodies, as well as the influencing factors. Finally, the article summarizes the main achievements and advantages of modified TiO2 photocatalysts in degrading organic pollutants in water bodies, points out the existing problems and challenges, and prospects for the development direction and future of this field.

Novel Sol-Gel Synthesis of TiO2 Spherical Porous Nanoparticles Assemblies with Photocatalytic Activity

For this study, the synthesis of TiO₂ nanomaterials was performed via a novel sol-gel method employing titanium butoxide as a metal precursor, Pluronic F127 as a templating agent, toluene as a swelling agent, and acidic water or ethanol as the reaction solvents. The method was designed by tailoring certain reaction parameters, such as the sequence of toluene addition, magnetic stirring, the type of reaction solvent, and the calcination conditions. Analysis of the specific surface area and porosity was carried out via N₂ physisorption, whereas the morphological features of the solids were investigated via transmission electron microscopy. The crystalline structure of both the dried powders and the calcined materials was evaluated using X-ray diffraction analysis. It transpired that the different phase compositions of the solids are related to the specific synthesis medium employed. Under the adopted reaction conditions, ethanol, which was used as a reaction solvent, promoted the local arrangement of dispersed anatase particles, the specific arrangement of which does not lead to rutile transformation. Conversely, the use of water alone supported high-particle packing, evolving into a rutile phase. The photodegradation of Rhodamine B was used as a target reaction for testing the photocatalytic activity of the selected samples.

Triple-Peak Photoluminescence of DNA-Hybrid Alq3 Crystals Emitting a Depressed Single Peak upon Bio-Recognition

The green organic semiconductor, tris-(8-hydroxyquinoline)aluminum (Alq₃), was hybridized with DNA growing in the shape of hexagonal prismatic crystals. In this study, we applied hydrodynamic flow to the fabrication of Alq₃ crystals doped with DNA molecules. The hydrodynamic flow in the Taylor-Couette reactor induced nanoscale pores in the Alq₃ crystals, especially at the side part of the particles. The particles exhibited distinctly different photoluminescence emissions divided into three parts compared to common Alq₃-DNA hybrid crystals. We named this particle a "three-photonic-unit". After treatment with complementary target DNA, the three-photonic-unit Alq₃ particles doped with DNAs were found to emit depressed luminescence from side parts of the particles. This novel phenomenon would expand the technological value of these hybrid crystals with divided photoluminescence emissions toward a wider range of bio-photonic applications.

Preparation of a Hybrid TiO2 and 1T/2H-MoS2 Photocatalyst for the Degradation of Tetracycline Hydrochloride

Water pollution caused by antibiotics is a growing problem. Semiconductor photocatalysis is an environmentally friendly technology that can effectively degrade organic pollutants in water. Therefore, the development of efficient photocatalysts is of great significance to solve the environmental pollution problem. In this paper, mixed-phase TiO₂ and 1T/2H-MoS₂ composite (1T/2H-MoS₂/TiO₂) were synthesized by the in situ growth method. The prepared compounds were characterized and applied to the visible-light degradation of tetracycline hydrochloride. The photocatalytic effect of 1T/2H-MoS₂/TiO₂ on tetracycline hydrochloride is significantly enhanced under visible light and has good stability. It has potential applications in the treatment of organic pollutants in water.

3D Flower-like TiO2 Nanostructures: Anatase-To-Rutile Phase Transformation and Photoelectrochemical Application

Flower-like TiO2 nanostructures were obtained by chemical oxidation of Ti foil using H2O2 combined with subsequent annealing. This paper offers an analysis of the phase transformation of 3D flower-like titanium dioxide nanostructures. The role of the annealing atmosphere, sample thickness, grain shape, and nanoflower size are discussed. The nanostructures were examined using SEM, XRD, and Raman spectroscopy. Due to the nature of these two processes, the morphology of these nanomaterials is complex, and is obtained through a reaction involving Ti foil and H2O2 at 80°C. A distinction is made between the layer composed of small grains at the substrate/oxide interface, elongated crystal-like structures, and outer spongle-like film. The annealing parameters, such as atmosphere (air or argon) and temperature (450 or 600 °C), affect phase composition. The photoelectrochemical performance of the anode based on flower-like TiO2 has been shown. The thickness and phase composition of the anodes are factors that strongly affect the photocurrent. The multiphase heterojunctions proposed for 3D flower-like TiO2 photoanodes in photoelectrochemical (PEC) cells suppose that the conduction band of anatase should be above rutile. The highest photoelectrochemical performance was obtained for a photoanode composed of 20–40% anatase and an associated thickness of 0.75–1.5 µm.

Sulfurized bimetallic biochar as adsorbent and catalyst for selective co-removal of cadmium and PAHs from soil washing effluents

Although biosurfactant enhanced soil washing is effective to remediate Polycyclic Aromatic Hydrocarbons (PAHs)-Heavy metals (HMs) co-contaminated soil, the treatment of soil washing effluents containing pollutant and biosurfactant remains a critical challenge. In this study, the sulfurized Fe-Mn bimetallic biochar, named FMSBC was prepared, which exhibited excellent performance in activating sodium percarbonate (SPC) to degrade phenanthrene and the good adsorption capacity of cadmium. A simple system using FMSBC adsorption and SPC oxidation (FMSBC/SPC) is thus developed to remove phenanthrene and cadmium from soil washing effluents. Although there was antagonistic behavior between PAHs and HMs in the FMSBC/SPC system, over 80% phenanthrene and cadmium can be simultaneously removed from soil washing effluents. Adsorption of cadmium was mainly driven by complexation and precipitation. Free radical quenching studies and electron paramagnetic resonance (EPR) analyses verified that the dominant radical in the FMSBC/SPC system was hydroxyl radical (·OH). The performances of adsorption and catalyst were stable across a wide pH range and in the presence of competitive metal ions or natural organic matters. The recovered biosurfactants could be further reused for three washing cycles. This study has suggested biosurfactant enhanced soil washing coupled with FMSBC/SPC system is a promising method for remediation of HMs-PAHs co-contaminated soil.

Room temperature bilayer water structures on a rutile TiO2(110) surface: hydrophobic or hydrophilic?

The lack of understanding of the molecular-scale water adsorbed on TiO2 surfaces under ambient conditions has become a major obstacle for solving the long-time scientific and applications issues, such as the photo-induced wetting phenomenon and designing novel advanced TiO2-based materials. Here, with the molecular dynamics simulation, we identified an ordered water bilayer structure with a two-dimensional hydrogen bonding network on a rutile TiO2(110) surface at ambient temperature, corroborated by vibrational sum-frequency generation spectroscopy. The reduced number of hydrogen bonds between the water bilayer and water droplet results in a notable water contact angle (25 ± 5°) of the pristine TiO2 surface. This surface hydrophobicity can be enhanced by the adsorption of the formate/acetate molecules, and diminishes with dissociated H2O molecules. Our new physical framework well explained the long-time controversy on the origin of the hydrophobicity/hydrophilicity of the TiO2 surface, thus help understanding the efficiency of TiO2 devices in producing electrical energy of solar cells and the photo-oxidation of organic pollutants.

Microwave-Assisted Photocatalytic Degradation of Organic Pollutants via CNTs/TiO2

Introducing microwave fields into photocatalytic technology is a promising strategy to suppress the recombination of photogenerated charge carriers. Here, a series of microwave-absorbing photocatalysts, xCNTs/TiO2, were prepared by combining titanium dioxide (TiO2) with carbon nanotubes (CNTs) using a typical alcoholic thermal method to study the promotion of microwave-generated thermal and athermal effects on the photocatalytic oxidation process. As good carriers that are capable of absorbing microwaves and conducting electrons, CNTs can form hot spots and defects under the action of the thermal effect from microwaves to capture electrons generated on the surface of TiO2 and enhance the separation efficiency of photogenerated electrons (e−) and holes (h+). Excluding the influence of the reaction temperature, the athermal effect of the microwave field had a polarizing effect on the catalyst, which improved the light absorption rate of the catalyst. Moreover, microwave radiation also promoted the activation of oxygen molecules and hydroxyl groups on the catalyst surface to generate more reactive oxygen radicals. According to the mechanism analysis, the microwave effect significantly improved the photocatalytic advanced oxidation process, which lays a solid theoretical foundation for practical application.

Hierarchically ordered macroporous TiO2 architecture via self-assembled strategy for environmental remediation

Hierarchical orderd macroporous TiO₂ architecture (HOMTA) was prepared with aid of ethylenediamine (EDA) and investigated the impact of amine molecules on the properties of TiO₂ architecture. The different variation of amine molecules (EDA) leads to tunning the morphology under hydrothermal approach which is confirmed by FESEM and TEM analysis. The XRD and Raman studies confirms the crystal structure of anatase and brookite phase of TiO₂. The surface of the architecture strongly depended on the concentration of EDA which plays a vital role in surface area which is revealed by Brunauer Emmett-Teller (BET) analysis. The obtained HOMTA was employed as photocatalyst and active photoanode in the dye sensitized solar cells (DSSC). The DSSC device exhibits excellent efficiency (η) of 5.27% for the EDA capped TiO₂ (S5) which had high surface area (167.11 m²/g) for better dye loading, whereas the lower concentration of EDA capped TiO₂ (S1, S2, S3 and S4) resulted the efficiency of 2.14, 3.90, 3.25 and 4.37%, respectively. The efficiency of photocatlysis degradation of the prepared samples (S1, S2, S3, S4 and S5) was 94.8, 90.47, 91.41, 91.32 and 93.75% under light source. The excellent photocatalysis property was achieved by S5 within 6 min due to high surface area which inducing more active site.

Metallic Copper-Containing Composite Photocatalysts: Fundamental, Materials Design, and Photoredox Applications

Semiconductor photocatalysis has long been regarded as a potential solution to tackle the energy and environmental challenges since the first discovery of water splitting by TiO₂ almost 50 years ago. The past few years have seen a tremendous flurry of research interest in the modification of semiconductors because of their shortcomings in the aspects of solar harvesting, electron-hole pairs separation, and utilization of photogenerated carriers. Among the various strategies, the introduction of metallic copper into the photocatalysis system can not only enhance the absorption of sunlight and the separation efficiency of photogenerated electrons and holes, but also increase the adsorption ability of substrate and the number of active sites, so as to realize the high solar to chemical energy conversion efficiency. This review focuses on the rational design of copper-based composites and their applications in photoredox catalysis. First, the preparation methods of metallic copper-containing composites are discussed. Then, the applications of different types of copper-based composites in the photocatalytic removal of pollutants, splitting of water to hydrogen production, reduction of carbon dioxide, and conversion of organic matter are introduced. Finally, the opportunities and challenges in the design and synthesis of copper-based composites and their applications in the photocatalysis are prospected.

Promoting photocatalytic CO2 reduction to CH4 via a combined strategy of defects and tunable hydroxyl radicals

A well-designed photocatalyst with excellent activity and selectivity is crucial for photocatalytic CO₂ conversion and utilization. TiO₂ is one of the most promising photocatalysts. However, its excessive surface oxidation potential and insufficient surface active sites inhibit its activity and photocatalytic CO₂ reduction selectivity. In this work, highly dispersed Bi₂Ti₂O₇ was introduced into defective TiO₂ to adjust its oxidation potential and the generation of radicals, further inhibiting reverse reactions during the photocatalytic conversion of CO₂. Moreover, an in situ topochemical reaction etching route was designed, which achieved defective surfaces, a contacted heterophase interface, and an efficient electron transfer path. The optimized heterophase photocatalyst exhibited 93.9% CH₄ selectivity at a photocatalytic rate of 6.8 μmol·g^-1·h^-1, which was 7.9 times higher than that of P25. This work proposes a feasible approach to fabricating photocatalysts with well-designed band structures, highly dispersed heterophase interfaces, and sufficient surface active sites to effectively modulate the selectivity and activity of CO₂ photoreduction by manipulating the reaction pathways.

Ti-Based porous materials for reactive oxygen species-mediated photocatalytic reactions

Reactive oxygen species (ROS) are highly reactive oxidants that are typically generated by the irradiation of semiconducting materials with visible or UV light and are widely used for the photocatalytic degradation of toxic substances, photodynamic therapy, and selective organic transformations. In this context, TiO2 is considered to be among the most promising photocatalysts due to its high redox activity, structural stability, and natural abundance. In view of the extensive development of highly active photocatalysts, we herein briefly introduce TiO2 and the mechanisms of TiO2-mediated ROS generation, subsequently focusing on key advances in the design and synthesis of Ti-containing porous materials, such as porous TiO2, Ti-based metal-organic frameworks, and Ti-based metal-organic aerogels. In particular, this review highlights the significance of porosity and the structure-function relationship for the development of Ti-based photocatalysts. The structures, porosities, and ROS generation mechanisms of these materials as well as the related efficiencies of ROS-mediated photocatalytic organic transformations are discussed in detail to provide a useful reference for future researchers and to inspire the exploration of high-performance photocatalysts.

Interfacial Assembly and Applications of Functional Mesoporous Materials

Functional mesoporous materials have gained tremendous attention due to their distinctive properties and potential applications. In recent decades, the self-assembly of micelles and framework precursors into mesostructures on the liquid-solid, liquid-liquid, and gas-liquid interface has been explored in the construction of functional mesoporous materials with diverse compositions, morphologies, mesostructures, and pore sizes. Compared with the one-phase solution synthetic approach, the introduction of a two-phase interface in the synthetic system changes self-assembly behaviors between micelles and framework species, leading to the possibility for the on-demand fabrication of unique mesoporous architectures. In addition, controlling the interfacial tension is critical to manipulate the self-assembly process for precise synthesis. In particular, recent breakthroughs based on the concept of the "monomicelles" assembly mechanism are very promising and interesting for the synthesis of functional mesoporous materials with the precise control. In this review, we highlight the synthetic strategies, principles, and interface engineering at the macroscale, microscale, and nanoscale for oriented interfacial assembly of functional mesoporous materials over the past 10 years. The potential applications in various fields, including adsorption, separation, sensors, catalysis, energy storage, solar cells, and biomedicine, are discussed. Finally, we also propose the remaining challenges, possible directions, and opportunities in this field for the future outlook.

Green preparation of porous hierarchical TiO2(B)/anatase phase junction for effective photocatalytic degradation of antibiotics

In this study, porous hierarchical bronze/anatase phase junction TiO₂ assembled by ultrathin two-dimensional nanosheets was prepared by a novel, green and simple deep eutectic solvent-regulated strategy. Due to its structural features, the TiO₂ sample exhibited enhanced photocatalytic activities for multiple kinds of antibiotics, including ofloxacin, ciprofloxacin and chloramphenicol.

Oxygen-Deficient WO3/TiO2/CC Nanorod Arrays for Visible-Light Photocatalytic Degradation of Methylene Blue

At present, TiO2 is one of the most widely used photocatalytic materials. However, the narrow response range to light limits the photocatalytic performance. Herein, we reported a successful construction of self-doped R-WO3/R-TiO2/CC nanocomposites on flexible carbon cloth (CC) via electrochemical reduction to increase the oxygen vacancies (Ovs), resulting in an enhanced separation efficiency of photo-induced charge carriers. The photocurrent of R-WO3/R-TiO2/CC at −1.6 V (vs. SCE) was 2.6 times higher than that of WO3/TiO2/CC, which suggested that Ovs could improve the response to sunlight. Moreover, the photocatalytic activity of R-WO3/TiO2/CC was explored using methylene blue (MB). The degradation rate of MB could reach 68%, which was 1.3 times and 3.8 times higher than that of WO3/TiO2/CC and TiO2/CC, respectively. Furthermore, the solution resistance and charge transfer resistance of R-WO3/R-TiO2/CC were obviously decreased. Therefore, the electrochemical reduction of nanomaterials enabled a promoted separation of photogenerated electron–hole pairs, leading to high photocatalytic activity.

Mesoporous TiO2 Microparticles with Tailored Surfaces, Pores, Walls, and Particle Dimensions Using Persistent Micelle Templates

Mesoporous microparticles are an attractive platform to deploy high-surface-area nanomaterials in a convenient particulate form that is broadly compatible with diverse device manufacturing methods. The applications for mesoporous microparticles are numerous, spanning the gamut from drug delivery to catalysis and energy storage. For most applications, the performance of the resulting materials depends upon the architectural dimensions including the mesopore size, wall thickness, and microparticle size, yet a synthetic method to control all these parameters has remained elusive. Furthermore, some mesoporous microparticle reports noted a surface skin layer which has not been tuned before despite the important effect of such a skin layer upon transport/encapsulation. In the present study, material precursors and block polymer micelles are combined to yield mesoporous materials in a microparticle format due to phase separation from a homopolymer matrix. The skin layer thickness was kinetically controlled where a layer integration via diffusion (LID) model explains its production and dissipation. Furthermore, the independent tuning of pore size and wall thickness for mesoporous microparticles is shown for the first time using persistent micelle templates (PMT). Last, the kinetic effects of numerous processing parameters upon the microparticle size are shown.

Morphology-Governed Performance of Multi-Dimensional Photocatalysts for Hydrogen Generation

In the past few decades, extensive studies have been performed to utilize the solar energy for photocatalytic water splitting; however, up to the present, the overall efficiencies reported in the literature are still unsatisfactory for commercialization. The crucial element of this challenging concept is the proper selection and design of photocatalytic material to enable significant extension of practical application perspectives. One of the important features in describing photocatalysts, although underestimated, is particle morphology. Accordingly, this review presents the advances achieved in the design of photocatalysts that are dedicated to hydrogen generation, with an emphasis on the particle morphology and its potential correlation with the overall reaction performance. The novel concept of this work—with the content presented in a clear and logical way—is based on the division into five parts according to dimensional arrangement groups of 0D, 1D, 2D, 3D, and combined systems. In this regard, it has been shown that the consideration of the discussed aspects, focusing on different types of particle morphology and their correlation with the system’s efficiency, could be a promising route for accelerating the development of photocatalytic materials oriented for solar-driven hydrogen generation. Finally, concluding remarks (additionally including the problems connected with experiments) and potential future directions of particle morphology-based design of photocatalysts for hydrogen production systems have been presented.

Engineering Z-scheme TiO2-OV-BiOCl via oxygen vacancy for enhanced photocatalytic degradation of imidacloprid

The development and application of photocatalysts with strong redox ability to degrade refractory pesticides is the key to eliminating pesticide contamination. In this work, we develop a facile, time-saving, and surfactant-assisted method to fabricate a new Z-scheme heterojunction based on TiO2/BiOCl. This photocatalyst is rich in oxygen vacancy defects (TiO2-OV-BiOCl), and displays an excellent photocatalytic degradation performance for imidacloprid (IMD), and a possible degradation pathway of IMD is provided. The surfactant F127 plays an essential role in regulating the oxygen vacancy defects (OVDs) of TiO2-OV-BiOCl, where the OVD mainly exists in 5 layer BiOCl ultrathin nanosheets. Free radical trapping experiments demonstrate that the introduction of an OVD in BiOCl as a 'charge mediator' changes the charge-transfer mode from a type-II mechanism to a Z-scheme mechanism. The formation of a Z-scheme heterojunction leads to an excellent light utilization and higher separation efficiency of photogenerated charge carriers with a prolonged lifetime compared to those of BiOCl and TiO2/BiOCl. This work highlights the critical role of an OVD in the construction of a Z-scheme heterojunction of TiO2/BiOCl, and it can be applied to construct efficient photocatalytic systems for pesticide degradation.

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

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

Simultaneous adsorption of Cd2+ and photocatalytic degradation of tris-(2-chloroisopropyl) phosphate (TCPP) by mesoporous TiO2

In this work, the prepared mesoporous TiO₂ was employed to eliminate the environmental risk induced by the combined pollution (tris-(2-chloroisopropyl) phosphate (TCPP) and Cd²⁺). The prepared material was characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (UV-DRS), Raman imaging spectrometer (Raman), N₂ adsorption/desorption isotherm and X-ray photoelectron spectroscopy (XPS). In the combined pollution system, the prepared TiO₂ simultaneously exhibited a higher adsorption and photocatalytic activity for Cd²⁺ and TCPP at neutral condition, respectively. The adsorption of Cd²⁺ and photo-degradation of TCPP by mesoporous TiO₂ followed pseudo-second-order and pseudo-first-order kinetics model, respectively. The removal efficiency of TCPP was improved from 67% to 100% when the concentration of co-existed Cd²⁺ increased from 0.5 mg L^-1 to 2 mg L^-1, due to the fact that the adsorbed Cd²⁺ on the surface of TiO₂ scavenged electron and thus inhibited the photo-generated electron-hole pairs recombination. In addition, six degradation intermediates were determined by high resolution mass spectrum (HRMS) and potential transformation pathways of TCPP under the co-existence of Cd²⁺ were proposed. The results suggested that rapid and high-efficient simultaneous removal of Cd²⁺ and TCPP was feasible, which laid the basis for the remediation of other combined pollution in the future.

Synergetic enhancement of surface reactions and charge separation over holey C3N4/TiO2 2D heterojunctions

Efficient charge separation and rapid interfacial reaction kinetics are crucial factors that determine the efficiency of photocatalytic hydrogen evolution. Herein, a fascinating 2D heterojunction photocatalyst with superior photocatalytic hydrogen evolution performance - holey C₃N₄ nanosheets nested with TiO₂ nanocrystals (denoted as HCN/TiO₂) - is designed and fabricated via an in situ exfoliation and conversion strategy. The HCN/TiO₂ is found to exhibit an ultrathin 2D heteroarchitecture with intimate interfacial contact, highly porous structures and ultrasmall TiO₂ nanocrystals, leading to drastically improved charge carrier separation, maximized active sites and the promotion of mass transport for photocatalysis. Consequently, the HCN/TiO₂ delivers an impressive hydrogen production rate of 282.3 μmol h^-1 per 10 mg under AM 1.5 illumination and an apparent quantum efficiency of 13.4% at a wavelength of 420 nm due to the synergetic enhancement of surface reactions and charge separation. The present work provides a promising strategy for developing high-performance 2D heterojunctions for clean energy applications.

Volatile-Organic-Compound-Intercepting Solar Distillation Enabled by a Photothermal/Photocatalytic Nanofibrous Membrane with Dual-Scale Pores

Solar distillation is emerging as a robust and energy-effective tool for water purification and freshwater production. However, many water sources contain harmful volatile organic compounds (VOCs), which can evaporate through the photothermal evaporators and be collected together with distilled water, or even be enriched in the distilled water. In view of the penetration of volatile organic compounds, herein, we rationally demonstrate a dual-scale porous, photothermal/photocatalytic, flexible membrane for intercepting volatile organic compounds during solar distillation, which is based on a mesoporous oxygen-vacancy-rich TiO_2-x nanofibrous membrane (m-TiO_2-x NFM). The dual-scale porous structure was constructed by micrometer-sized interconnected tortuous pores formed by the accumulation of m-TiO_2-x nanofibers and nanometer-sized pores in the m-TiO_2-x individual nanofibers. Consequently, the membrane can sustainably in situ intercept VOCs by providing more photocatalytic reactive sites for collision (mainly by mesopores) and longer tortuous channels for prolonging VOC retention (mainly by micrometer-sized pores); thus, it results in less than 5% of phenol residual in distilled water. As a proof of concept, when the m-TiO_2-x NFM is employed to purify practical river water in an evaporation prototype under real solar irradiation, complex volatile natural organic contaminants can be effectively intercepted and the produced distilled water meets the drinking water standards of China. This development will promote the application prospects of solar distillation.

Facile polyol-triggered anatase-rutile heterophase TiO2-x nanoparticles for enhancing photocatalytic CO2 reduction

Solar-driven CO₂ photoreduction into fuels has great potential in addressing the environmental and energy crisis. Heterophase TiO₂ has attracted increasing attention in photoenergy applications owing to its fascinating properties, but much more attention has been paid on photodegradation and photocatalytic water splitting than that of photocatalytic CO₂ reduction. Herein, anatase-rutile heterophase TiO₂ nanoparticles with oxygen vacancy (TiO_2-x) were successfully synthesized by involving proper amounts of polyols (EG, DEG, TEG, etc.) into the reaction system. The heterophase TiO_2-x nanoparticles could accelerate the electron-hole separation and exhibit superior photocatalytic activity for reducing CO₂ into methane. This work offers an alternative approach to simply fabricate TiO_2-x-based heterophase photocatalyst towards efficient CO₂ photoreduction.

Effects of Particle Size on the Structure and Photocatalytic Performance by Alkali-Treated TiO2

Particle size of nanomaterials has significant impact on their photocatalyst properties. In this paper, TiO₂ nanoparticles with different crystalline sizes were prepared by adjusting the alkali-hydrothermal time (0–48 h). An annealing in N₂ atmosphere after hydrothermal treatment caused TiO₂ reduction and created defects, resulting in the visible light photocatalytic activity. The evolution of physicochemical properties along with the increase of hydrothermal time at a low alkali concentration has been revealed. Compared with other TiO₂ samples, TiO₂-24 showed higher photocatalytic activity toward degrading Rhodamine B and Sulfadiazine under visible light. The radical trapping and ESR experiments revealed that O₂^•- is the main reactive specie in TiO₂-24. Large specific surface areas and rapid transfer of photogenerated electrons are responsible for enhancing photocatalytic activity. The above findings clearly demonstrate that particle size and surface oxygen defects can be regulated by alkali-hydrothermal method. This research will deepen the understanding of particle size on the nanomaterials performance and provide new ideas for designing efficient photocatalysts.

Preparation of Gd-Doped TiO2 Nanotube Arrays by Anodization Method and Its Photocatalytic Activity for Methyl Orange Degradation

Gd-doped TiO2 nanotube arrays with 3D ordered and high specific surface (176 m2/g) area are successfully prepared on a Ti foil surface via an anodizing method. The characterizations of Gd-doped TiO2 nanotube arrays are carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectrometer (EDX), optical contact angle measurer, and ultraviolet (UV) fluorescence spectrophotometer, respectively. The results reveal that the Gd-doped TiO2 nanotube arrays form on the Ti foil surface with a length of about 50.5 μm and 100 nm in diameter, and the growth direction grown along the (101) direction of anatase crystal. Under the optimized reaction conditions (60 V, 10 h, 0.01mol/L Gd3+), the crystal phase of Gd-doped TiO2 show an excellent nanotube structure, possess a beneficial photocatalytic performance for methyl orange (MO) (Degradation rate was 95.8%) and an excellent hydrophilic property (The optical contact angle was 4.9°). After doping with Gd, the hydrophilic and photocatalytic properties of the TiO2 nanotubes are further improved.

Recent advances in the synthesis of hierarchically mesoporous TiO2 materials for energy and environmental applications

Because of their low cost, natural abundance, environmental benignity, plentiful polymorphs, good chemical stability and excellent optical properties, TiO₂ materials are of great importance in the areas of physics, chemistry and material science. Much effort has been devoted to the synthesis of TiO₂ nanomaterials for various applications. Among them, mesoporous TiO₂ materials, especially with hierarchically porous structures, show great potential owing to their extraordinarily high surface areas, large pore volumes, tunable pore structures and morphologies, and nanoscale effects. This review aims to provide an overview of the synthesis and applications of hierarchically mesoporous TiO₂ materials. In the first section, the general synthetic strategies for hierarchically mesoporous TiO₂ materials are reviewed. After that, we summarize the architectures of hierarchically mesoporous TiO₂ materials, including nanofibers, nanosheets, microparticles, films, spheres, core-shell and multi-level structures. At the same time, the corresponding mechanisms and the key factors for the controllable synthesis are highlighted. Following this, the applications of hierarchically mesoporous TiO₂ materials in terms of energy storage and environmental protection, including photocatalytic degradation of pollutants, photocatalytic fuel generation, photoelectrochemical water splitting, catalyst support, lithium-ion batteries and sodium-ion batteries, are discussed. Finally, we outline the challenges and future directions of research and development in this area.

Controllable fabrication of TiO2 anatase/rutile phase junctions by a designer solvent for promoted photocatalytic performance

Highly active coin tree-like TiO₂ anatase–rutile phase junctions were constructed by tailored DESs and the two-phase ratios can be easily tuned.

Remarkable improvement of TiO2 for dye photocatalytic degradation by a facile post-treatment

A neutral, facile and universal hydrothermal post-treatment of TiO₂ was developed to significantly improve its photocatalytic activity.

Flower-like hydrogen titanate nanosheets: preparation, characterization and their photocatalytic hydrogen production performance in the presence of Pt cocatalyst

Flower-like hydrogen titanate nanosheets were prepared by a hydrothermal method and an assembling process. Then the Pt nanoparticles as cocatalysts were supported on the hydrogen titanate nanosheets through a photoreduction method. The samples were characterized by XRD, TG-DTA, ICP, SEM, TEM, XPS and UV-vis DRS. Their photocatalytic activity for H₂ production was also evaluated. The TEM results revealed that the as-prepared H₂Ti₂O₅·H₂O was with flower-like structure in which nanosheets were interlaced together. The formation mechanism of flower-like H₂Ti₂O₅·H₂O nanosheets was briefly proposed. With Pt cocatalyst, the flower-like H₂Ti₂O₅·H₂O had better photocatalytic activity (hydrogen production rate: 9.28 mmol g⁻¹ h⁻¹) and good cycling stability than original H₂Ti₂O₅·H₂O and commercial P25 under the same conditions. It was also found that the amount of cocatalyst Pt was positively correlated with photocatalytic performance.

Hydrogen titanate nanosheets were assembled into the flower-like hydrogen titanate nanosheets to obtain high photocatalytic performance.