Application of an Ion Beam Technique for the Design of Visible Light-Sensitive, Highly Efficient and Highly Selective Photocatalysts: Ion-Implantation and Ionized Cluster Beam Methods

As a new concept for the design of effective photocatalysts, an ion beam technology using accelerated metal ions, a metal ion implantation and an ionized cluster beam (ICB) method, have been applied to design unique photocatalysts. The metal ion implantation of TiO₂ and Ti-containing zeolites with highly accelerated metal ions (V⁺, Cr⁺, etc.) is useful in designing photocatalysts that can operate efficiently under visible light irradiation. Also, an ICB method with a low acceleration energy is useful in preparing transparent TiO₂ thin films on various types of substrates for the efficient photocatalytic degradation of pollutants diluted in water and air. The combination of the ICB method and metal ion implantation can develop the TiO₂ thin films that are able to operate not only under UV light but also under visible light irradiation.     

TiO2-assisted photocatalytic degradation of diclofenac, metoprolol, estrone and chloramphenicol as endocrine disruptors in water

The photocatalytic oxidation of diclofenac, metoprolol, estrone and chloramphenicol was tested in the tube reactor using different commercially available TiO₂. The photocatalysts were characterized using BET, XRD and SEM. The studied photocatalysts differed in S_BET, pore volume and rutile presence. It was observed that generally anatase TiO₂ possessed the highest activity in the photocatalytic oxidation of diclofenac, chloramphenicol and estrone. The presence of rutile enhanced the photooxidation of metoprolol. In case of the other pollutants, however, rutile diminished the photooxidation efficiency. The most effective in the reduction of the COD parameter of treated water was anatase with 21 nm crystals. The photooxidation of all studied pollutants can be described by the pseudo-first order kinetics with the values ranging from 0.46 × 10^?2 min^?1 in case of estrone removal over Tytanpol (Z.A. Police, Poland) to 1.87 × 10^?2 min^?1 for the removal of chloramphenicol over TiO₂ 21 nm (Sigma-Aldrich). The highest initial reaction rates were obtained for metoprolol removal over TiO₂ 21 nm (Sigma-Aldrich) 1.9 × 10^?6 mol dm³ min^?1 being three times higher than that determined for estrone photocatalytic oxidation over TiO₂ (Sigma-Aldrich).     

Two-dimensional blue-phase CX(X=S,Se) monolayers with high carrier mobility and tunable photocatalytic water splitting capability

Photocatalytic water splitting utilizing solar energy is considered as one of the most ideal strategies for solving the ene rgy and environmental issues.Recently,two-dimensional(2 D) materials with an intrinsic dipole show great chance to achieve excellent photocatalytic performance.In this work,blue-phase monolayer carbon monochalcogenides(CX,X=S,Se) are constructed and systematically studied as photocatalysts for water splitting by performing first-principles calculations based on density functional theory.After confirming the great dynamical,thermal,and mechanical stability of CX monolayers,we observe that they possess moderate band gaps(2.41 eV for CS and 2.46 eV for CSe) and high carrier mobility(3.23 × 10~4 cm~2 V~(-1) s~(-1) for CS and 4.27 × 10~3 cm~2 V~(-1) s~(-1) for CSe),comparable to those of many recently reported 2 D photocatalysts.Moreover,these two monolayer materials are found to have large intrinsic dipole(0.43 D for CS and 0.51 D for CSe),thus the build-in internal electric field can be selfintroduced,which can effectively drive the separation of photongenerated carriers.More importantly,the well-aligned band edge as well as rather pronounced optical absorption in the visible-light and ultraviolet regions further ensure that our proposed CX monolayers can be used as high efficient photocatalysts for water splitting.Additionally,the effects of external strain on the electronic,optical and photocatalytic properties of CX monolayers are also evaluated.These theoretical predictions will stimulate further work to open up the energy-related applications of CX monolayers.     

Pure and modified TiO2 photocatalysts and their environmental applications

Semiconductor photocatalysis is a process that harnesses light energy in chemical conversions. In particular, its applications to environmental remediation have been intensively investigated. The characteristics of TiO₂, the most popular photocatalyst, is briefly described and selected studies on the degradation/conversion of various recalcitrant pollutants using pure and modified TiO₂ photocatalysts, which were carried out in this group, are reviewed. Photocatalytic reactions are multi-phasic and take place at interfaces of not only water/TiO₂ and air/TiO₂ but also solid/TiO₂. Examples of photocatalytic reactions of various organic and inorganic substrates that are converted through the photocatalytic oxidation or reduction are introduced. TiO₂ has been modified in various ways to improve its photocatalytic activity. Surface modifications of TiO₂ that include surface platinization, surface fluorination, and surface charge alteration are discussed and their applications to pollutants degradation are also described in detail.     

Recent advances in BiOBr-based photocatalysts for environmental remediation

The efficient utilization of solar energy through photocatalysis is ideal for solving environmental issues and the development sustainable future. BiOBr-based semiconductors possess unique narrowed bandgaps and layered structures, thereby widely studied as photocatalysts for environmental remediation. However, a little has been focused on the comprehensive reviewing of BiOBr despite its extensive and promising applications. In this review, the state-of-the-art developments of BiOBr-based photocatalysts for environmental remediation are summarized. Particular focus is paid to the synthetic strategies for the control of the resulting morphologies, as well as efficient modification strategies for improving the photocatalytic activities. These include boosting the bulk phase by charge separation, enhancing the spatial charge separation, and engineering the surface states. The environmental uses of BiOBr-based photocatalysts are also reviewed in terms of purification of pollutants and CO₂ reduction. Finally, future challenges and opportunities of BiOBr-based materials in photocatalysis are discussed. Overall, this review provides a good basis for future exploration of high-efficiency solar-driven photocatalysts for environmental sustainability.     

Microwave-assisted synthesis of oxygen vacancy associated TiO2 for efficient photocatalytic nitrate reduction

The solar-driven photocatalytic technology has shown great potential in nitrate (NO₃^?) pollutants reduction, however, it has been greatly hindered by the complex preparation and high cost of photocatalysts. Herein, a relatively low-cost photocatalyst, rutile and anatase mixed phase TiO₂ was synthesized by a facile microwave-hydrothermal method. Meanwhile, oxygen vacancy is successfully generated, leading to an acidic surface for strong adsorption towards NO₃^?, which further improved the reduction activity. Compared with the commercial P25, a higher NO₃^? conversion of ca. 100% and nitrogen (N₂) selectivity of 87% were achieved under UV (365 nm) irradiation within 2 h. This research provides a promising strategy for designing efficient noble metal free photocatalyst in the NO₃^? reduction.     

Two‐Dimensional Layered Zinc Silicate Nanosheets with Excellent Photocatalytic Performance for Organic Pollutant Degradation and CO2 Conversion

Two‐dimensional (2D) photocatalysts are highly attractive for their great potential in environmental remediation and energy conversion. Herein, we report a novel layered zinc silicate (LZS) photocatalyst synthesized by a liquid‐phase epitaxial growth route using silica derived from vermiculite, a layered silicate clay mineral, as both the lattice‐matched substrate and Si source. The epitaxial growth of LZS is limited in the 2D directions, thus generating the vermiculite‐type crystal structure and ultrathin nanosheet morphology with thicknesses of 8–15 nm and a lateral size of about 200 nm. Experimental observations and DFT calculations indicated that LZS has a superior band alignment for the degradation of organic pollutants and reduction of CO₂ to CO. The material exhibited efficient photocatalytic performance for 4‐chlorophenol (4‐CP) degradation and CO₂ conversion into CO and is the first example of a claylike 2D photocatalyst with strong photooxidation and photoreduction capabilities.     

Constructing a novel Ag nanowire@CeVO4 heterostructure photocatalyst for promoting charge separation and sunlight driven photodegradation of organic pollutants

Exploiting efficient and recyclable photocatalysts is a vital matter for environmental purification.Herein,cerium vanadate（CeVO₄） sub-microspheres and silver nanowire（AgNW）@CeVO₄ with core-shell architecture as photocatalysts are rationally constructed by hydrothermal approach.The AgNW@CeVO₄ photocatalyst obtained by depositing CeVO₄ on the surface of Ag NWs possess one dimensional continuous structure,which expand the optical absorption range and redu...     

Carbon-based H2-production photocatalytic materials

Photocatalytic hydrogen production from water splitting is of promising potential to resolve the energy shortage and environmental concerns. During the past decade, carbon materials have shown great ability to enhance the photocatalytic hydrogen-production performance of semiconductor photocatalysts. This review provides a comprehensive overview of carbon materials such as CNTs, graphene, C₆₀, carbon quantum dots, carbon fibers, activated carbon, carbon black, etc. in enhancing the performance of semiconductor photocatalysts for H₂ production from photocatalytic water splitting. The roles of carbon materials including supporting material, increasing adsorption and active sites, electron acceptor and transport channel, cocatalyst, photosensitization, photocatalyst, band gap narrowing effect are explicated in detail. Also, strategies for improving the photocatalytic hydrogen-production efficiency of carbon-based photocatalytic materials are discussed in terms of surface chemical functionalization of the carbon materials, doping effect of the carbon materials and interface engineering between semiconductors and carbon materials. Finally, the concluding remarks and the current challenges are highlighted with some perspectives for the future development of carbon-based photocatalytic materials.     

A novel layered bismuth-based photocatalytic material LiBi3O4Cl2 with OH and h+ as the active species for efficient photodegradation applications

Developing new photocatalysts is of significant importance for their potential environmental and energetic applications. Herein, a novel layered bismuth-based photocatalytic material LiBi₃O₄Cl₂ was developed by a simple solid-state reaction. The morphology, microstructures and optical properties were investigated by XRD, SEM, TEM and DRS. The band gap of LiBi₃O₄Cl₂ has been determined to be 3.35 eV, and its E_CB and E_VB were also estimated. The photocatalytic property of LiBi₃O₄Cl₂ is surveyed by oxidative decomposition of rhodamine B (RhB), methyl orange (MO), methylene blue (MB) and phenol in aqueous solution. The results demonstrated that LiBi₃O₄Cl₂ is an efficient UV light active photocatalyst, which can destroy the contaminants with irradiation. It is also more effective in degrading pollutants than the related layered bismuth-based photocatalyst Bi₄NbO₈Br. The photocatalysis mechanism is detailedly investigated by active species trapping measurement and terephthalic acid photoluminescence probing technique (TA-PL). It revealed that powerful hydroxyl radicals (OH) and photogenerated holes (h⁺) are the two main active species and are responsible for the efficient degradation process. This study provides a new layered bismuth-based photocatalytic material for environmental and energetic applications.     

Construction of 2D-2D TiO2 nanosheet/layered WS2 heterojunctions with enhanced visible-light-responsive photocatalytic activity

Constructing nanocomposites that combine the advantages of composite materials, nanomaterials, and interfaces has been regarded as an important strategy to improve the photocatalytic activity of TiO₂. In this study, 2D-2D TiO₂ nanosheet/layered WS₂ (TNS/WS₂) heterojunctions were prepared via a hydrothermal method. The structure and morphology of the photocatalysts were systematically characterized. Layered WS₂ (～4 layers) was wrapped on the surface of TiO₂ nanosheets with a plate-to-plate stacked structure and connected with each other by W=O bonds. The as-prepared TNS/WS₂ heterojunctions showed higher photocatalytic activity for the degradation of RhB under visible-light irradiation, than pristine TiO₂ nanosheets and layered WS₂. The improvement of photocatalytic activity was primarily attributed to enhanced charge separation efficiency, which originated from the perfect 2D-2D nanointerfaces and intimate interfacial contacts between TiO₂ nanosheets and layered WS₂. Based on experimental results, a double-transfer photocatalytic mechanism for the TNS/WS₂ heterojunctions was proposed and discussed. This work provides new insights for synthesizing highly efficient and environmentally stable photocatalysts by engineering the surface heterojunctions.     

Two‐Dimensional Co@N‐Carbon Nanocomposites Facilely Derived from Metal–Organic Framework Nanosheets for Efficient Bifunctional Electrocatalysis

Metal–organic frameworks (MOFs) and MOF‐derived nanomaterials have recently attracted great interest as highly efficient, non‐noble‐metal catalysts. In particular, two‐dimensional MOF nanosheet materials possess the advantages of both 2D layered nanomaterials and MOFs and are considered to be promising nanomaterials. Herein, we report a facile and scalable in situ hydrothermal synthesis of Co–hypoxanthine (HPA) MOF nanosheets, which were then directly carbonized to prepare uniform Co@N‐Carbon nanosheets for efficient bifunctional electrocatalytic hydrogen‐evolution reactions (HERs) and oxygen‐evolution reactions (OERs). The Co embedded in N‐doped carbon shows excellent and stable catalytic performance for bifunctional electrocatalytic OERs and HERs. For OERs, the overpotential of Co@N‐Carbon at 10 mA cm^?2 was 400 mV (vs. reversible hydrogen electrode, RHE). The current density of Co@N‐Carbon reached 100 mA cm^?2 at an overpotential of 560 mV, which showed much better performance than RuO₂; the largest current density of RuO₂ that could be reached was only 44 mA cm^?2. The Tafel slope of Co@N‐Carbon was 61 mV dec^?1, which is comparable to that of commercial RuO₂ (58 mV dec^?1). The excellent electrocatalytic properties can be attributed to the nanosheet structure and well‐dispersed carbon‐encapsulated Co, CoN nanoparticles, and N‐dopant sites, which provided high conductivity and a large number of accessible active sites. The results highlight the great potential of utilizing MOF nanosheet materials as promising templates for the preparation of 2D Co@N‐Carbon materials for electrocatalysis and will pave the way to the development of more efficient 2D nanomaterials for various catalytic applications.     

Amino‐Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g‐C3N4 for Enhanced Photocatalytic CO2 Reduction

Halide perovskite quantum dots (QDs) have great potential in photocatalytic applications if their low charge transportation efficiency and chemical instability can be overcome. To circumvent these obstacles, we anchored CsPbBr₃ QDs (CPB) on NH_x‐rich porous g‐C₃N₄ nanosheets (PCN) to construct the composite photocatalysts via N?Br chemical bonding. The 20 CPB‐PCN (20 wt % of QDs) photocatalyst exhibits good stability and an outstanding yield of 149 μmol h^?1 g^?1 in acetonitrile/water for photocatalytic reduction of CO₂ to CO under visible light irradiation, which is around 15 times higher than that of CsPbBr₃ QDs. This study opens up new possibilities of using halide perovskite QDs for photocatalytic application.     

Hydrothermal synthesis of TiO2 nanorods: formation chemistry,growth mechanism,and tailoring of surface properties for photocatalytic activities

Titanium dioxide (TiO₂) is one of the best semiconductor photocatalysts with optical band gap of 3.2 eV. The optical band gap and photocatalytic properties could be further tuned by tailoring shape, size, composition, and morphology of the nanostructures. Hydrothermal synthesis methods have been applied to produce well-controlled nanostructured TiO₂ materials with different morphologies and improved optoelectronic properties. Among various morphologies, one-dimensional (1D) TiO₂ nanostructures are of great importance in the field of energy, environmental, and biomedical because of the directional transmission properties resulting from their 1D geometry. Particularly, TiO₂ nanorods (NRs) have gained special attention because of their densely packed structure, quantum confinement effect, high aspect ratio, and large specific surface area that could specially improve the directional charge transmission efficiency. This results in the effective photogenerated charge separation and light absorption, which are really important for potential applications of TiO₂-based materials for photocatalytic and other important applications. In this review, hydrothermal syntheses of TiO₂ NRs including the formation chemistry and the growth mechanism of NRs under different chemical environments and effects of various synthesis parameters (pH, reaction temperature, reaction time, precursors, solvents etc.) on morphology and optoelectronic properties have been discussed. Recent developments in the hydrothermal synthesis of TiO₂ NRs and tailoring of their surface properties through various modification strategies such as defect creation, doping, sensitization, surface coating, and heterojunction formation with various functional nanomaterials (plasmonic, oxide, quantum dots, graphene-based nanomaterials, etc.) have been reported to improve the photocatalytic activities. Furthermore, applications of TiO₂ NRs/tailored TiO₂ NRs as superior photocatalysts in degradation of organic pollutants and bacterial disinfection have been discussed with emphasis on mechanisms of action and recent advances in the fields.     

Multimetallic Oxynitrides Nanoparticles for a New Generation of Photocatalysts

A versatile synthetic strategy for the preparation of multimetallic oxynitrides has been designed and here exemplarily discussed considering the preparation of nanoscaled zinc–gallium oxynitrides and zinc–gallium–indium oxynitrides, two important photocatalysts of new generation, which proved to be active in key energy related processes from pollutant decomposition to overall water splitting. The synthesis presented here allows the preparation of small nanoparticles (less than 20 nm in average diameter), well-defined in size and shape, yet highly crystalline and with the highest surface area reported so far (up to 80 m² g⁻¹). X-ray diffraction studies show that the final material is not a mixture of single oxides but a distinctive compound. The photocatalytic properties of the oxynitrides have been tested towards the decomposition of an organic dye (as a model reaction for the decomposition of air pollutants), showing better photocatalytic performances than the corresponding pure phases (reaction constant 0.22 h⁻¹), whereas almost no reaction was observed in absence of catalyst or in the dark. The photocatalysts have been also tested for H₂ evolution (semi-reaction of the water splitting process) with results comparable to the best literature values but leaving room for further improvement.     

Development of TiO<Subscript>2</Subscript> photocatalysts suitable for practical use and their applications in environmental cleanup

Recently, environmental disruption is proceeding on a global scale through the consumption of huge amounts of fossil fuels and the emission of various chemical substances. However, these substances resist bio-treatment. TiO₂ generates electrons and holes by irradiation with light. Most organic micro-pollutants, including dioxins, are decomposed into carbon dioxide and water by the effect of the holes with high oxidative potential. By using such a photocatalytic reaction, various applications are feasible for environmental cleanup. In general, TiO₂ powder has been utilized as photocatalyst, although TiO₂ powder photocatalyst has several disadvantages: (1) it is difficult to handle, (2) photocatalytic reaction is slow and it takes a lot of time for treatment and (3) it is difficult to apply to plastics and textiles, because the photocatalyst decomposes them. We have developed a photocatalyst suitable for practical use and have developed high-activity photocatalysts such as TiO₂ photocatalytic transparent film, photocatalytic silica-gel, apatite-coated TiO₂ photocatalyst usable for plastics and textiles, photocatalytic paper, photocatalytic blue charcoal and photocatalytic oxygen scavenger. The application of these high-activity photocatalysts has been studied in deodorization, anti-bacterial, self-cleaning, anti-stain, water treatment, air purification such as photocatalytic decomposition of dioxins and VOC, and NO _x removal. Now various photocatalytic articles using these new photocatalyst materials are on the market in Japan. Photocatalytic technology can create many valuable products for environmental use all over the world.     

Degradation of toluene gas at the surface of ZnO/SnO2 photocatalysts in a baffled bed reactor

To eliminate volatile organic compounds (VOCs) from contaminated air, a novel medium-scale baffled photocatalytic reactor was designed and fabricated, using immobilized ZnO/SnO₂ coupled oxide photocatalysts. Toluene was chosen as a representative pollutant of VOCs to investigate the degradation mechanism and the parameters affecting photocatalytic degradation efficiency. The preliminary experimental results indicate that the degradation efficiency of toluene increased with the increase of the light irradiation dosage, while it decreased with the increase of concentrations of toluene. The degradation efficiency increased rapidly with the increase of the relative humidity in a low humidity range from 0 to 35%, but decreased gradually in a high relative humidity (i.e., >35%). The optimum experimental conditions for toluene degradation is a toluene concentration of 106 mg m^?3, a relative humidity of 35%, and an illumination intensity of ca. 6 mW cm^?2 at the surface of ZnO/SnO₂ photocatalysts. The intermediates produced during the gaseous photocatalytic degradation process were identified using the GC–MS technique. Based on these identified intermediates, the photocatalytic mechanism of toluene into ZnO/SnO₂ coupled oxide catalyst was also deduced.     

Z‐Scheme 2D/2D Heterojunction of Black Phosphorus/Monolayer Bi2WO6 Nanosheets with Enhanced Photocatalytic Activities

Black phosphorus (BP), a star‐shaped two‐dimensional material, has attracted considerable attention owing to its unique chemical and physical properties. BP shows great potential in photocatalysis area because of its excellent optical properties; however, its applications in this field have been limited to date. Now, a Z‐scheme heterojunction of 2D/2D BP/monolayer Bi₂WO₆ (MBWO) is fabricated by a simple and effective method. The BP/MBWO heterojunction exhibits enhanced photocatalytic performance in photocatalytic water splitting to produce H₂ and NO removal to purify air; the highest H₂ evolution rate of BP/MBWO is 21042 μmol g^?1, is 9.15 times that of pristine MBWO and the NO removal ratio was as high as 67 %. A Z‐scheme photocatalytic mechanism is proposed based on monitoring of ^.O₂^?, ^.OH, NO₂, and NO₃^? species in the reaction. This work broadens applications of BP and highlights its promise in the treatment of environmental pollution and renewable energy issues.     

A Hierarchical Nanostructured Carbon Nanofiber–In2S3 Photocatalyst with High Photodegradation and Disinfection Abilities Under Visible Light

Photocatalytic degradation of pollutants under visible light provides a new door to solve the water contamination problem by utilizing free and renewable sunlight. The search for highly efficient photocatalysts with hierarchical nanostructures remains crucial for accessing this new door. In this work, a new hierarchical nanostructured photocatalyst is designed and synthesized, for the first time, by anchoring In₂S₃ flower‐like nanostructures on non‐woven carbon nanofiber (CNF). The nanostructures of these CNF–In₂S₃ composites were fine‐tuned, with the aim of achieving the highest photocatalytic activity under visible light. The formation mechanism of the hierarchical nanostructure is also investigated. The results indicate that the optimized hierarchical CNF–In₂S₃ photocatalyst is superior in photodegradation and disinfection efficiency to that of pure In₂S₃ under visible‐light irradiation. The prominent photocatalytic activities of these hierarchical CNF–In₂S₃ photocatalysts can be attributed to the excellent properties of enhanced light absorption, large surface area, and efficient charge separation, which are all derived from the special three‐dimensional hierarchical nanostructures. Therefore, this work presents the great potential of this hierarchical nanostructured CNF–In₂S₃ photocatalyst in practical environmental remediation fields.     

Synthesis of nano-sized Ag3PW12O40/ZnO heterojunction as a photocatalyst for degradation of organic pollutants under simulated sunlight

With the rapid development of the world economy, water pollution has become increasingly serious. The photocatalytic degradation of pollutants is one of the most promising environmental treatment techniques. In this study, novel Ag₃PW₁₂O₄₀/ZnO nanoheterojunction was successfully constructed via a chemical process and was then characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, Brunauer-Emmett-Teller analysis, and photoluminescence measurements. The synthesized nanoheterojunction exhibited good crystallinity and dispersity. The particle diameter of the composite was approximately 800 nm, the bandgap was 2.92 eV, and the specific surface area was approximately 10.5 m².g^?1. Under optimum conditions, the photocatalyst degraded 82.1% RhB in 60 min. Moreover, the novel Ag₃PW₁₂O₄₀/ZnO heterojunction also exhibited an excellent recycling stability. Hydroxyl radicals, superoxide radicals, and holes played important roles in the photocatalytic degradation process. A possible mechanism for the enhanced photocatalytic performance of the nanoheterojunction was proposed. This work provides a strong foundation for the application of Ag₃PW₁₂O₄₀/ZnO nanoheterojunction for treating environmental organic pollutants.