Directional Change of Interfacial Electric Field by Carbon Insertion in Heterojunction System TiO2/WO3

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.

Constructing Heterojunction Photocatalyst Systems with Spatial Distribution of Au Single Atoms for CO2 Reduction

In single-atomic photocatalyst systems, the spatial distribution of single atoms on heterojunctions and its impact on photocatalytic processes, particularly on carrier dynamics and the CO2 reduction process involving multielectron reactions, remains underexplored. To address this gap, a WO3/TiO2 nanotube heterojunction with a spatially selective distribution of Au single atoms was developed using an oxygen vacancy anchoring strategy for CO2 photoreduction. By anchoring Au atoms onto the WO3 or TiO2 components, a substantial number of active sites are generated and the electron transfer pathways from the heterojunction toward Au sites are formed, thereby enhancing carrier separation and concentration. As a result, the total yield of CO2 reduction products increases by 6.3 times and 3.9 times, respectively. More importantly, due to significant differences in adsorption properties, energy band structures, and reaction energy barrier, as well as a 2-fold difference in carrier lifetime, the selective distribution of Au single-atom sites results in completely different CO2 photoreduction products: when Au atoms are anchored on WO3 and TiO2 components, the product selectivity is 67.6% CH4 and 82.9% CO, respectively. This study clarifies the vital role of the spatial distribution of single atoms on the selectivity of electron-demanding products.

Enhanced photocatalytic ammonia oxidation over WO3@TiO2 heterostructures by constructing an interfacial electric field

WO3 nanorods and xWO3@TiO2 (WO3/TiO2 mass ratio (x) = 1-5) photocatalysts were synthesized using the hydrothermal and sol-gel methods, respectively. The photocatalytic activities of xWO3@TiO2 for NH3 oxidation first increased and then decreased with a rise in TiO2 content. Among them, the heterostructured 3WO3@TiO2 photocatalyst showed the highest NH3 conversion (58 %) under the simulated sunlight irradiation, which was about two times higher than those of WO3 and TiO2. Furthermore, the smallest amounts of by-products (i.e., NO and NO2) were produced over 3WO3@TiO2. The enhancement in photocatalytic performance (i.e., NH3 conversion and N2 selectivity) of 3WO3@TiO2 was mainly attributed to the formed interfacial electric field between WO3 and TiO2, which promoted efficient separation and transfer of photogenerated charge carriers. Based on the results of reactive species trapping and active radical detection, photocatalytic oxidation of NH3 over 3WO3@TiO2 was governed by the photogenerated holes and superoxide radicals. This work combines two strategies of morphological regulation and interfacial electric field construction to simultaneously improve light utilization and photogenerated charge separation efficiency, which promotes the development of full-spectrum photocatalysts for the removal of ammonia.

Enhancing Photocatalytic Antibiotics Mineralization and Water Oxidation via Constructing Interfacial Electric Field in Plate-on-Plate BiOCl/WO3 Photocatalysts

Two-dimensional materials and related plate-on-plate interfacial heterostructures offer great flexibility for integrating different atomic layers, providing an attractive scheme for the construction of built-in electric fields in photocatalysts. Here, we developed an interfacial engineering strategy to construct well-interfaced plate-on-plate BiOCl/WO₃ heterojunctions for general enhanced photocatalytic oxidation reactions. BiOCl/WO₃ heterojunctions exhibited significant enhancements in oxygen evolution and antibiotic degradation, with a rate of 9.5 times and 14.7 times higher than that of WO₃. This enhancement is attributed to the well lattice matching contact surface of WO₃ {020} plane with BiOCl {001} plane, which integrates a strong built-in electric field induced by Bi-O chemically bonds, providing atomically fast transport channels for electrons. These findings offer new guidelines for designing interfacial structures for high-performance oxidative photocatalysts and provide insights into the underlying interfacial carrier transport mechanisms.

The interplay between acid-base properties and Fermi level pinning of a nano dispersed tungsten oxide - titania catalytic system

A series of WO₃/TiO₂ catalysts were synthesized, characterized, and evaluated for the NO selective catalytic reduction (SCR) with NH₃. Based on a wide range of characterization techniques, a detailed model was developed that describes the interfacial electron transfer between WO₃ and TiO₂ and defines a relationship between the acid-base properties of the catalytic surface and electronic structure modification. The electronic interactions at the WO₃/TiO₂ interface were quantified using variations in the system's electronic structure. Altering the dispersion and size of the WO₃ nanostructures results to drastic changes in titania's surface electron distribution, which are reflected in the pinning of Fermi level through an electron transfer process between WO₃ and TiO₂. The variations in the Fermi level were further related to changes in the point of zero charge (PZC) values and the activity towards NO SCR with NH_3, which was used as a test reaction. Temperature Programmed Surface Reaction (TPSR) was employed to study the catalytic activity at temperatures ranging from 30 °C to 500 °C and was quantitatively correlated to changes in coverage and interfacial charge transfer. We demonstrate that higher WO₃ loading on TiO₂ results in a stronger electronic interaction and a higher catalytic activity. This is because electron transfer increases the surface electron density, which enhances the surface basicity of TiO₂. The concomitant decrease in the adsorption energy of NH₃ results in a decrease in the activation energy, which is reflected in the SCR temperature onset.

Photoactive nanomaterials enabled integrated photo-rechargeable batteries

The research interest in energy storage systems (e.g. batteries and capacitors) has been increasing over the last years. The rising need for electricity storage and overcoming the intermittent nature of renewable energy sources have been potent drivers of this increase. Solar energy is the most abundant renewable energy source. Thus, the combination of photovoltaic devices with energy storing systems has been pursued as a novel approach in applications such as electric vehicles and smart grids. Among all the possible configurations, the "direct" incorporation of photoactive materials in the storing devices is most attractive because it will enhance efficiency and reduce volume/weight compared to conventional systems comprised two individual devices. By generating and storing electricity in a singular device, integrated photo-rechargeable batteries offer a promising solution by directly storing electricity generated by sunlight during the day and reversibly releasing it at night time. They hold a sizable potential for future commercialization. This review highlights cutting-edge photoactive nanomaterials serving as photoelectrodes in integrated photobatteries. The importance and influence of their structure and morphology and relevant photocatalytic mechanisms will be focal points, being strong influencers of device performance. Different architecture designs and working principles are also included. Finally, challenges and limitations are discussed with the aim of providing an outlook for further improving the performance of integrated devices. We hope this up-to-date, in-depth review will act as a guide and attract more researchers to this new, challenging field, which has a bright application prospect.

Evaluation of Ag@TiO2/WO3 heterojunction photocatalyst for enhanced photocatalytic activity towards methylene blue degradation

Methylene blue is a dye that is extensively used in the textile industry but it is a hazardous, carcinogenic, and mutagenic pollutant. Therefore, the treatment of wastewater containing methylene blue by photocatalytic degradation under visible light without using any sacrificial agent (H₂O₂) is an important method towards attaining an eco-friendly environment. Herein, the nanocomposite of Ag-doped TiO₂ on WO₃ nanoparticles (Ag@TiO₂/WO₃) was prepared by a modified sol-gel precipitation route, and their physicochemical properties were studied. The bandgap of Ag sensitized metal oxide nanocomposite in Ag@TiO₂/WO₃ was slightly reduced compared to the pristine titania due to the creation of interstitial energy states during colligation of titania and tungsten oxide. The ease of charge carrier transfers through the heterojunction of TiO₂/WO₃ increased the photocatalytic activity of the photocatalyst. Furthermore, in Ag@TiO₂/WO₃ the plasmonic Ag sensitization to the host semiconductor TiO₂ has further boosted the rate of photocatalytic degradation because of the surface plasmon resonance (SPR) and hindrance of charge carrier recombination. Due to the synergistic effect of SPR and the presence of heterojunction in Ag@TiO₂/WO₃, the photocatalytic activity was found to be 25 times higher for Ag@TiO₂/WO₃ than that of commercial DP25 photocatalyst under visible light towards methylene blue degradation.

A Review on the Properties and Applications of WO3 Nanostructure-Based Optical and Electronic Devices

Tungsten oxide (WO3) is a wide band gap semiconductor with unintentionally n-doping performance, excellent conductivity, and high electron hall mobility, which is considered as a candidate material for application in optoelectronics. Several reviews on WO3 and its derivatives for various applications dealing with electrochemical, photoelectrochemical, hybrid photocatalysts, electrochemical energy storage, and gas sensors have appeared recently. Moreover, the nanostructured transition metal oxides have attracted considerable attention in the past decade because of their unique chemical, photochromic, and physical properties leading to numerous other potential applications. Owing to their distinctive photoluminescence (PL), electrochromic and electrical properties, WO3 nanostructure-based optical and electronic devices application have attracted a wide range of research interests. This review mainly focuses on the up-to-date progress in different advanced strategies from fundamental analysis to improve WO3 optoelectric, electrochromic, and photochromic properties in the development of tungsten oxide-based advanced devices for optical and electronic applications including photodetectors, light-emitting diodes (LED), PL properties, electrical properties, and optical information storage. This review on the prior findings of WO3-related optical and electrical devices, as well as concluding remarks and forecasts will help researchers to advance the field of optoelectric applications of nanostructured transition metal oxides.

Construction of Ag/NaBiO3 with dual active sites for photocatalytic NO deep oxidation and long-lasting organic pollutants degradation in the dark

Ag/NaBiO₃ with dual active sites and high capacitance was prepared by the photo-deposition method. Upon light illumination, the reduction of Ag⁺ to Ag, the introduction of oxygen vacancies, and the electron storage in Ag nanoparticles simultaneously happened. NO, and O₂ adsorbed and activated at Ag site and oxygen vacancy site, respectively, to produce active ON* and •O₂^- radical species. The increased concentrations of the active oxygen species and the pre-oxidation of NO resulted in the enhanced NO removal with inhibited production of NO₂. Moreover, the high capacitance of Ag and the continuous charge transfer from defective NaBiO₃ to Ag offered the enhanced and long-lasting dark catalytic activity of the Ag/NaBiO₃. The stored electrons in Ag were directly released in dark to decompose methyl orange and/or tetracycline. This work provides a novel idea of designing and preparing a multifunctional catalytic material for environmental cleaning.

Excellent optoelectronic applications and electrical transport behavior of the n-WO3nanostructures/p-diamond heterojunction: a new perspective

Nanostructured n-type metal oxides/p-type boron-doped diamond heterojunctions have demonstrated a typical rectification feature and/or negative differential resistance (NDR) potentially applied in wide fields. Recently, the fabrication and electronic transport behavior of n-WO₃nanorods/p-diamond heterojunction at high temperatures were studied by Wanget al(2017Appl. Phys. Lett.110052106), which opened the door for optoelectronic applications that can operate at high-temperatures, high-power, and in various harsh environments. In this perspective, an overview was presented on the future directions, challenges and opportunities for the optoelectronic applications based on the n-WO₃nanostructures/p-diamond heterojunction. We focus, in particular, on the prospects for its high temperature NDR, UV photodetector, field emission emitters, photocatalyst and optical information storage for a wide range of new optoelectronic applications.

Facile one-pot synthesis of defect-engineered step-scheme WO3/g-C3N4 heterojunctions for efficient photocatalytic hydrogen production

Defect-engineered step-scheme WO₃/g-C₃N₄ heterojunctions synthesized by a facile one-pot method greatly improve the photocatalytic activity for hydrogen evolution.