Degradation of ammonia gas by Cu2O/{001}TiO2 and its mechanistic analysis

Design and Preparation of Heterostructured Cu2O/TiO2 Materials for Photocatalytic Applications

The extensive use of fossil fuels has sped up the global development of the world economy and is accompanied by significant problems, such as energy shortages and environmental pollution. Solar energy, an inexhaustible and clean energy resource, has emerged as a promising sustainable alternative. Light irradiation can be transformed into electrical/chemical energy, which can be used to remove pollutants or transform contaminants into high-value-added chemicals through photocatalytic reactions. Therefore, photocatalysis is a promising strategy to overcome the increasing energy and environmental problems. As is well-known, photocatalysts are key components of photocatalytic systems. Among the widely investigated photocatalysts, titanium dioxide (TiO2) has attracted great attention owing to its excellent light-driven redox capability and photochemical stability. However, its poor solar light response and rapid recombination of electron-hole pairs limit its photocatalytic applications. Therefore, strategies to enhance the photocatalytic activity of TiO2 by narrowing its bandgap and inhibiting the recombination of charges have been widely accepted. Constructing heterojunctions with other components, including cuprous oxide (Cu2O), has especially narrowed the bandgap, providing a promising means of solving the present challenges. This paper reviews the advances in research on heterostructured Cu2O/TiO2 photocatalysts, such as their synthesis methods, mechanisms for the enhancement of photocatalytic performance, and their applications in hydrogen production, CO2 reduction, selective synthesis, and the degradation of pollutants. The mechanism of charge separation and transfer through the Cu2O/TiO2 heterojunctions and the inherent factors that lead to the enhancement of photocatalytic performance are extensively discussed. Additionally, the current challenges in and future perspectives on the use of heterostructured Cu2O/TiO2 photocatalysts are also highlighted.

Preparation of a Z-Type g-C3N4/(A-R)TiO2 Composite Catalyst and Its Mechanism for Degradation of Gaseous and Liquid Ammonia

In this study, an (A-R)TiO2 catalyst (ART) was prepared via the sol-gel method, and g-C3N4 (CN) was used as an amendment to prepare the g-C3N4/(A-R)TiO2 composite catalyst (ARTCN). X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, N2 adsorption-desorption curves (BET), UV-Vis diffuse absorption spectroscopy (UV-Vis DRS), and fluorescence spectroscopy (PL) were used to evaluate the structure, morphology, specific surface area, optical properties, and photocarrier separation ability of the catalysts. The results showed that when the modifier CN content was 0.5 g, the dispersion of the ARTCN composite catalyst was better, with stronger light absorption performance, and the forbidden band width was smaller. Moreover, the photogenerated electrons in the conduction band of ART transferred to the valence band of CN and combined with the holes in the valence band of CN, forming Z-type heterostructures that significantly improved the efficiency of the photogenerated electron-hole migration and separation, thus increasing the reaction rate. Gaseous and liquid ammonia were used as the target pollutants to investigate the activity of the prepared catalysts, and the results showed that the air wetness and initial concentration of ammonia had a great influence on the degradation of gaseous ammonia. When the initial concentration of ammonia was 50 mg/m3 and the flow rate of the moist air was 0.9 mL/min, the degradation rate of gaseous ammonia by ARTCN-0.5 reached 88.86%, and it had good repeatability. When the catalytic dose was 50 mg and the initial concentration of NH4+ was 100 mg/L, the degradation rate of liquid ammonia by ARTCN-0.5 was 71.60% after 3 h of reaction, and small amounts of NO3- and NO2- were generated. The superoxide anion radical (·O2-) and hydroxyl radical (·OH) were the main active components in the photocatalytic reaction process.

The Preparation of {001}TiO2/TiOF2 via a One-Step Hydrothermal Method and Its Degradation Mechanism of Ammonia Nitrogen

{001}TiO₂/TiOF₂ photocatalytic composites with a high activity {001} crystal plane were prepared by one-step hydrothermal methods using butyl titanate as a titanium source and hydrofluoric acid as a fluorine source. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), raman spectroscopy, N₂ adsorption-desorption curve (BET), UV-Vis diffuse absorption spectroscopy (UV-Vis DRS), X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy (PL) were used to evaluate the structure, morphology, specific surface area, optical properties, and photocarrier separation ability of {001}TiO₂/TiOF₂. Ammonia nitrogen was taken as the target pollutant, and the degradation performance of the catalyst was investigated. The results show that hydrofluoric acid improves the content of {001} crystal plane of TiO₂ with high activity; it also improves the specific surface area and dispersion of the composite material and adjusts the ratio of {001}TiO₂ to TiOF₂ in the composite material to enhance the absorption capacity of the composite material and reduce the band gap width of the composite material. The degradation rate of ammonia nitrogen by 100 mg F15 is 93.19% when the initial concentration of ammonia nitrogen is 100 mg/L and pH is 10. Throughout the reaction process, the {001}TiO₂/TiOF₂ composite produces superoxide anion radical (·O₂^-) and hydroxyl radical (·OH) to oxidize NH₃·H₂O and generate N₂ accompanied by a small amount of NO₃^- and NO₂^-.

Dual Use of Copper-Modified TiO2 Nanotube Arrays as Material for Photocatalytic NH3 Degradation and Relative Humidity Sensing

In this paper, we emphasized the dual application of Cu-modified vertically aligned TiO2 nanotube arrays as photocatalyst and a relative humidity sensor. The TiO2 nanotube arrays were obtained by anodization of the titanium layer prepared using radio frequency magnetron sputtering (RFMS) and modified with different copper concentrations (0.5, 1, 1.5, and 2 M) by a wet-impregnation method. The sample modified with 2 M Cu(NO3)2 solution showed the highest efficiency for the NH3 photocatalytic degradation and the most pronounced humidity response in comparison to the other studied samples. In order to investigate the structure and impact of Cu modification, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used. The photocatalytic activity and the kinetic study of ammonia oxidation were studied in a mini-photocatalytic wind tunnel reactor (MWPT), while relative humidity sensing was examined by impedance spectroscopy (IS). Higher NH3 oxidation was a direct consequence of the increased generation of •OH radicals obtained by a more efficient photogenerated charge separation, which is correlated with the increase in the DC conductivity.

Novel, Simple and Low-Cost Preparation of Ba-Modified TiO2 Nanotubes for Diclofenac Degradation under UV/Vis Radiation

A novel low-cost synthesis of barium-modified TiO2 nanotube (TNT) arrays was used to obtain an immobilized photocatalyst for degradation of diclofenac. TNT arrays were prepared by electrochemical anodization of titanium thin films deposited on fluorine-doped tin oxide (FTO) coated glass by magnetron sputtering, ensuring transparency and immobilization of the nanotubes. The Ba-modifications were obtained by annealing solutions of Ba(OH)2 spin coated on top of TNT. Three different concentrations of Ba(OH)2 were used (12.5 mM, 25 mM and 50 mM). The crystalline structure, morphology and presence of Ba were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Ba-modified TiO2 nanotubes (BTNT) were tested for photocatalytic degradation of diclofenac under UV/Vis radiation and it was proven that all of the Ba-modified samples showed an increase in photocatalytic activity with respect to the unmodified TNTs. The most efficient photocatalyst was the sample prepared with 25 mM Ba(OH)2 which showed 90% diclofenac degradation after 60 min. This result was in agreement with cyclic voltammetry measurements that showed the largest increase in photo-oxidation current densities for the same sample due to the increased generation of •OH radicals obtained by a more efficient photogenerated charge separation.