Improved adsorption and degradation performance by S-doping of (001)-TiO2

Hollow S-Doped ZnFe2O4 Microcubes with Magnetic Separability for Photocatalytic Removal of Uranium(VI) under Different Light Intensity

Under xenon lamps, ZnFe2O4 (ZFO) has been shown to be effective in removing uranium through photocatalysis. However, its performance is still inadequate in low-light environments due to low photon utilization and high electron-hole complexation. Herein, S-doped hollow ZnFe2O4 microcubes (Sx-H-ZFO, x = 1, 3, 6, 9) were synthesized using the MOF precursor template method. The hollow morphology improves the utilization of visible light by refracting and reflecting the incident light multiple times within the confined domain. S doping narrows the band gap and shifts the conduction band position negatively, which enhances the separation, migration, and accumulation of photogenerated charges. Additionally, S doping increases the number of adsorption sites, ultimately promoting efficient surface reactions. Consequently, Sx-H-ZFO is capable of removing U(VI) in low-light environments. Under cloudy and rainy weather conditions, the photocatalytic rate of S3-H-ZFO was 100.31 μmol/(g·h), while under LED lamps (5000 Lux) it was 72.70 μmol/(g·h). More interestingly, a systematic mechanistic investigation has revealed that S doping replaces some of the oxygen atoms to enhance electron transfers and adsorption of O2. This process initiates the formation of hydrogen peroxide, which reacts directly with UO22+ to form solid studtite (UO2)O2·2H2O. Additionally, the promising magnetic separation capability of Sx-H-ZFO facilitates the recycling and reusability of the material. This work demonstrates the potential of ZnFe2O4 extraction uranium from nuclear wastewater.

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^-.

In situ composite of Co-MOF on a Ti-based material for visible light multiphase catalysis: synthesis and the photocatalytic degradation mechanism

A Co-MOF/Ti-based Z-type heterojunction prepared by an in situ growth method exhibits good photocatalytic activity for tetracycline.

Effect of Cu doping on the photocatalytic activity of InVO4 for hazardous dye photodegradation under LED light and its mechanism

Cu doped InVO₄ (xCu-InVO₄ (x = 0.06-0.15 wt %) was synthesized by a facile one-pot hydrothermal method for the removal of methylene blue (MB) under LED light irradiation. The X-ray photoelectron spectroscopy (XPS) analysis indicated the coexistence of V⁵⁺ and V⁴⁺ species due to the O-deficient nature of the xCu-InVO₄. The synthesized photocatalysts displayed a morphology of spherical and square shaped particles (20-40 nm) and micro-sized rectangle rods with a length range of 100-200 μm. The xCu-InVO₄ exhibited superior adsorption and photodegradation efficiency compared to pristine InVO₄ and TiO₂ due to the presence of O₂ vacancies, V⁴⁺/V⁵⁺ species, and Cu dopant. The optimum reaction conditions were found to be 5 mg L^-1 (MB concentration), pH 6, and 100 mg of photocatalyst mass with a removal efficiency and mineralization degree of 100% and 96.67%, respectively. The main active species responsible for the degradation of MB were ^•OH radicals and h⁺. Reusability studies indicated that the 0.13Cu-InVO₄ was deactivated after a single cycle of photocatalytic reaction due to significant leaching of V⁴⁺ and Cu²⁺ species.

C-,N- and S-Doped TiO2 Photocatalysts: A Review

This article presents an overview of the reports on the doping of TiO2 with carbon, nitrogen, and sulfur, including single, co-, and tri-doping. A comparison of the properties of the photocatalysts synthesized from various precursors of TiO2 and C, N, or S dopants is summarized. Selected methods of synthesis of the non-metal doped TiO2 are also described. Furthermore, the influence of the preparation conditions on the doping mode (interstitial or substitutional) with reference to various types of the modified TiO2 is summarized. The mechanisms of photocatalysis for the different modes of the non-metal doping are also discussed. Moreover, selected applications of the non-metal doped TiO2 photocatalysts are shown, including the removal of organic compounds from water/wastewater, air purification, production of hydrogen, lithium storage, inactivation of bacteria, or carbon dioxide reduction.

Transformation of novel TiOF2 nanoparticles to cluster TiO2-{001/101} and its degradation of tetracycline hydrochloride under simulated sunlight

The anatase type cluster TiO₂-{001/101} was rapidly generated by a one-step hydrothermal method. The transformation process of coral-like TiOF₂ nanoparticles to cluster TiO₂-{001/101} was investigated for the first time, and the sensitization between cluster TiO₂-{001/101} and tetracycline hydrochloride (TCH) was also discussed. The degradation rate of TCH by cluster TiO₂-{001/101} under simulated sunlight was 92.3%, and the total removal rate was 1.76 times that of P25. Besides, cluster TiO₂-{001/101} settles more easily than P25 in deionized water. The study showed that cluster TiO₂-{001/101} derived from coral-like TiOF₂ nanoparticles had a strong adsorption effect on TCH, which was attributed to the oxygen vacancy (O_v) and {001} facets of cluster TiO₂-{001/101}. The strong adsorption effect promoted the sensitization between cluster TiO₂-{001/101} and TCH, and widened the visible light absorption range of cluster TiO₂-{001/101}. In addition, the fluorescence emission spectrum showed that cluster TiO₂-{001/101} had a lower luminous intensity, which was attributed to the heterojunction formed by {001} facets and {101} facets that reduces the recombination rate of carriers. It should be noted that cluster TiO₂-{001/101} still has good degradation performance for TCH after five cycles of degradation. This study provides a new idea for the synthesis of cluster TiO₂-{001/101} with high photocatalytic performance for the treatment of TCH wastewater.

Degradation of tetracycline hydrochloride by cluster TiO₂-{001/101} under simulated sunlight.