Synthesis of polyoxometalates (POM)/TiO2/Cu and removal of nitrate nitrogen in water by photocatalysis.

Nitrate nitrogen is one of the vital issues needed to be addressed in the water purification process utilizing groundwater as a drinking water source. In this study, a sandwich-type polyoxometalate Na [α-SiW9O34] has been synthesized and SiW9/TiO2/Cu composite has been prepared by sol-gel method. Samples have been characterized by XRD, BET, FTIR, SEM, ED-Mapping, UV-Vis, XPS. The catalytic reduction of nitrate was performed in the presence of SiW9/TiO2/Cu composite as photocatalyst. The effects of catalyst loading, initial nitrate concentration, sandwich-type polyoxometalate loading, dissolved O2, and concentration of formic acid on nitrate removal have been investigated. The results showed that the prepared composite catalyst had better photocatalytic activity than the TiO2. 76.53% of nitrate removal with 82.09% of N2 selectivity was obtained under the following conditions: catalyst dosage 0.8 g/L, initial nitrate concentration of 30 mg/L, SiW9/Cu loading percentage of 10%, 30 mmol/L of formic acid, in presence of N2, and 6 h reaction time.

Removal of nitrate nitrogen from water by phosphotungstate-supported TiO2 photocatalytic method.

Nitrate nitrogen in water, especially in groundwater, is a major problem in the current drinking water environment. In this study, copper- and nickel-modified phosphotungstate catalysts supported on TiO2 were prepared by the sol-gel solvothermal method, and photocatalytic reduction by phosphotungstate was used to remove nitrate nitrogen in water under ultraviolet irradiation. The maximum removal rate was 59.60% with 0.8 g/L Cu-H3PW12O40/TiO2, 90 mg/L nitrate nitrogen, and 60 min reaction time. For Ni-H3PW12O40/TiO2, the maximum removal rate of nitrate nitrogen was 54.58%, achieved with a catalyst concentration of 0.8 g/L, nitrate nitrogen concentration of 120 mg/L, and reaction time of 30 min. Both catalysts could remove nitrate nitrogen from water under the condition of photocatalysis.

Preparation and characterization of a copper phosphotungstate/titanium dioxide (Cu-H3PW12O40/TiO2) composite and the photocatalytic oxidation of high-concentration ammonia nitrogen.

Currently, the majority of wastewater with a high concentration of ammonia nitrogen (NH4+/NH3) is treated using biological methods, which have poor biodegradability and low removal efficiency. In this paper, a composite photocatalyst of copper phosphotungstate/titanium dioxide (Cu-H3PW12O40/TiO2) was prepared by sol-gel hydrothermal synthesis, and the composite catalyst was characterized by X-ray diffraction (XRD), UV-vis-diffuse reflectance spectroscopy (UV-VIS-DRS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS)、scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The photocatalytic oxidation of a high-concentration NH4+/NH3 solution was carried out under ultraviolet (UV) light to explore the effects of different influencing factors on the photocatalytic effect and to optimize the reaction conditions. The prepared composite catalyst exhibited higher photocatalytic activity than that of TiO2. When the initial concentration of the solution was 300 mg·L-1, the initial pH was 11, the catalyst concentration was 1.5 g·L-1, the loading level of Cu-H3PW12O40 was 40%, and the aeration rate was 1.5 L·min-1, the removal rate of NH4+/NH3 by the composite photocatalyst could reach >80%. Very little NO2- and NO3- were produced, and N2 was the main product.