Performance and mechanism of Al, N co-doped carbon/nano-TiO2 photocatalytic oxidation for the removal of ammonia nitrogen and Ni/Co complexes from ternary precursor wastewater

The process of producing ternary precursors for new lithium batteries produces industrial wastewater containing high concentrations of ammonia nitrogen and metal ammonia complexes, which requires strict treatment. In this study, a simple and efficient photocatalyst (Al, N co-doped carbon/nano-TiO2) with excellent adsorption and photocatalytic properties was developed. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption-desorption test, UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), Energy Dispersive X-Ray Spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), which indicated that the catalyst had excellent specific surface area and strong light absorption properties. In addition, the performance of photocatalytic treatment of ternary precursor wastewater was investigated by varying the amount of Al doping, the loading of nano-TiO2, the amount of catalyst input, changing the adsorption and photocatalytic time. The results suggested that the 3.0 g/L of Al, N co-doped carbon/nano-TiO2 composite photocatalyst achieved 91.45% degradation efficiency of ammonia nitrogen and the removal efficiency of nickel and cobalt was 99.11% and 98.34%, respectively. EDS and XPS analyses showed that ammonia nitrogen pollutants in the wastewater were eventually degraded to nitrogen and nitrogen oxides, with nickel and cobalt adsorbed on the catalyst surface in the form of Ni2+ and Co2+.