Zinc oxide (ZnO) has been known as an excellent photocatalyst for the degradation of a variety of organic pollutants under UV irradiation. This work describes a synthesis of ZnO nanoparticles via a facile precipitation method, and Ag was doped into Ag/ZnO nanocomposite to improve the photocatalytic degradation of BPA under visible light irradiation. The obtained ZnO nanoparticles were 20 nm in size and had a relatively high surface area and pore volume, 26.2 m²/g and 0.48 cm³/g, respectively. The deposition of Ag led to a decrease in the surface area, pore volume, and band gap energy () of ZnO nanoparticles. However, the photocatalytic activity of Ag/ZnO composite in the case increased. The performance of ZnO was compared with Ag/ZnO composites at the different molar ratios, and the kinetic reaction of BPA in these catalysts was investigated by the first-order kinetic model. The sample of Ag/ZnO-10 composite had the highest catalytic activity and showed the degradation efficiency, reaction rate, and degradation capacity of 100% in 120 min, 0.014 min^-1, and 40 mg/g, respectively. In comparison, the effects of Ag/ZnO molar ratio, catalyst dosage, solution pH, and concentration of BPA on photocatalytic degradation were investigated. Additionally, the photocatalytic performance of Ag/ZnO-10 composite was evaluated by the degradation of other persistent organic compounds such as phenol, tartrazine, and methylene blue and compared to other catalysts in literature.

In this study, magnetic material based on graphene oxide (GO) was developed for enhanced adsorption capacity for heavy metals. The Fe₃O₄ nanoparticles were combined with the GO material using a chitosan (CS) binder to obtain the CS-Fe₃O₄/GO nanocomposite. The adsorption capacity of this nanocomposite was evaluated by removing heavy metals including Ni²⁺ ions. When GO was composed with Fe₃O₄ and CS, the GO films were densely covered with ferromagnetic particles, which were bound and densely distributed on the GO film surface due to the interaction between GO and CS. The optimal conditions for the complexation of Ni²⁺ and 4-(2-pyridyl azo)-rezoxine (PAR) are 1 ml Ni²⁺, 2 ml PAR 100 mg l⁻¹, pH = 6 (adjusted with 0.7 ml of the 0.1 M K₂HPO₄ solution) and a complexation time of 20 min. After 50 min of adsorption, the Ni²⁺ removal efficiency of the CS-Fe₃O₄/GO nanocomposite reached 81.21% and the corresponding adsorption capacity was 2.03 mg g⁻¹ . The Ni²⁺ removal process followed the first-order model and Freundlich isotherm. This process was spontaneous (ΔG ^o < 0) and an exothermic process (ΔH ^o = −1128.875 J·mol⁻¹). In addition, the factors affecting this process were investigated, including the pH solution, the dosage of the CS-Fe₃O₄/GO nanocomposite and the initial Ni²⁺ concentration. The CS-Fe₃O₄/GO nanocomposite showed a potential adsorption capacity in removing Ni²⁺ at low concentrations from wastewater.