Synthesis of Zinc Oxide-Kaolin Nanocomposite and Its Efficiency In the Photocatalytic Removal of Phosphate From Aqueous Solutions In the Presence of Visible Light Irradiation

The amount of phosphate in wastewater, lakes and seas are progressively on the rise. Since this nutrient is an essential macromolecule and a limiting factor for the growth of algae and cyanobacteria, thus, it could be a major factor in the occurrence of eutrophication.
The purpose of this study was to synthesize zinc oxide nanocomposite coating on the kaolin and determine its efficiency in photocatalytic removal of phosphate from aqueous environments in the presence of visible light.
ZnO-Kaolin was synthesized by a co-precipitation method and the effects of some parameters such as initial pH, initial nanocomposite dosage, initial phosphate concentration, hydrogen peroxide concentration, the presence of oxygen and nitrogen gases, and organic compounds on the removal of phosphate by ZnO-Kaolin/ visible light were investigated.
FT-IR and SEM analyses demonstrated favorable immobilization of ZnO onto Kaolin. The maximum removal efficiency of photocatalytic was attained in pH 3, initial concentration of phosphate 20 mgL-1 and nanocomposite dosage 0.5 gL-1 in 120 minutes. With increasing initial phosphate concentrations from 10 to 100 mgL-1, the reaction rate constant (kobs) decreased from 0.0604 to 0.0021 min-1 and electrical energy per order (EEo) increased from 158.940 to 4571.428 kWh.m-3. The efficiency of the zinc oxide – kaolin/ visible light process for reduction of phosphate was about 99.27.
According to the carried out tests, it was found that zinc oxide-kaolin/ visible light can be considered as an effective method for removing phosphate with high performance in a short time.