Degradation of naphthalene and anthracene using the CdS/ZnO with enhanced photocatalytic activities

Naphthalene and anthracene, as two common substances of polycyclic aromatic hydrocarbons (PAHs), have the harmful effects on human health (carcinogenic and mutagenic activity), and it is of great significance to remove them. In this paper, the CdS/ZnO nanocomposites were fabricated by the chemical bath deposition method. Its morphology and structure were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and so on. In addition, the photocatalytic degradation efficiency of naphthalene and anthracene was studied under different experimental conditions, including CdS-loading doses, pH, the dosage of photocatalyst and the initial concentrations of solution. Under the condition of pH 7.5, visible light irradiation and the optimal 4 mg nanocomposite, for 2 mg/L naphthalene solution, a maximum photocatalytic degradation efficiency was 98.75 % after 180 min and the corresponding pseudo-first order rate constant was 0.0214 min−1. Under the condition of pH 7.5, visible light irradiation and the optimal 8 mg nanocomposite, for 2 mg/L anthracene solution, the maximum photocatalytic degradation efficiency was 96.13 % after 300 min, and the rate constant was 0.0118 min−1. The above two rate constants were higher than those of their parent catalysts. Based on the free radical trapping experiments, the photocatalytic mechanism showed that •O2- and h+ were the major active radicals in the degradation process with the type-II heterostructure.