Effect of aqueous inorganic anions on the photocatalytic activity of CuO–Cu2O nanocomposite on MB and MO dyes degradation

Abstract

In this study, CuO–Cu2O nanocomposite was synthesized via a facile chemical-thermal oxidation method. The prepared nanocomposite was characterized by several techniques. X-ray diffraction (XRD) result affirmed that the synthesized nanocomposite was composed of CuO and Cu2O phases. X-Ray Photoelectron Spectroscopy (XPS) result confirmed the presence of Cu+, Cu2+, and O2− in the synthesized nanocomposite structure. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) results revealed the formation of string-bead-like nanoparticles with an average diameter of 40 nm. The optical band gap energy of 1.9 eV was estimated by diffuse reflectance spectroscopy (DRS). Besides, the photoluminescence (PL) spectrum shows the outstanding peak of the excitonic process at 550 nm. The photocatalytic performance of the synthesized compound was evaluated on methyl orange (MO) and methylene blue (MB) dyes. The degradation experiments were performed for 240 min under visible light irradiation. The photodegradation of the MB was higher than MO dye. Type II charge transfer was proposed for the photocatalytic mechanism of the synthesized nanocomposite. The degradation was further studied in the presence of sulfate, chloride, and nitrate ions in different concentrations. Sulfate anions had the most significant effect on MB inhibiting degradation, while chloride ions at the concentration of 0.5 mM increased the degradation of MB. Chloride anions also had the greatest inhibitory effect on the degradation of MO. Sulfate ions only negligibly affected MO degradation over CuO–Cu2O photocatalyst. Recyclability experiment revealed that the photodegradation process was only influenced 5 and 6%, respectively for MB and MO solutions after three runs.