Photodegradation of dyes in batch and continuous reactors by Cu2O-CuO nano-photocatalyst on Cu foils prepared by chemical-thermal oxidation

Abstract

In this study, CuO-Cu2O nanocomposite photocatalyst on Cu foils was synthesized by chemical-thermal oxidation. In the chemical step Cu(OH)2 forms and in the thermal step, it turns to CuO and Cu2O. The X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FESEM) showed the synthesized Cu/CuO-Cu2O nanocomposite contains nanorods distributing on the polyhedral copper oxide matrix. One-step thermal oxidation of Cu(OH)2 at 500 °C under nitrogen atmosphere has a denser distribution of the nanorods on the truncated octahedral matrix. Transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS) showed the formation of a heterostructure of CuO nanorods on the Cu2O matrix with the band gap energy of 1.35 eV. Photoluminescence spectroscopy (PL) indicated higher electron-hole separation efficiency in the presence of more nanorods. The photocatalytic activity was investigated by Methylene blue (MB) and Methyl orange (MO) degradation in two new batch and continuous reactors with and without air bubble flow under visible light irradiation. The continuous reactor not only was closer to the real application but also has faster kinetics and higher water purification capacity. The degradation in this reactor for 300 mL of 2 mg L−1 MB solution was 55 % within 5 h with 0.8 cm2 mL−1 of photocatalyst. X-ray photoelectron spectroscopy (XPS) revealed the increase in the CuO/Cu2O ratio and the adsorbed oxygen on the surface after the degradation process. Different colors of light-emitting diodes (LED) were used as an illumination source. The maximum photonic efficiency was obtained for the blue color.