Photocatalytic efficiency of ZnAl-layered double hydroxide on degradation of a cationic dye under UV and solar radiation

Abstract

UV and solar radiation photocatalytic degradation of basic dye Rhodamine B (RhB) using ZnAl-layered double hydroxide photocatalyst was investigated. ZnAl-layered double hydroxide (ZA4-HT) with a molar ratio of 4:1 was synthesized from zinc and aluminum salts by co-precipitation methods, followed by heat treatment at 500 °C (CZA4). Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) revealed that after heat treatment of ZA4-HT, the pristine structure collapsed resulting in ZnO particles and ZnAl2O4 spinel. The discoloration rate of RhB was lower than 8% through direct photolysis. The calcined ZA4-HT showed high photocatalytic efficiency with a discoloration rate of about 100% after 90 min exposure time to UV or sunlight radiation. The optimal catalyst loading was found to be 1 g/L and the discoloration time increased with the dye concentration. The photodiscoloration and the photodegradation kinetics data were described by pseudo-first-order and Langmuir–Hinshelwood models. The reusability study of the calcined material showed a stable efficiency after four successive uses.