Photocatalytic degradation of azo anionic dye (RR120) in ZnO-Ghezeljeh nanoclay composite catalyst/UV-C system: Equilibrium, kinetic and thermodynamic studies

This work presents the efficient photocatalytic decolorization of an anionic dye (RR120) by natural untreated Ghezeljeh nanoclay or “Geleh-Sar-Shoor” (means head-washing clay) and aqueous ZnO-natural Ghezeljeh nanoclay composite suspension catalysts. The physicochemical properties of these materials were determined by Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), X-ray fluorescence (XRF), cation exchange capacity (CEC) measurements, BET specific surface area and zeta potential. The UV radiation assisted decolorization/degradation kinetics of dye, has been studied and a number of parameters (amount of adsorbent, pH of the dye solutions, contact time, ionic strength, adsorbate medium temperature, and initial dye concentration) were optimized. The Ghezeljeh nanoclay exhibited a good ability during the photocatalytic reaction; the combination of nanoclay and ZnO made photooxidation more effective. The efficient photocatalytic removal of dye decreased with increasing pH or temperature and increased in the presence of inorganic salts; consequently, ZnO-Ghezeljeh clay nanocomposite is a suitable adsorbent to remove dyes from wastewater. Kinetic data revealed that the photocatalytic decolorization was controlled by the film diffusion, fitted by pseudo-first order model and followed with Langmuir isotherm. Calculation of ΔG0, ΔH0 and ΔS0 showed that the process was feasible, exothermic and spontaneous.