Green synthesis, characterisation, and performance evaluation of ZnO/TiO2 nanocomposite for cationic and anionic dye removal from aqueous solutions under solar irradiation

Abstract

Abstract Utilising plant extract for the synthesis of nanocomposite shows great potential as a viable substitute for conventional chemical method. In this study, ZnO/TiO2 composite of three different weight ratios (1:2, 1:1, and 2:1) were green synthesised using hibiscus leaf extract as the capping agent. The synthesised composites were characterised using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV–Vis Diffuse Reflectance Spectroscopy (UV–Vis DRS), Energy Dispersive X-ray Spectrometer (EDS), and Fourier Transform Infrared Spectroscopy (FTIR). XRD results confirmed the presence of wurtzite ZnO and anatase TiO2 in the composite. FTIR and FESEM analysis confirmed the formation of the composite. The composite was used for the removal of methylene blue and methyl orange dye under solar radiation. The degradation rate constant (k) of the composite with 1:2 weight ratio was 1.9 times the k value of pure TiO2. The effect of photocatalyst amount, initial pH of the dye solution, and reusability of the catalyst was investigated. The TiO2 and ZnO/TiO2 samples indicated a bandgap of 3.14 and 2.98 eV, respectively, which suggests better photocatalytic activity and also making the composite more active in the visible region.