Photocatalytic degradation of malachite green dye by ZnO and ZnO–β-cyclodextrin nanocomposite

Water, the primary source of life, is contaminated with various organic/inorganic impurities in the course of development. Organic dyes, a waste product from dying industries, have evolved as one of the major contributor to water pollution. The present work involves the photocatalytic degradation of malachite green dye as a model substrate using zinc oxide nanoparticles (ZnO NPs) and its composite with β-cyclodextrin (β-CD). ZnO NPs are found to be a worthy catalyst due to their bandgap and easy availability. The role of β-CD in ZnO photocatalyst is explored. With ZnO NPs, electron–hole recombination takes place very easily; hence, to restrict this recombination β-CD has been used. We have characterized the synthesized nanomaterials by using powder X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, diffuse reflectance spectroscopy (DSR), scanning electron microscopy and transmission electron microscopy (TEM). Various parameters, such as the concentration of dye, pH and amount of catalyst have optimized for the photocatalysis process. More basic medium adsorption is more favourable than degradation, which decreases the reusability of the catalyst. Based on the photodegradation efficiency and rate constant (k), we observed that ZnO–β-CD showed better photocatalytic activity than ZnO NPs. The plausible mechanism for photocatalytic degradation has also been reported with the help of photoluminescence spectra and scavenger activity.