Photocatalytic degradation of azo and anthraquinone dye using TiO₂/MgO nanocomposite immobilized chitosan hydrogels

Textile dyes are very toxic to human beings and environment. TiO₂ nanoparticles have been of great interest in treating the organic effluent dyes. While using TiO₂ nanoparticles, there is the electron-hole recombination, which decreases the degradation efficiency of photocatalyst. MgO nanoparticle, when used along with TiO₂, forming TiO₂/MgO nanocomposite act as a barrier for electron-hole recombination. Here, TiO₂/MgO nanocomposites have been immobilized in chitosan beads, where chitosan acts as a support for the nanocomposite. The photocatalysts have been characterized by scanning electron microscope, ultraviolet (UV), X-ray diffraction and Fourier transform infrared spectroscopy. Methyl orange (MO) and Alizarin Red S (ARS) were used as model dye compounds. For MO, the experimental data have a better fit with Langmuir adsorption model and for ARS, it has a better fit with Freundlich adsorption model. Photocatalytic degradation efficiency of TiO₂/MgO nanocomposite for a reaction time of 90 min towards degrading MO is 83.2% and ARS is 43.8%. Degradation efficiency of TiO₂/MgO/chitosan hydrogels towards degrading MO and ARS is 82.4% and 41.8%, respectively. 3 wt.% is found to be the optimum concentration of MgO in TiO₂/MgO nanocomposite . Degradation of the dye follows first-order kinetics and Langmuir-Hinshelwood model well suites in describing the kinetics of photocatalytic disappearance of the dyes. First-order rate constants for dye degradation under UV irradiation were calculated. TiO₂/MgO/chitosan hydrogels could efficiently degrade MO and ARS dyes with a little lesser efficiency than TiO₂/MgO nanocomposite making the process economically and environmentally a very suitable and favourable process for textile dye degradation.