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

Textile dyes are very toxic to human beings and environment. TiO nanoparticles have been of great interest in treating the organic effluent dyes. While using TiO nanoparticles, there is the electron-hole recombination, which decreases the degradation efficiency of photocatalyst. MgO nanoparticle, when used along with TiO, forming TiO/MgO nanocomposite act as a barrier for electron-hole recombination. Here, TiO/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 TiO/MgO nanocomposite for a reaction time of 90 min towards degrading MO is 83.2% and ARS is 43.8%. Degradation efficiency of TiO/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 TiO/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. TiO/MgO/chitosan hydrogels could efficiently degrade MO and ARS dyes with a little lesser efficiency than TiO/MgO nanocomposite making the process economically and environmentally a very suitable and favourable process for textile dye degradation.