Synthesis of a TiO2/zeolite composite: Evaluation of adsorption-photodegradation synergy for the removal of Malachite Green

Preparing by a simple method a versatile and sustainable material that can simultaneously perform effectively as an adsorbent/photocatalyst is a real challenge in wastewater treatment technology. In this work, a composite with 10% (wt%) TiO₂ nanoparticles supported on zeolite (TiO₂-Zeo) was synthesized by a facile-solid-state dispersion method, and characterized for their physicochemical, phase structure, microstructure, and optical properties. Characterization findings, showed that, for TiO₂-Zeo catalyst, the zeolitic matrix preserved its initial structure without any alteration, while its gap energy of 3.23 eV was similar to that of the starting TiO₂ material, showing that TiO₂ nanoparticles were simply deposited on the surface of the zeolite support. TiO₂-Zeo photocatalyst, as well as commercial TiO₂ nanoparticles, tested here as a photocatalyst model in view of comparison, were used for the removal of Malachite Green dye (MG) from aqueous solution. The adsorption and photodegradation potential of the catalysts was evaluated under the same operating conditions. It was found that the adsorption kinetics for the two materials were relatively slow, and the pseudo-first-order model can describe accurately the adsorption kinetics data. The equilibrium states were reached after 140 min and 150 min for MG/TiO₂-Zeo and MG/TiO₂ systems. At 0.5 g.L^-1 dose of TiO₂-Zeo, the adsorption capacity of MG at equilibrium, and the removal efficiency obtained with 25 mg.L^-1 and 35 mg.L^-1 were 41.2 mg.g^-1 (82.3%), and 46.9 mg.g^-1 (65.6%), respectively. Whereas, after 240 min UV irradiation, the obtained values in synergistic adsorption-photodegradation dye removal were superior, namely 47.4 mg.g^-1 (92.7%) and 63.6 mg.g^-1 (90.2%), respectively. On the other hand, within the range of operating conditions considered, the overall kinetic rate of synergistic adsorption-photodegradation was also simulated using the modified Elovich heterogeneous kinetic model in the two following scenarios: for strong and weak adsorption. Based on the goodness-of-fit criteria values obtained with the two used catalysts, the model appeared globally very consistent with kinetic data in both cases, with a perfect agreement in the strong adsorption case.