Photocatalytic Degradation of Methylene Blue with ZnO Nanoparticles; a Joint Experimental and Theoretical Study

Abstract

The present work focuses on the photocatalytic degradation and adsorption properties of Methylene Blue (MB) on ZnO nanoparticles from experimental and theoretical points of view. The photoreaction is carried out in a Pyrex photoreactor, equipped with a Krypton lamp. The kinetics of the degradation is explained in terms of Langmuir-Hinshelwood kinetic model. The results show that the pseudofirst-order equation is the model that gives the best fit to the experimental data. The value of the adsorption equilibrium constant is calculated as 0.128 L mg^-1. The quantum mechanical cluster approach is used to model the adsorption of MB on the ZnO (0001) facet. Geometrical optimizations and vibrational analysis are performed using density functional theory methods. The calculations show a negative charge transfer from the substrate to the photocatalyst. The calculated value of the adsorption energy is in the range of chemical adsorption energies.