Theoretical and experimental study of the adsorption characteristics of Methylene Blue on titanium dioxide surface using DFT and Monte Carlo dynamic simulation

In the present work, the experimental and theoretical studies of the adsorption of methylene blue (MB) on TiO2 were established. The geometry of MB was optimized by density functional theory (DFT) at the B3LYP/LanL2DZ level of theory using Gaussian software 09W, then after, the adsorption on anatase (110) TiO2 surface in aqueous solution was carried out by Monte Carlo dynamic simulation. Theoretical results show that the fully protonated MB in the three nitrogen atoms has a high negative PA which indicates their better tendency of chemical adsorption to TiO2 surface than neutral or partially protonated. Then, quantum chemical parameters, electronic distribution, total, average total, intermolecular, electrostatic, and van der Walls energies for the systems were evaluated and interpreted. According to the results, MB was chemisorbed in each case of neutral and protonated species. A systematic study of various parameters (amount of TiO2, contact time, initial concentration, temperature, pH), was performed. Experimental results show that the adsorption was rapid and was best fitted with the pseudo-second-order kinetic model instead of pseudo-first-order kinetic and Elovich models. The values of thermodynamic parameters Delta G degrees, Delta S degrees, and Delta H degrees indicate that the adsorption was spontaneous and exothermic in nature. The adsorption follows the Langmuir isotherm model in agreement with quantum chemical parameters obtained by DFT and MCDS.