Thermodynamic Study of Mehtylene Blue Adsorption and Photocatalytic Degradation on The N-Doped TiO₂ Thin Films: A DFT and Experimental Study

Abstract

N-Doped TiO2 coatings (N-TiO2) were synthesized and characterized. The effect of the doping process on the physical-chemical properties and photocatalytic efficiency of Methylene Blue (MB) under visible light irradiation were studied. The bare TiO2 showed only anatase crystalline structure. Furthermore, after the doping process, a slight transition from anatase to rutile was verified. The HRXPS confirmed that the doping process was effective. The N-2 sorption using the BET assay showed a slight increase in surface area after the doping process. MB adsorption kinetic showed also a slight increase for doped TiO2 films, showing as best fitting the Langmuir model. Furthermore, a modification on the electronic structure was observed, showed by the modification of the optical absorption profile in the doped material. The results showed that the MB adsorption on N-TiO2 thin films was endothermic (Delta H=11 kJ mol(-1)) and a spontaneous process (Delta G=-6.45 kJ mol(-1)). We performed DFT calculations to three simulated doped-structures. The Gap value, the global reactivity indexes and, the Fukui function isosurfaces are presented. Finally, the scavenger tests suggested that O-2(center dot<M->) and OH center dot could be the main ROS driving the photocatalytic process.