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

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 N2 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 (▵H=11 kJ mol−1) and a spontaneous process (▵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 O2. ${{{\rm O}}_{2}^{.\char60 M-\char62 }}$ and OH⋅ could be the main ROS driving the photocatalytic process. N‐TiO2 thin films improve its photocatalytic activity, showing the reduction of the MB concentration of 78 % after 180 min of visible irradiation. All the results were supported by means of DFT calculations. A schematic illustration of energy level diagram for bare TiO2 and N‐TiO2 thin films fabricated in this work.