Mesoporous dark brown TiO2 spheres for pollutant removal and energy storage applications

Abstract Colored TiO2 has tremendously attained significant interest worldwide due to its fascinating optical properties. Mesoporous dark brown TiO2 nanospheres with extremely high surface area (1246 m2/g) fabricated through the combined approach of thermal annealing with the sol–gel method. FESEM images inferred the creation of the spherical structure of 357 nm which transformed into defected mesoporous TiO2 spheres of 452 nm under annealing at 350 °C. UV-DRS PL and EPR studies confirm the bandgap narrowing due to the creation of oxygen defects sates in the TiO2 sample. Dark brown TiO2 exhibits remarkable sunlight-induced photodegradation activity for methylene blue and oxytetracycline hydrochloride molecules. Mesoporous TiO2 defect rich spheres adsorb the 32% of the MB pollutant molecules in just 30 min. Moreover, it decomposes the rest 67% of 15 µM MB dye solution and 0.5 mg/mL OTC solution in 30 min and 80 min respectively. Existences of high oxygen defect states in TiO2 were responsible for the bandgap narrowing and improve charge carriers separation and superior photocatalytic activity (PCA). Mesoporous dark brown TiO2 sample was also investigated for the energy storage application. Unusual high surface area also facilitated the accumulation of charges and led to the enhancement in charge storage properties.