Tunable band gap of Bi³⁺-doped anatase TiO₂ for enhanced photocatalytic removal of acetaminophen under UV-visible light irradiation

A series of Bi³⁺-doped TiO₂ photocatalysts has been prepared via the propylene oxide (PO) assisted sol-gel method. The effect of Bi³⁺ doping on structural surface morphology and optical properties of the as-prepared photocatalysts was characterized using UV-Visible (UV-Vis) diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller for determination of the specific surface area and porosity, and X-ray photoelectron spectroscopy. Increasing the Bi³⁺ doping percentage up to 10 mole percent, resulted in all as-prepared photocatalysts exhibiting pure anatase phase upon calcination at 400 °C for 3 hours. A red shift in optical band gap measurements was observed with increasing Bi³⁺ ion percent doping, which led to extension of the photocatalysts’ activity to the visible region. The enhanced photocatalytic activity for removal of the pharmaceutical compound acetaminophen under UV-Vis light irradiation was demonstrated by comparing bismuth doped as-prepared photocatalysts with pure TiO₂ photocatalysts prepared under the same conditions. Based on experimental conditions, the highest activity was achieved using 10 mole percent Bi³⁺-doped photocatalyst, where over a period of 4 hours more than 98% acetaminophen removal was achieved.