Multiple-homojunction gradient nitrogen doped TiO2 for photocatalytic degradation of sulfamethoxazole, degradation mechanism, and toxicity assessment

Abstract In this work, by using pulsed laser deposition (PLD) method, we incorporated nitrogen into the anatase TiO2 lattice to fabricate substitutional nitrogen doped TiO2 with different N content and film densities. All synthesized films were characterized in depth by X-ray diffraction (XRD), X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV–vis spectroscopy. In the next step, to fully leverage the band bending induced by nitrogen doping, we synthesized a six layer multiple-homojunction using gradient nitrogen doped TiO2 (g-N-TiO2) to extend the width of band bending over the bulk of the porous photocatalyst and induce an oriented electrical field perpendicular to the substrate. Following its higher photoelectrochemical (PEC) performance, the multiple-homojunction g-N-TiO2 prepared at 20 Pa with columnar-like nanostructure was used for the photocatalytic degradation of sulfamethoxazole (SMX) antibiotic in water under the simulated solar light irradiation. The results showed that compared to pristine TiO2 and non-gradient doped TiO2 (N-TiO2), the photocatalytic degradation performance of g-N-TiO2 dramatically improved in terms of SMX removal percentage, kinetics of degradation (10 times higher than TiO2) and detoxification of solution. We believe that the superior potential of the PLD technique in controlling the film density and gradient doping renders it a highly promising technique towards fabricating unique multiple-homojunctions based on gradient doped semiconductors. Besides water treatment, such formed, precisely controlled, multiple-homojunctions with low interfacial defects will provide novel insights into other applications such as solar fuels, sensors, water splitting, solar cells, etc.