Bio-based Au Doping with Dominant Oxygen Vacancies and Ti3+ Defects on Photocatalytic Functionalities of TiO2

The presence of pharmaceutically active compounds (PhACs) in waterways is a growing environmental concern. In fact, this is an open challenge for environmental scientists to develop an effective treatment technology for the abatement of pollution caused by PhACs. Herein, we have developed a novel bio-based and pH-independent steamed autoclaving method for synthesizing Au-doped TiO2 using vegetal analytes present inSechium edule. Au doping introduced new free excitons and shallow traps of AuNPs, and Ti3+ and oxygen vacancies in TiO2 facilitated an extended absorption range, better change transfer (charge transfer resistance, 15.60 → 5.77 kΩ), and surface hydrophilicity (water contact angle 16.8°) for enhanced visible-light-driven photocatalytic functionalities. Au doping took place in two steps as Au(III) → Au(I) → Au(0). Both the conduction and valence bands were shifted with a reduced band gap of 2.45 eV (from 3.29 eV) for Au1.00/TiO2(bio) (Au 1.00% w/w). With Au doping, the crystal size was increased, and a decrease in lattice strain and dislocation density was noted. Au1.00/TiO2(bio) exhibits increased electron density, facilitating charge transfer as evidenced from X-ray photoelectron spectroscopy analysis. Au1.00/TiO2(bio) exhibited four-fold higher photocurrent density (64.70 nA/cm2) than that of Au0.00/TiO2(bare). The optimally doped Au1.00/TiO2(bio) achieved 1.2–1.5-fold higher chloroquine (CLQ) degradation (94.59 ± 1.23%) and 1.5–1.9-fold higher TOC removal (69.57%) than Au0.00/TiO2(bare) and Au1.00/TiO2(chemically doped). The reused Au1.00/TiO2(bio) showed more than 90% degradation in three successive cycles, which decreased to 78.18% during the fifth cycle. CLQ was photodegraded in two different pathways by forming 16 intermediates as supported by a mass spectroscopic assay.