Bio-based Au Doping with Dominant Oxygen Vacancies and Ti<sup>3+</sup> Defects on Photocatalytic Functionalities of TiO<sub>2</sub>
Ravi Ravi, Animes Kumar Golder
Abstract
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 TiO 2 using vegetal analytes present in Sechium edule . Au doping introduced new free excitons and shallow traps of AuNPs, and Ti 3+ and oxygen vacancies in TiO 2 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 Au 1.00 /TiO 2 (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. Au 1.00 /TiO 2 (bio) exhibits increased electron density, facilitating charge transfer as evidenced from X-ray photoelectron spectroscopy analysis. Au 1.00 /TiO 2 (bio) exhibited four-fold higher photocurrent density (64.70 nA/cm 2 ) than that of Au 0.00 /TiO 2 (bare). The optimally doped Au 1.00 /TiO 2 (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 Au 0.00 /TiO 2 (bare) and Au 1.00 /TiO 2 (chemically doped). The reused Au 1.00 /TiO 2 (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.