Wavelength-dependent activity screening of reduced titania for photocatalytic degradation of imidacloprid in batch and flow-mode

Abstract

Water reuse is an emerging solution to decrease pressure on freshwater supplies and meet the increasing demand. This study explores the use of semiconductor photocatalysis for pesticide removal, focusing on extending TiO2 absorption to visible light and accelerating the screening of its wavelength-dependent photocatalytic activity. Grey to black TiO2 photocatalysts with lower direct and indirect band gap energies, up to 1.56 eV and 2.16 eV, respectively, were prepared by the chemical reduction of titania P25. The XPS analysis showed considerable oxygen vacancies, especially at the highest reduction temperature of 400 °C. The fraction of oxygen in the TiO2 lattice decreased from 90 % in the case of P25 to 53% for the photocatalyst obtained at 400 °C. The wavelength-dependent photocatalytic activity for the degradation of imidacloprid was screened in a batch photoreactor. TiO2 P25 presented higher photocatalytic activity than the reduced materials at 400 and 413 nm. At 443 nm, the material reduced at 400 °C exhibited the highest degradation efficiency of 16.8 % compared to 4.2 % as found for P25. Selected photocatalysts were then immobilized as thin films and tested in a 3D-printed flow photoreactor. Wavelength and photocatalyst’s impact on imidacloprid degradation in flow mode aligned with batch mode observations. The film activity remained stable after multiple reaction conditions and at least 150 min of operation. The proposed in-flow screening strategy is a promising approach to rapidly identify visible-light active catalysts, while minimizing the consumption of photocatalytic material and water contaminated with model pollutants.