TiO2-carbon microspheres as photocatalysts for effective remediation of pharmaceuticals under simulated solar light

Abstract

• Carbon microspheres were prepared by hydrothermal carbonization-pyrolysis of lignin. • Carbon microspheres were decorated by TiO 2 by solvothermal treatment. • Photocatalytic removal of pharmaceuticals under simulated solar light was tested. • High conversion and mineralization of diclofenac was achieved. • Diclofenac degradation routes involved C-N cleavage, hydroxylation and cyclization. In this work, novel carbon microspheres supported TiO 2 nanoparticles were prepared for the degradation of pharmaceuticals in water, selecting diclofenac, acetaminophen, and ibuprofen as target pollutants. Lignin, an important biomass byproduct from the paper industry and biorefineries, was transformed in carbon microspheres by a novel approach based on a Fe-activated hydrothermal carbonization followed by pyrolysis at 900 °C. These carbon microspheres were further covered with TiO 2 by a solvothermal treatment. The effects of several parameters including hydrothermal carbonization time and mass ratio (TiO 2 :carbon) on the catalytic activity of TiO 2 -carbon microspheres were investigated. The results revealed that the combination of long carbonization time and high TiO 2 :carbon ratio achieved superior TiO 2 -carbon microspheres (Ti2-C20) catalytic performance. Ti2-C20 achieved complete degradation of ibuprofen (5 mg·L −1 ) and diclofenac (5 mg·L −1 ) within 3 h under solar light and mineralization percentages close to 50%. Moreover, the photocatalytic performance remained high after five reuse cycles and was barely affected by the presence of common inorganic ions in treated wastewater (such as Cl – , NO 3 – and HCO 3 – ). The degradation pathway of diclofenac was proposed, involving C-N bond cleavage, and subsequent hydroxylation and cyclization reactions leading to the formation of aliphatic carboxylic acids. Overall, promising photocatalysts were obtained from a biomass byproduct for effective degradation of pharmaceuticals with the assistance of solar light.