Caffeine photocatalytic degradation using composites of NiO/TiO2-F and CuO/TiO2-F under UV irradiation

Abstract

The interest in the removal of emerging contaminants has increased in the last decade. Photocatalytic degradation using p-n heterojunctions could effectively provide the degradation of these type of substances that are persistent in the environment. In this work, the synthesis, characterization, and photocatalytic evaluation of TiO₂-F as well as CuO/TiO₂-F and NiO/TiO₂-F composite materials were studied in the photo-assisted degradation of caffeine using UV radiation. The fluorination of titanium dioxide induced changes in some physicochemical properties of the materials, which contributed to a decrease in surface area and bandgap energy as well as an increase in crystallite size as compared to pristine TiO₂. ≡Ti-F species were evidenced to be formed, which could favor charge separation processes. A highest segregation of CuO species in comparison with NiO on the surface of TiO₂-F could be formed, which could increase defect sites and decrease the band gap. The formation of a heterojunction between the semiconductors was evidenced, responsible for the observed improvements in photocatalytic properties of the composite materials. The photocatalytic tests evidenced an important degradation of caffeine; however, mineralization was incomplete. The stability of the composite materials and their potential use in the photocatalytic treatment of caffeine was evaluated by reuse tests.

Keywords: Caffeine; CuO/TiO(2)–F; Degradation; Emerging contaminants; NiO/TiO(2)–F; Photocatalysis.