MOF-derived core/shell C-TiO2/CoTiO3 type II heterojunction for efficient photocatalytic removal of antibiotics.

A novel core/shell C-TiO2/CoTiO3 type II heterojunction was successfully synthesized via a direct calcination method by using MIL-125/Co core-shell nanocakes as a sacrificial template and precursor. In the calcination process, the organic ligand in MIL-125 acts as an in-situ carbon doping source to form a carbon-doped TiO2 core (C-TiO2). At the same time, CoTiO3 nanoparticles are formed on the surface of C-TiO2 by an in-situ solid-state reaction between the C-TiO2 and Co2+ shell of MIL-125/Co. Due to such delicate core/shell structural features, carbon doping and type II heterojunctions, C-TiO2/CoTiO3 core/shell composites can effectively harvest visible light, facilitate the interfacial separation and suppress the recombination of photogenerated electron-hole pairs, leading to the remarkable photocatalytic activity for removal of ciprofloxacin (CIP). In particular, C-TiO2/CoTiO3-3 exhibits the best photocatalytic degradation activity of CIP with a degradation efficiency of 99.6% and a total carbon content removal percentage of 76% under visible-light illumination for 120 min. In addition, the proposed photocatalytic mechanism study illustrated that the main radical species in the photocatalytic degradation of CIP using C-TiO2/CoTiO3 as the photocatalyst is •OH. This work provides a new approach and insight for synthesizing core/shell heterojunction-based photocatalysts for various applications.