Adsorption and photocatalytic synergistic removal of ciprofloxacin on mesoporous ErFeO3/g-C3N4 heterojunction

The technology integrating adsorption and photocatalysis is regarded as the most promising strategy for the elimination of low concentration antibiotic contaminant. In this study, we firstly prepared the mesoporous g-C3N4 nanosheets (CN) with the thickness of 4–5 nm by the thermal etching and ultrasonic techniques. Then perovskite ErFeO3 nanoparticles (EF) were incorporated into CN to construct the 3/g-C3N4 (EFC) heterojunction. The heterojunction with EF content of 2 wt% (2-EFC) had the optimal adsorption and photocatalytic performance. 87.8% of ciprofloxacin (CIP) was eliminated via the adsorption–photocatalysis synergistic process over 2-EFC. The CIP adsorption capability of 2-EFC was 11.7 times that of CN, and the zero-order degradation reaction rate constant (k0) was 25.2 times of CN. The ultrathin and porous structure of CN increased the specific surface area and reaction active sites, shorten the diffusion distance of photoinduced charge carriers. And the construction of EFC heterojunction further accelerated the separation of charge carriers and inhibited its recombination. These two strategies ameliorated the adsorption and photocatalytic activity of EFC in removal of CIP. The CIP adsorption on the samples followed pseudo second order kinetics model, and the adsorption isotherm data complied with Langmuir isotherm model. The photocatalytic degradation process of CIP on 2-EFC could be divided into two phases. Due to the CIP concentration change in the degradation solution, the kinetics curve followed the zero order rate equation at 0 to 40 min. After that, it deferred to the first order rate equation. The h+, ⋅ OH and ⋅ O2– were involved in the photocatalytic degradation process. The structures of degradation intermediates and possible degradation pathways of CIP were proposed according to the HPLC-MS results. This research provided an alternative with high efficient synergetic effect of adsorption and photocatalytic degradation for the treatment of antibiotic wastewater.