Insights into adsorption and high photocatalytic oxidation of ciprofloxacin under visible light by intra-molecular Donor-Acceptor like p-n isotype heterojunction: Performance and mechanism

Antibiotics, e.g. ciprofloxacin (CIP) are frequently detected in natural waters and sewage, however, the con-ventional sewage treatment techniques presents a great challenge for efficient removal them due to the inhibition of bacterial proliferation. Herein, the intra-molecular Donor-Acceptor like p-n isotype heterojunction of phos-phorus and boron co-doped hollow tubular g-C3N4 (xB-PCN) was synthesized for high-efficiency visible light photocatalytic degradation of CIP. The Mott-Schottky curves showed that the xB-PCN exhibited both p and n -type conductivities, which probably because the doped boron has electron acceptor effect and the NH/NH2 groups could act as electron donors. This unique property enables xB-PCN to have excellent charge generation, separation and transfer ability for the highly efficient photodegradation of CIP, reaching 87.56% of decompo-sition efficiency within 1 h with the apparent rate constant (0.01151 min-1) of 6.85 times that of PCN. Furthermore, the 3B-PCN maintained high degradation percentage in tap water (84.63%) and aquaculture wastewater (78.41%). The results of LC-MS and TOC showed that CIP was gradually mineralized and the degradation pathways were proposed. Based on the radical trapping experiments and ESR characterization, the reactive oxygen species involved in the degradation of CIP were checked. This work offers a promising approach for treating antibiotics polluted water based on a metal-free conjugated polymeric g-C3N4.

Automated summary

In this study, a phosphorus-boron co-doped hollow tubular g-C3N4 (xB-PCN) with an intra-molecular Donor-Acceptor like p-n isotype heterojunction was synthesized for high-efficiency visible light photocatalytic degradation of ciprofloxacin (CIP) in water. The xB-PCN exhibited excellent charge generation, separation, and transfer ability, resulting in a decomposition efficiency of 87.56% within 1 hour, with an apparent rate constant 6.85 times higher than that of conventional g-C3N4 (PCN). Furthermore, xB-PCN maintained high degradation percentages in tap water (84.63%) and aquaculture wastewater (78.41%). The degradation pathways of CIP were proposed, and the reactive oxygen species involved in the degradation process were identified through radical trapping experiments and ESR characterization.