TiO2 supported on rice straw biochar as an adsorptive and photocatalytic composite for the efficient removal of ciprofloxacin in aqueous matrices

Ciprofloxacin (CIP) is a broad-spectrum antibiotic, but it is widely found in pharmaceutical wastewater, livestock wastewater, domestic sewage, and river sediments. CIP is not easy to be decomposed naturally and has high harm to human body. The development of cheap, environmental-friendly, and efficient biochar materials for antibiotic removal has certain practicability and applicability. The characteristics of rice straw biochar (RSB) and TiO2 modified rice straw biochar (Ti-RSB) were examined by BET, FTIR, UV-vis DRS, LRS, XPS, Zeta potential, SEM, EDS and XRD. Then the ability and mechanism of RSB and Ti-RSB to remove CIP were evaluated through kinetic and isotherm adsorption experiments. The results showed that the adsorption of CIP by RSB is more consistent with BET model. When pH= 5, the maximum adsorption capacity for CIP based on Langmuir model was 747.64 mg/g. The adsorption mechanism includes electrostatic interaction, 7C-7C interaction, and H bond interaction, in which C--O is the functional group that plays the main adsorption role. While using TiO2 to functionalize the surface of RSB, increasing the photocatalytic performance of the material, the composite Ti-RSB has a superior removal effect on CIP degradation at a wide pH from 5 to 9. The degradation mechanism belongs to the first defluorination reaction, and then the degradation of the piperazine ring. The recycling of rice straw into biochar and its functional modification into composite materials have application values in the removal of CIP.