Catalytic Ozonation of Ciprofloxacin with Cu–Al Layered Double Hydroxides Based on Response Surface Analysis

Abstract

Cu–Al layered double hydroxides (Cu–Al LDHs) were prepared by coprecipitation and used as a catalyst in heterogeneous a catalytic ozonation of ciprofloxacin. The structure of the synthesized Cu–Al LDHs was investigated by X-ray diffraction (XRD) patterns and Fourier-transform infrared spectra. Experimental results showed that the Cu3–Al LDHs had the best crystallization structure and the highest catalytic efficiency for ozonation. Response surface methodology (RSM) was used to optimize the operation conditions of ozone dose, ozone dosage, and initial pH. Under the optimal conditions (pH=9, LDH dosage 0.79 g/L, ozone dosage 61.2 mg/min), the total organic carbon (TOC) removal of ciprofloxacin by catalytic ozonation method can be as high as 72%. In addition, the TOC removal of ozone alone was about 30%, and the adsorption process contributed about 10%. Hydroxyl radicals, superoxide radicals, and singlet oxygen were proved to be involved in this process through electron paramagnetic resonance tests. Several degradation products were determined with LC-MS, suggesting that the pathway for ciprofloxacin degradation might include a substitution reaction, decarboxylation reaction, ring-opening reaction, and oxidation reaction.