Efficient removal of doxycycline by MnNb2O6/sulfite process: Response surface methodology optimization and mechanism analysis

Abstract

Sulfate radical-based advanced oxidation process could efficiently remove many emerging contaminants from wastewater. Considering the unique properties of MnNb2O6, an efficient MnNb2O6/sulfite system was developed to remove doxycycline residue from the aqueous environment. In this research, MnNb2O6 nanomaterial was successfully synthesized through a one-step hydrothermal route at 260 °C for 24 h. The paramagnetic behavior of MnNb2O6 was observed at 300 K. Scanning electron microscopy and transmission electron microscopy images showed that the size of petal-like MnNb2O6 crystals was 250–700 nm. The specific surface area of MnNb2O6 was 24.84 m2/g. Optimization of MnNb2O6/sulfite process was achieved by Box-Behnken Design based on response surface methodology. Under the predicted optimal conditions (pH of 8.7, MnNb2O6 dosage of 0.29 g/L, doxycycline concentration of 10.8 mg/L, and sodium sulfite concentration of 4.3 mM), the degradation efficiency of doxycycline could reach 85.1%. Mn species was found to be the dominant factor in MnNb2O6/sulfite system. Both SO4•− and •OH were identified as primary active radicals in MnNb2O6/sulfite system. Furthermore, six transformation products of doxycycline were elucidated. This work offers a simple water treatment process for efficiently removing doxycycline residue in the environment.