Oxidative degradation of sulfamethoxazole by different MnO2 nanocrystals in aqueous solution

•The crystal structure of MnO2 influenced its activity in SMX oxidative degradation.•The single-crystal α-MnO2 nanorods showed the highest SMX degradation efficiency.•The highest degradation efficiency of α-MnO2 nanorods resulted from its rich Osur.•A rapid degradation of SMX by α-MnO2 was achieved under lower pH conditions.

Several MnO2 nanomaterials synthesized at autoclave temperatures ranging from 130 to 210 °C were characterized and investigated for sulfamethoxazole (SMX) oxidative degradation in aqueous solution. The pure single-crystal α-MnO2 nanorods prepared at 150 °C showed the highest SMX degradation efficiency. We concluded that the crystallographic structure and the surface species of MnO2 were more important than BET surface area and crystallinity in influencing the activity in SMX oxidative degradation. The high degradation efficiency of α-MnO2 nanorods resulted from a (2 × 2) tunnel structure, rich surface adsorbed oxygen and high oxygen mobility. The degradation efficiency of α-MnO2 nanorods was also greatly influenced by the initial SMX concentration, MnO2 dosage and pH value. The particular reaction orders with respect to these three factors were 0.70, 0.54 and −0.15, respectively. Under lower pH conditions (e.g., pH < 2.4), a rapid oxidative degradation of SMX by α-MnO2 was achieved as well as generation of intermediate products and Mn2+. Moreover, α-MnO2 exhibited high stability in recycling tests, which demonstrated itself to be a good oxidant for oxidative degradation of SMX. These results may be useful in understanding the interaction of SMX and MnO2 in soil and water environments.

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