Synthesis of birnessite with adjustable electron spin magnetic moments for the degradation of tetracycline under microwave induction

•Birnessite, a manganese dioxide with varying Mn(II)/Mn(III)/Mn(IV) ratios were synthesized.•The birnessite was used for tetracycline (TC) degradation under microwave induction.•Higher Mn(II) and Mn(III) resulted in faster TC degradation due to better microwave response of Mn.•LC-MS analyses revealed progressive removal of N, C, and H for the reaction intermediates.•The catalyst could be regenerated under microwave induction.

Manganese dioxides (MOs) are excellent microwave absorbing materials and have been used as substrates or catalysts for enhanced degradation of organic compounds. In this study, we extended our research on using birnessite (Birn), a type of MOs, for the degradation of tetracycline (TC) in aqueous solution under microwave induction (MI). The Birns were fabricated to achieve different ratios of Mn(II)/Mn(III)/Mn(IV) in the crystal structure. Their physical and chemical characteristics were determined by X-ray diffraction, field-emission environmental scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption fine structure spectra, and a microwave network analyzer. Their removal of TC under MI was evaluated under different physicochemical conditions. Lower solution pH, higher MI power, and higher Mn(II) and Mn(III) in the structure resulted in more TC removal. And the Birns are regenerable. LC-MS analyses confirmed the presence of degradation intermediates. The better performances of TC removal by Birns under MI was attributed to the high magnetic spin moment of Mn(II) and Mn(III) in the structure that has higher MI response.

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