Construction of bionic sea urchin-like ZnFe2O4/Bi2S3 heterojunction for microwave-induced catalytic reduction of Cr(VI): Performance and mechanism insights

The construction of microwave-responsive catalysts with high reactivity for detoxifying heavy metal ions, specifically Cr(VI) in wastewater, poses a significant challenge. In this study, a novel microwave-responsive sea urchin-like ZnFe2O4/Bi2S3 heterojunction catalyst was designed for the rapid reduction of Cr(VI) from wastewater. Benefiting from the unique "tip" structure of the catalyst surface, coupled with its exceptional microwave absorption capabilities, the as-prepared sea urchin-like ZnFe2O4/Bi2S3 heterojunction removed 98 % pollutant from a 50 mg/L Cr(VI) solution under microwave irradiation for 40 min, even in a near-neutral aqueous environment. Importantly, this sea urchin-like ZnFe2O4/Bi2S3 heterojunction maintains an efficient microwave-induced catalytic removal performance of Cr(VI) in a complex water environment containing coexisting pollutants such as Methylene Blue (MB), Methyl Orange (MO), Crystal Violet (CV), Rhodamine B (RhB), Tetracycline (TC), Reactive Red X (RBR-X-3B), Congo Red (CR), Ketoprofen (KTP) drug, Norfloxacin (NOF) and Uranium(VI) (U(VI)). Furthermore, density functional theory (DFT) calculations revealed that the formation of the inhibited interface between ZnFe2O4 and Bi2S3 accelerates the transfer of electrons from ZnFe2O4 to Cr(VI) adsorbed on the surface of Bi2S3. Additionally, the synergistic interaction of ZnFe2O4 with Bi2S3 promotes the conversion of *Cr2O72- ions to *CrO3H3 ions and reduced the energy barrier of the rate determining hydrogenation step from −0.60 eV to −1.70 eV. This work not only provides a reference for designing highly active microwave-responsive heterojunction catalysts, but also offers theoretical guidance for a deeper understanding of the mechanism of microwave-induced catalytic reduction of heavy metal ions.