Construction of Hollow Porous Lychee-structured Ni/C/ZnFe₂O₄ MicrowaveResponsive Catalysts with Rapid Efficiently Reduction of Cr(VI) ions

Designing catalyst with high reactive efficiency is essential for the reduction of heavy metal Cr(VI) ions in wastewater via microwave induction. In this paper, a unique microwave-responsive lychee-like Ni/C/ZnFe₂O₄ composite catalyst with double-shell hollow porous heterojunction structure was constructed for the efficient reduction of Cr(VI). Benefiting from the novel hollow porous structure and "carbon nanocage" structure of the Ni/C/ZnFe₂O₄, coupled with excellent electromagnetic wave absorption ability, the prepared lychee-like Ni/C/ZnFe₂O₄ composite catalyst could remove up to 98% of Cr(VI) (50 mg/L, 50 mL) after 40 mins of microwave irradiation, even in nearly neutral water conditions. Additionally, density functional theory calculations indicated that the heterojunction interface between Ni/C and ZnFe₂O₄ enhances electron transfer from ZnFe₂O₄ to Ni/C, ultimately facilitating the removal of Cr(VI). Furthermore, the incorporation of Ni/C facilitated the acceleration of H ion transfer to *Cr₂O₇^2-, thereby expediting the conversion kinetics of the atter. This research aims to establish a theoretical and experimental foundation for the effective and stable microwave-assisted catalytic reduction of heavy metal Cr(VI) ions, presenting new insights and methods to combat heavy metal contamination.