Construction of hollow porous lychee-structured Ni/C/ZnFe2O4 microwave-responsive catalysts with rapid efficiently reduction of Cr(VI) ions

Designing catalysts with high reaction efficiency is essential for reducing heavy metal Cr(VI) ions in wastewater via microwave induction. In this paper, a unique microwave-responsive lychee-like Ni/C/ZnFe 2 O 4 composite catalyst with a 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/ZnFe 2 O 4 , coupled with excellent electromagnetic wave absorption ability, the prepared lychee-like Ni/C/ZnFe 2 O 4 composite catalyst could remove up to 98% of Cr(VI) (50 mg L −1 , 50 mL) after 40 min of microwave irradiation, even in nearly neutral water conditions. Additionally, density functional theory calculations indicated that the heterojunction interface between Ni/C and ZnFe 2 O 4 enhances electron transfer from ZnFe 2 O 4 to Ni/C, ultimately facilitating the removal of Cr(VI). Furthermore, the incorporation of Ni/C facilitated the acceleration of H ion transfer to ∗Cr 2 O 7 2− , thereby expediting the conversion kinetics of the latter. 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. A lychee-like Ni/C/ZnFe 2 O 4 catalyst with a double-shell hollow porous heterojunction structure achieves 98 % Cr(VI) removal under microwave irradiation, leveraging enhanced electron transfer and accelerated H + ion dynamics for efficient heavy metal reduction. • A novel MW-responsive lychee-like Ni/C/ZnFe 2 O 4 heterojunction catalyst was designed. • The Ni/C/ZnFe 2 O 4 catalysts have ultrafast MW catalytic performance for Cr(VI) reduction in pH∼7 environment. • Ni/C/ZnFe 2 O 4 composite exhibits excellent electromagnetic wave absorption capabilities. • The formation of an inhibited interface between Ni/C and ZnFe 2 O 4 accelerates the transfer of electrons. • The MW catalytic reduction mechanism of Cr(VI) was revealed by DFT calculations.