Green construction of MBI corrosion-resistant interfaces modified NZVI@MOFs-regulated 3D PAN cryogel film to enhance Cr(VI) removal

Nano zero-valent iron (NZVI) is an ideal material for treating chromium (VI). However, the NZVI's low loading and corrosion susceptibility in acidic Cr-containing industrial wastewater is the most pressing issue. Therefore, it is necessary to explore a method to construct novel NZVI composites with high loading, corrosion resistance, and outstanding activity. In this study, green 2-mercaptobenzimidazole (MBI) was employed for the first time as a corrosion inhibitor for NZVI to form a protective coating through chemisorption, thus blocking the corrosion of NZVI by reaction medium. Meanwhile, a novel multiphase green crystallization-assisted pore formation freeze-drying method was constructed to synthesize UiO-66-NH₂ regulated 3D network porous polyacrylonitrile (PAN) cryogel film for stabilizing NZVI, which is intended to remove Cr(VI) effectively and without secondary contamination. The synthesized MBI-Fe⁰@MOF/PAN possessed prominent activity, corrosion resistance, and considerable NZVI loading (45.9 mg/g). The Cr(VI) removal could still reach 82.7 % after 6 cycles, and the level of total dissolved iron ions was lowered to 0.255 mg/L. MBI-Fe⁰@MOF/PAN for rapid removal of Cr(VI) may be ascribed to the synergistic reaction of rapid protonation of MBI and strong reduction of NZVI. This study constructed the MBI corrosion-resistant interface and 3D PAN cryogel film concepts not only to broaden the horizons of designing efficient NZVI catalytic materials but also to promote the development of treatment technologies for acidic Cr-containing industrial wastewater.