[Enhanced Chromate (VI) Removal Characteristics and Mechanism Using Graphene Oxide Immobilized Nanoscale Zero-Valent Iron Coupled with a Weak Magnetic Field (GO-nFe0/WMF)].

A green, high-efficiency mesoporous magnetic material with strong reusability and oxidation resistance, named graphene oxide immobilized nanoscale zero-valent iron (GO-nFe0), was prepared by a co-precipitation method. The structure, appearance, surface elements, and valence of GO-nFe0 were characterized via FESEM, TEM, FTIR, BET, XRD, and XPS. The characteristics and mechanism of Cr(Ⅵ) treatment in water using a weak magnetic field (WMF) coupled with GO-nFe0 (GO-nFe0/WMF) were studied. Batch experiments established that when the load mass ratio of GO to nFe0 was 1:10 under 20 mT weak magnetic field strength, the GO-nFe0/WMF system could completely remove the 10 mg·L-1 of Cr(Ⅵ) solution in 30 min, consistent with first-order dynamics. With a decrease in initial pH value and an increase in material dosage, the removal efficiency of Cr(Ⅵ) increased significantly by enhancing the release rate of Fe2+. ClO4- had no effect on the reaction, Cl- could encourage corrosion and promote the corrosion of nFe0 to release Fe2+, CO32- restrained the reaction through an increase in initial pH of the solution, and SO42- could promote the dissolution of the nFe0 surface passivation film to accelerate the reaction process. The GO-nFe0/WMF system can maintain high activity after five reuses and 30 days of exposure to air. XRD, XPS, and 1,10-phenanthroline shielding experiments proved that its great conductivity allowed GO to provide electron transfer sites to accelerate the transfer of electrons, and nFe0 could quickly release Fe2+. WMF generated a magnetic gradient force (FΔB) that pushed the paramagnetic Fe2+ ions in the diffusion boundary layer concentrated on the two poles of GO-nFe0, where the most magnetic intensity was present, to exposed active sites on both sides. The high removal rate ability of GO-nFe0 to release Fe2+ continuously was maintained.