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

A green, high-efficiency mesoporous magnetic material with strong reusability and oxidation resistance, named graphene oxide immobilized nanoscale zero-valent iron (GO-nFe), was prepared by a co-precipitation method. The structure, appearance, surface elements, and valence of GO-nFe 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-nFe (GO-nFe/WMF) were studied. Batch experiments established that when the load mass ratio of GO to nFe was 1:10 under 20 mT weak magnetic field strength, the GO-nFe/WMF system could completely remove the 10 mg·L 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 Fe. ClO had no effect on the reaction, Cl could encourage corrosion and promote the corrosion of nFe to release Fe, CO restrained the reaction through an increase in initial pH of the solution, and SO could promote the dissolution of the nFe surface passivation film to accelerate the reaction process. The GO-nFe/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 nFe could quickly release Fe. WMF generated a magnetic gradient force () that pushed the paramagnetic Fe ions in the diffusion boundary layer concentrated on the two poles of GO-nFe, where the most magnetic intensity was present, to exposed active sites on both sides. The high removal rate ability of GO-nFe to release Fe continuously was maintained.