Facile synthesis of high iron content activated carbon-supported nanoscale zero-valent iron for enhanced Cr(VI)...

Nanoscale zero-valent iron (nZVI) based materials are considered as one of the most promising in situ remediation materials in the remediation of groundwater contaminated by a variety of pollutants. Supporting nZVI on activated carbon (AC) could reduce the aggregation of nZVI and lead to better utilization during application. The most used method for synthesizing nZVI/AC is liquid-phase reduction synthesis. However, the problem of nZVI shedding during the synthesis remains unsolved. In this study, an improved liquid-phase reduction synthesis method of nZVI/AC was developed. Compared to the conventional method, the improved method could significantly increase the Fe content of the obtain nZVI/AC (from 3.8% to 5.9%) and the utilization of reactant FeSO₄·7H₂O (from 49% to 77%) easily by changing the addition order and form of reactants, while using the same reaction precursors. The improved method reduced the shedding of nZVI from AC by taking advantage of the different solubility of FeSO₄ in ethanol and water, and the different reactivity of NaBH₄ in ethanol and water. The characterization results demonstrated that more nZVI was supported to the pores and outer surface of AC. The removal experiments of Cr(VI) (5.0 mg/L) from water showed that the nZVI/AC synthesized using the improved method exhibited better removal efficiency (85.6%) than that of the nZVI/AC synthesized using the conventional method (67.4%). These results suggested that selecting the appropriate solvent and optimizing the synthesis process may greatly improve the performance of nZVI-based materials.