Study on enhanced adsorption and reduction of hexavalent chromium in water by carbon-modified nano zero-valent iron
Nano zero-valent iron(nZVI)composites are widely used for the removal of hazardous hexavalent chromium[Cr(Ⅵ)]from water owing to their strong reducibility and high adsorption.To reduce the cost,the environmentally friendly carbon-modified nano-zero-valent iron(nZVI@GC)was successfully synthesized via facile carbonization and calculations of glucose and ferric chloride mixtures,which effectively solved the problem that nZVI was easy to agglomerate and easilyto oxidate in the preparation.Combined with the characterization results,XRD and TEM data showed that the zero-valent iron nanoparticles on the nZVI@GC were body-centered cubic α-Fe0 particles with an average particle size of 32 nm.The batch experiments were conducted to investigate the effects of nZVI@GC dosage,initial Cr(Ⅵ)concentration,and pH on the Cr(Ⅵ)adsorption and reduction.The results indicated that the maximum adsorption reduction capacity of Cr(Ⅵ)in water by nZVI@GC within 24 h was 178.6 mg/g,which was 5.7 times that of nZVI(31.5 mg/g).Kinetic studies indicated that the adsorption and reduction reaction of Cr(Ⅵ)by the nZVI@GC followed a pseudo-second-order rate equation(R2=0.9993).When the initial concentration of Cr(Ⅵ)was 50 mg/L and pH was 2-3,the Cr(Ⅵ)in the water were completely adsorbed and reduced after 0.5 g/L nZVI@GC were added for 30 min.After nZVI@GC was stored in dry air for a period of time,carbon on the composite material can effectively inhibit the erosion of zero-valent iron nanoparticles by oxygen.Compared with the newly synthesized material,the adsorption reduction rate of Cr(Ⅵ)in water by nZVI@GC stored for 30 days only decreased by 3.4％.The nZVI@GC exhibited a stronger adsorption reductionrate of Cr(Ⅵ)and was proved to be more stable in ambient conditions than nZVI.These results show that nZVI@GC has efficient and economical application potential in treating Cr(Ⅵ)-contaminated water.
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