Characterization and mechanism analysis of activated carbon fiber felt-stabilized nanoscale zero-valent iron for the removal of Cr(VI) from aqueous solution

Abstract

Nanoscale zero-valent iron (NZVI) loaded onto activated carbon fiber felt (ACFF) as a composite material (ACFF–NZVI) was developed to remove hexavalent chromium (Cr(VI)). The ACFF and ACFF–NZVI was characterized by X-ray diffraction, scanning electron microscopy and BET analysis. It is observed that synthetized NZVI had a majority of nanoscale with average particle size of 64.0nm.Batch experiments with variable pH values and initial concentration of Cr(VI) were conducted to evaluate the removal performance of ACFF, NZVI and ACFF–NZVI. The results showed that the removal rate of Cr(VI) was 67.0% for ACFF–NZVI, which was higher than that for ACFF (52.6%) and NZVI (59.4%). The concentration of total Cr was also recorded to study the reduction of Cr(VI). The difference of the residual concentration of total Cr and Cr(VI) indicated that part of Cr(VI) (56.6% for ACFF–NZVI, 18.9% for ACFF) was reduced to Cr(III). The removal was strongly pH dependent and showed an increase of removal efficiencies with the decrease of initial pH from 9.0 to 3.0. Ultrasonic (US) was used to enhance the removal of Cr(VI), higher removal efficiency (80.2%) would be obtained in the presence of US. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) were used to analyze the mechanisms of Cr(VI) removal. The results indicated that NZVI loaded on the surface was partial oxidized, and the removal of Cr(VI) was attributed to the adsorption of ACFF–NZVI and its reducibility.