Efficient batch and column removal of Cr(VI) by carbon beads with developed nano-network

Chromium removal is of significance to our daily life; however, the fabrication of high-performance sorbents with practicality remains a challenge. Herein, alginate-derived carbon beads (Alg-CB-X) with a developed nano-network were successfully prepared through a simple carbothermal reduction at different carbonization temperatures and acid treatment. The aim of this material was for easy separation and removal of Cr(VI) from water. The materials were characterized by FESEM, TEM, XRD, FTIR, XPS, EDS, Raman spectrometry and N2 sorption measurements. Parameters affecting the uptake of Cr(VI) ions by Alg-CB-X such as solution pH, initial concentration, contact time and coexisting anions were investigated systematically in batch experiments. The mechanism investigation showed that the removal of Cr(VI) involved electrostatic attraction and slightly involved redox reactions. However, it is emphasized that the reduction of Cr(VI) to Cr(III) was very slow and occurred only slightly because of the lack of oxygen-containing functional groups (caused by the pyrolysis process) and the short adsorption period. With increasing experiment time and initial concentration of Cr(VI), the amount of reduced Cr(III) increased gradually. Finally, Cr(VI) is deposited onto the carbon surface, and the formed Cr(III) is released into the aqueous phase due to electronic repulsion between the positively-charged groups and the Cr(III).