Enhance Cr(VI) removal by quaternary amine-anchoring activated carbons

• Quaternary amine-anchoring activated carbons (ACs) were prepared by epoxide-induced reactions.
• Cr(VI) and total Cr removal on AC-E was higher than that on AC-T and AC.
• Characterization experiments were used to investigate the Cr(VI) removal mechanisms.
• The stability and regeneration potential of AC-E was also examined.

Adsorbents quaternary amine-anchored were prepared from commercial activated carbon (AC) by epoxide-induced methods: AC-T and AC-E. The effect of pH, contact time, temperature and initial Cr(VI) concentration on adsorption was investigated to compare Cr(VI) removal capacity of those two modified ACs. The adsorption capacity for Cr(VI) of AC, AC-T and AC-E was 10.570, 26.247 and 112.360 mg/g, respectively. The rate of Cr(VI) adsorption onto AC-E was more rapid than that of AC and AC-T. In addition, AC-E performed a higher adsorption capacity during a wider range of pH (2.0–10.0). The physico-chemical properties of ACs were investigated by Zeta potential, elemental analysis, N2 adsorption/desorption, scanning electron microscope and Fourier transformed infrared. By means of multiple analyses, the authors surmised that (1) AC-T showed both pore-filling and electrostatic adsorption processes, while AC-E almost depended on the electrostatic attraction to remove Cr(VI); (2) the active quaternary ammonium sites within AC-E were more exposed and accessible for Cr(VI) removal than those within AC-T; (3) the desorption efficiencies of AC-E were 72.8–68.8% after five sorption–desorption cycles, 0.1 M HCl solution showed the best desorption capacity.

AC-T (Fig. a) had both intraparticle and boundary layer diffusion adsorption mechanisms, while the quaternary ammonium functionality (QAF) was hidden behind graphite layer, and that signified lesser availability and exposure of the amine sites; the adsorption of Cr(VI) by AC-E (Fig. b) almost depended on the electrostatic attraction between positively charged groups and negatively charged chromium ions, the amine groups could be sufficiently exposed to AC surface due to the anchoring carbon chain structure.Figure optionsDownload as PowerPoint slide