Enhancement of Cr(VI) removal by modifying activated carbon developed from Zizania caduciflora with tartaric acid during phosphoric acid activation

Tartaric acid (TA) was employed to modify Zizania caduciflora (ZC)-based activated carbon during phosphoric acid activation for improving its Cr(VI) removal from aqueous solutions. The original activated carbon (AC) and TA-modified activated carbon (AC-TA) were characterized by N-2 adsorption/desorption, Boehm's titration and X-ray photoelectron spectroscopy (XPS) analysis. The Cr(VI) removal abilities of AC and AC-TA were evaluated by batch sorption experiments. The residual Cr(VI) and total Cr concentration were determined to investigated the "Sorption-coupled reduction" mechanism. Equilibrium data for the Cr(VI) removal on AC and AC-TA were well described by the Freundlich model. The AC-TA exhibited much higher Cr(VI) and total Cr sorption capacities than AC. After blocking of carboxyl and hydroxyl functional groups, the carbons showed obviously higher Cr(VI) and total Cr removal than the original AC and AC-TA, indicating that electrostatic attraction played an important role on Cr(VI) removal. The higher Cr(VI) removal on AC-TA was attributed to its higher amount of oxygen-containing functional groups, which provided more electrons for Cr(VI) reduction and more positive sites for the produced Cr(III) sorption. (c) 2014 Elsevier B.V. All rights reserved.