Preparation and Characterization of Activated Carbons from Peanut Shell and Rice Bran and a Comparative Study for Cr(VI) Removal from Aqueous Solution

Low-cost activated carbons (AC) were prepared from peanut shell (PS) and rice bran (RB) by microwave heating with ZnCl2 as the activating agent and characterized by solid-state C-13-NMR, FT-IR, Boehm titration, and mass titration methods. The solid-state C-13-NMR spectra showed that aliphatic structures of the raw materials were almost completely transformed to condensed aromatic rings, a typical characteristic of AC. The potentials of ACs produced from peanut shell (PACs) and from rice bran (RACs) for Cr(VI) removal were examined by using iodine and methylene blue (MB) as adsorbates, respectively. The effects of solution pH, the dosage of AC, and the initial Cr(VI) concentration on Cr(VI) removal were investigated. The desorption experiments were also performed to examine the regeneration of AC. The results demonstrated that both PAC and RAC were excellent adsorbents for Cr(VI) removal. The maximum removal amounts of Cr(VI) by PAC and RAC reached to 96.27 and 76.04 mg/g, respectively. The adsorption capacity of PAC was higher than that of RAC because PAC held a larger surface area and a more microporous pore structure than RAC. The removal of Cr(VI) by PAC and RAC greatly depended on solution pH, with low pH (in a pH range of 2 to 6) being more conducive to the removal of Cr(VI). The adsorption-coupled reduction of Cr(VI) contributed to the removal of Cr(VI) by PAC and RAC.