Cr(VI) sequestration by activated carbon: experimental and theoretical study

Heavy metal ions in aqueous media are highly toxic even in minor quantity, and their removal from solution is considered as one of the serious issues in wastewater treatment. Cr(VI) in aquatic environment is a persistent challenge due to its mobility and severe toxicity. A coal-derived activated carbon (AC) with high surface area (3452.8 m2g-1) is prepared and explored for Cr(VI) ion elimination from water. The used and unused AC is characterized through FT-IR, SEM, XRD, TGA, TEM, zeta potential and BET. Maximum uptake (194 mgg-1) of Cr(VI) ions was attained from acidic medium. Values of the thermodynamics models such as increment G, increment H, Delta S were - 15.54 kJ mol-1, 32.74 kJ mol-1, and 161.95 J mol-1 K-1, respectively, show its spontaneous and endothermic nature. The obtained data show well applicability to D-R, Langmuir, and Freundlich models. The mass transfer of Cr(IV) is regulated by the pseudo-second-order kinetic model. The DFT analyses show that the activated carbon immensely senses and adsorbs the Cr(VI) from the prepared synthetic solutions. Larger negative adsorption energy values depicted the energetically favorable chemisorption nature of the process. The atom in molecule theory provides evidence of hydrogen bonding/weak van der Waals forces during adsorption. Total density of states analysis reveals that AC can be used efficiently for Cr(VI) removal from synthetic and real contaminated solutions.