Removal of azo dye from aqueous solution by a low-cost activated carbon prepared from coal: adsorption kinetics, isotherms study, and DFT simulation.

Abstract

The high-risk organic pollutants produced by industries are of growing concern. The highly porous coal-based activated carbon (AC) having a specific surface area of 3452.8m2/g is used for the adsorption of azo dye from synthetic solution. The sorbent is characterized through BET, SEM, TEM, XRD, FT-IR, TGA, and zeta potential. The sorbent exhibits -18.7mV surface charge, which is high enough for making suspension. The maximum dye uptake of 333mg/g is observed in sorbent under acidic medium. The thermodynamics parameters like ∆G, ∆H, and ΔS were found to be -12.40kJmol-1, 39.66kJmol-1, and 174.55Jmol-1K-1 at 293K, respectively, revealing that the adsorption mechanism is spontaneous, endothermic, and feasible. The experimental data follows the Langmuir and D-R models. The adsorption follows pseudo 2nd-order kinetics. DFT investigation shows that the dye sorption onto AC in configuration No. 4 (CFG-4) is more effective, as this configuration has high ∆H (enthalpy change) and adsorption energy (Eads). This is confirmed by Mullikan atomic charge transfer phenomenon.