Remediation of Cd (II) Ion from an Aqueous Solution by a Starch-Based Activated Carbon: Experimental and Density Functional Theory (DFT) Approach

Abstract

Heavy metal ion pollution is a serious threat for aquatic and terrestrial living beings. Adsorption is a facile process to encounter heavy metal pollution. Various types of adsorbents have been developed and used for environmental remediation. Activated carbon is one of the cheapest adsorbents derived from various biomass. In this work, the adsorption of cadmium ions (Cd (II)) with starch-based activated carbon (AC) having a specific surface area of 1600 m2 g−1 was investigated in a series of batch laboratory studies. The effective operating parameters, such as initial pH (pH0), initial concentration of metal ions, contact time, and temperature on the adsorption, were investigated. Validation of the kinetic study shows that the adsorption process is better predicted by the pseudo-second-order model. The extended Freundlich and Langmuir isotherms were applied to the study. The results show that the metal ion adsorption capacities of activated carbon increased with increasing pH, and it was found that maximum adsorption (284 mg g−1) of Cd (II) was achieved at pH solution of 5.5–6. The thermodynamic parameters, such as ∆G, ∆H, and ∆S, were found to be −17.42 kJ mol−1, 8.49 kJ mol−1, and 58.66 J mol−1 K−1, respectively, revealing that the adsorption mechanism is endothermic, spontaneous, and feasible. Furthermore, the density functional theory simulations demonstrated that the activated carbon strongly interacted with toxicity and mobility, so it is very urgent to remove this species from industrial wastewater before it is discharged into the environment. The adsorption energy calculated for all interactive sites was negative (−43.41 kJ mol−1 to −967.74 kJ mol−1), showing effective interaction between the adsorbate and adsorbent. The PDOS clearly shows that there is a stronger overlapping at the Femi level between the d orbital of the Cd ion and the p orbital of the O atom, showing a strong interaction and confirming the chemical bond formation between the Cd (II) ion and O atom.