Adsorptive removal of carbonyl sulfide by Fe-modified activated carbon: experiments and DFT calculations

摘要

Adsorptive removal of carbonyl sulfide (COS) by Fe-modified activated carbon was investigated in this study. A combination of experimental and theoretical method was used to elucidate the adsorption behavior and mechanism of COS. The sorbents were prepared by sol-gel method and the adsorptive performance for COS at 313, 323, 333 and 343 K was studied. Adsorption isotherms revealed that adsorption capacities increased with the increasing of temperature. Langmuir and Freundlich isotherm models were employed to analyze the equilibrium data. The Freundlich adsorption isotherm gave good fittings to the adsorption data. Also, free energy of adsorption, enthalpy, and entropy changes were determined to predict the nature of adsorption. The positive value (+ 68.394 kJ/mol) of the enthalpy change indicated that the adsorption is endothermic process and the adsorption process is a chemisorption. The mechanism of the chemisorption has been studied by using the density functional theory. The results showed that the adsorption of COS is dissociative adsorption. The cleavage of C-S bonds took place, and C-O bonds are adsorbed on the Fe top sites. Density of states analysis revealed that Fe-C-O interaction can be attributed to the bonding among Fe d orbitals, carbon s orbitals, and oxygen p orbitals.