Effect of liquid-phase O3 oxidation of activated carbon on the adsorption of thiophene

• We report liquid-phase O3 oxidation of activated carbon for thiophene adsorption.
• We examine the effect of O3 oxidation in various types of aqueous media.
• Oxygen functionalities on activated carbon increase thiophene adsorption.
• The adsorption mechanisms are illustrated by density functional theory.

In this work, a combined experimental and computational study is carried out to investigate the effect of O3 oxidation of activated carbon (AC) in various types of aqueous media (alkaline, acidic and neutral aqueous solutions) on the adsorption of thiophene. A high surface area AC (BET surface area of 2880 m2/g) is modified by ozone-oxidation in different aqueous media under ambient conditions. Experimental results show liquid phase ozone oxidation of AC introduces oxygen functional groups to the AC surface, resulting in enhanced adsorption capacity of thiophene. The impact of oxidation media on the adsorption capacity follows the order of NaOH > H2SO4 > H2O, consistent with the order of the concentrations of oxygen functionalities introduced on the carbon surface. Computational results suggest that phenol and carboxyl groups on the surface lead to stronger thiophene adsorption than the bare (unfunctionalized) graphite surface, corroborating our experimental results. Additionally, the presence of bridging-oxygen functionalities on the carbon surface leads to extremely exothermic adsorption energies of thiophene, which can be attributed to sulfoxide formation and H-bonding interactions. DFT calculations suggest the adsorption strength of thiophene follows the order of bridging-O-functionalized (Ads E = −1.51 eV) ≫ OH-functionalized (Ads E = −0.36 eV) > COOH-functionalized (Ads E = −0.27 eV) > bare graphite (Ads E = −0.26 eV). The combined experimental and computational study provides direction for carbon surface functionalization for adsorptive desulfurization.

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