Excellent adsorption performance of dibenzothiophene on functionalized low-cost activated carbons with different oxidation methods

Low-cost activated carbon (KAC) was functionalized by HNO₃, (NH₄)₂S₂O₈ and air oxidation, respectively, to remove dibenzothiophene (DBT) from model fuel. The changes in physical and chemical properties of these activated carbons were characterized by thermal analysis, elemental analysis, nitrogen adsorption apparatus, Raman spectra, scanning electron microscope and Boehm’s titration method. HNO₃ and (NH₄)₂S₂O₈ oxidation result in a significant decrease in pore structure, while air oxidation only causes slight pore reduction due to the re-activation by O₂. The oxygen-containing functional groups (OFGs) increase markedly after oxidative modification, in which (NH₄)₂S₂O₈ oxidation is considered as the most efficient method with respect to the introduction of OFGs. HNO₃ and (NH₄)₂S₂O₈ oxidation are more selective to generate carboxyls and lactones, whereas air oxidation creates more phenols, carbonyls and ethers. The DBT adsorption capacity follows the order: NAC (HNO₃-oxidized KAC) > OAC (air-oxidized KAC) > KAC > SAC ((NH₄)₂S₂O₈-oxidized KAC), implying the introduction of OFGs is beneficial for the DBT adsorption process, especially for selectivity, but excessive OFGs have a negative effect on the removal of DBT. Thus, to achieve high DBT adsorption performance, there should be a trade-off between the micropore volume and the OFGs amount.