The role of oxygen functional groups in the adsorption of heteroaromatic nitrogen compounds.

A wood-based activated carbon (AC) was oxidized using different oxidants. The resultant adsorbents were applied to adsorb nitrogen (N) containing compounds that appeared in light cycled oil. Appropriate oxidation treatment can increase oxygen functional groups on the surface of AC without much damage to its pore structure. Oxygen functional groups play a key role in enhancing adsorptive selectivity of carbons. Lactone groups can facilitate the selective removal of 1-ring N compounds. Phenolic groups, total CO2-releasing groups and total O groups show an improvement in the adsorption of 2-ring N compounds. Aldehyde groups favor the adsorption of 3-ring and 4-ring N compounds. However, excessive oxidation can result in the collapse of pore structure and closure of pore channels. For instance, the carbon oxidized by a mixture of concentrated H2SO4 and HNO3 has an extremely low adsorption performance.