Influence of oxygen-containing functional groups on active carbon adsorption of selected organic compounds

Two commercial activated carbons (AC) were treated with HNO3 and (NH4)2S2O8. The changes in surface area and pore size distribution resulting from the oxidising treatments were studied by means of nitrogen adsorption isotherms. The modifications in the surface chemistry were evaluated by means of the point of zero charge (PZC) and the oxygen content. Selective removal of oxygen complexes by heating under N2 and CO2 flow at 723 and 1123 K was also studied. The treatment with HNO3 was found to broaden the microporosity and mesoporosity of the carbons when low concentrations of the oxidising agent were employed. Severe oxidation conditions resulted in an almost total destruction of the texture of the carbons. The point of zero charge values changed systematically with the extent of the oxidation; the more oxidised the carbon, the lower its point of zero charge. Thermal treatment at high temperatures leads to an enhancement of the carbon basicity and a slight decrease in the textural properties of the original carbons.