[Effects of Acidic and Basic Modification on Activated Carbon for Adsorption of Toluene]

Activated carbons (ACs) were modified by acidic solutions (H₂SO₄, HNO₃, or H₃PO₄) and basic solutions (NaOH or NH₃·H₂O), then H₂SO₄modified ACs were re-modified by basic solutions, respectively, in order to investigate the key factors of physico-chemical properties that mainly affected the adsorption of ACs. BET surface area, micropore volume, and surface functional groups were characterized and the adsorption capacity of toluene on the modified ACs was measured. Results showed that BET area,micropore area and micropore volume decreased and the acidic functional groups increased by the acidic treatment, while the basic treatment showed the opposite changing trend in the physico-chemical properties of ACs. Such changes might be associated with the acidity/alkaline and oxidizability/reducibility of experimental solutions. The acidic treatment led to a reduce in toluene adsorption capacities by 9.6%-20.0%, while the capacity increased by 29.2%-39.2% using the basic treatment, compared to those in original ACs. Correlation analysis revealed that there was a positive relationship between toluene adsorption capacities and BET area, as well as micropore area and micropore volume, and a negative relationship between toluene adsorption capacities and acidic functional groups. Multiple regression analysis showed that micorpore volume and acidic functional groups were key factors influencing the toluene adsorption capacity. Furthermore, the adsorption capacity of toluene on re-modified ACs was influenced by the amount of acidic functional groups (-COOH, C=O, and -OH), of which -COOH was the most important factor affecting the adsorption capacity. It is generally suggested that the modification of ACs should focus on an increase in micorpore volume and a decrease in surface functional groups, especially the amount of -COOH, in order to gain the improvement of toluene adsorption capacities.