酸碱改性活性炭及其对甲苯吸附的影响

分别用酸溶液(H_2SO_4、HNO_3、H_3PO_4)和碱溶液(NaOH或NH_3·H_2O)浸渍方法对活性炭进行改性,并对酸改性活性炭进行碱溶液二次改性处理,通过表征改性前后活性炭BET比表面积、孔结构、表面官能团等理化特征和测定其对甲苯蒸气的饱和吸附量,研究了影响活性炭吸附甲苯蒸气的关键因素.结果表明,酸改性使BET比表面积、微孔面积、微孔容积减少、表面酸性官能团增加,而碱改性呈现相反的理化特征变化.活性炭理化特征的变化可能与改性溶液的酸碱性、氧化还原性有关,并且这种相反的变化直接关系到活性炭对甲苯蒸气的吸附.3种酸改性的活性炭对甲苯蒸气饱和吸附量相对于原活性炭减少9.6%~20.0%,而两种碱改性的活性炭则增加29.2%~39.2%.相关性分析显示甲苯吸附量与BET比表面积、微孔面积、微孔容积正相关,而与表面酸性官能团负相关;多元回归分析进一步表明微孔容积和酸性官能团数量是影响活性炭甲苯吸附的关键因素.二次改性活性炭甲苯吸附量与表面含氧酸性官能团拟合结果则表明,—COOH、C＝O和—OH都对活性炭甲苯吸附能力有影响,其中—COOH影响较大.研究结果表明有效提高活性炭对甲苯吸附能力,改性宜以提高活性炭微孔容积和减小活性炭表面酸性官能团数量,特别是—COOH数量为目标导向.

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.