梧桐叶活性炭对不同极性酚类物质的吸附

以梧桐枯叶为原料、磷酸为活化剂制备活性炭,研究了不同浸渍比、活化温度、活化时间对活性炭孔结构和表面化学性质的影响. 通过XRD(X射线衍射)、BET比表面积、红外图谱、XPS(X射线光电子能谱)等对梧桐叶活性炭进行表征,并对其表面零电荷点(pH_pzc)进行了测定,从热力学的角度研究了梧桐叶活性炭对水溶液中不同极性酚类物质的吸附行为. 结果表明,梧桐叶活性炭制备的最佳工艺条件为:浸渍比(质量比)为3∶1,活化温度为450℃,活化时间为2.5h. 浸渍比增大、活化温度升高和活化时间的延长,都有利于增加活性炭表面极性；活性炭的极性表面对酚类物质的吸附有重要影响,梧桐叶活性炭对苯酚、邻硝基苯酚和对硝基苯酚的吸附量分别达到79.2、93.9和95.8mg/g. 热力学研究表明,梧桐叶活性炭对不同极性酚类物质的吸附符合Frenundlich等温吸附方程,并且是一个自发的放热过程,其吸附焓变、吸附熵变、吸附自由能变均小于零. 

Adsorption Property of Activated Carbon from Leaves of Phoenix Tree on Different Polarity Phenols

The activated carbons from phoenix tree leaves were prepared by chemical activation with phosphoric acid. The influence of the impregnation ratio, activation temperature and activation time of the activated carbon on the pore structure and surface chemical properities were investigated. The activated carbon was analyzed using XRD, BET, FR-IR and XPS, and the surface point of zero charge (pH_pzc) was measured. The thermodynamic parameters for the adsorption of phenols of differert polarity in aqueous solution by phoenix tree leaves activated carbon were also studied. The results showed that the best activated carbon was obtained under the conditions with the ration of 3∶1(m/m) phosphoric acid to phoenix tree leaves, 450℃ activation temperature and 2.5h activation time. It would be helpful to increase the activated carbon surface polarity with high impregnation ratio, high activation temperature and long activation time. The polar surface of activated carbon grealy influenced on adsorption characteristics of phenols, and the adsorption of phenol, o-nitrophenol and p-nitrophenol reached the values of 79.2,3.9and 95.8mg/g, respectively. The thermodynamic results showed that the adsorption of different polarity phenols obeyed the Frenundlich isotherm model. The adsorption entrophy, entropy and Gibbs free energy were less then zero, and this is indicated the presence of an exothermic and spontaneous adsorption.