HNO_(3)改性活性炭对Cr(Ⅵ)的吸附性能及机理

Adsorption Property and Mechanism of Cr(Ⅵ)on HNO_(3) Modified Activated Carbon

活性炭的吸附性能与其表面化学密切相关,本研究为讨论活性炭表面氧化改性对其Cr(Ⅵ)吸附特性的影响,分析了Cr(Ⅵ)吸附过程与活性炭表面化学性质的关系,阐释吸附机理。结果表明,与未改性活性炭相比,硝酸氧化改性后活性炭对溶液中Cr(Ⅵ)的吸附性能提高,且改性后活性炭的比表面积和孔容积降低,表面的羧基、内酯基和酚羟基等酸性含氧官能团的数量增多。改性活性炭对Cr(Ⅵ)的吸附过程可用Langmuir、Freundlich、D-R和Temkin4种吸附模型模拟,吸附动力学数据与拟二级动力学模型吻合。采用X射线光电子能谱(XPS)表征了改性前后活性炭的表面化学性质。Cr(Ⅵ)在活性炭上的吸附机理主要为静电吸引、还原和配位络合等,与Cr(Ⅵ)发生络合作用的是活性炭表面含氧官能团。

Adsorption property is associated with surface chemistry of activated carbon(AC).In order to study the effect of surface oxidation modification of AC on adsorption,the relation of Cr(Ⅵ)adsorption process and surface chemistry of HNO_(3)modified activated carbon(HNO_(3)-AC)was analysized and the adsorption mechanism was illuminated.Specific surface area and pore volume decreased after modification.The number of oxygen-containing functional groups such as carboxyl,lactone and hydroxy on the surface of HNO_(3)-AC obviously increased.HNO 3-AC showed an increased adsorption capacities in the removal of Cr(Ⅵ).The adsorption behaviour obeyed four isotherm models such as Langmuir,Freundlich,D-R and Temkin.The adsorption kinetic data was found to fit well with a pseudo-second-order rate equation.Surface chemical properties of activated carbon before and after modification and adsorption were characterized by XPS.It could be seen that the adsorption mechanism of Cr(Ⅵ)included electrostatic attraction,reduction and formation of coordination complexes.It showed that just the oxygen-containing functional groups on the surface of HNO 3-AC were complexed with Cr(Ⅵ).