表面活性剂改性4A分子筛对Cr(VI)的吸附行为

Adsorption behavior of surfactant-modified molecular sieve 4A for Cr(VI)

采用浸渍法对4A分子筛进行表面改性,通过引入阳离子表面活性剂,使4A分子筛表面附着季铵型阳离子,并与反离子Br-形成"阴离子交换膜",从而促使更多的Cr(VI)阴离子通过离子交换吸附到改性4A分子筛上,通过X-射线衍射(XRD)和傅里叶变换红外光谱(FTIR)对样品的物相结构和组成进行表征分析。研究表明,表面活性剂的类型和疏水碳氢链结构会影响4A分子筛的吸附能力,十八烷基三甲基溴化铵(OTAB)碳氢链长,在分子筛表面形成的双分子层密,对Cr(VI)的吸附量最大。采用准一级、准二级、Elovich和Bangham动力学模型对六价铬的吸附数据进行拟合,其中准一级动力学方程最符合十八烷基三甲基溴化铵改性分子筛的吸附行为。同时,分别从Langmuir和Redlich-Peterson等温吸附模型获得六价铬的最大吸附量为13.98 mg/g,且改性分子筛以均一表面吸附为主。

The surface of molecular sieve 4A was modified with cationic surfactant by using impregnation method,and the adsorption of Cr( VI) on modified molecular sieve 4A was improved by forming the anion exchange membrane between quaternary ammonium cation and bromide anion. The phase structures and composition of the samples were characterized by the X-ray diffraction( XRD) and the Fourier transform infrared spectroscopy( FTIR). The study shows that the adsorption of modified molecular sieve 4A is affected by surfactant nature and chain structure of hydrophobic group,and the octadecy trimethyl ammonium bromide( OTAB) modified molecular sieve 4A with longer hydrophobic chain are provided with more dense bilayers and more adsorption capacities of dichromate anion. The Cr( VI) adsorption data were analyzed using pseudo-first-order,pseudo-sencondorder and Elovich as well as Bangham kinetic model,the pseudo-first-order was the most appropriate equation to predict the sorption behaviour of OTAB-modified molecular sieve 4A. The Cr( VI) uptake was also quantitatively evaluated using Langmuir,Freundlich,Redlich-Peterson,and Tempkin isotherm models,Cr( VI) sorption capacity of 13. 98 mg /g and the uniform adsorption playing a dominant role were derived from Langmuir and Redlich-Peterson isotherm.