改性MCM-41分子筛对阴离子偶氮染料的吸附作用机理

制备了改性介孔分子筛NH₃⁺-MCM-41,研究了其对阴离子偶氮染料甲基红的吸附效果。研究表明,通过氨基改性使介孔分子筛MCM-41表面电荷发生改变,从而利用静电吸附作用改善了脱除效果,使甲基红吸附率提高了1.1倍,达到90.4%。溶液pH值的改变会影响NH₃⁺-MCM-41的表面电荷,从而影响吸附效率,其最佳pH值为4。溶液中的杂质离子均会对吸附产生影响,当溶液中含有Cl^-、NO₃^-时,对吸附效果影响不大;而当溶液中含有CO₃^2-和HPO₄^2-等高价弱酸根离子时,对吸附效果影响很大,基本不吸附染料。此外,通过其吸附动力学研究发现,吸附过程中不符合准一级动力学模型,而较好符合准二级动力学,说明在该过程中存在化学吸附,这种化学吸附涉及吸附剂与吸附质之间的电子共用或电子转移。

Adsorption performance of anionic azo dye by the modified MCM-41 mesoporous molecular sieve

The adsorption efficiency of the anionic azo dye (methyl red) on amino-modified ordered mesoporous silica (NH₃⁺-MCM-41) have been investigated. The research results indicate that the surface charge of MCM-41 are redistributed after the amino modification. By means of the electrostatic effect, the adsorption efficiency of methyl red on NH₃⁺-MCM-41 was 90.4% which was 1.1 times more than that on the unmodified MCM-41. The pH value of the solution determines the surface charge of NH₃⁺-MCM-41 and then affects the adsorption efficiency, and the optimal pH value is 4. The impurity ions in the methyl red solution also influence the adsorption efficiency through competitive adsorption. When the solution contains only Cl^- and NO₃^-, there is little effect on the adsorption efficiency. But when the solution contains the weak acid anion with high valence, such as CO₃^2- and HPO₄^2-, the adsorption efficiency is greatly reduced and there is no methyl red adsorbed. Through the adsorption kinetics study, the adsorption rate is quasi second order rather than quasi first order, indicating the presence of chemical adsorption, which involves electron sharing or electron transfer between the agent and the adsorbate.