阳离子表面活性剂改性沸石对铬酸根的吸附机制

研究了由十六烷基三甲基溴化铵(CTAB)改性制成的有机沸石对水体中铬酸根的吸附性能及吸附机制.结果表明,与沸石原矿相比有机沸石对铬酸根的吸附容量更高,而铬酸根在有机沸石表面的吸附量随着体系离子强度的增加而显著减小,说明铬酸根的吸附以静电作用为主.研究还发现沸石经有机改性后表面Zeta电位由负变正,说明表面活性剂在沸石表面的吸附改变了沸石表面的电荷性质,这也是有机沸石能够对铬酸根发生静电吸附的主要原因.铬酸根的吸附量及吸附的铬酸根的解吸量均随着体系pH值的升高而增加,分别约在pH=5.0和pH=6.0时达最大,随后铬酸根的吸附量和解吸量随着pH值的进一步增加逐渐减小.铬酸根的吸附量与解吸量之间的差值随pH升高而减小,说明在低pH条件下非静电吸附所占比例较高pH值条件下有所增加.

Mechanisms of chromate adsorption by surfactant-modified zeolite

The adsorption of chromate on zeolite modified by cation surfactant CTAB and its mechanism were investigated. The results showed that the modified zeolite had a greater adsorption capacity for chromate as compared with non-modified zeolite. The amount of chromate absorbed by the modified zeolite decreased with the increase in ionic strength, which suggested that the electrostatic interaction between the modified zeolite and chromate was the major mechanism. The Zeta potential of zeolite changed from negative value to positive value after modified by cation surfactant, and this indicated that the adsorption of cation surfactant on zeolite induced a change in its surface charge properties. The increase in positive value of surface potential was the main reason for electrostatic adsorption of chromate on the modified zeolite. Both adsorption of chromate by the modified zeolite and desorption of pre-adsorbed chromate increased with the increase in pH, and reached a maximum value at pH 5.0 and 6.0, respectively, and then decreased. While after that, the difference between adsorption and desorption of chromate decreased with the increase of pH, suggesting that the adsorption through none electrostatic mechanisms increased at low pH value.