有机膨润土结构对吡虫啉吸附热力学和动力学的影响机理

Thermodynamic and Kinetic Investigation for Structural Effects of Organobentonites on Imidacloprid Adsorption

为深入了解有机膨润土结构对农药吸附性能的影响机理,制备了十六烷基三甲基氯化铵(HTMA)载量系列变化的有机膨润土,通过吸附热力学和动力学研究了新烟碱杀虫剂吡虫啉与有机膨润土的相互作用和影响农药分子在有机膨润土层间扩散的结构因素。结果显示,季铵盐改性削弱了膨润土片层与吡虫啉的静电结合,但是增强与吡虫啉的疏水相互作用。吡虫啉吸附动力学与有机膨润土层间结构密切相关,低载量(<0.8×CEC)的HTMA对膨润土层间距的影响很小,但是层间堆积密度的增加导致吡虫啉吸附速率常数急剧下降。HTMA载量的进一步增加导致其层间排列方式由单层平铺向双层平铺的转变,层间距急剧增加使得吡虫啉吸附速率常数略有增大。

To make a better understanding on the structural effects of organobentonite on its adsorption properties, organobentonite modified with hexadecyltrimethyl ammonium(HTMA) was prepared, and the interaction between the neonicotinoid insecticide imidacloprid and organobentonite and the structural factors affecting the diffusion of pesticide molecules between organobentonite layers were studied by adsorption thermodynamics and kinetics. Organic modification of bentonite resulted in a reduction of the electrostatic attraction, however led to an increase in the hydrophobic interaction with the pesticide. The adsorption kinetics was closely related to the structural features of organobentonite. A dramatic drop of adsorption kinetic rate constant was observed at HTMA loading level less than 0.8×CEC, due to the fact that the enhanced surfactant packing density significantly limited the migration of imidacloprid in interlayer. However, the increased basal spacing benefited the diffusion from the bulk solution into the interlayer gallery when the surfactant arrangement underwent a transition from lateral-monolayer to lateral-bilayer at higher loading level, leading to an increase of adsorption kinetic rate constant.