Wu Chou, Lou Xianfen, Xu Xiafan, Huang Aimin, Zhang Min, Ma Lin
School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, P. R. China.
ACS Omega. 2020 Feb 21;5(8):4191-4199. doi: 10.1021/acsomega.9b04025. eCollection 2020 Mar 3.
Thermodynamics and kinetics of pretilachlor adsorption on organobentonites modified with hexadecyltrimethyl ammonium chloride were investigated to reveal the structural effects of organobentonites on the interaction with pretilachlor and the diffusion of the herbicide and were related to the controlled release from organobentonites. The adsorption of pretilachlor was entropically driven by hydrophobic interaction. The entropy change dropped with increasing surfactant loading from 0.4 to 1.50 times the cation exchange capacity (CEC) of the bentonite used, corresponding to a decrease in the degree of freedom of pretilachlor molecules due to the enhanced order of surfactant in the interlayer. The kinetics of pretilachlor adsorption was well fitted to the pseudo-second-order model and related to the structural features of organobentonites. The enhanced packing density of the surfactant in the interlayer generally resulted in a reduction of the rate constant of the pretilachlor adsorption onto organobentonites. However, the stepwise increase in the basal spacing due to the surfactant arrangement transition, from lateral-monolayer to lateral-bilayer at a loading level of more than 0.8 × CEC, benefited the diffusion of pretilachlor and diminished the influence of the increase in surfactant packing density. The release of pretilachlor from organobentonites was predominated by Fickian diffusion, which could be understood from the adsorption thermodynamics and kinetics. The time taken for the release of 50% of active ingredient was 16-23 times that for the control formulation and exhibited a linear increase with the relative value of the equilibrium constant to the rate constant of pretilachlor adsorption.
研究了十六烷基三甲基氯化铵改性有机膨润土对丙草胺的吸附热力学和动力学，以揭示有机膨润土对与丙草胺相互作用及除草剂扩散的结构影响，并与有机膨润土的控释性能相关联。丙草胺的吸附是由疏水相互作用驱动的熵增过程。随着表面活性剂负载量从所用膨润土阳离子交换容量（CEC）的0.4倍增加到1.50倍，熵变下降，这对应于由于层间表面活性剂有序性增强导致丙草胺分子自由度降低。丙草胺吸附动力学很好地符合准二级模型，且与有机膨润土的结构特征相关。层间表面活性剂堆积密度的增加通常导致丙草胺在有机膨润土上吸附速率常数降低。然而，在负载量超过0.8×CEC时，由于表面活性剂排列从横向单层转变为横向双层，层间距逐步增加，有利于丙草胺的扩散，并减弱了表面活性剂堆积密度增加的影响。丙草胺从有机膨润土中的释放以菲克扩散为主导，这可以从吸附热力学和动力学来理解。活性成分释放50%所需的时间是对照制剂的16 - 23倍，且与丙草胺吸附平衡常数与速率常数的相对值呈线性增加。
