三种阴离子聚合物分散剂在吡虫啉颗粒表面的吸附热力学和动力学

通过振荡吸附实验研究了三种阴离子聚合物分散剂Morwet D-425、GYD-1252和LG-3在农药吡虫啉颗粒表面的吸附热力学和动力学,对比分析了三种分散剂吸附性能的差异。吸附等温线符合Langmuir和Freundlich吸附等温方程,前者拟合程度较高。由ΔG<0、ΔH<0、ΔS>0可知该吸附为自发、放热、熵增过程,高温不利于吸附进行,|ΔH|<40 kJ·mol^-1表明该吸附为物理吸附。通过对比可知Morwet D-425吸附稳定性最高,受温度影响最小;LG-3吸附稳定性最低,受温度影响最大;GYD-1252吸附稳定性介于两者之间。吸附动力学曲线最符合伪二级动力学方程,吸附过程包括颗粒外传质扩散和表面吸附两个步骤,不包括颗粒内微孔扩散。吸附速率由大到小的顺序为Morwet D-425、GYD-1252、LG-3.通过XPS测定不同温度下分散剂吸附层厚度可知Morwet D-425在吡虫啉颗粒表面的吸附致密,吸附层厚度较低但随温度升高变化很小;GYD-1252和LG-3在吡虫啉颗粒表面吸附疏松,低温下吸附层厚度较高但随温度升高明显降低。

Adsorption thermodynamics and kinetics of three anionic polymeric dispersants onto imidacloprid particle surface

The adsorption thermodynamics and kinetics of three dispersants(Morwet D-425,GYD-1252 and LG-3)onto pesticide imidacloprid particle surface were studied in order to compare adsorption properties.Adsorption data of three dispersants onto imidacloprid were fitted with Langmuir and Freundlich isotherm equations,and the former fitted better.The thermodynamic parameters:ΔH<0,ΔG<0,ΔS>0,indicated that the adsorption was a spontaneous exothermic process.Theoretically,higher temperature was not beneficial to adsorption process,|ΔH|<40 kJ·mol^-1 indicated that the adsorption process was physical adsorption.The conclusion obtained by comparing adsorption properties showed that Morwet D-425 had higher adsorption stability and was not susceptible to temperature effects,LG-3 had lower adsorption stability and was susceptible to temperature effects,adsorption stability of GYD-1252 was in between.The adsorption process followed the pseudo-second-order with a good correlation coefficient.The step of adsorption process included the external diffusion and adsorption onto particle surface,without intraparticle diffusion.Descending order of adsorption rate was Morwet D-425,GYD-1252 and LG-3.The result of adsorption layer thickness by XPS showed that Morwet D-425 had smaller adsorbed layer thickness which changed little with increasing temperature due to higher adsorption stability. GYD-1252 and LG-3 had larger adsorbed layer thickness which decreased significantly with increasing temperature due to weak adsorption stability.