ZSM-5分子筛对杜仲绿原酸的吸附行为研究

Adsorption of Chlorogenic Acid from Eucommia ulmoides Leaves on ZSM-5 Molecular Sieve

以杜仲叶中绿原酸为吸附对象,ZSM-5分子筛为吸附剂,通过分析吸附等温线、动力学及热力学,考察了分子筛对绿原酸的吸附行为。结果表明:在样品溶液pH值为5、20 mL溶液中加入2 g分子筛的条件下,分子筛对绿原酸的吸附量最大,吸附效果最好。动力学研究结果表明:在40℃下ZSM-5分子筛对绿原酸的平衡吸附量为2.075 mg/g,吸附符合准二级动力学模型,即吸附过程中化学吸附起主要作用,同时粒内扩散模型结果发现绿原酸分子向分子筛的扩散存在3个阶段,说明颗粒内扩散不是唯一的速率控制步骤,同时还存在外扩散及边界扩散的作用。吸附等温线研究发现:等温吸附曲线更加符合Freundlich模型,即吸附剂表面活性结合位点及能量分布不均匀,吸附易于进行。热力学研究发现:分子筛对绿原酸的吸附为自发过程(ΔG<0),且ΔH和ΔS分别为40.13 kJ/mol和157.58 J/(mol·K),表明吸附为吸热和熵增加过程。

The adsorption isotherm,kinetics and thermodynamics of chlorogenic acid in Eucommia ulmoides Oliv.leaves on ZSM-5 molecular sieve was investigated.Batch adsorption experiments revealed that the optimum solid-liquid ratio was 2∶20(g∶mL)and pH value was 5.The amount of absorbed chlorogenic acid reached 2.075 mg/g at 40℃.The results of kinetics study showed that the behavior of adsorption of chlorogenic acid on the adsorbent of molecular sieve accorded with the pseudo-second-order kinetic model;the chemisorption played a major role in the adsorption process;and there existed three regions of the diffusion of chlorogenic acid molecules into the molecular sieve depicted from the plot of intraparticle diffusion model,which meant it contained the effects of intraparticle diffusion,external diffusion and boundary diffusion.The result of thermodynamics study showed that theisothermal adsorption curve was more consistent with the Freundlich model,indicating that the adsorption process took place on a heterogeneous surface corresponding to a multilayer adsorption mechanism;the process of adsorption was spontaneous,the enthalpy and entropy were 40.13 kJ/mol and 157.58 J/(mol·K),respectively,which meant endothermic and entropy increased during the adsoption process.