铅(Ⅱ)离子印迹复合膜对重金属离子的吸附热力学与吸附动力学

Thermodynamics and dynamics for adsorption of heavy metal ions on Pb(Ⅱ)ion-imprinted composite membrane

以聚丙烯微孔膜(MPPM)为支撑,通过物理包埋和紫外线诱导共价键合组合法固定二苯甲酮,再通过紫外线引发丙烯酸和乙二醇二甲基丙烯酸酯接枝共聚制备了Pb(Ⅱ)离子印迹复合膜。采用平衡吸附和竞争渗透实验考察了印迹复合膜对Pb(Ⅱ)离子的吸附与选择能力。结果发现,印迹复合膜对Pb(Ⅱ)具有良好的吸附及渗透选择性,其对Pb(Ⅱ)的饱和吸附量分别为Cu(Ⅱ)和Zn(Ⅱ)的2.86倍和2.75倍,48h的渗透量分别为Cu(Ⅱ)和Zn(Ⅱ)的3.8倍和3.1倍;Langmuir等温吸附模型与平衡吸附数据相当吻合(R2≥0.991),吸附属于单分子层吸附;动力学研究结果表明,印迹复合膜对重金属离子的吸附过程符合Lagergren准二级动力学模型(R2≥0.998,ΔQ<10%),吸附过程主要受化学作用控制;印迹复合膜对重金属离子的吸附自由能变(ΔG)、吸附焓变(ΔH)及吸附熵变(ΔS)均为负值,说明吸附是一个自发、放热的过程;|ΔH|>|TΔS|,表明吸附过程是一个焓驱动过程。

A novel Pb（Ⅱ）ion-imprinted composite membrane with microporous polypropylene membrane（MPPM）as support was prepared by a modified UV-induced graft copolymerization.In the graft strategy,benzophenone was immobilized on membrane by combining physical entrapment and UV-induced covalent immobilization methods.The adsorption and selectivity capabilities of the imprinted composite membranes towards Pb（Ⅱ）were investigated with equilibrium adsorption and competitive permeation experiments.The imprinted composite membranes exhibit good adsorption and permselectivity towards Pb（Ⅱ）.The maximum adsorption capacity towards Pb（Ⅱ）is 2.86 and 2.75 times that towards Cu（Ⅱ）and Zn（Ⅱ）,respectively,and the permeation amount of Pb（Ⅱ）in 48 h is 3.8 and 3.1 times.Langmuir adsorption isotherm models fit the equilibrium experimental data well（R2≥0.991）,indicating that the sorption is of monolayer-mode.The kinetics of the adsorption towards heavy metal ions follow the Lagergren pseudosecond-order model（R2≥0.998,ΔQ10%）,and the adsorption process is dominated by chemical interaction.The thermodynamic parameters of Gibbs free energy change（ΔG）,enthalpy changes（ΔH）,and entropy change（ΔS）are calculated.Negative values of ΔH suggest exothermic nature of the adsorption,and negative values of ΔG indicate spontaneous nature of process.｜ΔH｜ ｜TΔS｜ suggests that the adsorption of heavy metal ions on the imprinted composite membranes is driven by enthalpy.