MOFs混合基质膜的制备及其对Co(Ⅱ)的分离研究

Preparation of MOFs Mixed Matrix Membrane and Its Separation Effect on Co(Ⅱ)

目的为了解决MOFs原料价格昂贵且吸附剂不易回收的问题,以废旧PET瓶为酸源制备UiO-66,在聚丙烯腈中掺杂UiO-66制备MOFs混合基质膜以提升膜材料对钴离子的分离性能。方法先将废旧PET瓶解聚制得对苯二甲酸,再以对苯二甲酸为原料制备MOFs材料UiO-66,利用MOFs与聚合物良好的相容性,将UiO-66分散到聚丙烯腈(PAN)中,制得MOFs混合基质膜UiO-66-PAN,通过XRD、FT-IR、BET、SEM等对UiO-66-PAN的表面形貌及结构进行分析。结果成功制备出UiO-66-PAN,当UiO-66掺杂量由0%增加到6%时,膜材料的比表面积随UiO-66的增加而增大;当UiO-66掺杂量继续增加到8%时,UiO-66出现明显聚集,导致材料的膜通量和截留率降低;当UiO-66的掺杂量为6%时,6%-UiO-66-PAN的膜通量和截留率最高,分别为2654L·m^(-2)·h^(-1)和49.71%。将UiO-66-PAN用于Co(Ⅱ)的分离研究,在pH值为8.3、温度为25℃时,6%-UiO-66-PAN对Co(Ⅱ)的吸附量为26.56mg/g,吸附过程自发吸热,符合准二级动力学模型和Freundlich吸附等温模型,经5次循环后对Co(Ⅱ)的去除率仍保持在80%以上。UiO-66-PAN具有良好的机械强度和稳定性,在金属离子分离方面具有潜在的应用价值。结论UiO-66的加入能增强膜材料对Co(Ⅱ)的吸附能力,多孔结构的MOFs材料能够增强混合基质膜对金属离子的分离性能。

Membrane separation method is considered as one of the methods with great potential for industrial application because of its advantages such as simple operation,energy saving and environmental protection,high efficiency and flexibility,small equipment footprint and scale-up ability of production.Therefore,the membrane separation method is used to separate cobalt ions.The work aims to solve the problem that MOFs raw materials are expensive and adsorbent is not easy to recover.Waste polyethylene terephthalate(PET)bottles are used as acid source to prepare UiO-66,and UiO-66 is doped into polyacrylonitrile to prepare MOFs mixed matrix membranes(MMMs),so as to improve the separation performance of the membrane material for cobalt ions.The synthesis process of the MMMs was divided into the following steps.Firstly,terephthalic acid was obtained by depolymerization of PET bottles.Then,the terephthalic acid was used as ligand to prepare zirconium-based MOFs UiO-66.Finally,combined with the good compatibility between MOFs and polymer,different contents of UiO-66 were dispersed into the polyacrylonitrile matrix,and UiO-66-PAN MMMs were prepared by solvent evaporation.Using waste PET bottles as acid source could not only reduce the cost of materials,but also turn waste into treasure,and realize the secondary utilization of resources.UiO-66 and UiO-66-PAN were characterized by XRD,FT-IR,BET and SEM,which proved that the material was successfully prepared and the addition of UiO-66 enhanced the thermal and mechanical stability of the membrane material.When the doping content of UiO-66 increased from 0%to 6%,the specific surface area of the membrane increased with the increasing content of UiO-66.As the doping content of UiO-66 continued to increase to 8%,UiO-66 showed obvious aggregation phenomenon,blocking the pore structure of the material and resulting in a significant decrease in membrane flux and rejection.Among all the materials,the best performance was achieved when the doping content was 6%,and the membrane flux and interception rate of the material were higher than those of other materials,reaching 2654 L·m^(-2)·h^(-1) and 49.71%,respectively.UiO-66-PAN was used for the separation of cobalt ions.When pH value was 8.3 and temperature was 25℃,the maximum adsorption capacity of 6%-UiO-66-PAN reached 26.56 mg/g.The separation of materials was a spontaneous endothermic process.By fitting the data,the material was more consistent with the quasi-second-order kinetic model and Freundlich adsorption isothermal model.It was found that the removal rate of cobalt ions remained above 80%after five cycles of experiment.UiO-66-PAN had good mechanical strength and stability.Finally,Co^(2+) adsorption mechanisms were discussed based on microstructure analysis and adsorption kinetics and isotherms,the result showed that chemical adsorption was the main adsorption method,and the formation of Co^(2+) and—COOH complex dominated the cobalt adsorption process.The experimental conclusion shows that the dispersion of UiO-66 in polymer matrix enhances both the separation performance of cobalt ions and the stability of the membrane and flux of the membrane.Besides,the addition of UiO-66 can enhance the adsorption capacity of membrane materials for Co(Ⅱ),and the porous MOFs can enhance the separation performance of mixed matrix membranes for metal ions,which has potential application value in the separation of metal ions.