聚偏氟乙烯与纳米二氧化钛复合超滤膜的研制

膜工艺是21世纪饮用水处理的优先发展技术之一,超滤膜技术与常规水处理工艺结合使用,可以有效地去除水体中的污染物。我国超滤膜的品种和质量与国际水准相比有一定的差距,而且由于成本问题还未能在水厂推广使用。因此,对超滤膜的研究有着重大的理论和实用价值。超滤膜的优先研究方向是提高膜的抗污染性能和降低成本。聚偏氟乙烯（PVDF）虽然价格昂贵,但热稳定性和化学稳定性很好。纳米材料被公认为重点发展的新型材料之一。本课题选择PVDF和纳米TiO2作为超滤膜材料,以期研制出抗污染性能较好的水处理用超滤膜。探讨了铸膜液组成及制备条件对膜性能和结构的影响,并采用现代仪器分析手段对膜的表面、截面和内部结构进行了研究和分析。PVDF超滤膜的固相含量以14%18%为宜。在前人研究的基础上,着重研究了铸膜液中无机添加剂LiCl的浓度（w（LiCl））较低时对PVDF膜性能和结构的影响。在实验条件下,w（PVDF）为16%,w（LiCl）为0.05%时,所得PVDF膜最薄,有最低的水通量（F）和水通量衰减系数（m）,以及最高的对牛血清白蛋白（BSA）的截留率（R）。w（LiCl）小于0.05%时, F和m随着w（LiCl）的增加而减小,R则增加。w（LiCl）大于0.05%时,F和m则随着w（LiCl）的增加而增加,R则有所降低。PAN超滤膜有同样的现象,在实验条件下,w（PAN）为18%,w（LiCl）为1%时,所得PAN膜最薄,F值和m值最低,R值最大。有机添加剂聚乙二醇（PEG）起致孔作用。然而,当w（PEG）为6%时,所得PVDF膜的水通量仅比无添加剂的PVDF膜的水通量增加20%左右。PEG和LiCl的协同作用优于它们单独使用的效果,但是膜的表面粗糙度增加。PVDF–TiO2复合超滤膜表面比PVDF超滤膜表面更致密。在无机和有机添加剂的协同作用下,复合超滤膜的内部结构和传质性能都有所改善。虽然PVDF–TiO2复合超滤膜的水通量没有明显增加,但截留率得到提高,即膜的抗污染能力增强。仪器分析表明,TiO2包埋在PVDF膜中,强化了PVDF分子的结晶,小粒径的纳米TiO2粒子对PVDF膜性能和结构的改善更显著。缺点是,TiO2纳米粒子在铸膜液中易发生团聚和沉积。首次从胶体的角度分析了铸膜液中各组成在高分子成膜过程中的作用机理。根据DLVO理论,铸膜液中低浓度的LiCl压缩高分子的溶剂化层,减小
电加热器
Membrane technology is one of the preferable ways for drinking water treatment in the 21st century. The pollutants in raw water can be removed when ultrafiltration （UF） is combined with conventional water treatment process. The quality of domestic UF membranes still need improving and is not widely used in water treatment plant due to costs. Therefore, research in UF membrane technology has great significance of theoretical and practical values.The most concentrated research focused on UF membranes is to enhance anti-fouling property and to reduce costs. Though costly, polyvinylidene fluoride （PVDF） has excellent thermal and chemical stability. Nano materials are considered as one of the most prospective material among new type materials. PVDF and TiO2 nanoparticles were chosen to develop UF membranes with good anti-fouling performance for water treatment. PVDF UF membrane and PVDF-TiO2 composite UF membranes were prepared by a phase inversion method. The effect of casting solution compositions and preparation conditions on membrane structure and performance was discussed. Modern instrumental analysis was used to investigate the membrane surface, cross-section and inner section.14%18% PVDF in the casting solution was appropriate to prepare PVDF UF membrane. Based on former studies, the effect of low LiCl concentration in casting solution （w（LiCl）） on membrane structure and performance was studied. PVDF membrane made from casting solution containing 16% PVDF and 0.05% LiCl was the thinnest, and it had the least flux （F） and flux reduction coefficients （m） and the most rejection （R） of blood serum albumen （BSA） under the experimental conditions. When w（LiCl） was less than 0.05%, F and m of the prepared membrane decreased with increasing w（LiCl）, while R increased. However, when w（LiCl） was more than 0.05%, F and m of the prepared membrane increased with increasing w（LiCl）, while R decreased. PAN UF membrane had the same phenomena. For example, PAN membrane made from the casting solution containing 18% PAN and 1% LiCl was the thinnest, and it had the least F and m and had the highest R under the experimental conditions.