碳纳米管负载层结构对复合膜分离性能的影响研究

Effects of carbon nanotubes mats structure on rejection performance of composite membranes

采用过滤涂敷法将多壁碳纳米管(MWCNTs)负载于氧化铝微滤(MF)膜表面,构建了一种新型复合膜。通过系统考察碳管投加量、外形尺寸对表面碳层结构的影响,建立了其与复合膜分离性能的响应关系,为传统MF膜的改进提供了重要参考。结果表明,借助高分子表面活性剂和超声波辅助技术,可以实现碳管在水溶液中的充分分散,这有利于在膜表面形成相对均匀的碳负载层。对于同类型碳管而言,增大负载量对碳层孔径分布和过滤比阻(rc)的影响较小。相比之下,使用低长径比(L/D)的碳管可以有效压缩负载碳层中的孔隙尺寸,导致复合膜渗透率降低。而高L/D比碳管在膜表面形成了高度缠绕的蓬松结构,对应的rc值最小。利用负载碳层的吸附作用,复合膜对小分子富里酸(FA)的截留能力与碳管负载量和比表面积呈现正相关,同时,碳层结构的致密程度也是影响FA截留率的重要因素。

A novel composite membrane was prepared by loading multiwalled carbon nanotubes（MWCNTs） on the surface of existing aluminum oxide micro-filtration（MF） membrane using filtration-coating method. The effects of both loading dosages and dimensional sizes of MWCNTs on the surface mats structure were investigated, while the responses to the rejection performance of composite membranes were also established for improving the conventional MF process. The results showed that the effective dispersion of MWCNTs could be achieved by combining large molecular surfactant and ultrasonic technology, which was beneficial to form homogeneous carbon nanotubes mats on the surface of MF membranes. For the same type of MWCNTs, increasing MWCNTs loading dosage would have no significant effects on the pore size distribution and specific filtration resistance（rc） of carbon nanotubes mats. When the MWCNTs with low length-diameter（L/D） ratio was used, the smaller pore size on the surface mats resulted in the decrease of membranes permeability. On the contrary, a highly twining and fluffy mat structure was observed with the high L/D ratio of MWCNTs, corresponding to the lowest value of rc. In addition, the positive correlations between the rejection of composite membranes for small molecular fluvic acid and both loading dosages and specific surface area of MWCNTs were found, which was also related to the mats compactness based on the main mechanism of adsorption.