A study on thermally and chemically stable multifunctional membranes

阳极氧化铝膜的孔隙结构是由一系列直径均匀的平行直通道组成。由于这种纳米通道的存在，该膜已被用作超滤的膜。然而，这种膜过滤器在酸性和碱性溶液中的化学稳定性都很差。为了避免这种差的稳定性，我们已经从阳极氧化膜制备了碳涂覆的膜，然后通过氧化或钝化处理对其碳表面进行化学改性。在本研究中，我们使用的膜渗透汽化分离水/乙醇混合物，并探讨这种改性对渗透汽化性能的影响，当丙烯进行热解在阳极氧化铝膜，膜上实现均匀的碳涂层。碳沉积过程将通道直径从30 nm减小到20 nm，但保持整个通道结构完整。进一步的Na 2SO 4或HNO_3处理并不改变通道结构。通过这些膜的气体渗透被发现主要由努森扩散。在水/乙醇混合物的渗透蒸发分离中，在氟化膜中观察到水的优先渗透，尽管未处理的和氧化的碳涂层膜没有显示出任何选择性。该工作表明，即使孔径大至20 nm，对孔壁进行适当的表面改性也可以赋予膜在渗透蒸发分离中的选择性。

The porosity of an anodic aluminum oxide film consists of an array of parallel and straight channels with a uniform diameter at nanometer level. Because of the presence of such nanochannels, the film has been used as a membrane for ultrafilitration. This membrane filter however, suffers from its poor chemical stability both in acid and alkaline solutions. In order to circumvent such poor stability, we have prepared a carbon-coated membrane from an anodic oxide film and then chemically-modified its carbon surface by either oxidation or fluorination treatment. In the present study, we use the membrane for pervaporation separation of water/ethanol mixture and investigate the effect of such modification on the pervaporation performance.When pyrolytic decomposition of propylene was carried out over an anodic aluminum oxide film, uniform carbon coating on the film was achieved. The carbon deposition process decreased the channel diameter from 30 to 20 nm, but left the whole channel structure intact. Further fluorination or HNO_3 treatment did not alter the channel structure. Gas permeation through these films was found to be principally governed by Knudsen diffusion. In the pervaporation separation of water/ethanol mixture, preferential permeation of water was observed in the fluorinated films, although the untreated and oxidized carbon-coated films did not show any selectivity. This work demonstrated that, even if pore diameter is as large as 20 nm, a suitable surface modification to pore wall makes it possible to endow a membrane with selectivity in pervaporation separation.