A study on thermally and chemically stable multifunctional membranes

阳极氧化铝膜的孔隙是由一组平行和直的通道组成的，这些通道具有纳米级的均匀直径。由于这些纳米通道的存在，该膜已被用作超滤膜。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。为了克服这种稳定性差的问题，我们从阳极氧化膜制备了碳涂层膜，然后通过氧化或氟化处理对其碳表面进行化学修饰。在本研究中，我们使用膜进行水/乙醇混合物的渗透汽化分离，并研究了这种改性对渗透汽化性能的影响。当丙烯在阳极氧化铝膜上进行热解分解时，薄膜上的碳涂层均匀。碳沉积过程将通道直径从30 nm减小到20 nm，但整个通道结构完好无损。进一步的氟化或HNO_3处理没有改变通道结构。通过这些薄膜的气体渗透主要受克努森扩散的支配。在水/乙醇混合物的渗透蒸发分离中，尽管未处理和氧化的碳包覆膜没有表现出任何选择性，但在氟化膜中观察到水的优先渗透。这项工作表明，即使孔径达到20 nm，对孔壁进行适当的表面修饰，也可以使膜在渗透蒸发分离中具有选择性。

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.