在大孔陶瓷管载体上引入ZnO连接层诱导合成稳定ZIF-8膜

Synthesis of stable ZIF-8 membranes on macroporousα-Al_2O_3 ceramic tubes by using ZnO layer as linker and induction sites

以平均孔径为3μm的大孔α-Al2O3陶瓷管为载体,采用载体表面预先引入一层ZnO作为连接和诱导成膜的策略,合成连续完整且性能稳定的ZIF-8膜.首先在载体的内表面通过溶剂热生长一层厚度约为5μm的连续多孔ZnO层,起到对载体表面的修饰、连接膜与载体和诱导成膜的多功能作用;然后,甲醇体系溶剂热法在ZnO表面合成得到连续的ZIF-8膜.考察和优化了ZnO层的活化、ZIF-8合成条件对成膜的影响,用SEM、XRD和气体渗透等分析方法对所得ZIF-8膜进行表征.研究表明,ZnO层的连续性和活化处理是成膜的关键,ZnO层不连续难以形成完整连续ZIF-8膜,不活化ZnO则起不到很好的诱导成膜作用.最佳条件下获得的ZIF-8膜的H2通量为2.14×10-7 mol/(s·m2·Pa),H2/CO2、H2/N2、H2/CH4的理想分离系数分别为5.18、8.32、8.30.该膜材料具有明显的筛分效应,且150℃条件下长时间测试稳定性良好.

ZIF-8membranes were synthesized on macroporousα-Al2O3 tubes with average pore size 3μm as supports,and by introducing a thin layer of ZnO as linker and induction sites.The preparation procedure involved a two-step process：firstly,the growth of a thin layer of ZnO on the inner surface of the macroporous tube,and then the formation of a continuous and dense ZIF-8membrane.The results showed that a continuous ZnO layer of around 5μm could be formed on the macroporous tube only in methanol/water solution.The ZnO layer acted as active sites to induce the uniform nucleation of ZIF-8nuclei on its surface to guide the growth of a dense ZIF-8membrane,an inorganic linker between the porous ceramic substrate and the membrane and a modification layer for the surface of the macroporous support.It was crucial to activate the ZnO layer with Hmim solution.Without activation,only some large ZIF-8crystals could grow on the ZnO surface.The characterization of SEM,XRD and single gas permeation indicated that the quality of the ZnO layer and its activation played a key role in growing a continuous and dense ZIF-8membrane.For the ZIF-8membrane achieved under the optimum condition,the H2 permeance was about2.14×10^-7 mol/（s·m^2·Pa）and the ideal selectivities of H2/CO2,H2/N2 and H2/CH4 were 5.18,8.32,8.30,respectively,which displays good molecular sieving effect.The membrane also demonstrates good stability at 150℃.