澄清溶液体系二次生长法NaA型沸石膜的生长机制及膜厚的控制合成

用晶种涂层二次生长成膜法研究了在含水量不同的澄清溶液合成体系中NaA型沸石膜的生长及沸石膜厚度的控制合成.用SEM,TEM和XRD表征手段分析了沸石膜的形成过程和微结构.在载体表面不涂晶种而直接合成则不易形成连续沸石膜;用晶种涂层二次法可以很容易形成均匀的连续膜.合成液中水量的高低强烈影响沸石膜的生长速率、形成结构和膜的厚度.在高水量(水硅摩尔比为2000)的合成体系中沸石生长速率慢,膜主要通过晶种层中的晶粒长大,交织成膜,且膜只有一层结构;而在低水量(水硅摩尔比为750)的合成体系中沸石生长速率快,膜则通过晶种层表面晶粒向外生长、交织成膜,而膜具有两层结构.通过调变合成液的水量可有效地控制沸石膜层的厚度,并能制得非常均匀、连续的膜.

Growth Mechanism of Zeolite NaA Membranes and the Thickness Control of the Membrane by Secondary Synthesis from Clear Solutions

The Effect of the water content on the growth of NaA zeolite membranes and the thickness control of the membrane were studied by secondary synthesis from clear solutions. The samples were characterized by SEM, TEM and XRD. It has been shown that different synthesis solutions resulted in the different growth process of NaA zeolite membranes. In the dilute synthesis solution n(H2O)/n(SiO2)=(2 000)], the thinner NaA membrane with single-layer structure was formed by zeolite crystals growing only within the seed layer. On the contrary, in the concentrated synthesis solution (n(H2O)/n(SiO2)=750],) the thicker NaA membrane with two-layer structure was formed by zeolite crystals growing outward from the topmost layer of the seeds. As the n(H2O)/n(SiO2) ratio was decreased from 1 500 to 500, the membrane thickness was increased from 1.7 μm to 10.8 μm. These results show that the membrane thickness could be easily adjusted mainly by varying the water content of the synthesis solution.