层层组装晶种法制备Mg-MOF-74膜及其分离性能

以2,5-二羟基对苯二甲酸和乙酸镁溶液为原料通过交替浸渍层层组装法在a-Al₂O₃载体表面预置晶种层, 再利用二次生长法制备出连续而致密的Mg-MOF-74晶体膜。采用X射线衍射(XRD)和扫描电镜(SEM)对膜进行了表征。实验结果表明:相比于原位溶剂热合成法, 通过2, 5-二羟基对苯二甲酸和乙酸镁交替浸渍层层组装法可以增强Mg-MOF-74与氧化铝基体之间的附着效果, 提高晶体薄膜的致密性与连续性, 实验发现4次交替浸渍层层组装预置晶种可以制备出具有分子筛分性能的Mg-MOF-74晶体膜, 单组分气体渗透测试表明其H₂/CO₂的理想选择性可以达到8.96, 高于其努森扩散选择性。XRD测试表明该晶体膜的特征衍射峰与文献报告的粉末MOF-74完全一致, 表明Mg-MOF-74晶粒以无取向形式生长于氧化铝载体表面。SEM表征表明Mg-MOF-74晶粒呈麦粒状微观外形, 其BET比表面积可以达到1182 m²·g^-1。

Preparation of Mg-MOF-74 membranes via layer-by-layer seeding and its separation properties

Continuous and dense Mg-MOF-74 membranes were prepared through a combined layer-by-layer seeding assembling and secondary growth method based on 2, 5-dihydroxybenzoic acid and magnesium acetate solution. The adhesion between Mg-MOF-74 crystals and a-Al₂O₃ support could be considerably improved by the alternate immersion assembling of 2, 5-dihydroxybenzoic acid and magnesium acetate solution. Compared with the in-situ crystallization technique, Mg-MOF-74 membranes synthesized by four-cycle layer-by-layer method exhibited improved molecule-sieving properties due to optimized membrane continuity and density. Single gas test indicated that the best Mg-MOF-74 membrane had H₂/CO₂ ideal selectivity as high as 8.96, higher than its Knudsen diffusion selectivity. XRD measurement proved that the XRD patterns of Mg-MOF-74 membranes were consistent with those of powdered Mg-MOF-74 from published papers, which implied that our membranes were composed of randomly oriented MOF-74 crystals. SEM characterization showed that the MOF-74 crystals possessed wheat-shaped morphology and specific BET surface area as high as 1182 m²·g^-1.