Metal-organic framework-functionalized alumina membranes for vacuum membrane distillation

Nature-mimetic hydrophobic membranes with high wetting resistance have been designed for seawater desalination via vacuum membrane distillation (VMD) in this study. This is achieved through molecular engineering of metal-organic framework (MOF)-functionalized alumina surfaces. A two-step synthetic strategy was invented to design the hydrophobic membranes: (1) to intergrow MOF crystals on the alumina tube substrate and (2) to introduce perfluoro molecules onto the MOF functionalized membrane surface. With the first step, the surface morphology, especially the hierarchical roughness, can be controlled by tuning the MOF crystal structure. After the second step, the perfluoro molecules function as an ultrathin layer of hydrophobic floss, which lowers the surface energy. Therefore, the resultant membranes do not only possess the intrinsic advantages of alumina supports such as high stability and high water permeability, but also have a hydrophobic surface formed by MOF functionalization. The membrane prepared under an optimum condition achieved a good VMD flux of 32.3 L/m²-h at 60 °C. This study may open up a totally new approach for design of next-generation high performance membrane distillation membranes for seawater desalination.