A Thermally Rearranged Poly(benzoxazole) Composite Membrane for Gas Separation Prepared by Vapor Phase Growth

Compositing metal organic framework (MOF) powder with a polymer substrate is an effective way to obtain an efficient gas separation membrane. However, the weak polymer-filler interaction usually leads to the formation of nonselective cracks in the composite material. Here, we report a MOF-polymer composite membrane with a continuous and dense MOF layer, which was synthesized by magnetron sputtering and vapor phase growth. A thermally rearranged poly(benzoxazole) (TR-PBO) membrane was converted from a hydroxy-polyimide precursor by a thermal rearrangement reaction, which was used as the polymer support of the composite membrane. An ultrathin ZnO seed layer was deposited on the TR-PBO support by magnetron sputtering technology, and then it was converted to a ZIF-8 layer by vapor phase growth. Scanning electron microscopy results confirm the formation of a dense, flat, and continuous ZIF layer with a thickness of about 450-600 nm. The ZIF-8 nanoparticles are uniform in size and evenly distributed. Furthermore, the attached ZIF layer significantly improves the gas selectivity of the composite membrane, which should be attributed to the sieving effect of the unique pore structure of ZIF-8. The method of magnetron sputtering combined with vapor phase growth is effective for improving the selectivity of the gas separation membrane and reducing the aggregation of MOF particles, which opens up a way for the design of flat and ultrathin gas separation composite membranes.