| Hierarchical porous films exhibit variousadvantages,including multi-porous structure,large specific surface area,high diffusion coefficient,high mass transfer coefficient and the characteristic of 2D continuity.The surface area and thickness are highly controlled.Furthermore,hierarchical porous films are applied to various substrates of different composition and shape.In the consequence,they show obvious superiority in the field of membrane reactor and membrane separation.This article aims at hierarchical porous films.The preparation methods of singleporous films were determined after choice of system and exploration of procedure.The preparation and structural analysis are attached importance.Then we used layer-by-layer method to prepare hierarchical porous films based on the synthesis process of single porous films,including microporous films,mesoporous films and macroporous films.Finally,the interlayer bonding force in the multi-porous films is analyzed.Mainly b-oriented,crystalline and dense ZSM-5 membrane was deposited on pure aluminum with in-site hydrothermal synthesis.The BET specific surface area and pore volume are examined to be 388.3 m~2/gand 0.146cm~3/g,respectively.The pore size is centrally distributed with the pore width(mode)of 0.446nm,which is referred to micropores.The continuous,crack-free and tightly attachedmesoporous silica films on glass slide were prepared by evaporation-induced self-assembly combined with dip-coating method.They exhibit typical three-dimensional cubic pore channel with the average diameter of 6.30nm.The 2D ordered and continuous macroporous silica filmswith opening structure,large windows as well as mesoporous wallon glass substrate were fabricated by colloid crystal templating combined with dip-coating method.The average size of macropores and windowsare326nm and 85nm,respectively.What's more,the wall possesses mesoporous channel with average diameter of4 nm.Themicro-mesoporousfilms,micro-macroporousfilmsand micro-meso-macroporous filmswith multi-layer structure were prepared by layer-by-layer method.The interconnected and 2D continuous micro-mesoporous films can be obtained by layer-by-layer method more than hydrothermal synthesis in the published papers.The BET specific surface area of the well-bonded micro-mesoporous filmsare examined to be 705.0m~2/g,which is higher than that of single ZSM-5 membrane.The pore volume and pore width(mode)of ZSM-5membrane are 0.263cm~3/g and 0.600nm,respectively.The same parameter of mesoporous layer with 3D cubic mesopore channel are 0.123cm~3/g and 5.627nm.The novel double-layered micro-macroporous films can be prepared by colloid crystal templating based on ZSM-5 membrane.The micro-macroporous filmswere obtained with the the BET specific surface area of 402.4m~2/g,which is similar to ZSM-5 membrane.The pore volume and pore width(mode)of ZSM-5 membrane are 0.162cm~3/g and 0.452nm,respectively.The average size of macropores,thickness of wall and windows are 260nm,50nm and 42nm,respectively.The triple-layered micro-meso-macroporous films with large pore volume of micropores can be obtained by introducing ZSM-5 as microporous layer in the layer-by-layer process,which differs from one pot method in papers.The micro-meso-macroporous films with connection among each level of poresand the BET specific surface area of 926.9m~2/g was fabricated.The pore volume and pore width(mode)of ZSM-5 membrane are 0.337cm~3/g and 0.572nm,respectively.The intermediate mesoporous layer with channel perpendicular to substrate possesses the pore volume and pore width(mode)of 0.220cm~3/g and 3.537nm.The average size of macropores and windows are 275nm and 70nm respectively.Moreover,mesopores can be found in the pore wall.The formation of multi-layer structure of hierarchical porous films can be fulfilled by Si-O-Si covalent bond.ZSM-5 membrane,mesoporous films and macroporous films contain some Si-OH on the surface.The condensation reaction between Si-OH is promoted in the high temperature calcination process,which forms Si-O-Si between each layer.As a result,the covalent bond guarantees excellent adherence among multi-porous films fabricated by layer-by-layer method. |
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