Fabrication And CO₂-Capturing Properties Of Multilayered Nanoporous Membrane Based On Nanoparticles' Self-assembly Technology

Organic porous materials have become one of the best adsorbent materials for the capture of carbon dioxide due to their high specific surface areas and excellent pore structure.At present,porous materials are mostly granular,and there is still a certain gap with the development of industrialization.Thin membrane is a kind of material with larger size,and its operation is flexible,small area and easy to expand.Therefore,the development of thin film solid adsorbents can make the application of porous materials more extensive.Layer by layer self-assembly technology is one of the technologies that can obtain large-scale membranes,which is precisely-controllable in nano-scale dimensional,programable in operation process and widely-suitable for various substrates regardless of their shapes and size.In this paper,the research progress of porous material and layer self-assembly technology is summarized.Nanoporous membranes were prepared by layer by layer self-assembly technology,and their pore properties,carbon dioxide adsorption and mechanical properties were studied.The effects of different modification conditions on the properties of porous membranes were explored.Firstly,nanoparticles with different size were prepared,and were alternatively assembled with polyelectrolytes on the substrate surface,and then the Friedel-Crafts reaction was employed to obtain the microporous membranes.The pore properties and gas adsorption properties of the membranes were studied,and the effects of different size of nanoparticles on the properties of the membranes were explored.Secondly,in order to improve the mechanical properties of nanoporous membranes,a buffer layer composed of polyelectrolytes is added between the adjacent microspheres layers to obtain composite nanoporous membrane(CS membrane),and the influence of the buffer layer on the properties of CS membrane is studied.Then,nanoporous membranes was crosslinked by the solution containing double bond monomers to obtain the pre-crosslinked nanoporous membrane(PC membrane),and the effects of the monomer introduction on the mechanical properties and gas adsorption were investigated.Finally,the performance of the nanoporous membrane was simultaneously modified by introducing the buffer layer and the monomer into the nanoparticle-assembled membranes.The change of mechanical properties is also studied.First,nanoparticles with core-shell structure were prepared by seed emulsion polymerization.The morphology and structure of the microspheres were characterized by transmission electron microscopy(TEM).The results showed that the size of the microspheres was about 200nm,400nm,and 600nm,with a negative charge on the surface of the microspheres,and the size of the particles was uniform.Scanning electron microscopy(SEM)and X ray photoelectron spectroscopy(XPS)were used to verify the layer-by-layer assembly behaviors of the microspheres.Finally,the porous structure and carbon dioxide adsorption properties of the membranes were tested by specific surface area analyzer.The results show that the maximum adsorption capacity of carbon dioxide is 3 5wt%?Secondly,in order to enhance the mechanical properties of the nanoporous membrane,polyelectrolyte buffer layers were deposited between the adjacent two microspheres layers to obtain composite nanoporous membrane(CS membrane).The buffer layers were verified by fluorescence labeling technique in florescent microscopy and XPS measurement.The surface elements detected by XPS showed that the addition of buffer layer did not affect the assembly of microspheres.Then the effects of different buffer layers on the performance of CS membrane were investigated.The results showed that the introduction of buffer layers had little effect on the morphology and structure of the microporous membrane.The specific surface area and CO2 adsorption capacity decreased slightly,while the mechanical properties obviously improved in these membranes with scalable thickness.It showed that after introducing 3 layers,6 layers and 9 layers of polyelectrolyte buffer layers,the mechanical properties of CS membrane increased to 0.083MPa,0.133MPa and 0.169MPa respectively,indicating that the buffer layer could improve the mechanical properties of the CS membranes.Then,in order to improve the mechanical properties of the film,the quaternary ammonium salt containing double bonds(DMC)was used to crosslink the nanoporous membrane,and pre-crosslinked nanoporous membrane(PC membrane)was obtained.The effects of different concentration of DMC on the pore properties,carbon dioxide adsorption and mechanical properties of the PC membrane were investigated.The results showed that with the increase of DMC concentration,the CO2 adsorption capacity of the PC membrane increased,because DMC was quaternary ammonium salt,which could combine with CO2 and increase the gas absorption capacity of the PC membrane.The mechanical properties of the PC membrane increase with the increase of the content of DMC.Finally,the mechanical properties of the PC membrane were improved by combining the buffer layer with DMC.The results showed that mechanical properties increased slightly.In this paper,a series of multilayer porous membranes are prepared,which have specific surface area,easy to get synthetic raw materials,simple preparation methods,good carbon dioxide adsorption performance,low energy consumption and industrial production prospects.