Preparation Of LDHs/polymer Hybrid Films With Gas Selective Transmission Properties

Recently,organic-inorganic gas selective transmission films have evoked widely attention due to their broad applications in natural gas sweetening,biogas upgrading and air dehumidification.However,the existing gas selective transmission films aspire after the satisfying gas selectivity with permeability sacrificing,which limited its industrial applications with large gas flow.Moreover,the ubiquitous plasticization of organic-inorganic films in high humidity limits the composite films to apply in separation of water vapor and other gas.For resolving the above two highlighted challenges,this study assembles the LDHs and special polymers into new organic-inorganic gas selective transmission hybrid films via the modified layer-by-layer self assembly,taking advantage of the unique feature of layered double hydroxides(LDHs)(such as adjustable two-dimensional layered structure and orientation)and characteristic response of polymer to exogenous stimulation.The two kinds of achieved composite films exhibit the outstanding CO2 and H2O selective transmission property,respectively,possessing the important theoretical value and practical application potential.The pivotal researches findings are shown as follows:(1)Multilayer films comprised by layered double hydroxides(LDH)nanosheets and carboxymethyl cellulose(CMC)were fabricated via layer-by-layer assembly.The resultant(LDH/CMC),films show excellent gas barrier property,which is ascribed to the largely increased pathway for gas permeation originating from the large aspect ratio and high orientation of two-dimensional LDH nanosheets.Unlike traditional gas barrier films with indiscriminate blocking effect to various gases(including water vapor),the(LDH/CMC),films exhibit unusual moisture permselective property.The moisture-permeable behaviour was related with the hygroscopicity of CMC and hydrophilicity of LDH,which can enrich the water molecule from surrounding and aggrandize the osmotic pressure for water vapor,resulting in an infrequent improvement of water vapor transmission.It is interesting to find that the(LDH/CMC),films exhibit enhanced gas(02,C02,CH4 and N2)barrier property upon treatment in humidity environment,due to the formation of hydrogen bond between the infiltrated water molecule and hydrophilic groups in CMC,padding the interstitial space of CMC molecular chains and increasing the gas diffusion length.The reduction of free volume and extension of gas transmission path further enhance the gas barrier property of(LDH/CMC)n films.In addition,the(LDH/CMC)n films represent water vapor permselective property in mixed gas(including O2,CO2,CH4,N2 and water vapor),while keeping barrier to other gases,which can be potentially applied in air dehydration and dehumidification of natural gas.(2)An organic-inorganic composite film was fabricated via modified layer-by-layer assembly,consisting of LDH nanoplate,formamidinesulfinic acid(FAC)and poly(dimethylsiloxane)(PDMS)as building blocks.The resultant(LDH/FAC)25-PDMS film exhibits a excellent CO2 selective transmission property with the high relative permeability factor of 147.91(C02/02)、159.51(C02/N2)、77.48(C02/H2)、and satisfying C02 transmission rate of 162.7 Barrer.The separation performance of(LDH/FAC)n-PDMS film is superior to lots of reported works and surpasses the Robinson upper bound(2008).The CO2 selective transmission property was mainly related with the physical barrier effect from LDHs and the protonation of FAC.Firstly,the unique protonation reaction between CO2 and the amidine group induces positively charge FAC.The resulting charge repulsion perturbs the high orientation of adjacent LDH nanoplate and makes the passageway for CO2 transmission.Secondly,as the other product of the protonation reaction,HCO3-is gravitated by positively charged LDH and interacts with the abundant alkaline groups on the LDH nanoplate,which makes the HCO3-moving fast to defect of LDH orientation.Finally,the CO2 reaches the next FAC layer and repeats the above reaction.Therefore the C2 could selectively and fast transmit through the multilayer of FAC and LDH.