Selective Adsorption Of The New Metal Organic Frameworks UTSA-74 And DMOF For C₂H₂

With the improvement of the human living standard and the development of industry,the demand for high purity acetylene is also increasing.In the preparation of high purity C₂H₂,it is difficult for traditional porous materials to separate impurities from the C₂H₂ gas,such as CO₂,C₂H₄ and so on.Based on the background of metal organic frameworks?MOFs?and adsorption and separation technology,the research on selective adsorption and separation of C₂H₂ gas has been carried out in this paper.In the first chapter,a new microporous MOF material UTSA-74?Zn₂?H₂O??dobdc?0.5?H₂O??is prepared through the accurate design of the central metal Zn?II?by hydrothermal method.The central metal Zn?II?in the UTSA-74 has two coordination structures:the Zn1?II?is four coordinated by organic ligands to built tetrahedron;and Zn2?II?site shows six coordinated octahedral geometry,and two terminal coordinated water molecules in the axis orientation which these terminal water molecules can be easily removed during thermal and/or vacuum activation obtained UTSA-74a with stable structure,so that,each of these Zn2 sites can carry two active metal sites.Based on the characteristics of UTSA-74a,a systematic gas adsorption experiment and characterization is carried out.And the abundant active metal sites have stronger interaction force for C₂H₂than CO₂,after than the C₂H₂ gas can be selectively adsorbed.UTSA-74a not only has better ability to separate C₂H₂,but also has high adsorption capacity for C₂H₂?UTSA-74a:145cm³/g,Zn-MOF-74:150cm³/g?.Compared with the other MOF with similar functions,UTSA-74 breaks through the barrier of selectivity and capacity.In the second chapter,the dithienylethene as ligands has been used to synthesize metal organic frameworks,DMOF,for researching the performance in the separation of C₂H₂gas.The diarylethene ligands from DMOF undergo photoinduced isomerization involving ring-opening/closing reactions triggered by UV and visible light,enduing characteristics of photochromism with DMOF.The gas adsorption experiments of C₂H₂ and C₂H₄ on DMOF show that the adsorption temperature and light can be used to efficiently control C₂H₂adsorption,furthermore,received the separation between C₂H₂ and C₂H₄.After ultraviolet light,the selectivity coefficient of DMOF for C₂H₂ and C₂H₄ was 3 at the 195K,however,this DMOF shows ultrahigh C₂H₂/C₂H₄ selectivity of 47.1 under UV light at the same temperature.Moreover,under open loop state,the selectivity ratio is decreasing,cooperated with the increase of adsorption temperature?47.1@195K,3.2@273K,2.2@293K?.Density functional theory?DFT?calculations show that the internal grooves in diarylethene from DMOF have the ability to trap the C₂H₂ molecules,but not C₂H₄molecules,leading selective preference of C₂H₂ molecules.However,as UV light is irradiated,the methyl bond on the thiophene ring in the structure and the grooves disappear,resulting in the decrease of the selectivity separation coefficient.A series of characterization experiments,such as the isosteric heat of adsorption,ideal adsorbed solution theory?IAST?calculations and industrial fixed-bed adsorbers,show that the DMOF has dual control adsorption on C₂H₂ gas.