Structural Transformation And NH₃ Adsorption Research On Isonicotinic Series Of MOFs

In recent years, haze pollution as one of the most focus pollution in our country has attracted great attention. After studying the causes of haze we found NH3 was an important factor in the formation of haze, ammonium salt content can be as high as 40%-60% in PM2.5. However,10.2 million tons of NH3 has been released into the atmosphere perennial in china, causing serious pollution hazard. But our emphasis on NH3 pollution is not enough, there is no NH3 emission reduction tasks and control measures. Therefore NH3 emission reduction or collection is especially important, so for science and green development, the attention and governance to NH3 is an urgent task. For NH3 emissions processing method, we used the porous adsorbent material to adsorb and collect NH3.Metal-organic framework materials (MOFs), having a special pore structure composed with metal and a multidentate organic ligand, has been researched actively in the last ten years. MOFs with structural diversity, large specific surface area, pore becomes adjustable, flexible structure can change features, making it has attractive application in shape selectivity and chiral catalysis, adsorption and separation, gas storage, optical and magnetic etc. M(INA)2 (M=Cu, Co, Ni, Zn, Cd) have excellent adsorption properties to polar molecules like NH3, and based on the flexible nature of MOFs, this adsorption can achieve reversible structure change. Therefore, this article obtained M(INA)2> M(INA)2(H2O)4 and M(INA)2(H2O)2(NH3)2 by hydrothermal synthesis or transformation, explored the influence of crystal formation laws about metal and ligand ratio, solvent, temperature, crystallization time; studied the adsorption conversion of Cu(INA)2 to I2 and NH3; discussed the NH3 adsorption-desorption transform properties of M(INA)2、M(INA)2(H2O)4 and M(INA)2(H2O)2(NH3)2. Their physical properties about constitute, pore structure, morphology and thermostability were characterized by XRD, SEM, FT-IR, TG-MS, NH3-TPD, BET and elemental analysis. The gas adsorption properties of these materials were tested by various characterization methods. The main contents and results are listed as follows:Firstly, Cu(INA)2 was synthesized through hydrothermal synthesis, with Cu(N(N3)2·3H2O and HINA as the raw material, under the conditions of a mixed solvent of water and ethanol. Studied the ratio of metal and ligand, solvent proportion, temperature and time influence of crystal synthesis, obtained optimum synthesis conditions:Cu(NO3)2·3H2O/HTNA=1:2, solvent H2O/ ethanol=1:1, reaction temperature 80 ℃, reaction time 1 day, synthesized under normal pressure conditions with 20-ml glass vial. What’ more, the by-product Cu(INA)2(H2O)4 was heated by 150℃ dehydration can also obtain Cu(INA)2. Explored the specific structural flexibility transformation properties of Cu(INA)2. Under normal temperature conditions, Three-dimensional Cu(INA)2 can be converted into supramolecular structure Cu(INA)2(H2O)2(NH3)2 through NH3 chemisorption in aqueous ammonia solution or ammonia steam environment, and after 150℃ heated it can be converted to the original structure. At the temperature of 60 ℃-120℃condition, Cu(INA)2 can be transformed into two-dimensional Cu(INA)2l2 by adsorbing I2. Its transformation process relate to transformation temperature and concentration of iodine, appropriate temperature increase and high concentration of iodine both contribute to the transformation. And the material transformed after 150℃heated can also be achieved reversibly converted. Flexible reversible transition properties imply these materials have potential applications in NH3,12 adsorption and storage.Secondly, by the extension of the reversible conversion properties of Cu(INA)2, through hydrothermal synthesis method, series materials M(INA)2(H2O)4(M= Co, Ni, Zn, Cd) and new materials M(INA)2(H2O)2(NH3)2 (M= Co, Ni) was obtained. M(INA)2(H2O)4 and M(INA)2(H2O)2(NH3)2 heated at 150 ℃, both can transform to corresponding M(INA)2 (M= Co, Ni, Zn, Cd). What’s more, M(INA)2 also can transform to M(INA)2(H2O)4 and M(INA)2(H2O)2(NH3)2 through the adsorption of H2O and NH3. Thus verified the reversibly transforming relation between M(INA)2(H2O)4、M(INA)2 and M(INA)2(H2O)2(NH3)2. The converted Cu(INA)2 still holds a good three-dimensional pore structure with a large adsorption capacity to CO2 and CH4, the adsorption is 45.91 cm3/g and 34.85 cm3/g (1 bar,298 K) respectively. The M(INA)2 (M= Cu, Co, Ni, Zn, Cd) series materials have a good NH3 adsorption in aqueous conditions or anhydrous conditions, adsorption effects are (1 bar,298 K):Absorption amount of NH3 in water environment respectively 6.4 mmol/g,6.5 mmol/g,6.4 mmol/g,6.0 mmol/g,5.2 mmol/g. Absorption amount of NH3 in anhydrous environment respectively 13.00 mmol/g,14.14 mmol/g,14.48 mmol/g,9.65 mmol/g,9.97 mmol/g.