| With the rapid development of society and the continuous improvement of people's living standards,the ecological environment has also been caused serious pollution and destruction,especially water pollution and greenhouse effect,which has threatened the survival and health of human beings.In view of the problem of water pollution,people urgently need to find efficient,safe,cheap and reliable methods to detect the pollutants such as metal ions,dyes and organic compounds in water.As for the greenhouse effect,CO2 is recognized as the main greenhouse gas in the world.Excessive CO2 emissions by human beings into the atmosphere lead to global warming and a series of environmental disasters,and even threaten the survival of human beings.On the other hand,CO2 as a chemical raw material is relatively cheap and easy to obtain,through the fixation and transformation of CO2to achieve CO2 emission reduction and resource utilization has important strategic significance.At present,the cycloaddition reaction of epoxide and CO2 to prepare cyclic carbonate is a very efficient way of CO2 resource application.The reaction meets the sustainability principle of green chemistry,and the atomic economy reaches 100%.However,due to the chemical inertness of CO2 itself,suitable catalysts must be found in order to catalyze CO2 conversion more efficiently.Therefore,it is of great theoretical and practical significance to design and synthesize fast and sensitive fluorescence sensing materials to detect metal ions and organic molecules in aqueous solution and catalysts that can fix CO2 efficiently and quickly.Metal-organic framework(MOFs)materials have been widely used in the fields of fluorescence sensing catalysis gas adsorption and separation.In this paper,two different metal-organic frameworks{[Zn Ho(TDP)(H2O)]·5H2O·3DMF}n(TIT-1)and{[Co Tb(TDP)(H2O)]·3H2O·4DMF}n(TIT-2)were constructed by d10metal Zn2+/Co2+ions and Ln metal Ho3+/Tb3+ions with the pyridne-containing ligand of2,4,6-tri(2',4'-dicarboxyphenyl)pyridine(H6TDP),which has excellent physical and chemical properties such as cellular nanochannels and good thermal and chemical stability of Lewis acid-base coexistence sites with high porosity and large specific surface area.The results showed that Fe3+(0.17?M)had fluorescence quenching effect on TIT-1,while tryptophan(0.11?M)in aqueous solution had fluorescence quenching effect on TIT-2,which due to the presence of a large amount of carboxyl O in its skeleton structure both atom and N atom,the detection limits of analytes in this paper are much better than those of MOFs previously reported.In addition,TIT-1 and TIT-2 have a conversion rate of more than 90%for the conversion of various epoxides into useful carbonates under mild conditions.A highly stable two-channel porous{[(CH3)2NH2]2[Tm3(BDCP)2(NO3)2(OH2)3]?4DMF?2H2O}n(TIT-3)was designed and synthesized with the ligand 2,6-bis(2,4-dicarboxylic phenyl)-4-(4-carboxyphenyl)pyridine(H5BDCP)and Ln series metal Tm(?).Due to the presence of both the Lewis acid site of Tm3+ion with 6/7 coordination and the Lewis base site of Npyridine atom,C=O group of COO-,which was endowed with high catalytic activity.In addition,Knoevenagel condensation reaction with aldehydes and malononitrile as substrates can also be greatly accelerated under the action of TIT-3.Therefore,these catalytic results prove that Lewis base site NO3-anions were introduced into the open metal site in MOFs,and could improve the catalytic efficiency,which should be attributed to the synergistic effect of the Lewis acid-base active site.The adsorption capacity of TIT-3 to CO2 at 273 K and 298 K was 91.8 cm3?g-1 and 55.6 cm3?g-1,respectively.The study showed that the Lewis acid-base site and porous structure in TIT-3 could greatly help to catalyze the conversion of CO2 and various small-sized epoxides into cyclic carbonate.Under the synergistic action of TIT-3 and co-catalyst n-Bu4NBr,CO2 and various epoxy compounds could be efficiently converted to cyclic carbonate under the reaction conditions of 60?,0.1 MPa and 6 h,and the conversion rate of propylene oxide is up to 99%.In addition,Knoevenagel condensation reaction also has a high yield under the reaction conditions of 50?and 18 h.The yield of condensation reaction between benzaldehyde and malononitrile is as high as 96%.On the basis of synthesis of TIT-3,the amount of solvent and dilute nitric acid in hydrothermal reaction was changed,{(Me2NH2)[Yb4(BDCP)2(?3-OH)2(?2-HCO2)(H2O)2]·5-DMF·H2O}n(TIT-4)and{(Me2NH2)[Ho4(BDCP)2(?3-OH)2(?2-HCO2)(H2O)2]·6DMF·3H2-O}n(TIT-5)were designed and constructed via the H5BDCP ligand.The framework structure of TIT-4 and TIT-5 consists of a unique six-row coplanar{Ln4}cluster of layered triangular micropores and hexagonal mesopores.The inner wall of the channels includes Lewis acid sites that open Ln metal center and Lewis base sites where N pyridine atoms,?3-OH and?2-HCO2 coexist.Due to its structural advantages such as rich bi-functional active sites and nanoscale channels,it has a high catalytic activity for the cycloaddition reaction of epoxy compounds and CO2 under mild conditions.In addition,it could also greatly speed up the Knoevenagel condensation reaction of aldehydes and malonitrile.In summary,five compounds were constructed by the reaction of nitrogen-containing pentahexaecarboxylic acid with metal ions Zn2+,Co2+,Ho3+,Tb3+,Tm3+and Yb3+,and their catalytic properties were studied.The effects of penta/hexadecarboxylic acid flexible ligand,transition metal ions and Ln series metal ions on the regulation of MOFs structure were investigated successively.Compounds TIT-1 and TIT-2 showed excellent fluorescence detection for metal Fe3+ions and tryptophan molecules in aqueous solution,as well as catalytic CO2 cycloaddition reaction.Compounds TIT-3,TIT-4 and TIT-5 had excellent performances in the catalytic cycloaddition reaction of CO2 and Knoevenagel condensation reaction,which provides a certain reference value for the design and construction of more porous MOFs used in the field of fluorescence sensing and catalysis in the future. |
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