Selective Capture And Detection Of Harmful Gases Based On Metal-organic Frameworks

With the rapid development of industrialization,more and more toxic and harmful gases are emitted into the atmosphere,which has not only brought tremendous impact on the human living environment but also seriously endanger the human health and safety.Among them,carbon dioxide and hydrogen sulfide are two representative hazardous gases.Carbon dioxide is mainly derived from power plants that burn fossil fuels and eacerbates the greenhouse effect,therefore,it is necessary to control and reduce carbon dioxide emission.Carbon capture and storage（CSS）technology is an important measure to reduce CO2 emission and precombustion capture,oxy-fule combustion and postcombustion capture are three main carbon capture options.Postcombustion capture is the most feasible and carbon dioxide adsorbents mostly are organic amines in this process.However,organic amines need a lot of energy to regenerated resulting in increased costs.Novel physical solid adsorbents should be developed.As for H2S,on the one hand it causes death at high concentration,on the other hand it is involved in many physiological processes,and abnormal concentration H₂S may be related to Huntington’s,Parkinson’s,and Alzheimer’s,thus the detection of H2S in living systems is of great importance.Fluorescence-based sensing method has been widely used due to high sensitivity,fast response,real-time detection,non-damaging sensing of biological analytes.Still,it have some drawbacks such as small organic molecule probes’toxicity,developing the new kind of H₂S fluorescent probe is needed.With the advantages like high specific surface area,controllable pore structure and various functional groups,metal organic frameworks（MOFs）have shown great potential in gas storage,separation and small molecule sensing.Therefore,considering MOF materials as the research object,we explored the synthesis of novel MOFs and new modification method of MOFs for post-combustion carbon dioxide capture as well as MOF-based probe for H2S heterogeneous fluorescence detection.The main contents of each chapter are summarized as follows:First,we choose 2-hydroxy-1,4-terephthalic acid,2-methyl 1,4-terephthalic acid and2,5-dimethyl-1,4-terephthalic acid as organic ligands to synthesize three new Al-MOFs,named as BIT-72,BIT-73 and BIT-74.These Al-MOFs share the similar crystal structures but different chemical environments inside.Three Al-MOFs are proved to have high thermal stability,high water stability and chemical stability.In addition,BIT-72 has the highest specific surface area of 1618 m²·g^-1 among these MOFs,and furthermore shows the highest CO2/N2 selectivity of 48 at 273 K,1 atm based on ideal adsorption solution theory（IAST）.The selectivity of BIT-73 and BIT-74 are slightly lower（only 36）,but their H2O capacity at P/P0=0.3,283 K are just one-third and one-fourth of the CAU-1 under the same conditions.This work achieves the balanced water sorption and CO2/N2 selectivity by changing the chemical environment inside the pores of Al-MOFs,and these stable Al-MOFs may have potential applications as a water-harvesting system in the dry regions or as water adsorbents for indoor moisture control.Secondly,by in-situ polymerization of 1,2-diethynylbenzene in the MOF-5 pores,composite material PN@MOF-5 were obtained,and its structure and properties were characterized.The pore of PN@MOF-5 is equally partitioned by polynaphthylene,and its CO2 adsorption capacity is doubled at 273 K and 1 atm compared with pristine MOF-5.Furethermore,the CO2/N2 IAST selectivity of PN@MOF-5 is 23 times higher than pristine MOF-5（9 for MOF-5,212 for PN@MOF-5）at 273 K,1 atm.In addition,stability to the humidity of PN@MOF-5 is largely improved compared with MOF-5.Exposure to humid air（>40 h,RH=40%）,its crystal structure,specific surface area and pore size distribution have no changes at all.What’s more,compared with MOF-5,MOF-199 and NH₂-Ui O-66,PN@MOF-5 exhibites good CO2/N2 selectivity and stable CO2 adsorption capacity both in dry and wet conditions simulating carbon dioxide capture in a real postcombustion environment.This abundant combinations of porous materials and conventional polymers will provide versatile material platforms for achieving multi-functions and practical applications.Finally,a new metal organic framework named MN-ZIF-90 was developed through Knoevenagel condensation reaction between free aldehyde groups in the ZIF-90 framework and malonitrile groups.Its structure and properties were investigated as follows.After the modification,the crystallinity and crystal structure of MN-ZIF-90 are the similar with ZIF-90.The malonitrile groups connected onto the ZIF-90 skeleton act as a fluorescence quencher of original frameworks.Based on the Michael addition reaction between HS^-and C=C double-bond of the functional groups of MN-ZIF-90,the fluorescence of the metal organic framework is recovered to achieve fluorescent detection of H2S in the liquid phase with the detection limit of 28μmmol·L^-1.And it can also selectively recognize L-cysteine among ten kinds of common amino acids with the detection limit of 25μmmol·L^-1.In addition,MN-ZIF-90 shows significant negligible cytotoxicity and biocompatibility due to the treatment of He La cells with MN-ZIF-90 in vitro viability assays.Futhermore,through laser scanning confocal microscopy studies,significant blue luminescent signal was observed for He La cells incubated with MN-ZIF-90,and overlay of bright field and fluorescent images further demonstrate that the fluorescence was evident in the intracellular region confirming the capability of MN-ZIF-90 for high-contrast in vitro cell imaging with negligible background.This work highlights the potential of using nano-scale functional MOFs as the novel platform for the design of nontoxic targeting biomolecules and long-term labeling of cells.