Directional Construction And Property Of S-containing MOF-5 Analogues,Crystalline Porous Materials With Moisture Resistance

In recent years,due to the wide application in molecular adsorption,separation and purification,energy storage,heterogeneous catalysis,drug delivery,etc.,a number of new porous materials were developed,for example,metal-organic framework（MOFs）,covalent organic porous polymer,mesoporous silica,porous graphene et al.Among them,the research of MOFs-based materials has been developed rapidly.As the research further develops,the stability of materials is becoming the key issues,which restricts the practical application of MOFs.Generally,MOFs do not have similar thermal and chemical stability of molecular sieves.Most of MOFs are sensitive to water molecules,and prone to lose its high specific surface area even skeletal structure when exposure to air or immersion in solvents containing little water molecules,which directly limit the practical application of MOFs in industry.Through the rational design and modulation,improving the moisture sensitivity of MOFs materials will help to promote the wide application of MOFs.Based on that,we try to develop resistance-moisture MOFs with expected structure and excellent property,and deeply research the functional properties of new MOFs materials.In this paper,we choose linear dicarboxylic acids with a hydrophobic substituent group（3-methyl-4-phenyl-thieno[2,3b]thiophene-2,5-dicarboxylic acid H₂CH₃PhTDC）as a organic ligand,directional synthesis zinc-based MOF-5 frameworks,it makes zinc-based metal-oxo clusters,which is sensitive to water molecules or other polar molecules,were covered by hydrophobic groups to reduce water molecules to attack quad-core zinc-oxo clusters and improve the stability of MOFs.Finally,the water-stability MOF-5 structure was obtained.In addition,holding the framework unchanged,transition metal ions Co²⁺ were successfully introducted to Zn₄O clusters by situ synthesis approach,and MOF-5 analogues consisting of heterometallic M₄O（COO）₆ cluster were obtained.We expect that some unique electrical and optical properties of this material are developed by doping metal ions.Considering that there are sulfur-rich atoms in the MOFs,we try to modify Ag⁺ metal ion to MOF-5 analogues directed by the sulfur atoms.Then study the selective absorption capability of Ag⁺ modified MOF-5 analogues.Around the above research,we obtained the following findings:（1）Using carboxylic acid with hydrophobic groups,3-methyl-4-phenyl-thiophene[2,3b]thiophene-2,5-dicarboxylic acid,as the organic ligand.Zn₄O-based metal-organic framework,Zn₄O（CH₃PhTDC）₃（1）,was synthesized by solvothermal method.We explore the stability of compound 1 by powder diffraction experiment and hydrophobic angle measurement experiment.The experimental results show that after introducing hydrophobic groups,moisture resistance of compound 1 was greatly improved in wet conditions.By gas adsorption tests,we systematically study CO2 adsorption property and hydrogen storage capacity of the materials.Surface photovoltage performance test（SPS）indicates that compound 1 is n-type semiconductor material.（2）Co²⁺ transition metal ions was successfully introducted to Zn₄O clusters by situ synthesis approach,and MOF-5 analogues containing heterometallic clusters,CoZn₃₀（CH₃PhTDC）₃（2）and Co1.4Zn_2.6O（CH₃PhTDC）₃（3）were obtained:UV and fluorescence spectra show that after Co2 + metal ions were doped,the UV-Vis absorption of MOFs material was explanded into the visible region.At the same time,the better fluorescence property of the material was given.Surface photovoltage performance test（SPS）indicates that the conductor type of compound 2 and 3 was changed comparing to 1.The type of conductor transform from n-type to p-type,and characteristic peak intensity was significantly enhanced,which shows that Co²⁺ metal ions were doped to make conductivity type changing,and the conductivity also is promoted.It may be caused by energy band changes of the system.（3）Ag⁺ modified classic MOF-5 analogue Ag_0.36Zn₄O（CH₃PhTDC）₃（i.e.Ag（I）@1）was successfully obtained by dipping method.We investigated the selective absorption properties of Ag（I）@1 for styrene molecules and toluene molecules.Preliminary results indicate that Ag（I）@1 have good selective absorption properties for styrene molecule by comparing with 1.Surface photovoltage performance test（SPS）shows that after modifying Ag⁺,the conductor type of crystals changed:the type of conductor transform from n-type to p-type,and characteristic peak intensity was significantly enhanced,which indicates that after modifying Ag⁺,the conductivity type of crystal material changes and the conductive ability also is promoted.