Study On The Construction Of New Metal-organic Framework Materials Based On Triangular Pyridine Carboxylic Acid Ligands And Their Photoelectric Properties

As a new type of functional porous materials,metal-organic frameworks(MOFs)have been a focus of inorganic chemistry in the past decade.The enormous internal surface areas,adjustable pore sizes,and abundant topological framework make them of potential applications in catalysis,magnetism,luminescence,adsorption and new energy storage media.Among the various organic ligands utilized to construct MOFs,pyridine carboxylic acid ligands have a lot of advantages due they combine the coordination modes of pyridine and carbloxylate groups.This dissertation reports the syntheses and properties of a series functional MOFs based on three tripodal pyridine carboxylic acid ligands.The preparation and capacitive performance of porous metal oxides decomposed from designed MOFs have also been investigated and discussed.This dissertation is composed of the following five chapters.Chaper 1 presents not only a brief introduction to MOFs,but also the development of MOFs on the base of pyridine carboxylic acid ligands.The main results of this work have also been outlined.In Chapter 2,pyridine-3,5-dicarboxylicacid(H2pdc),4,4'-(pyridine-3,5-diyl)dibenzoic acid(H2pbpc)and 4,4'-(4,4'-bipyridine-2,6-diyl)dibenzoic acid(H2bpydb)were selected and utilized to construct novel MOFs with lanthanide metal ions(Sm3+,Eu3+,Gd3+,Tb3+,Dy3+ Ho3+ and Er3+)and transition metal ions(Cu2+ and Cd2+)under hydrothermal condition,and fifteen novel MOFs were successfully obtained.Compounds 1-9 are of four type frameworks,which were assembled from H2pdc and small auxiliary ligands(Hga and Hoac).[Ln(pdc)(ga)]n(Ln = Gd(1),Tb(2),Dy(3),Er(4))are 2D isostructures.[Ln(pdc)(oac)(H2O)]n·nH2O(Ln = Sm(5),Eu(6),Gd(7))are 3D isostructures of 3,6-connected flu topological net.[Gd(pdc)(oac)(H2O)2]n·mH2O(8)is a 3D 3,6-connected rutile topological net,and[Tb(pdc)1.5(H2O)]n(9)is a 3D(3,8)-connected network with tfz-d topology.The emission spectra of MOFs 2,6,and 9 exhibit the characteristic bands of the corresponding Ln3+ and the intraligand emissions are absent.The emission spectra of MOFs 3 and 5 exhibit not only the characteristic bands of luminescent Ln3+ but also the emissions arising from the organic ligand,and 5 extra include ligand to Ln3+ fluorescence.The emissions of compounds 1 and 7 both are due to the intraligand charge transfer and ligand to Ln3+ fluorescence.The fluorescence of MOFs 4 and 8 shows the ligand-based emission.[Ho6(?4-OH)(pbpc)8(H2O)8]n·4nH2O(10)and Dy3+/Eu3+-doped largely[DyxEu6-x(?4-OH)-(pbpc)8(H2O)8]n·4nH2O(0 ? x ? 6)(11)are 3D isostructures withnew 3,8,8-connected topology.The emission spectra of MOF 10 show the ligand-based emission.Doped series of MOF 11 both exhibit the characteristic bands of pure Dy3+ and pure Eu3+ related to the ratio 'of Dy3+ and Eu3+.[Tb2(bpydb)2(Hbpydb)2(H2O)]n(12),[GdxEu1-x(bpydb)(HCOO)(H2O)]n·nH2O(0 ? x ? 1)(13),[Cu2(bpydb)2]n(14)and[Cd2(bpydb)2(H2O)]n(15)all are formed by H2bpydb ligands.MOFs 12,14 and 15 are constructed from 1D double helical chain motifs.12 and 15 are 3,5-connected networks but show different types of topology.14 is a 3,6-connected network with alb topology.MOF 13 is of 2D Gd3+/Eu3+-doped largely layer structure.The emission spectra of MOFs 12,14 and 15 all show the ligand-based emission due to the highly conjugated ligands and ???*effect in the double helical chains.In the emission spectra of doped series of MOF 13,when metal ions are pute Gd3+ or Eu3+,they exhibit ligand-based emission and the characteristic bands of corresponding Ln3+.The photoluminescence intensity varies with the ratio of Gd3+ to Eu3+,and reaches to the highest value at 1 to 1.Chapter 3 reported MOFs 16-20 with[M3O(COO)6]trimer building blocks,theircapacitance properties were investigated.[Co3(?3-O)(bpydb)3]n(16)was synthesized from H2bpydb and Co(NO3)2·6H2O,which exibited a 3D 3,3,9-connected 72 topology.MOFs 17-20 are isostructures[M3(?3-OH)(L)3]n(M = Ni(17,20),Fe(18),Co(19);L =H2bpydb(17)and H2pbpc(18,19,20,)),which were synthesized according to the literatures.The peudocapacitors performance of Ni-MOFs(17 and 20)exhibited high specific capacitance of 317 F g-1 and 200 F g-1 at 1 A g-1,respectively.Co-MOFs(16 and 19)exhibit the best cycling stability of constant current charge-discharge,which keep 94.71%and 90.16%of initial capacity over 3000 and 1000 cycles.Fe-MOF of 19 shows lower specific capacitance of 26 F g-1 at 1 A g-1 and the stability of constant current charge-discharge is acceptable,which keeps 87.5%of the initial capacity over 1000 cycles.In our opinion,the specific capacitance of these MOFs are also influenced the internal surface areas.The higher surface areas led to higher specific capacitance.The cycling stability is mianly determined by the metal ions.Mesoporous metallic oxides were prepared by simple solid-state thermolysis fromMOFs 16-20 in Chaper 4,that is,Co304-16(21),NiO-17(22),Fe203-18(23),Co3O4-19(24),and NiO-20(25).The effects of MOF-type and thermolysis temperature on the porosity and capacitance properties of metal oxides were investigated.The themolysis temperature is higher,the degree of crystallinity is higher,but reduced suface area led to lower specific capacitance.With regard to different metal oxides,the specific capacitance and cycling stability of Co3O4 both are the best,which are 114 F g-1(21)and 97 F g-1(24)at 1 A g-1,and keep 96.31%(21)and 105.59%(24)of initial capacity over 3000 cycles.The specific capacitance and cycling stability of NiO are lower than Co3O4.Fe2O3 shows the lowest specific capacitance of 24 F g-1 at 1 A g-1 and cycling stability with keeping 73.68%of initial capacity over 1000 cycles.Chapter 5 presents a brief summing-up and outlook on the work.