Synthesis,Structure Of MOFs Based On Pyridyl Triazine Ligands And Their Derived Carbon Materials' Electrocatalytic Properties For Oxygen Reduction Reaction

Metal-organic coordination polymer(MOCP)or metal-organic framework material(MOF)with an infinite network structure are self-assembled by metal ions or metal clusters and organic ligands through coordination bonds,due to its special structure as well as unique chemical and physical properties,it has received great attentions due to their potential applications in chemical sensing,gas storage and separation,drug delivery,magnetic materials and catalysis.In this paper,seventeen new coordination polymers were synthesized by solvothermal method under different self-assembly conditions based on pyridyl triazine ligands,aromatic carboxylic acid ligands and different metal salts.Two of them were selected as precursors to prepare porous carbon materials for application in electrocatalyzing oxygen reduction reaction.The main research contents and results are as follows:(1)By using 2,4,6-tris(3-pyridinyl)-1,3,5-triazine(3-tpt)as main ligand,aromatic carboxylic acid as ancillary ligand,and Co(II)/Ni(II)/Zn(II)/Mn(II)metal salts,12three-dimensional coordination polymers were synthesized under different self-assembly conditions.Among them,compounds 1-7 possess 1D chains constructed from aromatic carboxylate ligand and metal ion,which are further linked into 3D frameworks by 3-tpt ligands.While in compounds 8 and 9,trinuclear metal clusters are linked by aromatic carboxylate to genrate 3D frameworks,in which 3-tpt ligands are embedded.In compounds 10-12,the adjacent 2D layers constructed from aromatic carboxylic acid ligands and metal ions are further connected by 3-tpt ligands to build up 3D frameworks.(2)By exploiting 2,4,6-tris(4-pyridinyl)-1,3,5-triazine(4-tpt)as the main ligand,aromatic carboxylic acid as the ancillary ligand,and Mn/Zn/Cometal salts,five coordination polymers were synthesized under different self-assembly conditions.In compounds 13-15 and 17,metal ions connect with aromatic carboxylate ligands forming a 2D layer,such layers are further connected by 4-tpt ligands to obtain 3D frameworks.In compound 16,metal ions are linked up by aromatic carboxylate ligands to form 2D honeycomb-like network with 4-tpt residing in the grid.These 2D layers are connected by hydrogen bonds to generate a 3D supramolecular structure.(3)A cobalt-based MOF containing nitrogen atoms(compound 11)was used as the precursor to obtain porous carbon materials CoNC-T(T represents the pyrolysis temperature)and CoNC-800-x(x is the content of g-C₃N₄ in the precursor)through pyrolysis.Among these porous carbon materials,CoNC-800-0.75 exhibits the best catalytic activity for ORR with an onset potential of 0.90 V(vs.RHE),a half-wave potential of 0.79 V(vs.RHE)and a limiting current density of 5.24 m A/cm~2,which are almost equal to those of commercial Pt/C.Moreover,it exhibits much higher stability and better methanol tolerance than Pt/C.(4)A cobalt-based MOF containing nitrogen and sulfur atoms(compound 12)was used as the precursor to prepare porous carbon material CoSNC-T(T represents the pyrolysis temperature)and CoSNC-800-x[x=graphitic carbon nitride(g-C₃N₄),dicyandiamide(DCD),melamine(Mel)]by pyrolysis.Among these porous carbon materials,CoSNC-800-DCD exhibits superior catalytic activity for ORR with an onset potential of 0.94 V(vs.RHE),a half-wave potential of 0.79 V(vs.RHE),and a limiting current density of 6.02 m A/cm~2,indicating better catalytic activity,stability and methanol tolerance than Pt/C.