The Preparation And (Photo) Electrochemical Performance Of Metal-organic Complexes And Their Composite Or Derived Materials

Metal-organic complexes with periodic structures are composed by metal ions and active sites of organic ligands via self-assembly process.They can be applied in many fields such as gas adsorption,gas storage,chiral separation,ion exchange,biological imaging,drug slow-release,catalysis,photoelectric devices and solar cells,et al.It is ascribed to their novel and diverse topological structures.Thus the syntheses and applications of metal-organic complexes have become a hot research for scientists.In recent years,it emerges a large number of photoelectric materials including perovskite materials in the field of photoelectricity,and the perovskite itself is one of the outstanding optoelectronic materials.Perovskite refers to the material with the chemical general formula ABX₃ and has the identical crystal structure with that of calcium titanates.The perovskite materials possess excellent photoelectric properties,which is due to:?1?the appropriate band gaps;?2?the higher electron-hole mobility and diffusion length;?3?superior structural and point defects;?4?low recombination of electron-hole pairs.However,the perovskite materials have their intrinsic shortcomings themselves.Moisture?H₂O?is the factor which affects the performances of perovskite materials,lager amount of H₂O can destroy the structure of the perovskite,further deteriorating the photoelectric properties of perovskite.Therefore,the modification of perovskite materials has become the intensive research.Insoluble metal-organic complexes being deposited on perovskite materials is an important modifying method.In energy storage material,the metal-organic complex-derived energy storage materials have become the research focus owing to the structural diversity and tunability of metal-organic complexes.It has a profound impact on the fields of lithium ion batteries?Li-ion batteries?,supercapacitors and fuel cells,meanwhile,it provides a referable synthetic route for their electrode materials.Based on the excellent optical and electrochemical performances of metal-organic complexes,in this thesis,utilizing six nitrogen or oxygen-containing ligands,eight metal-organic complexes with novel structures have been successfully synthesized hydro?solvo?thermally.And they have been characterized by single-crystal X-ray diffraction,powder X-ray diffraction?PXRD?,infrared spectrum?IR?,elemental analyses?EA?,thermogravimetric analyses?TGA?,UV-vis spectra?UV-vis?,scanning electron microscope?SEM?and other modern analytic methods.Using Cambridge Sequential Total Energy Package?CASTEP?program,their band structures have been calculated,meanwhile,their thermal stabilities,photoelectric and electrochemical properties have also been investigated.In terms of metal-organic complex-derived materials,they have been characterized by transmission electron microscopy?TEM?,high-resolution transmission electron microscopy?HR-TEM?,selected area electron diffraction?SAED?,N₂ adsorption and desorption isotherm,Raman spectra,X-ray photoelectron spectroscopy?XPS?,energy-dispersive X-ray spectra?EDS?and the corresponding element mappings,meanwhile,the properties of the derived materials as supercapacitor electrode are investigated deeply.The main contents in this thesis are summarized as follows:Firstly,based on 3-?5-?5-?5-?pyridin-3-yl?-2H-1,2,4-triazol-3-yl?thiophen-2-yl?-1H-1,2,4-triazol-3-yl?pyridine?L1?,2,6-di?1H-imidazol-1-yl?pyridin-4-ol?L2?,and 2-?5-?5-bromopyridin-3-yl?-2H-1,2,4-triazol-3-yl?pyridine?L3?,three novel inorganic-organic hybrid materials formulated as[?N-ethyl-pyridine?⁺]₂?N-ethyl-1,3,4-triazole?⁺?Bi₂I₉?^3-?1?,?N-ethyl-pyridine?⁺?PbI₃?^-?2?and?Hpyridine?⁺?PbI₃?^-?3?were in situ-synthesized solvothermally.The N-donors,L1,L2 and L3 were decomposed into?N-ethyl-pyridine?⁺/?N-ethyl-1,3,4-triazole?⁺,?N-ethyl-pyridine?⁺,and?Hpyridine?⁺cations,respectively during the solvothermal process.In compound 1,the in situ-formed?N-ethyl-pyridine?⁺and?N-ethyl-1,3,4-triazole?⁺cations are linked with?Bi₂I₉?^3-via strong H bonds into three-dimensional?3D?supramolecular architecture.While the in situ-formed?N-ethyl-pyridine?⁺cations in compound 2 and?Hpyridine?⁺cations in compound 3 are linked with infinite one-dimensional?1D?Pb-??₂-I?₃-Pb-??₂-I?₃-Pb chains via strong H bonds.Density functional theory?DFT?calculations demonstrate the three compounds have different band structures.And among them,compound 1 possesses the narrowest band gap and it produces the largest photocurrent density under the visible light illumination.Moreover,compounds 1 and 2possess good water-proof properties in aqueous solution,which is probably due to the hydrophobic aromatic cations such as?N-ethyl-pyridine?⁺and?N-ethyl-1,3,4-triazole?⁺in their structures.Secondly,based on 2-?5-?3,5-dibromophenyl?-2H-1,2,4-triazol-3-yl?pyridine?HL?,threemetal?II?complexesformulatedasNi L₂?HL?·DMF?DMF=N,N-dimethylformamide??4?,NiL₂?5?and CuL₂?6?were solvothermally synthesized.Among them,complexes 5 and 6 are isostructural except different metal?II?centers in the structures?four-coordinated planar square geometry?,the metal ions in complexes 5and 6 are Ni?II?and Cu?II?cations,respectively.The three metal?II?complexes all exhibit the mononuclear structures.However,they possess different band structures.DFT calculations reveal complexes 5 and 6 are semiconductors,and they can produce visible light-driven photocurrent response.And their perovskite CH₃NH₃Pb I₃?P?composite materials,5@P and 6@P have yielded much larger photocurrent responses than the individual complexes.It is due to the proper band gap of P as light absorption layer and the matched energy levels between the complexes and P.In addition,the stable photocurrent responses of the two composite materials in aqueous solution suggest that the insoluble complex covered on the surface of P can improve the“water-resisting”property of P.Thirdly,based on 4-?4-oxopyridin-1?4H?-yl?phthalic acid?H₂L₁?and3-?4-oxopyridin-1?4H?-yl?phthalic acid?H₂L₂?,two novel Pb?II?coordination polymers?CPs?formulated as Pb₄Cl₄?L₁?₂?H₂O??7?and Pb₃Cl₄L₂·H₂O?8?were hydrothermally synthesized.DFT calculations revealed the two CPs are semiconductors but have different band gaps.Their valence band?VB?and conduction band?CB?positions were determined by Mott-Schottky curves and UV-visible diffuse reflectance spectra,demonstrating the feasibility of the CPs used in photo-and electro-catalysis for CO₂reduction.The photoelectrocatalytic performance of CP 8 was superior to that of CP 7owing to the more matched CB position of CP 8 with CO₂ reduction potentials.Fourthly,in the field of supercapacitor,according to the synthetic route of Cu/Mo-MOF in the literature,MnSO₄·4H₂O was utilized as Mn source to synthesize a Mn/Mo-MOF precursor[Mn?4,4?-bipyridine?_0.5MoO₄]·1.5H₂O,which possesses the same structure as that of Cu/Mo-MOF.And a bi-metallic MnS/MoS₂/C hybrid was synthesized through calcining and sulfurizing the Mn/Mo-MOF precursor with sulfur powder?S powder?as S source.SEM and TEM images demonstrate that this hybrid material is mainly constituted by MoS₂/C nanorods and MnS/MoS₂/C nanoflakes.The MnS/MoS₂/C hybrid delivers a high specific capacitance of 1162 F g^-1 at 0.5 A g^-1 in 2M KOH electrolyte,and it possesses good rate capacity with a retention of 75.7%(880F g^-1)at 10 A g^-1,which is due to the synergetic effects of the components MnS,MoS₂and carbon matrix in the hybrid material.The carbon matrix in the hybrid material not only can anchor the active components of MnS and MoS₂,but also transport electrons efficiently.The completely exposed Mo and S edges on the preferential 2H-?002?and3R-?003?facets of MoS₂ are beneficial for the electrolyte ion adsorption and the electrochemical reaction.An asymmetric supercapacitor constructed by the MnS/MoS₂/C hybrid?positive electrode?and activated carbon?AC??negative electrode?exhibited a capacitance retention of 81%after 5000 galvanostatic charge-discharge cycles?GCD?.During the GCD process,the metal sulfides were probably transformed into metal hydroxides or oxides in the presence of OH^-electrolyte ions,which can be seen from XPS and EDS analyses.Moreover,the MnS/MoS₂/C hybrid can exhibit visible light-driven photocurrent response.