Synthesis And Properties Of Novel Vanadoborates

Polyoxometalate?POM?material is an old topic that has been vigorously developed for more than 200 years,forming a distinctive class of inorganic metal-oxygen cluster compounds.Due to their novel structures and distinctive physical–chemical properties,POMs have been applied to many fields as diverse as catalysis,medicinal chemistry,electrochemistry,energy storage,optics,and as molecular and magnetic materials.Polyoxovanadoborates are a growing family among the polyoxometalates,which miraculously combine the structural characteristics of the borates and vanadates.Due principally to their structural plasticity that vanadium atoms present in different oxidation states,vanadoborates exhibit diverse structural architectures combined with multitude practical applications.Till now,a large number of vanadoborates have been observed,and their anionic structures have been extended from isolated clusters to 1D chain,2D layer and 3D framework structure.Although great progress has been made in the synthesis of vanadoborates,as well as the research of their properties in catalysis,magnetism and nonlinear optics,no investigation on their ion-conducting properties has been conducted up to now.Therefore,the design and synthesis of novel vanadoborates with ion/proton conduction properties are a promising and meaningful work,which may open new perspectives for developing novel electrode or electrolyte materials used for lithium batteries and other electrochemical devices.In this thesis,based on summary of literature search systematically,many vanadoborates with novel structures have been synthesized on the basis of hydrothermal method.And their synthesis conditions,structures and corresponding properties were also systematically studied.The main work is as follows:1.A new 3-D vanadoborate,Li₁₀[V₁₂B₁₈O₆₀H₆]·28H₂O?1?,was successfully prepared under hydrothermal conditions and structurally characterized.It provides a rare example of POMs constructed from the disordered Li⁺ions and hydrogen bonds.XRD demonstrates that the phase transition exists from crystal phase to glassy phase between 220°C and 400°C.After transformed into glass phase,this material exhibits high Li⁺ion conductivity.To the best of our knowledge,it is the first investigation of ionic conductivity properties in the vanadoborate series.In addition,we also studied the electrochemical properties of compound 1 and its glassy samples at 220°C as lithium battery cathode materials.The test result indicates that the glassy samples exhibited more excellent reversible capacity and rate capability.This finding is fundamentally important,which may open more opportunities for the discovery of novel vanadoborates materials with excellent properties.2.Four new vanadoborates?H₂en?₄H₂[V₁₂B₁₈O₅₄?OH?₆?H₂O?]·11H₂O?2?,?H₂en?₄[V₆B₂₀O₅₀H₈?H₂O?]·5H₂O?3?,H₁₀[V₁₂B₁₈O₅₄?OH?₆]·20H₂O?4?and Na₄[V₁₂B₁₈O₅₄?OH?₆?H₂O?]·?H₂en?₄·2?OH?·3H₂O?5?have been successfully synthesized under hydrothermal conditions.Their structures are all built up from discrete VBO polyanions,together with amine counterions or water molecules.Hydrogen bonds align the polyanions,cations or water molecules of our compounds,through which the respective anionic species are integrated into 3D architectures.Such structural features are particularly desirable for the development of proton conductors.The proton conduction behavior of the four compounds was studied by alternating current?AC?impedance techniques,and their performance in temperature-dependent?at 100%relative humidity?and humidity-dependent?at 293 K?proton conduction was simultaneously investigated.The proton conduction measurements showed that H₁₀[V₁₂B₁₈O₅₄?OH?₆]·20H₂O?4?exhibits more appreciable proton conductivity compared with other three samples.To the best of our knowledge,it is the first investigation of proton conductivity properties in the vanadoborate series.3.Anew3-Dopen-frameworkzincvanadoborate[Zn?en?]₃{V₁₂B₁₈O₅₄?OH?₆?H₂O?}·[ZnO₄H₈]·2H₃O·8H₂O?6?was hydrothermally obtained and structurally characterized.The framework of our compound is made up of trigonal-planar BO₂?OH?groups,BO₄ tetrahedra,VO₅ groups and ZnO₆ polyhedra.Along the a,b,or c axes of the framework,there are 1-D infinite plane-shaped channels constructed by four Zn²⁺cations and four vanadoborate anions,and the size of the pore opening is ca.11.8?7.1?.Magnetic measurement illustrates that compound 6 has antiferromagnetic exchange interactions between metal centers.The photocatalytic activity of compound 6 was evaluated by the degradation of methylene blue?MB?and Rhodamine B?RhB?.The result demonstrated that our compound displays selectively photocatalytic of MB under UV light irradiation.After 2 h of irradiation,the removal rate of MB could reach 92.5%.In addition,we also investigated the activity of compound 6 in the catalytic oxidation of?-Phenethyl alcohol.In order to achieve the optimal reaction conditions,we especially investigated the effect of H₂O₂ dosage on oxidation of?-Phenethyl alcohol to acetophenone.Through the analysis of the experimental results,we found that the 4mL is the ideal H₂O₂ dosage.4.A new vanadoborate[Co?en?₃]₄[V₁₁B₂₄O₆₉H₅]·H₃O·7H₂O?7?has been hydrothermally synthesized and structurally characterized.It is the first vanadoborate with a novel B/V ratio of 24/11.The structure of compound 7 is built up from discrete[V₁₁B₂₄O₆₉H₅]^13-clusters,with[Co?en?₃]³⁺complex groups floating around.These complex cations are further interact with the V₁₁B₂₄4 clusters by O-H···O and N-H···O H-bonds,which gives rise to a 3-D supramolecular structure.The pH value used in the synthesis played an important role in the structure of the resulting vanadoborate.