Microwave-Assisted Synthesis And Photothermal Conversion Properties Study Of Phosphite-Based Polymolybdates

Energy problem is one of the main problems in the world today.Solar energy is inexhaustible,and this green energy can solve the problem of energy shortage.Photothermal conversion materials,which can convert light into heat energy,are widely used in photothermal therapy,seawater desalination,photothermal catalysis,photothermal imaging and other fields.Polyoxometalates have been widely studied in the fields of catalysis,medicine and energy,because of their unique electronic properties and diversified structures.In this paper,the photothermal conversion properties of polyoxometalates have been investigated and their application prospects in the field of photothermal conversion materials have been expanded.The specific work mainly includes the following two parts:（1）Seven phosphomolybdenum heteropoly acids have been synthesized by microwave-assisted synthesis using phosphite as template.Na₈[Mo₆O₁₈（HPO₃）₄]·8H₂O（1）[（CH₃）₂NH₂]₄Na₁₁[Na Mo₁₂O₃₀（HPO₃）₈]·16H₂O（2）[（CH₃）₂NH₂]₄H₂[Mo₅O₁₅（HPO₃）₂]·2H₂O（3）[（CH₃）₂NH₂]₁Na₁₁[Ni₂Mo₈O₂₂（HPO₃）₁₀]·16H₂O（4）[（CH₃）₂NH₂]₁₂H₅[Ni₃Mo₁₈O₅₄（HPO₃）₁₀（PO₄）]·24H₂O（5）[（CH₃）₂NH₂]₄Na₈[Co₂Mo₈O₂₂（HPO₃）₁₀]·12H₂O（6）[（CH₃）₂NH₂]₁₂Na₅[Co₃Mo₁₈O₅₄（HPO₃）₁₀（PO₄）]·20H₂O（7）Reduced polyoxometalate（compound 2）has been obtained by introducing reducing agent,and four transition metal ions doped polyoxometalates have been synthesized by introducing transition metal salts（compound 4-7）.Compound 1-7 not only have near-infrared absorption and significant near-infrared photothermal conversion effect,but also have high photothermal conversion efficiency and high quality near-infrared photothermal imaging effect.Among them,compound 5shows the best photothermal conversion effect with a photothermal efficiency of 59.42%.The experimental results and theoretical calculations show that compound 5 is favorable for photothermal conversion due to its unique{（HPO₃）₃Mo₆}building unit and small HOMO-LUMO gap（0.317 e V）.The degree of electron delocalization and particle aggregation affect the photothermal conversion effect.It provides a meaningful model for studying the structure-activity relationship between the structure and photothermal conversion behavior of polyoxometalates at molecular level.（2）On the basis of phosphite template,the p H value has been finely adjusted,tellurite template has been introduced,and then three kinds of polymolybdates containing Te have been synthesized.The structures of compounds 8-10 have been accurately analyzed by single crystal X-ray diffraction.[（CH₃）₂NH₂]₂H₁₁[Na₃Mo₁₂O₃₉（HPO₃）_3.5（Te O₃）_1.5]·10H₂O（8）H₄[Na₂Te Mo₆O₂₄]·7H₂O（9）[（CH₃）₂NH₂]₂H₈[Na₆Mo₁₂O₃₉（HPO₃）₄（Te O₃）]·6H₂O（10）It is found that the p H value has a great influence on the structures of polyoxometalates.Their good stability and redox properties have been proved by infrared,ultraviolet,thermogravimetric and electrochemical characterization methods.The photothermal conversion performance of the three compounds have been studied,and it is found that the photothermal conversion effect is affected by the concentration of the compounds,the power density of the laser and the concentration of the reducing agent GSH.The structure-activity relationship between polyoxometalates structure and photothermal properties has been discussed.It is found that the structural elements and spatial dimensions of polyoxometalates affect the photothermal conversion effect.