Research On The Construction And Sensing Characteristics Of Thin Film Materials Containing Polyoxometalates

With the progress of society and economic development,people’s living standards are also improving day by day,and more and more attention is paid to human health status and living environment.However,problems such as food safety,environmental pollution and human diseases are restricting the balanced development of society,and even threatening the health and safety of animals,plants and human beings.Therefore,it is particularly important to develop fast and concise methods for monitoring the content of pollutants in the environment,detecting the content of biomolecules in food,and the content of substances required by the human body and harmful substances.Among many detection methods,electrochemical detection methods have attracted great attention due to their fast,portable,efficient,accurate,and low-cost characteristics.Electrochemical sensors can predict the occurrence of certain risks in advance,so that effective real-time monitoring can be carried out to fully reduce the harm caused by the problem.However,in terms of electrochemical detection,the most critical step is the preparation of the working electrode,because the working electrode directly determines the accuracy and sensitivity of the detection.The most common method for preparing working electrodes for electrochemical detection is to modify the sensing materials on the surface of the electrodes by certain techniques,thereby obtaining functionalized working electrodes.Polyoxometalates are a unique class of inorganic metal-oxygen cluster compounds with well-defined structures,good thermal stability,good solubility,strong acidity,high electron density,and electrochemical and photochemical reversible multi-electron redox activities,which can undergo multi-electron redox process while keeping the structure unchanged,thus showing excellent potential for application in electrochemical sensor research.In this thesis,starting from the preparation of polyoxometalate modified electrodes,various electrochemical sensing materials were prepared by using different synthetic methods and experimental methods,showing excellent electrochemical detection performance.Its main research contents are as follows:（1）Phosphomolybdate(PMo₁₂)with redox properties was selected to detect ascorbic acid（AA）through the redox reaction between it and AA with reducing properties.Through a simple electropolymerization method,mixed components ofβ-cyclodextrin（β-CD）,polyaniline（PANI）,and PMo₁₂ were deposited onto the electrode surface to construct a sensitive electrochemical sensor for the detection of AA.First,β-CD was electropolymerized on ITO to form a modified electrodeβ-CD/ITO,and then PANI and PMo₁₂ were copolymerized onβ-CD/ITO film to prepare a composite electrode PMo₁₂-PANI/β-CD/ITO.As a working electrode,it constitutes an electrochemical sensor.And by comparing with ITO,β-CD/ITO,PANI/ITO,PMo₁₂-PANI/ITO thin film electrodes,it is proved that the obtained electrode PMo₁₂-PANI/β-CD/ITO has high sensitivity for the electrochemical detection of AA,Low detection limit（15 n M）and wide linear range（0.01-3000μM）.Furthermore,the developed electrodes were used to detect AA in real samples,showing excellent accuracy and reproducibility,confirming good practicality,portability,and cost-effectiveness.（2）Four phosphotungstates(H₃PW₁₂O₄₀:PW₁₂,K₆P₂W₁₈O₆₂:P₂W₁₈,K_12.5Na_l.5[Na P₅W₃₀O₁₁₀]·15H₂O:P₅W₃₀,K₂₈Li₅H₇P₈W₄₈·92H₂O:P₈W₄₈)with the same composition and different structures were selected to realize the detection of 2,4-dinitrophenylhydrazine through the redox reaction between them.Four kinds of phosphotungstates were assembled on the electrode surface to make four kinds of thin-film electrodes by means of layer-by-layer self-assembly.The growth process of the components on the thin film was monitored and characterized by means of UV-Vis absorption spectroscopy.Their electrocatalytic reduction performance for 2,4-dinitrophenylhydrazine was investigated.The results showed that the thin film electrode containing P₈W₄₈ exhibited the best performance among the four thin film electrodes.Subsequently,the effects of the number of assembled layers of P₈W₄₈ and solution p H on the sensing performance of the P₈W₄₈-containing thin film electrode were investigated,and the results showed that the thin film electrode containing 7 layers of P₈W₄₈ exhibited the best electrocatalytic activity for the reduction of 2,4-dinitrophenylhydrazine at p H 7 of solution.Under optimized experimental conditions,the sensing performance of P₈W₄₈-based thin-film electrodes was evaluated by cyclic voltammetry（CV）and i-t curves,resulting in a linear concentration range of 1 to 700μM with a detection limit of 0.012μM.In addition,its selectivity,stability,reproducibility,and repeatability were also evaluated,and the results indicated that the developed sensor has good potential utility for the determination of 2,4-dinitrophenylhydrazine in the environment.（3）Four Cu-containing phosphotungstates(HCu PW₁₂O₄₀·n H₂O:Cu PW₁₂,Cu₃P₂W₁₈O₆₂·n H₂O:Cu₃P₂W₁₈,K₇Na₃P₂W₁₈Cu₄（H₂O）₂O₆₈·20H₂O:Cu₄P₂W₁₈,Na₁₆P₄W₃₀Cu₄（H₂O）₂O₁₁₂·n H₂O:Cu₄P₄W₃₀)were selected to detect 2,4-dinitrophenylhydrazine and its metabolites through the reduction peak of tungsten and the oxidation peak of Cu.First,the electrocatalytic performance of four Cu-containing phosphotungstates for the detection of 2,4-dinitrophenylhydrazine and its metabolites in solution was investigated;then,four kinds of Cu-containing phosphotungstates were assembled on the electrode surface to make four kinds of thin-film electrodes by means of layer-by-layer self-assembly.Their sensing properties for the detection of 2,4-dinitrophenylhydrazine and its metabolites were investigated by electrochemical means.The results show that the thin film electrode containing Cu₄P₄W₃₀ exhibits the best detection performance among the four Cu-containing phosphotungstates.Under the optimized experimental conditions,the sensing performance of the Cu₄P₄W₃₀ thin film electrode was investigated by CV technology,showing low detection limit and wide linear range.In addition,its selectivity,stability,reproducibility and repeatability were also evaluated.