Research On The Fabrications And Performances Of Sensors Based On Ionic Conductors Of Iron/niobium Oxide

Electrochemical sensor,as a branch of sensors,is an electrochemical analysis system that can analyze chemical components and generate an electrical signal which is proportional to the concentration of the compounds.The high sensitivity,rapid detection,specificity,stability,and miniaturization made it widely used in industrial production,environmental protection,medical diagnosis,bioengineering etc.Solid-state ionic conductors have been widely used in electrocatalysis,electrochemical capacitors,and rechargeable batteries due to their good chemical stability,thermal stability,wide electrochemical window,high ionic conductivity,high strength and hardness.However,there are few reports on the application of electrochemical biosensors.For the electrochemical dopamine sensor,the electrodes based on electronic conductors or the ionic liquid?IL?have been widely studied.Nevertheless,so far there has been no report on solid-state ionic conductor used as an electrode modifier for DA detection.In principle,the electrochemical redox reaction of dopamine involves the transfer of two protons and two electrons,thus,the development of electrodes based on new solid-state ion conductors is a new direction for the fabrication of electrochemical biosensors at present and in the future.In addition,the gas sensors based on YSZ,LSGM and NASICON electrolyte are by far the most commonly reported electrolyte sensors,but these sensors can not work at room temperature,and their performances will weaken with the increase of humidity,so they can not detect the concentration of exhaled gas in time,which limits their application in medical detection.Therefore,developing a new electrolyte with high ionic conductivity at room temperature and high humidity is an effective way to expand the application.Furthermore,with the rise of the automobile industry,there are more and more reports about the research and application of solid electrolyte oxygen sensors.Among them,the dense diffusion barrier limiting current oxygen sensors based on mixed oxide-ion/electron conductors aroused great interest of researchers,because they not only can make up the shortage of the concentration potential oxygen sensor in term of narrow oxygen concentration detected range,but also avoids the defects of easily blocked for small hole or porous diffusion barriers limiting current oxygen sensor.Compared to the limiting current oxygen sensors with porous diffusion barrier,the sensors exhibite narrrow oxygen concentration monitoring range due to the electrochemical reduction of diffusion barriers at low applied voltage.Therefore,it is necessary to develop new mixed oxide-ion/electron conductors with high decomposition voltage to widen the detection range.In this dissertation,based on the summary of the domestic and foreign literature,we used the hydrothermal method and ion exchange method to prepare K2Fe4O7,Na2Fe4O7 and AgTa0.5Nb0.5O2.52?ATN?.Using these materials,we fabricated new electrochemical dopamine sensors,H2S gas sensor and dense diffusion barrier limiting current oxygen sensor.The principle and performances of these sensors were studied systematically.The main research results are listed as follows:1.The potassium ferrite?K2Fe4O7?was synthesized under hydrothermal conditions and used to prepare the modified electrode?K2Fe4O7/GCE?Using 0.1M PBS?pH=7.6?as supporting electrolyte,K2Fe4O7/GCE electrode as working electrode,Ag/AgCl as reference electrode and Pt as counter electrode,we fabricated a new dopamine sensor.The sensing principle and properties of the electrode were studied by CV,DPV,EIS and chronoamperometry.The results showed that K2Fe4O7/GCE electrode had good electrocatalytic activity for the oxidation of dopamine and the transfer charge is ionic.Compared with published works based on electronic conductor,the sensing performance of the sensor has lower detection limit?0.22?m?S/N=3??,good reproducibility,repeatability and stability,and good selectivity under the interference of ascorbic acid,uric acid,glucose and inorganic ions.In addition,the sensor has been applied to the determination of dopamine in bovine serum and the results were satisfactory.This study provides a new approach for developing electrochemical biosensors based on ionic conducting solid materials.2.In view of the successful application of K2Fe4O7 in electrochemical dopamine sensor,and the disorder of K⁺in K2Fe4O7 crystal structure,we prepared Na2Fe4O7which has similar structure by ion exchange method.The crystal structure was determined by crystal analysis and material characterization.A new dopamine electrochemical sensor was fabricated with Na2Fe4O7.Compared with the dopamine sensor based on K2Fe4O7/GCE electrode,the detection principle of this sensor has not changed,but the electrocatalytic activity and sensing performance are better,the low detection limit is 0.11?m?S/N=3?.And the sensor can also be used to detect the dopamine concentration in bovine serum.3.We use the La0.5Sm0.5FeO3 as sensitive electrode and K2Fe4O7 as solid-state electrolyte to assemble a new solid-state electrolyte H2S gas sensor and the sensing performances at room temperature and high humidity were studied in detail.According to the polarization curve,it can be confirmed that the sensor belongs to mixed potential sensing mechanism.Moreover,the sensor is greatly affected by humidity.The response value of the sensor to 1 ppm H2S?97%RH?can reach 67 mV,and the detection limit is 5 ppb.Compared with the reported room temperature and high humidity H2S sensors,the performance of this sensor has made great progress.Under the condition of room temperature and high humidity,it still has good selectivity and repeatability.These advangtances are expected to be used to detect the concentration of H2S in the exhaled gas of patients with halitosis.The successful fabrication of this sensor provides a new candidate electrolyte material for solid electrolyte gas sensor.4.The oxygen vacancy was introduced by replacing Nb⁵⁺with Ta⁴⁺at B position of perovskite AgNbO3,and the mixed oxide-ion/electron conductor AgTa0.5Nb0.5O2.52?ATN?was prepared.ATN has high electrochemical decomposition voltage.Using ATN ceramic pellet as the dense diffusion barrier and 8YSZ as the solid electrolyte,we demonstrate a novel dense diffusion barrier limiting current oxygen sensor that exhibited a linear relationship between the limiting current and oxygen concentration in range of 1.3-100 mol%at 800?and 1 V.Furthermore,the sensor shows fast response,strong anti-interference,poisoning ability and good long-term stability.The sensor can significantly expand the detection range of dense diffusion barrier limiting current oxygen sensor.