Research On The Application Of Cerium-based Composite Materials In Electrochemical Detection Of Nitric Oxide

With the rapid growth of the global population,the production and safe storage of food have become one of the major issues.When some types of stored grains begin to deteriorate,a large amount of saprophytic and pathogenic filamentous fungi,Aspergillus flavus will be produced,and then Aspergillus flavus will produce small biological molecules such as active oxygen and nitrogen in the process of metabolism.Nitric oxide(NO)is one of typical products,so real-time monitoring the changes of NO concentration can be used to assess the storage status of food.However,NO is easy to be oxidized quickly,its biological half-life is short(6 s),and the concentration of NO in the early stage of grain deterioration is very low,which make it very difficult to evaluate the safety of stored grains through real-time monitoring of NO.Electrochemical sensor is a kind of biochemical analysis methods and has attracted much attention due to its low cost,simplicity,rapid analysis,ease of miniaturization,and high sensitivity.Electrochemical sensor provides the possibility of real time in-situ detection of low concentration of NO in complex biological systems.However,to achieve efficient and sensitive detection of low concentrations of NO,electrode modification materials for electrochemical sensors also face great challenges.Based on a lot of researches and summaries of previous works,this paper has carried out a series of research works on how to reduce the background noise of electrochemical sensor,improve the response signal,and realize fast and sensitive detection.Several cerium-based composite materials have been synthesized and the functionalized composite materials have been constructed to be corresponding electrochemical sensor.The main research contents and conclusions are as follow:1.Preparation of Ce-MOF and derived materials to apply in NO detection.Cerium-based materials(especially CeO₂)have abundant oxygen vacancies in the crystal structure,showing excellent adsorption performance for NO,and the reversible redox reaction of Ce between Ce³⁺and Ce⁴⁺can promote the electrochemical oxidation of NO.Therefore,they are often selected as the electroactive nanomaterials for the electrical analysis and detection of NO.In this work,wheat spike-like Ce-MOF materials are prepared by a simple and rapid liquid phase method,and then they are calcined in air and nitrogen atmospheres to derive materials CeO₂ and CeO₂/C.The effects of the composition and microstructure of these materials on the performance of the corresponding electrochemical sensors are discussed.As a result,it is found that the presence of carbon significantly improved the conductivity of CeO₂/C,however,its electrochemically active area also increase significantly,which results in a large background current and make it impossible to achieve sensitive detection of low concentration of NO.Although CeO₂ has a relatively small electrochemically active area,its conductivity is poor,and the response current can not be effectively collected,which greatly reduces the sensitivity of the sensor.Although Ce-MOF still generates a certain background current,it has a moderate electrochemically active area and conductivity,its catalytic activity is significantly improved,and it can effectively collect the response current.The results show that Ce-MOF sensor has a wider linear range(0.036-282?mol/L)and higher sensitivity than CeO₂ and CeO₂/C(0.403?A?M^-1 cm^-2)and the detection limit have also reached nanomolar(6 n M),which is expected to be used for the safety assessment of food storage.2.The construction of CeO₂/C coaxial nanocable and its detection of NOIn order to solve the contradiction between reducing the background current and improving the electrical conductivity of the material,in the subsequent work we are inspired by the unique structure of the optical fiber to detect low concentration NO sensitively.In order to explore the feasibility of this idea,by adjusting the solution composition,spinning parameters and calcination conditions,CeO₂/C coaxial cable and hollow CeO₂ nanotubes are finally synthesized,because of their high catalytic performance deriving from electrospinning technology.Due to the high conductivity of the carbon core and the excellent catalytic activity of the CeO₂ surface,the CeO₂/C sensor has a satisfactory detection limit(1.73 n M),which is 4 times lower than that of CeO₂ nanotubes.The sensor has good selectivity,high sensitivity(0.92?A?M^-1 cm^-2),and fast response time(2 s).When the CeO₂/C coaxial cable is used to detect NO released by aspergillus flavus,an obvious current response is also observed,which indicates that the coaxial cable structure can provide a very good analysis platform for biological detection.3.3D self-assembly MXene/Ce PA and its detection of NO released by Aspergillus flavusHow to overcome the problem of improving the conductivity of materials without increasing the background current becomes the key issue of the next research.According to literature reports,MXene(Ti₂C₃)has excellent conductivity,but the specific surface area is relatively small,which makes it likely to be an ideal sensor modification material.However,similar to other 2D materials,the problems of agglomeration and stacking greatly limit its performance.Therefore,in order to solve these problems,we design 3D MXene with a stable network structure directly from a single 2D MXene into.Through electrostatic self-assembly,and use it to anchor cerium phytate.We used electrostatic interaction to make Ce³⁺adsorb on the negatively charged MXene sheet,and then an environmentally friendly and naturally occurring phytic acid aqueous solution from grain are added to chelate it with Ce³⁺on the MXene sheet to form a cerium complex.The MXene sheets are connected together and self-assembled into a three-dimensional MXene/Ce PA composite material.Although pure 2D MXene has excellent conductivity,its catalytic activity is insufficient.Meanwhile,pure Ce PA has certain catalytic activity but poor conductivity makes it difficult to effectively collect response current.The MXene/Ce PA composite material has very low detection limit(0.28 n M)and good sensitivity(2.14?A?M^-1cm^-2)due to its excellent conductivity and good catalytic activity.Subsequently,the MXene/Ce PA sensor realized in situ monitoring of NO released from Aspergillus flavus under drug stimulation.This work shows that sensors modified electrode with excellent performance can be constructed by designing the function and structure of nanomaterials,which can be used for early detection of stored grain safety.