Construction Of Electrochemical Sensor Based On Metal Organic Framework And Graphene Composite And Its Detection Of NO₂^-

Nitrite,a salt containing NO₂^-,is not only widely present in our living environment,but also a common additive and preservative in the food industry.However,excessive nitrite will not only damage the environment,but also threaten human health.Therefore,it is of great significance for us to develop a method that can accurately measure the nitrite content in food.Through the efforts of the past ten years,a variety of analytical techniques have been developed,such as spectrophotometry^[1,2],fluorescence analysis method^[3],electrochemical method^[4,5],electrochemiluminescence method^[6],chemiluminescence^[7],chromatography^[8],capillary electrophoresis^[9],etc.Electrochemical methods are widely used due to their great advantages such as low cost,high accuracy,simple operation,and rapid on-site detection^[10].An electrochemical sensor is an analysis system composed of a sensor and a sensor based on the electrochemical properties of the sample to be tested.As one of the key technologies for analysis and detection,electrochemical sensors have incomparable advantages over traditional analysis technologies.Therefore,electrochemical sensors have been highly concerned and widely used in environmental monitoring,biomedicine,food safety,etc.In this paper,aluminum-based metal-organic framework materials（CAU-1）,Al-BTC and Al-BTC/r GO composites were used to modify the surface of glassy carbon electrodes,respectively.Three electrochemical sensors,CAU-1/r GO/CHIT/GCE,Al-BTC/CHIT/GCE and Al-BTC/r GO/CHIT/GCE,were constructed and used to detect nitrite.It was studied by electrochemical techniques such as cyclic voltammetry（CV）,chronoamperometry（i-t）,and characterization methods such as scanning electron microscopy（SEM）and X-ray diffraction（XRD）.The research contents are as follows:1.Aluminum-based metal framework CAU-1 material was successfully prepared by solvothermal method.CAU-1/r GO composites were prepared by compounding CAU-1 with graphene.It was characterized by SEM and XRD.The results show that the prepared CAU-1 is well mixed with graphene.Under the optimized experimental conditions,the sensor was used to measure NO₂^-.The results showed that the CAU-1/r GO sensor has a good linear relationship with NO₂^-in the range of 1.0×10^-6～5.0×10^-4 mol/L,and detection limit was1.1×10^-6 mol/L（S/N=3）.The prepared sensor was successfully applied for the detection of NO₂^-concentration in simulated water samples,the recovery rate reached 89.09%～92.77%,and the RSD was less than 2.9%.The good anti-interference and sensitivity of the sensor open up new ideas for the application of aluminum-based MOFs in electrochemical sensors.2.The Al-BTC material was synthesized using acidified aluminum hydroxide suspension and trimesic acid（BTC）under hydrothermal conditions,and characterized by SEM and XRD.The results showed that the prepared Al-BTC displays good crystallization.A new electrochemical sensor Al-BTC/CHIT/GCE was successfully constructed by using Al-BTC as the modification material.Under the optimal experimental conditions,the electrochemical response of the modified electrode to nitrite ions showed a good linear relationship in the concentration range of 1.0×10^-7～5.0×10^-3 mol/L,and the detection limit was 7.0×10^-8 mol/L（S/N=3）.The electrochemical sensor was used to detect the concentration of NO₂^-in simulated water samples,the recovery rate reached 91.7%～102.7%,and the relative standard deviation（RSD）was less than 5.9%,with high accuracy.Compared with the CAU-1/r GO/GCE modified electrode,the Al-BTC/CHIT/GCE has improved response range,sensitivity and accuracy.3.The Al-BTC/r GO composite was successfully prepared by adding 30:1 graphene during the synthesis of Al-BTC.A new electrochemical sensor Al-BTC/r GO/CHIT/GCE was successfully constructed by modifying Al-BTC/r GO composite on the surface of glassy carbon electrode.Under the optimal experimental conditions,the electrochemical response of the modified electrode to nitrite ions showed a good linear relationship in the range of1.0×10^-6～5.0×10^-3 mol/L,and the detection limit was 7.6×10^-7 mol/L（S/N=3）.The Al-BTC/r GO/CHIT/GCE electrochemical sensor was also applied to the detection of NO₂^-concentration in simulated water samples,and the recovery rate reached 101.0%～104.0%,RSD<5.5%,and displayed high accuracy.Although the sensor has no improvement in response range and sensitivity compared with Al-BTC/CHIT/GCE modified electrodes,it has improved in electron transfer speed and anti-interference ability.