Fabrication Of Nitrite Electrochemical Sensor Based On Oxidized Carbon Fiber Paper

Nitrite pollution caused by excessive use of agricultural fertilizer and food additive has posed serious harm to ecological environment and public health.Only a small amount of nitrite need be inhaled to cause acute poisoning,while the excessive intake of nitrite may cause cancer or even death.Thus,it is of great significance to monitor accurately and quantitatively the nitrite concentration in food products for food quality security as well as human health.Compared with traditional analytical techniques,nitrite electrochemical sensing has aroused more attention because of its simple operation,high sensitivity,fast analysis,and miniature on-site analysis.Commercialized carbon fiber paper（CFP）have been used widely in the fields of electroanalysis owing to their outstanding conductivity,high specific surface area,good stability and environmental friendliness.In this paper,an electrochemical nitrite sensor based on oxidized carbon fiber paper（OCFP）is constructed by simple thermal annealing for the fast and accurate detection of nitrite in mineral water and sausage.The main research contents and results are as follows:（1）Preparation and characterization of OCFP.Different OCFP electrode materials were fabricated via a thermal annealing under the regulation of oxidation temperature and time and investigated by a series of characterization methods.Field-emission scanning electron microscope（SEM）results showed that CFP and OCFP are features a three-dimensional（3D）network structure consisted of interweave carbon fiber bundles with the diameter of about 7.2μm,and the surface roughness of the material increases gradually with the degree of oxidation.X-ray diffractometer（XRD）patterns suggested OCFP has the crystalline structure of graphite.Raman spectra showed that the intensity ratio I_D/I_G for OCFP is substantially higher compared to CFP,indicating that the edge/plane defective sites can be increased by the oxidation treatment.The results of X-ray photoelectron spectrometer（XPS）analyses proved that oxidation can improve the oxygen content and introduce more oxygen-containing functional groups of this material.According to the methylene blue（MB）absorption test,it could be confirmed that OCFP has a larger adsorption surface area.The results of contact angle measurement indicated that the wettability of OCFP has been improved by the oxidation process,which conduce to the mass transfer of nitrite ions on the electrode.（2）The electrochemical performance evaluation of OCFP.The results showed that the excellent catalytic oxidation activity of OCFP may be ascribed to the increased active sites and specific surface areas.Optimal conditions of the detection system were obtained by exploring the effect of electrolyte p H,concentration and applied potential on the electrocatalytic oxidation activity of OCFP toward nitrite.The results of various scan rate test indicated that the oxidation reaction of nitrite is a diffusion-controlled process.I-T curve responses of OCFP under various treatment conditions were evaluated and the results showed that the optimum synthesis condition of annealing is 500℃,2 h.（3）Fabrication of nitrite electrochemical sensor based on OCFP.I-T curve studies suggested that OCFP exhibits excellent sensing performance compared to CFP,with a determination limit of 0.1μM,a limit of detection（LOD）of 0.07μM,a linear response concentration range of 0.1～3838.5μM,a response time of 1 s and a sensitivity of 930.4μA m M^-1 cm^-2.These performance values are comparable or better than those reported nitrite sensors based on noble-or transition-metal materials.The interference study results proved that OCFP electrochemical sensor possesses good anti-interference ability for most electroactive ions.Furthermore,the fabricated electrochemical sensor exhibits high stability,reproducibility,reliable sensing performance in food samples,as well as good practical application value.