Application Of Fe₂O₃ Semiconductor Gas Sensor For Rapid Detection Of Trimethylamine In Seafood And Fish

Seafood fish is rich in trace amino acids and unsaturated fatty acids,which are beneficial for strengthening the human immune system,maintaining the metabolic pathways of life and preventing neurological diseases.With the people’s pursuit of high-quality living standards,the demand for seafood and fish in China’s market and even the global market is increasing.However,spoiled seafood not only loses its original nutritional value,but also causes fever,dizziness,diarrhea and other symptoms due to spoilage of ingredients and proliferation of pathogenic bacteria,which seriously endangers people’s health.In recent years,the consumption of spoiled and expired seafood caused by food safety incidents have a bad impact,greatly reducing the public reputation of the brand and seriously endangering the lives of the people.Therefore,judging the freshness and quality of seafood fish is essential to ensure food safety.Trimethylamine（TMA）,as a product of oxidized trimethylamine degradation,is a precursor substance of the traditional carcinogen（nitrosamines）and one of the characteristic gases of seafood fish spoilage.Therefore,the establishment of on-site,accurate and nondestructive food safety techniques for the detection of TMA content in seafood fish is important for people to assess the quality of seafood fish and to protect their health.Gas sensors based on metal oxide semiconductor materials have attracted much attention in the field of detection of trace volatile organic compounds due to their ease of fabrication and high sensitivity.Among them,iron oxide material（Fe₂O₃）,as an environmentally friendly and self-stable n-type semiconductor（E_g=2.1 e V）,is widely used in various fields,including gas sensors,because of its unique physicochemical properties.However,pure Fe₂O₃as a gas-sensitive material has the disadvantages of high self-resistance and high operating temperature,and optimizing the morphology and structure of the material can improve the sensor response performance.In this paper,Fe₂O₃nanomaterials with various morphological structures,bimetallic nanoparticle modification and tin dioxide（Sn O₂）compound were prepared by controlling the morphology of Fe₂O₃,doping sensitizers and compounding other metal oxide materials,and further investigated the effects of the above gas-sensitive materials on the sensitive properties of TMA gas,and discussed the corresponding gas-sensitive mechanisms and the related sensitization mechanisms brought by different optimization methods.The corresponding gas-sensitive mechanisms brought by different optimization methods were discussed,and finally the prepared gas sensors were applied to the freshness detection of actual fish samples,in order to provide a solid theoretical basis and a new detection method for the rapid,portable and nondestructive detection of seafood fish freshness in the field.The main research of this paper is as follows:1.Preparation of Fe₂O₃nanocubes（NCs）based on different morphologies and their application in the freshness detection of Carassius auratus.In this chapter,Fe₂O₃with solid,nucleoshell and hollow cube morphology was prepared by controlled ion exchange reaction time using hydrothermal synthesis of Bruce blue.The hollow cube exhibited the best gas-sensitive performance for TMA,and the response of the sensor based on this material was 6.3 for 200 ppm TMA at the optimum operating temperature（230℃）with response recovery times of 14/91 s.In addition,the Fe₂O₃hollow cube based sensor was tested for the freshness variation of Carassius auratus under ambient storage conditions and based on the above results for the next experiments.Finally,this chapter discusses the sensing mechanism of the above three gas-sensitive materials for TMA gas.2.Bimetallic Au@Pt nanocrystal sensitization mesoporous Fe₂O₃hollow nanocubes for highly sensitive and rapid detection of pseudosciaena crocea freshness at low temperature.Based on the Fe₂O₃hollow NCs material in Chapter 2,it was synthesized Au@Pt bimetallic particles by oil amine reduction and ultrasonic impregnation method,the Au@Pt alloy modification concentrations were 0.5 wt%,1.0 wt%,1.5 wt%,2.0 wt%and 4.0 wt%,respectively.Au/Fe₂O₃and Pt/Fe₂O₃NCs materials were also prepared for comparative study.According to the gas sensing test results,The Au@Pt alloy can significantly improve the gas sensing performance of Fe₂O₃hollow NCs to TMA.The main reason for the enhancement of gas sensing performance may be that the hollow structure of the material provides more active sites,the chemical sensitization of Au and Pt metal elements and bimetallic Au@Pt synergy.Of which,1.0 wt%Au@Pt/Fe₂O₃hollow NCs material shows excellent gas sensing performance at the optimal working temperature of 150℃.The response to 100 ppm TMA is as high as 32,and the response time is shortened to 5s.It also has a good response to low concentration of 1 ppm TMA（response value is 2.1）.In addition,the freshness of pseudosciaena crocea was tested by Au@Pt/Fe₂O₃sensor under different storage time and storage temperature.The test results were verified by gas chromatography-mass spectrometry（GC-MS）,which provides a great possibility for the application of gas sensor in the detection of actual samples.Lastly,the sensing mechanism of Au@Pt/Fe₂O₃hollow NCs gas sensing material for trimethylamine test is also deeply discussed and analyzed.3.Bimetallic Au@Pd nanocrystal sensitization mesoporous Fe₂O₃-Sn O₂hollow nanocubes for highly sensitive and rapid detection of grouper freshness.In this chapter,Bruce blue was synthesized by hydrothermal method,and Fe₂O₃-Sn O₂nanocomposites with hollow cubic structure were prepared by full ion exchange reaction in potassium stannate solution;Then it was synthesized by in-situ reduction Au@Pd.The alloy modification concentrations were 0.5 wt%,1.0 wt%,1.5wt%and 2.0 wt%Au@Pd,respectively.At the same time,pure Fe₂O₃,pure Sn O₂,Fe₂O₃-Sn O₂,Au/Fe₂O₃-Sn O₂and Pd/Fe₂O₃-Sn O₂hollow NCs materials were also prepared for comparative study.According to the gas sensing test results,the Au@Pd/Fe₂O₃-Sn O₂composite can improve the gas sensing performance of Fe₂O₃NCs to TMA,which may be due to the n-n heterojunction structure formed on the surface of Fe₂O₃and Sn O₂,the sensitization of Au and Pd metal elements and bimetallic metals Au@Pd synergy.Of which,1.5 wt%Au@Pd/Fe₂O₃-Sn O₂hollow NCs material shows excellent gas sensing performance at the optimal working temperature of 210℃.The response to 100 ppm TMA is 72,the response recovery time is 4/59s,it also has a good response to low concentration of 1 ppm TMA（response value is 3.1）,and the detection limit is as low as 0.5 ppm.In addition,the freshness of grouper under different storage time and storage temperature was tested by Au@Pd/Fe₂O₃-Sn O₂sensor,and the test results were verified by gas chromatography-mass spectrometry（GC-MS）.Finally,the sensing mechanism of Au@Pd/Fe₂O₃-Sn O₂material for TMA test is also deeply discussed and analyzed.