Preparation Of Perovskite Quantum Dots And Its Application In Food Spoilage Gas Detection

As people’s standard of living improves,the demand for food is gradually changing from subsistence to safety and health.However,food spoilage due to improper storage,transportation and sale of food is a common occurrence,and there is an urgent need for a non-destructive,rapid and real-time method to monitor the freshness of food to ensure food safety.At present,sensory and physical and chemical testing methods are still the mainstream methods for evaluating food freshness,but they are complex,have long test cycles and are destructive to samples.In recent years,gas sensors,represented by electronic noses,have been gradually applied in the field of food safety,with the advantage of non-destructive,fast and real-time monitoring,working on the principle of detecting spoilage gases emitted when food is spoiled and thus evaluating its freshness.Nanotechnology and nanomaterials,as the core of the new generation of gas sensors,provide powerful tools and new development opportunities for the development of all types of sensors,and therefore new sensors with new nanomaterials as sensitive layers show great potential for food detection.With excellent optical properties,perovskite quantum dots are a novel and excellent quantum dot material with great potential as fluorescent probes.Therefore,the aim of this paper is to develop a gas sensor using perovskite quantum dots as a sensitive layer for the detection of food spoilage gases.The main research contents are as follows:1.Preparation and characterization of all-inorganic perovskite quantum dots CsPbX₃（X=Br^-,I^-）.Cesium oleate precursors were synthesized using oleic acid and oleylamine as ligands,and then injected into the corresponding salts（Pb Br₂,Pb I₂）by the hot injection method,and the CsPbBr₃ and CsPbI₃ quantum dots were obtained after purification by centrifugation.The quantum dots were characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM）,dynamic light scattering（DLS）and X-ray photoelectron spectroscopy（XPS）,which demonstrated that CsPbBr₃quantum dots were cubic in phase,CsPbI₃ quantum dots were mixed with cubic and tetragonal phase.The two types of quantum dots with a size of about 10 nm and uniform distribution.The PL peak of CsPbBr₃ quantum dots was about 510 nm and the sample were bright green,while the PL peak of CsPbI₃ quantum dots was about 686 nm and the sample was red,and both samples had good optical properties.Finally,time-resolved photoluminescence（TRPL）was used to analyze the exciton dynamics of the quantum dots.2.An ammonia gas sensor based on perovskite quantum dots was constructed,tested for its ability to detect ammonia gas and investigated for its fluorescence enhancement mechanism.The sensing system was designed and the sensing device based on perovskite quantum dots was prepared.The sensing capability of the sensor was tested at room temperature and the results showed that ammonia has a strong fluorescence enhancement effect on the sensor.The response value of the sensor is linearly dependent on the ammonia concentration in the operating range of 25-350 ppm and the fluorescence change value can be fully recovered.Four cycles of the response-recovery curve were tested at 50 ppm ammonia gas and demonstrated a stable fluorescence response with very fast response and recovery times（approximately 10 s and 30 s respectively）.The fluorescence enhancement of the perovskite quantum dots by ammonia gas was analyzed by TRPL and TA tests to determine the passivation of surface defects of perovskite quantum dots was from ammonia gas,which reduces the surface defects and suppresses nonradiative recombination,resulting in improved optical properties.3.A H₂S gas sensor based on perovskite quantum dots was constructed,tested for H₂S detection and its fluorescence quenching mechanism was investigated.The sensing device based on perovskite quantum dots was prepared and tested for H₂S sensing at room temperature.The results show that as the concentration of H₂S gradually increases,the quantum dots first show a fluorescence quenching effect and then a new gradually red-shifted fluorescence peak can be detected in the near-infrared spectral region,which is the production of Pb S quantum dots.The fluorescence quenching response of the sensor is proportional to the H₂S concentration at 0.1-0.3 ppm,with detection limits as low as 20 ppb;also in the 0.1-1 ppm concentration range,the shift of the fluorescence peak position in the NIR region is proportional to the H₂S concentration.Four cycles of the response-recovery curve were tested at 0.1 ppm H₂S and demonstrated a stable fluorescence response.The efficient fluorescence quenching effect was analyzed by TEM,TA and PL tests and was attributed to the generation of Pb S quantum dots,which causes an increase in the surface defects and the transfer of carriers from the perovskite quantum dots to the PbS quantum dots.