Preparation Of Sulfide Colloidal Quantum Dot Film And Study Of Saw Gas Sensor

Over the past 40 years of reform and opening up,China's industrial and society have developed rapidly,and the demand for energy is increasing.Petrochemical energy has long been a huge part of China's energy structure,resulting in increasingly serious air pollution.Nitrogen dioxide(NO₂)is a common outdoor air pollution gas,which can stimulate respiratory organs,cause acute and chronic poisoning,and seriously harm human health.Therefore,it is very important to realize the intelligent analysis of large-scale,real-time online monitoring and change trend of nitrogen dioxide in the atmosphere.In order to meet the needs of building the Internet of things for gas detection environment,it is urgent to develop high sensitivity and low power consumption nitrogen dioxide gas sensors.Surface acoustic wave(SAW)sensor has the characteristics of high detection accuracy,strong anti-interference ability and good stability,and is compatible with MEMS and COMS processes.It has obvious advantages in developing high sensitivity and low power consumption gas sensors.However,the current development ofSAW gas sensor is mostly limited by the sensitive materials deposited in the sensitive area of the sensor,because the preparation temperature and working temperature of these thin film materials are generally high,which hinders the sensor integration,large-scale networking and mobile intelligent terminal applications.The size of the Quantum Dots is small and the gas adsorption activity is high.The good room temperature film-forming property of the Quantum Dots is compatible withSAW devices.In this paper,a newSAW gas sensor based on the colloidal quantum dot film is constructed by using the unique surface effect,size effect andSolvability of the colloidal quantum dot,which can detect NO₂ gas efficiently at room temperature.Through systematic experimental research and mechanism analysis,it can provide experimental and theoretical reference for the development of a new generation ofSAW gas sensor technology for the Internet.The specific research work is as follows:1.Lead sulfide(PbS)colloidal quantum dots(CQDs)were successfully synthesized by cation exchange method.The liquid-phase PbS colloidal quantum dots were successfully integrated into the sensitive region ofSAW device by spin coating method and inorganic ligand replacement method.The effective fusion of the colloidal quantum dots andSAW sensor was realized at room temperature,and theSAW gas sensor based on PbS CQDs was prepared for the first time.The results of gas sensitivity test show that in the preparation process of PbS CQDs film,the use of the methanol solution of Pb(NO₃)₂ for ligand replacement not only changes the frequency response direction of the device to NO₂ gas,but also greatly improves the sensitivity(frequency shift)of the device.When the untreated PbS CQDsSAW gas sensor is exposed to 10 ppm NO₂ gas at room temperature,it shows a negative frequency shift of 2.2 k Hz,and the response recovery time is 487 s and 302 s respectively;while the devices treated with Pb(NO₃)₂ show a positive frequency shift of 9.8 k Hz at the same NO₂ concentration,and the response and recovery time are as low as 45 s and 58 s respectivelyS and showed good stability and selectivity.Finally,based on the classical theory of causingSAW sensor frequency drift and through the design of the contrast experiment,the mechanism of the gas sensing effect of the two devices is analyzed and discussed.It is found that the negative frequency drift of the devices without Pb(NO₃)₂ treatment is mainly due to the mass load effect,while the positive frequency drift of the devices with Pb(NO₃)₂ treatment is mainly due to the elastic effect of the quantum dot film.2.In view of the toxicity of PbS quantum dots,taking the environmentally friendlySnS quantum dots as the research object,SnS colloidal quantum dots were synthesized by heat injection method,and theSnS quantum dot basedSAW gas sensor which can detect NO₂ gas at room temperature was prepared.In order to study the influence of quantum dot size on the gas sensing performance of the sensor,SnS quantum dots with size ranging from 5 to 11 nm were successfully prepared by controlling the reaction time.The results show that when the size ofSnS quantum dots is in the range of 6 to 11 nm,the gas sensing response value of the quantum dots film increases with the decrease of the size.When the size of quantum dots is about 6±0.43 nm,the response to 10 ppm NO₂ reaches 6.6 k Hz frequency shift.The theoretical detection limit ofSnS quantum dot gas sensor is 52 ppb,and the corresponding gas sensing mechanism is discussed.It is found that theSnS quantum dotSAW gas sensor has good selectivity and repeatability.