Synthesis And Performance Study Of VOCs Gas-sensitive Materials With PAMAM As Template

The research of semiconductor gas sensors can be divided into two categories according to the research objectives:One is to synthesize a new gas-sensitive material,and then to explore the gas-sensing properties of the material after the successful preparation.The other is for the purpose of detection of the target gas,that is,to determine firstly the type of gas to be detected,and then to design and synthesize the gas sensing materials that meet the requirements of the target gas detection.The two focus on different problems and purposes,but the main work is basically the same,that is,the preparation of materials and the gas-sensing test to it.This paper focuses on the classical semiconductor gas sensing materials?Tin oxide,it was divided into three chapters according to research content.In the first chapter,a new semiconductor gas sensing material of self-assembled tin oxide microspheres?for short:NSM-SnO₂? was synthesized by a solvothermal method,and the growth behavior and gas-sensitivity of this kind of material are studied emphatically.The second chapter focuses on the detection of formaldehyde gas,which is the leading killer of indoor air pollution,Because the national standard requires that the detection of formaldehyde concentration is extremely low,so the tin oxide quantum dot with high sensitivity in terms of theory is designed and synthesized to realize the detection of formaldehyde under extremely low concentration.In the classification it belongs to the target gas detection for the purpose.In addition,in the field of semiconductor gas sensor,its complex gas sensitive mechanism has not been fully revealed and universally recognized,and the mechanism work has always been important and widely concerned.Therefore,in the third chapter,the author focuses on the exploration of the sensing mechanism.From the perspective of catalysis,the gas-sensitive mechanism of semiconductor gas sensor is discussed by taking the chemical oxygen adsorption reaction as the starting point,and the obtained results are extended appropriately to discuss the problems related to the catalytic treatment of polluted gas.The entire detailed research process and results are listed as follows:1.Study on the synthesis and growth behavior of self-assembled tin oxide microspheres?NSM-SnO₂? and its gas-sensitivity test at highest and lowest operating temperatures.Using Solvothermal Method,the medium polar aprotic tetrahydrofuran solvent,we synthesized a self-assembled tin oxide microspheres with a particle size of??2?m from SnO₂ nanocrystals???5 nm?.Through controlling the reaction temperature and time in the process of reaction,we successfully observed the growth behavior of the tin oxide microspheres.Because the gas-sensitive properties of the material,especially the selectivity and sensitivity of the material,ware largely affected by the operating temperature.Therefore,different from common tests,wer selected two extreme operating temperatures?lowest&highest?to test the gas sensing performance of NSM-SnO₂.It is found that the material has good gas-sensitivity to 0.1ppm H₂S at the operating temperature of 50?,high gas-sensitivity to 1ppm H₂,20ppm CH₄ and 80ppm CO at the operating temperature of 350?2.Synthesis of tin oxide quantum dots by polyamido-amine dendrimer?PAMAM?as a template and its application as a sensing material for formaldehyde gas sensor.Synthesis of PAMAM adopted ethylenediamine and acrylic acid methyl ester as raw materials by repeated the Michael addition and the end of the amidation reaction.We know that PAMAM is featured by multiple cavities,controllable molecular size and numerous metal ion coordination sites in the molecular framework.Tin oxide quantum dots with a particle size of about 3nm and good dispersion were synthesized by microwave assisted solvothermal method.The role of PAMAM template agent in the synthesis process is as follows:Many coordination groups in the molecular skeleton complexed with Sn⁴⁺,so that the decomposition reaction of Sn⁴⁺ was fully dispersed.At the same time,the existence of a large number of cavities and weak viscosity inside PAMAM sphere molecules will hinder the growth and aggregration of the decomposition products,thus the particle size of the tin oxide quantum dots synthesized can meet the requirements??<5.4 nm?,no reunion,and highly dispersed.Quantum dot materials have larger interface energy and larger specific surface area,which will increase the sensitivity of the materials to formaldehyde gas.Gas sensitivity test results show that when the operating temperature of this materials is 90?,the response value of this quantum dot materials to formaldehyde gas?0.1 ppm?is 30?40 times higher than that of other common VOCs gas.In addition,the possibility of PAMAM template reuse was explored,and it was found that 4.5 generation PAMAM could be reused for 3 times,which verified the economy of this synthesis method.3.Study on the mechanism of gas catalytic reaction based on chemisorbed oxygen reaction.In this chapter,the typical n-type metal oxide semiconductor tin oxide catalyst is used as the research object to explore the factors affecting the redox reaction between reducing gas and oxygen on the surface of solid catalyst.The influence factors of redox reaction between reducing gas and oxygen on the surface of solid catalyst which is based on chemical oxygen adsorption were investigated.By considering the four influencing factors of temperature?activation energy?,oxygen concentration,gas diffusion and reducing gas concentration,and combining with the experimental results,the mathematical formula for this chemical reaction was derived.Based on this mathematical model,the factors affecting the selectivity,sensitivity,response time and optimal operating temperature of the gas sensor are revealed,which provides a theoretical guidance for the design of sensitive materials for the gas sensor and the catalytic treatment for industrial?automobile?exhaust gas in the future.It is worth noting that limit to the author's knowledge level and cognitive deficiencies,this model is just one of numerous mechanism theory,its starting point is based on the effect of oxygen anion produced by chemical oxygen adsorption reaction on material resistance,It would be natural if the theoretical explanation contradicted some unknown fact or other mechanism explanation,please absorb selectively.