| With the development of society and the continuous rising of economic levels,people's lifestyles and dietary habits have undergone tremendous changes.The number and proportion of diabetes caused by this are increasing constantly.At present,the diagnosis and routine monitoring of diabetes are mostly achieved through invasive blood glucose detectors,which will bring great physical and mental burden to patients.Acetone is an important biomarker in the exhalation of diabetic patients,and the acetone gas sensor for exhalation detection has become a very potential noninvasive detection device for diabetes.In view of the high humidity,low acetone concentration and complex gas composition in human exhaled breath,the acetone gas sensor have practical application for needs to achieve:1)Humidity-insensitivity;2)Detection limit as low as 50 ppb;3)High selectivity for acetone;4)High Stability.In recent years,metal oxide semiconductor(MOS)sensors represented by ZnO nanorod arrays have been studied and applied widely.However,there are still shortcomings such as humidity interference,ppb level detection limit difficulty,and poor selectivity.At the same time,metal organic frameworks(MOF)as new functional materials have controlled pore structure and a large number of active metal sites,which can be used in the field of gas detection.Combining MOF and MOS can improve the gas sensor performance greatly.This paper is mainly based on ZnO@ZIF-71 nanorod array gas-sensing material,focusing on solving the problems in breath detection,establishing MOF functional gas-sensing mechanism models,and obtaining universal material design ideas.Firstly,the screening ideas of functional MOF materials for breath detection were discussed,and the hydrophobicity,preconcentration and molecular sieving role of MOF in gas sensor was demonstrated.And it is verified that ZIF-71 functional layer can improve the humidity insensitivity and sensitivity by synthesizing ZnO@ZIF-71 material.Then,the acetone sensing material with high sensitivity and selectivity was obtained through the introduction of metal ions and polymer separation membrane.And its catalytic gas sensing mechanism and diffusion gas sensing mechanism were explored based on the metal catalytic effect and the the selective separation of polymers.Finally,this work obtained a kind of acetone sensor with humidity insensitivity,high sensitivity,high selectivity and stability.First of all,according to the properties and structural characteristics of MOF materials,ZIF-71 were selected as a functional MOF material.By comparing the thermal and chemical stability of different MOF materials,the correlation between the pore size and the selectivity,ZIF-71was selected due to the appropriate pore size.It can avoid the interference of larger molecular gases to improve the selectivity to acetone.Then,the interaction between the pore structure of ZIF-71 and the target gas was analyzed through density functional theory,so as to predict that ZIF-71 has the potential to improve gas sensitivity.Combining the four dimensions of stability,humidity insensitivity,selectivity and sensitivity,ZIF-71 is a suitable functional MOF material for breath detection.Secondly,according to the material screening and pre-judgement results,this study prepared the ZnO@ZIF-71 nanorod array by self-templated solvothermal method to verify the ZIF-71 functional coating layer can improve the gas-sensing performance.Through the gas sensing performance test,the composite material has a higher response value(increased by 100%),a lower detection limit(reduced by 75%),and a faster response and recovery rate(increased by 48%and 31%)and humidity insensitive characteristics.The structure-activity relationship between ZIF-71 coating and acetone gas-sensitivity performance are discussed by in-situ infrared spectroscopy and temperature-programmed desorption test.It is proved that the metal sites in the ZIF-71 structure have physical adsorption of acetone molecules.Then,pre-concentration and enrichment of acetone is realized,so that a higher concentration of acetone gas is brought into contact with the surface of ZnO.By establishing pre-concentration gas sensing mechanism,it is proved that the ZIF-71 coating layer can improve the acetone gas sensing performance effectively.In addition,as regards to the low concentration of acetone in diabetic breath detection,the microstructure of ZnO@ZIF-71 is adjusted by introducing a metal ion Co2+doped ZIF-71 framework in this work.It can improve the sensitivity and reduce the detection limit from the perspective of the catalytic activity of metal ions.By comparing the gas-sensing performance of materials with different cobalt doping concentration at different operating temperature,the response value of ZnO@ZIF-71(Co)nanorod array sensing material is enhanced 100 times than that of the undoped material,and the response to 1 ppm acetone reaches 12.5,the experiment detection limit reaches 50 ppb.Through temperature programmed desorption and density functional theory calculation,the catalytic activation of adsorbed oxygen during the gas-sensing reaction,the catalytic decomposition process of acetone and the interaction of decomposition products on the surface of ZnO were analyzed to established catalytic gas sensing mechanism.Next,the ZnO@ZIF-71 nanorod structure coated with vapor deposited Polydimethylsiloxane(PDMS)nano film improved the anti-interference ability of ethanol in acetone detection.The selective separation of ethanol and acetone gas is achieved by using the difference in the dissolution and diffusion properties of ethanol and acetone in the separation membrane.Eventually,the response of ethanol is reduced,and the selectivity of acetone is improved.And by analyzing the solubility of ethanol and acetone in PDMS and molecular dynamics calculations to simulate the diffusion process and diffusion coefficient,a diffusion gas sensing mechanism is established.Acetone molecules have a higher affinity for PDMS molecules,resulting in better solubility than ethanol.And the hydrogen bonding force between the ethanol molecule and PDMS segment makes ethanol more difficult to diffuse in PDMS membrane than acetone.The selective separation of acetone and ethanol improves the selectivity.Finally,combined with multi-dimensional considerations,the ZnO@ZIF-71(Co)@PDMS nanorod array structure was prepared.And it was evaluated in the aspect of various indicators as an acetone sensor for breath detection comprehensively:1)Stable response under humidity conditions;2)The response value to 1 ppm acetone reaches 12;3)Outstanding selectivity to acetone;4)Good Stability.Finally,this work obtained a kind of acetone gas sensor with high-sensitivity,high selectivity,high stability and humidity insensitivity for breath detection. |
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