Research On Enhancement Method For Trace Exhalation Sensing Based On Functional Modification Of Metal Oxide

Highly sensitive detection of exhaled biomarkers for human diseases at the ppb level helps to improve the efficiency of early disease screening,diagnosis,and treatment,ensuring the physical health and life safety of the people.Gas sensors based on metal oxide semiconductors（MOS）is an effective technical means for trace detection application due to their advantages of flexible design,easy integration,fast response,and no dependence on sample processing.Design and optimization of sensor materials is the key to improving the performance of sensors to adapt to breathe detection.This thesis aims to detect the main exhaled biomarkers for human diseases,focusing on improving the receptor function,transducer function,and utility factor of gas sensitive materials.Through methods such as structure morphology construction,crystal structure regulation,heterogeneous doping modification,and photoexcitation,the gas sensitivity performance of the sensor is improved,achieving trace gas sensing.The main research contents of this thesis are as follows:A design method for porous microsphere heterostructures of Zn₂SnO₄/SnO₂ternary oxides is proposed.A kind of porous microsphere Zn₂SnO₄/SnO₂ ternary oxide heterojunction structure is constructed,and the"synergistic effect"and"interface effect"between the components are used to regulate the surface reaction path of sensitive materials,achieving specific receptor function.The interface heterojunction promotes charge transfer,increases carrier concentration,and improves gas sensitivity response performance.The porous microsphere structure improves the specific surface area,enhances the reaction activity,and improves the adsorption characteristics.The results show that based on the Zn₂SnO₄/SnO₂ porous microsphere composite structure,the response to 1 ppm H₂S is R_a/R_g=1850 at the optimal operating temperature of 160℃,and the detection limit is less than 0.2 ppm.At the same time,the sensor demonstrates excellent selectivity and good long-term stability.Through heterogeneous ion in situ doping technique,the crystal structure and electronic band structure of sensitive materials are regulated to improve the sensitivity performance of MOS gas sensors.2D NH₄⁺doped Mo O₃（AMO）is synthesized in situ by hydrothermal method,and free electrons are injected during the doping process to construct a hexagonal ring crystal structure,which increased the number of exposed active sites.The heterogeneous doping changes the position of the material’s Fermi energy level,reduces the free energy,and improves the conductivity of the sensitive material.The test results show that the sensing performance of 2D AMO for acetone is significantly improved after doping.2D AMO has good response and recovery characteristics to acetone in the range of 0.5-10 ppm,and the response to low-concentration acetone（0.5 ppm）is R_a/R_g=1.14.Constructing gas-sensitive material structure with high surface area,lowering the surface reaction activation energy,and achieving trace gas detection at room temperature.A design method of V₂O₅/PANI hierarchical composite structure NH₃sensitive materials is proposed,which constructed and improved the microstructure of the materials,and improved the utility factor of the materials based on the porous structure.The"coupling effect"of conductive polymers and oxides are utilized to regulate the gas adsorption path and improve the receptor function of materials.The reaction activation energy of the sensitive material is enhanced,and the detection of trace gas at room temperature is achieved.Test results show that V₂O₅/PANI of 20 mol%has good response and recovery characteristics for NH₃ with 0.8-20 ppm at room temperature.The response（R_g/R_a=2.5）for NH₃ with 10 ppm is 2 to 2.5 times higher than pure PANI（R_g/R_a=1.3）and V₂O₅（R_g/R_a=1.07）,and the sensor has better selectivity for NH₃.The rapid detection of ultra-trace gases is achieved by surface modification to increase reactive sites,coupled with excitation using visible light.2D ultrathin non-layered hydroxylated iron oxide（Fe OOH）nanosheets were synthesized using a soluble salt template（Na Cl）method.The introduction of hydroxyl groups through surface modification enriches the active sites of the 2D material surface,regulated the gas adsorption mode,and improved the receptor function and utility factor of the sensing material.By photoexcitation,accelerated gas adsorption/desorption rates,perfects the catalytic activity,and improves the gas sensor performance.The presence of photogenerated electrons holes pair and surface hydroxyl groups can effectively reduce the influence of humidity on the sensor.The test results show that the sensor obtains high response（R_g/R_a=94）to trace NO₂ concentrations（250 ppb）at low temperature（160℃）.By blue light excitation,the response is further enhanced to 138（R_g/R_a）for NO₂ at 250 ppb,and the detection limit is 0.38 ppb.At the same time,the sensor response recovery time is accelerated under blue light excitation.Moreover,it had good selectivity and long-term stability for NO₂,and could realize trace gas detection at room temperature.