Research On Gas Sensor Based On Cu_xO(x=1,2) Micro-Nano Structures

With the rapid development of artificial intelligence and Internet of Things technology,gas sensors have played a vital role in the fields of national defense security,environmental monitoring,medical health,and agricultural production as an important means of collecting gas information.Among them,metal oxide semiconductor gas sensors have the advantages of all-solid-state,high sensitivity,low cost,small size and easy fabrication,and have always been the focus of research in the field of gas sensors.However,the core of constructing high-performance gas sensors is the design and preparation of efficient metal oxide semiconductor sensitive materials,because the morphology,structure,and chemical composition of the sensing materials will significantly affect the performance of the sensor.Compared with N-type metal oxide semiconductors,most P-type oxide semiconductors are transition metal oxides,which show different oxidation states due to the electrons in their atomic d-shells,and show better catalysis effect on most toxic and harmful gases,which means that P-type oxide semiconductors have good potential as sensitive materials to construct high-performance gas sensors.Therefore,in this paper,Cu_xO(x=1,2)micro-nanostructures with different morphologies were prepared by hydrothermal and solvothermal synthesis methods,and research on how to improve their recognition function,conversion function and efficiency of sensitive body utilization and other scientific issues.On this basis,the selectivity and sensitivity of the sensor can be further improved by controlling the Fermi level position of Cu_xO(x=1,2)and the concentration of surface adsorbed oxygen through multi-component recombination and in-situ doping technology.The main research contents are as follows:(1)Double-shelled Cu₂O microspheres assembled from nanoparticles were prepared by one-step solvothermal method at 180?.Scanning and transmission electron microscopy images showed that the average diameter was about 5.2?m,and the thickness of the outer shell and inner sphere diameter were 0.8?m and 3.3?m,respectively.The N₂ adsorption/desorption isotherm curve and pore size distribution test results showed that the double-shelled Cu₂O microsphere-sensitive material had a large specific surface area(66.5 m²g^-1)and a pore size(9.9 nm).In addition,the formation mechanism of the double-shelled Cu₂O microspheres was investigated by controlling the reaction time.We coated the prepared material on the surface of the ceramic tube to make a side-heating sensitive element and test its gas-sensing properties.The test results showed that the double-shelled Cu₂O microspheres sensor exhibited high sensitivity and good selectivity to n-propanol gas(C₃H₈O)at an operating temperature of 187?.The response of the sensor to 100 ppm n-propanol gas(R_g/R_a=11)was twice that of the solid Cu₂O microsphere sensor,and it had fast response time(50s)and recovery time(40 s),good response-recovery properties and long-term stability.The excellent sensitive properties are attributed to the large specific surface area of its double-shell structure,which can provide more active sites,which is beneficial to the surface adsorption of oxygen and the redox reactions.At the same time,the hierarchical hollow structure effectively increases the diffusion of gas molecules and the utilization efficiency of sensitive bodies.(2)Three-dimensional(3D)hierarchical Cu₂O-CuO microflowers assembled from nanorods were fabricated by a one-step hydrothermal method.Scanning and transmission electron microscopy images showed that its average diameter was about2.1?m,and X-ray diffraction and X-ray photoelectron spectroscopy showed that the flower-like structure was composed of Cu₂O and CuO phases.The gas-sensing test results showed that the sensor based on Cu₂O-CuO microflowers not only exhibited a high response value to 100 ppb NO₂ gas(S=5.0)in the presence of various interfering gases(100 ppm)at an operating temperature of 187?,and its response changed by only 4.2%,indicating that the sensor exhibited excellent selectivity and good stability for NO₂.Meanwhile,the sensor had ultra-low detection limit(1.37-5 ppb),fast response(35 s)and recovery time(47 s)for NO₂.In addition,during the humidity interference test,it was found that the sensor still showed high sensitivity and good recovery characteristics to NO₂ even at relatively high humidity(90%RH).The response of the sensor to 10 ppb NO₂ was only reduced by 8.6%compared to 30%RH.The excellent sensing properties can be attributed to the existence of the P-P heterojunction,which modulates the Fermi level position and carrier migration at the interface,which promotes the adsorption and ionization of oxygen molecules,thereby enhancing the sensitive performance of the composite.(3)Cu₇S₄-CuO hierarchical microflowers were fabricated by a simple one-step hydrothermal method,and the effect of sulfur doping amount on the corresponding microstructures was investigated.Scanning and transmission electron microscopy images showed an average diameter of about 2.6?m.The obtained Cu₇S₄-CuO composites were used as a sensitive material to make a side-heating sensitive element,and its gas-sensing properties were tested.The results showed that by changing the ratio of Cu₇S₄ in the composite,the gas sensing performance of the sensor could be regulated.Among them,the ratio of the response of the sensor based on flower-like structure Cu₇S₄-CuO(S/Cu=27 mol%)to the same concentration of hydrogen sulfide and the response of other interfering gases(S_{hydrogen sulfide}/S_others)was between 2 and 20,which showed that the sensor had good selectivity for H₂S.In addition,the sensor had a fast response time(7 s)and recovery time(54 s)to 50 ppm hydrogen sulfide,and could detect H₂S on the order of ppb(1.8%-50 ppb)at 225?.The main reason for the highly sensitive and selective detection of hydrogen sulfide based on the flower-like structure Cu₇S₄-CuO(S/Cu=27 mol%)sensor can be attributed to the synergistic effect between CuO and Cu₇S₄.(4)Six CuO nanostructures with different morphologies were synthesized using Cu₂O nanocrystals as sacrificial templates.Six kinds of CuO sensitive materials with different microstructures were tested for gas sensitivity of straight chain monoalcohols.From the test results,it was found that the gas response values of the six CuO sensors with different structures increased first and then decreased with the increase of the carbon chain length of the monoalcohol molecule.However,when the carbon number of the straight chain monoalcohol was C5(n-pentanol),the response values of the six CuO sensors with different structures all reached the maximum value,especially,the CuO sensor based on the octahedral structure exhibited the best sensitivity to n-pentanol gas,its response and recovery time to 100 ppm n-pentanol were 8 s and 16 s,respectively,and the initial resistance of the sensor within 25 days,the variation range was only 8.9%,which showed that it has good stability.In order to explore the sensitive mechanism of CuO with different structures,we selected the(110)crystal plane of CuO to perform first-principles calculations.The theoretical calculation of the structure showed that the dissociative adsorption energy plays a more important role in the response of the(110)crystal face of CuO to monoalcohol molecules than the adsorption energy.The dissociative adsorption energies of CH₃(CH₂)_n-1OH(n=1-5)increased as the carbon chain increased from C1 to C5,but showed a small decrease in n-hexanol.This trend is consistent with the electrical signal enhancement from C1 to C5 in the sensitive performance test.