Heterogeneous Construction Of Copper Oxide Nanoarrays And Their Gas Sensing Properties

Hydrogen sulfide(H₂S)as an industrial raw material is widely used.At low concentrations,it has the odor of rotten eggs.Long-term exposure to low concentrations of hydrogen sulfide will cause damaging to the eyes,respiratory system and central nervous system of exposed personnel.High concentrations will paralyze the olfactory system,and inhalation of high concentrations of hydrogen sulfide will paralyze the respiratory nerve center,resulting in suffocation.Therefore,the detection of hydrogen sulfide gas in the living environment is very necessary.Advances in nanotechnology have enabled the development of nano-sensing materials with various properties,and gas sensors have developed rapidly.Due to the unique reaction of CuO with H₂S gas at different concentrations,various CuO nanomaterials have been developed and applied in H₂S gas detection.However,the current hydrogen sulfide gas sensors still have problems such as high working temperature,poor stability,low sensitivity,and complicated preparation methods.In this thesis,a simple method is applied to design a binder-free CuO nanoarray-based hydrogen sulfide gas sensor,which preserves the original morphology of the gas sensing material to the greatest extent,and can realize the detection of hydrogen sulfide gas at150?.On this basis,the experimental design was carried out from the three aspects of structure,surface and interface to improve its hydrogen sulfide sensing performance.A p/n heterojunction was constructed by sputtering In₂S₃ nanosheets,and the CuO/In₂S₃ heterojunction was transformed into a CuS/In₂S₃ Schottky junction to further improve the gas sensing performance of the CuO nanoarray-based hydrogen sulfide gas sensor,to achieve the detection of hydrogen sulfide gas at room temperature,but the detection concentration is high.On the basis of the previous two works,by optimizing the content of CuO nanoarrays and fabricating CuS shells by anion and cation exchange method to construct a CuO/CuS heterojunction,the sensor realizes the detection of low-concentration hydrogen sulfide gas at high temperature and room temperature.It can meet the needs of hydrogen sulfide gas detection in daily life.The specific research contents are as follows:(1)Binderless tubular H₂S gas sensor based on CuO nanoarrays.Firstly,Cumetal layer was prepared on the surface of Al₂O₃ ceramic tube by DC sputtering method,then Cu(OH)₂ nanoarray was prepared by chemical wet etching method,and then CuO nanoneedle array sensor was prepared by annealing in air.This is an effective method to prepare a binder-free sensor,and then a series of gas-sensing performance tests were carried out.The gas-sensing test results showed that the sensor based on the CuO nanoneedle array responded to 10 ppm H₂S at 150°C It is76.50%,and has good selectivity and long-term stability,which can meet the detection of hydrogen sulfide gas in daily life(2)Switching effect of p-CuO nanotube/n-In₂S₃ nanosheet heterostructures for high-performance room-temperature H₂S sensing.From the structural aspect,the CuO nanotube/In₂S₃ nanosheet heterostructure gas sensor was fabricated by sputtering,etching,subsequent annealing and secondary sputtering without using any binder.This promotes the reaction of the gas on the surface.The switching effect of hydrogen sulfide concentration on the response of CuO/In₂S₃ gas sensor was found during the gas sensing test,which made the carrier concentration at the interface changes,and the mechanism was explored.When exposed to low concentrations of H₂S(<20 ppm),the sensing mechanism can be explained by the gas adsorption model of the CuO/In₂S₃ p-n heterojunction.The sensing mechanism can be explained by the transformation of the CuO/In₂S₃ heterojunction into a CuS/In₂S₃ Schottky junction when exposed to high concentrations of H₂S(>20 ppm).The p-CuO nanotube/n-In₂S₃nanosheet heterostructure gas sensor has a unique potential to detect H₂S gas.This method provides an effective strategy for the fabrication of other binderless gas sensors,which is beneficial to the miniaturization and integration of gas sensors.(3)CuO/CuS core-shell heterostructure for high-sensitivity room-temperature H₂S gas sensing.On the basis of the previous research work,the sputtering time of the copper metal layer was optimized.The experiment was designed from the aspect of structure;the CuO/CuS core-shell heterostructure was prepared by the anion and cation exchange method.In this process,the anion and cation exchange time was controlled to improve the hydrogen sulfide sensing performance of CuO,and the reason of the CuS shell layer can enhance the hydrogen sulfide sensing performance was analyzed.With the increasing of ion exchange time,the surface of CuO will become rougher to provide more active sites for gas molecule adsorption;the reaction on the surface was promoted.Meanwhile,the CuS shell on the CuO surface will become thicker and thicker,and the electron transport on the CuO surface will be modulated at the interface.The sensing characteristics of CuO and CuO/CuS-based sensors at high temperature of 175°C are mainly affected by the concentration of hydrogen sulfide.At low temperature,the sulfurization reaction can proceed spontaneously,so both CuO and CuO/CuS-based sensors can detect hydrogen sulfide gas at high or low temperature.Compared with the pure CuO device,the CuO/CuS-7device exhibited the highest response to 5 ppm hydrogen sulfide at the optimum operating temperature of 25°C,107.63,which was 80.92 times higher than that of the CuO(1.33).XPS analysis results show that the amount of adsorbed oxygen in CuO is more than that in CuO/CuS-7.Therefore,the CuO/CuS-7 sample has better hydrogen sulfide sensing performance.