Preparation And Gas-sensing Properties Of 3D Flower-like MoS₂-ZnO Micro/Nanosphere Sensor

ZnO material has the characteristics of high stability,simple preparation process,low price and controllable morphology,so it is widely used in the detection of different gases.However,the application of pure ZnO sensors is limited due to factors such as higher operating temperature,lower sensitivity and poor selectivity.In this paper,3D flower-like ZnO micro/nanospheres are prepared by thermal evaporation,and the surface is coated with a layer of MoS₂,so as to achieve the purpose of improving the sensitivity of the sensor.The specific research contents are as follows:（1）ZnO nanomaterials with different morphologies were synthesized in different temperature zones,using the method of thermal evaporation,by controlling the ratio of source materials,the heating rate of the high-temperature tube furnace and the generation time and other factors.Among them,the generated 3D flower-like ZnO micro/nanospheres are flower-like micro/nanospheres composed of tapered micro-rod-like structures with a thick bottom and a thin top with uniform length.The flower-like structures are uniformly distributed and do not stack on each other.This unique flower-like structure can increase the specific surface area of nanomaterials and accelerate the transfer speed of gas molecules on the surface of the material.In order to improve the gas sensitivity of 3D flower-like ZnO micro/nanospheres,we evaporated a layer of MoS₂ on the surface of the 3D flower-like ZnO micro/nanospheres to form a 3D flower-like MoS₂-ZnO micro/nanosphere array.（2）The Raman spectrum test results of 3D flower-like MoS₂-ZnO micro/nanospheres show that the two Raman peaks at 383.3 cm^-1 and 407.1 cm^-1 correspond to the two Raman active vibration modes E¹_2g and A_1g of MoS₂,respectively,which indicates MoS₂ was successfully coated on the surface of 3D flower-like ZnO micro/nanospheres.The photoluminescence spectroscopy（PL）test results at room temperature showed that the intrinsic emission peak intensity of 3D flower-like MoS₂-ZnO micro/nanospheres at 385 nm increased,and the intensity of the deep-level emission peak at 499 nm decreased,indicating that the number of defects was reduced.The value of I_UV/I_DLE increases,which helps to reduce the recombination rate of carriers and promote the charge transfer at the MoS₂-ZnO interface.（3）The gas sensors of 3D flower-like ZnO micro/nanospheres and 3D flower-like MoS₂-ZnO micro/nanospheres were prepared by screen printing technology.Using these two gas sensors to test ethanol gas with a concentration of 500 ppm,the test results show that the best working temperature of the MoS₂-ZnO sensor is approximately 240 ^oC,the response time of the MoS₂-ZnO sensor is 30 s,the recovery time is 10 s,and the response intensity is 12.08.The optimal working temperature of the ZnO sensor is approximately 280^oC,the response time of the ZnO sensor is 35 s,the recovery time is 16 s,and the response intensity is 2.06.Compared with the gas sensing performance of the ZnO sensor,the optimal working temperature of the MoS₂-ZnO sensor is reduced by 40 ^oC,the response time is accelerated by 5 s,the recovery time is shortened by 6 s,and the response value of the MoS₂-ZnO sensor is greatly improved.Approximately 6 times the response value of the ZnO sensor.This means that the working temperature and response performance of the MoS₂-ZnO sensor have been well improved,and the sensor has good stability.（4）Sn O₂ nanomaterials and Sn O₂/Li₂Sn O₃ composite nanomaterials doped with different Li contents were synthesized via a simple one-step thermal evaporation method.With the increase of Li doping,the width of nanobelts gradually increased,with the morphology changing from banded structure to standard hexagonal sheet structure.X-ray diffraction patterns showed that with the increase of Li doping,the intensity of Li₂Sn O₃diffraction peaks gradually increased,while that of Sn O₂ diffraction peaks gradually decreased.The Raman scattering spectra indicated that with the increase of Li doping,the peak of Li₂Sn O₃ at 588.8 cm^-1 kept increasing,and the strongest vibration mode A_1g in Sn O₂gradually weakened.X-ray photoelectron spectroscopy revealed that with the increase of Li doping,the surface electrophilic oxygen species in Sn O₂/Li₂Sn O₃ composite nanomaterials greatly increased.Under the condition of light irradiation with a wavelength of 505 nm,the bright current of the Li-doped Sn O₂samples was higher than the dark current,while that of the Sn O₂/Li₂Sn O₃ composite nanomaterials was lower than the dark current.With the increase of Li doping,the positive photoconductivity of the material gradually weakened,and even negative photoconductivity emerged.