Research On Gas Sensors Based On Cadmium Sulfide Composite Nanomaterials

Monitoring and controlling the emission of flammable,explosive,toxic,and harmful gases in industrial production environments in real-time is crucial for preventing safety accidents,ensuring worker health and safety,and avoiding environmental pollution.Therefore,the development of high-performance sensors capable of accurately and rapidly detecting hazardous gases in industrial environments is of utmost importance.In response to the increasing demand for detection,the design and development of new sensitive materials are fundamental and critical for constructing high-performance semiconductor gas sensors.Semiconductor gas sensors demonstrate great potential in the field of gas detection due to their advantages such as low cost,simple manufacturing,easy manufacturing,all solid state,and small size.However,they still face challenges such as low sensitivity,high detection limits,long response/recovery times,and poor selectivity towards volatile organic compounds（VOCs）.This paper aims to address the practical detection needs of flammable,explosive and toxic gases:hydrogen sulfide（H₂S）,n-propanol,and n-butanol in the field of industrial production safety.With the goal of enhancing the sensitivity,selectivity,reducing the detection limits and improving response/recovery rates of gas sensors,using semiconductor metal sulfide cadmium sulfide（CdS）as the main sensing material,micro-nano structure regulation and surface modification strategies were employed to comprehensively improve the receptor function,transducer function and utility factor of sensing materials and developing functional composite nanomaterials to construct various high-performance gas sensors.The research explored the structure-activity relationship between the microstructure,chemical composition,surface defects,band structure and gas sensing performance,and summarized the sensing mechanisms of each sensor.The main research contents are as follows:（1）A highly sensitive H₂S sensor with a ppb-level detection limit was constructed using pine needles-like CdS/CdO as the sensitive material.Pine needles-like CdS was prepared by hydrothermal method,and an in-situ self-template oxidation method was employed to modify the CdS surface with an oxide layer,controlling the component ratio of the composite materialmaterial CdS/CdO by adjusting the annealing conditions.The response of the sensor based on CdS/CdO annealed at 400°C for 1 hour to 5 ppm H₂S at 200°C was 73.5,exhibiting a ppb-level detection limit（10 ppb）and excellent selectivity.Compared to sensors constructed with sensitive materials annealed under other conditions in this chapter,the sensitivity was increased by at least 4.9 times.The three-dimensional pine needles-like hierarchical structure improved the utility factor of the sensing material,providing a good growth scaffold for CdO.The introduction of CdO played a significant role in modulating the resistance of the sensing material in different gas environments,synergistically enhancing the performance of the sensor for H₂S and achieving precise detection of low concentrations of H₂S.（2）A n-butanol sensor capable of rapid response/recovery and effective detection at low concentrations was developed using tremella-like CdS/PdCu as the sensitive material.Two-dimensional nano-sheets self-assembled hierarchical tremella-like CdS,Pd and PdCu nanoparticles were prepared using solvothermal and co-reduction methods,respectively.The subsequent impregnation method was employed to regulate the content of metal particles on the surface of CdS.The CdS/PdCu sensor modified with 0.3 wt%PdCu nanoparticles exhibited the shortest response（4 s）and recovery（5s）times,as well as the highest response value（21.2）and a detection limit of 2 ppm to100 ppm n-butanol at 230°C.Compared to the sensor based on pristine CdS,sensitivity increased by 3.2 times,and response/recovery times were reduced by 3/1.8 times,respectively.The unique tremella-like morphology provided a large area supporting structure for the dispersion of metal particles and was conducive to the the diffusion of gas molecules.The synergistic effect of bimetallic nanoparticles exhibited stronger catalytic activity compared to single noble metals,leading to stronger chemical and electronic sensitization effects,significantly improving the gas-sensitive performance of the sensor for n-butanol and achieving efficient detection of the flammable and explosive gas n-butanol.（3）A n-butanol sensor with faster detection speed and lower detection limit was developed using one-dimensional rod-like CdS/Ag₂S as the sensitive material.One-dimensional CdS nanorods and CdS/Ag₂S composite nanomaterials with different molar ratios were prepared by one-step solvothermal method.The CdS/Ag₂S sensor with an Ag₂S content of 3 mol%exhibited a response value of 24.5 to 100 ppm n-butanol at 200°C,which is nearly 4 times higher than that of the single-component CdS sensor.Furthermore,the response time and recovery time were reduced to 4 s and 1 s,respectively,and the detection limit was lowered to 0.5 ppm.The one-dimensional single crystal nanorod structure of CdS provided an efficient pathway for electron transport along its axis.The electronic and chemical sensitization of Ag₂S are the main reasons for the improvement of sensor performance.Under the joint action of these two aspects,the sensor achieved rapid detection of low concentrations of n-butanol.And the impact of environmental humidity changes on sensor response has been reduced by introducing humidity compensation.（4）A n-propanol sensor was constructed using CdS/rGO as the sensitive material,which can achieve real-time and ultra-fast detection without being affected by humidity.One-dimensional single-crystal CdS nanorods were prepared by solvothermal method,and the modification content of rGO was regulated through subsequent water bath process.The CdS/rGO sensor modified with 0.5 wt%rGO exhibited a response value of 19.0 to 100 ppm n-propanol at 200°C,along with ultra-fast response/recovery time（1 s/1 s）and strong moisture-interference resistance.Compared to the sensor based on single component CdS,the sensor based on CdS/rGO composite material showed a 13-fold reduction in response time and a 2-fold reduction in recovery time,with an almost3-fold increase in response value.In addition to the structural advantages of CdS single-crystal nanorods,the introduction of flexible rGO layers with a large specific surface area and high charge carrier mobility provided more reactive sites and resistance modulation for the gas sensing process.Meanwhile,the hydrophobic nature of rGO enhanced the moisture-interference resistance of the sensor.Under the combined effect of the above aspects,the sensor achieved rapid and highly sensitive detection of n-propanol gas in high humidity environments.