Preparation And Gas Sensing Properties Of Branch/Spherical-like CdS/MoS₂ Composites

Cadmium sulfide(CdS)is a typical wide band gap n-type metal sulfide semiconductor.It is widely used in many fields,such as photodetector,gas sensor,photocatalysis and so on.Therefore,the synthesis and application of CdS materials are still the research hotspot of semiconductor materials.The main content of this thesis was the study of the CdS synthesis and the gas sensitive performance.The branch-like CdS materials,CdS/MoS₂composites and spherical-like MoS₂/CdS composites were respectively prepared by the hydrothermal method.After characterizing the samples by SEM,TEM,XRD,XPS,EDS,Raman and BET,we tested the gas sensitive properties of CdS and its composites after bonding with MoS₂to toxic and harmful gases and explored the sensitive mechanism.The details are as follows:(1)Synthesis,Characterization and gas sensing properties of branch-like CdSCdS materials were synthesized by hydrothermal method and found to be branch-like,uniform in morphology and well crystalline,which belongs to hexagonal wurtzite type single crystal structure without impurities.The CdS gas sensing detector was then fabricated and placed under an atmosphere of ethanol,propanol,iso-propanol,butanol,iso-butanol,and iso-amyl alcohol at 100 ppm,and the measured responses were 24,28,46,29,24,and 45,respectively,and those for benzene,methylbenzene,acetone,and methanal gases were only 1.5,1.6,2.8,and 12.The above data indicated that the CdS gas sensor exhibited unique selectivity toward alcohols.Then the concentration of alcohol gas above was set to 10,50,100,250,500and 800 ppm for testing,and it was found that it showed a good response in a wide range of concentration.The response and recovery time of CdS gas sensor to ethanol gas was subsequently investigated,and the measured response time was 50 s and recovery time of 20 s.In the repeatability cycle test for ethanol gas,it was found that this gas sensor exhibited good repeatability.(2)Synthesis,Characterization and gas sensitivity properties of branch-like CdS/MoS₂compositesThe CdS/MoS₂composites were synthesized by hydrothermal method with different Cd/Mo molar ratios.And from the characterization results,it was found that the branch-like CdS was tightly integrated with the leaf like MoS₂,and the composites exhibited a branch-like morphology.The BET results indicated that the composites possessed larger specific surface areas than CdS materials.Then the CdS/MoS₂composite gas sensor was made.The response of CM10 gas sensor to 100ppm ethanol and isopropanol was 51 and 94,respectively,which is 2 times higher than that of CdS gas sensor.The response time and recovery time to ethanol were 9 s and 6 s,and the response time and recovery time were shortened to 1/20 and 1/8 of the original respectively.The response of CM20 gas sensor to 100 ppm isopropanol is180,which is 4 times that of CdS gas sensor.From the above results,it can be seen that CdS/MoS₂composite gas sensor has unique selectivity and ultra-high response to alcohols,which may be caused by the special structure of the composite and more effective carrier mobility.Then ethanol,isopropanol and isoamyl alcohol were tested with formaldehyde and acetone as interference gases.It was found that the responsiveness of CdS/MoS₂composite gas sensor had little change,which showed that it had good anti-interference ability.Finally,in the repeated test of 100 ppm ethanol gas within 30 days,it was found that the responsiveness of CdS/MoS₂composite gas sensor did not decrease significantly,showing strong long-term stability.(3)Synthesis,Characterization and Gas sensitivity of spherical-like MoS₂/CdS CompositeOn the basis of the previous chapter,spherical-like MoS₂was successfully synthesized without adding Cd source and MoS₂gas sensor was prepared.It was found that pure MoS₂material hardly responds to alcohols,implying that the alcohol sensitive materials in composites are CdS.Spherical-like MoS₂/CdS composites were synthesized by hydrothermal method with different molar ratios of Mo/Cd.The characterization results show that the bulk CdS material was successfully attached to the spherical MoS₂surface.Then a MoS₂/CdS composite gas sensor was made,with a response of 75 to 100 ppm of propanol,three times that of the CdS gas sensor.Compared with the CdS gas sensor,the MC10 gas sensor shows a higher response to alcohols.The response time of MC10 gas sensor is 20 s and recovery time is 9 s,which is 1/2 of CdS gas sensor.Finally,the fitting curves of concentration and responsiveness are obtained by selecting the responsiveness values to various alcohols at 5,10,50,100 and 250 ppm.The limit of detection is calculated below 100ppb,which shows great application potential in the field of low concentration detection.