Research On The Controllable Preparation And NO₂ Gas Sensitivity Of Hierarchical Structure Of Cobalt-aluminum Double Metal Hydroxide

Aiming at the problems of high operating temperature and low sensitivity of semiconductor sensing materials,in this paper,the structural materials CoAl-LDHs with different morphologies were prepared by urea hydrolysis method,and the morphology was modified by using anionic surfactants?SDS:sodium dodecyl sulfate?and functional template?NH₄F?.Various characterization and test results showed that the layered double hydroxide materials with flower-like structure possessed a higher gas sensing performance for NO₂ gas.The CoAl-CO₃-LDHs materials with two dimensional nanosheet nanostructure were successfully prepared by adjusting the amount of substance between cobalt and aluminum through urea hydrolysis method.The results of XRD,SEM,BET and other characterizations showed that CoAl-CO₃-LDHs?amount of substance at 2:1?CA-2 had the best morphology.Its nanosheet thickness was about 40 nm and the edge length was about 4?m.Also,it had a larger surface area(16.90 m².g^-1)and higher chemisorbed oxygen content?39.9%?.Gas sensing tests illustrated that CA2 exhibited a good response towards 100-0.05 ppm NO₂ at room temperature,the response towards 100ppm NO₂ was 6.58,and the low detection limit could be reach to 0.05 ppm.The high gas sensing performance was due to its large specific surface area and high content of chemisorbed oxygen.In order to improve the gas sensing performance of CoAl-CO₃-LDHs,the three dimensional flower-like CoAl-SDS-LDHs nanostructure were controllable prepared by using anionic surfactants SDS.The results of XRD,SEM,BET and other characterizations showed that as-prepared CoAl-SDS-LDHs?amount of substance at 2:1?CAS-2 possessed thinner nanosheet?6 nm?,larger surface area(29.75 m².g^-1)and higher chemisorbed oxygen constent?35.79%?.Compared with CA-2 nanosheet,CAS-2exhibited much more excellent gas sensing properties in response and detection limit.The response of flower-like CAS-2 toward 100 ppm NO₂ was 18.11,which was 2.75times that of the CA-2 sample.And its detection limit was deduced from 0.05 ppm to0.01 ppm.The addtion of SDS was not only enlarged surface area but also effectively explanded the interlayer spacing.The change from two dimensional structure to three dimensional structure ultimately improved the gas sensing performance of the material.To further improve the gas sensing performance of the two dimensional materials,on the basic of CoAl-CO₃-LDHs nanosheet,the three dimensional CoAl-NHF-LDHs materials were controllable prepared by adding functional template agent NH₄F.The results of XRD,SEM,BET and other characterizations showed that as-prepared CoAl-NHF-LDHs?amount of substance at 2:1?CAF-2 presented the best morphology.It possessed ultrathinner nanosheet?3.068 nm?,much more larger surface area(49.45m².g^-1)and more higher chemisorbed oxygen content?24.91%?.Gas sensing test illustrated that the CAF-2 exhibited an excellent response towards 100-0.01 ppm NO₂ at room temperature.The response towards 100 ppm NO₂ was 26.11,which were 3.97 and1.45 times that of CA-2 and CAS-2,respectively.Its detection limit could reach to 0.01ppm.The addition of NH₄F not only made nanosheet easier to become ultrathin,and thus form three dimensional flower-like structure,led to increase the surface area,but also enhanced the carrier density and decreased the charge transfer resistance,which were the main reasons for further improving the gas sensing performances.Therefore,NH₄F as a template could be an effective way to improve NO₂ gas sensing performance.