Preparation Of Modified Co-LDHs Composites And Research On NO₂ Gas Sensing Properties

In view of the problems of high operating temperature,low responsiveness to gas at room temperature,and long-term device damage or even sintering of the traditional semiconductor sensor(MOS),monometallic cobalt layered double hydroxide(Co-LDHs)nanomaterials were first prepared by simple hydrothermal synthesis method in this paper,and modified Co-LDHs composites were prepared by adding surfactant hexadyl trimethylammonium bromide(CTAB)and Ti₃C₂T_x MXene.The material morphology and structures were analyzed by using XRD,SEM,TEM,FT-IR,BET and XPS.The gas sensitivity of materials to NO₂ was tested at room temperature.Furtheremore,the structure-effect relationship of the morphology and properties was analyzed,and the gas sensing mechanism was also discussed.Firstly,using cobalt hexahydrate and 2-methimidazole(MIm)as raw materials,MIm as the functional agent,monometallic Co-LDHs nanomaterials were prepared by adjusting the amount of functional agent MIm.The added addition CM-2 of 28.13 mmol showed a more regular layered sheet morphology structure,the less added CM-1 sample showed a tightly packed sheet structure,and the more added CM-3 showed a fragmented nanosheet structure.Among the three samples,the maximum specific surface area of CM-2 was 48.1 m~2·g^-1,showing superior NO₂ sensing performance over CM-1 and CM-3,and the response to 100 ppm NO₂ was 9.08,with a response time of3.97s and a minimum detection limit as low as 0.1 ppm.Furthermore,three-dimensional mesoporous Co-LDHs nanomaterials were controlled prepared by using CTAB as the template.Compared with monometallic Co-LDHs,modified Co-LDHs nanomaterials exhibited much better gas sensing performance to NO₂.Among them,CCM-2 with nanosheets thickness of 3.8-5.0 nm,had better gas sensing performance to NO₂at room temperature,it had larger surface area(91.4 m~2·g^-1),and better crystallinity in(003)crystal surface,and the gas response to 100 ppm NO₂ was about 2.6 times,higher than CM-2 without surfactant,with a response sensitivity of 23.7,response time below 2 s and detection limit was as low as0.05 ppm,significantly better than CCM-1 and CCM-3 samples.The excellent sensing performance of CCM-2 was attributed to the three dimensional mesoporous structure of ultrathin nanopsheet assembly mediated by CTAB and the presence of the rich chemosorbent oxygen on the surface of the material.Finally,Ti₃C₂T_x MXene,a two-dimensional material with high electrical conductivity,was selected as the base and combined with CTAB modified Co-LDHs to prepare a CCMX composite with a three dimensional hierarchical structure.SEM,TEM,BET and other tests showed that Ti₃C₂T_x MXene with addition of 18 mg had better gas sensing performance,with a gas sensing response of 29.36 to 100 ppm NO₂,which was4.33 times that of CM-2,the best sample of monometallic Co-LDHs,and 1.24 times of the best CCM-2 sample with CTAB modification.The response time of 1.31 s,and the detection limit was as low as 0.01 ppm.The reason was that CCMX composite has a larger specific surface area(127.2 m~2·g^-1),unique semiconductor-metal heterostructure and rich active site,and high electron transmission capacity of MXene interface,which not only improved the adsorption capacity of gas,but also accelerated the transmission speed of gas,which were conducive to improving the gas sensing performance of the material.In this paper,using a simple one-step hydrothermal synthesis method,the modified Co-LDHs composite material with there dimensional hierarchical structure was prepared by the modifying of surfactant and two dimensional plate layer materials.Due to the more active sites and more holes accumulation layer on the surface of the synthetic material,the conductivity was effectively improved.Thus,the modified material exhibits higher gas sensing performance for NO₂ at room temperature.