Controlled Synthesis Of Ordered Mesoporous Nickel Oxide-based Composite Materials And Their Gas-sensing Properties

Volatile organic compounds(VOCs)pollutants in the atmosphere affect the air quality of the environment,and detecting VOCs at low concentrations is crucial.At the same time,the design and construction of highly active gas-sensitive materials are essential.Ordered mesoporous nickel oxide has been widely used to detect VOCs,but its lower intrinsic activity and single carrier transport mode have severely limited its gas-sensitive performance.The doping modulation strategy effectively solves the problems mentioned earlier and is an essential tool for designing efficient gas-sensitive material systems.This thesis uses a combination of doping strategy and ordered mesoporous structure to optimize the gas sensing performance.A series of ordered mesoporous NiO and NiO ordered mesoporous materials with different Cr content doping(x-Cr-NiO)were synthesized using a nanocasting route.The effects of different Cr content doping ratios and calcination temperatures on the gas sensing properties were investigated.The results showed that the 0.2-Cr-NiO-300(0.2 is the doping ratio and 300 is the calcination temperature)gas sensor(Rgas/Rair=16.15)obtained a more considerable enhancement in response to 1 ppm p-xylene gas compared with the mesoporous NiO-300 sensor(Rgas/Rair<1.2).Meanwhile,the response of 0.2-Cr-NiO-600 gas sensor to 1 ppm p-xylene gas(Rgas/Rair=64.99)is 19.9 times higher than that of mesoporous NiO-600,with a lower detection limit and excellent selectivity.The excellent p-xylene sensing performance is mainly attributed to increased surface trivalent Ni and oxygen defects caused by Cr doping,which reduces NiO cavity concentration and improves gas-sensitive performance.A series of NiO ordered mesoporous materials x-Sn-NiO(x is the doping ratio)doped with different Sn contents were synthesized using a "solvent-free assisted infiltration" nanocasting route combined with calcination.The results showed that the ordered mesoporous Sn-doped NiO materials significantly improved in response to 1 ppm p-xylene.The 0.25-Sn-NiO gas sensor had a high sensitivity(Rgas/Rair=11.66),good selectivity,low detection limit,and excellent stability.Using a "solvent-assisted infiltration" nanocasting route in combination with calcination,an array of various Nb-doped NiO ordered mesoporous materials(x-Nb-NiO)were synthesized.The maximum specific surface area of the ordered mesoporous Nb-doped NiO materials was discovered to be 272 m2·g-1.Investigated were the gas-sensitive characteristics of NiO ordered mesoporous materials doped with various Nb concentrations.In comparison to the mesoporous NiO sensor response to p-xylene at 1 ppm,the results demonstrate that the 0.25-Nb-NiO gas sensor(Rgas/Rair=83.32)has excellent selectivity,a lower detection limit,and good stability.Due to valence differences,Nb species alteration can result in higher levels of oxygen defects and more sub-stable Ni3+,which increases their intrinsic activity.