Surface Control Of NiO Nanomaterials And Its Sensing Properties

Hydrogenated NiO nanoparticles and NiO octahedrons with exposed clean[111]facets were prepared by hydrogenation and solution thermal method.The morphology,crystal phase,specific surface area,pore structure and surface element composition of these products were characterized by scanning electron microscopy(SEM),field emission electron microscopy(FESEM),X-ray diffraction(XRD),transmission electron microscopy(TEM),infrared spectroscopy(IR),X-ray photoelectron spectra(XPS)and absorption-desorption porosimetry.The gas sensing properties of as obtained hydrogenated NiO nanoparticles and NiO octahedrons were investigated,and the influence of the surface structure on the sensing properties of the products was discussed.Fundamental reason for the enhanced sensing response was clarified,which afforded guidance to design and synthesize advanced gas sensing materials.The results are as follows:(1)The NiO nanoparticles aggregated from nanocrystals with irregular morphology were synthesized via baking the Ni(OIH)2 precursors obtained by mixing NiC12 and NaOH aqueous solutions,and then the as-prepared NiO samples were heated under a H2 gas flow to obtain hydrogenated NiO samples.The influence of hydrogenation on the gas sensing properties was studied,and it was found that the hydrogenated NiO particles exhibited better gas-sensing performance for acetone,formaldehyde,triethylamine and ethanol than NiO particles without hydrogenation,and the gas-sensing performance was further improved with an increase on the hydrogenation time.A concept of the unsaturated Ni atoms with dangling bonds serving as the active sites for the sensing reaction is proposed to explain the difference in the gas-sensing performances of hydrogenated and non-hydrogenated NiO particles.(2)NiO octahedrons with exposed[III]facets were prepared by solution thermal method,and then the as-prepared C1-ion capped NiO octahedrons were soaked by AgN03and NH3 H2O solutions to obtain NiO octahedrons with exposed clean[111]facets.Their gas sensing performances were studied,and it was found that the NiO octahedrons with exposed clean[111]facets exhibited far better gas-sensing performance for acetone,formaldehyde,triethylamine and ethanol than NiO particles and CI-ion capped NiO octahedrons.The excellent gas-sensing performance was attributed to an increase in the density of active sites of the enhanced NiO octahedral.A concept of unsaturated Ni3C atoms on the[111]surface serving as the active sites for the sensing reaction is proposed.In addition,the sensing mechanism is described in detail at atomic and molecule level,which afforded theoretical guidance to design and synthesize advanced gas sensing materials.