Study On The Gas-sensitivity And Photovoltaic Performance And Mechanism Of NiO Foam Structure With Exposed {111} Crystal Planes And [111] Oriented NiO Film

The NiO foam structures assembled from NiO nanosheets with exposed {111}facets,Al doped NiO foam structures assembled from NiO nanosheets with exposed{111} facets and[111]orientated NiO thin film were prepared by solution fast combustion method and sol-gel method.The crystal structure,morphology,surface structures,pore structure and specific surface area analyses of the as-fabricated NiO products were performed on X-ray diffraction(XRD),field scanning electron microscope(SEM),field transmission electron microscope(TEM),X-ray photoelectron spectra(XPS),absorption-desorption porosimetry and infrared spectroscopy(IR).The gas sensing properties and photovoltaic effects of as obtained NiO foam structures,Al doped NiO foam structures and[111]orientated NiO thin film were researched,and the impact of the surface structure on the sensing properties and photovoltaic effects of NiO foam structures was discussed.(1)The NiO foam structures assembled from NiO nanosheets with exposed {111}facets were successfully prepared by heating Ni(NO3)2 solution containing polyvinyl pyrrolidone(PVP)at 450-650?.In comparison with the NiO samples obtained at 450-650 ? and NiO particles,these NiO foam structures show significantly higher response to ethanol,formaldehyde and triethylamine than NiO particles,and with the increase of the preparation temperature of NiO foam structure samples,its gas sensing performance is gradually enhanced.We propose that the 3-coordinated unsaturated Ni atoms act as the sensing reaction active sites and present a gas sensing reaction mechanism at atomic and molecular level.(2)The Al doped NiO foam structures assembled from NiO nanosheets with exposed {111} facets were successfully synthesized by heating Ni(NO3)2 and Al(NO3)3 solution containing polyvinyl pyrrolidone(PVP)at 650 ?.The influence of different Al-doping concentrations on the VOC gas sensing performances of NiO foam structures were researched,it was found that the 5%Al doped NiO foam structure show higher sensing performance than other samples.The relationship between the surface atomic structure changes of NiO foam structure and the gas sensing properties was studied.We propose that the 3-coordinated unsaturated Ni atoms and Al atoms collectively act as the sensing reaction active sites and present a gas sensing reaction mechanism at atomic and molecular level.(3)Under the condition of pretreatment temperature are 200-400 ? and post-treatment temperature is 500 ?,different[111]orientated NiO thin film were synthesized on Au substrate by sol-gel method with Ni(CH3COO)2·4H2O,CH3CH2OH and PVP solutions.The influence of different[111]orientated NiO thin film on photovoltaic effect was studied.It was found that with the increase of the TC(111)of NiO thin film,its photovoltaic effect and rectifying properties are gradually enhanced.The relationship between the Ni-NiO(111)surface atomic structure and photovoltaic effect was studied.We propose that the concept of spontaneous electric field existing between polar semiconductor planes and a physical mechanism of photon-to-electron conversion.