Research On The Gas-sensing Properties And Regulation Mechanism Of Mesoporous Nickel Oxides

In recent years,the air pollution problem is becoming more and more serious,the inflammable,explosive,poisonous and harmful gases have seriously threatened industrial production safety and people's health.Therefore,it is urgent to develop gas sensors with high gas sensitivity and to realize effective monitoring and detection of dangerous gases in the environment.Noteworthily,owing to excellent chemical and electrical properties,NiO is considered to be an ideal gas-sensiting material.Howerver,the traditional NiO-based sensors with poor sensitivity still can not satisfy the practical application.In this paper,on the basis of its unique advantages,we adopted mesoporous-structure with high specific surface area,different valence state of metal doping to design and synthesize NiO,aiming to realize the efficient recognition of ethanol gases.At the same time,the physical mechanism of NiO nanostructures was studied.The detail methods are shown as follows:?1?Nickel oxides?NiO?nanowires were synthesized using the ordered mesoporous silica SBA-15 as hard templates with the nanocasting method,and then mesoporous NiO nanowires were separated from the dispersed NiO nanowires by the centrifugation technique.Mesoporous NiO NWs existed in bundles presented the higher mesopores percent.The specific surface area?92.61 m²/g?and bandgap?3.39eV?of the mesoporous NiO NWs were higher than those of the dispersed NiO NWs for the higher mesoporous-structure.Therefore,the mesoporous NiO NWs based sensor exhibited the good sensitivity and fast response-recovery to ethanol at 340?.?2?The mesoporous NiO NWs were synthesized by using SBA-15 silica as the hard templates with the nanocasting method,and then calcined from 550 to 750?.And the grain size increased and specific surface area decreased with the calcination temperature.The higher specific surface area created more active sites for the surface redox reaction,while the larger grain size led to the wider bandgap and thereby improved the material resistance and promoted the formation of a wider hole accumulation layer.The optimized results from the gas-sensing behavior indicated that NiO NWs-650 based sensor exhibited the highest sensitivity to ethanol.Therefore,650?could be used as the suitable calcination temperature foe the preparation of NiO NWs.?3?NiO and iron(Fe³⁺)-doped NiO NWs with the various doping content?from1 at%to 9 at%?were synthesized by using SBA-15 templates with the nanocasting method.All samples were synthesized in the same conditions and exhibited the same mesoporous-structures,uniform diameter and defects.Mesoporous-structures with high surface area created more active sites for the adsorption of oxygen on the surface of all samples,resulting in the smaller surface resistance in air.The impurity energy levels from the donor Fe-doping provided electrons to neutralize the holes of p-type Fe-doped NiO NWs,which greatly enhanced the total resistance.The comparative gas-sensing study between NiO NWs and Fe-doped NiO NWs indicated that the high-valence donor Fe-doping obviously improved the ethanol sensitivity and selectivity for Fe-doped NiO NWs.And Ni_0.94Fe_0.06O_1.03.03 NWs sensor presented the highest sensitivity of 14.30 toward ethanol gas at 320?.?4?Mesoporous NiO and stannum(Sn⁴⁺)-doped NiO NWs were synthesized by using SBA-15 templates with the nanocasting method.The gas-sensing analysis indicated that the Sn-doping could greatly improve the ethanol sensitivity for mesoporous NiO NWs.With the increasing Sn content,the ethanol sensitivity increased from 2.16 for NiO NWs up to the maximum of 15.60 for Ni_0.962Sn_0.038O_1.038,and then decreased to 12.24 for Ni_0.946Sn_0.054O_1.054.054 to 100 ppm ethanol gas at 340?.The high surface area from mesoporous-structure and the vacancies for the high valence Sn-doping both improved the adsorption of oxygen on the surface of NiO NWs,resulting in the smaller surface resistance in air.Owing to the recombination of the holes in hole-accumulation lay with the electrons from the donor impurity level and the increasing the body defects for Sn-doping,the total resistance in ethanol gas enhanced greatly.It was concluded that the sensitivity of Sn-doped NiO NWs based sensor could be improved by the Sn-doping.