| This paper focused on the synthesis of Tin dioxide (SnO2) nanowires viasolvothermal method. The effects of reaction temperature, reaction time and additiveagent on the structure and morphology of the samples were studied by a series ofcharacterization. The side-heating gas sensors were constructed from as-preparednanomaterials. The gas sensing properties of the side-heating gas sensors were tested.The relationships between the exposed crystal facets of the (SnO2) nanowires andtheir gas sensing properties were also experimentally and computationally studied bygas response investigation and first-principles calculation. The results can besummarized as follows:1. Single-crystalline SnO2nanowires with an average0.8μm in length and20-30nm in width were sovolthermally synthesized. The samples are characterizedby X-ray diffraction (XRD), transmission electron microscopy (TEM), highresolution transmission electron microscopy (HRTEM), and energy dispersivespectrometer (EDS) measurements. The effects of reaction temperature, reactiontime, additive agent on the structure and morphology of the samples were studied.The growth mechanisms of the one-dimensional tin oxide nanomaterials were alsoinvestigated. It was found that an intermediate phase (Na2Sn(OH)6) in ethanol/watermedia and difference in tin dioxide crystal facets energy played key role in theformation of (SnO2) nanowires. The sensors fabricated from (SnO2) nanowires showgood selectivity and nice sensitivity toward the50ppm ethanol at350℃. Thegasresponse of the sensors is39.7and response-recovery time is8s and10srespectively.2. Pd and Pt nanocrystals were all synthesized with solution-grown method. Itwas found that the modification result with noble metal nanocrystal method was moreeffective and convenient than the traditional impregnating-sintering method. Afterbeing modified by Pd nanocrystals, the gas response of the sensors toward50ppmhydrogen sulfide (H2S) increased to7times at290℃compared with unmodified SnO2nanowires. The sensors based on the SnO2nanowires which had been modifiedPd nanocrystal exhibit high stability owing to stable single crystal structure. When Pdnanocrystals were used, more depletion layer depth shift enhanced gas response. Afterbeing modified by Pt nanocrystals, the response of the sensors increased to2.8timestoward50ppm ethanol due to the catalytic properties of Pt.3. Solvothermal process have been used to prepare single-crystalline SnO2nanowires with dominant {110} or {100} exposed facets, respectively. Effects of theexposed crystallographic planes on gas sensing properties of SnO2nanowires wereexperimentally and computationally investigated. Our experimental results show thatthe sensors fabricated from SnO2nanowires with {110} exposed facets show thehigher sensing activity toward ethanol than those {100}. Agreeing well withexperimental results, first-principles calculations show that the ethanol absorptionenergy of (110) crystallographic plane is higher than those (100) crystallographicplane. This is because the difference in absorption energy and changes of electronstructure after absorb target gas. Our results indicated that the exposed facets of theSnO2nanowires play a key role in gas sensing among the size and shape of those.These presented a promising route to develop nanomatterials with high response andspecified gas selection crystallographic planes.4. Based on First-principles of density functional theory, the adsorptionproperties of ethanol, methanol, acetone, formaldehyde, hydrogen, hydrogen sulfideand carbon monoxide on SnO2(110) and (100) surface were calculated andinvestigated. The gases trend to locate the most stable adsorption site, such as thefive-coordinated Sn ion (Sn5) on (110) surface and six-coordinated Sn ion (Sn6s) on(100) surface. After the gas adsorbed to the adsorption site, the change of surfacedensity of state, new impurity energy level appearing in the band gap and the bandgap becoming narrow, resulted in the change of the surface conductance. Theelectron populations study indicated that the electron transfer from gas molecule tothe surface is helpful for releasing more electrons from adsorbing gas molecule reacted with adsorbed oxygen. Thus the sensors could display responsed signal.5. SnO2microplatelets with round corner square shape were fabricated byoxidizing SnO microplatelets synthesized via aqueous chemical sedimentation withaid of sonication radiation. The microplatelets were both characterized by XRD, TGand SEM. Our results show that the sensors exhibit the excellent gas-sensingproperties toward H2S，and can detect H2S as low as50ppb at290℃. |
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