简介:为了明确团聚现象及表面性质对ZnS纳米材料发光性质的影响,采用SiO2对ZnS材料进行了表面修饰,并对ZnS及ZnS/SiO2复合材料的光学性质进行对比研究。采用吸收光谱分析了包覆前后光吸收性质的差异,发现SiO2包覆后ZnS纳米材料的带边由333nm红移至360nm。为了研究ZnS纳米材料与ZnS/SiO2纳米复合材料的光发射性质,分别对含纳米材料的水溶液样品及粉末样品的发光光谱进行了采集。对比研究的结果表明,SiO2包覆后ZnS纳米材料在蓝紫光区的发光得到了明显增强。以氙灯作为激发光源所获得荧光光谱显示ZnS/SiO2粉末样品发光的积分强度增大为原来的17.5倍,但相同条件下针对溶液样品的测试结果显示其发光强度只增大了1.1倍,这种增强可用SiO2的存在抑制了ZnS纳米粒子间的团聚来解释,且这一推断由325nm紫外激光激发下获得的光致发光数据进行了验证。
简介:Variousagriculturalcropresiduesincludingcornstover,corncob,andsorghumstalkwithamoisturecontentof75wt%weresubjectedtoalongpretreatment(12-60h)withsupercriticalCO2(scCO2),atlowtemperature(50-80℃)andapressureof17.5-25.0Mpa.Thesugaryieldsfromtheenzymatichydrolysis(EH)ofthepretreatedsampleswereasmuchasthree-tofourfoldgreaterthanthoseaffordedbytherawmaterials.However,whenpretreatmentwasconductedwithinashorttime(e.g.0.5h),aspreviouslyreportedintheliterature,onlyaslightincreaseintheEHsugaryieldswasobserved.TheproposedscCO2pretreatmentmechanismdemonstratedtheroleofmoistureinthesystem.Wetting,softening,andswellingwereobservedtomainlyaffectthelignocellulosewhenasuitableamountofwaterwasadded.Finally,thesampleswereanalysedbyX-raydiffractionandscanningelectronmicroscopy,beforeandafterpretreatment,toinvestigatethechangesinthemicroscopicstructureofthebiomass.
简介:Inthisstudy,weattempttheanalysisofthepassageflowinthecentrifugalimpellerusingFEMwith/withouttheturbulencemodel,andcomparethisresultwiththeexperimentalresult.TheturbulencemodelisthelowReynoldsk-εmodelproposedbyChien.WeusetheGSMACmethodfortheReynoldsaveragedNavier-Stokesequations,theEulerexplicitmethodforthetransportequationsoftheturbulentkineticenergyandthedissipationrate.AllequationsarediscretizedbytheGalerkin'smethod.Atthemidpassageofthecentrifugalimpeller,thepassagewisevelocitycomponenttendstoincreaseinthepressure-to-suctiondirection,andtheothercomponenttowardthepressuresurfacetendstobelargeintheregionofthemiddleblade-to-bladetothehubside.Thetipleakagesappeararoundtheregionofthemiddleblade-to-bladenearthecasingtogetherwiththesecondaryflowtowardthesuctionsurface.Thesephenomenacorrespondwiththeexperimentalresult,qualitatively.
简介:In2010,theBESCollaboration[1]foundaclearenhancementintheK0K0massdistributionintheJ=ψ!ηK0K0decay.SuchanenhancementisusuallyasignatureofanL=0resonancearoundthreshold,whichinthiscasewouldcorrespondstoanh1statewithquantumnumbersIG(JPC)=0??(1+??).Thish1statewaspredictedbytheChiralUnitarytheoryintheKKinteraction.Becauseoftheconversationlaw,thisstatecanonlydecaytoK0K0channel,andcanbestudiedefficientlyintheJ=ψ!ηK0K0decay.
简介:Mixedalcoholisofgreatpromiseasoctaneimproverinautomotivefuel,andhopefultoreplacetheMTBEtoreducetheenvironmentalpollution,Inthisfield,alkali-promtedmolybdenum-basedcatalystshavebeengivenspecialinterestbecauseoftheirexcellentsulfur-toleranceforsynthesisofmixedalcoholfromCO+H2,Itwasreportedthatthecoblatisafavorablepromoterforenhancingalcoholproduction,especiallyforimprovingtheselectivityforC2+alcohol[1-3],moreover,stronginteractionbetweenConandMoisinfavorofmixedalcoholsynthesis[4].Recently,weprparedakindofK-Co-Moultrafineparticlesbysol-gelmethodanditshowsmuchsmallerparticlesizebuthigheractivtyandselectivitytowardalcoholformationthantheonepreparedbyconventionalmethod[5],TheaimofthepresentworkistoresearchthemicostructuresoftheMoandCospeciesintheK-Co-Mosamplespreparedbydifferentmethod.
简介:Anovelgas-phaseelectrocatalyticcellcontainingalow-temperatureprotonexchangemembrane(PEM)wasdevelopedtoelectrochemicallyconvertCO2intoorganiccompounds.TwodifferentCu-basedcathodecatalysts(CuandCu-C)werepreparedbyphysicalvapordepositionmethod(sputtering)andsubsequentlyemployedforthegas-phaseelectroreductionofCO2atdifferenttemperatures(70-90℃).ThepreparedelectrodesCuandCu-CwerecharacterizedbyX-raydiffraction(XRD),X-rayphotoemissionspectroscopy(XPS)andscanningelectronmicroscopy(SEM).Asrevealed,CuispartiallyoxidizedonthesurfaceofthesamplesandtheCuandCu-Ccathodiccatalystswerecomprisedofaporous,continuous,andhomogeneousfilmwithnanocrystallineCuwithagrainsizeof16and8nm,respectively.Theinfluenceoftheappliedcurrentandtemperatureontheelectro-catalyticactivityandselectivityofthesematerialswasinvestigated.Amongthetwoinvestigatedelectrodes,thepureCucatalystfilmshowedthehighestCO2specificelectrocatalyticreductionratesandhigherselectivitytomethanolformationcomparedtotheCu-Celectrode,whichwasattributedtothehigherparticlesizeoftheformerandlowerCuO/Curatio.Theobtainedresultsshowpotentialinterestforthepossibleuseofelectrical「enewableenergyforthetransformationofCO2intovaluableproductsusinglowmetalloadingCubasedelectrodes(0.5mgCucm2)preparedbysputtering.
简介:Inthiswork,MoOxpromotedIr/SiO2catalystswerepreparedandusedfortheselectivehydrogenolysisoftetrahydrofurfurylalcohol(THFA)to1,5-pentanediolinacontinuousflowreactor.Theeffectsofdifferentnoblemetals(Ir,Pt,Pd,Ru,Rh),supportsandIrcontentswerescreened.Amongtheinvestigatedcatalysts,4wt%Ir-MoOx/SiO2withaMo/Iratomicratioof0.13exhibitedthebestcatalyticperformance.ThesynergybetweenIrparticlesandthepartiallyreducedisolatedMoOxspeciesattachedonthemisessentialfortheexcellentcatalyticperformanceofIr-MoOx/SiO2.ThecatalystexhibitedabetterhydrogenolysisefficiencyofTHFAwiththeselectivityof1,5-pentanediolof65%–74%ataconversionofTHFAof70%–75%whentheinitialTHFAconcentrationisrangingfrom20wt%and40wt%.AndhighersystempressurewasalsoinfavoroftheconversionofTHFA.Duringastabilitytest,theconversionofTHFAand1,5-pentanediolyieldoverIr-MoOx/SiO2decreasedwithreactiontime,whichcanbeexplainedbytheleachingofMospeciesduringthereaction.
简介:Ingasturbineengines,laminar-turbulenttransitionoccurs.However,generally,theturbulencemodelstodescribesuchtransitionresultsintooearlyandtooshorttransition.Combiningaturbulencemodelwithadescriptionofintermittency,i.e.thefractionoftimetheflowisturbulentduringthetransitionphase,canimproveit.Bylettinggrowtheintermittencyfromzerotounity,startandevolutionoftransitioncanbeimposed.Inthispaper,amethodwhereadynamicequationofintermittencycombiningwithatwo-equationk-ωturbulencemodelisdescribed.Thisintermittencyfactorisapremultiplicatoroftheturbulentviscositycomputedbytheturbulencemodel.FollowingasuggestionbyMenteretal.[1],thestartoftransitioniscomputedbasedonlocalvariables.
简介:Catalyticpropertiesofthemetal-organicframeworkCr-MIL-101insolvent-freecycloadditionofCO2toepoxidestoproducecycliccarbonatesusingtetrabutylammoniumbromideasco-catalysthavebeenexploredundermildreactionconditions(8barCO2,25C).Styreneandpropylenecarbonateswereformedwithhighyields(95%and82%,respectively).CatalyticperformanceofCr-MIL-101wascomparedwithotherMOFs:Fe-MIL-101,Zn-MOF-5andHKUST-1.Thecatalyticpropertiesofdifferentquaternaryammoniumbromides,Cr-MIL-101aswellasPW12/Cr-MIL-101compositematerialhavebeenassessedinoxidativecarboxylationofstyreneinthepresenceofbothtert-butylhydroperoxideandH2O2asoxidantsat8100barCO2and2580Cwithselectivitytostyrenecarbonateupto44%at57%substrateconversion.
简介:Thenextgenerationofadvancedlightsourcesrequiresphotonswithlargeaveragefluxandhighbrightness,whichneedsadvancedelectrongunmatchedwithexcellentphotocathodematerials.K2CsSbphotocathodehastheadvantagesofhighquantumefficiency,longlifetimeandinstantaneousresponse.ThisstudyintroducesthedesignofasetofK2CsSbphotocathodepreparationsystemsanddetailedpreparationprocessofK2CsSbphotocathodes,includingsequentialdepositionprocessandco-depositionprocess,andfinallydevelopsaK2CsSbphotocathode.Theinfluenceoflaserpoweronthequantumefficiencyisalsoinvestigated.