氧化铈纳米粒子制备.ppt

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1、关于氧化铈纳米粒子的制备第一张，PPT共二十七页，创作于2022年6月1.Simply introduce the structure and applications of CeO23.Future works2.Synthesis of nanocrystalline CeO2 by different methodsOutline第二张，PPT共二十七页，创作于2022年6月Brief introductionCeO2属于萤石型氧化物。属于萤石型氧化物。CeO2晶胞中的晶胞中的Ce4+按面心立方点阵排按面心立方点阵排列，列，O2-占据所有的四面体位置，占据所有的四面体位置，每个每个Ce4

2、+被被8个个O2-包围，而每个包围，而每个O2-则与则与4个个Ce4+配位。配位。1.Structure of CeO22.功能特性功能特性 CeO2的结构中有的结构中有1/2立方体空隙，可称之为敞型结构。立方体空隙，可称之为敞型结构。敞型结构允许离子快速扩散。经高温敞型结构允许离子快速扩散。经高温(T950)还原后，还原后，CeO2转化为具有氧空位、非化学计量比的转化为具有氧空位、非化学计量比的CeO2-X氧化物氧化物(0 x0.5)，而在低温下，而在低温下(T450)CeO2可形成一系列组成各可形成一系列组成各异的化合物。异的化合物。值得注意的是，即使从晶格上失去相当数量的氧，值得注意的是

3、，即使从晶格上失去相当数量的氧，形成大量氧空位之后，形成大量氧空位之后，CeO2仍然能保持萤石型晶体结构，仍然能保持萤石型晶体结构，这种亚稳氧化物暴露于氧化环境时又易被氧化为这种亚稳氧化物暴露于氧化环境时又易被氧化为CeO2，因，因而而CeO2具有优越的储存和释放氧功能及氧化还原反应能力，具有优越的储存和释放氧功能及氧化还原反应能力，同时同时CeO2也有着良好的化学稳定性和高温快速氧空位扩散能也有着良好的化学稳定性和高温快速氧空位扩散能力。力。第三张，PPT共二十七页，创作于2022年6月Applications of CeO2 玻璃脱色剂氧化铈大颗粒氧化铈磨料氧化铈抛光粉/液晶显示屏氧化铈抛

4、光粉氧化铈抛光轮CeO2 Slurry 此此外外，CeO2还还用用作作催催化化材材料料、高高温温氧氧敏敏材材料料、pH传传感感材材料料、电电化化学学池池中中膜膜反反应应器器材材料料、燃燃料料电电池池 的的 中中 间间 材材 料料、中中 温温 固固 体体 氧氧 化化 物物 燃燃 料料 电电 池池(S O F C)用用 电电 极极 材材 料料第四张，PPT共二十七页，创作于2022年6月Synthesis of CeO21.Direct precipitationprecipitationStir and ageing stageScouring and dryingto calcine prec

5、ursorThe power of CeO2Ce3+or Ce4+technology of direct precipitationprecipitantNitrate:Ce(NO3)3 or(NH4)2Ce(NO3)6Precipitant:ammonia or NH4HCO3 Surface active agent:PEG-4000Process:nitrate and PEG-4000 were dissolved in distilled wate.Then ammonia or NH4HCO3 solution was added dropwise under vigorous

6、stirring till the pH reached 9.The precipitate was filtered,washed thrice with distilled water and alcohol and dried at 80 over night.第五张，PPT共二十七页，创作于2022年6月(a)(b)(c)(d)Results and discussion(a)(b)(c)(d)SEM photoes of precursorXRD of precursor(a):Ce(NO3)3+NH3H2O(b):(NH4)2Ce(NO3)6+NH3H2O(c):Ce(NO3)3+

7、NH4HCO3(d):(NH4)2Ce(NO3)6+NH4HCO3第六张，PPT共二十七页，创作于2022年6月(a)(c)XRD of CeO2 synthesized at 700(a)(b)(c)(d)XRD of CeO2 synthesized at 500(a)(c)XRD of CeO2 synthesized at 600第七张，PPT共二十七页，创作于2022年6月(a)(c)SEM photoes of CeO2 calcined at 600第八张，PPT共二十七页，创作于2022年6月Microwave homogeneous precipitationMicrowav

8、e reaction equipmentNitrate:Ce(NO3)3 or(NH4)2Ce(NO3)6Precipitant:urea Surface active agent:PEG-4000CO(NH2)2+H2O CO2+2NH3NH3+H2O NH4+OH-CO2+H2O CO32-+2H+水解生成的构晶离水解生成的构晶离子子OH-、CO32-,在微在微波辐照作用下波辐照作用下,与与Ce3+、Ce4+等结合生成等结合生成不溶前驱物不溶前驱物 第九张，PPT共二十七页，创作于2022年6月Results and discussionXRD of precursor calcined

9、at 500(a)(b)(c)XRD of precursor(a)Mean:(a)0.093um(b)0.171um(c)0.210umLS of CeO2 calcined at 600(a)Ce(NO3)3+urea,without PEG-4000(b)Ce(NO3)3+urea+PEG-4000(c)(NH4)2Ce(NO3)6+urea+PEG-4000第十张，PPT共二十七页，创作于2022年6月600700XRD of CeO2 synthesized at 600、700 SEM photo of CeO2 calcined at 600SEM photo of precur

10、sor(a)第十一张，PPT共二十七页，创作于2022年6月Hydrothermal synthesis of CeO2 nano-particles1.Cerium(IV)hydroxide precursorA.I.Y.Tok,et al(Nanyang Technological University),Journal of Materials Processing Technology 190(2007)217222H2O2+cerium(III)nitrate,stirred for 5 min under heat to convert Ce3+to Ce4+ammonia(pH=

11、8.8),stir continuously at 80 for 1 hthe pale yellow precipitates(Ce(OH)4)were washed,the conductivity of the supernatant=2ms30 ml of the washed precipitates(pH=10)were placed into the Teflon vessel of the hydrothermal bomb,then placed in the oven and heated at the respective durations(024 h)The fina

12、l products were re-washed,conductivity=2ms,dried at 75 第十二张，PPT共二十七页，创作于2022年6月2.Ceria acetate precursorhydrous cerium oxide stabilized by acetate ions(cerium acetate gel)was dissolved in deionized water to yield acetate stabilized colloidal ceria and will be identified as ceria acetateceria acetate

13、 was diluted,placing 30 ml of the solution into the Teflon vesselthe bomb was then placed in the oven and heated to 250 at different treatment timesthe products were later centrifuged and dried at 75 第十三张，PPT共二十七页，创作于2022年6月Fig.1.DTA/TG of Ce(OH)4 precursorResults and discussionThe total measured we

14、ight loss from 25 to 900 w a s 1 1.6 4%,w h i l e t h e t h e o r e t i c a lweight loss for the decomposition of cerium hydrate oxide is 17.3%,i.e.Ce(OH)4/CeO22H2O to CeO2The decomposition of the precursor is a form of dehydration process of the h y d r a t e d C e O2the difference in weight loss o

15、bserved could be due to the following reasons:(a)precipitate consisting of a partially hydrated form of ceria,(i.e.CeO2xH2O),for which a 11.64%weight loss on decomposition corresponds tox=1.35 or(b)the precipitate consisted of a m i x t u r e o f p h a s e sl i k e C e O22 H2O+C e O2第十四张，PPT共二十七页，创作

16、于2022年6月Fig.2 DTA/TG of ceria acetate precursorThe precursor measured a total weight loss of 12.55%with four distinct temperature peaksThe first endothermic peak was detected at around 100.This is attributed to the release of the water molecules present in the precursorFrom 100 to 200,the weight los

17、s was attribute to the removal of the surface acetate groups and later the formation of the acetic acid when surface acetate hydrolysis occurs.This also explains the very weak endothermic peak detected at 200There was a sharp weight loss from 200 to 400 and a corresponding exothermic peak.This exoth

18、ermic peak suggests the formation of oxyacetate and dioxocarbonate complexes with cerium,Ce(OH)(CH3COO)andCe2O2CO3As temperature increased to 700,the Ce2O2CO3decomposed endothermally to produce t h e f i n a l p r o d u c t C e O2第十五张，PPT共二十七页，创作于2022年6月Fig.3 DTA/TG for CeO2 synthesized from ceria a

19、cetate:(a)after 6 h treatment;(b)after 24 h treatmentafter 6 and 24 h of hydrothermal treatment,weight loss is dramatically reduced to 2.64 and 1.37%The distinct temperature peaks are similar to that of the precursor.However,the distinct exothermic peak for the hydrothermal treatedsamples is no long

20、er as pronounced as that o f t h e p r e c u r s o rThis could be due to the amount of acetate complexes formation being reduced considerably after hydrothermal treatment.Traces of cerium acetate complexes were still present in the samples after hydrothermal treatment.The amount is however,significa

21、ntly lower than that found in the precursor第十六张，PPT共二十七页，创作于2022年6月Fig.4 CeO2 using Ce(OH)4 precursor(250)as a function of timeFig.5 CeO2 using ceria acetate precursor(250)as a function of timeFig.4,the nano-particles exhibited some degree of crystallinity and displayed all of the major peaks of CeO

22、2 with a cubic structure after 6 h treatmentNo significant improvement in crystallinity was observed between 6 and 24 h,and the peaks were broad with weak intensities.This trend is similar with the ceria acetate systemFig.5,the peaks are significantly narrower with higher intensities suggesting larg

23、er crystallite sizes at an average of 15.5 nm as calculated and larger degree of crystallinity as compared to the cerium(IV)hydroxide system.The peaks at higher 2 angles can also be clearly observed for all samples第十七张，PPT共二十七页，创作于2022年6月Fig.6.Lattice constant of CeO2 after hydrothermal treatment at

24、 250 using Ce(OH)4 precursorFig.7 Lattice constant of CeO2 after hydrothermal treatment at 250 using ceria acetate precursorthe lattice parameter decreased by about 0.2%after hydrothermal treatment at 250 for 6 h.From 6 to 12 h at the same temperature,the lattice expanded.The lattice constant only v

25、aried within a narrow range(|a|/a0.03%)after 12 h,indicating that the structure became stable.The lattice constant decreased by about 0.5%after hydrothermal treatment at 250 C for 6 h.Further changes of lattice constant were very small when treatment duration was increased.The variation of lattice c

26、onstant was less than 0.03%第十八张，PPT共二十七页，创作于2022年6月Fig.8 CeO2 from Ce(OH)4(24 h)heat treated at(a)500,(b)1000Fig.9 CeO2 from ceria acetate(24 h)heat treated at(a)500,(b)1000 In both figures,it can be seen that the characteristic peaks are sharper and narrowerThe higher 2 peaks for the hydroxide syst

27、em can also be observed after heat treatment.This crystallite size after heat treatment at 500 and 1000 grew to 8.8 and 47.4 nm,respectivelyThe samples from the ceria acetate system exhibited a larger degree of crystallinity than cerium hydroxide system.The crystallite size for the ceria acetate sys

28、tem after heat treatment was 17.7 and 53.6 nm at 500 and 1000,respectively第十九张，PPT共二十七页，创作于2022年6月Fig.10 TEM and electron diffraction pattern of CeO2 from cerium(IV)hydroxide(a)and ceria acetate(b)after 24 h hydrothermal treatment.Fig.10(a)exhibited very fine particles,which were agglomerated.Crysta

29、llinity could be observed based on the particles and its corresponding electron diffraction pattern.Its crystallite size is about 56 nm as estimated from the TEM micrographs.The particles generally shown rounded edges but they are n o t w e l l-d e f i n e d d u e t o i t s s m a l l s i z eFig.10(b

30、),particles are very well-defined and relatively dispersed.Good crystalline faces and crystallinity state could be observedThe particle sizes,at about 1015 nm,are slightly bigger compared to the cerium(IV)hydroxide system.ceria acetate system appears to be less agglomerated than the cerium(IV)h y d

31、r o x i d e s y s t e m.H o w e v e r,agglomeration of the particles still a p p e a r s t o b e a p r o b l e m.第二十张，PPT共二十七页，创作于2022年6月Salt-assisted ultrasonic aerosol decompositionSalt-assisted aerosol decomposition(SAD)Conventional aerosol decomposition(CAD)the same operating conditions,the same

32、 experimental apparatus,without the saltsprecursor solution:cerium nitratewas dissolved in distilled watera mixture of potassium and sodium nitrates was added to the precursor solutionthe solution was misted by an ultrasonic transducer(1.7 MHz)into dropletscarried by air into a hot tubular reactor w

33、here they were rapidly heated and decomposed to form particles,heating time was less than five secondsCeO2 were obtained by washing the product in water to remove the salts or their derivativesB.Xia,I.W.Lenggoro and K.Okuyama,Hiroshima University,Japan,J.Mater.Chem.,2001,11,29252927第二十一张，PPT共二十七页，创作

34、于2022年6月Results and discussionFig.1 Submicron to micron CeO2 particles synthesized by the CAD method at 800:(a)lower magnification image;(b)higher magnification image of the particle marked A,comprising sintered nano-crystallites.The particles(Fig.1a)are solid and nearly spherical with a mean partic

35、le size o f 0.7 4 u mFig.1 shows the TEM images of the CeO2 particles,which were synthesized by theCAD method at 800 Consist of nanosized crystallites(Fig.1b)with mean size of 13.8 nm determined by the X-ray diffraction(XRD)technique.These nanosized crystallites are virtually inseparable due tosinte

36、ring第二十二张，PPT共二十七页，创作于2022年6月Fig.2 Nanometer nanosized CeO2 particles synthesized by the SAD method at(a)800,and(b)a typical high resolution TEM image of sample(a),showing the crystal lattice of a particleImportant differences between the CAD and the SAD products are indicated below:First,the SAD pr

37、oduct(Fig.2a)is composed of isolated nanoparticles(mean size 51 nm),while the CAD(mean size 0.74 mm)containing sintered nano-crystallitesSecond,the SAD CeO2 particles are single crystals while the CAD CeO2 particles are polycrystalline(as shown in Fig.1b)The single crystals are evidenced by the agre

38、ement between the particle sizes and the crystallite ones at all synthesis temperatures,as shown in Table 1.The typical crystal latticeimage shown in Fig.2b confirms the presence of singlecrystalline particlesClearly,the particle sizedistribution of the SAD product has been remarkably narrowed in co

39、mparison to the CAD product第二十三张，PPT共二十七页，创作于2022年6月Table 1 Comparison of particle and crystallite diameters(in anometers)of CeO2 synthesized by t h e C A D a n d t h e S A D p r o c e s s e sFig.3 Powder XRD patterns of roducts synthesized at(a)CAD,800 (CeO2);(b)SAD,800 (CeO2)Third,the SAD product

40、has a much higher crystallinity than the CAD product,as shown from the sharp peaks in Fig.3b.The crystallite size of the SAD 800 sample is 54.4 nm,as shown in Table 1.This is much larger than the corresponding CAD sampleD e t a i l s o f t h e S A D p r o c e s s:CeO2 can participate in dissolution

41、and precipitation in the liquid-state salt media,which can greatly facilitate mass transfer and thus material formation and crystallization processes A crystallite grows by depleting its adjacent crystallites and is then isolated from others due to theenergy-favorable interaction of the oxide surfac

42、e with the salts第二十四张，PPT共二十七页，创作于2022年6月Fig.2 CeO2 particles synthesized by the SAD method at(c)900,and(d)800 with addition of acetic acid to the s o l u t i o n p r i o r t o a e r o s o l d e c o m p o s i t i o nAs is shown in Table 1,the CAD CeO2 particle sizes change slightly with synthesis te

43、mperature,because it is well understood that the CAD particle size is primarily determined by the droplet size and concentration of the precursor solution.In the SAD process:many factors such as precursor(s),inert salts,additives and process parameters c a n b e u s e d t o c o n t r o l p a r t i c

44、 l e s i z e a n d m o r p h o l o g yFor example,Fig.2c and Table 1:the mean particle size of the SAD product increases from 51 nm(Fig.2a)to 119 nm when the synthesis temperature is increased from 800 to 900Fig.2d shows that the addition of acetic acid as an additive to the precursor solution resul

45、ted in a reduction in the final particle size from 51 nm to 21 nm.The b r o a d e n e d X R Dpeak is clearly seen in the inset of Fig.3第二十五张，PPT共二十七页，创作于2022年6月Future works1.1.改善颗粒间的团聚问题改善颗粒间的团聚问题2.2.对纳米对纳米CeOCeO2 2合成过程中其它影响合成过程中其它影响因素因素(如：反应时间、反应温度、搅如：反应时间、反应温度、搅拌速率、表面活性剂和热处理条件等拌速率、表面活性剂和热处理条件等)进行优化进行优化 第二十六张，PPT共二十七页，创作于2022年6月感谢大家观看第二十七张，PPT共二十七页，创作于2022年6月