氧化鈰納米粒子的制備

1、Members: Xianhong Rui Yu Chen Litao Yan Huamin Yao Liangjun YiSynthesis of ceriaDepartment of Materials Science and EngineeringUniversity of Science and Technology of ChinaJan 3, 2008Simply introduce the structure and applications of CeO23. Future works2. Synthesis of nanocrystalline CeO2 by differe

2、nt methodsOutlineBrief introductionCeO2屬于螢石型氧化物。 CeO2晶胞中的Ce4+按面心立方點陣排列，O2-占據(jù)所有的四面體位置，每個Ce4+被8個O2-包圍，而每個O2-則與4個Ce4+配位。1. Structure of CeO22.功能特性 CeO2的結構中有1/2立方體空隙，可稱之為敞型結構。敞型結構允許離子快速擴散。經(jīng)高溫(T950)還原后，CeO2轉化為具有氧空位、非化學計量比的CeO2-X氧化物(0 x0.5)，而在低溫下(T450) CeO2可形成一系列組成各異的化合物。 值得注意的是，即使從晶格上失去相當數(shù)量的氧，形成大量氧空位之后，C

3、eO2仍然能保持螢石型晶體結構，這種亞穩(wěn)氧化物暴露于氧化環(huán)境時又易被氧化為CeO2，因而CeO2具有優(yōu)越的儲存和釋放氧功能及氧化還原反應能力，同時CeO2也有著良好的化學穩(wěn)定性和高溫快速氧空位擴散能力。 Applications of CeO2 玻璃脫色劑氧化鈰大顆粒氧化鈰磨料氧化鈰拋光粉/液晶顯示屏氧化鈰拋光粉氧化鈰拋光輪CeO2 Slurry 此外， CeO2還用作催化材料、高溫氧敏材料、 pH傳感材料、電化學池中膜反應器材料、燃料電池的中間材料、中溫固體氧化物燃料電池(SOFC)用電極材料Synthesis of CeO21. Direct precipitationprecipitat

4、ionStir and ageing stageScouring and dryingto calcine precursorThe 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.The

5、n ammonia or NH4HCO3 solution was added dropwise under vigorous stirring till the pH reached 9. The precipitate was filtered, washed thrice with distilled water and alcohol and dried at 80 over night.(a)(b)(c)(d)Results and discussion(a)(b)(c)(d)SEM photoes of precursorXRD of precursor(a): Ce(NO3)3

6、+ NH3H2O(b): (NH4)2Ce(NO3)6 + NH3H2O(c): Ce(NO3)3 + NH4HCO3 (d): (NH4)2Ce(NO3)6 + NH4HCO3(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(a)(c)SEM photoes of CeO2 calcined at 600Microwave homogeneous precipitationMicrowave reaction eq

7、uipmentNitrate: 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+ 水解生成的構晶離子OH-、CO32-,在微波輻照作用下,與Ce3+、Ce4+等結合生成不溶前驅物 Results and discussionXRD of precursor calcined at 500(a)(b)(c)XRD of precursor (a)Mean:(a)0.0

8、93um(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-4000600700XRD of CeO2 synthesized at 600、700 SEM photo of CeO2 calcined at 600SEM photo of precursor(a)Hydrothermal synthesis of CeO2 nano-particles1

9、. 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 =8.8), stir continuously at 80 for 1 hthe pale yellow precipi

10、tates (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 final products were re-washed, conductivity=2ms, dried

11、at 75 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 was diluted, placing 30 ml of the solution into the Teflon vesselthe

12、bomb was then placed in the oven and heated to 250 at different treatment timesthe products were later centrifuged and dried at 75 Fig. 1. DTA/TG of Ce(OH)4 precursorResults and discussionThe total measured weight loss from 25 to 900 was 11.64%, while the theoreticalweight loss for the decomposition

13、 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 hydrated CeO2the difference in weight loss observed could be due to the following reasons: (a) precipitate consisting of a partially hydrated form of ceria, (i.e

14、. CeO2xH2O), for which a 11.64% weight loss on decomposition corresponds tox = 1.35 or (b) the precipitate consisted of a mixture of phaseslike CeO22H2O+ CeO2Fig. 2 DTA/TG of ceria acetate precursorThe precursor measured a total weight loss of 12.55% with four distinct temperature peaksThe first end

15、othermic 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 loss was attribute to the removal of the surface acetate groups and later the formation of the acetic acid when surface acetate hydrolysis occurs. Th

16、is 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 exothermic peak suggests the formation of oxyacetate and dioxocarbonate complexes with cerium, Ce(OH)(CH3COO) andCe2O2CO3As temperature increased to

17、700, the Ce2O2CO3decomposed endothermally to produce the final product CeO2Fig. 3 DTA/TG for CeO2 synthesized from ceria acetate: (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

18、peaks are similar to that of the precursor. However,the distinct exothermic peak for the hydrothermal treatedsamples is no longer as pronounced as that of the precursorThis could be due to the amount of acetate complexes formation being reduced considerably after hydrothermal treatment.Traces of cer

19、ium acetate complexes were still present in the samples after hydrothermal treatment. The amount is however,significantly lower than that found in the precursorFig. 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,

20、 the nano-particles exhibited some degree of crystallinity and displayed all of the major peaks of CeO2 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 th

21、e ceria acetate systemFig. 5, the peaks are significantly narrower with higher intensities suggesting larger 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 ob

22、served for all samplesFig. 6. Lattice constant of CeO2 after hydrothermal treatment at 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

23、. From 6 to 12 h at the same temperature, the lattice expanded. The lattice constant only varied 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 l

24、attice constant were very small when treatment duration was increased. The variation of lattice constant was less than 0.03%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

25、the characteristic peaks are sharper and narrowerThe higher 2 peaks for the hydroxide system 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

26、of crystallinity than cerium hydroxide system. The crystallite size for the ceria acetate system after heat treatment was 17.7 and 53.6 nm at 500 and 1000 , respectivelyFig. 10 TEM and electron diffraction pattern of CeO2 from cerium(IV) hydroxide (a) and ceria acetate (b) after 24 h hydrothermal tr

27、eatment.Fig. 10 (a) exhibited very fine particles, which were agglomerated. Crystallinity 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 edge

28、s but they are not well-defined due to its small sizeFig. 10 (b), 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 aceta

29、te system appears to be less agglomerated than the cerium(IV) hydroxide system. However, agglomeration of the particles still appears to be a problem.Salt-assisted ultrasonic aerosol decompositionSalt-assisted aerosol decomposition (SAD)Conventional aerosol decomposition (CAD)the same operating cond

30、itions , the same 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

31、hot tubular reactor where 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.,

32、2001, 11, 29252927Results 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 spherica

33、l with a mean particle size of 0.74 umFig. 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

34、 inseparable due tosinteringFig. 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, t

35、he SAD product (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 evi

36、denced by the agreement 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 rem

37、arkably narrowed in comparison to the CAD productTable 1 Comparison of particle and crystallite diameters (in anometers) of CeO2 synthesized by the CAD and the SAD processesFig. 3 Powder XRD patterns of roducts synthesized at (a) CAD, 800 (CeO2); (b) SAD, 800 (CeO2)Third, the SAD product has a much

38、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 sampleDetails of the SAD process:CeO2 can participate in dissolution and precipitation in the liquid-state salt media, which can greatly facilitate mass