1、關(guān)于氧化鈰納米粒子的制備第一頁(yè)，共27頁(yè)幻燈片3. 第二頁(yè)，共27頁(yè)幻燈片CeO2屬于螢石型氧化物。屬于螢石型氧化物。 CeO2晶胞中的晶胞中的Ce4+按面心立按面心立方點(diǎn)陣排列，方點(diǎn)陣排列，O2-占據(jù)所有的占據(jù)所有的四面體位置，每個(gè)四面體位置，每個(gè)Ce4+被被8個(gè)個(gè)O2-包圍，而每個(gè)包圍，而每個(gè)O2-則與則與4個(gè)個(gè)Ce4+配位。配位。1. Structure of CeO22.功能特性功能特性 CeO2的結(jié)構(gòu)中有的結(jié)構(gòu)中有1/2立方體空隙，可稱之為敞型結(jié)構(gòu)。立方體空隙，可稱之為敞型結(jié)構(gòu)。敞型結(jié)構(gòu)允許離子快速擴(kuò)散。經(jīng)高溫敞型結(jié)構(gòu)允許離子快速擴(kuò)散。經(jīng)高溫(T950)還原后，還原后，CeO2轉(zhuǎn)化為

2、具有氧空位、非化學(xué)計(jì)量比的轉(zhuǎn)化為具有氧空位、非化學(xué)計(jì)量比的CeO2-X氧化氧化物物(0 x0.5)，而在低溫下，而在低溫下(T450) CeO2可形成一系可形成一系列組成各異的化合物。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(dāng)數(shù)量的氧，值得注意的是，即使從晶格上失去相當(dāng)數(shù)量的氧，形成大量氧空位之后，形成大量氧空位之后，CeO2仍然能保持螢石型晶體結(jié)構(gòu)，仍然能保持螢石型晶體結(jié)構(gòu)，這種亞穩(wěn)氧化物暴露于氧化環(huán)境時(shí)又易被氧化為這種亞穩(wěn)氧化物暴露于氧化環(huán)境時(shí)又易被氧化為CeO2，因，因而而CeO2具有優(yōu)越的儲(chǔ)存和釋放氧功能及氧化還原反具有優(yōu)越的儲(chǔ)存和釋放氧功能及氧化還原反應(yīng)能力，同時(shí)應(yīng)能力

3、，同時(shí)CeO2也有著良好的化學(xué)穩(wěn)定性和高溫快速也有著良好的化學(xué)穩(wěn)定性和高溫快速氧空位擴(kuò)散能力。氧空位擴(kuò)散能力。 第三頁(yè)，共27頁(yè)幻燈片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，此外， CeO2還用作催化材料、高溫氧敏材料還用作催化材料、高溫氧敏材料、 pH傳感材料、電化學(xué)池中膜反應(yīng)器材料傳感材料、電化學(xué)池中膜反應(yīng)器材料、燃燃料 電 池 的 中 間 材 料 、 中 溫 固 體 氧 化 物 燃 料 電 池料 電 池 的 中 間 材 料 、 中 溫 固 體 氧 化 物 燃 料 電 池( S

4、O F C )用 電 極 材 料用 電 極 材 料第四頁(yè)，共27頁(yè)幻燈片Synthesis of CeO21. Direct precipitationprecipitationStir 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 ac

5、tive agent: PEG-4000Process: nitrate and PEG-4000 were dissolved in distilled wate.Then 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.第五頁(yè)，共27頁(yè)幻燈片(a)

6、(b)(c)(d)Results and discussion10203040506070 2(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 + NH4HCO3 (d): (NH4)2Ce(NO3)6 + NH4HCO3第六頁(yè)，共27頁(yè)幻燈片10203040506070050010001500200025003000 2(a)(c)XRD of CeO2 synthesized at 70010203040506

7、070 (a)(b)(c)(d)XRD of CeO2 synthesized at 50010203040506070 2(a)(c)XRD of CeO2 synthesized at 600第七頁(yè)，共27頁(yè)幻燈片(a)(c)SEM photoes of CeO2 calcined at 600第八頁(yè)，共27頁(yè)幻燈片Microwave homogeneous precipitationMicrowave reaction equipmentNitrate: Ce(NO3)3 or (NH4)2Ce(NO3)6Precipitant: urea Surface active agent: P

8、EG-4000CO(NH2)2 + H2O CO2 + 2NH3NH3 + H2O NH4+ + OH-CO2 + H2O CO32- + 2H+ 水解生成的構(gòu)晶離子水解生成的構(gòu)晶離子OH-、CO32-, ,在微波在微波輻照作用下輻照作用下, ,與與Ce3+、Ce4+等結(jié)合生成不等結(jié)合生成不溶前驅(qū)物溶前驅(qū)物 第九頁(yè)，共27頁(yè)幻燈片Results and discussion10203040506070 2XRD of precursor calcined at 500(a)(b)(c)10203040506070050100150200250 2XRD of precursor (a)Mean

9、:(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第十頁(yè)，共27頁(yè)幻燈片102030405060700500100015002000 2600700XRD of CeO2 synthesized at 600、700 SEM photo of CeO2 calcined at 600SEM photo of precurso

10、r(a)第十一頁(yè)，共27頁(yè)幻燈片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

12、 h)The final products were re-washed, conductivity=2ms, dried at 75 第十二頁(yè)，共27頁(yè)幻燈片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 ace

13、tate 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 第十三頁(yè)，共27頁(yè)幻燈片F(xiàn)ig. 1. DTA/TG of Ce(OH)4 precursorResults and discussionThe total measured weight

14、loss from 25 to 900 was 11.64%, while the theoreticalweight 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 observed could be due t

15、o 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 c o r r e s p o n d s t ox = 1.35 or (b) the precipitate consisted of a mixture of phasesl i k e C e O2 2 H2O + C e O2第十四頁(yè)，共27頁(yè)幻燈片F(xiàn)ig. 2 DTA/TG

16、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 i n t h e p r e c u r s o rFrom 100 to 200, the weight loss was a

17、ttribute 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 exothermic

18、 peak suggests the formation of oxyacetate and dioxocarbonate complexes with cerium, Ce(OH)(CH3COO) andCe2O2CO3As temperature increased to 700, the Ce2O2CO3decomposed endothermally to produce the final product CeO2第十五頁(yè)，共27頁(yè)幻燈片F(xiàn)ig. 3 DTA/TG for CeO2 synthesized from ceria acetate: (a) after 6 h treat

19、ment;(b) after 24 h treatmentafter 6 and 24 h of hydrothermal treatment, weight loss is dramatically r e d u c e d t o 2 . 6 4 a n d 1 . 3 7 %The distinct temperature peaks are similar to that of the precursor. However,the distinct exothermic peak for t h e h y d r o t h e r m a l t r e a t e dsampl

20、es is no longer as pronounced as t h a t 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

21、however,significantly lower than that f o u n d i n t h e p r e c u r s o r第十六頁(yè)，共27頁(yè)幻燈片F(xiàn)ig. 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

22、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 the ceria a c e t a t e s y s t e mFig. 5, the peaks are significantly narr

23、ower 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 b e c l e a r l y o b s e r v e d f o r a l l s a m p l e s第十七頁(yè)，共27頁(yè)幻燈片F(xiàn)ig.

24、 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. From 6 to 12 h at the sa

25、me 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 lattice constant were very

26、small when treatment duration was increased. The variation of lattice constant was less than 0.03%第十八頁(yè)，共27頁(yè)幻燈片F(xiàn)ig. 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 characteri

27、stic 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 of crystallini

28、ty 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 , respectively第十九頁(yè)，共27頁(yè)幻燈片F(xiàn)ig. 10 TEM and electron diffraction pattern of CeO2 from cerium(IV) hydroxide (a) and ceria acetate (b) after 24 h hydrothermal trea

29、tment.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 edges

30、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 acetate

31、 system appears to be less agglomerated than the cerium(IV) hydroxide system. However, agglomeration of the particles still appears to be a problem.第二十頁(yè)，共27頁(yè)幻燈片Salt-assisted ultrasonic aerosol decompositionSalt-assisted aerosol decomposition (SAD)Conventional aerosol decomposition (CAD)the same oper

32、ating conditions , 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 a

33、ir into a 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. Mate

34、r. Chem., 2001, 11, 29252927第二十一頁(yè)，共27頁(yè)幻燈片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 so

35、lid and nearly spherical with a mean particle size of 0.74 umFig. 1 shows the TEM images of the CeO2 particles, which were s y n t h e s i z e d b y t h eCAD 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

36、nanosized crystallites are virtually inseparable due tosintering第二十二頁(yè)，共27頁(yè)幻燈片F(xiàn)ig. 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

37、and the SAD products are indicated below:First, the SAD product (Fig. 2a) is composed of isolated nanoparticles (mean size 51 nm),while the CAD(mean size 0.74 mm) containing s i n t e r e d n a n o - c r y s t a l l i t e sSecond, the SAD CeO2 particles are single crystals while the CAD CeO2 particl

38、es are polycrystalline (as shown in Fig. 1b) The s i n g l e c r y s t a l s a r e e v i d e n c e d b y t h e 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

39、singlecrystalline particlesClearly, the particle sizedistribution of the SAD product has been remarkably narrowed in comparison to the CAD product第二十三頁(yè)，共27頁(yè)幻燈片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

40、sFig. 3 Powder XRD patterns of roducts synthesized at (a) CAD, 800 (CeO2); (b) SAD, 800 (CeO2)Third, the SAD product 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 c o r r e s p o n d i n g C A D s a m p l eDetails of the SAD process:CeO2 can participate in dissolution and precipitation in t