Research Article High Surface Area Ceria Nanoparticles via ...downloads.hindawi.com/journals/jnm/2016/7274949.pdf100 120 CNR1 CNR3 CNR4 CNR6 Relative pressure, p/p 0 Volume adsorbed

Research ArticleHigh Surface Area Ceria Nanoparticles via HydrothermalSynthesis Experiment Design

Stanislav Kurajica1 Iva Minga1 Martina Guliš1 Vilko MandiT2 and Ivan SimIiT3

1Faculty of Chemical Engineering and Technology University of Zagreb Marulicev Trg 19 10000 Zagreb Croatia2Ruđer Boskovic Institute Bijenicka Cesta 54 10000 Zagreb Croatia3Pliva Croatia doo Prilaz Baruna Filipovica 25 10000 Zagreb Croatia

Correspondence should be addressed to Stanislav Kurajica stankokfkithr

Received 30 March 2016 Revised 21 July 2016 Accepted 21 July 2016

Academic Editor Ajayan Vinu

Copyright copy 2016 Stanislav Kurajica et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Hydrothermal synthesis of CeO2was optimized on two reactant concentrations and synthesis temperature and duration in order

to achieve material having the greatest specific surface area (SSA) Taguchi method of experimental design was employed inevaluation of the relative importance of synthesis parameters CeO

2nanoparticles were characterized using X-ray diffraction

nitrogen adsorption-desorption isotherms and scanning electron microscopy Optimum conditions for obtaining particles withgreater SSA were calculated according to Taguchirsquos model ldquothe-higher-the-betterrdquo Synthesis temperature was found to be the onlyparameter significant for enabling nanoparticles with greater SSAMesoporous nanocrystalline ceria with SSA as great as 226m2 gminus1was achieved which is unprecedented for the hydrothermally synthesized ceria The reason for this achievement was found intemperature dependence of the diffusion coefficient which when low favors nucleation yielding with fine particles while whenhigh it favors crystal growth and formation of one-dimensional structuresThe occurrence of 1D-structure in sample exhibiting thesmallest SSA was confirmed Very fine crystallites with crystallite size as low as 59 nm have been obtained being roughly inverseproportional to SSA Selected samples were tested as catalyst for soot oxidation Catalyst morphology turned out to be decisivefactor for catalytic activity

1 Introduction

Ceria CeO2 has been investigated as catalyst for various

industrial and environmental applications [1] Recently theinvestigations have focused on nanostructured ceria and itsproperties and synthesis methods [2] since it has been shownthat nanostructured ceria is superior to bulk ceria in terms ofboth catalysis and support [3] Different synthesis approacheshave been used for synthesis of ceria nanoparticles [2 45] among which hydrothermal synthesis draws significantinterest [2 6ndash21]

Hydrothermal synthesis possesses numerous advantagesof one-pot one-step low-temperature low-cost and envi-ronmentally benign process enabling preparation of highpurity nanoparticles of desired size and morphology [11ndash13] Early investigations on hydrothermal synthesis for the

preparation of CeO2powders such as those conducted by

Hirano and Kato [14 15] have been concentrated on variousprocess precursors Shortly afterwards experimental condi-tions specifically precursor concentrations and reaction timeand temperature were studied [16 17] Later on focus inhydrothermal synthesis studies shifted from particle size tomorphology and ceria with various shapes such as nanorodsnanotubes nanoplates nanocubes and hollow nanosphereshas been prepared using hydrothermal method [11 18 19]Finally CeO

2nanostructured materials doped with various

elements have been prepared [20 21]One of the most beneficial properties for catalytic appli-

cation is the large surface area Commercial ceria specific sur-face area ranges below 10m2 gminus1 [7 22] while reports on SSAas high as 277m2 gminus1 could be found in literature for ceria pre-pared using combined sol-gel and solvothermal process [22]

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2016 Article ID 7274949 8 pageshttpdxdoiorg10115520167274949

2 Journal of Nanomaterials

Table 1 Process variables (factors) used

Assignation Variable Unit Lowervalue level 1

Highervalue level 2

119860 119888(NaOH) molL 8 12119861 119899(Ce(SO

4)2times3H2O) mmol 08 12

119862 Temperature ∘C 120 180119863 Duration h 16 24

Table 2 Experimental layout defined based on Taguchi L8 orthog-onal array

Experiment number 119860 119861 119862 119863

1 1 2 1 12 2 1 2 13 2 2 1 24 2 1 1 15 2 2 2 26 1 1 1 27 1 1 2 28 1 2 2 1

200m2 gminus1 for precipitation process [23] and 139m2 gminus1 forhydrothermally synthesized ceria [10]

The Taguchi method of experimental design is a methodfor testing the relative importance of parameters in the exper-iment outcome This approach is considered as very efficientsince a lot of information is obtained from a reduced set ofexperiments [24]

This study employs the experiment design in order toyield nanostructured CeO

2having favorable properties using

hydrothermal method of synthesis Thereby the relativeeffect of reactants concentrations synthesis temperature andduration on the specific surface area as well as on otherproperties of ceria was examined

2 Materials and Methods

In the course of the hydrothermal synthesis of ceria nanopar-ticles four process parameters were detected as potentiallysignificant concentration of two precursors NaOH andCe(SO

4)2times3H2O and temperature and duration of synthe-

sis In order to examine their effect on the properties ofceria nanoparticles a Taguchi experimental design has beenemployed Four factors (process variables) at two levels foreach factor (Table 1) were selected A common experimentaldesign including combinations of all input factors (full-factorial design) would require 24 = 16 experiments Onthe other hand Taguchi orthogonal design requires only 8experiments half of full-factorial design L8 orthogonal array(Table 2) is generated using JMP computer program for statis-tical analysis (JMP Version 11 SAS Institute Inc Cary NC1989ndash2013)

The typical synthesis procedure was as follows appropri-ate amount of Ce(SO

4)2times3H2O (Merck Germany) has been

dissolved in 56 cm3 of NaOH (Kemika Croatia) solution and

put in a 70mL capacity Teflon-lined stainless-steel auto-clave sealed tightly and thermally treated in temperature-controlled oven Eight samples were prepared the synthesisconditions used are shown in Tables 1 and 2 After cooling ofthe autoclave the product was centrifuged and obtained paleyellow precipitate was washed with demineralized water withthe aid of sonication Centrifugation and washing sequenceshave been repeated three times Finally yielded materialswere dried at 60∘C for 24 h in static air

The crystal phase in samples was identified by powder X-ray diffraction (XRD) analysis using Shimadzu XRD 6000diffractometer with CuK120572 radiation operated at 40 kV and30mA Data were collected between 5 and 70∘ 2120579 in a stepscan mode with steps of 002∘ and counting time of 2 s Thecrystallite size was estimated from XRD peak broadeningusing Scherrerrsquos formula

119863 =119896120582

120573 cos 120579 (1)

where 119863 is crystallite size 119896 is shape factor 120582 is CuK120572radiation wavelength 120573 is peak full width at half maximumcorrected for instrumental broadening and 120579 is Bragg angle

Surface properties of samples were determined by aBrunauer-Emmet-Teller (BET) N

2gas adsorption-desorp-

tion isotherms obtained on Micromeritics ASAP-2000 at77K Samples were previously degassed at 100∘C under adynamic vacuum of 13mPa to remove any surface adsorbedresidues Surface area was calculated by utilizing the desorp-tion data Pore size and pore volume were calculated by BJHmethod applied to the desorption branch of the isotherms

Morphology of the samples was investigated using fieldemission gun scanning electron microscopy (FESEM) deviceJEOL model 7000F The samples were sputtered with gold byQuorum SC 7620 sputter coater

The catalytic efficiency of the samples for soot oxidationwas examined according to the method of Sudarsanam et al[25] where 10 plusmn 1mg of catalyst was mixed with 10 plusmn 1mgof Norit DLC Super 30 carbon black (Cabot Norit NederlandBV) in 120572-alumina crucible with spatula for 2min and placedin a thermogravimetric analyzer (TGA) Netzsch STA409Oxidation experiment consisted of heating the catalyst-sootmixture at a rate of 10 Kminminus1 from ambient temperatureto 1300∘C under a 100 cm3minminus1 synthetic air purge gasflow Each test was repeated three times to ensure thereproducibility of the obtained results

3 Results and Discussion

The powder XRD patterns (Figure 1) of the prepared samplesare indexed to ceria CeO

2(ICDD PDF number 34-394)

Ceria adopts the fluorite crystal structure with space groupFm-3m In FCC ceria unit cell Ce4+ ions are close packedwhile O2minus ions occupy tetrahedral sites Beside peak anglespeak intensities also obey the profile of ICDD PDF number34-394 Broad peaks point out to formation of nanocrys-talline particles The differences among patterns presented inFigure 1 indicate that different synthesis conditions affect thecrystallite size of CeO

2 However no significant difference

Journal of Nanomaterials 3

Table 3 Average crystallite size calculated frombroadening of (220)XRD reflection using Scherrerrsquos formula and specific surface areacalculated from desorption isotherms by the BJH model

Sample Crystallitesize (nm)

Specific surfacearea (m2 gminus1)

Dominant poreradius (nm)

CNR1 59 plusmn 03 1817 plusmn 05 33CNR2 143 plusmn 10 1086 plusmn 10 62CNR3 75 plusmn 05 1750 plusmn 19 32 63CNR4 65 plusmn 04 1789 plusmn 15 32CNR5 214 plusmn 15 651 plusmn 08 63CNR6 62 plusmn 04 2267 plusmn 11 33CNR7 123 plusmn 09 1146 plusmn 15 37CNR8 125 plusmn 08 1067 plusmn 11 36

4000

3500

3000

2000

2500

1500

1000

500

0

20 30

(111)

Inte

nsity

(CPS

)

(200) (220)(222)

(311)

40 50 60

CNR1CNR2CNR3CNR4

CNR5CNR6CNR7

CNR8

2120579 (∘) CuK120572

Figure 1 Powder XRD patterns of the prepared samples

in background noise has been noted Excessive backgroundnoise would be a presence indication of great amount ofamorphous phase that is poor crystallinity

The only peak that is not partially overlapped reflection(220) was the basis for the average crystallite size calculationThe crystallite sizes calculated using Scherrerrsquos formula aregiven in Table 3 As can be seen sample 5 presents thegreatest while sample 6 have the smallest crystallite size

The nitrogen adsorption-desorption isotherms of theprepared samples are illustrated in Figure 2(a) (samplesCNR1 CNR3 CNR4 and CNR6) and Figure 2(b) (samplesCNR2 CNR5 CNR7 and CNR8) According to the IUPACclassification isotherms presented in Figure 2(b) could bewithout doubt classified as type IV [26] Shape of isothermspresented in Figure 2(a) does not allow such straightforwardclassification A typical feature of type IV isotherms is finalsaturation plateau of variable length despite being sometimesreduced to inflection point [26] As can be seen no plateaucould be observed in isotherms depicted in Figure 2(a) Itcould be speculated that isotherms presented in Figure 2(a)resemble to type II isotherms However the occurrence ofhysteresis loop is not consistent with this type of isothermsHysteresis is a consequence of capillary condensation [26](ie the initial monolayer-multilayer adsorption on the wallsof mesopores is followed by pore condensation) while type

II isotherms are associated with nonporous adsorbents [26]On the other hand completely reversible isotherms havingno hysteresis at all are rarely observable After careful con-sideration of presented arguments despite not being typicalisotherms in Figure 2(a) are classified as type IV ZagaynovandKutsev [27] in their study on ceria nanopowders also clas-sified isotherms similar to the ones depicted in Figure 2(a) astype IV

The hysteresis loop shapes are generally related to poresstructure Narrow hysteresis loops of isotherms presented inFigure 2(a) (samples CNR1 CNR3 CNR4 and CNR6) couldbe classified as H3 type while broader loops presented in Fig-ure 2(b) (samples CNR2 CNR5 CNR7 and CNR8) are of H2type [26] H3 loops are often associated with nonrigid aggre-gates of plate-like particles or pore network that consisted ofmacropores [26] H2 loops are given by complex pore struc-tures very often in solidsmade by aggregates or agglomeratesof spheroidal particles of nonuniform size and shape [5]

TheBET specific surface areas of the prepared samples aregiven within Table 3 As can be seen the specific surface areasvary significantly with the preparation conditions Amongthe prepared samples sample 5 provided the lowest and sam-ple 6 provided the highest specific surface area Obtained spe-cific surface areas corroborate well with the previously deter-mined average crystallite sizes being inversely proportionalTo the best of our knowledge for the ceria prepared usinghydrothermal synthesis SSA as great as 226m2 gminus1 was notreported before It is important to stress that such favorableoutcome has been achieved without any additive using justplane hydrothermal process while adjusting only the reac-tion parameters In such manner no organic contaminantswhich can reduce catalytic activity of ceria were introduced

The pore size distributions curves were calculated fromdesorption branch of the isotherms by the BJH modelDominant pore radiuses are presented within Table 3 Allsamples but sample 3 have monomodal pore size distributionwhile sample 3 displays bimodal pore size distribution Allpore diameters are within the range of mesopores which isconsistent with the existence of nanoparticles aggregates

Specific surface area was taken as the output of the exper-iment In order to determine the effect of each variable on theoutput the signal-to-noise (SN) ratio of theTaguchi approachhas to be calculated for each experiment There are three cat-egories of performance characteristics that is the-lower-the-better the-higher-the-better and the-nominal-the-better Inthis particular case maximizing the performance character-istic that is the-higher-the-better is required and thereforespecific surface area values were transformed into the signal-to-noise ratio using the following equation

SN = minus10 log[ 1119898

119898

sum

119894=1

1

1199102

119894

] (2)

where 119898 is the number of trials for each experiment and 119910119894

is the mean value of the observed performance characteristicfor a given experiment The SN ratio values for all samplescalculated on the basis of (2) are given in Table 4

Using Taguchi experimental design approach it is possi-ble to separate out the effect of each factor at each level [28]


00 02 04 06 08 10

40

60

80

100

120

CNR1CNR3

CNR4CNR6

Relative pressure pp0

Volu

me a

dsor

bed

(cm

3gminus

1)

(a)

00 02 04 06 08 100

20

40

60

80

100

120

CNR2 CNR5

CNR7 CNR8


Volu

me a

dsor

bed

(cm

3gminus

1)

(b)

Figure 2 Nitrogen adsorption-desorption isotherms of the prepared samples

Table 4 Signal-to-noise ratio according to (2) for each experiment

Experiment 1 2 3 4 5 6 7 8SN ratio 4519 4072 4486 4505 3627 4711 4118 4056

Table 5 SN ratio for each factor and level as well as influence of eachfactor to specific surface area

Factor SN1

SN2

119877

119860 4351 4173 178119861 4352 4172 180119862 4556 3968 588119863 4288 4236 052

First the average SN ratio value is calculated for each factorand level For example the average SN ratio values for factorA (concentration of NaOH) at level 1 (8mol Lminus1) can becalculated by averaging SN ratios fromexperiments 1 6 7 and8

SN1198601=SN1+ SN6+ SN7+ SN8

4 (3)

The influence of factor is defined as the absolute differencebetween the average SN ratios of the two levels For examplethe influence of factor 119860 is the absolute difference betweenthe effect of factor 119860 at level 1 SN

1198601 and the effect of factor

119860 at level 2 SN1198602

119877119860=1003816100381610038161003816SN1198601 minus SN1198602

1003816100381610038161003816 (4)

The larger the influence of factor 119877 the larger the effect thatthe variable has on the observed performance [28] SN ratiovalues for each factor and level as well as influence of eachfactor are tabulated in Table 5

Factor effect plots were used to visualize performancechanges as each individual factor level is changed (Figure 3)The slope of the line indicates the impact magnitude of

particular factor on specific surface area Based on Figure 4it could be estimated that the most influential factor was thetemperature of hydrothermal synthesis

In order to determine if the influence of any factor onspecific surface area is statistically significant the analysis ofvariance (ANOVA) has been performed Generally ANOVAis statistical technique for estimating the degree of differenceor similarity between two or more groups of data Here one-way ANOVA (JMP Version 11 SAS Institute Inc Cary NC1989ndash2013) providing calculation of the significance level ofeach process parameter on observed performance was used

From the SN ratios the overall SN ratio is expressed as

SN = 1119899

119899

sum

1

SN119899 (5)

where 119899 is the number of experiments according to orthogo-nal array SN is the overall mean of SN ratio and SN

119899is the

SN ratio for 119899th experiment In thatmanner the overall meanof SN ratio was calculated to be 4262

The total sum of squares of signal-to-noise ratio due tovariation about overall mean is

SS119905=

119899

sum

119899=1

(SN119899minus SN)

2

(6)

The value of SS119905is given in Table 6

The sum of squares for each factor due to variation aboutoverall mean is

SS119894=119899

119894

119895

sum

119895=1

(SN119894119895minus SN)

2

(7)

where 119894 denotes factor and 119895 denotes level so SN119894119895is the

average SN ratio of 119894th parameter of 119895th level The values ofSS119894have been given in Table 6


8 10 12

40

42

44

46

08 10 12 120 150 180 16 20 24

SN

40

42

44

46

SN

40

42

44

46

SN

40

42

44

46

SN

Time (h)Temperature (∘C)n(Ce2(SO4)3times4H2O)(mmol)c(NaOH) (mol Lminus1)

Figure 3 Factor effects plots for each individual factor level

500nm

(a)

500nm

(b)

Figure 4 FESEMmicrographs of (a) sample CNR5 and (b) sample CNR6

Table 6 Summary of ANOVA for SN ratio

Factor DoF SS119894

Mean SS119894119865-ratio 119901 value

119860 119888(NaOH) 1 638 638 338 016119861 119888(Ce(SO

4)2times3H2O) 1 644 644 342 016

119862 temperature 1 6889 6889 3654 001119863 duration 1 055 055 029 063SS119890

3 566 189SS119905

7 8792

The sum of squares of the errors correlated to all factorsis

SS119890= SS119905minus

119899

sum

119894=1

SS119894 (8)

The sum of squares of the errors is given in Table 6The mean square for each factor is obtained by dividing

the sum of squares by the degrees of freedom (Table 6) Insimilar manner the mean square of the error is obtainedby dividing the sum of squares of the residual error by thedegrees of freedom (Table 6)

Dividing the mean square for each factor by the meansquare error gives 119865-ratio

119865 =Mean SS

119894

Mean SS119890

(9)

A very large119865-ratiomeans that the effect variance exceeds theerror variance by a substantial amount

In order to determine whether any of the differencesbetween the means are statistically significant 119901 values foreach parameter have to be calculated and compared to sig-nificance level Large 119901 value suggests that data do not signifi-cantly differ but if119901 value is small it is likely that the observeddifference is practically significant Usually a significancelevel of 120572 = 005 is used as a boundary value indicating a5 risk of identifying a difference when actually none exists

The ANOVA results for SN ratio of achieving the greatestspecific surface area are given in Table 6 The analysis of theresults showed that for achieving great SSA the only signif-icant parameter is the temperature of the thermal treatmentwhile the influences of the other three parameters are statisti-cally irrelevant In order to achieve great SSA the temperatureof thermal treatment should be held at 120∘C It has to bestressed that these findings are based solely on the factorlevels considered in this study andmay vary if different factorlevels are used

The reasons why samples prepared at lower temperatureshave greater specific surface areas and smaller crystallite sizesare worth discussion Hydrothermal synthesis of ceria quitecommonly yields one-dimensional structures [2 7 9] It isbelieved that in the course of hydrothermal and solvothermalsynthesis diffusion coefficient is the key factor for the forma-tion of 1D-nanostructured materials [29] Any crystallizationfrom solution involves two steps nucleation and growth Lowdiffusion coefficient benefits nucleation while high diffusioncoefficient is beneficial for crystal growth and may influencethe preferred growth along certain direction [29]The intensenucleation further yields 0Dnanoparticles while growth due


to enhanced diffusion coefficient produces 1D nanorods[29] In other words the low synthesis temperature shouldbe beneficiary for crystallization of fine nanoparticles whilehigher temperatures should enable 1D structures formationThe importance of diffusion process to the ceria nanorodsformation has also been stressed by Soykal et al [30] indiscussion on oriented attachment mechanism that allowsceria nanocrystals to grow into a certain direction Proofsthat oriented attachment crystal growth is the main route forthe ceria nanorods formation have been presented by severalauthors [9 31]The fact that temperature is the key parameterfor hydrothermal synthesis of 1D ceria nanostructures hasbeen noted by several authors [9 29 32]

Representative FESEM micrographs of samples CNR5and CNR6 having the smallest and the greatest SSA areshown in Figure 4 Sample 6 consists of irregular-shaped andheavily agglomerated nanoparticles Morphology of sample 5is similar to that of sample 6 but additionally some 1D struc-ture could be observed Sample 5 is prepared at higher tem-perature (180∘C) so it seems that SEM analysis corroboratedassumed relationship between temperature and morphologyIn other words higher temperature enabled the formationof 1D structures despite being entangled with agglomeratedspherical nanoparticles Fine ceria nanoparticles yield greatSSA while coarser nanorods yield smaller SSA

The catalytic efficiency of the prepared ceria sampleswas studied for soot oxidation according to the methodof Sudarsanam et al [25] Four samples were selected forcatalytic test including samples CNR6 (selected since it hasthe greatest SSA) and CNR5 (selected since it has the smallestSSA) For comparison soot was oxidized under the sameconditions without ceria The curves showing percentage ofthe soot oxidized versus temperature are shown in Figure 5Regardless of catalyst presence the oxidation starts around450∘C However from Figure 5 it is obvious that without cat-alyst the oxidation process is the slowest and ends at the tem-perature of 995∘C In samples containing catalyst soot oxi-dation rate is greater and process is completed at lower tem-peratures in a range of 850 to 960∘C Surprisingly catalystswith greater SSA (samples CNR6 and CNR3) turned out tobe less active than catalysts with smaller SSA (samples CNR5and CNR8) Importance of morphology and exposed surfacecrystal plane for catalytic activity of nanocrystalline ceriais often reported [2 25 33] Ceria nanorods seem to showparticularly high catalytic activity [2 34] Therefore it seemsthat morphology has greater influence on catalytic activitythan SSA However relative importance of morphology andparticle size (and in turn SSA) in physical properties and cat-alytic activity of nanocrystalline ceria is still subject of debate[2]

4 Conclusions

Taguchi experimental design has been employed to examinethe effect of various hydrothermal synthesis parameters onthe specific surface area as well as on other properties ofceria Nanocrystalline ceria with SSA as great as 226m2 gminus1was prepared which is unprecedented for the hydrothermalsynthesis of ceria It was shown that the only significant factor

600 800 1000

0

20

40

60

80

100

CNR3CNR5CNR6

CNR8Pure soot

Con

vers

ion

()

T (∘C)

Figure 5 Soot conversion versus temperature for samples CNR3CNR5 CNR6 and CNR8 mixed with soot in ratio of 1 1 Pure sootconversion was added for comparison

for achieving high SSA is the hydrothermal synthesis temper-ature where lower temperature yields greater SSAThe reasonfor such behavior was found in diffusion coefficient whichis temperature dependent When low it favors nucleationwhile when high it favors crystal growth and formation ofone-dimensional structures The occurrence of 1D structurein sample obtained at higher temperature exhibiting thesmallest SSA has been confirmed Increase of SSA in sampleswas accompanied with proportional decrease of crystallitesto crystallite size as low as 59 nm Samples with smallerSSA turned out to possess better catalytic activity which isexplained with the influence of ceria catalyst nanoparticlesmorphology that is presence of 1D nanostructural entities

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The support of the University of Zagreb Faculty of ChemicalEngineering and Technology is gratefully acknowledgedTheauthors would like to thank G Matijasic for valuable discus-sion on adsorption-desorption isotherms

References

[1] A G Macedo S E M Fernandes A A Valente R A SFerreira L D Carlos and J Rocha ldquoCatalytic performance ofceria nanorods in liquid-phase oxidations of hydrocarbons withtert-butyl hydroperoxiderdquoMolecules vol 15 no 2 pp 747ndash7652010

[2] J M Lopez A L Gilbank T Garcıa B Solsona S Agouramand L Torrente-Murciano ldquoThe prevalence of surface oxygenvacancies over the mobility of bulk oxygen in nanostructured


ceria for the total toluene oxidationrdquo Applied Catalysis BEnvironmental vol 174-175 pp 403ndash412 2015

[3] X Gao C Chen S Ren J Zhang and D Su ldquoStructural effectsof cerium oxides on their thermal stability and catalytic perfor-mance in propane oxidation dehydrogenationrdquo Chinese Journalof Catalysis vol 33 no 7 pp 1069ndash1074 2012

[4] H Jin NWang L Xu and S Hou ldquoSynthesis and conductivityof cerium oxide nanoparticlesrdquoMaterials Letters vol 64 no 11pp 1254ndash1256 2010

[5] B Nematollahi M Rezaei and E Nemati Lay ldquoSynthesis ofnanocrystalline CeO

2with high surface area by the taguchi

method and its application inmethanationrdquoChemical Engineer-ing and Technology vol 38 no 2 pp 265ndash273 2015

[6] A Bumajdad J Eastoe and A Mathew ldquoCerium oxidenanoparticles prepared in self-assembled systemsrdquo Advances inColloid and Interface Science vol 147-148 pp 56ndash66 2009

[7] S Chowdhury M Yasir M A B Bustam and K-S LinldquoHydrothermal synthesis and characterization of one dimen-sional ceria nanorod for chromium ion removal from wastew-aterrdquo Journal of Energy Technologies and Policy vol 3 pp 489ndash494 2013

[8] X Ge Z Li and Q Yuan ldquo1D ceria nanomaterials versatilesynthesis and bio-applicationrdquo Journal of Materials Science andTechnology vol 31 no 6 pp 645ndash654 2015

[9] Z C Gernhart C M Marin J J Burke K O Sonnenfeldand C L Cheung ldquoAdditive-free synthesis of cerium oxidenanorods with reaction temperature-tunable aspect ratiosrdquoJournal of the AmericanCeramic Society vol 98 no 1 pp 39ndash432015

[10] N Ohtake Y Yamane K Nakagawa M Katoh and SSugiyama ldquoHydrothermally synthesized ceria with a high spe-cific surface area for catalytic conversion of ethanol to ethylenerdquoJournal of Chemical Engineering of Japan vol 49 no 2 pp 197ndash203 2016

[11] C-Y Cao Z-M Cui C-Q Chen W-G Song and WCai ldquoCeria hollow nanospheres produced by a template-freemicrowave-assisted hydrothermal method for heavy metal ionremoval and catalysisrdquo Journal of Physical Chemistry C vol 114no 21 pp 9865ndash9870 2010

[12] X Yin Y Zhang Z Fang Z Xu and W Zhu ldquoHydrothermalsynthesis of CeO

2nanorods using a strong basendashweak acid salt

as the precipitantrdquo Nanoscience Methods vol 1 no 1 pp 115ndash122 2012

[13] G Renu V V Divya Rani S V Nair K R V Subramanian andV-K Lakshmanan ldquoDevelopment of cerium oxide nanopar-ticles and its cytotoxicity in prostate cancer cellsrdquo AdvancedScience Letters vol 6 pp 17ndash25 2012

[14] M Hirano and E Kato ldquoHydrothermal synthesis of cerium(IV)oxiderdquo Journal of the American Ceramic Society vol 79 no 3pp 777ndash780 1996

[15] M Hirano and E Kato ldquoHydrothermal synthesis of nanocrys-talline cerium(IV) oxide powdersrdquo Journal of the AmericanCeramic Society vol 82 no 3 pp 786ndash788 1999

[16] J Wang Q Liu and Q Liu ldquoCeria- and Cu-doped ceriananocrystals synthesized by the hydrothermal methodsrdquo Jour-nal of the American Ceramic Society vol 91 no 8 pp 2706ndash2708 2008

[17] J Park J Kim JHan S-WNam andT-H Lim ldquoHydrothermalsynthesis and characterization of nanocrystalline ceria pow-dersrdquo Journal of Industrial and Engineering Chemistry vol 11no 6 pp 897ndash901 2005

[18] H-X Mai L-D Sun Y-W Zhang et al ldquoShape-selectivesynthesis and oxygen storage behavior of ceria nanopolyhedrananorods and nanocubesrdquo Journal of Physical Chemistry B vol109 no 51 pp 24380ndash24385 2005

[19] C Pan D Zhang and L Shi ldquoCTAB assisted hydrothermalsynthesis controlled conversion and CO oxidation propertiesof CeO

2nanoplates nanotubes and nanorodsrdquo Journal of Solid

State Chemistry vol 181 no 6 pp 1298ndash1306 2008[20] A I Y Tok S W Du F Y C Boey and W K Chong

ldquoHydrothermal synthesis and characterization of rare earthdoped ceria nanoparticlesrdquo Materials Science and EngineeringA vol 466 no 1-2 pp 223ndash229 2007

[21] S-F Wang C-T Yeh Y-R Wang and Y-C Wu ldquoChar-acterization of samarium-doped ceria powders prepared byhydrothermal synthesis for use in solid state oxide fuel cellsrdquoJournal of Materials Research and Technology vol 2 no 2 pp141ndash148 2013

[22] J Yang L Lukashuk H Li K Fottinger G Rupprechter and USchubert ldquoHigh surface area ceria for CO oxidation preparedfrom cerium t-butoxide by combined sol-gel and solvothermalprocessingrdquo Catalysis Letters vol 144 no 3 pp 403ndash412 2014

[23] Y Kamimura M Shimomura and A Endo ldquoSimple template-free synthesis of high surface areamesoporous ceria and its newuse as a potential adsorbent for carbon dioxide capturerdquo Journalof Colloid and Interface Science vol 436 pp 52ndash62 2014

[24] H Mohamed M Hisyam Lee M Sarahintu S Salleh and BSanugi ldquoThe use of Taguchi method to determine factors affect-ing the performance of destination sequence distance vectorrouting protocol in mobile ad hoc networksrdquo Journal of Mathe-matics and Statistics vol 4 no 4 pp 194ndash198 2008

[25] P Sudarsanam B Hillary D K Deepa et al ldquoHighly efficientcerium dioxide nanocube-based catalysts for low temperaturediesel soot oxidation The cooperative effect of cerium- andcobalt-oxidesrdquoCatalysis Science and Technology vol 5 no 7 pp3496ndash3500 2015

[26] M Thommes K Kaneko A V Neimark et al ldquoPhysisorptionof gases with special reference to the evaluation of surface areaand pore size distribution (IUPACTechnical Report)rdquo Pure andApplied Chemistry vol 87 no 9-10 pp 1051ndash1069 2015

[27] I V Zagaynov and S V Kutsev ldquoFormation of mesoporousnanocrystalline ceria from cerium nitrate acetate or acetylace-tonaterdquo Applied Nanoscience vol 4 no 3 pp 339ndash345 2014

[28] P J Ross Taguchi Technique for Quality Engineering McGraw-Hill New York NY USA 1988

[29] C Sun H Li H Zhang Z Wang and L Chen ldquoControlledsynthesis of CeO

2nanorods by a solvothermal methodrdquo Nan-

otechnology vol 16 no 9 pp 1454ndash1463 2005[30] I I Soykal H Sohn B Bayram et al ldquoEffect of microgravity on

synthesis of nano ceriardquo Catalysts vol 5 no 3 pp 1306ndash13202015

[31] Z Yang K Zhou X Liu Q Tian D Lu and S Yang ldquoSingle-crystalline ceria nanocubes size-controlled synthesis charac-terization and redox propertyrdquo Nanotechnology vol 18 ArticleID 185606 2007


[32] P X Huang F Wu B L Zhu et al ldquoCeO2nanorods and gold

nanocrystals supported on CeO2nanorods as catalystrdquo Journal

of Physical Chemistry B vol 109 no 41 pp 19169ndash19174 2005[33] S Chowdhury and K-S Lin ldquoSynthesis and characterization of

1D ceria nanomaterials for CO oxidation and steam reformingof methanolrdquo Journal of Nanomaterials vol 2011 Article ID157690 16 pages 2011

[34] K Zhou X Wang X Sun Q Peng and Y Li ldquoEnhancedcatalytic activity of ceria nanorods from well-defined reactivecrystal planesrdquo Journal of Catalysis vol 229 no 1 pp 206ndash2122005

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Table 1 Process variables (factors) used

Assignation Variable Unit Lowervalue level 1

Highervalue level 2

119860 119888(NaOH) molL 8 12119861 119899(Ce(SO

4)2times3H2O) mmol 08 12

119862 Temperature ∘C 120 180119863 Duration h 16 24

Table 2 Experimental layout defined based on Taguchi L8 orthog-onal array

Experiment number 119860 119861 119862 119863

1 1 2 1 12 2 1 2 13 2 2 1 24 2 1 1 15 2 2 2 26 1 1 1 27 1 1 2 28 1 2 2 1

200m2 gminus1 for precipitation process [23] and 139m2 gminus1 forhydrothermally synthesized ceria [10]

The Taguchi method of experimental design is a methodfor testing the relative importance of parameters in the exper-iment outcome This approach is considered as very efficientsince a lot of information is obtained from a reduced set ofexperiments [24]

This study employs the experiment design in order toyield nanostructured CeO

2having favorable properties using

hydrothermal method of synthesis Thereby the relativeeffect of reactants concentrations synthesis temperature andduration on the specific surface area as well as on otherproperties of ceria was examined

2 Materials and Methods

In the course of the hydrothermal synthesis of ceria nanopar-ticles four process parameters were detected as potentiallysignificant concentration of two precursors NaOH andCe(SO

4)2times3H2O and temperature and duration of synthe-

sis In order to examine their effect on the properties ofceria nanoparticles a Taguchi experimental design has beenemployed Four factors (process variables) at two levels foreach factor (Table 1) were selected A common experimentaldesign including combinations of all input factors (full-factorial design) would require 24 = 16 experiments Onthe other hand Taguchi orthogonal design requires only 8experiments half of full-factorial design L8 orthogonal array(Table 2) is generated using JMP computer program for statis-tical analysis (JMP Version 11 SAS Institute Inc Cary NC1989ndash2013)

The typical synthesis procedure was as follows appropri-ate amount of Ce(SO

4)2times3H2O (Merck Germany) has been

dissolved in 56 cm3 of NaOH (Kemika Croatia) solution and

put in a 70mL capacity Teflon-lined stainless-steel auto-clave sealed tightly and thermally treated in temperature-controlled oven Eight samples were prepared the synthesisconditions used are shown in Tables 1 and 2 After cooling ofthe autoclave the product was centrifuged and obtained paleyellow precipitate was washed with demineralized water withthe aid of sonication Centrifugation and washing sequenceshave been repeated three times Finally yielded materialswere dried at 60∘C for 24 h in static air

The crystal phase in samples was identified by powder X-ray diffraction (XRD) analysis using Shimadzu XRD 6000diffractometer with CuK120572 radiation operated at 40 kV and30mA Data were collected between 5 and 70∘ 2120579 in a stepscan mode with steps of 002∘ and counting time of 2 s Thecrystallite size was estimated from XRD peak broadeningusing Scherrerrsquos formula

119863 =119896120582

120573 cos 120579 (1)

where 119863 is crystallite size 119896 is shape factor 120582 is CuK120572radiation wavelength 120573 is peak full width at half maximumcorrected for instrumental broadening and 120579 is Bragg angle

Surface properties of samples were determined by aBrunauer-Emmet-Teller (BET) N

2gas adsorption-desorp-

tion isotherms obtained on Micromeritics ASAP-2000 at77K Samples were previously degassed at 100∘C under adynamic vacuum of 13mPa to remove any surface adsorbedresidues Surface area was calculated by utilizing the desorp-tion data Pore size and pore volume were calculated by BJHmethod applied to the desorption branch of the isotherms

Morphology of the samples was investigated using fieldemission gun scanning electron microscopy (FESEM) deviceJEOL model 7000F The samples were sputtered with gold byQuorum SC 7620 sputter coater

The catalytic efficiency of the samples for soot oxidationwas examined according to the method of Sudarsanam et al[25] where 10 plusmn 1mg of catalyst was mixed with 10 plusmn 1mgof Norit DLC Super 30 carbon black (Cabot Norit NederlandBV) in 120572-alumina crucible with spatula for 2min and placedin a thermogravimetric analyzer (TGA) Netzsch STA409Oxidation experiment consisted of heating the catalyst-sootmixture at a rate of 10 Kminminus1 from ambient temperatureto 1300∘C under a 100 cm3minminus1 synthetic air purge gasflow Each test was repeated three times to ensure thereproducibility of the obtained results

3 Results and Discussion

The powder XRD patterns (Figure 1) of the prepared samplesare indexed to ceria CeO

2(ICDD PDF number 34-394)

Ceria adopts the fluorite crystal structure with space groupFm-3m In FCC ceria unit cell Ce4+ ions are close packedwhile O2minus ions occupy tetrahedral sites Beside peak anglespeak intensities also obey the profile of ICDD PDF number34-394 Broad peaks point out to formation of nanocrys-talline particles The differences among patterns presented inFigure 1 indicate that different synthesis conditions affect thecrystallite size of CeO

2 However no significant difference







4000

3500

3000

2000

2500

1500

1000

500

0

20 30

(111)

Inte

nsity

(CPS

)

(200) (220)(222)

(311)

40 50 60

CNR1CNR2CNR3CNR4

CNR5CNR6CNR7

CNR8

2120579 (∘) CuK120572











119898

sum

119894=1

1

1199102

119894

] (2)





00 02 04 06 08 10

40

60

80

100

120

CNR1CNR3

CNR4CNR6


Volu

me a

dsor

bed

(cm

3gminus

1)

(a)

00 02 04 06 08 100

20

40

60

80

100

120

CNR2 CNR5

CNR7 CNR8


Volu

me a

dsor

bed

(cm

3gminus

1)

(b)





Factor SN1

SN2

119877

119860 4351 4173 178119861 4352 4172 180119862 4556 3968 588119863 4288 4236 052


SN1198601=SN1+ SN6+ SN7+ SN8

4 (3)



119860 at level 2 SN1198602

119877119860=1003816100381610038161003816SN1198601 minus SN1198602

1003816100381610038161003816 (4)






SN = 1119899

119899

sum

1

SN119899 (5)


119899is the



SS119905=

119899

sum

119899=1

(SN119899minus SN)

2

(6)



SS119894=119899

119894

119895

sum

119895=1

(SN119894119895minus SN)

2

(7)




8 10 12

40

42

44

46

08 10 12 120 150 180 16 20 24

SN

40

42

44

46

SN

40

42

44

46

SN

40

42

44

46

SN



500nm

(a)

500nm

(b)



Factor DoF SS119894


119860 119888(NaOH) 1 638 638 338 016119861 119888(Ce(SO

4)2times3H2O) 1 644 644 342 016


3 566 189SS119905

7 8792


SS119890= SS119905minus

119899

sum

119894=1

SS119894 (8)




119865 =Mean SS

119894

Mean SS119890

(9)









4 Conclusions


600 800 1000

0

20

40

60

80

100

CNR3CNR5CNR6

CNR8Pure soot

Con

vers

ion

()

T (∘C)



Competing Interests


Acknowledgments


References























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









4000

3500

3000

2000

2500

1500

1000

500

0

20 30

(111)

Inte

nsity

(CPS

)

(200) (220)(222)

(311)

40 50 60

CNR1CNR2CNR3CNR4

CNR5CNR6CNR7

CNR8

2120579 (∘) CuK120572











119898

sum

119894=1

1

1199102

119894

] (2)





00 02 04 06 08 10

40

60

80

100

120

CNR1CNR3

CNR4CNR6


Volu

me a

dsor

bed

(cm

3gminus

1)

(a)

00 02 04 06 08 100

20

40

60

80

100

120

CNR2 CNR5

CNR7 CNR8


Volu

me a

dsor

bed

(cm

3gminus

1)

(b)





Factor SN1

SN2

119877

119860 4351 4173 178119861 4352 4172 180119862 4556 3968 588119863 4288 4236 052


SN1198601=SN1+ SN6+ SN7+ SN8

4 (3)



119860 at level 2 SN1198602

119877119860=1003816100381610038161003816SN1198601 minus SN1198602

1003816100381610038161003816 (4)






SN = 1119899

119899

sum

1

SN119899 (5)


119899is the



SS119905=

119899

sum

119899=1

(SN119899minus SN)

2

(6)



SS119894=119899

119894

119895

sum

119895=1

(SN119894119895minus SN)

2

(7)




8 10 12

40

42

44

46

08 10 12 120 150 180 16 20 24

SN

40

42

44

46

SN

40

42

44

46

SN

40

42

44

46

SN



500nm

(a)

500nm

(b)



Factor DoF SS119894


119860 119888(NaOH) 1 638 638 338 016119861 119888(Ce(SO

4)2times3H2O) 1 644 644 342 016


3 566 189SS119905

7 8792


SS119890= SS119905minus

119899

sum

119894=1

SS119894 (8)




119865 =Mean SS

119894

Mean SS119890

(9)









4 Conclusions


600 800 1000

0

20

40

60

80

100

CNR3CNR5CNR6

CNR8Pure soot

Con

vers

ion

()

T (∘C)



Competing Interests


Acknowledgments


References























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




00 02 04 06 08 10

40

60

80

100

120

CNR1CNR3

CNR4CNR6


Volu

me a

dsor

bed

(cm

3gminus

1)

(a)

00 02 04 06 08 100

20

40

60

80

100

120

CNR2 CNR5

CNR7 CNR8


Volu

me a

dsor

bed

(cm

3gminus

1)

(b)





Factor SN1

SN2

119877

119860 4351 4173 178119861 4352 4172 180119862 4556 3968 588119863 4288 4236 052


SN1198601=SN1+ SN6+ SN7+ SN8

4 (3)



119860 at level 2 SN1198602

119877119860=1003816100381610038161003816SN1198601 minus SN1198602

1003816100381610038161003816 (4)






SN = 1119899

119899

sum

1

SN119899 (5)


119899is the



SS119905=

119899

sum

119899=1

(SN119899minus SN)

2

(6)



SS119894=119899

119894

119895

sum

119895=1

(SN119894119895minus SN)

2

(7)




8 10 12

40

42

44

46

08 10 12 120 150 180 16 20 24

SN

40

42

44

46

SN

40

42

44

46

SN

40

42

44

46

SN



500nm

(a)

500nm

(b)



Factor DoF SS119894


119860 119888(NaOH) 1 638 638 338 016119861 119888(Ce(SO

4)2times3H2O) 1 644 644 342 016


3 566 189SS119905

7 8792


SS119890= SS119905minus

119899

sum

119894=1

SS119894 (8)




119865 =Mean SS

119894

Mean SS119890

(9)









4 Conclusions


600 800 1000

0

20

40

60

80

100

CNR3CNR5CNR6

CNR8Pure soot

Con

vers

ion

()

T (∘C)



Competing Interests


Acknowledgments


References























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




8 10 12

40

42

44

46

08 10 12 120 150 180 16 20 24

SN

40

42

44

46

SN

40

42

44

46

SN

40

42

44

46

SN



500nm

(a)

500nm

(b)



Factor DoF SS119894


119860 119888(NaOH) 1 638 638 338 016119861 119888(Ce(SO

4)2times3H2O) 1 644 644 342 016


3 566 189SS119905

7 8792


SS119890= SS119905minus

119899

sum

119894=1

SS119894 (8)




119865 =Mean SS

119894

Mean SS119890

(9)









4 Conclusions


600 800 1000

0

20

40

60

80

100

CNR3CNR5CNR6

CNR8Pure soot

Con

vers

ion

()

T (∘C)



Competing Interests


Acknowledgments


References























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







4 Conclusions


600 800 1000

0

20

40

60

80

100

CNR3CNR5CNR6

CNR8Pure soot

Con

vers

ion

()

T (∘C)



Competing Interests


Acknowledgments


References























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Research Article High Surface Area Ceria Nanoparticles via ...downloads.hindawi.com/journals/jnm/2016/7274949.pdf100 120 CNR1 CNR3 CNR4 CNR6 Relative pressure, p/p 0 Volume adsorbed