Research Article Low-Temperature Synthesis and …downloads.hindawi.com/journals/jnm/2014/164380.pdfResearch Article Low-Temperature Synthesis and Gas Sensitivity of Perovskite-Type

Research ArticleLow-Temperature Synthesis and Gas Sensitivity ofPerovskite-Type LaCoO3 Nanoparticles

Lorenzo Gildo Ortiz1 Heacutector Guilleacuten Bonilla1 Jaime Santoyo Salazar2

M de la L Olvera3 T V K Karthik3 Enrique Campos Gonzaacutelez2 and Juan Reyes Goacutemez4

1 Facultad de Ciencias Quımicas Universidad de Colima 28400 Colima COL Mexico2Departamento de Fısica Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional07360 Mexico DF Mexico

3 Departamento de Ingenierıa Electrica-SEES Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional07360 Mexico DF Mexico

4 Facultad de Ciencias Universidad de Colima Bernal Dıaz del Castillo 340 28045 Colima COL Mexico

Correspondence should be addressed to Juan Reyes Gomez reyesgjucolmx

Received 29 January 2014 Revised 31 March 2014 Accepted 16 May 2014 Published 5 June 2014

Academic Editor Rakesh K Joshi

Copyright copy 2014 Lorenzo Gildo Ortiz 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

LaCoO3nanoparticles with perovskite-type structure were prepared by amicrowave-assisted colloidal method Lanthanumnitrate

cobalt nitrate and ethylenediamine were used as precursors and ethyl alcohol as solvent The thermal decomposition of theprecursors leads to the formation of LaCoO

3from a temperature of 500∘C The structural morphological and compositional

properties of LaCoO3nanoparticles were studied in this work by X-ray diffraction (XRD) scanning electron microscopy (SEM)

transmission electron microscopy (TEM) and atomic force microscopy (AFM) Pellets were manufactured in order to test the gassensing properties of LaCoO

3powders in carbonmonoxide (CO) and propane (C

3H8) atmospheres Agglomerates of nanoparticles

with high connectivity forming a porous structure were observed from SEM and TEM analysis LaCoO3pellets presented a high

sensitivity in both CO and C3H8at different concentrations and operating temperatures As was expected sensitivity increased

with the gas concentration and operation temperature increase

1 Introduction

In the last years inorganicmaterials have beenwidely studieddue to their attractive characteristics such as capacity tomodify its microstructure morphology and other physicalproperties as a function of the method and conditionsof synthesis [1ndash3] Novelty synthesis methods have beendeveloped for preparing inorganic materials such as aerosolsol-gel solution coprecipitation solution-polymerizationcolloidal method and solid-state reaction (ceramic method)among others [4ndash10] It is well known that a particularsynthesis route induces to physical changes in the volume andsurface characteristics of the material for example structuremorphology porosity and particle size [11] and consequentlythe electrical optical magnetic and sensing properties aremodified as well [12 13]

In particular diverse research groups have focused theirinterest in performing synthesis of materials through col-loidal routes since this method has led to process materialswith particle size around a few nanometers with attrac-tive morphologies of a great relevance due to its potentialapplications [14 15] For example Michel et al obtainedporous microspheres by using colloidal synthesis of trirutile-type CoSb

2O6[16] Sun et al also reported the formation

of nanostructured microspheres of organic-inorganic hybridmaterials by using the colloidal methods [17] Nanoparticlessynthesized by colloidal routes that can be applied in differentfields such as pigments for diverse applications record-ing materials ceramics catalysis drug delivery systemsbiosensors photonic crystals colloidal lithography porousmembranes and formation of hollow spheres among others[17ndash19]

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 164380 8 pageshttpdxdoiorg1011552014164380

2 Journal of Nanomaterials

On the other hand lanthanum cobalt oxide (LaCoO3)

with perovskite-type structure has acquired great importanceby its magnetic electrical and catalytic properties thatmake it attractive for different technological applicationsFor example it has been reported that LaCoO

3exhibits

catalytic activity in the oxidation of different compounds likecarbonmonoxide (CO) andmethane (CH

4) and also exhibits

photocatalytic activity in the oxidation of methyl orange andwater [20ndash27] In addition the LaCoO

3is a material that

presents good thermoelectric properties [28]In this work LaCoO

3nanoparticles were synthesized

by a colloidal route for studying their physical propertiesAdditionally the synthesized LaCoO

3powders were used to

manufacture pellets to be tested as gas sensors in two differentatmospheres namely CO and propane (C

3H8)

2 Experimental Procedures

21 Synthesis of LaCoO3Nanoparticles LaCoO

3nanoparti-

cles with perovskite-type structure were prepared employ-ing a colloidal method Firstly three different solutionswere separately prepared The first one consisted of 17316 gof La(NO

3)3sdot6H2O (Alfa Aesar) the second 1164 g of

Co(NO3)2sdot6H2O (Jalmek) both dissolved in 5mL of absolute

ethyl alcohol (CTR) and the third 2mL of ethylenediamine(Sigma) dissolved in 10mL of the same alcohol The threesolutions were stirred vigorously for 20min and then mixedall together Finally the resultant solution was kept in stirringfor 24 h at room temperature

Later the solution was put into a domestic microwaveoven (LGmodel MS1147 X) in order to evaporate the solventby a low power radiation of microwaves (sim145W) Theevaporation rate was controlled by applying the microwaveradiation in steps of 25 s in order to keep the solution at atemperature around 70∘C the temperature was monitored byan Extech IR 403255 thermometer The control of heatingtime and temperature was decisive to avoid the splashingand the consequent loss of material namely a better processyield After entire evaporation of solvents a yellow paste wasobtained which was dried at 200∘C during 8 h in a normalatmosphere The resultant powder was divided in five partsand theywere calcined at different temperatures namely 300400 500 600 and 700∘C The calcination process consistedof a heating rate of 100∘Ch up to reach the set point and thenan annealing for 5 h at constant temperatureThe calcinationswere carried out in an oven Vulcan 3ndash550 which has aprogrammable temperature controller

22 Physical Characterization of LaCoO3Powders All cal-

cined powders were analyzed by X-ray diffraction (XRD)by using a Siemens D500 diffractometer with a Cu-K120572radiation The 2120579 scanning range was from 10∘ to 70∘ witha step size of 002∘ and a step time of 1 s Lattice parameterswere calculated from the XRD patterns Powder Cell 24software [29] was employed for analyzing the XRD spectraMorphology of LaCoO

3powders was analyzed by scanning

electron microscopy (SEM) by using a JEOL JSM-6390LVmicroscope in modality of high vacuum and secondary

electron emission A surface composition analysis was devel-oped by energy dispersive X-ray spectroscopy (EDS-SEM)with an XFlash Detector 5010 from Bruker Surface areaanalysis was performed by nitrogen adsorption at 77K witha Minisorp II equipment from BEL Japan In this character-ization previous to the N

2adsorption process the chamber

with the sample was outgassed and kept in vacuum for 24 hat room temperature Surface area was calculated from theBET equation Size and shape of the nanoparticles wereanalyzed by transmission electron microscopy (TEM) in aJEM-2010 equipment from JEOLwith an acceleration voltageof 200 kV The surface topography was analyzed by atomicforce microscopy (AFM) by using a JSPM-5200 microscopefrom JEOL under intermittent contact operation For thetopographical study 01 g of LaCoO

3powder was dispersed

with isopropyl alcohol in a container by using an ultrasonicbath for 5 minutes Later by a syringe a drop of materialdisperse was deposited over the surface of a 15mm diameterbronze disc and finally dried at room temperature during24 h

23 Pellets Preparation for Gas Sensitivity Analysis The sens-ing properties of synthesized LaCoO

3powders were probed

in two different atmospheres namely carbonmonoxide (CO)and propane (C

3H8) at different gas concentrations and

operation temperaturesThe sensingmeasurements consistedof monitoring the electrical resistance of 12mm diameterand 05mm thick pellets manufactured by using a SimplexItal Equip-25 Tons pressing machine After several trialsoptimal pressing conditions were found for 15 tons during90min For electricalmeasurements twoohmic contactsweremanufactured onto the pellets by using pure silver paint(Alpha Aesar) Then these pellets were put onto a sampleholder in a chamber which allows the introduction of gasesin a controlled way For controlling gas concentration thepartial pressure into the chamber was monitored by a TM20Leybold detectorThe experimental setup used formeasuringthe sensing response is shown in Figure 1

The pellets sensitivity 119878 was estimated by the relative dif-ference of the electrical conductances (1electrical resistance)according to the following equation

119878 =

119866

119892minus 119866

119900

119866

119900

(1)

where 119866119892and 119866

119900are the electrical conductance of the

LaCoO3pellets measured in gas (CO or C

3H8) and air

respectively The conductance was measured by using aKeithley 2001 digital multimeter as a function of operatingtemperature and gas concentration Corresponding graphsare reporting results for three temperatures namely 150 250and 350∘C and five different gas concentrations 5 50 100200 and 300 ppmThis temperature range was selected sincelower operating temperatures do not lead to any conductancechanges

Journal of Nanomaterials 3

11

Gas

2

4

9

10

7

8

56

1

2

3

Display

35

4

(1) Vacuum chamber(2) Probes(3) Heating resistance plate (4) Sample(5) Thermocouple(6) Gas valves

(7) Vacuum valve (8) Pumping system(9) Temperature controller(10) Pressure meter(11) Multimeter

minus1

Figure 1 Schematic diagram of the system used for monitoring thesensing properties in controlled atmosphere and temperature

Inte

nsity

(au

)

10 20 30 40 50 60 70

2120579 (deg)

700∘C

600∘C

500∘C

400∘C

300∘C

200∘C

LaCoO3

La2O3

(012

)

(110

)

(104

)

(202

)(006

)(024

)

(122

)(116

)(214

)(018

)

(220

)

Figure 2 XRD patterns of the precursor material calcined from 200to 700∘C

3 Results and Discussion

31 XRD Analysis Figure 2 shows the X-ray diffractionpatterns of the LaCoO

3powders obtained after thermal treat-

ments carried out from 200 to 700∘C From the spectra arrayit can be observed that powders calcined at 200 and 300∘Care totally amorphous since the corresponding diffractionpatterns do not showdefined peaksThe spectrumof powderscalcined at 400∘C shows a weak peak corresponding to theLa2O3phase according to the JCPDS file number 05-0602

whereas the spectrum of powders calcined at 500∘C fit wellto the crystalline structure of LaCoO

3with the presence of

the (012) (110) (104) (202) (006) (024) (122) (116) (214)(018) and (220) planes according to the JCPDF file number48-0123 card At higher calcination temperatures 600 and700∘C the peaks in the spectra are higher and better definedThis result is associated with a better crystallinity Thesetwo spectra prove the formation of the LaCoO

3perovskite

with rhombohedral structure with space group R-3c Thesymmetry is consistent with other XRD studies reportedpreviously [28 30]The lattice parameters estimated were 119886 =5434 A and 119888 = 13110 A The wide peaks in the diffractionspectra indicate the nanocrystalline nature of the materialtherefore the mean size of crystal (119905) was estimated by usingthe Scherrer equation [31] 119905 = 09120582120573 cos 120579 where 120582 is thewavelength of the radiation used (15406 A) 120579 is the Braggangle and 120573 is the full width at half maximum (FWHM) ofthe diffraction peak Considering all reflections the crystalsize estimated was around 30 nm

Traditionally LaCoO3has been synthesized through a

solid-state reaction employing La2O3as precursor material

whereas Co2O3or Co

3O4were required to mix press and

calcinate the solid precursors at temperatures as high as1000∘C and long times for reactions (in the order of days)for having a complete formation of the compound [28 32]Comparing the solid-state reaction with the synthesis bycolloidal method the formation temperatures of 600 and700∘C and the annealing time of 5 h are relatively low for theformation of LaCoO

3

Recently other research groups have reported differentmethods for preparing LaCoO

3 where calcination temper-

atures between 600 and 700∘C were used Carabalı et al[33] synthesized LaCoO

3by the acrylamide polymerization

method using 120574 radiation reporting that the compoundbegins its formation at 500∘C and the formation of the singlephase was around 700∘C Jung and Hong [24] reported theformation of LaCoO

3at 650∘C when it was prepared from

an aqueous solution of metallic nitrate salts in presence ofmalic acid later a drying process by microwave radiationand finally a thermal treatment Similarly Sompech et al [34]synthesized perovskite at 600∘C employing a mechanochem-ical method In the present work LaCoO

3powders were

obtained employing a microwave-assisted colloidal methodin presence of ethylenediamine and a further calcinationprocess from a temperature of 500∘C and higher Then wecan state that temperatures around 600∘C are suitable for theformation of LaCoO

3employing soft synthesis methods

32 Scanning Electron Microscopy Analysis Figure 3 showstwo typical SEM images of LaCoO

3powders after calcination

at 700∘C These images present two different magnifications(a) 500x and (b) 15000x In Figure 3(a) it can be observed thatthe surface presents lots of pores with different sizes arounda few micrometers The smallest pores are around 05 120583mwhereas the biggest are around 30 120583m Also a grid of particleswas observed forming net-like structures and some particlesdisperse over the surface of materialThis can bemore clearlyobserved at higher magnifications as is shown in Figure 3(b)


50120583m

(a)

1120583m

(b)

Figure 3 SEM images of LaCoO3powders calcined at 700∘C at two different magnifications (a) 500x and (b) 15000x

1 2 3 4 5 6 7 8

C

Co

Co

Co

LaLa

La

LaLaLa

La

La

La

O

(Cou

nts

s)

LaCoO3

Energy (keV)

Figure 4 EDS-SEM spectrum of LaCoO3powders showing char-

acteristic lines of La Co and O

the gridding is due to the great connectivity among theparticles The porous microstructure obtained is attributedto the released gases during the thermal decomposition ofthe organic species mainly water vapor NO

119909 and CO

2

among others [35] BET surface area of LaCoO3was around

142m2gThe preparation of inorganic compounds employing

colloidal methods has been widely studied by Matijevic [36]The author states that these methods give rise to a bettercontrol on the nucleation process and the growth of theparticles Thus compounds with different morphologies canbe obtained These morphologies follow the crystallizationprinciples given by Lamer and Dinegar [37] which weredescribed in three theoretical stages the first stage statesthat the concentration of the reagents in colloidal dispersionsgradually increases the second one states that the concentra-tion of the reagents reaches a limiting state of supersaturationand the nucleation happens forming the nuclei of the crystalsand finally the third stage states that the growth of stablenuclei to form discrete particles is originated by diffusion ofthe dissolved species to nuclei

Figure 4 shows an EDS-SEM spectrum of LaCoO3oxide

From this it is possible to observe the characteristic peaks ofLa Co andO in concordance to the chemical composition of

thematerial For lanthanum (La)more intensive peaks corre-spond to the L120572 and L120573 lines localized at 465 and 504 keVrespectively For cobalt (Co) the three peaks present in thespectrum correspond to the characteristic lines L120572 K120572 andK120573 localized at 077 692 and 765 keV respectively Finally

for oxygen (O) the corresponding line is K120572 with an energyvalue of 0525 keV On the other hand the line localized closeto 028 keV indicates that carbon (C) element is present inthe composition which is a residue of the combustion of theorganicmaterial [38]This fact is a disadvantage of employingthe organic reagents in the synthesis of inorganic compounds

33 Transmission Electron Microscopy Analysis Figure 5shows typical images obtained by transmission electronmicroscopy and their corresponding particle size distributionof LaCoO

3perovskite powders In Figure 5(a) we observed

that LaCoO3oxide is constituted by nanoparticles that

present irregular shape and a rough surface texture Inaddition a continuous connectivity among the particles wasobserved as well in a similar way to that observed in the SEMimage Figure 3(b) This micrograph evidences the formationof necks for giving rise one more time to the coalescenceof particles Figure 5(b) shows the particle size distributionof LaCoO

3oxide obtained through the analysis of various

TEM images The particle size has been estimated in a rangeof 25 to 144 nm and around 78 of the particles were inthe 40ndash100 nm range with an average size estimated around68 nm with a standard deviation of 27 nm HRTEM wasperformed in a selected zone of the sample The HRTEMimage reveals that the interplanar distance is around 386 Awhich corresponds to (012) planes This image reports theelectron diffraction pattern where the characteristic rings ofthe reflections of the nanometric polycrystalline material canbe observed

34 Atomic Force Microscopy Analysis Topography of theLaCoO

3powders was analyzed by using the atomic force

microscopy (AFM) technique Figure 6 shows a typical AFMimage in a 322 nm times 322 nm scanned area From thismicrograph a topography can be observed that is conformedby grains of different height associated directly with thecontrast of the image The estimated particle size of thescanned area was around 64 nm These results are consistent


200nm

(a)

33

29

24

20

16

12

8

4

0

Part

icle

s (

)

Particle size (nm)20 40 60 80 100 120 140 160

(b)

10nm

sim386 A

(c)

Figure 5 TEM analysis of LaCoO3powders (a) LaCoO

3nanoparticles and electron diffraction pattern (inset) (b) particle size distribution

and (c) HRTEM image showing the lattice fringes

(nm)

(nm

)

(nm

)

7

0

0

3220

322

Figure 6 Topographical image obtained by AFM of LaCoO3

powders

with those obtained from TEM shown in Figure 5(a) Themean planar roughness estimated over the scanning areawas around 484 nm From AFM analysis it is evident that

the texture observed from TEM images can be associated tothe roughness on the nanoparticles surface

35 Sensing Properties Figure 7 shows the sensitivities ofthe LaCoO

3pellets as a function of the CO and C

3H8

concentration LaCoO3pellets are clearly sensible to both

gas concentration and operating temperature neverthelessat temperatures below 150∘C no resistance changes wereregistered We observed an increase in the sensitivity mag-nitude with increase in the operation temperature for bothCO and C

3H8 This result is associated to the increase

of the oxygen desorption at higher temperatures Changreported the adsorption of different oxygen species as afunction of the temperature [39] So at temperature below150∘C the O

2

minus oxygen species is present in a dominant waywhereas other oxygen species like Ominus and O2minus are presentat higher temperatures which are more reactive species thanprevious ones At room temperature no resistance changesare registered since there is not enough thermal energy toproduce the desorption of oxygen species irrespective of thegas concentration


0 50 100 150 200

0

2

4

6

8

CO concentration (ppm)

150 350

250

Tamb

Sens

itivi

ty

Operation temperature (∘C)

(a)


50 100 150 200 250 300 350

0

2

4

6

8

0 5 50

100200

Sens

itivi

ty


(b)

0 50 100 150 200 250 300

0

10

20

30

40

150250

350Tamb

Sens

itivi

ty

C3H8 concentration (ppm)


(c)

50 100 150 200 250 300 350

0

10

20

30

40

Operation temperature (degC)

0 5 50

100200300

Sens

itivi

ty


(d)

Figure 7 Sensitivity of LaCoO3pellets versus (a) CO concentration (b) operating temperature and CO (c) propane (C

3H8) concentration

and (d) operating temperature and propane (C3H8) concentration

At 350∘C and 200 ppm of CO and C3H8 the sensitivities

calculated were around 10 and 15 respectively Neverthe-less in case of C

3H8 the sensitivity was around 42 at

300 ppm thus it was thrice increased On the other handthe sensitivity was increased with the gas concentrationirrespective of the gas type as was expected since the moregas concentration the more desorption reactions

4 Conclusions

LaCoO3nanoparticles with perovskite-type structure were

successfully synthesized employing a colloidal method Thissynthesis route is a convenient way to synthesize the com-pound at temperatures relatively low LaCoO

3nanoparticles

are clearly sensible to both operating temperature and gas


concentration As was expected sensitivity of LaCoO3pellets

increased by increasing the CO and C3H8concentration

and the operation temperatureMaximum sensitivity around42 was obtained in C

3H8at 350∘C for a concentration of

300 ppm

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Lorenzo Gildo Ortiz and Hector Guillen Bonilla expresstheir gratitude to Consejo Nacional de Ciencia y Tecnologıa(CONACyT) for the scholarships received The technicalassistance of Darıo Pozas Zepeda and Miguel Angel LunaArias is thankedThisworkwas partially supported by Projectno 784-12 FRABA and Project no 155996 from CONACyTmanaged by M de la L Olvera

References

[1] R Betancourt-Galindo P Y Reyes-Rodriguez B A PuenteUrbina et al ldquoSynthesis of copper nanoparticles by thermaldecomposition and their antimicrobial propertiesrdquo Journal ofNanomaterials vol 2014 Article ID 980545 5 pages 2014

[2] S Wannapop T Thongtem and S Thongtem ldquoCharac-terization of donut-like SrMoO

4produced by microwave-

hydrothermal processrdquo Journal of Nanomaterials vol 2013Article ID 474576 6 pages 2013

[3] A Phuruangrat T Thongtem and S Thongtem ldquoInfluence ofPVP on the morphologies of BiS

3nanostructures synthesized

by solvothermal methodrdquo Journal of Nanomaterials vol 2013Article ID 314012 6 pages 2013

[4] J Ortega T T Kodas S Chadda D M Smith M Ciftciogluand J E Brennan ldquoFormation of dense Ba

086Ca014

TiO3parti-

cles by aerosol decompositionrdquo Chemistry of Materials vol 3no 4 pp 746ndash751 1991

[5] J D Jordan R A Dunbar D J Hook et al ldquoProductioncharacterization and utilization of aerosol-deposited sol-gel-derived filmsrdquo Chemistry of Materials vol 10 no 4 pp 1041ndash1051 1998

[6] C R Michel E Delgado G Santillan A H Martınez and AChavez-Chavez ldquoAn alternative gas sensor material synthesisand electrical characterization of SmCoO

3rdquoMaterials Research

Bulletin vol 42 pp 84ndash93 2007[7] C R Michel A H Martınez and S Jimenez ldquoGas sensing

response of nanostructured trirutile-type CoSb2O6synthesized

by solution-polymerization methodrdquo Sensors and Actuators Bvol 132 no 1 pp 45ndash51 2008

[8] D Wang and F Caruso ldquoPolyelectrolyte-coated colloid spheresas templates for sol-gel reactionsrdquo Chemistry of Materials vol14 no 5 pp 1909ndash1913 2002

[9] R J Hunter Foundations of Colloid Science Oxford UniversityPress New York NY USA 2005

[10] S W You I H Kim S M Choi and W S Seo ldquoSolid-statesynthesis and thermoelectric properties of Mg

2+119909Si07Sn03Sb119898rdquo

Journal of Nanomaterials vol 2013 Article ID 815925 4 pages2013

[11] Y Zhu W Zhao H Chen and J Shi ldquoA simple one-potself-assembly route to nanoporous and monodispersed Fe

3O4

particles with oriented attachment structure and magneticpropertyrdquo Journal of Physical Chemistry C vol 111 no 14 pp5281ndash5285 2007

[12] M J Molaei A Ataie S Raygan et al ldquoMagnetic propertyenhancement and characterization of nano-structured bariumferrite bymechano-thermal treatmentrdquoMaterials Characteriza-tion vol 63 pp 83ndash89 2012

[13] L da Conceicao C R B Silva N F P Ribeiro and M M VM Souza ldquoInfluence of the synthesis method on the porositymicrostructure and electrical properties of La

07Sr03MnO

3

cathode materialsrdquo Materials Characterization vol 60 no 12pp 1417ndash1423 2009

[14] S Libert D V Goia and E Matijevic ldquoInternally compositeuniform colloidal cadmium sulfide spheresrdquo Langmuir vol 19no 26 pp 10673ndash10678 2003

[15] S-M Yang S-H Kim J-M Lim and G-R Yi ldquoSynthesis andassembly of structured colloidal particlesrdquo Journal of MaterialsChemistry vol 18 no 19 pp 2177ndash2190 2008

[16] C R Michel H Guillen-Bonilla A H Martınez-Preciado andJ P Moran-Lazaro ldquoSynthesis and gas sensing properties ofnanostructured CoSb

2O6microspheresrdquo Sensors and Actuators

B vol 143 no 1 pp 278ndash285 2009[17] X Sun S Dong and E Wang ldquoCoordination-induced forma-

tion of submicrometer-scale monodisperse spherical colloidsof organic-inorganic hybrid materials at room temperaturerdquoJournal of the American Chemical Society vol 127 no 38 pp13102ndash13103 2005

[18] E Matijevic ldquoPreparation and properties of uniform sizecolloidsrdquoChemistry of Materials vol 5 no 4 pp 412ndash426 1993

[19] M G Han and S H Foulger ldquoCrystalline colloidal arrays com-posed of poly(34-ethylenedioxythiophene)-coated polystyreneparticles with a stop band in the visible regimerdquo AdvancedMaterials vol 16 no 3 pp 231ndash234 2004

[20] F Teng S Liang B Gaugeu R Zong W Yao and Y ZhuldquoCarbon nanotubes-templated assembly of LaCoO

3nanowires

at low temperatures and its excellent catalytic properties for COoxidationrdquo Catalysis Communications vol 8 no 11 pp 1748ndash1754 2007

[21] B Seyfi M Baghalha and H Kazemian ldquoModified LaCoO3

nano-perovskite catalysts for the environmental application ofautomotive CO oxidationrdquo Chemical Engineering Journal vol148 no 2-3 pp 306ndash311 2009

[22] A Baiker P E Marti P Keusch E Fritsch and A RellerldquoInfluence of the A-site cation in ACoO

3(A = La Pr Nd and

Gd) perovskite-type oxides on catalytic activity for methanecombustionrdquo Journal of Catalysis vol 146 no 1 pp 268ndash2761994

[23] Y Wang J Ren Y Wang et al ldquoNanocasted synthesis ofmesoporous LaCoO

3perovskite with extremely high surface

area and excellent activity in methane combustionrdquo Journal ofPhysical Chemistry C vol 112 no 39 pp 15293ndash15298 2008

[24] W Y Jung and S-S Hong ldquoSynthesis of LaCoO3nanoparticles

by microwave process and their photocatalytic activity undervisible light irradiationrdquo Journal of Industrial and EngineeringChemistry vol 19 no 1 pp 157ndash160 2013

[25] Y Yamada K Yano D Hong and S Fukuzumi ldquoLaCoO3

acting as an efficient and robust catalyst for photocatalytic wateroxidation with persulfaterdquo Physical Chemistry Chemical Physicsvol 14 no 16 pp 5753ndash5760 2012


[26] A V Salker N-J Choi J-H Kwak B-S Joo and D-D LeeldquoThick films of In Bi and Pd metal oxides impregnated inLaCoO

3perovskite as carbon monoxide sensorrdquo Sensors and

Actuators B vol 106 no 1 pp 461ndash467 2005[27] M Ghasdi and H Alamdari ldquoCO sensitive nanocrystalline

LaCoO3

perovskite sensor prepared by high energy ballmillingrdquo Sensors and Actuators B vol 148 no 2 pp 478ndash4852010

[28] L Fu and J-F Li ldquoPreparation and thermoelectric properties ofLaCoO

3ceramicsrdquo Key Engineering Materials vol 434-435 pp

404ndash408 2010[29] W Kraus and G Nolze PowderCell For Windows Version 24

Federal Institute for Materials Research and Testing BerlinGermany 2000

[30] J Prado-Gonjal A M Arevalo-Lopez and E MoranldquoMicrowave-assisted synthesis a fast and efficient route toproduce LaMO

3(M =Al Cr Mn Fe Co) perovskite materialsrdquo

Materials Research Bulletin vol 46 no 2 pp 222ndash230 2011[31] U Holzwarth andN Gibson ldquoThe Scherrer equation versus the

lsquoDebye-Scherrer equationrsquordquoNature Nanotechnology vol 6 no 9p 534 2011

[32] O Myakush V Berezovets A Senyshyn and L VasylechkoldquoPreparation and crystal structure of new perovskite-typecobaltites R

1minus119909R1015840119909CoO3rdquo Chemistry of Metals and Alloys vol 3

pp 184ndash190 2010[33] G Carabalı E Chavira I Castro E Bucio L Huerta and J

Jimenez-Mier ldquoNovel sol-gel methodology to produce LaCoO3

by acrylamide polymerization assisted by 120574-irradiationrdquo Radia-tion Physics and Chemistry vol 81 no 5 pp 512ndash518 2012

[34] S Sompech A Srion and A Nuntiya ldquoThe effect of ultrasonictreatment on the particle size and specific surface area ofLaCoO

3rdquo Procedia Engineering vol 32 pp 1012ndash1018 2012

[35] C R Michel A H Martınez F Huerta-Villalpando and J PMoran-Lazaro ldquoCarbon dioxide gas sensing behavior of nanos-tructured GdCoO

3prepared by a solution-polymerization

methodrdquo Journal of Alloys and Compounds vol 484 no 1-2 pp605ndash611 2009

[36] E Matijevic ldquoUniform inorganic colloid dispersions Achieve-ments and challengesrdquo Langmuir vol 10 no 1 pp 8ndash16 1994

[37] V K Lamer and R H Dinegar ldquoTheory production andmechanism of formation of monodispersed hydrosolsrdquo Journalof the American Chemical Society vol 72 no 11 pp 4847ndash48541950

[38] V V Gorbunov A A Shidlovskii and L F Shmagin ldquoCombus-tion of transition-metal ethylenediamine nitratesrdquoCombustionExplosion and Shock Waves vol 19 no 2 pp 172ndash173 1983

[39] S C Chang ldquoOxygen chemisorption on tin oxide correlationbetween electrical conductivity and EPR measurementsrdquo Jour-nal of Vacuum Science and Technology vol 17 no 1 pp 366ndash3691979

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BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


On the other hand lanthanum cobalt oxide (LaCoO3)

with perovskite-type structure has acquired great importanceby its magnetic electrical and catalytic properties thatmake it attractive for different technological applicationsFor example it has been reported that LaCoO

3exhibits

catalytic activity in the oxidation of different compounds likecarbonmonoxide (CO) andmethane (CH

4) and also exhibits

photocatalytic activity in the oxidation of methyl orange andwater [20ndash27] In addition the LaCoO

3is a material that

presents good thermoelectric properties [28]In this work LaCoO

3nanoparticles were synthesized

by a colloidal route for studying their physical propertiesAdditionally the synthesized LaCoO

3powders were used to

manufacture pellets to be tested as gas sensors in two differentatmospheres namely CO and propane (C

3H8)

2 Experimental Procedures

21 Synthesis of LaCoO3Nanoparticles LaCoO

3nanoparti-

cles with perovskite-type structure were prepared employ-ing a colloidal method Firstly three different solutionswere separately prepared The first one consisted of 17316 gof La(NO

3)3sdot6H2O (Alfa Aesar) the second 1164 g of

Co(NO3)2sdot6H2O (Jalmek) both dissolved in 5mL of absolute

ethyl alcohol (CTR) and the third 2mL of ethylenediamine(Sigma) dissolved in 10mL of the same alcohol The threesolutions were stirred vigorously for 20min and then mixedall together Finally the resultant solution was kept in stirringfor 24 h at room temperature

Later the solution was put into a domestic microwaveoven (LGmodel MS1147 X) in order to evaporate the solventby a low power radiation of microwaves (sim145W) Theevaporation rate was controlled by applying the microwaveradiation in steps of 25 s in order to keep the solution at atemperature around 70∘C the temperature was monitored byan Extech IR 403255 thermometer The control of heatingtime and temperature was decisive to avoid the splashingand the consequent loss of material namely a better processyield After entire evaporation of solvents a yellow paste wasobtained which was dried at 200∘C during 8 h in a normalatmosphere The resultant powder was divided in five partsand theywere calcined at different temperatures namely 300400 500 600 and 700∘C The calcination process consistedof a heating rate of 100∘Ch up to reach the set point and thenan annealing for 5 h at constant temperatureThe calcinationswere carried out in an oven Vulcan 3ndash550 which has aprogrammable temperature controller

22 Physical Characterization of LaCoO3Powders All cal-

cined powders were analyzed by X-ray diffraction (XRD)by using a Siemens D500 diffractometer with a Cu-K120572radiation The 2120579 scanning range was from 10∘ to 70∘ witha step size of 002∘ and a step time of 1 s Lattice parameterswere calculated from the XRD patterns Powder Cell 24software [29] was employed for analyzing the XRD spectraMorphology of LaCoO

3powders was analyzed by scanning

electron microscopy (SEM) by using a JEOL JSM-6390LVmicroscope in modality of high vacuum and secondary

electron emission A surface composition analysis was devel-oped by energy dispersive X-ray spectroscopy (EDS-SEM)with an XFlash Detector 5010 from Bruker Surface areaanalysis was performed by nitrogen adsorption at 77K witha Minisorp II equipment from BEL Japan In this character-ization previous to the N

2adsorption process the chamber

with the sample was outgassed and kept in vacuum for 24 hat room temperature Surface area was calculated from theBET equation Size and shape of the nanoparticles wereanalyzed by transmission electron microscopy (TEM) in aJEM-2010 equipment from JEOLwith an acceleration voltageof 200 kV The surface topography was analyzed by atomicforce microscopy (AFM) by using a JSPM-5200 microscopefrom JEOL under intermittent contact operation For thetopographical study 01 g of LaCoO

3powder was dispersed

with isopropyl alcohol in a container by using an ultrasonicbath for 5 minutes Later by a syringe a drop of materialdisperse was deposited over the surface of a 15mm diameterbronze disc and finally dried at room temperature during24 h

23 Pellets Preparation for Gas Sensitivity Analysis The sens-ing properties of synthesized LaCoO

3powders were probed

in two different atmospheres namely carbonmonoxide (CO)and propane (C

3H8) at different gas concentrations and

operation temperaturesThe sensingmeasurements consistedof monitoring the electrical resistance of 12mm diameterand 05mm thick pellets manufactured by using a SimplexItal Equip-25 Tons pressing machine After several trialsoptimal pressing conditions were found for 15 tons during90min For electricalmeasurements twoohmic contactsweremanufactured onto the pellets by using pure silver paint(Alpha Aesar) Then these pellets were put onto a sampleholder in a chamber which allows the introduction of gasesin a controlled way For controlling gas concentration thepartial pressure into the chamber was monitored by a TM20Leybold detectorThe experimental setup used formeasuringthe sensing response is shown in Figure 1

The pellets sensitivity 119878 was estimated by the relative dif-ference of the electrical conductances (1electrical resistance)according to the following equation

119878 =

119866

119892minus 119866

119900

119866

119900

(1)

where 119866119892and 119866

119900are the electrical conductance of the

LaCoO3pellets measured in gas (CO or C

3H8) and air

respectively The conductance was measured by using aKeithley 2001 digital multimeter as a function of operatingtemperature and gas concentration Corresponding graphsare reporting results for three temperatures namely 150 250and 350∘C and five different gas concentrations 5 50 100200 and 300 ppmThis temperature range was selected sincelower operating temperatures do not lead to any conductancechanges


11

Gas

2

4

9

10

7

8

56

1

2

3

Display

35

4



minus1


Inte

nsity

(au

)

10 20 30 40 50 60 70

2120579 (deg)

700∘C

600∘C

500∘C

400∘C

300∘C

200∘C

LaCoO3

La2O3

(012

)

(110

)

(104

)

(202

)(006

)(024

)

(122

)(116

)(214

)(018

)

(220

)









3perovskite




whereas Co2O3or Co



3








3powders were







50120583m

(a)

1120583m

(b)


1 2 3 4 5 6 7 8

C

Co

Co

Co

LaLa

La

LaLaLa

La

La

La

O

(Cou

nts

s)

LaCoO3

Energy (keV)




119909 and CO

2


















200nm

(a)

33

29

24

20

16

12

8

4

0

Part

icle

s (

)

Particle size (nm)20 40 60 80 100 120 140 160

(b)

10nm

sim386 A

(c)




(nm)

(nm

)

(nm

)

7

0

0

3220

322


powders





3H8





2



0 50 100 150 200

0

2

4

6

8


150 350

250

Tamb

Sens

itivi

ty


(a)


50 100 150 200 250 300 350

0

2

4

6

8

0 5 50

100200

Sens

itivi

ty


(b)

0 50 100 150 200 250 300

0

10

20

30

40

150250

350Tamb

Sens

itivi

ty



(c)

50 100 150 200 250 300 350

0

10

20

30

40


0 5 50

100200300

Sens

itivi

ty


(d)


3H8) concentration






4 Conclusions



3nanoparticles







300 ppm



Acknowledgments


References









086Ca014

TiO3parti-











2+119909Si07Sn03Sb119898rdquo



3O4




07Sr03MnO

3











3nanowires





3(A = La Pr Nd and













LaCoO3































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




11

Gas

2

4

9

10

7

8

56

1

2

3

Display

35

4



minus1


Inte

nsity

(au

)

10 20 30 40 50 60 70

2120579 (deg)

700∘C

600∘C

500∘C

400∘C

300∘C

200∘C

LaCoO3

La2O3

(012

)

(110

)

(104

)

(202

)(006

)(024

)

(122

)(116

)(214

)(018

)

(220

)









3perovskite




whereas Co2O3or Co



3








3powders were







50120583m

(a)

1120583m

(b)


1 2 3 4 5 6 7 8

C

Co

Co

Co

LaLa

La

LaLaLa

La

La

La

O

(Cou

nts

s)

LaCoO3

Energy (keV)




119909 and CO

2


















200nm

(a)

33

29

24

20

16

12

8

4

0

Part

icle

s (

)

Particle size (nm)20 40 60 80 100 120 140 160

(b)

10nm

sim386 A

(c)




(nm)

(nm

)

(nm

)

7

0

0

3220

322


powders





3H8





2



0 50 100 150 200

0

2

4

6

8


150 350

250

Tamb

Sens

itivi

ty


(a)


50 100 150 200 250 300 350

0

2

4

6

8

0 5 50

100200

Sens

itivi

ty


(b)

0 50 100 150 200 250 300

0

10

20

30

40

150250

350Tamb

Sens

itivi

ty



(c)

50 100 150 200 250 300 350

0

10

20

30

40


0 5 50

100200300

Sens

itivi

ty


(d)


3H8) concentration






4 Conclusions



3nanoparticles







300 ppm



Acknowledgments


References









086Ca014

TiO3parti-











2+119909Si07Sn03Sb119898rdquo



3O4




07Sr03MnO

3











3nanowires





3(A = La Pr Nd and













LaCoO3































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




50120583m

(a)

1120583m

(b)


1 2 3 4 5 6 7 8

C

Co

Co

Co

LaLa

La

LaLaLa

La

La

La

O

(Cou

nts

s)

LaCoO3

Energy (keV)




119909 and CO

2


















200nm

(a)

33

29

24

20

16

12

8

4

0

Part

icle

s (

)

Particle size (nm)20 40 60 80 100 120 140 160

(b)

10nm

sim386 A

(c)




(nm)

(nm

)

(nm

)

7

0

0

3220

322


powders





3H8





2



0 50 100 150 200

0

2

4

6

8


150 350

250

Tamb

Sens

itivi

ty


(a)


50 100 150 200 250 300 350

0

2

4

6

8

0 5 50

100200

Sens

itivi

ty


(b)

0 50 100 150 200 250 300

0

10

20

30

40

150250

350Tamb

Sens

itivi

ty



(c)

50 100 150 200 250 300 350

0

10

20

30

40


0 5 50

100200300

Sens

itivi

ty


(d)


3H8) concentration






4 Conclusions



3nanoparticles







300 ppm



Acknowledgments


References









086Ca014

TiO3parti-











2+119909Si07Sn03Sb119898rdquo



3O4




07Sr03MnO

3











3nanowires





3(A = La Pr Nd and













LaCoO3































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




200nm

(a)

33

29

24

20

16

12

8

4

0

Part

icle

s (

)

Particle size (nm)20 40 60 80 100 120 140 160

(b)

10nm

sim386 A

(c)




(nm)

(nm

)

(nm

)

7

0

0

3220

322


powders





3H8





2



0 50 100 150 200

0

2

4

6

8


150 350

250

Tamb

Sens

itivi

ty


(a)


50 100 150 200 250 300 350

0

2

4

6

8

0 5 50

100200

Sens

itivi

ty


(b)

0 50 100 150 200 250 300

0

10

20

30

40

150250

350Tamb

Sens

itivi

ty



(c)

50 100 150 200 250 300 350

0

10

20

30

40


0 5 50

100200300

Sens

itivi

ty


(d)


3H8) concentration






4 Conclusions



3nanoparticles







300 ppm



Acknowledgments


References









086Ca014

TiO3parti-











2+119909Si07Sn03Sb119898rdquo



3O4




07Sr03MnO

3











3nanowires





3(A = La Pr Nd and













LaCoO3































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 50 100 150 200

0

2

4

6

8


150 350

250

Tamb

Sens

itivi

ty


(a)


50 100 150 200 250 300 350

0

2

4

6

8

0 5 50

100200

Sens

itivi

ty


(b)

0 50 100 150 200 250 300

0

10

20

30

40

150250

350Tamb

Sens

itivi

ty



(c)

50 100 150 200 250 300 350

0

10

20

30

40


0 5 50

100200300

Sens

itivi

ty


(d)


3H8) concentration






4 Conclusions



3nanoparticles







300 ppm



Acknowledgments


References









086Ca014

TiO3parti-











2+119909Si07Sn03Sb119898rdquo



3O4




07Sr03MnO

3











3nanowires





3(A = La Pr Nd and













LaCoO3































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








300 ppm



Acknowledgments


References









086Ca014

TiO3parti-











2+119909Si07Sn03Sb119898rdquo



3O4




07Sr03MnO

3











3nanowires





3(A = La Pr Nd and













LaCoO3































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







LaCoO3































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 Low-Temperature Synthesis and …downloads.hindawi.com/journals/jnm/2014/164380.pdfResearch Article Low-Temperature Synthesis and Gas Sensitivity of Perovskite-Type