research article averrhoa carambola : a renewable...

Research ArticleAverrhoa carambola A Renewable Source ofOxalic Acid for the Facile and Green Synthesis of Divalent Metal(Fe Co Ni Zn and Cu) Oxalates and Oxide Nanoparticles

Nguimezong Nguefack Marius Borel1 Josepha Foba-Tendo1 Divine Mbom Yufanyi1

Ekane Peter Etape1 Jude Namanga Eko2 and Lambi John Ngolui3

1 Department of Chemistry Faculty of Science University of Buea PO Box 63 Buea Cameroon2 Institute of Physics Department of Chemical Physics and Material Science University of Augsburg 86153 Augsburg Germany3Department of Chemistry ENS Yaounde PO Box 47 Yaounde Cameroon

Correspondence should be addressed to Josepha Foba-Tendo jnfobagmailcom

Received 27 June 2014 Accepted 2 September 2014 Published 17 September 2014

Academic Editor Hongxing Dai

Copyright copy 2014 Nguimezong Nguefack Marius Borel et alThis is an open access article distributed under theCreativeCommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

A green simple and environmentally benign synthetic approach has been utilised to obtain some bivalent metal oxalates fromAverrhoa carambola juice extract without any purification or special treatment of the juiceThemain acid components (oxalic acidand ascorbic acid) of the juice were identified by HPLC technique The effect of temperature on the purity of the product has beeninvestigated The as-synthesized metal oxalates were thermally decomposed at low temperatures to their respective metal oxidenanoparticles The metal oxalates and their respective thermal decomposition products were characterized by Fourier TransformInfrared spectroscopy X-ray diffraction analysis and thermogravimetry

1 Introduction

Metal carboxylates have been widely investigated and havebeen used as precursors in the production of metal oxidenanomaterials [1ndash6] Generally these metal carboxylates arethermally decomposed at relatively low temperatures into thecorrespondingmetal oxide nanomaterialsThe precursors areusually obtained when the metal salt reacts with the free acidor any of its labile carboxylates The reactants are generallysynthetic but many of these carboxylates are readily availablein our environment (mostly in plants) and need only to beharnessed They include amongst others citric acid tartaricacid and oxalic acid The latter is known to be one of themajor acids in many plants (eg Rhubarb and Averrhoacarambola)

Averrhoa carambola known as carambola or star fruitis an attractive exotic tropical and shrub-like ornamentaltree of the Oxalidaceae family [7ndash10] The ripe fruits canbe eaten fresh or used to produce juice jelly or wine [11]

The fruit is also widely used in traditional medicine for thetreatment of a wide range of ailments [10 12] It is also apotential source of pectin [12] Carambola fruit juice has beenshown [7 13] to contain active constituents such as vitaminsamino acids ascorbic acid oxalic acid tartaric acid citricacid carbohydrates fats and proteins Assessment of thephysicochemical properties of carambola fruit juice from ripeand unripe fruits showed that the pH of the fruits increasedwith advance in maturity being 24 for green mature 27 forhalf-ripe and 344 for ripe fruits [7] Averrhoa carambola is avery good source of oxalic acid with oxalic acid contents thatcan be as high as 1 wt of wet mass (representing about 74of the total acid content depending on the level of maturity ofthe fruits) [7 14 15]

The high concentration of oxalic acid in this fruit isresponsible for its toxicity Star fruit and other plants con-taining high amounts of oxalates can cause neurotoxic andnephrotoxic effects in humans and animals [16ndash19] It willtherefore be very useful to develop an approach that can

Hindawi Publishing CorporationJournal of Applied ChemistryVolume 2014 Article ID 767695 9 pageshttpdxdoiorg1011552014767695

2 Journal of Applied Chemistry

reduce the amount of acid in the fruit prior to its consump-tion We here explore the feasibility of using this naturallyavailable and sustainable resource (Averrhoa carambola L)rather than the commercial sources for the synthesis of metaloxalates The use of these natural renewable resources is ofenvironmental significance and in the case of free oxalicacid rich fruits (eg Averrhoa carambola L) could resultin a significant reduction in the level of the free acid thusadding value to the elimination of toxic components throughreaction with metal ions of biological and technologicalimportance This could also open up the possibility of highvalue exploitation of spoiled fruits

In order to render the synthesis cost effective and eco-friendly we decided to proceed with a synthetic pathwaywhere the fruit juice is used directly without initial purifi-cation steps or prior extraction of the acid This decisionwas guided by the fact that in the natural condition of thejuice (pH 26ndash31) oxalic acid has a better chance to reactpreferentially with the metal ions owing to its relative highacidic strength (pKa

1(123) and pKa

2(419)) In comparison

with the other carboxylic acids present in the juice oxalic acidrequires no initial alkaline deprotonation step to precipitatewith the metal ions and the precipitation can therefore occurat the natural pH of the juice

The synthesis of metal (Mn Fe Co Ni Cu Zn andCd) oxalates by solvothermal [4] microemulsion [2] reversemicellar route [13] solid state route [20] and by singlediffusion technique in agar gel [6] has been reported Theseoxalate nanorods have been used as precursors for thesynthesis of oxide nanoparticles Thermal decomposition ofthese precursors in the temperature range 450ndash500∘C yieldedhomogeneous oxide nanoparticles In the different synthesismethods a reaction of the appropriate metal salts and oxalicacid from commercial sources was used

Herein we present a facile and green approach for thesynthesis of metal oxalates and their subsequent thermaldecomposition to the oxide nanoparticles Our approach isbased on mixing the metal ion solution and the fruit juiceextract without the use of hazardous organic compounds orsurfactants In this preliminary study five divalent 3d metalions (Fe2+ Co2+ Ni2+ Zn2+ and Cu2+) were used for theproof of conceptThe as prepared complexes and their variousthermal decomposition products have been characterized byFTIR powder XRD and TGA

2 Experimental

21 Chemicals Fe(II) Co(II) Ni(II) Cu(II) and Zn(II)chlorides were obtained from Sigma Aldrich The chemicalswere of analytical grade and were used without furtherpurification HPLC grade oxalic ascorbic citric lactic malicmalonic and succinic acids were also used

22 Processing of the Fruit Juice Ripe carambola fruits wereharvested from the campus of CRTV Buea in the South-West Region of Cameroon The fruits were washed underrunning tap water and crushed in a blender The juice wasextracted by squeezing through cheese cloth The collectedjuice was centrifuged for 20min at 3000 rpm the supernatant

Table 1 Summary of sample codes synthesis time and colour ofprecipitates

Sample (code) Synthesistime (min)

Colour ofprecipitate formed

Fe2+ (P1) 45 YellowCo2+ (P2) 30 PinkNi2+ (P3) 60 Light greenCu2+ (P5) 60 Light blueZn2+ (P4) 60 White

was filtered and the filtrate collected and kept in a freezer forfurther use

23 Characterization of the Juice Theacid content of the juicewas investigated using HPLC The HPLC system (DEGASYDG-1210) with an autosampler was coupled to a GynkotekUV-detector (UVD340S) set at three wavelengths (214 230and 254 nm) The data was collected and processed withChromeleon software The analyses were performed isocrat-ically at 12mLmin at room temperature with an AltimaC18 column (250 times 10mm 5 120583m) The mobile phase was01WVH

3PO4acidified distilled water Standard solutions

of several acids (oxalic ascorbic citric lactic malic malonicand succinic acids) were prepared and their chromatogramsrecorded as described above with a run time of 25minand compared to that of the juice extract Identification ofthe peaks enabled us to determine the nature of the acidscontained in the juice The amount of oxalic acid in the juicewas determined by a spectrophotometric method based onthe catalytic oxidation of bromophenol blue by dichromateusing oxalic acid as the catalyst [21]

24 Synthesis of the Metal Oxalates Prior to the synthesisthe pH of the juice was measured with Fisherdrand Hydrus500 pH meter

Solutions (01M) of the various metal ions (Fe2+ Co2+Ni2+ Zn2+ and Cu2+) were prepared by dissolving theappropriate amount of the metal chloride in 100mL distilledwater 30mL of the juice extract was poured into a 250mLround bottomflask immersed into a water bathmaintained at80∘C The appropriate metal ion solution (40mL) was addedslowly into the juice while stirring and the mixture wasstirred for a given period of time as summarized in Table 1Themixture was allowed to cool to room temperature and theprecipitates obtained were filtered washed several times withdistilled water (to remove any undesired ions) allowed to air-dry overnight and finally dried in a desiccator over calciumchloride

In order to study the effect of temperature on thesynthesis product we synthesized Co2+ complexes at varioustemperatures (room temperature 45∘C 60∘C and 80∘C) andcompared their XRD patterns Based on our observations80∘C was chosen as synthesis temperature for the precursors

25 Thermal Decomposition of the Complexes A sample ofthe dry precursor (05 g) was ground placed in a ceramic

Journal of Applied Chemistry 3

00

13

25

38

50

63

75

88

100

00 13 25 38 50 63 75 88 100 113 125 138 150 163 175 188 201

(mAU

)

1- 00942- 05853- 0678 4- 14745- 15796- 17977- 21138- 23799- 598110- 6478 11- 8761 12- 10100

13- Oxalic acid- 11052

14- 1409215- 1428216- 14536

17- 15897

18- 1638919- 17399

20- Ascorbic acid-19041

21- 1970622- 1984023- 19908

minus40

minus25

minus13

UV VIS 4

WVL 230nm

(min)

Figure 1 HPLC chromatogram of the juice

crucible and the crucible was placed in the furnace that hadbeen heated to the desired calcination temperature of 550∘Cand calcination in air continued for 4 h The sample wasallowed to cool down to room temperature in the furnaceThe residues (Dp1 Dp2 Dp3 and Dp4 resp from P1 P2 P3and P4) obtained were weighed and kept for further analysesThey represent respectively 439 444 429 and 409of the precursors

26 CharacterizationTechniques FTIR spectrawere recordedfrom 4000 to 400 cmminus1 on a PerkinElmer Spectrum TwoUniversal Attenuated Total Reflectance Fourier TransformInfrared (UATR-FTIR) spectrometer Thermogravimetricanalysis (TGA) was obtained using a Pyris 6 PerkinElmerTGA 4000 thermal analyser The TGA analysis was con-ducted between 30 and 900∘C under nitrogen atmosphereat a flow rate of 20mLmin and a temperature ramp of10∘Cmin The XRD diffractograms of the precursors andthe decomposition products were recorded on a BrukerD8 advance X-ray diffractometer using a Cu K120572 radiationsource (120582 = 015406 nm 40 kV and 40mA) Scans were takenover the 2120579 range from 10∘ to 100∘ in steps of 001∘ atroom temperature in open quartz sample holders The phasewas identified with the help of the BrukerDIFFRACplusevaluation software in combination with the ICDD powderdiffraction data base (International Centre for DiffractionData)

3 Results and Discussion

Reaction of the respectivemetal salts with the carambola juiceat 80∘Cgenerally leads to coloured complexes (except the zinccomplex P4) in high yields The metal complexes are lessintense in colour than the respective metal salts from which

they were derived The complexes are crystalline solids thatare air stable and nonhygroscopic as opposed to the startingsalts Physical data for the complexes are presented in Table 1

31 HPLC Analysis of Juice Extract Figure 1 shows the HPLCchromatogram of the juice Only two peaks appear after 22minutes of run These peaks are compared with those ofthe standard oxalic acid (RT 10966min) and ascorbic acid(RT 18938min) The absence of the peaks of other acidsindicates that they are either absent or if present they are intrace proportions This observation supports that of severalauthors who found that the principal acids in the maturefruits are ascorbic and oxalic acids [7 14 15] It has beenobserved that as the fruits mature the relative content ofoxalic acid increases while that of other acids decrease [7 15]The amount of oxalic acid in the juice as determined byspectrophotometry was found to be in the range of 76ndash116 gLminus1 in agreement with the literature reports where thecontent is generally in the range of 63 to 12 gLminus1 of the juice[7 14]The pH of the juice was found to be in the range 26 to31 This falls within the range observed by Patil et al [7] andNarain et al [15] These authors both observed an increase ofpH as the fruit mature

32 FTIR Spectral Characterisation The formation of pureoxalate phases is indicated by FTIR analysis Figure 2((a)ndash(e)) shows the FTIR spectra of all the metal complexessynthesized from carambola juice They all exhibit similarcharacteristics and comparable patterns except that of P5The bands observed are similar to those reported in theliterature for metal oxalate dihydrates [22 23] The broadband at 3343 cmminus1 is attributed to the stretching vibrationof the OndashH bond of water molecules of crystallisation Theabsence of this band in the spectrum of the copper complex


5001000150020002500300035004000

Wavelength (cmminus1)

(a)(b)(c)

(d)(e)

Figure 2 FTIR spectra of the complexes (spectra (a) (b) (c) (d)and (e) are for P1 P2 P3 P4 and P5 resp)

(P5) attests to the reduced amount of water of crystallisationin this complex The strong band at 1614 cmminus1 is due tothe antisymmetric stretching mode of the carbonyl groupC=O of the oxalate The two bands at 1359 and 1314 cmminus1are those of CndashO symmetric stretching mode The differencebetween ]as(COO) and ]sym(COO) stretching frequencies is255 cmminus1 indicating a bidentate or a terminal monodentatecoordination mode of the oxalate ligand in the complexes[24] The bands at 822 cmminus1 is attributed to the bendingvibration of OndashCndashO and the band at 745 cmminus1 (absent inthe spectrum of the Cu complex) is attributed to HndashOndashHrocking The fact that no other bands are present attests tothe identity and purity of the samples

Figure 3((a)ndash(d)) shows the FTIR spectra of the decom-position products (DPi) of the various complexes Thebands present on the spectrum of the precursor complexes(Figure 2) have disappeared and new bands have appearedThe disappearance of the bands is attributed to the completedecomposition of the complexes We observed the appear-ance of new bands in all the spectra suggesting the formationof new products These bands are all around 500 cmminus1 andare attributed to the stretching vibration of the MndashO bondThe spectra of Dp1 and Dp2 show two bands in this vicinityIn the case of cobalt product (Dp2) the bands are at 660and 550 cmminus1 which suggest the formation of spinel Co

3O4

that is (Co2+)(Co3+)2(O2minus)

4[25] These bands have been

attributed respectively to (Co2+)ndashOndash(Co3+) and to (Co3+)ndashOndash(Co3+) vibrations [16ndash18 25] The presence of two bandsinstead of one or three bands in the spectrum of the ironproduct excludes the possibility of having Fe

3O4or 120574-Fe

2O3

and suggests that the product is likely to be pure 120572-Fe2O3

[19 26]

33 X-Ray Diffraction The XRD spectra of the cobalt com-plexes synthesised at different temperatures are shown inFigure 4 The observed XRD patterns are similar to that ofthe standard prepared from commercial oxalic acid as wellas to those reported in the literature [20 24] This indicatesthat cobalt oxalate dihydrate was obtained at the differentsynthesis temperatures However a close look at the XRDpatterns reveals that some of the peaks such as (400) are notwell resolved at lower temperatures (RT 45 and 60∘C) The

5001000150020002500300035004000

Wavenumber (cmminus1)

520430

(a)

(b)

(c)(d)

660 550

Figure 3 FTIR spectra of the thermal decomposition products(spectra (a) (b) (c) and (d) are for Dp1 Dp2 Dp3 and Dp4 resp)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

StandardJCPDS card no 25-0250

25∘C

45∘C

60∘C

80∘C

lowast

(202

)

(004

)

(400

)

(022

)(404

)

(310

)

(224

)

(602

)(026

)(130

)

(426

)

lowast lowast lowast

Figure 4 XRD patterns of CoOX synthesised at different tempera-tures

spectra of the samples synthesized at lower temperatures alsoexhibit unidentified peaks (lowast) This suggests that despite thepossibility to obtain the complexes at low temperatures purephases that compare to the standard are obtained at 80∘CThisprompted our decision to run all of the subsequent synthesesat 80∘C

The XRD patterns of the metal complexes and their cor-responding decomposition products are shown in Figure 5The peaks have been indexed as shown on the spectra Thepatterns of the complexes (a1 b1 c1 and d1 respectively forP1 P2 P3 and P4) are in good agreement with the JCPDScards reported for the various metal oxalate dihydrates(except the pattern e which is not that of a dihydrate) TheXRD spectrum of sample P1 matches the JCPDS card no 72-1305 for FeC

2O4sdot2H2O [19] The XRD pattern of sample P2

matches the JCPDS card no 25-0250 for 120573-CoC2O4sdot2H2O

[20 24 27]Thepattern of the nickel complex (P3) agreeswiththe JCPDS card no 14-0742 for NiC

2O4sdot2H2O [20] The zinc

complex is identified as ZnC2O4sdot2H2O [28] its pattern agrees

with JCPDS card no 25-1029 and the pattern of P5 is indexedin an orthorhombic cell with parameters described in JCPDScard no 21-0297 for CuC

2O4sdot 119909H2O (119909 lt 1) [20] All of the

peaks are attributed to the corresponding MIIC2O4sdot 2H2O

and confirm that our products are the expectedmetal oxalatesas already suggested from FTIR results

The XRD pattern of the thermal decomposition products(Dp1 Dp2 Dp3 and Dp4) matched the patterns of the metal


15 20 25 30 35 40 45 50 55 60 65 70

(012

)(202

)

(104

)(110

)

(113

)

(024

)

(116

)

(214

)(300

)

(018

)

(110

)

(004

)

(400

)

(022

)

(206

)(116

)(224

)

(602

)

(026

)

(426

)

(a1)

(a2)

2120579 (deg)

120572-Fe2O3 JCPDS 33-0664

Fe2O4 middot H2O JCPDS 72-1305

(a)

(111

)

(220

) (311

)(222

)

(400

)

(422

)(511

)

(440

)

(002

)

(004

)

(400

)

(022

)(206

)(315

)(224

)(602

)(026

)(130

)

(426

)

Co3O4 JCPDS 42-1467

CoC2O4middot2H2O JCPDS 25-0250

(b2)

(b1)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(b)

(c2)

(c1)

(202

)

(111

) (200

)

(220

)

(311

)

(222

)

(004

)

(400

)

(115

) (022

)(206

)(510

)(512

)(602

)(026

)(515

)

(426

)

(624

)

NiO JCPDS 73-1519

NiC2O4middot2H2O JCPDS 25-5810

15 20 25 30 35 40 45 50 55 60 65 7570 80

2120579 (deg)

(c)(202

)

(402

) (100

)(002

) (101

)

(102

)

(110

)

(103

)

(200

) (112

)(201

)

(002

)(111

)

(113

) (021

)

(022

)(221

)(421

)(023

)

ZnO JCPDS 36-1451

ZnC2O4middot2H2O JCPDS 25-1029(d1)

(d2)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(d)

(110

)

(120

)

(011

)

(101

)

(220

)

(130

)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

CuC2O4middotxH2O JCPDS 21-0297

(e)

Figure 5 XRD spectra for the complexes (a1ndashe) and of their decomposition products (a2ndashd2)

oxides as follows the pattern of Dp1 compares with JCPDScard no 33-0664 for pure rhombohedral 120572-Fe

2O3[19 26]

The pattern of Dp2 compares with JCPDS card no 42-1467 forthe spinel Co

3O4(space group Fd3m lattice parameter) [27]

The pattern of Dp3 agrees with JCPDS card no 73-1519 forNiO [29] and the XRD pattern of Dp4 is indexed with respectto the parameters of JCPDS card no 36-1451 corresponding toZnO [28 30] The purity of the products is evidenced by theabsence of any impurity peaks

The average crystallite sizes of the complexes were esti-mated using the Debye-Scherrer equation

119863 =

09120582

120573 cos 120579 (1)

where 120582 is the wavelength of the X-ray 120573 is the full widthat half maximum (FWHM) of the diffraction peak and 120579is the Bragg diffraction angle The FWHM and the otherparameters of the peaks were determined with OriginLab7

fitting wizard by using the Amplitude version of Gaussianpeak function Calculations were done with three peaks foreach of the samples and averagedThe as-determined averageparticle sizes for both the complexes and their decompositionproducts are shown inTable 2The products are of nanometresize with average crystallite size in the range 14ndash25 nm

The thermograms of the complexes are shown in Figure 6and summarised in Table 3 To better elucidate the ther-mal behaviour of the complexes a graph of the weightdifference for consecutive rows against the temperature wasplotted (Figure 7)The thermograms of four of the complexes(MC2O4sdot 119909H2O where M = Fe2+ Co2+ Ni2+ and Zn2+)

show two well defined steps of weight loss in agreement withreports in literature [24 28 31] The first weight loss forFeC2O4sdot 119909H2O (209) occurs in the range 170ndash218∘C This

is attributed to the elimination of two molecules of waterof crystallization according to the theoretical value (1969)The same is true for the first weight loss of CoC

2O4sdot 119909H2O


Table 2 Average crystallite sizes of the complexes and their decomposition products obtained using Debye-Scherrer equation

Metal ion Metal oxalate Metal oxidePeak Size (nm) Average (nm) Peak Size (nm) Average (nm)

Fe2+(202) 2308

249(012) 2334

226(224) 2710 (104) 2435(022) 2457 (024) 2103

Co2+(002) 2165

225(220) 2174

203(022) 2406 (311) 2198(224) 2167 (400) 1723

Ni2+(202) 1742

197(111) 1480

145(004) 2254 (200) 1450(022) 1917 (220) 1405

Zn2+(002) 2464

233(100) 2072

193(402) 2212 (101) 1976(022) 2328 (102) 1740

Cu2+(110) 1625

150(011) 1599 Not available(220) 1278

544

381009080706050

3040

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

CuC2O4 middotxH2O

(a)

389

178

ZnO

10090807060504030

Rela

tive m

ass

Temperature (∘C)

ZnC2O4

ZnC2O4

middot2H2O

0 100 200 300 400 500 600

(b)

419

2026

NiO

10090807060504030

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

NiC2O4

NiC2O4middot2H2O

(c)

10090807060504030

Rela

tive m

ass

1934

397

CoC2O4

CoC2O4

middot2H2O

Co3O4

Temperature (∘C)0 100 200 300 400 500 600

(d)

10090

70605040

80

357

209

Rela

tive m

ass

FeC2O4

FeC2O4middot2H2O

Temperature (∘C)0 100 200 300 400 500 600

(e)

Figure 6 TG thermograms of the metal oxalates


Table 3 Thermal decomposition temperatures and weight loss

(a)

First weight loss Second weight lossTemp (∘C) Obs () Calc () Temp (∘C) Obs () Calc () Possible MO

119909formed

FeC2O4sdot2H2O 170ndash218 209 2095 242ndash330 3574003 FeO3559 Fe2O3

3707 Fe3O4

CoC2O4sdot2H2O 170ndash232 193 1969 350ndash436 3973936 CoO3499 Co2O3

3644 Co3O4

NiC2O4sdot2H2O 210ndash285 206 1972 370ndash434 419 3941 NiOZnC2O4sdot2H2O 132ndash198 178 1902 385ndash445 389 3802 ZnO

(b)

Sloppy weight loss Sharp weight lossTemp (∘C) Obs () Calc () depends on 119909 Temp (∘C) Obs () Calc () depends on 119909 MO

119909

CuC2O4sdotxH2O 272 38119909 = 0 0

272ndash360 544119909 = 0 4689 CuO

119909 = 1 2125 119909 = 1 4247119909 = 03 392 119909 = 03 555 Cu

50 100 150 200 250 300 350 400 450 500 550 600

Temperature (∘C)

000

005

010

015

020

025

030

035

Mas

s diff

eren

ce p

er ro

w (g

)

Df TG CoC2O4middotxH2ODf TG NiC2O4middotxH2ODf TG FeC2O4middotxH2O

Df TG ZnC2O4middotxH2ODf TG CuC2O4middotxH2O

Figure 7 Df-TG plots of the difference in weight in consecutiverows against temperature

(1934 170ndash232∘C) NiC2O4sdot 119909H2O (2061 210ndash285∘C)

and ZnC2O4sdot 119909H2O (1783 132ndash198∘C) according to their

respective theoretical values (1969 1971 and 1902)This confirms the XRD observation that the complexes aremetal oxalate dihydrates (MC

2O4sdot2H2O where M = Fe Co

Ni or Zn)Thedehydration reaction can bewritten as follows

MC2O4sdot 2H2O 997888rarr MC

2O4+ 2H2O (2)

On the other hand the thermogram of CuC2O4sdot 119909H2O

shows a single well-defined weight loss portion There is aregion of gradual weight loss (38) between 245 and 310∘Cimmediately followed by the sharp portion hat end at 360∘CThis decomposition pattern has been observed by Jongenet al [32] The absence of a well-defined dehydration stepsuggests that there is a very little amount of water of crys-tallization in CuC

2O4sdot 119909H2O Using the observed weight

loss the amount of water was estimated and the followingmolecular formula proposed CuC

2O4sdot03H2O This agrees

with its FTIR spectrum which shows no clear bands that canbe assigned to water The sharp weight loss portion on thethermogramofCuC

2O4sdot03H2Ocorresponds to 544which

is very close to 555 expected for the loss of two moleculesof CO

2and the formation of metallic copper As shown by

the TG and Df-TG graphs there is an increase in weight thatoccurs around 460∘CWe attribute this event to the oxidationof the metallic copper As can be seen on Table 2 this is theprocess that best agrees with the observed valuesThis weightloss portion corresponds to the second weight loss portionsof FeC

2O4sdot 119909H2O (357 between 242 and 330∘C) CoC

2O4sdot

119909H2O (3968 350ndash436∘C) NiC

2O4sdot 119909H2O (419 370ndash

434∘C) andZnC2O4sdot119909H2O(389 385ndash445∘C)As observed

in the literature [28] some of these complexes will likelydecompose in pathways which involve the decompositionof the anhydrous metal oxalate (NiC

2O4and ZnC

2O4) into

(NiO and ZnO resp) with the elimination of CO2and CO

As for FeC2O4sdot2H2O and CoC

2O4sdot2H2O this decomposition

step might result in the production of a variety of products(MOM

2O3 orM

3O4)TheDf-TGofCoC

2O4sdot2H2Osuggests

that its second weight loss proceeds in two steps Based onthis observation and on the report made by Wu (2011) [33]we suggest that CoC

2O4undergoes both decomposition and

oxidation reactions to produce CO2and Co

3O4(3)

3CoC2O4+ 2O2997888rarr Co

3O4+ 6CO

2 (3)

4 Conclusion

We have been able to use Averrhoa carambola juice assource of oxalic acid for the synthesis of some divalent metaloxalates The synthesis required no special treatment of thejuice as the product was obtained by directlymixing themetal


ion solution and the juice The products were all identifiedas the expected metal oxalates Both the complexes and theirdecomposition productswere found to be nanomaterials withtheir crystallite size ranging from 14 to 25 nm

Conflict of Interests

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

References

[1] T Palacios-Hernandez G A Hirata-Flores O E Contreras-Lopez et al ldquoSynthesis of Cu and Co metal oxide nanoparticlesfrom thermal decomposition of tartrate complexesrdquo InorganicaChimica Acta vol 392 pp 277ndash282 2012

[2] J Ahmed T Ahmad K V Ramanujachary S E Lofland andAK Ganguli ldquoDevelopment of a microemulsion-based processfor synthesis of cobalt (Co) and cobalt oxide (Co3O4) nano-particles from submicrometer rods of cobalt oxalaterdquo Journal ofColloid and Interface Science vol 321 no 2 pp 434ndash441 2008

[3] Y Zhang J Zhu X Song and X Zhong ldquoControlling thesynthesis of CoO nanocrystals with various morphologiesrdquoJournal of Physical Chemistry C vol 112 no 14 pp 5322ndash53272008

[4] X Wang X Chen L Gao H Zheng Z Zhang and Y QianldquoOne-dimensional arrays of Co3O4 nanoparticles Synthesischaracterization and optical and electrochemical propertiesrdquoJournal of Physical Chemistry B vol 108 no 42 pp 16401ndash16404 2004

[5] D N Bhosale V M S Verenkar K S Rane P P Bakare and SR Sawant ldquoInitial susceptibility studies on Cu-Mg-Zn ferritesrdquoMaterials Chemistry and Physics vol 59 no 1 pp 57ndash62 1999

[6] P V Dalal ldquoNucleation controlled growth of cadmium oxalatecrystals in agar gel and their characterizationrdquo Indian Journal ofMaterials Science vol 2013 Article ID 682950 5 pages 2013

[7] A G Patil D A Patil A V Phatak and N Chandra ldquoPhys-ical and chemical characteristization of carambola (averrhoacarambola L) fruit at three stages of maturityrdquo InternationalJournal of Applied Biology and Pharmaceutical Technology vol1 no 2 pp 624ndash629 2010

[8] P Dasgupta P Chakraborty and N N Bala ldquoAverrhoa caram-bola an updated reviewrdquo International Journal of PharmaResearch and Review vol 2 no 7 pp 54ndash63 2013

[9] C J Wagner Jr W L Bryan R E Berry W Haven and R JKnight Jr ldquoCarambola Selection for Commercial ProductionrdquoFlorida State Horticultural Society vol 88 pp 466ndash469 1975

[10] G Payal K Pankti C Manodeep and K V Jagadish ldquoPhyto-chemical and pharmacological profile of averrhoa carambolaLinn an overviewrdquo International Research Journal of Pharmacyvol 3 no 1 pp 88ndash92 2012

[11] S Napahde A Durve D Bharati and N Chandra ldquoWineproduction from Carambola (Averrhoa carambola) juice usingSaccharomyces cerevisiaerdquo Asian Journal of Experimental Bio-logical Science pp 20ndash23 2010

[12] A Patil S Koli D Patil and A Phatak ldquoA comprehensivereview of an important medicinal plantmdashAverrhoa carambolaLrdquo Pharmacognosy Communications vol 2 no 2 pp 13ndash172012

[13] A Ganguly P Trinh K V Ramanujachary T Ahmad AMugweru and A K Ganguli ldquoReverse micellar based synthesis

of ultrafineMgO nanoparticles (8ndash10 nm) characterization andcatalytic propertiesrdquo Journal of Colloid and Interface Science vol353 no 1 pp 137ndash142 2011

[14] C W Wilson III P E Shaw and R J Knight Jr ldquoAnalysisof oxalic acid in carambola (Averrhoa carambola L) andspinach by high-performance liquid chromatographyrdquo Journalof Agricultural and Food Chemistry vol 30 no 6 pp 1106ndash11081982

[15] N Narain P S Bora H J Holschuh M A Da and SVasconcelo ldquoPhysical and chemical composition of carambolafruit (Averrhoa carambola L) at three stages of maturityrdquoCiencia y Tecnologıa Alimentaria vol 3 no 3 pp 144ndash148 2001

[16] M T Makhlouf B M Abu-Zied and T H Mansoure ldquoNano-crystalline Co

3O4fabricated via the combustion methodrdquo

Metals and Materials International vol 19 no 3 pp 489ndash4952013

[17] M Salavati-Niasari NMir and FDavar ldquoSynthesis and charac-terization of Co

3O4nanorods by thermal decomposition of

cobalt oxalaterdquo Journal of Physics and Chemistry of Solids vol70 no 5 pp 847ndash852 2009

[18] TOzkaya A BaykalM S Toprak Y Koseoglu andZDurmusldquoReflux synthesis of Co

3O4nanoparticles and its magnetic

characterizationrdquo Journal ofMagnetism andMagneticMaterialsvol 321 no 14 pp 2145ndash2149 2009

[19] N Du Y Xu H Zhang C Zhai and D Yang ldquoSelectivesynthesis of Fe

2O3and Fe

3O4nanowires via a single precursor a

general method for metal oxide nanowiresrdquoNanoscale ResearchLetters vol 5 no 8 pp 1295ndash1300 2010

[20] H Luo D Zou L Zhou and T Ying ldquoIonic liquid-assistedsynthesis of transition metal oxalates via one-step solid-statereactionrdquo Journal of Alloys and Compounds vol 481 no 1-2 ppL12ndashL14 2009

[21] X-Q Xu and Z-Q Zhang ldquoKinetic spectrophotometric deter-mination of oxalic acid based on the catalytic oxidation ofbromophenol blue by dichromaterdquoMikrochimica Acta vol 135no 3-4 pp 169ndash172 2000

[22] M C DrsquoAntonio A Wladimirsky D Palacios et al ldquoSpectro-scopic investigations of iron(II) and iron(III) oxalatesrdquo Journalof the Brazilian Chemical Society vol 20 no 3 pp 445ndash4502009

[23] A Wladimirsky D Palacios M C DrsquoAntonio A C Gonzalea-Baro and E J Baran ldquoVibratinal spectra of the 120572-M119868119868C2O42H2O Oxalato complexes with M119868119868 = Co Ni Znrdquo The

Journal of the Argentine Chemical Society vol 98 pp 71ndash77 2011[24] E Romero M E Mendoza and R Escudero ldquoWeak ferromag-

netism in cobalt oxalate crystalsrdquo Physica Status Solidi (B) BasicResearch vol 248 no 6 pp 1519ndash1525 2011

[25] M T Makhlouf B M Abu-Zied and T H Mansoure ldquoDirectfabrication of cobalt oxide nanoparticles employing sucrose asa combustion fuelrdquo Journal of Nanoparticles vol 2013 ArticleID 384350 7 pages 2013

[26] W Qin C Yang R Yi and G Gao ldquoHydrothermal synthesisand characterization of single-crystalline 120572-Fe

2O3nanocubesrdquo

Journal of Nanomaterials vol 2011 Article ID 159259 5 pages2011

[27] L Ren P Wang Y Han C Hu and B Wei ldquoSynthesis ofCOC2O4sdot2H2O nanorods and their thermal decomposition to

CO3O4nanoparticlesrdquo Chemical Physics Letters vol 476 no 1ndash

3 pp 78ndash83 2009[28] L Ni L Wang B Shao Y Wang W Zhang and Y Jiang ldquoSyn-

thesis of flower-like zinc oxalate microspheres in ether-water


bilayer refluxing systems and their conversion to zinc oxidemicrospheresrdquo Journal of Materials Science and Technology vol27 no 6 pp 563ndash569 2011

[29] V P Patil S Pawar M Chougoule et al ldquoEffect of annealingon structural morphological electrical and optical studies ofnickel oxide thin filmsrdquo Journal of Surface Engineered Materialsand Advanced Technology vol 1 no 2 pp 35ndash41 2011

[30] C Chen B Yu P Liu J F Liu and L Wang ldquoInvestigationof nano-sized ZnO particles fabricated by various synthesisroutesrdquo Journal of Ceramic Processing Research vol 12 no 4pp 420ndash425 2011

[31] M Hermanek R Zboril M Mashlan L MacHala and OSchneeweiss ldquoThermal behaviour of iron(II) oxalate dihydratein the atmosphere of its conversion gasesrdquo Journal of MaterialsChemistry vol 16 no 13 pp 1273ndash1280 2006

[32] N JongenHHofmann P Bowen and J Lemaıtre ldquoCalcinationand morphological evolution of cubic copper oxalate particlesrdquoJournal ofMaterials Science Letters vol 19 no 12 pp 1073ndash10752000

[33] C-H Wu ldquoPreparation of ultrafine Co3O4powders by con-

tinuous and controllable combustion synthesisrdquo Transactions ofNonferrous Metals Society of China vol 21 no 3 pp 679ndash6842011

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


reduce the amount of acid in the fruit prior to its consump-tion We here explore the feasibility of using this naturallyavailable and sustainable resource (Averrhoa carambola L)rather than the commercial sources for the synthesis of metaloxalates The use of these natural renewable resources is ofenvironmental significance and in the case of free oxalicacid rich fruits (eg Averrhoa carambola L) could resultin a significant reduction in the level of the free acid thusadding value to the elimination of toxic components throughreaction with metal ions of biological and technologicalimportance This could also open up the possibility of highvalue exploitation of spoiled fruits

In order to render the synthesis cost effective and eco-friendly we decided to proceed with a synthetic pathwaywhere the fruit juice is used directly without initial purifi-cation steps or prior extraction of the acid This decisionwas guided by the fact that in the natural condition of thejuice (pH 26ndash31) oxalic acid has a better chance to reactpreferentially with the metal ions owing to its relative highacidic strength (pKa

1(123) and pKa

2(419)) In comparison

with the other carboxylic acids present in the juice oxalic acidrequires no initial alkaline deprotonation step to precipitatewith the metal ions and the precipitation can therefore occurat the natural pH of the juice

The synthesis of metal (Mn Fe Co Ni Cu Zn andCd) oxalates by solvothermal [4] microemulsion [2] reversemicellar route [13] solid state route [20] and by singlediffusion technique in agar gel [6] has been reported Theseoxalate nanorods have been used as precursors for thesynthesis of oxide nanoparticles Thermal decomposition ofthese precursors in the temperature range 450ndash500∘C yieldedhomogeneous oxide nanoparticles In the different synthesismethods a reaction of the appropriate metal salts and oxalicacid from commercial sources was used

Herein we present a facile and green approach for thesynthesis of metal oxalates and their subsequent thermaldecomposition to the oxide nanoparticles Our approach isbased on mixing the metal ion solution and the fruit juiceextract without the use of hazardous organic compounds orsurfactants In this preliminary study five divalent 3d metalions (Fe2+ Co2+ Ni2+ Zn2+ and Cu2+) were used for theproof of conceptThe as prepared complexes and their variousthermal decomposition products have been characterized byFTIR powder XRD and TGA

2 Experimental

21 Chemicals Fe(II) Co(II) Ni(II) Cu(II) and Zn(II)chlorides were obtained from Sigma Aldrich The chemicalswere of analytical grade and were used without furtherpurification HPLC grade oxalic ascorbic citric lactic malicmalonic and succinic acids were also used

22 Processing of the Fruit Juice Ripe carambola fruits wereharvested from the campus of CRTV Buea in the South-West Region of Cameroon The fruits were washed underrunning tap water and crushed in a blender The juice wasextracted by squeezing through cheese cloth The collectedjuice was centrifuged for 20min at 3000 rpm the supernatant

Table 1 Summary of sample codes synthesis time and colour ofprecipitates

Sample (code) Synthesistime (min)

Colour ofprecipitate formed

Fe2+ (P1) 45 YellowCo2+ (P2) 30 PinkNi2+ (P3) 60 Light greenCu2+ (P5) 60 Light blueZn2+ (P4) 60 White

was filtered and the filtrate collected and kept in a freezer forfurther use

23 Characterization of the Juice Theacid content of the juicewas investigated using HPLC The HPLC system (DEGASYDG-1210) with an autosampler was coupled to a GynkotekUV-detector (UVD340S) set at three wavelengths (214 230and 254 nm) The data was collected and processed withChromeleon software The analyses were performed isocrat-ically at 12mLmin at room temperature with an AltimaC18 column (250 times 10mm 5 120583m) The mobile phase was01WVH

3PO4acidified distilled water Standard solutions

of several acids (oxalic ascorbic citric lactic malic malonicand succinic acids) were prepared and their chromatogramsrecorded as described above with a run time of 25minand compared to that of the juice extract Identification ofthe peaks enabled us to determine the nature of the acidscontained in the juice The amount of oxalic acid in the juicewas determined by a spectrophotometric method based onthe catalytic oxidation of bromophenol blue by dichromateusing oxalic acid as the catalyst [21]

24 Synthesis of the Metal Oxalates Prior to the synthesisthe pH of the juice was measured with Fisherdrand Hydrus500 pH meter

Solutions (01M) of the various metal ions (Fe2+ Co2+Ni2+ Zn2+ and Cu2+) were prepared by dissolving theappropriate amount of the metal chloride in 100mL distilledwater 30mL of the juice extract was poured into a 250mLround bottomflask immersed into a water bathmaintained at80∘C The appropriate metal ion solution (40mL) was addedslowly into the juice while stirring and the mixture wasstirred for a given period of time as summarized in Table 1Themixture was allowed to cool to room temperature and theprecipitates obtained were filtered washed several times withdistilled water (to remove any undesired ions) allowed to air-dry overnight and finally dried in a desiccator over calciumchloride

In order to study the effect of temperature on thesynthesis product we synthesized Co2+ complexes at varioustemperatures (room temperature 45∘C 60∘C and 80∘C) andcompared their XRD patterns Based on our observations80∘C was chosen as synthesis temperature for the precursors

25 Thermal Decomposition of the Complexes A sample ofthe dry precursor (05 g) was ground placed in a ceramic


00

13

25

38

50

63

75

88

100

00 13 25 38 50 63 75 88 100 113 125 138 150 163 175 188 201

(mAU

)

1- 00942- 05853- 0678 4- 14745- 15796- 17977- 21138- 23799- 598110- 6478 11- 8761 12- 10100


14- 1409215- 1428216- 14536

17- 15897

18- 1638919- 17399


21- 1970622- 1984023- 19908

minus40

minus25

minus13

UV VIS 4

WVL 230nm

(min)










5001000150020002500300035004000


(a)(b)(c)

(d)(e)




3O4




3O4or 120574-Fe

2O3


[19 26]


5001000150020002500300035004000


520430

(a)

(b)

(c)(d)

660 550


15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)


25∘C

45∘C

60∘C

80∘C

lowast

(202

)

(004

)

(400

)

(022

)(404

)

(310

)

(224

)

(602

)(026

)(130

)

(426

)
















15 20 25 30 35 40 45 50 55 60 65 70

(012

)(202

)

(104

)(110

)

(113

)

(024

)

(116

)

(214

)(300

)

(018

)

(110

)

(004

)

(400

)

(022

)

(206

)(116

)(224

)

(602

)

(026

)

(426

)

(a1)

(a2)

2120579 (deg)

120572-Fe2O3 JCPDS 33-0664


(a)

(111

)

(220

) (311

)(222

)

(400

)

(422

)(511

)

(440

)

(002

)

(004

)

(400

)

(022

)(206

)(315

)(224

)(602

)(026

)(130

)

(426

)

Co3O4 JCPDS 42-1467


(b2)

(b1)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(b)

(c2)

(c1)

(202

)

(111

) (200

)

(220

)

(311

)

(222

)

(004

)

(400

)

(115

) (022

)(206

)(510

)(512

)(602

)(026

)(515

)

(426

)

(624

)

NiO JCPDS 73-1519


15 20 25 30 35 40 45 50 55 60 65 7570 80

2120579 (deg)

(c)(202

)

(402

) (100

)(002

) (101

)

(102

)

(110

)

(103

)

(200

) (112

)(201

)

(002

)(111

)

(113

) (021

)

(022

)(221

)(421

)(023

)

ZnO JCPDS 36-1451


(d2)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(d)

(110

)

(120

)

(011

)

(101

)

(220

)

(130

)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)


(e)



2O3[19 26]





119863 =

09120582

120573 cos 120579 (1)






2O4sdot 119909H2O




Fe2+(202) 2308

249(012) 2334

226(224) 2710 (104) 2435(022) 2457 (024) 2103

Co2+(002) 2165

225(220) 2174

203(022) 2406 (311) 2198(224) 2167 (400) 1723

Ni2+(202) 1742

197(111) 1480

145(004) 2254 (200) 1450(022) 1917 (220) 1405

Zn2+(002) 2464

233(100) 2072

193(402) 2212 (101) 1976(022) 2328 (102) 1740

Cu2+(110) 1625

150(011) 1599 Not available(220) 1278

544

381009080706050

3040

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

CuC2O4 middotxH2O

(a)

389

178

ZnO

10090807060504030

Rela

tive m

ass

Temperature (∘C)

ZnC2O4

ZnC2O4

middot2H2O

0 100 200 300 400 500 600

(b)

419

2026

NiO

10090807060504030

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

NiC2O4

NiC2O4middot2H2O

(c)

10090807060504030

Rela

tive m

ass

1934

397

CoC2O4

CoC2O4

middot2H2O

Co3O4

Temperature (∘C)0 100 200 300 400 500 600

(d)

10090

70605040

80

357

209

Rela

tive m

ass

FeC2O4

FeC2O4middot2H2O

Temperature (∘C)0 100 200 300 400 500 600

(e)




(a)


119909formed


3707 Fe3O4


3644 Co3O4


(b)


119909

CuC2O4sdotxH2O 272 38119909 = 0 0

272ndash360 544119909 = 0 4689 CuO

119909 = 1 2125 119909 = 1 4247119909 = 03 392 119909 = 03 555 Cu

50 100 150 200 250 300 350 400 450 500 550 600

Temperature (∘C)

000

005

010

015

020

025

030

035

Mas

s diff

eren

ce p

er ro

w (g

)










2O4+ 2H2O (2)












2O4sdot

119909H2O (3968 350ndash436∘C) NiC

2O4sdot 119909H2O (419 370ndash



2O4and ZnC

2O4) into





2O3 orM

3O4)TheDf-TGofCoC

2O4sdot2H2Osuggests




3O4(3)


3O4+ 6CO

2 (3)

4 Conclusion






References



























2O3and Fe











2O3nanocubesrdquo























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


00

13

25

38

50

63

75

88

100

00 13 25 38 50 63 75 88 100 113 125 138 150 163 175 188 201

(mAU

)

1- 00942- 05853- 0678 4- 14745- 15796- 17977- 21138- 23799- 598110- 6478 11- 8761 12- 10100


14- 1409215- 1428216- 14536

17- 15897

18- 1638919- 17399


21- 1970622- 1984023- 19908

minus40

minus25

minus13

UV VIS 4

WVL 230nm

(min)










5001000150020002500300035004000


(a)(b)(c)

(d)(e)




3O4




3O4or 120574-Fe

2O3


[19 26]


5001000150020002500300035004000


520430

(a)

(b)

(c)(d)

660 550


15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)


25∘C

45∘C

60∘C

80∘C

lowast

(202

)

(004

)

(400

)

(022

)(404

)

(310

)

(224

)

(602

)(026

)(130

)

(426

)
















15 20 25 30 35 40 45 50 55 60 65 70

(012

)(202

)

(104

)(110

)

(113

)

(024

)

(116

)

(214

)(300

)

(018

)

(110

)

(004

)

(400

)

(022

)

(206

)(116

)(224

)

(602

)

(026

)

(426

)

(a1)

(a2)

2120579 (deg)

120572-Fe2O3 JCPDS 33-0664


(a)

(111

)

(220

) (311

)(222

)

(400

)

(422

)(511

)

(440

)

(002

)

(004

)

(400

)

(022

)(206

)(315

)(224

)(602

)(026

)(130

)

(426

)

Co3O4 JCPDS 42-1467


(b2)

(b1)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(b)

(c2)

(c1)

(202

)

(111

) (200

)

(220

)

(311

)

(222

)

(004

)

(400

)

(115

) (022

)(206

)(510

)(512

)(602

)(026

)(515

)

(426

)

(624

)

NiO JCPDS 73-1519


15 20 25 30 35 40 45 50 55 60 65 7570 80

2120579 (deg)

(c)(202

)

(402

) (100

)(002

) (101

)

(102

)

(110

)

(103

)

(200

) (112

)(201

)

(002

)(111

)

(113

) (021

)

(022

)(221

)(421

)(023

)

ZnO JCPDS 36-1451


(d2)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(d)

(110

)

(120

)

(011

)

(101

)

(220

)

(130

)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)


(e)



2O3[19 26]





119863 =

09120582

120573 cos 120579 (1)






2O4sdot 119909H2O




Fe2+(202) 2308

249(012) 2334

226(224) 2710 (104) 2435(022) 2457 (024) 2103

Co2+(002) 2165

225(220) 2174

203(022) 2406 (311) 2198(224) 2167 (400) 1723

Ni2+(202) 1742

197(111) 1480

145(004) 2254 (200) 1450(022) 1917 (220) 1405

Zn2+(002) 2464

233(100) 2072

193(402) 2212 (101) 1976(022) 2328 (102) 1740

Cu2+(110) 1625

150(011) 1599 Not available(220) 1278

544

381009080706050

3040

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

CuC2O4 middotxH2O

(a)

389

178

ZnO

10090807060504030

Rela

tive m

ass

Temperature (∘C)

ZnC2O4

ZnC2O4

middot2H2O

0 100 200 300 400 500 600

(b)

419

2026

NiO

10090807060504030

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

NiC2O4

NiC2O4middot2H2O

(c)

10090807060504030

Rela

tive m

ass

1934

397

CoC2O4

CoC2O4

middot2H2O

Co3O4

Temperature (∘C)0 100 200 300 400 500 600

(d)

10090

70605040

80

357

209

Rela

tive m

ass

FeC2O4

FeC2O4middot2H2O

Temperature (∘C)0 100 200 300 400 500 600

(e)




(a)


119909formed


3707 Fe3O4


3644 Co3O4


(b)


119909

CuC2O4sdotxH2O 272 38119909 = 0 0

272ndash360 544119909 = 0 4689 CuO

119909 = 1 2125 119909 = 1 4247119909 = 03 392 119909 = 03 555 Cu

50 100 150 200 250 300 350 400 450 500 550 600

Temperature (∘C)

000

005

010

015

020

025

030

035

Mas

s diff

eren

ce p

er ro

w (g

)










2O4+ 2H2O (2)












2O4sdot

119909H2O (3968 350ndash436∘C) NiC

2O4sdot 119909H2O (419 370ndash



2O4and ZnC

2O4) into





2O3 orM

3O4)TheDf-TGofCoC

2O4sdot2H2Osuggests




3O4(3)


3O4+ 6CO

2 (3)

4 Conclusion






References



























2O3and Fe











2O3nanocubesrdquo























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


5001000150020002500300035004000


(a)(b)(c)

(d)(e)




3O4




3O4or 120574-Fe

2O3


[19 26]


5001000150020002500300035004000


520430

(a)

(b)

(c)(d)

660 550


15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)


25∘C

45∘C

60∘C

80∘C

lowast

(202

)

(004

)

(400

)

(022

)(404

)

(310

)

(224

)

(602

)(026

)(130

)

(426

)
















15 20 25 30 35 40 45 50 55 60 65 70

(012

)(202

)

(104

)(110

)

(113

)

(024

)

(116

)

(214

)(300

)

(018

)

(110

)

(004

)

(400

)

(022

)

(206

)(116

)(224

)

(602

)

(026

)

(426

)

(a1)

(a2)

2120579 (deg)

120572-Fe2O3 JCPDS 33-0664


(a)

(111

)

(220

) (311

)(222

)

(400

)

(422

)(511

)

(440

)

(002

)

(004

)

(400

)

(022

)(206

)(315

)(224

)(602

)(026

)(130

)

(426

)

Co3O4 JCPDS 42-1467


(b2)

(b1)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(b)

(c2)

(c1)

(202

)

(111

) (200

)

(220

)

(311

)

(222

)

(004

)

(400

)

(115

) (022

)(206

)(510

)(512

)(602

)(026

)(515

)

(426

)

(624

)

NiO JCPDS 73-1519


15 20 25 30 35 40 45 50 55 60 65 7570 80

2120579 (deg)

(c)(202

)

(402

) (100

)(002

) (101

)

(102

)

(110

)

(103

)

(200

) (112

)(201

)

(002

)(111

)

(113

) (021

)

(022

)(221

)(421

)(023

)

ZnO JCPDS 36-1451


(d2)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(d)

(110

)

(120

)

(011

)

(101

)

(220

)

(130

)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)


(e)



2O3[19 26]





119863 =

09120582

120573 cos 120579 (1)






2O4sdot 119909H2O




Fe2+(202) 2308

249(012) 2334

226(224) 2710 (104) 2435(022) 2457 (024) 2103

Co2+(002) 2165

225(220) 2174

203(022) 2406 (311) 2198(224) 2167 (400) 1723

Ni2+(202) 1742

197(111) 1480

145(004) 2254 (200) 1450(022) 1917 (220) 1405

Zn2+(002) 2464

233(100) 2072

193(402) 2212 (101) 1976(022) 2328 (102) 1740

Cu2+(110) 1625

150(011) 1599 Not available(220) 1278

544

381009080706050

3040

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

CuC2O4 middotxH2O

(a)

389

178

ZnO

10090807060504030

Rela

tive m

ass

Temperature (∘C)

ZnC2O4

ZnC2O4

middot2H2O

0 100 200 300 400 500 600

(b)

419

2026

NiO

10090807060504030

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

NiC2O4

NiC2O4middot2H2O

(c)

10090807060504030

Rela

tive m

ass

1934

397

CoC2O4

CoC2O4

middot2H2O

Co3O4

Temperature (∘C)0 100 200 300 400 500 600

(d)

10090

70605040

80

357

209

Rela

tive m

ass

FeC2O4

FeC2O4middot2H2O

Temperature (∘C)0 100 200 300 400 500 600

(e)




(a)


119909formed


3707 Fe3O4


3644 Co3O4


(b)


119909

CuC2O4sdotxH2O 272 38119909 = 0 0

272ndash360 544119909 = 0 4689 CuO

119909 = 1 2125 119909 = 1 4247119909 = 03 392 119909 = 03 555 Cu

50 100 150 200 250 300 350 400 450 500 550 600

Temperature (∘C)

000

005

010

015

020

025

030

035

Mas

s diff

eren

ce p

er ro

w (g

)










2O4+ 2H2O (2)












2O4sdot

119909H2O (3968 350ndash436∘C) NiC

2O4sdot 119909H2O (419 370ndash



2O4and ZnC

2O4) into





2O3 orM

3O4)TheDf-TGofCoC

2O4sdot2H2Osuggests




3O4(3)


3O4+ 6CO

2 (3)

4 Conclusion






References



























2O3and Fe











2O3nanocubesrdquo























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


15 20 25 30 35 40 45 50 55 60 65 70

(012

)(202

)

(104

)(110

)

(113

)

(024

)

(116

)

(214

)(300

)

(018

)

(110

)

(004

)

(400

)

(022

)

(206

)(116

)(224

)

(602

)

(026

)

(426

)

(a1)

(a2)

2120579 (deg)

120572-Fe2O3 JCPDS 33-0664


(a)

(111

)

(220

) (311

)(222

)

(400

)

(422

)(511

)

(440

)

(002

)

(004

)

(400

)

(022

)(206

)(315

)(224

)(602

)(026

)(130

)

(426

)

Co3O4 JCPDS 42-1467


(b2)

(b1)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(b)

(c2)

(c1)

(202

)

(111

) (200

)

(220

)

(311

)

(222

)

(004

)

(400

)

(115

) (022

)(206

)(510

)(512

)(602

)(026

)(515

)

(426

)

(624

)

NiO JCPDS 73-1519


15 20 25 30 35 40 45 50 55 60 65 7570 80

2120579 (deg)

(c)(202

)

(402

) (100

)(002

) (101

)

(102

)

(110

)

(103

)

(200

) (112

)(201

)

(002

)(111

)

(113

) (021

)

(022

)(221

)(421

)(023

)

ZnO JCPDS 36-1451


(d2)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)

(d)

(110

)

(120

)

(011

)

(101

)

(220

)

(130

)

15 20 25 30 35 40 45 50 55 60 65 70

2120579 (deg)


(e)



2O3[19 26]





119863 =

09120582

120573 cos 120579 (1)






2O4sdot 119909H2O




Fe2+(202) 2308

249(012) 2334

226(224) 2710 (104) 2435(022) 2457 (024) 2103

Co2+(002) 2165

225(220) 2174

203(022) 2406 (311) 2198(224) 2167 (400) 1723

Ni2+(202) 1742

197(111) 1480

145(004) 2254 (200) 1450(022) 1917 (220) 1405

Zn2+(002) 2464

233(100) 2072

193(402) 2212 (101) 1976(022) 2328 (102) 1740

Cu2+(110) 1625

150(011) 1599 Not available(220) 1278

544

381009080706050

3040

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

CuC2O4 middotxH2O

(a)

389

178

ZnO

10090807060504030

Rela

tive m

ass

Temperature (∘C)

ZnC2O4

ZnC2O4

middot2H2O

0 100 200 300 400 500 600

(b)

419

2026

NiO

10090807060504030

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

NiC2O4

NiC2O4middot2H2O

(c)

10090807060504030

Rela

tive m

ass

1934

397

CoC2O4

CoC2O4

middot2H2O

Co3O4

Temperature (∘C)0 100 200 300 400 500 600

(d)

10090

70605040

80

357

209

Rela

tive m

ass

FeC2O4

FeC2O4middot2H2O

Temperature (∘C)0 100 200 300 400 500 600

(e)




(a)


119909formed


3707 Fe3O4


3644 Co3O4


(b)


119909

CuC2O4sdotxH2O 272 38119909 = 0 0

272ndash360 544119909 = 0 4689 CuO

119909 = 1 2125 119909 = 1 4247119909 = 03 392 119909 = 03 555 Cu

50 100 150 200 250 300 350 400 450 500 550 600

Temperature (∘C)

000

005

010

015

020

025

030

035

Mas

s diff

eren

ce p

er ro

w (g

)










2O4+ 2H2O (2)












2O4sdot

119909H2O (3968 350ndash436∘C) NiC

2O4sdot 119909H2O (419 370ndash



2O4and ZnC

2O4) into





2O3 orM

3O4)TheDf-TGofCoC

2O4sdot2H2Osuggests




3O4(3)


3O4+ 6CO

2 (3)

4 Conclusion






References



























2O3and Fe











2O3nanocubesrdquo























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




Fe2+(202) 2308

249(012) 2334

226(224) 2710 (104) 2435(022) 2457 (024) 2103

Co2+(002) 2165

225(220) 2174

203(022) 2406 (311) 2198(224) 2167 (400) 1723

Ni2+(202) 1742

197(111) 1480

145(004) 2254 (200) 1450(022) 1917 (220) 1405

Zn2+(002) 2464

233(100) 2072

193(402) 2212 (101) 1976(022) 2328 (102) 1740

Cu2+(110) 1625

150(011) 1599 Not available(220) 1278

544

381009080706050

3040

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

CuC2O4 middotxH2O

(a)

389

178

ZnO

10090807060504030

Rela

tive m

ass

Temperature (∘C)

ZnC2O4

ZnC2O4

middot2H2O

0 100 200 300 400 500 600

(b)

419

2026

NiO

10090807060504030

Rela

tive m

ass

50 150 250 350 450 550Temperature (∘C)

NiC2O4

NiC2O4middot2H2O

(c)

10090807060504030

Rela

tive m

ass

1934

397

CoC2O4

CoC2O4

middot2H2O

Co3O4

Temperature (∘C)0 100 200 300 400 500 600

(d)

10090

70605040

80

357

209

Rela

tive m

ass

FeC2O4

FeC2O4middot2H2O

Temperature (∘C)0 100 200 300 400 500 600

(e)




(a)


119909formed


3707 Fe3O4


3644 Co3O4


(b)


119909

CuC2O4sdotxH2O 272 38119909 = 0 0

272ndash360 544119909 = 0 4689 CuO

119909 = 1 2125 119909 = 1 4247119909 = 03 392 119909 = 03 555 Cu

50 100 150 200 250 300 350 400 450 500 550 600

Temperature (∘C)

000

005

010

015

020

025

030

035

Mas

s diff

eren

ce p

er ro

w (g

)










2O4+ 2H2O (2)












2O4sdot

119909H2O (3968 350ndash436∘C) NiC

2O4sdot 119909H2O (419 370ndash



2O4and ZnC

2O4) into





2O3 orM

3O4)TheDf-TGofCoC

2O4sdot2H2Osuggests




3O4(3)


3O4+ 6CO

2 (3)

4 Conclusion






References



























2O3and Fe











2O3nanocubesrdquo























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



(a)


119909formed


3707 Fe3O4


3644 Co3O4


(b)


119909

CuC2O4sdotxH2O 272 38119909 = 0 0

272ndash360 544119909 = 0 4689 CuO

119909 = 1 2125 119909 = 1 4247119909 = 03 392 119909 = 03 555 Cu

50 100 150 200 250 300 350 400 450 500 550 600

Temperature (∘C)

000

005

010

015

020

025

030

035

Mas

s diff

eren

ce p

er ro

w (g

)










2O4+ 2H2O (2)












2O4sdot

119909H2O (3968 350ndash436∘C) NiC

2O4sdot 119909H2O (419 370ndash



2O4and ZnC

2O4) into





2O3 orM

3O4)TheDf-TGofCoC

2O4sdot2H2Osuggests




3O4(3)


3O4+ 6CO

2 (3)

4 Conclusion






References



























2O3and Fe











2O3nanocubesrdquo























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





References



























2O3and Fe











2O3nanocubesrdquo























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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