Materials Letters 63 (2009) 2355–2357

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Materials Letters

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Synthesis and characterization of uniform fine particles of copper oxalate

Ikram ul Haq ⁎, Farzana HaiderNational Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar-25120, NWFP, Pakistan

⁎ Corresponding author. Fax: +92 91 9216671.E-mail address: ikramhq@yahoo.com (I. Haq).

0167-577X/$ – see front matter © 2009 Elsevier B.V. Adoi:10.1016/j.matlet.2009.08.008

a b s t r a c t

a r t i c l e i n f o

Article history:Received 1 May 2009Accepted 4 August 2009Available online 10 August 2009

Keywords:Copper oxalateIsoelectric point (IEP)Fine particles

Copper oxalate particles were synthesized in various shapes and sizes by mixing appropriate volumes ofknown concentration of oxalic acid and copper nitrate at 25 and 85 °C. Temperature and reactantsconcentration had significant effect on the morphology of the precipitated particles and therefore extensiveoptimizations of the experimental parameters were carried out in order to obtain maximum uniformity inparticles' morphological features. Selected batch of the copper oxalate particles was characterized by variousphysical methods.

© 2009 Elsevier B.V. All rights reserved.

1. Introduction

Uniformity in particle size and shape is considered an essentialparameter for the powder materials being used in applications wherespecific output and reproducible performance are desirable. Tomention a few, these applications include gas sensors [1], catalysts[2], adsorbents [3], pigments [4], lubricants [5], drugs [6], prostheticdentistry [7], etc. As such, a number of research groups of materialscientists and engineers in different parts of the world [8,9] havefocused on establishing scientific principles under which functionalpowders of tailored characteristics could be generated.

Copper oxalate is believed to have unusual antiferromagneticproperties [10] and is also a potential precursor material for theproduction of CuO and Cu particles [11]. As such, some of the materialscientists published [12–14] useful work on this material. However,following those findings, we believe that there exists room for furtherresearch work in this area. As such, attempts were made in this studyto explore more about the production of uniform fine particles ofcopper oxalate by precipitation process under different experimentalconditions.

2. Experimental details

2.1. Materials

Copper nitrate (Cu(NO3)2·3H2O) and oxalic acid (H2C2O4) werereceived fromMerck and usedwithout any further purification. All thestock and working solutions were made with doubly distilled waterusing Pyrex glass vessels. Working solutions were filtered through

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membrane filter before use in order to remove any insolubleimpurities.

2.2. Precipitation

For this purpose, experiments were performed in which equalvolumes of copper nitrate (0.02–0.2 mol/L) and oxalic acid (0.01–0.03 mol/L) solutions were mixed at 25 and 85 °C in open reactionvessels and then aged for various intervals of times (10–60 min). Theprecipitated solids were separated from the mother liquor byfiltration through 0.2 µm membrane filter and then washed severaltimes with copious amount of triply distilled water. The obtainedsolids were dried in air and then stored in a desiccator before furtherstudy.

2.3. Characterization

Particle morphology of the powders was inspected with ScanningElectron Microscope (SEM; JEOL, JSM-5910) at the acceleratingvoltage of 20 keV. Before examination, the powder sample wassputtered with gold. The crystallinity of the solids was assessed fromthe XRD patterns, obtained with X-ray diffractometer (XRD, JEOL JDX-3532) using Cu-Kα radiations. The XRD was operated with 40 kVvoltage and 20 mA current. The sample was scanned in the 2θ range5–80° with step angle of 0.05°. The thermogravimetric/differentialanalysis of the selected samples was performed with TGA/DTAanalyzer (Diamond TG/DTA, Perkin Elmer). The sample was heatedfrom 30 to 800 °C at the heating rate of 5 °C min−1 in the flow ofnitrogen. The infrared spectra were recorded with FTIR (Schimadzue,IR Prestige-21, FTIR-8400S) in the range 400–4000 cm−1. Calcinationof the desired powder was carried out in a programmable furnace inair at 400 °C for 1 h at a heating rate of 5 °C/min, and then cooleddown to room temperature at the same rate.

Fig. 1. Scanning electron micrographs (SEM) of copper oxalate particles, obtained by aging the reactant mixtures, 0.240 mol/L copper nitrate and 0.014 mol dm−3 oxalic acid (A);0.240 mol dm−3 copper nitrate and 0.019 mol/L oxalic acid (B); 0.023 mol/L copper nitrate and 0.023 mol/L oxalic acid (C) for 1 h at 25 °C. Particles in D were obtained by aging thereactant mixture in C at 85 °C for 1 h.

Fig. 2. X-ray diffraction (XRD) patterns of the particles in Fig. 1 D before (A) and after(B) heat treatment at 350 °C.

2356 I. Haq, F. Haider / Materials Letters 63 (2009) 2355–2357

Moreover, Zetaphoremeter-IV (CAD instrument, Z4000) wasemployed for determining the isoelectric point (IEP) of the desiredsample. For zetaphoretic measurements, dispersions of the powdersample were prepared in 0.1 mol dm−3 NaNO3 solution in the pHrange ~1.0 to 10.0.

3. Results and discussion

Precipitation experiments were conducted under a wide range ofexperimental conditions. SEM analysis indicated that morphology ofthe precipitated particles was dependent upon the concentration ofthe reactants, aging time and temperature. In most of the cases,regular shaped particles were obtained. Uniformity in particles shapeand size was achieved under narrow set of experimental conditions.

SEM images at A and B in Fig. 1 exemplifies some of the solidsobtained at 25 °C under thementioned conditions. As can be seen fromthe micrograph in Fig. 1(A), the powder is composed of cubic particleswith pits [13] on some of the particles' surfaces. The absence of pits inother particles in the same picture points to the fact that pits werepossibly present only on one face of each cubic particle; otherwise, itshould have been present on all of them. As such, we believe thatformation of pits on particles in Fig. 1(A) was probably due toinsufficient amount of the precipitant (oxalic acid) in the reactionmedium, essential for particles' build up. In order to support this idea,we increased the concentration of oxalic acid in the starting reactantsolution, while keeping the amount of copper nitrate constant. Thesolids obtained in the latter case are depicted in Fig. 1(B). It can benoted from this figure that the pits disappeared on the particles'surface, which demonstrated the full growth of the particles in thepresence of rather large amount of the precipitant in the startingreaction mixture.

Synthesis temperature also affected particle size and shape. Forexample, the micrographs in Fig. 1(C) and (D) reveals that the

particles produced from the same type of recipe at 85 °C were smallerin size than those produced at 25 °C, and having almost identicalshapes. It was observed during the precipitation experiments that at85 °C the induction time of the precipitation was shorter than that at25 °C. The shorter induction time at high temperature indicated thatthe formation of primary particles and their subsequent growth tookplace in relatively short time, most probably due to the endothermicnature of the precipitation reaction. The particles shown in Fig. 1(D)were selected for further study in this work.

Fig. 2(A) shows XRD pattern of particles shown in Fig. 1(D), whichindicated their crystalline nature. Location of the major peaks clearlyconfirmed composition of this material to be copper oxalate.

Fig. 3. Differential thermal (A) and thermogravimetric analysis (B) curves obtained forthe particles shown in Fig. 1D. Inset shows zeta potential of the same particles as afunction of pH in 0.1 mol/L NaNO3 solution.

Fig. 4. FTIR spectra of the particles in Fig. 1D before (A) and after (B) heat treatment at350 °C.

2357I. Haq, F. Haider / Materials Letters 63 (2009) 2355–2357

Crystallite size was estimated (~82.146 nm) from the peak at 2θ~22.8using the well known Scherrer equation. This suggested the fact thatthe particles in Fig. 1(D) were polycrystalline materials, andoriginated from the aggregation process of the nanosized crystallineparticles.

Similarly, TGA [Fig. 3(B)] indicated that this material powder lostits thermally decomposable components mostly at ~350 °C, whichwas attributed to the loss of water contents and phase transition. Theweight became nearly constant after loosing 51.0% of the materialweight in the temperature range 330–800 °C which indicated thecompleteness of the temperature dependent weight losses in theheated solid. The DTA data, recorded in parallel with the thermo-gravimetric data showed (see, Fig. 3A) exothermic peak with maximaat 286–300 °C which may be ascribed to the exothermic nature of thereaction responsible for the material loss and phase transition. Theappearance of the shoulder with the sharp-tipped DTA peak on thehigh temperature side demonstrated the possibility of formation ofdifferent solid phases in the indicated temperature range. We believethat the formation of sharp-tipped DTA peak corresponded to theformation of low valence state Cu2O, some of which converted to CuO.The transformation of Cu2O to CuO could be held responsible for theappearance of shoulder in the DTA peak in Fig. 3(A). It is added thatCu2O is considered to be formed as an intermediate product duringthe phase transition from copper oxalate to copper oxide [15].

Another heat treatment experiment was performed in which aknown amount of the powder sample of the particles, shown Fig. 1(D),was heated in a furnace at 350 °C for 1 h at the rate of 5 °C/min whichresulted in 51.2 wt.% material loss. The observed weight agreed wellwith the weight loss registered in the TGA experiment. XRD analysis[Fig. 2(B)] indicated that heat-treated powder composed of Cu2O andCuO.

The transformation from CuC2O4·xH2O to Cu2O/CuO compositewas very well compatible with the following phase transformationreaction:

3CuC2O4�0:1H2O→51:6k;350 ˚C

CuO + Cu2O + 2CO + 4CO2 + 0:3H2O:

ð1Þ

The theoretical weight loss indicated in Eq. (1) agreed well withtheweight loss determined in heat treatment experiment with copper

oxalate particles. As such, the particles in Fig. 1D were formulated asCuC2O4·0.1H2O.

Zeta potential of the particles shown in Fig. 1(D) was evaluated in0.1 mol dm−3 NaNO3 solution in pH range 2.0–6.8 and the data areplotted in the inset of Fig. 3, which indicated the IEP of these particlesat pH~2.8. It is worth mentioning that we report IEP of this materialfor the first time and therefore no comparison could be made withother studies.

IR spectrum (see Fig. 4A) of the latter compound showed thepresence of absorption bands at various locations due to vibrationalmodes of different groups, i.e. 3533.59 cm−1 and 1643.35 cm−1

(stretching and bending vibrations of OH group, emerged from theindicated water of crystallization); 1363.67 and 1319.31 cm−1

(stretching and bending vibrations of CfO group); and 821.68 and507.28 cm−1 (vibration of metal–oxygen bond). Most of the abovementioned absorption bands almost disappeared in the IR spectrum(Fig. 4B) of the heated sample, except the metal–oxygen bond, whichin much broader form. The metal–oxygen corresponded to Cu2O/CuO.

Acknowledgement

We are thankful to the NCE in Physical Chemistry, University ofPeshawar, Pakistan and Higher Education Commission of Pakistan forsupporting this work.

References

[1] Ahmed J,VaidyaS,AhmadT,DeviPS,DasD,GanguliAK.MaterResBull 2008;43:264–71.[2] Ramnani SP, Sabharwal S, Kumar JV, Prasad RKH, Rama KS, Prasad PS. Catal Commun

2008;5:756–61.[3] Ciesielczyk F, Krysztafkiewicz A, Jesionowski T. Appl Surf Sci 2007;253:8435–42.[4] Haq I, Fraser I, Matijević E. Colloid Polym Sci 2003;281:542–9.[5] Hudson LK, Eastoe J, Dowding PJ. Adv Colloid Interface Sci 2006;123–126:425–31.[6] Liu L, Guo K, Lu J, Venkatraman SS, Luo D, Ng KC, et al. Biomater 2008;29:1509–17.[7] Denry I, Kelly JR. Dent Mater 2008;24:299–307.[8] Uskoković V, Matijević E. J Colloid Interface Sci 2007;315:500–11.[9] Carneya CS, Gumpa CJ, Weimer AW. Mater Sci Eng A 2006;431:1–12.[10] Michalowicz A, Girerd JJ, Goulon J. Inorg Chem 1979;18:3004–10.[11] Zhang X, Zhang D, Nia X, Zheng H. Solid-State Electron 2008;52:245–8.[12] Soare LC, Bowen P, Lemaitre J, Hofmann H. Mater Res Soc Symp Proc, vol. 788.

Material research Society; © 2004.[13] Zhao X, Yu J. J Cryst Growth 2007;306:366–72.[14] Jongen N, Hofmann H, Bowen P, Lemaitre J. J Mater Sci Lett 2000;19:1073–5.[15] Jia Z, Yue L, Zheng Y, Xu Z. Mater Res Bull 2008;43:2434–40.