Synthesisof Copper Nanoparticles at Room Temperature Using Hydrazine in Glycerol

HueiRuey Ong1,2,a, Maksudur Rahman Khan1,b, Ridzuan Ramli2,c, RosliMohd Yunus1,d

1Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang, LebuhrayaTunRazak, 26300 Kuantan, Pahang, Malaysia.

2Malaysian Palm Oil Board (MPOB), No. 6, PersiaranInstitusi, Bandar barubangi, 43000 Kajang, Selangor, Malaysia.

aroi_rui86@hotmail.com, bmrkhancep@yahoo.com, cridzco@gmail.com, drmy@ump.edu.my

Keywords: Copper nanoparticles; Hydrazine; Chemical reduction; Glycerol.

Abstract. Copper nanoparticles (CuNPs) have been prepared by the reduction of copper chloride in glycerol using hydrazine at ambient conditions. The reduction process takes place under vigorous stirring for 8 h. The formation of CuNPs and size were confirmed by UV/Vis analysis and TEM imaging respectively. The experiment result showed that, 7.062 mM of hydrazine solution and 0.0147 mM of Cu

2+ solution were needed to synthesize narrow size monodisperseCuNPs.The

presence of nanoparticle was found after an induction period of 4 h and further reaction time, complete Cu

0 state nanoparticle was obtained as deep red wine colour was observed. Stability study

of CuNPs showed that the nanoparticles were stable up to 4 days. The particle size of the nanoparticles have been analysed by transmission electron microscopy (TEM) and the average size of CuNPs was in the range 2 to 10 nm.

Introduction

In recent years, many efforts have been made in the synthesis of metal nanoparticles (NPs) because of their unusual properties and potential applications in physical, chemical, electronic, magnetic, catalytic and optical [1,2]. Among various metal, copper nanoparticles (CuNPs) attracted more attention due to catalytic, optical, electrical, antifungal application and low cost [3–5]. A number of methods have been developed in metal nanoparticles preparation, such as chemical reduction, co-precipitation, sol-gel methods, template synthesis, thermal reduction, microwave irradiation methods, vacuum vapour deposition and laser ablation[6–10]. Among these methods, chemical reduction is the most preferred because it is simple, economical and easily in control nanoparticle size. A chemical reduction method usually involves metal salts and reducing agent.

In most of the work, CuNPs was prepared in aqueous medium [5,11]. However, aqueous medium is needed high amount of capping agent to stabilize the nanoparticles. Moreover, some specifically area especially material synthesis, nanoparticles in aqueous medium cannot be applied directly. Many renewable reagent sources such as alcohol, plant extracts and polyols have been demonstrated as successful reducing agent or capping agent or solvent. To our existing knowledge, limited studies have been reported regarding formation of CuNPs in glycerol medium and hydrazine as reducing agent at low temperature.

In this work, we report a new environmentally friendly, low temperature method to obtain a homogeneous population of CuNPs. The effect of parameters such as concentration of hydrazine, concentration of copper salt solution, stability and reaction time were investigated. The resultant nanoparticles were characterized by UV-visible spectroscopy and transmission electron microscopy (TEM) techniques.

Experimental

Materials. Copper (II) chloride salt (CuCl2●2H2O), hydrazine monohydrate (N2H4●H2O), ascorbic

acid and anhydrous glycerol were obtained from Sigma-Aldrich, USA and used without further

purification.

Applied Mechanics and Materials Vol. 481 (2014) pp 21-26Online available since 2013/Dec/19 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.481.21

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 130.207.50.37, Georgia Tech Library, Atlanta, USA-15/11/14,03:51:44)

Preparation and characterization of Cu nanoparticles. The CuNPs were synthesized in glycerol.

Then, CuCl2●2H2O (0.012 – 0.023mmol) and ascorbic acid were subsequently added in 10 mL

glycerol with vigorous stirring. About 6.0 mL solution of hydrazine monohydrate (1.177–

7.062mmol) was injected into the reaction mixture with continuous stirring for 8 hr. Ultraviolet-

visible (UV-vis) absorption spectroscopy was performed by Hitachi U 1800 UV-visible dual

wavelength. The particle sizes were determined by transmission electron microscopy (TEM) using a

LEO 912 AB EFTEM operating at 120 kV. The sample for TEM analysis was obtained by diluting

the dispersed solution with ethanol and then placing a drop of the diluted solution on a holey carbon

film supported on a copper grid and drying it under vacuum condition.

4 → 4 1

Results and discussion

The results in Fig. 1a) and b) shown that, the colour appearance of effect of reaction time and

stability of sols respectively. The sols colour change from pale yellow into wine red colour, which

indicating the formation of CuNPs in the sols while reaction time was increased (Fig. 1a). Sols

colour change from red wine into yellow colour, indicating that metallic CuNPs were oxidized into

Cu2O (Fig. 1b).

Fig. 1 The change of colour appearance a) Effect of reaction time, and b) Effect of stability.

Fig. 2 UV/Vis adsorption spectra of Cu nanoparticles at various hydrazine concentrations. [CuCl2] =

0.0147mM, [N2H2] = a)1.177, b)2.354, c)3.531, d)4.708, e)5.885, and f)7.062 mM.

22 Quantum, Nano, Micro Technologies and Applied Researches

Fig.2 shows the UV/Vis absorption spectra for CuNPsat various hydrazine concentrations. The

spectra were recorded after 8h of reaction in addition of different concentration of hydrazine into

Cu2+

solution with constant amount of ascorbic acid. The results showed that the intensity of the

adsorption band increased as the concentration of hydrazine increased. The result obtained was in

agreement with Díaz-Visurraga et al. [12] which reported that, the UV/Vis spectrum intensity of

CuNPs formation increased as concentration of reducing agent increased. When the concentration

of hydrazine increased up to 7.062 mM, a characteristic plasmon peak was observed at 502 nm.

This corresponds to the formation of CuNPs. However it is known that, the plasmon resonance peak

of nanosized copper particles is observed at approximately 580 nm [13]. The exact position of the

band may shift depending on the individual particle properties including size, shape, solvent used

and capping agent employed [14]. In this case, the peak maximum was observed at 502 nm, smaller

size nanoparticles may be synthesized [15]. Thisresult implied that, molar concentration of

hydrazine in the reaction was important for synthesis nanoparticle. Sufficient concentration of

hydrazine is needed for reduction of Cu2+

to Cu0.

Fig. 3 UV/Vis adsorption spectra of Cu nanoparticles at various copper ion concentrations. [N2H2] =

7.062mM, [CuCl2] = a)0.0235, b)0.0205, c)0.0176, d)0.0147, and e)0.0117 mM.

Fig. 3 shows the UV/Vis absorption spectra for CuNPs at Cu2+

solution concentrations. The

spectra were recorded after 8h of reaction in addition of hydrazine into different concentration Cu2+

solution with constant amount of ascorbic acid. The results showed that the intensity of the

adsorption band increased as the concentration of Cu2+

solution decreased. When the concentration

of Cu2+

decreased up to 0.0147mM, a characteristic plasmon peak was observed at 502 nm, while

Cu2+

concentration at 0.0117 mMtwo plasmon peak were observed at 514 and 555 nm. This

corresponds to the formation of CuNPs. The spectrum of 0.0117 mM with two plasmon peak (514

and 555 nm) and asymmetric peak indicated that, the particles were polydisperse and relatively

large[13,15]. This result implied that, molar concentration of Cu2+

in the reaction was important for

nanoparticlesynthesis andsize can be control with this approach.

Applied Mechanics and Materials Vol. 481 23

Fig. 4 UV/Vis adsorption spectra of Cu nanoparticles at various reaction times.

Fig. 4 has shown that, the growth of CuNPsduring the reaction. The reaction went through

several steps was observed from a set of colour changes, from pale yellow to red wine (Fig. 1a). A

light blue colour solution was initially formed. Further addition of hydrazine solution into the

reaction mixture produced a pale yellowish solution which containing Cu2O particles. There is no

characteristic plasmon peak was observed for the spectra 0 – 3h, while the solution colour was in

yellow. These Cu2O nanoparticles were further reduced by excess hydrazine and yield a red colour

solution containing colloidal CuNPs after 4h reaction. A characteristic peak was observed at 530

nm. The colour of solution turned into deep red after stirring the reaction mixture up to 8h which

indicated the growth of colloidal CuNPsand two plasmon peaks were observed at 514 and 555 nm.

The intensity of the peak was increased as the reaction time increased indicated that the reduction of

Cu2+

came to completion. These results suggested that size controlled synthesis of CuNPswith

narrow size distribution can be possible with this approach.

Fig. 5 UV/Vis adsorption spectra of Cu nanoparticles at stability.

Fig. 5 shown that, the synthesized copper sols was stabilized up to 4 days and red shift were

occurred as compared to fresh prepared sols, it shifted from 514 nm and 555 nm to 480 nm region.

The shifted plasmon band indiacted that metallic CuNPs were oxidized into Cu2Oor CuO[16,17].

Besides that, after 4 days, the intensity of the surface plasmon band (SPB) decreased compared to

24 Quantum, Nano, Micro Technologies and Applied Researches

previous day. The sols was gradually changed the colour from deep red wine into brown and then

yellow (Fig. 1b). This result suggested that, the particles size might be aggregated into bigger size

and glycerol can used as capping agent. Highly monodisperseCuNPs in a size range of 2-10 nm

were obtained as shown by TEM (Fig. 6).

Fig. 6 TEM micrograph of Cu nanoparticles. [N2H2] = 7.062 mM, [CuCl2] = 0.0147 mM.

Conclusion

MonodisperseCuNPs in glycerol medium was synthesized at ambient temperature with average size

2-10 nm. The formation of CuNPs and size were confirmed by UV/Vis analysis and TEM imaging

respectively. Effect of hydrazine concentration and Cu2+

solution concentration were investigated. It

was found that, 7.062 mM of hydrazine concentration was needed for the CuNPs formation.

Besides that, 0.0147 mM of Cu2+

solution was needed to synthesize narrow size

monodisperseCuNPs. The growth process of nanoparticles showed that yellow Cu2O seed

nanoparticles were initially formed, which further converted to Cu0 nanoparticles as reaction

progressed up to 8h. Stability studies of CuNPs showed that the nanoparticles were stable up to 4

days. This suggested that, glycerol can be used as a promising capping agent to reduce the oxidation

process. The TEM studies indicated that the average size of the nanoparticles were 2-10 nm.

Acknowledgement

The authors thank Universiti Malaysia Pahang and Ministry of Higher Education, Malaysia for

ERGS Grant RDU120611 and Malaysian Palm Oil Board for the GSAS scholarship.

References

[1] X. Peng, L. Manna, W. Yang, J. Wickham, E. Scher, A. Kadavanich, et al., Nature, Vol.

404(2000), p.59–61.

[2] A.P.Alivisatos, Science, Vol. 271(1996), p. 933–937.

[3] A.A.Ponce andK.J.Klabunde, Journal of Molecular Catalysis A: Chemical, Vol.255(2005), p.

1–6.

[4] Z.Huang, F.Cui, H.Kang, J.Chen, X.Zhang and C. Xia, Chemistry of Materials, Vol. 20(2008),

p. 5090–5099.

[5] M.N.K.Chowdhury, M.D.H.Beg, M.R.Khan andM.F.Mina, Materials Letters, Vol. 98(2013), p.

26–29.

Applied Mechanics and Materials Vol. 481 25

[6] N.A.Dhas, C.P.Raj andA.Gedanken, Chemistry of Materials, Vol. 10(1998), p. 1446–1452.

[7] Z.Liu andY.Bando, Advanced Materials, Vol. 15(2003), p. 303–305.

[8] Y.Zhao, J.J.Zhu, J.M.Hong, N.Bian andH.Y.Chen, European Journal of Inorganic Chemistry,

Vol. 20(2004), p. 4072–4080.

[9] M.Yang andJ.J.Zhu, Journal of Crystal Growth, Vol. 256(2003), p. 134–138.

[10] M.S.Yeh, Y.S.Yang, Y.P.Lee, H.F.Lee, Y.H.Yeh andC.S.Yeh, The Journal of Physical

Chemistry B, Vol. 103(1999), p. 6851–6857.

[11] S.H.Wu andD.H.Chen, Journal of Colloid and Interface Science, Vol., 273(2004), p. 165–169.

[12] J.Díaz-Visurraga, C.Daza, C.Pozo, A.Becerra, C.von Plessing andA.García, International

Journal of Nanomedicine, Vol. 7(2012), p. 3597–3612.

[13] J.Kim, S.W.Kang, S.H.Mun andY.S.Kang, Industrial & Engineering Chemistry Research, Vol.

48(2009), p. 7437–7341.

[14] D.Mott, J.Galkowski, L.Wang, J.Luo andC.J.Zhong, Langmuir, Vol. 23(2007), p. 5740–5745.

[15] G.H.Hong andS.W.Kang, Industrial & Engineering Chemistry Research, Vol. 52(2013), p.

794–797.

[16] M.Salavati-Niasari andF.Davar, Materials Letters, Vol. 63(2009), p. 441–443.

[17] W.Yu, H.Xie, L.Chen, Y.Li andC.Zhang, Nanoscale Research Letters, Vol. 4(2009), p. 465–

470.

26 Quantum, Nano, Micro Technologies and Applied Researches

Quantum, Nano, Micro Technologies and Applied Researches 10.4028/www.scientific.net/AMM.481 Synthesis of Copper Nanoparticles at Room Temperature Using Hydrazine in Glycerol 10.4028/www.scientific.net/AMM.481.21