International

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Nanoparticles

Volume 3, No.2, 2010

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Contents

93 Effects of current density on copper nanoparticle prepared by electrochemical method Jianlin Xu, Jidong Chen, Shuhua YangLihui Zhang and Jianbang Lu

104 Size-controlled preparation of ruthenium nanoparticles using polyaromatic amine-containing compounds as hydrogenation nanocatalyst precursors Katarzyna Morawa Eblagon, Teresa Valdes-Solis, K.M. Kerry Yu, Anibal J. Ramirez-Cuesta, Shik Chi Tsang

123 Optimal synthesis and nitrate and mercury removal ability of microemulsion-made iron nanoparticles M. Shekarriz, S. Taghipoor, F. Haji-Aliakbari, M. Soleymani-Jamarani, R. Kaveh-Ahangar, M. Eslamian

138 Effects of magnetic field on Rashba spin-orbit interaction in spin dependent resonant transmission in a ZnSe/Zn1-xMnxSe heterostructure A. John Peter

149 Temperature dependent thermal conductivity enhancement of copper oxide nanoparticles dispersed in propylene glycol-water base fluid M.T. Naik, G. Ranga Janardhana

160 Potential energy curves, permanent and transition dipole moments for numerous electronic excited states of CaAr Walid Gaied, Brahim Oujia

173 Structure and magnetic properties of nano-sized HoFe2O4 material A. Jaafar, A. Al-Saie, M. Bououdina

179 Protein-loaded chitosan nanoparticles modulate uptake and antigen presentation of hen egg-white lysozyme by murine peritoneal macrophages S. Madrigal-Carballo, M. Esquivel, M. Sibaja, J. Vega-Baudrit

192 Gelation rate of silica nanoparticles at different supersaturation with and without ammonium fluoride additive E.A. Abdel-Aal, M.M. Rashad, R.M. Mohamed

Int. J. Nanoparticles, Vol.3, No.2, 2010

Int. J. Nanoparticles, Vol. 3, No. 2, 2010 93

Copyright 2010 Inderscience Enterprises Ltd.

Effects of current density on copper nanoparticle prepared by electrochemical method

Jianlin Xu* State Key Laboratory of Gansu Advanced Non-Ferrous Metal Materials, Lanzhou University of Technology, Lanzhou 730050, China and Key Laboratory of Non-Ferrous Metal Alloys and Processing, The Ministry of Education, Lanzhou University of Technology, Lanzhou 730050, China E-mail: ggdjlxu@sina.com E-mail: xujl@lut.cn *Corresponding author

Jidong Chen ShaoXing Testing Institute of Quality Technical Supervision, ShaoXing 312017, China E-mail: chenjd421@163.com

Shuhua Yang and Lihui Zhang State Key Laboratory of Gansu Advanced Non-Ferrous Metal Materials, Lanzhou University of Technology, Lanzhou 730050, China E-mail: yangshuhua78@163.com E-mail: v208@foxmail.com

Jianbang Lu Heat Treatment Workshop of Forging Plant, China National Erzhong Group Co., Deyang 618000, China E-mail: lujianbang2009@163.com

Abstract: Copper nanoparticles are prepared by electrochemical method with various current density in emulsion containing sodium dodecyl sulfate, tween80, dodecyl mercaptan, CuSO45H2O. The resulting copper nanoparticles are investigated by XRD, TEM and FT-IR. The result shows that great changes have taken place in the size, the dispersibility, and the distribution of particles size as the current density goes up. According to analysis, it can be found that the copper nanoparticle can be obtained in smaller size, better dispersibility and narrower distribution of particle size under the current density of 0.01 A/cm2. At the same time, current density eventually affects the size of the nanoparticles as well as overpotential and the size of water droplet.

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Keywords: current density; copper; nanoparticle; emulsion; electrochemical.

Reference to this paper should be made as follows: Xu, J., Chen, J., Yang, S., Zhang, L. and Lu, J. (2010) Effects of current density on copper nanoparticle prepared by electrochemical method, Int. J. Nanoparticles, Vol. 3, No. 2, pp.93103.

Biographical notes: Jianlin Xu is a Professor at State Key Lab of Gansu New Non-Ferrous Metal Materials of Lanzhou University of Technology of China. His main areas of researching are new metal materials and computer application in materials. He has accomplished eight research projects planned by Gansu Province of China. More than 40 research papers have been published. He is a Technology Committee Member of Chinese Heat Treatment Society, and was awarded The 555 Innovative Researcher of Science and Technology by Gansu Province of China.

Jidong Chen is an Engineer at ShaoXing Testing Institute of Quality Technical Supervision of China. He obtained his Masters degree from Lanzhou University of Technology of China in 2009. His main area of research is nano-particles preparation.

Shuhua Yang obtained his BSc from Inner Mongolia University of Technology in 2008. He is a Master candidate as student under the direction of Dr. Xu. His current research direction is material science and preparation of nanomaterials.

Lihui Zhang obtained his BSc from Henan University of Science & Technology in 2006. He is a Master candidate as student under the direction of Dr. Xu. He is now working mainly on nano-powder preparation.

Jianbang Lu is an Associate Engineer at China National Erzhong Group Co. of China. He completed his Bachelors degree as a graduate student at Lanzhou University of Technology of China in 2008. His current research direction is metal materials engineering.

1 Introduction

Nanometre metal material performs satisfactorily in the fields of lubrication, electromagnetism, absorbing material, magneto fluid, catalyse, sensing element, adding toughness to ceramics, biomedicine, combustion supporting and so on. To grant potential values of application to the nanometre metal material is a new direction for material research and chemical engineering research. And great importance is universally attached to this field by the academic circles of material science, physics, chemistry and industry (Edelstein et al., 1997; Braos et al., 2003; Takimoto et al., 2004; Andrievski and Glezer, 2001).

With their unique performance, the applications of Cu nanoparticles span over catalyst, electron conduction slurry, microelectronics, metal alloy, solid lubricant, and so on. In recent years, the researches on the preparation, the performance and the application of nanoparticles of Cu are paid great attention both at home and abroad, with the value in theory and in practice.

Now, the main methods to produce Cu nanoparticles have been categorised as gas phase evaporation (Huang et al., 2003), plasma (Bica, 1999), machine-chemical (Ding et

Effects of current density on copper nanoparticle 95

al., 1996), sol-gel (Epifani et al., 2001), inverse microemulsion (Cason et al., 2001), chemical reduction (Wu and Chen, 2004), microwave irradiation (Tu and Liu, 2000), supercritical extraction (Ziegler et al., 2001) and so on. But since Cu is relatively low in redox potential, easy to be oxidised, and bad in outcome dispersibility without a modified stabiliser, especially when more expensive strong reducing materials like NaBH4 reacted with cupric salt, in liquid phase reducing method, more cost outcome and more serious pollution of environment result. At the same time, it is indeed a complicated process to declutch nanometre particles of Cu from reducing materials. So all the methods mentioned above are not idealistic.

The preparation of copper nanoparticle by electrochemical deposition is an environmentally better process. Besides, the as-prepared copper nanoparticle is deposited on the electrode surface, which is easy to collect. At present, the copper nanoparticle prepared by the electrochemical method is dendrite, some researches indicate that the fractal growth is a diffusion limited aggregate and its activity is also weaker than that of spherical copper nanoparticle (Zhu et al., 2000; Jacob and Garik, 1990). Our team adjusted the preparing technique after a preliminary research, and spherical copper nanoparticle are prepared by electrochemical process.

The initial research shows that the current density, the main salt solubility, the value of pH, and the added organic solvent can affect the shape of the final copper nanoparticle in the process of the preparation of copper nanoparticle by electrochemical method. In the paper, spherical copper nanoparticle is prepared by electrochemical method in containing sodium dodecyl sulfate, tween80, dodecyl mercaptan, CuSO45H2O and various current density. The effects of current density on final copper nanoparticle, chemical mechanism of surface dispersant and current density were investigated.

2 Experimental

2.1 Chemicals

There are some chemicals as follows: bluestone (CuSO45H2O, AR grade), dodecyl mercaptan (C12SH, 96%, CP grade), sodium dodecyl sulfate, tween80 and absolute ethanol. All the organic solvents in the experiments were analytically pure and were used without further purification. Deionised and distilled water was used in the work.

2.2 Preparation of copper nanoparticles

First, Primrose emulsions containing sodium dodecyl sulfate, tween80, dodecyl mercaptan and CuSO45H2O were mixed into well-proportioned light yellow emulsion by magnetic stirrer. Then, titrate it to 1.0 of pH by using strong sulphuric acid. Secondly, using this emulsion as electrolyte, pure copper as anode with its acreage being 2 cm 4 cm and stainless steel net as cathode with its acreage being 3 cm 8 cm, space between the two patches being about 4550 mm, electrolysis time being 60 min. After this, cathode is cleaned in an absolute ethanol ultrasonic bath for five minutes. Then some brown solid powder was collected and repeatedly cleaned with absolute ethanol. Finally, the solid powder was dried by DZF-6050 vacuum drying cabinet for two hours. Hereto, spherical copper nanoparticles were obtained. Properties of the copper nanopaticle prepared in various current densities are presented in Table 1.

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Table 1 Preparation conditions and properties of the copper nanopaticle

Sample Precursor amount CuSO4 (mol/L)

Current density (A/cm2)

Modifier amount Average particle size(nm)

Particle size distribution(nm)

R1 0.05 0.05 SDS + Tween80; 1g + 5ml

35 2040

R2 0.05 0.075 SDS + Tween80; 1g + 5ml

35 2050

R3 0.05 0.10 SDS + Tween80; 1g + 5ml

25 1540

R4 0.05 0.125 SDS + Tween80; 1g + 5ml

70 40100

R5 0.05 0.15 SDS + Tween80; 1g + 5ml

75 6090

R6 0.05 0.175 SDS + Tween80; 1g + 5ml

110 80150

2.3 Sample analysis

Phases of the copper nanoparticle was analysed using Japan Rigaku D8 ADVANCE X-ray diffraction with Cu-K radiation ( = 0.1540598 nm). The particle size and morphology were characterised using a HITACHI H-600 transmission electron microscope (TEM). The process of TEM samples were as follows: First, copper nanoparticles was dissolved in absolute ethanol with ultrasonic for 20 minutes. Then, deposit them on a carbon-coated TEM grid. Lastly, the copper nanoparticle was observed by the TEM when absolute ethanol was volatilised completely. Infrared absorption spectrum of copper nanoparticles was examined by an infrared spectroscopy of Fourier transform (NICOLEF FTIR-360 FTIR). Measured sample and KBr powder were evenly mixed and dried by infrared light, then were pressed into flake. The infrared analysis was made using pure KBr flake as background.

3 Results analysis

3.1 XRD analysis

Figure 1 shows the spherical copper nanoparticle X-ray diffraction in different current density. According to Figure 1, it can be found that diffraction peaks with strong intensities appear at 2 = 43.3, 50.4 and 74.1 assign to the (111), (200) and (220) crystal diffractions plane of metal copper (fcc), respectively. Therefore, the as-prepared nanoparticles are copper powder with face-centred cubic structure. Furthermore, no other oxide diffraction peaks of copper appear in XRD, which means spherical copper powders are not oxidised in the air. It is because of the absorption of organic compounds on the surface of copper powder, so as to improve its stability.

Effects of current density on copper nanoparticle 97

Figure 1 X-ray diffraction patterns of the copper sample of R1, R2, R3, R4, R5 and R6

Figure 2 TEM images of the copper sample of R1, R2, R3, R4, R5 and R6

98 J. Xu et al.

3.2 TEM analysis

Figure 2 shows TEM photos of copper nanoparticle prepared in different current density. It can be seen from Figure R1 and Figure R2 that distribution of copper nanoparticles are more even with smaller spherical particles, an average diameter of about 35 nm and no clear aggregation. In Figure R3, the copper nanoparticles are well-distributed with no aggregation, the average diameter being about 25 nm. They are better in distribution of particle size than other samples. In Figure R4, the copper nanoparticles take an average diameter of about 70 nm, they distributed unevenly. In Figure R5 great aggregation appears, the grain looks like ball, some take the shape of triangle, stick or polygon. In Figure R6, the grain is much bigger than those in the other photos and could not be seen clearly. This may be results from too much coating agent on the surface. From the above analysis, 0.10 A/cm2 of current density is the best process parameter to prepare copper nanoparticles.

3.3 Infrared absorption spectrum analysis

Figure 3 is the infrared absorption spectrum of dodecyl mercaptan and samples prepared under different current density. In Figure 3, curve (1) is the infrared absorption spectrum of dodecyl mercaptan and curve (2) is the infrared absorption spectrum of R1, R2, R3, R4, R5, R6, respectively. According to curve (1) of Figure 3(a), it can be found that the peak at 2,955cm1 is belongs to the CH3 dissymmetry stretching vibration, and peaks at 2,853cm1 and 2,924cm1 of CH2 to symmetric stretching vibration and absorbing appeared, respectively. The peak at 1,493cm1 is corresponded to the CH2 distortion and wagging vibration-absorbing and this absorbing peak belongs to CH3 shearing vibration. The absorption peak at 721 cm1 is belongs to vibration-absorbing peak of sulphate compound. The curve (2) is the infrared absorption spectrum of R1 sample in the Figure 3(a) when surface dispersant is dodecyl mercaptan and current density is 0.05 A/cm2. There are several peaks at 2,947 cm1, 2,917 cm1, 2,845 cm1 and 1,469 cm1 of the spectrum. There are several peaks at 2,917 cm1, 2,848 cm1 and 1,498 cm1 of the absorption spectrum of R2 sample with dodecyl mercaptan as surface dispersant and 0.075 A/cm2 of current density in the Figure 3(b). The characteristic peaks of R3 sample appears obviously at 2,952 cm1, 2,918 cm1, 2,848 cm1, 1,465 cm1 and 723 cm1 with dodecyl mercaptan as surface dispersant and 0.10 A/cm2 of current density in the Figure 3(c). When surface dispersant is dodecyl mercaptan and current density is 0.125 A/cm2, the characteristic peaks of the spectrum line of R4 emergence at 2,914 cms1 and 2,843 cms1 as showed in Figure 3(d). Using the same surface dispersant with 0.15 A/cm2 and 0.175 A/cm2 of current density, the characteristic peaks of R5 appears at 2,953 cm1, 2,919 cm1, 2,848 cm1, 1,466 cm1 and 719 cm1 and that of R6 appears at 2,919 cm1, 2,850 cm1, 1,465 cm1 and 717 cm1, respectively, as showed in Figure 3(e) and Figure 3(f). Compared curve (2) of the as-prepared Cu nanoparticles with curve (1) of pure dodecyl mercaptan in Figure 3, the characteristic peak of coating agent (namely dodecyl mercaptan) still exists, but can present some excursion due to coating agent absorption and combination with copper nanoparticle, which is due to of fewer surface atoms and higher surface energy of copper nanoparticle.

Effects of current density on copper nanoparticle 99

Figure 3 Fourier transformation infrared absorption spectra of dodecyl mercaptan solution and the nanoparticle R1, R2, R3, R4, R5 and R6 under different current density (see online version for colours)

100 J. Xu et al.

4 Discussion

4.1 Analysis of the current density on copper nanoparticles

According to the electrolysis principle, as to certain electrolyte, an upper and lower limits range of current density is often allowed to use. If this range is exceeded, crystallisation layer, not particulate matter will be formed. The current density exerts a great influence on thickness of the crystallisation. When the current density is lower than that of the lower limit of the current density, the crystallisation is thicker; this is because of low current density and small overpotential and slow formation of crystal nucleus, so that only a few crystals grow up. With the increase of the current density, and the overpotential, when the upper limit of the current density is reached, the formation of crystal nucleus speeds up notably, the crystallisation is relatively thin. When the current density exceeds the upper limit of the current density, because there is few discharging ion near the cathode, usually discharging occurs in the raised angle and salient part, and nodulation or dendrite as well. If the current density continues rising, because hydrogen evolution makes cathode region pH value rise, the basic salt or the hydroxide will form, these materials will be absorbed or mixed with near the cathode and inhibitory coating, so as to form the spongy precipitate.

4.2 Function of emulsion in preparing nanometre copper powder

The copper nanoparticles prepared by the simple sulphate system has accumulated a large number of positive and negative electric charges on its surface because after the getting thinning order of magnitude of nanometre of particle. The particle shape is extremely irregular, the surface energy is with not energy stable state, and acting force between particles like Van der Waals force makes it easy for them to aggregate and reach stable state, so as to cause the aggregation of large number of nanoparticle. To this situation, we substitute electrolytic emulsion for the single electrolytic liquid to carry out the reaction. Before or at the beginning of reduction of particles, surfactant in the form of micelles in the emulsion can makes the better separation of participles thus, prevents their aggregation effectively (lipophilic group assembles within the micelles, and hydrophilic group base moves towards water). Mechanism can be seen Figure 4, among which:

a is electrolytic emulsion before reaction, it reaches temporary balance under the repulsion of electric charges and Van der Waals force

b is the ultra thin powder particles surrounded by emulsion drops when the reaction happens; when in order to reflect that happens, the ultra thin powder body particle produced is surrounded by the emulsification drop

c Because of the relative instability of thermodynamics of the emulsion, in order to reduce the free energy in the system, the emulsion drops collide with the ultra thin powder body each other and cause the subsiding flocculation adsorption and aggregation of emulsion, in the course of core shape and, crystallisation of the powder, the poor conductor coatings formed on the metal crystal nucleus.

Because the spherical surface area is minimum, and the interface tension is relatively lower, the powder membrane changes from (c) to (d) in form, up to now, the metal crystal nucleus stop further growing and aggregating because of prevention of covering

Effects of current density on copper nanoparticle 101

coat. As a result, little and steady nanoparticles are available. The surface dispersant is not a simple physical absorption on the surface of copper nanoparticle, but there is strong adsorptive action between them due to some bridge oxygen chemical bond of c-o-c, c-o and s = o in the surface dispersant and copper nanoparticles. The absorption can be verified by infrared absorption spectra diagram. For example, when copper adsorbed nanoparticle dodecyl mercaptan, its characteristic peaks take place some excursion as showed in Figure 3(a). The peak at 2,955 cm1 of CH3 shifts to 2,947 cm1, the peak of CH2 changes from 2,924 cm1 and 2,853 cm1 to 2,917 cm1 and 2,845 cm1, respectively. And the distortion and wagging vibration-absorbing peak of CH2 removes to 1,469 cm1.The peak at 721 cm1 of sulphate compound also changes. Same phenomenon also appear in infrared absorption spectra diagram of other samples, as shown in Figure 3(b), Figure 3(c), Figure 3(d), Figure 3(e) and Figure 3(f). Therefore, the result of the strong adsorption is forming a coating of dodecyl mercaptan on the surface of copper nanoparticles. The surface coating not only can obstruct oxidation, but also can repress the growth of copper nanoparticles. The structure of absorbed dodecyl mercaptan do not changed, which is validate by Figure 3. All long carbon chain alkenes part and relevant absorption of functional group of samples still exist with no obvious variation, which showed that all the prepared samples include ligands, and have no variation in structure. Besides, the table taking appeared in 1,150 cm11,400 cm1 is belongs to the curve and shake-vibration of the dodecyl mercaptan, and in the area bands is often used as an effective evidence that the alkyl chain rule is exactly arranged of the dodecyl mercaptan.

Figure 4 Schematic diagram of coating mechanism of powder particle

(a) (b) (c) (d)

4.3 effect of current density on nano-copper prepared by the emulsion

Emulsion is composed of surfactants, aid-surfactants, oil (usually hydrocarbons), water (or electrolyte solution) ordinarily. Small puddle in emulsion is surrounded by monolayer of surfactants and aid-surfactants, so as to form emulsion particles, which are sphericity or polygon, the size of which is between dozens and hundreds of nano. Emulsion particles are in continuous Brownian motion, taking advantage of self-dissociation and absorption makes particle itself electrically charged. In a collision with other particles, the hydrocarbon chain of surfactant and aid-surfactant forming interface get to another particle infiltrate each other, at the same time, materials in puddle can pass through the interface, and so that the reaction happens. As the reaction occurred in tiny water nuclear, and the growth of reaction product is restricted by radius of water nuclear, therefore, the size of water nuclear directly determines the size of the nano-powder.

102 J. Xu et al.

When DC current passes into the emulsion prepared, dissociation will take place in emulsion itself, so will the copper anode under the reaction of electrolyte solution and electric current. As the time goes by, there will be a large number of ionising Cu2+ and free electrons in solution, and the water in the solution will be electrolysed so as to produce H+ and OH, as well as free electrons. Thus, a large number of free electrons, emulsion surfactant ion in the emulsion are adsorbed on the interface; the hydrophobic part is inserted into Oil phase, polarity in phase of water, forming pervasion dual-layer with Cu2+. As some of the charged particles get together to, form a certain electrical energy barrier, or large number of potential difference, result in all the system so that surfactant ion adsorption is greatly enhanced. With enhance absorption, the surface molecules movement can be easily carried out from lower surface tension to higher one. Therefore, the nuclear membrane coating of water is pressed and thickened under larger surface tension so as to make the size of puddle relatively smaller, which supply a nano-size environment for nano-copper formation. The variational trend of average particle size with changing current density reflected the circumstance in Table 1. The average particle size minishes from 35 nm to 25 nm as current density increases from 0.05 A/cm2 to 0.10 A/cm2; But when the current is too strong and exceeds a certain limit, the influence of over the potential impact will be dominant, surfactant activity in emulsion will be greatly decreased, and the goal of restraining copper particles growth is beyond expectation. In Table 1, beyond 0.10 A/cm2 of current density, the average particle size shows an increasing trend with increasing current density. The morphology of resulting copper nanoparticles are shown in Figure 3.

From the analysis above we can learn that the influence of current density to an average electrolyte process is more obvious and direct. With the help of inter-reaction of surfactant and dispersant agents, emulsion plays an important role in the electrochemical preparation of nano-copper powder, coating nanoparticle and prevention of their aggregation. Also, the influence of current density on water nucleus size indirectly affects the particle size of powder.

5 Conclusions

Copper nanoparticles were prepared by electrochemical method and different current density in emulsion mixed with sodium dodecyl sulphate, tween80, dodecyl mercaptan and certain concentration of CuSO45H2O. It can be concluded by analysis of XRD, TEM and FT-IR.

1 on condition that there is no technique change, current density is about 0.1 A/cm2, spherical nanoparticles are available with small size, distribution of particles size and good separation.

2 current density works in potential and water nucleus size respectively, finally affects particle size of nano-copper.

Acknowledgements

The work was supported by Doctor Research Fund of Lanzhou University of Technology.

Effects of current density on copper nanoparticle 103

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