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Current Applied Physics 13 (2013) 1496e1501

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Current Applied Physics

journal homepage: www.elsevier .com/locate/cap

Preparation of CueAg coreeshell particles with their anti-oxidationand antibacterial properties

Kuan-ting Chen a, Dahtong Ray a, Yu-hsien Peng b,c,d,*, Yu-Chi Hsu a

aDepartment of Resources Engineering, National Cheng Kung University, No.1, Da-Hsueh Road, Tainan, Taiwan 70101, ROCbDepartment of Environmental Engineering, Dayeh University, 168 University Rd., Dacun, Changhua, Taiwan 51591, ROCcDepartment of Research & Development, Oriental Happy Enterprise Co., No.27, Xin’ai Rd., South Dist., Tainan, Taiwan 70255, ROCdCenter for General Education, Kun Shan University, No.949, Dawan Rd., Yongkang Dist., Tainan, Taiwan 71003, ROC

a r t i c l e i n f o

Article history:Received 30 November 2012Received in revised form6 May 2013Accepted 7 May 2013Available online 21 May 2013

Keywords:Coreeshell particlesComposite particlesAntibacteria materialsX-ray diffraction spectroscopySEM analysis

Abbreviations: TA, tartaric acid; S. aureus, StaEscherichia coli.* Corresponding author. Department of Environme

versity, 168 University Rd., Dacun, Changhua, Taiwan1338, þ886 6 261 8328; fax: þ886 6 2616003.

E-mail addresses: pengyuhsien@hotmail.com(Y.-h. Peng).

1567-1739/$ e see front matter Crown Copyright � 2http://dx.doi.org/10.1016/j.cap.2013.05.003

a b s t r a c t

CueAg coreeshell particles were fabricated from Cu particles and silver sulphate with theenvironmental-friendly TA (tartaric acid, C4H6O6) as reducing and chelating agent in an aqueous system.The influences of [TA]/[Ag] and [Ag]/[Cu] molar ratios on the formation of Ag coatings on the Cu particleswere investigated. The SEM images and SEMeEDS analyses showed that [TA]/[Ag] ¼ 0.5 and [Ag]/[Cu]�0.2, the Cu particles were coated with uniform Ag nanoparticles. XRD analyses revealed that for theseCueAg particles heated at 250 �C, the oxidation of Cu was significantly reduced. Both anti-Staphylococcusaureus (Gram-positive) and anti-Escherichia coli (Gram-negative) characteristics of this CueAg compositeparticles showed satisfactory antibacterial ability. The characteristics of the composite CueAg particleswere discussed in detail.

Crown Copyright � 2013 Published by Elsevier B.V. All rights reserved.

1. Introduction

The coreeshell particles have received intense attentionbecause of the improved physical and chemical properties overtheir single-component particles. Many efforts have been maderecently to synthesize such special coreeshell structures [1,2].There are also many advantages of the coreeshell particles in theapplication of an antibacterial agent, such as high antibacterialactivity, long lasting effects, high chemical stability and low toxicityto human [3]. Nowadays, due to the low toxicity and high anti-bacterial properties of copper and silver, they are widely used asbactericide in the typical antibacterial treatment [4e6].

Guzman et al. [7] reported antibacterial activity of Ag nano-particles against E. coli (Escherichia coli), Pseudomonas aeruginosaand S. aureus (Staphylococcus aureus) by the KirbyeBauer method.The results demonstrated that there are strong antibacterial

phylococcus aureus; E. coli,

ntal Engineering, Dayeh Uni-51591, ROC. Tel.: þ886 4 851

, timchen317@gmail.com

013 Published by Elsevier B.V. All

activities against aforementioned bacteria at very low silver con-centration (below 7 ppm). Xue et al. [8] fabricated Ag nanoparticles(100e300 nm) coated textiles and found that there are high anti-bacterial ability against the Gram-negative bacteria, E. coli. ShateriKhalil-Abad and Yazdanshenas [9] fabricated the super hydropho-bic antibacterial surfaces on the cotton textiles by introducing Agnanoparticles (200e500 nm) to the woven fiber network. Themodified cotton textiles were capable of killing both Gram-negativeand Gram-positive bacteria on the surfaces. Gu et al. [10] andBurket et al. [11] reported that there are effective antibacterial ac-tivities on copper loaded carboxymethyl chitosan nanoparticles.The copper-deposited activated carbon fibers were for antibacterialaction.

Generally, coreeshell structure particles can be fabricated byelectroplating [12], electroless plating (also called spontaneousdisplacement reaction) [13,14] and vacuum process (e.g. evapora-tion, sputtering [15] etc.). It is well known that silver can bedeposited on many substrates by electroplating [16]. For commer-cial purposes, however, the electroplating and vacuummethods aretoo expensive and time-consuming. Therefore, the spontaneousdisplacement reaction method of the Ag coating is a betterapproach for commercial purposes. According to the literature, therate of replacement reaction is the determining factor and hasmajor influences on the properties of the final product [17e20].

rights reserved.

Table 1The parameters of the CueAg particle preparation reactions.

Sample Cuparticles(g)

0.023MeAg2SO4

(ml)[Ag]/[Cu]molar ratio

TA (g) [TA]/[Ag]molar ratio

1 2.92 200 0.2 0 02 2.92 200 0.2 0.69 0.53 2.92 200 0.2 1.38 14 2.92 200 0.2 2.76 25 2.92 200 0.2 5.52 46 2.92 200 0.1 0.69 0.57 2.92 200 0.2 0.69 0.58 2.92 200 0.3 0.69 0.5

K.-t. Chen et al. / Current Applied Physics 13 (2013) 1496e1501 1497

Mancier et al. [17] reported that the CueAg coreeshell nano-particles can be synthesized by displacement reaction of theultrasound-assisted electrochemistry. The rate of AgeCu displace-ment could be controlled by ethylenediaminetetraacetic acid(EDTA) which was the chelating agent. Xu et al. [18] reported thatthe fine Cu particles were coated by Ag nanoparticles via displacingCu by silver nitrate in ammonium hydroxide solution. The rate of Cudissolutionwas controlled by the dosage of ammonia. Hai et al. [19]reported that commercial Cu particles (2e40 mm) were mixed withammonium hydroxide solution, and then silver nitrate and potas-sium tartrate as reduction agent were added. The results showedthat the surface of the CueAg particles was controlled by theadding rate of silver nitrate solution. The porous structure had beenformed if the adding rate of silver nitrate solution was too fast ortoo slow. Peng et al. [20] reported that commercial Cu particles(7.36 mm) and Ag2SO4 were individually mixed with sodium citratesolution, then these two solutions were mixed together and aspontaneous reaction followed. It was found that the size of Agparticles deposited on the surface of the Cu particles was influencedby the concentration of sodium citrate.

In this article, we reported a simple and novel method tofabricate CueAg coreeshell particles at room temperatures, inwhich copper particles and silver sulphate were the starting ma-terials together with TA (tartaric acid, C4H6O6) as reducing andchelating agent. Furthermore, the CueAg particles prepared by thismethod showed good antibacterial characteristics, which providespromising applications in the antibacterial treatment.

2. Experimental

2.1. Materials

Copper powders, aggregated from primary particles of sizes lessthan 2 mm, with a median size of 7.36 mm (Laser Diffraction ParticleSize Analyzer, Baite Instruments Ltd.) was afforded by OrientalHappy Enterprise Co., Ltd., Taiwan. Silver sulphate (Ag2SO4) wasmanufactured by Solar Technology Inc., Taiwan. Tartaric acid(C4H6O6) was manufactured by Katayama Chemical, Japan. Allchemicals were used as received without further purification.

2.2. Preparation of the CueAg particles

One suspension and one solution, denoted as Sa and Sb,respectively, were prepared first. For Sa, 2.92 g Cu particles wasmixed with 100 ml deionized water and then stirred continuouslyat room temperature; for Sb, Ag2SO4 (1.43, 2.46 and 4.29 g,respectively) and TA (0, 0.69, 1.38, 2.76 and 5.52 g, respectively)were mixed with 200 ml deionized water. The detailed experi-mental parameters are listed in Table 1. The solution Sb was addedinto Sa using a syringe pump set at 20 ml/min with continuedstirring at 500 rpm. The reactions according to Eqs. (1)e(3), whichare similar to the reactions with citrate ions [21,22] will proceedimmediately.

H2C4H4O6#C4H4O2�6 þ 2Hþ; (1)

2Agþ þ C4H4O2�6 #

hAg2þ2 .C4H4O

2�6

i; (2)

hAg2þ2 .C4H4O

2�6

iþ n C4H4O

2�6 #

hAg2þ2 .

�C4H4O

2�6

�nþ1

i2n�:

(3)

When Agþ was reduced, the Cu2þ was simultaneously chelatedby the tartrate ion according to Eq. (4).

Cu2þ þ C4H4O2�6 � CuC4H4O6: (4)

During the process of the above reactions, it was observedthat the color of the solution after mixing turned from red topurple and finally to dark green, suggesting the coating of silveron copper particles. When the reaction finished, the mixture wasimmediately filtrated and washed for at least three times withdeionized water and the solids obtained were dried in a vacuumoven.

2.3. Preparation of samples for SEM cross-sectional images

The cross-sectional images of the coated CueAg particles wereexamined using an SEM. The CueAg particles producedweremixedwith epoxy resin and solidified. The solidified resinwas polished bythe Grinder and Polisher (PM2-200SA).

2.4. Test of the antibacterial ability

S. aureus (ATCC 15285) and E. coli (ATCC 15480) were selected asindicators in the antibacterial experiments, in which the concen-tration of the broth was set at 1.5 � 106 (Colony Forming Units/ml,CFU/ml). The prepared broth was uniformly coated on a MuellerHinton Agar. The CueAg particles (0.01 g) were mixed with steril-izedwater (100 ml) and then dropped on a disk filter paper (8mm indiameter) by a pipette. The disk was dried at room temperature for24 h and was used as the antibacterial disk samples. One blank andthree CueAg doped disks were put on the center of the MuellerHinton Agar and then maintained in an incubator at 37 �C for 24 h.The growth extents of S. aureus and E. coli were recorded withphotography and followed bymeasurements of the diameter of theinhibition zones.

2.5. Characterization

The morphology of the CueAg particles was observed by SEM(JEOL JSM-7001F, Japan). The phases identification of powders weredetermined by XRD (DX-2500, Fangyuan Co., PRC) using Cu Ka(l ¼ 1.5418 Å) radiation. The micro-chemical analysis was done bythe energy dispersive spectrometry (EDS) of SEM.

3. Results and discussions

3.1. Effects of [TA]/[Ag] molar ratio on the CueAg compositeparticles

Fig. 1 shows the XRD patterns of the Cu, Ag and CueAg particlesprepared at [TA]/[Ag] ¼ 0, 0.5, 1, 2 and 4, respectively. Three crystalphases can be identified in Fig. 1, i.e. Cu, Cu2O and Ag. At [TA]/[Ag]¼ 0 (XRD pattern 1c), Cu2O phase is produced together with Cu

Fig. 2. SEM images of the CueAg particles: (a) [TA]/[Ag

Fig. 1. XRD patterns of the Cu, Ag and the CueAg particles: (a) Cu; (b) Ag; (c)e(g) CueAg particles at [TA]/[Ag]: (c) 0; (d) 0.5; (e) 1; (f) 2; (g) 4 ([Ag]/[Cu] ¼ 0.2).

K.-t. Chen et al. / Current Applied Physics 13 (2013) 1496e15011498

and Ag, the appearance of Cu2O is probably due to the random andfast oxidation by Agþ ions. When TA was added (XRD patterns 1de1g), Cu2O phase disappeared, indicating that by chelating Agþ ions,the oxidation of Cu may be controlled or slow down. Besides, thepeaks of Ag and Cu phases are more distinct than that without TA,and are consistent for all TA concentrations.

The SEM images of the CueAg particles, prepared at [TA]/[Ag] ¼ 0, 0.5, 1, 2 and 4, are shown in Fig. 2. The particles canobviously be divided into two size-categories. The 50e150 nm Agparticles, and the 1e1.5 mm CueAg particles. Without TA, the re-action rate of Ag reduction and Cu replacement probably is too fast,so the Ag particles grew randomly on the surface of the Cu particles,even resulted in smaller independent Ag particles separated fromthe Cu particles as shown in Fig. 2a. The sizes of the Ag particles area little larger than 50e150 nm and the morphologies are variedincluding dendritic, platy and spherical. With the addition of TAand [TA]/[Ag] ¼ 0.5 and 1, smaller and uniform Ag particles aredeposited on the surface of the Cu particles, as shown in Fig. 2b andc. The addition of TA presumably reduce the rate of replacement

] ¼ 0; (b) 0.5; (c) 1; (d) 2; (e) 4 ([Ag]/[Cu] ¼ 0.2).

K.-t. Chen et al. / Current Applied Physics 13 (2013) 1496e1501 1499

reaction between Ag and Cu, and resulting in uniform and sphericalAg particles. For [TA]/[Ag] ratio larger than 1, as shown in Fig. 2dand e, there are more adhesive connections between Cu and Agparticles. Also, the morphology of the Ag particles becomes moreirregular. Obviously overdosed TA is deleterious to the formation ofcoreeshell CueAg particles and the optimum dosage is [TA]/[Ag] ¼ 0.5e1.0.

Fig. 4. XRD patterns of the CueAg particles heated at 250 �C for 2 h: (a) [Ag]/[Cu] ¼ 0;(b) 0.1; (c) 0.2; (d) 0.3 ([TA]/[Ag] ¼ 0.5).

3.2. Characterization of the CueAg composite particles

Fig. 3 shows the cross-sectional SEM pictures together withEDS analyses of CueAg particles prepared at [TA]/[Ag] ¼ 0.5 and[Ag]/[Cu] ¼ 0.1, 0.2 and 0.3, respectively (M and L are the electronshells of atoms. CuL: L-shell of copper; AgL: L-shell of silver; PtM:M-shell of platinum.). At [Ag]/[Cu] ¼ 0.1, there seems to be someformation of Janus particle (Fig. 3a) as well as independent Agnanoparticles. When [Ag]/[Cu] ¼ 0.2, however the coreeshellstructure of the CueAg particles can be identified by the cross-sectional SEM pictures showing the image of dimmer Cu corewith lighter Ag rim. The EDS analyses further afford evidences ofthe coreeshell structure with the results of centrally concentratedCu spectrum and peripherally concentrated Ag spectrum. Thischaracteristic becomes more prominent for the sample of [Ag]/[Cu] ¼ 0.3.

The anti-oxidation test, i.e. heat treatment of the CueAg parti-cles, on the other hand is a practical check of the rigidity of coreeshell structure. Fig. 4 shows the XRD patterns of the CueAg parti-cles heated at 250 �C for 2 h. It can be seen that without Ag, Cu2Opeak appears immediately (Fig. 4a). When Ag forms a shell on Cu,the Cu2O peak reduces remarkably (Fig. 4aed) and the trend ismaintained with increasing [Ag]/[Cu] molar ratio. However, the Agcoating may still not be densified enough at [Ag]/[Cu] ¼ 0.3 to

Fig. 3. Cross-sectional SEM pictures and EDS analyses of the CueAg particles prepared at [Tatoms. CuL: L-shell of copper; AgL: L-shell of silver; PtM: M-shell of platinum.).

render complete prevention of the Cu core from oxidation in pre-sent experiment.

3.3. Antibacterial ability of the CueAg particles

Agþ and Cuþ ions which are released from the nanoparticlesmay connect to the negatively charged bacterial cell wall andrupture it. Therefore, they can cause protein denaturation andcell death [23]. Both Agþ ions and Ag nanoparticles caused theaccumulation of envelope protein precursors to the cell walland resulted in dissipation of the proton motive force. Ag

A]/[Ag] ¼ 0.5 and [Ag]/[Cu] ¼ (a) 0.1; (b) 0.2; (c) 0.3 (M and L are the electron shells of

Fig. 5. Pictures of the antibacterial test disks for S. aureus at [Ag]/[Cu] ¼ (a) 0; (b) 0.1; (c) 0.2; (d) 0.3 ([TA]/[Ag] ¼ 0.5).

K.-t. Chen et al. / Current Applied Physics 13 (2013) 1496e15011500

nanoparticles also exhibited destabilization of the outer mem-brane and rupture of the plasma membrane. Therefore, theycaused the depletion of intracellular ATP (adenosine triphos-phate) [24].

Antibacterial ability tests were carried out for CueAg particlesprepared at [Ag]/[Cu] ¼ 0.1, 0.2 and 0.3 ([TA]/[Ag] ¼ 0.5). Thepictures of the disks are shown in Fig. 5 (S. aureus) and Fig. 6(E. coli). The relationship between the inhibition zone diameterand CueAg particles prepared at different [Ag]/[Cu] molar ratiowas presented in Fig. 7. It can be seen that the antibacterial

Fig. 6. Pictures of the antibacterial test disks for E. coli at [A

ability of CueAg particles are effective for both E. coli (Gram-negative) and S. aureus (Gram-positive). However, the antibac-terial ability on S. aureus (Gram-positive) is superior to E. coli(Gram-negative). This result is consistent with that observed byGuzman et al. [7]. It is expected that gram-negative bacteria ismore vulnerable due to its thin membrane. However, gram-positive bacteria though have thicker membrane walls, butdoes not have second membrane layer and lipopolysaccharidelayer (LPS). This may explain the weaker resistance of gram-positive bacteria to Ag nanoparticles.

g]/[Cu] ¼ (a) 0; (b) 0.1; (c) 0.2; (d) 0.3 ([TA]/[Ag] ¼ 0.5).

Fig. 7. The relationship between the inhibition zone diameter and [Ag]/[Cu] ratio ofthe CueAg particles for: S. aureus (curve a) and E. coli (curve b).

K.-t. Chen et al. / Current Applied Physics 13 (2013) 1496e1501 1501

4. Conclusions

The coreeshell structure CueAg composite particles can beproduced at room temperatures using tartaric acid (TA) as thechelating agent to control the reduction and coating of Ag on Cuand less environmental impact is expected. The CueAg compositeparticles present both antibacterial and anti-oxide properties. At[TA]/[Ag] ¼ 0.5 and [Ag]/[Cu] ¼ 0.3, the antibacterial and anti-oxidation abilities of CueAg particles reaches a peak. Theenhancement of the antibacterial and anti-oxidation abilities of theCueAg powder make possible of its replacement of pure Ag pow-ders in the manufacture of conductive paste, electronic slurry,catalyst and antibacterial materials.

Acknowledgements

The financial support for this research was provided by the In-dustrial Development Bureau, Ministry of Economic Affairs of the

Republic of China under Grant no. M10000121-222 in the Con-ventional Industry Technology Development (CITD) program.

Ms. H.J. Shih of the Instrument Center of National Cheng KungUniversity, performing the SEM and EDS analyses is greatlyappreciated.

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