Synthesis and Growth Mechanism of Silver Nanowires through

Research ArticleSynthesis and Growth Mechanism of Silver Nanowires throughDifferent Mediated Agents (CuCl2 and NaCl) Polyol Process

Mohd Rafie Johan Nurul Azri Khalisah Aznan Soo Teng Yee Ing Hong HoSoo Wern Ooi Noorsaiyyidah Darman Singho and Fatihah Aplop

Nanomaterials Engineering Research Group Advanced Materials Research Laboratory Department of Mechanical EngineeringUniversity of Malaya 50603 Kuala Lumpur Malaysia

Correspondence should be addressed to Noorsaiyyidah Darman Singho ieyda putriumedumy

Received 6 February 2014 Revised 23 April 2014 Accepted 23 April 2014 Published 22 May 2014

Academic Editor Zhenhui Kang

Copyright copy 2014 Mohd Rafie Johan et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Silver nanowires (AgNWs) have been synthesized by polyol process through different mediated agents (CuCl2and NaCl) The

presence of cations and anions (Cu(II) Na+ and Clminus) has been shown to have a strong impact on the shape of silver nanostructuresThe field emission scanning electronmicroscopy (FESEM) and transmission electronmicroscopy (TEM) show uniform nanowiresThe UV-vis spectra show that plasmon peak indicated the formation of nanowires The X-ray diffraction (XRD) pattern displayedthat final product was highly crystallized and pure The growth mechanism of AgNWs was proposed

1 Introduction

One-dimensional (1-D) metal nanostructures such as nano-wires have attracted extensive attention due to their uniquemagnetic optical and electronic properties compared tozero-dimensional (0-D) nanostructures [1ndash6] Among these1-Dmetal nanostructures silver nanowires (AgNWs) are par-ticularly of interest because the bulk Ag exhibits the highestelectrical and thermal conductivity among all metals Thereare many applications where nanowires could be exploited togreatly enhance the functionality of a material [7ndash9] In theseregards the synthesis of nanowires has attracted attentionfrom a broad range of researchers [10ndash14] Over the lastdecade variousmethods had been used to synthesizeAgNWssuch as polyol process [12ndash14] wet chemical synthesis [15 16]hydrothermal method [17 18] and ultraviolet irradiationphotoreduction techniques [19 20] Among these methodsthe polyol process is considered due to simple effective lowcost and high yield In the polyol process an exotic reagentleads to the formation of wire like structure Xia and Sun [13]have modified the polyol process by generating AgNWs withdiameters in the range of 30ndash50 nm By controlling theparameters such as reaction time molar ratio between cap-ping agent and metallic precursor temperature and addition

of control agent a reasonable control growth of AgNWs maybe achieved In this work AgNWs were synthesized throughreducing silver nitrate (AgNO

3) with 12-propanediol (Sam-

ple 1) and ethylene glycol (EG) (Samples 2 and 3) in the pres-ence of polyvinylpyrrolidone (PVP) as the surfactant whichcan direct the growth of AgNWs and protect them fromaggregation The mediated agents such as CuCl

2(Sample 2)

and NaCl (Sample 3) are added to facilitate the growth ofAgNWs We believe Cu(II) Na+ and Clminus ions are necessaryfor AgNWs production

2 Experimental Method

Anhydrous 12-propandiol (99) AgNO3(99) and polyvi-

nylpyrrolidonewere purchased fromAcros All the chemicalswere used as received without any further purificationThe first sample (Sample 1) is without any mediated agent10mL of 12-propanediol was added into a 50mL three-necked flask at 170∘C for 2 h Then 05mL of 12-propanediolsolution of AgNO

3(0005M) was injected into the 12-

propanediol under vigorous magnetic stirring Later 3mL of12-propanediol solution of AgNO

3(01M) and 3mL of 12-

propanediol solution of PVP (045M) were added dropwise

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 105454 7 pageshttpdxdoiorg1011552014105454

2 Journal of Nanomaterials

simultaneously over a period of 5 minutes The solutionimmediately turned from colorless to light yellow The reac-tion was continued for 1 h and heated at 170∘C for 30min Agrey suspensionwas obtained and allowed to cool at the roomtemperature Then the mixture was diluted by acetonecentrifuged washed by deionized water and dried in avacuum for 24 hours at room temperature

The second sample (Sample 2) is with CuCl2as the

mediated agent Firstly 5mL of ethylene glycol was addedinto a beaker and heated for 1 hour using silicon oil bathat 150∘C Then 40120583L of a 4mM CuCl

2sdotH2Oethylene glycol

was added into the solution stirred and allowed to heat for15 minutes After that 15mL of 114mM PVPethylene glycolwas added into the beaker followed by 15mL of 94mMAgNO

3ethylene glycol The color changed to yellow and

became brownish grey after AgNO3ethylene glycol was

added The solution was heated for another 1 hour Then thesolution was taken out and let to cool at room temperatureThe solution was centrifuged at 3000 rpm and 30min eachwith acetone and deionized water The final product waspreserved in deionized water until characterization

The third sample (Sample 3) is with NaCl as the mediatedagent 15mL of 036M of ethylene glycol (EG) solution ofpolyvinylpyrrolidone (PVP) was heated and stirred for 15minutes It was then followed by microwave heating at 170∘Cfor an hour Then 20120583L of 01M EG solution of NaCl and20120583L of 006MEG solution of AgNO

3were injected into

this EG solution of PVP to produce AgCl as seeds After15 minutes of injection 15mL of 006M of EG solution ofAgNO

3was injected into mixture solution within 5 minutes

The mixture solution was stirred to obtain a homogeneoussolutionThe color ofmixture solution slowly changes to lightyellow The mixture solution was then heated undermicrowave irradiation with temperature maintained at 170∘Cfor approximately 30minutes It is allowed to cool naturally toroom temperature and turn to gray color The resultingsolution was washed several times using acetone and ethanoland then dried in vacuum at 60∘C

The X-ray diffraction (XRD) patterns were recordedusing a Siemens D5000 X-ray diffractometer (Cu-K120572 radia-tion 120582 = 0154 nm) The transmission electron microscopy(TEM) images were taken on a Libra 120 model TEMusing accelerating voltage of 400 kV Field emission scanningelectronmicroscopy (FE-SEM) imageswere takenusingZeissAurigaTheUV-visible spectrum of the as-prepared productswas recorded on a Varian Cary 50UV-vis spectroscopy

3 Results and Discussion

31 Mechanism for the Formation of AgNWs

311 Scheme 1 (Sample 1 without any Mediated Agent) Theformation of anisotropic AgNWs involves two steps In thefirst step 12-propanediol was converted to propionaldehydeat high temperature (170∘C) as shown in (1) Then it reducesAg+ ions to Ag atoms as shown in (2) Consider

HOCH3CH2CHOH 170∘C997888997888997888997888rarr CH3CH2CHO +H2O (1)

2Ag+ + 2CH3CH2CHO 997888rarr CH3CH2COOH3 + 2Ag + 4H+

(2)

In the second step AgNO3and PVP were added dropwise

to the reaction system allowing the nucleation and growth ofAgNWs

Ag + (--CH2--CH--) (--CH2--CH--)

N N

2HC

2HC

2HC

2HC

C=O C=O

CH2 CH2

Ag

nn

(3)

Ag atoms are nucleated through the homogeneous nucleationprocessTheseAgNpswerewell dispersed because of the pres-ence of a polymeric surfactant PVP that could be chemicallyadsorbed onto the surfaces of Ag through OndashAg bonding (3)PVP has an affinity toward many chemicals to form coordi-native compounds due to the structure of polyvinyl skeletonwith strong polar group (pyrrolidone ring) In this caseC=O polar groups were interacted with Ag+ ions and formcoordinating complex as shown in (3) When this dispersionof AgNps was continuously heated at 170∘C the smallnanoparticles progressively disappeared to the benefit oflarger ones viaOstwald ripening process [21]The critical par-ticle radius increased with temperature As the reaction con-tinued the small AgNpswere no longer stable in solution andthey started to dissolve and contribute to the growth of largerones With the assistance of PVP some of the larger nanopar-ticles were able to grow into rod-shaped structures Thegrowth process would continue until all the AgNps werecompletely consumed and only nanowires survived

312 Scheme 2 (Sample 2 with CuCl2Mediated Agent) In the

initial step high temperature is crucial for the conversion ofethylene glycol to glycolaldehyde as shown in

2HOCH2CH2OH +O2150∘C997888997888997888997888rarr 2CH3CHO + 2H2O (4)

AgNps were formed by reducing Ag+ ions with glycolalde-hyde as shown in

2CH3CHO + 2Ag+ 997888rarr CH3COndashOCCH3 + Ag + 2H+

(5)

It was found that a small amount of Clminus must be added to apolyol synthesis to provide electrostatic stabilization for theinitially formed Ag seeds [4]

2HOCH2CHO + CuCl2 997888rarr 2CH2COOH + Cu + 2HCl

(6)

Ag+ + Clminus lArrrArr AgCl (7)

In addition to electrostatically stabilizing the initiallyformed Ag seeds the high Clminus concentrations during CuCl

2

Journal of Nanomaterials 3

mediated synthesis help reduce the concentration of free Ag+ions in the solution through the formation of AgCl Sub-sequent it will slowly release the Ag+ and subsequent slowrelease of Ag+ effectively These facilitate the high-yieldformation of the thermodynamically more stable multiplytwinned Ag seeds that are required for wire length Valencymetal ions (Cu2+) were reduced by EG to low valence (Cu+)which in turn reacted with and scavenged adsorbed atomicoxygen from the surface of AgNps Here Cu2+ can removeoxygen from the solvent which prevents twinned seedsdissolved by oxidative etching and scavenging adsorbedatomic oxygen from the surface of the Ag seeds facilitatingmultiply twinned seeds growth [12]

In the final step AgNO3and PVP were added dropwise

to the reaction system allowing the nucleation and growth ofsilver nanowires as shown in (3) AgNps were well dispersedbecause of the presence of PVP a polymeric surfactant thatcould be chemically adsorbed onto the surfaces of Ag throughOndashAg bonding As the reaction continued the small Agnanoparticles were no longer stable in solution and theystarted to dissolve and contribute to the growth of largerones When multiple twinned form the nanoparticles duringa nuclei period the PVP was bounded preferently on 100then 111 [22 23] This inhibited the growth along 111direction So the growth took place only in the 110 directionresulting in the fivefold twinned nanowires (Figure 1)

313 Scheme 3 (Sample 3 with NaCl Mediated Agent) Likein Scheme 2 the formation of anisotropic AgNWs involves anumber of steps The first two steps are similar to (4) and (5)Like in Scheme 2 chloride ions were added (8) to stabilizeAgNps and prevented the growth of nanoparticles [10] As aresult nanoparticles that can grow will dissolve via Oswaldripening

2HOCH2CHO + 2NaCl 997888rarr 2CH2COOH + 2Na+ + 2HClminus

(8)


The high Clminus concentration during NaCl mediated syn-thesis helps reduce the concentration of free Ag+ in the solu-tion through the formation of AgCl (9) Subsequent it willslowly release the Ag+ and subsequent slow release of Ag+effectivelyThis facilitates the high yield formation of the ther-modynamically stable multiply twinned Ag seeds So AgClprecipitate that forms in the early stages of the reaction servesas a seed for multitwin particles The formed AgCl nanopar-ticles can be reduced slowly and decreased reaction ratemakes anisotropic growth of Ag nanowires favorable [24]Meanwhile Na+ can remove oxygen from the solvent whichprevents twinned seeds dissolved by oxidative etching andscavenging adsorbed atomic oxygen from the surface of thesilver seeds facilitating multiply twinned seeds growth [12]In the final step AgNO

3and PVP were added dropwise to

the recreation system allowing the nucleation and growth ofAgNWs as shown in (3)

With passivation of some facets of particles by PVPsome nanoparticles can grow into multitwin particles PVP is

111

100

Figure 1 Schematic of 5-fold twinned pentagonal nanowires con-sisting of five elongated 100 facets and 10 111 end facets

Figure 2 FESEM image of AgNWs (without any mediated agent)

believed to passivate (100) faces of these multitwin particlesand leave (111) planes achieve for anisotropic growth at [110]direction [13] (Figure 1) As the addition of Ag+ continuesmultitwin particles grow into Ag nanowires

32 FESEM Analysis Figure 2 shows the FESEM image ofAgNWs without any mediated agents The image showsstraightness along the longitudinal axis the level of perfec-tion and the copiousness in quantity that we could routinelyachieve using this synthetic approach The presence of silvernanoparticles (AgNps) is also evident in the figure indicatingthat not all of AgNps are transformed into nanowires

Figure 3 shows the FESEM image of AgNWs with CuCl2

as the mediated agent The image reveals that the product isentirely composed of a large quantity of uniform nanowireswith a mean diameter of 65 nmThe high faces of PVP on allfaces of the seeds lead to anisotropic growth mode

Figure 4 shows the FESEM image of AgNWswithNaCl asthe mediated agentThe image shows well-defined wires withmean diameter of 80 nm

33 TEM Analysis Figure 5 shows the TEM image of indi-vidual AgNWs without any mediated agents with 84 nm indiameter and 1119 nm in length

Figure 6 shows a TEM image of an individual AgNW(CuCl

2mediated agent) with 87 nm in diameter and 3 120583m


Figure 3 FESEM image of AgNWs (with CuCl2mediated agent)

Figure 4 FESEM image of AgNWs (with NaCl mediated agent)

in length The insert of Figure 6 reveals a pentagonal cross-section of AgNWs and indicates the multiple-twinned struc-ture of the AgNWs [24]

Figure 7 shows the TEM image of AgNWs with NaClmediated agent The TEM image displayed a twin boundaryin the middle of nanowires and pentagon shape cross-sectionat the end of nanowires

34 XRD Analysis Figure 8 shows the XRD pattern ofAgNWswith andwithoutmediated agentThepeaks at anglesof 2120579 = 381∘ 442∘ 643∘ and 775∘ correspond to the (111)(200) (220) and (311) crystal planes of the face center cubic(FCC) Ag respectively The lattice constant calculated fromthe diffraction pattern was 04086 nm which is in agreementwith the reported value of silver (JCPDS 04-0783) Further-more the intensity ratio of the (111) to (200) peaks is 20 ingood agreement with the theoretical ratio that is 25 [14]

Figure 9 shows the XRD pattern of highly crystallineAgNWs with CuCl

2mediated agent It has a similar pattern

with AgNWs without mediated agent (Figure 8) The XRDpattern reveals that the synthesis AgNWs through polyolprocess comprise pure phase The lattice constant 119886 was407724 A which is almost approaching the literature value of4086 A The ratio of intensity between (111) and (200) peaksreveals a relatively high value of 32 compared to the theoret-ical ratio value of 25 This high value of ratio indicates theenchancement of 111 crystalline planes in the AgNWs

Figure 10 shows the XRD pattern of AgNWs with NaClmediated agent It exhibits well-defined peaks without anyimpurity element peaks detected This indicated the success

Figure 5 TEM image of AgNWs without any mediated agent

Figure 6 TEM image ofAgNWswithCuCl2mediated agent (insert

pentagon cross-section of AgNWs)

Figure 7 TEM image of AgNWs (with NaCl mediated agent)

0

20

40

60

80

100

120

140

160

20 25 30 35 40 45 50 55 60 65 70 75 80

Inte

nsity

(au

)

(200)(220) (311)

(111)

2120579

Figure 8 XRD pattern of AgNWs without any mediated agent


0

50

100

150

200

250

300

350

400

30 40 50 60 70 80

Inte

nsity

(au

)

(200)

(220) (311)

(111)

2120579 (deg)

Figure 9 XRD pattern of AgNWs (with CuCl2mediated agent)

0

02

04

06

08

1

12

20 30 40 50 60 70 80

Coun

ts (s

)

(111)

(200)(220) (311)

2120579

Figure 10 XRD patterns of the as-synthesized AgNWs (with NaClmediated agent)

in the formation of the crystalline silver nanowires The fourdiffraction peaks obtained are similar to peaks in Figures 8and 9 It is worth noting that the ratio of intensity between(111) and (200) peaks exhibits a relative value of 205 (thetheoretical ratio is 25) It indicated that the sample becomesless crystalline with NaCl mediated agent

35 UV-Vis Spectroscopy Analysis Figure 11 shows the absor-ption spectra of AgNWs without mediated agent at differentmolar ratio of PVP to AgNO

3 The appearance of a weak

surface plasmon resonance (SPR) at 425 nm indicated theformation of AgNps [17] This implies that the final productsynthesized under this particular condition was a mixture ofAgNps and AgNWs As the molar ratio increases from 45 to75 the intensity of the SPR is slightly decreased Furthermorethe SPR peak around 425 nm is blue-shifted to 404 nm Theshoulder peak at 380 nm could be considered as the opticalsignature of AgNWs At this point optical signatures similarto those of bulk Ag also began to appear as indicated by the

3000 3500 4000 4500 5000 5500 6000

Abso

rban

ce (a

u)

Wavelength (nm)

minus05

minus04

minus03

minus02

minus01

00

01

02

03

04

05

06

Molar ratio = 45

Molar ratio = 6

Molar ratio = 75

425nm

380nm

350nm

Figure 11 Absorption spectra of AgNWs (without any mediatedagent) with different molar ratio of PVP and AgNO

3

0

002

004

006

008

01

012

014

300 350 400 450 500 550 600

Abso

rban

ce (a

u)

Wavelength (nm)

Figure 12 Absorption spectra of AgNWs (with CuCl2mediated

agent)

shoulder peak around 350 nm With increasing molar ratiothe intensity of absorption bands at 350 and 380 nm increasedapparently due to increased density of AgNWs

Figure 12 shows the UV-vis absorption spectra forAgNWs with CuCl

2mediated agent The peak positions at

391 nm could be considered as the optical signature of rela-tively long AgNWs At this point optical signatures similar tothose of bulk silver also began to appear as indicated by theshoulder peak around 357 nm [25] Compared to the previousabsorption spectra (Figure 11) no peak for AgNps existedThis indicates that the sample is completely of AgNWs

Figure 13 shows the absorption spectra of ANWs (withNaCl mediated agent) synthesized with different molar ofAgNO

3 The appearance of a story peak at 384 nm could be

considered as the transverse mode of relatively long AgNWs


0

05

1

15

2

300 350 400 450 500 550 600

Abso

rban

ce (a

u)

Wavelength (nm)minus05

minus1

Ag 006MAg 008M

Figure 13 Absorption spectra of the as-synthesized AgNWs (withNaClmediated agent) at differentmolar of AgNO

3 (a) 006 (b) 008

At this point optical signatures similar to those of bulk Agalso began to appear as indicated by the shoulder peak around350 nm As the concentration of AgNO

3increases from 006

to 008M the intensity of these peaks increased significantlyand red-shifted to 394 and 351 nm respectively This resultindicated that theAgNWs increased in numberwith apparentgrowth in length Again the spectra show that the sample iscompletely AgNWs

4 Conclusion

AgNWs were successfully synthesized by using polyol tech-niquewith andwithoutmediated agents It was found that theaddition of CuCl

2or NaCl to the polyol reduction of AgNO

3

in the presence of PVP greatly facilitated the formation ofAgNWs Without the mediated agents the final productsynthesized was a mixture of AgNps and AgNWs Both thecation and the anions are crucial for the successful productionof AgNWs

Conflict of Interests

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

Acknowledgment

The financial support received from University of MalayaResearch Grant (RP011C-13AET) is gratefully acknowledged

References

[1] Y Xia P Yang Y Sun et al ldquoOne-dimensional nanostructuressynthesis characterization and applicationsrdquo Advanced Mate-rials vol 15 no 5 pp 353ndash389 2003

[2] Z L Wang ldquoCharacterizing the structure and properties ofindividual wire-like nanoentitiesrdquo Advanced Materials vol 12no 17 pp 1295ndash1298 2000

[3] P J Cao Y S Gu H W Lin et al ldquoHigh-density alignedcarbon nanotubes with uniformdiametersrdquo Journal ofMaterialsResearch vol 18 pp 1686ndash1690 2003

[4] J Hu T W Odom and C M Lieber ldquoChemistry and physicsin one dimension synthesis and properties of nanowires andnanotubesrdquo Accounts of Chemical Research vol 32 no 5 pp435ndash445 1999

[5] N A C Lah and M R Johan ldquoFacile shape control synthesisand optical properties of silver nanoparticles stabilized byDaxad 19 surfactantrdquoApplied Surface Science vol 257 no 17 pp7494ndash7500 2011

[6] N A C Lah and M R Johan ldquoOptical and thermodynamicstudies of silver nanoparticles stabilized byDaxad 19 surfactantrdquoInternational Journal of Materials Research vol 102 no 3 pp340ndash347 2011

[7] C M Lieber ldquoOne-dimensional nanostructures chemistryphysicsamp applicationsrdquo Solid State Communications vol 107 no11 pp 607ndash616 1998

[8] M S Gudiksen L J Lauhon J Wang D C Smith and C MLieber ldquoGrowth of nanowire superlattice structures for nano-scale photonics and electronicsrdquo Nature vol 415 no 6872 pp617ndash620 2002

[9] Y Cui and C M Lieber ldquoFunctional nanoscale electronicdevices assembled using silicon nanowire building blocksrdquoScience vol 291 no 5505 pp 851ndash853 2001

[10] C R Martin ldquoNanomaterials a membrane-based syntheticapproachrdquo Science vol 266 no 5193 pp 1961ndash1966 1994

[11] A M Morales and C M Lieber ldquoA laser ablation method forthe synthesis of crystalline semiconductor nanowiresrdquo Sciencevol 279 no 5348 pp 208ndash211 1998

[12] K E Korte S E Skrabalak and Y J Xia ldquoRapid synthesis ofsilver nanowires through a cucl- or cucl2-mediated polyolprocessrdquo Journal of Materials Chemistry vol 18 pp 437ndash4412008

[13] Y Xia and Y Sun ldquoLarge-scale synthesis of uniform silvernanowires through a soft self-seeding polyol processrdquoAdvanced Materials vol 14 no 11 pp 833ndash837 2002

[14] Y Sun Y Yin B T Mayers T Herricks and Y Xia ldquoUniformsilver nanowires synthesis by reducing AgNO

3with ethylene

glycol in the presence of seeds and poly(vinyl pyrrolidone)rdquoChemistry of Materials vol 14 no 11 pp 4736ndash4745 2002

[15] K K Coswell C M Bender and C J Murply ldquoSeedlesssurfactantless wet chemical synthesis of silver nanowiresrdquoNanoLetters vol 3 no 5 pp 667ndash669 2003

[16] P S Mdluli and N Revaprasadu ldquoAn improved NN-dim-ethylformamide and polyvinyl pyrrolidone approach for thesynthesis of long silver nanowiresrdquo Journal of Alloys andCompounds vol 469 no 1-2 pp 519ndash522 2009

[17] Z Wang J Liu X Chen J Wan and Y Qian ldquoA simple hyd-rothermal route to large-scale synthesis of uniform silvernanowiresrdquo ChemistrymdashA European Journal vol 11 no 1 pp160ndash163 2005

[18] J Xu J Hu C Peng H Liu and Y Hu ldquoA simple approach tothe synthesis of silver nanowires by hydrothermal process in thepresence of gemini surfactantrdquo Journal of Colloid and InterfaceScience vol 298 no 2 pp 689ndash693 2006

[19] Y Zhou S H Yu C Y Wang X G Li Y R Zhu and ZY Chen ldquoA novel ultraviolet irradiation photoreduction tech-nique for the preparation of single-crystal Ag nanorods and AgdendritesrdquoAdvancedMaterials vol 11 no 10 pp 850ndash852 1999

[20] K Zou X H Zhang X F Duan X M Meng and S KWu ldquoSeed-mediated synthesis of silver nanostructures and


polymer silver nanocables by UV irradiationrdquo Journal of Crys-tal Growth vol 273 no 1-2 pp 285ndash291 2004

[21] A R Roosen andW C Carter ldquoSimulations of microstructuralevolution anisotropic growth and coarseningrdquo Physica A vol261 no 1-2 pp 232ndash247 1998

[22] W A Al-Saidi H Feng and K A Fichthorn ldquoAdsorption ofpolyvinylpyrrolidone on Ag surfaces insight into a structure-directing agentrdquo Nano Letters vol 12 no 2 pp 997ndash1001 2012

[23] W A Al-Saidi H Feng and K A Fichthorn ldquoThe binding ofPVP to Ag surfaces insight into a structure-directing agentfrom dispersion-corrected density-functional theoryrdquoThe Jour-nal of Physical Chemistry C vol 117 pp 1163ndash1171 2013

[24] K E Korte S E Skrabalak andY Xia ldquoRapid synthesis of silvernanowires through a CuCl- or CuCl

2-mediated polyol processrdquo

Journal of Materials Chemistry vol 18 no 4 pp 437ndash441 2008[25] T You S Xu S Sun and X Song ldquoControllable synthesis of

pentagonal silver nanowires via a simple alcohol-thermalmethodrdquoMaterials Letters vol 63 no 11 pp 920ndash922 2009

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Journal ofNanomaterials


simultaneously over a period of 5 minutes The solutionimmediately turned from colorless to light yellow The reac-tion was continued for 1 h and heated at 170∘C for 30min Agrey suspensionwas obtained and allowed to cool at the roomtemperature Then the mixture was diluted by acetonecentrifuged washed by deionized water and dried in avacuum for 24 hours at room temperature

The second sample (Sample 2) is with CuCl2as the

mediated agent Firstly 5mL of ethylene glycol was addedinto a beaker and heated for 1 hour using silicon oil bathat 150∘C Then 40120583L of a 4mM CuCl

2sdotH2Oethylene glycol

was added into the solution stirred and allowed to heat for15 minutes After that 15mL of 114mM PVPethylene glycolwas added into the beaker followed by 15mL of 94mMAgNO

3ethylene glycol The color changed to yellow and

became brownish grey after AgNO3ethylene glycol was

added The solution was heated for another 1 hour Then thesolution was taken out and let to cool at room temperatureThe solution was centrifuged at 3000 rpm and 30min eachwith acetone and deionized water The final product waspreserved in deionized water until characterization

The third sample (Sample 3) is with NaCl as the mediatedagent 15mL of 036M of ethylene glycol (EG) solution ofpolyvinylpyrrolidone (PVP) was heated and stirred for 15minutes It was then followed by microwave heating at 170∘Cfor an hour Then 20120583L of 01M EG solution of NaCl and20120583L of 006MEG solution of AgNO

3were injected into

this EG solution of PVP to produce AgCl as seeds After15 minutes of injection 15mL of 006M of EG solution ofAgNO

3was injected into mixture solution within 5 minutes

The mixture solution was stirred to obtain a homogeneoussolutionThe color ofmixture solution slowly changes to lightyellow The mixture solution was then heated undermicrowave irradiation with temperature maintained at 170∘Cfor approximately 30minutes It is allowed to cool naturally toroom temperature and turn to gray color The resultingsolution was washed several times using acetone and ethanoland then dried in vacuum at 60∘C

The X-ray diffraction (XRD) patterns were recordedusing a Siemens D5000 X-ray diffractometer (Cu-K120572 radia-tion 120582 = 0154 nm) The transmission electron microscopy(TEM) images were taken on a Libra 120 model TEMusing accelerating voltage of 400 kV Field emission scanningelectronmicroscopy (FE-SEM) imageswere takenusingZeissAurigaTheUV-visible spectrum of the as-prepared productswas recorded on a Varian Cary 50UV-vis spectroscopy

3 Results and Discussion

31 Mechanism for the Formation of AgNWs

311 Scheme 1 (Sample 1 without any Mediated Agent) Theformation of anisotropic AgNWs involves two steps In thefirst step 12-propanediol was converted to propionaldehydeat high temperature (170∘C) as shown in (1) Then it reducesAg+ ions to Ag atoms as shown in (2) Consider

HOCH3CH2CHOH 170∘C997888997888997888997888rarr CH3CH2CHO +H2O (1)

2Ag+ + 2CH3CH2CHO 997888rarr CH3CH2COOH3 + 2Ag + 4H+

(2)

In the second step AgNO3and PVP were added dropwise

to the reaction system allowing the nucleation and growth ofAgNWs

Ag + (--CH2--CH--) (--CH2--CH--)

N N

2HC

2HC

2HC

2HC

C=O C=O

CH2 CH2

Ag

nn

(3)

Ag atoms are nucleated through the homogeneous nucleationprocessTheseAgNpswerewell dispersed because of the pres-ence of a polymeric surfactant PVP that could be chemicallyadsorbed onto the surfaces of Ag through OndashAg bonding (3)PVP has an affinity toward many chemicals to form coordi-native compounds due to the structure of polyvinyl skeletonwith strong polar group (pyrrolidone ring) In this caseC=O polar groups were interacted with Ag+ ions and formcoordinating complex as shown in (3) When this dispersionof AgNps was continuously heated at 170∘C the smallnanoparticles progressively disappeared to the benefit oflarger ones viaOstwald ripening process [21]The critical par-ticle radius increased with temperature As the reaction con-tinued the small AgNpswere no longer stable in solution andthey started to dissolve and contribute to the growth of largerones With the assistance of PVP some of the larger nanopar-ticles were able to grow into rod-shaped structures Thegrowth process would continue until all the AgNps werecompletely consumed and only nanowires survived

312 Scheme 2 (Sample 2 with CuCl2Mediated Agent) In the

initial step high temperature is crucial for the conversion ofethylene glycol to glycolaldehyde as shown in

2HOCH2CH2OH +O2150∘C997888997888997888997888rarr 2CH3CHO + 2H2O (4)

AgNps were formed by reducing Ag+ ions with glycolalde-hyde as shown in

2CH3CHO + 2Ag+ 997888rarr CH3COndashOCCH3 + Ag + 2H+

(5)

It was found that a small amount of Clminus must be added to apolyol synthesis to provide electrostatic stabilization for theinitially formed Ag seeds [4]

2HOCH2CHO + CuCl2 997888rarr 2CH2COOH + Cu + 2HCl

(6)


In addition to electrostatically stabilizing the initiallyformed Ag seeds the high Clminus concentrations during CuCl

2







(8)






111

100

























0

20

40

60

80

100

120

140

160

20 25 30 35 40 45 50 55 60 65 70 75 80

Inte

nsity

(au

)

(200)(220) (311)

(111)

2120579



0

50

100

150

200

250

300

350

400

30 40 50 60 70 80

Inte

nsity

(au

)

(200)

(220) (311)

(111)

2120579 (deg)


0

02

04

06

08

1

12

20 30 40 50 60 70 80

Coun

ts (s

)

(111)

(200)(220) (311)

2120579






3000 3500 4000 4500 5000 5500 6000

Abso

rban

ce (a

u)

Wavelength (nm)

minus05

minus04

minus03

minus02

minus01

00

01

02

03

04

05

06

Molar ratio = 45

Molar ratio = 6

Molar ratio = 75

425nm

380nm

350nm


3

0

002

004

006

008

01

012

014

300 350 400 450 500 550 600

Abso

rban

ce (a

u)

Wavelength (nm)


agent)









0

05

1

15

2

300 350 400 450 500 550 600

Abso

rban

ce (a

u)


minus1

Ag 006MAg 008M


3 (a) 006 (b) 008


3increases from 006


4 Conclusion



3




Acknowledgment


References















3with ethylene
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









(8)






111

100

























0

20

40

60

80

100

120

140

160

20 25 30 35 40 45 50 55 60 65 70 75 80

Inte

nsity

(au

)

(200)(220) (311)

(111)

2120579



0

50

100

150

200

250

300

350

400

30 40 50 60 70 80

Inte

nsity

(au

)

(200)

(220) (311)

(111)

2120579 (deg)


0

02

04

06

08

1

12

20 30 40 50 60 70 80

Coun

ts (s

)

(111)

(200)(220) (311)

2120579






3000 3500 4000 4500 5000 5500 6000

Abso

rban

ce (a

u)

Wavelength (nm)

minus05

minus04

minus03

minus02

minus01

00

01

02

03

04

05

06

Molar ratio = 45

Molar ratio = 6

Molar ratio = 75

425nm

380nm

350nm


3

0

002

004

006

008

01

012

014

300 350 400 450 500 550 600

Abso

rban

ce (a

u)

Wavelength (nm)


agent)









0

05

1

15

2

300 350 400 450 500 550 600

Abso

rban

ce (a

u)


minus1

Ag 006MAg 008M


3 (a) 006 (b) 008


3increases from 006


4 Conclusion



3




Acknowledgment


References















3with ethylene
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

















0

20

40

60

80

100

120

140

160

20 25 30 35 40 45 50 55 60 65 70 75 80

Inte

nsity

(au

)

(200)(220) (311)

(111)

2120579



0

50

100

150

200

250

300

350

400

30 40 50 60 70 80

Inte

nsity

(au

)

(200)

(220) (311)

(111)

2120579 (deg)


0

02

04

06

08

1

12

20 30 40 50 60 70 80

Coun

ts (s

)

(111)

(200)(220) (311)

2120579






3000 3500 4000 4500 5000 5500 6000

Abso

rban

ce (a

u)

Wavelength (nm)

minus05

minus04

minus03

minus02

minus01

00

01

02

03

04

05

06

Molar ratio = 45

Molar ratio = 6

Molar ratio = 75

425nm

380nm

350nm


3

0

002

004

006

008

01

012

014

300 350 400 450 500 550 600

Abso

rban

ce (a

u)

Wavelength (nm)


agent)









0

05

1

15

2

300 350 400 450 500 550 600

Abso

rban

ce (a

u)


minus1

Ag 006MAg 008M


3 (a) 006 (b) 008


3increases from 006


4 Conclusion



3




Acknowledgment


References















3with ethylene
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

50

100

150

200

250

300

350

400

30 40 50 60 70 80

Inte

nsity

(au

)

(200)

(220) (311)

(111)

2120579 (deg)


0

02

04

06

08

1

12

20 30 40 50 60 70 80

Coun

ts (s

)

(111)

(200)(220) (311)

2120579






3000 3500 4000 4500 5000 5500 6000

Abso

rban

ce (a

u)

Wavelength (nm)

minus05

minus04

minus03

minus02

minus01

00

01

02

03

04

05

06

Molar ratio = 45

Molar ratio = 6

Molar ratio = 75

425nm

380nm

350nm


3

0

002

004

006

008

01

012

014

300 350 400 450 500 550 600

Abso

rban

ce (a

u)

Wavelength (nm)


agent)









0

05

1

15

2

300 350 400 450 500 550 600

Abso

rban

ce (a

u)


minus1

Ag 006MAg 008M


3 (a) 006 (b) 008


3increases from 006


4 Conclusion



3




Acknowledgment


References















3with ethylene
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

05

1

15

2

300 350 400 450 500 550 600

Abso

rban

ce (a

u)


minus1

Ag 006MAg 008M


3 (a) 006 (b) 008


3increases from 006


4 Conclusion



3




Acknowledgment


References















3with ethylene
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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