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RESEARCH

ARTIC

LE

Copyright copy 2011 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 11 6429ndash6432 2011

Effect of Synthetic Temperature on theDispersion Stability of Gold NanocolloidProduced via Electrical Explosion of Wire

G S Yun1 L H Bac1 J S Kim1 Y S Kwon1 H S Choi2 and J C Kim1lowast1School of Materials Science and Engineering University of Ulsan Daehak-ro 102 Nam-gu Ulsan 680-749 South Korea

2School of Biological Sciences University of Ulsan Daehak-ro 102 Nam-gu Ulsan 680-749 South Korea

In this study gold nanocolloid was produced via the electrical explosion of wire in water for thepurpose of medical treatment Thus the use of other additives was avoided to stabilize the goldnanocolloid The temperature of the water that was to be used for explosion was changed andits effect on the stability of the gold nanocolloid was investigated The synthetic temperature wasvaried from ice temperature to 80 C The morphology and particle size were studied using a trans-mission electron microscope The UV-Vis spectra confirmed the formation of gold nanoparticles inthe water The stability of the gold nanocolloid was estimated using the zeta-potential and Turbis-can methods The results showed that the synthetic temperature affected the stability of the goldnanocolloid The TEM images of the gold nanoparticles prepared at low temperatures (0 and 20 C)have several big particles But when the synthetic temperature was increased to 80 C most ofthe nanoparticles formed a spherical shape without neck connection Better stability was obtainedin the gold nanocolloid sample prepared at a higher temperature The gold nanocolloid that wassynthesized at 80 C was stable for more than three months with small sedimentation

Keywords Electrical Explosion of Wire (EEW) Gold Nanocolloid Turbiscan Stability

1 INTRODUCTION

Gold nanocolloids have attracted much attention of latedue to their potential applications in various fields suchas in catalysis sensors biology and medicine1ndash4 Theypresent fascinating aspects such as their assembly of mul-tiple types involving materials science the behavior of theindividual particles size-related electronic magnetic andoptical properties (quantum size effect) and their appli-cations to catalysis and biology5 In these applicationsthe stability of the nanocolloids is one of the importantparameters The main approach for obtaining higher stabil-ity is through chemical surface treatment using surfactantsandor dispersants The absorbance of these agents on thegold nanoparticlesrsquo surfaces can keep the nanocolloids sta-ble and will allow them to be used as sensors catalystsetc Nevertheless the surfactants andor dispersants willbe destroyed or will produce bad effects on the cells oron a living body Therefore it is important to synthesizea stable nanocolloidal gold without impurities like surfac-tants or dispersants In addition there has been increasedemphasis on the development and use of ldquogreenrdquo synthesis

lowastAuthor to whom correspondence should be addressed

methods aiming at the total elimination or at the very leastthe minimization of hazardous waste and toxic chemicalsElectric explosion of wire (EEW) is a top-down phys-

ical method for fabricating nanostructure materials6 Theproducts of wire explosion depend on the current densitywire dimension and medium in which the explosion is car-ried out Electrical explosion of wire in gas has been usedfor preparing various metal and ceramic nanopowders7ndash10

Electrical explosion of wire in liquid is useful for thepreparation of nanocolloids In this process the nanoparti-cles directly disperse into the liquid and it can be regardedas a one-step technique that can minimize the aggregationof the nanoparticles and therefore increase the stability ofthe nanocolloidsIn this study the preparation of gold nanocolloid in

deionized (DI) water and was focused on the effect of thesynthetic temperature on the dispersion properties of thenanocolloid was investigated A green method of preparingnanocolloid using non-toxic chemicals was also introduced

2 EXPERIMENTAL DETAILS

A thin gold wire with a 02 mm diameter was used as astarting material for the explosion process The experiment

J Nanosci Nanotechnol 2011 Vol 11 No 7 1533-48802011116429004 doi101166jnn20114394 6429

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

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Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW Yun et al

Table I Summary of the experimental details

Capacitance (F) 30Charging voltage (V) 30Material AuWire diameter (mm) 02Length of each explosion (mm) 27Ambient liquid Water

details have been described elsewhere11 Briefly gold wirewas submerged in water and a pulsed high-density cur-rent from a 3-kV-charged capacitor was injected into itby closing the spark gap As the resistance of water ismuch smaller than that of gold the electrical energy wasdeposited only onto the gold wire The gold wire wasmelted evaporated due to Joule heating and then turnedinto plasma Gold nanoparticles were formed in the liquidafter the vapor was cooled and condensed by the ambientwater The experiment parameters are shown in Table IAfter 25-time explosion the suspension was collected foranalysisThe morphologies and the sizes of the prepared gold

nanoparticles were observed via transmission electronmicroscopy (TEM) A drop of gold suspension wasdropped onto a carbon-coated copper grid was flow-driedunder vacuum at room temperature and was then placedin an electron-microscopic chamber for observation Theabsorption spectrum of the gold nanocolloid was investi-gated through the UV-Vis method within the wavelengthrange of 300ndash800 nm The dispersion stability was esti-mated using a Turbiscan Lab (Formulaction Co France)instrument based on the multiple light-scattering methodit detected the concentration variation in the nanocolloidby scanning the whole height of the sample in transmis-sion and backscattering The zeta potential of the goldnanocolloid was measured using a zeta potential analyzer(ELS-Z Japan) At least ten different runs were carriedout to obtain the average zeta potential value

3 RESULTS AND DISCUSSION

Gold nanocolloid was prepared in water via electricalexplosion of wire in DI water The formation of goldnanoparticles in the aqueous colloidal solution was con-firmed through UV-Vis spectra analysis Figure 1 showsthe absorption UV-Vis spectra of the gold nanocolloidsprepared in water at different temperatures It can be seenin the figure that there was an absorption peak in allthe samples that were prepared The spectra exhibited thecharacteristics of a surface plasmon band at sim530 nmwhich was reported in many papers12ndash15 The absorptionspectra were essentially the same in all the samples Theplasmon absorption wavelengths of all the gold nanocol-loidal solutions are listed in Table II It is well known thatthe plasmon band maximum and its bandwidth of metallicnanoparticles depend on the particle size shape and sol-vent media It can be seen in Figure 1 that the absorption

Fig 1 UV-Vis absorption plasmon spectra of the gold nanocolloidalsolutions synthesized at different temperatures (a) 0 C (b) 20 C(c) 40 C (d) 60 C and (e) 80 C

spectra of all the prepared samples were similar The wave-length band positions and the bandwidths did not clearlychange clearly (shown in Table II) These behaviors canbe explained in two ways First as the samples were pre-pared using the same solvent (DI water) the effect of theambient media can be neglected Second although the par-ticle sizes of the gold nanoparticles prepared at differenttemperatures were not the same (seen in the TEM imagesin Fig 2) the particles that were prepared at low tem-peratures seem smaller than those that were prepared athigh temperatures The particles connected however andformed a chain and cluster of nanoparticles which resultedin a bigger average sizeFigure 2 shows the TEM images of the gold nanopar-

ticles prepared at different synthetic temperatures Thenanocolloids that were prepared at low temperatures (0 and20 C) have several big particles with sizes of about40 nm The big particles had spherical shapes and wereseparated while the small nanoparticles seemed to haveconnected and formed a chain across the particles Therewere less small particles in the samples that were pre-pared at higher temperature but the particles nonethelessbecame more spherical When the synthetic temperaturewas increased to 80 C most of the nanoparticles formeda spherical shape without neck connection There were big

Table II Plasmon absorption wavelengths and zeta potentials of thegold nanocolloids formed at different synthetic temperatures

Plasmon absorption Zeta-potentialTemperature (C) wavelength (nm) FWHM (mV)

0 534 6775 minus6220 532 7456 minus8140 530 7277 minus22360 529 7359 minus28180 529 7130 minus315

6430 J Nanosci Nanotechnol 11 6429ndash6432 2011

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

ARTIC

LE

Yun et al Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW

(a)

(d) (e)

(b) (c)

Fig 2 TEM images of the nanoparticles prepared at different temperatures (a) 0 C (b) 20 C (c) 40 C (d) 60 C and (e) 80 C

particles in samples that were prepared at higher tempera-tures The difference in particle size and shape may be dueto the cooling rate of the vapor After explosion the vapor-ized gold material collided with the water molecules andcooled down after which it condensed to form nanoparti-cles The cooling rates of the vapor at different synthetictemperatures were not equal The cooling rate was higherwhen the temperature of the surrounding liquid was lowerThe high cooling speed of the vapor for condensing theparticles could have created smaller particles at lower syn-thetic temperaturesTo understand the stability of gold nanocolloids in the

absence of surfactants their zeta potentials were measuredA zeta potential value will make a repulsion force andwill keep the gold nanoparticles away from one anotherwhich will result in the high stability of the nanocolloidsTable II shows the zeta potentials of the gold nanocolloidsthat were prepared via EEW in water at different syn-thetic temperatures All the gold nanocolloids were nega-tively charged with zeta potential values within the rangeof minus62 to minus315 mV It was found that the absolute zetapotential value increases with increasing synthetic temper-ature and reaches the highest value of minus315 mV Basedon the zeta potential values the nanocolloids that wereprepared at 80 C had the best stability among all the goldnanocolloids Their zeta potentials remained at minus302 mVafter three months slightly smaller than that of the as-synthesized sample This result is in agreement with theresult of the Turbiscan measurement which will be pre-sented later The negative values of the gold nanoparticlesreveal that the nanoparticles were negatively charged in

water As no surfactants were used in these nanocolloidsthe surfaces of the gold nanoparticles are attributed to theoxygen chemisorptions1617 Electrons were injected intothe gold nanoparticles during the explosion causing nega-tively charged surfaces These charged surfaces were satu-rated by atomic oxygen which can create hydrogen bondswith water particles in a water medium18 As the oxygenchemisorption on a gold surface at a higher temperaturecan be greater than that at a lower temperature the zetapotential of the charged surface is thus greaterFigure 3 presents the typical transmission (T) and

backscattering (BS) intensities as a function of sampleheight and time in the case of the gold nanocolloidprepared at 80 C in three days In this case the BS

Fig 3 Typical transmission and backscattering profiles of the goldnanocolloid produced at 80 C

J Nanosci Nanotechnol 11 6429ndash6432 2011 6431

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

ARTIC

LE

Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW Yun et al

Fig 4 Variation of transmission signal (T ) versus time for the goldnanocolloids produced via electrical explosion of wire in water at differ-ent temperatures

intensities almost did not change while the T intensitiesdecreased as a function of time The first important obser-vation is that the BS and T signals were constant over thesample length The T and BS curves were flat The per-centage of light going across the sample decreased overtime The decrease was small however only 025 inthree days Figure 4 compares the variation of the T signalas a function of time for the five samples prepared at dif-ferent temperatures This figure indicates that the variationof the T signal depends much on the synthetic tempera-ture In all the cases the T variation increased as a func-tion of time but the speeds of change were different TheT variation of the samples that were prepared at highertemperatures increased more slowly than that of the sam-ples that were prepared at lower temperatures In two sam-ples that were prepared at 0 and 20 C respectively thevariation rose fast for less than 10 h and then became toconstant This means that the gold nanoparticles settledindicating that the colloid was unstable The gold nanopar-ticles agglomerated into big clusters that can be seen bythe naked eyes These clusters then rapidly settled at thebottom of the bottle which made the transmission sig-nal go up eventually reaching a constant value due onlyto water The fast agglomeration can be attributed to thefact that gold nanofluids have small zeta potential at alow synthetic temperature The zeta potential values wereonly minus62 and minus81 mV at the synthetic temperatures of0 and 20 C respectively They were not high enough tocreate force strong enough to repulse one another and tokeep the nanoparticles far away from one another The sta-bility of the gold nanocolloid was much better at a highsynthetic temperature It can be clearly seen in Figure 4that the T variation of the gold nanocolloid that wasprepared at 80 C synthetic temperature is much smaller

compared to that of the gold nanocolloids prepared atother temperatures The high zeta potential of the goldnanocolloid prepared at 80 C created repulsive electro-static forces between the nanoparticles and protected themagainst agglomeration and sedimentation in the water Thegold nanocolloids were stable for more than three monthswithout noticeable aggregation

4 CONCLUSIONS

The effect of the liquid temperature on the dispersion sta-bility of gold nanocolloids produced via electrical explo-sion of wire in water was studied The dispersion stabilitywas found to depend much on the synthetic temperatureThe gold nanocolloid is more stable at a high synthetictemperature The results of the study show that withoutsurfactants the gold nanocolloids prepared at 80 C canbe stable up to more than three months This stability canbe attributed to the highly negative charge of the goldnanoparticles It is believe that this method is the mostsimple effective and green way of preparing stable goldnanocolloids

References and Notes

1 S Chah M R Hammond and R N Zare Chem Biol 12 323(2005)

2 S Aryal S Pilla and S Gong J Nanosci Nanotechnol 9 5701(2009)

3 P K Jain K S Lee I H El-Sayed and M A El-Sayed J PhysChem B 110 7238 (2006)

4 D P OrsquoNeal L R Hirsch N J Halas J D Payne and J L WestCancer Lett 209 171 (2004)

5 M C Daniel and D Astruc Chem Rev 104 293 (2004)6 Y A Kotov J Nanopart Res 5 539 (2003)7 Y S Kwon Y H Jung N A Yavorovsky A P Illyn and J S

Kim Scripta Mater 44 2247 (2001)8 W Jiang and K Yatsui IEEE Trans Plasma Sci 26 1498 (1998)9 R Sarathi T K Sindhu and S R Chakravarthy Mater Lett

61 1823 (2007)10 Y Kinemuchi K Murai C Sangurai C H Cho H Suematsu

W Jiang and K Yatsui J Am Ceram Soc 86 420 (2003)11 L H Bac Y S Kwon J S Kim Y I Lee D W Lee and J C

Kim Mater Res Bull 45 352 (2010)12 J P Sylvestre S Poulin A V Kabashin E Sacher M Meunier

and J H T Luong J Phys Chem B 108 16864 (2004)13 F Mafuneacute J Kohno Y Takeda T Kondow and H Sawabe J Phys

Chem B 105 5114 (2001)14 D Philip Spectrochim Acta Part A 71 80 (2008)15 A Mishra P Tripathy S Ram and H J Fecht Nanosci Nanotech-

nol 9 4342 (2009)16 A Franceschetti S J Pennycook and S T Pantelides Chem Phys

Lett 374 471 (2003)17 S D Puckett J A Heuser J D Keith W U Spendel and G E

Pacey Talanta 66 1242 (2005)18 J K Lung J C Huang D C Tien C Y Liao K H Tseng T T

Tsung W S Kao T H Tsai C S Jwo H M Lin and L StobinskiJ Alloys Compd 434 655 (2007)

Received 27 August 2010 Accepted 28 January 2011

6432 J Nanosci Nanotechnol 11 6429ndash6432 2011

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

ARTIC

LE

Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW Yun et al

Table I Summary of the experimental details

Capacitance (F) 30Charging voltage (V) 30Material AuWire diameter (mm) 02Length of each explosion (mm) 27Ambient liquid Water

details have been described elsewhere11 Briefly gold wirewas submerged in water and a pulsed high-density cur-rent from a 3-kV-charged capacitor was injected into itby closing the spark gap As the resistance of water ismuch smaller than that of gold the electrical energy wasdeposited only onto the gold wire The gold wire wasmelted evaporated due to Joule heating and then turnedinto plasma Gold nanoparticles were formed in the liquidafter the vapor was cooled and condensed by the ambientwater The experiment parameters are shown in Table IAfter 25-time explosion the suspension was collected foranalysisThe morphologies and the sizes of the prepared gold

nanoparticles were observed via transmission electronmicroscopy (TEM) A drop of gold suspension wasdropped onto a carbon-coated copper grid was flow-driedunder vacuum at room temperature and was then placedin an electron-microscopic chamber for observation Theabsorption spectrum of the gold nanocolloid was investi-gated through the UV-Vis method within the wavelengthrange of 300ndash800 nm The dispersion stability was esti-mated using a Turbiscan Lab (Formulaction Co France)instrument based on the multiple light-scattering methodit detected the concentration variation in the nanocolloidby scanning the whole height of the sample in transmis-sion and backscattering The zeta potential of the goldnanocolloid was measured using a zeta potential analyzer(ELS-Z Japan) At least ten different runs were carriedout to obtain the average zeta potential value

3 RESULTS AND DISCUSSION

Gold nanocolloid was prepared in water via electricalexplosion of wire in DI water The formation of goldnanoparticles in the aqueous colloidal solution was con-firmed through UV-Vis spectra analysis Figure 1 showsthe absorption UV-Vis spectra of the gold nanocolloidsprepared in water at different temperatures It can be seenin the figure that there was an absorption peak in allthe samples that were prepared The spectra exhibited thecharacteristics of a surface plasmon band at sim530 nmwhich was reported in many papers12ndash15 The absorptionspectra were essentially the same in all the samples Theplasmon absorption wavelengths of all the gold nanocol-loidal solutions are listed in Table II It is well known thatthe plasmon band maximum and its bandwidth of metallicnanoparticles depend on the particle size shape and sol-vent media It can be seen in Figure 1 that the absorption

Fig 1 UV-Vis absorption plasmon spectra of the gold nanocolloidalsolutions synthesized at different temperatures (a) 0 C (b) 20 C(c) 40 C (d) 60 C and (e) 80 C

spectra of all the prepared samples were similar The wave-length band positions and the bandwidths did not clearlychange clearly (shown in Table II) These behaviors canbe explained in two ways First as the samples were pre-pared using the same solvent (DI water) the effect of theambient media can be neglected Second although the par-ticle sizes of the gold nanoparticles prepared at differenttemperatures were not the same (seen in the TEM imagesin Fig 2) the particles that were prepared at low tem-peratures seem smaller than those that were prepared athigh temperatures The particles connected however andformed a chain and cluster of nanoparticles which resultedin a bigger average sizeFigure 2 shows the TEM images of the gold nanopar-

ticles prepared at different synthetic temperatures Thenanocolloids that were prepared at low temperatures (0 and20 C) have several big particles with sizes of about40 nm The big particles had spherical shapes and wereseparated while the small nanoparticles seemed to haveconnected and formed a chain across the particles Therewere less small particles in the samples that were pre-pared at higher temperature but the particles nonethelessbecame more spherical When the synthetic temperaturewas increased to 80 C most of the nanoparticles formeda spherical shape without neck connection There were big

Table II Plasmon absorption wavelengths and zeta potentials of thegold nanocolloids formed at different synthetic temperatures

Plasmon absorption Zeta-potentialTemperature (C) wavelength (nm) FWHM (mV)

0 534 6775 minus6220 532 7456 minus8140 530 7277 minus22360 529 7359 minus28180 529 7130 minus315

6430 J Nanosci Nanotechnol 11 6429ndash6432 2011

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

ARTIC

LE

Yun et al Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW

(a)

(d) (e)

(b) (c)

Fig 2 TEM images of the nanoparticles prepared at different temperatures (a) 0 C (b) 20 C (c) 40 C (d) 60 C and (e) 80 C

particles in samples that were prepared at higher tempera-tures The difference in particle size and shape may be dueto the cooling rate of the vapor After explosion the vapor-ized gold material collided with the water molecules andcooled down after which it condensed to form nanoparti-cles The cooling rates of the vapor at different synthetictemperatures were not equal The cooling rate was higherwhen the temperature of the surrounding liquid was lowerThe high cooling speed of the vapor for condensing theparticles could have created smaller particles at lower syn-thetic temperaturesTo understand the stability of gold nanocolloids in the

absence of surfactants their zeta potentials were measuredA zeta potential value will make a repulsion force andwill keep the gold nanoparticles away from one anotherwhich will result in the high stability of the nanocolloidsTable II shows the zeta potentials of the gold nanocolloidsthat were prepared via EEW in water at different syn-thetic temperatures All the gold nanocolloids were nega-tively charged with zeta potential values within the rangeof minus62 to minus315 mV It was found that the absolute zetapotential value increases with increasing synthetic temper-ature and reaches the highest value of minus315 mV Basedon the zeta potential values the nanocolloids that wereprepared at 80 C had the best stability among all the goldnanocolloids Their zeta potentials remained at minus302 mVafter three months slightly smaller than that of the as-synthesized sample This result is in agreement with theresult of the Turbiscan measurement which will be pre-sented later The negative values of the gold nanoparticlesreveal that the nanoparticles were negatively charged in

water As no surfactants were used in these nanocolloidsthe surfaces of the gold nanoparticles are attributed to theoxygen chemisorptions1617 Electrons were injected intothe gold nanoparticles during the explosion causing nega-tively charged surfaces These charged surfaces were satu-rated by atomic oxygen which can create hydrogen bondswith water particles in a water medium18 As the oxygenchemisorption on a gold surface at a higher temperaturecan be greater than that at a lower temperature the zetapotential of the charged surface is thus greaterFigure 3 presents the typical transmission (T) and

backscattering (BS) intensities as a function of sampleheight and time in the case of the gold nanocolloidprepared at 80 C in three days In this case the BS

Fig 3 Typical transmission and backscattering profiles of the goldnanocolloid produced at 80 C

J Nanosci Nanotechnol 11 6429ndash6432 2011 6431

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

ARTIC

LE

Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW Yun et al

Fig 4 Variation of transmission signal (T ) versus time for the goldnanocolloids produced via electrical explosion of wire in water at differ-ent temperatures

intensities almost did not change while the T intensitiesdecreased as a function of time The first important obser-vation is that the BS and T signals were constant over thesample length The T and BS curves were flat The per-centage of light going across the sample decreased overtime The decrease was small however only 025 inthree days Figure 4 compares the variation of the T signalas a function of time for the five samples prepared at dif-ferent temperatures This figure indicates that the variationof the T signal depends much on the synthetic tempera-ture In all the cases the T variation increased as a func-tion of time but the speeds of change were different TheT variation of the samples that were prepared at highertemperatures increased more slowly than that of the sam-ples that were prepared at lower temperatures In two sam-ples that were prepared at 0 and 20 C respectively thevariation rose fast for less than 10 h and then became toconstant This means that the gold nanoparticles settledindicating that the colloid was unstable The gold nanopar-ticles agglomerated into big clusters that can be seen bythe naked eyes These clusters then rapidly settled at thebottom of the bottle which made the transmission sig-nal go up eventually reaching a constant value due onlyto water The fast agglomeration can be attributed to thefact that gold nanofluids have small zeta potential at alow synthetic temperature The zeta potential values wereonly minus62 and minus81 mV at the synthetic temperatures of0 and 20 C respectively They were not high enough tocreate force strong enough to repulse one another and tokeep the nanoparticles far away from one another The sta-bility of the gold nanocolloid was much better at a highsynthetic temperature It can be clearly seen in Figure 4that the T variation of the gold nanocolloid that wasprepared at 80 C synthetic temperature is much smaller

compared to that of the gold nanocolloids prepared atother temperatures The high zeta potential of the goldnanocolloid prepared at 80 C created repulsive electro-static forces between the nanoparticles and protected themagainst agglomeration and sedimentation in the water Thegold nanocolloids were stable for more than three monthswithout noticeable aggregation

4 CONCLUSIONS

The effect of the liquid temperature on the dispersion sta-bility of gold nanocolloids produced via electrical explo-sion of wire in water was studied The dispersion stabilitywas found to depend much on the synthetic temperatureThe gold nanocolloid is more stable at a high synthetictemperature The results of the study show that withoutsurfactants the gold nanocolloids prepared at 80 C canbe stable up to more than three months This stability canbe attributed to the highly negative charge of the goldnanoparticles It is believe that this method is the mostsimple effective and green way of preparing stable goldnanocolloids

References and Notes

1 S Chah M R Hammond and R N Zare Chem Biol 12 323(2005)

2 S Aryal S Pilla and S Gong J Nanosci Nanotechnol 9 5701(2009)

3 P K Jain K S Lee I H El-Sayed and M A El-Sayed J PhysChem B 110 7238 (2006)

4 D P OrsquoNeal L R Hirsch N J Halas J D Payne and J L WestCancer Lett 209 171 (2004)

5 M C Daniel and D Astruc Chem Rev 104 293 (2004)6 Y A Kotov J Nanopart Res 5 539 (2003)7 Y S Kwon Y H Jung N A Yavorovsky A P Illyn and J S

Kim Scripta Mater 44 2247 (2001)8 W Jiang and K Yatsui IEEE Trans Plasma Sci 26 1498 (1998)9 R Sarathi T K Sindhu and S R Chakravarthy Mater Lett

61 1823 (2007)10 Y Kinemuchi K Murai C Sangurai C H Cho H Suematsu

W Jiang and K Yatsui J Am Ceram Soc 86 420 (2003)11 L H Bac Y S Kwon J S Kim Y I Lee D W Lee and J C

Kim Mater Res Bull 45 352 (2010)12 J P Sylvestre S Poulin A V Kabashin E Sacher M Meunier

and J H T Luong J Phys Chem B 108 16864 (2004)13 F Mafuneacute J Kohno Y Takeda T Kondow and H Sawabe J Phys

Chem B 105 5114 (2001)14 D Philip Spectrochim Acta Part A 71 80 (2008)15 A Mishra P Tripathy S Ram and H J Fecht Nanosci Nanotech-

nol 9 4342 (2009)16 A Franceschetti S J Pennycook and S T Pantelides Chem Phys

Lett 374 471 (2003)17 S D Puckett J A Heuser J D Keith W U Spendel and G E

Pacey Talanta 66 1242 (2005)18 J K Lung J C Huang D C Tien C Y Liao K H Tseng T T

Tsung W S Kao T H Tsai C S Jwo H M Lin and L StobinskiJ Alloys Compd 434 655 (2007)

Received 27 August 2010 Accepted 28 January 2011

6432 J Nanosci Nanotechnol 11 6429ndash6432 2011

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

ARTIC

LE

Yun et al Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW

(a)

(d) (e)

(b) (c)

Fig 2 TEM images of the nanoparticles prepared at different temperatures (a) 0 C (b) 20 C (c) 40 C (d) 60 C and (e) 80 C

particles in samples that were prepared at higher tempera-tures The difference in particle size and shape may be dueto the cooling rate of the vapor After explosion the vapor-ized gold material collided with the water molecules andcooled down after which it condensed to form nanoparti-cles The cooling rates of the vapor at different synthetictemperatures were not equal The cooling rate was higherwhen the temperature of the surrounding liquid was lowerThe high cooling speed of the vapor for condensing theparticles could have created smaller particles at lower syn-thetic temperaturesTo understand the stability of gold nanocolloids in the

absence of surfactants their zeta potentials were measuredA zeta potential value will make a repulsion force andwill keep the gold nanoparticles away from one anotherwhich will result in the high stability of the nanocolloidsTable II shows the zeta potentials of the gold nanocolloidsthat were prepared via EEW in water at different syn-thetic temperatures All the gold nanocolloids were nega-tively charged with zeta potential values within the rangeof minus62 to minus315 mV It was found that the absolute zetapotential value increases with increasing synthetic temper-ature and reaches the highest value of minus315 mV Basedon the zeta potential values the nanocolloids that wereprepared at 80 C had the best stability among all the goldnanocolloids Their zeta potentials remained at minus302 mVafter three months slightly smaller than that of the as-synthesized sample This result is in agreement with theresult of the Turbiscan measurement which will be pre-sented later The negative values of the gold nanoparticlesreveal that the nanoparticles were negatively charged in

water As no surfactants were used in these nanocolloidsthe surfaces of the gold nanoparticles are attributed to theoxygen chemisorptions1617 Electrons were injected intothe gold nanoparticles during the explosion causing nega-tively charged surfaces These charged surfaces were satu-rated by atomic oxygen which can create hydrogen bondswith water particles in a water medium18 As the oxygenchemisorption on a gold surface at a higher temperaturecan be greater than that at a lower temperature the zetapotential of the charged surface is thus greaterFigure 3 presents the typical transmission (T) and

backscattering (BS) intensities as a function of sampleheight and time in the case of the gold nanocolloidprepared at 80 C in three days In this case the BS

Fig 3 Typical transmission and backscattering profiles of the goldnanocolloid produced at 80 C

J Nanosci Nanotechnol 11 6429ndash6432 2011 6431

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

ARTIC

LE

Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW Yun et al

Fig 4 Variation of transmission signal (T ) versus time for the goldnanocolloids produced via electrical explosion of wire in water at differ-ent temperatures

intensities almost did not change while the T intensitiesdecreased as a function of time The first important obser-vation is that the BS and T signals were constant over thesample length The T and BS curves were flat The per-centage of light going across the sample decreased overtime The decrease was small however only 025 inthree days Figure 4 compares the variation of the T signalas a function of time for the five samples prepared at dif-ferent temperatures This figure indicates that the variationof the T signal depends much on the synthetic tempera-ture In all the cases the T variation increased as a func-tion of time but the speeds of change were different TheT variation of the samples that were prepared at highertemperatures increased more slowly than that of the sam-ples that were prepared at lower temperatures In two sam-ples that were prepared at 0 and 20 C respectively thevariation rose fast for less than 10 h and then became toconstant This means that the gold nanoparticles settledindicating that the colloid was unstable The gold nanopar-ticles agglomerated into big clusters that can be seen bythe naked eyes These clusters then rapidly settled at thebottom of the bottle which made the transmission sig-nal go up eventually reaching a constant value due onlyto water The fast agglomeration can be attributed to thefact that gold nanofluids have small zeta potential at alow synthetic temperature The zeta potential values wereonly minus62 and minus81 mV at the synthetic temperatures of0 and 20 C respectively They were not high enough tocreate force strong enough to repulse one another and tokeep the nanoparticles far away from one another The sta-bility of the gold nanocolloid was much better at a highsynthetic temperature It can be clearly seen in Figure 4that the T variation of the gold nanocolloid that wasprepared at 80 C synthetic temperature is much smaller

compared to that of the gold nanocolloids prepared atother temperatures The high zeta potential of the goldnanocolloid prepared at 80 C created repulsive electro-static forces between the nanoparticles and protected themagainst agglomeration and sedimentation in the water Thegold nanocolloids were stable for more than three monthswithout noticeable aggregation

4 CONCLUSIONS

The effect of the liquid temperature on the dispersion sta-bility of gold nanocolloids produced via electrical explo-sion of wire in water was studied The dispersion stabilitywas found to depend much on the synthetic temperatureThe gold nanocolloid is more stable at a high synthetictemperature The results of the study show that withoutsurfactants the gold nanocolloids prepared at 80 C canbe stable up to more than three months This stability canbe attributed to the highly negative charge of the goldnanoparticles It is believe that this method is the mostsimple effective and green way of preparing stable goldnanocolloids

References and Notes

1 S Chah M R Hammond and R N Zare Chem Biol 12 323(2005)

2 S Aryal S Pilla and S Gong J Nanosci Nanotechnol 9 5701(2009)

3 P K Jain K S Lee I H El-Sayed and M A El-Sayed J PhysChem B 110 7238 (2006)

4 D P OrsquoNeal L R Hirsch N J Halas J D Payne and J L WestCancer Lett 209 171 (2004)

5 M C Daniel and D Astruc Chem Rev 104 293 (2004)6 Y A Kotov J Nanopart Res 5 539 (2003)7 Y S Kwon Y H Jung N A Yavorovsky A P Illyn and J S

Kim Scripta Mater 44 2247 (2001)8 W Jiang and K Yatsui IEEE Trans Plasma Sci 26 1498 (1998)9 R Sarathi T K Sindhu and S R Chakravarthy Mater Lett

61 1823 (2007)10 Y Kinemuchi K Murai C Sangurai C H Cho H Suematsu

W Jiang and K Yatsui J Am Ceram Soc 86 420 (2003)11 L H Bac Y S Kwon J S Kim Y I Lee D W Lee and J C

Kim Mater Res Bull 45 352 (2010)12 J P Sylvestre S Poulin A V Kabashin E Sacher M Meunier

and J H T Luong J Phys Chem B 108 16864 (2004)13 F Mafuneacute J Kohno Y Takeda T Kondow and H Sawabe J Phys

Chem B 105 5114 (2001)14 D Philip Spectrochim Acta Part A 71 80 (2008)15 A Mishra P Tripathy S Ram and H J Fecht Nanosci Nanotech-

nol 9 4342 (2009)16 A Franceschetti S J Pennycook and S T Pantelides Chem Phys

Lett 374 471 (2003)17 S D Puckett J A Heuser J D Keith W U Spendel and G E

Pacey Talanta 66 1242 (2005)18 J K Lung J C Huang D C Tien C Y Liao K H Tseng T T

Tsung W S Kao T H Tsai C S Jwo H M Lin and L StobinskiJ Alloys Compd 434 655 (2007)

Received 27 August 2010 Accepted 28 January 2011

6432 J Nanosci Nanotechnol 11 6429ndash6432 2011

Delivered by Ingenta toKorea Institute of Science amp Technology (KIST)

IP 16112273158Thu 04 Oct 2012 123824

RESEARCH

ARTIC

LE

Effect of Synthetic Temperature on the Dispersion Stability of Gold Nanocolloid Produced via EEW Yun et al

Fig 4 Variation of transmission signal (T ) versus time for the goldnanocolloids produced via electrical explosion of wire in water at differ-ent temperatures

intensities almost did not change while the T intensitiesdecreased as a function of time The first important obser-vation is that the BS and T signals were constant over thesample length The T and BS curves were flat The per-centage of light going across the sample decreased overtime The decrease was small however only 025 inthree days Figure 4 compares the variation of the T signalas a function of time for the five samples prepared at dif-ferent temperatures This figure indicates that the variationof the T signal depends much on the synthetic tempera-ture In all the cases the T variation increased as a func-tion of time but the speeds of change were different TheT variation of the samples that were prepared at highertemperatures increased more slowly than that of the sam-ples that were prepared at lower temperatures In two sam-ples that were prepared at 0 and 20 C respectively thevariation rose fast for less than 10 h and then became toconstant This means that the gold nanoparticles settledindicating that the colloid was unstable The gold nanopar-ticles agglomerated into big clusters that can be seen bythe naked eyes These clusters then rapidly settled at thebottom of the bottle which made the transmission sig-nal go up eventually reaching a constant value due onlyto water The fast agglomeration can be attributed to thefact that gold nanofluids have small zeta potential at alow synthetic temperature The zeta potential values wereonly minus62 and minus81 mV at the synthetic temperatures of0 and 20 C respectively They were not high enough tocreate force strong enough to repulse one another and tokeep the nanoparticles far away from one another The sta-bility of the gold nanocolloid was much better at a highsynthetic temperature It can be clearly seen in Figure 4that the T variation of the gold nanocolloid that wasprepared at 80 C synthetic temperature is much smaller

compared to that of the gold nanocolloids prepared atother temperatures The high zeta potential of the goldnanocolloid prepared at 80 C created repulsive electro-static forces between the nanoparticles and protected themagainst agglomeration and sedimentation in the water Thegold nanocolloids were stable for more than three monthswithout noticeable aggregation

4 CONCLUSIONS

The effect of the liquid temperature on the dispersion sta-bility of gold nanocolloids produced via electrical explo-sion of wire in water was studied The dispersion stabilitywas found to depend much on the synthetic temperatureThe gold nanocolloid is more stable at a high synthetictemperature The results of the study show that withoutsurfactants the gold nanocolloids prepared at 80 C canbe stable up to more than three months This stability canbe attributed to the highly negative charge of the goldnanoparticles It is believe that this method is the mostsimple effective and green way of preparing stable goldnanocolloids

References and Notes

1 S Chah M R Hammond and R N Zare Chem Biol 12 323(2005)

2 S Aryal S Pilla and S Gong J Nanosci Nanotechnol 9 5701(2009)

3 P K Jain K S Lee I H El-Sayed and M A El-Sayed J PhysChem B 110 7238 (2006)

4 D P OrsquoNeal L R Hirsch N J Halas J D Payne and J L WestCancer Lett 209 171 (2004)

5 M C Daniel and D Astruc Chem Rev 104 293 (2004)6 Y A Kotov J Nanopart Res 5 539 (2003)7 Y S Kwon Y H Jung N A Yavorovsky A P Illyn and J S

Kim Scripta Mater 44 2247 (2001)8 W Jiang and K Yatsui IEEE Trans Plasma Sci 26 1498 (1998)9 R Sarathi T K Sindhu and S R Chakravarthy Mater Lett

61 1823 (2007)10 Y Kinemuchi K Murai C Sangurai C H Cho H Suematsu

W Jiang and K Yatsui J Am Ceram Soc 86 420 (2003)11 L H Bac Y S Kwon J S Kim Y I Lee D W Lee and J C

Kim Mater Res Bull 45 352 (2010)12 J P Sylvestre S Poulin A V Kabashin E Sacher M Meunier

and J H T Luong J Phys Chem B 108 16864 (2004)13 F Mafuneacute J Kohno Y Takeda T Kondow and H Sawabe J Phys

Chem B 105 5114 (2001)14 D Philip Spectrochim Acta Part A 71 80 (2008)15 A Mishra P Tripathy S Ram and H J Fecht Nanosci Nanotech-

nol 9 4342 (2009)16 A Franceschetti S J Pennycook and S T Pantelides Chem Phys

Lett 374 471 (2003)17 S D Puckett J A Heuser J D Keith W U Spendel and G E

Pacey Talanta 66 1242 (2005)18 J K Lung J C Huang D C Tien C Y Liao K H Tseng T T

Tsung W S Kao T H Tsai C S Jwo H M Lin and L StobinskiJ Alloys Compd 434 655 (2007)

Received 27 August 2010 Accepted 28 January 2011

6432 J Nanosci Nanotechnol 11 6429ndash6432 2011