- Email: [email protected]
Discovery of ionic silver in silver nanoparticle suspension fabricated by arc discharge method
Journal of Alloys and Compounds 463 (2008) 408–411
Discovery of ionic silver in silver nanoparticle suspension fabricated by arc discharge method Der-Chi Tien a,∗ , Kuo-Hsiung Tseng b , Chih-Yu Liao b , Jen-Chuen Huang b , Tsing-Tshih Tsung a a Graduate Institute of Mechanical and Electrical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan, R.O.C. b Department of Electrical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan, R.O.C.
Received 25 April 2007; received in revised form 3 September 2007; accepted 9 September 2007 Available online 18 September 2007
Abstract As a result of mankind’s over-reliance on antibiotics, germs are becoming more drug-resistant every year. The gradual but inexorable decline in the efficacy of traditional antibiotics is forcing scientists and doctors to search for new weapons in the fight against germs. Metallic silver nanoparticle (Ag0 ) and ionic silver (Ag+ ) are the future of the post-antibiotic era, with the latter playing perhaps the central role in this fight. Using the arc discharge method (ADM), our research has allowed us to fabricate silver nanoparticle suspension (SNPS) in deionized water with no added surfactants. Most related research in this field is confined to explore the composition of nanoparticle, ignoring ions. However, we aim to identify and measure the proportion of ionic silver in ADM-SNPS, using conductivity meters, centrifuges, titrator, and atomic absorption spectrophotometer (AA). The results of our experiments show that SNPS fabricated by means of ADM with no added surfactants contains metallic silver nanoparticle and ionic silver. The fabrication consumes silver rods at a rate of 100 mg/min, yielding metallic silver nanoparticle and ionic silver with concentrations of approximately 11 ppm and 19 ppm, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: Metallic; Nanofabrications; Nanostructured materials; Precipitation
1. Introduction Since the days of the Egyptian and Roman empires, silver has been used to preserve drinking water from germs. In the 18th century, immigrants to America put silver coins in milk to preserve it; in 1884, Cred´e proposed the use of drops of silver nitrate eye solution (1% silver nitrate) to prevent ophthalmia neonatorum in newborns [1]; during World War I, silver foil was used to protect wounds from infection; a method that is still used today; and in the 1970s, the National Aeronautics and Space Administration (NASA) used silver containers to preserve the purity of drinking water on spacecraft. These varied uses illustrate the antibiotic and bacteriostatic properties of silver.
∗
Corresponding author. Tel.: +886 2 2771 2171x2173/968 612 760/ 926 645 301; fax: +886 2 2776 4017. E-mail address: [email protected] (D.-C. Tien). 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.09.048
With the discovery of antibiotics at the beginning of the 20th century, silver became less widely used for medicinal purposes. However, due to over-reliance on antibiotics over the last century, some bacteria – such as MRSA (methicillin-resistant Staphylococcus aureus) [2] and VRSA (vancomycin-resistant Staphylococcus aureus) [3] – have become resistant to antibiotics. The growing ineffectiveness of traditional antibiotics has renewed interest in the antibiotic properties of silver. By raising the surface-to-volume ratio [4] of metallic silver nanoparticle, it can alter their physical and chemical properties and increase their efficacy in killing bacteria. It seems clear that metallic silver nanoparticle [5] will play an increasingly important role in the fight against germs. Recognizing the potential health benefits of silver nanoparticle suspension (SNPS), our lab has created a new method for synthesizing SNPS that is fast, simple, and easily adaptable to mass production: the arc discharge method (ADM) [6,7]. Experimental data also show that ADM-SNPS contains ionic silver components, which increase its germ-killing ability [8]. It is
D.-C. Tien et al. / Journal of Alloys and Compounds 463 (2008) 408–411
409
Table 1 Key parameters for silver nanoparticle suspension production Parameter
Value
Initial voltage (V) Peak current (A) On-pulse duration (s) Off-pulse duration (s) Temperature of deionized water (◦ C) Fabrication pressure (atm) Volume of deionized water (mL) Fabrication time (s)
135 6.4 50 50 25 1 500 60
safe to assume that ionic silver will become a major weapon against germs in the post-antibiotic era [9]. 2. Experimental setup
Fig. 1. Diameter of silver nanoparticle suspension.
2.1. SNPS preparation
20,000 × g. Using Formula 2, Stokes’ law, we can calculate the minimum time required for the centrifuge to separate the ions—100 min. Under these conditions, we can ensure that at least 96% of the metallic silver nanoparticle will be separated from the ionic silver.
Silver wires (Gredmann, 99.99%, 1 mm in diameter) were submerged in deionized water and used as electrodes. The SNPS preparation process proposed by ADM is based on parameters including initial voltage, peak current, on- and off-pulse duration, pressure, volume of deionized water, and fabrication time, as shown in Table 1.
RCF = 1.118 × 10−5 rN 2
where RCF is the relative centrifugal force (cm/s2 ); r the rotational radius (cm); and N is the rotating speed (revolutions per minute, rpm).
2.2. Experimental apparatus The main apparatuses used for identifying metallic silver nanoparticle and ionic silver were (a) a conductivity meter (JENCO 6307), to measure the number of ions in the solution and quickly perform qualitative analysis; (b) a particle sizer (Malvern Instruments ZS-90), to analyze the distribution of metallic silver nanoparticle in suspension, enabling us to calculate the velocity and time required to achieve the optimal conditions for the centrifuge; (c) a centrifuge (Hettich, Mikro 22R), to separate the SNPS into particles and ions—in the centrifuge, the particles would precipitate and the ions would dissolve in the water, resulting in a straightforward separation process; (d) a titrator (METTLER TOLEDO-DL50), to estimate the concentration of the ionic silver—using NaCl of a predetermined molar concentration that reacts with the ionic silver to form a precipitate, we can calculate the concentration of ionic silver in the solution before it is measured; and (e) an atomic absorption spectrophotometer (Shimadzu AA-680), to measure the concentration of ionic silver below the threshold of 6 ppm in order to check the accuracy of the estimate made with the titrator.
2.3. Experimental setup Applying a conductivity meter to the SNPS produced with ADM, we discovered that its conductivity (20.1 S/cm) was greater than that of deionized water (0.5 S/cm), suggesting that the SNPS contained ions. However, the conductivity test we carried out did not allow us to distinguish between the different types of ions. Using a centrifuge, we were able to separate the ions from the particles and to perform individual qualitative and quantitative analyses in an attempt to explore the nature of the ions. The centrifuge separates the ions from the particles, which causes the particles to precipitate but has no effect on the ions. The disadvantage of this method is that if the particles in the suspension are too small (less than a few nanometers) for sedimentation to occur, it is impossible to complete the separation process in a short period of time. To overcome this problem, we first measured the diameter of the SNPS particles; the particles’ sizes and distribution are shown in Fig. 1. In this diagram we can also see that in order to remove at least 96% of the metallic silver nanoparticle, we must first separate at least 10 nm of silver particles in the centrifuge. Using Formula 1, we can infer that, using a centrifuge with a radius of 7.5 cm running at 18,000 rpm, we can achieve a relative centrifugal force (RCF) of
(1)
Vs =
2rp2 (ρp − ρf ) × RCF
(2)
9η
where Vs is the particles’ settling velocity (cm/s); rp the Stokes radius of the particles (cm); ρp the density of the particles (g/cm3 ); ρf the density of the deionized water (g/cm3 ); and η is the viscosity of the deionized water (dyn s/cm2 ). Identification of ionic silver is done using a process illustrated in Fig. 2. First, ADM is used to fabricate SNPS from deionized water and a silver rod. A centrifuge running at 18,000 rpm for 100 min is then used to extract the ionic silver (which is contained in the supernatant—Ag+ ) and the metallic silver nanoparticle (which are contained in the sediment—Ag0 ). Quantitative analysis of the ionic silver can be carried out directly on the supernatant (Ag+ ). However, quantitative analysis of the metallic silver nanoparticle requires the addition of an appropriate amount of nitric acid (65%) so that the sediment (Ag0 ) will be fully dissolved; the mixture is then diluted with deionized water in order to get it back up to the original volume.
3. Results and discussion Our experiment used a conductivity meter, centrifuge, titrator, and atomic absorption spectrophotometer (AA) to identify SNPS. As shown in Table 2, our results indicate that the conductivity of SNPS (20.1 S/cm) and the conductivity of the supernatant (Ag+ ) (19.0 S/cm) are very similar. This suggests that SNPS contains ions and that the conductivity of SNPS is Table 2 Experimental data Sample
Conductivity (S/cm)
Titrator (ppm)
AA (ppm)
Deionized water Silver nanoparticle suspension Supernatant (Ag+ ) Sediment (Ag0 ) dissolved by HNO3
0.5 20.1 19.0 n/aa
0 19.9 18.6 11.2
0 26.4 19.2 11.4
a
The use of HNO3 voids the conductivity measurement.
410
D.-C. Tien et al. / Journal of Alloys and Compounds 463 (2008) 408–411
Fig. 3. Plasma and electrical discharge.
Fig. 2. Experimental procedure.
due to these ions. It also suggests that some of these ions change into atoms in the centrifuge, reducing the conductivity of the supernatant (Ag+ ). We measured the conductivity of the SNPS to confirm that it contained ions; then, using the titrator and an AA, it’s found that the concentration of the ionic silver in the SNPS was 19.9 ppm and 26.4 ppm, respectively. This proves that the ions in SNPS are ionic silver. The measurement taken with the AA is greater than the measurement taken with the titrator because the AA is sensitive to both the ionic silver and the metallic silver nanoparticle, whereas the titrator is sensitive solely to the ionic silver. Because ionic silver dissolve only in the supernatant, therefore can determine silver ions concentration of SNPS through the use of titration and AA. These gave us measurements of 18.6 ppm and 19.2 ppm, respectively. The measurement taken with the AA was slightly greater than that taken with the titrator because the supernatant (Ag+ ) contained less than 10 nm of metallic silver nanoparticle. After the sediment (Ag0 ) dissolved fully in the nitric acid, the titrator and the AA gave measurements of 11.2 ppm and 11.4 ppm, respectively. This suggests that the metallic silver nanoparticle suspended in the SNPS had a concentration of approximately 11 ppm. In the SNPS production by ADM, ionic silver is produced as a by-product of generating the metallic silver nanoparticle. During the spark discharge occurs as represented in Fig. 3, the following four individual effects of the system arise simultaneously (1) a
strong electric field, (2) a high-plasma temperature, (3) active silver atoms given off from the silver rod and (4) hydrogen and oxygen atoms given off from the water molecules. When these active atoms react, we can see that a silver-ion-like compound will form, which will dissolve in the deionized water. Furthermore, during the spark discharge bombardment, we can presume that atomic oxygen adheres to the surface of the charged silver nanoparticles, due to hydrogen bond, marked here by dashed line (- - -), and water molecules have been bonded with the oxygen atoms on the surface of silver nanoparticle to form a steady colloid. 4. Conclusion Metallic silver nanoparticle offer hope for the fight against germs, and they will likely bring an end to the era of antibiotics. This research assesses the use of arc discharge method (ADM) to produce SNPS, and the identification of ADM products: ionic silver and metallic silver nanoparticle. The research employed centrifugal force, along with measuring instruments such as a conductivity meter, a titrator, and an AA for the identification purpose. Our findings permit us to draw the following two conclusions: 1. This is the first discovery that ADM-SNPS has been identified to contain ionic silver as by-product of this nanoparticle manufacturing process. 2. With a silver rod consumption rate of 100 mg/min, concentrations of approximately 19 ppm and 11 ppm which are associated with ionic silver and metallic silver nanoparticle contained in ADM-SNPS, respectively, have been observed. Acknowledgments The authors thank Prof. Teh-Hua Tsai (Institute of Chemical Engineering, NTUT) for the particle size analysis and Prof. S.P. Rwei (Institute of Organic and Polymeric Materials, NTUT) for AA measurement. We also thank master student Shang Chin
D.-C. Tien et al. / Journal of Alloys and Compounds 463 (2008) 408–411
(Graduate Institute of Mechanical and Electrical Engineering) for technical assistance and stimulating discussions. References [1] [2] [3] [4]
J. Rungby, Exp. Eye Res. 42 (1986) 93–94. S.R. Norrby, C.E. Nord, R. Finch, Lancet Infect. Dis. 5 (2005) 115–119. F.C. Tenover, Clin. Microbiol. Newslett. 27 (2005) 35–40. N. Ichinose, Y. Ozaki, S. Kashu, Superfine Particle Technology, Springer Verlag, New York, 1992.
411
[5] Y. Li, P. Leung, L. Yao, Q.W. Song, E. Newton, J. Hosp. Infect. 62 (2006) 58–63. [6] 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, L. Stobinski, J. Alloys Compd. 434/435 (2007) 655–658. [7] C.H. Lo, T.T. Tsung, H.M. Lin, J. Alloys Compd. 434/435 (2007) 659–662. [8] D.C. Tien, C.Y. Liao, Y.C. Chen, H. Beem, K.H. Tseng, T.T. Tsung, L. Stobinski, Proceedings of the International Symposium on Biomedical Engineering, Taiwan, 2006. [9] Q.L. Feng, J. Wu, G.Q. Chen, F.Z. Cui, T.N. Kim, J.O. Kim, J. Biomed. Mater. Res. 52 (2000) 662–668.
Discovery of ionic silver in silver nanoparticle suspension fabricated by arc discharge method Der-Chi Tien a,∗ , Kuo-Hsiung Tseng b , Chih-Yu Liao b , Jen-Chuen Huang b , Tsing-Tshih Tsung a a Graduate Institute of Mechanical and Electrical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan, R.O.C. b Department of Electrical Engineering, National Taipei University of Technology, Taipei 10608, Taiwan, R.O.C.
Received 25 April 2007; received in revised form 3 September 2007; accepted 9 September 2007 Available online 18 September 2007
Abstract As a result of mankind’s over-reliance on antibiotics, germs are becoming more drug-resistant every year. The gradual but inexorable decline in the efficacy of traditional antibiotics is forcing scientists and doctors to search for new weapons in the fight against germs. Metallic silver nanoparticle (Ag0 ) and ionic silver (Ag+ ) are the future of the post-antibiotic era, with the latter playing perhaps the central role in this fight. Using the arc discharge method (ADM), our research has allowed us to fabricate silver nanoparticle suspension (SNPS) in deionized water with no added surfactants. Most related research in this field is confined to explore the composition of nanoparticle, ignoring ions. However, we aim to identify and measure the proportion of ionic silver in ADM-SNPS, using conductivity meters, centrifuges, titrator, and atomic absorption spectrophotometer (AA). The results of our experiments show that SNPS fabricated by means of ADM with no added surfactants contains metallic silver nanoparticle and ionic silver. The fabrication consumes silver rods at a rate of 100 mg/min, yielding metallic silver nanoparticle and ionic silver with concentrations of approximately 11 ppm and 19 ppm, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: Metallic; Nanofabrications; Nanostructured materials; Precipitation
1. Introduction Since the days of the Egyptian and Roman empires, silver has been used to preserve drinking water from germs. In the 18th century, immigrants to America put silver coins in milk to preserve it; in 1884, Cred´e proposed the use of drops of silver nitrate eye solution (1% silver nitrate) to prevent ophthalmia neonatorum in newborns [1]; during World War I, silver foil was used to protect wounds from infection; a method that is still used today; and in the 1970s, the National Aeronautics and Space Administration (NASA) used silver containers to preserve the purity of drinking water on spacecraft. These varied uses illustrate the antibiotic and bacteriostatic properties of silver.
∗
Corresponding author. Tel.: +886 2 2771 2171x2173/968 612 760/ 926 645 301; fax: +886 2 2776 4017. E-mail address: [email protected] (D.-C. Tien). 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.09.048
With the discovery of antibiotics at the beginning of the 20th century, silver became less widely used for medicinal purposes. However, due to over-reliance on antibiotics over the last century, some bacteria – such as MRSA (methicillin-resistant Staphylococcus aureus) [2] and VRSA (vancomycin-resistant Staphylococcus aureus) [3] – have become resistant to antibiotics. The growing ineffectiveness of traditional antibiotics has renewed interest in the antibiotic properties of silver. By raising the surface-to-volume ratio [4] of metallic silver nanoparticle, it can alter their physical and chemical properties and increase their efficacy in killing bacteria. It seems clear that metallic silver nanoparticle [5] will play an increasingly important role in the fight against germs. Recognizing the potential health benefits of silver nanoparticle suspension (SNPS), our lab has created a new method for synthesizing SNPS that is fast, simple, and easily adaptable to mass production: the arc discharge method (ADM) [6,7]. Experimental data also show that ADM-SNPS contains ionic silver components, which increase its germ-killing ability [8]. It is
D.-C. Tien et al. / Journal of Alloys and Compounds 463 (2008) 408–411
409
Table 1 Key parameters for silver nanoparticle suspension production Parameter
Value
Initial voltage (V) Peak current (A) On-pulse duration (s) Off-pulse duration (s) Temperature of deionized water (◦ C) Fabrication pressure (atm) Volume of deionized water (mL) Fabrication time (s)
135 6.4 50 50 25 1 500 60
safe to assume that ionic silver will become a major weapon against germs in the post-antibiotic era [9]. 2. Experimental setup
Fig. 1. Diameter of silver nanoparticle suspension.
2.1. SNPS preparation
20,000 × g. Using Formula 2, Stokes’ law, we can calculate the minimum time required for the centrifuge to separate the ions—100 min. Under these conditions, we can ensure that at least 96% of the metallic silver nanoparticle will be separated from the ionic silver.
Silver wires (Gredmann, 99.99%, 1 mm in diameter) were submerged in deionized water and used as electrodes. The SNPS preparation process proposed by ADM is based on parameters including initial voltage, peak current, on- and off-pulse duration, pressure, volume of deionized water, and fabrication time, as shown in Table 1.
RCF = 1.118 × 10−5 rN 2
where RCF is the relative centrifugal force (cm/s2 ); r the rotational radius (cm); and N is the rotating speed (revolutions per minute, rpm).
2.2. Experimental apparatus The main apparatuses used for identifying metallic silver nanoparticle and ionic silver were (a) a conductivity meter (JENCO 6307), to measure the number of ions in the solution and quickly perform qualitative analysis; (b) a particle sizer (Malvern Instruments ZS-90), to analyze the distribution of metallic silver nanoparticle in suspension, enabling us to calculate the velocity and time required to achieve the optimal conditions for the centrifuge; (c) a centrifuge (Hettich, Mikro 22R), to separate the SNPS into particles and ions—in the centrifuge, the particles would precipitate and the ions would dissolve in the water, resulting in a straightforward separation process; (d) a titrator (METTLER TOLEDO-DL50), to estimate the concentration of the ionic silver—using NaCl of a predetermined molar concentration that reacts with the ionic silver to form a precipitate, we can calculate the concentration of ionic silver in the solution before it is measured; and (e) an atomic absorption spectrophotometer (Shimadzu AA-680), to measure the concentration of ionic silver below the threshold of 6 ppm in order to check the accuracy of the estimate made with the titrator.
2.3. Experimental setup Applying a conductivity meter to the SNPS produced with ADM, we discovered that its conductivity (20.1 S/cm) was greater than that of deionized water (0.5 S/cm), suggesting that the SNPS contained ions. However, the conductivity test we carried out did not allow us to distinguish between the different types of ions. Using a centrifuge, we were able to separate the ions from the particles and to perform individual qualitative and quantitative analyses in an attempt to explore the nature of the ions. The centrifuge separates the ions from the particles, which causes the particles to precipitate but has no effect on the ions. The disadvantage of this method is that if the particles in the suspension are too small (less than a few nanometers) for sedimentation to occur, it is impossible to complete the separation process in a short period of time. To overcome this problem, we first measured the diameter of the SNPS particles; the particles’ sizes and distribution are shown in Fig. 1. In this diagram we can also see that in order to remove at least 96% of the metallic silver nanoparticle, we must first separate at least 10 nm of silver particles in the centrifuge. Using Formula 1, we can infer that, using a centrifuge with a radius of 7.5 cm running at 18,000 rpm, we can achieve a relative centrifugal force (RCF) of
(1)
Vs =
2rp2 (ρp − ρf ) × RCF
(2)
9η
where Vs is the particles’ settling velocity (cm/s); rp the Stokes radius of the particles (cm); ρp the density of the particles (g/cm3 ); ρf the density of the deionized water (g/cm3 ); and η is the viscosity of the deionized water (dyn s/cm2 ). Identification of ionic silver is done using a process illustrated in Fig. 2. First, ADM is used to fabricate SNPS from deionized water and a silver rod. A centrifuge running at 18,000 rpm for 100 min is then used to extract the ionic silver (which is contained in the supernatant—Ag+ ) and the metallic silver nanoparticle (which are contained in the sediment—Ag0 ). Quantitative analysis of the ionic silver can be carried out directly on the supernatant (Ag+ ). However, quantitative analysis of the metallic silver nanoparticle requires the addition of an appropriate amount of nitric acid (65%) so that the sediment (Ag0 ) will be fully dissolved; the mixture is then diluted with deionized water in order to get it back up to the original volume.
3. Results and discussion Our experiment used a conductivity meter, centrifuge, titrator, and atomic absorption spectrophotometer (AA) to identify SNPS. As shown in Table 2, our results indicate that the conductivity of SNPS (20.1 S/cm) and the conductivity of the supernatant (Ag+ ) (19.0 S/cm) are very similar. This suggests that SNPS contains ions and that the conductivity of SNPS is Table 2 Experimental data Sample
Conductivity (S/cm)
Titrator (ppm)
AA (ppm)
Deionized water Silver nanoparticle suspension Supernatant (Ag+ ) Sediment (Ag0 ) dissolved by HNO3
0.5 20.1 19.0 n/aa
0 19.9 18.6 11.2
0 26.4 19.2 11.4
a
The use of HNO3 voids the conductivity measurement.
410
D.-C. Tien et al. / Journal of Alloys and Compounds 463 (2008) 408–411
Fig. 3. Plasma and electrical discharge.
Fig. 2. Experimental procedure.
due to these ions. It also suggests that some of these ions change into atoms in the centrifuge, reducing the conductivity of the supernatant (Ag+ ). We measured the conductivity of the SNPS to confirm that it contained ions; then, using the titrator and an AA, it’s found that the concentration of the ionic silver in the SNPS was 19.9 ppm and 26.4 ppm, respectively. This proves that the ions in SNPS are ionic silver. The measurement taken with the AA is greater than the measurement taken with the titrator because the AA is sensitive to both the ionic silver and the metallic silver nanoparticle, whereas the titrator is sensitive solely to the ionic silver. Because ionic silver dissolve only in the supernatant, therefore can determine silver ions concentration of SNPS through the use of titration and AA. These gave us measurements of 18.6 ppm and 19.2 ppm, respectively. The measurement taken with the AA was slightly greater than that taken with the titrator because the supernatant (Ag+ ) contained less than 10 nm of metallic silver nanoparticle. After the sediment (Ag0 ) dissolved fully in the nitric acid, the titrator and the AA gave measurements of 11.2 ppm and 11.4 ppm, respectively. This suggests that the metallic silver nanoparticle suspended in the SNPS had a concentration of approximately 11 ppm. In the SNPS production by ADM, ionic silver is produced as a by-product of generating the metallic silver nanoparticle. During the spark discharge occurs as represented in Fig. 3, the following four individual effects of the system arise simultaneously (1) a
strong electric field, (2) a high-plasma temperature, (3) active silver atoms given off from the silver rod and (4) hydrogen and oxygen atoms given off from the water molecules. When these active atoms react, we can see that a silver-ion-like compound will form, which will dissolve in the deionized water. Furthermore, during the spark discharge bombardment, we can presume that atomic oxygen adheres to the surface of the charged silver nanoparticles, due to hydrogen bond, marked here by dashed line (- - -), and water molecules have been bonded with the oxygen atoms on the surface of silver nanoparticle to form a steady colloid. 4. Conclusion Metallic silver nanoparticle offer hope for the fight against germs, and they will likely bring an end to the era of antibiotics. This research assesses the use of arc discharge method (ADM) to produce SNPS, and the identification of ADM products: ionic silver and metallic silver nanoparticle. The research employed centrifugal force, along with measuring instruments such as a conductivity meter, a titrator, and an AA for the identification purpose. Our findings permit us to draw the following two conclusions: 1. This is the first discovery that ADM-SNPS has been identified to contain ionic silver as by-product of this nanoparticle manufacturing process. 2. With a silver rod consumption rate of 100 mg/min, concentrations of approximately 19 ppm and 11 ppm which are associated with ionic silver and metallic silver nanoparticle contained in ADM-SNPS, respectively, have been observed. Acknowledgments The authors thank Prof. Teh-Hua Tsai (Institute of Chemical Engineering, NTUT) for the particle size analysis and Prof. S.P. Rwei (Institute of Organic and Polymeric Materials, NTUT) for AA measurement. We also thank master student Shang Chin
D.-C. Tien et al. / Journal of Alloys and Compounds 463 (2008) 408–411
(Graduate Institute of Mechanical and Electrical Engineering) for technical assistance and stimulating discussions. References [1] [2] [3] [4]
J. Rungby, Exp. Eye Res. 42 (1986) 93–94. S.R. Norrby, C.E. Nord, R. Finch, Lancet Infect. Dis. 5 (2005) 115–119. F.C. Tenover, Clin. Microbiol. Newslett. 27 (2005) 35–40. N. Ichinose, Y. Ozaki, S. Kashu, Superfine Particle Technology, Springer Verlag, New York, 1992.
411
[5] Y. Li, P. Leung, L. Yao, Q.W. Song, E. Newton, J. Hosp. Infect. 62 (2006) 58–63. [6] 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, L. Stobinski, J. Alloys Compd. 434/435 (2007) 655–658. [7] C.H. Lo, T.T. Tsung, H.M. Lin, J. Alloys Compd. 434/435 (2007) 659–662. [8] D.C. Tien, C.Y. Liao, Y.C. Chen, H. Beem, K.H. Tseng, T.T. Tsung, L. Stobinski, Proceedings of the International Symposium on Biomedical Engineering, Taiwan, 2006. [9] Q.L. Feng, J. Wu, G.Q. Chen, F.Z. Cui, T.N. Kim, J.O. Kim, J. Biomed. Mater. Res. 52 (2000) 662–668.