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Preparation of Aqueous Gold Colloid by Vapor Deposition Method
JOURNAL OF COLLOID AND INTERFACE SCIENCE ARTICLE NO.
185, 285–286 (1997)
CS964569
NOTE Preparation of Aqueous Gold Colloid by Vapor Deposition Method Gold vapor and water vapor were co-condensed on a cooled surface and then the ice was melted to obtain highly pure aqueous gold colloid. After removing gold aggregate, we obtained a supernatant solution of gold which is transparent and purple in color. A surface plasmon resonance absorption peak appeared at about 550 nm. The gold colloid was stable for more than a year without any additives. q 1997 Academic Press Key Words: gold; fine particle; colloid; vapor deposition; surface plasmon absorption.
It is well known that the physical properties of nano-scale materials are quite different from that of bulk materials ( 1 – 3 ) . In the case of gold metal, its fine particles are expected to be highly efficient third nonlinear optics ( 4, 5 ) or a unique catalyst ( 6 ) . They can also be used for microanalysis of protein ( 7, 8 ) . Usually, they are prepared by vapor deposition ( 9 ) or the sol – gel method ( 10, 11 ) . In these methods, fine gold particles are obtained with a solid matrix in a thin film. Solution-type gold colloid was prepared by the reduction of aqueous chloroauric acid ( HAuCl4 ) by an aqueous solution of sodium citric acid ( Na3C6H5O7 ) ( 12 ) . It has been used for protein microanalysis and as the raw material of a gold-doped glass. However, impurities due to chloroauric acid and sodium citric acid remain in the resultant colloid. The presence of impurities decreases the sensitivity in protein analysis. Organic solvent also decreases the sensitivity. Since a highly pure gold colloid is desired for the protein analysis, water would be the most desirable medium. We report here an attempt to prepare an aqueous gold colloid by utilizing a vapor deposition process. Vapor deposition processes generally produce highly pure materials. A variety of metal colloid was prepared by a solvated metal atom dispersion ( SMAD ) method developed by Matsuo and Klabunde ( 13 ) . In contrast to the preparation of metal particles by reduction with hydrogen, the SMAD method does not need high temperature. Therefore, it is used to prepare nonaggregated metal colloid ( 13, 14 ) . Metal colloid is prepared in organic reagents such as toluene or tetrahydrofuran. It has, however, never been reported on the preparation of metal colloid dispersed in water by the SMAD method. In this study, we tried to use this technique to produce gold colloid in water without any other components. Figure 1 shows a schematic diagram of the apparatus. Two water cooled electrodes were set in a glass reactor. An alumina-coated tungsten crucible was connected with the two electrodes. Gold metal powder, 0.3 g, was put into the crucible. Gold powder was vaporized by heating the crucible under vacuum. At the same time, water vapor was introduced into the reactor from a glass tube having many small holes. We used purified water with an electric resistance of more than 5 MV and the content of silicates was less than 0.5 ppm. The total weight of water introduced was 10 g. Gold vapor condensed together with water vapor on the reactor wall that was cooled with liquid nitrogen. After the cocondensation, the reactor was slowly warmed to room temperature. The
ice melted and dropped to the reactor bottom together with gold colloid. The absorption spectrum of the solution in the ultraviolet and visible range was recorded on a Hitachi U-3500 photometer. During the co-condensation, it was observed by the naked eye that the condensed solid was purple in color. Purple color is characteristic of gold fine particles. Thus at least a part of the gold seemed to be incorporated into the ice matrix as fine particles. When the ice melted away, fine gold particles were dispersed in the water. Since these particles can move in water rather freely, some fine particles would contact with others and form aggregates. However, a small portion of gold was left in the supernatant solution which was transparent and purple in color. The gold concentration in this solution was estimated to be 2 1 10 03 mol / liter. This value is comparable to that obtained by the reduction of AuCl 04 ( 12 ) . The absorption spectrum of the solution in the ultraviolet and visible range is presented in Fig. 2 which shows a broad peak at about 550 nm. A peak in this range is generally observed for gold colloid prepared by the methods mentioned above and it is attributed to surface plasmon resonance absorption of fine gold particles ( 15 ) . Anion species such as Cl 0 and – COO 0 or surface active reagents, which make gold particles stable in water, are not added in the present colloid solution. Nevertheless, no aggregates were observed in the supernatant solution even after 1 year. There is some possibility that the surfaces of the fine gold particles are charged due to the presence of a tiny amount of impurity. The reason for the stability of the fine gold particles should be clarified in future study. In conclusion, gold colloid containing only gold and water could be prepared by the SMAD method. The resultant gold colloid was very stable for more than 1 year and no aggregates were formed in the solution in spite of the absence of anions and surface active reagents.
FIG. 1. Schematic diagram of the apparatus.
285
AID
JCIS 4569
/
6g19h$$761
12-18-96 02:41:17
0021-9797/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
coidas
286
NOTE
6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
Rentzepis, P. M., Shen, T. P., and Rogovin, D., J. Phys. Chem. 94, 1100 (1990). Haruta, M., Yamada, N., Kobayashi, T., and Iijima, S., J. Catal. 115, 301 (1989). Moeremans, M., Daneels, G., and De Mey, J., Anal. Biochem. 145, 315 (1985). Stoscheck, C. M., Anal. Biochem. 160, 301 (1987). Tan, B. J., Sherwood, P. M. A., and Klabunde, K. J., Langmuir 6, 105 (1990). Matsuoka, J., Mizutani, R., Nasu, H., and Kamiya, K., J. Ceram. Soc. Jpn. 100, 599 (1992). Kozuka, H., and Sakka, S., Chem. Mater. 5, 222 (1993). Chow, M. K., and Fukoski, C. F., J. Colloid Interface Sci. 165, 97 (1994). Matsuo, K., and Klabunde, K. J., J. Catal. 73, 216 (1982). Klabunde, K. J., Ralston, D. H., Zoellner, R. W., Hattori, H., and Tanaka, Y., J. Catal. 55, 213 (1978). Creighton, J. A., and Eadon, D. G., J. Chem. Soc., Faraday Trans. 87, 3881 (1991).
FIG. 2. Absorption spectrum of the resultant Au colloid.
REFERENCES 1. Brus, L., J. Phys. Chem. 90, 2555 (1986). 2. Ekimov, A. I., Efros, Al. L., and Onushchenko, A. A., Solid State Commun. 88, 947 (1993). 3. Kimura, K., Zeit. Phys. D 11, 327 (1989). 4. Hache, F., Ricard, D., Flytzanis, C., and Kreibig, K., Appl. Phys. A 47, 347 (1988). 5. Dutton, T., Van Wontergheim, B., Saltiel, S., Chestnoy, N. V.,
AID
JCIS 4569
/
6g19h$$761
12-18-96 02:41:17
YOSHIO KOBAYASHI AKIRA TOMITA 1 Institute for Chemical Reaction Science Tohoku University Katahira, Aoba-ku Sendai 980-77, Japan Received April 29, 1996; accepted August 22, 1996
1
To whom correspondence should be addressed.
coidas
185, 285–286 (1997)
CS964569
NOTE Preparation of Aqueous Gold Colloid by Vapor Deposition Method Gold vapor and water vapor were co-condensed on a cooled surface and then the ice was melted to obtain highly pure aqueous gold colloid. After removing gold aggregate, we obtained a supernatant solution of gold which is transparent and purple in color. A surface plasmon resonance absorption peak appeared at about 550 nm. The gold colloid was stable for more than a year without any additives. q 1997 Academic Press Key Words: gold; fine particle; colloid; vapor deposition; surface plasmon absorption.
It is well known that the physical properties of nano-scale materials are quite different from that of bulk materials ( 1 – 3 ) . In the case of gold metal, its fine particles are expected to be highly efficient third nonlinear optics ( 4, 5 ) or a unique catalyst ( 6 ) . They can also be used for microanalysis of protein ( 7, 8 ) . Usually, they are prepared by vapor deposition ( 9 ) or the sol – gel method ( 10, 11 ) . In these methods, fine gold particles are obtained with a solid matrix in a thin film. Solution-type gold colloid was prepared by the reduction of aqueous chloroauric acid ( HAuCl4 ) by an aqueous solution of sodium citric acid ( Na3C6H5O7 ) ( 12 ) . It has been used for protein microanalysis and as the raw material of a gold-doped glass. However, impurities due to chloroauric acid and sodium citric acid remain in the resultant colloid. The presence of impurities decreases the sensitivity in protein analysis. Organic solvent also decreases the sensitivity. Since a highly pure gold colloid is desired for the protein analysis, water would be the most desirable medium. We report here an attempt to prepare an aqueous gold colloid by utilizing a vapor deposition process. Vapor deposition processes generally produce highly pure materials. A variety of metal colloid was prepared by a solvated metal atom dispersion ( SMAD ) method developed by Matsuo and Klabunde ( 13 ) . In contrast to the preparation of metal particles by reduction with hydrogen, the SMAD method does not need high temperature. Therefore, it is used to prepare nonaggregated metal colloid ( 13, 14 ) . Metal colloid is prepared in organic reagents such as toluene or tetrahydrofuran. It has, however, never been reported on the preparation of metal colloid dispersed in water by the SMAD method. In this study, we tried to use this technique to produce gold colloid in water without any other components. Figure 1 shows a schematic diagram of the apparatus. Two water cooled electrodes were set in a glass reactor. An alumina-coated tungsten crucible was connected with the two electrodes. Gold metal powder, 0.3 g, was put into the crucible. Gold powder was vaporized by heating the crucible under vacuum. At the same time, water vapor was introduced into the reactor from a glass tube having many small holes. We used purified water with an electric resistance of more than 5 MV and the content of silicates was less than 0.5 ppm. The total weight of water introduced was 10 g. Gold vapor condensed together with water vapor on the reactor wall that was cooled with liquid nitrogen. After the cocondensation, the reactor was slowly warmed to room temperature. The
ice melted and dropped to the reactor bottom together with gold colloid. The absorption spectrum of the solution in the ultraviolet and visible range was recorded on a Hitachi U-3500 photometer. During the co-condensation, it was observed by the naked eye that the condensed solid was purple in color. Purple color is characteristic of gold fine particles. Thus at least a part of the gold seemed to be incorporated into the ice matrix as fine particles. When the ice melted away, fine gold particles were dispersed in the water. Since these particles can move in water rather freely, some fine particles would contact with others and form aggregates. However, a small portion of gold was left in the supernatant solution which was transparent and purple in color. The gold concentration in this solution was estimated to be 2 1 10 03 mol / liter. This value is comparable to that obtained by the reduction of AuCl 04 ( 12 ) . The absorption spectrum of the solution in the ultraviolet and visible range is presented in Fig. 2 which shows a broad peak at about 550 nm. A peak in this range is generally observed for gold colloid prepared by the methods mentioned above and it is attributed to surface plasmon resonance absorption of fine gold particles ( 15 ) . Anion species such as Cl 0 and – COO 0 or surface active reagents, which make gold particles stable in water, are not added in the present colloid solution. Nevertheless, no aggregates were observed in the supernatant solution even after 1 year. There is some possibility that the surfaces of the fine gold particles are charged due to the presence of a tiny amount of impurity. The reason for the stability of the fine gold particles should be clarified in future study. In conclusion, gold colloid containing only gold and water could be prepared by the SMAD method. The resultant gold colloid was very stable for more than 1 year and no aggregates were formed in the solution in spite of the absence of anions and surface active reagents.
FIG. 1. Schematic diagram of the apparatus.
285
AID
JCIS 4569
/
6g19h$$761
12-18-96 02:41:17
0021-9797/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
coidas
286
NOTE
6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
Rentzepis, P. M., Shen, T. P., and Rogovin, D., J. Phys. Chem. 94, 1100 (1990). Haruta, M., Yamada, N., Kobayashi, T., and Iijima, S., J. Catal. 115, 301 (1989). Moeremans, M., Daneels, G., and De Mey, J., Anal. Biochem. 145, 315 (1985). Stoscheck, C. M., Anal. Biochem. 160, 301 (1987). Tan, B. J., Sherwood, P. M. A., and Klabunde, K. J., Langmuir 6, 105 (1990). Matsuoka, J., Mizutani, R., Nasu, H., and Kamiya, K., J. Ceram. Soc. Jpn. 100, 599 (1992). Kozuka, H., and Sakka, S., Chem. Mater. 5, 222 (1993). Chow, M. K., and Fukoski, C. F., J. Colloid Interface Sci. 165, 97 (1994). Matsuo, K., and Klabunde, K. J., J. Catal. 73, 216 (1982). Klabunde, K. J., Ralston, D. H., Zoellner, R. W., Hattori, H., and Tanaka, Y., J. Catal. 55, 213 (1978). Creighton, J. A., and Eadon, D. G., J. Chem. Soc., Faraday Trans. 87, 3881 (1991).
FIG. 2. Absorption spectrum of the resultant Au colloid.
REFERENCES 1. Brus, L., J. Phys. Chem. 90, 2555 (1986). 2. Ekimov, A. I., Efros, Al. L., and Onushchenko, A. A., Solid State Commun. 88, 947 (1993). 3. Kimura, K., Zeit. Phys. D 11, 327 (1989). 4. Hache, F., Ricard, D., Flytzanis, C., and Kreibig, K., Appl. Phys. A 47, 347 (1988). 5. Dutton, T., Van Wontergheim, B., Saltiel, S., Chestnoy, N. V.,
AID
JCIS 4569
/
6g19h$$761
12-18-96 02:41:17
YOSHIO KOBAYASHI AKIRA TOMITA 1 Institute for Chemical Reaction Science Tohoku University Katahira, Aoba-ku Sendai 980-77, Japan Received April 29, 1996; accepted August 22, 1996
1
To whom correspondence should be addressed.
coidas