Aggregation state of silver nanoparticles dispersed in an aqueous solution greatly varies with storage and treatment conditions. In this study, silver nanoparticles synthesized in chitosan solution by a chemical reduction method were hydrothermally treated at different temperatures. The variation in the aggregation state of silver nanoparticles in the solution was observed by UV-Vis spectroscopy and field emission transmission electron microscopy. Results indicated that a phase transition occurred while silver nanoparticles were hydrothermally treated for 5 h at 100 and ; however, they aggregated and completely precipitated at . Mesoporous silver powder obtained by hydrothermal treatment at was characterized by using X-ray diffraction technique, BET analyzer, and scanning electron spectroscope. 1. Introduction Silver nanoparticles have become the most widely commercialized nanomaterials due to thier unique physicochemical and biological properties [1]. Silver nanoparticles can be synthesized and stabilized in the presence of polymers [2–7] in an aqueous solution or organic solvents. They can also be stabilized in the pores of porous materials where tiny spaces or channels act as spatial hindrance, which inhibits the growth of silver particles [8–11]. The size and shape of silver nanoparticles in porous materials depend on their pore diameters and are almost stable after synthesis, whereas that of silver nanoparticles in solutions is affected by various factors including storing conditions, the type and concentration of stabilizer, the concentration of silver nanoparticles, and synthetic routes. The properties, applicability and efficiency of final products are greatly related to the size, the shape, and the aggregation state of silver nanoparticles. Silver powder has been widely used in catalysis, electronics, chemical industry, and biomedical application [12]. Electronic industry consumes large amounts of silver powder that is usually used as conductive paste [13–16]. Several studies have indicated that mesoporous silver powders with higher porosity and larger surface area engender higher application efficiencies such as reducing firing temperature of conductive film [17], enhancing the resistance of heat exchanger material at ultralow temperature [18], or increasing catalytic activity of an oxidation reaction [19, 20]. Recently, due to the rapid development of electronic industry, it demands a huge amount of high quality silver powder. Thus, scientists have investigated and proposed different methods such as spray pyrolysis [21–23], sonochemical
References
[1]
October 2012, http://www.nanotechproject.org/inventories/consumer/analysis_draft/.
[2]
D. Long, G. Wu, and S. Chen, “Preparation of oligochitosan stabilized silver nanoparticles by gamma irradiation,” Radiation Physics and Chemistry, vol. 76, no. 7, pp. 1126–1131, 2007.
[3]
H. Wang, X. Qiao, J. Chen, and S. Ding, “Preparation of silver nanoparticles by chemical reduction method,” Colloids and Surfaces A, vol. 256, no. 2-3, pp. 111–115, 2005.
[4]
A. Zielińska, E. Skwarek, A. Zaleska, M. Gazda, and J. Hupka, “Preparation of silver nanoparticles with controlled particle size,” Procedia Chemistry, vol. 1, no. 2, pp. 1560–1566, 2009.
[5]
H. N. Chau, L. A. Bang, N. Q. Buu, T. T. N. Dung, H. T. Ha, and D. V. Quang, “Some results in manufacturing of nanosilver and investigation of its application for disinfection,” Advances in Natural Sciences, vol. 9, pp. 241–248, 2008.
[6]
Y.-K. Twu, Y.-W. Chen, and C.-M. Shih, “Preparation of silver nanoparticles using chitosan suspensions,” Powder Technology, vol. 185, no. 3, pp. 251–257, 2008.
[7]
H. Huang and X. Yang, “Synthesis of polysaccharide-stabilized gold and silver nanoparticles: a green method,” Carbohydrate Research, vol. 339, no. 15, pp. 2627–2631, 2004.
[8]
D. V. Quang, P. B. Sarawade, A. Hilonga et al., “Synthesis of silver nanoparticles within the pores of functionalized-free silica beads: the effect of pore size and porous structure,” Materials Letters, vol. 68, pp. 350–353, 2012.
[9]
D. V. Quang, P. B. Sarawade, A. Hilonga et al., “Preparation of amino functionalized silica micro beads by dry method for supporting silver nanoparticles with antibacterial properties,” Colloids and Surfaces A, vol. 389, no. 1–3, pp. 118–126, 2011.
[10]
D. V. Quang, J. E. Lee, J.-K. Kim, Y. N. Kim, G. N. Shao, and H. T. Kim, “A gentle method to graft thiol-functional groups onto silica gel for adsorption of silver ions and immobilization of silver nanoparticles,” Powder Technology, vol. 235, pp. 221–227, 2013.
[11]
D. V. Quang, P. B. Sarawade, A. Hilonga et al., “Preparation of silver nanoparticle containing silica micro beads and investigation of their antibacterial activity,” Applied Surface Science, vol. 257, no. 15, pp. 6963–6970, 2011.
[12]
X. Chen and H. J. Schluesener, “Nanosilver: a nanoproduct in medical application,” Toxicology Letters, vol. 176, no. 1, pp. 1–12, 2008.
[13]
P. K. Khanna and V. V. V. S. Subbarao, “Nanosized silver powder via reduction of silver nitrate by sodium formaldehydesulfoxylate in acidic pH medium,” Materials Letters, vol. 57, no. 15, pp. 2242–2245, 2003.
[14]
Z. Liu, X. Qi, and H. Wang, “Synthesis and characterization of spherical and mono-disperse micro-silver powder used for silicon solar cell electronic paste,” Advanced Powder Technology, vol. 23, no. 2, pp. 250–255, 2012.
[15]
J.-T. Tsai and S.-T. Lin, “Silver powder effectiveness and mechanism of silver paste on silicon solar cells,” Journal of Alloys and Compounds, vol. 548, no. 105, 109 pages, 2013.
[16]
G. Guo, W. Gan, F. Xiang et al., “Effect of dispersibility of silver powders in conductive paste on microstructure of screen-printed front contacts and electrical performance of crystalline silicon solar cells,” Journal of Materials Science: Materials in Electronics, vol. 22, no. 5, pp. 527–530, 2011.
[17]
J. C. Lin and C. Y. Wang, “Effect of surface properties of silver powder on the sintering of its thick-film conductor,” Materials Chemistry and Physics, vol. 45, no. 3, pp. 253–261, 1996.
[18]
W. Itoh, A. Sawada, A. Shinozaki, and Y. Inada, “New silver powders with large surface area as heat exchanger materials,” Cryogenics, vol. 31, no. 6, pp. 453–455, 1991.
[19]
J. K. Shon, S. S. Kong, J. M. Kim et al., “Facile synthesis of highly ordered mesoporous silver using cubic mesoporous silica template with controlled surface hydrophobicity,” Chemical Communications, no. 6, pp. 650–652, 2009.
[20]
J. K. Shon, J.-N. Park, S. H. Hwang et al., “Pretreatment effect on CO oxidation over highly ordered mesoporous silver catalyst,” Bulletin of the Korean Chemical Society, vol. 31, no. 2, pp. 415–418, 2010.
[21]
H. Lu, “Fabrication and characterization of porous silver powder prepared by spray drying and calcining technology,” Powder Technology, vol. 203, no. 2, pp. 176–179, 2010.
[22]
K. C. Pingali, D. A. Rockstraw, and S. Deng, “Silver nanoparticles from ultrasonic spray pyrolysis of aqueous silver nitrate,” Aerosol Science and Technology, vol. 39, no. 10, pp. 1010–1014, 2005.
[23]
X. Shi, S. Wang, X. Duan, and Q. Zhang, “Synthesis of nano Ag powder by template and spray pyrolysis technology,” Materials Chemistry and Physics, vol. 112, no. 3, pp. 1110–1113, 2008.
[24]
V. Sáez and T. J. Mason, “Sonoelectrochemical synthesis of nanoparticles,” Molecules, vol. 14, no. 10, pp. 4284–4299, 2009.
[25]
Z. Yingjie, Q. Yitai, Z. Manwei, C. Zuyao, L. Bin, and W. Changsui, “Preparation of nanocrystalline silver powders by γ-ray radiation combined with hydrothermal treatment,” Materials Letters, vol. 17, no. 5, pp. 314–318, 1993.
[26]
Y. Dai, T. Deng, S. Jia, L. Jin, and F. Lu, “Preparation and characterization of fine silver powder with colloidal emulsion aphrons,” Journal of Membrane Science, vol. 281, no. 1-2, pp. 685–691, 2006.
[27]
K. D. Kim, D. N. Han, and H. T. Kim, “Optimization of experimental conditions based on the Taguchi robust design for the formation of nano-sized silver particles by chemical reduction method,” Chemical Engineering Journal, vol. 104, no. 1–3, pp. 55–61, 2004.
[28]
H. H. Nersisyan, J. H. Lee, H. T. Son, C. W. Won, and D. Y. Maeng, “A new and effective chemical reduction method for preparation of nanosized silver powder and colloid dispersion,” Materials Research Bulletin, vol. 38, no. 6, pp. 949–956, 2003.
[29]
K. Byrappa and T. Adschiri, “Hydrothermal technology for nanotechnology,” Progress in Crystal Growth and Characterization of Materials, vol. 53, no. 2, pp. 117–166, 2007.
[30]
M. Yoshimura and K. Byrappa, “Hydrothermal processing of materials: past, present and future,” Journal of Materials Science, vol. 43, no. 7, pp. 2085–2103, 2008.
[31]
Z. Wang, J. Liu, X. Chen, J. Wan, and Y. Qian, “A simple hydrothermal route to large-scale synthesis of uniform silver nanowires,” Chemistry: A European Journal, vol. 11, no. 1, pp. 160–163, 2005.
[32]
J. Zou, Y. Xu, B. Hou, D. Wu, and Y. Sun, “Controlled growth of silver nanoparticles in a hydrothermal process,” China Particuology, vol. 5, no. 3, pp. 206–212, 2007.
[33]
G. Wei, C.-W. Nan, Y. Deng, and Y.-H. Lin, “Self-organized synthesis of silver chainlike and dendritic nanostructures via a solvothermal method,” Chemistry of Materials, vol. 15, no. 23, pp. 4436–4441, 2003.
[34]
M. J. Rosemary and T. Pradeep, “Solvothermal synthesis of silver nanoparticles from thiolates,” Journal of Colloid and Interface Science, vol. 268, no. 1, pp. 81–84, 2003.
[35]
X.-L. Tang, P. Jiang, G.-L. Ge, M. Tsuji, S.-S. Xie, and Y.-J. Guo, “Poly(N-vinyl-2-pyrrolidone) (PVP)-capped dendritic gold nanoparticles by a one-step hydrothermal route and their high SERS effect,” Langmuir, vol. 24, no. 5, pp. 1763–1768, 2008.
[36]
S. Wang and G. Shi, “Uniform silver/polypyrrole core-shell nanoparticles synthesized by hydrothermal reaction,” Materials Chemistry and Physics, vol. 102, no. 2-3, pp. 255–259, 2007.
[37]
L.-B. Luo, S.-H. Yu, H.-S. Qian, and T. Zhou, “Large-scale fabrication of flexible silver/cross-linked poly(vinyl alcohol) coaxial nanocables by a facile solution approach,” Journal of the American Chemical Society, vol. 127, no. 9, pp. 2822–2823, 2005.
[38]
Q. Zhang, N. Li, J. Goebl, Z. Lu, and Y. Yin, “A systematic study of the synthesis of silver nanoplates: is citrate a “magic” reagent?” Journal of the American Chemical Society, vol. 133, no. 46, pp. 18931–18939, 2011.
[39]
S. Lowell, J. E. Shields, M. A. Thomas, and M. Thommes, Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2004.
