Poly(4-styrenesulfonic acid-co-maleic acid)를 이용한

Ag 나노입자 제조 및 안정화

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

화학공학의 이론과 응용 제8권 제1호 2002년

김기정, 신승일, 오성근

한양대학교 화학공학과

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

화학공학의 이론과 응용 제8권 제1호 2002년

화학공학의 이론과 응용 제8권 제1호 2002년

Preparation and Stabilization of Silver Nanoparticles protected

by Poly(4-styrenesulfonic acid-co-maleic acid)

Gi-Jeong Kim, Seung-Il Shin, Seong-Geun Oh

Department of Chemical Engineering and CUPS, Hanyang University

INTRODUCTION

The concern with metal nanoparticles has been growing for the last several years. The most considerable feature of metal nanoparticles is that their chemical and physical properties are quite different from those of bulk metals and metal nanoparticles. The unique properties of nano-sized materials make them really attractive for a number of technological applications, including photonic devices, microelectronic devices, catalysis, liquid and solid composites, non-linear optics and so on.

Preparation and characterization of nanoparticles is a very critical point for a fundamental understanding and application of practical use. Changes in the optical properties and chemical reactivity of metal nanoparticles have been correlated to size and surface effects.

Metal nanoparticles have been synthesized in the micrometre and sub-micrometre size ranges by the polyol process. The reaction for producing stable and monodisperse silver nanoparticles by polyol process involves the reduction of the soluble silver salts by ethylene glycol, nucleation of metallic silver, and growth of the individual nuclei in the presene of a suitable protective agent. The protective agent interact with the small particles, preventing their agglomeration and precipitation. A number of polymers can be used as protective agents(e.g. poly(viniylalcohol), poly(methylviniylether), sodium polyacrylate, poly(N-vinylpyrrolidone)(PVP)).

Silver nanoparticles are very sensitive to environmental factors(light, heat, pH, etc). Thus, it is important to select protective agent for advanced stability of silver nanoparticles.

In this study, we prepared positively charged silver nanoparticles by polyol process. The particle size distribution and UV-absorption of silver nanoparticles was investigated. The stability of silver colloid according to polymer species was estimated relatively.

화학공학의 이론과 응용 제8권 제1호 2002년

EXPERIMENTAL

Silver nitrate(AgNO3, KOJIMA Chemicals CO. LTD.,99.9%) was the starting material for silver colloid and ethylene glycol(C2H6O2, DUKSAN Chemicals CO. LTD., First grade) used as a solvent for AgNO3 and as a reducing agent. Polyvinylpyrrolidone(PVP, Aldrich, average Mw ca. 10000) and polystyrenesulfonic acid-co-maleic acid(PSSA-MA, Aldrich, 3:1 styrene/maleic acid mole ratio) used as a protective agent. The chemicals were used as received without further purification. Deionized water(electrical resistivity 18.2M□) from a Millipore(Milli-Q) system was used in all preparations.

Polymer-protected, monodispersed silver nanoparticles have been obtained through spontaneous nucleation by the polyol process as follow. PVP(1.5g) and AgNO3(50mg) were dissolved in ethylene glycol(75mL) at room temperature. Then the solution was heated up to 120℃ and the reaction was carried out for 1h at this temperature. After cooling, the silver colloids can be separated from the polyol after the addition of a large amount of acetone followed by centrifugation and can be eventually redispersed in ethanol. The same method applies to PSSA-MA as protective agent. But it is different with PVP that silver colloid was redispersed in water.

To compare stabilities which depend on polymer species, absorption spectra of the silver particles in solution were recorded at intervals of 5 minute with a variable radiation wavelenth between 300 and 800nm and sodium chlorides were used as destabilizing agent.

The morphology and size of particles were investigated by transmission electron microscopy(TEM, Jeol-model JEM-2000EXⅡ). A drop of dispersed samples was placed on the carbon coated TEM grid. Photomicrographs were obtained operating at 200kV  and 200,000 magnifications. The stability of silver colloid was measured by UV-visible spectroscope(Scinco CO. LTD. S-2150) equipped with a PMMA cuvette(Pathlength 10mm).

RESULTS AND DISCUSSION

Monodispersed and homogeneous silver colloid were synthesed by polyol process as shown in Fig. 1. The N and O atoms of polar group in PVP have a strong affinity for the silver ions and metallic silver. A polymer in solution, which most likely has a pseudo-random coil conformation, may take part in some form of complex with the metal silver atoms. Consequently, PVP prohibits silver particles aggregation and grain growth as a result of its steric effect.

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

화학공학의 이론과 응용 제8권 제1호 2002년

Otherwise, in the case of PSSA-MA as protective agent, sulfur atom in PSSA-MA interact with the silver particles. Sulfur atom is larger and more polarizable than the oxygen atom, And it can also stabilize a negative charge on an adjacent atom. The silver particle charged positively in aqueous solution. Thus, formation of coordinative bonding between PSSA-MA and silver ion is occured spontaneously and PSSA-MA effectively prevents agglomeration and precipitation of the silver particles.

Variations of absorption spectra of silver colloid provide important information on size-dependent chemical properties of the particles. The presence of Ag0 in solution is related to a absorbance peak whose maximum occurs at 400nm. The peak height is directly proportional to the quantity of Ag0 present in solution. Thus, we can estimate the stability of silver colloid by reduction rate of absorbance maximum peak. Fig. 2 and Fig. 3 show the variation of absorption spectra according to polymer species. The variation of the absorbance maximum peak as a function of time has been plotted as shown in Fig. 4. In the case of PVP, the slope was decreased rapidly. Otherwise in the case of PSSA-MA, it remained constant value as a function of time. From what has been discussed above, we can conclude that the silver colloid stabilized by PSSA-MA is more stable than PVP.

ACKNOWLEDGMENT

This researh was funded by Center for Ultramicrochemical Process Systems sponsored by KOSEF.

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