계면활성제 및 환원제 첨가 조건이 Ag 나노입자의 합성에 미치는 영향

Abstract

최근 들어 나노입자에 대한 관심이 고조되면서 여러 가지 나노입자의 제조에 대한 연구가 활발히 진행되고 있다. 나노크기의 물질들은 마이크로 크기에서 나타나지 않는 고유의 광학적, 전기적, 자기적, 화학적, 기계적 특성을 가지고 있다. 이러한 성질들은 입자의 크기와 모양에 의해 영향을 받기 때문에 나노물질들은 형상제어가 매우 중요하다. 최근 전자, 정보통신의 발달과 더불어 각종 디바이스의 소형화, 복합화에 대한 요구가 증대되고, 그에 따른 분야에 나노기술을 접목하려는 연구가 시도되고 있다. Ag 입자는 우수한 열전도성, 항균 및 살균효과도 지니고 있어 마이크로 전자, 센서디바이스 및 촉매 등 응용분야가 매우 넓다. 나노 입자를 제조법으로는 광화학적 환원법, 화학환원법, 열 분해법등 많은 방법이 있다. 본 실험은 단순하면서 쉽게 제조할 수 있는 액상환원법 중 계면활성제 첨가에 의한 화학환원법을 사용하여 질산은과 계면활성제의 농도의 변화 그리고 환원제 첨가 조건에 따른 Ag 입자를 합성하고 특성을 연구하였다. 계면활성제로 PVP(plyvinylpyrrolidone K-30)과 SDS(sodium dodecyl sulfate)를 사용하여 질산은과의 충분한 혼합을 한 용액에 환원제를 서서히 첨가하여 나노크기의 Ag 입자를 합성하였다. 합성된 Ag 입자는 계면활성제와 환원제 첨가 농도에 따라 입자의 크기 및 형상에 크게 영향을 주었다. PVP와 질산은과의 몰비의 변화를 주어 Ag 입자를 합성한 경우, 몰비가 0.5와 1에서의 비교적 15-20 nm 의 크기를 갖는 구형의 입자가 이루어 졌으며 좁은 입도를 가지고 있었으나 몰비가 1.5에서는 80 nm 정도의 크기를 가진 응집된 입자와 대부분 육각형을 이루는 입자가 형성되는 것을 활 수 있었다. 반면에 SDS와 질산은의 몰비 변화에서는 PVP를 사용한 결과와는 다르게 몰비가 증가할수록 입자의 크기는 감소하여 10-20 nm 정도였으며, 입자의 형상도 일정한 구형을 이루며 높은 분산성을 나타내었다. 따라서 계면활성제로 PVP 보다는 SDS를 사용하였을 경우 입자의 크기 및 형상에 크게 작용함을 관찰할 수 있었다. 계면활성제와 질산은의 몰비가 일정한 용액에 환원제 첨가량을 각각 5, 10, 20 ml를 첨가하여 Ag 입자를 합성하였다. 환원제의 첨가량이 증가 할수록 입자의 크기는 PVP와 SDS를 사용한 경우 모두 입자의 크기는 물론 응집 역시 증가 하여 시간적인 콜로이드의 안정성도 감소하였다. 5 ml의 첨가하였을 경우 20 nm 의 크기를 가졌으나 첨가량이 20 ml 까지 증가하였을 경우 입자의 크기는 80 nm 이상까지 조대한 입자를 형성하였다. 또한 환원제 첨가속도를 각각 분당 5 ml에서 1 ml로 제어하여 Ag 입자를 제조하였는데, 환원제의 첨가 속도가 감소할수록 입자의 크기는 80 nm에서 10 nm 까지 감소하였으며 입자의 형상도 구형을 이루고 있었다. UV-visible spectrophotometer를 사용하여 합성된 콜로이드의 핵과 입자의 형성를 관찰한 결과 수용액상에서 합성된 Ag 나노입자는 400 nm 부근에서 maximum peak를 가지는 것을 확인할 수 있었다. 이러한 Ag 나노입자는 고농도로 하여 전자재료 분야에 적용할 수 있고, 특히 이 방법은 단순하고 실온에서 진행되기 때문에 다른 금속물질에 적용할 경우 쉽고 저가로 나노입자를 제조할 수 있어 많은 응용이 기대된다.|Recently, research on nanosized particles has received considerable attention because of the unique properties that they exhibit as a result of the reduced filler dimension and quantum size effects which may arise and influence all physical properties of such materials. Nanoscale materials are of great interest due to their unique optical, electrical and magnetic properties. These properties are strongly dependent on the size and shape of the particles and therefore it is very important to be able to finely control the morphology of the nanomaterials. The prospect of exploiting size-dependent properties opens in turn the way toward the development of new functional materials and advanced devices. Nanoparticles of Ag and other noble metals are attracting much attention because of their potential applications in microelctronic, sensing devices, and catalysis. A number of methods have been developed for preparing metal colloids, such as radiation chemical reduction, chemical reduction with or without stabilizing polymers, chemical or photoreduction in reverse micelles, and thermal decomposition in organic solvents. We present here a simple and convenient method for the preparing colloidal silver nanoparticles using surfactant as a reducing agent. We also describe here in the effect of concentration of silver salt and surfactant on the colloidal silver formation. This study has focused on the preparation of silver nanoparticles by chemical reduction method and the effect of surfactants such as polyvinylpyrrolidone K-30 (noted by PVP) and sodium dodecyl sulfate (noted by SDS) on the morphology of nanosized silver particles. The size and shape of silver particles were strongly dependent on the concentration of surfactant and reduction agent. The silver colloids were prepared by following procedure. Silver nitrate and reduction agent were reacted to prepare silver colloids. PVP or SDS was added to the solution and then, a selected surfactant was dropwisely added at room temperature to promote a reduced reaction. In the case of silver nanoparticles prepared from the PVP/AgNO₃ solution, the spherical nanoparticles with 15-20 nm in size was formed and the size distribution was narrow with well dispersion when the molar ratio was 0.5 and 1. However, as the molar ratio increased to 1.5, the large particles with the size of 80 nm above were formed due to particle agglomeration and the shape of the particle was irregular. On the other hand, upon increasing the molar ratio of SDS/AgNO₃, the particle size decreased to 10-20 nm, which showed an opposite phenomenon to the PVP case. When the molar ratio was 1.5, the fine particles with uniform shape were obtained and the particles were well-dispersed. The PVP and SDS surfactants during the reduced reaction had an opposite influence on the morphology of silver nanoparticles, especially on the particle size. The amount of reduction agents had an influence on the particle size and agglomeration between silver particles. The well dispersed silver colloids could be easily obtained by using SDS surfactant. Silver colloids prepared from SDS/AgNO₃ solution with hydrazine consisted of spherical fine particles with narrow size distribution. SDS as a stabilizing agent had superior protection ability of silver nanoparticles against particle growth and agglomeration. Silver particles which were prepared with a surfactant had spherical shape of 10-30 nm in size. The colloids was stable for at least 24 hours. Silver nanoparticles prepared from AgNO₃/surfactant solution with the amount of hydrazine of 5, 10 and 20 ml. The morphology of silver particle changed to the irregular shape with the addition of hydrazine as a reduction agent. Also the particle size increased from 10 to 80 nm with increasing the reduction agent from 5 to 20 ml and the agglomerates between silver particles also increased. Silver nanoparticles obtained from AgNO₃/surfactant solution with the drop speed of 1 or 5 ml/min. With increasing the drop speed of hydrazine, the particle size increased to 10-80 nm and the shape of silver particle became spherical with the addition speed of hydrazine. Additionally, the particle size increased from 10 to 80 nm with increasing the reduction agent from 1 to 5 ml/min. UV-visible spectra were measured with a UV-Vis spectrophotometer to observe the nucleation and particle growth in solution. UV-visible absorption spectra have been proven to be quite sensitive to the formation of silver colloids since silver particles exhibit and intense absorption peak around 400 nm due to the surface plasmon excitation. Therefore, silver nanoparticles protected by a surfactant, such as SDS, can give potential for preparation of silver paste with high concentration. These silver nanoparticles with spherical shape may have important applications especially in electro materials, and this method extend its potential for preparation of other noble metal nanoparticles.