Nanocrystals (NCs) have received attention due to their wide applications, such as sensing, catalysis, en-ergy storage and photoenery conversion. This is due to their distinct and unique physical and chemical proper-ties. These NCs could be precisely tuned by adjusting their shape, size, composition, and surface structure. Therefore, during the past decade, there are enormous efforts to synthesize optimized NCs in various fields. In practice, developed NCs have exhibited superior performance compared to existing NCs. Accordingly, the main objective of this thesis focused on the synthesis of shape- and composition-controlled NCs and study on their various properties.
In chapter 2, bimetallic alloy Au-Pd nanoparticles with an unprecedented octapodal shape have been prepared by a one-pot aqueous synthesis method. This unique structure was produced through selective etching of {100} facets by in situ generated Br- ions. The octapodal Au-Pd nanoparticles exhibited efficient electrocatalytic properties toward ethanol oxidation.
In chapter 3, Pd-Pt alloy NCs with hollow structures such as nanocages with porous walls and dendritic hollow structures and Pd@Pt coreshell dendritic NCs could be selectively synthesized by a galvanic replacement method with uniform Pd octahedral and cubic NCs as sacrificial templates. Fine control over the degree of gal-vanic replacement of Pd with Pt allowed the production of Pd-Pt NCs with distinctly different morphologies. The synthesized hollow NCs exhibited considerably enhanced oxygen reduction activities compared to those of Pd@Pt core-shell NCs and a commercial Pt/C catalyst, and their electrocatalytic activities were highly dependent on their morphologies. The Pd-Pt nanocages prepared from octahedral Pd NC templates exhibited the largest improvement in catalytic performance. We expect that the present work will provide a promising strategy for the development of efficient oxygen reduction electrocatalysts and can also be extended to the preparation of other hybrid or hetero-nanostructures with desirable morphologies and functions.
In chapter 4, Au NCs with an unprecedented hexoctahedral structure enclosed exclusively by high-index {321} facets have been prepared for the first time. Manipulating the NC growth kinetics by controlling the amount of reductant and the reaction temperature in the presence of a suitable surfactant was the key synthetic lever for controlling the morphology of the Au NCs. The hexoctahedral Au NCs exhibited efficient optical and surface-enhanced Raman scattering activities due to their unique morphological characteristics.
나노결정은 센싱, 촉매, 에너지 저장, 및 태양에너지 변환과 같은다양한 분야에서 많은 관심을 받아오고 있다. 이는 그들의 차별되고 독특한 물리적, 화학적 특성 때문이다. 이러한 나노결정들은 정교한 모양, 크기, 성분 및 표면 구조 조절을 통해서 제어될 수 있다. 이 때문에 지난 10년 동안 여러 분야에서 최적의 나노결정을 합성하기 위해서 많은 노력을 해왔다. 실제로 이렇게 개발된 나노결정은 기준의 나노결정보다 뛰어난 성능을 나타내고 있다. 따라서 이번 학위의 주요 목표는 모양과 성분이 제어된 나노결정의 합성과 그의 다양한 활성을 연구하는 것이다.
2장에서는 octapodal 모양의 Au-Pd 합금 이종 나노결정이 물에서 합성되었다. 이 모양의 나노결정은 Br- 이온에 의한 선택적 에칭을 통해서 만들어 졌다. Octapodal 나노결정은 높은 에탄올 산화 반응 활성을 나타내었다.
4장에서는 속이 빈 구조의 Pd-Pt 나노결정을 Pd 정팔면체와 정육면체 나노결정을 씨드로 이용하고galvanic replacement의 정도를 조절하면서 합성에 성공하였다. 이 때 galvanic replacement의 정도에 따라서 구별되는 속이 빈 Pd-Pt 나노결정이 합성되었고, 이중에 Pd 정팔면체를 이용하여 합성한 Pd-Pt 나노케이지가 가장 뛰어난 산소환원반응 활성을 나타내었다.
5장에서는 표면이 {321} 고지수 표면구조를 가지는 hexoctahedral Au나노결정이 환원제와 온도를 조절함에 따른 kinetics에 의해 합성됨을 확인하였다. 제조된 hexoctahedral Au나노결정는 독특한 구조로 인해 높은 surface-enhanced Raman scattering 활성을 나타내었다.
