Complex-shaped Metal Nanoparticles

Bottom-Up Syntheses and Applications

Tapan K. Sau, Andrey L. Rogach

• Publisher: Wiley-VCH
• Year: 2012
• Print ISBN:
  9783527330775
• Edition: 1
• eBook ISBN:
  9783527652594
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The past few years have witnessed the development of non-spherical metal nanoparticles with complex morphologies, which offer tremendous potential in materials science, chemistry, physics and medicine.
Covering all important aspects and techniques of preparation and characterization of metal nanoparticles with controlled morphology and architecture, this book provides a sound overview - from the basics right up to recent developments. Renowned research scientists from all over the world present the existing knowledge in the field, covering theory and modeling, synthesis and properties of these nanomaterials.
By emphasizing the underlying concepts and principles in detail, this book enables researchers to fully recognize the future research scope and the application potential of the complex-shaped metal nanoparticles, inspiring further research in this field.

Chapter 1

Colloidal Synthesis of Noble Metal Nanoparticles of Complex Morphologies

Tapan K. Sau and Andrey L. Rogach

1.1 Introduction

Interesting properties and small volume of nanoparticles (NPs) have made them desirable for numerous studies and applications in many frontier scientific and technological fields. Synthesis plays crucial roles in tuning the volume as well as the properties of NPs. Many properties, which are known to be constant for bulk materials, vary with the size, shape, and surface structure of the nanomaterials. Therefore, one needs to develop the synthesis methodologies that can produce NPs of precisely controlled size, shape, crystal structure, surface chemistry, and chemical composition. This has prompted the researchers to produce an impressive range of NPs through various physical and (bio)chemical methods of synthesis. With the progress in synthesis, many exciting new nanomaterials with unique properties have been generated, which in turn has initiated numerous new scientific studies and technological applications.

NPs can be produced in the solid, liquid, solution, or gaseous state, following two broad, basic approaches, classified as “top-down” and “bottom-up” in the literature. In the top-down approach, one achieves structure sizes in the medium to lower nanometer range starting from large materials entity by using the physical and lithographic principles of micro- and nanotechnology. In the bottom-up approach, ionic, atomic, and molecular units assemble through various processes to form structures of nanometer length scale. The bottom-up approach in essence is the chemical synthesis method. In this approach, chemical synthesis principles are primarily employed starting from the generation of the constituents to their growth into nanoentity. The bottom-up approach allows, in principle, designing and producing NPs of any size and morphology via unit-by-unit deposition of the constituents. This approach offers an opportunity to understand the atomic/molecular-level aspects of the morphology development and the structure–property relationship in a particle. The bottom-up solution-phase synthesis methods are often denoted as “chemical colloidal” (or “colloid chemical”) methods, because they involve precipitation of nanometer-sized particles within a continuous solvent matrix forming colloidal sols. These methods of syntheses are inexpensive, versatile, and technologically simple to implement. Chemical colloidal methods and the materials thus produced are suitable for further processing, which is essential for integrating NPs in complex systems and devices. Therefore, chemical colloidal methods have been preferred methods for producing a wide-ranging NPs and nanocomposites of a variety of materials (e.g., metals, alloys, intermetallics, semiconductors, and ceramics).

Chemical colloidal synthesis routes have been extensively employed to prepare metal NPs, especially noble metal nanoparticles (NMNPs). NMNPs preparation via the chemical colloidal synthesis routes basically involves the (bio)chemical reduction of metal salts, photochemical and electrochemical pathways, or sonochemical/thermal decomposition of metallic compounds in aqueous or organic solvents in the presence of a variety of additives, such as surfactants, ligands, polymers, etc. In this chapter, we provide an overview of the chemical, photochemical, biochemical, and electrochemical synthesis routes that have been used to prepare NMNPs of “complex morphologies” (of mainly Ag, Au, Pd, and Pt metals). In our complex morphology terminology, we exclude single-component spherical NPs. Readers are referred to other chapters of this book as well as to a few excellent review articles for further reading [1–6]. Particle synthesis by sonochemical and thermal decomposition or hydrothermal methods is not considered here. Interested readers are referred to Refs [7, 8].

This chapter aims to provide a state-of-the-art overview of the morphology-controlled colloidal synthesis of NMNPs. In Section 1.2, we will discuss the classifications of NMNPs based on their general appearance. In Section 1.3, the synthesis methods generally employed for the preparation of NMNPs of controlled morphologies are described. In Section 1.4, some of the NP characterization techniques are briefly mentioned. The factors that influence the particle morphologies are highlighted in Section 1.5. Finally, in Section 1.6, the proposed mechanisms of development of various morphologies are discussed. Throughout the text, we will also refer readers to other chapters of this book for more comprehensive treatment of some specific aspects related to the synthesis, morphology, and properties of NMNPs that are briefly introduced/discussed here.

1.2 Classification of Noble Metal Nanoparticles

A diverse spectrum of NMNPs has become available due to the numerous synthetic efforts over the years. However, no commonly accepted nomenclature and classification systems are followed at present. Composition of nanomaterials (viz., monometallic, bimetallic, metal oxide, magnetic, semiconductor, hybrid, composite, etc.) has been used frequently as the basis for their classifications. Naming particles according to their geometrical shapes and general appearance is a very common trend. As examples, one finds nanorods [9–13], nanowires [13–18], nanodumbbells [19, 20], nanocubes [9, 10, 21–30], tetrahedra [31–33], decahedra [31, 34, 35], icosahedra [31, 36–38], octahedra [10, 23–25, 29, 33, 39–41], prisms [42–50], pyramids [51], stars [9, 17, 52–55], multipods [9, 56–61], nanocages [27], striped particles [62, 63], core–shell [64, 65], heterodimers [64, 65], tadpoles [66], tubular [67–69], and so on [44, 58, 70–85]. Glotzer and Solomon recently put forward several possible classifying principles as a way of unifying the practically infinite number of different particle shapes and types that are already made or will be made in the near future [86]. We follow here the classification that is based on the major growth directions as well as on the morphology or general appearance. Based on the major growth directions, one can classify anisometric nanomaterials broadly into three kinds: (i) one-dimensional (1D) NPs, (ii) two-dimensional (2D) NPs, and (ii) three-dimensional (3D) NPs. In 1D NPs, the major growth occurs in one dimension, whereas it is confined in two other dimensions, namely, rods, wires, tubes, and so on. Two-dimensional NPs are those where major growth occurs in two dimensions (the growth is confined in one dimension), namely, planar triangles, hexagons, plates, disks, ribbons, belts, and so on. In 3D NPs, major growth occurs in all three dimensions, namely, Platonic, Archimedean, Poisont shapes, such as tetrahedra, octahedra, decahedra, icosahedra, cubes, prisms, nanocages, branched NPs (e.g., bipod, tripod, tetrapod, multipod, bumpy, thorny, and sea-urchin) and so on. Figure 1.1 shows a few examples of 1D, 2D, and 3D nonspherical NMNPs. We refer the readers to Chapter 8 for a comprehensive treatment of thermodynamic cartography of major NP morphologies.

Figure 1.1 A few examples of 1D, 2D, and 3D NMNPs of complex morphologies synthesized by colloid chemical synthetic approach. First row shows the TEM (a–d) or SEM (e) images of NPs where major growth has taken place in one dimension. (a) Nanorods. (b) Nanoshuttles. (c) Nanobipyramids of Au/Ag. (d) Silver nanowires. (e) Au nanotubule. Middle row shows some examples of 2D NPs. TEM images of triangular Au nanoplate (f), silver nanodisk (g), and Au ribbons (h), and SEM image of Au belts (i). Bottom row shows TEM or SEM images of some typical 3D (e.g., polyhedral, branched, and hollow/porous) NPs. (j) Nanocubes. (k) Tetrapods. (l and m) Star-shaped Au particles. (n) Ag nanohexapods. (o) Au–Ag nanocage. Reproduced with permission: Parts (a) from Ref. [11], Copyright 2004 American Chemical Society; (b) from Ref. [20], Copyright 2008 OSA; (c) from Ref. [87], Copyright 2007 Taylor & Francis Group; (d) from Ref. [14], Copyright 2003 American Chemical Society; (e) from Ref. [68], Copyright 2001 American Chemical Society; (f) from Ref. [88]; (g) from Ref. [89], Copyright 2002 American Chemical Society; (h and i) from Ref. [90], Copyright 2008 American Chemical Society; (j–m) from Ref. [9], Copyright 2004...

Table of contents

• Cover
• Related Titles
• Title Page
• Copyright
• Dedication
• Foreword
• Preface
• List of Contributors
• Metal Nanoparticles of Complex Morphologies: A General Introduction
• Chapter 1: Colloidal Synthesis of Noble Metal Nanoparticles of Complex Morphologies
• Chapter 2: Controlling Morphology in Noble Metal Nanoparticles via Templating Approach
• Chapter 3: Shape-Controlled Synthesis of Metal Nanoparticles of High Surface Energy and Their Applications in Electrocatalysis
• Chapter 4: Shape-Controlled Synthesis of Copper Nanoparticles
• Chapter 5: Size- and Shape-Variant Magnetic Metal and Metal Oxide Nanoparticles: Synthesis and Properties
• Chapter 6: Structural Aspects of Anisotropic Metal Nanoparticle Growth: Experiment and Theory
• Chapter 7: Colloids, Nanocrystals, and Surface Nanostructures of Uniform Size and Shape: Modeling of Nucleation and Growth in Solution Synthesis
• Chapter 8: Modeling Nanomorphology in Noble Metal Particles: Thermodynamic Cartography
• Chapter 9: Platinum and Palladium Nanocrystals: Soft Chemistry Approach to Shape Control from Individual Particles to Their Self-Assembled Superlattices
• Chapter 10: Ordered and Nonordered Porous Superstructures from Metal Nanoparticles
• Chapter 11: Localized Surface Plasmons of Multifaceted Metal Nanoparticles
• Chapter 12: Fluorophore–Metal Nanoparticle Interactions and Their Applications in Biosensing
• Chapter 13: Surface-Enhanced Raman Scattering Using Complex-Shaped Metal Nanostructures
• Chapter 14: Photothermal Effect of Plasmonic Nanoparticles and Related Bioapplications
• Chapter 15: Metal Nanoparticles in Biomedical Applications
• Chapter 16: Anisotropic Nanoparticles for Efficient Thermoelectric Devices
• Index