Noble Metal-Based Nanocomposites E-Book

Jun Yang

• Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 822

Veröffentlichungsjahr: 2019

Beschreibung

Provides a systematic and coherent picture of the solution-based methods for the preparation of noble metal-based composite nanomaterials, their characterization, and potential applications in electrocatalysis Within the last decade, the development of wet-chemistry methods has led to the blossom of research in composite nanomaterials. However, the design and synthesis of composite nanomaterials with controlled properties remains a significant challenge. This book summarizes the solution-based methods for the preparation of noble metal-based composite nanomaterials. It examines their characterization, as well as their use in electrocatalysis. It also discusses the intrinsic relationship between the catalytic properties and the physical /chemical effects in the composite materials, and offers some perspectives for the future development of metal-based composite nanomaterials. In addition, the book not only provides a systematic and coherent picture of this field, but also inspires rethinking of the current processing technologies. Noble Metal-Based Nanocomposites: Preparation and Applications offers in-depth chapter coverage of ethanol-mediated phase transfer of metal ions and nanoparticles. It presents the full range of nanocomposites consisting of chalcogenide semiconductors and gold, silver sulfide, or other noble metals. It also examines core-shell structured cadmium selenide-platinum nanocomposites; Pt-containing Ag2S-noble metal nanocomposites for direct methanol fuel cells operated at high fuel concentrations; and nanocomposites consisting of metal oxides and noble metals. In addition, the book looks at scientific issues derived from noble metal-based nanocomposites. -Covers all of the preparations of noble metal-based nanocomposites and their numerous applications -Highlights some of the recent breakthroughs in the design, engineering, and applications of noble metal-based nanocomposites -Appeals to a wide range audience, especially researchers in the areas of catalysis, chemistry, chemical engineering, materials synthesis and characterization, and fuel cell Noble Metal-Based Nanocomposites: Preparation and Applications is an excellent book for inorganic chemists, materials scientists, catalytic chemists, chemical engineers, and those interested in the subject.

Leseprobe

Table of Contents

Cover

About the Author

Preface

Acknowledgments

List of Abbreviations

1 An Introduction to Noble Metal‐Based Composite Nanomaterials

1.1 Materials at Nanometer Scales

1.2 Emergence of Composite Nanomaterials

1.3 General Concepts in Wet Chemistry Synthesis of Composite Nanomaterials

1.4 Characterizations of Composite Nanomaterials

1.5 The Scope of This Book

1.6 The Road Ahead

References

2 Ethanol‐Mediated Phase Transfer of Metal Ions and Nanoparticles

2.1 Introduction

2.2 Early Studies in Phase Transfer of Noble Metal Nanoparticles

2.3 Brust–Schiffrin Method

2.4 Phase Transfer Through Ligand Exchange

2.5 Phase Transfer Through Electrostatic Interaction

2.6 Phase Transfer of Nanoparticles from Organic to Aqueous Phase

2.7 Ethanol‐Mediated Phase Transfer

2.8 Recent Advances in Phase Transfer

2.9 Summary

References

3 Nanocomposites Consisting of Chalcogenide Semiconductors and Gold

3.1 Introduction

3.2 Phosphine‐Free Synthesis of Metal Selenide Nanocrystals

3.3 Deposition of Au on Chalcogenide Semiconductor Nanocrystals

3.4 Growth of Chalcogenide Semiconductors on Gold Nanoparticles

3.5 Semiconducting Metal Sulfide–Gold Nanocomposites upon Ethanol‐Mediated Phase Transfer

3.6 Semiconductor–Gold Nanocomposites by a Two‐phase Strategy

3.7 Special Gold‐Related Nanocomposites

3.8 Semiconductor–Gold Nanocomposites for Efficient Three‐component Coupling of Aldehyde, Amine, and Alkyne in Water

3.9 Summary

References

4 Nanocomposites Consisting of Chalcogenide Semiconductors and Other Noble Metals

4.1 Introduction

4.2 Semiconductor–Silver Nanocomposites

4.3 Semiconductor–Platinum Nanocomposites

4.4 Nanocomposites Consisting of Semiconductors and Other Noble Metals

4.5 Semiconductor–Dual Metal Nanocomposites

4.6 Summary

References

5 Nanocomposites Consisting of Silver Sulfide and Noble Metals

5.1 Introduction

5.2 Aqueous Synthesis of Ag

2

S Nanocrystals

5.3 Binary Ag

2

S–Noble Metal Nanocomposites

5.4 Multiple Ag

2

S–Noble Metal Nanocomposites

5.5 Electrocatalytic Property of Pt‐Containing Ag

2

S–Noble Metal Nanocomposites for Methanol Oxidation Reaction and Oxygen Reduction Reaction

5.6 Electrocatalytic Property of Pt‐Containing Ag

2

S–Noble Metal Nanocomposites for Formic Acid Oxidation Reaction

5.7 Summary

References

6 Nanocomposites Consisting of Chalcogenide Semiconductors and Noble Metals by Structural Transformations

6.1 Introduction

6.2 Inside‐Out Diffusion of Ag in Core–Shell Nanoparticles with Ag Residing in the Core or Internal Shell Regions

6.3 Nanocomposites Consisting of Ag

2

S and Hollow Noble Metal Nanoparticles

6.4 Nanocomposites Consisting of Ag

2

S and Bimetallic Au–Pt Cage‐Bell Structures

6.5 Ternary Nanocomposites Consisting of Ag

2

S, Au, and Hollow Pt Nanoparticles

6.6 Electrochemical Properties of the Binary and Ternary Nanocomposites and Their Core–Shell Precursors

6.7 Nanocomposites Consisting of Ag

2

S and Palladium Nanoparticles and Their Electrochemical Properties

6.8 Nanocomposites Consisting of Ag

2

Se and Hollow Platinum Nanoparticles

6.9 Nanocomposites Consisting of CuS and Platinum Nanoparticles

6.10 Strategies for Further Enhancing the Catalytic Performance of Pt‐Containing Noble Metal‐Based Nanocomposites in Electrochemical Reactions

6.11 Summary

References

7 Core–Shell‐Structured Cadmium Selenide–Platinum Nanocomposites

7.1 Introduction

7.2 Reversible Phase Transfer of Semiconductor and Noble Metal Nanoparticles

7.3 CdSe–Pt Nanocomposites with Core–Shell Constructions

7.4 Further Efforts in Core–Shell‐Structured Semiconductor–Noble Nanocomposites

7.5 Summary

References

8 Pt‐Containing Ag

2

S–Noble Metal Nanocomposites for Direct Methanol Fuel Cells Operated at High Fuel Concentrations

8.1 Introduction

8.2 Ternary Au@Ag

2

S–Pt Nanocomposites as Selective Electrocatalysts at DMFC Anode

8.3 Core–Shell–Shell Au@Ag

2

S@Pt Nanocomposites as Selective Electrocatalysts at DMFC Anode

8.4 Cage‐Bell‐Structured Pt–Ru Nanoparticles as Selective Electrocatalysts at DMFC Cathode

8.5 Core–Shell‐Structured Au@Pd Nanoparticles with Thin Pd Shells as Selective Electrocatalysts at DMFC Cathode

8.6 A Prototype of the Membraneless Direct Methanol Fuel Cell

8.7 A Selective Electrocatalyst‐Based Direct Methanol Fuel Cell (DMFC) Operated at High Concentration of Methanol

8.8 Summary

References

9 Nanocomposites Consisting of Metal Oxides and Noble Metals

9.1 Introduction

9.2 Gold‐Based Nanocomposites for CO Oxidation at Low Temperature

9.3 Early Studies in Metal Oxide–Noble Metal Nanocomposites

9.4 Dumbbell‐Like Metal Oxide–Noble Metal Nanocomposites

9.5 High‐Order Nanocomposites

9.6 RuO

2

–Au Nanocomposites as Electrode Materials for Supercapacitors

9.7 Hollow‐Structured MO

x

–RuO

2

(M = Co, Cu, Fe, Ni, CuNi) Nanocomposites as Highly Efficient Electrodes for Supercapacitors

9.8 CuO–Pd Nanocomposites with Atomic Dispersion of Pd for Catalytic Removal of Benzene

9.9 Strategies for Determining the Influence of Noble Metals on the Catalytic Performance of Nanocomposites

9.10 Summary

References

10 Scientific Issues Derived from Noble Metal‐Based Nanocomposites

10.1 Introduction

10.2 Diffusion of Gold from the Inner Core to the Surface of Ag

2

S Nanocrystals

10.3 Coalescence of Au and Ag

2

S Nanocrystals at Room Temperature

10.4 Synthesis of PbSe–Au Nanocomposites with Different Morphologies

10.5 Fine Ag

2

S–Pt Nanocomposites Supported on Carbon Substrates for Methanol Oxidation Reaction

10.6 Summary

References

11 Conclusion and Perspectives

11.1 Creating a Favorable Solvent Environment for the Growth of Noble Metal‐Based Nanocomposites

11.2 Synthesis of Composite Nanosystems and Understanding Their Underlying Chemistry

11.3 Exploring the Catalytic Properties of the Noble Metal‐Based Nanocomposites for Energy Conversion and Storage

11.4 Investigating Other Scientific‐Related Issues

References

Index

End User License Agreement

List of Tables

Chapter 2

Table 2.1 The phase‐transfer efficiency of metal ions from water to toluene.

Chapter 4

Table 4.1 Metal deposition on colloidal semiconductor nanorods.

a

Chapter 5

Table 5.1 The facets and lattice spacing of monoclinic Ag

2

S (JCPDS 140072).

Table 5.2 Electrochemical measurements of methanol oxidation on commercial Pt/C ...

Chapter 7

Table 7.1 Electrochemical measurements of methanol oxidation on small core–shell...

Chapter 8

Table 8.1 Electrochemical measurements of methanol oxidation on ternary Au@Ag

2

S–...

Table 8.2 Comparison of the DMFC with selective electrocatalysts and those repor...

Chapter 9

Table 9.1 The mass ratios of transition metal oxides and RuO

2

in the final hMO

x

–...

Table 9.2 Specific capacitance of hMO

x

–RuO

2

/C and hMO

x

–RuO

2

/CNT electrode materi...

Table 9.3 Specific capacitance of hMO

x

–RuO

2

/C and hMO

x

–RuO

2

/CNT electrode materi...

Table 9.4 Retention ratios of specific capacitance of symmetric supercapacitors ...

Table 9.5 The equivalent series resistance of symmetric supercapacitors based on...

Table 9.6 Binding energies and area percentage of Cu 2p

3/2

, Pd 3d

5/2

and O 1s ana...

Table 9.7 The characteristic temperature of catalysts for the oxidation of benze...

Chapter 10

Table 10.1 Electrochemical measurements of methanol oxidation over alloy Au/Pt n...

Table 10.2 Electrochemical measurements of oxygen reduction over alloy Au/Pt nan...

Table 10.3 Synthesis conditions for different PbSe–Au nanocomposites.

List of Illustrations

Chapter 1

Figure 1.1 Schematic illustration of different shapes of Pt nanocrystals deriv...

Figure 1.2 Schematic illustration to show the synthesis of noble metal nanomate...

Figure 1.3 The main milestones in wet chemistry‐based syntheses of noble metal‐...

Figure 1.4 Plot of atomic concentration against time, illustrating the generati...

Figure 1.5 Comparative sketches illustrating possible heterogeneous deposition ...

Figure 1.6 TEM images of (a) 3–7 nm, (b) 3–10 nm, (c) 5–12 nm, and (d) 5–17 nm ...

Figure 1.7 (a) High‐magnification HAADF‐STEM image showing a representative Ag–...

Chapter 2

Figure 2.1 TEM images of colloidal Au dispersions in hexanes: (a) colloidal Au...

Figure 2.2 TEM images of Pt nanocrystals obtained by the phase‐transfer method ...

Figure 2.3 Schematic illustration to show the three‐step route for the synthesi...

Figure 2.4 Schematic illustration to show the ligand exchange‐based phase trans...

Figure 2.5 The dynamic covalent approach to reversible nanoparticle property tu...

Figure 2.6 Schematic illustration to show the ligand exchange on the surface of...

Figure 2.7 TEM images of ODA‐stabilized, surface‐modified gold nanoparticles: (...

Figure 2.8 Photographs showing the successful transfer of Co(II), Os(III), Rh(I...

Figure 2.9 FT‐IR spectra of pure DDA and metal ion–DDA complexes.

Figure 2.10 TEM images of metal nanoparticles. (a) Ag derived with HDD. (b) Au,...

Figure 2.11 TEM images of (a) alkylamine‐stabilized Ag nanoparticles of c. 7.09...

Figure 2.12 TEM images of alkanethiol‐stabilized Au nanoparticles of 6.24 nm an...

Figure 2.13 Schematic illustration to show the process of displacing citrate fr...

Figure 2.14 Schematic illustration of the process to generate highly fluorescen...

Figure 2.15 TEM images of metal nanoparticles in chloroform (CHCl

3

). (a) Au5 sc...

Figure 2.16 TEM images of self‐assembled AuNP@PSSH films (

d

AuNP

 = 28 nm). (a) L...

Chapter 3

Figure 3.1 Schematic illustration to show the synthesis of CdSe and core–shell...

Figure 3.2 TEM images showing controlled growth of Au onto the tips of CdSe qua...

Figure 3.3 Effect of increasing Au

/

rod molar ratio on the growth. Top panels sh...

Figure 3.4 Schematic illustration to show the growth process of Au nanocrystals...

Figure 3.5 (a) Scheme of a light‐induced charge separation mechanism in a CdSe–...

Figure 3.6 Understanding size‐dependent hydrogen production yield. (a) Hydrogen...

Figure 3.7 TEM images of (a) as‐synthesized 5‐nm InAs nanocrystals, (b) InAs na...

Figure 3.8 (a and b) TEM images of the ordered array of PbS–Au

4

heterogeneous n...

Figure 3.9 TEM images (a, c, d) and HRTEM image (b) of Fe

3

O

4

–Au–PbSe (a and b) ...

Figure 3.10 (a) Optical absorbance of 4.6‐nm Au nanoparticles and Cu

2−

x

Se...

Figure 3.11 (a) A TEM image of PbS nanostars. (b and c) TEM images, (d and e) H...

Figure 3.12 TEM images of CdSe‐seeded CdS nanorods with c. 40‐nm length and an ...

Figure 3.13 (a) Reaction schematic to obtain hierarchically complex CdSe‐seeded...

Figure 3.14 Schematic illustration for the synthesis of CdS–Au nanocomposites u...

Figure 3.15 (a) Schematic illustration to show the self‐assembly process used t...

Figure 3.16 (a) TEM image of PbTe nanocrystals initially coated with a thick am...

Figure 3.17 (a) Schematic illustration to show the synthesis of dimeric Cu

2

S–Au...

Figure 3.18 (a–d) TEM images of Bi

2

S

3

–Au heterogeneous nanocomposites at differ...

Figure 3.19 (a–c) TEM and HRTEM images showing smaller SnS cubes decorated by s...

Figure 3.20 (a) TEM image of a typical Au–ZnSe heteronanostructure; (b−d) prese...

Figure 3.21 Schematic illustration to show different pathways and outcomes of A...

Figure 3.22 Bright‐field (a and c), dark‐field (b), and HRTEM image (d) of CZTS...

Figure 3.23 Schematic representation of the matching of the periodic distances ...

Figure 3.24 Two charge separation mechanisms in CdS–Au nanocomposites: Mechanis...

Figure 3.25 TEM images of (a) PbS nanocrystals and (b–d) Au@PbS core–shell nano...

Figure 3.26 Schematic illustration showing the synthetic method for growth of A...

Figure 3.27 (a) Reaction protocol and schematic presentation of formation of fl...

Figure 3.28 (a) Typical TEM, (b) HRTEM, and (c) STEM image as well as element m...

Figure 3.29 (a) Schematic representation of the synthesis of Au@Cu

2−

x

Se (

Figure 3.30 Nonepitaxial growth process and mechanism of composite core–shell n...

Figure 3.31 Schematic illustration showing the growth of Au@CdS core–shell nano...

Figure 3.32 (a and b) TEM images, (c) HRTEM image, and (d) SAED pattern of the ...

Figure 3.33 XRD pattern of the as‐prepared Ag

2

S nanocrystals. Inset shows the p...

Figure 3.34 TEM images of different times for Ag

2

S nanocrystals obtained by rea...

Figure 3.35 Schematic illustration to show the growth mechanism of Ag

2

S nanocry...

Figure 3.36 (a, c, e) Representative TEM and (b, d, f) HRTEM images of Ag

2

S nan...

Figure 3.37 (a) TEM, (b) HRTEM, and (c) STEM images of Ag

2

S–Au heterodimers der...

Figure 3.38 (a) TEM and (b) HRTEM images of core–shell Au@Ag

2

S nanocomposites (...

Figure 3.39 (a) TEM and (b) HRTEM image of the HgS nanocrystals synthesized by ...

Figure 3.40 (a, c, e, g, i) TEM and (b, d, f, h, j) HRTEM images of (a and b) A...

Figure 3.41 TEM images of CdS–Au nanocomposites synthesized after physically mi...

Figure 3.42 (a, c, e, g, i) TEM and (b, d, f, h, j) HRTEM images of CdS–Au nano...

Figure 3.43 TEM image (a) and HRTEM image (b) of CdS–Au nanocomposites at CdS/A...

Figure 3.44 (a, c, e, g, i) TEM and (b, d, f, h, j) HRTEM images of Ag

2

S–Au (a ...

Figure 3.45 X‐ray diffraction (XRD) patterns of monoclinic Ag

2

S, hexagonal CuS,...

Figure 3.46 (a) TEM, (b) HRTEM, (c) STEM image of PbS–Ag nanocomposites, and (d...

Figure 3.47 (a) TEM, (b) HRTEM, (c) STEM image of PbS–Ag–Au nanocomposites, and...

Figure 3.48 Schematic illustration to demonstrate the mechanism for serially de...

Figure 3.49 Schematic illustration showing the formation of semiconducting meta...

Figure 3.50 (a) SEM image, (b) TEM image, (c) size distribution of Au dots, and...

Figure 3.51 TEM images of (a) CdS, (b) CdSe, and (c) PbS semiconductor nanocrys...

Figure 3.52 Schematic illustration to show the tentative mechanism for the PbS–...

Chapter 4

Figure 4.1 (a) Schematic illustration of the formation of Ag

2

S–Ag dimeric nano...

Figure 4.2 Characterization of the dimeric Ag

2

S–Ag nanocomposites: (a) TEM imag...

Figure 4.3 Structural characterizations of the sulfidation products and schemat...

Figure 4.4 (a–c) Proposed pathway of sulfidation processes as a function of Na

2

Figure 4.5 Schematic representation showing the synthesis of CdSe–Ag aerogels: ...

Figure 4.6 Photodeposition of Pt on CdS nanorods: (a) TEM images of CdS nanorod...

Figure 4.7 (a) Schematic illustration showing the three‐step synthetic process ...

Figure 4.8 Characteristic fluence‐dependent photoluminescence obtained in gaseo...

Figure 4.9 (a–d) TEM images of Pt growth onto CdSe nanorods in aqueous solution...

Figure 4.10 Selective growth of Pt nanoparticles with different sizes on CdS na...

Figure 4.11 Metal deposition pathways.

Figure 4.12 Schematic illustration and associated TEM images of CuInS

2

–Pt nanoc...

Figure 4.13 Schematic illustration showing the band alignment of CdSe–Au and Cd...

Figure 4.14 Schematic illustration showing the reaction pathways for the photoc...

Figure 4.15 Synthesis of Ru nanoinorganic caged Cu

2

S nanocomposites and hollow ...

Figure 4.16 (a) Synthetic illustration showing the routes to nanocomposites con...

Figure 4.17 Schematic illustration showing the morphologies of noble metal doma...

Figure 4.18 (a) TEM image of ∼2.8‐nm‐diameter core Au nanoparticles with a ∼3.3...

Figure 4.19 Schematic illustration summarizing the options directing the deposi...

Figure 4.20 (a) TEM, (b) HAADF‐STEM, and (c) HRTEM images, along with a (d) STE...

Figure 4.21 Schematic representation showing the morphologies of the composite ...

Figure 4.22 HRTEM images of two sets of seeded rods, taken before and after the...

Figure 4.23 Relative efficiency for the photocatalytic hydrogen production half...

Figure 4.24 (a) Schematic illustration showing the multistep synthesis; TEM ima...

Figure 4.25 (a) Transient absorption (TA) spectra of Au–CdSe–Pt nanodumbbells w...

Chapter 5

Figure 5.1 TEM images of the Ag

2

S sample prepared with low molar ratio of dode...

Figure 5.2 TEM images of Ag

2

S nanocrystals synthesized from Ag nanoclusters in ...

Figure 5.3 (a) TEM and (b) HRTEM images of the as‐prepared Ag

2

S nanocrystals in...

Figure 5.4 Binary Ag

2

S–noble metal nanocomposites. (a) TEM image, (b) HRTEM ima...

Figure 5.5 (a and c) TEM and (b and d) HRTEM images of Ag

2

S–Au nanocomposites s...

Figure 5.6 (a and c) TEM and (b and d) STEM images of Ag

2

S–Pt nanocomposites sy...

Figure 5.7 (a) TEM, (b) HRTEM, and (c) STEM images of Ag

2

S–Ir nanocomposite, an...

Figure 5.8 (a) TEM, (b) HRTEM, and (c) STEM images of Ag

2

S–Rh nanocomposite, an...

Figure 5.9 Multicomponent Ag

2

S–noble metal nanocomposites prepared at a metal/A...

Figure 5.10 Cyclic voltammograms of Pt‐containing nanocomposites and commercial...

Figure 5.11 (a) Pt 4f XPS spectra of the Pt/C catalyst and Pt‐containing Ag

2

S–n...

Figure 5.12 4f XPS spectra of Au in monometallic Au particles and the Pt‐contai...

Figure 5.13 CO stripping over the commercial Pt/C catalyst, binary Ag

2

S–Pt and ...

Figure 5.14 (a) Cyclic voltammograms of Pt‐containing Ag

2

S–noble metal nanocomp...

Figure 5.15 Oxygen reduction reaction polarization curves over the commercial P...

Figure 5.16 TEM images of (a) Ag

2

S–Au, (b) Ag

2

S–Pt, (c) Ag

2

S–Au–Pt nanocomposit...

Figure 5.17 (a) Cyclic voltammograms of pure Pt nanoparticles and Pt‐containing...

Chapter 6

Figure 6.1 Inside‐out diffusion of Ag in core–shell Ag–Pt nanoparticles: (a) T...

Figure 6.2 (a) TEM image and (b) HRTEM image of Ag seed nanoparticles synthesiz...

Figure 6.3 Schematic illustration showing the mechanism for the inside‐out diff...

Figure 6.4 TEM images of hollow‐structured (a) Ru, (b) Rh, (c) Os, (d) Pt, (e) ...

Figure 6.5 Schematic illustration showing the formation of nanocomposites consi...

Figure 6.6 TEM images of core–shell (a) Ag–Ir, (e) Ag–Pt, (i) Ag–Rh, (m) Ag–Ru,...

Figure 6.7 EDX analyses of core–shell (a and b) Ag–Ir, (c and d) Ag–Pt, (e and ...

Figure 6.8 TEM images of carbon‐supported hollow (a) Pt, (b) PtRh, (c) PtRu, (d...

Figure 6.9 Schematic illustration showing the synthesis of Ag

2

S–cage‐bell Au–Pt...

Figure 6.10 TEM images of (a) core–shell–shell Au–Ag–Pt nanoparticles, (b) Ag

2

S...

Figure 6.11 (a) TEM image, (b) HRTEM image, (d) line‐scanning analysis, and (e–...

Figure 6.12 TEM images of (a) core–shell Ag@Pt nanoparticles, (b) Ag

2

S–hPt hete...

Figure 6.13 (a) Cyclic voltammograms of the core–shell Ag–Pt nanoparticles, Ag

2

Figure 6.14 TEM image (a), HRTEM image (b), STEM image (c and d), and elemental...

Figure 6.15 Schematic illustration showing the synthesis of heterogeneous Ag

2

S–...

Figure 6.16 (a) Cyclic voltammograms of Ag

2

S–hPd nanocomposites, core–shell Ag–...

Figure 6.17 (a, g, m) TEM images, (b, h, n) HRTEM image, and (c–f, i–l, o–r) el...

Figure 6.18 (a) TEM image, (b) HRTEM image, (c–g) elemental mapping analyses, (...

Figure 6.19 Schematic illustration showing the synthetic routes and experimenta...

Figure 6.20 TEM images of (a) 12–10 nm CuS–Pt nanocomposites from Cu‐seeded CuP...

Figure 6.21 Schematic illustrations showing the synthetic strategies for hetero...

Chapter 7

Figure 7.1 Schematic illustration showing the strain and the associated shift ...

Figure 7.2 Chemical structure of glutathione tetramethylammonium salt.

Figure 7.3 Schematic illustration showing the functionalization of semiconducto...

Figure 7.4 Photographs under of (1–4) CdSe‐CdZnS nanocrystals under UV irradiat...

Figure 7.5 TEM images of CdSe–CdZnS nanocrystals: (a) as‐prepared (7.2 nm), (b)...

Figure 7.6 Photoacoustic FT‐IR spectra of core–shell CdSe–CdZnS nanocrystals wi...

Figure 7.7 TEM image of (a) Au (13 nm), (b) Ag (11 nm), (c) CdS rods (50 nm), a...

Figure 7.8 Room‐temperature (a) UV–visible and (b) photoluminescent spectra of ...

Figure 7.9 UV–vis spectra of Au nanoparticles as‐prepared (1–O) and after

n

rou...

Figure 7.10 (a and c) TEM and (b and d) HRTEM images of CdSe nanocrystals with ...

Figure 7.11 XRD patterns of CdSe nanocrystals of different sizes and CdSe refer...

Figure 7.12 Core–shell CdSe–Pt nanocomposites synthesized in aqueous phase usin...

Figure 7.13 XRD patterns core–shell CdSe–Pt nanocomposites synthesized using 10...

Figure 7.14 Pt 4f XPS spectrum of (a) Pt/C catalysts, (b–d) core–shell CdSe–Pt ...

Figure 7.15 Electrochemical characterization of the core–shell CdSe–Pt nanocomp...

Figure 7.16 ECSA‐based specific ORR polarization curves for the core–shell CdSe...

Figure 7.17 Core–shell CdSe–Pt nanocomposites synthesized using 5 nm CdSe cores...

Figure 7.18 XRD patterns of core–shell CdSe–Pt nanocomposites using 5‐nm CdSe: ...

Figure 7.19 Electrochemical characterization of the core–shell CdSe–Pt nanocomp...

Figure 7.20 Cyclic voltammograms of core–shell CdSe–Pt nanocomposites synthesiz...

Figure 7.21 Possible structures for further efforts in semiconductor–noble meta...

Chapter 8

Figure 8.1 (a) Schematic illustration showing the energy‐level alignment in Ag

Figure 8.2 (a) TEM image and (b) HRTEM image of Au seeds synthesized by NaBH

4

r...

Figure 8.3 (a) TEM image, (b) HRTEM image, (c) STEM image, (d) EDX analysis of ...

Figure 8.4 Core–shell–shell Au@Ag

2

S@Pt nanocomposites: (a) TEM image, (b) aberr...

Figure 8.5 Electrochemical measurements of core–shell–shell Au@Ag

2

S@Pt nanocomp...

Figure 8.6 Schematic illustration showing the differential diffusion and reacti...

Figure 8.7 (a) TEM image and (b) HRTEM image of Pt seeds synthesized in oleylam...

Figure 8.8 (a) TEM image, (b) HRTEM image, (c) STEM image, (d) EDX‐based line‐s...

Figure 8.9 Core–shell Au@Pd nanoparticles: (a) TEM image, (b) aberration‐correc...

Figure 8.10 Electrochemical measurements of core–shell Au@Pd nanoparticles: (a)...

Figure 8.11 (a) Schematic illustration showing the membraneless DMFC, (b) the o...

Figure 8.12 The open circuit voltage of membraneless DMFC with core–shell–shell...

Figure 8.13 Schematic illustration showing the DMFC fabricated with core–shell–...

Figure 8.14 Performance of the assembled DMFC with selective or commercial cata...

Chapter 9

Figure 9.1 Oxidation efficiency of CO as a function of duration time: ○, 5 ato...

Figure 9.2 A representation of the early stages of the oxidation of carbon mono...

Figure 9.3 Activity for CO oxidation at room temperature as a function of Au co...

Figure 9.4 High‐magnification aberration‐corrected STEM‐HAADF images of (a and ...

Figure 9.5 Schematic illustration showing the synthesis of yolk–shell Au@Void@T...

Figure 9.6 Schematic illustration showing the synthesis of the Au/TiO

2

nanocomp...

Figure 9.7 Schematic illustration showing a composite nanoparticle with dumbbel...

Figure 9.8 TEM and STEM images of the dumbbell‐like Au–Fe

3

O

4

nanoparticles: (a)...

Figure 9.9 Magneto‐optical Faraday rotation of dimers and monomers in hexane at...

Figure 9.10 (a) T

2

‐weighted MRI images of (i) 20‐nm Fe

3

O

4

, (ii) 3‐ to 20‐nm Au–...

Figure 9.11 Tug‐of‐war in Au

2

–Au

1

–Fe

3

O

4

nanocomposites: (a) schematic illustrat...

Figure 9.12 Schematic illustration showing the selective etching of Au–Fe

3

O

4

na...

Figure 9.13 Schematic illustration showing the controlled synthesis of Au–MnO n...

Figure 9.14 Schematic illustration showing the proposed energy storage mechanis...

Figure 9.15 Schematic illustration showing the synthesis of dimeric Au–Fe nanop...

Figure 9.16 TEM images of (a) 3‐ to 7‐nm, (b) 3‐ to 10‐nm, (c) 5‐ to 12‐nm, and...

Figure 9.17 (i) Schematic illustration showing the synthetic strategy; TEM imag...

Figure 9.18 Schematic illustration showing the synthesis of dimeric Ag–Fe

3

O

4

na...

Figure 9.19 Snapshots of bright‐field images of macrophage cells labeled with F...

Figure 9.20 Schematic illustration showing the mechanism of the temperature‐con...

Figure 9.21 Schematic illustration showing kinetic growth model of dimeric nano...

Figure 9.22 (a–k) TEM and HRTEM images and corresponding selected area electron...

Figure 9.23 Schematic illustration showing the high‐order nanocomposites, in wh...

Figure 9.24 Schematic illustration showing the various products staring from Zn...

Figure 9.25 Stepwise construction of M–Pt–Fe

3

O

4

heterotrimers (M = Ag, Au, Ni, ...

Figure 9.26 HRTEM images of the three distinct Pt–Fe

3

O

4

–Ag heterotrimer morphol...

Figure 9.27 Schematic illustration showing the stepwise reaction sequences used...

Figure 9.28 Schematic illustration showing the formation of ternary Ni–Au–ZnO n...

Figure 9.29 (a) Schematic illustration showing the synthesis of Fe

3

O

4

–CdS–Au te...

Figure 9.30 (a) TEM image, (b) HRTEM image, and (c) Ru 3p XPS spectrum of RuO

2

/...

Figure 9.31 (a) 3p XPS spectrum of Ru and (b) 4f XPS spectrum of Au in the prec...

Figure 9.32 (a) TEM and (b) HRTEM images of RuO

2

–Au/C nanocomposites as‐prepare...

Figure 9.33 Cyclic voltammograms of (a) RuO

2

/C and (b) RuO

2

–Au/C nanocomposites...

Figure 9.34 Schematic illustration showing the formation of hMO

x

–RuO

2

/C or hMO

x

Figure 9.35 (a

1

–e

1

) TEM images, (a

2

–e

2

) HRTEM images, (a

3

–a

6

, b

3

–b

6

, c

3

–c

6

, d

3

–...

Figure 9.36 TEM images of as‐prepared (a and c) hCo–Ru, (b and d) hCoO–RuO

2

, (e...

Figure 9.37 XPS spectra of Ru in (a and b) hCo–Ru, (c and d) hCu–Ru, h(e and f)...

Figure 9.38 Cyclic voltammograms of (a

1

, c

1

) hCoO–RuO

2

, (a

2

, c

2

) hCuO–RuO

2

, (a

3

Figure 9.39 Plots of specific capacitance for hMO

x

–RuO

2

and commercial RuO

2

sup...

Figure 9.40 A laboratory demonstration showing the application of the hollow‐st...

Figure 9.41 (a, c, e) TEM images and (b, d, f) HRTEM images of bimetallic Cu–Pd...

Figure 9.42 TEM images of Pd–CuO/γ‐Al

2

O

3

samples with Pd/Cu molar ratios of (a)...

Figure 9.43 XPS spectra of Pd 3d (a), Cu 2p (b), and O 1s (c) of γ‐Al

2

O

3

‐suppor...

Figure 9.44 H

2

‐temperature‐programmed reduction (H

2

‐TPR) profiles of γ‐Al

2

O

3

‐su...

Figure 9.45 (a) Conversion rate and (b) TOF showing the benzene oxidation over ...

Figure 9.46 The stability of the Cu–Pd/γ‐Al

2

O

3

catalysts after calcination with...

Figure 9.47 Schematic illustration showing the deposition of different noble me...

Figure 9.48 (a, c, e) TEM images and (b, d, f) UV–vis spectra of the TiO

2

–Ag (a...

Chapter 10

Figure 10.1 Diffusion of Au from the inner core to the surface of core–shell A...

Figure 10.2 HRTEM images of (a) the starting core–shell Au@Ag

2

S nanoparticles, ...

Figure 10.3 (a) Au 4f XPS spectra of Au seeds, core–shell Au@Ag

2

S nanoparticles...

Figure 10.4 Schematic illustration showing the Au diffusion in Ag

2

S from the co...

Figure 10.5 Schematic illustration showing the synthesis of a complicated semic...

Figure 10.6 (a) TEM and (b) HRTEM images of 4‐nm Pt nanoparticles synthesized i...

Figure 10.7 (a) TEM and (b) HRTEM images of core–shell–shell Pt@Au@Ag

2

S nanopar...

Figure 10.8 TEM image of Ag

2

S nanocrystals (in gray tone) synthesized in the pr...

Figure 10.9 Ostwald ripening observed during the diffusion of Au in Ag

2

S. Initi...

Figure 10.10 (a, c, e) TEM images and (b, d, f) HRTEM images of (a and b) Ag

2

S ...

Figure 10.11 Coalescence of Ag

2

S and Au nanocrystals: (a–e) TEM images of the p...

Figure 10.12 (a, b, c) TEM images of the physical mixture of Ag

2

S and 5‐nm Au n...

Figure 10.13 (a) Au 4f XPS spectra of the original Au nanoparticles and resulti...

Figure 10.14 (a) Schematic illustration showing the removal of Au from QD–Au hy...

Figure 10.15 Removal of Au from QD–Au hybrids using the coalescence of Au and A...

Figure 10.16 (a) Schematic illustration showing the extraction of Au from Au/Pt...

Figure 10.17 Extraction of Au from Au/Pt alloy nanoparticles using the coalesce...

Figure 10.18 (a) Cyclic voltammograms over alloy Au/Pt nanoparticles before and...

Figure 10.19 (a) TEM image, (b) HRTEM image, (c) SAED pattern, and (d) XRD patt...

Figure 10.20 (a and c) TEM images and (b and d) HRTEM images of PbSe–Au nanocom...

Figure 10.21 (a) TEM images and (b) HRTEM images of “pineapple‐like” PbSe–Au na...

Figure 10.22 Schematic illustration showing the synthesis of PbSe–Au nanocompos...

Figure 10.23 TEM images of PbSe–Au nanocomposites synthesized at PbSe/Au molar ...

Figure 10.24 Schematic illustration showing the synthesis of Ag

2

S–Pt nanocompos...

Figure 10.25 (a, c, e) TEM images and (b, d, f) histograms showing the size dis...

Figure 10.26 (a) TEM image, (b) HRTEM image, (c–g) nanoscale element mappings, ...

Figure 10.27 (a) Cyclic voltammograms of Ag

2

S–PtNCs/C and commercial Pt/C catal...

Guide

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E1

Noble Metal-Based Nanocomposites

Preparation and Applications

Jun Yang

Copyright

Author

Prof. Jun Yang

Institute of Process Engineering, CAS

1 North 2nd Street

Zhongguancun, Haidian District

100190 Beijing

China

Cover Image:

© ALFRED PASIEKA/SCIENCE

PHOTOLIBRARY/Science Photo

Library/Getty Images

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Print ISBN: 978‐3‐527‐34452‐9

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About the Author

Prof. Jun YANG was born in Hebei, China, in 1972. He received his Ph.D. in Chemical and Biomolecular Engineering in 2006 from the National University of Singapore (with Professor Jim Yang LEE). After postdoctoral research at Boston College and University of Toronto with Prof. Shana O. Kelley, he joined the Institute of Bioengineering and Nanotechnology, Singapore, in 2007. In 2010, he moved to the Institute of Process Engineering, Chinese Academy of Sciences, as the group leader of Materials for Energy Conversion and Environmental Remediation (MECER). He is also a joint professor of School of Materials Science and Opto‐Electronic Technology, University of Chinese Academy of Sciences. His main research interests include electrocatalysis, nanocomposites for energy conversion, synthesis and application of novel nanocrystalline materials, and separation techniques.

Preface

Nanocomposites consisting of noble metals and semiconductors or metal oxides represent an important type of heterogeneous nanostructures, which often exhibit improved physical and chemical properties than those of isolated individual nanoparticles. The enhancement might be attributed to the synergistic effect that occurs at the permanent inorganic interface of metal and semiconductor/metal oxide domains in the composite nanoparticles. Over the past two decades, there have been tremendous developments in the high degree of control over nanocomposites in terms of their domain size, morphology, and composition. Naturally, extensive applications emerge in the field of photocatalysis, as nanoscale sections of certain semiconductors or metal oxides combined with appropriate noble metals as cocatalysts could allow the photogenerated charge carriers to separate effectively for performing redox reactions with high efficiency. In addition, noble metal‐based nanocomposites would be particularly useful for electrocatalytic applications. Adjacent domains of semiconductors or metal oxides having different electron affinity and, appropriately, energy‐level alignments could either donate or withdraw electrons from the noble metal domains through the solid‐state interfaces of the nanocomposites, thus inducing the changes of the electron density around the metal atoms. The changes in electron density would tune the catalytic property of noble metals by altering the adsorption/desorption of reactants on the same.

Following the groundbreaking study made by the Banin group in 2004, who demonstrated a solution‐based synthesis of nanohybrids via the selective growth of gold tips on the apexes of hexagonal‐phase CdSe nanorods at room temperature, the efforts of many leading research groups have led to a rich variety of noble metal‐based nanocomposites, e.g. ZnO–Ag, ZnO–Au, ZnO–Au–Ni, CdS–Au, InAs–Au, TiO2–Ag, TiO2–Au, Fe3O4–Au, α‐Fe2O3–Au, Fe3O4–Ag, VO2–Au, MnO–Au, SiO2–Au, CuO–Ag, Cu2O–Ag, Cu2O–Au, CdO–Au, In2O3–Au/Ag, CoFe2O4–Ag, AgGaO2–Ag, Bi2S3–Au, CdSe–Au, CdTe–Au, CdSe–Ag, Ag2S–Au, Ag2S–Ag, AgBr–Ag, Cu2S–Au, Cu2−xSe–Au, PbS–Au, PbSe–Au, PbTe–Au, SnS–Au, ZnS–Au, ZnSe, CuInS2–Au, Cu2ZnSnS4–Au, Si–Au, and Pt, Pd, or other noble metal‐based composite nanosystems, by anisotropic growth of noble metals on semiconductor/metal oxides through photo‐ or thermal reduction. The accumulation creates great opportunities and also a tremendous challenge to apply these materials in diverse realms, e.g. optics, energy conversion/storage, and environmental remediation. We therefore prefer to devote this book to summarize the developments of solution‐based methods for the preparation of noble metal‐based nanocomposites and their characterization and potential applications in diverse catalysis so as to provide the readers with a systematic and coherent picture of the field. We hope that through this research effort, one can learn and expect the future progress in synthetic ability would open up access to new breeds of nanomaterials with multiple functionalities, which could enable optical, optoelectronic, magnetic, biomedical, photovoltaic, and specifically catalytic applications with a high level of performance.

The contents benefit greatly from the communications between the authors and colleagues and peers in a number of conferences and forums. We are grateful in particular to our staff/students: Dong Chen, Penglei Cui, Hui Liu, Jianglan Qu, Feng Ye, Junyu Zhong, Yan Feng, Pengfei Hou, Weiwei Hu, Chengyin Li, Jiaqi Li, Danye Liu, Jiayi Tang, and Linlin Xu, Niuwa Yang, and Hong Zhang, who took care of the format of figures and references, went through the details to correct the typos and to clarify many points in the presentation, and got all the copyright permissions. We are also indebted to all our colleagues/collaborators in research laboratories at the National University of Singapore, Boston College, University of Toronto, Institute of Bioengineering and Nanotechnology, and Institute of Process Engineering, Chinese Academy of Sciences. Without their helpful suggestions and valuable contributions, this book would not have been possible. Dr. Lifen Yang at Wiley‐VCH is particularly acknowledged for her initiation of this book. The writing of this book started with the beginning of the new semester and was fulfilled by the end of the summer holidays. The author thanks his wife Lijing Wang and sons Renxiao and Renzhe for their unending love and support and their understanding of why Dad was always not able to enjoy time with them.

September 2018

Jun Yang

Institute of Process Engineering

Chinese Academy of Sciences

University of Chinese Academy of Sciences

Beijing, China

Acknowledgments

The authors gratefully acknowledge the financial support from the 100 Talents Program of the Chinese Academy of Sciences, National Natural Science Foundation of China (Grant Nos.: 21173226, 21376247, 21476246, 21506225, 21506234, 21573240, 21706265, 21776292), the Center for Mesoscience, Institute of Process Engineering, Chinese Academy of Sciences (COM2015A001), State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences (MPCS‐2012‐A‐11, MPCS‐2017‐A‐02), National Natural Science Foundation of Beijing, China (Grant No.: 2173062), the importation and development of High‐Caliber Talents Project of Beijing Municipal Institutions (CIT&TCD201704049), the development of Beijing Excellent Talents Project (2016000026833ZK01), and the Technology Innovation Project of Beijing Municipal Institutions (KM201610020001).

List of Abbreviations

CA

chronoamperometry

CBS

cage‐bell structure

CZTS

Cu

2

ZnSnS

4

BSPCD

backward scan peak current density

BSPP

bis(

p

‐sulfonatophenyl)phenylphosphine or backward scan peak potential

CNT

carbon nanotubes

CTAB

cetyltrimethyl ammonium bromide

CVs

cyclic voltammograms

CVD

chemical vapor deposition

DDA

dodecylamine

DDAB

dodecyldimethylammonium

DENs

dendrimer‐encapsulated nanoparticles

DFAFC

direct formic acid fuel cell

DIBAL

diisobutylaluminumhydride

DIPEA

diisopropylethylamine

DMFC

direct methanol fuel cell

DSC

differential scanning calorimetry

ECSAs

electrochemically active surface areas

EDX

energy‐dispersive X‐ray spectroscopy

EGFRA

epidermal growth factor receptor antibody

EIS

electrochemical impedance spectroscopy

EPR

electron paramagnetic resonance

FAOR

formic acid oxidation reaction

FBS

fetal bovine serum

fcc

face‐centered cubic

FDTD

finite‐difference time‐domain

FSPCD

forward scan peak current density

FSPP

forward scan peak potential

FT‐IR

Fourier‐transform infrared

GSH

L

‐glutathione

GTMA

glutathione tetramethylammonium salt

HAADF

high‐angle annular dark‐field

HRTEM

high‐resolution transmission electron microscopy

ICO

indium‐doped cadmium oxide

ICP‐AES

inductively coupled plasma atomic emission spectroscopy

ILs

ionic liquids

LSPR

localized surface plasmon resonance

LUMO

lowest unoccupied molecular orbital

MBE

molecular beam epitaxy

MOR

methanol oxidation reaction

MPCs

monolayer‐protected clusters

MS

mass spectroscopy

MPA

3‐mercaptopropionic acid

MSA

mercaptosuccinic acid

MUA

mercaptoundecanoic acid

NIR

near‐infrared

NMR

nuclear magnetic resonance

NTs

nanotubes

NWs

nanowires

OA

oleic acid

OCV

open circuit voltage

ODA

octadecylamine

ODPA

octadecylphosphonic acid

OLA

oleylamine

ORR

oxygen reduction reaction

PBS

phosphate‐buffered saline

PEI

polyethylenimine

PEM

polymer electrolyte membrane

PVP

polyvinylpyrrolidone

QDs

quantum dots

ROS

reactive oxygen species

SAED

selected area electron diffraction

SERS

surface‐enhanced Raman scattering

SPR

surface plasmon resonance

STEM

scanning transmission electron microscopy

STM

scanning tunneling spectroscopy

TBAB

tetrabutylammonium borohydride

TBOT

tetrabutyl titanate

TBP

tributylphosphine

TDW

triple distilled water

TEA

trimethylamine

TEM

transmission electron microscopy

TEOS

tetraethyl orthosilicate

TGA

thermogravimetric analysis

TMAD

tetramethylammonium decanoate

TMNPs

transition metal nanoparticles

TOA

trioctylamine

TOAB

tetraoctylammonium bromide

TOF

turnover frequency

TOP

trioctylphosphine

TTAB

tetradecyltrimethylammonium bromide

UV–vis

ultraviolet–visible

VOCs

volatile organic compounds

XAFS

X‐ray absorption fine‐structure

XPS

X‐ray photoelectron spectroscopy

XRD

X‐ray diffraction

1An Introduction to Noble Metal‐Based Composite Nanomaterials

1.1 Materials at Nanometer Scales

Materials including semiconductors, metals, and oxides at nanometer scales, in terms of nanomaterials, nanoparticles, or nanocrystals with controlled sizes/morphologies, have garnered a great deal of research interest due to their immense potential for various applications, e.g. catalysis and photonics [1–19]. Owing to the quantum confinement effect and/or the large surface‐to‐volume ratio, the physical and chemical properties of materials at nanometer scale are usually dependent on size and shape [4,512–1420–25]. One typical example to indicate the size influence on the chemical property of nanometer materials is the catalytic reduction of p‐nitrophenol to p‐aminophenol over gold (Au) nanoparticles stabilized by cetyltrimethyl ammonium bromide (CTAB) with average sizes in the range of 3.5–56 nm. The results suggest that the activity of the CTAB‐stabilized Au nanoparticles is neither very efficient for the smallest particles (3.5 nm) nor for the larger ones (28 and 56 nm). Instead, it turns out that the CTAB‐stabilized Au nanoparticles of an intermediate size (13 nm) are the most active ones for the catalytic reduction of p‐nitrophenol to p‐aminophenol [26]. In addition, for noble metal nanoparticles with different shapes, they could display different activities for the same catalytic reaction due to their different crystallographic surfaces [2,3,512–14,27,28]. In other words, noble metal nanoparticles with different shapes often display quite different catalytic behaviors [12,13]. For instance, Wang and coworkers demonstrated that the monodispersed Pt nanoparticles with controlled sizes of 3–7 nm and shapes of polyhedron, truncated cube, or cube are active catalysts for the oxygen reduction reaction (ORR) in acidic medium. However, the measured current density for 7‐nm Pt nanocubes is four times that of 3‐nm polyhedral (or 5‐nm truncated cubic) Pt nanoparticles, manifesting a significant effect of particle shape on the oxygen reduction [8].

We are currently witnessing the impressive successes in preparation of materials at nanometer scale. Over the past decades, a vast number of wet‐chemistry approaches, including the reduction of appropriate precursors in solution phases [1429–34], in microemulsions [35], or in sol–gel processes [36], have been developed to obtain various nanoparticles with well‐defined sizes and shapes. Further, the size/shape control of the nanoparticles could also be achieved through control of the nucleation and growth by varying the synthetic parameters, including the activity of the reducing agents, the type and concentration of the precursors, and the nature and amount of surfactants or protective reagents [3337–43]. As an important noble metal used in a wide variety of catalytic applications, single‐crystalline platinum (Pt) nanoparticles with diverse shapes, as summarized in Figure 1.1, have been synthesized in the presence of a capping agent through reducing a Pt precursor, decomposing an organometallic complex, or combining these two routes such as hydrogenated decomposition of platinum(II) acetylacetonate (Pt(acac)2) [12].

Figure 1.1 Schematic illustration of different shapes of Pt nanocrystals derived from conventional single‐crystal polyhedrons enclosed by the low‐index planes {100} and {111}. The first column represents the perfect polyhedrons, while the second column contains the truncated forms of the perfect polyhedrons. The third and fourth columns compromise the overgrown nanostructures and highly branched nanostructures grown from the corners of the perfect polyhedrons, respectively. The yellow and blue colors represent the {100} and {111} facets, respectively.

Source: Chen et al. 2009 [12]. Adapted with permission of Elsevier.

Another common strategy used to generate nanomaterials with controlled sizes/shapes is the seed‐mediated growth method. The core particle in this case is overlaid with a single shell of another material to realize the preparation of nanoparticles with desired sizes/shapes [44–50]. The core of the nanoparticles could be subsequently removed by calcination or with a solvent for further tailoring of the particle structures [51–57]. As schematically shown in Figure 1.2, in a typical example, core–shell silver (Ag)–noble metals including ruthenium (Ru), rhodium (Rh), platinum (Pt), osmium (Os), iridium (Ir), and their alloys or core–shell–shell nanoparticles with Ag residing in the inner shell region were firstly synthesized in an organic solvent. The Ag was then extracted from the core or the inner shell by an aqueous solution of bis(p‐sulfonatophenyl)phenylphosphine, which binds strongly with Ag atoms or Ag+ ions to allow the complete removal of the Ag component, leaving behind an organosol of hollow‐ or cage‐bell‐structured noble metal nanoparticles [53].

Figure 1.2 Schematic illustration to show the synthesis of noble metal nanomaterials with hollow or cage‐bell structure based on the inside‐out diffusion of Ag in core–shell nanoparticles with Ag residing in the core or inner shell region.

Source: Liu et al. 2012 [53]. Adapted with permission of American Chemical Society.

1.2 Emergence of Composite Nanomaterials

After close to decades of intense effort in determining dominant experimental conditions, e.g. suitable precursors, templates, stabilizer molecules, relative concentration ratios, reaction media, and temperature, many nanoparticles can now be produced with fairly good control of sizes and shapes [58–64]. A number of nanoparticle geometries such as wires [65–70], rods [71–77], cubes [66,78,79], stars [80–83], disks [84–86], dendrites [87–94], and prisms [95,96] can be routinely synthesized by solution chemistry methods in polar and nonpolar environments. Following the extensive progress in synthetic control achieved for nanoparticles of metals, semiconductors, and oxides, naturally, there is an increased interest in producing more sophisticated nanostructures because of the promise of tunable properties for a new generation of technology‐driven applications in catalysis [97–100], chemical and biological sensing [101–105], and optics [100,106,107]. The increase in degree of complexity may mean increase in functionalities. As an example, the core–shell nanoparticles, in which an additional inorganic material is uniformly grown around a nanocrystal core, can be used to enhance the robustness and fluorescence efficiency of a semiconductor core [108–112], to tailor the magnetic properties of the overall particle [113,114], and also to provide a surface to which molecules can attach easily [115].

After remarkable successes in synthesizing more conventional hybrid nanomaterials, which are featured by their combination of same type of materials, e.g. core–shell [44116–121], alloy [122–135], and bimetallic heterostructures with controlled dimensions and intriguing morphologies [45,83,90,94136–141], there has been increasing interest devoted toward the development of composite nanomaterials (also called hybrid nanoparticles) that consist of different classes of materials with intimate contacts [142–161]. The lure of these composite nanostructures is that they combine disparate materials with distinctly different physical and chemical properties onto a single nanosystem, thus providing a powerful approach for the bottom‐up design of novel architectures. Beyond the fundamental development in synthesis, the interest in nanocomposites arises from their combined and synergistic properties exceeding the functionality of the individual components, which yield a unique hybrid platform with tunable optical properties [162–176], enhanced photocatalytic activities [177–187], ultrafast carrier dynamics [188–195], and photothermal therapy or cell destruction functions [196–198]. Furthermore, the interactions among their different domains can greatly improve the overall application performance of the nanocomposites. These ideas are well demonstrated by the application of metal‐based nanocomposites in photocatalysis. Upon ideal combination, the solid‐state interfaces among different domains in the nanocomposites can assist quick transfer of the photogenerated charge carriers from one to the other; and can delocalize the photoelectrons over the excited states of both metal and semiconductor or oxide, which in turn hinders carrier recombination, offering a better opportunity for their utilization in activating the chemical reactions [147,156,177,181,199,200]. Further, these composite materials also provide various combinations of facets on their surfaces, which can give rise to more chances for the substrate molecules getting adsorbed [147,201,202]. These advantages make these metal‐based nanocomposites more efficient photocatalysts than the only‐metal or semiconductor/oxide catalysts. For example, the metal ingredients in semiconductor–metal nanocomposites can enhance both the photocatalytic and light‐harvesting efficiencies of semiconductors by improving the charge separation and by increasing the light absorption [203–205]. In addition, as presented by Talapin et al., contrary to the n‐type lead sulfide (PbS) semiconductor, core–shell‐structured Au–PbS nanocomposites exhibit strong p‐type gate effects due to the intraparticle charge transfer between Au core and PbS shell regions. The energy‐level alignment of PbS and Au is favorable for the electron transfer from the highest occupied 1Sh quantum confined state of the PbS shell to the Au core, which is something like the injection of mobile holes into the PbS shell [206].

The early studies on noble metal‐based nanocomposites involve the deposition or doping of different noble metals (e.g. Au, Ag, and Pt) in titanium dioxide (TiO2) powders for photocatalytic applications [180207–213]. In these structures, the metal domain induces the charge equilibrium in photoexcited TiO2 substrates to affect the energetics of the nanocomposites by shifting the Fermi level to more negative potentials. The shift in Fermi level is indicative of improved charge separation in TiO2–noble metal systems, and is effective in enhancing the efficiency of photocatalysis [177,178,214,215].

As shown in Figure 1.3, the syntheses for most of the noble metal‐based nanocomposites were achieved after the year 2000. Indeed, only within the past two decades have wet chemistry methods blossomed and become a powerful approach toward the synthesis of composite nanomaterials [147,150,154,156159–161]. In 2004, the Banin group at the Hebrew University of Jerusalem, Israel, made a major breakthrough in fabricating semiconductor–metal nanocomposites [216]. They demonstrated a solution‐based synthesis for nanohybrids via the selective growth of Au tips on the apexes of hexagonal‐phase cadmium selenide (CdSe) nanorods at room temperature. The novel nanostructures display modified optical properties due to the strong coupling between the Au and semiconductor domains. The Au tips show increased conductivity, as well as selective chemical affinity for forming self‐assembled chains of rods. The architecture of these composite nanostructures is qualitatively analogous to bifunctional molecules such as dithiols, which provide two‐sided chemical connectivity for self‐assembly and for electrical devices, and contacting points for colloidal nanorods and tetrapods. The researchers in the Banin group later reported the synthesis of asymmetric semiconductor–noble metal heterostructures, whereby Au is grown on one side of the CdSe nanocrystalline rods and dots. Theoretical modeling and experimental analysis show that the one‐sided nanocomposites are transformed from the two‐sided architectures through a ripening process [217]. Subsequently, a large number of wet chemistry‐based approaches were developed for the synthesis of semiconductor or metal oxide–noble metal nanocomposites, e.g. ZnO–Ag [218–224], ZnO–Au [198225–230], ZnO–Au–Ni [231], CdS–Au [167,168,192,195232–249], InAs–Au [250,251], TiO2–Ag [252–256], TiO2–Au [257–267], Fe3O4–Au [268–280], α‐Fe2O3–Au [281,282], Fe3O4–Ag [283–285], VO2–Au [286], MnO–Au [287,288], SiO2–Au [170,289,290], CuO–Ag [187,291], Cu2O–Ag [172], Cu2O–Au [292–294], CdO–Au [295], In2O3–Au/Ag [173,296], CoFe2O4–Ag [297], AgGaO2–Ag [298], Bi2S3–Au [299], CdSe–Au [165,201300–312], CdTe–Au [313], CdSe–Ag [314], Ag2S–Au [163315–317], Ag2S–Ag [169,171,176318–321], AgBr–Ag [322,323], Cu2S–Au [324,325], Cu2−xSe–Au [326], PbS–Au [269327–329], PbSe–Au [330], PbTe–Au [331], SnS–Au [332], ZnS–Au [333–337], ZnSe [338], CuInS2–Au [339], Cu2ZnSnS4–Au [340,341], Si–Au [175,197,342,343], and Pt, Pd, or other noble metal‐based composite nanosystems [344–412], by anisotropic or epitaxial growth of noble metals on various semiconductors/metal oxides or vice versa through reduction, physical deposition, or photochemistry.

Figure 1.3 The main milestones in wet chemistry‐based syntheses of noble metal‐based composite nanomaterials.

We are interfacing a number of forefront research areas in this period of technology development. The invention and development in characterization and measurement techniques such as high‐resolution transmission electron microscopy (HRTEM) offer the opportunity to study in great detail and manipulate the nanostructures or nanomaterials often down to the atomic level, which enables us to establish the synthesis–structure–performance relationship and further direct the design of new materials with the desired performance. Noble metal‐based composite nanomaterials, which represent a powerful paradigm for bottom‐up construction of advanced materials, have emerged in the past decade, and their progress is expected to further continue and intensify in the coming years. The nanocomposites in their constituents are not new, and they are the combination of existing materials and our synthetic capability to manipulate at nanometer or atomic scale, which makes the composite nanomaterials so compelling from the scientific viewpoint.

1.3 General Concepts in Wet Chemistry Synthesis of Composite Nanomaterials

The understanding of the formation mechanism accounting for monodispersed nanoparticles is necessary because it is helpful to develop improved synthetic methods that can be universally applicable to various kinds of metal, semiconductor, and oxide materials.

For single materials, the study on preparing uniform colloidal particles could be dated back to the 1940s. LaMer and Dinegar proposed the concept of “burst nucleation” through investigating the preparation of a variety of oil aerosols and sulfur hydrosols [14,413,414]. In this process, they divided the formation of colloidal particles into three stages (Figure 1.4), and assumed that many nuclei are generated at the same time, and then these nuclei start to grow without the need for additional nucleation. Because all of the particles are nucleated almost simultaneously, their growth histories are nearly the same. This is the essence of the “burst‐nucleation” process, which makes it possible to control the size distribution of the ensemble of particles as a whole during the process of growth. Otherwise, if the nucleation process also occurs during the formation of particles, the growth histories of the particles would differ largely from one another, and would consequently make a great difference to the size distribution.

Figure 1.4 Plot of atomic concentration against time, illustrating the generation of atoms, nucleation, and subsequent growth.

Source: Adapted from Xia et al. [14] and Carbone and Cozzoli [413].

In the “burst‐nucleation” theory, it is necessary to induce a single nucleation event and prevent additional nucleation during the subsequent growth process for the preparation of highly uniform colloidal solution. This synthetic strategy, often referred to as “separation of nucleation and growth” has been extensively used to synthesize monodispersed semiconductor nanoparticles, e.g. CdSe and InAs [415,416]. The seed‐mediated growth method is the most apparent case for the separation of nucleation and growth, wherein nucleation is physically separated from growth using preformed nanoparticles as seed nuclei. This method utilizes heterogeneous nucleation to suppress the formation of additional nuclei by homogeneous nucleation [417–420]. In this method, the preformed nuclei, which have to be uniform in size, are introduced into the reaction solution and then the monomers, which refer to the highly reactive species generated as the synthesis is activated, are supplied to precipitate on the surface of the existing nuclei. The monomer concentration is kept low during growth to suppress homogeneous nucleation. Seed‐mediated growth is further divided into two categories: the synthesis of homogeneous particles [417,420] and the production of heterogeneous structures, such as core@shell structures [418,419].

In the growth stage of nanoparticles, the agglomeration or aggregation of small particles is inevitable in the absence of stabilizers as the thermodynamics favor the minimization of the surface/volume ratio. Alternatively, the surface energy can be well controlled by absorbing some capping agents [14,21,421]. The capping agents play several key roles during the synthesis of the nanoparticles. Indeed, they form complexes with the monomers, thereby tuning their reactivity, while they simultaneously participate in an adsorption/desorption dynamics at the surface of the growing clusters, which prevents them from aggregation and uncontrolled growth [143]. In this sense, knowledge and studies in surface science would be helpful in designing nanoparticles with desired sizes/shapes, which might be featured with specific facets. In addition, both thermodynamics and kinetics can affect the growth of metal nanoparticles. Compared with the growth tendency, which is determined by thermodynamics, the crystal growth paths are mainly dependent on the kinetics. Therefore, metal nanoparticles at various transition states that are metastable thermodynamically could be generated by carefully controlling the growth kinetics.

A number of suitable techniques have been developed to satisfactorily tailor the size and size distribution of nanoparticles through balancing the relative depletion of monomers between the nucleation and growth stages, e.g. hot injection, delayed nucleation, and digestive ripening [5422–430]. It is also noteworthy that the capping agents can affect the specific surface energy of the growing nanoparticles, which has important implications in the tuning of their shape [5,142,428]. In brief, facet‐preferential ligand adhesion can modify the relative growth rates along the various crystallographic directions and/or can favor the selective elimination of unstable surfaces by triggering oriented attachment of particles. In the absence of additional circumstances that can interrupt growth symmetry (e.g. the presence of foreign particle catalysts or the application of external electric or magnetic fields), the capping agents remain mostly responsible for the formation of nanoparticles in a variety of anisotropic shapes, such as cubes, polyhedrons, rods, wires, polypods, and rings [142,143].