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Y. Min et al.
remarkable impact on their catalytic properties [1–4]. In this sense, a lot of effort has
been devoted to understanding and tuning these characteristics. On the other hand,
supramolecular catalysis allows creating unique catalyst–substrate interactions that
can be tailored to direct substrates along particular reaction paths and selectivities
[5–7]. The assembly of metal NP could also permit to direct substrates, or to create
confined spaces in order to produce better catalysts. Nevertheless, the assembly of
metal NP has received relatively little attention for applications in catalysis. Several
approaches have been described for the directed self-assembly of metallic NP [8]
that involves manipulation of: (i) molecular interaction forces such as van der Waals
(vdW) [9], electrostatic interactions [10], zwitterion-type electrostatic interactions,
[11–14] hydrogen bonding, [15–19] host–guest interactions [20], or DNA-assisted
assemblies [21], and (ii) covalent interactions (i.e., coordination bonds, bifunctional
linkage), or external fields [22] (i.e., capillary forces, magnetic [23] and electric
field). Herein, we will focus on the creation of covalent interactions between NP,
since they may provide robust NP networks, which are desirable for applications
in catalysis. Covalent assemblies of metal NP have been obtained following several
methodologies: direct cross-linking methods, indirect cross-linking methods, and
stimuli-responsive reversible covalent networks of NP, which are described below.
Finally, their applications in catalysis are discussed.
5.2 Synthesis of Covalent Assemblies of Metal
Nanoparticles
We can distinguish two approaches for creating covalent bonds between metallic NP,
the direct and indirect cross-linking methods, described herein.
5.2.1 Direct Cross-Linking Methods
This section provides an overview of metal NP covalent assemblies through directed
linkage, i.e., the ligand molecules bearing two or more anchoring groups (dithiol,
dicarboxylic, etc.) bound on the surface of adjacent metal NP to establish various
dimensional networks (1-D, 2-D, 3-D). The covalent metal NP assemblies have
been investigated for more than thirty years. For a large portion of the research
reported, the synthesis process involved a ligand exchange procedure. Thus, a ditopic
ligand achieving cross-linking would replace the monofunctional ligand stabilizing
the isolated metal NP (monolayer-protected NP). Different methods can be used to
build covalent NP networks such as the layer-by-layer method (LBL), the two-phase
method, the one-phase method, Langmuir–Blodgett (LB) method, among others.
Among them, the first three methods (Fig. 5.1) are the most frequently employed
ones.
Y. Min et al.
remarkable impact on their catalytic properties [1–4]. In this sense, a lot of effort has
been devoted to understanding and tuning these characteristics. On the other hand,
supramolecular catalysis allows creating unique catalyst–substrate interactions that
can be tailored to direct substrates along particular reaction paths and selectivities
[5–7]. The assembly of metal NP could also permit to direct substrates, or to create
confined spaces in order to produce better catalysts. Nevertheless, the assembly of
metal NP has received relatively little attention for applications in catalysis. Several
approaches have been described for the directed self-assembly of metallic NP [8]
that involves manipulation of: (i) molecular interaction forces such as van der Waals
(vdW) [9], electrostatic interactions [10], zwitterion-type electrostatic interactions,
[11–14] hydrogen bonding, [15–19] host–guest interactions [20], or DNA-assisted
assemblies [21], and (ii) covalent interactions (i.e., coordination bonds, bifunctional
linkage), or external fields [22] (i.e., capillary forces, magnetic [23] and electric
field). Herein, we will focus on the creation of covalent interactions between NP,
since they may provide robust NP networks, which are desirable for applications
in catalysis. Covalent assemblies of metal NP have been obtained following several
methodologies: direct cross-linking methods, indirect cross-linking methods, and
stimuli-responsive reversible covalent networks of NP, which are described below.
Finally, their applications in catalysis are discussed.
5.2 Synthesis of Covalent Assemblies of Metal
Nanoparticles
We can distinguish two approaches for creating covalent bonds between metallic NP,
the direct and indirect cross-linking methods, described herein.
5.2.1 Direct Cross-Linking Methods
This section provides an overview of metal NP covalent assemblies through directed
linkage, i.e., the ligand molecules bearing two or more anchoring groups (dithiol,
dicarboxylic, etc.) bound on the surface of adjacent metal NP to establish various
dimensional networks (1-D, 2-D, 3-D). The covalent metal NP assemblies have
been investigated for more than thirty years. For a large portion of the research
reported, the synthesis process involved a ligand exchange procedure. Thus, a ditopic
ligand achieving cross-linking would replace the monofunctional ligand stabilizing
the isolated metal NP (monolayer-protected NP). Different methods can be used to
build covalent NP networks such as the layer-by-layer method (LBL), the two-phase
method, the one-phase method, Langmuir–Blodgett (LB) method, among others.
Among them, the first three methods (Fig. 5.1) are the most frequently employed
ones.