3
Moving Nanoparticles Around: Phase-Transfer
Processes in Nanomaterials Synthesis
M. Sastry
3.1
Introduction
We are witnessing impressive advances in understanding the unusual physicochemical and optoelectronic properties of nanomaterials, their synthesis, assembly
and packaging for commercial application [1]. One important area of nanotechnology is concerned with the development of reliable processes for the synthesis
of nanomaterials over a range of sizes (with good monodispersity) and chemical
compositions. Realizing that shape anisotropy could lead to interesting variation in
the electronic and catalytic properties of nanoparticles [2, 3], much current research is directed towards development of experimental methods for the synthesis
of nanoparticles of varying shapes. Nanorods and nanowires of silver [4, 5]/gold
[6–12]/Au-core–Ag-shell [13]/CdSe [14]/tungsten sulfide [15], nanoprisms of silver
[16]/gold [17, 18] and CdS [19] are some of the exotic nanocrystalline shapes that
may be routinely synthesized in the laboratory today. From a fundamental angle,
the ability to control the shape of nanocrystals is particularly exciting and has led to
the first observation of two distinct quadrupole plasmon resonance modes in silver
nanoprisms [16]. The need to develop eco-friendly synthesis protocols that do away
with the use of toxic chemicals has also fuelled research in this direction and biorelated processes that use microorganisms such as bacteria [20–23], fungi [24–27]
and actinomycete [28] have been developed to grow nanocrystals of silver and gold
both inside and outside the biomass.
Gold nanoparticles have, in particular, been the subject of considerable attention
over the ages and enjoy an interesting history dating back to the pioneering work
of Faraday on the synthesis of gold hydrosols (gold nanoparticles dispersed in
water) [29]. Gold nanoparticles find application in a variety of fields such as catalysis [30], as electron microscopy markers [31] and in DNA sequence determination. It is of little surprise, therefore, that there are many recipes for the synthesis
of gold nanoparticles over a range of sizes in an aqueous environment. The procedures for synthesis of gold hydrosols include, (1) reduction of aqueous chloroaurate ions by a variety of reducing agents such as citric acid [33], sodium borohydride [34], and alkaline tetrakis(hydroxymethyl)phosphonium chloride [35]; (2)
31
Moving Nanoparticles Around: Phase-Transfer
Processes in Nanomaterials Synthesis
M. Sastry
3.1
Introduction
We are witnessing impressive advances in understanding the unusual physicochemical and optoelectronic properties of nanomaterials, their synthesis, assembly
and packaging for commercial application [1]. One important area of nanotechnology is concerned with the development of reliable processes for the synthesis
of nanomaterials over a range of sizes (with good monodispersity) and chemical
compositions. Realizing that shape anisotropy could lead to interesting variation in
the electronic and catalytic properties of nanoparticles [2, 3], much current research is directed towards development of experimental methods for the synthesis
of nanoparticles of varying shapes. Nanorods and nanowires of silver [4, 5]/gold
[6–12]/Au-core–Ag-shell [13]/CdSe [14]/tungsten sulfide [15], nanoprisms of silver
[16]/gold [17, 18] and CdS [19] are some of the exotic nanocrystalline shapes that
may be routinely synthesized in the laboratory today. From a fundamental angle,
the ability to control the shape of nanocrystals is particularly exciting and has led to
the first observation of two distinct quadrupole plasmon resonance modes in silver
nanoprisms [16]. The need to develop eco-friendly synthesis protocols that do away
with the use of toxic chemicals has also fuelled research in this direction and biorelated processes that use microorganisms such as bacteria [20–23], fungi [24–27]
and actinomycete [28] have been developed to grow nanocrystals of silver and gold
both inside and outside the biomass.
Gold nanoparticles have, in particular, been the subject of considerable attention
over the ages and enjoy an interesting history dating back to the pioneering work
of Faraday on the synthesis of gold hydrosols (gold nanoparticles dispersed in
water) [29]. Gold nanoparticles find application in a variety of fields such as catalysis [30], as electron microscopy markers [31] and in DNA sequence determination. It is of little surprise, therefore, that there are many recipes for the synthesis
of gold nanoparticles over a range of sizes in an aqueous environment. The procedures for synthesis of gold hydrosols include, (1) reduction of aqueous chloroaurate ions by a variety of reducing agents such as citric acid [33], sodium borohydride [34], and alkaline tetrakis(hydroxymethyl)phosphonium chloride [35]; (2)
31