ABSTRACT
Only a few reports are available in the area of nanolarvae. Thus, the shape-controlled Cu-In sul£de heterostructured nanocrystals were synthesized by thermal decomposition of a mixture of Cu-oleate and In-oleate complex in dodecanethiol.1,2 Varying the reaction temperature and time, it was possible to prepare Cu-InS nanocrystals not only with larva (Figure 8.1) but also with acorn and bottle shapes. Precisely when the reaction was carried out for 1 h at 250°C, the Fannia canicularis larvashaped nanocrystals (nanolarvae) of 45 nm × 185 nm were produced (composition CuIn1.30S1.24). The following Reaction 8.1 was established to be responsible for the production of Cu2S nanocrystals; the formation mechanism was discussed including generation of Cu2S seeds, and subsequent growth of indium sul£de (In2S3) occurred on these seeds via a so-called seed-mediated growth mechanism. The authors proved that the initially formed polydisperse Cu2S nanoparticles were aggregated via a process similar to the oriented attachment mechanism, and subsequent incorporation of In2S3 species-generated larva-shaped nanostructures with a constant Cu/In atomic ratio:
C H SH Cu-OC O -C H Cu S C H C O OH C H12 25 17 33 2 17 33 12 242 2+ == → + == +( ( ) ( ) (8.1)
In contrast to larva-like nanostructures, “nanoworms”3 (or nanostructures with worm-like pores) are much more widespread in nanotechnological reports and represented, as well as other lesscommon nanoforms, mainly by inorganic metal oxides and salts, although elemental nanoworms (metals or nonmetals, alone or supported on composites) have also been obtained. Among them, gold nanostructures with different morphologies including spheres, rods, and worm-like nanostructures (Figure 8.2) were prepared by a three-step process treating an aqueous solution of chloroauric acid with sodium citrate and poly(vinyl pyrrolidone) (PVP).4 Two possible growth mechanisms were proposed in the formation of these worm-like particles: the £rst is related to the stage of formation of nanorods from spherical colloids, and the second described the formation of worm-like particles from nanorods. Au catalysts were supported on wormhole hexagonal mesoporous silica (HMS) for the CO oxidation reaction, and the effect of support modi£cation with cerium on the catalysts for this reaction was studied.5 The highest activity of the Au/Ce-HMS catalyst in CO oxidation was associated with its higher gold dispersion and larger degree of coverage of HMS by CeO2, thereby increasing the effectiveness of oxygen mobility. The in–uence of 20 kHz ultrasound waves of high intensity (40 W/cm2) on preformed citrate-protected gold nanoparticles (GNPs) (25 nm) in water and in the presence of surfactants6 after 60 min of sonication led to a worm-like or ring-like structure. This effect could be of interest for ultrasonic melting of inorganic materials on a nanoscale to produce metal structures with different morphologies and properties.
