Hollow nanospheres

Even though Ti02-based materials have been far more investigated than any other photocatalyst and this chapter is dedicated to these systems, it is important at least to mention here some of the promising alternative materials studied for wastewater treatment. CdS hollow nanospheres were prepared in a single-step hydrothermal route by Li et al. [109] using the ionic liquid l-butyl-3-methylimidazolium... 

Li, X., Gao, Y., Yu, L., and Zheng, L. (2010) Template-free synthesis of CdS hollow nanospheres based on an ionic liquid assisted hydrothermal process and their application in photocatalysis. Journal of Solid State Chemistry, 183 (6), 1423-1432. 

Preparation of Cu20 hollow nanospheres under reflux conditions. European Journal of Inorganic Chemistry, 3841-3844. 

Cao, C., Cui, Z., Chen, C., Song, W. and Cai, W. (2010) Ceria hollow nanospheres produced by a template-free microwave-assisted hydrothermal method for heavymetal ion removal and catalysis. Journal of Physical Chemistry C, 114, 9865-9870. 

Figure 6.4 The preparation of nanostructured materials in solution evolves from (a) the classic examples of suspension, dispersion, or emulsion polymerization, to the methods that include the covalent crosslinking of select domains within supramolecular polymer assemblies (b) core crosslinking of polymer micelles (c) shell crosslinking of polymer micelles (SCKs) (d) nanocages from core-eroded SCKs (e) shaved hollow nanospheres from outer shell/core-eroded vesicles.

Figure 6.5 Illustrations of nanoscale spherical assemblies resulting from block copolymer phase separation in solution are shown, along with the chemical compositions that have been employed to generate each of the nanostructures (a) core crosslinked polymer micelles (b) shell crosslinked polymer micelles (SCKs) with glassy cores (c) SCKs with fluid cores (d) SCKs with crystalline cores (e) nanocages, produced from removal of the core of SCKs (f) SCKs with the crosslinked shell shielded from solution by an additional layer of surface-attached linear polymer chains (g) crosslinked vesicles (h) shaved hollow nanospheres produced from cleavage of the internally and externally attached linear polymer chains from the structure of (g)...

The advances in nanotechnology and synthesis methods have enabled nanomaterials to be produced in various shapes and structures. Coating of a luminescent layer activated by lanthanide ions on nanoparticles such as SiC>2 or AI2O3 is one of such approaches to develop new nanophosphors. In section 6, we review recent work on interesting spectroscopic features and luminescence dynamics of lanthanide ions in other novel low-dimensional nanostructures including core-shell, one-dimensional (ID) nanowires and nanotubes, two-dimensional (2D) nanofilms, hollow nanospheres, 2D nanosheet and nanodisk which have also attracted extensive attention. 

It is possible to alter the intrinsic properties of materials by chemical nanocoating, which cannot be achieved by conventional methods. Generally the core-shell nanostructures are divided into two categories (1) lanthanides doped in the core (2) lanthanides doped in the shell. The former are synthesized in order to improve the quantum efficiency of lanthanide ions or design bio-labels, while the latter are meant for the study of surface modifications on the lanthanide luminescence or the synthesis of lanthanide-doped hollow nanospheres. 

Liu et al. synthesized hollow nanospheres of Eu Y2C>3 (20 nm shell thickness) by etching SiC /Y2O3 Eu core-shell nanoparticles with NaOH solution (Liu and Hong, 2005). No significant difference in emission spectrum was observed for both the hollow nanospheres and their core-shell counterparts. 

Zhou P, Li Y, Sun P, Zhou J, Bao J (2007) A novel Heck reaction catalyzed by Co hollow nanospheres in ligand-free condition. Chem Commun 1418-1420... 

By using polymer-controlled growth in ethylenediamine at 170°C, very long CdS nanowires (100px40 nm) were synthesized (Fig. 9a) [36]. Cadmium sulfide with different morphologies, such as nanoparticles and nanorods (Fig. 9b) [39], peanut-like nanostructures [37] and hollow nanospheres [38] (Fig. 9c) were prepared via solvothermal routes. 

In order to improve the kinetics of the Li-N-H system, Xie et al. [96] prepared Li2NH hollow nanospheres by plasma metal reaction based on the Kirkendall effect. The special nanostructure showed significantly improved hydrogen storage kinetics compared to that of the Li2NH micrometer particles. The absorption temperature decreased markedly, and the absorption rate was enhanced dramatically because... 

Fig. 15.24. Schematic depiction of the polymerization of monomers within the vesicle bilayer leading to the formation of hollow nanospheres. (Reprinted with permission from Langmuir, 1998, 14, 1031. 1998 American Chemical Society [87].)...

Coupling reactions. Hollow nanospheres of cobalt can substitute for Pd species in Sonogashira coupling. The catalyst system still contains Cul, Ph3P, and K2C03. ... 

G.Z. Shen, D. Chen, K.B. Tang, Y.T. Qian, and S.Y. Zhang, Silicon carbide hollow nanospheres, nanowires and coaxial nanowires, Chem. Phys. Lett., 375,177-184(2003). 

PbS hollow nanospheres with diameters of 80-250 nm have been synthesized by a surfactant-assisted sonochemical route from Pb(CH3COO)2, thioacetamide, and sodium dodecylbenzenesulfonate [3]. 200-400 nm hollow silica spheres with mesoporous walls were prepared by the application of ultrasound to a mixture of nonionic polyoxyethylene surfactant and tetraethylorthosilicate. The presence of surface-active agents during ultrasonic synthesis was proved to be effective because surfactants can act as soft templates as well as structure directing agents for the assembly and subsequent... 

Spherical, and size) of the nanopores in the mesoporous silica defines the width of the polymer distribution. This approach, in which the polymers are degraded to convert them to carbon and the silica template is dissolved, permits the preparation of ordered arrays of hollow nanospheres and nanotubes. 

D.M. Cheng, X. Zhou, H. Xia, and H.S.O. Chan, Novel method for the preparation of polymeric hollow nanospheres containing silver cores with different sizes, Chem. Mater., 17(14), 3578-3581 (2005). 

Hu, Y, Chen, Y, Chen, Q., Zhang, L., Jiang, X., and Yang, C. Synthesis and stirnuU-responsive properties of chitosan/poly(acrylic acid) hollow nanospheres. Polymer, 46(26), 12703-12710 (2005). 

It is worth noting that the boundaries between numerous bottom-up approaches are sometimes ambiguous, so combining multiple approaches to obtain desirable or complex nanostructures is often necessary. For example, the colloidal process is often combined with template-assisted self-assembly to produce hollow nanospheres and other complex structures [42,43]. This versatility of bottom-up approaches opens many opportunities to fabricate a myriad of nanomaterials with extraordinary properties. 

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