Hollow inorganic nanoparticles

Long hollow inorganic nanoparticle nanotubes with a nanoscale brick wall structure of clay mineral platelets have been... 

Figure 11.1 (a) Soft-templating and (b) hard-templating routes to hollow inorganic nanoparticles. 

The sacrificial core approach entails depositing a coating on the surface of particles by either the controlled surface precipitation of inorganic molecular precursors from solution or by direct surface reactions [2,3,5,6,8,9,33-35,38], followed by removal of the core by thermal or chemical means. Using this approach, micron-size hollow capsules of yttrium compounds [2], silica spheres [38], and monodisperse hollow silica nanoparticles [3,35] have been generated. 

Inorganic nanoparticles themselves can be assembled into mesoscopic structures. Dinsmore et al. proposed an approach for the fabrication of solid capsules from colloidal particles with precise control of size, permeability, mechanical strength, and compatibility (Fig. 2.9).44 This unusual mesoscopic structure is called colloidosome and is prepared through emulsion droplets at a water-oil interface. Following the locking together of the particles to form elastic shells, the emulsion droplets were transferred to a fresh continuous-phase fluid identical to that contained inside the droplets. The resultant structures are hollow, elastic shells whose permeability and elasticity can be precisely controlled. 

In addition to applications as surfactants and in personal care prodncts, block copolymer micelles have been extensively investigated as nanoparticles for solubilizing active agents for drug delivery (100,101,126,127), or as nanoreactors for the production of inorganic nanoparticles, eg, of metals with potential applications in catalysis (128,129). An alternative approach is to form vesicles (bilayers wrapped round into a spherical shell) (130,131). These may be cross-linked or polymerized to form hollow shell nanoparticles (132-134). 

Emulsified droplets and micelles/vesicles formed by surfactant and amphiphilic block copolymers are often used as soft templates (Figure 11.1a). An inorganic shell can be formed on these templates if certain attractive interactions exist between the inorganic species and template surfeces. Pickering emulsions -emulsions stabilized by inorganic nanoparticles instead of amphiphilic molecules -can be converted to hollow particles by connecting the nanoparticles to each other. The templates are finally removed by solvent extraction, calcination, or simple... 

Fuji, M Shin, T., Watanabe, H., and Takei, T. (2012) Shape-controlled hollow silica nanoparticles synthesized by an inorganic particle template method. Adv. Powder TechnoL, 23, 562-565. 

Li Q, Walter EC, van der Veer WE, Murray BJ, Newberg JT, Bohannan EW, Switzer JA, Hemminger JC, Penner RM (2005) Molybdenum disulfide nanowires and nanoribbons by electrochemical/chemical synthesis. J Phys Chem B 109 3169-3182 Tenne R, Homyonfer M, Feldman Y (1998) Nanoparticles of layered compounds with hollow cage structures (inorganic fuUerene-like structures). Chem Mater 10 3225-3238 Shibahara T (1993) Syntheses of sulphur-bridged molybdenum and tungsten coordination compounds. Coord Chem Rev 123 73-147... 

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