Nanoparticle hollow

Keywords. Self-organization, Nanoparticles, Hollow spheres, Mesoporous materials. Liquid crystals, Morphosynthesis, Kinetic models. Surfactant templating... 

Although lots of methodologies for MOP synthesis have been explored, only little attention has been paid to MOPs with controllable micromorphology. There are only a few reports of MOPs with tunable micromorphology such as nanoparticles,hollow capsules, 2D films and monoliths. 

The carbon-arc plasma of extremely high temperatures and the presence of an electric field near the electrodes play important roles in the formation of nanotubes[ 1,2] and nanoparticles[3]. A nanoparticle is made up of concentric layers of closed graphitic sheets, leaving a nanoscale cavity in its center. Nanoparticles are also called nanopolyhedra because of their polyhedral shape, and are sometimes dubbed as nanoballs because of their hollow structure. 

Filled nanocapsules, as well as hollow nanoparticles, are synthesized by the dc arc-evaporation method that is commonly used to synthesize fullerenes and... 

Fig. 2. A model of growth processes for (a) a hollow nanoparticle and, (b) a nanotube curved lines depicted around the tube tip show schematically equal potential surfaces.

Nanotechnology has led to very efficient versions of liposomes. Tiny hollow spheres only nanometers in diameter hold even tinier capsules of medicine. The spheres are made of silica covered with gold nanoparticles and when they are coated with antibodies they attach to tumor cells. The spheres are sensitive to light of specific wavelengths and when the light is applied, either heat up and destroy the tumor, or burst, releasing the drugs within the capsules directly into the tumor. 

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. 

Another method to synthesize hollow nanocapsules involves the use of nanoparticle templates as the core, growing a shell around them, then subsequently removing the core by dissolution [30-32]. Although this approach is reminiscent of the sacrificial core method, the nanoparticles are first trapped and aligned in membrane pores by vacuum filtration rather than coated while in aqueous solution. The nanoparticles are employed as templates for polymer nucleation and growth Polymerization of a conducting polymer around the nanoparticles results in polymer-coated particles and, following dissolution of the core particles, hollow polymer nanocapsules are obtained. 

FIG. 10 SEM micrographs of (a) sUica nanoparticle/polymer [Si02/PDADMAC)3]-coated PS lat-ices and (b) hollow silica capsules. The hollow sUica capsules were obtained by calcining coated particles as shown in (a). The calcination process removes the PS core and the polymer bridging the silica nanoparticles, while at the same time fusing the silica nanoparticles together. Some of the silica capsules were deliberately broken to demonstrate that they were hollow (b). (From Ref. 106.)... 

FIG. 13 TEM micrograph of a hollow composite nanoparticle/polymer capsule dried on a carbon grid. The hollow composite capsule was obtained after removal of the ME core from Si02/PDAD-MAC-coated ME particles by treatment with hydrochloric acid. The shadowing seen is a result of collapse and overlapping of the hollow capsule upon drying. (From Ref. 110.)... 

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... 

By changing the ultrasound power, changes in the mesoporosity of ZnO nanoparticles (average pore sizes from 2.5 to 14.3 nm) have been observed. In addition to the changes in mesoporosity, changes in the morphology have also been noted [13]. Recently, Jia et al. [14] have used sonochemistry and prepared hollow ZnO microspheres with diameter 500 nm assembled by nanoparticles using carbon spheres as template. Such specific structure of hollow spheres has applications in nanoelectronics, nanophotonics and nanomedicine. 

Wong, M.C., Cha, J.N., Choi, K.S., Deming, T.J. and Stucky, G.D. (2002) Assembly of nanoparticles into hollow spheres using block copolypeptides. Nano Letters, 2, 583—587. 

Figure 14.24 Fluorescent silica nanobubbles have been created using gold nanoparticle seeds that initially are coated by adsorption with a fluorescent dye. The particles then are capped by a layer of silica by polymerizing TEOS and entrapping the dye molecules within it. Finally, the gold core is dissolved by reaction with cyanide, leaving behind hollow fluorescent silica nanobubbles.

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