Nanomaterials core-shell

The Stober method can be used to form core-shell silica nanoparticles when a presynthesized core is suspended in a water-alcohol mixture. The core can be a silica nanoparticle or other types of nanomaterials [46, 47]. If the core is a silica nanoparticle, before adding silicon alkoxide precursors, the hydroxysilicates hydrolyzed from precursors condense by the hydroxide groups on the surface of the silica cores to form additional layers. If the core is a colloid, surface modification of the core might be necessary. For example, a gold colloid core was modified by poly (vinylpyrrolidone) prior to a silica layer coating [46]. 

Figure 5 shows two typical core-shell structures (a) contains a metal core and a dye doped silica shell [30, 32, 33, 78-85] and (b) has a dye doped silica core and a metal shell [31, 34]. There is a spacer between the core and the shell to maintain the distance between the fluorophores and the metal to avoid fluorescence quenching [30, 32, 33, 78-80, 83]. Usually, the spacer is a silica layer in this type of nanostructures. Various Ag and Au nanomaterials in different shapes have been used for fluorescence enhancement. Occasionally, Pt and Au-Ag alloys are selected as the metal. A few fluorophores have been studied in these two core-shell structures including Cy3 [30], cascade yellow [78], carboxyfluorescein [78], Ru(bpy)32+ [31, 34], R6G [34], fluorescein isothiocyanate [79], Rhodamine 800 [32, 33], Alexa Fluor 647 [32], NIR 797 [82], dansylamide [84], oxazin 725 [85], and Eu3+ complexes [33, 83]. 

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. 

Synthesis forms a vital aspect of the science of nanomaterials. In this context, chemical methods have proved to be more effective and versatile than physical methods and have therefore, been employed widely to synthesize a variety of nanomaterials, including zero-dimensional nanocrystals, one-dimensional nanowircs and nanotubes as well as two-dimensional nanofilms and nanowalls. Chemical synthesis of inorganic nanomaterials has been pursued vigorously in the last few years and in this article we provide a perspective on the present status of the subject. The article includes a discussion of nanocrystals and nanowires of metals, oxides, chalcogenides and pnictides. In addition, inorganic nanotubes and nanowalls have been reviewed. Some aspects of core-shell particles, oriented attachment and the use of liquid-liquid interfaces are also presented. 

When HRTEM is used for examining nanoparticles of oxides, in which the proportion of surface area greatly increases, most structural information concerns the surface. For example, HRTEM images of core-shell quantum dots can show the shell structure and its thickness directly. HRTEM images of metal oxide nanotubes can also be regarded as surface profile images. The appHcation of TEM in nanomaterials will be further discussed below. 

Two different nanomaterials, namely colloidal core / shell Quantum Dots (QDs) and Quantum Rods (QRs) were synthesized as described in [51]. In the case of CdSe / ZnS QDs, the synthesis yielded samples emitting at Inux = 580 nm widi a spectral width of the fluorescence emission of 40 nm. CdSe quantum rods showed an emission peak centered at l x = 567 nm with similar linewidth. The NCs were subsequently dispersed in PMMA and deposited onto the substrate by spin-coating. In order to study tiie influence of the average fluorophore-metallic surface distance on the MEF efi t, several thicknesses of the active layer were investigated, finding an o(Aimum value of 35 nm, as measured from the surface of the metallic nanostructures. 

Bimetallic nanomaterials Currently used monometallic SERS tags such as gold and silver NPs have a main drawback in that the metal surface is unprotected. The assays are therefore unreliable as components of the analyte can adsorb on the metal surface, leading to the possibility of replacing the label species. One way to overcome this problem is to encapsulate the metal particle/label molecule in a protective shell. Bimetallic nanostructures, with two different metals in a single particle, such as core-shell-type nanomaterials are gaining importance as Raman tags [1]. 

Typically, core/shell magnetic nanomaterials synthesized according to steps of Subheading 3.1 consist predominantly of a magnetite core with a mean crystallite size of 9-11 nm that can be calculated from the broadening of the X-ray... 

The further study of Cho et al. [107] has showed that the structure of Fe/Au core/shell nanomaterials is somewhat complex. Mossbauer spectra were best interpreted as Fe speciation of a-Fe, Fe11, Fem and Fe-Au alloy. The Au shell was suggested to grow by nucleating from small nanoparticles on the Fe-core surface before it develops the shell structure. These nanoparticle nucleation sites form islands for the growth and coalescence... 

The core-shell polyelectrolyte brushes can serve as the one-dimensional templates for different nanomaterials since different metal ions or small molecules can be... 

Song et al. [67] prepared PLA/CNT nanocomposites by one step based on in situ polycondensation of the commercially available lactic acid monomer in the presence of purified CNTs. The TEM image (Fig. 11.5) of core/shell nanostructures clearly indicates that the coating of grafted polymer was uniform both on the CNT s sidewall and tip. It was suggested that the incorporation of CNT into PL A will improvement its solubility and biocompatibility as it may promise a good future in biomedical systems and the development of bio-nanomaterials. The researchers also suggested that the current method of PLA/CNT nanocomposites preparation should be favored in industrialization as it takes less steps and cheaper. 

---