Ultraviolet/visible nanoparticles

A potentially new separation method called held flow fractionation has been introduced only on a preliminary basis for the determination of adsorbed substances to particles [182]. A novel method was developed by Ilium et al. [68] to determine both free and bound drug on PBCA nanoparticles without prior separation. For example, a bathochromic shift was observed in the ultraviolet/visible (UV/vis) spectrum of Rose Bengal after binding to PBCA nanoparticles. The amount of free drug was determined at 540 nm and bound drug at 548 nm. This type of analysis is very specific to the drug under investigation. 

Coreduction of Mixed Ions. Coreduction of mixed ions is the simplest method to synthesize bimetallic nanoparticles. However, this method cannot be always successful. Au/Pt bimetallic nanoparticles were prepared by citrate reduction by Miner et al. from the corresponding two metal salts, such as tetrachloroauric(III) acid and hexachloroplatinic(IV) acid (24). Reduction of the metal ions is completed within 4 h after the addition of citrate. Miner et al. studied the formation of colloidal dispersion by ultraviolet-visible (UV-Vis) spectrum, which is not a simple sum of those of the two monometallic nanoparticles, indicating that the bimetallic nanoparticles have an alloy structure. The average diameter of the bimetallic nanoparticles depends on the metal composition. By a similar method, citrate-stabilized Pd/Pt bimetallic nanoparticles can also be prepared. 

Further, Wu et al. (2004) exploited radiation chemical technique to synthesize CdS/polystyrene nanocomposite hollow spheres with diameters between 240 and 500 nm under ambient conditions in which the polymerization of styrene and the formation of CdS nanoparticles were initiated by y-irradiation. It was demonstrated that the walls of the hollow spheres were porous and composed of polystyrene containing homogeneously dispersed CdS nanoparticles (Figure 23.14). The quantum-confined effect of the CdS/polystyrene nanocomposite hollow spheres was confirmed by the ultraviolet-visible (UV-vis) and PL spectra. They proposed that the walls of these nanocomposite hollow spheres originated from the simultaneous synthesis of polystyrene and CdS nanoparticles at the interface of microemulsion droplets. 

T.R. Jensen, G.C. Schatz, and R.P. Van Duyne, Nanosphere lithography Surface plasmon resonance spectrum of aperiodic array of silver nanoparticles by ultraviolet-visible extinction spectroscopy and electrodynamic modeling, J. Phys. Chem. B, 103(13), 2394—2401 (1999). 

The final section Part IV is concerned with physical properties of polymeric nanocomposites (PNCs). Two types of nanoparticles, leading to two different characters and applicabilities of PNC, are discussed layered silicates (with natural or synthetic clays), used in structural-type PNCs and the others used in functional PNCs. Sender et al. in Chapter 13 describe the performance of PNCs with acicular ferroelectric particles producing PNCs with good electroactive (dc conductivity) and mechanical properties. In Chapter 15, Nicolais and Carotenuto focus on metal clusters in polymeric matrices, which combine optical transparency with magnetism, luminescence. Ultraviolet-visible absorption, thermochromism, and so on. 

Microscopy (TEM), UltraViolet-Visible (UV-vis) Spectroscopy, Nuclear Magnetic Resonance (NMR) Spectroscopy, and Fourier Transform Infrared (FTIR) Spectroscopy are among others deeply used and X-ray Photoelectron Spectroscopy (XPS) has become an increasingly available and powerful tool for imderstanding the nature of different surfaces and chemical and electronic structure of functionalized molecules or polymers upon coordination for example of metallic nanoparticles or biological systems. 

Presence of silicon hydride groups grafted to the silica surface was confirmed by Fourier transform infr ed (FTIR) spectra data (NEXUS FT-IR) Nanoparticles of metals were recorded using x-ray powder diffraction (DRON-4-07, CuK(j-radiation). Ultraviolet-visible (UV-Vis) spectra of metal-containing composites were recorded on Carl Zeiss Jena spectrophotometer. 

Particles are known to scatter light as well as absorb it and this produces the white or pale appearance of fine powders. The even smaller nano-sized particles, however, are transparent because the scattering efficiency is reduced. This effect has led to the use of nanoparticles in sunscreens and cosmetics. These will still absorb ultraviolet light but will scatter less visible light. 

Nanoparticles in the form of quantum dots are reaching a mature stage in the development of medical applications. Their fluorescent yields are in the visible and infrared. They outperform organic dyes in the narrow emission linewidths, they have the capability to excite a wide range of useful emissions with a single ultraviolet (UV) excitation, and they are resistant to photobleaching. 

The ultraviolet (UV) - visible spectrophotometer is another important tool in the characterisation of vegetable oil-based polymer nanocomposites and is particularly effective for metal nanocomposites. The formation of metal nanoparticles in the matrix can be easily detected by UV-visible spectroscopy. Every metal nanoparticle has its own characteristic surface plasmon resonance value. This band is attributed to the collective oscillation of electron gas in the nanoparticles, with a periodic change in the electronic density at the surface. Parameters such as particle size, shape and dielectric constant of the medium and surface adsorbed species determine the position and shape of the plasmon absorption. When the particles become significantly smaller than the mean free path of electrons in the bulk metal, the plasmon oscillation is dampened. The plasmon absorption peak shifts to a higher wavelength than expected with an increase in aggregation of the nanoparticles. The sharpness of the peak indicates the narrow size distribution. 

SiO nanoparticle has features of small particle size, narrow particle size distribution, porous, large surface area and owns a large number of hydroxyl groups and unsaturated residual bonds on its surface and shows high reflectivity to long wave, visible light and ultraviolet ray [36]. 

Polyaniline-ZnO nanocomposites were synthesized by in-situ oxidative polymerization of aniline monomer in the presence of different amounts of ZnO nanostructures. ZnO nanostructures were prepared in the absence and presence of surfactant. The effect of ZnO nanostructure concentration on the conducting behaviour of nanocomposites was evaluated by a two-probe method. The results showed that the conductivity of nanocomposites was increased with an increased concentration of ZnO nanostmctures as compared with neat polyaniline. Optimum conductivity was observed with incorporation of 60% ZnO nanostructures into the polyaniline matrix [248].Polymethylmethacrylate-ZnO nanocomposites were fabricated by solution radical copolymerization of methyl methacrylate and oleic acid-modified ZnO nanoparticles using 2,2 -azobisisobutylonitile as initiator in toluene. The UV-vis analysis showed that resulting nanocomposites exhibited high absorption in the ultraviolet region and low absorption in the visible region [249]. 

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