Well-dispersed nanoparticles

Yu, K.M.K., Steele, A.M., Zhu, J Fu, Q.J. and Tsang, S.C. (2003) Synthesis of well-dispersed nanoparticles within porous solid structures using surface-tethered surfactants in supercritical CO2-Journal of Materials Chemistry, 13 (1), 130-134. 

The applicability of this technique is limited to metal hydroxides or carbonates that can be co-precipitated with Au(OH)g. Gold can be supported in the form of well-dispersed nanoparticles, by CP, on a-Fe203, C03O4, NiO and ZnO, but not on Ti02, Cr203, MnO, and CdO [28]. 

Although, the reasons for the catal3dic activity of gold are not as yet fully understood, the presence of gold as well-dispersed nanoparticles (<10nm)... 

In conclusion, the treatment of supported catalysts in an aqueous medium seems therefore unfavorable to the presence of well dispersed nanoparticles. Nevertheless, an in situ reduction of the parent catalyst allows one to prevent or restrict metal sintering, depending on the nature of the support. However, in the absence of any contact of the catalyst with air, many parameters can also influence the metal particle size. Then, for example it is better to avoid especially very acidic (pH 2) or very basic (pH 10) solutions [13, 72]. 

Figure 39.4 shows the effect of urea addition on the morphology and nanoparticle formation of YAH (hexagonal YAIO3, an intermediate phase of YAG). The urea-nitrate ratio, in which the nitrate represents the precursor solution, was varied from 0 to 30. Figure 39.4a shows that most of the particles prepared from a precursor without a urea addition were in the submicron size (400-700 pm) with a small amount of nano-sized particles. When 1 M of urea (urea-nitrate ration is 10) was added, the quantity of nanoparticles increased while the size of larger particles was reduced. Well-dispersed nanoparticles, with an average size of 20 nm, were produced from the addition of 2 M urea in the nitrate precursor, as shown in Fig. 39.4c. The addition of more than 2 M of urea produced nanoparticles with an agglomerated morphology, as shown in Fig. 39.4d (urea addition of 3 M). These results show that the addition of 2 M urea into 0.1 M nitrate precursor is an effective way to produce...

Figure 9.28 Transmission electron microscopy (TEM) images of (a) BaTiOj, (b) PBTll along with SAED patterns (inset) and HRTEM images of (c) BaTiOj, (d) PBTl 1 along with lattice spacing, show well-dispersed nanoparticles of BT. Reprinted from Ref [6] with permission from RSC.

In the case of commercial MWCNTs as ftRu support, Jeng et al. [31] used this kind of support previously activated by chemical treatment. Well dispersed PtRu 1 1 nanoparticles of 3.5-4 nm were obtained by a polyol synthesis method. The fuel cell test showed a performance 50 % higher than that of a commercial PtRu on Vulcan support (E-TEK). Similar results were found by Prabhuram et al. [32] for PtRu on oxidized MWCNT, where well dispersed nanoparticles of 4 nm were obtained by the NaBH4 method. The DMFC performance test of PtRu supported on MWCNTs showed a power density ca. 35 % higher than that using the Vulcan carbon support. Outstanding results were obtained by Tsuji et al. [33] with PtRu nanoparticles supported on carbon nanofibers prepared by polyol method and tested in a DMFC. They obtained a performance 200 % higher than standard PtRu on Vulcan carbon from Johnson Matthey. 

In addition to particle breakup, the coalescence process may be affected as well. It has been speculated that exfoliated clay platelets or well-dispersed nanoparticles may hinder particle coalescence by acting as physical barriers [19,22]. Furthermore, it has been suggested that an immobilized layer, consisting of the inorganic nanoparticles and bound polymer, forms around the droplets of the dispersed phase [50]. The reduced mobility of the confined polymer chains that are bound to the fillers likely causes a decrease in the drainage rate of the thin film separating two droplets [44]. If this is the case, this phenomenon should be dependent on filler concentration this is shown in Figure 2.8, which shows the effect of nanoclay fillers on the dispersed particle size of a 70/30 maleated EPR/PP blend [19]. 

In this chapter, the study carried out on nanofillers reinforced natural/synthetic rubber has been discussed. After a description on the NR rubber and CaCOs as filler, the development of synthetic composites with the incorporation of micro and nano-CaC03 as a filler material has also been discussed for comparative study. In particular, the role of fillers on the property modification of rubber properties, such as surface properties, mechanical strength, thermal conductivity, and permittivity has been mentioned. The effectiveness of this coating was demonstrated. The importance of well-dispersed nanoparticles on the improvement of the mechanical and electrical properties of polymers is also emphasized. However, one of the problems encountered is that the nanoparticles agglomerate easily because of their high surface energy. 

Fujihara used BINAP derived ligands as stabilizers for Pd NPs, giving well dispersed nanoparticles with narrow size distribution. Using chiral phosphine ligands, including S-BINAP in the asymmetric Suzuki-Miyaura coupling of naphtyl bromides and aiylboronic acids at room temperature, moderate ees of up to 74% could be achieved (Scheme 2). ... 

The addition of an inert salt in a mixture of redox solution for combustion synthesis may result in the formation of well dispersed nanoparticles with... 

Sol-gel - organic monomers, oligomers or polymers and inorganic nanoparticle precursors are mixed together in the solution. The inorganic precursors then hydrolyze and condense into well-dispersed nanoparticles in the pol3rmer matrix. 

Nanocomposite conventional mesoscale fibers (textile fibers that carry nanoparticulate filler) are produced via conventional fiber-spinning techniques by incorporating well-dispersed nanoparticles into the spinning dope. For instance, an intercalated poly(ethylene terephthalate) (PET)/organo-montmorillonite (MMT) nanocomposite prepared by in situ polymerization of the polyester in the presence of MMT clay was successfully melt spun into microfibers (Guan, G.-H., et al. 2005). Melt-spun conventional fibers of... 

When the dispersion of MPMS nanoparticles modified with surface proteins was observed microscopically, the addition of GPP to a MPMS nanoparticle solution led to well-dispersed nanoparticles with a distinct fluorescence. This indicated that, compared to TEOS nanoparticles, the GPP modified the MPMS nanoparticles very effectively while retaining good dispersion. MPMS nanoparticles modified with GPP were also detected and observed using fluorescence microscopy. 

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