Silica nanoparticles, synthesis using technique

From our research group Santra et al. [11,41,42] reported the development of novel luminescent nanoparticles composed of inorganic luminescent dye RuBpy, doped inside a sihca network. These dye-doped silica nanoparticles were synthesized using a w/o microemulsion of Tx-lOO/cyclohexane/ n-hexanol/water in which controlled hydrolysis of the TEOS leads to the formation of mono dispersed nanoparticles ranging from 5-400 nm. This research illustrates the efficiency of the microemulsion technique for the synthesis of uniform nanoparticles. These nanoparticles are suitable for biomarker application since they are much smaller than the cellular dimension and they are highly photostable in comparison to most commonly used organic dyes. It was shown that maximum liuninescence intensity was achieved when the dye content was around 20%. Moreover, for demonstration... 

One merit of special attention in this chapter is the fact that sol-gel synthesis offers a convenient method for hosting chemical reactions, a process which is not possible using other synthesis techniques. Typically, in sol-gel encapsulation, silica nanoparticles surround the captive molecules during gel formation. In principle, the sol-gel process can be considered as a phase separation by sol-reactions, sol-gelation and finally, removal of the solvent resulting in a ceramic material Depending on the preparation, dense oxide particles or polymeric clusters will be obtained [16]. 

Fig. 4.13 Depiction of the two nanoparticle synthesis techniques used and the initial reactivity results for electrophilic catalysis, (a) In the top scheme, Pt ions are loaded onto a PAMAM den-drimer and reduced to form a dendrimer-encapsulated NP. Sonication deposits the NPs on the mesoporous silica, SBA-15, to generate the NP catalysts. In the bottom scheme, polyvinylpyrrolidone (PVP) encapsulates the NP. Deposition on SBA-15 follows to produce the catalyst. In both cases, the NPs are synthesized before loading onto SBA-15. (b) Hydroalkoxylation of 1 with Pt NPs. To obtain electrophilic activity from the Pt NPs, treatment with the mild oxidant PhlClj is required. Pt4o/G40H/SBA-15 NPs must be further reduced under H atmosphere at 100 °C for 24 h before reaction. This treatment generates catalytically active NPs that activate the jc-bond in 1, resulting in hydroalkoxylation to benzofuran 2. Yields were determined by comparing peaks in NMR against an internal standard. Reprinted with permission from ref. [100]. Copyright 2009 Nature Publishing Group...

Widely used methods in the synthesis of silica nanoparticles are the sol-gel process and flame synthesis [5]. The latter is an effective synthetic route to continuously produce extremely pure nanoparticles, but in many cases the final products are agglomerated or show low reactive surfaces that make them difficult to functionalize. Nevertheless, flame synthesis is a prominent method to commercially produce silica nanopartides in powder form [6]. It is being used since decades for the production of the so-called fumed siUca, which is a filler in many applications, for example, in the pharmaceutical or polymeric business [7]. The extension of this preparation route is the so-called flame spray pyrolysis that has expanded in the last two decades to many other material compositions and is a promising rapid technique for the production of nanopowders [8]. 

Zeolites have ordered micropores smaller than 2nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique (Figure 1) [1,2], and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16 [3,4], MCM-41 [5], and SBA-15 [6] have been used as catalyst supports, because they have large pores (2-10 nm) and high surface area (500-1000 m g ) [7,8]. The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications [9]. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noble-metal nanoclusters in mesoporous silicas. 

Various metal and metal oxide nanoparticles have been prepared on polymer (sacrificial) templates, with the polymers subsequently removed. Synthesis of nanoparticles inside mesoporus materials such as MCM-41 is an illustrative template synthesis route. In this method, ions adsorbed into the pores can subsequently be oxidized or reduced to nanoparticulate materials (oxides or metals). Such composite materials are particularly attractive as supported catalysts. A classical example of the technique is deposition of 10 nm particles of NiO inside the pore structure of MCM-41 by impregnating the mesoporus material with an aqueous solution of nickel citrate followed by calicination of the composite at 450°C in air [68]. Successful synthesis of nanosized perovskites (ABO3) and spinels (AB2O4), such as LaMnOs and CuMn204, of high surface area have been demonstrated using a porous silica template [69]. 

The applicability of the Pt deposition precipitation technique (DP) on mesoporous silica has been evaluated and discussed. A detailed synthesis procedure is given, and a suitable support from the SBA-15 family has been identified. The material synthesized at the conditions described here was clearly able to withstand the severe conditions of the DP treatment, indicating improved hydrothermal stability. The incorporation of the active species was accomplished without compromising the structural integrity of the parent material, as monitored by XRD and N2-sorption measurements. Using UV-Vis diffuse reflectance spectroscopy we were able to detect the platinum surface complex that coexists with platinum nanoparticles on the impregnated solid. 

In this chapter, we present an overview of our experience in the organometallic synthesis of ruthenium nanoparticles of controlled size and surface state. We also give insights on the study of their surface chemistry by using simple techniques, mainly IR and NMR both in solution and in solid state, hi addition, model hydrogenation reactions have been used. We also discuss the performances of these materials as catalysts in solution (organic and aqueous phases) and on a support (alumina, silica, or carbon materials). 

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