Organofunctionalized silicas

Table 2. Organofunctionalized silicas in pre-concentration of noble metal ions.

It has been shown that organofunctionalized silica surfaces further modified with in situ synthesized copper complexes can be used to produce new stationary phases for HPLC [4]. The immobilized copper complexes provide new sites in the stationary phase that can interact strongly with basic organic compounds. A test mixture of compounds such as benzene, toluene, naphthalene, anthracene, pyrene, and nitrobenzene shows that the presence of copper ion complexes on the modified surface strongly affects the retention factor (fe) of the stationary phases. 

Organofunctionalized silica was prepared as follows 50 cm of tetraethylortho-silicate (TEOS) was dissolved in 38 cm of 3-chloro(propyl)trimethoxysilane. To the resulting solution, 400 cm of a 0.3 mol dm HCl solution was added. The obtained gel was mechanically stirred for 30 min. The resulting mixture was aged for 24 h, the supernatant was discarded, and 400 cm was deionized water was added. This sequence of operations was repeated three times. The obtained powder was then dried at room temperature in a fume hood and then dried under vacuum at 40°Cfor4h. 

The in situ organofunctionalized silica complexes were prepared by reacting the eta-modified sihca with an ethanolic solution of EUCI3. Schematic representations of the in situ synthesized complexes are shown in Fig. 3.6. 

Figure 3.6 Schematic representation of eta (a) and eta—phen (b) of in situ organofunctionalized silica europium complexes.

The emission spectra for free and in situ organofunctionalized silica prepared complexes are shown in Figs. 3.9 and 3.10. As can be seen from Figs. 3.9a and 3.9b,... 

Figure 3-9 Emission spectra for free and insitu organofunctionalized silica prepared Eu-eta-phen complexes.

The experimental results indicate that the substitution of water molecules by a phen molecule into the coordination sphere of a Eu-eta complex enhances the luminescence intensity due to the lowering of the number of OH oscillators (which suppress the luminescence), as well as the ability of phen to act as a good chromo-phor. Furthermore, the in situ organofunctionalized silica-eta complex exhibits an optimization of optical properties, in comparison with the free complex, mainly an enhancement of the emission intensity. The experimental parameters show that the dynamic coupling mechanism is predominant. 

In a preliminary experiment to study the adsorption of Cu(II) on organofunctionalized silica surfaces (obtained when Si-OH groups on the silica surface bind with alcoxysilanes), the fractional factorial design whose data are presented in Table 4A.1 was carried out (Cestari et al., 1996). 

CESTARI, A. R. BRUNS, R. E. and AIROLDI, C. A fractional factorial design applied to organofunctionalized silicas for adsorption optimization. Colloids Surfaces A Physicochem. Eng. Aspects 117, 1996, pp. 7-13. 

Fyfe, C.A., Zhang, Y., and Aroca, P. 1992. An alternative preparation of organofunctionalized silica gels and their characterization by twodimensional high-resolution solid-state heteronuclear NMR correlation spectroscopy, y. Am. Chem. Soc. 114 3252-3255. 

The adsorption of MN4-MC on the surface of organofunctionalized silica has also shown to be an efficient way to prepare hybrid materials useful in electroanalysis. Fujiwara et al. [70] described the surface modification of porous Si02/ AI2O3 (SiAl) with a thin layer of 3-n-propylpyridiniumsilsesquioxane polymer (SiPy-) (Fig. 19a). 

The concentration of Cd(II) was determined using a carbon paste electrode modified with organofunctionalized amorphous silica with 2-benzothiazolethiol [402] or diacetyldioxime [403] and differential pulse anodic stripping voltammetry. The same method was used for determination of Cd(II) ion using GC electrode modified by antraquinone improved Na-montmorillonite nanoparticles [404]. 

Cavalheiro ETG, Marino G, Cesarino I (2006) Differential pulse anodic stripping voltammetric determination of mercury(II) in natural water at a carbon paste electrode modified with organofunctionalized amorphous silica. Anal Chem Indian J 2 37-44... 

Popa DE, Buleandra M, Mureseanu M, lonica M, Tanase IG (2010) Carbon paste electrode modified with organofunctionalized mesoporous silica for electrochemical detection and quantitative determination of cadmium(II) using square wave anodic stripping voltammetry. 

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