Rafael López-Castañares

Silver Nanoparticles Obtained by Laser Ablation Using Different Stabilizers

We have synthesized silver nanoparticles by laser ablation in water using three stabilizers: hexadecyltrimethylammonium (CTAB) surfactant, polyamidoamine dendrimer second generation (PAMAM 2G) and polyamidoamine dendrimer fourth generation (PAMAM 4G) at different concentrations. We obtained spherical nanoparticles with narrow size distributions and average sizes ranging from 6 to 20 nm depending on the type of stabilizer and its concentration. For all cases the highest stabilizer concentration yielded the lowest average particle size; 15.5, 9.5, and 5.6 nm for CTAB, PAMAM 2G and PAMAM 4G respectively. We have also studied the stability of the nanoparticle colloids over a period of 30 days. Only the colloids of CTAB 10-3 M, all the concentrations of PAMAM 4G and pure water were stable after this time. This is explained in terms of steric hindrance of the stabilizer molecules and particle charge from Zeta potential measurements. All the results from transmission electron microscopy correlate well with those observed from the ultraviolet and visible spectra of each sample in terms of absorbance, peak width and peak maximum.

Synthesis and structural characterization of tris (methacrylato)chromium(III)

A straightforward synthetic route to produce tris(methacrylato)chromium(III), Cr(O2C(CH3)C=CH2)3, by reacting sodium methacrylate with an aqueous solution of CrCl3 gave a blue microcrystalline powder, insoluble in most common solvents. Electronic spectroscopy (UV-Vis), electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), were employed to characterize Cr(O2C(CH3)C=CH2)3. Morphology and elemental composition of this compound were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX), respectively. Spherical particles of approximately 2.5 µm in diameter were obtained. Thermal stability of the product was investigated via thermogravimetric analysis (TGA). The spectroscopic studies revealed that the coordination sphere around the chromium ion corresponds to a chelating bidentate carboxylate-Cr(III) complex. Thermal stability above 350°C, and spherical shape particles of few micrometers in diameter, suggest a potential application of this novel compound as a catalyst in oxidation reactions.