Characterization of Porous Nanocomposites Formed by Cobalt Ferrites Dispersed in Sol-Gel Silica Matrix

Composites of cobalt ferrite particles dispersed in a silica matrix (CoFe₂O₄/SiO₂) were prepared by the sol-gel process using tetraethylorthosilicate (TEOS) as a precursor of silica and metallic nitrates as precursors of ferrite. Samples of SiO₂ and CoFe₂O₄/SiO₂ were prepared in monolithic shape, dried at 110^∘C, treated at various temperatures and their characteristics were compared. After the thermal treatment, the surface area of the silica matrix decreased, above 700^∘C it densified, and above 1100^∘C it crystallized. The same heat treatment in the composite led to the crystallization of CoFe₂O₄ particles in the SiO₂ matrix and the increase in particle size, with the consequent increase in magnetization. The presence of particles in the matrix reinforced its structure, avoiding large changes in surface area and porosity and in the structure of the matrix after high temperature thermal treatment.     

An automated system for liquid-liquid extraction based on a new micro-batch extraction chamber with on-line detection: Preconcentration and determination of copper(II)

An automated system to perform liquid-liquid extraction is proposed, in which the effective mixture (the intimate contact) between the aqueous phase and the organic phase, as well as the separation of the phases, are carried out in a micro-batch glass extraction chamber. Sample, reagents and organic solvent are introduced into the glass extraction chamber by a peristaltic pump using air as carrier. The detection of the extracted species from the aqueous phase is made in a small volume (120-150 μl) of isobutyl methyl ketone (MIBK). The system allows enrichment factors of 2-10-fold. The proposed automatic system was evaluated for Cu(II) extraction based on complex formation between copper(II) and 1-(2′-pyridylazo)naphthol (PAN) in MIBK. When a volumetric ration of 2:1 (aqueous:organic) was implemented, copper was detected in the concentration range of 100-1600 μg l⁻¹ (r = 0.9995) with a relative standard deviation of 2% (200 μg l⁻¹, n = 5) and a detection limit of 20 μg l⁻¹. The analytical curve was linear over the concentration range 25-500 μg l⁻¹ (r = 0.9994) when a volumetric ratio of 10:1 was employed. With this ratio, the detection limit was 5.0 μg l⁻¹ and the relative standard deviation was 6% (50 μg l⁻¹, n = 5).     

Electrochemical evaluation of lectin-sugar interaction on gold electrode modified with colloidal gold and polyvinyl butyral

In this work, ConA and CramoLL lectins were immobilized on gold nanoparticles (AuNp) with polyvinyl butyral (PVB), and adsorbed on the surface of gold (Au) electrodes. Electrochemical impedance spectroscopy (EIS), in the frequency range from 100mHz to 100KHz, and cyclic voltammetry (CV), from -0.2 to 0.7V, were performed on these electrodes, in phosphate buffer (PBS) solution containing 10mM K(3)[Fe(CN)(6)]/K(4)[Fe(CN)(6)] (1:1) mixture as a redox probe. EIS and CV measurements showed that redox probe reactions on the modified Au electrodes were partially blocked due to the adsorption of AuNp-ConA-PVB and AuNp-CramoLL-PVB. SEM images showed the presence of aggregates of AuNp-ConA on PVB spherules in a tridimensional structure on the surface of the Au electrode. Bovine serum albumin (BSA) was adsorbed on the AuNp-Lectin-PVB modified electrode in order to block the remaining free gold sites. Both EIS and CV techniques yielded results that confirm positive responses of the lectins to ovalbumin agglutination. These results indicate an improvement of the sensitivity for detection of sugars that can be applicable to construction of a biosensor sensitive to glycoproteins in solution.     

Characterisation of Xerogels Derived from Sucrose Templated Sol-Gel Synthesis

This work presents the results of the nanostructural characterisation of the effect of sucrose as a template added to a sol derived from a tetraethoxysilane acid catalysed process. By increasing the sucrose template ratio, N₂ adsorption isotherms showed that the xerogel samples changed from a micropore to a mesopore nanostructure as evidenced by the formation of hysteresis at 0.5 partial pressure. In turn, this led to a direct increase in surface areas, pore volumes and average pore sizes. Sucrose has two molecular components of the same molecular weight: D-fructose and D-glucose. D-fructose resulted in the formation of higher pore volumes and pore sizes, while D-glucose formed higher surface area xerogels. Depending of the template ratio employed in the xerogel synthesis, average pore radius ranged from 8.8 to 26 Å, while surface areas increased by over two fold up to 750 m²·g^?1. However, pore volumes increased by as much as six fold, from 0.15 to almost 1 cm³·g^?1.