Leliz T. Arenas

3-n-Propyl-1-azonia-4-azabicyclo[2.2.2]octanechloride Silsesquioxane: A New Water Soluble Polymer

A water soluble silsesquioxane polymer, with different grades of 3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octanechloride pendant group, was obtained using the sol-gel method and it was analyzed using infrared and thermogravimetric techniques. The silsesquioxane polymer solubility was investigated and it was related to the amount of the incorporated organic groups in the polymer network. The polymer was impregnated on the surfaces of silica, alumina and silica modified with alumina (Al/SiO2). The resulting dispersed polymer film was strongly adhered onto the Al/SiO2 surface.

3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octanechloride/silica hybrid polymer. A morphologic study in relation to the organic content

Abstract The 3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octanechloride/silica hybrid polymer was synthesized, using the sol–gel method, by varying the organic content. The samples were characterized using infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N2 adsorption–desorption isotherms and thermogravimetric analysis. The polymer morphology could be controlled by the choice and amount of the organic precursor added. The dispersion of the organic/inorganic phases was shown to be in molecular or nanometric level. The organic content elevation produced a decrease in the surface area and pore volume due to the organic pore blocking effect.

Niobium oxide dispersed on a carbon–ceramic matrix, SiO2/C/Nb2O5, used as an electrochemical ascorbic acid sensor

A film of niobium oxide was immobilized on a SiO(2)/C carbon-ceramic matrix (specific surface area 270 m(2)g(-1)) and characterized by N(2) adsorption-desorption isotherms, scanning electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. This new carbon-ceramic material, SiO(2)/C/Nb(2)O(5), was used for construction of electrodes, and it shows ability to improve the electron-transfer between the electrode surface and ascorbic acid. The electrocatalytic oxidation of ascorbic acid was made by differential pulse and cyclic voltammetry techniques, making it potentially useful for developing a new ascorbic acid sensor.

Mesoporous Nb2O5/SiO2 material obtained by sol–gel method and applied as adsorbent of crystal violet dye

ABSTRACT In this work, SiO2/Nb2O5 (SiNb) material was prepared using sol–gel method and employed as adsorbent for removal of crystal violet dye (CV). The material was characterized using nitrogen adsorption–desorption isotherms, FTIR spectroscopy, pHpzc, and SEM-EDS. The analysis of N2 isotherms revealed the presence of micro- and mesopores in the SiNb sample with specific surface area as high as 747 m2 g−1. For the CV adsorption process, variations of several parameters such as of pH, temperature, contact time, and concentration of dye of the process were evaluated. The optimum initial pH of the CV dye solution was 7.0. The adsorption kinetic and equilibrium data for CV adsorption were suitably represented by the general-order and Liu models, respectively. The maximum adsorption capacity of the CV dye by SiNb was achieved at 303 K, which attained 116 mg g−1 at this temperaure. Dye effluents were simulated and used to check the applicability of the SiNb material for treatment of effluents – the material showed very good efficiency for decolorization of dye effluents.

TiO2 and TiO2/SiO2 nanoparticles obtained by sol–gel method and applied on dye sensitized solar cells

Abstract In this work we show the synthesis and characterization of TiO2 and TiO2/SiO2 nanoparticles synthesized by sol–gel method using HF and HCl as catalysts. The obtained nanoparticles were analyzed by N2 adsorption–desorption isotherms, transmission electronic microscopy, Ultraviolet–visible spectroscopy and X-ray diffractometry. Mesoporous, homogeneously polycondensed TiO2/SiO2 materials, containing nanocrystalline anatase phase with band gap similar to pure titania were obtained. Films of the powdered oxides were applied to assemble dye sensitized solar cells that presented electrical parameters, Fill Factor and efficiencies similar to devices obtained by only TiO2. The sol–gel route arises as an alternative way to prepare TiO2/SiO2 materials for solar cells.

Synthesis of silica xerogels with high surface area using acetic acid as catalyst

The influence of acetic acid on the pore structure and surface area of silica prepared by the sol-gel method was investigated. Experimental conditions of synthesis, such as gelation temperature and solvents, were also studied. N2 adsorption isotherms of the samples were type 1, typical of microporous materials, explaining the high surface area values (BET) observed. The simultaneous addition of acetic and hydrochloric acids as catalysts and of acetone as solvent, together with the use of a gelation temperature of 20 oC, made it possible to prepare amorphous silica materials with surface area values up to 850 m2 g-1. The high surface area value of these samples could be explained by the microporosity and the nanometric size of the particles.

A water soluble 3-n-propyl-1-azonia-4-azabicyclo[2.2.2]octanechloride silsesquioxane grafted onto Al/SiO2 surface: chromium adsorption study

The water soluble material, 3-n-propyl-1-azonia-4-azabicyclo(2.2.2)octanechloride silsesquioxane (dabcosil silsesquioxane) was obtained. The dabcosil silsesquioxane was grafted onto a silica surface, previously modified with aluminum oxide. The resulting solid, dabcosil-Al/SiO 2 , pres- ents 0.15 mmol of dabco groups per gram of material. The product of the grafting reaction was ana- lyzed by infrared spectroscopy and N 2 adsorption-desorption isotherms. The dabcosil-Al/SiO 2 materi- al was used as sorbent for chromium (VI) adsorption in aqueous solution.

Chitosan-stabilized gold nanoparticles supported on silica/titania magnetic xerogel applied as antibacterial system

AbstractThe sol-gel method is an excellent choice to produce composite materials with enhanced performance by efficiently combining the individual features of their components. In this work, chitosan-stabilized gold nanoparticles (ChAuNPs) were immobilized onto a SiO2/TiO2 magnetic xerogel, which was synthesized through hetero-condensation of silica and titania precursors in the presence of magnetite particles covered with a silica shell. This system allies the antimicrobial capacity of ChAuNP, the surface reactivity of titania, porous structure of silica, and magnetic response of the magnetite particles. The magnetite phase was characterized by X-ray diffraction and the shape and size of the particles were observed by scanning and transmission electron microscopy. ChAuNPs were obtained in spherical shape with size below 10 nm, as characterized by UV–Vis spectroscopy and transmission electron microscopy. SiO2/TiO2 magnetic xerogel containing the ChAuNP was also characterized by thermogravimetric and textural analysis, transmission electron microscopy, and magnetism. The ChAuNP-SiO2/TiO2 magnetic xerogel is mesoporous with facile magnetic recovering and its performance as antimicrobial agent was assessed against the pathogen E. coli. The ChAuNP-SiO2/TiO2 magnetic xerogel presented inhibitory effect against the tested bacteria, even with such low gold content. After the magnetic recovering, the material was reused and maintained its antibacterial activity. HighlightsMagnetic composite embedding magnetite particles in silica/titania network.Adhesion of chitosan-stabilized gold nanoparticles to silica/titania surface.Porous and high surface area material containing gold nanoparticles as antimicrobial agent.Efficient and reusable antimicrobial system against E. coli bacteria.