E. Fachini

Highly Organized Nanofiber Formation from Zero Valent iron Nanoparticles After Cadmium Water Remediation

Many studies have used nanoscale zero valent iron (nZVI) nanoparticles to remove redox-sensitive metals (e.g., As, Cr, U, Se, Ni, Cu) from aqueous systems by absorption or reduction processes. However, very few investigations present a detailed study of the product formed after the remediation process. In order to quantify the efficiency of nZVI particles as a possible cadmium remediation agent, we prepared nZVI by sodium borohydride reduction of an iron complex, FeCl3·6H2O, at room temperature and ambient pressure. Fe0 and nanocrystalline structures of iron oxides and oxyhydroxides were obtained with this method. We exposed the nZVI to 6 ppm of Cd2+ and characterized the products with X-ray diffraction, X-ray absorption and X-ray photoelectron spectroscopy. Inductively coupled plasma analysis showed that the nZVI remediation efficiency of cadmium ions was between 80% and 90% in aqueous media. All of the physical characterization results confirmed the presence of Fe0, α-Fe2O3 and FeOOH. High resolution transmission electron microscopy images showed nanofiber formation of a mixture of Fe0, oxyhydroxides and oxides iron formed after interacting with cadmium ions, possibly forming CdFe2O4. These results suggest that the FeOOH shell and other iron oxides in nZVI could enhance Cd2+ removal. This removal is observed to cause a change of the initial structure of nZVI to nanofibers due to possible formation of CdFe2O4 as a waste product.

Nanofibers and thin films as a selective membrane for sensors and microTAS

A composite material of PAN (polyacrylonitrile), starch granules and dimethylformamide as solvent was used as a selective membrane for volatile organic compounds (VOCs) in gaseous phase. This composite was produced as a thin film obtained by spin-casting and as a fiber mat produced by electrospinning. The fiber mat was tested for adsorption of VOCs and water. Characterization used microscopy (electron scanning and optical) in order to evaluate the fiber morphology and the starch incorporation in the PAN matrix. Infrared spectroscopy was intended to determine the starch presence. Relative viscosity of the starch/PAN suspensions was measured in order to provide a model of composite fiber formation. Quartz crystal microbalance experiments determined VOCs and water adsorption. Fibers incorporated the starch granules, making the composite sensible to water; but VOCs were not detected. Therefore, the composite was found to be a good choice as selective barrier on sensors or microTAS protection purposes.

Large Surface Area of HMDS Plasma Polymerized Thin Film Used for Production of Miniaturized Structures

The aim of this work was the production of a large surface area of hexamethyldisilazane (HMDS) plasma-deposited thin films and their applicability in a miniaturized structure useful for preliminary analysis of organic mixtures. The HMDS plasma films were produced with different surface areas and morphologies, and all films adsorbed polar and non-polar organic compounds. A low cost miniaturized structure was manufactured in glass using a Milling cutter and covered with HMDS plasma films. Good agreement was observed between simulation and experimental results on those microstructures. The observed different performance between pure and mixtures of organic compound samples suggests that the proposed system is a simple setup that could be useful for rough analysis of a fuel.

Composites in small and simple devices to increase mixing on detector surfaces

This work aims at three different applications for the betterment of plasma generated-composite thin films: pre-mixing, spray formation in miniaturized structures and an increase in the performance of detector surfaces. Miniaturized structures were projected, simulated with FEMLAB® 3.2 software and then constructed. Clustered films made from tetraethoxysilane (TEOS) and nonafluoro(iso)butyl ether (HFE®) precursors were deposited on silicon, acrylic and quartz substrates for different kinds of film characterization/or in the projected structures. Physical and chemical characterization guided the selection of best films previous to/after UVC exposure. The active surfaces (plasma-deposited films) in structures were modified by UVC exposure and then tested. The applications include pre-mixing of liquids and/or spray formation, best results being obtained with surface covered by derivative-HFE films, which acted as passivation layers. Preliminary results show good humidity sensing for TEOS-derivative films.

P2.9.2 Small and Simple Devices for Increase Mixing on Detector Surfaces

Due to transport phenomena, analyte adsorption on the detector surface can be hindered, which increases the detection limit. Therefore, this work aims the simulation, production and tests of a simple miniaturized structure that favors mixing on detector surfaces. The conception of the manufactured device is based on passive mixers. Mixing is improved by changing the surfaces properties of plasma deposited thin films. Hexamethyldisilazane (HMDS) and nonafluoro(iso)butyl ether (HFE) and codeposited HMDS/HFE plasma films were modified by ultraviolet (UVC) or beta radiation exposure (electron beam, 2 MeV, from 10 nA to 100 nA). Silicon, acrylics and piezoelectric quartz crystal (PQC) were used as substrates. Film characterization used profilemeter for thickness and ellipsometer for refractive index determinations; Raman, infrared (FTIR) and x-ray photoelectron (XPS) spectroscopies determined chemical composition. Optical, scanning electron (SEM) and atomic force (AFM) microscopies evaluated the film resistance toward ultraviolet light or beta radiation and cluster formation; cluster size were estimated using ImageJ software. Contact angle measurements tested hydrophobicity and the adsorption of volatile organic compounds (VOCs). Simulations of detector surfaces (based on PQC detection) and respective package used FEMLAB 3.2 software. All films are hydrophobic and adsorbent, even after exposition to ultraviolet radiation. HMDS films exposed to ultraviolet form a silicone-like structure whereas beta radiation exposure leads to carbon nodules formation. HFE films act as passive layer, even for beta radiation. Best design for surface modification has approximately a sinoidal shape.

Perfluorocompound and Hexamethyldisilazane Thin Film Composite Material Used for Surface Modification

The aim of this work was to produce, to characterize and test selective membranes based on derivatives from organic fluorinated/silicon compounds. The produced composites presented silicon and fluorinated species on the surface. The morphology of these non uniform surfaces showed big domains in the micrometer scale but a closer view reveals structures also in the nanometer range. Contact angle measurements showed a mildly hydrophobic and organophilic surface. Polymeric tapes treated with this composite showed an increase on permeation rate for the organic compounds. An acrylic device that employed this modified polymeric tape was manufactured and used for sample pretreatment during chemical analysis.