Robert Bjorklund

Some properties of polypyrrole-paper composites

It is shown that porous materials such as paper can be impregnated with a conducting polymer by first soaking the paper in a solution of metal salt which acts as an initiator for subsequent polymerization. By using this procedure the conductivity of filter paper can be raised to as high as 2 (ohm cm)−1 for an FeCl3/H20/pyrrole combination. The role of the metal ion is discussea and it is pointed out that the impregnated papers exhibit both ionic and electronic conductivity. The polypyrrole paper composites exhibit some properties similar to carbon black-polymer composites.

Hydrogen production from organic waste

The extraction of pure hydrogen from the fermentation of household waste by a mixed anaerobic bacterial flora is demonstrated. Simulated household waste (600 g) was fermented in a bioreactor, which ...

Vapor sensitivity of thin porous silicon layers

Spectroscopic ellipsometry has been used to study optical changes in thin porous silicon layers due to exposure to vapors from different liquids. The changes in the ellipsometric parameters Ψ and Δ were caused by changes in the total refractive index of the layers. The detection limit threshold for acetone vapors by the layers was 12 ppm. Using a 4-layer optical model, it was determined that capillary condensation was involved in the vapor sensitivity of the layers. Based on these findings, it was concluded that thin porous silicon layers can be used as an optical sensor material for gas sensing purposes.

An infrared and electrical conductance study of V2O5/SIO2-TIO2 catalysts active for the reduction of NO by NH3

Abstract A series of V 2 O 5 SiO 2 TiO 2 catalysts (vanadia content 2–30 wt%) was evaluated for the selective reduction of NO by NH 3 . Activities at 200 °C determined on a per gram vanadia basis were nearly equal for catalysts containing 5–20% vanadia. The 10% catalyst exhibited the highest activity at 350 °C. Characterization of the catalysts with FTIR and XRD showed that the vanadia was highly dispersed on the carrier as an amorphous phase for all catalysts with 20% or less vanadia. Electrical conductance measurements were made to study the dispersion of the vanadia on the support and the effect of different gases on the degree of vanadia reduction. Conductances for the catalysts in 1.5% O 2 Ar carrier gas increased with increasing vanadia content for catalysts with 15% or more vanadia indicating a decreasing distance between V(IV) centers. Exposure of the catalysts to NH 3 in the carrier gas resulted in reversible increases in conductance for all vanadia concentrations. Exposure of the catalysts to NO resulted in reversible conductance increases for the 15, 20, and 30% catalysts. Exposure of the catalysts to NH 3 + NO resulted in conductance changes which indicated a reaction at 350 °C between adsorbed, laterally mobile NH 3 and gaseous NO for all catalysts with the most effective reaction occurring on the 10% catalyst. At 200 °C, the conductance measurements indicated a reaction between strongly bound NH 3 , which exhibited little lateral movement, and gaseous NO.

Protein adsorption in thermally oxidized porous silicon layers

Abstract Variable angle spectroscopic ellipsometry was employed for multilayer characterization of thermally oxidized porous silicon layers and for quantitative adsorption studies of human serum albumin and fibrinogen in these layers. The oxidized samples were used either as prepared or were hydrated in a deionized water bath prior to their use. Hydration decreased the volume percentage of adsorbed albumin from 24 to 13% in the sublayer next to the ambient but resulted in an increase of the amount of adsorbed protein deeper in the film. Hydration did not, however, affect the adsorption behavior of fibrinogen which was found to adsorb only in the outermost sublayer. This phenomenon was attributed to the larger size of this protein. The amount of adsorbed fibrinogen depended on the concentration of the protein in the stock solution.

COLOR CHANGES IN THIN POROUS SILICON FILMS CAUSED BY VAPOR EXPOSURE

Thin films of porous silicon formed by electrochemically etching silicon wafers changed color when exposed to an ambient atmosphere saturated in various organic solvent vapors. The degree of the color change was related to the refractive indices of the solvents. Analysis of the data using a four‐layer optical model indicated that the film refractive index increased up to 15% when solvent molecules replaced air in the pores. Solvent condensing from the saturated atmosphere filled up to 45% of the total void volume. Thermally oxidizing the films to make them hydrophilic resulted in surfaces which changed color upon exposure to water.

Kinetics of pyrrole polymerisation in aqueous iron chloride solution

The chemical oxidation of pyrrole by iron(III) chloride in aqueous solutions of methylcellulose has been investigated. The kinetics of the reaction were studied by following the absorption of the soluble (colloidal), oxidised poly(pyrrole) product at 800 nm. In the pH interval 0–0.5 the reaction was first-order in FeIII and pyrrole concetrations and zero-order in proton concentration. For pH > 1.3, the kinetic curves exhibited behaviour characteristic of autocatalytic reactions. A mechanism is proposed in which the rate-limiting step is the oxidation of pyrrole to a radical cation by an outer-sphere activated-complex mechanism. The observed pH dependence on the rate is attributed to the hydrolysis equilibrium for FeIII in solution, in which lower pH decreases the concentration of OH–, which can hinder pyrrole from approaching the oxidant. The observed autocatalytic behaviour at higher pH is caused by the fact that the polymerisation produces protons. A brief comparison with oxidation by ammonium persulphate is given.

Colorimetric analysis of water and sand samples performed on a mobile phone

Analysis of water and sand samples was done by reflectance measurements using a mobile phone. The phones screen served as light source and front view camera as detector. Reflected intensities for white, red, green and blue colors were used to do principal component analysis for classification of several compounds and their concentrations in water. Analyses of colored solutions and colorimetric reactions based on widely available chemicals were performed. Classification of iron(III), chromium(VI) and sodium salt of humic acid was observed using reflected intensities from blue and green light for concentrations 2-10mg/l. Addition of complex forming sodium salt of ethylenediaminetetraacidic acid enabled the discrimination of Cu(II) ions in the 2-10mg/l concentration range based on reflection of red light. An alternate method using test strips for copper solutions with the phone as reader also demonstrated a detection limit of 2mg/l. Analysis of As(III) from 25 to 400 μg/l based on reflection of red light was performed utilizing the bleaching reaction of tincture of iodine containing starch. Enhanced sensitivity to low concentrations of arsenic was obtained by including reflected intensities from white light in the analysis. Model colored sand samples representing discoloration caused by the presence of arsenic in groundwater were analyzed as a complementary method for arsenic detection.

A Potential Soot Mass Determination Method from Resistivity Measurement of Thermophoretically Deposited Soot

Miniaturized detection systems for nanometer-sized airborne particles are in demand, for example in applications for onboard diagnostics downstream particulate filters in modern diesel engines. A soot sensor based on resistivity measurements was developed and characterized. This involved generation of soot particles using a quenched co-flow diffusion flame; depositing the particles onto a sensor substrate using thermophoresis and particle detection using a finger electrode structure, patterned on thermally oxidized silicon substrate. The generated soot particles were characterized using techniques including Scanning Mobility Particle Sizer for mobility size distributions, Differential Mobility Analyzer—Aerosol Particle Mass analyzer for the mass–mobility relationship, and Transmission Electron Microscopy for morphology. The generated particles were similar to particles from diesel engines in concentration, mobility size distribution, and mass fractal dimension. The primary particle size, effective density and organic mass fraction were slightly lower than values reported for diesel engines. The response measured with the sensors was largely dependent on particle mass concentration, but increased with increasing soot aggregate mobility size. Detection down to cumulative mass as small as 20–30 μg has been demonstrated. The detection limit can be improved by using a more sensitive resistance meter, modified deposition cell, larger flow rates of soot aerosol and modifying the sensor surface.

Electrically conducting composites of colloidal polypyrrole and methylcellulose

The oxidation of pyrrole by iron(III) chloride in aqueous solutions of methylcellulose yields colloidal solutions of conducting polypyrrole which can be used to prepare thin films with maximum conductivity of 0.2 S/cm.