Dean J. Campbell

Synthesis of palladium colloids within polydimethylsiloxane and their use as catalysts for hydrogenation

The presence of unreacted silanes within cured polydimethylsiloxane (PDMS) leads to the reduction of tetrachloropalladate(II) ions, generating encapsulated palladium colloids. The resulting colloids had varied morphology and were typically less than 80 nm in size. The Pd/PDMS vessels, which contained 0.10±0.01% Pd, were effective catalysts for the hydrogenation of carbon-carbon multiple bonds for at least ten successive runs with no loss of catalytic activity, and the catalyst does not exhibit the same pyrophoric behavior as Pd on carbon after use in hydrogenation reactions. In addition, storage of previously used Pd/PDMS vessels for 6 months in air did not affect the catalytic activity, and the overall morphology of the catalysts after use was the same as those that have not been involved in catalytic reactions.

Demonstrations of Magnetism and Oxidation by Combustion of Iron Supplement Tablets

Iron supplement tablets containing iron(II) sulfate can be used in chemistry demonstrations as a convenient, household source of small quantities of iron(II) ions. When the tablet is burned in air, oxygen converts the iron(II) in the tablet ultimately to iron(III) oxide in the hematite phase. Heating pure iron(II) sulfate heptahydrate also produces hematite. However, for the tablet, and for mixtures of iron(II) sulfate heptahydrate and starch, other iron oxide species such as magnetite and maghemite are produced before complete conversion to hematite. The presence of the starch, and cellulose in the tablets, appears to slow the oxidation of the iron(II). Magnetite and maghemite can be captured, observed by X-ray diffraction, and are much more strongly attracted to a magnet than hematite. The changes in color and magnetic susceptibility during iron supplement tablet combustion enable it to be used as an interesting demonstration of oxidation.

Infrared Spectroscopic Analysis of the Adsorption of Pyridine Carboxylic Acids on Colloidal Ceria

Surface adsorption of a homologous series of pyridine carboxylic acids on a hydrated colloidal cerium dioxide (ceria) film is characterized using the combination of experimental and computationally determined infrared (IR) spectra. Experimental analyses employ attenuated total reflectance (ATR) IR spectroscopy of deposited colloidal ceria thin films equilibrated with three pyridine carboxylic acids at pH 3.0, 5.5, and 8.5. The corresponding computational IR spectra for the energy-minimized intermediate and base forms of the pyridine carboxylic acids use density functional theory calculations at the B3LYP/6-311++G** level of theory. Solvent effects are modeled using both the COSMO implicit solvation model and the inclusion of explicit water molecules. Experimental IR spectra show that the adsorptive interactions between the pyridine carboxylic acids and ceria surface are due to the outer-sphere coordination of cerium ions in the films. Vibrational assignments based on combined experimental and computational results indicate that both pyridyl ring nitrogen and carboxylate functional groups account for the interaction of pyridine carboxylic acids at ceria surfaces. Experimentally determined Langmuir constants point to the intermediate form of picolinic acid (pyridine-2-carboxylic acid) as having the strongest adsorption to ceria compared to the other pyridine carboxylic acids investigated. The enhanced adsorption of picolinic acid is attributed to the adjacency of the protonated pyridyl nitrogen and the carboxylate group relative to nicotinic acid (pyridine-3-carboxylic acid) and isonicotinic acid (pyridine-4-carboxylic acid).

Exploring Materials Science with LEGO ® Brick Models

Various physical and chemical principles related to materials science and technology can be demonstrated with LEGO ® models. Three-dimensional models are excellent tools for grasping structure-function relationships. Additionally, many people are familiar with LEGO ® bricks, and most models can be built with a level of mechanical sophistication that does not intimidate or frustrate the user. LEGO ® bricks typically have many connection sites, allowing tremendous flexibility in the structures that can be built. The bricks can be used to model both the structures of materials and the techniques used to study them. Many models can be built with varying degrees of sophistication, even incorporating electronics, enabling the user to focus on relatively simple concepts or more subtle details. The variety of models available also enables LEGO ® bricks to fit into a variety of user budgets. This paper features models of the structures of materials, including unit cells, discrete molecules, and polymers. It also features models of analytical tools used to study materials, including models of a scanning probe microscope and a photometer. Details and building instructions of these and other models are featured in the book “Exploring the Nanoworld with LEGO ® Bricks”. This book may be downloaded from the Internet at: http://mrsec.wisc.edu/edetc/LEGO/index.html .

An Alternative Thermochemical Container

A polystyrene foam egg carton (or even multiple nested cartons) is an adequate container for mixing the solutions and performing thermochemical measurements.