Biomedical subjects

Dominick J Casadonte

Publications and source records attributed to Dominick J Casadonte.

6 recordsLinked to original sources

PubMed2006

PtRu nanoparticle electrocatalyst with bulk alloy properties prepared through a sonochemical method.

Properties of PtRu nanoparticles prepared using high-intensity sonochemistry are reported. Syntheses were carried out in tetrahydrofuran (THF) containing Ru3+ and Pt4+ in a fixed mole ratio of either 1:10 or 1:1. X-ray diffraction measurements confirmed sonocation produces an alloy phase and showed that the composition of the nanometer scale metal particles is close to the mole fraction of Ru3+ and Pt4+ in solution with deviations that tend toward Ru enrichment in the alloy phase. The materials gave responses that are similar in terms of peak potential and current density, referenced to the catalyst active surface area, to those of bulk alloys in voltammetry experiments involving CO stripping and CH3OH electrochemical oxidation in 0.1 M H2SO4. The results show that sonochemical methods have the potential to produce nanometer scale bimetallic electrocatalysts that possess alloy properties. The materials have application in mechanistic studies of fuel cell reactions and as platforms for the development of CO tolerant fuel cell catalyst.

Journal Article↗

PubMed2006

Hydration and interfacial water in Nafion membrane probed by transmission infrared spectroscopy.

Infrared spectroscopy was applied to probe water inside pores and channels of Nafion membrane exchanged with either proton (H+) or sodium ions (Na+). Transmission measurements were performed on freestanding Nafion 112 (approximately 50 microm thickness) in a cell that enabled adjustment of the relative humidity. Experiments that employed Na+-exchanged Nafion focused on relative humidity environments at or below about 32% generated through the use of humectants. Under these conditions, narrow features in the O-H stretching spectral region near 3650-3720 cm(-1), previously attributed to interfacial water, were detected and matched to bands in vibrational sum frequency (VSF) spectra of water/air, water/organic, and salt-solution/air interfaces. The features correspond to the stretching mode of the "free" OH group of water oriented with one hydrogen atom toward other water molecules and interacting through hydrogen bonding and the other straddling the interface extending into fluorocarbon-rich regions (approximately 3668 cm(-1)) or air-filled segments (approximately 3700 cm(-1)) in the membrane. For membrane exchanged with H+, -SO3- groups were easily shifted to -SO3H as water was removed upon exposure to a few Torr of vacuum at 95 degrees C. In contrast, residual water was retained by membrane exchanged with Na+ after exposure to these conditions for up to 72 h. The permeation of methanol and acetone into Na+-exchanged Nafion 112 was also examined. The C-H and O-H stretching modes of methanol were perturbed in a manner that suggests the polymer disrupts hydrogen bonding interactions within the solvent, similar to the effect it exerts on pure water. For acetone, the C-H stretching modes were not shifted appreciably compared to those of the bulk liquid. However, the carbonyl band was affected, indicating the likely importance of dipolar interactions between solvent molecules and polar groups on the polymer. Control experiments performed with poly(hexafluoropropylene-co-tetrafluoroethylene) (FEP) membrane did not show evidence for water or methanol permeation, which demonstrates the critical role played by the ion-filled channels and pores in facilitating solvent transport within Nafion membrane.

Journal Article↗

PubMed2005

Enhancing sonochemical activity in aqueous media using power-modulated pulsed ultrasound: an initial study.

Relatively little is known about the effects of pulsed ultrasound on the facilitation of chemical reactivity. Previous studies have indicated that sonochemistry using pulses is generally less effective than continuous ultrasonic irradiation. However, the pulse trains employed were such that the peak power of the pulses was the same as the maximum power used in continuous irradiation. As a result, less acoustic energy was transmitted to the solutions over the same period of time. The effectiveness of ultrasound when the pulse is adjusted so that the same amount of acoustic energy is input compared to continuous irradiation over a given time has not been previously explored. In this study we have embarked on an examination of the efficacy of power-modulated pulsed (PMP) sonochemistry. Specifically, we have explored the effects of pulse type and pulse frequency on the oxidation of potassium iodide and the degradation of acid orange, a common industrial colorant. A rate increase by a factor of three was observed compared with continuous irradiation under conditions of equivalent acoustic input power.

Journal Article↗

PubMed2004

Facile sonochemical synthesis of graphite intercalation compounds.

[reaction: see text] Graphite intercalation compounds (GICs) are useful as powerful reducing agents in organic chemistry and are typically prepared by anaerobic solid-state reactions at high temperatures for 1-8 h. We have been able to prepare KC(8) in situ in toluene using ultrasound in less than 5 min. This allows for a convenient approach to reductive chemical syntheses involving GICs.

Journal Article↗

PubMed2002

Design and calibration of a single-transducer variable-frequency sonication system.

The design of a novel single-transducer variable-frequency sonication system capable of operating at constant acoustic power over the range 20-500 kHz is described. The system employs a mass-loaded sandwich transducer arrangement and a series of transformers to provide an accurate impedance matching circuit. Approximately 0-5 W of acoustic power are produced by the system at typical operating frequencies of 20, 40, 150, 200, 300, and 450 kHz. As a first test of the single-transducer variable-sonication system we have re-examined the frequency dependence of the sonochemical oxidation of potassium iodide. Previous investigators have monitored the frequency dependence using a multi-transducer system to obtain the different frequencies required. In accordance with the earlier findings, we have observed an eightfold increase in the rate of potassium iodide oxidation at 300 kHz compared to 20 kHz, as well as an inversion in the rate of oxidation for argon and air-saturated solutions at 300 kHz. Possible reasons for the rate variations are discussed.

Journal Article↗

PubMed2002

Frequency effect on the sonochemical remediation of alachlor.

The effect of ultrasonic frequency on the sonodegradation of alachlor is described. The rate observed for the destruction of alachlor is approximately 25 times faster at 300 kHz under argon saturation than at 20 kHz under comparable acoustic input energy. The effect of variation of a number of extrinsic parameters such as dissolved gases, radical scavengers and hydroxyl radical promoters is also explored. Argon-saturated solutions display an enhancement in rate by a factor of two compared to either oxygen- or air-saturated solutions upon sonication at 300 kHz. The principal ultrasonic degradation products have been determined in air, argon, and oxygen. The products results primarily from cleavage of the N-methoxymethyl unit when sonication occurs in argon and air. Oxygen addition has been observed when the saturating gas is oxygen. The nature of the active site for reactivity of alachlor is discussed.

Acetamides↗