Search

Your search keyword '"Peak, John D."' showing total 14 results
Start Over Author "Peak, John D."
14 results on '"Peak, John D."'

3. The Effect of Oxyanions on the Oxalate-Promoted Dissolution of Goethite

Author

Eick, Matthew J., Peak, John D., and Brady, Warren D.

Subjects
Soil science -- Research, Soil mineralogy -- Research, Soil research -- Analysis, Earth sciences
Abstract

Organic ligand-promoted dissolution of oxide minerals can be enhanced or inhibited in the presence of specifically adsorbed oxyanions. It has been proposed that an oxyanion inhibits or enhances dissolution depending on the type of surface complex formed and the strength of the bond. Mononuclear complexes (especially if they are bidentate) accelerate dissolution, while binuclear complexes inhibit dissolution. Recent spectroscopic evidence indicates that chromate and arsenate form different surface complexes depending on surface coverages. This study examined the influence of chromate and arsenate on the oxalate promoted dissolution of goethite. Based on a previous spectroscopic study, oxyanion surface coverages were varied to generate both mononuclear and binuclear surface complexes. Chromate and arsenate inhibited the oxalate promoted dissolution of goethite at all surface coverages investigated except at pH 6 ([[Gamma].sub.arsenate] = 1.70 x [10.sup.-6] and [[Gamma].sub.chromate = 1.66 x [10.sup.-6] mol [m.sup.-2]). It is proposed that chromate and arsenate inhibit goethite dissolution by decreasing oxalate adsorption. This is accomplished because arsenate and chromate are more effective competitors for goethite surface sites than oxalate and upon adsorption increase the negative charge of the goethite surface. At pH 6 the adsorption of chromate and arsenate increases the negative charge of the goethite surface which in turn increases proton adsorption. Since proton adsorption is a necessary step for oxalate-promoted dissolution of goethite, and since proton activity at pH 6 is low, an increase in the negative charge of goethite upon adsorption of the oxyanions accelerates dissolution.

Published
1999

4. Dual Mechanism Nonlinear Response of Selected Metal Organic Chromophores

Author

FLORIDA UNIV GAINESVILLE, Peak, John D., FLORIDA UNIV GAINESVILLE, and Peak, John D.

Abstract

13 The goal for the research described herein is the development of a series of transition metal based metal organic chromophores that display both two-photon and excited state absorption (TPA/ESA) character. With this goal in mind, we present the preparation and photophysical characterization for a series of metal-organic chromophores containing a two photon absorbing bipyridine core combined with a transition metal component which yields a long-lived triplet excited state. The combination of these two photophysical properties represents a dual mode nonlinear optical (NLO) mechanism. Three major areas of interest for this project are addressed here. First, to develop and instrument an in-house photophysical apparatus with the ability to evaluate and measure two photon activity as well as detect nonlinear optical responses. Second, to synthesize, characterize and evaluate an all organic chromophore system, centered on a bipyridine core, which utilizes known TPA architecture. Lastly, to synthesize, characterize and evaluate the metal organic analogs of the TPA chromophore system utilizing transition metals with high spin-orbit coupling values which help create long-lived triplet excited states leading to a possible ESA. The metalorganic analogs in turn should exhibit a dual mechanism for NLO response comprised of both TPA and ESA.

Published
2007

Catalog

Books, media, physical & digital resources
See catalog results