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203. Comparative Study of Four TiO2-Based Photocatalysts to Degrade 2,4-D in a Semi-Passive System.

Author

Heydari, Gisoo, Hollman, Jordan, Achari, Gopal, and Langford, Cooper H.

Subjects
TITANIUM dioxide, PHOTOCATALYSTS, DICHLOROPHENOXYACETIC acid, LIGHT emitting diodes, ENERGY consumption
Abstract

In this study, the relative efficiency of four forms of supported titanium dioxide (TiO2) as a photocatalyst to degrade 2,4-dichlorophenoxyacetic acid (2,4-D) in Killex®, a commercially available herbicide was studied. Coated glass spheres, anodized plate, anodized mesh, and electro-photocatalysis using the anodized mesh were evaluated under an ultraviolet – light-emitting diode (UV-LED) light source at λ = 365 nm in a semi-passive mode. Energy consumption of the system was used to compare the efficiency of the photocatalysts. The results showed both photospheres and mesh consumed approximately 80 J/cm3 energy followed by electro-photocatalysis (112.2 J/cm3), and the anodized plate (114.5 J/cm3). Although electro-photocatalysis showed the fastest degradation rate (K = 5.04 mg L−1 h−1), its energy consumption was at the same level as the anodized plate with a lower degradation rate constant of 3.07 mg L−1 h−1. The results demonstrated that three-dimensional nanotubes of TiO2 surrounding the mesh provide superior degradation compared to one-dimensional arrays on the planar surface of the anodized plate. With limited broad-scale comparative studies between varieties of different TiO2 supports, this study provides a comparative analysis of relative degradation efficiencies between the four photocatalytic configurations. [ABSTRACT FROM AUTHOR]

Published
2019
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204. ON THE SOLVATION OF IONS IN DIPOLAR APROTIC SOLVENTS. CHLORINE-35 NUCLEAR MAGNETIC RESONANCE STUDIES OF CHLORIDE ION IN MIXED SOLVENTS

Author

MASSACHUSETTS UNIV AMHERST DEPT OF CHEMISTRY, Stengle,Thomas R., Langford,Cooper H., MASSACHUSETTS UNIV AMHERST DEPT OF CHEMISTRY, Stengle,Thomas R., and Langford,Cooper H.

Abstract

The chemical shift of the Cl-35 NMR signal was used as a probe for the investigation of the solvation of the chloride ion in solvent mixtures of water-acetonitrile and water-dimethyl sulfoxide. First it was shown that the chemical shift is independent of the nature of the cation and the salt concentration; that is, the counter ion has no effect on the experimental parameter. The chemical shift then should reflect the composition of the solvation sphere. In acetonitrile-water mixtures, chloride ion shows a strong preference for water; presumably the result of hydrogen bonding between H2O and Cl(-). In DMSO-water mixtures however, there appears to be nearly equal competition for Cl(-) solvation sites. A possible explanation of this unexpected behavior is advanced. (Author), Prepared in cooperation with Carleton Univ., Ottawa (Ontario), Dept. of Chemistry.

Published
1969

205. RATES OF EXCHANGE OF SOLVENT MOLECULES WITH PARAMAGNETIC IONS.

Author

MASSACHUSETTS UNIV AMHERST DEPT OF CHEMISTRY, Stengle,Thomas R., Langford,Cooper H., MASSACHUSETTS UNIV AMHERST DEPT OF CHEMISTRY, Stengle,Thomas R., and Langford,Cooper H.

Abstract

A summary is given of a program aimed at the elucidation of the factors which determine the rate of solvent exchange (and ligand substitution) reactions with transition metal ions in solution. In many octahedral complexes it has become apparent that the reaction is mainly dissociative in nature, and that it is relatively independent of the entering group. Hence the composition of the second coordination sphere (solvation shell) plays an important role in the reaction rate. It was necessary to work out techniques for the determination of the composition of the solvation shell of a complex ion. Several methods of accomplishing this were developed; all of them depending on nuclear magnetic resonance measurements. Then exchange rates with metal ions and dimethylformamide were studied in depth. Some other systems were examined in less detail. There has resulted from the work a useful technique for the study of the kinetics and mechanisms of solvolysis reactions. (Author)

Published
1967

206. Ligand Substitution Processes

Author

Langford, Cooper H., Gray, Harry B., Langford, Cooper H., and Gray, Harry B.

Abstract

From the preface: The subject of the mechanistic study of ligand substitution reactions is currently undergoing an exciting growth. New fast-reaction techniques have removed the upper limit on rates that can be measured, and extension to less familiar central metal atoms has begun in earnest. This might seem the wrong moment for review of the field. As yet, definitive treatment is possible only for those complexes involving monodentate ligands with cobalt(III) and platinurn(II). But, because information is so extensive for these systems, it is clear that they are functioning as models from which concepts and experiments are generated for application over the fast-growing range of the subject. We believe that this is an important moment to reopen debate on fundamentals so that concepts will be most felicitously formulated to aid growth of understanding. This monograph is centrally concerned with three aspects of those fundamentals. We have attempted to develop an approach to classification of ligand substitution reactions that is adapted to what seem to have emerged as the characteristic features of these reactions and is susceptible to operational tests. (We do recognize that any such scheme of ideas is necessarily obsolescent once it is formulated since new experiments will certainly follow immediately.) We have tried to evaluate the basis for making generalizations about ligand substitution processes and to formulate tests to show whether new reactions fall within familiar patterns. Finally, we have sought to base the models of ligand substitution processes in the language of molecular-orbital theory. We believe that MO theory is most useful, because it may be used to correlate rate data on complexes with the extensive information available from spectral and magnetic studies, yet differs from crystal-field theory in providing a natural place for consideration of the bonding electrons, which must be a principal determinant of reaction processes. To keep this essay

Published
1966

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