Issue 7, 2011

Microwave discharge electrodeless lamps (MDEL)

Part VII. Photo-isomerization of trans-urocanic acid in aqueous media driven by UV light from a novel Hg-free Dewar-like microwave discharge thermally-insulated electrodeless lamp (MDTIEL). Performance evaluation

Abstract

A novel mercury-free Dewar-like (double-walled structure) microwave discharge thermally-insulated electrodeless lamp (MDTIEL) was fabricated and its performance evaluated using the photo-isomerization of trans-urocanic acid (trans-UA) in aqueous media as a test process driven by the emitted UV light when ignited with microwave radiation. The photo-isomerization processes trans-UA → cis-UA and cis-UA → trans-UA were re-visited using light emitted from a conventional high-pressure Hg light source and examined for the influence of UV light irradiance and solution temperature; the temperature dependence of the transcis process displayed a negative activation energy, Ea = −1.3 cal mol−1. To control the photo-isomerization of urocanic acid from the heat usually dissipated by a microwave discharge electrodeless lamp (single-walled MDEL), it was necessary to suppress the microwave-initiated heat. For comparison, the gas-fill in the MDEL lamp, which typically consists of a mixture of Hg and Ar, was changed to the more eco-friendly N2 gas in the novel MDTIEL device. The dynamics of the photo-isomerization of urocanic acid driven by the UV wavelengths of the N2-MDTIEL light source were compared to those from the more conventional single-walled N2-MDEL and Hg/Ar-MDEL light sources, and with those from the Hg lamp used to irradiate, via a fiber optic, the photoreactor located in the wave-guide of the microwave apparatus. The heating efficiency of a solution with the double-walled N2-MDTIEL was compared to the efficiency from the single-walled N2-MDEL device. Advantages of N2-MDTIEL are described from a comparison of the dynamics of the trans-UA → cis-UA process on the basis of unit surface area of the lamp and unit power consumption. The considerably lower temperature on the external surface of the N2-MDTIEL light source should make it attractive in carrying out photochemical reactions that may be heat-sensitive such as the photothermochromic urocanic acid system.

Graphical abstract: Microwave discharge electrodeless lamps (MDEL) Part VII. Photo-isomerization of trans-urocanic acid in aqueous media driven by UV light from a novel Hg-free Dewar-like microwave discharge thermally-insulated electrodeless lamp (MDTIEL). Performance evaluation

Supplementary files

Article information

Article type
Paper
Submitted
02 Feb 2011
Accepted
18 Mar 2011
First published
26 Apr 2011

Photochem. Photobiol. Sci., 2011,10, 1239-1248

Microwave discharge electrodeless lamps (MDEL)

S. Horikoshi, T. Sato, K. Sakamoto, M. Abe and N. Serpone, Photochem. Photobiol. Sci., 2011, 10, 1239 DOI: 10.1039/C1PP05059A

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