title: 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 trans → cis process displayed a negative activation energy, E(a) = -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 N(2) gas in the novel MDTIEL device. The dynamics of the photo-isomerization of urocanic acid driven by the UV wavelengths of the N(2)-MDTIEL light source were compared to those from the more conventional single-walled N(2)-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 N(2)-MDTIEL was compared to the efficiency from the single-walled N(2)-MDEL device. Advantages of N(2)-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 N(2)-MDTIEL light source should make it attractive in carrying out photochemical reactions that may be heat-sensitive such as the photothermochromic urocanic acid system.
authors.affiliation: Department of Material & Life Science, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyodaku, Tokyo 102-8554, Japan. horikosi@sophia.ac.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Horikoshi
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Sato
authors.forename: Kazutami
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
authors.forename: Nick
authors.initials: N
authors.lastname: Serpone
mesh_terms: D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D008872:Microwaves; D013696:Temperature; D014466:Ultraviolet Rays; D014560:Urocanic Acid / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D014560:Urocanic Acid