Recebido em 13/1/04; aceito em 27/1/05; publicado na web em 30/6/05 CONSTRUCTION AND PERFORMANCE STUDIES OF A CPC TYPE PHOTOCHEMICAL REACTOR. A CPC (Compound Parabolic Concentrator) reactor was projected and constructed aiming to promote the degradation of the organic matter present in considerable volumes of aqueous effluents, under the action of solar radiation. The essays were done using a model effluent which consists of a mixture of fragments of a sodium salt of lignosulphonic acid possessing a mean molecular weigth of 52,000 Daltons, and a real effluent, from a chip board industry. The volume of effluent in each test was about 50 L. The tests involved heterogeneous (TiO 2 P25 Degussa and formulations made from the association of TiO 2 with a photosensitiser), and homogeneous (thermal and photochemical Fenton reactions) catalysis of the effluents. The results demonstrate the viability of application of this kind of reactor even when the load of organic pollutants is high.
The photophysics of 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one was studied in different solvents and in SDS micelles. This compound presents characteristics which include an S(0)---> S(1) ( pi,pi*) transition with a (1)(n,pi*) perturbative component, due to the electronic coupling between the diethylamino group and the coumarin ring, considerable solvatochromism, dual fluorescence and high fluorescence quantum yields in almost all solvents studied. The electronic structure of the S(1) and S(2) excited states permits vibronic coupling between them, making configurational changes of the S(2) excited state possible, leading to the formation of an S(2)(TICT) state. Analysis of the TCSPC data indicates an equilibrium between the S(2)(TICT) and S(1)(LE) states in favour of the former. In protic solvents, the hydrogen bonding between the solvent and the diethylamino moiety results in the formation of an S(2)(HICT) state, making internal conversion an important deactivation process. Quantum mechanical calculations for the isolated molecule show that the diethylamino group in the S(2)(TICT) state is twisted at least 56 degree from the plane of the coumarin ring, with partial electronic decoupling between -NEt(2) and the coumarin ring. This twisting angle must be positively influenced by solute-solvent interactions. [capital Phi](ST) is found to be small, but not negligible. However, Phi (delta) can be considered negligible, an indication that T(1) is a short-lived state. Based on the experimental data and theoretical calculations, the most probable sequence for the first excited states, including the TICT state, is T(1)(n, pi*) < S(2)(TICT) < S(1)(pi,pi*) approximate S(2) (n,pi*).
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