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Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology

Optimisation of the chemical generation of singlet oxygen (1O2, 1Deltag) from the hydrogen peroxide-lanthanum(III) catalytic system using an improved NIR spectrometer.


PMID 19582279

Abstract

A near-IR chemiluminescence spectrometer designed to study chemical sources of singlet oxygen ((1)O(2), (1)Delta(g)), was built by coupling a reactor compartment to a nitrogen-cooled Ge diode through a bundle of optical fibres. This device was used to optimise the generation of (1)O(2) from the hydrogen peroxide-lanthanum(iii) catalytic system. The reaction kinetics were studied with a 2(3)3(3)//12 screening experimental design comprising twelve experiments. The influence of six factors was examined: the nature of the lanthanum salt (hydroxide, oxide or nitrate) and its concentration (0.05 or 0.1 mol L(-1)), the pH value (5, 7 or 9), the concentration of H(2)O(2) (0.5, 1 or 2 mol L(-1)), the temperature (20 or 30 degrees C) and the concentration of EDTA (0 or 5 mmol L(-1)). Two responses were measured: the rate of H(2)O(2) disproportionation and the intensity of the luminescence of (1)O(2) at 1270 nm. The essential factor is the nature of the lanthanum salt since La(NO(3))(3) induces the disproportionation of H(2)O(2) about 60 x faster than La(2)O(3) or La(OH)(3). Other influencing factors are the pH value, the concentration of H(2)O(2), the temperature and the concentration of the lanthanum salt whereas the concentration of EDTA has no effect on the reaction. The catalytic activity of La(NO(3))(3) was then investigated in further detail by studying the influence of two factors (pH and [H(2)O(2)]) thanks to a Doehlert design.

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