Optimisation of the chemical generation of singlet oxygen (1O2, 1Δg) from the hydrogen peroxide–lanthanum(iii) catalytic system using an improved NIR spectrometer

Abstract

A near-IR chemiluminescence spectrometer designed to study chemical sources of singlet oxygen (¹O₂, ¹Δ_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 ¹O₂ from the hydrogen peroxide–lanthanum(III) catalytic system. The reaction kinetics were studied with a 2³3³//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 H₂O₂ (0.5, 1 or 2 mol L⁻¹), the temperature (20 or 30 °C) and the concentration of EDTA (0 or 5 mmol L⁻¹). Two responses were measured: the rate of H₂O₂ disproportionation and the intensity of the luminescence of ¹O₂ at 1270 nm. The essential factor is the nature of the lanthanum salt since La(NO₃)₃ induces the disproportionation of H₂O₂ about 60 × faster than La₂O₃ or La(OH)₃. Other influencing factors are the pH value, the concentration of H₂O₂, 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(NO₃)₃ was then investigated in further detail by studying the influence of two factors (pH and [H₂O₂]) thanks to a Doehlert design.