Studies on Kinetics and Thermodynamics of Effects of Primary Colours on Photochemical Reactions: Degradation of Hydrogen Peroxide in Focus

Abstract

Green as one of the primary colours of white light in sunlight is reflected alongside absorption of other wavelengths of electromagnetic radiation by leaf before photosynthesis can take place, with no application of extra external energy and without pollutants. Given that green is one of the primary colours of white light, effect of irradiating H2O2 with primary colours was investigated. [H2O2] used ranged from 0.055Mdm-3to 0.075Mdm-3, duration of irradiation with LEDs and sunlight ranged from 300s to 1800s, while temperature during irradiation ranged from 293k to 313k. Primary colours were absorbed with 0.01M KMnO4, 0.01M methyl orange 1M CuSO4 and 1M NiSO4. Titre of KMnO4 consumed by H2O2 after irradiation was a measure of [H2O2] degraded. It was observed that low [H2O2] had negative Eas, while high [H2O2] had positive Eas, for S-g. For W-r, low [H2O2] had positive Eas while high [H2O2] had negative Eas. Although negative and positive Eas for other LED and sunlight irradiations showed no trend, magnitude of Eas decreased in the order; W-g>GLED>BLED>W-r; and S-g>S. There was increase in ?G as temperature increased for both LED and sunlight irradiations.?Gs for BLED were all positive, while the rest of LED and sunlight irradiation had at most two negative ?Gs. Although irradiations from both LEDs and sunlight showed no degradation trend, the magnitude of ?Gs decreased in the order; BLED>GLED>W-g>W-r; and S-g>S. WLED>RLED>W-b>W-br induced no observable degradation of H2O2. W-g and S-g did not degrade H2O2 at 313k. S-b, S-r and S-br degraded H2O2 in at most two temperatures. W-g and S-g degraded 0.075Mdm-3 H2O2 and 0.070Mdm-3 H2O2, just like all [H2O2] under sunlight irradiation, in second order pattern, while the rest degraded H2O2 in first order pattern. W-r, that is equivalent to combining BLED and GLED in subsequent researches is most favorable to H2O2 degradation and could lead to smearing light absorption materials on surfaces of devices like solar panels.