0000000000001281
AUTHOR
Jean-pierre Aguer
Photoinductive efficiency of soil extracted humic and fulvic acids
Humic and fulvic acids extracted from soils of different genesis were investigated for their ability to photoinduce the transformation of fenuron (2 x 10(-4) mol(-1)) at 365 nm. The ratio of the initial rate of fenuron consumption over the rate of light absorption by humic substances was found to be higher for fulvic acids (range 2.0 x 10(-3) to 9.0 x 10(-5)) than for humic acids (range 1.7 x 10(-4) to - 3.6 x 10(-5)). Within the FAs population, this ratio decreased as the specific absorption coefficient at 365 nm increased. It seems therefore that most of 365-nm absorbing components have no photoinductive activity and even reduce that of photoinductive chromophores.
Transformation of monuron photosensitized by soil extracted humic substances: energy or hydrogen transfer mechanism?
The humic and fulvic acids extracted from a Ranker type soil sensitize the transformation of monuron. When monuron is irradiated at 365 nm in the presence of the fulvic acid, its degradation is faster in deoxygenated medium than in air-saturated solution. Chloride ions are released, and the para-hydroxylated derivative is formed as upon direct photolysis. It is deduced that the consumption of monuron observed in the absence of oxygen is due to an energy transfer from reactive triplet states of the fulvic acid to monuron. Energy transfer reactions also take place when hydroquinone or acetophenone are used as sensitizers, showing that the energy level of the triplet state of monuron is lower …
Comparison of the photoinductive properties of commercial, synthetic and soil-extracted humic substances
Abstract The photochemical behavior of a fulvic acid (FA) and several humic acids (HAs) were studied. These synthetic, commercial or soils-extracted humic substances were compared according to their abilities to sensitize the formation of singlet oxygen and to photoinduce the transformation of aromatic compounds such as 2,4,6-trimethylphenol (TMP) and 1,1-dimethyl-3-phenylurea (fenuron). Singlet oxygen was detected by ESR experiments, and quantum yields of singlet oxygen formation were measured by using 1,2-difuranyl-2-hydroxyethanone (furion) as a probe molecule. The photoinductive capacities were evaluated from the kinetics of TMP and fenuron disappearance. The humic substances that showe…