Abstract
Solid-phase micro-extraction has been used for identifying, quantifying and following the evolution of intermediate products of octanol degradation by two advanced oxidation treatments (AOTs), photocatalytic and ultrasound processes, inducing mainly the same active species.
Headspace extraction enabled direct extraction of the organic compounds in a heterogeneous process like photocatalysis. The presence of a solid does not affect the extraction percentage of alkanes, alkenes and aldehydes while alcohols and carboxylic acids are not completely extracted if the extraction time is too short.
To extract C
3–C
8 alkanes, alkenes and aldehydes a Carboxen/PDMS fiber and an extraction time of 25
min are used. The presence of alcohol and carboxylic acids requires the use of the presence of salt under acidic conditions, a longer extraction time and a polyacrylate fiber (PA), having a polar fiber. The in situ derivatization—pyrenyldiazomethane on a PA fiber—increases the carboxylic acid extraction containing smaller hydrocarboned chain while diazomethane derivatization is not as efficient due to its volatility.
Whatever be the treatment, photocatalysis or ultrasound processes, aldehydes are the main intermediate products, which is not surprising since the same oxidation species (HO
2°, O
2°
−, OH°) are formed. Alkanes and alkenes are also detected in both processes; however, alkane formation is more important in photocatalysis while alkenes are formed in higher amounts by ultrasound. Moreover, the presence of carboxylic acids in more important amounts by ultrasound than by photocatalysis is attributed to the presence of holes (h
+) in photocatalysis which induces photo-Kolbe degradation. The sonochemical formation of small-chained dienes and alkynes is probably due to pyrolysis of hydrophobic compounds in cavitation bubbles.