Enhanced monitoring of photocatalytic reactive oxygen species: using electrochemistry for rapid sensing of hydroxyl radicals formed during the degradation of coumarin

Many recent research studies have reported indirect methods for the detection and quantification of OH radicals generated during photocatalysis. The short lifespan and high reactivity of these radicals make indirect detection using probes such as coumarin a more viable quantification method. Hydroxyl radical production is commonly monitored using fluorescence spectroscopy to determine the concentration of the compound 7-hydroxycoumarin, which is formed from hydroxyl radical attack on coumarin. There are, however, a number of additional hydroxylated coumarins generated during this process, which are less amenable to detection by fluorescence spectroscopy. Consequently, limitations and inaccuracies of this method have previously been reported in the literature. As an alternative approach to those previously reported, this work has developed an electrochemical screening method using coumarin as a OH radical trap, that is capable of in situ monitoring of not only 7-hydroxycoumarin, but all the main mono-hydroxylated products formed. As a result, this technique is a more representative and comprehensive method for the quantification of OH radicals produced by photocatalysts using coumarin as a probe molecule. Moreover, the electroanalytical method provides a portable, rapid, sensitive, and accurate in situ method for the monitoring of OH radical formation without the need for sample preparation.