Confirming the Formation of Hydroxyl Radicals in the Catalytic Decomposition of H₂O₂ on Metal Oxides Using Coumarin as a Probe

Abstract

Hydrogen peroxide can be catalytically decomposed to O2 and H2O on metal oxide surfaces in contact with aqueous solutions containing H2O2. The initial step in this process has been proposed to be the formation of surface‐bound hydroxyl radicals which has recently been verified using tris as a radical scavenger. Here, we make use of the unique fluorescent product 7‐hydroxycoumarin formed in the reaction between hydroxyl radicals and coumarin to probe the formation of surface‐bound hydroxyl radicals. The experiments clearly show that 7‐hydroxycoumarin is formed upon catalytic decomposition of H2O2 in aqueous suspensions containing ZrO2‐particles and coumarin, thereby confirming the formation of surface‐bound hydroxyl radicals in this process. The results are quantitatively compared to results on the same system using tris as a probe for hydroxyl radicals. The effects of the two probes on the system under study are compared and it is concluded that coumarin has a significantly lower impact on the system.

Oxidative Coupling of Coumarins by Blue‐LED‐Driven in situ Activation of Horseradish Peroxidase in a Two‐Liquid‐Phase System

“…To exclude the specific presence of ⋅OH radicals in the blue‐LED driven oxidation of 1 to hydroperoxide 2 , the reaction was repeated in the absence of HRP using coumarin 3 b as a well‐recognized ⋅OH acceptor (“coumarin method”) (Figure 4). [53,54] In accordance with the literature, 3 b invariably reacts with ⋅OH at the C‐7 position of the aromatic ring to yield fluorescent derivative 3 a [55] . Under our experimental conditions no traces of 3 a were detected by HPLC analysis (Materials and methods and SI#4).…”

Quantification of hydroxyl radicals in photocatalysis and acoustic cavitation: Utility of coumarin as a chemical probe

“…but not [OH]T when assessing AOPs. Although it has been suggested that coumarin is more useful as a qualitative probe for OH radicals [42], it may be employed quantitatively to determine [OH]1 with the appropriate deliberations. It is first established that coumarin reacts to form a variety of hydroxylation products upon contact with OH [43].…”

Anion effects on the catalytic decomposition of H2O2 on ZrO2(s) in aqueous systems

“…[15] The formation of hydroxyl radicals in the catalytic decomposition of H 2 O 2 on ZrO 2 -powder in aqueous suspension has previously been demonstrated by tris and methanol, and quite recently by the use of coumarin as a probe. [16] In the latter case, the OH radicals react with coumarin mainly by addition, which eventually gives rise to a number of stable hydroxylated products. One of these, 7-hydroxycoumarin, is strongly fluorescent, and can for this reason be detected spectroscopically.…”