Caveats in the Use of Tertiary Butyl Alcohol as a Probe for Hydroxyl Radical Involvement in Conventional Ozonation and Catalytic Ozonation Processes

In this study, we enunciate the limitations associated with the use of tert-butanol (TBA) to deduce the contribution of hydroxyl radicals (•OH) in organic oxidation during conventional ozonation and/or heterogeneous catalytic ozonation (HCO). Our results show that TBA is unable to access surface-located •OH formed during HCO. Furthermore, TBA may also interfere with the adsorption of organic compounds on the catalyst surface and decrease the adsorptive as well as concomitant oxidative removal of organics via nonradical-mediated pathways (if important). Our results also demonstrate that TBA scavenging results are inconclusive for mildly ozone reactive compounds due to switching from O3/•OH-mediated oxidation in the absence of TBA to O3-driven oxidation in the presence of TBA. The presence of TBA may also decrease the rate of ozone decay with the increased stability of O3 in the presence of TBA, facilitating (i) direct oxidation of ozone-reactive organics in the bulk solution and/or (ii) diffusion of O3 to the catalyst surface and subsequent surface-mediated oxidation of organics. Overall, we conclude that caution needs to be exercised when interpreting the observations made in the presence of TBA and also describe the further experimentation required to confirm/reject the role of •OH in organic oxidation. The findings of this work should assist in preventing researchers from reaching erroneous conclusions regarding the involvement of •OH in catalytic or conventional ozonation processes.