Photocatalytic OH radical formation and quantification over TiO2 P25: producing a robust and optimised screening method

The development of photocatalytic technology has grown significantly since its initial publication and as such, a number of screening methods have been developed to assess activity. In the field of environmental remediation, a crucial factor is the formation of highly oxidising species such as OH radicals. These radicals are often the primary driving force for the removal and breakdown of organic and inorganic contaminants. The quantification of such compounds is challenging due to the nature of the radical, however indirect methods which deploy a chemical probe to essentially capture the radical have been shown to be effective. As discussed in the work presented here, optimisation of such a method is fundamental to the efficiency of the method. A starting concentration range of coumarin from 50 μmol/L to 1000 μmol/L was used along with a catalyst loading of 0.01g/L to 1 g/L TiO2 to identify that 250 μmol/L and 0.5 g/L TiO2 were the optimum conditions for production. Under these parameters a maximum production rate of 35.91 μmol/L (Rmax = 0.4 μmol/L OH• min-1) was achieved which yielded at photonic efficiency of 4.88 OH• moles photon-1 under UV irradiation. The data set presented also highlighted the limitations which are associated with the method which included; rapid exhaustion of the probe molecule and process inhibition through UV light saturation. Identifying both the optimum conditions and the potential limitations of the process were concluded to be key for the efficient deployment of the photocatalytic screening method.