Photocatalytic degradation and pollutant-oriented structure-activity analysis of carbamazepine, ibuprofen and acetaminophen over faceted TiO2

Photocatalytic degradation of carbamazepine, ibuprofen, acetaminophen and phenol was studied in the presence of anatase photocatalyst, exposing three different crystal facets in the majority of {0 0 1}, {1 0 0} or {1 0 1}. It was found that octahedral anatase particles exposing {1 0 1} facets allow to achieve the best degradation and mineralization of all persistent organic pollutants. This confirms that the previous findings, showing high {1 0 1} activity, are not limited to phenol and could be generalized for other water pollutants. Based on the obtained results, a correlation model including exposed TiO2 crystal facet and chemical hardness of the pollutant was developed to predict the degradation rate of pollutants with a possibly diverse electronic structure. The structure-activity analyses, based on the reactivity predictors obtained from the DFT calculations for all tested compounds, have shown that pollutants with higher chemical hardness react faster with the photocatalyst. Alternatively, a similar effect was observed for the higher HOMO-LUMO energy gap of the compound. This relation indicates that for compounds with a low energy position of LUMO orbital, e.g., carbamazepine, process efficiency is not strictly dependent on the stability of h+ generated organic radical, which is often pointed out as an initial reactive form. Based on these results, a correlation model was developed for the first time to quantitatively describe the effect of the facet-pollutant interactions based on their independent electronic properties. Finally, this was followed by the detailed degradation study of the pharmaceuticals mixture, showing the impact of the total concentration and role of active species on the degradation efficiency over facet-engineered TiO2 photocatalysts.