Comparison of TiO 2 and ZnO for Heterogeneous Photocatalytic Activation of the Peroxydisulfate Ion in Trimethoprim Degradation.

The persulfate-based advanced oxidation process is a promising method for degrading organic pollutants. Herein, TiO 2 and ZnO photocatalysts were combined with the peroxydisulfate ion (PDS) to enhance the efficiency. ZnO was significantly more efficient in PDS conversion and SO 4 •- generation than TiO 2 . For ZnO, the PDS increased the transformation rate of the trimethoprim antibiotic from 1.58 × 10 -7 M s -1 to 6.83 × 10 -7 M s -1 . However, in the case of TiO 2 , the moderated positive effect was manifested mainly in O 2 -free suspensions. The impact of dissolved O 2 and trimethoprim on PDS transformation was also studied. The results reflected that the interaction of O 2 , PDS, and TRIM with the surface of the photocatalyst and their competition for photogenerated charges must be considered. The effect of radical scavengers confirmed that in addition to SO 4 •- , • OH plays an essential role even in O 2 -free suspensions, and the contribution of SO 4 •- to the transformation is much more significant for ZnO than for TiO 2 . The negative impact of biologically treated domestic wastewater as a matrix was manifested, most probably because of the radical scavenging capacity of Cl - and HCO 3 - . Nevertheless, in the case of ZnO, the positive effect of PDS successfully overcompensates that, due to the efficient SO 4 •- generation. Reusability tests were performed in Milli-Q water and biologically treated domestic wastewater, and only a slight decrease in the reactivity of ZnO photocatalysts was observed.