Comparison of TiO2 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, TiO2 and ZnO photocatalysts were combined with the peroxydisulfate ion (PDS) to enhance the efficiency. ZnO was significantly more efficient in PDS conversion and SO4 center dot- generation than TiO2. For ZnO, the PDS increased the transformation rate of the trimethoprim antibiotic from 1.58 x 10(-7) M s(-1) to 6.83 x 10(-7) M s(-1). However, in the case of TiO2, the moderated positive effect was manifested mainly in O2-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 SO4 center dot-, center dot OH plays an essential role even in O-2-free suspensions, and the contribution of SO4 center dot-- to the transformation is much more significant for ZnO than for TiO2. The negative impact of biologically treated domestic wastewater as a matrix was manifested, most probably because of the radical scavenging capacity of Cl- and HCO3-. Nevertheless, in the case of ZnO, the positive effect of PDS successfully overcompensates that, due to the efficient SO4 center dot-- 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.

Automated summary

The persulfate-based advanced oxidation process is a promising method for degrading organic pollutants. The combination of TiO2 and ZnO photocatalysts with PDS enhances the efficiency. ZnO is more efficient in PDS conversion and SO4 center dot- generation than TiO2. The interaction between O-2, PDS, and TRIM and their competition for photogenerated charges are important factors to consider. SO4 center dot- and center dot OH both play essential roles in the transformation. The negative impact of biologically treated domestic wastewater is due to the radical scavenging capacity of Cl- and HCO3-, but the positive effect of PDS compensates for this.