Accurate Removal of Trace 17β-Estradiol and Estrogenic Activity in Blended Systems under a Photoelectrocatalytic Circulating Flow.

Trace 17β-estradiol (E2) is persistent against advanced treatment when blended with higher concentrations of low-toxicity organics, thus wasting energy. A circulating-flow selective photoelectrocatalysis (CF-SPEC) system is established with a selective E2-TiO2-NR photoanode, accurately reducing 1 μg L-1 E2 to less than 0.1 ng L-1 along with eliminating estrogenic activity even when blended with natural organic matter (NOM) at a thousand times higher concentration. Such high efficiency is derived from the augmented selectivity and activity of E2-TiO2-NRs toward E2 during CF-SPEC. Under a flow, the difference in adsorption capacity between NOM and E2 is further amplified 5.6-fold. Furthermore, the higher initial •OH concentration and faster mass transfer jointly endow CF-SPEC with a stronger oxidation capacity. As a result, the removal of E2 increases by 58.7%, and the elimination of estrogenic activity increases 5.8-fold. In addition, deeper mineralization and less homo- and heterocoupling under CF-SPEC are observed, leading to more thorough estrogenic activity removal. Although additional energy is needed to maintain the flow, there is a 55% decrease in energy consumption due to the accurate removal capacity. This work suggests a combination of flow degradation and surface engineering that can be expanded for the selective removal of toxic trace pollutants in blended systems.