Efficacy and reusability of mixed-phase TiO2?ZnO nanocomposites for the removal of estrogenic effects of 17?-Estradiol and 17?-Ethinylestradiol from water

Photocatalytic removal of estrogenic compounds (ECs), 17?-estradiol (E2), and 17?-ethinylestradiol (EE2) were assessed using a TiO2?ZnO nanocomposite (NC) over a range of initial EC concentration (Co; 10 mg/L ? 0.05 mg/ L). Photocatalytic removal was evaluated under UV and visible irradiation using 10 mg/L NC over 240 min duration. After 240 min, analysis using GCxGC TOF MS revealed 100% transformation at Co < 1 mg/L and ?25% transformation at Co < 10 mg/L under visible irradiation. Degradation was accompanied by breakdown of the fused ring structure of E2, generating smaller molecular weight by-products which were subsequently mineralized as revealed through TOC removal. With UV photocatalysis, -30% and -20% mineralization was attained for E2 and EE2, respectively, for Co of 10 mg/L. Under visible irradiation, -25% and -10% mineralization was achieved for E2 and EE2, respectively. Estrogenicity variation was estimated using the E-screen assay conducted with estrogen receptor-positive MCF-7 breast cancer cells. Complete removal of estrogenicity of ECs was confirmed after 240 min of photocatalysis under UV and visible irradiation. FTIR spectroscopy-based analysis of the NC after E2 photocatalysis revealed the presence of sorbed organics. Desorption, followed by GC ? GC TOFMS analysis revealed these organics as by-products of photocatalysis. Desorption of sorbed organics followed by recalcination at 600 ?C for 1 h regenerated the active sites on the NC, enabling its efficient reuse for 3 cycles under visible irradiation without loss in activity.