Surface Catalyzed Oxidative Oligomerization of 17β-Estradiol by Fe3+-Saturated Montmorillonite

With widespread detection of endocrine disrupting compounds including hormones in wastewater, there is a need to develop cost-effective remediation technologies for their removal from wastewater. Previous research has shown that Fe3+-saturated montmorillonite is effective in quickly transforming phenolic organic compounds such as pentachlorophenol, phenolic acids, and triclosan via surface-catalyzed oligomerization. However, little is known about its effectiveness and reaction mechanisms when reacting with hormones. In this study, the reaction kinetics of Fe3+-saturated montmorillonite catalyzed 17 beta-estradiol (beta E2) transformation was investigated. The transformation products were identified using liquid chromatography coupled with mass spectrometry, and their structures were further confirmed using computational approach. Rapid beta E2 transformation in the presence of Fe3+-saturated montmorillonite in an aqueous system was detected. The disappearance of beta E2 follows first-order kinetics, while the overall catalytic reaction follows the second-order kinetics with an estimated reaction rate constant of 200 +/- 24 (mmol beta E2/g mineral)-1 h(-1). The half-life of beta E2 in this system was estimated to be 0.50 +/- 0.06 h. beta E2 oligomers were found to be the major products of beta E2 transformation when exposed to Fe3+-saturated montmorillonite. About 98% of beta E2 were transformed into beta E2 oligomers which are >107 times less water-soluble than beta E2 and, therefore, are much less bioavailable and mobile then beta E2. The formed oligomers quickly settled from the aqueous phase and were not accumulated on the reaction sites of the interlayer surfaces of Fe3+-saturated montmorillonite, the major reason for the observed >84% beta E2 removal efficiency even after five consecutive usages of the same of Fe3+-saturated montmorillonite. The results from this study clearly demonstrated that Fe3+-saturated montmorillonite has a great potential to be used as a cost-effective material for efficient removal of phenolic organic compounds from wastewater.