Oxidative Coupling Processes on Fe(III)-Montmorillonite Surfaces: Polymerization of 17β-Estradiol and Cross-Coupling with Natural Organic Matter.

A systematic investigation of surface mediated 17β-estradiol polymerization via oxidative coupling on Fe(III)-montmorillonite surfaces was described  in this study. It was demonstrated that 17β-estradiol can be effectively polymerized on Fe(III)-montmorillonite surfaces into dimers, trimers and tetramers, which were identified and confirmed by LC/MS. Carbon mass balance result suggested that polymers longer than tetramers were possibly formed. Moreover, computational modeling based on density functioned theory displayed the most stable 17β-estradiol dimer and trimer conformers and proposed most possible Fe(III)-montmorillonite surfaces-catalyzed 17β-estradiol polymerization pathways. Our study demonstrated that Fe(III)-montmorillonite remained effective for 17β-estradiol polymerization after at least 5 repetitive uses. Using catechol as model compound that mimics the phenolic moieties of natural organic matter, we confirmed by EPR spin trapping technique possible cross-coupling between catechol and 17β-estradiol on Fe(III)-montmorillonite surface. The cross coupling products were confirmed using LC/MS. This result suggests the possibility of using Fe(III)-montmorillonite to catalyze 17β-estradiol polymerization and the formation of stable natural organic matter-17β-estradiol complexes during wastewater treatment processes.