Turning thiophene contaminant into polymers from wastewater by persulfate and CuO

Turning heterocyclic contaminants into polymers from industrial wastewater is a promising method that opens a new door for feasible and cost-effective treatment for aromatic wastewater. In this study, CuO shows the high reactivity in the catalytic oxidation of thiophene by persulfate (PS) under pH-neutral condition, and the observed rate constant (kobs) in the PS-CuO system is about 10 times of that in the PS-alone system at pH 7.0. The linear relationship between the consumed PS and the removed thiophene reveals that a complete removal of 1.0 mM thiophene from solution requires 1.11 mM PS in the PS-CuO system, indicating that thiophene has not been completely mineralized into CO2 and H2O. Quenching experiments and EPR analysis rule out contributions of O2•− and 1O2 to thiophene oxidation, and suggest that although both SO4•− and •OH contribute to thiophene oxidation to some extent, they are not the primary oxidants in the PS-CuO system at pH 7.0. Meanwhile, the presence of thiophene radical cation indicates that electron abstraction from thiophene is an important pathway in the oxidation. The produced thiophene radical cations are then polymerized into polymers. Solid characterizations further confirm that polythiophene S,S-dioxide is the primary oxidation product. The electrochemical analysis indicates that the produced polythiophene S,S-dioxide polymers show pseudocapacitive characteristics and can be used for capacitors.