Polydopamine coated polyvinyl alcohol sponges as floatable co-catalysts for boosting the CaO2/Fe3+ system in dye degradation

Polydopamine (PDA) has shown charming co-catalytic activity in the classical Fenton and Fenton-like reactions. However, the improvement is merely attributed to the Fe 2+ regeneration ability of PDA. The co-catalytic role and cycling stability of PDA in the CaO 2 based Fenton-like reaction have been rarely explored despite CaO 2 is considered safer than the liquid H 2 O 2 . In this study, floatable co-catalysts were fabricated by coating PDA on polyvinyl alcohol (PVA) sponges. It is proven that in the composite can accelerate not only the Fe 3+ reduction but also the reaction between Fe 2+ and H 2 O 2 released by CaO 2 . Therefore, lower concentrations of Fe 2+ and H 2 O 2 in the CaO 2 /Fe 3+ Fenton-like system were detected respectively, along with higher efficiency in Rhodamine B (RhB) removal. In addition, in the reusing test, the RhB degradation still maintained at 81.2% after the fifth cycle. The reasons for the decreased activity were carefully investigated. First, the RhB adsorption is largely disturbed by the Ca 2+ and Fe 3+ /Fe 2+ ions adsorbed during the reaction. Secondly, both declined Fe 2+ regeneration and H 2 O 2 consumption were observed, due to the reduced content of phenolic hydroxyl groups on the PDA surface.