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 Fe2+ regeneration ability of PDA. The co-catalytic role and cycling stability of PDA in the CaO2 based Fenton-like reaction have been rarely explored despite CaO2 is considered safer than the liquid H2O2. 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 Fe3+ reduction but also the reaction between Fe2+ and H2O2 released by CaO2. Therefore, lower concentrations of Fe2+ and H2O2 in the CaO2/Fe3+ 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 Ca2+ and Fe3+/Fe2+ ions adsorbed during the reaction. Secondly, both declined Fe2+ regeneration and H2O2 consumption were observed, due to the reduced content of phenolic hydroxyl groups on the PDA surface.