Sulfonated Pentablock Copolymer with Graphene Oxide for Co2+ Ions Removal: Efficiency, Interaction Mechanisms and Secondary Reaction Products

In this work, sulfonated pentablock copolymer (s-PBC) and s-PBC mixed with graphene oxide (s-PBC_GO) layers were deposited on polypropylene (PP) fibrous filters and tested as active coatings for the removal of cobalt ions from water using adsorption and filtration processes. Some of the coated filters were treated by UV light irradiation to modify their hydrophilic properties. The filters were characterized, before and after the processes, by energy-dispersive X-ray (EDX) analysis and Fourier transform infrared spectroscopy (FT-IR). The Qt (mg/g) values, defined as the weight ratio between the removed ions and the coating layer, were evaluated. In the case of adsorption processes, the best results for the removal of Co2+ ions were achieved by the s-PBC_GO coating, with a Qt of 37 mg/g compared to 21 mg/g obtained by the s-PBC. This was ascribed to the presence of GO, which contains more favorable sites able to adsorb positive ions from the solution. Vice versa, for filtration processes, the s-PBC coated filters show similar or slightly better results than the s-PBC_GO coated ones. Such differences can be ascribed to the shorter contact time between the solution and the coating layer in the case of filtration, with respect to adsorption processes, thus reducing the chance for the ions to be adsorbed on the GO layers before passing through the filter. A collateral effect, observed in this study and enhanced in the case of UV-treated coatings, is the release of radical oxysulfur species. The mechanisms involved in this effect are discussed and identified as a consequence of the interaction between the coating layers and metal ions. In order to identify the mechanism of oxysulfur radicals formation and considering a water sample closer to real water, the Co2+ ions adsorption experiments were conducted in the presence of a competitive organic contaminant (i.e., methyl orange, MO).