Floating smart materials for water decontamination under solar light

Recently, environmental remediation became a global concern due to fresh-water scarcity and groundwater pollution. Various organic and inorganic molecules, derived from both anthropic and natural sources, lower drinking-water quality. Within emerging contaminants, persistent organic pollutants (POPs) raise researchers’ interest because of their bio-accumulation and toxicity. Therefore, it has been necessary to develop innovative and inexpensive materials able to degrade these toxic compounds. In this regard, heterogeneous photocatalysis offers a green solution for the production of photoactive devices for water remediation. Titanium dioxide (TiO2), an inexpensive semiconductor highly photoactive in the UV region, is the most used photocatalyst. However, its efficiency is severely limited under solar light due to its wide band-gap (3.2 eV). For this reason, researchers are willing to improve its activity by doping it, for example with noble metals or non-metals compounds. In particular, it has been proved that doping TiO2 with conductive polymers, such as polyaniline (PANI), is able to broaden its band-gap extending the photo-response to the visible region. Moreover, the catalyst can be immobilized on a suitable substrate to decrease costs and difficulties related to material recovery and recycling. The substrate needs to be physico-chemically stable, transparent to UV radiation and with an high surface area. In this context, floating supports are attracting great interest due to their ability to maximize the light utilization and the water oxygenation increasing the efficiency of the overall photocatalytic process. Synthetic polymers, such as polyurethane (PU), have been commonly employed as floating materials thanks to their light-weight, stability and low cost. In the present work, visible light photoactive devices were prepared immobilizing PANI/TiO2 with PANIcomposites on floating PU foams. The activity of these materials, under solar light irradiation, have been monitored through the degradation of an organic model molecule (rhodamine B). Additionally, recycle tests have been performed in order to verify floating photocatalysts activity and stability after numerous experiments.