Innovative Floating Materials For Water Remediation Under Sunlight

In the last decades, environmental remediation became an imperative issue due to fresh-water scarcity and groundwater pollution. Several organic and inorganic compounds, derived from both anthropic and natural activities, lower drinking-water quality. Among the emerging contaminants, persistent organic pollutants (POPs) raise concerns because of their bio-accumulation and toxicity. Therefore, the field of research has been led towards the production of innovative and inexpensive materials. In this context heterogeneous photocatalysis provides a green path for the development of photoactive devices for water remediation. The most used catalyst is titanium dioxide (TiO2), an inexpensive semiconductor highly photoactive in the UV region. However, under solar light its efficiency is severely limited due to its wide band-gap (3.2 eV). For this reason, researchers are willing to improve its activity by extending the photo-response to the visible region. If on the one hand it has been proved that TiO2 band-gap can be decreased by different approaches (e.g., by doping with noble metals), on the other hand new metal-free materials, highly active under sunlight, have also been developed. Moreover, to overcome difficulties related to material recovery and recycling when the photocatalyst is used dispersed into the water medium, it can be immobilized on a suitable substrate. The substrate has to be transparent to UV radiation, physico-chemically stable and with an high surface area. In this regard, the use of floating supports is attracting great interest thank to their ability to maximize the light utilization and the water oxygenation improving the efficiency of the overall photocatalytic process. Recently, synthetic and natural polymers, such as polystyrene (PS), polyurethane (PU) and modified alginic acid obtained from brown seaweeds, inorganic materials such as expanded perlites and light expanded clay aggregates (LECA) have been commonly employed as floating materials. In the present study, photoactive materials were prepared immobilizing a visible light responsive catalyst on floating supports. The activity of these materials have been followed through the degradation of an organic model molecule (rhodamine B) and for the reduction of Cr(VI) under solar light irradiation. Additionally, floating photocatalysts were subjected to recycle tests in order to verify their activity and stability after several experiments.