Advanced sustainable floating photocatalysts for wastewater remediation

Water is one of Earth’s most important molecules: it is essential for life in our world. Climate change is reshaping water access by causing both droughts and floods: there is not enough water, and the amount that is available is usually tainted with some level of pollutants [1]. In this drastic scenario, treating wastewater contaminated by different pollutants is of crucial environmental and commercial importance and urgently requires fast and highly efficient solutions. Heterogeneous photocatalysis has emerged as an interesting strategy for its ability to degrade mixtures of pollutants without the addition of chemical oxidants under mild conditions [2]. However, photocatalytic processes are less effective when used to treat trace concentrations of pollutants in a large volume of contaminated matrices due to the large reactor sizes, the limited light penetration, the high energy cost, and the difficulties in recycling/reusing the photocatalysts. To facilitate the degradation of pollutants traces, different composites have been studied [3]. However, they are nano-sized materials that, although common, raises concerns about nanotoxicity. The ideal photocatalyst should possess activity, selectivity, stability, non-toxicity, cheapness, and easy handling. Achieving all these requirements is a difficult task. Herein, we present our results related to the development of sustainable photoactive materials obtained by immobilizing innovative adsorptive photocatalysts (i.e., bismuth oxyhalides), on eco-friendly floating supports (e.g., alginate spheres, and Lightweight Expanded Clay Aggregate, LECA). Their obtained performances in the degradation of different pollutants (e.g., dyes, drugs, polyphenols) after exposure to solar light irradiation will be illustrated. A targeted study of the role of water matrix (ultrapure or simulated drinking water), catalyst dosage, type of floating support and recycling tests, approaching the actual application, will be presented with the aim to provide an insight on potential and limitations of each floating device selected for the real application. The promising results obtained open the view toward the future real use of these innovative systems, acting as a bridge between environmental remediation and water reuse. [1] https://www.who.int/news-room/fact-sheets/detail/drinking-water. [2] Djellabi, R. et al., Curr. Opin. Chem. Eng., 2021, 1, 100696. [3] Galloni, M.G. et al., Catalysts 2022, 12(8), 923.