Innovative floating photocatalysts for wastewater remediation

Nowadays, water crisis caused by insufficient water supply and pollution leads to several problems related to drought, famine, and death. In fact, about 1.1 billion people worldwide suffer from poor access to water, and ca. 2.7 billion experience water scarcity for at least one month per year [1]. In this scenario, the treatment of wastewater contaminated by different pollutants is of significant environmental and commercial importance and it urgently requires fast and efficient solutions. Among all the possibilities, heterogeneous photocatalysis has recently emerged as an interesting strategy, operating under mild conditions, and degrading many pollutants without the addition of chemical oxidants [2, 3]. In this perspective, photocatalytic floating devices can be exploited with the final aim to overcome issues related to the use of catalyst-based slurry systems and to maximize light utilization, and photocatalyst aeration. [4] In addition, an unavoidable challenge is to be able to develop alternative photocatalytic systems to TiO2, which has been recently recognized as carcinogenic substance. [5] Herein we present our recent results in the framework of the development and optimization of photoactive materials obtained by immobilizing visible light responsive catalysts (e.g., polyaniline, bismuth oxyhalides) on floating supports characterized by environmentally friendly features (e.g., expanse polyurethane, luffa, a common natural fiber, alginates’ spheres, and Lightweight Expanded Clay Aggregate, LECA). In addition, studies on the photocatalytic activity towards different classes of pollutants (i.e., dyes, drugs, polyphenols) after exposure to solar or visible light irradiation will be described with a special focus on the study of the effect of water matrix (ultrapure or simulated drinking water) and catalyst dosage together with recycling tests in the view of a real application. All the samples were able to almost full degrade the selected model pollutant after 210 min of photocatalytic test under irradiation. These encouraging results open the view towards the future use of the studied innovative systems in real applications, acting as a bridge between environmental protection and circular economy. We thank Velux Stiftung Foundation for the financial support through project 1381 "SUNFLOAT – Water decontamination by sunlight-driven floating photocatalytic systems". [1] https://www.worldwildlife.org/threats/water-scarcity; [2] R. Djellabi, R. Giannantonio, E. Falletta, C. L. Bianchi, Curr. Opin. Chem. Eng., 1, 2021, 100696; [3] G. Ren, H. Han, Y. Wang, S. Liu, J. Zhao, X. Meng, Z. Li, Recent Advances of Photocatalytic Application in Water Treatment: A Review, Nanomaterials, 11(7), 2021, 1804; [4] https://www.sunfloat.unimi.it/; [5] M. Skocaj, M. Filipic, J. Petkovic, S. Novak, Radiol. Oncol., 45 (4), 2011, 227-247.