Investigating the role of bismuth oxyhalides immobilized onto environmentally friendly floating devices in wastewater remediation

Nowadays, the water crisis caused by insufficient water supply and pollution leads to several problems. Indeed, ca. 1.1 billion people worldwide suffer from poor access to water, and 2.7 billion experience water scarcity for at least one month per year [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 traces of pollutants, different composites combine high adsorption capacity and photoreactivity [3]. In this context, a recent unavoidable challenge is to develop sustainable and efficient TiO2-free photocatalytic systems since TiO2 has been recognized as a carcinogenic substance [4]. Herein we present our results related to the development of photoactive materials obtained by immobilizing bismuth oxyhalides (BiOX, where X is Cl, Br, and I), innovative adsorptive photocatalysts, on eco-friendly floating supports (e.g., loofah, and Lightweight Expanded Clay Aggregate, LECA). BiOX are able to concentrate on their surface different pollutants (e.g., dyes, drugs, polyphenols) also in the dark and quantitatively degrade them after exposure to solar light irradiation. A targeted study of the role of water matrix (ultrapure or simulated drinking water), catalyst dosage, and recycling tests, approaching the actual application, will be discussed. All the studied samples almost entirely degrade the selected model pollutant after 210 min of the photocatalytic test under irradiation. By way of example, Figure 1 summarizes some results obtained on a sample consisting of 3 wt.% BiOBr deposited on loofah in experiments of pollutant abatement under solar light irradiation. These evidences open the view toward the future use of these innovative systems in real applications, acting as a bridge between environmental protection and sustainability.