Sunlight-powered device for drug degradation: Pioneering sustainable water remediation in vulnerable communities

Nowadays, the preservation of freshwater is a pivotal issue for both human and environment. Pharmaceutical and personal care products (PPCPs), steroids, and hormones are pollutants found in water.1 Among the former, nonsteroidal anti-inflammatory drugs (NSAIDs) are characterized by a broad scope of properties widely used in medicine. Ibuprofen (IBU) and diclofenac (DCF) belong to this category: their consumption has drastically increased due to the rapid growth and aging of world population, thus contributing to the increase of their concentration in surface waters, consequently destroying the aquatic ecosystems and organisms.2 In the above-depicted panorama, the possible purification/reuse of wastewater still represents an unavoidable challenge, since the demand for freshwater due to the population growth and consumption in the agricultural/industrial sectors is continuously increasing. Researchers are hardly working on the development of novel efficient strategies aimed at the NSAIDs abatement from the environment: among them, advanced oxidation processes (AOPs) have emerged.3 In this frame, photodegradations of IBU and DCF have been investigated by several authors, but the most part of photocatalytic systems are in powder form, starting from the conventional titanium dioxide, zinc oxide to more sophisticated-ones (e.g., heterojunctions, etc.).4 This still remains a practical limitation needed to be overcome, since the difficult photocatalyst recovery from the reaction mixture for its reuse can result in incomplete recovery, causing contamination issues and additional costs. In the present scenario, floating photocatalysts are interesting alternatives to be exploited because, thanks to the floatability on the air-water interface, maximize both light utilization and surface aeration, enhancing the pollutant abatement performances and, at same time, decreasing the post-treatment cost.3 In addition, if properly developed in the way to be sustainable and efficient, they could represent a novel innovative paradigm towards the sustainable water remediation for vulnerable communities. Herein, we propose the development of an innovative sunlight-driven device composed by bismuth oxybromide (BiOBr) grown on a man-made material derived from natural sources (Lightweight Expanded Clay Aggregate, LECA), to clean surface waters under natural solar irradiation. The photodegradation of IBU and DCF was investigated under various environmental conditions. Laboratory- and real-scale experiments reveal that the fabricated floating BiOBr/LECA photocatalyst is able to fully degrade diclofenac, whereas restricted abatement of ibuprofen is observed (Figure 1).5 Based on the identification of specific transformation products (TPs) during the degradation reaction, this behaviour seems to be strongly related to the different structures of the two drugs. The main TP produced during DCF degradation derives from dechlorination and rings condensation. This type of photocatalytic degradation pathway is generally easier than breaking of C-C bonds, the unique possible for IBU abatement. Finally, the reusability tests demonstrate the high stability of the floating composite.