Can sunlight effectively clean water? That was the challenge the Solar2Clean project, led by professors and researchers at Instituto Superior Técnico, set out to address. The project aimed to develop sustainable, solar-powered strategies to transform polluted water – contaminated with antibiotics, dyes, and microplastics – into treated water.
Led by Ana C. Marques (in the photo) and Susete Dias, professors at Técnico and researchers at CERENA, the Solar2Clean project focused on photocatalysis, a process where light activates a material – the photocatalyst – that can break down harmful pollutants into non-toxic by-products. Photocatalysis has since shown great promise in laboratory settings. However, translating this technology into effective real-world applications remains challenging. Solar2Clean aimed to overcome the main obstacles through material innovation and reactor design.
The developed materials were successfully applied to the degradation of antibiotics – a growing concern due to their persistence in wastewater and their contribution to antibiotic resistance. This issue is particularly relevant in Portugal, where pharmaceutical companies producing these compounds are seeking effective treatment solutions to re-move antibiotic residues from their process effluents before discharge into municipal wastewater systems.
The project brought together a multidisciplinary team across Técnico, partnering with ETH Zurich. The nearly four-year long project combined advanced materials science, environmental engineering, and international collaboration to overcome key limitations of traditional water treatment technologies. It welcomed students and researchers from eight countries, resulting in 13 publications in peer-reviewed journals, 15 oral communications, and 9 academic theses.
One major difficulty with photocatalysts is that they are usually nanoscale particles, which are hard to recover after use and may pose environmental risks themselves. To address this, the team developed and optimised the synthesis of MICROSCAFS® (the international brand was granted for the support material developed in the project) – microspheres primarily made of silica with coral-like macroporosity that act as scaffolds for the photocatalytic nanoparticles. These structures not only simplify handling and re-cycling but can be partially made of titanium dioxide – the photocatalyst itself – making them active on their own. Moreover, through an international collaboration with Ca’ Foscari University of Venice, the team developed a more sustainable synthesis route using rice husk silica, further improving the project’s environmental impact, through waste valorisation.
Another limitation of conventional photocatalysts is their dependency on ultraviolet (UV) light, which accounts for only about 5% of solar radiation. To broaden their usability, the team engineered doped photocatalysts that can absorb visible and infrared light and convert it into usable UV light, significantly improving the system’s overall solar efficiency.
This FCT-funded project also demonstrated how a combined approach of gamma irradiation and photocatalysis can make microplastics, such as polyethylene, susceptible to biodegradation. This setup enabled continuous operation and highlighted the practical applicability of the materials in diverse real-world scenarios, including industrial wastewater treatment.
