Sunlight-mediated photocatalytic upcycling of microplastics - SOLMUP

During the last two decades, scientists have increasingly highlighted a critical environmental issue associated with the excessive use of plastics in modern society: the widespread presence of micrometer-sized plastic fragments in natural ecosystems. These particles, known as microplastics (MPs), have raised significant concerns due to their persistence and bioaccumulation potential, which may lead to detrimental long-term effects on ecological balance and environmental health. Consequently, researchers from various scientific disciplines are actively investigating effective strategies for the removal, degradation, and upcycling of MPs.

Current methods for MP degradation can be broadly classified into biodegradation, chemical degradation, thermal degradation, and photodegradation. Biodegradation is primarily carried out by microorganisms such as bacteria; however, microbial growth has often been shown to be inhibited by the presence of plastic materials, limiting the efficiency and long-term viability of this approach. Chemical degradation relies on the use of catalysts specifically tailored to the polymer composition of MPs, while thermal degradation requires substantial energy input to induce polymer decomposition. Similarly, many chemical degradation processes depend on external energy sources to activate catalytic reactions. In this context, photocatalytic degradation represents a promising alternative, as it exploits visible light—the most abundant component of solar radiation—as a renewable and readily available energy source.

Photocatalysis is widely employed for the degradation and removal of water contaminants, particularly organic pollutants, and therefore holds considerable potential for the upcycling of MPs. The photocatalytic degradation of organic compounds is driven by the generation of reactive oxygen species (ROS), which are produced by photocatalysts possessing suitable electronic structures and band-gap energies. These highly reactive species can promote the oxidation and transformation of plastic materials into value-added products.

Accordingly, this project proposes a photocatalytic strategy for the upcycling of MPs through photoreforming (SOLMUP). Photoreforming (PR) offers a sustainable pathway for converting unwanted plastic waste into high-value chemicals, fully aligning with the principles of the circular economy. To date, TiO₂ and ZnO have been the most extensively investigated photocatalysts for plastic degradation; however, their application in photoreforming remains limited. In many reported studies, MPs were degraded without a clear understanding or control of the resulting products. As a consequence, PR has emerged as a challenging research area, with only a limited number of studies dedicated to its investigation. This highlights the need for fundamental research aimed at developing new photocatalysts and innovative approaches for selective MP photoreforming.

To address this challenge, the project proposes the use of Fe-based materials, which have not yet been explored for MP photoreforming. These materials will be investigated with the goal of enhancing photocatalytic performance while exploiting their favorable properties for ROS generation. Furthermore, to overcome one of the major limitations of photocatalytic systems—namely, the rapid recombination of photogenerated charge carriers—Fe-based materials will be engineered into heterostructured photocatalysts. For the first time, heterojunction photocatalysts will be applied to MP photoreforming, with the aim of improving light harvesting, charge separation efficiency, catalyst durability, and product selectivity. This strategy is expected to achieve higher yields of targeted products compared with the limited number of previous reports in the field.

In addition, advanced in situ characterization techniques will be employed to monitor catalyst evolution under operating conditions. Combined with mechanistic studies aimed at identifying reaction intermediates, these investigations will provide unprecedented insights into the photocatalytic process and elucidate the fundamental reaction pathways governing MP photoreforming.

The project will be carried out within the highly active, international, and multidisciplinary environment of the NANOMO Research Unit at the University of Oulu. This stimulating research setting will provide an excellent platform for scientific development and will support the successful implementation of all project activities.

Ultimately, SOLMUP brings together two highly relevant themes in environmental sustainability: the upcycling of plastic waste and the utilization of renewable solar energy. By integrating fundamental chemistry with advanced materials science, the project adopts an interdisciplinary approach to address one of the most pressing environmental challenges of our time while contributing to the development of sustainable and circular technologies.