From Microplastics to Acetic Acid: University of Waterloo Innovation

Dr Yimin Wu, Professor of Mechanical and Mechatronics Engineering and Tang Family Chair in New Energy Materials and Sustainability at the University of Waterloo, is leading a research effort that reframes how plastic waste might be handled in the future. In a study published in Advanced Energy Materials, Wu and his team report a sunlight powered catalytic process that converts common plastic waste into acetic acid, a widely used industrial chemical. The work, led experimentally by doctoral researcher Wei Wei, proposes a route that combines environmental remediation with chemical manufacturing.

Wei, W., Du, C., Ge, J., Wang, X., Chen, Z., Zhang, M., Guo, T., Wang, L., Wang, M., Liu, Y., Zhou, H., Sun, C., Chen, N., Chen, W., Billinghurst, B., Shakouri, M., Sprenger, P., Sani, F. F., Quan, Y., … Wu, Y. A. (2025). Bio‐Inspired Cascade Photocatalysis on Fe Single‐Atom Carbon Nitride Upcycles Plastic Wastes for Effective Acetic Acid Production. Advanced Energy Materials. https://doi.org/10.1002/aenm.202505453

Plastic waste management remains one of the defining engineering challenges of this century. Mechanical recycling is limited by contamination and polymer degradation. Thermal processes such as incineration recover energy but release carbon dioxide and other emissions. Chemical recycling techniques can depolymerize plastics, yet they often require high temperatures, high pressures or fossil derived inputs. Against this backdrop, photocatalysis offers a different direction. It uses light energy to drive chemical transformations, potentially lowering energy demand and reducing process emissions.

Dr Yimin Wu, at University of Waterloo stated,

“Our goal was to solve the plastic pollution challenge by converting microplastic waste into high-value products using sunlight.”

The Waterloo team developed a catalyst composed of isolated iron atoms embedded within a carbon nitride matrix. Carbon nitride is a semiconductor material known for its ability to absorb visible light. By dispersing single iron atoms across its surface, the researchers created active sites capable of initiating controlled oxidation reactions under sunlight. The catalyst design was informed by biological systems, particularly enzymatic cascades used by certain fungi to degrade organic matter into smaller, useful molecules.

When exposed to simulated sunlight in an aqueous environment, the catalyst initiates a sequence of reactions that break long polymer chains into smaller fragments. Rather than fully oxidizing the material into carbon dioxide, the system directs the reaction pathway toward acetic acid formation. The reported selectivity is significant because uncontrolled oxidation is a common limitation in photocatalytic systems. Achieving targeted partial oxidation represents an engineering milestone in reaction control.

The process was demonstrated on several commercially important plastics, including polyethylene, polypropylene, polyvinyl chloride and polyethylene terephthalate. These materials account for a substantial share of global plastic production and are frequently found in mixed waste streams. One practical challenge in recycling is the need to separate plastics by type before processing. The study reports that the photocatalytic system maintains performance even when multiple polymer types are present together. That tolerance to feedstock variability suggests potential compatibility with real world waste conditions.

Acetic acid is a commodity chemical with a broad industrial footprint. It is used in food preservation, solvent production, polymer synthesis and emerging energy technologies. Global demand reaches millions of tonnes annually, with established supply chains and downstream markets. Converting plastic waste into acetic acid does not simply remove waste from the environment. It inserts recovered carbon into an existing industrial loop. From an engineering perspective, this positions the technology within the framework of circular material flows rather than waste disposal.

An additional point of interest is the reaction medium. The photocatalytic conversion occurs in water, which opens the possibility of addressing microplastic contamination directly in aquatic environments. Microplastics present unique challenges because their small size makes collection difficult. By targeting chemical degradation rather than physical retrieval, the process could offer an alternative remediation strategy. The concept remains at laboratory scale, yet it highlights how materials engineering can intersect with environmental systems engineering.

The research also included a techno economic assessment conducted in collaboration with environmental economists. Early modeling indicates that using abundant solar energy as the primary energy input could reduce operational emissions compared to thermal recycling pathways. While commercial viability depends on scale, catalyst stability and reactor design, preliminary analysis suggests that integrating solar driven photocatalytic reactors into existing waste management infrastructure may be feasible under certain conditions.

From a materials science standpoint, the use of single atom catalysts is central to the reported performance. Isolated metal atoms maximize atomic efficiency and can provide highly uniform active sites. Advanced characterization techniques, including electron microscopy and spectroscopy, were used to confirm the dispersion of iron atoms and to track structural changes during reaction cycles. Maintaining catalyst stability under repeated illumination and in the presence of heterogeneous plastic feedstock is a critical requirement for future scale up.

Scaling the system presents engineering challenges that extend beyond catalyst chemistry. Photocatalytic processes require efficient light delivery, mass transport control and reactor geometries that balance exposure with throughput. Designing reactors capable of handling solid plastic particles suspended in water while maintaining consistent irradiation is nontrivial. The transition from laboratory photoreactors to pilot scale solar installations will require collaboration across chemical engineering, materials science and environmental engineering disciplines.

The work aligns with broader institutional efforts focused on sustainable technologies and circular manufacturing. It contributes to a growing body of research exploring solar driven chemical transformations as a tool for decarbonization. In recent years, photocatalysis has been investigated for hydrogen production, carbon dioxide reduction and wastewater treatment. Extending these principles to plastic upcycling reflects an expansion of the field into solid waste management.

The findings do not imply an immediate replacement for existing recycling infrastructure. Mechanical recycling remains energy efficient for certain clean plastic streams. However, for contaminated, mixed or degraded plastics that are difficult to recycle conventionally, a light driven chemical route may offer an additional pathway. The emphasis on selective production of a marketable chemical distinguishes this approach from processes aimed solely at waste destruction.

Further research will focus on improving catalyst efficiency, enhancing reaction rates under natural sunlight and assessing long term durability. Engineering optimization will likely include refining the carbon nitride support structure, adjusting iron loading levels and tailoring reactor configurations. Life cycle assessment will also be necessary to quantify overall environmental impact, including material inputs and end of life catalyst management.

In practical terms, the study demonstrates how advances in catalyst design can reshape discussions around waste. By treating plastic not only as refuse but as a carbon resource, the research reframes the problem as one of conversion rather than elimination. Whether deployed in centralized facilities or adapted for distributed treatment systems, sunlight driven photocatalysis introduces a concept that merges renewable energy with materials recovery.

As engineering communities continue to address the global accumulation of plastic waste, solutions that combine environmental remediation with value creation will attract attention. The work led by Dr Yimin Wu illustrates how targeted materials innovation, informed by biological systems and supported by economic analysis, can contribute to that objective. The next phase will determine whether the laboratory proof of concept can translate into scalable infrastructure capable of operating within the constraints of real waste streams and variable solar conditions.