Artificial Enzymes for Chemical Recycling and Upcycling of Aromatic Polycarbonates

In this project, Professor Yan Zhao of the Department of Chemistry at Iowa State University is developing new chemical tools to make plastic recycling more effective. Plastic waste is a growing environmental and public health challenge. Global plastic production exceeds 500 million metric tons each year, yet less than 30 percent of waste plastic is recycled because collection and processing are costly and many plastics are difficult to separate and reuse. One especially challenging plastic is bisphenol A-based polycarbonate, which is widely used in electronics, automobile parts, and consumer products. Because it is often mixed with other plastics during collection, it is difficult to recycle efficiently, and its breakdown can release bisphenol A, a compound associated with health and environmental concerns. This project develops new catalysts that imitate useful features of natural enzymes to break down polycarbonate and related plastics under mild conditions. These catalysts are based on small polymer nanoparticles that recognize a target plastic and selectively cut its chemical bonds. The research aims to create faster and more effective methods for recycling and upcycling plastic waste, including strategies that selectively break down one plastic in a mixture or convert waste plastic into useful building blocks for new materials. If successful, the work will advance sustainable chemistry, support new approaches in materials manufacturing, and help reduce the environmental burden of plastic waste. The project also trains student researchers in organic synthesis, catalysis, supramolecular chemistry, and polymer chemistry, while showing how fundamental science connects to real problems in recycling and manufacturing. Outreach activities engage students interested in science and engineering, and training in patents and intellectual property helps prepare students for industrial careers. These efforts strengthen the scientific workforce, broaden public understanding of science, and serve the national interest by advancing technologies relevant to efficient use of materials, environmental protection, and health. In this project, Professor Yan Zhao of the Department of Chemistry at Iowa State University is developing molecularly imprinted nanoparticles as synthetic hydrolase catalysts for the depolymerization and selective transformation of bisphenol A-based polycarbonate and other hydrolyzable plastics. These water-soluble, protein-sized polymeric receptors contain imprinted binding sites that can be equipped with catalytic groups to achieve enzyme-like activity and substrate selectivity under mild conditions. Building on preliminary results in which a first-generation synthetic polycarbonate hydrolase shows higher activity than a commercial lipase in polycarbonate degradation, the project seeks more active and selective catalysts for plastic recycling and upcycling. The research has three aims. The first aim optimizes the active site of the first-generation catalyst to improve polycarbonate bond cleavage. The second aim develops catalysts that remain associated with the polymer chain during hydrolysis to increase catalytic efficiency. The third aim exploits the designable selectivity of these synthetic catalysts to cleave polycarbonate and other hydrolyzable polymers with site selectivity for functional upcycling or selective depolymerization of one polymer within mixed plastic streams. Broader impacts include multidisciplinary student training, outreach through Iowa State University, and professional development in intellectual property and patents, thereby linking catalysis, sustainability, and biotechnology to workforce preparation and public engagement. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.