CAREER: Photocatalytic Optical Fibers

Because light can be collected freely or produced efficiently, driving chemical transformations with light instead of heat can have significant advantages over traditional chemical production methods. However, challenges remain in bringing these mostly academic findings to the scale necessary for industrial adoption, limiting the benefits to society that would result from safer and milder chemical processing conditions. An important factor in restricting the scalability of photochemical processes is that while high light absorptivity of the feedstocks is desirable for reaction efficiency, it also limits light penetration depth into the reaction medium. Commonly used photocatalysts can also be prohibitively expensive, and residual catalyst impurities in the final products often leads to discoloration or degradation. To address these limitations, this CAREER project will study the use of photocatalyst-coated optical fibers to guide light into the reactor vessels. If successful, the proposed work will lay the scientific foundations to facilitate the implementation of modern photochemistry on an industrial scale and enhance the impact of academic photo-reaction engineering innovations. Immobilizing photocatalysts on optical fibers is anticipated to improve light-penetration and efficiency of the catalytic process. Because the catalysts are immobilized and will not be added continuously with the reactor feed, the proposed approach will improve the process economics and will provide a path to manufacturing both pristine small molecules and polymers free of catalyst impurities. Eliminating such impurities is of importance for synthesis of high purity chemicals in biomedical and electronic applications where trace metals can introduce toxicity or be detrimental to device performance. The research plans have the potential to accelerate the implementation of modern and mild photochemistries on large scales and benefit society by helping to bridge the academia-industry divide. Education and outreach activities will also benefit from the close academia-industry ties to be developed, connecting undergraduate and graduate students and potential employers through field trips and panel discussions with industry leadership. Further, this program will develop and distribute inexpensive polymer science laboratory kits that will benefit underserved middle and high school students by improving access to a quality STEM education experience.

This CAREER project will provide the fundamental engineering knowledge needed to translate academic advances in modern photochemistry to large-scale industrial applications. The objectives of this research program are to identify critical chemical structure-property relationships for organic photoredox catalysts that will enable surface-grafting to immobilizing substrates without affecting catalytic activity. By investigating a range of approaches to control the optical fiber evanescent field, optical fiber surface-tethered catalysts will subsequently be tested as heterogeneous photocatalysts in both batch and continuous-flow reactor systems. Catalyst surface density will be controlled through a combination of surface monolayer grafting and the use of bottlebrush polymer tethers. Once an optimal fiber unit spacing and distribution is identified, process throughput and scalability will no longer limited by light absorption, but exclusively by the size of the reactor. By bringing light into the reactor, Beer-Lambert absorption limitations will be circumvented to provide a highly scalable continuous throughput methodology. Because the photocatalyst is immobilized within the reactor (and not continuously added), it can be recycled for multiple reactions; furthermore, the final chemical product will be free of catalyst impurities, a condition necessary in many pharmaceutical and electronics chemical products. From an educational and outreach perspective, this program will broadly impact students of all ages and backgrounds by forming a coalition between university entities, rural schools, and industrial partners. The principal investigator will increase interfaces between undergraduate and graduate students and potential employers through field trips and panel discussions with industry leadership. Further, this program will pilot and distribute inexpensive at-cost polymer science laboratory kits to secondary students to benefit underserved middle and high school students by improving their access to quality STEM education. Finally, targeted community outreach events will promote university enrollment of socioeconomically challenged students while communicating scientific principles and the importance of sustainability and plastic waste recycling to non-technical audiences.

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.