Due to their extensive use in coatings, chemical and materials processing, and aqueous firefighting foams, per- and polyfluoroalkyl substances (PFAS) have a ubiquitous presence in the environment. PFAS is a health hazard, and is difficult to destroy due to the extreme stability of the C-F bonds. Compared to the various treatment options being studied and developed, photocatalytic oxidation offers the advantages of needing no additional reagents, and needing only a light source. Many materials have been investigated for photocatalytic PFAS (e.g., perfluorooctanoic acid [PFOA]) degradation, including TiO₂ and more exotic In- and Bi-based materials. However, these typically require either additional chemicals or high light intensities to achieve minimal degradation rates. TiO₂ is commercially available but not effective; the composite catalysts are more effective but are not commercially available. The objective of this project is to further develop boron nitride (BN)-based materials, which have recently demonstrated remarkable chemical-free PFAS photocatalytic degradation activity, to economically and efficiently treat PFAS-impacted sites.

BN is inexpensive, non-toxic, and widely used as a ceramic component, solid lubricant, and a bright-white ingredient for cosmetics. Until last year, it was not known to have any ability to degrade PFAS. In this project, the project team will better assess the unusual PFAS degrading capabilities of BN — a material discovered to photocatalytically oxidize PFOA and Gen-X in water under ambient conditions using ultraviolet — C light (254 nanometers) — to treat a much wider range of PFAS materials, in a much wider range of concentration, co-occurring chemicals, and water quality conditions.

The project team will extend the investigations to a more complete PFAS library that encompasses 29 PFAS that are commonly found in aqueous film-forming foam (AFFF) concentrates. Whereas earlier studies were performed at the part per million concentration level, the project team will study degradation efficacy down to the much lower regulatory part per trillion levels, as well as the much higher concentration found in typical AFFF concentrates (3-6 wt%). The project team will explore strategies for deployment of this technology to the treatment of waters and other media. They will further identify appropriate strategies to treat AFFF-impacted waters.

This study will extend scientific knowledge of the photocatalytic degradation capabilities of BN-based materials, including their general applicability to the wide range of PFAS species present in AFFF and other sources. By testing simulated and natural waters as well as wash streams, the project team will determine field applicability of the BN photocatalytic approach for PFAS-impacted Department of Defense sites. These learnings may further translate into application of the technology for other PFAS-impacted matrices, such as drinking water, and may be generalizable to point-of-use sources and water treatment plants. (Anticipated Project Completion - 2024)

Chen, Y., M. Bhati, B.W. Walls, B. Wang, M.S. Wong, and T.P. Senftle. 2022. Mechanistic Insight into the Photo-Oxidation of Perfluorocarboxylic Acid over Boron Nitride. Environmental Science & Technology, 56(12):8942-8952. doi.org/10.1021/acs.est.2c01637.

Duan, L., B. Wang, K.N. Heck, C.A. Clark, J. Wei, M. Wang, J. Metz, G. Wu, A. Tsai, S. Guo, J. Arrendondo, A.D. Mohite, T.P. Senftle, P. Westerhoff, P.J.J. Alvarez, X. Wen, Y. Song, and M.S. Wong. 2022. Titanium Oxide Improves Boron Nitride Photocatalytic Degradation of Perfluorooctanoic Acid. Chemical Engineering Journal, 448:137735. doi.org/10.1016/j.cej.2022.137735.

Qanbarzadeh, M., L. DiGiacomo, E. Bouteh, E.Z. Alhamdan, M.M. Mason, B.Wang, M.S. Wong, and E.L. Cates. 2023. An Ultraviolet/Boron Nitride Photocatalytic Process Efficiently Degrades Poly-/Perfluoroalkyl Substances in Complex Water Matrices. Environmental Science & Technology Letters, 10(8):705-710. doi.org/10.1021/acs.estlett.3c00363.

Dissertations and Theses

Wang, B. 2023. Boron Nitride Based Photocatalysts for the Efficient PFAS Degradation (Ph.D. Dissertation). Rice University.