(186b) Catalyst Design Strategies for Photo-Oxidative PFOA Degradation over Boron Nitride

Perfluorooctanoic acid (PFOA), a common member of the per/polyfluoroalkyl substance (PFAS) family of water contaminants, is pervasive, persistent, and harmful to human health. Heterogeneous photocatalysis is a promising and environmentally friendly way to degrade PFOA. We recently reported that hexagonal boron nitride (hBN) can photo-catalytically degrade PFOA under UVC illumination, with a catalyst activity ~2 times higher than TiO₂. [1] In this work, we demonstrated that the 2D properties of hBN are responsible for its enhanced photo-catalytic activity for PFAS degradation. We applied density functional theory (DFT) to investigate the thermodynamics and kinetics of PFAS adsorption and degradation over hBN. This analysis reveals that the initial elementary step of the oxidative PFOA degradation cycle over hBN is a one electron transfer yielding a perfluoroalkyl radical: C_nF_2n+1COO^- + h⁺ → C_nF_2n+1• + CO₂. By analyzing the density of states (DOS) of defective hBN surface models, we found that nitrogen-boron substitutional defects (N_B) and nitrogen vacancies (V_N) introduce mid-gap states that enable UVC light absorption and enhance charge carrier separation. Therefore, we propose that introducing more N_B and V_N defects can enhance the performance of hBN. [2] We also compared the semiconductor/electrolyte reaction interface of TiO₂ anatase and hBN, and we found that the hydrophobicity of hBN is responsible for its better performance than TiO₂. Dissociative water adsorption on the TiO₂ surface inhibits oxidation of PFOA, as the dissociated water scavenges the holes required to activate PFOA. Therefore, enhancing the hydrophobicity of hBN by passivating edge sites is also a promising catalyst design strategy. [3]

[1] Environ. Sci. Technol. Lett. 2020, 7, 8, 613–619

[2] Environ. Sci. Technol. 2022, 56, 12, 8942–8952

[3] Chem. Eng. J. 2024, 483, 149134