Carbon Adsorbent Properties Impact Hydrated Electron Activity and Perfluorocarboxylic Acid (PFCA) Destruction

Hosea A Santiago-Cruz; Zimo Lou; Jiang Xu; Ryan C Sullivan; Bailey B Bowers; Rachel A Molé; Wan Zhang; Jinghao Li; Joshua S Yuan; Susie Y Dai; Gregory V Lowry

doi:10.1021/acsestengg.4c00211

Carbon Adsorbent Properties Impact Hydrated Electron Activity and Perfluorocarboxylic Acid (PFCA) Destruction

ACS ES T Eng. 2024 Aug 2;4(9):2220-2233. doi: 10.1021/acsestengg.4c00211. eCollection 2024 Sep 13.

Authors

Hosea A Santiago-Cruz¹, Zimo Lou^{1

2}, Jiang Xu^{1

3}, Ryan C Sullivan^{4

5}, Bailey B Bowers^{4

6}, Rachel A Molé¹, Wan Zhang⁷, Jinghao Li^{7

8}, Joshua S Yuan⁸, Susie Y Dai⁷, Gregory V Lowry¹

Affiliations

¹ Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
² Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, Hangzhou 310014, China.
³ College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China.
⁴ Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15217, United States.
⁵ Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15217, United States.
⁶ Department of Chemistry and Biochemistry, Oberlin College, Oberlin, Ohio 44074, United States.
⁷ Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843, United States.
⁸ Department of Energy, Environmental, and Chemical Engineering, McKelvey School of Engineering, Washington University in St. Louis, St. Louis, Missouri 63130-4899, United States.

Abstract

Carbon-based adsorbents used to remove recalcitrant water contaminants, including perfluoroalkyl substances (PFAS), are often regenerated using energy-intensive treatments that can form harmful byproducts. We explore mechanisms for sorbent regeneration using hydrated electrons (e_aq ^-) from sulfite ultraviolet photolysis (UV/sulfite) in water. We studied the UV/sulfite treatment on three carbon-based sorbents with varying material properties: granular activated carbon (GAC), carbon nanotubes (CNTs), and polyethylenimine-modified lignin (lignin). Reaction rates and defluorination of dissolved and adsorbed model perfluorocarboxylic acids (PFCAs), perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA), were measured. Monochloroacetic acid (MCAA) was employed to empirically quantify e_aq ^- formation rates in heterogeneous suspensions. Results show that dissolved PFCAs react rapidly compared to adsorbed ones. Carbon particles in solution decreased aqueous reaction rates by inducing light attenuation, e_aq ^- scavenging, and sulfite consumption. The magnitude of these effects depended on adsorbent properties and surface chemistry. GAC lowered PFOA destruction due to strong adsorption. CNT and lignin suspensions decreased e_aq ^- formation rates by attenuating light. Lignin showed high e_aq ^- quenching, likely due to its oxygenated functional groups. These results indicate that desorbing PFAS and separating the adsorbent before initiating PFAS degradation reactions will be the best engineering approach for adsorbent regeneration using UV/sulfite.