Photocatalytic degradation of GenX in water using a new adsorptive photocatalyst

Yangmo Zhu; Haodong Ji; Ke He; Lee Blaney; Tianyuan Xu; Dongye Zhao

doi:10.1016/j.watres.2022.118650

Photocatalytic degradation of GenX in water using a new adsorptive photocatalyst

Water Res. 2022 Jul 15:220:118650. doi: 10.1016/j.watres.2022.118650. Epub 2022 May 23.

Authors

Yangmo Zhu¹, Haodong Ji², Ke He³, Lee Blaney³, Tianyuan Xu⁴, Dongye Zhao⁵

Affiliations

¹ Department of Civil & Environmental Engineering, Auburn University, Auburn, AL 36849, USA.
² School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China.
³ Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland Baltimore County, MD 21250, USA.
⁴ School of Resource and Geosciences, China University of Mining and Technology, Xuzhou, Jiangsu 221116, China. Electronic address: xutianyuan@cumt.edu.cn.
⁵ Department of Civil & Environmental Engineering, Auburn University, Auburn, AL 36849, USA. Electronic address: zhaodon@auburn.edu.

PMID: 35640506
DOI: 10.1016/j.watres.2022.118650

Abstract

GenX, the ammonium salt of hexafluoropropylene oxide dimer acid, has been used as a replacement for perfluorooctanoic acid. Due to its widespread uses, GenX has been detected in waters around the world amid growing concerns about its persistence and adverse health effects. As relevant regulations are rapidly evolving, new technologies are needed to cost-effectively remove and degrade GenX. In this study, we developed an adsorptive photocatalyst by depositing a small amount (3 wt.%) of bismuth (Bi) onto activated-carbon supported titanate nanotubes, Bi/TNTs@AC, and tested the material for adsorption and subsequent solid-phase photodegradation of GenX. Bi/TNTs@AC at 1 g/L was able to adsorb GenX (100 µg/L, pH 7.0) within 1 h, and then degrade 70.0% and mineralize 42.7% of pre-sorbed GenX under UV (254 nm) in 4 h. The efficient degradation also regenerated the material, allowing for repeated uses without chemical regeneration. Material characterizations revealed that the active components of Bi/TNTs@AC included activated carbon, anatase, and Bi nanoparticles with a metallic Bi core and an amorphous Bi₂O₃ shell. Electron paramagnetic resonance spin-trapping, UV-vis diffuse reflectance spectrometry, and photoluminescence analyses indicated the superior photoactivity of Bi/TNTs@AC was attributed to enhanced light harvesting and generation of charge carriers due to the UV-induced surface plasmon resonance effect, which was enabled by the metallic Bi nanoparticles. ^•OH radicals and photogenerated holes (h⁺) were responsible for degradation of GenX. Based on the analysis of degradation byproducts and density functional theory calculations, photocatalytic degradation of GenX started with cleavage of the carboxyl group and/or ether group by ^•OH, h⁺, and/or e_aq^-, and the resulting intermediates were transformed into shorter-chain fluorochemicals following the stepwise defluorination mechanism. Bi/TNTs@AC holds the potential for more cost-effective degradation of GenX and other per- and polyfluorinated alkyl substances.

Keywords: Adsorption; Adsorptive photocatalyst; Defluorination; GenX; PFAS; Photocatalysis.

MeSH terms

Adsorption
Bismuth / chemistry
Charcoal
Nanotubes* / chemistry
Photolysis
Water*

Substances

Water
Charcoal
Bismuth