Compared to the legacy long-chain PFAS, short-chain PFAS are often more persistent, less adsorbable, and more mobile in the environment. In April 2024, the US EPA issued the legally enforceable maximum contaminant levels for 6 priority PFAS in drinking water, including GenX and perfluorobutanesulfonic acid (PFBS). Due to their widespread uses, these short-chain PFAS have been widely detected in waters at the ppt or ppb levels. Yet, cost-effective technologies have been lacking for removing and degrading GenX and PFBS in contaminated waters. To address this challenge, we prepared a new class of adsorptive photocatalysts by depositing a small amount (2-3 wt.%) of bismuth (Bi), gallium (Ga) and/or copper (Cu) onto activated-carbon supported titanate nanotubes, denoted as Bi/TNTs@AC and Cu-Ga/TNTs@AC, and tested the materials for adsorption and subsequent solid-phase photocatalytic degradation of GenX, PFBS, and perfluorobutanoic acid (PFBA). Bi/TNTs@AC at 1 g/L was able to nearly completely adsorb GenX (100 µg/L, pH 7.0) within 1 h, and subsequently, when the GenX-laden solids were subjected to UV (254 nm, 9-10 mW cm^-2, 25 ^oC), 70.0% of the pre-sorbed GenX was degraded and 42.7% was defluorinated/mineralized 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 high 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. Likewise, Cu-Ga/TNTs@AC was able to adsorb >90% of the initial 100 µg L^-1 PFBS and PFBA in 4 h. When the PFAS-laden material was subjected to the UV irradiation and in the presence of 2 mM ascorbic acid and 2 mM KI, 67.0% and 63.0% of PFBS and PFBA were defluorinated. The trap-&-zap technology enabled by the adsorptive photocatalysts holds the potential for more cost-effective degradation of highly persistent PFAS in water.

Nelson Rodney Leary

Appearances