Confined water–encapsulated activated carbon for capturing short-chain perfluoroalkyl and polyfluoroalkyl substances from drinking water

Abstract

The global ecological crisis of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water has gradually shifted from long-chain to short-chain PFASs; however, the widespread established PFAS adsorption technology cannot cope with the impact of such hydrophilic pollutants given the inherent defects of solid–liquid mass transfer. Herein, we describe a reagent-free and low-cost strategy to reduce the energy state of short-chain PFASs in hydrophobic nanopores by employing an in situ constructed confined water structure in activated carbon (AC). Through direct (driving force) and indirect (assisted slip) effects, the confined water introduced a dual-drive mode in the confined water–encapsulated activated carbon (CW-AC) and completely eliminated the mass transfer barrier (3.27 to 5.66 kcal/mol), which caused the CW-AC to exhibit the highest adsorption capacity for various short-chain PFASs (C-F number: 3-6) among parent AC and other adsorbents reported. Meanwhile, benefiting from the chain length– and functional group–dependent confined water–binding pattern, the affinity of the CW-AC surpassed the traditional hydrophobicity dominance and shifted toward hydrophilic short-chain PFASs that easily escaped treatment. Importantly, the ability of CW-AC functionality to directly transfer to existing adsorption devices was verified, which could treat 21,000 bed volumes of environment-related high-load (~350 ng/L short-chain PFAS each) real drinking water to below the World Health Organization’s standard. Overall, our results provide a green and cost-effective in situ upgrade scheme for existing adsorption devices to address the short-chain PFAS crisis.

Exceptionally High Perfluorooctanoic Acid Uptake in Water by a Zirconium-Based Metal–Organic Framework through Synergistic Chemical and Physical Adsorption

“…Positive binding energies were observed with a higher proportion of PFOA molecules forming coordination bonds (Figure S27), whereas negative binding energies were found when more PFOA molecules were physically adsorbed (Figure S28). Remarkably, a lower adsorption energy was observed upon increasing the adsorbed PFOA molecules, indicating a synergistic effect between the coordinated and free PFOA molecules due to their hydrophobicity, which can facilitate the adsorption process . The maximum adsorption capacity was calculated to be 52.58 PFOA molecules per unit cell (Figure S29), corresponding to 3.29 PFOA molecules per ligand, thereby matching the experimental adsorption capacity.…”

“…Remarkably, a lower adsorption energy was observed upon increasing the adsorbed PFOA molecules, indicating a synergistic effect between the coordinated and free PFOA molecules due to their hydrophobicity, which can facilitate the adsorption process. 41 The maximum adsorption capacity was calculated to be 52.58 PFOA molecules per unit cell (Figure S29), corresponding to 3.29 PFOA molecules per ligand, thereby matching the experimental adsorption capacity. Overall, these calculations further highlight the crucial role of the additional open coordination sites and a favorable porous environment in facilitating the adsorption of PFOA.…”

Modification of activated carbon for enhanced treatment of per‐ and polyfluoroalkyl substances: A focused review

“…The efficiency of AC decreases significantly for shorter‐chain PFAS (Inyang & Dickenson, 2017; Xiao et al, 2013). Short‐chain PFAS compounds, which have lower potential energy in water, tend to remain dissolved in water rather than binding to adsorbents (Shi et al, 2023). When dealing with drinking water, it was observed that AC's removal efficiency decreases from about 80% for long‐chain PFAS to around 40% for short‐chain compounds, and short‐chain PFAS desorb readily from adsorbents (Park et al, 2020).…”