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

What is it about?

The global ecological crisis of per- 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 in-situ constructing confined water structure in activated carbon (AC). Through direct (driving force) and indirect (assisted slip) effects, the confined water introduced an unprecedented dual-drive mode in the confined water-encapsulated AC (CW-AC) and completely eliminated the mass transfer barrier (3.27-5.66 kcal/mol), which caused the CW-AC to exhibit the highest adsorption capacity for various short-chain PFAS (chain length: C4-C6, functional group: -COOH or -SO3H) 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 PFAS that easily escaped treatment. Importantly, the ability of CW-AC functionality to directly transfer to existing adsorption devices was verified, which could treat 21000 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.

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Photo by engin akyurt on Unsplash

Photo by engin akyurt on Unsplash

Why is it important?

Adsorption is the most established method used to block human exposure through drinking water to the notorious per- and polyfluoroalkyl substances (PFASs), yet is challenged by the increasing short-chain PFAS crisis due to the inherent defects of solid‒liquid mass transfer. Herein, by assembling the confined water structure in-situ in hydrophobic nanopores, we introduce an unprecedented dual-drive mode in the activated carbon to completely eliminate the mass transfer barrier and dramatically enhance its adsorption performance for various short-chain PFASs. Significantly, the methodology demonstrated is a potential in-situ upgrade of existing adsorption devices. This work will thus revolutionize the understanding of the role of confined water in mass transfer and enable an in-situ solution for the short-chain PFASs crisis in drinking water.