Lower Critical Solution Temperature-Driven Catch and Release of Perfluoroalkyl Substances from Water: Remediation and Sampling

Abstract

Water pollution by per- and polyfluoroalkyl substances (PFASs) is a rising issue for the environment and human health because PFASs are persistent and nonbiodegradable. Recent studies have revealed that the concentration of PFASs found in contaminated water is in the order of the parts per trillion (i.e., 10–12) scale. This can result in a grand challenge for scientists not only to remove PFASs from water but to detect them. Various methodologies including functionalized nanoparticles, bioassay, activated carbon, anion exchange resin, and molecularly imprinted polymers have been employed to detect or remove PFASs from water. Dynamic adsorbents have demonstrated that they can adsorb PFASs from water while releasing them on demand for reuse upon an external trigger. This enables one to remove PFASs from water and retain them for preconcentration, while on-demand releasing allows for regenerating the adsorbent for reuse. Herein, a poly­(isopropylmethacrylamide) (P-NIPMAM)-based adsorbent that can adsorb and retain PFASs at a temperature higher than its lower critical solution temperature (LCST) while releasing them at a lower temperature is reported. Perfluorooctanoic acid (PFOA) and perfluorohexanoic acid (i.e., PFHxA) are utilized as a representative PFAS with a long and short fluoroalkyl chain, respectively. The adsorption capacity for PFOA and PFHxA is measured as ≈37 and ≈18 mg g–1 at 75 °C, respectively. When the adsorbent is submerged in water at a lower temperature (e.g., 23 °C < LCST), it starts to release the adsorbed compounds resulting in the desorption efficiency of ≈0.66 and ≈0.81 for PFOA and PFHxA, respectively. Finally, a prototype PFAS sampler was engineered by utilizing P-NIPMAM that can demonstrate the LCST-driven reversible adsorption and desorption of PFASs.

Thermoresponsive Polymers for Water Treatment and Collection

“…In contrast to traditional regeneration processes that occur under strongly acidic or basic conditions, the regeneration of PNIPAm-based adsorbents is acid free and environmentally friendly. In order to improve the mechanical properties of PNIPAm hydrogels, nanomaterials such as clay and graphene oxide have been introduced into poly­(NIPAm- co -maleic acid) and PNIPAm/alginate (Alg) cryogels, which provide a promising way for recycling rare earth elements such as La 3+ from wastewater. , In addition, PNIPAm-based adsorbents have been developed to treat emerging per- and polyfluoroalkyl substances (PFASs) organic pollutants such as perfluorohexanoic acid and perfluorooctanoic acid . Adsorption of pollutants is primarily driven by the hydrophobic interaction between the fluoroalkyl chain of PFASs and isopropyl or methyl groups of PNIPAm at temperatures above the LCST.…”

Review of Recent Computational Research on the Adsorption of PFASs with a Variety of Substrates

“…One way of addressing this ongoing issue is using adsorbents to physically remove PFASs from various water supplies. Experimental evidence using various adsorbents has shown promise to varying degrees, but challenges arise due to the relatively low concentrations of PFASs in some sources as well as the propensity of PFASs to resist chemical reactions [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Computational methods can be utilized to complement ongoing experimental findings or even to drive new research to find novel materials, and have been increasing in complexity given the enormous growth of computing power over the last few decades.…”