# Encapsulation of Perfluoroalkyl Carboxylic Acids (PFCAs) Within Polymer Microspheres for Storage in Supercritical Carbon Dioxide: A Strategy Using Dispersion Polymerization of PFCA-Loaded Monomers

## TL;DR

This paper introduces a method to encapsulate harmful PFCAs in polymer microspheres that dissolve in supercritical CO2, offering a new approach for PFAS storage and removal.

## Contribution

A novel strategy for PFCA encapsulation using PFCA-loaded monomers and their dissolution in supercritical CO2 is presented.

## Key findings

- PFCAs were effectively captured by TPMA monomer through acid-base reaction in methanol.
- PFCA-loaded microspheres dissolved in supercritical CO2 under mild conditions.
- Perfluoroalkyl chains migrated to microsphere surfaces, aiding dissolution in scCO2.

## Abstract

The removal of per- and polyfluoroalkyl substances (PFAS) from global aquatic environments is an emerging issue. However, little attention has been paid to addressing accumulated PFAS through their removal. This study demonstrates the encapsulation of perfluoroalkyl carboxylic acids (PFCAs) within polymer microspheres that dissolve in supercritical carbon dioxide (scCO2). PFCAs were effectively captured by a hindered amine-supported monomer, 2,2,6,6-tetramethyl-4-piperidyl methacrylate (TPMA), in methanol (MeOH) through a simple acid-base reaction. The PFCA-loaded TPMA underwent dispersion polymerization in MeOH in the presence of poly(N-vinylpyrrolidone) (PVP) as a surfactant, producing microspheres with high monomer conversions. The microsphere size depended on the molecular weight and concentration of PVP, as well as the perfluoroalkyl chain length of the PFCAs. X-ray photoelectron spectroscopy (XPS) revealed that the perfluoroalkyl chains migrated from the interior to the surface of the microspheres when exposed to air. These surface perfluoroalkyl chains facilitated dissolution of the microspheres in scCO2, with cloud points observed under relatively mild conditions. These findings suggest the potential for managing PFCA-encapsulated microspheres in the scCO2 phase deep underground via CO2 sequestration.