Highly efficient preconcentration using anodically generated shrinking gas bubbles for per- and polyfluoroalkyl substances (PFAS) detection.

Abstract

Here we report a highly efficient PFAS preconcentration method that uses anodically generated shrinking gas bubbles to preconcentrate PFAS via aerosol formation, achieving ~ 1400-fold enrichment of PFOS and PFOA-the two most common PFAS-in 20min. This new method improves the enrichment factor by 15 to 105% relative to the previous method that uses cathodically generated H2 bubbles. The shrinking gas bubbles are in situ electrogenerated by oxidizing water in an NH4HCO3 solution. H+ produced by water oxidation reacts with HCO3- to generate CO2 gas, forming gas bubbles containing a mixture of O2 and CO2. Due to the high solubility of CO2 in aqueous solutions, the CO2/O2 bubbles start shrinking when they leave the electrode surface region. A mechanistic study reveals two reasons for the improvement: (1) shrinking bubbles increase the enrichment rate, and (2) the attractive interactions between the positively charged anode and negatively charged PFAS provide high enrichment at zero bubble path length. Based on this preconcentration method, we demonstrate the detection of ≥ 70ng/L PFOA and PFOS in water in ~ 20min by coupling it with our bubble-nucleation-based detection method, fulfilling the need of the US Environmental Protection Agency.