Final Report: Development of “Smart” Polymer Nanofiber Mats for Selective andEfficient Removal of PFAS from Landfill Leachate

EPA Contract Number: 68HERD19C0016
Title: Development of “Smart” Polymer Nanofiber Mats for Selective andEfficient Removal of PFAS from Landfill Leachate
Investigators: Feng, Maoqi M
Small Business: Polykala Technologies, LLC
EPA Contact: Richards, April
Phase: I
Project Period: May 1, 2019 through October 31, 2019
Project Amount: $99,815
RFA: Small Business Innovation Research (SBIR) - Phase I (2019) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , Small Business Innovation Research (SBIR): Phase 1 (2019) , SBIR - Water Quality

Description:

This project developed two novel functionalized nanofiber mats fabricated by electrospinning of polymer nanofibers for "smart" (selective) removal of per- and polyfluoroalkyl substances (PFAS) from wastewater such as landfill leachate. Extensive tests of the nanofiber mats using two PFAS model compounds, perfluorooctanoic acid (PFOA, CF3(CF2)6COOH) and heptadecafluorooctanesulfonic acid (PFOS, CF3(CF2)7SO3H), showed that the materials have high efficiency (over 91%) for PFOA and PFOS removal at various total PFAS concentrations.

The first functionalized nanofiber mat is amine-functionalized polyimide nanofibrous mat, which was prepared by electrospinning of polyamic acid (the precursor of polyimide) followed by amine-functional group treatment. Figure 1 shows the nanofibrous mat before and after treatment, and their SEM images are shown in Figure 2.

Figure 1. Electrospun polymide nanofiber mats before (A) and after amine-functional group treatment (B)

The color difference in Figure 1, and the circles marked on Figure 2 clearly show the successful functionalization.

Figure 2. SEM images acquired from electrospun polymide nanofirous mats before (A) and aftger amine-functional group treatment (B).

The second functionalized nanofiber mat is clay-incorporated amine-functionalized polyimide nanofibrous mat, which was prepared by infiltration of clay into the amine-functionalized polyimide nanofibrous mat. The SEM images are shown in Figure 3.

Figure 3. SEM images of clay-containing mat surface (A) and (B) cross-section (B).

The amine group can form hydrogen-bond with the carboxylic acid and sulfonic acid to facilitate PFAS selective removal. Although there are no straight-through pores in the mats, the particles with small sizes can permeate through the mat via tortuous pathways; hence, the mat has pore size in sub-micron range. Some large pollutant particles can be removed via physical blocking mechanism.

Two analytical methods were used for the PFAS analysis: 1) the EPA 537 Rev. 1.1 Method for quantitative analysis, and 2) the Relay Electrospray Ionization High Resolution Mass Spectrometry for fast screening.

Summary/Accomplishments (Outputs/Outcomes):

  1. PFOA and PFOS removal efficiency.

Tests of the nanofiber mats on PFAs removal using two PFAS model compounds, PFOA and PFOS, showed that the materials have high efficiency for PFOA (91.2%) and PFOS (92.5%) removal.

The nanofiber mats were able to treat water containing high PFAS concentration up to 6,500 ng/L and removed over 91-92 wt.% of the PFAS. At lower PFAS concentration, the materials were able to reduce the PFAS concentration to below EPA threshold value 70 ng/L.

  1. PFOA and PFOS selectivity.

The nanofiber mats had higher selectivity for PFOA than that of PFOS. The reason is that amine forms stronger hydrogen bonding with the carboxylic acid in PFOA than that of sulfonic acid in PFOS because of the size difference.

  1. Polyimide nanofiber mats stability in water.

The polyimide-based nanofiber mats were immersed in de-ionized water for 3 months at room temperature, no swelling or decoloring was observed, indicating the materials are very stable in water.

  1. Polyimide nanofiber mats regeneration with acetone.

The polyimide-based nanofiber mats were regenerated with acetone washing. For each piece, a small amount (10-15 mL) of acetone was used immerse the mat for 10 minutes. The regenerated mats can be reused. After the acetone was evaporated in a rotavapor, the residue was collected.

Conclusions:

The nanofiber mats developed in this project were proved to be very promising for PFAS removal in a smart and selective adsorption feature, and energy-efficient regeneration can be achieved with PFAS recovery for destruction.

The commercialization effort is summarized as follows:

Registered trademark "PFAS Shield" .

Price quotations for commercial scale (over 100 square meter) manufacturing of polyimide substrate mats had been obtained.

The products are currently being marketed as "syringe filter media" to provide PFAS-free water.

Journal Articles:

No journal articles submitted with this report: View all 3 publications for this project

SBIR Phase II:

Development of 'Smart' Polymer Nanofiber Mats for Selective and Efficient Removal of PFAS from Wastewater  | Final Report