Functionalized-MXene Thin-Film Nanocomposite Hollow Fiber Membranes for Enhanced PFAS Removal from Water

Abstract

Due to adverse health effects and the broad sources of per-and polyfluoroakyl substances (PFAS), PFAS removal is a critical research area in water purification. We demonstrate the functionalization of thin-film composite (TFC) hollow fiber nanofiltration (HFN) membranes by MXene nanosheets during the interfacial polymerization (IP) process for enhanced removal of perfluorooctane sulfonic acid (PFOS) from water. A MXenepolyamide (PA) selective layer was fabricated on top of a polysulfone (PSF) hollow fiber support via IP of trimesoyl chloride (TMC) and a mixture of piperazine (PIP) and MXene nanosheets to form MXene-PA thin-film nanocomposite (TFN) membranes. Incorporating MXene nanosheets during the IP process tuned the morphology and negative surface charge of the selective layer, resulting in enhanced PFOS rejection from 72% (bare TFC) to more than 96% (0.025 wt % MXene TFN), while the water permeability was also increased from 13.19 (bare TFC) to 29.26 LMH/bar (0.025 wt % MXene TFN). Our results demonstrate that both electrostatic interaction and size exclusion are the main factors governing the PFOS rejection, and both are determined by PA selective layer structural and chemical properties. The lamella structure and interlayer of MXene nanosheets inside the PA layer provided different transport mechanisms for water, ions, and PFAS molecules, resulting in enhanced water permeability and PFAS rejection due to traveling through the membrane by both diffusions through the PA layer and the MXene intralayer channels. MXene nanosheets showed very promising capability as a 2D additive for tuning the structural and chemical properties of the PA layer at the permeability-rejection tradeoff.

A Review on Removal and Destruction of Per- and Polyfluoroalkyl Substances (PFAS) by Novel Membranes

“…In the case of PFAS removal via an adsorption-based process coupled with membranes, the membrane’s surface is coated with adsorbent materials and the process is controlled by the characteristics of adsorbents, such as adsorbent particle size, surface area, pore-volume, etc. In such cases, the electrostatic force between the membrane surface and the PFAS mostly depends on the adsorbent material and not the membrane’s properties [ 112 ].…”

“…Functionalized-MXene (Ti 2 C 3 T x , 0–0.05 wt% MXene) thin-film nanocomposite hollow fiber membranes ( Figure 9 ) were successfully developed by Le et al, for PFOS removal from water. The thin film was formed through interfacial polymerization [ 112 ], and the coated polyamide-MXene layer (optimum at 0.025 wt% MXene) on polysulfone hollow fiber support was able to increase PFOS rejection from 72 to 96% in comparison to a PES polyamide hollow fiber. Furthermore, the addition of an MXene layer increased the permeability from 13.9–29.26 LMH/bar.…”

“… SEM and AFM images of ( a ) bare thin film composite membrane (Cross-section (left) and top surface (right)), ( b ) 0.025 MXene−Membrane, and ( c ) 0.050 MXene—Membrane (reprinted with permission from Ref. [ 112 ]. Copyright 2022 ACS).…”

Rational Design of MXene Hollow Fiber Membranes for Gas Separations

“…32 And Milad et al demonstrated one composite MXene hollow fiber membrane using an interfacial polymerization method. 33 However, the random distribution of MXene nanosheets in membranes could increase the molecular transport resistance. To better control the interlayer spacing, dip-coating is a viable technology for fabricating conformational 2D hollow fiber membranes, since the film thickness can be well regulated by controlling the coating speed and cycles, which can achieve a precise selective layer with controlled configurations (thickness or structures).…”

“…For MXene membranes based on a polymeric support, Zhang et al designed one hydrophobic–hydrophilic MXene/PVDF hollow fiber membrane using a chemical grafting method . And Milad et al demonstrated one composite MXene hollow fiber membrane using an interfacial polymerization method . However, the random distribution of MXene nanosheets in membranes could increase the molecular transport resistance.…”