Addressing Short-Chain PFAS Contamination in Water with Nanofibrous Adsorbent/Filter Material from Electrospinning.

ConspectusPer- and polyfluoroalkyl substances (PFAS) stand for thousands of fully/highly fluorinated aliphatic chemicals, which have been widely manufactured and used in consumer products. Due to easy deprotonation of headgroups and high strength of C-F bonds in their molecules, PFAS are water-soluble and extremely stable in our environment. Significant accumulation of PFAS in water bodies started as early as the beginning of their production in the late 1940s. Recent studies confirmed the occurrence and accumulation of PFAS in all human tissues as well as their harmful health effects. Upon environmental regulations and health advisories, the PFAS industry quickly shifted to short-chain PFAS, e.g., hexafluoropropylene oxide dimer acid and its ammonium salt (GenX), to replace traditional long-chain PFAS. According to the recent fact sheet by the U.S. Environmental Protection Agency (EPA) in October 2021, however, GenX turned out to be more toxic than people originally thought and has shown health effects on liver, kidney, immune system, and so forth upon animal tests. On June 15, 2022, the EPA released the final health advisory for GenX, which is just 10 ppt. Thus, there is an urgent need of novel adsorbents for highly effective GenX remediation from water.Until now, there have been just a few reports on the remediation of GenX from water despite its popular use. In this Account, we reviewed current technology on PFAS remediation and illustrated our research on how to use polyacrylonitrile (PAN), a common and economic polymer for water filtration, in the form of nanofibrous membrane with handy chemical surface modification to develop innovative adsorbent/filter material for effective and scalable GenX remediation from water at the largest HBCU in the nation together with opportunities and challenges that are associated with this research. For the first time, we compared the GenX removal capability of electrospun PAN (ESPAN) nanofibrous membrane and amidoxime surface-functionalized ESPAN (ASFPAN) nanofibrous membrane. By modifying the surface of ESPAN nanofibrous membrane and introducing amidoxime functional group, the maximum GenX removal capacity (weight-normalized GenX removal) was almost doubled and reached ∼0.6 mmol/g at pH 4, which is higher than or comparable to that of most reported adsorbents for GenX removal. Hydrophobic interaction and dipole-dipole interaction could be the GenX adsorption mechanism on the ESPAN nanofibrous membrane while surface hydrophilicity and electrostatic interaction play major roles in GenX adsorption on the ASFPAN nanofibrous membrane. Our research shed light on understanding the GenX adsorption mechanism and developing new adsorbent/filter materials for practical short-chain PFAS remediation from water.

Adsorptive removal of organophosphate pesticides from aqueous solution using electrospun carbon nanofibers.

Organophosphate pesticides (OPPs) are widely prevalent in the environment primarily due to their low cost and extensive use in agricultural lands. However, it is estimated that only about 5% of these applied pesticides reach their intended target organisms. The remaining 95% residue linger in the environment as contaminants, posing significant ecological and health risks. This underscores the need for materials capable of effectively removing, recovering, and recycling these contaminants through adsorption processes. In this research, adsorbent materials composed of electro-spun carbon nanofibers (ECNFs) derived from polyacrylonitrile was developed. The materials were characterized through several techniques, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) analysis, and contact angle measurements. SEM analysis revealed details of the structural properties and inter-fiber spacing variations of the carbon nanofibers. The results revealed that ECNFs possess remarkable uniformity, active surface areas, and high efficiency for adsorption processes. The adsorption studies were conducted using batch experiments with ethion pesticide in aqueous solution. High-Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD) was utilized to quantify the concentrations of the OPP. Various parameters, including adsorbent dosage, pH, contact time, and initial ethion concentration, were investigated to understand their impact on the adsorption process. The adsorption isotherm was best described by the Freundlich model, while the kinetics of adsorption followed a non-integer-order kinetics model. The adsorption capacity of the ECNFs for OPP removal highlights a significant advancement in materials designed for environmental remediation applications. This study demonstrates the potential of ECNFs to serve as effective adsorbents, contributing to the mitigation of pesticide contamination in agricultural environments.

Meso-Microporous Carbon Nanofibrous Aerogel Electrode Material with Fluorine-Treated Wood Biochar for High-Performance Supercapacitor.

A supercapacitor is an electrical energy storage system with high power output. With worldwide awareness of sustainable development, developing cost-effective, environmentally friendly, and high-performance supercapacitors is an important research direction. The use of sustainable components like wood biochar in the electrode materials for supercapacitor uses holds great promise for sustainable supercapacitor development. In this study, we demonstrated a facile and powerful approach to prepare meso-microporous carbon electrode materials for sustainable and high-performance supercapacitor development by electrospinning polyacrylonitrile (PAN) with F-treated biochar and subsequent aerogel construction followed by stabilization, carbonization, and carbon activation. The resultant carbon nanofibrous aerogel electrode material (ENFA-FBa) exhibited exceptional specific capacitance, attributing to enormously increased micropore and mesopore volumes, much more activated sites to charge storage, and significantly greater electrochemical interaction with electrolyte. This electrode material achieved a specific capacitance of 407 F/g at current density of 0.5 A/g in 1 M H2SO4 electrolyte, which outperformed the state-of-the-art specific capacitance of biochar-containing electrospun carbon nanofibrous aerogel electrode materials (<300 F/g). A symmetric two-electrode cell with ENFA-FBa as electrode material showed an energy density of 11.2 Wh/kg at 125 W/kg power density. Even after 10,000 cycles of charging-discharging at current density of 10 A/g, the device maintained a consistent coulombic efficiency of 53.5% and an outstanding capacitance retention of 91%. Our research pointed out a promising direction to develop sustainable electrode materials for future high-performance supercapacitors.

Algae-Enhanced Electrospun Polyacrylonitrile Nanofibrous Membrane for High-Performance Short-Chain PFAS Remediation from Water.

As a short-chain PFAS (per- and polyfluoroalkyl substance), GenX was produced in recent years to replace traditional long-chain PFASs, such as perfluorooctanoic acid (PFOA). However, GenX turns out to be more toxic than people originally thought, posing health risks as a persistent environmental pollutant. In this research, for the first time, we incorporated chlorella, a single-celled green freshwater microalga that grows worldwide, with polyacrylonitrile (PAN) in equal amounts in electrospun nanofibers and studied the capability of the electrospun PAN/Algae bicomponent nanofibrous membrane (ES(PAN/Algae)) to bind and remove GenX from water. The incorporation of algae demonstrated a synergistic effect and significantly improved the GenX removal efficiency of the nanofibrous membrane. The maximum GenX removal capacity reached 0.9 mmol/g at pH 6, which is significantly higher than that of most of the reported GenX adsorbents as well as activated carbon. The GenX removal mechanism was investigated and discussed by using water contact angle, zeta potential, FTIR, and XPS techniques. This research demonstrated the potential to make highly efficient adsorbent/filter materials from common and economic materials to practically remediate short-chain PFASs from various water bodies.

Surface-Modified Electrospun Glass Nanofibers from Silane Treatment and Their Use for High-Performance Epoxy-Based Nanocomposite Materials.

As a new and promising reinforcing filler, electrospun glass nanofibers (EGNFs) have attracted attention in the field of polymer composite materials. However, the reinforcing effectiveness of surface-modified EGNFs using different silane coupling agents in epoxy resin is still not quite clear. In this research, a series of silane coupling agents with increasing chain lengths in the order of methyl trimethoxysilane (MTMS), (3-aminopropyl) triethoxysilane (APTES), (3-glycidyloxypropyl) trimethoxysilane (GPTMS), and dual silane coupling agent APTES-GPTMS were employed to carry out surface treatment on the EGNFs. The pristine and silane functionalized EGNFs were then incorporated into epoxy resin as reinforcing fillers at low loading levels, i.e., 0.25 wt.%, 0.5 wt.%, and 1 wt.%, and the mechanical properties of the resultant epoxy nanocomposites, including strength, stiffness, ductility, and toughness, were evaluated. A commercial product of glass nanoparticles (GNPs) was used as a control to compare the reinforcing effectiveness of the EGNFs and the GNPs. This study revealed that the EGNFs could provide significant reinforcing and toughening effects at ultra-low loading (0.25 wt.%) in epoxy nanocomposite materials. Furthermore, surface modification of the EGNFs with silane coupling agents with long chain lengths, e.g., by using dual silane coupling agents, APTES-GPTMS, could enhance the interfacial bonding between the EGNFs and the epoxy matrix and further increase the mechanical performance of the EGNF-reinforced epoxy nanocomposite materials. Through this research, we realized epoxy nanocomposite materials with much-improved mechanical properties, i.e., 37%, 24%, 18%, 57% improvement in strength, stiffness, ductility, and toughness, respectively, with respect to those of the cured neat epoxy material with an ultra-low loading (0.25 wt.%) of APTES-GPTMS-EGNFs. Our research paves the road for developing lighter and stronger epoxy nanocomposite materials with EGNFs.

Remediation of GenX from water by amidoxime surface-functionalized electrospun polyacrylonitrile nanofibrous adsorbent.

As a short-chain PFAS, GenX has gained increasing attention in recent years as a hazardous and emerging contaminant in water bodies. However, there is only limited research outcome up to date to address GenX remediation from water. In this research, we investigated amidoxime surface-functionalized PAN nanofibrous material from electrospinning as adsorbent to remove GenX from water. The nanofibrous adsorbent from 10 min treatment of electrospun PAN nanofibrous material in hydroxylamine (ASFPAN10) realized 35% GenX removal from a 100 mg/L aqueous solution at pH = 4 and 0.24 g/L loading after a simple one-time filtration with a GenX removal capacity of ~0.6 mmol/g. The mechanism study indicated that the GenX adsorption on PAN nanofibrous adsorbent could be mainly ascribed to hydrophobic interaction and dipole-dipole interaction between CN and C-F while the GenX adsorption on ASFPAN10 nanofibrous adsorbent could be mainly attributed to coulomb force between positive-charged CN+(OH)-H from ASFPAN10 and negative-charged COO- from GenX. Compared to that of PAN, the more hydrophilic surface of ASFPAN10 facilitated water access to the nanofibrous adsorbent surface and also contributed to the higher GenX removal efficiency. For the first time, this research pointed out a direction to use common economic materials for effective remediation of short-chain PFAS from water bodies especially at relatively high PFAS centration.