Tailoring physical and chemical properties of electrospun nanofiber and nanofiber composite mats for applications as passive sampling materials
Creators: name: Nagorzanski, Matthew R
Publisher: name: University of Iowa
Year: 2024
Subjects: subject: carbon nanotubes
subject: electrospinning
subject: passive sampling
subject: public abstract
subject: Nanotechnology
subject: FOS: Nanotechnology
subject: Pesticides

description: Today’s chemically dependent society sees a large, diverse amount of chemicals used in agriculture, industry, and in medicine, which can inevitably end up in the environment. Whether agrochemicals from runoff into water ways, or pharmaceuticals and personal care products that are released via wastewater treatment plant effluent, surface waters are often contaminated with a number of diverse chemicals resulting in a range of potential fates. This widespread contamination represents a significant environmental and human health concern that is often challenging to assess due to the unknown level and characterization of exposure that can shift temporally and spatially.
description: Passive sampling technology is often used to determine contaminant exposure profiles and can be deployed into surface waters to passively (i.e., without any addition energy input) accumulate contaminants into the sampler matrix over time. Despite recent advances in passive sampling technology, there remain challenges, and current technologies require long deployment times (i.e., weeks to months), can miss high intensity, short duration contaminant spikes, and can often struggle with smaller, more polar, organic chemicals or charged species. To address these challenges, there remain opportunities to develop fast, equilibrium passive sampling materials to supplement current technologies.
description: With these goals in mind, this work demonstrates the potential viability of polymer and polymer-nanoparticle composite materials fabricated via electrospinning as fast equilibrium passive samplers due to their high surface area to volume ratio. The studies reported herein focus on (1) demonstrating the ability to fabricate various electrospun nanofiber mats (ENMs) and tailor their properties to target organic micropollutants, including those with high polarity and high water solubility that can prove challenging for more tradition sorbent media, and (2) evaluating the viability of using these tailored ENMs as fast equilibrium passive samplers for field monitoring of organic micropollutants.
description: First, this work studied the effect of surface chemistries of carbon nanotubes (CNTs) as model substrates for more complex carbon-based sorbent media using the neonicotinoid family of insecticides as a model pollutant class. CNTs demonstrated rapid (&lt; 20 minutes) uptake of neonicotinoids, and neonicotinoid sorption trends loosely followed observed trends for other carbon sorbents such as granulated activated carbon. Surface chemistries of the CNTs played a noticeable role in neonicotinoid sorption, with charged surface chemistries seemingly interfering with sorption in most cases. Notably, differences in parent neonicotinoid imidacloprid (more electronegative pharmacophore) and its metabolite desnitro-imidacloprid (more positively charged pharmacophore) were observed to considerably influence sorption, with opposite trends in sorption to charged surface chemistries observed for this parent and metabolite compound pair.
description: These results with CNTs informed the fabrication of a variety of ENM-CNT composites to tailor sorption of neonicotinoids in a three-dimensional network of nanofibers. A variety of polymer (i.e., polyacrylonitrile, PAN) and carbon nanofiber (CNF) ENM-CNT composites were fabricated, and neonicotinoid sorption increased with the addition of CNTs and the cationic surfactant tertabutyl ammonium bromide (TBAB), and sorption further increased upon the carbonization of the PAN nanofibers to CNFs. Neonicotinoid sorption capacity generally increased with increasing carbon content of CNF-ENMs, and the benefits of different additives in PAN-ENMs was additive between addition of TBAB and/or CNTs. These results provide new insights into the tailored design of ENMs for the targeted removal of chemical pollutants.
description: Building upon this work demonstrating the ability to tailor ENM composition, surface chemistry, and bulk material properties, these findings were extended to other common organic micropollutants, atrazine, metolachlor, diuron, and 2,4-dichlorophenoxyacetic acid (2,4-D). ENM-CNT composites demonstrated sorption of all analytes. Composite materials containing TBAB sorbed significantly higher amounts of 2,4-D, and also increased uptake of metolachlor and diuron. Addition of the surfactant sodium dodecyl sulfate, SDS, with its subsequent washing and leaching from nanofibers increased ENM surface area, thereby increasing sorption of atrazine, diuron, and metolachlor. Sorption reversibility studies demonstrated that while a fraction of atrazine sorption is more permanently bound, atrazine sorption is largely reversible, particularly in ENMs with lower CNT content and added surfactants. An ideal ENM formulation, PAN / 10% COOH-CNT / 20% SDS, demonstrated near complete reversibility (96% desorption after 24 hours) and was deemed optimal for field testing.
description: Finally, using the optimal SDS-modified ENM-CNT composite, we conducted a proof-of-concept field trial for measurement of atrazine and metolachlor as a fast equilibrium passive sampler. Laboratory validation reported mostly reversible sorption of metolachlor (90% desorbed after 24 hours), and partition coefficients KENM-W were developed for atrazine and metolachlor (0.052 ± 0.006 L/g and 0.034 ± 0.004 L/g respectively) across environmentally relevant concentrations. The ENM-CNT composites were deployed at Muddy Creek in North Liberty, Iowa, where they reported atrazine aqueous concentrations in good agreement with concurrent grab sample analysis, but largely overpredicted aqueous metolachlor concentrations. Despite these disparate results from field trials, we maintain that ENM-CNT composites merit future development for potential use as a fast equilibrium passive sampler to complement existing integrative samplers that are typically deployed over longer timescales.