22 Feb 2024

2D Fluorinated Graphene Oxide (FGO)-Polyethyleneimine (PEI) Based 3D Porous Nanoplatform for Effective Removal of Forever Toxic Chemicals, Pharmaceutical Toxins, and Waterborne Pathogens from Environmental Water Samples

Abstract: Although water is essential for life, as per the United Nations, around 2 billion people in this world lack access to safely managed drinking water services at home. Herein we report the development of a two-dimensional (2D) fluorinated graphene oxide (FGO) and polyethylenimine (PEI) based three-dimensional (3D) porous nanoplatform for the effective removal of polyfluoroalkyl substances (PFAS), pharmaceutical toxins, and waterborne pathogens from contaminated water. Experimental data show that the FGO-PEI based nanoplatform has an estimated adsorption capacity (qm) of ∼219 mg g−1 for perfluorononanoic acid (PFNA) and can be used for 99% removal of several short- and long-chain PFAS. A comparative PFNA capturing study using different types of nanoplatforms indicates that the qm value is in the order FGO-PEI > FGO > GO-PEI, which indicates that fluorophilic, electrostatic, and hydrophobic interactions play important roles for the removal of PFAS. Reported data show that the FGO-PEI based nanoplatform has a capability for 100% removal of moxifloxacin antibiotics with an estimated qm of ∼299 mg g−1. Furthermore, because the pore size of the nanoplatform is much smaller than the size of pathogens, it has a capability for 100% removal of Salmonella and Escherichia coli from water. Moreover, reported data show around 96% removal of PFAS, pharmaceutical toxins, and pathogens simultaneously from spiked river, lake, and tap water samples using the nanoplatform.

20 Dec 2023

Graphene in Cementitious Materials

Abstract: This project aims to determine the influence of laboratory-generated graphene (LGG) and commercial-grade graphene (CGG) on the chemical structure and compressive strength of graphene-cement mixtures. Determining the graphene-cement structure/processing/property relationships provides the most useful information for attaining the highest compressive strength. Graphene dose and particle size, speed of mixing, and dispersant agent were found to have important roles in graphene dispersion by affecting the adhesion forces between calcium silicate hydrate (CSH) gels and graphene surfaces that result in the enhanced strength of cement-graphene mixtures. X-ray diffraction (XRD), Raman, and scanning electron microscope (SEM) analyses were used to determine chemical microstructure, and compression testing for mechanical properties characterization, respectively. Based on observed results both LGG and CGG graphene cement mixtures showed an increase in the compressive strength over 7-, 14-, and 28-day age curing periods. Preliminary dispersion studies were performed to determine the most effective surfactant for graphene dispersion. Future studies will continue to research graphene—cement mortar and graphene—concrete composites using the most feasible graphene materials. These studies will prove invaluable for military programs, warfighter support, climate change, and civil works.

28 Mar 2023

Exploration of Two Polymer Nanocomposite Structure-Property Relationships Facilitated by Molecular Dynamics Simulation and Multiscale Modeling

Abstract: Polyamide 6 (PA6) is a semi-crystalline thermoplastic used in many engineering applications due to good strength, stiffness, mechanical damping, wear/abrasion resistance, and excellent performance-to-cost ratio. In this report, two structure-property relationships were explored. First, carbon nanotubes (CNT) and graphene (G) were used as reinforcement molecules in simulated and experimentally prepared PA6 matrices to improve the overall mechanical properties. Molecular dynamics (MD) simulations with INTERFACE and reactive INTERFACE force fields (IFF and IFF-R) were used to predict bulk and Young's moduli of amorphous PA6-CNT/G nanocomposites as a function of CNT/G loading. The predicted values of Young's modulus agree moderately well with the experimental values. Second, the effect of crystallinity and crystal form (α/γ) on mechanical properties of semi-crystalline PA6 was investigated via a multiscale simulation approach. The National Aeronautics and Space Administration, Glenn Research Center's micromechanics software was used to facilitate the multiscale modeling. The inputs to the multiscale model were the elastic moduli of amorphous PA6 as predicted via MD and calculated stiffness matrices from the literature of the PA6 α and γ crystal forms. The predicted Young's and shear moduli compared well with experiment.

1 Oct 2020

Method Selection Framework for the Quantitation of Nanocarbon Scientific Operating Procedure Series (SOP-C-3): Selection of Methods for Release Testing and Quantitation of Solids, Suspensions, and Air Samples for Carbon-Based Nanomaterials

Abstract: There is significant concern regarding the health and safety risk of nanocarbon (for example, nanotubes, graphene, fullerene), and the cur-rent capability gap for accurately determining exposure levels encumbers risk assessment, regulatory decisions, and commercialization. Given the various analytical challenges associated with the detection and quantitation of nanocarbon, it is unlikely that a single method or technique will prove effective for all forms of nanocarbon, all exposure scenarios, or all possible environmental systems. The optimal approach, or series of techniques, will likely depend on the nature of the material being measured, its concentration, and the matrix in which it is contained. In this work, a preliminary decision framework is presented that assists the user in deter-mining which analytical methods are best suited for a given sample.