Polyvinyl alcohol-montmorillonite composites for water purification: Analysis of clay mineral cation exchange and composite particle synthesis.

Municipal and residential water purification rely heavily on activated carbon (AC), but regeneration of AC is costly and cannot be performed at the point-of-use. Clay minerals (CMs) comprise a class of naturally abundant materials with known capacities for analyte adsorbance. However, the gel-forming properties of CMs in aqueous suspension pose problems for these materials being used in water-purification. In this study, we have taken three main steps to optimize the use of CMs in these applications. First, we produced several variants of montmorillonite CMs to evaluate the effect of interstitial cation hydrophobicity on the ability of the CM to uptake chargecarrying organic pollutants. These variants include CMs with the following cations: sodium, hexyl(triphenyl) phosphonium, hexyadecyl(triphenyl)phosphonium, and hexyl(tributyl)phosphonium. Second, we synthesized polymer-clay mineral composite films composed of polyvinyl alcohol (PVA), crosslinked in the presence of a CM variant. These films were evaluated for their ability to uptake malachite green (MG). Finally, we developed a one-pot synthetic method for the generation of polymer-clay particles for use in a continuous column process. We synthesized polymer-clay mineral particles using the highest performing CM (based on the film experiments) and evaluated the equilibrium capacity and kinetics of MG uptake from solution.

Multiplex surface-enhanced Raman scattering detection of deoxynivalenol and ochratoxin A with a linear polymer affinity agent.

A linear, methacrylamide polymer affinity agent was explored to capture two mycotoxins, deoxynivalenol (DON) and ochratoxin A (OTA), for multiplex surface-enhanced Raman scattering (SERS) detection. These mycotoxins are naturally occurring small molecules from fungi that can be dangerous at low concentrations. SERS detection was completed for each polymer-toxin complex at concentrations relevant to current safety regulation by the FDA: 1 ppm for DON and 5 ppb for OTA. Visibly distinguishable vibrational modes were observed in the multiplex spectra that were attributed to each mycotoxin individually, thus, not requiring any additional chemometric analysis. Density functional theory (DFT) was used to model DON and OTA to accurately label the vibrational modes in the experimental spectra as well as provide insight on the binding between both targets and the affinity agent. Fully modeled vibrations of these toxins are novel contributions due to OTA never being modeled and only a few published vibrational modes of DON. DFT guides empirical observations regarding hydrogen bonding at multiple sites of each mycotoxin target molecule through the amine groups on the polymer, confirming the capabilities of a single polymer affinity agent to facilitate multiplex detection of a class of molecules through less-specific interactions than traditional affinity agents.

Coating iron oxide nanoparticles with mesoporous silica reduces their interaction and impact on S. oneidensis MR-1.

Here, we investigate the impact of iron oxide nanoparticles (IONPs) and mesoporous silica-coated iron oxide nanoparticles (msIONPs) on Shewanella oneidensis in an aerobic environment, which is likely the main environment where such nanoparticles will end up after use in consumer products or biomedical applications. Monitoring the viability of S. oneidensis, a model environmental organism, after exposure to the nanoparticles reveals that IONPs promote bacterial survival, while msIONPs do not impact survival. These apparent impacts are correlated with association of the nanoparticles with the bacterial membrane, as revealed by TEM and ICP-MS studies, and upregulation of membrane-associated genes. However, similar survival in bacteria was observed when exposed to equivalent concentrations of released ions from each nanomaterial, indicating that aqueous nanoparticle transformations are responsible for the observed changes in bacterial viability. Therefore, this work demonstrates that a simple mesoporous silica coating can control the dissolution of the IONP core by greatly reducing the amount of released iron ions, making msIONPs a more sustainable option to reduce perturbations to the ecosystem upon release of nanoparticles into the environment.

Stabilization of Silver and Gold Nanoparticles: Preservation and Improvement of Plasmonic Functionalities.

Noble metal nanoparticles have been extensively studied to understand and apply their plasmonic responses, upon coupling with electromagnetic radiation, to research areas such as sensing, photocatalysis, electronics, and biomedicine. The plasmonic properties of metal nanoparticles can change significantly with changes in particle size, shape, composition, and arrangement. Thus, stabilization of the fabricated nanoparticles is crucial for preservation of the desired plasmonic behavior. Because plasmonic nanoparticles find application in diverse fields, a variety of different stabilization strategies have been developed. Often, stabilizers also function to enhance or improve the plasmonic properties of the nanoparticles. This review provides a representative overview of how gold and silver nanoparticles, the most frequently used materials in current plasmonic applications, are stabilized in different application platforms and how the stabilizing agents improve their plasmonic properties at the same time. Specifically, this review focuses on the roles and effects of stabilizing agents such as surfactants, silica, biomolecules, polymers, and metal shells in colloidal nanoparticle suspensions. Stability strategies for other types of plasmonic nanomaterials, lithographic plasmonic nanoparticle arrays, are discussed as well.

Isothermal Titration Calorimetry for the Screening of Aflatoxin B1 Surface-Enhanced Raman Scattering Sensor Affinity Agents.

In this work, isothermal titration calorimetry (ITC) is employed as an affinity agent screening method for the surface-enhanced Raman scattering (SERS) detection of aflatoxin B1 (AFB1). AFB1, a potent carcinogen produced by a fungus that infects crops, is an important target due to the monitoring required based on its FDA regulation. Polymer affinity agents, like those studied here, have the potential to enable separation and detection of relevant small molecules such as pesticides, drugs, and biological toxins, like AFB1, especially when paired with a vibrational spectroscopy technique such as SERS. Herein, seven homopolymers were synthesized to be evaluated as AFB1 affinity agents based on hypothetical hydrogen bonding interactions. Nitrogen-inclusive poly( N-(2-aminoethyl) methacrylamide) (pAEMA) polymers and their oxygen analogs, poly(2-hydroxyethyl methacrylate) (pHEMA) were evaluated. ITC was demonstrated as an effective method for rapid screening among the polymer affinity agents. Chain lengths between seven and 39 repeat units were synthesized to study length-based variance in affinity agent performance. An ITC method was optimized and used for the rapid screening of polymer affinity agents. The results were compared to those generated by SERS. Good agreement between the ITC results and follow-up SERS sensing experiments showcased ITC's screening potential for analytical applications such as separation and detection.

Molecular Affinity Agents for Intrinsic Surface-Enhanced Raman Scattering (SERS) Sensors.

Research at the interface of synthetic materials, biochemistry, and analytical techniques has enabled sensing platforms for applications across many research communities. Herein we review the materials used as affinity agents to create surface-enhanced Raman spectroscopy (SERS) sensors. Our scope includes those affinity agents (antibody, aptamer, small molecule, and polymer) that facilitate the intrinsic detection of targets relevant to biology, medicine, national security, environmental protection, and food safety. We begin with an overview of the analytical technique (SERS) and considerations for its application as a sensor. We subsequently describe four classes of affinity agents, giving a brief overview on affinity, production, attachment chemistry, and first uses with SERS. Additionally, we review the SERS features of the affinity agents, and the analytes detected by intrinsic SERS with that affinity agent class. We conclude with remarks on affinity agent selection for intrinsic SERS sensing platforms.

Simultaneously Tailoring Surface Energies and Thermal Stabilities of Cellulose Nanocrystals Using Ion Exchange: Effects on Polymer Composite Properties for Transportation, Infrastructure, and Renewable Energy Applications.

Cellulose nanocrystals (CNCs) have great potential as sustainable reinforcing materials for polymers, but there are a number of obstacles to commercialization that must first be overcome. High levels of water absorption, low thermal stabilities, poor miscibility with nonpolar polymers, and irreversible aggregation of the dried CNCs are among the greatest challenges to producing cellulose nanocrystal-polymer nanocomposites. A simple, scalable technique to modify sulfated cellulose nanocrystals (Na-CNCs) has been developed to address all of these issues. By using an ion exchange process to replace Na+ with imidazolium or phosphonium cations, the surface energy is altered, the thermal stability is increased, and the miscibility of dried CNCs with a nonpolar polymer (epoxy and polystyrene) is enhanced. Characterization of the resulting ion exchanged CNCs (IE-CNCs) using potentiometry, inverse gas chromatography, dynamic vapor sorption, and laser scanning confocal microscopy reveals that the IE-CNCs have lower surface energies, adsorb less water, and have thermal stabilities of up to 100 °C higher than those of prepared protonated cellulose nanocrystals (H-CNCs) and 40 °C higher than that of neutralized Na-CNC. Methyl(triphenyl)phosphonium exchanged cellulose nanocrystals (MePh3P-CNC) adsorbed 30% less water than Na-CNC, retained less water during desorption, and were used to prepare well-dispersed epoxy composites without the aid of a solvent and well-dispersed polystyrene nanocomposites using a melt blending technique at 195 °C. Predictions of dispersion quality and glass transition temperatures from molecular modeling experiments match experimental observations. These fiber-reinforced polymers can be used as lightweight composites in transportation, infrastructure, and renewable energy applications.