Conference Agenda

Nanopores are ubiquitous in environmental systems such as shale in the sediments and membranes for separations, and chemical functional groups always play a fundamental role in regulating ion behaviors there. However, it is unclear whether interactions between an aqueous solution and functional groups on unconfined surfaces can be applied in functionalized nanoporous systems. Here, we designed a core-shell nanosensor with a gold nanorod (AuNR) core and functionalized mesoporous silica shell. Using surface-enhanced Raman spectroscopy, we measured the local pH and concentrations of toxic cations (Hg²⁺, Cu²⁺, and Pb²⁺) in functionalized nanopores. Our results showed that the physical interaction originating from ion polarization dominates the hydrophobic functionalized nanopores (methyl- and phenyl-). In hydrophobic functionalized nanopores, enhanced anion concentrations and suppressed cation concentrations occurred concurrently and could further result in a much lower pH in nanopores (as much as 2.5 pH units compared to bulk solutions), even in a well-buffered system. In contrast, in hydrophilic functionalized nanopores (amine-, carboxyl-, and thiol-), pH and concentrations of toxic metals are respectively dependent on pK_a values of the functional groups and chemical affinities of toxic metals towards these functional groups. Our new findings can provide guidelines for controlling heavy metal contamination in sediments and membranes, and help to design new remediation approaches that can utilize the unique characteristics of nanopore chemistry.

Switchable solvents are emerging platforms for green chemistry, promising efficient separations and tunable chemical environments for a diverse list of environmental applications. However, the molecular-level interactions in switchable mixtures, such as molecular orientation, patterns of bonding, and clustering, are still poorly understood, hindering further progress in the field. Amine-based switchable solvents are particularly promising, with applications in desalination, water softening, biorefinery separations, and oil extraction. In this study, we develop a novel use of the double-differential pair distribution function (ddPDF) technique and apply this technique to the switchable diisopropylamine (DIPA)-water system. The ddPDF technique revealed ordered, temperature- and composition-sensitive structures reminiscent of a co-crystal of water and amine. Small angle x-ray scattering further revealed that water formed nanoscale, inverse micelle-like regions inside the diisopropylamine-rich phase, and molecular dynamics showed that amine-water hydrogen bonds were much more temperature-sensitive than water-water bonds, pointing to the breakage of amine-water hydrogen bonds as the mechanism for the high temperature phase separation of the mixture. In sum, this study revealed the fundamental mechanisms behind the temperature-switchable DIPA-water phase behavior: for the first time, the nanoscale structures in the DIPA-water mixture were elucidated, and the extent of hydrogen bonding in the DIPA-water mixture was quantified. The techniques developed here can be extended to other systems, such as ionic liquids, deep eutectic solvents, proteins, or microemulsions, unlocking powerful tools for interpreting molecular interactions in complicated mixtures.

Self-healing materials are materials that can recover from physical or chemical damage autonomously. These smart materials can be instrumental in improving the safety and resilience of civil and environmental engineering systems. Thus far, they have been explored for applications such as structural materials (self-healing concrete), protective coatings, and water filtration membranes. While much effort has been made to improve the stability and mechanical properties of self-healing materials, work to understand how complex environments impact self-healing behavior and ability remains limited. To be applied in underwater applications such as water treatment, self-healing materials need to demonstrate sufficient self-healing ability in complex water matrices. Herein we investigated how monovalent (NaCl) and divalent (MgSO₄) ions impact the self-healing efficiency of a model 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and N,N-methylene bis(acrylamide) (MBA) hydrogel. Poly AMPS relies on interchain diffusion along with hydrogen bonding to facilitate self-healing. Our study showed NaCl and MgSO₄ ions inhibit hydrogen bonding but enhance interchain diffusion. In the absence of ions, the ultimate tensile (UT) strength and UT strain self-healing efficiency of a 0.003 MBA:AMPS hydrogel was 67.5 ± 21.6% and 15.0 ± 3.6%, respectively. However, in the presence of 35 g/L NaCl the UT strength self-healing efficiency dropped to 44.1 ± 10.4% while the UT strain self-healing efficiency increased to 43.9 ± 16.9%. This general trend was also observed for 0.006 MBA:AMPS hydrogels and under MgSO₄ conditions. Surprisingly, this study shows that divalent ions may not act as a crosslinker between partially or fully charged oxygen groups.

Tubular structures at the nanoscale possess remarkable advantages for a broad range of environmental applications, including for example, catalysis, sensing, microencapsulation, selective mass transport and ultrafiltration. While the fields of carbon nanotubes and nanotubes made of several non-carbon materials (e.g., metals, oxides, and semiconductors) have been progressing rapidly, proteinaceous nanotubes of customized biodegradability remained largely underexplored. Here, by integrating a template wetting approach with multiple silk-based solutions, we present a rapidly scalable and robust technology for fabricating large arrays (e.g., 20 cm × 20 cm) of well-aligned 1D nanostructures made of silk proteins. Benefitting from the polymorphic nature of silk, precise control over the size, density, aspect ratio, morphology (nanotubes versus nanopillars) and polymorphs of silk nanostructures are achieved, which then allows for programmable regulation of the end materials’ functions and properties (e.g., hydrophobicity, oleophilicity and gas permeability). The silk nanotube arrays fabricated present great utility as anti-fouling coatings against marine algae, in oil extraction from oil-water mixtures, and as a food packaging material with improved gas barrier property. Because of the biodegradable, non-toxic and edible nature of silk proteins, we believe that such nanostructured arrays will provide innovative solutions for a variety of environmental issues, such as oil spill and food waste.

Identifying unknown small molecules using tandem mass spectrometry (MS/MS) from a complex chemical mixture still has challenges. Some of the bottlenecks include determining the structure and understanding the reaction kinetics and reaction mechanisms; such challenges are far from solved. The reaction rate constants and reaction pathways are important variables that are used to inform the fate of contaminants in the environment. However, estimating these parameters is always considered an analytical challenge and often time-consuming, requiring significant costs, and technical personnel. The main objective of this study is to develop automated models that can be used to predict major reaction rate constants, reaction pathways, and other properties for identified features in complex chemical systems under chlorination. The specific objectives include (i) identifying the chemical features (or chemical/functional groups) in complex chemical systems using LC-MS/MS, and (ii) developing and successfully applying models that can perform kinetic analysis and reaction pathway modeling on the identified features from the non-targeted screening analysis. As model chemical complex systems, we used leached material from commonly used plastic materials (polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyvinyl acetate (PVA), poly(R)-hydroxybutyric acid (PHBA), poly L-lactide (PL) and rubber powder). Suwannee River natural organic matter (SRNOM) was used as a representative for the aquatic DOM. Samples were subjected to chlorination, and aliquots were taken at selected time intervals for further molecular characterization. Results on the emergent reaction dynamics will be reported. This research is contributing to the advancement of molecular characterization of complex chemical systems.