skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Quantitative Spectroscopic Analysis of Water Populations in the Hydrated Nanopore Environments of a Natural Montmorillonite
Title: Quantitative Spectroscopic Analysis of Water Populations in the Hydrated Nanopore Environments of a Natural Montmorillonite
Smectite clays are implicated in solute trapping in natural and engineered processes. Here we evaluated 23Na solid-state nuclear magnetic resonance (NMR) and thermogravimetric analysis-coupled mass spectrometry (TGA–MS) for quantitative analysis of a hydrated natural Na-montmorillonite equilibrated at different relative humidity (RH). Using X-ray diffraction, we determined predominantly large-sized (∼1.55 nm) interlayers at 93% and 75% RH, 2:1 ratio of medium-sized (∼1.23 nm) to large-sized interlayers at 55% RH, and 2:1 ratio of small-sized (<0.96 nm) to medium-sized interlayers at 11% RH. Informed by simulated NMR of differently hydrated model Na-MONT systems, the experimental 23Na NMR data revealed only fully hydrated Na+ populations at 93% RH, a 2:1 ratio of partially hydrated (outer-sphere) to mineral-bound (inner-sphere) Na+ populations at 55% RH and, remarkably, a near-equal proportion of these latter two Na+ populations at 11% RH. Between 93% and 11% RH, the TGA–MS data captured a 57% increase in tightly bound waters (water loss at 100–300 °C) but only a 22% decrease in freely exchangeable waters (water loss below 40 °C). The addition of exogenous NaCl altered the aforementioned hydration behaviors, particularly at low RH. Our findings of persisting hydrated environments despite interlayer collapse implied water populations incongruent with predictions from smectite interlayer nanopore size distributions.  more » « less
Award ID(s):
1646815
PAR ID:
10337137
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Journal of physical chemistry
Volume:
125
Issue:
48
ISSN:
1932-7455
Page Range / eLocation ID:
26552-26565
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, AIP Advances)
    Data are presented on strain compensation in InGaN-based multiple quantum wells (MQW) using AlGaN interlayers (ILs). The MQWs consist of five periods of InxGa1-xN/AlyGa1-yN/GaN emitting in the green (λ ∼ 535 nm ± 15 nm), and the AlyGa1-yN IL has an Al composition of y = 0.42. The IL is varied from 0 - 2.1 nm, and the relaxation of the MQW with respect to the GaN template layer varies with IL thickness as determined by reciprocal space mapping about the (202¯5) reflection. The minimum in the relaxation occurs at an interlayer thickness of 1 nm, and the MQW is nearly pseudomorphic to GaN. Both thinner and thicker ILs display increased relaxation. Photoluminescence data shows enhanced spectral intensity and narrower full width at half maximum for the MQW with 1 nm thick ILs, which is a product of pseudomorphic layers with lower defect density and non-radiative recombination. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; (, Materials Advances)
    Small molecule guests influence the functional properties of supramolecular hydrogels. Molecular-level understanding of such sol-gel compositions and structures is challenging due to the lack of long-range order and inherently heterogeneous sol-gel interface. In this study, insight into the uptake process of biologically relevant small molecules into guanosine-quartet(G4) borate hydrogels is obtained by gel-state magic-angle spinning (MAS) NMR spectroscopy. G4∙K + borate hydrogel can absorb up to 0.3 equivalent of cationic methylene blue (MB) without a significant disruption of the G4 fibrils that make up the gel, whereas the addition of over 0.3 equivalents of MB to the same gel leads to a gel-to-sol transition. The gel-to-sol transition process is characterized ex situ by analyzing and comparing the 1 H and 11 B MAS NMR spectra acquired before and after the MB uptake. In particular, 11 B isotropic chemical shifts and quadrupole interactions were determined by analyzing the 11 B MAS NMR spectra acquired at different magnetic fields, 11.7 T, 14.1 T and 20 T, which enable the different local bonding environments of borate anions in sol- and gel domains to be distinguished and identified. By comparison, uptake of heterocyclic molecules such as adenine, cytosine and 1-methylthymine into G4∙Na + borate hydrogels lead to stiff and clear gels while increasing the solubility of the nucleobases as compared to the solubility of the same compounds in water. G4∙Na + gel can uptake one equiv. of adenine with minimal disruption to the sol-gel framework, thus enhancing the adenine solubility up to an order of magnitude as compared to water. Combined multinuclear ( 1 H, 11 B and 23 Na) NMR spectroscopy analysis and vial inversion tests revealed that the nucleobases are embedded into pores of the sol phase rather than being closely interacting with the G-4 fibrils that make up the gel phase. These results indicate that G-4 hydrogels have potential applications as carrier systems for small molecules. Gel-state MAS NMR spectroscopy can be used to gain insight into host-guest interactions in complex heterogeneous sol-gel systems, which is often difficult to obtain from the conventional techniques such as X-ray scattering, electron microscopy and optical spectroscopy. 
    more » « less
  3. ; ; ; ; ; ; ; (, Ecosphere)
    Abstract Ticks are vectors of many diseases and are expanding in geographic distribution. However, how ticks will fare in their new environments, where they may experience stressful climatic conditions at the expansion front, remains unclear. Since there is a trade‐off in ticks between behaviors that promote longevity and behaviors that promote reproduction, we hypothesized that extreme climatic stress reduces the survivorship of ticks but increases the frequency of tick host‐seeking behavior, or questing. Here, we used a novel method to simulate climatic stress on individual ticks of three species—Amblyomma americanum,Dermacentor variabilis, andIxodes scapularis—to evaluate their survival, physiology, and questing behavior. The first experiment involved placing 144 adult ticks of each species in two temperature ranges (15–25°C and 25–35°C) and three relative humidity (RH) treatments (32%, 58%, and 84% RH). We assessed the ticks daily for survivorship and questing, and we measured water loss by comparing the mass of each tick when it died to when it was fully hydrated. In this first experiment, ticks in warmer and less humid conditions generally died faster than those in cooler and more humid conditions. Ticks of all three species were more likely to quest shortly before their death and consistently died after losing approximately 50%–56% of their total body water content, butIxodesreached that threshold much faster than the other two species. The second experiment involved placing 18 ticks of each species at 35°C and 32% RH. We assessed the ticks every 3 h for survivorship, questing, and water loss. Ticks again were more likely to quest shortly before their death. With frequent checks, we were able to measure the dehydration tolerance more accurately and the rate of water loss. Ticks of all three species consistently died after losing approximately 51% of their total body water content. However,Ixodeslost water approximately 5 times faster thanAmblyommaand 11 times faster thanDermacentor. These results demonstrate that severe climatic stress tilts the trade‐off toward higher questing rates but not higher overall questing time because of reduced survival rates. 
    more » « less
  4. ; ; ; ; ; ; (, Journal of Geophysical Research: Atmospheres)
    Abstract Three climate models are evaluated using in situ airborne observations from the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) campaign. The evaluation targets cloud phases, microphysical properties, thermodynamic conditions, and aerosol indirect effects from −40°C to 0°C. Compared with 580‐s averaged observations (i.e., 100 km horizontal scale), the Community Atmosphere Model version 6 (CAM6) shows the most similar result for cloud phase frequency distribution and allows more liquid‐containing clouds below −10°C compared with its predecessor—CAM5. The Energy Exascale Earth System Model (E3SM) underestimates (overestimates) ice phase frequencies below (above) −20°C. CAM6 and E3SM show liquid and ice water contents (i.e., LWC and IWC) similar to observations from −25°C to 0°C, but higher LWC and lower IWC than observations at lower temperatures. Simulated in‐cloud RH shows higher minimum values than observations, possibly restricting ice growth during sedimentation. As number concentrations of aerosols larger than 500 nm (Na500) increase, observations show increases of LWC, IWC, liquid, and ice number concentrations (Nliq, Nice). Number concentrations of aerosols larger than 100 nm (Na100) only show positive correlations with LWC and Nliq. From −20°C to 0°C, higher aerosol number concentrations are correlated with lower glaciation ratio and higher cloud fraction. From −40°C to −20°C, large aerosols show positive correlations with glaciation ratio. CAM6 shows small increases of LWC and Nliqwith Na500and Na100. E3SM shows small increases of Nicewith Na500. Overall, CAM6 and E3SM underestimate aerosol indirect effects on ice crystals and supercooled liquid droplets over the Southern Ocean. 
    more » « less
  5. ; ; ; ; ; (, AIChE Journal)
    Abstract Portlandite (Ca(OH)2; also known as calcium hydroxide or hydrated lime), an archetypal alkaline solid, interacts with carbon dioxide (CO2) via a classic acid–base “carbonation” reaction to produce a salt (calcium carbonate: CaCO3) that functions as a low‐carbon cementation agent, and water. Herein, we revisit the effects of reaction temperature, relative humidity (RH), and CO2concentration on the carbonation of portlandite in the form of finely divided particulates and compacted monoliths. Special focus is paid to uncover the influences of the moisture state (i.e., the presence of adsorbed and/or liquid water), moisture content and the surface area‐to‐volume ratio (sa/v, mm−1) of reactants on the extent of carbonation. In general, increasing RH more significantly impacts the rate and thermodynamics of carbonation reactions, leading to high(er) conversion regardless of prior exposure history. This mitigated the effects (if any) of allegedly denser, less porous carbonate surface layers formed at lower RH. In monolithic compacts, microstructural (i.e., mass‐transfer) constraints particularly hindered the progress of carbonation due to pore blocking by liquid water in compacts with limited surface area to volume ratios. These mechanistic insights into portlandite's carbonation inform processing routes for the production of cementation agents that seek to utilize CO2borne in dilute (≤30 mol%) post‐combustion flue gas streams. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email