Search for: All records

Abstract Water‐mediated proton conductivity in nanoporous materials is influenced by channel water ordering and the hydrophobicity/hydrophilicity of interior walls, making metal‐organic nanotubes (MONTs) useful systems for exploring these relationships due to their high crystallinity and tunable hydrophobicity. In the current study, electrochemical impedance spectroscopy is utilized to explore the proton conductivity on two metal organic nanotubes (UMONT and Cu‐LaMONT) with weak hydrophobic behavior that possess extended water networks within the 1‐D channels. Measurements performed at 95% RH and 20 °C indicate values of 1.63 × 10⁻⁴S cm⁻¹for UMONT and 3.80 × 10⁻⁴S cm⁻¹for Cu‐LaMONT, which is lower than values for walls with acidic, hydrophilic functional groups or nanotubular materials with strictly hydrophobic behavior. Proton conductivity decreases sharply with lower humidity, with Cu‐LaMONT being more sensitive to humidity changes. At low temperatures, UMONT outperforms LaMONT due to its well‐established hydrogen bonding network and hydrophobic interior. The anisotropic nature of proton conduction is also confirmed through pelletized powder sample analysis, emphasizing that the conductivity occurs through the water networks located within the 1‐D MONT channels. These findings emphasize the importance of understanding water–pore interactions and the resulting proton conductivity mechanisms to understand complex systems and design advanced materials. 

Abstract Hybrid materials, such as metal organic nanotubes (MONTs) can possess nanoconfined water molecules within their pore space and the overall behavior of the water within the material may be tuned based upon interactions with the inner channel walls. We have previously developed a range of methods (electron density mapping, kinetic models, and water interaction enthalpies) to evaluate water behavior under nanoconfinement using a uranium‐based metal organic nanotube (UMONT) but have not explored their applicability across a range of materials. In the current study, we test our methodologies on two additional MONT materials (LaMONTandCu‐LaMONT) to determine if the techniques can be utilized in other systems to predict behavior within complex hybrid materials. In addition, we explored how to use Hirshfeld surface maps generated by the CrystalExplorer software in the visualization and prediction of water behavior within complex hybrid materials. 

Thermosalience in an anthracene-thiocarboxamide occurs due to strong anisotropic thermal expansion, and the solid responds uniquely to different external stimuli. 

Through a combination of many analytical approaches, we show that a metal organic nanotube (UMON) displays selectivity for H 2 O over all types of heavy water (D 2 O, HDO, HTO). Water adsorption experiments combined with vibrational and radiochemical analyses reveal significant differences in uptake and suggest that surface adsorption processes may be a key driver in water uptake for this material. 

Uranium (U) contamination of drinking water often affects communities with limited resources, presenting unique technology challenges for U 6+ treatment. Here, we develop a suite of chemically functionalized polymer (polyacrylonitrile; PAN) nanofibers for low pressure reactive filtration applications for U 6+ removal. Binding agents with either nitrogen-containing or phosphorous-based ( e.g. , phosphonic acid) functionalities were blended (at 1–3 wt%) into PAN sol gels used for electrospinning, yielding functionalized nanofiber mats. For comparison, we also functionalized PAN nanofibers with amidoxime (AO) moieties, a group well-recognized for its specificity in U 6+ uptake. For optimal N-based (Aliquat® 336 or Aq) and P-containing [hexadecylphosphonic acid (HPDA) and bis(2-ethylhexyl)phosphate (HDEHP)] binding agents, we then explored their use for U 6+ removal across a range of pH values (pH 2–7), U 6+ concentrations (up to 10 μM), and in flow through systems simulating point of use (POU) water treatment. As expected from the use of quaternary ammonium groups in ion exchange, Aq-containing materials appear to sequester U 6+ by electrostatic interactions; while uptake by these materials is limited, it is greatest at circumneutral pH where positively charged N groups bind negatively charged U 6+ complexes. In contrast, HDPA and HDEHP perform best at acidic pH representative of mine drainage, where surface complexation of the uranyl cation likely drives uptake. Complexation by AO exhibited the best performance across all pH values, although U 6+ uptake via surface precipitation may also occur near circumneutral pH values and at high (10 μM) dissolved U 6+ concentrations. In simulated POU treatment studies using a dead-end filtration system, we observed U removal in AO-PAN systems that is insensitive to common co-solutes in groundwater ( e.g. , hardness and alkalinity). While more research is needed, our results suggest that only 80 g (about 0.2 lbs.) of AO-PAN filter material would be needed to treat an individual's water supply (contaminated at ten-times the U.S. EPA maximum contaminant level for U) for one year.