Synthesis, Characterization, and Magnetic Properties of Lanthanide-Containing Paramagnetic Ionic Liquids: An Evan's NMR Study.

The present study focuses on the synthesis and characterization of lanthanide-containing paramagnetic ionic liquids (ILs), [CnC1Im]3[MCl3X3] (n = 4, 6, and 8; M = Gd, Dy, and Ho; X = Br and Cl), derived from 1-alkyl-3-methylimidazolium anions. These paramagnetic ILs exhibit low vapor pressure, high thermal stability, physiochemical stability, and tunability, along with significant magnetic susceptibility, making them of interest in advanced material applications that may take advantage of neat liquids with magnetic susceptibility. Structural and physical properties were determined using FTIR, 1H NMR, DSC, and TGA. The room temperature density and viscosity of the iron paramagnetic ILs were also reported. Accompanying this report of paramagnetic IL products, we reintroduce and highlight Evan's NMR technique, an accessible magnetic susceptibility measurement technique that can utilize any available proton NMR to characterize the magnetic susceptibility of ILs. This work demonstrates the robustness of Evan's technique by demonstrating the ability to account for the IL water content, a common issue for hygroscopic materials, during the measurement of magnetic susceptibility. A detailed comparison of the ILs is presented, with dysprosium- and holmium-containing paramagnetic ILs exhibiting the highest magnetic susceptibility reported for mononuclear ILs reported to date. These materials have been studied with an eye on applications for mass transfer, eventually seeking to optimize magnetic susceptibility and viscosity using magnetic field gradients to move paramagnetic ILs carrying solute or heat. The study of paramagnetic ILs is important not only for understanding the magnetic properties of these materials but also for potential applications in areas such as magnetic resonance imaging, biomedicine, environmental remediation, and mass transfer. These unique materials have the potential to bring about new advances and technologies in the fields of materials science and analytical chemistry.

Thermal conductivity of ethylene glycol and propylene glycol nanofluids with boron nitride nano-barbs.

This study investigates the potential of composite allotrope boron nitride nanobarbs (BNNBs) as nanoparticles for enhancing the thermal conductivity of nanofluids based on mixtures of ethylene glycol and propylene glycol with water. BNNBs are allotrope composites composed of boron nitride nanotube cores with walls decorated with attached hexagonal boron nitride crystals, creating a jagged morphology that facilitates the formation of a connected network and contributes to the enhancement of thermal conductivity in nanofluids. BNNBs exhibit high thermal conductivity due to efficient phonon transfer and they are electrical insulators owing to their wide bandgap. The effect of BNNB concentration in carrier fluids on nanofluid thermal conductivity was investigated by introducing BNNBs into ethylene glycol-water and propylene glycol-water mixtures at 0-10 wt%. The results showed that BNNBs enhanced thermal conductivity of carrier fluids up to 45%, and the enhancement was proportional to the concentration of BNNBs in the carrier fluid. The study also investigated the dispersion stability of BNNBs in different solvents using Hansen Solubility Parameters, revealing that propylene glycol mixtures demonstrated better long-term stability compared to ethylene glycol mixtures. The findings suggest that BNNBs have great potential for use as thermally conductive nanoparticles in nanofluids for various heat transfer applications. Future research should focus on enhancing the dispersion stability of BNNB nanofluids and exploring the influence of BNNB morphology on the thermal conductivity and other thermophysical properties of nanofluids.

Synthesis and disassembly of an organometallic polymer comprising redox-active Co4S4 clusters and Janus biscarbene linkers.

Here, we show for the first time that main-chain organometallic polymers (MCOPs) can be prepared from Janus N-heterocyclic carbene (NHC) linkers and polynuclear cluster nodes. The crosslinked framework Co4S4-MCOP is synthesized via ligand displacement reactions and undergoes reversible electron transfer in the solid state. Discrete molecular cluster species can be excised from the framework by digesting the solid in solutions of excess monocarbene. Finally, we demonstrate a synthetic route to monodisperse framework particles via coordination modulation.

Quantification of hexagonal boron nitride impurities in boron nitride nanotubes via FTIR spectroscopy.

Preparation of high-quality boron nitride nanotubes (BNNTs) from commercially available stock is critical for eventual industry adoption and to perform comprehensive experimental studies of BNNTs. Separation of hexagonal boron nitride (h-BN) and BNNTs is a significant challenge, and equally so, quantification of h-BN content in mixed samples is a major challenge due to their nearly identical properties. This work introduces a simple method of quantifying h-BN content in BNNTs based on FTIR analysis. Quantification is achieved by "spiking" a BNNT sample with pure nanoscale h-BN as an internal standard. To demonstrate the efficacy of the quantification technique two BNNT enrichment methods, surfactant wrapping and centrifugation, and a novel sonication-assisted isovolumetric filtration are introduced. FTIR spectra of enriched samples show clear trends throughout the processes. We propose and demonstrate that FTIR peak ratios of the transverse and buckling modes of mixed h-BN/BNNT samples can be used to calibrate and quantify h-BN content in any BNNT sample. Hopefully, this method enables as-received BNNTs to be quantifiably enriched from low purity commercial feedstocks, enabling future development and study of BNNTs and related technology.

Adsorption studies of divalent, dinuclear coordination complexes as molecular spacers on SWCNTs.

In order to enhance the electrical energy storage capabilities of nanostructured carbon materials, inter-particle spacer strategies are needed to maintain ion-accessible surface area between the nanoparticles. This paper presents a comparison between different classes of divalent, dinuclear coordination complexes which both show strong adsorption to SWCNTs and have molecular spacer properties that maintain electrochemical activity. We find that a novel, dinuclear zinc hydrazone complex binds as an ion-pair at very high loading while not inducing significant aggregation as compared to our previously studies of dinuclear ruthenium complexes. These conclusions are supported by conductivity and dispersion stability data. Moreover, since zinc is an earth abundant metal, these complexes can be used as components in sustainable energy storage materials. Binding kinetics and binding equilibrium data are presented. Modeling of the adsorption isotherm is best fit with the BET model. Kinetics data support an independent binding model. Preliminary capacitance and membrane resistance data are consistent with the complexes acting as molecular spacers between the SWCNTs in a condensed thin film.

Aggregation kinetics of single-walled carbon nanotubes investigated using mechanically wrapped multinuclear complexes: probing the tube-tube repulsive barrier.

The rational design of supraparticle assemblies requires a detailed understanding of directed assembly processes. The stability of dispersions of nanoscale materials, like single-walled carbon nanotubes (SWCNTs), is still not fully understood, nor are the mechanisms of aggregation and assembly. A detailed balance of attractive van der Waals type interactions with various repulsive barrier mechanisms is needed to control the assembly of industrially viable and functional hybrid-nanoscale supraparticles. We report a detailed study of SWCNT dispersion stability and aggregation kinetics as a function of the nature of the coagulant used in various solvent systems. We explore three classes of coagulants that vary in charge, size, shape, solvation energy, and the ability to bind to the SWCNTs. We use these kinetic data to assess the tube-solvent-coagulant-tube interactions. We compare the relative contributions from two types of repulsive barriers. We find that tube-mediated structured solvent around the SWCNTs does not sufficiently describe our measured kinetic data. A DLVO type, electrical double layer repulsion is used to rationalize our observations. The data presented in this paper require a more detailed theoretical understanding of the physico-chemical environment near nanoparticle surfaces such as aggregating SWCNTs.

Direct measurement of the interactions of amide solvents with single-walled carbon nanotubes using isothermal titration calorimetry.

The interaction enthalpy of amide solvents with single-walled carbon nanotube (SWCNT) dispersions is measured using isothermal titration calorimetry (ITC). N,N-Dimethyl-formamide (DMF) and N-methyl-2-pyrilidone (NMP) were used to make dispersions of highly purified (6,5) SWCNTs. Using isothermal titration calorimetry, the ΔH and K(A) terms related to the solvent-nanotube interactions were measured, and ΔG and ΔS of the interaction were determined. It was found that the interaction enthalpy of NMP with SWCNTs dispersed in DMF was exothermic. The addition of a second solvent into a NMP or DMF dispersion produced spontaneous exfoliation of SWCNT bundles as the solvent properties became more favorable. During the titration, a positive change in interaction entropy within the dispersed system due to the unbundling of SWCNTs was measured. From blank titrations of pure DMF into pure NMP and the reverse, dilution enthalpies were also calculated and compared to the literature, along with the corresponding enthalpic interaction coefficients, h(xx) and h(xxx). From our results, ITC appears to be a viable technique for measuring the interaction of solvent molecules with the surface of SWCNTs and for measuring the effect of mixed solvent properties on SWCNT dispersions.