Nuclear Magnetic Resonance Spectra Of Liquids Research Articles

Diffusional Motion of Solvated Ions in Super-Concentrated Electrolytes

The evolution of solvation structure and dynamics of aqueous LiTFSI based electrolytes with varying salt concentration and competing divalent (Zn2+, Mg2+ and Ca2+) and ammonium based (Me3EtN+) cations were studied using 7Li, 19F and 1H nuclear magnetic resonance (NMR) spectroscopy and pulsed-field gradient (PFG) NMR methods. The NMR peak intensity analysis (Figure 1(a)), reveals that more than half of Li+, TFSI- and H2O molecules are invisible in liquid NMR spectra, likely due to the loss of mobility (broader NMR line width) associated with formation of bigger solvate clusters at higher salt concentrations. The 7Li, 19F and 1H chemical shift values (Figure 1(b)), were shifted to the higher field (more negative chemical shift values) with salt concentration, indicating the interaction between Li+ cations and TFSI- anions became stronger, while the hydrogen bonding network between H2O molecules became weaker resulting from the localization of water clusters in the solutions. The mobility of the remaining species were analyzed through the PFG-NMR based diffusion measurements (Figure 1(c)). It showed that Li+ cation diffuses relatively faster than TFSI- anion (D H2O>D Li>D TFSI) for these aqueous electrolytes, and differ from non-aqueous electrolyte solutions which traditionally register higher anion diffusion rates (D anion > D Li) [1-4]. The D H2O/D TFSI diffusion ratio showed that the relative mobility of water molecules increases with LiTFSI concentration and by addition of multivalent (Zn2+, Mg2+ and Ca2+) cation salt. The D Li/D TFSI diffusion ratio reaches the maximum value of ~3.4 for the 20 m LiTFSI/H2O solution, and the addition of competing cations tends to minimally affect the lithium diffusion. The different behavior between D H2O/D TFSI and D Li/D TFSI values suggest that the localized water molecules diffuse freely in the higher concentration electrolytes, while the diffusion motions of Li+ cation and TFSI- anion depend strongly on the total composition of the competing ions in the solution. The structural and diffusional properties of high concentration electrolytes will be discussed based on diffusion and chemical shift analysis. References Frömling, T., et al., Enhanced Lithium Transference Numbers in Ionic Liquid Electrolytes. J. Phys. Chem. B, 2008. 112(41): p. 12985-12990.Hayamizu, K., Temperature Dependence of Self-Diffusion Coefficients of Ions and Solvents in Ethylene Carbonate, Propylene Carbonate, and Diethyl Carbonate Single Solutions and Ethylene Carbonate + Diethyl Carbonate Binary Solutions of LiPF6 Studied by NMR. J. Chem. Eng. Data, 2012. 57(7): p. 2012-2017.Hayamizu, K., et al., Pulse-Gradient Spin-Echo 1H, 7Li, and 19F NMR Diffusion and Ionic Conductivity Measurements of 14 Organic Electrolytes Containing LiN(SO2CF3)2. J. Phys. Chem. B, 1999. 103(3): p. 519-524.Wu, T.-Y., et al., Influence of LiTFSI Addition on Conductivity, Diffusion Coefficient, Spin–Lattice Relaxation Times, and Chemical Shift of One-Dimensional NMR Spectroscopy in LiTFSI-Doped Dual-Functionalized Imidazolium-Based Ionic Liquids. J. Chem. Eng. Data, 2015. 60(3): p. 471-483. Figure 1

Photomineralization of Effluent Organic Phosphorus to Orthophosphate under Simulated Light Illumination.

Organic phosphorus (OP), one of the main forms of phosphorus in effluent from biological wastewater treatment plants, may contribute to the bioavailable phosphorus pool as well as water eutrophication. However, little is known about the photomineralization of OP or the possible impacts on the phosphorus cycle in water bodies. Herein, the photomineralization of effluent OP was investigated. An increase in orthophosphate concentration was observed under illumination. The 31P liquid nuclear magnetic resonance spectra demonstrated that the release of orthophosphate resulted from photomineralization of OP. Furthermore, the photoproduced hydroxyl radicals (·OH) were proved to play a dominant role in the OP photomineralization. Nitrate, effluent organic matter (EfOM), and Fe(III) presented in effluent were the main chromophores for ·OH photoproduction, and their contributions to ·OH production and photomineralization of OP followed the order: nitrate > EfOM > Fe(III). Additionally, the carbonate (or bicarbonate) in the effluent and high pH were unfavorable for OP photomineralization. The present study revealed the photomineralization behavior of OP in actual effluent, suggesting that photomineralization of OP might contribute to eutrophication and may play a non-negligible role in phosphorus turnover in water bodies.

Structural studies of zinc polyphosphate glasses by nuclear magnetic resonance

Nuclear magnetic resonance (NMR) spectroscopy of solids and of liquids was used to study the structure of xZnO+(1− x)P 2O 5 glasses prepared from a glass melt in the composition range 0.35⩽ x⩽0.70. Relative concentrations of Q n units in the solid glasses have been compared with the liquid NMR spectra and with the predictions based on the reorganization theory. Disproportionation reactions in glass liquids of meta- and pyrophosphates are evident. Anisotropies of chemical shift tensor for all phosphorus units are given. Structural changes associated with CSA parameters, including the presence of rings and chains are discussed. Both solid and liquid state NMR spectra show that ultraphosphate glasses consist mainly of ring structures, while only chains are present in metaphosphates.