Three in One: The Versatility of Hydrogen Bonding Interaction in Halide Salts with Hydroxy-Functionalized Pyridinium Cations.

The paradigm of supramolecular chemistry relies on the delicate balance of noncovalent forces. Here we present a systematic approach for controlling the structural versatility of halide salts by the nature of hydrogen bonding interactions. We synthesized halide salts with hydroxy-functionalized pyridinium cations [HOCn Py]+ (n=2, 3, 4) and chloride, bromide and iodide anions, which are typically used as precursor material for synthesizing ionic liquids by anion metathesis reaction. The X-ray structures of these omnium halides show two types of hydrogen bonding: 'intra-ionic' H-bonds, wherein the anion interacts with the hydroxy group and the positively charged ring at the same cation, and 'inter-ionic' H-bonds, wherein the anion also interacts with the hydroxy group and the ring system but of different cations. We show that hydrogen bonding is controllable by the length of the hydroxyalkyl chain and the interaction strength of the anion. Some molten halide salts exhibit a third type of hydrogen bonding. IR spectra reveal elusive H-bonds between the OH groups of cations, showing interaction between ions of like charge. They are formed despite the repulsive interaction between the like-charged ions and compete with the favored cation-anion H-bonds. All types of H-bonding are analyzed by quantum chemical methods and the natural bond orbital approach, emphasizing the importance of charge transfer in these interactions. For simple omnium salts, we evidenced three distinct types of hydrogen bonds: Three in one!

Enhanced Furfural Production in Deep Eutectic Solvents Comprising Alkali Metal Halides as Additives.

The addition of alkali metal halide salts to acidic deep eutectic solvents is here reported as an effective way of boosting xylan conversion into furfural. These salts promote an increase in xylose dehydration due to the cation and anion interactions with the solvent being a promising alternative to the use of harsh operational conditions. Several alkali metal halides were used as additives in the DES composed of cholinium chloride and malic acid ([Ch]Cl:Mal) in a molar ratio of 1:3, with 5 wt.% of water. These mixtures were then used as both solvent and catalyst to produce furfural directly from xylan through microwave-assisted reactions. Preliminary assays were carried out at 150 and 130 °C to gauge the effect of the different salts in furfural yields. A Response Surface Methodology was then applied to optimize the operational conditions. After an optimization of the different operating conditions, a maximum furfural yield of 89.46 ± 0.33% was achieved using 8.19% of lithium bromide in [Ch]Cl:Mal, 1:3; 5 wt.% water, at 157.3 °C and 1.74 min of reaction time. The used deep eutectic solvent and salt were recovered and reused three times, with 79.7% yield in the third cycle, and the furfural and solvent integrity confirmed.

Effect of halide salts on development of surface browning on fresh-cut 'Granny Smith' (Malus × domestica Borkh) apple slices during storage at low temperature.

BACKGROUND: The postharvest life of fresh-cut apple slices is limited by browning on cut surfaces. Dipping in halide salt solutions was examined for their inhibition of surface browning on 'Granny Smith' apple slices and the effects on biochemical factors associated with browning. RESULTS: Delay in browning by salts was greatest with chloride = phosphate > sulfate > nitrate with no difference between sodium, potassium and calcium ions. The effectiveness of sodium halides on browning was fluoride > chloride = bromide > iodide = control. Polyphenol oxidase (PPO) activity of tissue extracted from chloride- and fluoride-treated slices was not different to control but when added into the assay solution, NaF > NaCl both showed lower PPO activity at pH 3-5 compared to control buffer. The level of polyphenols in treated slices was NaF > NaCl > control. Addition of chlorogenic acid to slices enhanced browning but NaCl and NaF counteracted this effect. There was no effect of either halide salt on respiration, ethylene production, ion leakage, and antioxidant activity. CONCLUSION: Dipping apple slices in NaCl is a low cost treatment with few impediments to commercial use and could be a replacement for other anti-browning additives. The mode of action of NaCl and NaF is through decreasing PPO activity resulting in reduced oxidation of polyphenols.

Halide salts induced the photodegradation of a fat-burning compound 2, 4-dinitrophenol by iron-montmorillonite.

Natural montmorillonite clay and anthropogenic organic pollutants frequently coexist in the estuarine environment where freshwater from rivers mixes with saltwater from the ocean. In this environment, the sharply changed aqueous chemistry especially salt content could significantly alter the photochemical behaviors of pollutants. However, this process was rarely investigated. In this study, the photodegradation of a representative anthropogenic weight-loss compound 2,4-dinitrophenol in the presence of Fe3+-montmorillonite and different halide salts was systematically investigated. Results show that 2,4-dinitrophenol was resistant to photodegradation by Fe3+-montmorillonite alone, but the presence of NaCl, NaBr, and sea salts in the system can evoke significant 2,4-dinitrophenol degradation. The enhancement effect was further elucidated as the replacement reaction between the clay associated Fe3+ and Na + which leads to the release of more interlayer Fe3+ from montmorillonite, resulting in increased production of high active hydroxyl radicals (˙OH) that can substantially damage 2,4-dinitrophenol molecule. In addition, halogen radicals from the reaction of halide ions with ˙OH were also confirmed to participate in 2,4-dinitrophenol degradation. Overall, this study implied that the changed salty condition in the estuarine water could induce the rapid transformation of organic pollutants that move from freshwater and have relatively stable photochemical properties.

Surface Passivation of MAPbBr3 Perovskite Single Crystals to Suppress Ion Migration and Enhance Photoelectronic Performance.

Recently, organometal halide perovskites (OHPs) have achieved significant advancement in photovoltaics, light-emitting diodes, X-ray detectors, and transistors. However, commercialization and practical applications were hindered by the notorious ion migration issue of OHPs. Here, we report a simple solvent-based surface passivation strategy with organic halide salts (methylammonium bromide (MABr) and phenylethylammonium bromide (PEABr)) to suppress the ion migration of MAPbBr3 single crystals. The surface passivation effect is evidenced by the stronger photoluminescence (PL) intensity and extended PL lifetime. Using the pulse voltage and continuous voltage current-voltage measurements, we found that single crystals with surface passivation showed negligible hysteresis on the surface due to the suppression of ion migration. As a result, the dark current stability of coplanar structure devices was significantly improved. Moreover, the vertical structure X-ray detectors with PEABr treatment exhibited a high sensitivity of 15 280 µC Gyair-1 cm-2 and a low detection limit of 87 nGyair s-1 under 5 V bias. The proposed technology would be a versatile tool to improve the performance of perovskite photoelectronic devices.

Reducing Open-Circuit Voltage Deficit in Perovskite Solar Cells via Surface Passivation with Phenylhydroxylammonium Halide Salts.

Suppressing non-radiative recombination via passivating surface defects of perovskite films has demonstrated an excellent strategy for high-performance perovskite solar cells (PSCs). However, it is still hard to realize both high open-circuit voltage (Voc ) of >1.2 V and high power conversion efficiency (PCE) of >22%, because the optimized bandgap of perovskite films is less than 1.60 eV for efficient light harvesting and Voc deficit is generally unavoidable due to carriers recombination. Here, the surface of the perovskite film is treated with a series of phenylhydroxylammonium halide salts and it is found that all of them can remarkably prolong the carrier lifetime owing to their excellent capability of surface defects passivation. The best PSC with phenylbutylammonium bromide treatment realizes a PCE of 22.67% with a Voc of 1.216 V, corresponding to a small Voc deficit of ≈344 mV.

Single Additive with Dual Functional-Ions for Stabilizing Lithium Anodes.

The dendritic lithium formation and sustained lithium consumption caused by the uncontrollable side reactions between lithium and electrolytes seriously restrict the applications of lithium anodes in high-energy density batteries, especially in carbonate electrolytes. Ameliorating the surface status of lithium anodes is critical for modulating lithium deposition behavior and improving the cycling stability of lithium metal batteries. Herein, magnesium chloride salt is first reported as a carbonate electrolyte additive for lithium surface modification by in situ reaction. It is proved that both Cl- and Mg2+ play important roles in building a stable electrode/electrolyte interface with a fast Li+ diffusion property. The coexistence of inorganic LiCl and metallic Mg species in the interface can effectively decrease the surface side reactions, lower interphase resistance, promote Li ions diffusion, and result in uniform lithium deposition. The electrochemical tests show that the reversible utilization rate of lithium for Li/Cu asymmetrical cells increases by 10% and the polarization of Li/Li symmetrical cells is reduced noteworthily with such an additive. Furthermore, a significant improved cycling performance of Li/Li4T5O12 full cells is also achieved.