Chuanyu Yan

A PEGylated deep eutectic solvent for controllable solvothermal synthesis of porous NiCo2S4 for efficient oxygen evolution reaction

As ionic liquid analogues or quasi-ionic liquids, deep eutectic solvents (DESs) have been applied in many fields in the past few years. Herein, a novel PEGylated DES composed of PEG 200 and thiourea was formed for the first time and used for solvothermal synthesis of nickel cobalt sulfides. The structure and composition of the as-synthesized sulfides can be tuned by adjustment of the ratio of the reactants. The PEGylated DES plays multiple roles as a solvent, a shape-control agent, and a sulfur source in the synthesis of sulfides. Compared with traditional sulfuration routes, this proposed route is cost-effective and energy-efficient by combining solvothermal synthesis and the sulfuration process. The prepared sulfides were used as catalysts for electrochemical water oxidation and they exhibited excellent oxygen evolution reaction (OER) performance, especially for NiCo2S4 with hierarchical pores. The overpotential (η) demand was 337 mV for the current density reaching 10 mA cm−2 and the Tafel slope was 64 mV dec−1 in an alkaline medium (1 M KOH) for NiCo2S4. In addition, NiCo2S4 demonstrated long-term stability with little deactivation after either thirty hours of continuous operation or two thousand cycles and a high faradaic efficiency of 95.8%. Synergistic effects including a relatively high Brunauer–Emmett–Teller area, abundant active sites, easy diffusion of electrolytes and oxygen gas, and strong structural integrity contribute to the high activity and long-term stability of the catalyst for OER. This study provides a new method for the synthesis of hierarchically structured metal sulfides for energy conversion and storage applications.

Highly efficient I2 capture by simple and low-cost deep eutectic solvents

The efficient removal and storage of radioactive nuclear contaminants including an isotope of iodine (131I) has attracted great concern especially after the explosion of the Fukushima nuclear power plant. In this study, deep eutectic solvents (DESs) are proposed for the removal and storage of iodine (I2). These DESs can be obtained by simply mixing two simple components (also cheap and biodegradable), which form liquids with melting points far below that of the individual components. A series of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) are selected for the preparation of DESs. The properties and I2 capture efficiency of the prepared DESs have been investigated. The results indicate that some DESs have higher efficiencies for I2 removal than the previously reported materials. Among them, ChI–methylurea shows the best I2 uptake efficiency of approximately 100% within 5 hours. Moreover, ChI–methylurea exhibits a good capability of I2 storage with only 4.6% of the iodine evaporated after 10 hours of strong N2 sweeping, which is also important since I2 is easy to sublimate. Additional calculations also suggest that the high efficiency for I2 capture by DESs mainly comes from the formation of halogen bonding (XB) between DESs and I2. This work opens a new way for the application of DESs.

Ionicity of acetate-based protic ionic liquids: evidence for both liquid and gaseous phases

Low ionicity at high temperatures has been detected for a series of acetate-based protic ionic liquids (PILs), which form neutral components as a result of back proton transfer through an equilibrium shift. By utilising temperature dependence of 15N NMR, neutral and ionised species are observed. In the meantime, 15N NMR and Attenuated Total Reflection Fourier Transform Infra Red (ATR-FTIR) spectroscopy indicates that the strength of directional hydrogen bonds is weakened at high temperatures, and ions form aggregates rather than precursor molecules. In situ FT-IR and gas chromatography-electron ionization mass spectrometry (GC-EI-MS) investigations show that the acetate-based PILs exist as both precursor molecules and ion pairs in the gaseous phase. Theoretical FT-IR vibrational mode analysis, the potential energy surface profile and Atom in Molecular (AIM) analysis of the PILs have been utilized to reveal the essential bonding information, which provides a guide for further application of the PILs.

The dynamic process of atmospheric water sorption in [BMIM][Ac]: quantifying bulk versus surface sorption and utilizing atmospheric water as a structure probe.

The dynamic process of the atmospheric water absorbed in acetate-based ionic liquid 1-butyl-3-methyl-imidazolium acetate ([BMIM][Ac]) within 360 min could be described with three steps by using two-dimensional correlation infrared (IR) spectroscopy technique. In Step 1 (0-120 min), only bulk sorption via hydrogen bonding interaction occurs. In Step 2 (120-320 min), bulk and surface sorption takes place simultaneously via both hydrogen bonding interaction and van der Waals force. In Step 3, from 320 min to steady state, only surface sorption via van der Waals force occurs. Specifically, Step 2 could be divided into three substeps. Most bulk sorption with little surface sorption takes place in Step 2a (120-180 min), comparative bulk and surface sorption happens in Step 2b (180-260 min), and most surface sorption while little bulk sorption occurs in Step 2c (260-320 min). Interestingly, atmospheric water is found for the first time to be able to be used as a probe to detect the chemical structure of [BMIM][Ac]. Results show that one anion is surrounded by three C4,5H molecules and two anions are surrounded by five C2H molecules via hydrogen bonds, which are very susceptible to moisture water especially for the former one. The remaining five anions form a multimer (equilibrating with one dimer and one trimer) via a strong hydrogen bonding interaction, which is not easily affected by the introduction of atmospheric water. The alkyl of the [BMIM][Ac] cation aggregates to some extent by van der Walls force, which is moderately susceptible to the water attack. Furthermore, the proportion of bulk sorption vs surface sorption is quantified as about 70% and 30% within 320 min, 63% and 37% within 360 min, and 11% and 89% until steady-state, respectively.

The dynamic process of radioactive iodine removal by ionic liquid 1-butyl-3-methyl-imidazolium acetate: discriminating and quantifying halogen bonds versus induced force

With the increasing demand for nuclear energy and the Fukushima Daiichi nuclear disaster in 2011, the removal of radioactive and hazardous iodine has attracted more and more attention. Here, we investigate the dynamic process of radioactive iodine sorption in a representative acetate-based ionic liquid (AcIL), 1-butyl-3-methyl-imidazolium acetate [BMIM][Ac], via in situ UV-Vis spectroscopy in combination with a two-dimensional correlation technique. More importantly, the halogen bonds (including interior and exterior types) and induced force (only possessing an exterior form) resulting in iodine sorption in [BMIM][Ac] at specific time points are discriminated and quantified. The results show that the iodine sorption in [BMIM][Ac] can be divided into three zones. In the first 140 min, only halogen bonds occur (Zone 1). From 140 to 240 min, (exterior) halogen bonds and induced force occur simultaneously (Zone 2). After 240 min, only induced force occurs (Zone 3). Specifically, Zone 1 consists of two subzones, i.e., Zone 1a (before 90 min) and Zone 1b (90–140 min), corresponding to interior and exterior halogen bonds, respectively. Zone 2 is composed of three subzones, i.e., Zone 2a (140–180 min), Zone 2b (180–200 min), and Zone 2c (200–240 min), with (exterior) halogen bonds taking up the majority, approximately one half, and a small part of the total iodine sorption, respectively. The proportion of halogen bonds and induced force resulting in iodine sorption by [BMIM][Ac] can be approximately derived as 100% and 0% within 140 min, 96% and 4% within 240 min, and 91% and 9% within 570 min, respectively. Furthermore, the proportion of interior and exterior halogen bonds resulting in iodine sorption by [BMIM][Ac] could be approximately derived as 85% and 15% within 140 min, 80% and 20% within 240 min, and 80% and 20% within 570 min, respectively. These processes and quantifications can provide insight into the radioactive iodine removal by ILs in addition to the [BMIM][Ac] that we investigated here, and may motivate further experimental or theoretical studies on the application of halogen bonds for removal of iodine by designing new types of ILs.

The Dynamic Process of Atmospheric Water Sorption in [EMIM][Ac] and Mixtures of [EMIM][Ac] with Biopolymers and CO2 Capture in These Systems

There are mainly three findings related to the dynamic process of atmospheric water sorption in the ionic liquid (IL) 1-ethyl-3-methlyl-imidazolium acetate ([EMIM][Ac]) and its mixtures with biopolymers (i.e., cellulose, chitin, and chitosan), and CO2 capture in these systems above. The analytical methods mainly include gravimetric hygroscopicity measurement and in situ infrared spectroscopy with the techniques of difference, derivative, deconvoluted attenuated total reflectance and two-dimensional correlation. These three findings are listed as below. (1) Pure [EMIM][Ac] only shows a two-regime pattern, while all the mixtures of [EMIM][Ac] with biopolymers (i.e., cellulose, chitin, and chitosan) present a three-regime tendency for the dynamic process of atmospheric water sorption. Specifically, the IL/chitosan mixture has a clear three-regime mode; the [EMIM][Ac]/chitin mixture has an unclear indiscernible regime 3; and the [EMIM][Ac]/cellulose mixture shows an indiscernible regime 2. (2) [EMIM][Ac] and its mixtures with biopolymers could physically absorb a trace amount of and chemically react with a much larger amount of CO2 from the air. The chemisorption capacity of CO2 in these pure and mixed systems is ordered as chitosan/[EMIM][Ac] mixture > chitin/[EMIM][Ac] mixture > cellulose/[EMIM][Ac] mixture > pure [EMIM][Ac] (ca. 0.09 mass ratio % g/g CO2/IL). (3) The CO2 solubility in [EMIM][Ac] decreases about 50% after being exposed to the atmospheric moist air for some specific time period.

Water sorption in protic ionic liquids: correlation between hygroscopicity and polarity

The hygroscopicity of nine protic ionic liquids (PILs) was first measured in air for 24 h at ambient temperature (ave. 28.9 °C) and relative humidity (ave. 56.6%). The hygroscopic process was qualitatively described by a sorption triangle, which connects well the three types of water sorption parameters, i.e., sorption capacity (C, W24h, W∞), sorption rate (R, kW∞, 1/t0.01, R30min), and sorption equilibrium (E, 1/k). Then, the hydrophilicity of the PILs was derived by the steady-state sorption capacity 100W∞. The results show that PILs are highly hygroscopic and have greater hydrophilicity compared to aprotic ionic liquids. Finally, the polarity of the PILs was indicated by Nile Red with λmax and was found to be positively correlated with their hygroscopicity capacity (W24h, W∞) and initial rate (R30min), while being negatively correlated with the average equilibrium (1/k), average rate (kW∞, 1/t0.01) and OH asymmetric stretching modes of water (νOH) in PILs. The results show that the correlation between the hygroscopicity and polarity of PILs is complicated.

Fine regulation of cellulose dissolution and regeneration by low pressure CO2 in DMSO/organic base: dissolution behavior and mechanism

In this study, the fine regulation of the dissolution and regeneration of microcrystalline cellulose (MCC) using very low pressure (0-0.2 MPa) CO2 in a mixed solvent of dimethyl sulfoxide (DMSO) and 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) at a very low temperature (30 °C) was achieved. The solubility of MCC in DMSO/DBU (weight ratio of DMSO WDMSO = 0.90) could reach 9.0% at 30 °C and under CO2 pressure of 0.2 MPa. A similar phenomenon was observed in the mixed solvent DMSO/1,1,3,3-tetramethylguanidine (TMG). Moreover, ATR-FTIR, NMR, UV-Vis, TGA, XRD and DFT computational analyses were used to investigate the dissolution mechanism. It was concluded that in the mixed solvent (DMSO and organic base), DMSO helped to dissociate ion-pairs into free ions by balancing the concentration of free ions and the number of hydrogen bonds at WDMSO = 0.90. Interactions between CO2 and the solvent mixture were explored, and the results indicate that the optimum CO2 pressure not only promotes the formation of ionic bonds but also accelerates the formation of covalent bonds. In this way, these interactions prevent the MCC molecules from aggregating and facilitate the dissolving of MCC. This study gives a thorough insight into the dissolution mechanism and specificity of MCC in the CO2-DMSO/organic base solvent system, which could be helpful for the utilization and transformation of cellulose.