Fluorine Induced In Situ Formation of High Valent Nickel Species for Ultra Low Potential Electrooxidation of 5-Hydroxymethylfurfural.

The Nickel-based catalysts have a good catalytic effect on the 5-hydroxymethylfurfural electrooxidation reaction (HMFOR), but limited by the conversion potential of Ni2+ /Ni3+ , 1.35 V versus RHE, the HMF electrooxidation potential of nickel-based catalysts is generally greater than 1.35 V versus RHE. Considering fluorine has the highest Pauling electronegativity and similar atomic radius of oxygen, the introduction of fluorine into the lattice of metal oxides might promote the adsorption of intermediate species, thus improving the catalytic performance. F is successfully doped into the lattice structure of NiCo2 O4 spinel oxide by the strategy of hydrothermal reaction and low-temperature fluorination. As is confirmed by in situ electrochemical impedance spectroscopy and Raman spectroscopy, the introduction of F weakens the interaction force of metal-oxygen covalent bonds of the asymmetric MT -O-MO backbone and improves the valence of Ni in tetrahedra structure, which makes it easier to be oxidized to higher valence active Ni3+ under the action of electric field and promotes the adsorption of OH- , while the decrease of Co valence enhances the adsorption of HMF with the catalyst. Combining the above reasons, F-NiCo2 O4 shows superb electrocatalytic performance with a potential of only 1.297 V versus RHE at a current density of 20 mA cm-2 , which is lower than the most catalyst.

Quantification of alkalinity of deep eutectic solvents based on (H-) and NMR.

Alkaline deep eutectic solvents (DESs) have been widely employed across diverse fields. A comprehensive understanding of the alkalinity data is imperative for the comprehension of their performance. However, the current range of techniques for quantifying alkalinity is constrained. In this investigation, we formulated a series of alkaline DESs and assessed their basicity properties through a comprehensive methodology of Hammett functions alongside 1H NMR analysis. A correlation was established between the composition, structure and alkalinity of solvents. Furthermore, a strong linear correlation was observed between the Hammett basicity (H-) of solvents and initial CO2 adsorption rate. Machine learning techniques were employed to predict the significant impact of alkaline functional components on alkalinity levels and CO2 capture capacity. This study offers valuable insights into the design, synthesis and structure-function relationship of alkaline DESs.

Operando Forming of Lattice Vacancy Defect in Ultrathin Crumpled NiVW-Layered Metal Hydroxides Nanosheets for Valorization of Biomass.

The 2D layered metal hydroxides (LMHs) have been developed for electrooxidation of 5-hydroxymethylfurfural (HMF). In this work, an effective strategy is proposed to tailor the electronic structure of active sites at the atomic level, which is by introducing defects into the lattice structure. As an example, a series of ultrathin crumpled ternary NiVW-LMH electrocatalysts with abundant lattice vacancies (denoted as NiVWv -LMH) are prepared in this way. The introduction of tungsten (W) endows the catalyst with a special crumpled structure, which promotes the generation of lattice vacancies and thus exposes more unsaturated Ni activity sites. The NiVWv -LMH displays superb performance in the electrooxidation of HMF. The Tafel slope for electrodehydrogenation of Ni2+ OH bond to Ni(OH)O species is 12.04 mV dec-1 . The current density at 1.43 V versus reversible hydrogen electrode (RHE) toward the oxidation reaction of HMF reaches about 193 mA cm-2 , which is better than most of the common electrocatalysts, with an 5.37-fold improvement compared with Ni(OH)2 electrode. The preparation strategy demonstrates in this work can be useful for developing highly efficient electrocatalysts.

Yet another perspective on hole interactions, part II: lp-hole vs. lp-hole interactions.

Most of the experimental and theoretical work in hole interactions (HIs) is mainly focused on exploiting the nature and characteristics of σ and π-holes. In this perspective, we focus our attention on understanding the origin and properties of lone-pair holes. These holes are present on an atom opposite to its lone-pair region. Utilizing some new and old examples, such as X3N/P⋯F- (X = F/Cl/Br/I), F-Cl/Br/I⋯H3P⋯NCH and H3B-NBr3 along with other molecular systems, we explored to what extent these lp-holes participate in lp-hole interactions, if they participate at all.

Analysis of the oxygen evolution activity of layered double hydroxides (LDHs) using machine learning guidance.

Layered double hydroxides (LDHs) are excellent catalysts for the oxygen evolution reaction (OER) because of their tunable properties, including chemical composition and structural morphology. An interplay between these adjustable properties and other (including external) factors might not always benefit the OER catalytic activity of LDHs. Therefore, we applied machine learning algorithms to simulate the double-layer capacitance to understand how to design/tune LDHs with targeted catalytic properties. The key factors of solving this task were identified using the Shapley Additive explanation and cerium was identified as an effective element to modify the double-layer capacitance. We also compared different modelling methods to identify the most promising one and the results revealed that binary representation is better than directly applying atom numbers as inputs for chemical compositions. Overpotentials of LDH-based materials as predicted targets were also carefully examined and evaluated, and it turns out that overpotentials can be predicted when measurement conditions about overpotentials are added as features. Finally, to confirm our findings, we reviewed additional experimental literature data and used them to test our machine algorithms to predict LDH properties. This analysis confirmed the very credible and robust generalization ability of our final model capable of achieving accurate results even with a relatively small dataset.

Acidity scales of deep eutectic solvents based on IR and NMR.

Acidic deep eutectic solvents (ADESs) have been utilized in various applications. Clearly, it is crucial to obtain acidity information that could reveal the relationship with performance. However, appropriate methods for measuring acidity are limited. Herein, we developed two promising approaches (without additional solvents) to identify and characterize both Lewis and Brønsted acidities by applying acetonitrile as an infrared probe and trimethylphosphine oxide (TMPO) as a nuclear magnetic resonance (NMR) probe. The acetonitrile IR approach is suitable for measuring the acidity of Lewis ADESs by monitoring the peak of ν(CN) around 2300 cm-1, and the 31P-TMPO NMR approach could identify and scale both Lewis and Brønsted acidities precisely. Moreover, a perfect linear relationship between the IR shift of ν(CN) and the effective charge density of metal cations was established, which provides a better understanding of Lewis acidity. In short, this study not only offers two efficient acidity measurement methods but also provides a molecular basis for optimizing the performance of ADESs in applications.

Calorimetric effect and thermokinetics in the formation process of a deep eutectic solvent.

For the first time, we report the calorimetric effect and thermokinetics in the formation process of a model deep eutectic solvent (DES), ChCl:urea. Mixing of a 1-to-2 molar ratio of choline chloride and urea shows a rapid endothermic process under stirring. The rate constants and reaction orders are determined by analyzing the thermokinetic curves at several constant temperatures. Low activation energy and activation parameters demonstrate that the formation of this DES is a rapid process. Other thermodynamic parameters are also estimated.

Magnetic deep eutectic solvents: formation and properties.

Deep eutectic solvents (DESs) are well-known as novel solvents due to their unique properties, which are indispensable for the development of green chemistry in the future. CoCl2·6H2O and NiCl2·6H2O-based DESs, which could be called magnetic DESs (MDESs) for short in view of their responsive behavior to an external magnetic field, have been widely used in many industrial applications, such as biomass treatment, electrolytes, and material preparation. For better application and full-scale development of these MDESs in various fields, eleven MDESs were prepared in this work by using CoCl2·6H2O and NiCl2·6H2O as hydrogen bond acceptors (HBAs) with alcohols, carboxylic acids and amides as hydrogen bond donors (HBDs), respectively. The intermolecular interactions between the components of MDESs were characterized via FTIR, 1H NMR and DSC analysis. In addition, physicochemical properties including density, viscosity, conductivity, ionicity, pH values, surface tension, thermostability and solvatochromic parameters were investigated. All MDESs exhibit acid characteristics and have good conductivity comparable with ionic liquids (ILs) and other DESs used for electrolytes. The results show that stronger H-bonding networks in Ni-based MDESs make them have higher density, viscosity, polarity and surface tension values than Co-based MDESs. Moreover, all prepared MDESs possess a good conductivity behavior which could be comparable to that of common organic solvents and ILs. According to this work, we could better comprehend the behavior of Co/Ni-based MDESs and choose the appropriate one for particular applications.

Deep insights into the viscosity of deep eutectic solvents by an XGBoost-based model plus SHapley Additive exPlanation.

Deep eutectic solvents (DESs) are emerging as novel green solvents for the processes of mass transport and heat transfer, in which the viscosity of DESs is important for their industrial applications. However, for DESs, the measurement of viscosity is time-consuming, and there are many factors influencing the viscosity, which impedes their wider application. This study aims to develop a data-driven model which could accurately and rapidly predict the viscosity of diverse DESs at different temperatures, and furthermore boost the design and screening of novel DESs. In this work, we collected 107 DESs with 994 experimental values of viscosity from published works. Given the significant effect of water on viscosity, the water content of each collected DES was labeled. The Morgan fingerprint was first employed as a feature to describe the chemical environment of DESs. And four machine learning algorithms were used to train models: support vector regression (SVR), random forest (RF), neural network (NN), and extreme gradient boosting (XGBoost), and XGBoost showed the best predictive performance. In combination with the powerful interpretation method SHapley Additive exPlanation (SHAP), we further revealed the positive or negative effect of features on viscosity. Overall, this work provides a machine learning model which could predict viscosity precisely and facilitate the design and application of DESs.

Eutectics: formation, properties, and applications.

Various eutectic systems have been proposed and studied over the past few decades. Most of the studies have focused on three typical types of eutectics: eutectic metals, eutectic salts, and deep eutectic solvents. On the one hand, they are all eutectic systems, and their eutectic principle is the same. On the other hand, they are representative of metals, inorganic salts, and organic substances, respectively. They have applications in almost all fields related to chemistry. Their different but overlapping applications stem from their very different properties. In addition, the proposal of new eutectic systems has greatly boosted the development of cross-field research involving chemistry, materials, engineering, and energy. The goal of this review is to provide a comprehensive overview of these typical eutectics and describe task-specific strategies to address growing demands.

Correction: Eutectics: formation, properties, and applications.

Correction for 'Eutectics: formation, properties, and applications' by Dongkun Yu et al., Chem. Soc. Rev., 2021, DOI: .

Thermal properties and cold crystallization kinetics of deep eutectic solvents confined in nanopores.

Herein, the phase behaviors of both bulk and confined deep eutectic solvents in controlled pore glasses were first investigated. Glass transition, cold crystallization and melting behaviors alter significantly in the nanopores due to the size effect and interfacial interactions. Kinetic analysis of the crystallization reveals increased effective activation energies and pre-exponential factors under nanoconfinement.

High volatility of superbase-derived eutectic solvents used for CO2 capture.

High volatility would lead to a highly flammable hazard, explosion danger, low regeneration efficiency and air pollution. Eutectic solvents (ESs) are assumed to be nonvolatile; however, the assumption is not correct. Here, we, for the first time, find that superbase-derived ESs are highly volatile. Even at room temperature (i.e., 25 °C) and atmospheric pressure, the mass loss of ESs could reach as high as 43.5% after 20 h of exposure. Superbase-derived ESs are promising solvents for CO2 capture, and they are also highly volatile after CO2 capture. We found that typical ethylene glycol : 1,8-diazabicyclo[5.4.0]undec-7-ene (EG : DBU (4 : 1)) has a three-stage volatilizing mechanism. EG and DBU volatilize first by breaking weak hydrogen-bonding interactions (1st stage), followed by the destruction of strong hydrogen-bonding interactions (2nd stage), and finally by destroying much stronger hydrogen-bonding interactions (3rd stage). This work presents a new horizon that ESs and their mixture with CO2 are highly volatile, which is helpful for mitigating laboratory explosion, combustion hazards, air pollution and designing new types of ESs with negligible volatility.

Ionicity of deep eutectic solvents by Walden plot and pulsed field gradient nuclear magnetic resonance (PFG-NMR).

Deep eutectic solvents (DESs) have attracted considerable attention due to their unique properties. Owing to similar structures and properties, DESs are also called "quasi-ionic liquids" or "ionic liquid analogous". However, for a deeper understanding and application of DESs, a comprehensive investigation on the ionicity of DESs is crucial. In this work, the effects of the structure and components of typical DESs on the ionicity were investigated. Moreover, the ionicity was discussed by using Walden plot, and the validity of applying it to DESs was verified using pulsed field gradient nuclear magnetic resonance (PFG-NMR). We found that the lack of free charged species and high viscosities make it difficult to achieve optimal conductivities for DESs, and thus most of them exhibit "poor ionic" nature. Fortunately, with an in-depth understanding of its microstructure and physicochemical properties, the properties of DESs can be finely tailored by selecting or even designing suitable parent compounds for functional applications. In particular, the ionicity of Li-based DESs was investigated for their potential application as electrolytes in Li-ion batteries.

Rhodium-catalyzed reductive carbonylation of aryl iodides to arylaldehydes with syngas.

The reductive carbonylation of aryl iodides to aryl aldehydes possesses broad application prospects. We present an efficient and facile Rh-based catalytic system composed of the commercially available Rh salt RhCl3·3H2O, PPh3 as phosphine ligand, and Et3N as the base, for the synthesis of arylaldehydes via the reductive carbonylation of aryl iodides with CO and H2 under relatively mild conditions with a broad substrate range affording the products in good to excellent yields. Systematic investigations were carried out to study the experimental parameters. We explored the optimal ratio of Rh salt and PPh3 ligand, substrate scope, carbonyl source and hydrogen source, and the reaction mechanism. Particularly, a scaled-up experiment indicated that the catalytic method could find valuable applications in industrial productions. The low gas pressure, cheap ligand and low metal dosage could significantly improve the practicability in both chemical researches and industrial applications.

Are Ionic Liquids Chemically Stable?

Ionic liquids have attracted a great deal of interest in recent years, illustrated by their applications in a variety of areas involved with chemistry, physics, biology, and engineering. Usually, the stabilities of ionic liquids are highlighted as one of their outstanding advantages. However, are ionic liquids really stable in all cases? This review covers the chemical stabilities of ionic liquids. It focuses on the reactivity of the most popular imidazolium ionic liquids at structural positions, including C2 position, N1 and N3 positions, and C4 and C5 positions, and decomposition on the imidazolium ring. Additionally, we discuss decomposition of quaternary ammonium and phosphonium ionic liquids and hydrolysis and nucleophilic reactions of anions of ionic liquids. The review aims to arouse caution on potential decomposition of ionic liquids and provides a guide for better utilization of ionic liquids.

Water absorption by deep eutectic solvents.

Deep eutectic solvents (DESs) are one type of green solvents. Most of the DESs could absorb water from air. However, even a trace amount of water can affect the chemical structure and physical properties of DESs. To date, no study has been reported on the hygroscopicity of DESs. Consequently, in this study, a comprehensive investigation was performed on the capacity, kinetics, mechanism, and furthermore the dynamic process (by PCMW2D-COS IR spectra) of atmospheric water absorption from air by DESs. The results show that most DESs are highly hygroscopic. Surface absorption enhances the overall water absorption capacity by DESs in spite of decreasing the initial water absorption rate. In the beginning, the water absorption increases with an increase in the number of hydrophilic groups in DESs due to the retained DES nanostructure during this period. Therefore, DESs with more hydrophilic groups (ChCl:glucose than ChCl:xylitol) possess a higher water absorption initial rate. However, when the water absorption capacity is high, the hindrance from the H-bond strength from inner DESs needs to be overcome for the absorption of more water. In this case, DESs with stronger H-bonds (ChCl:glucose than ChCl:xylitol) have a lower steady-state water absorption capacity and an easier equilibrium.

The dynamic evaporation process of the deep eutectic solvent LiTf2N:N-methylacetamide at ambient temperature.

Lithium-based deep eutectic solvents (DESs) are potential and promising electrolytes for energy-storing devices such as the lithium-ion battery and supercapacitor due to their greenness, low cost, favorable stability, and ease of synthesis. LiTf2N (lithium bis(trifluoromethylsulfonyl)imide):NMA (N-methylacetamide) is a liquid due to the strong intermolecular H-bonding interaction between the H-bonding acceptor (HBA, LiTf2N) and H-bonding donor (HBD, NMA). The properties (melting point, conductivity, viscosity, etc.) of LiTf2N:NMA change with the evaporation of NMA from LiTf2N:NMA, which would further influence the performance of the energy-storing devices. The evaporation of DES should be determined by the intermolecular interactions. Here, for the first time, the dynamic process of evaporation and intermolecular interactions of the DES LiTf2N:NMA at room temperature were investigated and we find that the evaporation mechanism of the DES LiTf2N:NMA can be divided into three stages. In the first stage (before 110 min), the H-bonding interaction between O in LiTf2N and NH in NMA is disrupted before destruction of the coordinating interaction related to amide II C[double bond, length as m-dash]O and Li cation. In the second stage (from 110 min to 270 min), the change of coordinating interaction related to amide II C[double bond, length as m-dash]O and Li cation is also higher than that of the H-bonded interaction. In the third stage (after 270 min), evaporation of NMA from LiTf2N:NMA has very little influence on the environment of LiTf2N:NMA. This work provides a guide for designing DESs as electrolytes for energy-storing devices such as the lithium-ion battery and supercapacitor.

Thermal, electrochemical and radiolytic stabilities of ionic liquids.

Research on ionic liquids has achieved rapid progress in the last several decades. Stability is a prerequisite for the application of ionic liquids. Ionic liquids may be used at elevated temperature, as electrolytes, or under irradiation. Therefore, the thermal, electrochemical, and radiolytic stabilities of ionic liquids are important and need to be known before their usage. Many research papers and some reviews on the stabilities of ionic liquids have been published. However, new results are continuously being published and a comprehensive review and perspective on this topic are still urgently needed. In this perspective, we intend to provide a comprehensive review including characterization methods, the effects of chemical composition of the ionic liquids on the thermal, electrochemical, and radiolytic stabilities of ionic liquids, respectively. Moreover, the thermal stability of some special types of ionic liquids such as poly(ionic liquids) and mixed ionic liquids, and the thermal and electrochemical stabilities of protic ionic liquids are discussed too. For thermal stability, the interactions between ions are less important than the individual anions and cations. The decomposition temperature is mainly determined by the less-stable ion, usually the anion. For electrochemical stability, the electrochemical window is determined by both the cation and anion. The less stable ion could influence the stability by interaction between the generated species from the decomposition with the more stable ion (opposite ion). This perspective is helpful for people to avoid using unstable ionic liquids and choose suitable ionic liquids.

Surprising Hofmeister Effects on the Bending Vibration of Water.

The Hofmeister series, which originally described the specific ion effects on the solubility of macromolecules in aqueous solutions, has been a long-standing unsolved and exceptionally challenging mystery in chemistry. The complexity of specific ion effects has prevented a unified theory from emerging. Accumulating research has suggested that the interactions among ions, water and various solutes play roles. However, among these interactions, the binding between ions and solutes is receiving most of the attention, whereas the effects of ions on the hydrogen-bond structure in liquid water have been deemed to be negligible. In this study, attenuated-total-reflectance Fourier transform infrared spectroscopy is used to study the infrared spectra of salt solutions. The results show that the red- and blue-shifts of the water bending band are in excellent agreement with the characteristic Hofmeister series, which suggests that the ions' effects on water structure might be the key role in the Hofmeister phenomenon.