Suojiang Zhang

Physical Properties of Ionic Liquids: Database and Evaluation

A comprehensive database on physical properties of ionic liquids (ILs), which was collected from 109 kinds of literature sources in the period from 1984 through 2004, has been presented. There are 1680 pieces of data on the physical properties for 588 available ILs, from which 276 kinds of cations and 55 kinds of anions were extracted. In terms of the collected database, the structure-property relationship was evaluated. The correlation of melting points of two most common systems, disubstituted imidazolium tetrafluoroborate and disubstituted imidazolium hexafluorophosphate, was carried out using a quantitative structure-property relationship method.

Dual Amino‐Functionalised Phosphonium Ionic Liquids for CO2 Capture

A series of 20 dual amino-functionalised phosphonium ionic liquids, (3-aminopropyl)tributylphosphonium amino acid salts ([aP(4443)][AA], in which [AA](-) = [Ala](-), [Arg](-), [Asn](-), [Asp](-), [Cys](-), [Gln](-), [Glu](-), [Gly](-), [His](-), [Ile](-), [Leu](-), [Lys](-), [Met](-), [Phe](-), [Pro](-), [Ser](-), [Thr](-), [Trp](-), [Tyr](-) and [Val](-)), has been prepared. Their physicochemical properties, such as density, viscosity, glass transition and thermal decomposition temperatures and conductivity, have been determined. In particular, the [aP(4443)][AA] ionic liquids (ILs) have low glass transition temperatures ranging from -69.7 to -29.6 degrees C and high decomposition temperatures (all above 200 degrees C). The effects of the variation of the structure of [AA](-) on the above physicochemical properties are discussed. Furthermore, the CO(2) absorption of [aP(4443)][Gly], [aP(4443)][Ala], [aP(4443)][Val] and [aP(4443)][Leu], taken as examples, was investigated. It was found that the supported absorption of CO(2) by the [aP(4443)][AA] ILs almost reaches equilibrium within 80 min, the chemical absorption of CO(2) by the [aP(4443)][AA] ILs approaches 1 mol CO(2) per mol ionic liquid (twice that reported before) and the [aP(4443)][AA] ILs can be repeatedly recycled for CO(2) uptake.

Review of recent advances in carbon dioxide separation and capture

This review provides a comprehensive assessment of recently improved carbon dioxide (CO2) separation and capture systems, used in power plants and other industrial processes. Different approaches for CO2 capture are pre-combustion, post-combustion capture, and oxy-combustion systems, which are reviewed, along with their advantages and disadvantages. New technologies and prospective “breakthrough technologies”, for instance: novel solvents, sorbents, and membranes for gas separation are examined. Other technologies including chemical looping technology (reaction between metal oxides and fuels, creating metal particles, carbon dioxide, and water vapor) and cryogenic separation processes (based on different phase change temperatures for various gases to separate them) are reviewed as well. Furthermore, the major CO2 separation technologies, such as absorption (using a liquid solvent to absorb the CO2), adsorption (using solid materials with surface affinity to CO2 molecules), and membranes (using a thin film to selectively permeate gases) are extensively discussed, though issues and technologies related to CO2 transport and storage are not considered in this paper.

Chitosan functionalized ionic liquid as a recyclable biopolymer-supported catalyst for cycloaddition of CO2

Development of efficient, cheap and recyclable catalysts for a reaction under green reaction conditions is still a very attractive topic. In this work, the cycloaddition reactions of CO2 with various epoxides to form five-membered cyclic carbonates catalyzed by chitosan functionalized 1-ethyl-3-methyl imidazolium halides (CS-EMImX, X = Cl, Br) without additional solvent and metal co-catalyst were achieved in high yield and selectivity. The catalyst could be easily recovered and reused five times with high catalytic activity and selectivity. Besides, a possible catalytic cycle for the hydrogen bond assisted ring-opening of epoxide and activation of CO2 induced by the nucleophilic tertiary nitrogen of the chitosan was also proposed. The process represents a simple, ecologically safe and cost-effective route to synthesize cyclic carbonates with high product yield, as well as easy catalyst recycling.

Hydrogen Bonds: A Structural Insight into Ionic Liquids

Ionic liquids (ILs) have attracted intensive attention in academia and industry due to their unique properties and potential applications. Nowadays, much interest is focused on finding out what is the main force that determines the properties of ionic liquids. Intuitively like NaCl, in high-temperature molten salt (HTMS) the electrostatic Coulomb force is regarded as the dominant factor that determines the behaviors of ILs. However, a large amount of evidence indicates that such a molten-salt-based simplified explanation is not consistent with the corresponding experimental results. Besides the Coulomb force, the hydrogen bond is another important noncovalent interaction in the IL and is closely related to some important properties and applications, as suggested in some new research results. Therefore in this review, we present results concerning the hydrogen bond in ILs, from the perspective of experiment and calculation, to shed light on its effects and roles. The deep insights into structure, in particular the hydrogen bonds, can provide us with a rational design for the new ILs to fulfill the demands in some complicated chemical processes.

Fixation of CO2 into cyclic carbonates catalyzed by ionic liquids: a multi-scale approach

Fixation of CO2 to cyclic carbonates is one of the most important reactions since it represents a much greener alternative to the traditional phosgene process. In this context, the transformation of CO2 with epoxides into cyclic carbonates with respect to the newly emerged ionic liquid (IL) technology is discussed from a multi-scale viewpoint, including (1) the mechanism considering the “cooperative effect” at the basic atom and molecule level; (2) the reactor configuration at the unit level; (3) and the related process integration at the system level.

Facile Synthesis of Au-Nanoparticle/Polyoxometalate/Graphene Tricomponent Nanohybrids: An Enzyme-Free Electrochemical Biosensor for Hydrogen Peroxide

A green, facile, one-pot synthesis of well-defined Au NPs@POM-GNSs tricomponent nanohybrids is reported (POM stands for polyoxometalate and GNSs for graphene nanosheets). The synthesis is convenient, rapid and environmentally friendly. The POMs serve as both reducing, encapsulating molecules, and bridging molecules; this avoids the introduction of other organic toxic molecules. Characterization using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy analysis is performed, and the structure of the prepared nanohybrids of Au NPs@POM-GNSs is verified. Most importantly, the amperometric measurements show the Au NPs@POM-GNSs nanohybrids have high catalytic activity with good sensitivity, good long-term stability, wide linear range, low detection limit, and fast response towards H(2)O(2) detection for application as an enzyme-free biosensor. Transformation of the POMs during H(2)O(2) detection does not affect the catalytic activities of the nanohybrids. Thus, the synergistic effect of Au NPs and GNSs in the nanohybrids leads to the enhanced catalytic property.

Efficient Acid–Base Bifunctional Catalysts for the Fixation of CO2 with Epoxides under Metal‐ and Solvent‐Free Conditions

A series of acid-base bifunctional catalysts (ABBCs) that contain one or two Brønsted acidic sites in the cationic part and a Lewis-basic site in the anionic part are used as efficient catalysts for the synthesis of cyclic carbonates by cycloaddition of CO(2) to epoxides, without the use of additional co-catalyst or co-solvent. The effects of the catalyst structures and various reaction parameters on the catalytic performance are investigated in detail. Almost complete conversion can be achieved in 1 h for propylene oxide using [{(CH(2))(3)COOH}(2) im]Br under mild reaction conditions (398 K and 2 MPa). Furthermore, the catalyst can be recycled over five times without substantial loss of catalytic activity. This protocol is found to be applicable to a variety of terminal epoxides, producing the corresponding cyclic carbonates in good yields and high selectivities. A synergistic effect of the acidic and the basic sites as well as suitable hydrogen-bonding strength of ABBCs are considered crucial for the reaction to proceed smoothly. The activities of the ABBCs increase remarkably with increasing carboxylic-acid chain length of the cation. This metal- and solvent-free process thus represents an environmentally friendly process for BTC-catalyzed conversion of CO(2) into value-added chemicals.

Biodegradable Naphthenic Acid Ionic Liquids: Synthesis, Characterization, and Quantitative Structure–Biodegradation Relationship

It has been confirmed that commonly used ionic liquids are not easily biodegradable. When ultimately disposed of or accidentally released, they would accumulate in the environment, which strongly restricts large-scale industrial applications of ionic liquids. Herein, ten biodegradable ionic liquids were prepared by a single, one-pot neutralization of choline and surrogate naphthenic acids. The structures of these naphthenic acid ionic liquids (NAILs) were characterized and confirmed by (1)H and (13)C NMR spectroscopy, IR spectroscopy, and elemental analysis, and their physical properties, such as densities, viscosities, conductivities, melting points (T(m)), glass transition points (T(g)), and the onset temperatures of decomposition (T(d)), were determined. More importantly, studies showed that these NAILs would be rapidly and completely biodegraded in aquatic environments under aerobic conditions, which would make them attractive candidates to be utilized in industrial processes. To explore the underlying mechanism involved in the NAIL biodegradation reaction and seek prediction of their biodegradability under environmental conditions, four molecular descriptors were chosen: the logarithm of the n-octanol/water partition coefficient (log P), van der Waals volume (V(vdW)), energies of the highest occupied molecular orbital (E(HOMO)), and energies of the lowest unoccupied molecular orbital (E(LUMO)). Through multiple linear regression, a general and qualified model including the biodegradation percentage for NAILs after the 28-day OECD 301D test (%B(28)) and molecular descriptors was developed. Regression analysis showed that the model was statistically significant at the 99 % confidence interval, thus indicating that the %B(28) of NAILs could be explained well by the quantum chemical descriptor E(HOMO), which might give some important clues in the discovery of biodegradable ionic liquids of other kinds.

Understanding Structures and Hydrogen Bonds of Ionic Liquids at the Electronic Level

Due to their unique properties, ionic liquids (ILs) have attracted the academic and industrial attentions. However, recent controversies have focused on what are the main forces to determine the behaviors of ILs. In this work, a detailed DFT calculation was carried out to investigate the intermolecular interactions in two typical ILs, [Emim][BF(4)] and [Bmim][PF(6)]. The results indicate that hydrogen bonds (H-bonds) are the major intermolecular structural feature between cations and anions. Although the electrostatic force remains the major noncovalent force (70% of the total energy by energy decomposition calculation), the interaction energies calculated at different theoretical levels indicate that H-bond and van der Waals interactions cannot be ignored. However, the H-bonded capacities from natural bond orbital (NBO) delocalization energies do not show the consistent changes in the total interaction energies and number of H-bonds. Based on the canonical orbitals analysis, it is found that the σ-type orbital overlap and the partial charges transfer between anion and cation, finally, result in the significant energy reduction and rationalize the preferable location of anion, which is an essential understanding for the interaction and structure in the ion pair. Additionally, the strong agreement between the experimental IR spectra and the calculated vibrations implies that the structures of the larger ion clusters provide a reasonable depiction for bulk ILs at room temperature condition.