Shiguo Zhang

Recent advances in ionic liquid catalysis

Due to their unique properties, ionic liquids have offered great potential for developing clean catalytic technologies. After a short introduction of their advantages in green catalysis, recent advances in ionic liquid catalysis are reviewed with emphasis on four hot fields, viz. biomass conversion in ionic liquids, catalytic production of fine chemicals in ionic liquids, supported ionic liquid phase catalysis, as well as Friedel–Crafts reactions in ionic liquids. In particular, through selected samples, we show here the advantages and potential of ionic liquids in exploring cleaner catalytic technologies, as compared to traditional catalytic processes. Finally, further development of ILs in catalysis is briefly prospected.

Protic Ionic Liquids and Salts as Versatile Carbon Precursors

Instead of traditional polymer precursors and complex procedures, easily prepared and widely obtainable nitrogen-containing protic ionic liquids and salts were explored as novel, small-molecule precursors to prepare carbon materials (CMs) via direct carbonization without other treatments. Depending on the precursor structure, the resultant CMs can be readily obtained with a relative yield of up to 95.3%, a high specific surface area of up to 1380 m(2)/g, or a high N content of up to 11.1 wt%, as well as a high degree of graphitization and high conductivity (even higher than that of graphite). One of the carbons, which possesses a high surface area and a high content of pyridinic N, exhibits excellent electrocatalytic activity toward the oxygen reduction reaction in an alkaline medium, as revealed by an onset potential, half-wave potential, and kinetic current density comparable to those of commercial 20 wt% Pt/C. These low-cost and versatile precursors are expected to be important building blocks for CMs.

Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices

Ionic liquids (ILs) are liquids consisting entirely of ions and can be further defined as molten salts having melting points lower than 100 °C. One of the most important research areas for IL utilization is undoubtedly their energy application, especially for energy storage and conversion materials and devices, because there is a continuously increasing demand for clean and sustainable energy. In this article, various application of ILs are reviewed by focusing on their use as electrolyte materials for Li/Na ion batteries, Li-sulfur batteries, Li-oxygen batteries, and nonhumidified fuel cells and as carbon precursors for electrode catalysts of fuel cells and electrode materials for batteries and supercapacitors. Due to their characteristic properties such as nonvolatility, high thermal stability, and high ionic conductivity, ILs appear to meet the rigorous demands/criteria of these various applications. However, for further development, specific applications for which these characteristic properties become unique (i.e., not easily achieved by other materials) must be explored. Thus, through strong demands for research and consideration of ILs unique properties, we will be able to identify indispensable applications for ILs.

Upper limit of nitrogen content in carbon materials.

Nitrogen-doped carbon materials (NDCs) play an important role in various fields. A great deal of effort has been devoted to obtaining carbon materials with a high nitrogen content; however, much is still unknown about the structure of the nitrogen-doped materials and the maximum nitrogen content possible for such compounds. Here, we demonstrate an interesting relationship between the N/C molar ratio and the N content of NDCs. The upper limit for the nitrogen content of NDCs that might be achieved was estimated and found to strongly depend on the carbonization temperature (14.32 wt% at 1000 °C and 21.66 wt% at 900 °C), irrespective of the precursor or preparation conditions. Simulations suggest that, especially in the carbon architectures obtained at high temperatures, nitrogen atoms are always located on separate hexagon moieties in a graphitic configuration, thereby yielding a critical N/C molar ratio very close to the value estimated from the experimental results.

Clean Beckmann rearrangement of cyclohexanone oxime in caprolactam-based Brønsted acidic ionic liquids

The Beckmann rearrangement of cyclohexanone oxime to afford caprolactam in a novel caprolactam-based Bronsted acidic ionic liquid as catalyst and reaction medium proceeded with high conversion and selectivity at 100 °C. The occurrence of the Beckmann rearrangement of cyclohexanone oxime in such a Bronsted acidic IL was also confirmed with in situ FT-Raman observation. The key point is that the caprolactam product was one component of the ionic liquid, and a dynamic exchange between the resulting caprolactam product and the caprolactam from the ionic liquid is expected. Therefore, the strong chemical combination between the caprolactam product and the acidic ionic liquid was greatly decreased and the desired product in the solid was recovered through extraction with organic solvent after the reaction.

Nanoconfined Ionic Liquids

Ionic liquids (ILs) have been widely investigated as novel solvents, electrolytes, and soft functional materials. Nevertheless, the widespread applications of ILs in most cases have been hampered by their liquid state. The confinement of ILs into nanoporous hosts is a simple but versatile strategy to overcome this problem. Nanoconfined ILs constitute a new class of composites with the intrinsic chemistries of ILs and the original functions of solid matrices. The interplay between these two components, particularly the confinement effect and the interactions between ILs and pore walls, further endows ILs with significantly distinct physicochemical properties in the restricted space compared to the corresponding bulk systems. The aim of this article is to provide a comprehensive review of nanoconfined ILs. After a brief introduction of bulk ILs, the synthetic strategies and investigation methods for nanoconfined ILs are documented. The local structure and physicochemical properties of ILs in diverse porous hosts are summarized in the next sections. The final section highlights the potential applications of nanoconfined ILs in diverse fields, including catalysis, gas capture and separation, ionogels, supercapacitors, carbonization, and lubrication. Further research directions and perspectives on this topic are also provided in the conclusion.

Protic-salt-derived nitrogen/sulfur-codoped mesoporous carbon for the oxygen reduction reaction and supercapacitors

Nitrogen/sulfur-co-doped mesoporous carbon (Phen-HS) was obtained through direct carbonization of a single protic salt, that is, 1,10-phenanthrolinium dibisulfate ([Phen][2 HSO4 ]), in the presence of a colloidal silica template without the use of additional acid or metal catalysts for prepolymerization prior to carbonization. Phen-HS was prepared in a relatively high yield (30.0 %) and has a large surface area (1161 m(2)  g(-1) ), large pore volume (2.490 cm(3)  g(-1) ), large mesopores (≈12 nm), narrow pore-size distribution (7-16 nm), and high nitrogen (7.5 at %) and sulfur (1.3 at %) contents. The surface area/pore-size distribution is much higher/narrower than that of most reported carbon materials obtained from traditional precursors by using the same template. Phen-HS was directly used as an electrocatalyst for the oxygen reduction reaction (ORR) and as an electrode material for supercapacitors. As an efficient metal-free catalyst, Phen-HS exhibited good electrocatalytic activity toward the ORR in a 0.1 M KOH aqueous solution, which is comparable to the activity of a commercial Pt/C catalyst. Electrochemical measurements for Phen-HS used in a double-layer capacitor showed high specific capacitances of 160 and 140 F g(-1) in 1 M H2 SO4 and 6 M KOH, respectively, with good rate capabilities and high cycling stabilities.

The influence of the acidity of ionic liquids on catalysis.

In the past 20 years, the concept of ionic liquids (ILs) have been extensively applied in the fields of chemistry, materials, and life sciences. Undoubtedly, the ionic liquids composed of quaternary ammonium cations and anions, such as BF4 , PF6 , Cl , and NTf2 , have been the backbone of this area since immidazolium cation ionic liquids were synthesized by Zaworotko et al. and were brought into catalysis and synthesis by Seddon, Rogers, Welton, Wasserscheid, and others. Thousands of reactions have been performed in these ionic liquids and many of them exhibited better behavior than organic solvents. Normally, the fine performance of these ionic liquids was attributed to the specific ionic environment of the ionic liquid. Nevertheless, the acidity of the airand moisture-stable ionic liquids and its effect on catalysis is an interesting topic. As it is well known, a large amount of organic reactions can be catalyzed or promoted by an acid environment. During our investigation of the function of ionic liquids in catalysis, especially airand moisture-stable ones, we found that these ILs normally exhibit weak acidity in the presence of a small amount of water. That means the interpretations about the function of airand moisture-stable ionic liquids in catalytic reactions are possibly wrong because the presence of trace amount of water is not avoidable in reality. Herein, we present our results on the study of acidity of airand moisture-stable ionic liquids and their activity in some known acid-catalyzed reactions. We hope these results could be helpful for researchers in this area to reconsider the influence of the acidity of airand moisture-stable ionic liquids on catalysis and also in other fields. At the initial stage, the acidity of ionic liquids–water with different cations and anions were measured with a pH meter. The concentration of ionic liquid in water was 0.1 m. The operation was performed with methods given in the Annual Book of American Society for Testing and Materials Standards (ASTM) with slight modification. As shown in Figure 1, ionic liquid–water mixtures with BF4 anions were all acidic. Interestingly, the acidity of the ionic liquids could be tuned via substituted alkyl variation. The pH value of EMImBF4 ionic liquid reached 3.44(0.03) but the pH value of BMImBF4 and HMImBF4 were 4.27(0.14) and 6.61(0.03) respectively. BMImBF4 ionic liquids purchased from Merck (lot code: S5204049909) and Sigma–Aldrich (lot code: 0001415814) were also measured for comparison. Under the same condition, their pH values were 4.70(0.05) and 4.30(0.09), respectively, which are exactly the same as the acidity of the ionic liquids that we synthesized. The incorporation of an hydroxyl group would further enhance the acidity of ionic liquids with BF4 anion. The pH value reached 3.12(0.01) and 3.11(0.02) with hydroxyethyl or hydroxypropyl groups. The substitution of the C2 position with a methyl group weakens the acidity of this kind of ionic liquid. For the ionic liquid BMMImBF4, the pH value was 6.51(0.04). This was almost the same as that with the ionic liquid from Merck, that is, 6.46(0.23) (lot code: EQ005416). For ionic liquids with tetrabutyl ammonium and tetrabutyl phosphonium cations, the IL solutions were close to Figure 1. pH values of the aqueous phase of ionic liquids with BF4 as anion (0.1 m). The numbers in the parentheses are the values of the standard deviation.

Catalytic growth of single-walled carbon nanotubes with a narrow distribution of diameters over Fe nanoparticles prepared in situ by the reduction of LaFeO3

Abstract Bundles of single-walled carbon nanotubes (SWNTs) with a narrower distribution of diameter have been produced by catalytic decomposition of methane at 1010 °C on a newly developed catalyst LaFeO 3 . The SWNTs were characterized by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The diameter of the SWNTs is in the range of 0.8–1.8 nm. This result shows for the first time that SWNTs could be produced by catalytic decomposition of hydrocarbons without Al 2 O 3 , or SiO 2 or MgO support.

Sonochemical formation of iron oxide nanoparticles in ionic liquids for magnetic liquid marble

Ionic liquids (ILs)-stabilized iron oxide (Fe(2)O(3)) nanoparticles were synthesized by the ultrasonic decomposition of iron carbonyl precursors in [EMIm][BF(4)] without any stabilizing or capping agents. The Fe(2)O(3) nanoparticles were isolated and characterized by X-ray powder diffraction, transmission electron microscopy and susceptibility measurements. The physicochemical properties of ILs containing magnetic Fe(2)O(3) nanoparticles (denoted as Fe(2)O(3)@[EMIm][BF(4)]), including surface properties, density, viscosity and stability, were investigated in detail and compared with that of [EMIm][BF(4)]. The Fe(2)O(3)@[EMIm][BF(4)] can be directly used as magnetic ionic liquid marble by coating with hydrophobic and unreactive polytetrafluoroethylene (PTFE), for which the effective surface tension was determined by the puddle height method. The resulting magnetic ionic liquid marble can be transported under external magnetic actuation, without detachment of magnetic particles from the marble surface that is usually observed in water marble.