Guanying Yang

Absorption of CO2 by ionic liquid/polyethylene glycol mixture and the thermodynamic parameters

Absorption/desorption of CO2 by ionic liquid (IL) where both cation and anion are from renewable materials, (2-hydroxyethyl)-trimethyl-ammonium (S)-2-pyrrolidine-carboxylic acid salt [Choline][Pro], and [Choline][Pro]/polyethylene glycol 200 (PEG200) mixture, were studied in the 308.15 K to 353.15 K range at ambient pressure. It was demonstrated that both the neat ionic liquid (IL) and the IL/PEG200 mixture could capture CO2 effectively and could be easily regenerated under vacuum or by bubbling nitrogen through the solution, and the molar ratio of CO2 to the IL could exceed 0.5 slightly, which is the theoretical maximum for absorption of CO2 chemically, indicating that both chemical and physical absorption existed. Addition of PEG200 in the IL could enhance the rates of absorption and desorption of CO2 significantly. The solubility of CO2 in [Choline][Pro]/PEG200 at different pressures from 0 to 1.1 bar was also measured, and the enthalpy and entropy of solution of CO2 were calculated from the solubility data. At all the conditions, the enthalpy and entropy of solution were large negative values, indicating that the absorption process is exothermic.

Hydrogenation of CO2 to Formic Acid Promoted by a Diamine‐Functionalized Ionic Liquid

Amines to an end: The basic diamine-functionalized ionic liquid 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium trifluoromethanesulfonate was prepared and used in the hydrogenation of CO(2) to formic acid. One mole of the ionic liquid coordinates two moles of formic acid to promote the reaction. Both the ionic liquid and catalyst can be reused directly after their separation from the formic acid produced.

Highly Selective Synthesis of Phenol from Benzene over a Vanadium‐Doped Graphitic Carbon Nitride Catalyst

Design and preparation of efficient and economical catalysts for direct hydroxylation of benzene to phenol is an important topic. In this work, a series of metal‐doped graphitic carbon nitride catalyst (Cu‐, Fe‐, V‐, Co‐, and Ni‐g‐C3N4) were successfully synthesized by using urea as the precursor through a facile and efficient method. The catalysts were characterized systematically using N2 adsorption–desorption, FTIR, thermogravimetric analysis, powder X‐ray diffraction, and X‐ray photoelectron spectroscopy techniques. It was found that the vanadium‐doped graphitic carbon nitride catalyst V‐g‐C3N4 was the most efficient catalyst for the direct synthesis of phenol from benzene with hydrogen peroxide as the oxidant and it could be recycled at least 4 times. The influence of reaction conditions such as the solvent, reaction temperature, reaction time, and the amounts of catalyst and hydrogen peroxide were investigated. Under optimized conditions, 18.2 % yield of phenol was obtained with the selectivity to phenol as high as 100 %.

Efficient synthesis of quinazoline-2,4(1H,3H)-diones from CO2 using ionic liquids as a dual solvent–catalyst at atmospheric pressure

The highly efficient transformation of CO2 into value-added chemicals is an interesting topic in green chemistry. In this work, we studied the synthesis of quinazoline-2,4(1H,3H)-diones from CO2 and 2-aminobenzonitriles in a series of ionic liquids (ILs). It was found that 1-butyl-3-methylimidazolium acetate ([Bmim]Ac), a simple and easily prepared IL, could act as both solvent and catalyst, the reactions could be carried out very efficiently at atmospheric pressure of CO2, and a high yield of the products was obtained. Further study indicated that the IL was also very efficient for converting other 2-aminobenzonitriles into their corresponding quinazoline-2,4(1H,3H)-diones in high yields at atmospheric pressure. Moreover, the separation of the products from the IL was very easy, and the IL could be reused at least five times without considerable loss in catalytic activity.

Recovery of Silver Nanoparticles Synthesized in AOT/C12E4 Mixed Reverse Micelles by Antisolvent CO2

Silver nanoparticles were synthesized in sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles in isooctane with tetraethylene glycol dodecyl ether (C(12)E(4)) as a cosurfactant. Recovery of the Ag particles from the reverse micelles by dissolving antisolvent CO(2) in the micellar solution was investigated. All the Ag particles in the reverse micelles could be precipitated by compressed CO(2) at suitable pressures, while the surfactants remained in the isooctane continuous phase, and well-dispersed Ag nanoparticles were obtained. The effects of operating conditions on the size and size distribution of the Ag particles were investigated. The particle size decreased with decreasing molar ratio (w) of water to surfactant. A higher CO(2) pressure in the recovery process favored production of smaller particles. A decrease in the molar ratio of reductant KBH(4) to AgNO(3) resulted in larger Ag particles with higher polydispersity.

Efficient SO2 absorption by renewable choline chloride–glycerol deep eutectic solvents

The utilization of cheap and renewable materials is an important topic in green chemistry. In this work we studied the absorption of SO2 by choline chloride (ChCl)–glycerol deep eutectic solvents (DESs) at various temperatures and SO2 partial pressures, and the molar ratios of ChCl and glycerol ranged from 1 : 4 to 1 : 1. It was demonstrated that the solubility of SO2 in the DESs increased as the ChCl concentration in the DESs increased. The SO2 absorption capacity of the DESs with a ChCl–glycerol molar ratio of 1 : 1 could be as high as 0.678 g SO2 per g DES at 20 °C and 1 atm. Moreover, the absorbed SO2 could be easily released, and their excellent properties of high absorption capacity and rapid absorption/desorption rates remained during the five consecutive absorption/desorption cycles. The Henrys constants of SO2 in the DESs were calculated based on the solubility data.

Highly mesoporous metal–organic framework assembled in a switchable solvent

The mesoporous metal–organic frameworks are a family of materials that have pore sizes ranging from 2 to 50 nm, which have shown promising applications in catalysis, adsorption, chemical sensing and so on. The preparation of mesoporous metal–organic frameworks usually needs the supramolecular or cooperative template strategy. Here we report the template-free assembly of mesoporous metal–organic frameworks by using CO2-expanded liquids as switchable solvents. The mesocellular metal–organic frameworks with large mesopores (13–23 nm) are formed, and their porosity properties can be easily adjusted by controlling CO2 pressure. Moreover, the use of CO2 can accelerate the reaction for metal–organic framework formation from metal salt and organic linker due to the viscosity-lowering effect of CO2, and the product can be recovered through CO2 extraction. The as-synthesized mesocellular metal–organic frameworks are highly active in catalysing the aerobic oxidation of benzylic alcohols under mild temperature at atmospheric pressure.

Supercritical CO2-facilitating large-scale synthesis of CeO2 nanowires and their application for solvent-free selective hydrogenation of nitroarenes

Ceria nanowires were synthesized on a large scale by a simple, efficient, and environmentally benign strategy using supercritical (SC) CO2 expanded ethanol as reaction medium. Morphological characterization by SEM and TEM showed that most of the nanowires were bundles composed of individuals oriented parallel to each other throughout the whole length of the nanowires. Statistical data from AFM measurements showed that approximately 10% ceria nanowires (bundles/individuals) were ultrafine ones with diameters less than 5 nm. The effects of precursor concentration, reaction time and CO2 pressure on the formation of nanowires were studied, and it was found that SC CO2 played a key role in the evolution of the nanowires. As such, a possible formation mechanism for the as-prepared nanowires was provided. Moreover, the synthesis strategy was proved to be applicable to other rare earth oxide (La2O3, Eu2O3) nanowire preparation. Additionally, we successfully decorated ceria nanowires with ultrafine Pt nanoparticles via a sonication-facilitating deposition method. The as-prepared Pt-CeO2 showed superior catalytic activity and good selectivity for the solvent-free hydrogenation of nitrobenene and o-chloronitrobenzene.

Large-scale production of high-quality graphene using glucose and ferric chloride

Graphene and its derivatives have great potential for a variety of applications. The large-scale production of high-quality graphene using simple methods with cheap feedstocks is crucial for its wide applications. Glucose is an abundant and renewable carbon resource and FeCl3 is a very cheap salt. Herein, we proposed a new method to prepare graphene that is simply composed of the dissolution of glucose and FeCl3 in water, vaporization of water, and calcination. It was found that graphene with up to a few layers could be prepared and its electrical conductivity was similar to that of the graphene sheets synthesized using the chemical vapor deposition (CVD) method. Further studies indicated that FeCl3 was the key to the generation of high-quality graphene, because it acted as both the template and catalyst, for the formation of graphene.

Synthesis of dimethyl carbonate using CO2 and methanol: enhancing the conversion by controlling the phase behavior

The critical parameters and phase behavior of the multi-component system CO2-CH3OH–CH3I–H2O–CH3OC(O)OCH3 (dimethyl carbonate, DMC) were determined. The concentrations of the components were selected in such a way that they simulated the compositions of the reaction system at different conversions for synthesizing DMC using CO2 and methanol in a batch reactor. The critical density of the reaction system decreases with the conversion of methanol. The critical temperature and critical pressure of the reaction system increase with the conversion. Based on the determined critical parameters and phase behavior, DMC synthesis using CO2 and methanol was run at various pressures that corresponded to conditions in the two-phase region, the critical region as well as the single-phase supercritical region. The original ratios of the reactants CO2∶CH3OH were 8∶2 and 7∶3, and the corresponding reaction temperatures were 353.2 and 393.2 K, respectively, which were slightly higher than the critical temperatures of the reaction systems. The results indicate that the phase behavior affects the equilibrium conversion of methanol significantly and the conversion reaches a maximum in the critical regions of the reaction system. At 353.2 K, the equilibrium conversion in the critical region is about 7%, and can be about three times as large as those in other phase regions. At 393.15 K, the equilibrium conversion in the critical region is also much higher and can be twice as large as those in other phase regions.