Silica-supported Ionic Liquids Research Articles

Removal of mercury by silica-supported ionic liquids: Efficiency and ecotoxicological assessment

Anthropogenic impacts have affected the coastal environment and contributed to its contamination. Mercury (Hg) is widespread in nature and has been shown to be toxic in even the smallest amounts, negatively affecting not only the marine ecosystem but also the entire trophic chain due to its biomagnification. Mercury ranks third on the Agency for Toxic Substances and Diseases Registry (ATSDR) priority list and it is therefore imperative to develop more effective methods than those currently available to avoid the persistence of this contaminant in aquatic ecosystems. The present study aimed to evaluate the effectiveness of six different silica-supported ionic liquids (SIL) in removing Hg from contaminated saline water, under realistic conditions ([Hg] = 50 µg/L), and to ecotoxicologically evaluate the safety of the SIL-remedied water, using as test model the marine macroalga Ulva lactuca. The results revealed that SIL [Si][C3C1im][SCN] (250 mg/L) was the most effective in removing Hg from solution, with a efficiency up to 99 % in just 6 h, that enable to obtain < 1 µg/L Hg (European guideline in drinking water). U. lactuca exposed to either the SIL and/or the remedied water showed no significant changes in relative growth rate and chlorophyll a and b levels, compared to the control condition. Biomarker analysis (LPO, GSH, GSSG, SOD, GPx, CAT and GRed) also showed no significant changes in the biochemical performance of U. lactuca. Therefore, it could be assumed that water treatment with SIL or its presence in an aqueous environment does not pose toxicity levels that could inhibit the metabolism or cause cell damage to U. lactuca.

Mesoporous Silica-Supported Ionic Liquids as Catalysts for Styrene Carbonate Synthesis from CO2

Various types of mesoporous silica were used as carriers to synthesize a series of immobilized imidazolium-based ionic liquids. Their activity was tested in the synthesis of styrene carbonate from CO2 and styrene. This is one-pot process, whereby two stages are carried out in one reactor and there is no need to isolate the intermediate product, epoxide. A systematic study on the influence of parameters such as temperature, the reaction time, CO2 pressure, as well as the amount and type of catalyst used was carried out. A strong synergistic catalytic effect of ionic liquid and Lewis acid was observed in promoting this reaction. The addition sequence of regents and amount of immobilized catalyst were considered crucial for the synthesis of styrene carbonate from CO2 and styrene. The tested silica-supported ionic liquids gave an easily-recyclable system which under the most favorable conditions ([mtespim]Cl/@SiO2; ZnBr2, 0.1 mol%; 110 °C, 4 h, 1 MPa) can be reused without a significant loss of catalytic activity nor selectivity.

Silica-Supported Ionic Liquids for Heat-Powered Sorption Desalination.

This work investigates the application of novel sorption materials to heat-powered desalination systems. Two ionic liquids 1-ethyl-3-methylimidazolium acetate (Emim-Ac) and 1-ethyl-3-methylimidazolium methanesulfonate (Emim-Oms) were impregnated in two silica supports, namely, Syloid AL-1FP and Syloid 72FP. Emim-Ac and Emim-Oms composite sorbents have been compared on morphology, water vapor sorption equilibrium, and heat of sorption. Fourier-transform infrared spectroscopy shows that the ionic liquid partly self-organizes on the silica surface. When used in a sorption desalination process powered by low grade heat at 60 °C, these composites have exceptionally high theoretical working capacities ranging from 1 to 1.7 gwater gsorbent-1. Experimental tests on a lab scale desalinator show that Emim-Ac/Syloid 72FP in real operating conditions can produce 25 kgwater kgsorbent-1 day-1. To date, this yield is 2.5 times higher than the best achieved with silica gel.

Polyoxometalate-based silica-supported ionic liquids for heterogeneous oxidative desulfurization in fuels

With the aim of deep desulfurization, silica-supported polyoxometalate-based ionic liquids were successfully prepared by a one-pot hydrothermal process and employed in heterogeneous oxidative desulfurization of various sulfur compounds. The compositions and structures of the hybrid samples were characterized by various methods such as FT-IR, XPS, Raman, UV–Vis, wide-angle XRD and N2 adsorption–desorption. The experimental results indicated that the hybrid materials presented a high dispersion of tungsten species and excellent catalytic activity for the removal of 4,6-dimethyldibenzothiophene without any organic solvent as extractant, and the sulfur removal could reach 100.0% under mild conditions. The catalytic performance on various substrates was also investigated in detail. After cycling seven cycles, the sulfur removal of the heterogeneous system still reached 93.0%. The GC-MS analysis results demonstrated that the sulfur compound was first adsorbed by the catalyst and subsequently oxidized to its corresponding sulfone.

Continuous Conversion of Carbon Dioxide to Propylene Carbonate with Supported Ionic Liquids

We present the use of silica-supported ionic liquids as catalysts for the continuous production of propylene carbonate from propylene oxide using supercritical carbon dioxide as solvent and reagent. Considerable differences in the catalytic activity of ionic liquids in homogeneous catalysis in batch mode and in continuous-flow using supported species processes were found, suggesting that a synergistic effect between ionic liquid and silica support material takes place. While supported ionic liquids prepared via physisorption of [C2mim]Br showed the highest catalytic activity, studies on long-term stability showed a rapid loss in yield due to the formation of undesired polypropylene carbonate that agglomerated in the ionic liquid layer. Improved long-term stability was found for ionic liquids covalently bound to the silica support materials, suggesting that a compromise between activity and stability is the best solution for the continuous production of propylene carbonate.

Effect of immobilization methods and the pore structure on CO2 separation performance in silica-supported ionic liquids

The CO2 separation performance in ionic liquids modified porous silica gels prepared by the impregnation and grafting methods were investigated. The effects of impregnation amount and pore size distribution of adsorbents with different types of ionic liquids on the CO2/N2 selectivity and water vapour adsorption and diffusion coefficient were analyzed in detail. The porous structures were characterized by CO2 adsorption isotherms at 0 °C. Adsorption behavior of CO2 (at 25, 40 and 60 °C) and N2 (at 40 °C) was measured using a gravimetric method. Compared with the impregnated samples, the grafting of ILs on the support surface only causes a weak loss of microporosity, leading to a slight decrease in CO2 adsorption capacity, and has much better recycling. CO2/N2 selectivity and water resistance are however enhanced, especially samples with the longer chain on imidazolium cation. A conventional homogeneous surface diffusion model for ILs grafted silica was used to estimate the diffusivities and good agreement between experimental values and fitting curves were obtained. For ILs modified silica prepared with impregnation method, the CO2 diffusivity constants include diffusion coefficients in ionic liquid phase and silica phase simultaneously. The diffusion coefficients are at a level of 10−7-10−9 m2 s−1 and about two or three orders of magnitude higher than that of neat ILs. The grafted silica exhibits diffusivities faster than those of the impregnated silica, indicating that more ionic liquids accessed into inner pore is unfavorable for CO2 diffusion.

Silica-Supported Ionic Liquids Prompted One-Pot Four-Component Synthesis of Pyrazolopyranopyrimidines, 3-methyl-4-aryl-4,5-dihydro-1H-pyrano[2,3-c]pyrazol-6-ones, and 1,6-diamino-2-oxo-1,2,3,4-tetrahydropyridine-3,5-dicarbonitriles

ABSTRACTThree methods have been used for synthesis of pyrazolopyranopyrimidines, 3-methyl-4-aryl-4,5-dihydro-1H-pyrano[2,3-c]pyrazol-6-ones, and 1,6-diamino-2-oxo-1,2,3,4-tetrahydropyridine-3,5-dicarbonitrile derivatives via four-component reactions under solvent-free conditions. Silica-bonded 5-n-propyl-octahydro-pyrimido[1,2-a]azepiniumchloride (SB-DBU+Cl−), silica-bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO+Cl−), and nano silica-bonded 5-n-propyl-octahydro-pyrimido[1,2-a]azepinium chloride (NSB-DBU+Cl−) as silica-supported ionic liquids catalyzed these reactions. These green, heterogeneous catalysts are separated from the reactions by simple filtration. The catalysts were recovered for at least four times without significant loss of their catalytic activities.

Immobilizing Penicillin G Acylase Using Silica-Supported Ionic Liquids: The Effects of Ionic Liquid Loadings

The supported ionic liquids (SILs) were prepared via immobilizing silane-functionalized ionic liquids (IL) onto the monodispersive silica nanoparticles, and the composite material was then applied in the immobilization of penicillin G acylase (PGA, EC 3.5.1.11), an important industrial enzyme for the production of semisynthetic antibiotics. This was a novel approach of immobilizing PGA proposed in our previous report, in which we had studied the effects of IL types on the performance of this novel support. Here, we focused on the effects of IL loading on the properties of the SILs and their performance in PGA immobilization. The effects of silica sizes and routes of preparing SILs (the solvent route and the sol–gel route) on IL loading were investigated. The results showed that (1) the IL loading could be tuned efficiently by changing the silica sizes. (2) As compared with the solvent route, the sol–gel route is more simple, time-saving, and ecofriendly in operation. What's more, it has a higher IL loading. Among the factors affecting the IL loading, the reaction time was the most feasible factor to control to tune the IL loading, as compared with the temperature and the dosage of ILs. (3) With the increase of IL loading, the surface ζ-potential of silicas changed from negative to positive, and the isoelectronic point (IEP) increased accordingly, which caused the decrease of the protein loading but the increase of apparent and specific activity. A reusability experiment showed that the sol–gel 1 sample maintained approximately 55% of the initial activity even after 10 consecutive operation cycles under the experimental conditions. This activity was 3.7 times higher than that of the sol–gel 2 sample.

Synthesis of cyclic carbonate through microwave irradiation using silica-supported ionic liquids: Effect of variation in the silica support

Microwave-assisted cycloaddition of CO 2 to phenyl glycidyl ether (PGE) was carried out under solvent-free conditions using silica-supported ionic liquids as catalysts. Various immobilized ionic liquid catalysts were prepared with different silica supports such as commercial and amorphous silica, SBA-15, and MCM-41. The effect of these supports on the cycloaddition reactions of CO 2 to PGE was studied under optimized reaction conditions of microwave power and irradiation time. The catalytic activity was found to depend strongly on the morphology of the support. Comparative studies with conventional heating reactions showed that microwave-induced reactions were greatly superior, with very high PEG conversion and high selectivity of cyclic carbonate within 15 min of reaction time.

Microwave Assisted Synthesis of Cyclic Carbonate Using Homogeneous and Heterogeneous Ionic Liquid Catalysts

A comparative study was effectuated between the catalytic performance of homogeneous and silica supported ionic liquids (SSILs) for the cycloaddition of epoxides and CO2 under microwave irradiation by varying the reaction parameters. Compared to the classical heating mode, both catalysts showed higher activity at moderate reaction condition through microwave irradiation.

Synthesis of dimethyl carbonate from ethylene carbonate and methanol using immobilized ionic liquid on amorphous silica

Ionic liquid immobilized on mesoporous amorphous silica was prepared from the coupling of 1-(triethoxysilylpropyl)-3- n-alkyl-imidazolium halides with tetraethyl orthosilicate (TEOS) through template-free condensation under strong acidic conditions. The immobilized 1- n-butyl-3-methyl imidazolium bromide ionic liquid on amorphous silica (BMImBr-AS) was characterized by EA, N 2 adsorption, FT-IR, 13C NMR and 29Si NMR. The immobilized amount of IL was 1.27 mmol/g-SiO 2 and surface area was 652 m 2/g with bimodal distribution of pores. The average pore diameter was 3.3 and 24.6 nm, respectively. The silica-supported ionic liquids were proved to be an effective heterogeneous catalyst for the synthesis of dimethyl carbonate (DMC) from transesterification of ethylene carbonate (EC) with methanol. High temperature, high carbon dioxide pressure, and longer reaction time were favorable for the reactivity of BMImBr-AS. The catalyst can be reused for the reaction up to three consecutive runs with a slight decrease of its catalytic activity.

Synthesis of cyclic carbonate from allyl glycidyl ether and carbon dioxide using ionic liquid-functionalized amorphous silica

Ionic liquid functionalized mesoporous silica (IFMS) was prepared from the coupling of 1-(triethoxysilylpropyl)-3- n-alkylimidazolium halides with tetraethyl orthosilicate (TEOS) through template-free condensation under strong acidic conditions. The immobilized ionic liquid (IM-IL) catalysts showed 0.61–0.93 mmol of ionic liquid on SiO 2 and surface area in the range of 189–647 m 2/g with pore sizes from 3.2 to 4.2 nm. Elemental analysis and SEM image showed that the immobilized ionic liquid groups were well incorporated on the support. The silica-supported ionic liquids were proved to be an effective heterogeneous catalyst for the solventless synthesis of cyclic carbonate from allyl glycidyl ether (AGE) and carbon dioxide. Im-IL of longer alkyl chain length and more nucleophilic nature showed higher conversion of AGE. High temperature, high carbon dioxide pressure, and the presence of ZnBr 2 co-catalyst were favorable for the conversion of AGE. Im-IL can be reused for the reaction up to three consecutive runs without any considerable loss of its catalytic activity.

Solventless synthesis of cyclic carbonates from carbon dioxide and epoxides catalyzed by silica-supported ionic liquids under supercritical conditions

A silica-supported ionic liquid proved to be an efficient heterogeneous catalyst for solventless synthesis of cyclic carbonates from epoxides and carbon dioxide under supercritical conditions, which requires no additional organic solvents either for the reaction or for the separation of product. The effects of reaction time, temperature and other reaction parameters on the reaction are investigated. High yields with excellent selectivity were obtained. The purity of product separated directly by filtration from the reaction mixture, reached 99% without further purification process. Moreover, the catalyst can be easily recovered by filtration and reused over four times with slight loss of its catalytic activity. The process represents a simple, ecologically safer, cost-effective route to cyclic carbonates with high product quality, as well as easy product recovery and catalyst recycling.