SXI route to mesostructured materials from Fau and Beta zeolite precursors: A comparative study of their assembly behaviors in extremely acidic media

Mesoporous molecular sieves were synthesized from Beta and Fau zeolite precursors through S⁺X⁻I⁺ route under extremely acidic conditions in parallel (designated as M_Beta and M_Fau, respectively). The textural properties of M_Fau were different from its M_Beta counterpart but resembled normal MCM-41 silica from TEOS. Al content in M_Beta was almost equivalent to that in the initial Beta zeolite precursors, whereas only trace Al species was present in M_Fau from elemental analysis results. The hydrothermal stability of M_Beta after post-synthesis ammonia treatment was considerably improved compared with normal MCM-41 aluminosilicates, whereas the M_Fau after the same procedure was as unstable as normal MCM-41 silica. Thus, the assembly behaviors of Beta and Fau zeolite precursors were comparatively studied based on these results. The microstructure of Fau zeolite precursors were degraded by the extremely acidic condition, and Al species was dissolved into the synthesis mixture. However, Beta zeolite precursors survived the chemical attack of extremely acidic media and were incorporated into mesostructured framework as primary building units.     

Open-Framework Rubidium Halides Incorporated in Cadmium Oxalate Host Lattices

The metathetic reaction between CdBr₂ and rubidium oxalate under hydrothermal conditions yields [RbBr] [Cd₆(C₂O₄)₆]·2H₂O, I, containing Cd₆O₂₄ clusters with the Br⁻ ions in the center. The RbBr moiety forms a three-dimensional Fm3m structure, but with a unit cell double that of the normal stable phase. The hydrothermal reaction between rubidium oxalate and CdCl₂ in the presence of NO⁻₃ ions gives [Rb₂Cd(NO₃)(Cl)(C₂O₄)(H₂O)], II, containing cadmium chloro-oxalate layers. The Rb⁺ ions present between the layers interact with the Cl atoms to form a one-dimensional RbCl chain decorated by NO⁻₃ groups.     

Silver nanoplates-based colorimetric iodide recognition and sensing using sodium thiosulfate as a sensitizer

A colorimetric method for the recognition and sensing of iodide ions (I⁻) has been developed by utilizing the reactions between triangular silver nanoplates (TAg-NPs) and I⁻ in the presence of sodium thiosulfate (Na₂S₂O₃). Specifically, I⁻ together with Na₂S₂O₃ can induce protection of TAg-NPs owing to the formation of insoluble AgI, as confirmed by the high-resolution transmission electron microscopy (HRTEM). In the absence of Na₂S₂O₃, the etching reactions on TAg-NPs were observed not only by I⁻ but also other halides ions. The Na₂S₂O₃ plays as a sensitizer in this system, which improved the selectivity and sensitivity. The desired colorimetric detection can be achieved by measuring the change of the absorption peak wavelength corresponding to localized surface plasmon resonance (LSPR) with UV–vis spectrophotometer or recognized by naked eye observation. The results show that the shift of the maximum absorption wavelength (Δλ) of the TAg-NPs/Na₂S₂O₃/I⁻ mixture was proportional to the concentration of I⁻ in the range 1.0 × 10⁻⁹–1.0 × 10⁻⁶ mol L⁻¹. Moreover, no other ions besides I⁻ can induce an eye discernible color change as low as 1.0 × 10⁻⁷ mol L⁻¹. Finally, this method was successfully applied for I⁻ determination in kelp samples.     

The intercalation of cetyltrimethylammonium cations into muscovite by a two-step process: II. The intercalation of cetyltrimethylammonium cations into Li-muscovite

The alkylammonium cations were successively intercalated into the interlayer of muscovite. It was achieved by inorganic-organic ion exchange in the hydrothermal reaction of the LiNO₃-treated muscovite with cetyltrimethylammonium bromide solution. One-dimensional Patterson plots and electron density calculations show that hydrated Li⁺ and CTA⁺ cations entered the interlayer of muscovite successively. The CTA⁺-intercalated muscovite was characterized by powder X-ray diffraction and elemental analysis, in conjunction with FTIR, nuclear magnetic resonance, X-ray photoelectron spectra, high-resolution transmission electron microscopy, etc. The experiments show that organo-muscovite composite with ordered structure has been obtained. The CTA⁺ headgroups are distributed in the interlayer uniformly. However, the arrangement and conformation of CTA⁺ chains are strongly dependent upon the reaction temperature. At lower reaction temperature, the chains of CTA⁺ ions adopt a little more disordered arrangement and have higher gauche/trans conformer ratio, resulting in the disturbance to the interlayer symmetry. Whereas at higher reaction temperature, the sample with paraffin-like arrangement of CTA⁺ chains could be obtained, in which the methylene chains of CTA⁺ adopt a fully stretched, all-trans conformation.     

Anion-π interactions—interactions between benzo-crown ether metal cation complexes and counter ions

The loss of X^· radical from [M + Cu + X]⁺ ions (copper reduction) has been studied by the so called in-source fragmentation at higher cone voltage (M = crown ether molecule, X⁻ = counter ion, ClO₄⁻, NO₃⁻, Cl⁻). The loss of X^· has been found to be affected by the presence/lack of aromatic ring poor/rich in electrons. Namely, the loss of X^· occurs with lower efficiency for the [NO₂-B15C5 + Cu + X]⁺ ions than for the [B15C5 + Cu + X]⁺ ions, where NO₂-B15C5 = 3-nitro-benzo-15-crown-5, B15C5 = benzo-15-crown-5. A reasonable explanation is that Anion-π interactions prevent the loss of X^· from the [NO₂-B15C5 + Cu + X]⁺ ions. The presence of the electron-withdrawing NO₂ group causes the aromatic ring to be poor in electrons and thus its enhances its interactions with anions. For the ion containing the aromatic ring enriched in electrons, namely [NH₂-B15C5 + Cu + ClO₄]⁺ where NH₂-B15C5 = 3-amino-benzo-15-crown-5, the opposite situation has been observed. Because of Anion-π repulsion the loss of X^· radical proceeds more readily for [NH₂-B15C5 + Cu + X]⁺ than for [B15C5 + Cu + X]⁺. Iron reduction has also been found to be affected by Anion-π interactions. Namely, the loss of CH₃O^· radical from the ion [B15C5 + Fe + NO₃ + CH₃O]⁺ proceeds more readily than from [NO₂⁻B15C5 + Fe + NO₃ + CH₃O]⁺.     

Reduction of nitric oxide,nitrous acid and nitrogen dioxide at platinum electrodes in acidic solutions: Review and new voltammetric results

The literature concerning the chemical and electrochemical reactions of nitric oxide, nitrous acid and nitrogen dioxide in aqueous solutions is reviewed briefly, with emphasis on electrochemical reductions at platinum electrodes in acidic solutions. The voltammetric behavior of NO and NO₂ at a Pt electrode in perchloric acid is virtually identical to that for HNO₂ and this is explained on the basis of a common electroactive precursor concluded to be NO⁺. Three cathodic waves are obtained for acidic solutions of NO, HNO₂ and NO₂. The first two waves correspond to reduction of NO⁺ to NO and N₂O₃ to NO, respectively. The presence of N₂O₃ results from decomposition of the parent compounds. The presence of Br^- or Cl^- in acidic solutions of the title compounds promotes the voltammetric reductions at lower H⁺ concentrations. This probably results from formation of electroactive nitrosyl halides.     

A label-free colorimetric detection of lead ions by controlling the ligand shells of gold nanoparticles

We have developed a simple, colorimetric and label-free gold nanoparticle (Au NP)-based probe for the detection of Pb²⁺ ions in aqueous solution, operating on the principle that Pb²⁺ ions change the ligand shell of thiosulfate (S₂O₃²⁻)-passivated Au NPs. Au NPs reacted with S₂O₃²⁻ ions in solution to form Au⁺·S₂O₃²⁻ ligand shells on the Au NP surfaces, thereby inhibiting the access of 4-mercaptobutanol (4-MB). Surface-assisted laser desorption/ionization time-of-flight ionization mass spectrometry (SALDI-TOF MS) and inductively coupled plasma mass spectrometry (ICP-MS) measurements revealed that PbAu alloys formed on the surfaces of the Au NPs in the presence of Pb²⁺ ions; these alloys weakened the stability of the Au⁺·S₂O₃²⁻ ligand shells, enhancing the access of 4-MB to the Au NP surfaces and, therefore, inducing their aggregation. As a result, the surface plasmon resonance (SPR) absorption of the Au NPs red-shifted and broadened, allowing quantitation of the Pb²⁺ ions in the aqueous solution. This 4-MB/S₂O₃²⁻-Au NP probe is highly sensitive (linear detection range: 0.5-10 nM) and selective (by at least 100-fold over other metal ions) toward Pb²⁺ ions. This cost-effective sensing system allows the rapid and simple determination of the concentrations of Pb²⁺ ions in real samples (in this case, river water, Montana soil and urine samples).     

The supramolecular chemistry of metal complexes with heavily substituted imidazoles as ligands: Cobalt(II) and zinc(II) complexes of 1-methyl-4,5-diphenylimidazole

An investigation of the M^II/X⁻/L [M^II = Co, Ni, Cu, Zn; X⁻ = Cl⁻, Br⁻, I⁻, NCS⁻, NO₃⁻, N₃⁻, CH₃COO⁻; L = 1-methyl-4,5-diphenylimidazole] general reaction system towards the detailed study of the intermolecular interactions utilized for controlling the supramolecular organization and the structural consequences on the structures produced has been initiated. Three representative complexes with the formulae [Co(NO₃)₂(L)₂] (1), [Zn(NO₃)₂(L)₂] (2) and [Co(NCS)₂(L)₂]·EtOH (3·EtOH) have been synthesized and characterized by spectroscopic methods and single-crystal X-ray analysis. Compounds 1 and 2 are isomorphous (tetragonal, I4₁cd) with their metal ions in a severely distorted octahedral Co/ZnN₂O₄ environment, while 3·EtOH crystallizes in P2₁/c with a tetrahedral CoN₄ coordination. The structural analysis of 1, 2 and 3·EtOH reveals a common mode of packing among neighbouring ligands (expressed through intramolecular π–π interactions between the 4,5-diphenylimidazole moieties), enhancing thus the rigidity and stability of the complexes. The bent coordination of the two isothiocyanates in 3 [Co–NCS angles of 173.8(2) and 160.8(2)°] seems to be caused by intermolecular hydrogen bonding and crystal packing effects.     

A new tool for inorganic nitrogen speciation study: simultaneous determination of ammonium ion, nitrite and nitrate by ion chromatography with post-column ammonium derivatization by Nessler reagent and diode-array detection in rain water samples

The paper presents a new method for a simultaneous determination of inorganic nitrogen species in the oxidized (NO₂⁻, NO₃⁻) and reduced (NH₄⁺) form in rain water samples. The method is based on a system of nitrogen species separation employing ion exchange and diode-array detection. The ions are separated in a strong ion-exchanger, nitrites and nitrates are determined directly at 208 and 205 nm, respectively, while the ammonium ions are determined in the column hold-up time after a post-column derivatization by the Nessler reagent, at 425 nm. The use of a diode-array detector permits a simultaneous identification of the inorganic nitrogen species in 8 min. The detection limits obtained are: NO₂⁻, 0.1 mg L⁻¹; NO₃⁻, 0.05 mg L⁻¹; NH₄⁺, 1 mg L⁻¹. The method proposed has been successfully used for speciation analysis of inorganic nitrogen in precipitation.     

A new semi-empirical kinetic method for the determination of ion exchange constants for the counterions of cationic micelles

A new method, based upon semi-empirical kinetic approach, for the determination of ion exchange constant for ion exchange processes occurring between counterions at the cationic micellar surface is described in this review article. Basically, the method involves a reaction kinetic probe which gives observed pseudo-first-order rate constants (k_obs) for a nucleophilic substitution reaction between the nonionic and anionic reactants (R and S) in the presence of a constant concentration of both reactants as well as cationic micelles and varying concentrations of an inert inorganic or organic salt (MX). The observed data (k_obs, versus [MX]) fit satisfactorily (in terms of residual errors) to an empirical equation which could be derived from an equation explaining the mechanism of the reaction of the kinetic probe in terms of pseudophase micellar (PM) model coupled with another empirical equation. This (another) empirical equation explains the effect of [MX] on cationic micellar binding constant (K_S) of the anionic reactant (say S) and gives an empirical constant, K_X/S. The magnitude of K_X/S is the measure of the ability of X⁻ to expel S⁻ from a cationic micellar pseudophase to the bulk aqueous phase through ion exchange X⁻/S⁻. The values of K_X/S and K_Y/S (where Y⁻ is another inert counterion) give the ion exchange constant, K_X^Y (= K_X/K_Y where K_X and K_Y represent cationic micellar binding constants of X⁻ and Y⁻, respectively). The suitability of this method is demonstrated by the use of three different reaction kinetic probes and various MX.     

A reversible chemosensor for nitrite based on the fluorescence quenching of a carbazole derivative

The carbazole derivative, with an amino group in 9-position (9-methylacryloylamino carbazole (MAC), has been utilized to prepare a fluorescent sensor and used for the determination of NO₂⁻ based on the reaction between nitrite (NO₂⁻) and excess I⁻ to form I₃⁻, which can quench the fluorescence of carbazole derivative. MAC, as a fluorescent carrier, has a terminal double bond and is covalently immobilized on a quartz glass plate surface by photo-polymerization to prevent the leakage of the dye. The sensor shows sufficient repeatability, selectivity, operational lifetime of 8 weeks, and a fast response of less then 30 s. NO₂⁻ can be determined in the range between 1.0×10⁻⁶ and 1.0×10⁻⁴ mol l⁻¹ with a detection limit of 8.0×10⁻⁷ mol l⁻¹ at pH of 2.0. The quenching mechanism is discussed. Most commonly coexisting ions do not interfer with the NO₂⁻ assay.     

Reduction of iodine by hydroxylamine within the pH range 0.7–3.5

The reduction of iodine by hydroxylamine within the [H⁺] range 3×10⁻¹–3×10⁻⁴ mol.L⁻¹ was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH₃OH⁺]₀/[I₂]₀ ratio below 15, [H⁺] around 0.1 mol.L⁻¹, and ionic strength around 0.1 mol.L⁻¹), the [I₂] and [I₃⁻] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I₂+I⁻⇔︁I₃⁻, 2 I₂+NH₃OH⁺+H₂O→HNO₂+4 I⁻+5 H⁺, NH₃OH⁺+HNO₂→N₂O+2 H₂O+H⁺, and 2 HNO₂+2 I⁻+2 H⁺→2 NO+I₂+2 H₂O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H⁺] is above 4×10⁻² mol.L⁻¹ at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH₂OH and NH₃OH⁺ as the reducing reactive species. The additional rate suppression by H⁺ at low pH would be connected to the existence of H₂OI⁺ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998     

Synthèse et structures cristallines de Cs3MI4NO3 (M = Zn,Co, Cd): Un exemple de substitution sélective

The compounds Cs₃MX₅ (M is a bivalent metal, and X an halogen) consist of Cs⁺, I⁻, and distorted (MI₄)²⁻ ions. The separate X⁻ ion suggests a possible substitution by another monovalent anion. The new compounds Cs₃MI₄NO₃ (M = Zn, Co, Cd) have been synthesized and characterized by X-ray diffraction. They are orthorhombic Pnma, a = 10.114(4), b = 11.601(5), c = 14.290(9) Å for Cs₃ZnI₄ NO₃; a = 10.078(8), b = 11.621(4), c = 14.262(6) Å for Cs₃CoI₄NO₃; a = 10.177(4), b = 11.784(5), c = 14.336(7) Å for Cs₃CdI₄NO₃; Z = 4. The crystal structures are described. The NO₃ groups surrounded by six Cs⁺ cations occupy the same sites as the separate I⁻ ion in the Cs₃MI₅ compounds.     

Electronic absorption spectra of palladium(II) in concentrated nitric acid solutions

Palladium complexation in concentrated nitric acid solutions was studied by UV/Vis absorption spectrophotometry. The ionic strength of the solutions was fixed to I = 1, 3, or 5 mol dm⁻³ (M) by mixing of HNO₃ and HClO₄. The major palladium species were found to be Pd²⁺, PdNO₃ ⁺, and Pd(NO₃)₂. The formation constant of PdNO₃ ⁺ was determined to be β ₁ = 1.32 (I = 1 M), 1.49 (I = 3 M), or 1.47 (I = 5 M), while that of Pd(NO₃)₂ to be β ₂ = 0.45 (I = 3 M) or 0.14 (I = 5 M).     

Ion-exclusion chromatography with the direct UV detection of non-absorbing inorganic cations using an anion-exchange conversion column in the iodide-form

An ion-exclusion chromatographic method for the direct UV detection of non-absorbing inorganic cations such as sodium (Na⁺), ammonium (NH₄⁺) and hydrazine (N₂H₅⁺) ions was developed by connecting an anion-exchange column in the I⁻-form after the separation column. For example, NH₄⁺ is converted to a UV-absorbing molecule, NH₄I, by the anion-exchange column in the I⁻-form after the ion-exclusion separation on anion-exchange column in the OH⁻-form with water eluent. As a result, the direct UV detection of Na⁺, NH₄⁺ and N₂H₅⁺ could be successfully obtained as well as the well-resolved separation. The calibration graphs of the analyte cations detected with UV at 230 nm were linear in the range of 0.001-5.0 mM. The detection limits at S/N = 3 of the cations were below 0.1 μM. This method was applied to real water analysis, the determination of NH₄⁺ in river and rain waters, or that of N₂H₅⁺ in boiler water, with the satisfactory results. This could be applied also to low- or non-absorbing anions such as fluoride or hydrogencarbonate ions by the combination of a weakly acidic cation-exchange resin in the H⁺-form as the separation column and the anion-exchange conversion column.     

Structural and thermodynamic characteristics of ionic associates in vapors over sodium bromide and iodide

Nonempirical methods are used to calculate the geometric parameters, the frequencies of normal vibrations, and thermochemical characteristics of ions existing in saturated vapors over sodium bromide and iodide: Na₂X⁺, NaX₂⁻, Na₃X₂⁺, and Na₂X₃⁻ (X = Br, I). According to the calculations, Na₂X⁺ and NaX₂⁻ triatomic ions have a linear equilibrium configuration of D _∞h symmetry. Pentaatomic ions can exist in the form of three isomers: linear with D _∞h symmetry, planar cyclic with C _2v symmetry, and bipyramidal with D _3h symmetry. At a temperature of ∼1000 K, Na₃X₂⁺ and NaX₃⁻ pentaatomic ions are shown to be present in vapor mainly in the form of linear isomers. The energies and enthalpies of ion molecular reactions with the participation of the above ions are calculated, and the formation enthalpies of the ions are determined, Δ _f H ^o(0 K): 293±2 kJ/mol (Na₂Br⁺), 354±2 kJ/mol (Na₂I⁺), −536±2 kJ/mol (NaBr₂⁻, −458±2 kJ/mol (NaI₂⁻, 24±5 kJ/mol (Na₃Br₂⁺, 143±5 kJ/mol (Na₃I₂⁺, −810±5 kJ/mol (Na₂Br₃⁻, and −675±5 kJ/mol (Na₂I₃⁻.     

Aluminum phosphate dispersed on a cellulose acetate fiber surface: Preparation, characterization and application for Li, Na and K separation

Cellulose acetate fibers with supported highly dispersed aluminum phosphate were prepared by reacting aluminum-containing cellulose acetate (Al₂O₃=3.5 wt.%; 1.1 mmol g⁻¹ aluminum atom per gram of the material) with phosphoric acid. Solid-state NMR spectra (CPMAS ³¹P NMR) data indicated that HPO₄²⁻ is the species present on the fiber surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.50 mmol g⁻¹. The ion exchange capacities for Li⁺, Na⁺ and K⁺ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g⁻¹): Li⁺=0.03, Na⁺=0.44 and K⁺=0.50. The H⁺/Li⁺ exchange corresponds to the model of the ideal ion exchange with a small value of the corresponding equilibrium constant K=1.1×10⁻². Due to the strong cooperative effect, the H⁺/Na⁺ and H⁺/K⁺ ion exchange is non-ideal. These ion exchange equilibria were treated with the use of models of fixed bi- or tridentate centers, which consider the surface of the sorbent as an assemblage of polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants were discussed by taking into consideration the sequence of the ionic hydration radii for Li⁺, Na⁺ and K⁺. The matrix affinity order for the ions decreases as the hydration radii of the cations increase, i.e. Li⁺>Na⁺>K⁺. The high values of the separation factors S_Na⁺/Li⁺ and S_K⁺/Li⁺ (up to several hundred) provide quantitative separation of Na⁺ and K⁺ from Li⁺ from a mixture containing these three ions.     

Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid

In this work, molecular dynamics simulations were performed to study the pH-induced structural transitions for a CTAB/p-toluic acid solution. Spherical and cylindrical micelles were obtained for aqueous surfactants at pH 2 and 7, respectively, which agrees well with the experimental observations. The structural properties of two different micelles were analyzed through the density distributions of components and the molecular orientations of CTA⁺ and toluic acid inside the micelles. It was found that the bonding interactions between CTA⁺ and toluic in spherical and cylindrical micelles are very different. Almost all the ionized toluic acid (PTA⁻) in the solution at pH 7 was solubilized into the micelles, and it was located in the CTA⁺ headgroups region. Additionally, the bonding between surfactant CTA⁺ and PTA⁻ was very tight due to the electrostatic interactions. The PTA⁻ that penetrated into the micelles effectively screened the electrostatic repulsion among the cationic headgroups, which is considered to be crucial for maintaining the cylindrical micellar shape. As the pH decreased, the carboxyl groups were protonated. The hydration ability of neutral carboxyl groups weakened, resulting in deeper penetration into the micelles. Meanwhile, their bonding interactions with surfactant headgroups also weakened. Accompanied by the strengthen of electrostatic repulsion among the positive headgroups, the cylindrical micelle was broken into spherical micelles. Our work provided an atomic-level insights into the mechanism of pH-induced structural transitions of a CTAB/p-toluic solution, which is expected to be useful for further understanding the aggregate behavior of mixed cationic surfactants and aromatic acids.     

A novel spectrophotometric method for batch and flow injection determination of cyanide in electroplating wastewater

A sensitive and highly selective spectrophotometric method is described for the determination of cyanide. It is based on a reaction of cyanide with aquacyanocobyrinic acid heptamethyl ester (ACCbs) reagent (orange color) at pH 9.5 to give dicyanocobester (DCCbs) (violet color). The increase of the absorption bands of the reaction product at 368 and 580 nm and the decrease of the reagent band at 353 nm are linearly proportional to the cyanide concentration. The method is used in static mode for determining cyanide over the concentration range 0.04-1.20 μg ml⁻¹ with a detection limit of 0.02 μg ml⁻¹ and for hydrodynamic analysis of 0.4-5.2 μg ml⁻¹ cyanide. Application for batch and flow injection monitoring of cyanide in electroplating wastewater samples gives results agree within ± 1.2% with those obtained by the standard potentiometry using the cyanide ion selective electrode. The method is practically free from interferences by PO₄³⁻, NO₃⁻, NO₂⁻, SO₄²⁻, F⁻, Cl⁻, Br⁻, I⁻, S²⁻ and SCN⁻ ions and gives results with average recoveries of 97.6-99.2%. Advantages offered by using ACCbs as a chromogen for cyanide assay are: (i) high selectivity and sensitivity of the coordination site of the reagent towards cyanide ion; (ii) fast reaction, since legation takes place at the axial position of the reagent; (iii) good solubility and stability of the reagent in aqueous solutions over a wide pH range; (iv) high stability of the reagent (ACCbs) and the colored complex product (DCCbs) and (v) possible absorbance measurements at three different wavelengths.     

Effect of the polarity of silver nanoparticles induced by ionic liquids on facilitated transport for the separation of propylene/propane mixtures

The effect of ionic liquids on the formation of a partial positive charge on the surface of silver nanoparticle and its subsequent effect on facilitated olefin transport were investigated. Three different ionic liquids of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM⁺BF₄⁻), 1-butyl-3-methylimidazolium triflate (BMIM⁺Tf⁻), and 1-butyl-3-methylimidazolium nitrate (BMIM⁺NO₃⁻) were employed to control the positive charge density of the surface of silver nanoparticles. The positive charge density of the silver nanoparticles, as characterized by the binding energy of the silver atom, was in the following order: BMIM⁺BF₄⁻/Ag ? BMIM⁺Tf⁻/Ag > BMIM⁺NO₃⁻/Ag. This order was consistent with the tendency of ionic liquids to form free ions. The best separation performance for the propylene/propane mixtures was a mixed gas selectivity of 17 and a permeance of 7 GPU through a composite membrane consisting of BMIM⁺BF₄⁻/Ag. A better separation performance for olefin/paraffin mixtures was observed with a higher positive charge density of the silver nanoparticles. It was therefore concluded that facilitated olefin transport was a direct consequence of the surface positive charge of the silver nanoparticles induced by ionic liquids.