Solid-state Ion-exchange Reaction Research Articles

All solid-state fabrication strategy of CdS@ZnS nanocomposites and their photocatalytic performance in water purification

Herein a systematic study of two-step solid-phase synthesis of CdS@ZnS nanocomposites and their photocatalytic activity is presented. First, CdS nanoparticles were synthesized in a planetary ball mill through a solid-state ion exchange reaction. In the second step, Cd2+ ions were partially replaced by Zn2+ ions at the surface of the nanoparticles using solvent free long-term activation in a high-energy planetary ball mill. The optimal activation time in a ball mill was determined to be 45 min. Spherical CdS nanoparticles with a diameter of 10 nm and modified CdS@ZnS (45 min) nanocomposites were characterized by X-ray diffraction analysis, Raman and UV-vis spectroscopy, and scanning electron microscopy. The ability of nanocomposites for photocatalytic water purification was tested on the degradation of the model organic dye Orange II in an aqueous solution under the visible light irradation. The modified CdS@ZnS nanocomposites showed higher photocatalytic activity compared to the original CdS nanoparticles.

A new molybdenum nitride catalyst with rhombohedral MoS2 structure for hydrogenation applications.

Nitrogen-rich transition-metal nitrides hold great promise to be the next-generation catalysts for clean and renewable energy applications. However, incorporation of nitrogen into the crystalline lattices of transition metals is thermodynamically unfavorable at atmospheric pressure; most of the known transition metal nitrides are nitrogen-deficient with molar ratios of N:metal less than a unity. In this work, we have formulated a high-pressure route for the synthesis of a nitrogen-rich molybdenum nitride through a solid-state ion-exchange reaction. The newly discovered nitride, 3R-MoN2, adopts a rhombohedral R3m structure, isotypic with MoS2. This new nitride exhibits catalytic activities that are three times more active than the traditional catalyst MoS2 for the hydrodesulfurization of dibenzothiophene and more than twice as high in the selectivity to hydrogenation. The nitride is also catalytically active in sour methanation of syngas with >80% CO and H2 conversion at 723 K. Our formulated route for the synthesis of 3R-MoN2 is at a moderate pressure of 3.5 GPa and, thus, is feasible for industrial-scale catalyst production.

Ionic Transport and Surface Morphological Studies on SbI3 - Ag2WO4 Mixed System for Solid State Battery Applications

Detailed experimental data pertaining to ionic transport and micro structural investigations on new superionic materials formed in the mixed system (SbI3) x - (Ag2WO4)1- x (0.1 ≤ x ≤ 0.5) have been described in this paper. Temperature-dependent electrical conductivity analysis yielded the activation energy values for various compositions as confirmed by means of frequency- dependent conductivity results as well. Evaluation of transport properties carried out in terms of ionic transport number (ti ) measurements by Wagner's dc polarization method and silver ionic transport number ( tAg+) measurements by EMF method has revealed that a typical ti value of 0.99 along with a silver ionic transport number of 0.95 would be exhibited by the best conducting composition (SbI3) 0.4 - (Ag2WO4)0.6 having the room temperature electrical conductivity of 5.7×10 -2 Scm -1 . The surface morphological results obtained by scanning electron microscopy (SEM) have suggested the presence of AgI micro-crystals as dispersoids within the silver oxysalt matrix formed as a result of probable solid state ion exchange reactions occurring between SbI3 and Ag2WO4 in accordance with hard and soft acids and bases (HSAB) principle. The measured open circuit voltage, OCV for an all-solid-state electrochemical cell fabricated using the best conducting composition (SbI3) 0.4-(Ag2W04) 0.6 as solid electrolyte is found to be 603 mV at room temperature.

Thermal FT-IRmicrospectroscopy for rapid detection of solid-state ion-exchange reaction between metoclopramide HCl monohydrate and potassium bromide

The combination of Fourier transform infrared (FT-IR) microspectroscopy with a thermal analyzer was applied to quickly investigate the solid-state ion-exchange reaction of metoclopramide HCl monohydrate (MCP H(2)O) by clipping MCP H(2)O powder between two KBr or KCl pellets. The physical and ground mixtures of MCP H(2)O or 150 °C-preheated MCP powder and KBr or KCl powders with a weight ratio of 1 : 100 were also prepared and determined by FT-IR microspectroscopy. The samples of MCP H(2)O or 150 °C-preheated MCP were identified by using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The results of present study indicate that the ion-exchange reaction was easily induced between MCP H(2)O and KBr by grinding and heating processes. The possible mechanism of ion-exchange reaction may take place between the HCl salt of MCP H(2)O and a KBr matrix by grinding or heating to yield a mixture of HCl and HBr salts of the MCP sample in the presence of hydrated water. The crystal hydrate played an important role to improve this ion-exchange reaction between MCP H(2)O and KBr. However, no ion-exchange reaction occurred between MCP H(2)O and KCl or between 150 °C-preheated MCP and KBr. The solid-state ion-exchange reaction was more easily determined by this novel thermal FT-IR microspectroscopy than other conventional methods.

Influence of the cobalt salt precursors on the cobalt speciation and catalytic properties of H-ZSM-5 modified with cobalt by solid-state ion exchange reaction

Abstract Co-ZSM-5 catalysts prepared by either aqueous or solid-state ion exchange using different cobalt precursors (acetate, chloride, nitrate or formate) were studied in the selective ammoxidation of ethylene and ethane to acetonitrile. Co 2+ supported catalysts were characterized by chemical analysis, X-ray powder diffraction, N 2 adsorption (BET), TEM/EDX, FTIR, XANES and EXAFS spectroscopy, H 2 TPR and TPD of ammonia. It was found that all the preparations led to cobalt exchanged metal ion at the bridging oxygen of Si–OH–Al groups or to Co oxide or phyllosilicate. XRD, TEM and H 2 TPR indicated the presence of cobalt oxide when cobalt chloride, formate or nitrate was used. TPD of ammonia and FTIR of pyridine, used respectively as probe molecules showed that solid-state exchange catalysts exhibited new Lewis acid sites. The catalyst resulting from cobalt acetate, which contained mostly isolated Co 2+ ions in cationic exchange position and cobalt phyllosilicate, showed high activity and selectivity toward acetonitrile.

Synthesis of layered sodium lanthanum selenide through ion exchange reactions

Layered hexagonal KLaSe2 (α-NaFeO 2-type) was synthesized using the reactive flux method and analyzed by powder XRD to determine its lattice constants (space group R-3m, a = 4.40508(5) Å, c = 22.7838(5) Å). NaLaSe 2, which normally crystallizes as a disordered rock salt structure with mixed Na+/La + 3 sites, was synthesized through a solid state ion exchange reaction at 585 °C from a 1:3 molar ratio mixture of KLaSe 2:NaI. The product of this reaction was hexagonally layered NaLaSe 2 (space group R-3m, a = 4.3497(3) Å, c = 20.808(2) Å) isostructural to KLaSe 2. This product was analyzed by comparison with members of the set of solid solutions Na (1− x) K ( x) LaSe 2 to confirm that the extent ion exchange in this reaction was complete. Cubic (disordered) NaLaSe 2 was also reacted with KI to yield the poorly crystalline hexagonally layered product with the approximate formula Na 0.79K 0.21LaSe 2.

Prototype electrostatic ground state approach to predicting crystal structures of ionic compounds: Application to hydrogen storage materials

We have developed a procedure for crystal structure generation and prediction for ionic compounds consisting of a collection of cations and rigid complex anions. Our approach is based on global optimization of an energy functional consisting of the electrostatic and soft-sphere repulsive energies using Metropolis Monte Carlo (MMC) simulated annealing in conjunction with smoothing of the potential energy landscape via the distance scaling method. The resulting structures, or prototype electrostatic ground states (PEGS), are subsequently relaxed using first-principles density-functional theory (DFT) calculations to obtain accurate structural parameters and thermodynamic properties. This method is shown to produce the ground state structures of $\mathrm{Na}\mathrm{Al}{\mathrm{H}}_{4}$ and $\mathrm{Mg}{(\mathrm{Al}{\mathrm{H}}_{4})}_{2}$, as well as the mixed cation alanate ${\mathrm{K}}_{2}\mathrm{Li}\mathrm{Al}{\mathrm{H}}_{6}$. For $\mathrm{Li}\mathrm{Al}{\mathrm{H}}_{4}$, the PEGS search produces a structure with a static DFT total energy equal to that of the experimentally observed structure; the latter is stabilized by vibrational contributions to the free energy. For mixed-valence hexa-alanates, $XY$ $\mathrm{Al}{\mathrm{H}}_{6}$, where $X=(\mathrm{Li},\mathrm{Na},\mathrm{K})$, and $Y=(\mathrm{Mg},\mathrm{Ca})$, the PEGS method predicts six unsuspected structure types, which are not found in the existing structure databases. The PEGS search yields energies that are, on the average, better than the best database structures with the same number of atoms per unit cell, demonstrating the predictive power and usefulness of the PEGS structures. In addition to the recently synthesized $\mathrm{Li}\mathrm{Mg}\mathrm{Al}{\mathrm{H}}_{6}$ compound, we predict that $\mathrm{Li}\mathrm{Ca}\mathrm{Al}{\mathrm{H}}_{6}$, $\mathrm{Na}\mathrm{Ca}\mathrm{Al}{\mathrm{H}}_{6}$, and $\mathrm{K}\mathrm{Ca}\mathrm{Al}{\mathrm{H}}_{6}$ are also thermodynamically stable with respect to phase separation into other alanates and metal hydrides. In contrast, $\mathrm{Na}\mathrm{Mg}\mathrm{Al}{\mathrm{H}}_{6}$ and $\mathrm{K}\mathrm{Mg}\mathrm{Al}{\mathrm{H}}_{6}$ are slightly unstable (by less than $3\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}∕\mathrm{mol}$) relative to the phase separation into $\mathrm{Na}\mathrm{Al}{\mathrm{H}}_{4}$, $\mathrm{K}\mathrm{Al}{\mathrm{H}}_{4}$, and $\mathrm{Mg}{\mathrm{H}}_{2}$. We suggest that solid-state ion-exchange reactions between ${X}_{3}\mathrm{Al}{\mathrm{H}}_{6}$ $(X=\mathrm{Li},\mathrm{Na},\mathrm{K})$ and $Y{\mathrm{Cl}}_{2}$ $(Y=\mathrm{Mg},\mathrm{Ca})$ could be used to synthesize the predicted mixed-valence hexa-alanates.

Preparation of cerium-loaded Y-zeolites for removal of organic sulfur compounds from hydrodesulfurizated gasoline and diesel oil

Ce(IV)-loaded Y-zeolites (CeY) were prepared for selective removal of the trace amount of organic sulfur compounds from hydrodesulfurization (HDS)-treated diesel oil. The CeY samples can be obtained from NH 4–Y-zeolite (NH 4Y) using liquid-phase ion-exchange and solid-state ion-exchange methods. The ion-exchange reactions, structures, and selective adsorptions of organic sulfur compounds of the CeY samples were investigated using XRD, IR, XPS, TEM, and GC sulfur analyzer. The organic sulfur compound uptakes strongly depend on the amount and the valency of Ce in the zeolite structure. Ce(IV) shows much higher adsorptive ability than Ce(III). A CeY–S sample prepared by solid-state ion-exchange reaction of NH 4Y and Ce(NO 3) 3 with Ce/NH 4 mole ratio of 0.63 at 250 °C showed a maximum sulfur uptake from a model solution of HDS-treated gasoline containing thiophene [ S = 5 ppm (ppm = mg/L)]. A desulfurization from a HDS-treated diesel oil containing organic sulfur compounds ( S = 1.87 ppm ) and H 2S ( S = 0.73 ppm ) was investigated with a combination of the CeY–S and a CuO adsorbent for removal of H 2S by a batch method. The sulfur content was reduced to below 0.01 ppm for the first time. This method provides a promising desulfurization process to prepare a clean fuel for fuel cells.

Solid State Ion Exchange Reactions of Co with Zeolites

Co cations were introduced into ZSM5 and faujasite type zeolites by solid state ion exchange. On both types of zeolites the solid state reaction led to an exchange of all protons. On ZSM5 one proton was exchanged with one Coe} cation, while on the faujasite samples two protons were exchanged with one Coe} cation. After the incorporation of cobalt two new Lewis acid sites were observed on the CoZSM5 and CoY samples.

Solid-state ion exchange reactions between homoionic-montmorillonites and organoammonium salts

Organoammonium-montmorillonite intercalation compounds were prepared by solid-state ion exchange reactions which we have developed recently in order to understand the nature of the solid-state intercalation reactions. The reactions were carried out by grinding the mixtures of homoionic-montmorillonites and organoammonium (dodecyltrimethylammonium, tetramethylammonium, and tetrabutylammonium) halides (chloride, bromide, and iodide) at room temperature. Both of the counter anions of the organoammonium salts and the interlayer exchangeable cations of montmorillonite are concerned with the solid-state ion exchange reactions, indicating that the solid-solid reactions are thermodynamically governed. The solid-state ion exchange reactions lead to novel and different reactivities and intercalation compounds from those of conventional solution methods.

Solid-state ion exchange in zeolites. Part 5.—NH4-Y–iron(II) chloride

Solid-state ion-exchange reactions proceeding upon grinding of hydrated NH4-Y zeolite and FeCl2·4H2O in air and subsequent heating in vacuum have been followed by X-ray diffraction (XRD) and temperature-programmed evolution of volatile reaction products (H2O, NH3 and HCl) monitored by mass spectrometry (MS). Changes in valence state and coordination environment of the exchanged iron ions upon heat treatment up to 720 K in vacuum and air, as well as in hydrogen after treatment in air, were studied by Mossbauer spectroscopy. Partial ion exchange and oxidation to cationic hydroxy-iron(III) species proceed upon mere grinding. Heat treatment in vacuum results in partial autoreduction and characteristic environmental changes of di- and tri-valent Fe species, especially in the temperature range between 620 and 720 K. In an oxidizing atmosphere, autoreduction is suppressed; however, at temperatures >520 K, iron(III) oxide is formed in increasing amounts. Reduction by hydrogen subsequent to heat treatment in air at 720 K results in the formation of a magnetite-like oxide phase and some metallic α-iron.

Characterization of Zn centers in ZSM-5 zeolites with X-ray absorption spectroscopy

In the analysis of Zn K XANES of a ZnO + Na-ZSM-5 zeolite, the appearance of a solid state ion exchange reaction was shown. The ZSM-5 zeolites modifed by zinc exhibit enhanced catalytic activity.

Preparation of acidic forms of montmorillonite clay via solid-state ion-exchange reactions

A solid-state procedure has been developed which enables A13+ and Fe3+ ion-exchanged montmorillonite to be prepared via co-grinding of the clay with the appropriate metal nitrate at room temperature. Pyridine adsorption/infrared spectroscopic studies indicate that montmorillonite treated in this manner contains Bronsted and Lewis acid sites in significant quantities, suggesting that these easily prepared materials may be of interest as acid catalysts.

In situ investigation of solid state lon exchange in zeolites using Fourier transform infrared spectroscopy

The solid-state ion-exchange reaction in H-ZSM-5 zeolite was investigated in situ up to a temperature of 550 °C by diffuse reflectance Fourier transform infrared spectroscopy. At 550 °C, the exchange rate of the framework OH groups inside the zeolite channels is faster than that of the terminal OH groups at the crystallite surface. The positions of the OH stretching bands are not shifted during the exchange process. The relationship between the OH groups and a constant acid strength during the exchange of Zn2+ ions is discussed.

Potentiometric study of the solid state ion-exchange reaction between α-AgI and β″-alumina

The ion-exchange reaction between β″-alumina and solid α-AgI was investigated by measuring the EMF of a galvanic cell with a β″-alumina solid electrolyte. The following cell was assembled and EMF measurements were taken in a temperature range between 342 to 816 K: Mo, Na(s, 1)| β″-alumina|Ag+AgI+ β″-alumina, Mo (I). Ag, AgI and β″- alumina powders were mixed in a molar ratio of Ag : AgI : Na (in β″-alumina powder) of 1.00 : 1.00 : 1.00. The cell was heated and maintained at 630 K for 30 d. The ion-exchange between Ag + ion in α-AgI and Na + ion in β″-alumina powder gradually proceeded and formed two solid solutions of (Ag + −Na + )I − and (Na + −Ag + )-β″-alumina. The resulting EMF was higher than that of cell ( II) : Mo, Na(s, 1)| β″-alumina|NaI+Ag+AgI, Mo(II). The 30 days retention at 630 K gave a cell EMF of 2.1370 V which was higher than the EMF of cell (II) by 9.6 mV. When the cell temperature was decreased below 600 K, a NaI saturated with AgI, (Na + −Ag + )I − sat. phase appeared and the EMFs of cell (I) agreed with the EMFs of cell (II). By heating the cell to a particular temperature on the liquidus line on the AgI side of the AgINaI system, a liquid phase appeared and the ion-exchange between α-AgI and β″-alumina smoothly proceeded via the liquid. After that, two kinds of three-phase-equilibria of (Ag −Na−I) sat.+(Ag + −Na + )I − sat.+(Na + −Ag + )I − sat. and (Ag −Na−I) sat.+ (Ag + −Na + )I − sat.+liquid (Ag + −Na + )I − were attained below and above 657 K, respectively. Then, the EMFs of cell (I) agreed with the value of cell (II) below 657 K.