Zn Al Cl Research Articles

Role of Anions in Stabilizing the [Zn–Al] Layered Double Hydroxides: A Thermodynamic Study

Room-temperature acid solution calorimetry, high-temperature oxide melt solution calorimetry, and low-temperature heat capacity measurements were employed to calculate the thermodynamic stabilities of the [Zn–Al–X] layered double hydroxides (LDH) containing different anions (X = Cl–, CO32–, and SO42–). Cryogenic heat capacity measurements demonstrated a Schottky-type anomaly in the heat capacity of all three LDHs below 11 K. This anomaly is attributed to the tunneling of protons between adjacent oxygen atoms in the LDH interlayer as this creates an energy system similar to a two-level system modeled with a Schottky term. These heat capacity measurements were also used to determine vibrational entropies which, when combined with configurational entropies, provide standard entropies of these LDHs. Enthalpies of formation of LDHs from binary components were determined and combined with the entropies of formation to calculate Gibbs free energies. Based on these values, the order of stability is [Zn–Al–SO4] > [Zn–Al–CO3] > [Zn–Al–Cl]. This trend results from a combination of the interlayer spacing, amount of water in the interlayer, interactions among the interlayer species, and interactions between the metal hydroxide layer and the interlayer.

Utilization of Zn–Al–Cl layered double hydroxide as an adsorbent for the removal of anionic dye Remazol Red 23 in aqueous solutions: kinetic, equilibrium, and thermodynamic studies

Utilization of Zn–Al–Cl layered double hydroxide as an adsorbent for the removal of anionic dye Remazol Red 23 in aqueous solutions: kinetic, equilibrium, and thermodynamic studies

Layered Double Hydroxide-Based Gas Sensors for VOC Detection at Room Temperature.

Miniaturized low-cost sensors for volatile organic compounds (VOCs) have the potentiality to become a fundamental tool for indoor and outdoor air quality monitoring, to significantly improve everyday life. Layered double hydroxides (LDHs) belong to the class of anionic clays and are largely employed for NOx detection, while few results are reported on VOCs. In this work, a novel LDH coprecipitation method is proposed. For the first time, a study comparing four LDHs (ZnAl–Cl, ZnFe–Cl, ZnAl–NO3, and MgAl–NO3) is carried out to investigate the sensing performances. As explored through several microscopy and spectroscopy analyses, LDHs show a morphology characterized by a large surface area and a three-dimensional hierarchical flowerlike architecture with micro- and nanopores that induce a fast diffusion and highly effective surface interaction of the target gases. The fabricated sensors, operating at room temperature, are able to reversibly and selectively detect acetone, ethanol, ammonia, and chlorine vapors, reaching significant sensing response values up to 6% at 21 °C. The results demonstrate that by changing the LDHs’ composition, it is possible to modulate the sensitivity and selectivity of the sensor, helping the discrimination of different analytes, and the consequent integration on a sensor array paves the way for electronic nose development.

Removal of Remazol Blue 19 from wastewater by zinc–aluminium–chloride-layered double hydroxides

Layered double hydroxides (LDHs), also called anionic clays, consist of cationic brucite-like layers and exchangeable interlayer anions. These hydrotalcite-like compounds, with Zn and Al in the layers and chloride in the interlayer space, were prepared following the coprecipitation method at constant pH. The affinity of this material for Remazol Blue 19, RB19 [2-(3-(4-Amino-9,10-dihydro-3-sulpho-9,10-dioxoanthracen-4-yl) aminobenzenesulphonyl) vinyl) disodiumsulphate], was studied as a function of contact time, pH of the solutions LDH dose and the RB19/[Zn–Al–Cl] mass ratio. It was found that 48 h is enough time for the equilibrium state to be reached with maximum RB19 retention at pH of 9 for an LDH dose equal to 100 mg and with an RB19/[Zn–Al–Cl] mass ratio higher than 3. The adsorption isotherm, described by the Langmuir model, is of L-type. The results demonstrate that RB19 retention on LDHs occurs by adsorption on external surface when RB19/[Zn–Al–Cl] mass ratio is equal or <3 and by both adsorption and interlayer ion exchange for ratios higher than 3. A mechanism for removal of RB19 anion has been confirmed by X-ray diffraction, IR spectroscopy and TG analysis (TG and DTG curves).

Synthesis and physicochemical characterization of Zn/Al chloride layered double hydroxide and evaluation of its nitrate removal efficiency

Deleterious effects of nitrate on health are well known. A laboratory study was conducted to investigate the ability of Zn–Al–Cl layered double hydroxide for the removal of nitrate from synthetic nitrate solution. In the present study Zn–Al–Cl LDH was synthesized by co-precipitation method and was characterized using SEM, XRD, FTIR and TGA–DSC. To know the practical applicability, a detailed nitrate removal study was carried out. The removal of nitrate was 85.5% under neutral conditions, using 0.3 g of LDH in 100 mL of nitrate solution having initial concentration of 10 mg/L. Adsorption kinetic study revealed that the adsorption process followed first order kinetics. Adsorption data were fitted to linearly transformed Langmuir isotherm with R 2 (correlation coefficient) >0.99. Thermodynamic parameters were also calculated to study the effect of temperature on the removal process. In order to understand the adsorption type, equilibrium data were tested with Dubinin–Radushkevich isotherm. The percentage removal was found to decrease gradually with increase in pH and the optimum pH was found to be 6. The presence of competitive anions reduced the nitrate adsorption in the order of carbonate > phosphate > chloride > sulphate. The Zn–Al–Cl LDH exhibited low desorption and poor regeneration.

Cyclic voltammetry of metal bipyridyl cations at redox active Ni–Al–Cl layered double hydroxide films

A very large increase in the [Os(bpy)3]2+ cathodic peak was observed when an electrode modified with a Ni–Al–Cl LDH film was cycled in solution of the cation. The cathodic charge increased from 0.16 mC to 3.0 mC when the switching potential was increased from 0.9 to 1.4 V. This was not observed for Zn–Al–Cl LDH films. Addition of [Ru(bpy)3]2+ resulted in an additional doubling the [Os(bpy)3]2+ cathodic peak. Similar results were obtained for [Co(bpy)3]2+. When [Os(bpy)3]2+ was added to a [Co(bpy)3]2+ solution however, the enhancement of [Co(bpy)3]2+ cathodic peak was completely suppressed at the expense of the [Os(bpy)3]2+ cathodic peak. This is the first report on the electrochemistry of metal bipyridyl cations, or of any electroactive cations at LDH-modified electrodes. Since LDHs have positively charged layers separated by exchangeable anions, they were not expected to adsorb large amounts of cations. This was confirmed by UV–Visible spectroscopy and elemental analysis of films that had been soaked in solution of the metal bipyridyl cations. The large voltammetric peaks observed for the bipyridyl complexes are therefore attributed to mediation of the oxidation or reduction of the LDHs nickel sites by the trace amounts of theses cations that were present at the interface between the films and the solutions. Preliminary measurements show that a similar mediation occurs for [Fe(CN)6]4− anions and for a mixture of [Fe(CN)6]4− and [Ru(bpy)3]2+.

Anion-exchange and thermal change of layered zinc hydroxides formed in the presence of Al(III)

Zinc hydroxide chloride particles of ZHC (simonkolleite, Zn 5(OH) 8Cl 2·H 2O) and layered double hydroxides (LDH, Zn–Al–Cl) were prepared by hydrolysis of ZnCl 2 solutions dissolving AlCl 3 at Al/Zn = 0.1 and 0.6 in atomic ratio, respectively. The anion-exchange and thermal change of ZHC and LDH were investigated by XRD, TEM, FTIR, analysis of Zn, Al, and Cl and gas adsorption of N 2, H 2O, and CCl 4. The formed ZHC and LDH particles were hexagonal thin plates and irregularly shaped thin plates, respectively. LDH was more easily ion-exchanged with CO 3 2− and SO 4 2− compared to ZHC. The layered structure of LDH was damaged by the ion-exchange with SO 4 2− but not CO 3 2−, whereas that of ZHC was kept after the ion-exchange with both the anions. The TEM observation of the ZHC and LDH particles outgassed at different temperatures of 75–400 °C revealed that exfoliation takes place on outgassing ZHC at 100–150 °C but not occurs in LDH. ZHC showed a high H 2O adsorption selectivity when outgassed below 100 °C, however the adsorption selectivity completely disappeared above 125 °C where the exfoliation took place. On the other hand, LDH exhibited less adsorption selectivity than ZHC though the selectivity was held after outgassed at 400 °C. The facilitated delamination of ZHC indicates that ZHC exhibits weaker interlalyer attractive force than LDH in vacuo.

Synthesis of layered zinc hydroxide chlorides in the presence of Al(III)

Zinc hydroxide chloride particles were synthesized by hydrolysis of ZnCl 2 solutions dissolving AlCl 3 at different atomic Al/Zn ratios from 0 to 1.0 and characterized by various techniques. Increasing Al/Zn ratio changed the crystal phases of the products as ZnO→ZnO+ZHC (Zn 5(OH) 8Cl 2·H 2O)→ZHC→LDH (layered double hydroxides, Zn–Al–Cl) and the particle morphology as agglomerates (ZnO)→fine particles (ZnO)→plates (ZHC)+rods (ZnO)→plates (ZHC)→plates (LDH). The atomic Cl/Zn ratios of LDH particles formed at Al/Zn⩾0.3 were ca. 0.3 despite the increase of Al/Zn ratio, being due to the intercalation of CO 3 2− into the LDH crystal. The OH − content of LDH estimated by TG was reduced by the deprotonation of OH − to counteract the excess positive charge produced by replacing Zn(II) with Al(III). ZHC exhibited a high adsorption selectivity of H 2O.

Removal of the herbicide 2,4-dichlorophenoxyacetate from water to zinc–aluminium–chloride layered double hydroxides

Batch sorption studies were conducted to investigate the potential of [Zn–Al–Cl] layered double hydroxides (LDHs) for the removal of the herbicide 2,4-dichlorophenoxyacetate (2,4-D) from contaminated aqueous solutions. Experiments were performed at different pH values, initial pesticide concentration, solid/pesticide ratio and anion exchange capacity of LDHs. The LDH samples evaluated had very high retention capacity for 2,4-D whose removal was a rapid process, as a quasi-equilibrium state was reached after 1-h reaction time. The adsorption can be described by Langmuir-type isotherms, with an average affinity constant of 12.5 L mmol −1. At initial 2,4-D concentrations between 0.08 and 4 mmol L −1, the solids removed up to 98% of the pesticide. Physicochemical characterization of the LDH solids, both fresh and after removal of 2,4-D, by X-ray diffraction, infrared spectroscopy and thermogravimetry, indicates that the retention of 2,4-D is done by adsorption on the surface of the solid for low 2,4-D concentrations. However, a combination of surface adsorption and interlayer ion exchange takes place when the 2,4-D concentration is high.

Palladium‐Catalyzed Reaction of Acylzirconocene Chloride and Stereoselective Formation of Bicyclo[3.3.0] Compounds.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Intercalation of dicarboxylate anions into a Zn–Al–Cl layered double hydroxide: microcalorimetric determination of the enthalpies of anion exchange

The enthalpies of anion exchange in a chloride-intercalated zinc aluminium layered double hydroxide (LDH) in suspension in water have been studied at 25 °C. The heat effects associated with the exchange of the chloride anions for dicarboxylate anions (oxalate, succinate, adipate and tartrate) have been determined by titration microcalorimetry for different amounts of LDH. Except for tartrate, the exchange processes are endothermic, in contrast to the exchange processes involving only inorganic anions. The enthalpies of exchange vary linearly with the number of carbon atoms, suggesting that the intercalated dicarboxylate anions are perpendicular to the layers. The energetic parameters show, for the first time, hydrophobic interactions between the CH2 groups of the parallel succinate or adipate anions and hydrogen bonding between the OH groups of the parallel tartrate anions.

Palladium-catalyzed reaction of acylzirconocene chloride and stereoselective formation of bicyclo[3.3.0] compounds.

The acylzirconocene chloride complex as an acyl group donor reacts with omega-unsaturated alpha,beta-enones and -ynones under Pd-Me(2)Zn(Me(2)AlCl)-catalyzed conditions to give stereoselectively bicyclo[3.3.0] compounds through (i) formation of a Pd(II) intermediate by an oxidative addition of the Pd(0) catalyst to an enone function, (ii) cyclization of the Pd intermediate to an omega-unsaturated group, (iii) an acyl group transfer from zirconium to Pd metal, (iv) reductive elimination of the Pd metal, and (v) intramolecular cis-selective aldol reaction. [reaction: see text]

Intercalation of a nitronyl nitroxide radical into layered inorganic hosts.: Preparation and physico-chemical characterization

The synthesis of new intercalation compounds obtained introducing the organic radical 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H-imidazol-1-oxyl-3-oxide (NITpBAH) in layered inorganic hosts via topotactic anion exchange reactions or exchange of anionic ligands is presented. Three different inorganic hosts were employed, two LDH-phases (MgAlCO 3 and ZnAlCl) and the butanoxy derivative of λ-zirconium phosphates. In all cases the intercalation procedure was successfully accomplished. The percentage of exchanged anions obtained was 27, 45, 40% for MgAlLDH, ZnAlLDH and λ-ZrPO 4[O(CH 2) 3CH 3]DMSO, respectively. The magnetic properties of the intercalated compounds were measured with a SQUID magnetometer and compared to those of a polycrystalline powder of the pure radical. The intercalation process does not change the nature of magnetic intermolecular interactions which remain antiferromagnetic but reduces their magnitude.

Electrochemical impedance spectroscopy of electrodes modified with thin films of NiAlCl layered double hydroxides

The impedance spectra of NiAlCl LDH-modified electrodes after oxidation at different dc potentials were recorded. The data were fitted to a simple Randles type cell by replacing the Warburg impedance with a mass transfer resistance in parallel with a constant phase element. The film charge transfer resistance decreased dramatically at the onset of nickel oxidation, from more than 10 6 Ω for the unoxidized films, to a minimum of about 60 Ω in a film oxidized to Ni 2.5+, before increasing slightly for more extensively oxidized films. For the partially oxidized films, the Nyquist plots consisted of depressed semicircles at high frequency, followed by larger capacitive loops at lower frequency where the impedance was dominated by mass transport. Effective diffusion coefficients estimated from the low frequency impedance varied between 1 and 5×10 −9 cm 2 s −1, in agreement with previous reports for proton diffusion in nickel hydroxide films. The resistive component of the mass transport impedance decreased with increase in the nickel oxidation state. The addition of [Mo(CN) 8] 4− caused an increase of 140 mV in the dc potential required to affect the changes in the NiAlCl film impedance spectra associated with oxidation of the nickel sites. The impedance of a redox inactive ZnAlCl film was unaffected by the use of dc conditioning potentials.

Evolution of protonic conduction in [Zn–Al–Cl] Lamellar Double Hydroxide phases with temperature and trivalent metal content

The conduction properties of a series of [Zn–Al–Cl] Lamellar Double Hydroxides (LDHs) with different amounts of trivalent metal are studied by impedance spectroscopy. The structural evolution of these samples is characterized by Rietveld analysis on powder X-ray diffraction diagrams. The conduction properties appear clearly related to the structural evolution of the interlayer domains.

Synthesis and characterization of a new ruthenium containing LDH: [Zn–Al–RuCl5H2O2−

A new ruthenium containing LDH has been synthesized by exchanging chloride anions in [Zn–Al–Cl] with the aquapentachlororuthenate(III) complex: [RuCl5H2O]2−. This intercalation has been investigated by various analytical methods such as powder X-ray diffraction, chemical analysis, FT-IR, thermogravimetric analysis and cyclic voltammetry. The exchange, carried out in acidic media, led to a decrease in the Zn/Al molar ratio suggesting a dissolution–reconstruction process or the formation of defective hydroxyl sheets. The interlayer free spacing and the presence of water molecules make it impossible to determine the orientation of the complex anion. The electrochemical study confirms the oxidation state as +3 for the ruthenium ions and demonstrates the difficulty in reducing them once intercalated.

X-Ray Diffraction Pattern Simulation for Thermally Treated [Zn–Al–Cl] Layered Double Hydroxide

Thermal analyses and X-ray diffraction (XRD) were combined with refinement and simulation of the XRD patterns in order to elucidate the evolution of the atom distribution in the interlayer domain of the [Zn–Al–Cl] layered double hydroxide during heating. Rietveld refinement indicates that the structure is composed of [Zn1−xAlx(OH)2]0.33+ layers separated by water molecules and chloride ions. Zn and Al are randomly distributed among the octahedral positions. The OH layer sequence is –BC–CA–AB–BC–. Oxygen of water molecules and chloride ions, also randomly distributed, prefer positions at about 0.76 Å of the threefold axis. The simulation of the XRD patterns shows that these positions were imposed by geometric constraints of water molecules connecting two OH groups of adjacent brucite-like layers.

Preparation of a new stable hybrid material by chloride–2,4-dichlorophenoxyacetate ion exchange into the zinc–aluminium–chloride layered double hydroxide

A new hybrid material with the composition [Zn1.9Al(OH)5.8][Cl2C6H3OCH2CO2·2.83H2O] has been synthesised via ion exchange of chloride by ions of a molecule belonging to the pesticide family, 2,4-dichlorophenoxyacetate (2,4D). The ion exchange in the zinc–aluminium–chloride layered double hydroxide, [Zn–Al–Cl], was investigated by X-ray diffraction and infrared spectroscopy. The effects of the anion concentration in solution, the 2,4D/[Zn–Al–Cl] molar ratio, the ageing time and the temperature on the ion exchange were studied. The best sample, in terms of crystallinity and extent of ion exchange, was obtained at 100 °C in a 0.004 M 2,4D solution in which the 2,4D/[Zn–Al–Cl] molar ratio was equal to 11, with 24 h of stirring time. This hybrid material was further characterised by chemical analyses and its thermal behaviour was also studied.

Shape and size determination for zinc–aluminium–chloride layered double hydroxide crystallites by analysis of X-ray diffraction line broadening

The Rietveld method, extended by a Fourier analysis of line profiles on the basis of the Warren–Averbach method, has been used for analysing the powder X-ray diffraction (PXRD) pattern of a [Zn–Al–Cl] layered double hydroxide, in order to separate size and strain effects. Assuming a given size distribution (Cauchy) and an adjustable strain variation in space, this method allows the simultaneous determination of structural parameters and the size and strain parameters of the sample. The shape, size, size distribution and orientation of the crystallites are determined. It is found that the shape is markedly anisotropic and compatible with plate-like crystallites with a hexagonal symmetry; the structure being described in the Rm space group. The strain parameter, i.e. the distribution of atomic positions around their equilibrium positions, varies by a factor of 2 while the mean particle size changes from 120 A to 2200 A in the [001] and [110] directions, respectively. Such shape and size are in good agreement with the transmission electron microscopy (TEM) observations.

Ion exchange of different phosphate ions into the zinc–aluminium–chloride layered double hydroxide

A well-crystallised [Zn–Al–Cl] layered double hydroxide was prepared by coprecipitation at constant pH. The chloride ion of this solid was then exchanged in solution with a series of phosphate ions having different sizes and charges; namely, PO 3 −, H 2PO 4 −, HPO 4 2−, PO 4 3−, P 2O 7 4− and P 3O 10 5−. Powder X-ray diffraction and Fourier transform infrared spectroscopy have allowed a correlation to be made of the structural features of the precursor and the exchanged materials.