Synthesis and characterization of layered zinc hydroxychlorides

Layered material of zinc hydroxychlorides (Zn₅(OH)₈Cl₂·nH₂O: ZHC), which is one of the basic zinc salts (BZS), was synthesized from ZnO nano-particles aged with aqueous ZnCl₂ solutions at different temperatures ranging from 6 to 140 °C for 48 h. X-ray diffraction (XRD) results indicated that the diffraction peaks of ZnO completely disappeared by aging at 6 °C and the ZHC peaks were developed. By increasing the aging temperature, crystallinity of the layered structure was improved. At 6 °C, the ZHC particles were thin hexagonal plate particles with sizes ranging from 1 to 3 μm. The particle size of ZHC was independent of aging temperature. The atomic Cl/Zn ratios of all the ZHC materials were almost 0.2 less than 0.4 of the theoretical ratio, indicating that the synthetic ZHC is Cl-deficient. It seemed that half of Cl atoms in the layer were replaced with HCO₃⁻ and/or OH⁻. The specific surface areas of ZHC estimated from N₂ adsorption isotherms were ca. 10 m² g⁻¹ and were independent of the aging temperature. However, the H₂O monolayer adsorption capacity per unit surface area (n_w) for all the samples was higher than that of ZnO particles, revealing the high affinity of ZHC to H₂O molecules. The n_w values were increased by reducing the crystallinity of ZHC. This enhancement of H₂O adsorption selectivity was thought to be related with less-crystallized parts of the particles.     

Intercalation studies of zinc hydroxide chloride: Ammonia and amino acids

Zinc hydroxide chloride (ZHC) is a layered hydroxide salt with formula Zn₅(OH)₈Cl₂·2H₂O. It was tested as intercalation matrix for the first time and results were compared with intercalation products of the well-known zinc hydroxide nitrate and a Zn/Al layered double hydroxide. Ammonia was intercalated into ZHC, while no significant intercalation occurred in ZHN. Aspartic acid intercalation was only achieved by co-precipitation at pH=10 with ZHC and pH=8 with zinc hydroxide nitrate. Higher pH resistance in ZHC favored total deprotonation of both carboxylic groups of the Asp molecule. ZHC conferred more thermal protection against Asp combustion presenting exothermic peaks even at 452 °C while the exothermic event in ZHN was 366 °C and in the LDH at 276 °C.     

Formation of Zn–Al layered double hydroxide thin films intercalated with sulfonated spiropyran

We prepared Zn–Al layered double hydroxide (LDH) thin films intercalated with sulfonated 1,3′,3′-trimethyl-6-nitrospiro[2H-chromene-2,2′-indoline] anions (SP-SO₃ ^?) by immersion of sol–gel derived amorphous Al₂O₃–ZnO thin films in hot water containing SP-SO₃H. Extended interlayer spacing, in comparison to the Zn–Al LDH with carbonate anions, was observed after immersion in distilled water containing SP-SO₃H at 60 °C for 30 min, indicating that we formed Zn–Al LDH films with SP-SO₃ ^? directly on glass substrates. The merocyanine form of SP-SO₃ ^? was shown by UV spectra to have stabilized in the hydroxide layers of LDH.     

Alkaline hydrolysis of dimethyl terephthalate in the presence of [LiAl2(OH)6]Cl·2H2O

The alkaline hydrolysis of dimethyl terephthalate (DMT) in the presence of [LiAl₂(OH)₆]Cl has been investigated to demonstrate a possible application of anion exchange facility of layered double hydroxides (LDHs) to control chemical reactions. The results show that (i) in the alkaline hydrolysis of DMT in the presence of [LiAl₂(OH)₆]Cl, most of the interlayer Cl⁻ of [LiAl₂(OH)₆]Cl is quickly replaced by OH⁻ in the alkaline solution because the LDH host favors OH⁻ more; (ii) the alkaline hydrolysis of DMT in the presence of [LiAl₂(OH)₆]Cl is faster than the reaction of DMT and [LiAl₂(OH)₆]OH; (iii) The hydrolysis of DMT in a buffer solution of pH≈8 takes longer time to reach equilibrium than the alkaline hydrolysis of DMT in the presence of [LiAl₂(OH)₆]Cl. It is believed that the selective anion exchange chemistry of the LDH plays a key role in storage and controlled release of active reactant, that is, OH⁻, thus make the hydrolysis proceeds in a controlled way.     

Fabrication and characterization of Meldola's blue/zinc oxide hybrid electrodes for efficient detection of the reduced form of nicotinamide adenine dinucleotide at low potential

We report the synthesis and the electrochemical properties of hybrid films made of zinc oxide (ZnO) and Meldola's blue dye (MB) using cyclic voltammetry (CV). MB/ZnO hybrid films were electrochemically deposited onto glassy carbon, gold and indium tin oxide-coated glass (ITO) electrodes at room temperature (25 ± 2 °C) from the bath solution containing 0.1 M Zn(NO₃)₂, 0.1 M KNO₃ and 1 × 10⁻⁴ M MB. The surface morphology and deposition kinetics of MB/ZnO hybrid films were studied by means of scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical quartz crystal microbalance (EQCM) techniques, respectively. SEM and AFM images of MB/ZnO hybrid films have revealed that the surfaces are well crystallized, porous and micro structured. MB molecules were immobilized and strongly fixed in a transparent inorganic matrix. MB/ZnO hybrid films modified glassy carbon electrode (MB/ZnO/GC) showed one reversible redox couple centered at formal potential (E⁰′) −0.12 V (pH 6.9). The surface coverage (Γ) of the MB immobilized on ZnO/GC was about 9.86 × 10⁻¹² mol cm⁻² and the electron transfer rate constant (ks) was determined to be 38.9 s⁻¹. The MB/ZnO/GC electrode acted as a sensor and displayed an excellent specific electrocatalytic response to the oxidation of nicotinamide adenine dinucleotide (NADH). The linear response range between 50 and 300 μM NADH concentration at pH 6.9 was observed with a detection limit of 10 μM (S/N = 3). The electrode was stable during the time it was used for the full study (about 1 month) without a notable decrease in current. Indeed, dopamine (DA), ascorbic acid (AA), acetaminophen (AP) and uric acid (UA) did not show any interference during the detection of NADH at this modified electrode.     

Supramolecular networks through second-sphere coordination based on 1D metal-4,4′-dipyridyldisulfide coordination polymers and hydrogenfumarate or sulfonate anions

Four hydrogen-bonded assemblies of formula [M(dpds)₂(OH₂)₂]A₂·nH₂O (A = anion) are described. These assemblies result from the second-sphere coordination interactions between the 1D coordination polymers [M(dpds)₂(OH₂)₂]²⁺, M = Zn(II) and Cu(II), dpds = 4,4′-dipyridyldisulfide, and the pyridine-3-sulfonate (3pySO₃⁻) or hydrogenfumarate (Hfum⁻) anions. Significantly, supramolecular structural variations are observed depending on the presence of water lattice molecules, which formed discrete aggregates when the Hfum⁻ anion was used. The effects of geometrical variations in the building blocks are also evident on using Jahn-Teller-distorted divalent Cu(II) ions or regular octahedral species based on Zn(II) ions. The second-sphere effects on the stabilization of the compounds are illustrated by TGA experiments.     

ZnO–Al2O3–CeO2–Ce2O3 mixed metal oxides as a promising photocatalyst for methyl orange photocatalytic degradation

In this research article, ZnO–Al₂O₃–CeO₂–Ce₂O₃ mixed metal oxides phases were prepared by calcination of Zn–Al/Ce–CO₃ layered double hydroxides (LDH) precursors, and evaluated for the photocatalytic degradation of methyl orange (MO) as a model textile dye from aqueous solution under UV irradiation. First, Zn–Al–CO₃ and a series of Zn–Al/Ce–CO₃ with different Ce content (5, 10, 15, 20%) were synthesized through co-precipitation method at Zn/(Al+Ce) molar ratio (r) of 3, then subjected to calcination at 500 °C for 6 h. Samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray analysis and pH point of zero charge. The experimental results of the photodegradation reveal that the photocatalyst developed from Zn–Al–Ce10%-CO₃ LDH exhibits the highest photocatalytic activity, with a degradation efficiency of 99.8% after 300 min of irradiation. This performance was mainly ascribed to the presence of difference state of Ce, leading a highest separation efficiency of electrons and holes. The recycling tests suggests a much high photostability and reusability of the photocatalyst.     

Solution decomposition of the layered double hydroxide (LDH) of Zn with Al

The layered double hydroxides (LDH) of Zn with Al containing intercalated CO₃²⁻ and NO₃⁻ ions undergo solution decomposition to yield a highly crystalline oxide mixture comprising ZnO and ZnAl₂O₄ at temperatures as low as 150–180 °C under hydrothermal conditions. In contrast solid-state decomposition takes place at a much higher temperature (240–315 °C) in air. Solution decomposition is not only guided by the low octahedral crystal field stabilization energy of Zn²⁺ ions, a factor that also affects solid-state decomposition, but also by solubility considerations. The LDHs of Mg and Ni with Al do not undergo solution decomposition.     

Preparation of ultrathin membranes by layer-by-layer (LBL) deposition of oppositely charged inorganic colloids

Nanofilms were prepared by alternating deposition of Mg–Al (2:1) NO ₃ ⁻ layered double hydroxide (LDH), hectorite and silica particles present study. The charge density of the oppositely charged materials strongly affect film properties like thickness and ordering. The specific charge of the colloidal particles was measured with the particle charge detector. The sequential build up of the thin films was followed by spectrophotometry and X-ray diffraction (XRD). The surface morphology of the formed multilayers was characterized and film thickness determination was performed by atomic force microscopy. The influence of the charge density of hectorite and silica particles on the LDH/hectorite, LDH/silica film thickness was studied. The results reveal that the LDH concentration has a significant effect on the film thickness while the hectorite and silica concentration were not important. Films prepared from the different types of negatively charged inorganic particles in the same concentration range (0.25–1.0%) have similar thickness because of the much higher surface charge relative to the LDH lamellae.     

Effect of water vapor on the thermal decomposition process of zinc hydroxide chloride and crystal growth of zinc oxide

Thermal decomposition process of zinc hydroxide chloride (ZHC), Zn₅(OH)₈Cl₂·H₂O, prepared by a hydrothermal slow-cooling method has been investigated by simultaneous X-ray diffractometry and differential scanning calorimetry (XRD-DSC) and thermogravimetric-differential thermal analysis (TG-DTA) in a humidity-controlled atmosphere. ZHC was decomposed to ZnO through β-Zn(OH)Cl as the intermediate phase, leaving amorphous hydrated ZnCl₂. In humid N₂ with P_H2O=4.5 and 10 kPa, the hydrolysis of residual ZnCl₂ was accelerated and the theoretical amount of ZnO was obtained at lower temperatures than in dry N₂, whereas significant weight loss was caused by vaporization of residual ZnCl₂ in dry N₂. ZnO formed by calcinations in a stagnant air atmosphere had the same morphology of the original ZHC crystals and consisted of the c-axis oriented column-like particle arrays. On the other hand, preferred orientation of ZnO was inhibited in the case of calcinations in 100% water vapor. A detailed thermal decomposition process of ZHC and the effect of water vapor on the crystal growth of ZnO are discussed.     

Mechanism of Formation of Nanocrystalline ZnO Particles through the Reaction of [Zn(acac)2] with NaOH in EtOH

The mechanism of formation of nanocrystalline ZnO particles from the reaction of zinc acetylacetonate ([Zn(acac)₂]) with 2-equivalent NaOH in boiling EtOH was investigated by characterizing the particles and following the transformation of acac moieties. The reaction was found to proceed via hydrolysis of zinc ethoxide derivatives, followed by dehydration–condensation reactions. High-resolution solid-state CP-MAS¹³C NMR measurements indicate that the ZnO particles are produced through Zn (acac)(OZn)_n(acac) (3). Furthermore, it was suggested that acac⁻ligands play an important role in the generation of nanocrystalline ZnO particles by suppressing the hydrolysis–condensation of Zn(acac)(OZn)_n(acac).     

In and Ex Situ Studies of the Formation of Layered Microspherical Hydrozincite as Precursor for ZnO

Layered ZnO microspheric particles were prepared by the thermal decomposition of layered hydrozincite (LZnHC), which was synthesized from zinc nitrate and urea in a water/PEG400 mixture. The influence of the starting reagents, their concentrations, and the amount of PEG in the water/PEG400 mixture on the particle growth was observed. The chemical aspect of the particle growth was proposed in the frame of the partial charge model (PCM), and the formation of [Zn(OH)₂(OH₂)₄]⁰ and [Zn(OH)(HCO₃)(OH₂)₃]⁰ was predicted for the solid phase. The assumed growth mechanism, which follows the “nonclassical crystallization” concept of a self‐assembling mechanism, was observed in situ by small‐angle X‐ray scattering (SAXS) and predicts the rapid formation of approximately 6 nm sized building units. The size of these nano building units, stable only in the reaction medium, remains nearly constant during the synthesis, as the concentration of the nano building units increases throughout the reaction. The nano building units connect into leaves of LZnHC with a thickness of 20 nm. These leaves of LZnHC are further agglomerated into porous, microsphere‐like particles with sizes up to 4 μm.     

Thermally Induced Growth of ZnO Nanocrystals on Mixed Metal Oxide Surfaces

An in situ method for the growth of ZnO nanocrystals on Zn/Al mixed metal oxide (MMO) surfaces is presented. The key to this method is the thermal treatment of Zn/Al layered double hydroxides (Zn/Al LDHs) in the presence of nitrate anions, which results in partial demixing of the LDH/MMO structure and the subsequent crystallization of ZnO crystals on the surface of the forming MMO layers. In a first experimental series, thermal treatment of Zn/Al LDHs with different fractions of nitrate and carbonate in the interlayer space was examined by thermogravimetry coupled with mass spectrometry (TG‐MS) and in situ XRD. In a second experimental series, Zn/Al LDHs with only carbonate in the interlayer space were thermally treated in the presence of different amounts of an external nitrate source (NH₄NO₃). All obtained Zn/Al MMO samples were analysed by electron microscopy, nitrogen physisorption and powder X‐ray diffraction. The gas phase formed during nitrate decomposition turned out to be responsible for the formation of crystalline ZnO nanoparticles. Accordingly, both interlayer nitrate and the presence of ammonium nitrate led to the formation of supported ZnO nanocrystals with mean diameters between 100 and 400 nm, and both methods offer the possibility to tailor the amount and size of the ZnO crystals by means of the amount of nitrate.     

Preparation and Studies of ZnO:Al Films and Powders

ZnO:Al (0–10 at% Al) films and powders were produced using acac-modified methoxy-ethoxide precursors, obtained from Zn(C₂H₅)₂ and Al₄(OPr ⁱ )₁₂. The conversion to oxide powders was monitored with TGA and DSC, and the phase development was investigated with XRD, FT-IR spectroscopy, and TEM-EDS. The gels obtained by air-hydrolysis contained ca 0.5 acac/(Zn + Al) and a small amount of water and hydroxyls. All residual groups were removed to yield ZnO:Al by heating to ca 400°C. The powders obtained at 400 and 500°C were elementally homogeneous, and consisted of hex-ZnO:Al as ca 3–5 (10 at% Al) or 20–30 (3 at% Al) nm sized crystalline particles. Spin-coating on quartz, Si/SiO₂, and window glass, followed by heating to 500°C resulted in 150–200 nm thick films of hex-ZnO:Al. 500 nm thick films were obtained by repeating the deposition and heat-treatment twice. The films were visually very clear and the measured transmittance high over the 400–800 nm range (91–93% at 800 nm) for ca 300 nm thick films.     

Real-time tracking of hydrogen peroxide secreted by live cells using MnO2 nanoparticles intercalated layered doubled hydroxide nanohybrids

We report a facile and green method for the fabrication of new type of electrocatalysts based on MnO₂ nanoparticles incorporated on MgAl LDH P-type semiconductive channel and explore its practical applications as high-performance electrode materials for electrochemical biosensor. A series of MgAl layered doubled hydroxide (LDH) nanohybrids with fixed Mg/Al (M²⁺/M³⁺ atomic ratio of 3) and varied amount of MnCl₂.4H₂O are fabricated by a facile co-precipitation method. This approach demonstrates the combination of distinct properties including excellent intercalation features of LDH for entrapping nanoparticles and high loading of MnO₂ nanoparticles in the host layers of LDH. Among all samples, Mn5–MgAl with 0.04% loaded manganese has a good crystalline morphology. A well-dispersed MnO₂ nanoparticles encapsulated into the host matrix of hydrotalcite exhibit enhanced electrocatalytic activity towards the reduction of H₂O₂ as well as excellent stability, selectivity and reproducibility due to synergistic effect of good catalytic ability of MnO₂ and conductive MgAl LDH. Glass carbon electrode (GCE) modified with Mn5–MgAl possesses a wide linear range of 0.05–78 mM, lowest detection limit 5 μM (S/N = 3) and detection sensitivity of 0.9352 μAmM⁻¹. This outstanding performance enables it to be used for real-time tracking of H₂O₂ secreted by live HeLa cells. This work may provide new insight in clinical diagnosis, on-site environmental analysis and point of care testing devices.     

In situ dielectric measurements of Zn–Al layered double hydroxide with anionic nitrate ions

Zn–Al–NO₃–layered double hydroxide (Zn–Al–NO₃–LDH) was prepared by the co-precipitation method with a ratio of Zn/Al = 4 and at a constant pH of 7. Powder XRD patterns showed the characteristic peaks of layered structure of the LDH sample. Thermogravimetric analysis (TGA) and infrared spectra of the sample were investigated. Because of the existence of water molecules and anionic NO₃⁻ in the interlayer of the LDH, the in situ dielectric spectroscopy of the LDH can be described by an anomalous low frequency dispersion using the second type of Universal Power Law. Novel measurements of activation energy of LDH have been obtained at five different frequencies. The energy value increased from 0.05 eV at 1 MHz to 0.37 eV at 134 Hz. The conductivity spectra of sample were studied as a function in temperature of the in situ measurements. The ionic conductivity (dc) of LDH increased as the in situ temperature increased.     

Synthesis and Thermal Decomposition of Mn-Al Layered Double Hydroxides

In this paper, the synthesis and thermal decomposition behavior of hydrotalcite-like Mn-Al layered double hydroxide (LDH) have been investigated. First, the Mn-Al LDH was synthesized by the coprecipitation method using various anions such as Cl⁻, CO²⁻₃, NO⁻₃, SO²⁻₄ or dicarboxylic acids (DCA). The single phase of the Mn-Al LDH was obtained when Cl⁻, NO⁻₃ or DCA was used as a guest anion. In the case of CO²⁻₃ or SO²⁻₄, the solid products included MnCO₃ or shigaite as a by-product. The crystallinity of the Cl/Mn-Al LDH was greatly influenced by a drying temperature and that the crystallinity of the Cl/Mn-Al LDH dried at room temperature was found to rise about 6 times in comparison with that dried at 333 K. The DCA/Mn-Al LDH was found to have an expanding LDH structure, supporting that the LDH basal layers were bridged by the intercalated DCA anion. Then, the thermal decomposition of the DCA/Mn-Al LDH has been examined, and the intercalated DCA was found to be decomposed at lower temperature than DCA itself. The oxidation number of Mn ion rose with increasing the heat treatment temperature and was +2.70 with crystallizing Mn₃O₄ after being heated at 973 K. The thermal decomposition of guest DCA was thought to be accelerated by the strong catalytic action of Mn ion in the host hydroxide basal layers.     

A method for Ca, Fe, Ga, Na, Si and Zn determination in alumina by inductively coupled plasma optical emission spectrometry after aluminum precipitation

In this present work a method for the determination of Ca, Fe, Ga, Na, Si and Zn in alumina (Al₂O₃) by inductively coupled plasma optical emission spectrometry (ICP OES) with axial viewing is presented. Preliminary studies revealed intense aluminum spectral interference over the majority of elements and reaction between aluminum and quartz to form aluminosilicate, reducing drastically the lifetime of the torch. To overcome these problems alumina samples (250 mg) were dissolved with 5 mL HCl + 1.5 mL H₂SO₄ + 1.5 mL H₂O in a microwave oven. After complete dissolution the volume was completed to 20 mL and aluminum was precipitated as Al(OH)₃ with NH₃ (by bubbling NH₃ into the solution up to a pH ~ 8, for 10 min). The use of internal standards (Fe/Be, Ga/Dy, Zn/In and Na/Sc) was essential to obtain precise and accurate results. The reliability of the proposed method was checked by analysis of alumina certified reference material (Alumina Reduction Grade-699, NIST). The found concentrations (0.037% w w⁻¹ CaO, 0.013% w w⁻¹ Fe₂O₃, 0.012% w w⁻¹ Ga₂O₃, 0.49% w w⁻¹ Na₂O, 0.014% w w⁻¹ SiO₂ and 0.013% w w⁻¹ ZnO) presented no statistical differences compared to the certified values at a 95% confidence level.     

Investigation of Fe-based oxyhydroxy-fluoride with hollandite-type structure

Well crystallized Fe-based oxyhydroxy-fluoride with the FeO(OH_0.2F_0.8)·0.2H₂O chemical composition has been prepared from hydrolysis of Fe trifluoride under supercritical CO₂ conditions. Investigation by Mössbauer spectroscopy and neutron diffraction show that this compound crystallize in the monoclinic symmetry (SG: I2/m, a = 10.447(7) Å, b = 3.028(2) Å, c = 10.445(4) Å, β = 90.00(3)°). Taking into account the Fe-O(F) bond distances, F⁻ anions are mainly located on the common vertices of Fe octahedra whereas OH⁻ groups occupy mainly the shared edges of the Fe octahedra. Two various highly distorted octahedral sites have been identified with Fe-O/F bond distances varying from 1.90 Å to 2.31 Å. One Fe site is more distorted than in FeO_0.8OH_1.2·0.2Cl akaganeite because of the random distribution of F⁻/OH⁻/O²⁻ in the vicinity of this Fe cation.     

Sensors based on galvanic cell generated electrochemiluminescence and its application

In this paper, a novel electrochemiluminescence (ECL) imaging sensor array was developed for determination of hydrogen peroxide (H₂O₂), which was based on Cu/Zn alloy galvanic cell generated ECL. In alkaline solution, Cu/Zn galvanic cell was formed because of corrosion effect, the galvanic cell could supply stable potential for ECL generation of luminol, and the weak ECL emission could be enhanced by H₂O₂. The galvanic cell sensor array was designed by putting Cu/Zn alloy in 96-well microtiter plates separately. The relative ECL intensity was proportional with the concentration of hydrogen peroxide in the range of 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol l⁻¹ and the detection limit was 3.0 × 10⁻⁷ mol l⁻¹ (3σ), the relative standard deviation (R.S.D.) for 11 parallel measurements of 1.0 × 10⁻⁵ mol l⁻¹ H₂O₂ was 4.0%.