Preparation and characterization of nanocrystalline ZnO by direct precipitation method

Nanocrystalline ZnO was prepared with ZnCl₂·2H₂O and (NH₄)₂CO₃ as raw materials by direct precipitation method. The precursor was proved to be [Zn₅(OH)₆(CO₃)₂] by TG-DTG-DTA and IR analysis. This precursor was calcined at 300°C for 1, 2 and 3 hours respectively, and then the nanocrystalline ZnO of different grain size were obtained. The nanocrystalline ZnO was characterized using X-ray diffraction (XRD), TEM and Brunner-Emmett-Teller method (BET). Experimental results for nanocrystalline ZnO showed that the minimum size was about 8nm, the maximum was about 15 nm and the mean grain size was 12 nm, the surface area was 80.56 m²/g and the purity was 99.9% when the precursor was calcined at 300°C for 2 h. __________ Translated from Journal of Inner Mongolia Normal University (Natural Science Edition), 2006, 35(1) (in Chinese)     

Hydrothermal Synthesis and Optical Properties of ZnO Nanostructured Films Directly Grown from/on Zinc Substrates

Uniform ZnO nanorods arrays are grown directly from and on Zn foils in pure water under hydrothermal conditions at a relatively low temperature. The nanorods are 80–200 nm in diameter and ∼ 1 μm in length, which grow on the Zn foil along the [001] direction. By changing the pure water to a urea solution, a Zn compound ([Zn₅(OH)₆(CO₃)₂], a precursor of ZnO nanoflowers film, is created by self-assembly. The ZnO nanoflowers film can be easily obtained by heating the [Zn₅(OH)₆(CO₃)₂] compound in N₂ at 350∘C for 5–6 hours. Possible growth processes of the ZnO nanorods arrays and the [Zn₅(OH)₆(CO₃)₂] nanoflowers are discussed. Photoluminescence properties of the as-prepared ZnO nanostructures have been measured. The ZnO nanorods array synthesized using our method has minimal defects so that only band-gap emission is observed. However, the ZnO nanoflowers film, obtained by heating the [Zn₅(OH)₆(CO₃)₂] nanoflower precursor in N₂, is polycrystalline and displays strong defect-related emission.     

Synthesis of ZnO microcrystals and their photocatalytic ability in the degradation of textile azo dyes

Flower and broken sheet-like zinc oxide (ZnO) microcrystals have been prepared via a thermal decomposition process, using Zn₅(CO₃)₂(OH)₆ as the precursor in the presence of glycerol at 300 and 600 °C. The ZnO products were examined as a photocatalyst for the UV-induced degradation of Yellow 181 and Red 245 (textile azo dyes) in water solution. The applicability of the Langmuir–Hinshelwood kinetic equation revealed that the degradation of dyes occurred mainly on the surface of the photocatalyst.     

Fabrication of mesoporous ZnO nanosheets from precursor templates grown in aqueous solutions

Mesoporous ZnO nanosheets were successfully prepared by pyrolytic transformation of zinc carbonate hydroxide hydrate, Zn₄CO₃(OH)₆·H₂O. The nanosheets were initially formed as assemblies on glass substrates during chemical bath deposition (CBD) in aqueous solutions of urea and zinc acetate dihydrate, zinc chloride, zinc nitrate hexahydrate, or zinc sulfate heptahydrate at 80°C. It was key to induce heterogeneous nucleation of Zn₄CO₃(OH)₆·H₂O by promoting a gradual hydrolysis reaction of urea and controlling the degree of supersaturation of zinc hydroxide species. Morphology of Zn₄CO₃(OH)₆·H₂O was largely influenced by the anions present in the CBD solutions. The Zn₄CO₃(OH)₆·H₂O nanosheets were transformed into wurtzite ZnO by heating at 300°C in air without losing the microstructural feature.     

微波辐射对浆态床合成甲醇CuO/ZnO/Al2O3催化剂前驱体晶相转变的影响

在微波辐射条件下,对CuO/ZnO/Al2O3催化剂的沉淀母液进行老化,通过XRD、TG、H2-TPR,FTIR、HR-TEM和XPS对前驱体及催化剂微观结构的进行表征,探讨了CuO/ZnO/Al2O3催化剂前驱体晶相转变过程中微波辐射的作用。结果表明,微波辐射有利于Cu2+取代Zn5(CO3)2(OH)6中Zn2+的同晶取代反应。微波辐射的老化过程中,首先发生Cu2+取代Zn5(CO3)2(OH)6中Zn2+生成(Cu,Zn)5(CO3)2(OH)6的同晶取代反应,并于1.0 h内基本完成;随着老化时间继续延长,主要进行Zn2+取代Cu2(CO3)(OH)2中Cu2+生成(Cu,Zn)2(CO3)(OH)2的同晶取代反应,同时(Cu,Zn)5(CO3)2(OH)6进一步结晶。与常规老化1 h制备的前驱体相比,微波辐射老化1.0 h制备的前驱体含有较多的(Cu,Zn)5(CO3)2(OH)6物相,有助于增强焙烧后CuO/ZnO/Al2O3催化剂中CuO-ZnO协同作用,提高表面铜含量,进而提高CuO/ZnO/Al2O3催化剂在浆态床合成甲醇的催化活性和稳定性,在400 h浆态床合成甲醇评价期间,甲醇时空收率最大达318.9 g.kg-1.h-1,失活率仅为0.11%.d-1。     

Evidence for the formation of anhydrous zinc acetate and acetic anhydride during the thermal degradation of zinc hydroxy acetate,Zn5(OH)8(CH3CO2)2·4H2O to ZnO

Zinc hydroxy acetate, Zn₅(OH)₈(CH₃CO₂)₂·4H₂O, has been prepared by the precipitation method. It has been demonstrated by FTIR analysis that, contrary to previous reports, the interaction of the acetate anion with the matrix cation is ionic. TG analysis, mass spectral analysis of the evolved gases, and in situ variable temperature PXRD and FTIR analysis have shown that decomposition of the material to ZnO involves the formation of Zn₅(OH)₈(CH₃CO₂), Zn₃(OH)₄(CH₃CO₂)₂ and anhydrous zinc acetate (Zn(CH₃CO₂)₂) as some of the acetate-containing intermediate solid products. The acetate anion is finally lost, at temperatures below 400 °C, as acetic anhydride, (CH₃CO)₂O.     

Preparation of ZnO nanoparticle‐reinforced polyamide 6 composite by in situ‐coproduced method and their properties

Polyamide 6/ZnO nanocomposites (noted as PA6/ZnO) were prepared by an in situ co‐producing method, during which Zn₂(OH)₂CO₃ decomposed into nano‐ZnO in the process of the opening‐ring polymerization of caprolactam at high temperature. Transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were used to analyze the size and dispersive properties of nano‐ZnO, the crystallization and melting properties, the thermal properties, and crystal structure of PA6/ZnO composite, respectively. The results showed that the nano‐ZnO derived from Zn₂(OH)₂CO₃ via in situ polymerization of PA6‐ZnO was uniformly dispersed in PA6 matrix. However, the overall nano‐ZnO crystallization rate and crystal size in the PA6 matrix were hindered by the bulky PA6 molecular chains. The mechanical properties were evaluated using universal tensile and impact testing instruments. The results revealed that PA6/ZnO composite with 0.2% nano‐ZnO content possessed excellent tensile strength, enhanced by 75% in comparison with the pure PA6. The nano‐ZnO had little influence on the impact strength of PA6. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 165–170     

溶剂极性对微波辐射老化制备前驱体及CuO/ZnO/Al2O3催化剂结构的影响

在制备CuO/ZnO/Al2O3催化剂的老化过程中,采用微波辐射老化技术,着重研究了溶剂极性对前躯体物相组成,烧后CuO/ZnO/Al2O3催化剂结构及其在浆态床合成甲醇工艺中催化性能的影响。通过XRD、DTG、H2-TPR,FTIR、HR-TEM和XPS对前驱体及催化剂表征表明,沉淀母液在微波辐射条件下进行老化,溶剂的极性对前躯体物相组成及催化剂结构影响显著。随着溶剂极性的增大,Zn2+/Cu2+取代Cu2(CO3)(OH)2/Zn5(CO3)2(OH)6中Cu2+/Zn2+的取代反应增强,使得前躯体中(Cu,Zn)5(CO3)2(OH)6和(Cu,Zn)2(CO3)(OH)2物相的含量增多,结晶度提高,导致烧后CuO/ZnO/Al2O3催化剂中CuO-ZnO协同作用增强,且CuO晶粒减小,表面Cu含量增加,催化剂活性和稳定性提高。水溶剂的极性最大,制备的催化剂活性和稳定性最好,甲醇的时空收率(STY)和平均失活率分别为320 mg.g-1.h-1和0.11%.d-1。     

The role of anhydrous zinc nitrate in the thermal decomposition of the zinc hydroxy nitrates Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O

The steps associated with the thermal decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O and ZnOHNO₃·H₂O are re-examined. Previous reports have suggested that Zn₅(OH)₈(NO₃)₂·2H₂O decomposes to ZnO via two intermediates, Zn₅(OH)₈(NO₃)₂ and Zn₃(OH)₄(NO₃)₂ whereas ZnOHNO₃·H₂O has been reported to decompose to ZnO via a Zn₃(OH)₄(NO₃)₂ intermediate. In this study, we demonstrate using TG, mass spectral analysis of evolved gases and in situ variable temperature powder X-ray diffraction analysis that, in fact, in the decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O an anhydrous zinc nitrate intermediate is also involved. We, additionally, show that the decomposition of ZnOHNO₃·H₂O to ZnO also involves the formation of an anhydrous zinc nitrate intermediate. The anhydrous zinc nitrate formed in both cases is poorly crystallised and this observation may explain why this phase could not be observed by PXRD analysis in the previous studies.     

Doping-induced emission of infrared light from Co2+-doped ZnSe quantum dots

ZnSe quantum dots doped with Co²⁺ have been prepared in aqueous solution by a one-pot method using thioglycolic acid as stabilizer. The quantum dots were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV?Cvisible spectrophotometry, and spectrofluorimetry. The results confirmed the quantum dots formed a single cubic phase with zinc blende structure. The average particle size of the quantum dots was approximately 5 nm. Co²⁺ ions were doped into ZnSe lattice sites by substitution. As a result, infrared (IR) emission of Co^{2+ 4}T₂(F) ?? ⁴A₂(F) at approximately 3.5 ??m was detected on excitation with 755 nm radiation.     

An Effective Method to Construct Cluster‐based Frameworks with Multifarious Structures,Luminescence, and Sorption Properties

An effective method was developed for the synthesis of three cluster‐based frameworks with multifarious secondary building units (SBUs) and various structures, which were formulated as [Me₂NH₂]₂[Zn₁₀(BTC)₆(μ₃‐O)(μ₄‐O)(H₂O)₅] · 3DMA · 9H₂O ( FJI ‐ 3 ), [Me₂NH₂]₂[Zn₉(μ₃‐OH)₂(BTC)₆(H₂O)₃] · 5DMA · 6H₂O ( FJI ‐ 4 ) and [Me₂NH₂][Zn₃(μ₃‐OH)(BTC)₂DMF] · H₂O ( FJI ‐ 5 ) (H₃BTC = 1,3,5‐benzenetricarboxylic acid, DMA = N,N′‐dimethyl acetamide and DMF = N,N′‐dimethyl formamide), respectively. X‐ray structural analysis reveals that FJI ‐ 3 displays 3D highly porous metal‐organic framework with four kinds of microporous cages constructed by two paddle‐wheel Zn₂(CO₂)₄, trimeric Zn₃O(CO₂)₆, and tetrameric Zn₄O(CO₂)₆ SBUs. FJI ‐ 4 exhibits 3D microporous MOFs with a dodecahedral cavities built by paddle‐wheel Zn₂(CO₂)₄ and trimeric Zn₃O(CO₂)₆. FJI ‐ 5 shows 3D microporous MOFs with an 1D channel assembled by the Zn₃O(CO₂)₆ SBUs. In addition, the fluorescence and sorption properties in these cluster‐based frameworks were also investigated. Furthermore, the method employed in this work may provide an useful approach to the design and synthesis of novel cluster‐based frameworks.     

Pulse annealing electron paramagnetic resonance with probing transition ions

The analysis of the sequence of electron paramagnetic resonance (EPR) spectra of trace amounts of substitutional probing paramagnetic ions incorporated in (nano)crystalline samples submitted to isothermal and isochronal pulse annealing treatments can offer a wealth of information on the thermally induced compositional and structural changes of the host material. The potential of this new thermal analysis method is illustrated here with results of such investigations on the thermal decomposition of crystalline zinc hydroxide (Zn(OH)₂) and anhydrous zinc carbonate basic (Zn₅(CO₃)₂(OH)₆) precursors containing trace amounts of substitutional Mn²⁺ probing ions into nanostructured zinc oxide-ZnO. The quantitative analysis of the sequence of isochronal pulse annealing EPR spectra could provide, besides the thermal decomposition curves of the two precursors, additional information about the structure of the resulting nanostructured ZnO, some of it hard to get by standard structural diffraction techniques. The analysis of both isochronal and isothermal pulse annealing EPR data was further used to investigate the crystallization mechanism of the initially formed nanostructured disordered ZnO and to quantitatively describe the further growth of the resulting ZnO nanocrystals with the increasing annealing temperature and duration.     

Zur Thermodynamik der Metallcarbonate 3. Mitteilung [1]. Löslichkeitskonstanten und Freie Bildungsenthalpien von ZnCO3 und Zn5(OH)6(CO3)2 bei 25°

The solubilities of ZnCO₃ and Zn₅(OH)₆(CO₃)₂ have been investigated at 25°C in solutions of the constant ionic strength 0,2 M consisting primarily of sodium perchlorate. From experimental data the following values for equilibrium constants and GIBBS free energies of formation are deduced: A predominance area diagram for the ternary system Zn²⁺–H₂O–CO_2(g) including ZnO, ZnCO₃, Zn₅(OH)₆(CO₃₎₂, and Zn²⁺ is given.     

Structural Effects of Cu/Zn Substitution in the Malachite–Rosasite System

Synthetic zincian malachite samples (Cu_1–xZn_x)₂(OH)₂CO₃ with x = 0, 0.1, 0.2 and 0.3 were characterized by powder X‐ray diffraction and optical spectroscopy. The XRD patterns of the samples up to x = 0.2 indicate single phase materials with an approximately linear dependence of the refined lattice parameters on the zinc content. In contrast, the sample with a nominal zinc content x = 0.3 shows the formation of a small amount of aurichalcite (Zn,Cu)₅(OH)₆(CO₃)₂ as an additional phase. Based on the lattice parameter variations, the zinc content of the zincian malachite component in this sample is estimated to be x ≈? 0.27, which seems to represent the maximum possible substitution in zincian malachite under the synthesis conditions applied. The results are discussed in relation to preparation of Cu/ZnO catalysts and the crystal structures of the minerals malachite and rosasite. One striking difference between these two structurally closely related phases is the orientation of the Jahn–Teller elongated axes of the CuO₆ octahedra in the unit cell, which seems to be correlated with the placement of the monoclinic β angle. The structural and chemical relationship between these crystallographically distinct phases is discussed using a hypothetical intermediate Zn₂(OH)₂CO₃ phase of higher orthorhombic symmetry. In addition to the crystallographic analysis, optical spectroscopy proves to be a useful tool for estimation of the Cu:Zn ratio in (Cu_1–xZn_x)₂(OH)₂CO₃ samples.     

Basische Carbonate des Dysprosiums: Dy2O2(CO3) und Dy(OH)(CO3)

Basic Carbonates of Dysprosium: Dy₂O₂(CO₃) and Dy(OH)(CO₃) Single crystals of the basic carbonates Dy₂O₂(CO₃) and Dy(OH)(CO₃) are obtained via hydrothermal synthesis from a mixture of DyCl₃ · 6 H₂O and K₂CO₃ and Cs₂CO₃, respectively, as well as CO₂ and H₂O in a steel autoclave at 480 and 400 °C, respectively. The crystal structures are isotypic with those of II‐Nd₂O₂(CO₃) and B–Nd(OH)(CO₃), respectively; Dy₂O₂(CO₃): hexagonal, P6₃/mmc, Z = 2; a = 386.9(2), c = 1516.3(3) pm; Dy(OH) · (CO₃): hexagonal, P‐6, Z = 18; a = 1201.0(1), c = 971.8(9) pm.     

Syntheses, crystal structures, thermal stabilities and luminescence of six M(II)-hydroxyphosphonoacetate materials

Hydrothermal reactions of Zn^II, Ba^II or Co^II ion with 2-hydroxyphosphonoacetic acid (H₃L) afforded six metal phosphonates, namely, [Zn₅(O₃PCH(OH)CO₂)₄(C₆H₉N₂)₂] (1), [(C₄H₁₂N₂)Zn₅(O₃PCH(OH)CO₂)₄(H₂O)₂] (2), [(C₃H₁₂N₂)_0.5Zn₅(HO₃PCH(OH)CO₂)(O₃PCH(OH)CO₂)₃(H₂O)₂]·0.75H₂O (3), [BaZn₂(O₃P CH(OH)CO₂)₂] (4), [Ba(HO₃PCH(OH)CO₂)] (5) and [(NH₄)₂Co₇(HO₃PCH(OH) CO₂)₆(HPO₄)₂(H₂O)₆]·4H₂O (6). In 1, zinc tetrahedra ([ZnO₄]) and octahedra ([ZnO₅N], [ZnO₆]) are bridged by 2-hydroxyphosphonoacetate with penta- and hexadendate modes into a hybrid layer, which is further pillared by the 3-picolylamines to form a 3D structure through Zn-N bonds and hydrogen bondings. Both 2 and 3 are 3D framework encapsulating piperazine and 1,2-propanediamine cations, respectively. In solids 4-6, the cross-linkages of [ZnO₄], [BaO₁₀] and [CoO₆] polyhedral with 2-hydroxyphosphonoacetate form 3D frameworks. Solids 3 and 4 behave thermally stable up to 250 and 300 °C under air atmosphere, respectively. It is interesting that the peak emission of solid 3 displays a 10 nm red-shift after simple heat-treatment.     

Aluminum-calcium based three-component systems with addition of zinc and magnesium compounds for absorption of the hydrochloric acid vapor

To prepare granulated sorbents for absorption of the hydrochloric acid vapor, the formulations ZnO-CaO-Al(OH)₃, Zn₄CO₃(OH)₆-CaO-Al(OH)₃, and MgO-CaO-Al(OH)₃ with a 1: 1: 1 molar ratio of the oxides were studied. Mechanical processing of the mixtures leads to amorphization of compounds of the bivalent metals and to an increase in the size of gibbsite crystallites, accompanied by deformation of its crystal lattice. The composition of the chemisorbent has no effect on the number of basic surface centers, but determines the mechanical strength of grains and their absorbing capacity. The most promising formulation for preparing the chemisorbent is the Zn₄(CO₃(OH)₆-CaO-Al(OH)₃ system possessing the highest absorbing capacity for HCl vapor and retains its mechanical strength in tests.     

Effect of surface modification of zinc oxide on the electrochemical performances of [Ni4Al(OH)10]OH electrode

Surface modification of zinc oxide on the [Ni₄Al(OH)₁₀]OH has been performed by a chemical surface precipitation method. Inductively coupled plasma measurements show that the amount of ZnO of prepared samples increases with the increase of initial concentration of Zn²⁺ in the mother solution. Powder X-ray diffraction measurements and scanning electron microscope images show that the modification of ZnO has little effects on the lattice parameters and the particle sizes of the [Ni₄Al(OH)₁₀]OH, but does change the morphology. The charge–discharge cycles results show that the deterioration rate of discharge capacity for the electrode with ZnO is only 4.0 % after 255 cycles, which is lower than that of electrode without ZnO (8.5 %); meanwhile, the maximal numbers of exchanged electrons per nickel atom for the electrodes with ZnO are basically over 1.83, which are higher than that of the electrode without ZnO (1.73), indicating that the modification of ZnO can improve the utilization of active material. In addition, the cyclic voltammogram tests results show that the modification of ZnO not only improves electrochemical cyclic reversibility but also elevates the oxygen evolution potential. Electrochemical impedance spectroscopy measurements show that the modification of ZnO can lower the double layer capacitance and the charge transfer resistance.     

Mild solution synthesis of plate-like and rod-like ZnO crystals

Micro-disks and micro-rods of ZnO were successfully synthesized by a mild solution process using zinc chloride as starting material. The morphology of the ZnO crystals changed substantially, depending on the concentrations of the Zn²⁺ ion and organic additives in the solution. A plate-like Zn₅(OH)₈Cl₂·H₂O precursor with a layered structure could be produced in solutions with high concentrations of chloride ions. The thermal stability, including phase composition and morphology, of the as-prepared Zn₅(OH)₈Cl₂·H₂O in air and water was investigated.     

Effects of sodium dodecyl sulfate on the electrochemical behavior of supercapacitor electrode MnO2

Supercapacitor electrode material MnO₂ was prepared by liquid co-precipitation with different concentration of anionic surfactant sodium dodecyl sulfate (SDS). As evidenced by X-ray diffraction, the obtained MnO₂ are all typical amorphous α-MnO₂ with poor crystallinity. Scanning electron microscopy reveals that the dispersity of MnO₂ initially get better and then worse with the increase of SDS, and the particle sizes first become smaller then larger as well. It is worthwhile noting that the morphology of MnO₂ tested by transmission electron microscopy undergoes a changeable process: fibrous, pine needle like, cotton like, round bubble like, flocculent, and nervous tissue like as SDS increases. Through cyclic voltammetry and galvanostatic charge/discharge tests, SDS addition amount 0.2 g (0.017 mol L^?1) is found to be the optimal effect value, and the as-prepared Mn-0.2 obtains the highest specific capacitance (C _sp) of 154.5 F g^?1 at a current density of 500 mA g^?1. Compared with the sample Mn-0 synthesized without SDS, the C _sp increases by about 50 % (±5 %), which can be attributed to its largest Brunauer–Emmett–Teller–specific surface area of 255.9 m² g^?1, best particle dispersity, and smallest particle size of approximately 50–80 nm. Meanwhile, the rate capability and cycle stability of Mn-0.2 also improves obviously, and the equivalent series resistance decreases a lot, only 0.120 Ω.