Preparation of pure ZnO nanoparticles by a simple solid-state reaction method

ZnO nanoparticles are synthesized by the one-step solid-state reaction using ZnSO₄·7H₂O and NaOH as the reagents. By adjusting the molar ratio of the reagents, the unwanted component Zn(OH)₂, which is the intermediate product of the reaction, can be fully removed in the final product, and the preparation of pure ZnO nanoparticles are achieved at room temperature. The X-ray diffraction pattern and transmission electron microscopic observations show that these nanoparticles are of hexagonal phase ZnO mostly in round shapes with a minority of rod shape with a mean grain size of about 40 nm. PACS  61.46.Df; 81.07.-b; 61.46.-w; 81.07.wx; 81.16.-c     

Effect of the reaction conditions on the formation of the ZnO nanostructures

ZnO nanorods were synthesized through a simple chemical method by reacting Zn(C₂H₃O₂)₂·2H₂O and NaOH at low temperature and the effects of changing the order of addition of reactants on the morphological evolution of ZnO nanorods were investigated. The samples were characterized by using XRD, SEM, EDX, TEM, BET and Raman techniques. Optical properties of the ZnO nanostructures were too investigated by UV–Vis spectroscopy at room temperature.The hexagonal wurtzite phase of ZnO was confirmed by X-ray diffraction (XRD) for all the samples. SEM and TEM analysis indicated that different morphologies were obtained by changing the order of addition of reactants.     

A Simple method to prepare multi-walled carbon nanotube/ZnO nanoparticle composites

A multi-wall carbon nanotube (MWCNT)/ZnO nanoparticle composite is fabricated by the thermal decomposition of a mixture of Zn(NH₃)₄CO₃, MWCNTs and polyvinyl pyrrolidone (PVP). From the infrared spectra of dried samples of Zn(NH₃)₄CO₃, PVP, and the mixture of Zn(NH₃)₄CO₃ and PVP, we show that there is a coordination interaction between the Zn of Zn(NH₃)₄CO₃ and the carbonyl of PVP. Thermal decomposition of the mixture of Zn(NH₃)₄CO₃ and PVP with MWCNTs results in the decomposition of Zn(NH₃)₄CO₃ to ZnO nanoparticles which are well-dispersed on the outer walls of the MWCNTs. The results show that PVP can be used to control the ZnO nanoparticle size and its dispersion on the MWCNTs walls during decomposition. This method is favorable for large scale synthesis. PACS 61.10.Nz; 61.46.Fg; 61.46.Df; 78.30.-j     

Growth mechanism of ZnO nanorod/Fe3O4 nanoparticle composites and their photocatalytic properties

ZnO nanorods/Fe₃O₄ nanocomposites as the recyclable photocatalyst were synthesized by a co-precipitation method, with microwave assistant by dropping alkaline solution with Fe₃O₄ nanoparticles into the aqueous of zinc salt. These Fe₃O₄ nanoparticles were the nucleated centers for the ZnO nanorods growth so that these nanorods ended with aggregated Fe₃O₄ nanoparticles. The growth processes and mechanism are explained as those insoluble zinc hydroxides prefer to nucleate on the surface of Fe₃O₄ nanoparticles (heterogeneous nucleation) rather than nucleated as isolated ZnO nanostructures (homogeneous nucleation). These nanocomposites have strong photocatalytic ability to reduce RhB and moderate magnetization, which make them being good recyclable photocatalysts.     

Synthesis of dimension-tunable ZnO nanostructures via the design of zinc hydroxide precursors

A facile synthesis route is presented to achieve dimension-tunable ZnO nanostructures by the design of zinc hydroxide precursors under the surfactant-free condition. From three types of zinc hydroxide precursors, namely, crystalline Zn(OH)(NO₃)(H₂O) nanobelts, amorphous zinc hydroxides microparticles and soluble Zn(OH)^2-₄\mathrm{Zn}(\mathrm{OH})^{2-}_{4} species, the porous ZnO nanosheets, ZnO nanoparticles and ZnO nanowires can be achieved, respectively. The porous ZnO nanosheets exhibit large polar surface area. Thermal analysis indicates that the crystalline Zn(OH)(NO₃)(H₂O) nanobelts were converted to the porous ZnO nanosheets by in situ lattice reconstruction, which was attributed to the unique fibrous structure of Zn(OH)(NO₃)(H₂O) nanobelts. The as-prepared dimension-tunable ZnO nanostructures have potential applications in solar cells, photocatalysis, novel chemical and biological sensors, etc.     

Micro-structural investigations and paramagnetic susceptibilities of zinc oxide, europium oxide and their nanocomposite

Nanoparticles of zinc oxide (ZnO), europium oxide (Eu₂O₃) and their nanocomposite system {(ZnO)_0.55(Eu₂O₃)_0.45} have been prepared by pyrophoric reaction and chemical co-precipitation methods. The precursor materials used for the synthesis were Zn(NO₃)₂·6H₂O and bulk Eu₂O₃. For nanocrystallization, the as-prepared samples were annealed at 500 and 600 °C for 6 h. The X-ray diffractograms (XRD) confirmed the formation of desired phases of the nanoparticles of ZnO, Eu₂O₃ and nanocomposite of {(ZnO)_0.55 (Eu₂O₃)_0.45}. Particle sizes of all the samples have been estimated from the width of the XRD peaks using the Debye-Scherrer equation. Particle sizes, crystallographic phases, etc. extracted from the high resolution transmission electron microscopy of a few selected samples are in agreement with those obtained from the XRD. Field emission scanning electron microscopy showed that ZnO nanoparticles are more-or-less spherical in shape. Average magnetic susceptibilities of all the annealed samples measured in the temperature range of 300-14 K indicate that all the samples including the zinc oxide, which is normally diamagnetic in the bulk state, are paramagnetic and the data are tried to analyze by the Curie-Weiss law. Photo-luminescence data recorded at room temperature of all the samples indicate that the optical property of the ZnO nanoparticles are not affected by Eu₂O₃ nanoparticles in the nanocomposite system though its bulk magnetization is substantially enhanced by incorporating the Eu₂O₃ nanoparticles.     

Studies of luminescence properties of ZnO and ZnO:Zn nanorods prepared by solution growth technique

Pyramidal ZnO nanorods with hexagonal structure having c-axis preferred orientation are grown over large area silica substrates by a simple aqueous solution growth technique. The as-grown nanorods were studied using XRD, SEM and UV-vis photoluminescence (PL) spectroscopy for their structural, morphological and optical properties, respectively. Further, the samples have also been annealed under different atmospheric conditions (air, O₂, N₂ and Zn) to study the defect formation in nanorods. The PL spectra of the as-grown nanorods show narrow-band excitonic emission at 3.03 eV and a broad-band deep-level emission (DLE) related to the defect centers at 2.24 eV. After some mild air annealing at 200 °C, fine structures with peaks having energy separation of ∼100 meV were observed in the DLE band and the same have been attributed to the longitudinal optical (LO) phonon-assisted transitions. However, the annealing of the samples under mild reducing atmospheres of N₂ or zinc at 550 °C resulted in significant modifications in the DLE band wherein high intensity green emission with two closely spaced peaks with maxima at 2.5 and 2.7 eV were observed which have been attributed to the V_O and Zn_i defect centers, respectively. The V-I characteristic of the ZnO:Zn nanorods shows enhancement in n-type conductivity compared to other samples. The studies thus suggest that the green emitting ZnO:Zn nanorods can be used as low voltage field emission display (FED) phosphors with nanometer scale resolution.     

ZnO nanoparticle creating in a SiO2/Si structure using the Zn ion implantation with subsequent heat treatment

The distribution profiles of the dopant in the surface layer of a SiO₂/Si structure implanted with Zn and O ions are studied via Rutherford backscattering spectroscopy for He²⁺ ions using the channeling technique. The redistribution of implanted impurities in the Si surface layer during the formation process of zinc oxide (ZnO) nanoparticles is analyzed. The effect of the annealing temperature on the formation process and growth of ZnO nanoparticles is studied. The sample-surface morphology is examined via atomic force microscopy. The optical absorption and photoluminescence of the implanted layers are studied.     

Two-step synthesis and characterization of ZnO nanoparticles

A novel two-step procedure has been employed for the synthesis of ZnO nanoparticles: (1) mechanochemical synthesis of ZnC₂O₄2H₂O nanoparticles by grinding a mixture of zinc acetate and oxalic acid in an agate mortar at 27 °C and (2) thermal decomposition of ZnC₂O₄2H₂O nanoparticles at 400 °C to form ZnO nanoparticles. XRD and FESEM characterize the final product as highly crystalline ZnO with wurtzite structure and crystallite sizes in the range 5–20 nm. FTIR and EPR are used to identify molecular species during thermal decomposition and impurity/defect status of the ZnO powder respectively.     

Controllable synthesis and shape-dependent photocatalytic activity of ZnO nanorods with a cone and different aspect ratios and of short-and-fat ZnO microrods by varying the reaction temperature and time

ZnO nanorods with a cone and different aspect ratios and short-and-fat ZnO microrods were synthesized via a hydrothermal reaction of Zn with Zn(CH₃COO)₂ and H₂O. The control over these ZnO nanocrystals with a wurtzite structure and different shapes was achieved by adjusting only the reaction temperature and time. A possible kinetic mechanism was proposed to account for the growth of these ZnO nanocrystals with different shapes. Photocatalytic activities of ZnO nanocrystals with distinctive shapes in the degradation of methyl orange were investigated. The results indicate that the photocatalytic ability of the ZnO nanorods with a cone and different aspect ratios is stronger than that of the short-and-fat microrods.     

Selective Synthesis of Wurtzite CdSe Nanorods and Zinc Blend CdSe Nanocrystals through a Convenient Solvothermal Route

By simply changing the reactants’ compositions, wurtzite CdSe nanorods and zinc blend CdSe nanoparticles were selectively synthesized through a convenient solvothermal route with the reaction of cadmium nitrate (Cd(NO₃)₂· 4H₂O), hydrazine hydrate (N₂H₄· H₂O), and Se in ethylenediamine (en) at 140°C. Effects of temperature and composition of the reactants were detected and the amount and gaining rate of Se²⁻ ions were found to determine the morphology and structure of the final product. Dong Wu and Guo-Qiao Lai contributed equally to this paper     

CdSe nanocrystals in novel phosphate glass matrix

The CdSe nanoparticles have been prepared in the novel glass matrix P₂O₅–Na₂O–ZnO–Li₂O. The prepared nanoparticles and glass matrix are characterized by differential thermal analysis, X-rays diffraction, UV–vis optical absorption, and infrared spectroscopy. X-rays diffraction and optical absorption show that both of the annealing temperature and time play an important role in nanoparticles’ growth. The well-annealed and high-temperature-annealed samples suggest Zn atoms to substitute Cd atoms to form an additional ZnSe–CdSe system. Infrared spectroscopy confirms the decrease of the Zn-content in the host glass due to growing of nanoparticles, causing long phosphate chains within.     

ZnO/cubic (Mg,Zn)O radial nanowire heterostructures

The formation and properties of radial heteroepitaxial ZnO/(Mg,Zn)O nanowires is reported in which the (Mg,Zn)O is cubic. Synthesis is achieved via a catalyst-driven molecular beam epitaxy technique. The nanowires were grown on Ag-coated Si substrates at growth temperatures ranging from T_g=300 to 500 °C, using Zn, Mg, and O₃/O₂ as the reactive flux. Structural and compositional analyses indicate that the core of the nanowire is ZnO possessing the hexagonal wurtzite structure, with the (Mg,Zn)O sheath assuming the cubic rock salt structure. Since (Mg,Zn)O has a larger band-gap energy (up to 7.8 eV) than that of ZnO (3.37 eV), these radial heterostructure nanorods provide an interesting system for quantum confinement and one-dimensional nanoscale device studies. PACS 81.05.Dz; 81.07.Vb     

Sonochemical synthesis and characterization of three nano zinc(II) coordination polymers; Precursors for preparation of zinc(II) oxide nanoparticles

Nanostructures of three Zinc(II) coordination polymers, [Zn(NNO)₂(H₂O)₄]_n (1), [Zn(PNNO)₂(H₂O)₂]_n (2) and [Zn(H₂O)₆]·(INNO)₂ (3) {NNO: Nicotinic acid N-oxide, PNNO: Picolinic acid N-oxide and INNO: Isonicotinic acid N-oxide}, have been synthesized by a sonochemical process and reaction of ligands with Zn(CH₃COO)₂. The Zinc(II) oxide nano-particles have been synthesized from thermolysis of [Zn(NNO)₂(H₂O)₄]_n (1), [Zn(PNNO)₂(H₂O)₂]_n (2) and [Zn(H₂O)₆]·(INNO)₂ (3) at two different methods (with surfactant and without surfactant) and two temperatures (200 and 600 °C). The ZnO nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Comparison of the SEM images of ZnO nano-particles at two different methods and temperatures shows that higher temperature results in an increasing of agglomeration and thus small and spherical ZnO particles with good separation were produced by thermolysis of compounds at 200 °C and by use of surfactant.     

水热法合成ZnO纳米棒图案及其场增强效应

利用水热合成方法在图案化的Au岛上合成了ZnO纳米棒图案,采用的溶液体系为六次甲基四胺和硝酸锌溶液,ZnO纳米棒的基底是ITO导电玻璃上的有序Au岛. 由于ZnO的异相成核速度在Au和ITO基底上具有不同的成核速度,因此ZnO优先生长在成核速度快的Au岛上,同时由于受到了溶液中前驱物种扩散的限制,纳米棒继续生长也被受到了约束. 通过调控六次甲基四胺和硝酸锌的浓度,可以调整不同的图案. 此外,利用X射线衍射、光致发光谱和场发射特性性能对水热合成的ZnO纳米棒图案进行了研究. ZnO纳米棒表现出良好的场增强性     

Nanoporous ZnO nanostructures for photocatalytic degradation of organic pollutants

ZnO porous bamboo-leave-like nanorods and nanoporous networks were prepared by thermal conversion from Zn₂CO₃(OH)₂?H₂O bamboo-leave-like nanorods, Zn(OH)₂ nanoparticle networks and Zn(OH)₂ long nanostrand networks, respectively. Among them, the ZnO nanoporous networks prepared from Zn(OH)₂ nanostrands had the highest surface area of 78.57 m²/g and presented the best photocatalytic decomposition of organics. The morphologies of the Zn(OH)₂ nanostructures significantly depended on the solvent used for the precursors of aminoethanol and Zn(NO₃)₂ and then determined the corresponding structures and properties of the final ZnO nanostructures. The ethanol/water mixture solvent dramatically increased the stability of Zn(OH)₂ nanostrands. This is very beneficial for the collection and application of Zn(OH)₂ nanostrands.     

Characterizations of octahedral zinc oxide synthesized by sonochemical method

The ultrasonic reaction of zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (C₆H₁₂N₄) was investigated by varying the concentration of the reactants, the irradiation time, and the type of sonicator. The morphology, composition, and phase structure of the products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopy. Octahedral zinc oxide (ZnO) micropowders were formed at low concentrations, 0.05 M, of Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ in both lab-made sonicator and commercial ultrasonic bath. However, at concentrations between 0.1 and 1.0 M Zn(NO₃)₂-C₆H₁₂N₄ mainly plate-like zinc hydroxide nitrate hydrate (Zn₅(OH)₈(NO₃)₂(H₂O)₂) resulted with only a small fraction of ZnO, irrespective of the irradiation time employed, highlighting the sensitivity of the system to the concentration of the starting materials. Heat treatment of Zn₅(OH)₈(NO₃)₂(H₂O)₂ at 350 °C in air affords a ZnO phase of irregular morphology. Octahedral ZnO is found to exhibit slightly lower IR absorption and similar UV absorption to that of commercial prismatic hexagonal ZnO, although an extra peak due to small quantities of Zn₅(OH)₈(NO₃)₂(H₂O)₂ is observed.     

Hydrothermal growth of ZnO on annealed electrodeposited titanate film: Influence of zinc nitrate and methenamine

Hydrothermal growth of hexagonal ZnO nanorods on the annealed titanate nanotube films is reported as a function of molar ratio of Zn(NO₃)₂ and methenamine (1:1-1:4). The molar ratio of 1:4 results in a dense and thinner rod in comparison with other molar ratios. Corn-like structures of the rods are believed to be due to the higher amine concentration. Raman peaks at 437 and 331 cm⁻¹ are assigned to E₂ and E_2H-E_2L modes. Near band gap edge and green photoluminescence emission indicates the structural and oxygen vacancy. O 1s peak is found built-up of sub-peaks at 530.62, 531.8 and 532.84 eV corresponding to O²⁻ on normal wurtzite structure and OH and oxygen vacancies of ZnO, respectively.     

Structural and photoluminescence properties of ZnO nanoparticles on silicon oxide

Isolated, self assembled ZnO nanoparticles are grown in two steps: by the electron beam evaporation of Zn on oxidised silicon wafers, during which isolated Zn nanodots are grown, and a subsequent annealing in oxygen that results in the desired ZnO nanodots. Low temperature PL measurements of the ZnO nanodots show that the near band edge part of the spectra is dominated by a zero phonon line near 3.36 eV which is an overlap of two emitting lines near 3.363 eV and 3.367 eV. Characterization by TEM and EELS shows that the nanoparticles are zinc oxide single crystals grown with their c-axis perpendicular to the substrate; their distribution, size and crystallinity depend on the deposition parameters of zinc and the growth substrate. We discuss the effect of these parameters on the morphology of the resulting material. Our approach demonstrates a simple method for the growth of high purity isolated ZnO nanodots of similar sizes, distributed uniformly on a large surface. PACS 61.46.Df; 81.05.Dz; 81.07.-b     

Hydrothermal synthesis and photocatalytic properties of WO3 nanorods by using capping agent SnCl4·5H2O

Hexagonal tungsten trioxide (h-WO₃) nano-rods of different sizes are prepared via hydrothermal synthesis using a capping agent of SnCl₄·5H₂O. The size of the synthesized WO₃ nanoparticles can be controlled by changing concentration of the capping agent SnCl₄·5H₂O alone. We also investigate microstructures and optical properties of the WO₃ nanorods and propose a synthesis mechanism for the nanorods. The photocatalytic activities of the h-WO₃ nanorods are evaluated by degradation of Rhodamine-B (RhB), revealing that these nanorods exhibit excellent photocatalytic properties. The capping agent SnCl₄·5H₂O is found to be critical to governing sizes and properties of the h-WO₃ nanorods. Our results demonstrate that functional nano-crystallites with tunable size and morphology can be synthesized via a facile hydrothermal synthesis process by adjusting the concentration of capping agent alone. Such a facile hydrothermal synthesis process should be applicable to other types of nanomaterials and relevant to a wide range of applications.