Nanostructured Colloidal Crystals from Forced Hydrolysis Methods (original) (raw)
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Optimum between purification and colloidal stability of ZnO nanoparticles
Advanced Powder Technology, 2010
Crystalline ZnO quantum dots have been synthesized by hydrolysis of zinc acetate dihydrate with lithium hydroxide in ethanolic solution. By varying different parameters of the synthesis process, the size of the ZnO particles can be controlled. Detailed investigation of the ripening of the nanoparticles evidenced that despite of the well-known influence of ageing temperature and time, the presence of the reaction byproduct lithium acetate strongly affects the ripening behaviour. In particular, the particle size can be almost completely arrested by the removal of this byproduct via reversible flocculation of the ZnO nanoparticles using heptane as an antisolvent. A closer analysis of the repeated washing process shows an initial improvement of the colloidal stability of the ZnO nanoparticles during the first purification cycle as it mainly removes the lithium acetate from the suspension and not the stabilizing acetate groups directly bound to the particle surface. With further washing the remaining acetate ligands are unable to maintain the stabilization against agglomeration of the ZnO nanoparticles. Thus, there exists an optimum between purification progress and colloidal stability. These findings are also confirmed by calculations according to the DLVO theory, which show that there exists nearly no primary minimum of small ZnO nanoparticles below 5 nm in the presence of stabilizing acetate ions whereas the decrease in acetate ions bound to the particle surface leads to a more and more pronounced primary minimum. The present work is of particular significance for the preparation of purified colloidal ZnO nanoparticles for studies of their electrical and optical properties with respect to their wide range of potential applications.
ZnO Inverse Opals Using Colloidal-Crystal Template Assisted Hydrothermal Method
Proceedings of the 4th 2016 International Conference on Material Science and Engineering (ICMSE 2016), 2016
Both two-dimensional (2D) ZnO nanobowl arrays and three-dimensional (3D) ZnO inverse opals were fabricated using hydrothermal method with assistance of the three-dimensional colloidal crystal templates. Scanning electron microscope measurements showed the morphological evolutions of ZnO from rods to 2D monolayer nanobowl arrays and 3D porous films by controlling the concentration of hydrothermal solutions and reaction time. The photonic stop b and was characterized using reflections spectra presenting the 3D periodic geometry. The photoluminescence spectra indicate good crystalline quality via the hydrothermal route.
ZnO/Liquid Crystalline Nanohybrids: From Properties in Solution to Anisotropic Growth
Chemistry - A European Journal, 2012
Over the past decade, composites based on the dispersion of nanoparticles (NPs) in liquid crystals have been of growing interest. The driving force of research in this field is the possible development of new materials or devices with multiple or improved properties. Indeed, NPs may influence the state or the surface anchoring of doped LCs. The electro-optical behavior of LC/NP systems may then be adjusted by changing the NP content. Conversely, the properties of the nanomaterial may be modified and even controlled by the LC matrix. Achieving such a goal often requires functionalization of NPs with LC moieties to improve compatibility between NPs and LC or to obtain new LC nanohybrids. Indeed, LC hybrids involving gold, cobalt, cadmium selenide or cadmium telluride, and iron oxide NPs have been described. In a previous article we reported the first successful hybridization of small-sized ZnO NPs with a mesogenic molecule. Due to the presence of fluxional ligands, the hybridized material presented mesomorphic behavior even with a high content of inorganic material. However, the fluxionality of these ligands at the surface of the NP may hinder their application due to the presence of excess free ligands present in solution. In addition, in most cases these hybrids were obtained in a two-step process. Recently, branched capping agents have attracted special interest in the field of nanohybrids due to their effective stabilization properties for ZnO nanoparticles in polar and non-polar solvents. These stabilizers are characterized by their threedimensional molecular shapes; they also have low mobility at the NP surface and present a large number of functional end groups, which makes them easy to tailor for end-user purposes.
Superlattices and Microstructures, 2015
ABSTRACT ZnO colloidal spheres were prepared using a simple surfactant mediated approach via a two-stage reaction process, involving the synthesis of nanoparticles and the assembly of the nanoparticles to obtain nanospheres. The present work pointed out a simple and ‘green’ way of converting ZnO nanoparticles into ZnO nanospheres. The structural properties and the crystalline phase of the synthesized nanospheres were characterized by transmission electron microscopy (TEM), scanning electronic microscopy (SEM), and powder X-ray diffraction (XRD). The morphology of the colloidal ZnO nanosphere observed at high resolution showed a nanocrystalline substructure, and XRD indicated the hexagonal phase of zinc oxide with a high purity. The dielectric properties were studied over a frequency range of 1 Hz–1 MHz at room temperature, and in the framework of complex dielectric permittivity and complex electric modulus formalisms. The evolution of the complex dielectric permittivity as a function of frequency at room temperature was investigated.
European Journal of Inorganic Chemistry, 2009
A facile and reproducible route to nanostructured colloidal ZnO nanoparticles was developed by controlled hydrolysis and condensation of zinc acetylacetonate in alkaline conditions. By reaction of an ethanolic solution of Zn(acac) 2 with NaOH in a 1:2 molar ratio, after reflux, ZnO spherical nanoparticles were obtained that displayed a homogeneous size distribution; particle diameters ranged from 6 to 10 nm, as evidenced by transmission electron microscopy (TEM) analysis. The same reaction was carried out also in water, glycerol and 1,2-propanediol, to investigate the effect of the solvent viscosity and dielectric constant on the final features of the obtained material. Irrespective of the nature of the solvent, X-ray diffraction (XRD) analysis shows the formation of hexagonal ZnO, whereas the presence of residual unreacted Zn(acac) 2 could be ruled out. Indeed, different particle sizes and very different morphologies were obtained. Also the reflux step was shown to be a key factor in avoiding the fast precipitation of a floc and achieving a pure compound, which
ZnO nanoparticles synthesized by co-precipitation method; Morphology and optoelectronic study
2021
In this study, zinc oxide (ZnO) nanoparticles (NPs) were first synthesized using the co-precipitation method at the presence of Zn(NO3)2.6H2O precursor and calcined at 450 °C and 1000 °C. Then, the samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). The XRD analysis was performed to evaluate the crystal structure. SEM and TEM analyses were also conducted to assess the morphology and the particle size of the material. Finally, the chemical compositions of the samples were investigated by energy dispersive x-rays (EDX) analyses. In this work, the crystallite Polygon shape ZnO NPs were fabricated in the range of 70-100 nm. We found that the intensity of the crystal plane of (002) increased by raising the temperature to 1000 °C.
Advanced Materials Research, 2013
Intensive and innovative research is focused on the preparation of various nanostructured materials especially nanostructured metal oxides as applicable to number of applications.The present work mainly emphasis a single step synthesis of ZnO nanoparticles by employing surfactant free forced condensation method. Surface morphology of the sample was precisely controlled by varying the calcination conditions. Investigation on the structure, surface and composition of ZnO nanoparticles is of both fundamental interest and technological importance. X-ray diffraction (XRD) analysis reviled that the ZnO nanoparticles exhibits crystalline with the preferential orientation along (1 0 0) plane. SEM image shows the nanoparticles are in the range of 75 to 150 nm with spherical shape. The room temperature PL spectra of ZnO particles exhibited strong ultraviolet photoluminescence around 380 nm at room temperature.
Journal of Nanomaterials, 2014
Flower-like bundles of ZnO nanosheets have been prepared by using preheating hydrothermal process without any surfactants. The flower-like bundles consist of many thin and uniform hexagonal-structured ZnO nanosheets, with a thickness of 50 nm. The selected area electronic diffraction (SAED) and high-resolution transmission electron microscope (HRTEM) images indicate that the ZnO nanosheets are single crystal in nature. The growth mechanism of the flower-like bundles of ZnO nanosheets is discussed based on the morphology evolution with growth times and reaction conditions. It is believed that the formation of flower-like bundles of ZnO nanosheets is related to the shielding effect of OH−ions and the self-assembly process, which is dominated by a preheating time. Room temperature photoluminescence spectra results show that the annealing atmosphere strongly affects the visible emission band, which is sensitive to intrinsic and surface defects, especially oxygen interstitials, in flower...