Low Cost, Fast Solution Synthesis of 3D Framework ZnO Nanosponges.

An efficient, template-free solution-chemical route to nanostructured ZnO sponges is presented: A mixture of Zn(NO3)2·6H2O, Zn(OAc)2·2H2O, and triethanolamine in methanol was evaporated to a highly viscous liquid and rapidly heated to >200 °C for 1-3 min to achieve highly porous, nanocrystalline sponges of ZnO. The viscous precursor concentrate obtained on evaporation in air was characterized by TG, DSC, and IR spectroscopy, and the product ZnO sponges by XRD, SEM, TEM, and IR spectroscopy. The fast reaction forming ZnO started at 140 °C and finished within a few seconds. Scherrer analysis of the XRD peak broadening showed average crystallite sizes of 8 to 11 nm for ZnO prepared by annealing at 200-450 °C (3 min), while grain growth to 134 nm was observed from 500 to 900 °C (3 min). The ZnO powders obtained at 200-900 °C had cell dimensions of a = 3.25 Å and b = 5.21 Å, matching the ZnO literature data well. SEM and TEM analyses showed highly porous, bread-like 3D nanostructures built by ca. 30-70 nm thick walls of ZnO crystallites of the approximate average sizes given by the XRD Scherrer analysis. It seems that the crystal growth above 450 °C takes place within the ZnO 3D structure obtained at lower temperatures without much sintering of the larger porous structure.

In situ and ex situ TEOS coating of ZnO nanoparticles and the preparation of composite ZnO/PMMA for UV-VIS absorbers.

ZnO nanoparticles were prepared in a typical single-step experimental procedure, in different water-to-ethylene glycol volume ratios at a moderate temperature. Morphological studies performed by SEM and TEM have revealed two different types of nanosized particles: hexagonal facetted nanoparticles and spherical ones. The obtained ZnO nanoparticles were further coated with the coupling reagent tetraethyl orthosilicate (TEOS), in situ and ex situ. The thickness of the silica layer around the ZnO nanoparticles varied between 4 and 18 nm. The coated as well as the bare ZnO nanoparticles were thoroughly characterized by different characterization methods. They were also incorporated into poly-methylmethacrylate (PMMA). The obtained PMMA/ZnO nanocomposites showed relatively high transmittance for visible light but also relatively high absorbance in the UV region between 250-370 nm.

A critical assessment of the specific role of microwave irradiation in the synthesis of ZnO micro- and nanostructured materials.

A rapid, microwave-assisted hydrothermal method has been developed to access ultrafine ZnO hexagonal microrods of about 3-4 µm in length and 200-300 nm in width by using a 1:5 zinc nitrate/urea precursor system. The size and morphology of these ZnO materials can be influenced by subtle changes in precursor concentration, solvent system, and reaction temperature. Optimized conditions involve the use of a 1:3 water/ethylene glycol solvent system and 10 min microwave heating at 150 °C in a dedicated single-mode microwave reactor with internal temperature control. Carefully executed control experiments ensuring identical heating and cooling profiles, stirring rates, and reactor geometries have demonstrated that for these preparations of ZnO microrods no differences between conventional and microwave dielectric heating are observed. The resulting ZnO microrods exhibited the same crystal phase, primary crystallite size, shape, and size distribution regardless of the heating mode. Similar results were obtained for the ultrafast preparation of ZnO nanoparticles with diameters of approximately 20 nm, synthesized by means of a nonaqueous sol-gel process at 200 °C from a Zn(acac)(2) (acac=acetylacetonate) precursor in benzyl alcohol. The specific role of microwave irradiation in enhancing these nanomaterial syntheses can thus be attributed to a purely thermal effect as a result of higher reaction temperatures, more rapid heating, and a better control of process parameters.

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)(OH(2))(4)](0) and [Zn(OH)(HCO(3))(OH(2))(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.

Morphology and particle size of di(ethylene glycol) mediated metallic copper nanoparticles.

Cu nanoparticles were prepared in di(ethylene glycol) by a reduction reaction of Cu (II) acetate precursor to metallic Cu. The size and morphology of the synthesized particles were studied in dependence of the concentration of the starting compound and the temperature conditions of reaction were varied to determine the correlation with the size and morphology of the synthesized particles. The morphology and size of the resulting copper (I) oxide as an intermediate product and metallic Cu particles as a final product are strongly dependent on the concentration of the starting compound, thus indicating differences in the mechanism of the reduction reaction and, consequently, the mechanism of particle formation. At low concentrations (0.01 and 0.1 mol/L), an organo-metallic copper complex intermediate forms crystalline 10-100 nm thick and up to 10 microm long nanowires organized in dendritic spheres with a diameter of 5-50 microm, which further transform into Cu2O. Cu-di(ethylene glycolate) complex has an as yet undescribed crystalline structure. At a high precursor concentration (1 mol/L), the intermediate forms partly amorphous and partly crystalline Cu20. The reduction of Cu2O to metallic Cu takes place between 190-200 degrees C. The smallest average particle size (100 nm) and the narrowest particle size distribution was obtained at a Cu (II) acetate concentration of 0.1 mol/L.

Amino- and ionic liquid-functionalised nanocrystalline ZnO via silane anchoring - an antimicrobial synergy.

The synthesis of highly antimicrobial nanocrystalline zinc oxide and its covalent modifications are presented. In order to achieve further improvement of antimicrobial activity, the surface of ZnO was effectively modified with selected silanes comprising amino- and ionic liquid-functionalities. We demonstrate for the first time ionic liquid surface immobilization on ZnO and the application of this hybrid material for antimicrobial purposes. Different microscopic and spectroscopic techniques as well as size, surface and elemental composition analyses were employed to prove these modifications. Characterization revealed that surface and antimicrobial properties strongly depend on the modification employed. Most of the amino- and ionic liquid-functionalised nanocrystalline ZnO exhibited improved antimicrobial activity compared to commercially available silane-containing antimicrobial agents attached to nanocrystalline ZnO. Bacterial growth reduction was assessed by following the optical density of bacterial growth with different concentrations of the novel antimicrobial nanomaterials. Complete bacterial inactivation was achieved for specific amino- and ionic liquid-modifications at 0.125 g L-1, revealing the synergistic effect of ZnO and its modifications, exhibiting up to 2-fold improvement compared to unmodified ZnO.

Morphological impact of zinc oxide particles on the antibacterial activity and human epithelia toxicity.

ZnO nanoparticles are utilized in an ever growing number of products and can, therefore, be readily encountered in our everyday life. Human beings' outermost tissues consist of different epithelia and are, therefore, the most exposed to materials from the environment. In this paper, Caco-2 and Calu-3 cell lines were used, having been previously broadly applied for in vitro modelling of intestinal and respiratory epithelia, respectively. The toxicity of synthesized micro-, submicro- and nanoparticulate ZnO on these epithelia was measured and compared to the efficacy of the same ZnO particles as antibacterial agents. An approximately four-fold excess in antibacterial activity of ZnO nanoparticles over ZnO granulate was observed. The results of this paper reveal a sharp distinction between toxic nanoparticulate ZnO and safe ZnO particles of larger sizes in intestinal and airway in vitro epithelial models. In contrast, ZnO of larger particle sizes had only modestly lower antibacterial activity, which can be compensated for with higher dosing. These results show that nanoparticulate ZnO requires critical in vivo assessment before application.

Interplay between the structural and magnetic probes in the elucidation of the structure of a novel 2D layered [V4O4(OH)2(O2CC6H4CO2)4]·DMF.

The title compound has been synthesized under solvothermal conditions by reacting vanadium(V) oxytriisopropoxide with terephthalic acid in N,N-dimethylformamide. A combination of synchrotron powder diffraction, infrared spectroscopy, scanning and transmission electron microscopy, and thermal and chemical analysis elucidated the chemical, structural and microstructural features of a new 2D layered inorganic-organic framework. Due to the low-crystallinity of the final material, its crystal structure has been solved from synchrotron X-ray powder diffraction data using a direct space global optimization technique and subsequent constraint Rietveld refinement. [V(4)O(4)(OH)(2)(O(2)CC(6)H(4)CO(2))(4)]·DMF crystallizes in the monoclinic system (space group P2/m (No. 10)); cell parameters: a = 20.923(4) Å, b = 5.963(4) Å, c = 20.425(1) Å, ß = 123.70(6)°, V = 2120.1(9) Å(3), Z = 2. The overall structure can be described as an array of parallel 2D layers running along [-101] direction, consisting of two types of vanadium oxidation states and coordination polyhedra: face-shared trigonal prisms (V(4+)) and distorted corner-shared square pyramids (V(5+)). Both configurations form independent parallel chains oriented along the 2-fold symmetry crystallographic b-axis mutually interlinked with terephthalate ligands in a monodentate mode perpendicular to it. The morphology of the compound exhibits long nanofibers, with the growth direction along the layered [-101] axis. The magnetic susceptibility measurements show that the magnetic properties of [V(4)O(4)(OH)(2)(O(2)CC(6)H(4)CO(2))(4)]·DMF can be described by a linear antiferromagnetic chain model, with the isotropic exchange interaction of J = -75 K between the nearest V(4+) neighbours of S = 1/2.

The synthesis of zinc oxide nanoparticles from zinc acetylacetonate hydrate and 1-butanol or isobutanol.

ZnO nanoparticles of different sizes, from 20 to 200 nm in length, and morphologies, nanorods and coral-like structures, were synthesized via a simple one-pot synthesis by refluxing an oversaturated solution of zinc acetylacetonate hydrate in 1-butanol and isobutanol. On the basis of (1)H and (13)C NMR experiments, the reactions in both alcohols were found to proceed via the alcoholytic C-C cleavage of the acetylacetonate ligand, followed by the hydrolytic formation of the reactive Zn-OH intermediate from the water molecules present in the precursor hydrate species and/or those released during the condensation cycle. The zinc acetylacetonate conversion into ZnO in isobutanol is significantly slower than in the case when 1-butanol was used as both the medium and the reagent. FE-SEM studies showed that in 1-butanol the growth of the rod-shaped particles occurs via the agglomeration of ZnO primary particles that are less than 10 nm in size. The morphology of the particles formed in the isobutanol is time dependent, with the final coral-like structures developing from initially formed bundle-like structures.