Zorica Crnjak Orel

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.

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.

Polyol-mediated synthesis of zinc oxide nanorods and nanocomposites with poly(methyl methacrylate)

ZnO nanorods (length 30-150 nm) were synthesized in di(ethylene glycol) using Zn(CH3COO)2 as a precursor and para-toluene sulphonic acid, p-TSA, as an end-capping agent. Increasing the concentration of p-TSA above 0.1M causes the reduction of the ZnO length. Nanocomposites with poly(methyl methacrylate) were prepared using unmodified nanorods. They enhanced the UV absorption of nanocomposites (∼98%) at low ZnO concentrations (0.05-0.1wt.%), while visible light transparency was high. At concentrations of 1wt.% and above, nanorods enhanced the thermal stability of nanocomposites. At low concentrations (0.05- 0.1wt.%), they increased the storage modulus of material and shifted Tg towards higher temperatures as shown by dynamic mechanical analysis, DMA, while at higher concentrations (1.0wt.%) this effect was deteriorated. DMA also showed that spherical ZnO particles have a more pronounced effect on the storage modulus and Tg than nanorods.

Nanocrystalline hybrid inorganic–organic one-dimensional chain systems tailored with 2- and 3-phenyl ring monocarboxylic acids

Two novel nanosized hybrid inorganic–organic frameworks, VO(C14H9COO)2, and VO(C10H7COO)2 have been solvothermally synthesized and their structures elucidated using a combination of powder XRD and DFT geometry optimization. They contain one-dimensional chains of corner-sharing tetrahedra in the case of VO(C10H7COO)2, and corner-sharing octahedra for VO(C14H9COO)2 oriented along orthorhombic/monoclinic c-axis, respectively. While VO(C14H9COO)2 exhibits bidentate bridging binding of organic moiety to the metal center, VO(C10H7COO)2 shows a monodentate mode as evidenced from DFT and infrared spectroscopy. Both hybrids exhibit fiber-like morphology, consisting of smaller individual single crystals aligned in parallel to the growth direction along the c-axis. They are thermally stable up to 350 °C having even more stable impurities containing vanadium in its highest oxidation state. The magnetic properties have also been investigated and indicate antiferromagnetic ordering along the chains characterized by rather low spin exchange parameters.

Poly(zinc dimethacrylate) as a precursor in the low-temperature formation of ZnO nanoparticles.

We present a simple, low-temperature synthesis of pure ZnO nanoparticles and polymer-ZnO hybrid materials formed by the NaOH-mediated conversion of poly(zinc dimethacrylate) in 1-butanol. The polymer poly(zinc dimethacrylate) was used as a precursor to prepare neat ZnO particles. It has a double role in the ZnO formation process, acting as a template and simultaneously controlling the crystal growth. The obtained single-crystalline ZnO nanorods show a low tendency to aggregate. The reaction mechanism of ZnO formation was proposed on the basis of a model system of the base-mediated conversion of a monomer zinc dimethacrylate Zn(MA)(2).