The dumbbell- and flower-like Au−Fe3O4 heterostructures by thermal decomposition of the iron−oleate complex in the presence of Au nanoparticles (NPs) have been successfully fabricated using different sizes of Au NPs as the seeds for magnetically recyclable catalysis of p-nitrophenol and 2,4-dinitrophenol reduction. The heterostructures exhibit bifunctional properties with high magnetization and excellent catalytic activity toward nitrophenol reduction. The epitaxial linkages in dumbbell- and flower-like heterostructures are different, leading to the change in magnetic and catalytic properties of the heterostructured nanocatalysts. The pseudo-first-order rate constants for nitrophenol reduction are 0.63−0.72 min−1 and 0.38−0.46 min−1 for dumbbell- and flower-like Au−Fe3O4 heterostructures, respectively. In addition, the heterostructured nanocatalysts show good separation ability and reusability which can be repeatedly applied for nearly complete reduction of nitrophenols for at least six successive cycles. The reaction mechanism for nitrophenol reduction by Au−Fe3O4 nanocatalysts is also proposed and confirmed by XPS and FTIR analyses. These unique properties make Au−Fe3O4 heterostructures an ideal platform to study various heterogeneous catalytic processes which can be potentially applied in a wide variety of fields in purification, catalysis, sensing devices, and green chemistry.

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The application of nanoparticles in the processes of making commercial products has increased in recent years due to their unique physical and chemical properties. With increasing amount of commercial nanoparticles released into nature, their fate and effects on the ecosystem and human health are of growing concern. This study investigated the stability and morphology of three metal oxide nanoparticles in aqueous solutions. The commercially available nanoparticles, TiO(2), ZnO, SiO(2), aggregated quickly into micrometer-size particles in aqueous solutions, which may not threaten human health. Their changes in morphology and characteristics were further examined by dynamic light scattering (DLS) method and transmission electron microscopy (TEM). Among the several dispersion approaches, ultrasonication was found to be the most effective for disaggregating nanoparticles in water. For these three selected nanoparticles, ZnO could not remain stable in suspensions, presumably due to the dissolution of particles to form high concentration of ions, resulting in enhanced aggregation of particles. In addition, the existence of dissolved organic matters stabilized nanoparticles in lake water and wastewater for several hours in spite of the high concentration of cations in these real-water samples. The fate of metal oxide nanoparticles in natural water bodies would be determined by the type and concentration of cations and organic matters. Results obtained in this study revealed that the stability of nanoparticles changed under different aqueous conditions and so did their fate in the environment.

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Highly crystalline and surface-modified Zr-doped TiO(2) nanorods were successfully prepared using a nonhydrolytic sol-gel method that involves the condensation of metal halides with alkoxides in anhydrous trioctylphosphine oxide (TOPO) at either 320 or 400 degrees C. In addition, the interaction of the cross-condensation between the Ti and Zr species was studied by characterizing the morphologies, crystalline structures, chemical compositions, surface properties, and band gaps of the nanocrystals obtained at different reaction temperatures and Zr-to-Ti stoichiometric ratios. Increases in the concentration of Zr(4+) and in the reaction temperature led to large nanorods and regular shapes, respectively. In addition, only the anatase form was observed in the Zr-doped TiO(2) nanorods. The Zr-to-Ti ratios obtained ranged from 0.01 to 2.05, all of which were far below the stoichiometric ratios used during the preparation of the samples (0.25-4). Moreover, the Zr(4+) units accumulated mainly at the surface of the TiO(2) nanocrystals. The band gaps of the Zr-doped TiO(2) nanorods ranged from 2.8 to 3.8 eV, which are smaller than those of pure TiO(2) (3.7 eV) or ZrO(2) (5.2 eV). The Zr-doped anatase TiO(2) nanorods prepared at 400 degrees C at an initial stoichiometric Zr-to-Ti ratio of 2:3 exhibited the highest photoactivities for the decomposition of rhodamine B because of the presence of trace amounts of Zr(4+) (Zr/Ti = 0.03) in the TiO(2) and the regular shapes of these particles. DSC analysis indicated that the temperatures for forming nanocrystalline TiO(2) and ZrO(2) were 207 and 340 degrees C, respectively. Moreover, the reactivities of condensation between the Ti species were reduced when Zr species were involved in the NHSG reactions. The results obtained in this study clearly demonstrate that the faster kinetics for the generation of TiO(2) controls the material properties as well as the photoactivities of the nonhydrolytic sol-gel-derived nanocrystals.

The good stability, low cytotoxicity, and excellent photoluminescence property of graphene quantum dots (GQDs) make them an emerging class of promising materials in various application fields ranging from sensor to drug delivery. In the present work, the dopamine-functionalized GQDs (DA-GQDs) with stably bright blue fluorescence were successfully synthesized for low level Fe(3+) ions detection. The as-synthesized GQDs are uniform in size with narrow-distributed particle size of 4.5 ± 0.6 nm and high quantum yield of 10.2%. The amide linkage of GQDs with dopamine, confirmed by using XPS and FTIR spectra, results in the specific interaction between Fe(3+) and catechol moiety of dopamine at the interfaces for highly sensitive and selective detection of Fe(3+). A linear range of 20 nM to 2 μM with a detection limit of 7.6 nM is obtained for Fe(3+) detection by DA-GQDs. The selectivity of DA-GQDs sensing probe is significantly excellent in the presence of other interfering metal ions. In addition, the reaction mechanism for Fe(3+) detection based on the complexation and oxidation of dopamine has been proposed and validated. Results obtained in this study clearly demonstrate the superiority of surface functionalized GQDs to Fe(3+) detection, which can pave an avenue for the development of high performance and robust sensing probes for detection of metal ions and other organic metabolites in environmental and biomedical applications.

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