A simple solution-based method to prepare mainly flowerlike zinc oxide (ZnO) nanostructures using the ascorbate ion as a shape-directing/capping agent at relatively low temperature (ca. 30 and 60 degrees C) was described. However, we observed that different shapes of hierarchical ZnO nanostructures such as flowerlike, spindlelike, and spherical could be obtained with an increase in the synthesis temperature from 60 to 90 degrees C. The effects of other organic capping agents on the shape of hierarchical ZnO nanostructures were also studied. FTIR, FESEM, and XRD characterization were performed on the formed ZnO nanostructures to understand the role of ascorbate in the growth of flowerlike morphology. The nucleation and growth process can regulate by changing the metal precursor and ascorbate ion concentrations. We were able to identify intermediate nanostructures such as spherical/quasi-spherical and spindle that are very much on the pathway of formation of large, flowerlike ZnO nanostructures. Electron microscopy results indicated that these spherical/quasi-spherical ZnO nanoparticles might aggregate through oriented attachment to produce spindlelike and flowerlike nanostructures. On the basis of these results, a possible growth mechanism for the formation of flowerlike ZnO nanostructures was described. The optical properties of these differently shaped ZnO nanostructures were also described. The catalytic activities of the as-synthesized spherical and flowerlike ZnO nanostructures were tested in the Friedel-Crafts acylation reaction of anthracene with benzoyl chloride. The catalysis results indicated that the catalytic activity of flowerlike ZnO nanostructures is slightly higher than the spherical counterpart.

While molecular water-oxidation catalysts are remarkably rapid, oxidative and hydrolytic processes in water can convert their active transition metals to colloidal metal oxides or hydroxides that, while quite reactive, are insoluble or susceptible to precipitation. In response, we propose using oxidatively-inert ligands to harness the metal oxides themselves. This approach is demonstrated by covalently attaching entirely inorganic oxo-donor ligands (polyoxometalates) to 3-nm hematite cores, giving soluble anionic structures, highly resistant to aggregation, yet thermodynamically stable to oxidation and hydrolysis. Using orthoperiodate (at pH 8), and no added photosensitizers, the hematite-core complex catalyzes visible-light driven water oxidation for seven days (7600 turnovers) with no decrease in activity, far exceeding the documented lifetimes of molecular catalysts under turnover conditions in water. As such, a fundamental limitation of molecular complexes is entirely bypassed by using coordination chemistry to harness a transition-metal oxide as the reactive center of an inherently stable, homogeneous water-oxidation catalyst.

Although metal oxide nanocrystals are often highly active, rapid aggregation (particularly in water) generally precludes detailed solution‐state investigations of their catalytic reactions. This is equally true for visible‐light‐driven water oxidation with hematite α‐Fe2O3 nanocrystals, which bridge a conceptual divide between molecular complexes of iron and solid‐state hematite photoanodes. We herein report that the aqueous solubility and remarkable stability of polyoxometalate (POM)‐complexed hematite cores with 275 iron atoms enable investigations of visible‐light‐driven water oxidation at this frontier using the versatile toolbox of solution‐state methods typically reserved for molecular catalysis. The use of these methods revealed a unique mechanism, understood as a general consequence of fundamental differences between reactions of solid‐state metal oxides and freely diffusing “fragments” of the same material.

The uptake of molecular guests, a hallmark of the supramolecular chemistry of cages and containers, has yet to be documented for soluble assemblies of metal nanoparticles. Here we demonstrate that gold nanoparticle-based supraspheres serve as a host for the hydrophobic uptake, transport and subsequent release of over two million organic guests, exceeding by five orders of magnitude the capacities of individual supramolecular cages or containers and rivalling those of zeolites and metal-organic frameworks on a mass-per-volume basis. The supraspheres are prepared in water by adding hexanethiol to polyoxometalate-protected 4 nm gold nanoparticles. Each 200 nm assembly contains hydrophobic cavities between the estimated 27,400 gold building blocks that are connected to one another by nanometre-sized pores. This gives a percolated network that effectively absorbs large numbers of molecules from water, including 600,000, 2,100,000 and 2,600,000 molecules (35, 190 and 234 g l ) of para-dichorobenzene, bisphenol A and trinitrotoluene, respectively.H ost-guest phenomena that involve the uptake of gases and small molecules are associated with the supramolecular chemistry of soluble capsules, cages and containers [1][2][3][4][5] or, alternatively, with heterogeneous reactions of porous solid-state materials such as zeolites 6 and metal-organic frameworks 7 . Only now, however, are organized assemblies of metal nanoparticles beginning to serve in a similar capacity as hosts for molecular guests. In organic solvents, for example, light-induced dipoledipole interactions between gold nanoparticles with azobenzenefunctionalized thiolate ligands were recently used to entrap and catalyse the reactions of polar and alkylaromatic substrates 8 . By design, substrates were entrapped during nanoparticle aggregation to overcome the poor uptake and diffusion of molecular guests into colloidal nanocrystal assemblies. However, the uptake of molecular guests, a trait of supramolecular and solid-state chemistry, has so far not been achieved for colloidal nanoparticle assemblies.For that to occur, a thermodynamically favourable driving force must be combined with a porous structure whose interior architecture features host cavities, along with pathways for the effective diffusion of molecular guests from the exterior (bulk solution) to host domains deeply buried in the assembly's interior. If this were achieved, colloidal metal-nanoparticle assemblies could emerge as a new class of functional nano-engineered structures that are uniquely positioned between supramolecular containers and porous solid-state materials.We report a new class of functional assemblies, wherein the hydrophobic effect 9,10 drives the spontaneous uptake of alkyl and alkylaromatic guests 11 by porous 200 nm diameter supraspheres whose host capacities are orders of magnitude larger than those of individual cages or containers. On a mass-per-volume basis, the level of uptake rivals those of zeolites and metal-organic frameworks, which, for methane at elevated pressures, r...

Well-defined amphiphilic poly(ε-caprolactone)-b-poly(N-vinylpyrrolidone) (PCL-b-PNVP) block copolymers were successfully prepared via the combination of ring-opening polymerization (ROP) and xanthate-mediated reversible additionÀfragmentation chain transfer (RAFT) polymerization. Well-defined poly(ε-caprolactone) (PCLÀOH) was synthesized by ROP in bulk at 110 °C using benzyl alcohol as initiator and stannous octate [Sn(Oct) 2 ] as catalyst . The ÀOH end group was then converted into its corresponding xanthate (PCLÀX) via the conversion to its corresponding bromide (PCLÀBr). These are verified by 1 H NMR spectroscopy. PCL-b-PNVP block copolymers were synthesized via RAFT polymerization in tetrahydrofuran (THF) at 80 °C using PCLÀX as macro-chain transfer agent and characterized by 1 H NMR spectroscopy and gel permeation chromatography (GPC). The amphiphilic diblock copolymer PCL 63 -b-PNVP 90 forms spherical micelles of ∼34 nm diameter in water as shown by transmission electron microscopy (TEM), supported by 1 H NMR spectroscopy, and light scattering. The critical micellar concentrations were determined by fluorescence spectroscopy using pyrene as probe. The critical micelle concentration (cmc) value of the block copolymers increases with the increase in the chain length of PNVP block. The overall hydrodynamic radius (R h ) of the micelles remains almost constant over the concentration range above the cmc value and over the angles of scattering measurement.

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The synthesis of solvent-adoptable monometallic Ni and NiCo alloy nanochains by a one-pot solution phase reduction method in the presence of poly(4-vinylphenol) (PVPh) is demonstrated. The elemental compositions of the as-prepared alloys are determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS), which are matching well with the target compositions. The morphology analysis by TEM and FESEM confirms that the nanochains are made up of organized spherical monometallic Ni or bimetallic NiCo alloy nanoparticles (NPs). However, there is no nanochain formation when the alloy is prepared without the polymer PVPh. A possible mechanism for the formation of such NiCo alloy nanochains is discussed. The X-ray diffraction and selected area electron diffraction patterns reveal that the Ni/NiCo alloys are polycrystalline with fcc structure. The obtained Ni or NiCo alloy nanostructures are ferromagnetic with very high coercivity. The polymer Ni/NiCo alloy nanochains are dispersible in both water and organic media that makes them versatile enough to use as catalysts in the reactions carried out in both types of media. The catalytic activities of these Ni/NiCo alloy nanochains are extremely high in the borohydride reduction of p-nitrophenol in water. In organic solvents, these nanochains can act as efficient catalysts, under ligand-free condition, for the C-S cross-coupling reactions of various aryl iodides and aryl thiols for obtaining the corresponding cross-coupled products in good to excellent yield up to 96%. The NiCo nanochain also successfully catalyzes the C-O cross-coupling reaction in organic medium. A possible mechanism for NiCo alloy nanochain-catalyzed cross-coupling reaction is proposed.

Carboxylated peptide-functionalized gold nanoparticles (peptide-GNPs) self-assemble into two- and three-dimensional nanostructures in the presence of various heavy metal ions (i.e. Pb(2+), Cd(2+), Cu(2+), and Zn(2+)) in aqueous solution. The assembly process is monitored by following the changes in the surface plasmon resonance (SPR) band of gold nanoparticles in a UV/Vis spectrophotometer, which shows the development of a new SPR band in the higher-wavelength region. The extent of assembly is dependent on the amount of metal ions present in the medium and also the time of assembly. TEM analysis clearly shows formation of two- and three-dimensional nanostructures. The assembly process is completely reversible by addition of alkaline ethylenediaminetetraacetic acid (EDTA) solution. The driving force for the assembly of peptide-GNPs is mainly metal ion/carboxylate coordination. The color and spectral changes due to this assembly can be used for detection of these heavy-metal ions in solution.