Au-induced polyvinylpyrrolidone aggregates with bound water for the highly shape-selective synthesis of silica nanostructures

Novel Au-induced polyvinylpyrrolidone (PVP) aggregates with bound water (PVP-water) were created for the highly shape-selective synthesis of distinctive silica nanostructures, such as core-shell spheres, rods, snakes, tubes, capsules, thornlike, and dendritic morphologies. A water/PVP/n-pentanol system was first designed to bind water to PVP, and then Au nanoparticles were used to induce the PVP-water species to aggregate into distinctive soft structures by exploiting the interplay between PVP and gold. This was confirmed by the IR absorption spectra. The bound water in the soft structures was consumed during the hydrolysis of tetraethylorthosilicate and the target silica nanostructures were obtained. The soft structures, and therefore, the silica morphologies, can be readily tuned by adjusting the experimental parameters. The tunable Au-induced PVP-water soft structures reported herein open up new dimensions for the synthesis of distinctive nanomaterials (other than silica) that have new physicochemical properties and applications. These soft structures were also successfully extended to synthesize ZnO and SnO(2) particles with remarkable shapes, such as spheres, leaves, T-shaped structures, and dendritic morphologies.     

Synthesis and Morphogenesis of Organic and Inorganic Polymers by Means of Biominerals and Biomimetic Materials

We have studied the simultaneous synthesis and morphogenesis of polymer materials with hierarchical structures from nanoscopic to macroscopic scales. The morphologies of the original materials can be replicated to the polymer materials. In general, it is not easy to achieve the simultaneous synthesis and morphogenesis of polymer material even using host materials. In the present work, four biominerals and three biomimetic mesocrystal structures are used as the host materials or templates and polypyrrole, poly(3‐hexylthiopehene), and silica were used as the precursors for the simultaneous syntheses and morphogenesis of polymer materials. The host materials with the hierarchical structure possess the nanospace for the incorporation of the monomers. After the incorporation of the monomers, the polymerization reaction proceeds in the nanospace with addition of the initiator agents. Then, the dissolution of the host materials leads to the formation and morphogenesis of the polymer materials. The scheme of the replication can be classified into the three types based on the structures of the host materials (types I–III). The type I template facilitates the hierarchical replication of the whole host material, type II mediates the hierarchical surface replication, and type III induces the formation of the two‐dimensional nanosheets. Based on these results, the approach for the coupled synthesis and morphogenesis can be applied to a variety of combinations of the templates and polymer materials.     

Chelation-mediated aqueous synthesis of metal oxyhydroxide and oxide nanostructures: combination of ligand-controlled oxidation and ligand-cooperative morphogenesis

We have synthesized nanostructures of iron and cobalt oxyhydroxides and manganese oxides in aqueous solution containing a chelating agent. Nanosheets of FeOOH and NaxMnO2 and nanoflakes of CoOOH were generated from the corresponding divalent metal salts and ethylenediaminetetraacetate (EDTA) by one-pot synthesis under ambient conditions. The chelating agent fulfilled multiple roles in the reaction process and morphogenesis leading to two-dimensional nanostructures. Coordination to the divalent metal ions inhibited rapid precipitation of metal hydroxides and mediated oxidation to tri- and tetravalent species by dissolved oxygen. Along with the deposition, the two-dimensional and single-crystal nanostructures were also associated with interactions of the chelating agent. Therefore, this approach can be regarded as a combination of ligand-controlled oxidation and ligand-cooperative morphogenesis. Parallel control of the reaction and the morphology was achieved by a simple approach. The model cases suggest that tailoring chelation can facilitate the design of other metal oxide nanomaterials.     

Morphology-controlled assembly of ZnO nanostructures: a bioinspired method and visible luminescence

In a bioinspired methodology, positively charged polypeptides and polyamines directly catalyse ZnO mineralization under "green" conditions of room temperature and neutral pH. The polyamines not only act as mineralizing agents for the formation of ZnO nanoparticles, but also self-assemble the nanoparticles to form spindle-like morphologies at these very ambient conditions. Both the directional growth of ZnO and its luminescent property have a pH dependency. At higher pH, the ZnO shape changes to a rodlike morphology that exhibits green photoluminescence with different intensity than that for ZnO spindles.     

Zn2+ and EDTA Cooperative Switchable Nanofluidic Diode Based on Asymmetric Modification of Single Nanochannel

Design and fabrication of smart switchable nanofluidic diodes remains a challenge in the life and materials sciences. Here, we present the first example of a novel Zn²⁺/EDTA switchable nanofluidic diode system based on the control of one‐side of the modified hourglass‐shaped nanochannel with salicylaldehyde Schiff base (SASB). The nanofluidic diode can be turned on in the response of Zn²⁺ and turned off in response to EDTA solution with good reversibility and recyclability.     

Controlled Orientation in a Bio‐Inspired Assembly of Ag/AgCl/ZnO Nanostructures Enables Enhancement in Visible‐Light‐Induced Photocatalytic Performance

In a bio‐inspired approach, polyamine‐mediated mineralization of ZnO was explored to develop an environmentally benign methodology for synthesizing Ag/AgCl/ZnO nanostructures. The assembling properties displayed by the polyamines to create composite structures was utilized to have the nanocomponents effectively interact with each other in a way that is desirable for the application envisaged. The polyamines, which act as a mineralizing agent for ZnO nanoparticles, also facilitate the formation of Ag/AgCl within ZnO under ambient conditions. Thus synthesized Ag/AgCl/ZnO nanostructures represent a multi‐heterojunction system in which the nanocomponents lead in a synergistic way to enhancement in the photocatalytic activity under visible‐light irradiation.     

Hierarchical,Titania‐Coated,Carbon Nanofibrous Material Derived from a Natural Cellulosic Substance

Hierarchical, titania‐coated, nanofibrous, carbon hybrid materials were fabricated by employing natural cellulosic substances (commercial filter paper) as a scaffold and carbon precursor. Ultrathin titania films were firstly deposited by means of a surface sol–gel process to coat each nanofiber in the filter paper, and successive calcination treatment under nitrogen atmosphere yielded the titania–carbon composite possessing the hierarchical morphologies and structures of the initial paper. The ultrathin titania coating hindered the coalescence effect of the carbon species that formed during the carbonization process of cellulose, and the original cellulose nanofibers were converted into porous carbon nanofibers (diameters from tens to hundreds of nanometers, with 3–6 nm pores) that were coated with uniform anatase titania thin films (thickness ≈12 nm, composed of anatase nanocrystals with sizes of ≈4.5 nm). This titania‐coated, nanofibrous, carbon material possesses a specific surface area of 404 m² g^?1, which is two orders of magnitude higher than the titania–cellulose hybrid prepared by atomic layer deposition of titania on the cellulose fibers of filter paper. The photocatalytic activity of the titania–carbon composite was evaluated by the improved photodegradation efficiency of different dyes in aqueous solutions under high‐pressure, fluorescent mercury‐lamp irradiation, as well as the effective photoreduction performance of silver cations to silver nanoparticles with ultraviolet irradiation.     

Oriented morphogenesis of ZnO nanostructures from water-soluble zinc salts under environmentally mild conditions and their optical properties

Herein, we report a bottom-up, mineralization strategy, which borrows key principles from biomineralization processes, to synthesize nanostructured materials. A long-chain polyamine simultaneously mineralizes and assembles ZnO nanoparticles directly from water-soluble zinc salts under sustainable synthesis conditions. These thus-generated oriented structures undergo interesting morphogenesis that is controlled by changing the ratio of polyamine/Zn(2+) ions. As the ratio increases, the morphology changes from a spherical shape to oval-, dumbbell-, and finally hexagonal-rod-shaped structures that contain unique hollow rod structures. Using XPS, XRD, FT-IR, Raman spectroscopy, DLS, and confocal fluorescence microscopic analysis, we elucidate the mechanism of structural evolution; this mechanism involves the initial formation of a zinc/amine complex that is furnished with polyamine chains. These chains facilitate the condensation process to form ZnO nanoparticles and their assembly in aqueous medium at neutral pH. Further, the presence of defects in the thus-morphogenized ZnO structures leads to blue luminescence and efficient photoinduced activity, assisted by the surface-hole-trapping effect of polyamines.