Daoai Wang

Spontaneous phase and morphology transformations of anodized titania nanotubes induced by water at room temperature.

We report a spontaneous phase transformation of titania nanotubes induced by water at room temperature, which enables the as-anodized amorphous nanotubes to be crystallized into anatase mesoporous nanowires without any other post-treatments. These mesoporous TiO(2) nanomaterials have a markedly improved surface area, about 5.5 times than that of the as-anodized TiO(2) nanotubes, resulting in a pronounced enhanced photocatalytic activity. The present approach not only allows a flexible control over the morphology of TiO(2) nanostructures but can fundamentally eliminate the need for high temperature operations for crystallizing amorphous TiO(2).

Towards a tunable and switchable water adhesion on a TiO2 nanotube film with patterned wettability

Tunable water adhesion was realized on a TiO(2) nanotube film with patterned wettability formed via selective illumination through a mask. Meanwhile, the adhesion can be switched between sliding superhydrophobicity and sticky superhydrophobicity by masked illumination and heat annealing.

Highly Flexible Coaxial Nanohybrids Made from Porous TiO2 Nanotubes

Anatase TiO(2), an n-type semiconductor, has gained considerable research interest over several decades due to its photocatalytic activity. Most recently, its properties for photoelectrical conversion in solar cells has been explored. Anodized TiO(2) nanotube (NT) arrays have been developed and possess improved photocatalytic, sensing, photoelectrolystic, and photovoltaic properties. The present work describes using TiO(2) as the building block to form ordered heterojunctions via simple electrodeposition with materials of potential interest, including conducting polymers (polypyrrole, poly(3-hexylthiophene)), inorganic semiconducting materials (CdS), and metals (Ni and Au, etc.). A key finding is that the synthesized TiO(2) NT-nanowires(nanotubes) nanohybrids are highly flexible after being peeled off from mother substrates, which is in contrast to more fragile pure TiO(2) NTs. These highly flexible coaxial nanohybrids are expected to have potent applications.

Electrostatic Self-Assembly of Au Nanoparticles onto Thermosensitive Magnetic Core-Shell Microgels for Thermally Tunable and Magnetically Recyclable Catalysis

A facile route to fabricate a nanocomposite of Fe3O4@poly[N-isopropylacrylamide (NIPAM)-co-2-(dimethylamino)ethyl methacrylate (DMAEMA)]@Au (Fe3O4@PND@Au) is developed for magnetically recyclable and thermally tunable catalysis. The negatively charged Au nanoparticles with an average diameter of 10 nm are homogeneously loaded onto positively charged thermoresponsive magnetic core-shell microgels of Fe3O4@poly(NIPAM-co-DMAEMA) (Fe3O4@PND) through electrostatic self-assembly. This type of attachment offers perspectives for using charged polymeric shell on a broad variety of nanoparticles to immobilize the opposite-charged nanoparticles. The thermosensitive PND shell with swollen or collapsed properties can be as a retractable Au carrier, thereby tuning the aggregation or dispersion of Au nanoparticles, which leads to an increase or decrease of catalytic activity. Therefore, the catalytic activity of Fe3O4@PND@Au can be modulated by the volume transition of thermosensitive microgel shells. Importantly, the mode of tuning the aggregation or dispersion of Au nanoparticles using a thermosensitive carrier offers a novel strategy to adjust and control the catalytic activity, which is completely different with the traditional regulation mode of controlling the diffusion of reactants toward the catalytic Au core using the thermosensitive poly(N-isopropylacrylamide) network as a nanogate. Concurrent with the thermally tunable catalysis, the magnetic susceptibility of magnetic cores enables the Fe3O4@PND@Au nanocomposites to be capable of serving as smart nanoreactors for thermally tunable and magnetically recyclable catalysis.

Towards chemically bonded p–n heterojunctions through surface initiated electrodeposition of p-type conducting polymer inside TiO2 nanotubes

Improving the interfacial adhesion is the key to improve and to guarantee stable performance of organic–inorganic solar cells. In this paper, we demonstrate a proof-of-concept approach by using a biomimetic initiator to initiate on-site electrochemical polymerization of pyrrole inside TiO2 nanotubes so as to improve the adhesion during formation of coaxial p–n nanohybrids. The new bifunctional anchor of N-(3,4-dihydroxyphenethyl)-pyrrole-2-carboxamide (Dop-Py) is inspired by mussel adhesive proteins and can strongly anchor to TiO2, and so provides a grafted monomer for initiation of electropolymerization. Much quicker polymerization rate and larger density of polypyrrole (PPy) are achieved than that without the biomimetic initiator. In addition, interface adhesion between PPy and TiO2 is dramatically enhanced, and so the improved charge transfer efficiency as indicated by impedance characterization, suggesting that this is a promising strategy for fabricating ordered organic/inorganic p–n heterojunctions.

Fabrication and characterization of extended arrays of Ag2S/Ag nanodot resistive switches

Well-ordered Ag2S/Ag nanodot arrays with a density of >60 Gbit/in.2 have been fabricated by sputtering Ag on a silicon substrate using ultrathin porous anodic aluminum oxide membranes as shadow masks, followed by sulfurization treatment at room temperature. The morphology, microstructure, and electrical properties of the as-prepared nanodots were characterized by scanning electron microscopy, x-ray diffractometry, transmission electron microscopy, and conductive atomic force microscopy, respectively. Well-defined resistive switching behavior was observed in these nanodots, and the ON/OFF ratio was found to be higher than 102. The Ag2S/Ag nanodot arrays hold substantial promise for use as ultrahigh density nonvolatile memory devices.

Novel Three‐Dimensional Nanoporous Alumina as a Template for Hierarchical TiO2 Nanotube Arrays

Hierarchical micro-/nano-structures made easy. By using extremely rough, chemically etched microstructured aluminium foils, anodization in phosphoric acid under very harsh conditions, e.g., 10 wt% phosphoric acid and room temperature, can be repeatedly accomplished without suffering from breakdown. As a result, an alumina membrane with a three-dimensionally distributed nanopore structure is formed, which can be used as a general template to fabricate hierarchical micro-/nano-structures.

The fabrication of nanoporous Pt-based multimetallic alloy nanowires and their improved electrochemical durability

A general approach for the fabrication of nanoporous Pt-based multimetallic alloy nanowires is reported, which involves electrodeposition of corresponding precursor alloys into porous anodic alumina templates, followed by a mild dealloying process. Nanoporous ternary PtCoNi and PtCoAu as well as quaternary PtRuCoNi nanowires were successfully fabricated, and their microstructure and composition were examined by transmission electron microscopy. Electrochemical tests showed that these porous nanowires exhibit higher electrochemically active surface area and much improved durability compared to commercially available Pt black, and may find potential applications in electrocatalysis and electrochemical sensing.

Bioinspired Self-Healing Organic Materials: Chemical Mechanisms and Fabrications

Design and preparation of organic materials having the ability to automatically restore their mechanical and physical properties are of great importance because of the extensive application ranging from aerospace components to microcircuitry, where the accessibility is highly limited and the reparability of materials is lower. The self-healing behavior is actually a dynamic property of material, resembling what is possessed by nature living systems. Therefore, fabrication of most self-healing materials is actually inspired by nature. This tutorial review focuses on the basic chemical mechanisms that have been successfully adopted in designing self-healing organic materials. It specially covers recent development in the design of materials with durable, easy repairable or self-healing superhydrophobic surfaces and coatings.

Gecko-inspired but chemically switched friction and adhesion on nanofibrillar surfaces.

Chemically switched friction nano-fibrillar surfaces (SiNWAs-PSPMA & SiNWAs-PMAA arrays) can be constructed by finely decorating ordered Si nanowire arrays with responsive polymer brushes. As expected, these surfaces sense humidity or pH smartly and show reversible friction switching, based on swelling and shrinking of the polymer brushes, which is successfully monitored by AFM in liquid media.