Nanoporous Metal Oxide Research Articles

Tailored 3D Interface for Efficiency Improvement in Encapsulation-Free Hybrid Light-Emitting Diodes

The modification of the planar organic/inorganic interface of the hybrid light-emitting diodes by the addition of a tailored nanoporous crystalline metal oxide increases up to 1 order of magnitude the efficiency of the resulting devices. In this Letter, we present the preparation and characterization of the novel controlled 3D interface and discuss how the interaction between the metal oxide and the polymer at the interface results in such an improvement.

Size-Selective Incorporation of DNA Nanocages into Nanoporous Antimony-Doped Tin Oxide Materials

A conductive nanoporous antimony-doped tin oxide (ATO) powder has been prepared using the sol-gel method that contains three-dimensionally interconnected pores within the metal oxide and highly tunable pore sizes on the nanoscale. It is demonstrated that these porous materials possess the capability of hosting a tetrahedral-shaped DNA nanostructure of defined dimensions with high affinity. The tunability of pore size enables the porous substrate to selectively absorb the DNA nanostructures into the metal oxide cavities or exclude them from entering the surface layer. Both confocal fluorescence microscopy and solution FRET experiments revealed that the DNA nanostructures maintained their integrity upon the size-selective incorporation into the cavities of the porous materials. As DNA nanostructures can serve as a stable three-dimensional nanoscaffold for the coordination of electron transfer mediators, this work opens up new possibilities of incorporating functionalized DNA architectures as guest molecules to nanoporous conductive metal oxides for applications such as photovoltaics, sensors, and solar fuel cells.

Synthesis of nanoporous metal oxides through the self-assembly of phloroglucinol–formaldehyde resol and tri-block copolymer

A versatile route to synthesize nanoporous crystalline metal oxides has been developed through the self-assembly of phloroglucinol–formaldehyde resol and tri-block copolymer templates. Materials were characterized by a complementary combination of X-ray diffraction, nitrogen sorption, and transmission electron microscopy. Metal oxides synthesized using this route have remarkably high surface area when compared with the commercial samples. The surface area of metal oxides decreased upon calcination at higher temperatures. However, the surface area was still much higher when compared with the commercial samples. TEM investigation reveals that upon calcination at higher temperature, the size of the crystal increased but the short range order was merely disturbed. The analyses show that the present method is suitable as a direct route to synthesize crystalline nanoporous metal oxides. Hydrogen bonding plays a key role in the preferential arrangement of porous metal–carbon structure in the domain of tri-block copolymer. The nanoporous metal oxides with ordered mesoporous structure, high surface area, and crystalline framework are expected to show significant improvement in catalysis and nano-technology.

Single-crystal ZnO nanorod/amorphous and nanoporous metal oxide shell composites: Controllable electrochemical synthesis and enhanced supercapacitor performances

Single-crystal ZnO nanorod/amorphous and nanoporous metal oxide shell composites were facilely prepared by electrochemical deposition and tested as promising electrode materials for supercapacitor applications.

Low temperature crystallization of transparent, highly ordered nanoporous SnO2 thin films: application to room-temperature hydrogen sensing

High surface area highly ordered nanoporous thin films are the current gold standard for gas sensor use, however the nanostructure of such films is prone to collapse at annealing temperatures as low as 250 °C resulting in formation of a dense layer of limited utility. We report on a templating method used to deposit highly ordered nanoporous platinum (Pt)-doped tin dioxide (SnO(2)) thin films that are crystallized by a 100 °C water vapor hydrothermal treatment, with the low temperature process being compatible with a large variety of substrates including plastic. The resulting highly ordered nanoporous, transparent Pt-SnO(2) thin films are mechanically stable and can be annealed, as desired, at temperatures up to 800 °C for removal of the templating materials and tailoring of gas sensitivities without damage to the nanoporous structure. The synthesis method is general, offering a promising strategy for preparing high performance nanoporous metal oxide crystalline films for applications including gas sensing, photocatalysis, and 3(rd) generation photovoltaics. In our example application of the synthesized materials, we find that these Pt-SnO(2) films exhibit exceptional hydrogen gas sensing behavior, rapidly detecting low-level hydrogen concentrations at room temperature; for example, an eight order of magnitude change in electrical resistance is seen in response to 10 000 ppm H(2), with only minimal sensitivity to humidity.

Crystalline nanoporous metal oxide thin films by post-synthetic hydrothermal transformation: SnO2 and TiO2

Nanostructured and nanoporous metal oxide thin films are rarely accessible by standard synthetic approaches but highly desired for many applications, e.g. as electrodes, transparent conducting coatings, sensors or surface catalysts. Template based sol–gel chemistry combined with post-synthetic hydrothermal treatment allows now the synthesis of nanocrystalline mesostructured porous thin films of metal oxides, e.g. tin oxide and titania. Even in cases where the crystallization cannot be induced highly stable thin films can be achieved, e.g. niobium oxide thin films. We demonstrate how the size of the nanocrystallites influences and stabilizes the mesostructure at temperatures as low as 100 C and thereby in the case of titania or tin dioxide even prevents it from deterioration at higher temperatures up to 400–600 C.

Controlled growth and monitoring of tantalum oxide nanostructures

Nanoporous metal oxide structures produced by the electrochemical anodization of valve metals, such as Zr, Ti, W, Nb, Al, and recently Ta, have attracted increasing interest because of their potential use as catalysts, waveguides, and three-dimensionally arranged Bragg-stack reflectors. Here we demonstrate the formation of either supported nanotubular Ta oxide films or free-standing Ta oxide membranes, produced by controlling the conditions of Ta anodization in organic-free aqueous HF/H(2)SO(4) solutions. The supported oxide nanotubes, which are at least 15 mum in length, are characterized by very good adhesion to the Ta substrate, and extremely smooth and homogeneous walls. It is also reported here, for the first time, that these nanotubular films can be removed as free-standing Ta oxide membranes that are easily transferable to other substrates, making them potentially useful in sensors, optics, and catalysis. We also show that, when the Ta oxide nanotubes detach to form the membranes, they leave behind an ordered array of dimples in the Ta surface, with the dimples having the identical distribution and size as the pores in the previously attached nanotubes. Finally, we demonstrate how the in situ electrochemical response during anodization can be used to determine which of these highly useful Ta surface morphologies (nanotubes vs. dimples) are formed, without the need for post factum microscopic analysis. Knowledge of the meaning of these in situ signals can now serve to accelerate the controlled formation of oxide nanotubes or dimpled surfaces using other combinations of metals and anodization conditions.

Thermosetting polymer templated nanoporous sinter-active layer for low temperature solid oxidefuelcells

A facile synthesis method was developed to form a nanoporous metal oxide layer using poly(furfuryl alcohol) (PFA) as a thermosetting polymer template. A nanoporous Ce0.8Sm0.2O1.9 (SDC) layer with high sinterability was prepared on an anode-supported electrolyte film at 900 °C, and used as a sinter-active layer in cell fabrication to improve the interface between the inert electrolyte surface and the cathode layer of a solid oxide fuel cell (SOFC). The resulting saw-like interface improved the maximum powder density of the cell by 51% at 600 °C and 162% at 500 °C compared with that of the unmodified cell. The cell with the saw-like electrolyte–cathode interface exhibited lower electrode polarization resistance than those reported in the literature, and such improvement was much more significant at reduced operating temperatures (400–500 °C). Our study shows that the operating temperature of solid oxide fuel cells can be substantially lowered by simply improving the electrode–electrolyte interfaces.

A General Single‐Source Route for the Preparation of Hollow Nanoporous Metal Oxide Structures

A hole in one: Hollow nanoporous structures are prepared by controlled decomposition–dissolution. The partial thermal decomposition of transition-metal salts forms a metal oxide shell on the surface of the metal salt particles. Acid washing removes the metal salt cores, resulting in hollow nanoporous metal oxide shells (see picture). This new strategy provides a template-free single-source route to hollow structures.

A General Single‐Source Route for the Preparation of Hollow Nanoporous Metal Oxide Structures

A General Single‐Source Route for the Preparation of Hollow Nanoporous Metal Oxide Structures

A Simple Template‐Free Strategy to Synthesize Nanoporous Manganese and Nickel Oxides with Narrow Pore Size Distribution, and Their Electrochemical Properties

AbstractA facile method has been developed to synthesize nanoporous manganese and nickel oxides with polyhedron particle morphologies, high surface areas and narrow pore distributions by controlled thermal decomposition of the oxalate precursors. This method can be extended to using other kinds of salt precursors to prepare a series of nanoporous metal oxides. The heating rate, calcination temperature and controlled particle size of the oxalate precursors are important factors to get well‐defined pore structures. XRD, TG‐DTA, TEM, SEM, XPS, wet chemical titration and N2 sorption isotherm techniques are employed for morphology and structure characterizations. High surface area microporous manganese oxide (283 m2 g−1) and mesoporous nickel oxide (179 m2 g−1) with narrow pore distribution at around 1.0 nm and 6.0 nm, respectively, are obtained. Especially, we can tune the pore size of manganese oxides from microscope to mesoscope by controlling the thermal procedure. Electrochemical properties of manganese and nickel oxides are studied by cyclic voltammetry measurements in a mild aqueous electrolyte, which shows a high specific capacitance of 309 F g−1 of microporous manganese oxide and a moderately high specific capacitance of 165 F g−1 of mesoporous NiO due to their nanoporous structure, presenting the promising candidates for super capacitors (SC).

In situ STM of pulsed laser nanostructured deposits: First stages of film formation

In the synthesis of nanostructured thin films the characterization of the growth processes plays a fundamental role for the control of the film and surface properties. Moreover when the deposition technique is based on the production and the assembling of nanoparticles/clusters the characterization of the precursor size distribution is of fundamental importance. We have designed a pulsed laser deposition (PLD) apparatus for the production of nanostructured thin films and surfaces, connected to a UHV variable temperature scanning tunneling microscope (STM). The whole system is devoted to the synthesis and in situ study of nanostructured and nanoporous functional metal and metal oxide films and surfaces. We have deposited W nanoparticles produced by a few hundreds laser pulses in order to investigate the initial mechanisms of the film growth. Different deposition conditions have been explored by controlling the laser generated plasma expansion through a background gas in the PLD chamber. STM measurements have been performed on W thin films deposited on different substrates to study both the size distribution and the aggregation of the precursors on the surface. Although substrate effects must be taken into account, the control of the background gas pressure and of the target-to-substrate distance allows to produce surfaces with different morphologies. This opens the possibility to tailor the material properties through the control of the size and deposition energy of the building nano-units.

Spectrophotochemical and electrochemical characterization of perylene derivatives adsorbed on nanoporous metaloxide films

Electrochemistry of perylene imide and anhydride derivatives adsorbed on semiconductor TiO 2 (NT) and insulator Al 2 O 3 (NA) metal oxide films were presented. Adsorption rates on metal oxide surface are observed to be strongly depending on molecular structure. Monoanhydride-monoimide derivatives show two reversible reductions in solution and one reversible reduction in films. Color change from red to blue and violet is observed indicating the formation of monoanion and dianion radicals. Spectroelectrochemical measurements support this interpretation. The color reversal is quite stable in NA films in comparison with NT films.

Synthesis of Nanoporous Metal Oxide Particles by a New Inorganic Matrix Spray Pyrolysis Method

In this paper we describe a new approach for the formation of nanoporous particles in which a thermally stable, water-soluble, and therefore easily leached second component is employed during spray pyrolysis to produce a composite particle. We demonstrate the new synthetic approach for synthesizing nanoporous aluminum oxide (Al2O3) by spray pyrolysis of aluminum nitrate (Al(NO3)3·9H2O) and sodium chloride (NaCl) solutions. The characteristics of the nanoporous material such as surface area, pore volume, and particle morphology are investigated as a function of relative humidity, temperature, and salt fractions. Specific surface area of the product particles increased significantly from 10 m2/g for the produced composite particles to over 370 m2/g for the remaining Al2O3 particles following aqueous leaching to remove the NaCl filler. Nanoporous particles could be produced at relatively low temperature (<550 °C) and high relative humidity (or low evaporation rate of aerosolized droplets) when followed by th...

Nanoporous iron oxide membranes: layer-by-layer deposition and electrochemical characterisation of processes within nanopores

A versatile procedure for the formation of nanoporous metal oxide membranes is reported, based on a layer-by-layer deposition procedure (‘directed assembly’) of metal oxide nanoparticles with appropriate ‘linker’ molecules; here Fe2O3 particles and phytic acid. Two types of nanoporous Fe2O3 membranes have been prepared and characterised: (A) a nanofilm deposit composed of 4–5 nm diameter Fe2O3 particles linked by phytic acid and (B) a nanoporous film formed after calcination of the type A deposit at 500 °C in air. The nanofilm deposits are characterised by microscopy (SEM and AFM) and by electrochemical methods.

Nanoporous Metal Oxides Synthesized by the Nanoscale Casting Process Using Supercritical Fluids

Nanoporous metal oxides (TiO2, Al2O3) have been synthesized using activated carbon templates with supercritical fluid solvents by using the nanoscale casting (NC) process. The precursors were dissolved in supercritical CO2 and attached to activated carbon fibers or powders as templates. After removal of the activated carbon templates by calcination in air at 873 K or by treatment in oxygen plasma, the nanoporous TiO2 or Al2O3 replicating the macroscopic shapes of the activated carbon templates was obtained. The surface area of the titania sample was 387 m2/g. The titania sample crystallized in the anatase form. The alumina samples have mesopores corresponding to the graphene crystallite size of the activated carbon. The alumina samples crystallized in the γ-alumina form.

Pulsed Laser Ablation of Low-Density Nanoporous Metal Oxides

AbstractPulsed laser ablation has been employed to generate thin films of low density metal oxides, including nanoporous molecular sieves. An excimer laser (KrF*, 248 nm) was used to deposit molecular sieve films onto a variety of substrates including polished silicon, platinum, tantalum, titanium nitride, glass, indium-doped tin oxide, copper and Mylar. Recent results for the deposition of microporous UTD-1 and FeAPO-5 as well as mesoporous aluminosilicate MCM-41 and Nb-TMSI molecular sieve films are presented. The order (crystallinity) of the laser deposited films has been shown to be enhanced by a brief post hydrothermal treatment. A vapor phase treatment of the laser deposited FeAPO-5 films allows for increases in film crystallinity without an increase in film thickness. Hydrothermal treatment of laser deposited Nb-TMSI results in “worm hole” pore motif which is new for this composition. Silicate based molecular sieves such as UTD-1 and aluminosilicate MCM-41 require a UV-absorbing guest molecule for laser ablation giving rise to a phenomenon referred to as guest assisted laser ablation (GALA). The molecular sieve films were characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy.