Macroporous Tungsten Research Articles

Confined catalysis of MOF-818 nanozyme and colorimetric aptasensing for cardiac troponin I

Understanding the catalytic performance of nanozymes assembled in confined environment is an interesting topic. Herein, a three-dimensional nanozyme-catalytic nanoreactor was constructed by confining MOF-818 nanozyme in the pore of macroporous tungsten trioxide (p-WO3). The catalytic activity of MOF-818 assembled in-situ for the oxidation of 3,5-Di-tert-butylcatechol (3,5-DTBC) could be regulated by changing the pore size of p-WO3. Only when being confined in the pores of p-WO3 with an appropriate pore size, MOF-818 could exhibit high affinity towards 3,5-DTBC, and excellent catalytic activity for 3,5-DTBC oxidation, the catalytic rate constant kcat and Michaelis constant Km were determined to be 31.47 s−1 and 1.42 mM, respectively, and the maximum yield of 3,5-DTBC oxidation reached 95.2%. Furthermore, the as-constructed nanozyme-catalytic nanoreactor could be designed to construct a colorimetric aptasensor for selective determining cardiac troponin I based on the enzymatic inhibition effect and the exonuclease I-assisted target recycling signal amplification, which exhibited a good linear range of 50 fg mL−1 - 100 ng mL−1, low detection limit of 18 fg mL−1, and was applied for human serum analysis with RSD less than 5.2% and the recoveries ranged from 95% to 107%.

Temperature-dependent mechanical behavior of three-dimensionally ordered macroporous tungsten

Abstract

Porous WS2 and W2N powders by hard templating with colloidal silica

Meso- and macroporous tungsten disulfide (WS2) and tungsten nitride (W2N) powders were successfully synthesized by reduction of [WO3/colloidal silica] composites under hydrogen sulfide and ammonia gases respectively. The colloidal silica, marketed as Ludox®, was used as a hard template and its removal from the composite led to a porosity release. The products were characterized by X-ray diffraction, nitrogen adsorption, mercury porosimetry and electron microscopy. Well-crystallized samples with specific surfaces areas close to ~40m2g−1 were thus synthesized. The present approach might be easily extended to the synthesis of other nitrides and sulfides materials.

Electrochromic Properties of Sol-Gel Synthesized Macroporous Tungsten Oxide Films Doped with Gold Nanoparticles

Macroporous tungsten oxide thin films were prepared by using a polystyrene microsphere template and the peroxitungstic acid precursor. Gold nanoparticles were introduced into the tungsten oxide film by two different methods, either in the polystyrene template, through a self-assembly process, or they were cast on the surface of the annealed film. Raman imaging experiments showed an enhancement effect of the intensity of the major tungsten oxide bands by the gold nanoislands. The electrochromic properties of gold-doped macroporous tungsten oxide are described and compared to those of the standard porous sol-gel film. The films with gold nanoparticles on the surface of the tungsten oxide film were found to have better electrochromic properties than the standard sol-gel tungsten oxide films and the ones doped with gold in the polystyrene template. The diffusion coefficients of protons in the gold-doped tungsten oxide films were determined from both Cyclic Voltammetry (CV) and Electrical Impedance Spectroscopy (EIS) measurements. The results indicate a faster diffusion of the proton in the porous film, compared with a compact tungsten oxide film. The model that evolves from the EIS data, involves fast charge transfer rates at the electrolyte/tungsten oxide film interface. The results demonstrated an enhancement of the coloration efficiency of the macroporous tungsten oxide films with Au nanoparticles on the surface of the film. The possible involvement of plasmon resonance of Au nanoparticles in the electrochromic process is discussed.

Physical Properties of Macroporous Tungsten Oxide Thin Films and Their Impact on the Photocurrent Density

Tungsten trioxide (WO3) films were prepared using polystyrene spheres of two different diameters as a template in order to create porous layers. X-ray diffraction data and electron microscopy images show that annealed films exhibit polycrystalline structure with monoclinic phase and pore size of approximately hundred nanometers. The optical band gap energies have been determined by photoacoustic spectroscopy as 3.17 eV, and this value was not affected by sample morphology. Low temperature photoluminescence spectra exhibit broad band in the blue region. Deconvolutions of PL spectra show that there are two transitions which intensity depends on thin film pore size. We discuss the possible origin of this emissions associated with oxygen vacancies and surface states. A comparative study of the WO3films used as photoanodes is presented and correlated with PL results.

Improved electrochromic performance of ordered macroporous tungsten oxide films for IR electrochromic device

Electrochromic performance of tungsten oxide (WO3) has attracted extensive interest due to its applications in smart windows, spacecraft thermal control and other optical devices. Here we report ordered macroporous WO3 thin films prepared by the template-assisted sol–gel method. The principle finding of the paper is that the ordered multi-layer interconnected porous structure facilitates the diffusion of ions/electrons as well as the light transmission. Consequently we see improved IR optical modulation and faster response time in the macroporous WO3 films. Moreover, both small pore size and perfection of ordered porous structure contribute to the improved electrochromic performance. These results have obvious practical relevance for fast near IR electrochromic devices exemplified by aerospace thermal control systems.

Enhanced electrochromic performance of macroporous WO 3 films formed by anodic oxidation of DC-sputtered tungsten layers

Self-organized macroporous tungsten trioxide (WO 3) films are obtained by anodic oxidation of DC-sputtered tungsten (W) layers on 10 mm × 25 mm indium tin oxide (ITO)-coated glass. Under optimized experimental conditions, uniformly macroporous WO 3 films with a thickness of ca. 350 nm are formed. The film shows a connected network with average pore size of 100 nm and a pore wall thickness of approximately 30 nm. The anodized film becomes transparent after annealing without significant change in macroporous structure. In 0.1 M H 2SO 4, the macroporous WO 3 films show enhanced electrochromic properties with a coloration efficiency of 58 cm 2 C −1. Large modulation of transmittance (∼50% at 632.8 nm) and a switching speed of about 8 s are also achieved with this macroporous film.

Preparation of 3-D ordered macroporous tungsten oxides and nano-crystalline particulate tungsten oxides using a colloidal crystal template method, and their structural characterization and application as photocatalysts under visible light irradiation

Three-dimensionally ordered macroporous (3DOM) tungsten(VI) oxide (WO3) was prepared using a colloidal crystal template method. Well-ordered 3DOM WO3 was prepared with a high pore fraction using ammonium metatungstate ((NH4)6H2W12O40), a Keggin-type dodecatungstate, as a tungsten precursor; WO3 materials prepared by other commercially available W precursors, tungsten chloride (WCl6), tungsten(V) ethoxide (W(OEt)5), and phosphotungstic acid (H3PW12O40), have a low 3DOM pore fraction. These WO3 materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) analysis of nitrogen adsorption isotherm, and Raman spectroscopy. Non-porous WO3 prepared from ammonium metatungstate without a poly(methyl metacrylate) (PMMA) template grew to crystal sizes of up to several micrometres with a low specific surface area (ca. 1–2 m2 g−1). In the presence of a colloidal crystal template of PMMA spheres, WO3 crystal grew in the nanometre-sized voids between the PMMA spheres, and the specific surface area thus increased up to ca. 30 times compared to non-porous WO3. The surface area is tunable by changing the PMMA sphere diameter. Calcination of the 3DOM WO3 produced WO3 nano-crystalline particles by sintering-induced disassembly. After Pt-loading, these WO3 materials showed higher photocatalytic activity compared to non-porous WO3 for decomposition of acetic acid in air under visible light irradiation.

Construction and characterization of tunable meso-/macroporous tungsten oxide-based transmissive electrochromic devices

Recent developments in the processing of porous transition metal oxide thin films have opened up new opportunities in the construction of electrochromic (EC) devices with enhanced properties. Tungsten oxide (WO3) is one of the most promising materials for EC devices. In this work, we report on the synthesis of meso-/macroporous WO3 thin films using tungstic acid as precursor and organically modified silane (ORMOSIL) as a templating agent. Calcination of the film at 500 °C resulted in nanocrystalline monoclinic tungsten oxide (m-WO3) with crystallite sizes of ~16 nm. The meso-/macroporous structure is retained after calcination. An asymmetric EC device based on the meso-/macroporous m-WO3 thin film was constructed. Thus constructed EC device was characterized by micro-Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction (XRD). Detailed micro-Raman and XRD studies of the intercalation and deintercalation of lithium (Li) in the meso-/macroporous m-WO3 layer of the EC device as a function of the applied voltage were performed. The meso-/macroporous WO3 layer, which was found to be monoclinic before Li intercalation, transforms to its higher symmetric phase of tetragonal and toward cubic phase when Li is intercalated into it. Upon complete deintercalation, these phase transitions were reversed and m-WO3 is recovered. Optical transmission studies were performed in conjunction with Raman and XRD studies. This study shows that meso-/macroporous m-WO3 layer-based EC device exhibit a high color contrast during the coloration and bleaching.

Synthesis and Characterization of Three-Dimensionally Ordered Macroporous (3DOM) Tungsten Carbide: Application to Direct Methanol Fuel Cells

Three-dimensionally ordered macroporous tungsten carbide (3DOM WC) with varying pore size was synthesized using the “inverse-opal” method. Poly{methyl methacrylate} (PMMA) colloidal crystal template with sphere diameters ranging from 180 to 490 nm was used. Two synthesis procedures were performed, the first requiring calcination of tungsten impregnated PMMA colloidal template in air followed by carburization in H2/CH4/N2 atmosphere. The second procedure involved direct carburization of the tungsten impregnated template without prior calcination. The effect of Pt-modification of the template prior to carburization on the resulting material composition was also investigated. The material properties were evaluated using surface and bulk characterization techniques. Finally, cyclic voltammetry was used to investigate the methanol electro-oxidation activity of the 3DOM WC and Pt-modified 3DOM WC in acidic electrochemical environment.

A Study of the Effects of Thermal Emission and Heating of Macroporous Tungsten Photonic Crystals

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Synthesis and Characterization of Macroporous Tungsten Oxide Films for Electrochromic Application

Macroporous tungsten oxide films have been prepared by combining a nonhydrolytic sol-gel method with a molecular assembly templating strategy. The material has been prepared by hydrolysis of an ethanolic solution of tungsten ethoxide in the presence of polyethylene glycol (PEG), followed by calcination of the dip-coated films. AFM images indicated that an important morphological diversity can be obtained by simply varying the amount of PEG in the coating solution and the conditions of the heat-treatment. The formation of nanostructures of controlled shapes and patterns (fibrils or striped phases) with relatively uniform channel spacings is accounted for by strong hydrogen bonding interactions between the PEG and the partially hydrolyzed tungsten oxide oligomers. XRD and FTIR data showed that PEG delays the crystallization of WO3. When compared to sol-gel prepared tungsten oxide fims prepared without PEG, the coloration efficiency of the macroporous films appears to be significantly improved especially in the near-infrared region.

Electrochemical Change of the Photonic Stop Band of the Ordered Macroporous WO3 Films

Abstract Three-dimensional macroporous tungsten trioxide (WO3) was electrochemically prepared by using the polystyrene opal as a template. The photonic stop band of the porous WO3 film could be changed when the WO3 was intercalated with lithium cation by the electrochemical method. The change of the stop band was attributed to the change of the refractive indices accompanied with the electrochromism of WO3.

DECOMPOSITION OF HYDRAZINE BY TUNGSTEN OXYCARBIDES: THE INFLUENCE OF MACROPOROSITY AND MECHANICAL STRENGTH ON A 2 N MICROTHRUSTER ENGINE

The aim of this work was to prepare tungsten oxycarbides by Temperature Programmed Reaction (TPR), starting with previously molded macroporous tungsten oxide (WO3). The tungsten oxycarbides were prepared by one of two different methods: direct carburization with CH4/H2 to obtain WC or preliminary formation of nitrides with NH3 to obtain W2N, followed by carburization to W2C and WC with CH4/H2. Results suggested that the carburization of the W2N was incomplete, resulting in an oxycarbonitride, or did not occur at all, with the end material being W2N. From among the materials prepared, two catalysts were selected as a function of their mechanical properties, and their performances were compared with a 2 N microthruster using the Shell 405 commercial catalyst in the reaction of hydrazine decomposition.