Macroporous Films Research Articles

Photocatalytic activity of erbium-doped TiO 2 nanoparticles immobilized in macro-porous silica films

A macro-porous silica film served as mechanical support to immobilize TiO 2 nanoparticles, which were doped with erbium. The films and the nanoparticles were prepared by sol–gel route. The nanoparticles exhibited photocatalytic activity under visible light. We obtained a degradation rate of methylene blue that followed first order kinetics. The sensitization of the nanoparticles to visible light was attributed to a red shift in the band-gap of the TiO 2 due to the addition of erbium ions.

Electrodeposition of Lithium/Polystyrene Composite Electrodes from an Ionic Liquid: First Attempts

Abstract One challenge in the use of metallic lithium in secondary lithium ion or lithium air batteries is the dendritic growth of lithium upon repeated cycling which might either lead to a short circuit or at least to an uneven current distribution and bad cycling stability. In the present paper we present our first results on the electrodeposition of lithium from an ionic liquid within the voids of a polystyrene opal structure on copper. For this purpose polystyrene spheres with an average diameter of about 600 nm were applied onto a copper sheet by a simple dipping process resulting in a layer thickness of about 10 μm. Lithium can be deposited within this polymer structure without damaging it and the subsequent dissolution of the polystyrene spheres delivers a macroporous lithium film, proving that a mechanically stable composite electrode is feasible.

Synthesis of Structured Macroporous TiO2 Thin Films and Investigation on Their Photocatalytic Activities

Synthesis of structured macroporous TiO2 thin films on quartz substrate (macro-TiO2/Q) was performed by a dip-coating method using poly(methyl methacrylate) (PMMA) microspheres as template. Obtained TiO2 thin films kept high transparency and had anatase crystalline structure. SEM observations revealed that the macropores were uniformly formed on the film surface. The size of macropores was quite similar to the diameter of PMMA microspheres as template. In comparison to the nonporous TiO2 thin films (TiO2/Q), macro-TiO2/Q exhibited twice higher photocatalytic activity for decolorization of methylene blue in water. Decomposition of acetaldehyde in gas phase also proceeded efficiently on macro-TiO2/Q. Moreover, the surface of macro-TiO2/Q was easily hydrophilized after a short period of UV light irradiation and maintained lower water contact angle in the dark for a long period as compared to those of TiO2/Q.

Printable and flexible macroporous organosilica film with high protein adsorption capacity

An approach for creating a flexible and macroporous silsesquioxane film using phase separation method is described. The porous film was prepared by a simple coating method where sol–gel solution containing polyacrylic acid (PAA) and 1,6-bis(trimethoxysilyl)hexane in water was applied on boehmite silica coated polymethylmethacrylate (PMMA) film. After drying, the water soluble PAA template was removed by washing the film with water revealing the porous film. With certain ratios of PAA and water, fully co-continuous pore system with open surface was obtained. Porous films with 3–4 μm thickness were found to be highly flexible. The biocompatibility of the porous film was tested by immobilizing a high affinity biotin-binding chimeric avidin (ChiAVD(I117Y)) into the porous matrix The porous film was found to adsorb higher amounts of functional chimeric avidin compared to the pure PMMA film or a boehmite silica coated PMMA film.

Enhancing Sensitivity and Selectivity of Long-Period Grating Sensors using Structure-Switching Aptamers Bound to Gold-Doped Macroporous Silica Coatings

High surface area, sol-gel derived macroporous silica films doped with gold nanoparticles (AuNP) are used as a platform for high-density affinity-based immobilization of functional structure-switching DNA aptamer molecules onto Michelson interferometer long-period grating (LPG) fiber sensors, allowing for label-free detection of small molecular weight analytes such as adenosine triphosphate (ATP). The high surface area afforded by the sol-gel derived material allowed high loading of DNA aptamers, while the inclusion of gold nanoparticles within the silica film provided a high refractive index (RI) overlay, which is required to enhance the sensitivity of the LPG sensor according to our numerical simulations. By using a structure-switching aptamer construct that could release an oligonucleotide upon binding of ATP, the effective change in RI was both enhanced and inverted (i.e., binding of ATP caused a net reduction in molecular weight and refractive index), resulting in a system that prevented signals originating from nonspecific binding. This is the first report on the coupling of aptamers to LPG fiber sensors and the first use of high RI AuNP/silica films as supports to immobilize biomolecules onto the LPG sensor surface. The dual functionality of such films to both improve binding density and LPG sensor cladding refractive index results in a substantial enhancement in the sensitivity of such sensors for small molecule detection.

Morphological modification of nanostructured ultrathin-layer chromatography stationary phases

Ultrathin-layer chromatography (UTLC) provides the high sensitivities and rapid separations over short distances desirable in many analytical applications. The dependence of these performance benefits on UTLC layer microstructure motivates continued stationary phase engineering efforts. A new method of modifying the elution behaviours of nanostructured thin film UTLC stationary phases is investigated in this report. Macroporous normal phase silica thin films ∼5 μm thick were fabricated using glancing angle deposition (GLAD). Reactive ion etching (RIE) and a subsequent annealing treatment modified stationary phase morphology to tune migration velocity, analyte retention, and overall separation performance. Combining this technique with a RIE shadow mask enabled fabrication of adjacent concentration and separation zones with markedly different elution properties. Although produced using an entirely new approach, GLAD UTLC concentration zone media behaved in a manner consistent with traditional thin-layer chromatography (TLC) and high-performance TLC (HPTLC) concentration zone plates. In particular, these new media focused large volume, low concentration dye mixture spots into narrow bands to achieve high-quality separations. The described approach to modifying the morphology and resultant elution behaviours of nanostructured stationary phases expands the capabilities of the GLAD UTLC technique.

Flexible and Ordered Macroporous PMMA Polymers Films

The ordered colloidal crystals were prepared by sedimentation of a solution of silica colloidal spheres of 298nm. Colloidal crystals were obtained after evaporation at 50°Cfor eight days while solution evaporates. These colloidal crystals were used to be templates and MMA was filled in the gap of silica spheres. SiO2/PMMA structures with a overlayer of PMMA were obtained by polymerization reaction carried out at 80°C for 24 h. After etched with the hydrofluoric acid (HF) for 24h, a piece of bluish violet film can be obtained. The film is flexible and free-standing and is enough tough to be curled to various shape. This kind of film can extend the usage of macroporous structures and have various potential applications in flexible photoelectronic device.

Macroporous conductive polymer films fabricated by electrospun nanofiber templates andtheir electromechanical properties

We demonstrate a facile method to fabricate macroporous poly (3,4-ethylenedioxythiophene)/poly(4-styrene sulfonate) (PEDOT/PSS) films with empty channels by using electrospunnanofiber as a sacrificial template. The channels within the PEDOT/PSS filmswere prepared by depositing PEDOT/PSS aqueous dispersion onto poly (vinylpyrrolidone)/poly(methyl methacrylate) (PVP/PMMA) nanofiber template, and then thenanofibers were removed by solvent extraction. The average diameter of the channels is313 ± 45 nm, which is almost the same as the parent PVP/PMMA nanofibers. The macroporousPEDOT/PSS film with the empty channels showed an enhancement of electromechanicalproperties compared to the nonporous PEDOT/PSS film.

Well-defined meso- to macro-porous film of tin oxides formed by an anodization process

Anodically formed tin oxide typically displays a self-ordered porous structure with a large degree of cracking. In addition, its surface pores are frequently closed, especially in the case where the deposited tin film is anodized. Herein, we report a simple way of eliminating virtually all the inner cracks and ensuring that the surface pores are totally open, leading to well-defined one-dimensional anodic tin oxide. The current efficiency ratio of oxygen gas generation to tin oxide formation and the amount of charge allocated for pore initiation are suggested to be the key factors affecting the internal crack development and pore opening, respectively. Pulsed anodization proved to be quite an effective way to create a well-defined structure with few inner cracks and completely open pores.

Tailored Assembly of Carbon Nanostructures: Tailored Assembly of Carbon Nanotubes and Graphene (Adv. Funct. Mater. 8/2011)

AbstractThis Feature Article reviews recent progress in the tailored assembly of carbon nanotubes and graphene into three‐dimensional architectures with particular emphasis on our own research employing self‐assembly principles. Carbon nanotubes and graphene can be assembled into macroporous films, hollow spherical capsules, or hollow nanotubes, via directed assembly from solvent dispersion. This approach is cost‐effective and beneficial for large‐scale assembly, but pre‐requests stable dispersion in a solvent medium. Directed growth from a nanopatterned catalyst array is another promising approach, which enables the control of morphology and properties of graphitic materials as well as their assembly. In addition, the aforementioned two approaches can be synergistically integrated to generate a carbon hybrid assembly consisting of vertical carbon nanotubes grown on flexible graphene films. Tailored assembly relying on scalable self‐assembly principles offer viable routes that are scalable for mass production towards the ultimate utilization of graphitic carbon materials in nanoelectronics, displays, sensors, energy storage/conversion devices, and so on, including future flexible devices.

Tailored Assembly of Carbon Nanotubes and Graphene

AbstractThis Feature Article reviews recent progress in the tailored assembly of carbon nanotubes and graphene into three‐dimensional architectures with particular emphasis on our own research employing self‐assembly principles. Carbon nanotubes and graphene can be assembled into macroporous films, hollow spherical capsules, or hollow nanotubes, via directed assembly from solvent dispersion. This approach is cost‐effective and beneficial for large‐scale assembly, but pre‐requests stable dispersion in a solvent medium. Directed growth from a nanopatterned catalyst array is another promising approach, which enables the control of morphology and properties of graphitic materials as well as their assembly. In addition, the aforementioned two approaches can be synergistically integrated to generate a carbon hybrid assembly consisting of vertical carbon nanotubes grown on flexible graphene films. Tailored assembly relying on scalable self‐assembly principles offer viable routes that are scalable for mass production towards the ultimate utilization of graphitic carbon materials in nanoelectronics, displays, sensors, energy storage/conversion devices, and so on, including future flexible devices.

Optical and electrochemical properties of ordered macroporous gold array on the ITO surface

The electrochemical and optical properties of transparent, two-dimensional macroporous gold film were investigated. Colloidal crystal templates were assembled onto indium-doped tin oxide (ITO) glass surface through vertical depositing method. Following gold electrodeposition, they were removed by dissolution with tetrahydrofuran (THF). The highly ordered macroporous gold array was achieved. It was characterized by scanning electron microscope (SEM) and ultraviolet visible (UV–vis) spectrophotometry. The optical transparency of the gold film was near 25% and fairly constant between 300 and 900 nm. The macroporous gold film electrode was mounted into a thin-layer transmission cell. The electrochemical response was evaluated by thin-layer cyclic voltammograms (CV) of the Fe (CN) 6 3−/Fe (CN) 6 4− couple. Thin-layer cell exhibits good shape of waves and nearly symmetric cathodic and anodic waves. E 0′ value and n of TMPD + /TMPD (TMPD is acronyms for N,N,N′,N′-tetramethyl-p-phenylenediamine, and TMPD + is its mono-cation radical) couple were determined. Furthermore, results demonstrated electrolytic equilibrium was faster reached in macroporous gold film than ITO electrode.

A non-template hydrothermal route to uniform 3D macroporous films with switchable optical properties

Here we report the direct synthesis of long-range uniform 3D macroporous film on the surface of glass via a non-template strategy by reacting silica with a mixture solution of HCl and H 2O 2 under hydrothermal conditions. The size of macropores can be tuned from 1 μm to 7 μm by changing the hydrothermal temperature. Followed by the impregnation or release of water, the 3D porous films showed a high-contrast optical switchable property. The maximum optical transmittance modulation of these 3D porous films was up to 50% over the visible and near IR wavelength range. Furthermore, liquid-induced optical switching device were designed as a sandwich structure. The average transmittance of the device was varied between 62.3% (from 350 to 1100 nm) at the transparent state and 13.2% (from 350 to 1100 nm) at the opaque state, respectively. Such a wide modulation range of optical transmittance is suitable for application of this porous film to energy saving smart windows.

Regulation of cellular responses to macroporous inorganic films prepared by the inverse-opal method

Regenerative medicine for repairing damaged body tissues has recently become critically important. Cell culture scaffolds are required for the control of cell attachment, proliferation, and differentiation in in vitro cell cultures. A new strategy to control cell adhesion, morphology, and proliferation was developed by culturing mouse osteoblast-like MC3T3-E1 cells on novel cell culture scaffolds fabricated using ordered nanometer-sized pores (100, 300, 500, and 1000nm).Results of this study indicate that after 72h of incubation, the number of cells cultured on a silica film with a pore size of 1000nm was similar to or slightly lower than that cultured on a non-porous control silica film. Films with 100–500nm pore sizes, however, resulted in the cell growth inhibition. Morphology of the cultured cells revealed increased elongation and the formation of actin stress fibers was virtually absent on macroporous silica films with 100–500nm pore size. Vinculin molecules expressed in cells cultured on the non-porous silica films showed many clear focal adhesions, whereas focal contacts were insufficiently formed in cells cultured on macroporous films. The influence of hydroxyapatite (HAp) and alumina scaffolds on the behavior of MC3T3-E1 cells was also evaluated. The proliferation rate of MC3T3-E1 cells cultured on HAp films with 1000nm pore size was increased to approximately 20% above than that obtained of cells cultured on non-porous HAp films. These results demonstrate that the pore size and constituents of films play a role in controlling the morphology and proliferation rate of MC3T3-E1cells.

Surface Immobilization of Structure-Switching DNA Aptamers on Macroporous Sol−Gel-Derived Films for Solid-Phase Biosensing Applications

Structure-switching signaling aptamers (ss-aptamers) are single-stranded DNA molecules that are generated through in vitro selection and have the ability to switch between a duplex composed of a quencher-labeled DNA strand (QDNA) hybridized adjacent to a fluorophore label on the aptamer, and an aptamer-target complex wherein the QDNA strand is released, generating a fluorescence signal. While such species have recently emerged as promising biological recognition and signaling elements, very little has been done to evaluate their potential for solid-phase assays. In this study, we demonstrate that high surface area, sol-gel-derived macroporous silica films are suitable platforms for high-density affinity-based immobilization of functional ss-aptamer molecules, allowing for binding of both large and small target analytes with robust signal development. These films are formed using a poly(ethylene glycol) (PEG)-doped sodium silicate material, and we show that it is possible to control the pore size distribution and surface area of the silica film by varying the amount of PEG. Materials with the highest surface area are shown to be able to immobilize up to 6-fold more ss-aptamer than planar glass surfaces, providing greater detection sensitivity and somewhat improved detection limits as compared to immobilization on conventional glass. The solid-phase assay is performed using two different structure-switching signaling aptamers with high selectivity for adenosine 5'-triphosphate and platelet-derived growth factor, respectively, demonstrating that this immobilization scheme should be suitable for a variety of target ligands.

Filtration-assembling colloidal crystal templates for ordered macroporous nanoparticle films

Ordered macroporous nanoparticle thin films are achieved on porous substrates by combining ultrathin metal hydroxide nanostrands, colloidal crystal templates and the advantage of filtration technique. The preformed nanostrands layer plays two key roles for both uniform formation of hexagonal close-packed latex colloidal crystals on macroporous substrate and efficiently filling the interstitial voids of the colloidal crystal templates with nanoparticles. The stacking number of the colloids is simply controlled by the filtration volume. The uniformity of the film was guaranteed by the filtration process. After removing the latex templates and copper hydroxide nanostrand layer, free-standing ordered macroporous nanoparticle films were obtained. The robust free-standing gold nanoparticle films could be easily transferred onto various solid substrates and has potential application for electrodes, surface enhanced Raman detectors and catalyst. This method could be extended for the other ordered macroporous functional nanoparticle thin films.

Dye-sensitized biosystem sensing using macroporous semiconducting metal oxide films

Transparent semiconducting oxide (TiO2, SnO2 and ZnO) films having highly interconnected pores in the range of 30–200 nm were fabricated in one-pot using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer. Such porous structures were helpful for efficient transport of bulky guest species such as proteins. Biosensing protocols were constructed in the films by using bulky biomolecules, namely, adsorbed DNA, adsorbed antibody and adsorbed antigen–antibody (immunoassay). In the DNA-based system, the macroporous TiO2 film was the most useful among porous anatase films such as mesoporous and mesoporous/PS beads derived macroporous ones, leading to significant detection of 125 times higher photocurrent generated from a dye (Cy5) attached to DNA than those observed for the others. Macroporous SnO2 and ZnO films were also available for the construction of similar biomolecule immobilized electrodes. Extremely complicated immunoassay reactions involving bulky proteins (antigen, antibody, etc.) were also established using the macroporous TiO2 and SnO2 films. Especially photocurrent for electron transfer from Cy5 attached to the second antibody was successfully detected by using the SnO2 film for exceptionally selective sensing applications.

Design of macroporous TiO2 thin film photocatalysts with enhanced photofunctional properties

TiO2 thin films with uniform macropores were successfully prepared on quartz substrates by a dip-coating method using poly(methyl methacrylate) (PMMA) microspheres as a template. SEM observations revealed that the diameter of the macropores showed a good correspondence with the size of the PMMA microspheres. These thin films had anatase crystalline structures and maintained relatively high transparency. The degradation of organic pollutants such as 2-propanol and acetaldehyde under UV light was significantly enhanced by the construction of the macropores. It was also found that TiO2 thin films with macropores exhibited good photoinduced hydrophilicity after a short period of UV light irradiation, and a slow recovery of water contact angles in the dark as compared to those of non-porous TiO2 thin films.

Multicolor Polymer‐Dispersed Liquid Crystal

The potential of a self-assembled phase-separated macroporous polymer film filled with an appropriate solvent for application in a functional multicolor polymer-dispersed liquid crystal (PDLC) display is explored. The findings dem-onstrate that a phase-separated porous MMAA-BIS polymer network filled with mixed LCs of 5CB and 5PCH can exhibit changes in structural color covering the whole visible region and an opaque milky color upon temperature variation. This system may be available for energy-saving multicolor displays.

Gas sensing properties of p-type hollow NiO hemispheres prepared by polymeric colloidal templating method

This work presents a simple and versatile route to produce macroporous p-type metal oxide thin films. Two-dimensional arrays of p-type NiO films with a hollow hemisphere structure were fabricated by colloidal templating and RF-sputtering followed by a subsequent heat treatment. The diameter and shell thickness of the NiO hemisphere were 800 nm and 20 nm, respectively. X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the pure NiO phase with grain size of 10 nm was obtained at calcination temperatures that exceeded 450 °C. Close-packed arrays of hollow NiO hemispheres were found to exhibit p-type gas sensing properties against (CO, H 2, C 3H 8, CH 4, NO 2, and C 2H 5OH), leading to significantly enhanced responses to C 2H 5OH ( R gas / R air = 5.0 at 200 ppm).