Morphological control of surfactant-templated metal oxide films

The Effect of Novel Synthetic Methods and Parameters Control on Morphology of Nano-alumina Particles

Alumina is an inorganic material, which is widely used in ceramics, catalysts, catalyst supports, ion exchange and other fields. The micromorphology of alumina determines its application in high tech and value-added industry and its development prospects. This paper gives an overview of the liquid phase synthetic method of alumina preparation, combined with the mechanism of its action. The present work focuses on the effects of various factors such as concentration, temperature, pH, additives, reaction system and methods of calcination on the morphology of alumina during its preparation.

Enhanced photoelectrochemical performance of novel p-type MoBiCuSe4 thin films deposited by a simple surfactant-mediated solution route

Nanostructured MoBiCuSe₄ thin films with different morphologies deposited using different surfactants, such as PEG, SDS and TOPO, through a surfactant-mediated modified chemical route for PEC application.

Template-free synthesis of mesoporous CeO2 powders by integrating bottom-up and top-down routes for acid orange 7 adsorption

A combined bottom-up and top-down route was developed for the template-free synthesis of mesoporous CeO₂ powders.

Mesoscopically structured nanocrystalline metal oxide thin films

This review describes the main successful strategies that are used to grow mesostructured nanocrystalline metal oxide and SiO₂ films via deposition of sol-gel derived solutions. In addition to the typical physicochemical forces to be considered during crystallization, mesoporous thin films are also affected by the substrate-film relationship and the mesostructure. The substrate can influence the crystallization temperature and the obtained crystallographic orientation due to the interfacial energies and the lattice mismatch. The mesostructure can influence the crystallite orientation, and affects nucleation and growth behavior due to the wall thickness and pore curvature. Three main methods are presented and discussed: templated mesoporosity followed by thermally induced crystallization, mesostructuration of already crystallized metal oxide nanobuilding units and substrate-directed crystallization with an emphasis on very recent results concerning epitaxially grown piezoelectric structured α-quartz films via crystallization of amorphous structured SiO₂ thin films.

Electrochemically assisted generation of highly ordered azide-functionalized mesoporous silica for oriented hybrid films

One key challenge in inorganic mesoporous films is the development of oriented mesostructures with vertical channels, and even more challenging is their functionalization while maintaining accessible the selected surface groups. Combining the electrochemically assisted deposition of ordered and oriented azide-functionalized mesoporous silica with alkyne-azide click chemistry enables such nanostructured and vertically aligned hybrid films to be obtained with significant amounts of active organic functional groups, as illustrated for ferrocene and pyridine functions. A good level of mesostructural order was obtained, namely up to 40% of organosilane in the starting sol. The method could be applied to a wide variety of functional groups, thus offering numerous new opportunities for applications in various fields.

Control of ordering and structure in soft templated mesoporous carbon films by use of selective solvent additives

The structure of ordered mesoporous carbons fabricated using poly(styrene-block-N,N,-dimethyl-n-octadecylamine p-styrenesulfonate) (PS-b-PSS-DMODA) as the template and phenolic resin (resol) as the carbon source can be easily manipulated by inclusion of low concentrations of low volatility selective solvents in the casting solution. Casting from neat methyl ethyl ketone yields a disordered structure even upon thermal annealing. However, addition of both dioctyl phthalate (DOP, PS selective) and dimethyl sulfoxide (DMSO, resol and PSS-DMODA selective) at modest concentrations to this casting solution provides sufficient mobility to produce highly ordered films with cylindrical mesopores. The DOP acts to swell the hydrophobic domain and can more than double the mesopore size, while the DMSO acts to swell the resol phase. Moreover, the surface area of the mesoporous carbons increases significantly as the meosopore size increases. This is a result of the decrease in wall thickness, which can be ascertained by the constant d-spacing of the mesostructure as the pore size increases. This behavior is counter to the typical effect of pore swelling agents that increase the pore size and decrease the surface area. Moreover, with only 4 wt % DOP/DMSO in the solution (20 wt % relative to solids), the scattering profiles exhibit many orders of diffraction, even upon carbonization, which is not typically observed for soft templated films. Variation in the concentration of DOP and DMSO during casting enables facile tuning of the structure of mesoporous carbon films.

Morphology control in mesoporous carbon films using solvent vapor annealing

Ordered mesoporous (2-50 nm) carbon films were fabricated using cooperative self-assembly of a phenolic resin oligomer with a novel block copolymer template (poly(styrene-block-N,N-dimethyl-n-octadecylamine p-styrenesulfonate), (PS-b-PSS-DMODA)) synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Due to the high Tg of the PS segment and the strong interactions between the phenolic resin and the PSS-DMODA, the segmental rearrangement is kinetically hindered relative to the cross-linking rate of the phenolic resin, which inhibits long-range ordering and yields a poorly ordered mesoporous carbon with a broad pore size distribution. However, relatively short exposure (2 h) to controlled vapor pressures of methyl ethyl ketone (MEK) yields significant improvements in the long-range ordering and narrows the pore size distribution. The average pore size increases as the solvent vapor pressure during annealing increases, but an upper limit of p/p0 = 0.85 exists above which the films dewet rapidly during solvent vapor annealing. This approach can be extended using mesityl oxide, which has similar solvent qualities to MEK, but is not easily removed by ambient air drying after solvent annealing. This residual solvent can impact the morphology that develops during cross-linking of the films. These results illustrate the ability to fine-tune the mesostructure of ordered mesoporous carbon films through simple changes in the processing without any compositional changes in the initial cast film.

X-ray lithography and small-angle X-ray scattering: a combination of techniques merging biology and materials science

The advent of micro/nanotechnology has blurred the border between biology and materials science. Miniaturization of chemical and biological assays, performed by use of micro/nanofluidics, requires both careful selection of the methods of fabrication and the development of materials designed for specific applications. This, in turn, increases the need for interdisciplinary combination of suitable microfabrication and characterisation techniques. In this review, the advantages of combining X-ray lithography, as fabrication technique, with small-angle X-ray scattering measurements will be discussed. X-ray lithography enables the limitations of small-angle X-ray scattering, specifically time resolution and sample environment, to be overcome. Small-angle X-ray scattering, on the other hand, enables investigation and, consequently, adjustment of the nanostructural morphology of microstructures and materials fabricated by X-ray lithography. Moreover, the effect of X-ray irradiation on novel materials can be determined by use of small-angle X-ray scattering. The combination of top-down and bottom-up methods to develop new functional materials and structures with potential in biology will be reported.

Synthesis of hierarchically nanoporous silica films for controlled drug loading and release

Films with well-controlled porous structures provide many exciting application opportunities in chemistry and biology. Here we report the synthesis of a highly uniform, hierarchically nanoporous silica film structure, and its application in drug loading and release for antibacterial surface coating. Templated by both sub-micron poly-styrene (PS) particles and a triblock copolymer (F127), this hierarchically nanoporous film has two distinct pore sizes of 200 nm and 7 nm. The 7-nm mesopores provide high surface area and thus high adsorption capacity for drug molecules, and the 200-nm macropores facilitate the adsorption rate of drug molecules, especially for molecules with comparable sizes to mesopores. Fluorescence measurement of rhodamine release demonstrates that this hierarchically porous film has a higher adsorption capacity, efficiency and much longer molecule releasing time window than both the inverse opal film and the mesoporous film. When loaded with Ampicillin, this hierarchically porous film shows over 8 times longer of inhibition of E. coli growth than both the inverse opal film and the mesoporous film. This simple and versatile process allows for fabrication of a variety of surface-coated, hierarchically nanoporous films with different chemical compositions and applications.

Impact of film thickness on the morphology of mesoporous carbon films using organic-organic self-assembly

Mesoporous polymer and carbon thin films are prepared by the organic-organic self-assembly of an oligomeric phenolic resin with an amphiphilic triblock copolymer template, Pluronic F127. The ratio of resin to template is selected such that a body-centered cubic (Im3m) mesostructure is formed in the bulk. However, well-ordered mesoporous films are not always obtained for thin films (<100 nm), and this behavior is found to be directly correlated with the initial phenolic resin to template ratio. Furthermore, the symmetry of ordered phases is highly dependent on the number of layers of spheres in the film: Monolayers and bilayers are characterized by hexagonal close-packed (HCP) symmetry, while films with approximately 5 layers of spheres exhibit a mixture of HCP and face-centered orthorhombic (FCO) structures. Ultrathick films having more than 30 layers of spheres are similar to the bulk body-centered cubic symmetry with a preferential orientation of the closest-packed (110) plane parallel to the substrate. Film thickness and initial composition of the carbonizable precursors in the template are critical factors in determining the morphology of mesoporous carbon films. These results provide insight into why difficulties have been reported in producing ultrathin ordered mesoporous carbon films using cooperative organic-organic self-assembly.

Aerosol route to functional nanostructured inorganic and hybrid porous materials

The major advances in the field of the designed construction of hierarchically structured porous inorganic or hybrid materials wherein multiscale texturation is obtained via the combination of aerosol or spray processing with sol-gel chemistry, self-assembly and multiple templating are the topic of this review. The available materials span a very large set of structures and chemical compositions (silicates, aluminates, transition metal oxides, nanocomposites including metallic or chalcogenides nanoparticles, hybrid organic-inorganic, biohybrids). The resulting materials are manifested as powders or smart coatings via aerosol-directed writing combine the intrinsic physical and chemical properties of the inorganic or hybrid matrices with defined multiscale porous networks having a tunable pore size and connectivity, high surface area and accessibility. Indeed the combination of soft chemical routes and spray processing provides "a wind of change" in the field of "advanced materials". These strategies give birth to a promising family of innovative materials with many actual and future potential applications in various domains such as catalysis, sensing, photonic and microelectronic devices, nano-ionics and energy, functional coatings, biomaterials, multifunctional therapeutic carriers, and microfluidics, among others.

Mesoporous silica hybrid membranes for precise size-exclusive separation of silver nanoparticles

One-dimensional (1D) nanomaterials have unique applications due to their inherent physical properties. In this study, hexagonally ordered mesoporous silica hybrid anodic alumina membranes (AAM) were synthesized using template-guided synthesis with a number of nonionic n-alkyl-oligo(ethylene oxide), Brij-type (C(x)EO(y)), which are surfactants that have different molecular sizes and characteristics. The hexagonal mesoporous silicas are vertically aligned in the AAM channels with a predominantly columnar orientation. The hollow mesostructured silicas had tunable pore diameters varying from 3.7 to 5.1 nm. In this synthesis protocol, the surfactant molecular natures (corona/core features) are important for the controlled generation of ordered structures throughout AAM channels. The development of ultrafiltration membranes composed of silica mesostructures could be used effectively in separating silver nanoparticles (Ag NPs) in both aqueous and organic solution phases. This would be relevant to the production of well-defined Ag NPs with unique properties. To create a size-exclusive separation system of Ag NPs, we grafted hydrophobic trimethylsilyl (TMS) groups onto the inner pores of the mesoporous silica hybrid AAM. The immobilization of the TMS groups allowed the columnar mesoporous silica inside AAM to retain this inner pore order without distortion during the separation of solution-phase Ag NPs in organic solvents that may cause tortuous-pore membranes. Mesoporous TMS-silicas inside 1D AAM channels were applicable as a size-exclusive separation system to isolate organic solution-phase Ag NPs of uniform morphology and size.

Impact of nanopore morphology on cell viability on mesoporous polymer and carbon surfaces

Topography at the nanoscale can lead to dramatic changes in the adhesion of cells to surfaces and their subsequent viability. For biological applications, including tissue engineering and cell-based sensing, the large internal surface area of ordered mesoporous carbons provides an opportunity for enhanced sensitivity and performance, but the mesostructure also affects the topography of the material. In this work, we probe the viability and adhesion of osteoblasts on ordered mesoporous materials with different morphologies and matrix chemistries. FDU-15 (hexagonal) and FDU-16 (cubic) films were processed at either 350 degrees C (polymeric) or 800 degrees C (carbon) to provide these different materials. For the films processed at 350 degrees C, the cell adhesion was markedly improved on the mesoporous films in comparison to a dense film analog, consistent with many reports in the literature that nanostructuring of surfaces improves the viability and adhesion of osteoblasts. Conversely, osteoblast adhesion was reduced on the carbonized surfaces processed at 800 degrees C when ordered mesopores were introduced, particularly for the cubic mesostructure (FDU-16). We attribute the decrease in cell adhesion to the propensity of the ordered mesoporous carbon films to sorb organics from aqueous solution, which could lead to removal of adhesion-promoting compounds at the film surface. These results suggest that cell viability on mesoporous polymer and carbon films can be controlled through simple changes in the pyrolysis temperature.

Computer simulation of the epitaxy of surfactant-templated inorganic nanomaterials on patterned surfaces

For a surfactant-inorganic-water system, we study systemically the epitaxy process of the surfactant-templated inorganic nanomaterial on a patterned surface with a lattice Monte Carlo method. It is found that by using ring-patterned substrate as a template, vertically oriented inorganic material may be formed through the nanometer-scale epitaxy. For all the cases studied in this work, a hemicylinder initially formed on the ring pattern behaves as nucleation sites for the following growth process. Different parameters, such as surfactant architecture, bulk surfactant concentration, fraction of inorganic component, and pattern size, are found to affect the epitaxial growth process of the inorganic nanomaterial. The change of surfactant architecture alters the structure of formed aggregates significantly, thus affecting the epitaxial growth. For the effects of surfactant concentration, it is found that there exists a critical value. If and only if the bulk surfactant concentration is higher than the critical value is the epitaxial growth of inorganic material nucleated from the patterned substrate possible. For the effects of the fraction of the inorganic component, simulation results indicate that there also exists a volume fraction above which the nanomaterial growth is dominated by macrophase separation but not templated by the substrate pattern. The geometry of the chemical modification of the surface also shows significant effects on the nanometer-scale epitaxy, depending on whether its sizes are commensurate with the morphology of the formed inorganic nanomaterials or not.

Vertically oriented hexagonal mesoporous films formed through nanometre-scale epitaxy

Polymer- and surfactant-templated mesoporous inorganic materials offer a unique combination of controllable nanoscale architecture, materials variation and low-cost solution processing. Inorganic materials can be produced with a range of periodic pore structures, with feature size ranging from 2 to 30 nm, and from a diverse set of materials. Unfortunately in thin-film form, the pores of the ubiquitous hexagonal honeycomb phase tend to lie in the plane of the substrate making these materials unsuitable for applications where diffusion into the pores is required. Here, we show that nanometre-scale epitaxy on a patterned substrate can be used to form vertically oriented pores in honeycomb-structured films. We use the surface of cubic mesoporous films to form the pattern; as such, our method does not sacrifice the simple processing advantages of a self-assembled system. A precise lattice match between the hexagonal and cubic films is needed for vertical orientation, a condition that can be achieved using mixed templates or selective pore swelling. Pore orientation is characterized by a combination of microscopy and diffraction. Here, we present alignment data on oriented nanopores in the 10-15 nm range, but the method should be applicable across the 2-30 nm pore size range of these self-organized materials.

Photochromic hybrid organic-inorganic liquid-crystalline materials built from nonionic surfactants and polyoxometalates: elaboration and structural study

This work reports the elaboration and structural study of new hybrid organic-inorganic materials constructed via the coupling of liquid-crystalline nonionic surfactants and polyoxometalates (POMs). X-ray scattering and polarized light microscopy demonstrate that these hybrid materials, highly loaded with POMs (up to 18 wt %), are nanocomposites of liquid-crystalline lamellar structure (Lalpha), with viscoelastic properties close to those of gels. The interpretation of X-ray scattering data strongly suggests that the POMs are located close to the terminal -OH groups of the nonionic surfactants, within the aqueous sublayers. Moreover, these materials exhibit a reversible photochromism associated to the photoreduction of the polyanion. The photoinduced mixed-valence behavior has been characterized through ESR and UV-visible-near-IR spectroscopies that demonstrate the presence of W(V) metal cations and of the characteristic intervalence charge transfer band in the near-IR region, respectively. These hybrid nanocomposites exhibit optical properties that may be useful for applications involving UV-light-sensitive coatings or liquid-crystal-based photochromic switches. From a more fundamental point of view, these hybrid materials should be very helpful models for the study of both the static and dynamic properties of nano-objects confined within soft lamellar structures.

Electrochemically assisted self-assembly of mesoporous silica thin films

Supported mesostructured thin films are of major importance for applications in optical, electrochemical and sensing devices. However, good performance is restricted to mesostructured phases ensuring good accessibility from the film surface, which would be straightforward with cylindrical pores oriented normal to the underlying support, but this remains challenging. Here, we demonstrate that electrochemistry is likely to induce self-assembly of surfactant-templated (organo)silica thin films on various conducting supports, homogeneously over wide areas. The method involves the application of a suitable cathodic potential to an electrode immersed in a surfactant-containing hydrolysed sol solution to generate the hydroxyl ions that are necessary to catalyse polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the electrode surface. The method is compatible with controlled and localized deposition on heterogeneous supports, opening the way to electrochemically driven nanolithography for designing complex patterns of widely accessible mesostructured materials.