Mesoporous Titania Thin Films Research Articles

Structural and Mechanical Evolution of Mesoporous Films with Thermal Treatment: The Case of Brij 58 Templated Titania

Mesoporous titania thin films (MTTFs) with well ordered cubic array of mesopores were synthesized on glass and silicon substrates using Brij 58 as a template. The effect of the thermal treatment and the substrate on the structural parameters (thickness, porosity, pore order, and crystallinity) and the mechanical properties of MTTFs were determined by electron microscopy, X-ray diffraction, Raman spectroscopy, 2D-small angle X-ray scattering, ellipsometric porosimetry, and nanoindentation. Clear differences in the mesostructural order evolution and crystallization behavior were observed as a function of the substrate and the thermal treatment. In particular, the anatase crystallization process occurs at lower temperatures for samples prepared on silicon when compared with samples prepared on glass, due to the balance between nanocrystals formation, mass diffusion, and Na+ migration from the substrate. As a consequence of such phenomena, the MTTFs mechanical properties are also dependent on the substrate. F...

Mesoporous thin film structures as metal nanoparticle reactors for electronic circuits: Effects of matrix crystallinity and nanoparticle functionalization

There is an increasing interest in versatile nanoelectronic structures based on stable, accessible and spatially located arrays of metal nanoparticles. In this study, the influences of mesoporous titania thin film crystallinity and pore features over electrical conductivity of embedded Ag-nanoparticles were analyzed. Although matrices treated at lower temperatures have shown less pore connectivity, less extensive anatase fraction and lower silver content, they revealed higher electrical conductivity than matrices treated at higher temperatures. This was interpreted as better connectivity among particles from plasmon behavior. The stability of this system was significantly enhanced through upon chemisorption of 1-octanethiol self-assemble monolayers over Ag-nanoparticles. The maximum plasmon absorbance remained practically unaltered after storage for at least 15 days and the current remains stable up to 20 voltage cycles. This demonstrates that a stable and accessible conductive nanocomposite circuit consisting of alkanethiol-functionalized metal nanoparticles embedded in a mesoporous oxide thin film matrix can be produced.

Gold Nanoparticles Supported on Mesoporous Titania Thin Films with High Loading as a CO Oxidation Catalyst.

In the present work, 2.4 nm gold nanoparticles (Au NPs) are uniformly dispersed on mesoporous titania thin films which are structurally tuned by controlling the calcination temperature. The gold content of the catalyst is as high as 27.8 wt %. To our knowledge, such a high loading of Au NPs with good dispersity has not been reported until now. Furthermore, the reaction rate of the gold particles is enhanced by one order of magnitude when supported on mesoporous titania compared to non-porous titania. This significant improvement can be explained by an increase in the diffusivity of the substrate due to the presence of mesopores, the resistance to agglomeration, and improved oxygen activation.

2D-SAXS In Situ Measurements as a Tool To Study Elusive Mesoporous Phases: The Case of p6mm TiO2

Mesoporous titania thin films (MTTF) with p6mm pore array are currently attracting a great interest because of their 2D-hexagonal arrangement of close-packed cylindrical pores, but they are difficult to synthesize. This work seeks to understand such apparent elusiveness of the p6mm phase for MTTF. To that end, a wide variety of MTTF were prepared using different precursors, templates, aging and stabilization conditions, according to procedures reported in the literature and several variations thereof. Initially, the obtained MTTF were cross-characterized by ex situ transmission electron microscopy, two-dimensional small-angle X-ray scattering (2D-SAXS), and grazing incidence SAXS, with no clear evidence of a well-organized p6mm pore structure in the final system. In view of the difficulty of obtaining the desired pore array, the mesophase evolution was monitored during the synthesis, aging, stabilization, and calcination stages, resorting to in situ 2D-SAXS experiments. The performed experiments indicate ...

Magnetic Gold Confined in Ordered Mesoporous Titania Thin Films: A Noble Approach for Magnetic Devices.

In the past decade, the surprising magnetic behavior of gold nanoparticles has been reported. This unexpected property is mainly attributed both to size and surface effects. Mesoporous thin films are ideal matrices for metallic nanoparticles inclusion, because of their highly accessible and tailorable pore systems that lead to completely tunable chemical environments. Exploiting these features, we synthesized Au nanoparticles within mesoporous titania thin films (film thickness of ∼150 nm and pore diameter of ∼5 nm), and we studied their magnetic properties under confinement. Here, we present the results of the magnetization as a function of temperature and magnetic field for this system, which are consistent with the previously reported for free (unconfined) thiol-capped gold nanoparticles. The successful inclusion of stable magnetic Au nanoparticles within transparent mesoporous thin films opens the gates for the application of these nanocomposites in two-dimensional (2D) microdevices technology and magneto-optical devices.

Stem cell homing using local delivery of plerixafor and stromal derived growth factor-1alpha for improved bone regeneration around Ti-implants.

Triggering of the early healing events, including the recruitment of progenitor cells, has been suggested to promote bone regeneration. In implantology, local drug release technologies could provide an attractive approach to promote tissue regeneration. In this study, we targeted the chemotactic SDF-1α/CXCR4 axis that is responsible e.g. for the homing of stem cells to trauma sites. This was achieved by local delivery of plerixafor, an antagonist to CXCR4, and/or SDF-1α, from titanium implants coated with mesoporous titania thin films with a pore size of 7.5 nm. In vitro drug delivery experiments demonstrated that the mesoporous coating provided a high drug loading capacity and controlled release. The subsequent in vivo study in rat tibia showed beneficial effects with respect to bone-implant anchorage and bone-formation along the surface of the implants when plerixafor and SDF-1α were delivered locally. The effect was most prominent by the finding that the combination of the drugs significantly improved the mechanical bone anchorage. These observations suggest that titanium implants with local delivery of drugs for enhanced local recruitment of progenitor cells have the ability to promote osseointegration. This approach may provide a potential strategy for the development of novel implant treatments. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2466-2475, 2016.

Antimicrobial performance of mesoporous titania thin films: role of pore size, hydrophobicity, and antibiotic release.

Implant-associated infections are undesirable complications that might arise after implant surgery. If the infection is not prevented, it can lead to tremendous cost, trauma, and even life threatening conditions for the patient. Development of an implant coating loaded with antimicrobial substances would be an effective way to improve the success rate of implants. In this study, the in vitro efficacy of mesoporous titania thin films used as a novel antimicrobial release coating was evaluated. Mesoporous titania thin films with pore diameters of 4, 6, and 7 nm were synthesized using the evaporation-induced self-assembly method. The films were characterized and loaded with antimicrobial agents, including vancomycin, gentamicin, and daptomycin. Staphylococcus aureus and Pseudomonas aeruginosa were used to evaluate their effectiveness toward inhibiting bacterial colonization. Drug loading and delivery were studied using a quartz crystal microbalance with dissipation monitoring, which showed successful loading and release of the antibiotics from the surfaces. Results from counting bacterial colony-forming units showed reduced bacterial adhesion on the drug-loaded films. Interestingly, the presence of the pores alone had a desired effect on bacterial colonization, which can be attributed to the documented nanotopographical effect. In summary, this study provides significant promise for the use of mesoporous titania thin films for reducing implant infections.

Correction: Mesoporous titania thin films as efficient enzyme carriers for paraoxon determination/detoxification: effects of enzyme binding and pore hierarchy on the biocatalyst activity and reusability.

Correction for 'Mesoporous titania thin films as efficient enzyme carriers for paraoxon determination/detoxification: effects of enzyme binding and pore hierarchy on the biocatalyst activity and reusability' by N. Frančičet al., Analyst, 2014, 139, 3127-3136.

Three-Dimensional Electrochemical Lithography in Mesoporous TiO2 Thin Films

Fil: Linares Moreau, Maria de Las Mercedes. Comision Nacional de Energia Atomica. Centro Atomico Constituyentes. Gerencia de Investigacion y Aplicaciones; Argentina. Universidad Nacional de San Martin. Instituto Sabato; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

The effect of alendronate on biomineralization at the bone/implant interface.

A recent approach to improve the osseointegration of implants is to utilize local drug administration. The presence of an osteoporosis drug may influence both bone quantity and quality at the bone/implant interface. Despite this, the performance of bone-anchoring implants is traditionally evaluated only by quantitative measurements. In the present study, the osteoporosis drug alendronate (ALN) was administrated from mesoporous titania thin films that were coated onto titanium implants. The effect that the drug had on biomineralization was explored both in vitro using simulated body fluid (SBF) and in vivo in a rat tibia model. The SBF study showed that the apatite formation was completely hindered at a high concentration of ALN (0.1 mg/mL). However, when ALN was administrated from the mesoporous coating the surface became completely covered with apatite. Ex vivo characterization of the bone/implant interface using Raman spectroscopy demonstrated that the presence of ALN enhanced the bone mineralization, and that the chemical signature of newly formed bone in the presence of ALN had a higher resemblance to the pre-existing mature bone than to the bone formed without drug. Taken together, this study demonstrates the importance of evaluating the quality of the formed bone to better understand the performance of implants. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A 104A: 620-629, 2016.

Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy.

The osseointegration capacity of bone-anchoring implants can be improved by the use of drugs that are administrated by an inbuilt drug delivery system. However, to attain superior control of drug delivery and to have the ability to administer drugs of varying size, including proteins, further material development of drug carriers is needed. Mesoporous materials have shown great potential in drug delivery applications to provide and maintain a drug concentration within the therapeutic window for the desired period of time. Moreover, drug delivery from coatings consisting of mesoporous titania has shown to be promising to improve healing of bone-anchoring implants. Here we report on how the delivery of an osteoporosis drug, alendronate, can be controlled by altering pore size and surface energy of mesoporous titania thin films. The pore size was varied from 3.4 nm to 7.2 nm by the use of different structure-directing templates and addition of a swelling agent. The surface energy was also altered by grafting dimethylsilane to the pore walls. The drug uptake and release profiles were monitored in situ using quartz crystal microbalance with dissipation (QCM-D) and it was shown that both pore size and surface energy had a profound effect on both the adsorption and release kinetics of alendronate. The QCM-D data provided evidence that the drug delivery from mesoporous titania films is controlled by a binding–diffusion mechanism. The yielded knowledge of release kinetics is crucial in order to improve the in vivo tissue response associated to therapeutic treatments.

Macro-/mesoporous titania thin films: analysing the effect of pore architecture on photocatalytic activity using high-throughput screening

The photocatalytic behaviour of titania thin films was studied using a high-throughput method to correlate the effect of pore and thickness modification.

Mechanical behavior of mesoporous titania thin films

Nanoindentation is used to assess mechanical properties of ordered mesoporous titania thin films with pore sizes in the range of 8–16 nm. Estimates of strut properties are obtained under the standard scaling assumptions widely used in porous media. The inferred hardness and fracture toughness of individual struts are found to correspond to anatase titania, indicating the absence of obvious size effects in the nanostructured ceramic. This is in marked contrast to nanoporous metals, where size effects often play a crucial role in determining material properties at similar length scales.

Direct Spectroscopic Evidence for Constituent Heteroatoms Enhancing Charge Recombination at a TiO2−Ruthenium Dye Interface

A series of three bis(tridentate) cycloruthenated sensitizers with furyl, thiophene, or selenophene units attached to the cyclometalated ligand were designed to examine how chalcogen atoms effect interfacial electron transfer events that occur following the absorption of visible light by the sensitizers when attached to mesoporous titania thin films immersed in CH3CN electrolytes. Spectroelectrochemistry established that the RuIII/II reduction potentials were confined to the 0.954–0.965 V vs NHE range for the series and that the density of TiO2 acceptor states were sensitizer-independent. Pulsed light excitation into the metal-to-ligand charge transfer band of the sensitized thin films resulted in rapid excited state injection, kinj > 108 s–1. Charge recombination (RuIII/TiO2(e–) → RuII/TiO2) rate constants were insensitive to the identity of the cyclometalated compound, yet the open circuit photovoltages were markedly lower for the compound containing selenophene. These lower photovoltages appear to be a...

Tailoring the Morphology of Mesoporous Titania Thin Films through Biotemplating with Nanocrystalline Cellulose

The tunable porosity of titania thin films is a key factor for successful applications in photovoltaics, sensing, and photocatalysis. Here, we report on nanocrystalline cellulose (NCC) as a novel shape-persistent templating agent enabling the straightforward synthesis of mesoporous titania thin films. The obtained structures are highly porous anatase morphologies having well-defined, narrow pore size distributions. By varying the titania-to-template ratio, it is possible to tune the surface area, pore size, pore anisotropy, and dimensions of titania crystallites in the films. Moreover, a post-treatment at high humidity and subsequent slow template removal can be used to achieve pore widening; this treatment is also beneficial for the multilayer deposition of thick films. The resulting homogeneous transparent films can be directly spin- or dip- coated on glass, silicon, and transparent conducting oxide (TCO) substrates. The mesoporous titania films show very high activity in the photocatalytic NO conversion and in the degradation of 4-chlorophenol. Furthermore, the films can be successfully applied as anodes in dye-sensitized solar cells.

Nano‐Designed Enzyme–Functionalized Hierarchical Metal–Oxide Mesoporous Thin Films: En Route to Versatile Biofuel Cells

A versatile bioelectronic system is presented, based on Ag nanoparticle assemblies embedded into hierarchically mesoporous titania thin films on which electroactive enzymes are simply immobilized by a fast adsorption process. This strategy enables straightforward, cost effective, high-performance, thin-film enzymatic fuel cell technology with foreseeable applications in self-powered microfluidic and electronic devices.

Mesoporous titania thin films as efficient enzyme carriers for paraoxon determination/detoxification: effects of enzyme binding and pore hierarchy on the biocatalyst activity and reusability.

In this work we demonstrate the efficient immobilization of histidine 6-tagged organophosphate hydrolase (His6-OPH), an organophosphate-degrading enzyme, on mesoporous titania thin films. This permits the use of the biocatalyst films as efficient tools in the detection/detoxification of paraoxon. His6-OPH was immobilized on mesoporous thin films with uniform (9 nm) and bimodal (13-38 nm) pore size distribution, through covalent attachment and physical adsorption. The biocatalyst films show good activity, and enhanced stability with respect to the free enzyme at extreme conditions of pH and temperature, especially around neutral pH and room temperature. In addition, the bioactive films can be easily separated from the reaction media and reused multiple times without significant loss of activity.

Reduced Titania Films with Ordered Nanopores and Their Application to Visible Light Water Splitting

We report on the photoelectrochemical properties of partially reduced mesoporous titania thin films. The fabrication is achieved by synthesizing mesoporous titania thin films through the self-assembly of a titania precursor and a block copolymer, followed by aging and calcination, and heat-treatment under a (1 torr) environment. Depending on the temperature used for the reaction with , the degree of the reduction (generation of oxygen vacancies) of the titania is controlled. The oxygen vacancies induce visible light absorption, and decrease of resistance while the mesoporosity is practically unaltered. The photoelectrochemical activity data on these films, by measuring their photocurrent-potential behavior in 1 M NaOH electrolyte under AM 1.5G 100 mW illumination, show that the three effects of the oxygen vacancies contribute to the enhancement of the photoelectrochemical properties of the mesoporous titania thin films. The results show that these oxygen deficient mesoporous thin films hold great promise for a solar hydrogen generation. Suggestions for the materials design for improved photoelectrochemical properties are made.

Preparation of Ordered Mesoporous Alumina‐Doped Titania Films with High Thermal Stability and Their Application to High‐Speed Passive‐Matrix Electrochromic Displays

Ordered mesoporous alumina-doped titania thin films with anatase crystalline structure were prepared by using triblock copolymer Pluronic P123 as structure-directing agent. Uniform Al doping was realized by using aluminum isopropoxide as a dopant source which can be hydrolyzed together with titanium tetraisopropoxide. Aluminum doping into the titania framework can prevent rapid crystallization to the anatase phase, thereby drastically increasing thermal stability. With increasing Al content, the crystallization temperatures tend to increase gradually. Even when the Al content doped into the framework was increased to 15 mol %, a well-ordered mesoporous structure was obtained, and the mesostructural ordering was still maintained after calcination at 550 °C. During the calcination process, large uniaxial shrinkage occurred along the direction perpendicular to the substrate with retention of the horizontal mesoscale periodicity, whereby vertically oriented nanopillars were formed in the film. The resulting vertical porosity was successfully exploited to fabricate a high-speed and high-quality passive-matrix electrochromic display by using a leuco dye. The vertical nanospace in the films can effectively prevent drifting of the leuco dye.

Controlled Synthesis of Well‐Ordered Mesoporous Titania Films with Large Mesopores Templated by Spherical PS‐b‐PEO Micelles

AbstractWe focus on the effects of solvent and the hydrolysis rate of inorganic precursors in the synthesis of ordered mesoporous titania thin film with uniform and large‐sized pores. The amphiphilic diblock copolymer poly(styrene‐b‐ethylene oxide) was used as the structure‐directing agent. The formation of orderly arranged polymeric micelles is primarily necessary to obtain well‐ordered mesoporous titania. Here, we achieve both large‐sized mesopores and long‐range ordering by precisely controlling the properties of the precursor solution. The mesostructural domains successfully extend up to the micrometer scale, which has never seen in previous reports.