No abstract

Periodically ordered mesoporous titania thin films (MTTF) present a high surface area, controlled porosity in the 2-20 nm pore diameter range and an amorphous or crystalline inorganic framework. These materials are nowadays routinely prepared by combining soft chemistry and supramolecular templating. Photocatalytic transparent coatings and titania-based solar cells are the immediate promising applications. However, a wealth of new prospective uses have emerged on the horizon, such as advanced catalysts, perm-selective membranes, optical materials based on plasmonics and photonics, metamaterials, biomaterials or new magnetic nanocomposites. Current and novel applications rely on the ultimate control of the materials features such as pore size and geometry, surface functionality and wall structure. Even if a certain control of these characteristics has been provided by the methods reported so far, the needs for the next generation of MTTF require a deeper insight in the physical and chemical processes taking place in their preparation and processing. This article presents a critical discussion of these aspects. This discussion is essential to evolve from know-how to sound knowledge, aiming at a rational materials design of these fascinating systems.

Mesoporous titania thin films with accessible porosity and anatase structure were synthesized on conductive glass or silicon substrates. Ti K-edge XANES was used to assess Ti local coordination. Analysis of the pre-edge region permitted accurate quantification of the degree of crystalline nature of the inorganic walls upon thermal treatment. The substrate has a marked effect:  film crystallization takes places at temperatures 100 °C lower in the crystalline Si, with respect to conductive glass. Accordingly, remarkable photocatalytic properties are found in well-crystallized mesoporous titania deposited onto conductive silicon.

A novel optical sensor is proposed, based on the normal-incidence excitation of Tamm plasmons at the interface between a multilayer of porous SiO 2 and TiO 2 , acting as a permeable Bragg reflector, and a flat gold film.Transmittance spectra reveal a sharp Tamm mode within the stop-band of the distributed Bragg reflector, the spectral position of which was monitored upon exposure to various solvents, demonstrating the sensitivity of the device to changes of refractive index.

Organic molecules have been incorporated into the pore system of mesoporous TiO 2 and ZrO 2 xerogels and thin films. Surface-modifying functions include alkyl, aryl, amino, sulfonate, thiol, and polyol. Phosphate, phosphonate, carboxylate, and polyphenol were used as grafting groups. The incorporation of these functions into the mesoporous network (typically 2-8 µmol/m 2 ) was monitored by crossing FTIR and EDS. In particular, the cases of dihexadecyl phosphate, monododecyl phosphate, 3-nitrophthalic acid, TIRON (disodium 1,2-dihydroxybenzene, 3,5-disulfonate), and thiol-bearing carboxylates are discussed. Uptake experiments suggest that the pore structure plays a key role in the accessibility of the pore system. Leaching experiments in different solvents and conditions were performed to assess the anchoring of the grafted functions. This permits tailoring of the molecule grafting, from firmly anchored functions to groups with controlled lability.

A first study of the behavior of amino functions in mesoporous hybrid thin films M 1-x (Si-(CH 2 ) 3 NH 2 ) x O 2-x/2 (M ) Si, Ti, Zr; 0.05 e x e 0.2) with accessible Im3 j m-or Fm3 j m-derived pore mesostructures is presented. An XPS study of surface nitrogen species shows two different sites corresponding to amino and ammonium groups. The ratio of these species changes with pH and is related to the nature of M, suggesting that the interaction between the organic functions and the surface M-OH groups can be tailored to tune the surface acid-base behavior. Density functional theory (DFT) calculations were used to rationalize the XPS observations showing that -NH 3 + functions irreversibly transfer a proton to neighboring M-Osurface groups. The acid-base surface properties can be further modified by adding a phosphonate "capping" on the M surface sites. Our findings have a series of interesting implications in surface functionalization: attachment of biomolecules to surfaces, design of perm-selective or philicity-selective membranes, or design of catalysts that show a well-defined organic reactive function near surface hydroxyl groups.

Application of surface-enhanced Raman scattering (SERS) spectroscopy to the ultrasensitive analysis of small molecules in biological samples is complicated by signal contamination by ubiquitous macromolecules such as proteins, nucleic acids, or lipids. We present a proof-of-concept study of the application of composite films comprising branched gold nanoparticles embedded in mesoporous thin films, which act as molecular sieves. The inorganic mesoporous layer only allows the diffusion of small molecules toward the plasmonic particles while preventing the contact of macromolecules in solution with the optical sensor.Fil: López-Puente, Vanesa. Universidad de Vigo; EspañaFil: Abalde-Cela, Sara. Universidad de Vigo; EspañaFil: Angelome, Paula Cecilia. Comisión Nacional de Energía Atómica. Gerencia del Área de Seguridad Nuclear y Ambiente. Gerencia de Química (CAC); ArgentinaFil: Álvarez Puebla, Ramón. Universitat Rovira I Virgili; España. Centro de Tecnología Química de Cataluña; España. Institució Catalana de Recerca i Estudis Avancats (ICREA); EspañaFil: Liz-Marzán, Luis M.. Universidad de Vigo; España. Bionanoplasmonics Laboratory; Españ

No abstract