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.

The adsorption and photooxidation of salicylic acid on dispersed TiO2 (Degussa P-25) particles was studied as a function of substrate concentration and pH. Salicylic acid chemisorbs at the particle interface, forming inner-sphere titanium(IV) salicylate surface complexes. The visible differential diffuse reflectance spectra of the surface complexes present a band, with maximum absorption at 420 nm, which is assigned to the internal ligand to metal charge-transfer transition. The surface excess of salicylic acid increases with decreasing pH and levels off around pK a1. At constant pH, the surface excess increases with the concentration of salicylic acid, the isotherm reflecting surface site heterogeneity. Photooxidation rates in air-saturated solutions, on the other hand, are independent of both pH and salicylic acid concentration, in the entire studied range. Chemisorption results are accounted for by a multisite surface complexation model in which two different surface titanium sites and three complexation modes are considered. The mismatch between salicylic acid surface excess values and photooxidation rates is interpreted in terms of the different reactivities of the titanium(IV) salicylate surface complexes and is attributed to the fastest hole capture by bidentate salicylate binding a single surface titanium ion. The advanced rationale illustrates the importance of the basic principles of coordination chemistry in the interpretation of apparent kinetic orders in photolyte concentration.

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The photo-electro-oxidation on titanium dioxide film electrodes of methanol, 2-propanol, and tert-butyl alcohol has been studied by measuring the transient photocurrents observed during the early stages of illumination. Transients and steady-state photocurrents, measured at different applied potentials and methanol concentrations, were compared with model predictions. The numerical solution of the differential equations corresponding to methanol photo-electro-oxidation, as well as the advanced experimental evidence, supports the hypothesis that surface hole trapping as −OH• mediates the charge transfer to methanol. Formation of −OH• accounts for the high initial photocurrents, its rapid decay being due to recombination. The rate of oxidation of methanol is then determined by the rate of reaction between −OH• and CH3OH located in the interfacial region. The oxidation of •CH2OH to CH2O, through the injection of an electron into the conduction band (current doubling), gives rise to an increase in photocurrent; steady state values are later attained. As a consequence, a minimum transient is observed. The minimum is marginally observable in tert-butyl alcohol solutions, in line with the properties of the respective radicals.

An interconnected Au nanoparticle arrangement is obtained by electrodeposition from Au(III) soluble complexes within the pore system of block-copolymer templated mesoporous titania films. The resulting Au@TiO2 nanocomposites (5 nm Au particles, 5.5 nm amorphous titania walls) have the electrochemical behavior of a gold electrode of high surface area. The attenuation of Au surface plasmon due to -OH electroadsorption and the existence of mixed localized states in these Au@TiO2 nanocomposites are observed by in situ spectroelectrochemistry.

We introduce a nanoparticle-mesoporous oxide thin film composite (NP-MOTF) as low-cost and straightforward sensing platforms for surface-enhanced Raman Spectroscopy (SERS). Titania, zirconia, and silica mesoporous matrices templated with Pluronics F-127 were synthesized via evaporation-induced self-assembly and loaded with homogeneously dispersed Ag nanoparticles by soft reduction or photoreduction. Both methods give rise to uniform and reproducible Raman signals using 4-mercaptopyridine as a probe molecule. Details on stability and reproducibility of the Raman enhancement are discussed. Extensions in the design of these composite structures were explored including detection of nonthiolated molecules, such as rhodamine 6-G or salicylic acid, patterning techniques for locating the enhancement regions and bilayered mesoporous structures to provide additional control on the environment, and potential size-selective filtration. These inorganic oxide-metal composites stand as extremely simple, reproducible, and versatile platforms for Raman spectroscopy analysis.

Processes that occur in the TiO2-photocatalysis of binary aqueous solutions containing model photolytes with different affinity for the TiO2 surface (methanol and oxalic and salicylic acids) are analyzed from the photoelectrochemical response of TiO2 films under bias in a time window of 1-100 s. Long-lived oxidized intermediates produced upon illumination at 0.6 VSCE are detected by cathodic sweep run in the dark after irradiation. The main conclusion derived from this work is that a scheme of competitive kinetics describes only those cases in which one of the components is weakly or nonadsorbed on TiO2, whereas for two photolytes with high affinity for the surface cooperative effects may occur. The methanol-oxalate system is quantitatively modeled by considering that oxalate forms surface complexes with different reactivity and a parallel pathway for hole transfer to -OH and adsorbed oxalate. In this case as well as for electrolytes containing methanol and salicylate photooxidation of methanol (with low affinity for the surface) via intermediates formed by reaction with trapped holes (-*OH) is partially or fully suppressed. For electrolytes containing oxalic and salicylic acids in which both components chemisorb on TiO2 the photoelectrochemical response depends on preadsorption, the photooxidation pathways deviates those of single component systems, and there is remotion of salicylate adsorbed byproducts assigned to cooperative effects.

The encapsulation of living cells in materials with good optical and mechanical properties often produces death or stress due to the release of toxic byproducts originated during the synthesis. We present here a method to assess the cellular stress that silica entrapment exerts over living cells taking into account the main preparation variables such as the nature of the silica source, protecting functional groups, total solid concentration, or indirect procedures. Measurement of the cellular stress status of genetically modified Sacharomyces cereVisiae, a true biological probe, allowed us to perform a quantitative analysis of cellular stress in a short time basis (compared to conventional long-term viability tests), opening the gate for a more sophisticated approach to optimize the synthesis conditions. In addition, the aforementioned findings allowed the preparation of novel materials with enhanced optical and mechanical properties. The relation of cellular stress with initial viability is also discussed.