Surface structure and reactivity study of phosphotungstic acid-nitrogenated ormosils

Supramolecular interactions between nitrogenated groups in hybrid ormosils bearing phosphotungstate nanocatalyst were used to tune the photocatalytical activity of these class-II hybrid materials obtained through sol–gel chemistry. Surface chemistry and morphology of the materials was studied by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and water contact angle measurements. The photocatalytic efficiency of these hybrid films, measured by the degradation of crystal violet over-layer deposited on ormosils films, is higher for ormosils bearing neutral, more polar and less H-bonding nitrile groups than those bearing alkylamine/alkylammonium functionalities, despite the lower W/Si atomic ratio on the surface and lower tungsten percentage of the pure nitrile bearing ormosils. Such higher surface reactivity of the nitrile bearing ormosils is due to weaker interaction with the phosphotungstate and the lower activity of amine bearing ormosils is attributed to the competition among reversible photochromism and photocatalysis pathways in these materials.     

Photophysical properties of corrphycenes

The photophysical properties of the Zn salt of octaethylcorrphycene (compound 1) and the doubly protonated octaethylcorrphycene (compound 2) were determined in benzene solutions. Fluorescence spectra and fluorescence quantum yields of phiF (1) = 0.03+/-0.02 and PF (2) = 0.06+/-0.02 were measured. The triplet-triplet absorption spectra were obtained by means of flash-photolysis experiments. The triplet quantum yield values phiT (1) = 0.79+/-0.08 and phiT (2) = 0.82+/-0.08 were obtained by using laser-induced optoacoustic spectroscopy. The quantum yield of singlet molecular oxygen generation in air-saturated solutions, phidelta (1) = 0.55+/-0.07 and phidelta (2) = 0.38+/-0.05, were also measured using time resolved NIR luminescence.     

Photophysical Methods for the Study of Sol-Gel Transition and Structure of Titania Gels

The sol to gel evolution of titania based systems in AOT (sodium 2-etil-hexil sulfosuccinate) reverse micelles is monitored by the fluorescence anisotropy of molecular probes located in the different phases of the system. In contrast with processes in homogeneous systems, hydrolysis and condensation reactions occur in different time windows. The obtained results allow to describe the location of the hydrolysis, the reorganisation of the surfactant and to predict the formation of precipitates.     

Uncertainty studies of topographical measurements on steel surface corrosion by 3D scanning electron microscopy

Pitting corrosion is a damage mechanism quite serious and dangerous in both carbon steel boiler tubes for power plants which are vital to most industries and stainless steels for orthopedic human implants whose demand, due to the increase of life expectation and rate of traffic accidents, has sharply increased. Reliable methods to characterize this kind of damage are becoming increasingly necessary, when trying to evaluate the advance of damage and to establish the best procedures for component inspection in order to determine remaining lives and failure mitigation. A study about the uncertainties on the topographies of corrosion pits from 3D SEM images, obtained at low magnifications (where errors are greater) and different stage tilt angles were carried out using an in-house software previously developed. Additionally, measurements of pit depths on biomaterial surfaces, subjected to two different surface treatments on stainless steels, were carried out. The different depth distributions observed were in agreement with electrochemical measurements.     

Photoacoustic characterization of phase transitions in amorphous metal alloys

Received: 24 February 1997     

Growth of gold nanoparticle arrays in TiO2 mesoporous matrixes

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.