Time-resolved Energy Dispersive X-ray Research Articles

Morphological variations as nonstandard test parameters for the response to pollutant gas concentration: An application to Ruthenium Phthalocyanine sensing films

A systematic time-resolved energy dispersive x-ray reflectometry study was performed in situ on Ruthenium Phthalocyanine thin fims to estimate the morphological detection limits of this material as NO2 transducer and the influence of the gas concentration on the gas-film interaction mechanisms. The work validates the use of this unconventional method—based on the observation of the morphological parameters change—for evaluating the response of novel sensing materials in alternative to more standard procedures. Indeed, the morphological monitoring is shown to be sensitive to the gas concentration in a range comparable to the usual electroresistive measurements. Moreover, while the latter is only able to give the information on whether the gas is interacting with the sensor, the former is also able to discriminate among interaction processes of a different nature (in the present case the interaction limited to the film surface and the one involving the material bulk).

In situ energy dispersive x-ray reflectometry measurements on organic solar cells upon working

The change in the morphology of plastic solar cells was studied by means of time-resolved energy dispersive x-ray reflectivity (XRR). This unconventional application of the XRR technique allowed the follow up of in situ morphological evolution of an organic photovoltaic device upon working. The study consisted of three steps: A preliminary set of XRR measurements on various samples representing the intermediate stages of cell construction, which provided accurate data regarding the electronic densities of the different layers; the verification of the morphological stability of the device under ambient condition; a real-time collection of XRR patterns, both in the dark and during 15h in artificial light conditions which allowed the changes in the system morphology at the electrode-active layer interface to be monitored. In this way, a progressive thickening of this interface, responsible for a reduction in the performances of the device, was observed directly.

A new experimental setup for the study of lipid hydration by energy dispersive X-ray diffraction

A new hydration cell has been constructed that allows to fully hydrate aligned lipid multibilayers as well as to study lipid hydration by using in situ time-resolved energy dispersive X-ray diffraction. The cell has been used to investigate the evolution of the lamellar d-spacing of dioleoylphosphocoline oriented membranes as a function of both relative humidity (RH) and time. The extreme sensitivity of d to RH was shown and two hydration regimes were detected.

Effect of hydration on the structure of oriented lipid membranes investigated by in situ time-resolved energy dispersive x-ray diffraction

In situ time-resolved energy dispersive x-ray diffraction (EDXD) was applied to investigate the effect of hydration on the structure of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)-oriented membranes. The measurements allowed a very high density time sampling of the evolution of the structural properties of the DOTAP bilayer such as the lamellar d-spacing, the membrane thickness, and the size of the interbilayer water region. Time-resolved EDXD has been found to provide important information on the role played by free water molecules on the structure and fluidity of lipid bilayer.

Effect of hydration on the long-range order of lipid multilayers investigated by in situ time-resolved energy dispersive X-ray diffraction

In situ time-resolved energy dispersive X-ray diffraction (EDXD) was applied to investigate the hydration kinetics of oriented dioleoylphosphocoline (DOPC) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) membranes. The long-range order in the investigated lipid multilayers has been found to vary as a function of hydration in a nonmonotic way. In the first stage, water adsorption increased the long-range order along the normal to the lipid bilayer whereas, in the second one, a progressive loss of interbilayer coherence was observed. Possible molecular mechanisms underlying the experimental observations are discussed.

In situ formation of solid-supported lipid/DNA complexes

Solid-supported lipid/DNA complexes were prepared by using highly aligned 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) multibilayers as a template. The complex formation was promoted in situ and followed in time. The resulting DOTAP/DNA complex shows a good degree of orientation along the normal to the support as revealed by combined time-resolved energy dispersive X-ray diffraction (EDXD) and surface synchrotron small angle X-ray scattering (SAXS) measurements.

Structural investigation of the bridged activated complex in the reaction between hexachloroiridate(iv) and pentacyanocobaltate(ii)

Time resolved energy dispersive X-ray absorption spectroscopy has been used to follow the structural evolution of the inner-sphere electron transfer reaction between [IrCl6]2- and [Co(CN)5]3-, and to characterise the local structure of the iridium metal centre in the bridged activated complex formed during the reaction.

Time-resolved energy dispersive x-ray reflectometry measurements on ruthenium phthalocyanine gas sensing films

The energy dispersive (ED) variant of the conventional x-ray reflectivity (XR) provides an atomic scale determination of the morphological characteristics of thin films, such as their thickness and surface roughness. We report on the in situ EDXR measurements of the (minimal) morphological changes of ruthenium phthalocyanine gas sensing thin films. A series of reflectivity spectra have been collected, during the exposure of the films to a gas flux of nitrogen oxides (NOx) molecules. The measurements allowed a very high density time sampling of the evolution of the two morphological parameters, providing important information on the gas-film interaction.

A kinetic investigation of gibbsite precipitation using in situ time resolved energy dispersive X-ray diffraction

The precipitation of gibbsite Al(OH)3 from a supersaturated caustic aluminate solution is the rate determining step in the production of alumina (Al2O3) by the Bayer process. Seeded secondary nucleation and ordered growth experiments of gibbsite from sodium, potassium and deuterated sodium aluminate solutions, at 60 and 80°C, have been investigated for the first time using the in situ energy dispersive X-ray diffraction (EDXRD) technique. Gibbsite was the only phase precipitated from sodium and potassium aluminate solutions under all experimental conditions investigated. A mixture of gibbsite and bayerite was precipitated from deuterated sodium aluminate solution at 60°C while gibbsite was the only phase observed at 80°C. Bayerite persisted over the duration of the experiment, suggesting that bayerite and gibbsite precipitated independently and that bayerite did not undergo polymorphic transformation to gibbsite. Kinetic calculations using the Cardew model indicate that seeded precipitation at 60°C is a nucleation controlled reaction with nucleation occurring more readily in potassium aluminate solutions than in corresponding sodium aluminate solutions. Calculations of the growth rate for experiments at 80°C suggest that growth occurred preferentially over nucleation. These calculations confirm that suitable experimental conditions were chosen for the promotion of either nucleation or ordered growth over the other growth processes from caustic aluminate solutions.

Time-resolved in situ X-ray diffraction study of the liquid-phase reconstruction of Mg–Al–carbonate hydrotalcite-like compounds

The brucite-like Mg2+/Al3+ layered double hydroxide (LDH) was synthesized by using the coprecipitation method and calcined at a variety of temperatures. The starting LDH and the calcination products (mixtures of binary oxides and spinels) were characterized by X-ray diffraction, IR spectroscopies and thermogravimetric analysis. These techniques allowed us to confirm that the double hydroxide possesses a brucite-like structure in which cations are octahedrally arranged. At moderate temperatures, the calcination products have a MgO-like structure where Al ions are dissolved in the lattice to form a solid solution. Calcination at high temperatures (up to 1000 °C) yields a mixture of well-crystallized phases corresponding to MgO and MgAl2O4 (spinel). The reconstruction of layered double hydroxides from material calcined at 400 °C has been studied in situ by time resolved energy dispersive X-ray diffraction (EDXRD). Kinetic data for the reaction have been determined and modelled using the Avrami–Erofe'ev nucleation–growth model, consistent with the process taking place by dissolution of the starting material and crystallisation of the LDH from the solution.

Time-resolved energy-dispersive XAS studies of photoinduced electron transfer intermediates in electron donor-acceptor complexes.

The structure around the Fe atom of a photoinduced electron transfer intermediate in a di-porphyrin electron donor/acceptor complex is studied with time-resolved energy dispersive X-ray absorption spectroscopy. Photoinduced electron transfer from the lowest excited triplet state ofa Zn porphyrin attached at a fixed 25 D distance by means of a long spacer molecule to an Fe(III) porphyrin occurs with a 6 ms time constant at 77 K. Time domain X-ray absorption measurements show that Fe(III) is transiently photoreduced to Fe(II) and that the bond between the Fe atom and a pyridine molecule ligated to it weakens substantially upon reduction of the Fe. Coupling of ligand loss to reduction of Fe(III) to Fe(II) provides a mean of stabilizing the reduced intermediate.

Time-Resolved In-Situ Energy and Angular Dispersive X-ray Diffraction Studies of the Formation of the Microporous Gallophosphate ULM-5 under Hydrothermal Conditions

The hydrothermal synthesis of the large-pore oxy-fluorinated gallophosphate ULM-5 has been followed in situ using time-resolved energy dispersive and angular dispersive X-ray diffraction. A variety of synthetic parameters such as temperature, reagent stoichiometry, source materials, and pH have been studied, and their effect on the crystallization determined. The nature of the phosphorus source used, either orthophosphoric acid or phosphorus pentoxide, is found to have a profound influence on the reaction pathway. Using orthophosphoric acid, ULM-5 is found to form very rapidly following a short induction period. A kinetic analysis of the crystallization of ULM-5 using orthophosphoric acid under isothermal hydrothermal conditions has been performed. Comparison of the experimentally determined extent of reaction (R) versus time data with those predicted by various theoretical models indicates that over a wide range of temperatures and pH the crystallization can be modeled by a three-dimensional diffusion-controlled process. This process occurs at a rate essentially independent of temperature and pH. In contrast, using phosphorus pentoxide, the formation of ULM-5 is found to proceed via the formation of either of two distinct crystalline intermediate phases, which subsequently react to form the ULM-5 final product at a rate which is strongly dependent on temperature. The relative quantities of each intermediate phase formed depend critically on the precise reagent stoichiometry used. Conditions have been identified in which ULM-5 can be formed exclusively via either intermediate phase. The mechanism of transformation of intermediate to product phases appears to be either a direct solid- solid transformation, or via the dissolution or amorphorization of only a small quantity of material at the surface of the intermediate crystallites.