Interaction of nitrogen dioxide (NO2) with a monolayer of oleic acid at the air–water interface – A simple proxy for atmospheric aerosol

The reactions between atmospheric oxidants and organic amphiphiles at the air water interface of an aerosol droplet may affect the size and critical supersaturation required for cloud droplet formation. We demonstrate that no reaction occurs between gaseous nitrogen dioxide (1000 ppm in air) and a monolayer of an insoluble amphiphile, oleic acid (cis-9-octadecenoic acid), at the air water interface which removes material from the air water interface. We present evidence that the NO2 isomerises the cis-9-octadecenoic (oleic) acid to trans-9-octadecenoic (elaidic) acid. The study presented here is important for future and previous studies of (1) the reaction between the nitrate radical, NO3, and thin organic films as NO2 is usually present in high concentrations in these experimental systems and (2) the effect of NO2 air pollution on the unsaturated fatty acids and lipids found at the air liquid surface of human lung lining fluid.

Using phospholipid Langmuir and Langmuir-Blodgett films as matrix for urease immobilization

The immobilization of enzymes in organized two-dimensional matrices is a key requirement for many biotechnological applications. In this paper, we used the Langmuir-Blodgett (LB) technique to obtain controlled architectures of urease immobilized in solid supports, whose physicochemical properties were investigated in detail. Urease molecules were adsorbed at the air-water interface and incorporated into Langmuir monolayers of the phospholipid dipalmitoyl phosphatidyl glycerol (DPPG). Incorporation of urease made DPPG monolayers more flexible and caused the reduction of the equilibrium and dynamic elasticity of the film. Urease and DPPG-urease mixed monolayers could be transferred onto solid substrates, forming LB films. A close packing arrangement of urease was obtained, especially in the mixed LB films, which was inferred with nanogravimetry and electrochemistry measurements. From the blocking effect of the LB films deposited onto indium tin oxide (ITO) substrates, the electrochemical properties of the LB films pointed to a charge transport controlled by the lipid architecture. (c) 2007 Elsevier Inc. All rights reserved.

Adsorption kinetics and charge inversion in layer-by-layer films from nickel tetrasulfonated phthalocyanine and poly(allylamine hydrochloride)

Layer-by-layer (LBL) films of nickel tetrasulfonated phthalocyanine (NiTsPc) alternated with poly(allylamine hydrochloride) (PAH) have been prepared, whose surface charge has been evaluated using surface potential measurements. From adsorption kinetics results, we obtained the immersion time of similar to 40 s, which was used to assemble layers of NiTsPc. The effect of gold (Au) and aluminum (Al) electrodes on the charge behavior was examined. We found that the surface potential (i.e. surface charge) was inverted each time a layer of PAH was alternated with another of NiTsPc molecules for the two types of electrodes, which was attributed to charge overcompensation between positive charges of PAH molecules, and negative charges from NiTsPc molecules. (C) 2009 Elsevier B.V. All rights reserved.

Immobilization of Poly(propylene imine) Dendrimer/Nickel Phtalocyanine as Nanostructured Multilayer Films To Be Used as Gate Membranes for SEGFET pH Sensors

We describe the assembly of layer-by-layer films based on the poly(propylene imine) dendrimer (PPID) generation 3 and nickel tetrasulfonated phthalocyanine (NiTsPc) for application as chemically sensitive membranes in sepal alive extended-gate field effect transistor (SEGFET) pH sensors PPID/NiTsPc films wet e adsorbed on quartz, glass. indium tin oxide. or gold (Au)-covered glass substrates Multilayer formation was monitored via UV-vis absorption upon following the increment in the Q-band intensity (615 nm) of NiTsPc The nanostructured membranes were very stable in a pH range of 4-10 and displayed a good sensitivity toward H(+), ca 30 mV/pH for PPID/N(1)TsPc films deposited on Au-covered substrates For films deposited on ITO, the sensitivity was ca 52 4 mV/pH. close to the expected theoretical value for ton-sensitive membranes. The use of chemically stable PPID/NiTsPc films as gate membranes in SEGFETs, as introduced here, may represent an alternative for the fabrication of nanostructured, porous platforms for enzyme immobilization to be used in enzymatic biosensors.

Absorption and emission properties of LBL PPV films deposited on ITO electrodes

In this work we studied the properties of absorption and emission line shape of layer-by-layer (LBL) poly(p-phenylene vinylene) (PPV) on indium-tin oxide (ITO) electrode. To minimize the PPV thermal conversion effects during the polymer processing, we used a less aggressive leaving group in the precursor polymer; minimizing electrode degradation. LBL ITO/PPV films showed the same absorption and emission line shape compared with LBL PPV films deposited on non-metallic substrates (glass). With this analysis we indirectly observe the decrease in the ITO degradation. Atomic force microscopy (AFM) technique was used to analyze quantitatively the microscopic morphology of the film surface. Results indicated that the substrate topology is not affected, to a large extent, by the use of dodecylbenzensulfonate (DBS) ion. (C) 2008 Elsevier B.V. All rights reserved.

N3-Dye-Induced Visible Laser Anatase-to-Rutile Phase Transition on Mesoporous TiO(2) Films

Titanium dioxide has been extensively used in photocatalysis and dye-sensitized solar cells, where control of the anatase-to-rutile phase transformation may allow the realization of more efficient devices exploiting the synergic effects at anatase/rutile interfaces. Thus, a systematic study showing the proof of concept of a dye-induced morphological transition and an anatase-to-rutile transition based on visible laser (532 nm) and nano/micro patterning of mesoporous anatase (Degussa P25 TiO(2)) films is described for the first time using a confocal Raman microscope. At low laser intensities, only the bleaching of the adsorbed N3 dye was observed. However, high enough temperatures to promote melting/densification processes and create a deep hole at the focus and an extensive phase transformation in the surrounding material were achieved using Is laser pulses of 25-41 mW/cm(2), in resonance with the MLCT band. The dye was shown to play a key role, being responsible for the absorption and efficient conversion of the laser light into heat. As a matter of fact, the dye is photothermally decomposed to amorphous carbon or to gaseous species (CO(x), NO(x), and H(2)O) under a N(2) or O(2) atmosphere, respectively.

Unravelling the Chemical Morphology of a Mesoporous Titanium Dioxide Interface by Confocal Raman Microscopy: New Clues for Improving the Efficiency of Dye Solar Cells and Photocatalysts

The presence of anatase and rutile domains on nanocrystalline films of P25 TiO(2), as well as the distinct coordination modes of carboxylates on those phases, were revealed by confocal Raman microscopy, a technique that showed to be suitable for imaging the chemical morphology down to submicrometric size.

Lithium Ion Electro-Insertion and Spectroelectrochemical Properties of Films from Hexaniobate

Layer-by-layer (LbL) films from K(2)Nb(6)O(17)(2-) and polyallylamine (PAH) and dip-coating films of H(2)K(2)Nb(6)O(17) were prepared on a fluorine-doped tin-oxide (FTO)-coated glass. The atomic force microscopy (AFM) images were carried out for morphological characterization of both materials. The real surface area and the roughness factor were determined on the basis of pseudocapacitive processes involved in the electroreduction/electrooxidation of gold layers deposited on these films. Next, lithium ion insertion into these materials was examined by means of electrochemical and spectroelectrochemical measurements. More specifically, cyclic voltammetry and current pulses under visible light beams were used to investigate mass transport and chromogenic properties. The lithium ion diffusion coefficient (D(Li)) within the LbL matrix is significantly higher than that within the dip-coating film, ensuring high storage capacity of lithium ions in the self-assembled electrode. Contrary to the LbL film, the potentiodynamic profile of absorbance change (Delta A) as a function of time is not similar to that obtained in the case of current density for the dip-coating film. Aiming at analyzing the rate of the coloration front associated with lithium ion diffusion, a spectroelectrochemical method based on the galvanostatic intermittent titration technique (GITT) was employed so as to determine the ""optical"" diffusion coefficient (D(op)). In the dip-coating film, the method employed here revealed that the lithium ion rate is higher in diffusion pathways formed from K(2)Nb(6)O(17)(2-) sites that contribute more significantly to Delta A. Meanwhile, the presence of PAH contributed to the increased ionic mobility in diffusion pathways in the LbL film, with low contribution to the electrochromic efficiency. These results aided a better understanding of the potentiodynamic profile of the temporal change of absorbance and current density during the insertion/deinsertion of lithium ions into the electrochromic materials.

Layer-by-layer TiO(2) films as efficient blocking layers in dye-sensitized solar cells

Charge recombination at the conductor substrate/electrolyte interface has been prevented by using efficient blocking layers of TiO(2) compact films in dye-sensitized solar cell photoanodes. Compact blocking layers have been deposited before the mesoporous TiO(2) film by the layer-by-layer technique using titania nanoparticles as cations and sodium sulfonated polystyrene, PSS, as a polyanion. The TiO(2)/PSS blocking layer in a DSC prevents the physical contact of FTO and the electrolyte and leads to a 28% increase in the cell`s overall conversion efficiency, from 5.7% to 7.3%. (C) 2009 Elsevier B.V. All rights reserved.

Electrostatic layer-by-layer deposition and electrochemical characterization of thin films composed of MnO(2) nanoparticles in a room-temperature ionic liquid

Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly (diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.

Electrodeposition and characterization of undoped and nitrogen-doped ZnSe films

Semiconducting films of (n-type) ZnSe and (p-type) nitrogen-doped ZnSe were electrodeposited by a linear-sweep voltammetric technique on to a substrate of fluorine-tin oxide (FM) glass ceramics. The films were characterized by scanning electron microscopy, energy-dispersive X-ray analysis and grazing-incidence X-ray diffraction. The results indicated that the material was deposited uniformly over the substrate, forming clusters when the Zn content of the bath was 0.1 mol L(-1) and a film when it was 0.2 or 0.3 mol L(-1). The effectiveness of doping the films with nitrogen by adding ammonium sulfate to the deposition solution was assessed by measuring the film-electrolyte interface capacitance (C) at various applied potentials (E(ap)) and plotting Mott-Schottky curves (C(-2) vs E(ap)), whose slope sign was used to identify p-type ZnSe. (C) 2009 Elsevier B.V. All rights reserved.

Ascorbate electro-oxidation by modified electrodes: Polypyrrole and polypyrrole/Ni(OH)(2) composite thin films

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Immobilization of uricase in layer-by-layer films used in amperometric biosensors for uric acid

The layer-by-layer technique was exploited to immobilize the enzyme uricase onto indium tin oxide substrates coated with a layer of Prussian Blue. Uricase layers were alternated with either poly(ethylene imine) or poly(diallyidimethylammoniumchloride), and the resulting films were used as amperometric biosensors for uric acid. Biosensors with optimum perfomance had a limit of detection of 0.15 mu A mu mol 1(-1) cm(-2) with a linear response between 0.1 and 0.6 mu M of uric acid, which is sufficient for use in clinical tests. Bioactivity was preserved for weeks, and there was negligible influence from interferents, as detection was carried out at 0.0 V vs saturated calomel electrode.

Molecular architecture and electrical properties in evaporated films of cobalt phthalocyanine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Deposition and characterization of BiVO4 thin films and evaluation as photoanodes for methylene blue degradation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)