Search

A systematic cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) study on titanium dioxide (TiO2) and silver–TiO2 surfaces was performed in order to decouple electrochemical reduction processes of carbon dioxide in aqueous solutions. CV studies indicate cathodic current increase on Ag–TiO2 compared to bare TiO2 surfaces. An equivalent circuit based on transmission line model was applied in order to adjust EIS data, and a modification of this model was made to account for Ag particle interaction with the electrolyte solution. Electrochemical processes were then decoupled upon applied potential where the role of TiO2 surface states was identified and separated from (a) silver reduction, (b) electronic transport on TiO2, and (c) charge transfer on TiO2 and Ag surfaces. The Ag–electrolyte interface impedance has considerably lower values than the TiO2–electrolyte interface, suggesting that the silver particles may be considered as favorable reaction sites for the electrochemical reduction of water and carbon dioxide.

BACKGROUND: PEGylation reactions often result in a heterogeneous population of conjugated species and unmodified proteins that presents a protein separations challenge. Aqueous two-phase systems (ATPS) are an attractive alternative for the potential fractionation of native proteins from their PEGylated conjugates. The present study characterizes the partition behaviors of native RNase A and α-Lac and their mono and di-PEGylated conjugates on polyethylene glycol (PEG)—potassium phosphate ATPS. RESULTS: A potential strategy to separate unreacted native protein from its PEGylated species was established based upon the partition behavior of the species. The effect of PEG molecular weight (400–8000 g mol−1), tie-line length (15–45% w/w) and volume ratio (VR; 0.33, 1.00 and 3.00) on native and PEGylated proteins partition behavior was studied. The use of ATPS constructed with high PEG molecular weight (8000 g mol−1), tie-line lengths of 25 and 35% w/w, and VR values of 1.0 and 3.0 allowed the selective fractionation of native RNase A and α-Lactalbumin, respectively, from their PEGylated conjugates on opposite phases. Such conditions resulted in an RNase A bottom phase recovery of 99%, while 98% and 88% of mono and di-PEGylated conjugates, respectively were recovered at the top phase. For its part, α-Lac had a bottom phase recovery of 92% while its mono and di-PEGylated conjugates were recovered at the top phase with yields of 77% and 76%, respectively. CONCLUSIONS: The results reported here demonstrate the potential application of ATPS for the fractionation of PEGylated conjugates from their unreacted precursors. Copyright © 2010 Society of Chemical Industry

TiO2 thin films supported on transparent conductive glass plates were modified by silver particles (250 nm diameter) deposited by electrochemical double pulse from an aqueous solution of silver nitrate. Selective formation of Ag particles on TiO2 surface could be seen from SEM and AFM images and topography. Rugosity and particle size analyses were performed on the modified surface. Benefits of silver particle modification are discussed based on the enhanced electrochemical reduction of carbon dioxide in aqueous solution.

Silver nanoparticles were deposited on titanium oxideIV (TiO2) thin films supported on FTO (fluorine-doped tin oxideIV) glass using a double pulse electrochemical deposition method. A systematic study of particle nucleation and growth is presented as a function of applied potential and time. Samples were analyzed by grazing-angle X-ray diffraction (GIXRD) technique and morphology was observed using Scanning Electron Microscopy and Energy Dispersive Spectroscopy device (SEM–EDS). Our results confirm the possibility of controlled electrochemical homogeneous deposition of metallic silver particles over TiO2 surface, which exhibit a potential application in catalytic processes.

The effect of electrochemical reduction of CO2 on the structure and morphology of titanium(IV) oxide thin films was examined after a fixed-potential bulk electrolysis process. Films deposited on ITO (Indium-Tin Oxide) substrates were used as the working electrodes and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) as solvent and as supporting electrolyte. Grazing incidence X-ray diffraction analysis performed before and after the electrolysis process indicated no microstructural changes of the anatase films. X-ray photoelectron spectroscopy revealed peaks associated with adsorbed carbonate ions at 288 eV and CO2 species at 293 eV, whereas Ti2p peaks displacements for CO2-saturated TiO2/ITO surfaces in [BMIm][BF4] revealed chemical bonding effects. Auger electron spectroscopy revealed a high carbon content on CO2-exposed films, and suggested a strong chemisorption of CO2 and CO32− species on the TiO2/ITO surface in [BMIm][BF4] solvent system. A significant decrease in carbon content after bulk electrolysis indicated that the CO2 electroreduction process is not controlled by either diffusion or by adsorption of CO2 on the TiO2/ITO electrode surface.

This article reports the optical and morphological properties of dip-coated TiO{sub 2} and ZrO{sub 2} thin films on soda-lime glass substrates by metal-organic decomposition (MOD) of titanium{sup IV} and zirconium{sup IV} acetylacetonates respectively. Thermogravimetric and differential thermal analysis (DTA-TG) were performed on the precursor powders, indicating pure TiO{sub 2} anatase and tetragonal ZrO{sub 2} phase formation. Phase crystallization processes took place in the range of 300-500 deg. C for anatase and of 410-500 deg. C for ZrO{sub 2}. Fourier Transform Infrared Spectroscopy (FT-IR) was used to confirm precursor bidentate ligand formation with keno-enolic equilibrium character. Deposited films were heated at different temperatures, and their structural, optical and morphological properties were studied by grazing-incidence X-ray Diffraction (GIXRD) and X-Ray Photoelectron Spectroscopy (XPS), Ultraviolet Visible Spectroscopy (UV-Vis), and Atomic Force Microscopy (AFM) respectively. Film thinning and crystalline phase formation were enhanced with increasing temperature upon chelate decomposition. The optimum annealing temperature for both pure anatase TiO{sub 2} and tetragonal ZrO{sub 2} thin films was found to be 500 deg. C since solid volume fraction increased with temperature and film refractive index values approached those of pure anatase and tetragonal zirconia. Conditions for clean stoichiometric film formation with an average roughness value ofmore » 2 nm are discussed in terms of material binding energies indicated by XPS analyses, refractive index and solid volume fraction obtained indirectly by UV-Vis spectra, and crystalline peak identification provided by GIXRD.« less

This study is concerned with the influence of biological suspension on the position of the binodal curve in aqueous two-phase systems (ATPSs). Three different biological suspensions (i.e., disrupted yeast, E. coli homogenate and fermentation broth from Trichoderma harzianum) were selected and their impact upon ATPS performance was evaluated on the basis of changing volume ratio (Vr) and the position of the binodal curve of biological ATPSs (added with biomass). Biological ATPSs with initial Vr greater than 1 and long (>40%, w/w) tie-line length (TLL), exhibited significant changes in Vr when compared with that from non-biological systems. Such behaviour was associated with the top phase biomass accumulation. It was shown that the addition of the biological suspensions used in this study to ATPSs caused the binodal curve to displace towards the origin, which was associated with the critical contribution of the bio-polymer (present in the systems) to the phase formation. The practical implementation of ATPSs for the purification of biological materials exploiting the information reported in this study is discussed.

Sol-Gel, dip-coated titaniumIV and zirconiumIV dioxide monolayered films were deposited on soda-lime glass using titanium and zirconium acetylacetonates as precursors, respectively, and their structural and morphological characterization carried out. The films were heat-treated at different temperatures, 25°C, 150°C, 300°C, and 500°C and, according to Low-angle X-Ray Diffraction analyses (XRD), it was found that TiO2 (anatase) and tetragonal zirconia were present on the substrate, when heated at 500°C. Yoshida and Yajima's method, based on optical information given by the films transmittance UV-Vis spectra, was used to estimate film thickness, refractive index, and, using the Lorentz-Lorentz relationship, their volume fraction. Film thinning and phase formation with increasing temperature was observed, and both titania and zirconia films showed similar behavior during firing. Smooth films with a roughness value of around 2 nm are obtained for the two cases as indicated by Atomic Force Microscopy (AFM) of the surface. Also, formation temperature at around 500°C resulted in the optimum condition to obtain clean stoichiometric TiO2 and ZrO2 thin films on glass substrates as confirmed by X-Ray Photoelectron Spectroscopy (XPS) measurements.