[Show abstract][Hide abstract] ABSTRACT: Ruthenium (II) complex-sensitized TiO2 electrodes were chemically coated with NH2-terminatedpoly(amidoamide) dendrimers generation 4.0 in order to improve the performance of dye-sensitized solar cells using these photoanodes. The presence of dendrimers in these photodevices produced a global photovoltaic conversion efficiency of 6.78%, which was higher than that obtained for photocells without them (5.43%). The experimental results indicated that this treatment of the dye-sensitized TiO2 electrodesallowed for controlling the concentrations of I3− anions and Li+ cations into the dendrimers-modified dyed-TiO2 pores during operation of the photocells. Consequently, the charge interception reaction and the charge accumulation process at the conduction band of the TiO2 electrodes were simultaneously balanced by the establishment of I2···NH2, NH···I− and C = O···Li+ bonds at the branches of the confined dendrimers for increasing their global conversion efficiency.
Full-text · Article · Oct 2014 · Electrochimica Acta
[Show abstract][Hide abstract] ABSTRACT: a b s t r a c t An air diffusion activated carbon packed electrode was used to promote the in-situ generation of hydro-gen peroxide (H 2 O 2) to support an electro-Fenton based method for the degradation of a typical dye, Methyl Orange (MO) at two different concentrations in an aqueous effluent (250 mg L −1 and 97 mg L −1). Electrochemical experiments were carried out using a one compartment cylindrical cell with granular activated carbon (GAC) configured as an air diffusion cathode. The efficiency of the electrode was explored as a function of H 2 O 2 produced reaching a maximum value of 10 mM. Experimental parameters such as applied current (300, 200, 100 and 50 mA), initial Fe 2+ concentration (0.2, 0.5 and 0.8 mM) and electrode stability (10 cycles) were studied. High Total Organic Carbon (TOC) decay (90%) and color removal (100%) were obtained using this electrode under appropriate operation conditions. Consecutive degradation cycles of electro-Fenton process were performed in the electrochemical cell without great loss of the removal efficiency. Considering that, in the proposed packed electrode, the use of air diffusion GAC as cathode results in efficient degradation and cost reduction for the conventional electro-Fenton process, this electrode approach could constitute an excellent alternative for H 2 O 2 generation when compared to conventional carbon electrodes.
[Show abstract][Hide abstract] ABSTRACT: A review on different arrangements and reactor designs for Advanced Oxidation Processes based on the use of the Fenton reagent is presented. The review focuses on reports that include publications and patents dealing with water contaminated with different recalcitrant pollutants. The work includes a brief introduction that deals with the basics of the Fenton reagent use for the oxidation of pollutants of water effluents, followed by a set of sections in which some of the reports and patents of the different forms in which the Fenton reagent is employed for water treatment processes are presented. In this way, this review includes a section dealing with processes in which the components of the Fenton reagent is administered by means of H 2 O 2 and Fe salts addition, in which it is photo-assisted with UV light and in which it is electro-generated in-situ and photo-assisted taking advantage of the electrochemical reduction of dissolved oxygen on a carbonaceous cathode.
[Show abstract][Hide abstract] ABSTRACT: Glassy carbon electrodes (GCE) were sequentially modified by cysteamine-capped gold nanoparticles (AuNp@cysteamine) and PAMAM dendrimers generation 4.5 bearing 128-COOH peripheral groups (GCE/AuNp@cysteamine/PAMAM), in order to explore their capabilities as electrochemical detectors of uric acid (UA) in human serum samples at pH 2. The results showed that concentrations of UA detected by cyclic voltammetry with GCE/AuNp@cysteamine/PAMAM were comparable (deviation <±10%; limits of detection (LOD) and quantification (LOQ) were 1.7×10(-4) and 5.8×10(-4)mgdL(-1), respectively) to those concentrations obtained using the uricase-based enzymatic-colorimetric method. It was also observed that the presence of dendrimers in the GCE/AuNp@cysteamine/PAMAM system minimizes ascorbic acid (AA) interference during UA oxidation, thus improving the electrocatalytic activity of the gold nanoparticles.
Full-text · Article · Feb 2014 · Analytica chimica acta
[Show abstract][Hide abstract] ABSTRACT: The conductivity mechanism of non-illuminated n-type TiO2 semiconductor films (prepared by electrophoretic deposition) modified with either terpyridine “tpy-Ru(II)” or bipyridine “bpy-Ru(II)” ruthenium complexes, has been investigated using Electrochemical Impedance Spectroscopy (EIS) measurements at different temperatures. While all the films (bare TiO2 and TiO2/Dye) showed that the electronic conductivity in a low temperature window (T < 313.24 K) can be described by a mechanism that follows the Mott equation (3D Variable Range Hopping, 3D-VRH), in a high temperature window (T >313.24 K), the conduction mechanism corresponds to the Nearest Neighbor Hopping (NNH) mechanism. The effect of the complexes is reflected in changes of the energetic parameters caused by the modifications in the distribution of energetic sites induced by the electronic overlapping of the π- molecular orbitals in the bpy or tpy ligands and the TiO2 films.
Full-text · Article · Oct 2013 · Journal of The Electrochemical Society
[Show abstract][Hide abstract] ABSTRACT: CdS nanoparticles (CdS-nps) were synthesized employing charged and neutral polyamidoamide (PAMAM) dendrimers (generation G3.5, G4.0 and G4.0-OH with 64 –COO−, –NH3+ and –OH peripheral groups, respectively) as templates. The morphological characterization of CdS-nps was carried out using TEM measurements that showed spherical nanoparticles characterized by average diameter values between 3.6 and 4.7 nm. Using UV–vis experiments, CdS-nps formation was evaluated using a diffusion controlled growth model where the S2− diffusion coefficient throughout the external and internal functional groups of dendrimers was found to be an important parameter. In this way, the results indicate that nanoparticle formation is primarily affected by the charged nature of the external functional groups of the dendrimer template.
Full-text · Article · Dec 2012 · Journal of Crystal Growth
[Show abstract][Hide abstract] ABSTRACT: This study presents the synthesis of TiO2 doped with different amounts of Co and Ni, starting from a simple metallic titanium powder. A successful electrophoretic
deposition of these materials on ITO electrodes was achieved for its potential application as photoanodes. EDX, diffuse reflectance
UV–Vis spectroscopy, and XRD measurements gave information on the chemical composition of the material and the location of
the Ni or Co within the crystal structure of TiO2. Raman spectroscopy suggests that for a higher content of doping metal above a defined percentage, the formation of metal
oxide is promoted. A preliminary study of photoelectrocatalytic orange dye degradation shows higher color removal efficiency
as compared to the commercial TiO2 material.
–X-ray diffraction–Rietveld refinement–Raman spectroscopy–Nanocomposites
Full-text · Article · Aug 2011 · Journal of Nanoparticle Research
[Show abstract][Hide abstract] ABSTRACT: Advanced oxidation processes (AOPs), on the basis of photoelectrochemical reactions, constitute a good alternative for treating wastewaters contaminated with refractory organic compounds such as dyes. For this purpose, different approaches have been explored to develop novel photoanodes that can be efficiently used in these systems. In this context, this study deals with a comparison of indium tin oxide (ITO) thin films deposited at room temperature by pulsed laser deposition on flat glass and on silica optical fiber (SiO2 core, 600 mu m diameter) substrates. Characterization data reveal that nanostructured ITO thin films with resistivity values from 4.4 x 10(-2) to 5.6 x 10(-4) Omega.cm were obtained. To build the photoanode, the ITO thin films were coated with a TiO2 layer deposited by using the electrophoretic method. The prepared TiO2/ITO bilayers on optical fibers showed a better photocatalytic performance than those deposited on flat glass substrates according to TOC and color removal measurements from dye contaminated water samples. These results suggest that the deposited materials exhibit suitable properties for their application in photoelectrocatalytic devices that, employing optical fiber as support and light transmitter, can be efficiently used for the elimination of organic contaminants in industrial wastewaters. DOI: 10.1061/(ASCE)EE.1943-7870.0000340. (C) 2011 American Society of Civil Engineers.
Full-text · Article · May 2011 · Journal of Environmental Engineering
[Show abstract][Hide abstract] ABSTRACT: Electrochemical advanced oxidation processes (EAOPs) are used to chemically burn non biodegradable complex organic compounds that are present in polluted effluents. A common approach involves the use of TiO2 semiconductor substrates as either photocatalytic or photoelectrocatalytic materials in reactors that produce a powerful oxidant (hydroxyl radical) that reacts with pollutant species. In this context, the purpose of this work is to develop a new TiO2 based photoanode using an optic fiber support. The novel arrangement of a TiO2 layer positioned on top of a surface modified optical fiber substrate, allowed the construction of a photoelectrochemical reactor that works on the basis of an internally illuminated approach. In this way, a semi-conductive optical fiber modified surface was prepared using 30 microm thickness SnO2:Sb films on which the photoactive TiO2 layer was electrophoretically deposited. UV light transmission experiments were conducted to evaluate the transmittance along the optical fiber covered with SnO2:Sb and TiO2 showing that 43% of UV light reached the optical fiber tip. With different illumination configurations (external or internal), it was possible to get an increase in the amount of photo-generated H(2)O(2) close to 50% as compared to different types of TiO2 films. Finally, the electro-Fenton photoelectrocatalytic Oxidation process studied in this work was able to achieve total color removal of Azo orange II dye (15 mg L(-1)) and a 57% removal of total organic carbon (TOC) within 60 min of degradation time.
[Show abstract][Hide abstract] ABSTRACT: This paper reports the capacity of polypyrrole to reduce toxic hexavalent chromium (Cr(VI)). The influence of using different electrolytes during the polymer's synthesis has been studied. To improve the reduction of Cr(VI), the parameters considered were the polypyrrole morphology and the amount of conducting polymer. Polypyrrole obtained by cyclic voltammetry at a low sweep rate using KBr as supporting electrolyte showed better performance for Cr(VI) reduction compared to coatings obtained by constant potential or cyclic voltammetry at high sweep rates.
Full-text · Article · Nov 2007 · Progress in Organic Coatings