Mineralization of Acid Yellow 36 azo dye by electro-Fenton and solar photoelectro-Fenton processes with a boron-doped diamond anode.

The degradation of the Acid Yellow 36 (AY36) azo dye is studied by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) using a recirculation flow plant with an undivided cell containing a boron-doped diamond anode and an air-diffusion cathode for H2O2 electrogeneration, coupled with a solar photoreactor. A solution of 2.5L with 108 mg L⁻¹ of the dye and 0.5 mM Fe²(+) at pH 3.0 was comparatively treated at constant current. Hydroxyl radicals formed from Fenton's reaction and at the anode surface are the main oxidants. Total mineralization is almost achieved in SPEF, while EF yields poor TOC removal. Both processes are accelerated with increasing current. AY36 decays with similar rate in EF and SPEF following a pseudo first-order reaction, but the solution is more slowly decolorized because of the formation of conjugated byproducts. NH4(+) ion is released in SPEF, while NO3⁻ ion is mainly lost in EF. Tartronic, maleic, fumaric, oxalic, formic and oxamic acids are detected as generated carboxylic acids. Fe(III)-oxalate complexes are largely accumulated in EF and their quick photodecomposition in SPEF explains its higher oxidation power. The SPEF method yields greater current efficiency and lower energy cost as current decreases, and then it is more viable at low currents.

Comparative efficiencies of the decolourisation of Methylene Blue using Fenton's and photo-Fenton's reactions.

The decolourisation and mineralization of Methylene Blue azo dye (MB) under Fenton's and photo-Fenton's conditions have been studied. Some parameters, such as initial concentrations of iron (Fe(2+)) and fixed hydrogen peroxide (H(2)O(2)), were evaluated to find the optimal conditions for the efficient degradation of azo dye. The experimental assays showed better efficiency for the photo-Fenton's system. Pseudo-first order degradation rate constants were obtained from batch experimental set up. It is suggested that photo-Fenton's reactions are viable processes for treatment of azo dye MB, according to the high levels of colour (UV(665)) and total organic carbon (TOC) removal.

Enhancing the electrochemical oxidation of acid-yellow 36 azo dye using boron-doped diamond electrodes by addition of ferrous ion.

This work shows preliminary results on the electrochemical oxidation process (EOP) using boron-doped diamond (BDD) electrode for acidic yellow 36 oxidation, a common azo dye used in textile industry. The study is centred in the synergetic effect of ferrous ions and hydroxyl free radicals for improving discoloration of azo dye. The assays were carried out in a typical glass cell under potentiostatic conditions. On experimental conditions, the EOP was able to partially remove the dye from the reaction mixture. The reaction rate increased significantly by addition of Fe(2+) (1mM as ferrous sulphate) to the system and by (assumed) generation of ferrate ion [Fe(VI)] over BDD electrode. Ferrate is considered as a highly oxidizing reagent capable of removing the colorant from the reaction mixture, in synergistic action with the hydroxyl radicals produced on the BDD surface. Further increases in the Fe(2+) concentration lead to depletion of the reaction rate probably due to the hydroxyl radical scavenging effect of Fe(2+) excess in the system.

Water vapor permeability, mechanical properties and antioxidant effect of Mexican oregano-soy based edible films.

Water-soluble extracts from Mexican oregano (Lippia graveolens) were incorporated into soy protein isolate (SPI) films. Water vapor permeability, mechanical properties, and antioxidant ability were evaluated. All the extracts were capable of scavenging DPPH radicals in a concentration-dependent fashion; the IC50 values were obtained. Oregano extracts were incorporated into SPI films plasticized with sorbitol, glycerol, and glycerol-sorbitol 1:1. The addition of the extracts resulted in an increase in the water vapor permeability values and provided a dark reddish film appearance. Changes in tensile strength as well as elongation values were observed. The oregano SPI films exhibited antioxidant properties in a concentration-dependent fashion.

Photocatalytic properties of nano-structured TiO2-carbon films obtained by means of electrophoretic deposition.

Recent studies have shown that the light-absorption and photocatalytic efficiencies of TiO2 can be improved by coupling TiO2 nano-particles with nonmetallic dopants, such as carbon. In this paper, we describe the electrophoretic preparation of a novel TiO2-carbon nano-composite photocatalyst on a glass indium thin oxide (ITO) substrate. The objective is to take better advantage of the (e-/h+) pair generated by photoexcitation of semiconducting TiO2 particles. The transfer of electrons (e-) into adjacent carbon nano-particles promotes reduction of oxygen to produce hydrogen peroxide (H2O2) which, in the presence of iron ions, can subsequently form hydroxyl radicals (*OH) via the Fenton reaction. At the same time, *OH is formed from water by the (h+) holes in the TiO2. Thus, the *OH oxidant is produced by two routes. The efficiency of this photolytic-Fenton process was tested with a model organic compound, Orange-II (OG-II) azo dye, which is employed in the textile industry.

In situ electrochemical and photo-electrochemical generation of the fenton reagent: a potentially important new water treatment technology.

In this work, the design and construction of an annular tube reactor for the electrochemical and photo-electrochemical in situ generation of H2O2 are described. By cathodic reduction of dissolved oxygen and the coupled oxidation of water at a UV-illuminated nanocrystalline-TiO2 semiconductor anode, it was found that the electrochemically generated H2O2 can be employed to readily oxidize the model compound Direct Yellow-52 in dilute acidic solution at high rates in the presence of small quantities of dissolved iron(II). Although, the model organic compound is chemically stable under UV radiation, its electrochemical oxidation rate increases substantially when the semiconductor anode is illuminated as compared to the same processes carried out in the dark.