Anodic oxidation of wastewater containing the Reactive Orange 16 Dye using heavily boron-doped diamond electrodes

Boron-doped diamond (BDD) films grown on the titanium substrate were used to study the electrochemical degradation of Reactive Orange (RO) 16 Dye. The films were produced by hot filament chemical vapor deposition (HFCVD) technique using two different boron concentrations. The growth parameters were controlled to obtain heavily doped diamond films. They were named as E1 and E2 electrodes, with acceptor concentrations of 4.0 and 8.0 × 10²¹ atoms cm⁻³, respectively. The boron levels were evaluated from Mott-Schottky plots also corroborated by Raman's spectra, which characterized the film quality as well as its physical property. Scanning Electron Microscopy showed well-defined microcrystalline grain morphologies with crystal orientation mixtures of (1 1 1) and (1 0 0). The electrode efficiencies were studied from the advanced oxidation process (AOP) to degrade electrochemically the Reactive Orange 16 azo-dye (RO16). The results were analyzed by UV/VIS spectroscopy, total organic carbon (TOC) and high-performance liquid chromatography (HPLC) techniques. From UV/VIS spectra the highest doped electrode (E2) showed the best efficiency for both, the aromaticity reduction and the azo group fracture. These tendencies were confirmed by the TOC and chromatographic measurements. Besides, the results showed a direct relationship among the BDD morphology, physical property, and its performance during the degradation process.     

Adsorption kinetics and thermodynamics of azo-dye Orange II onto highly porous titania aerogel

We report herein a kinetic and thermodynamic study of the adsorption of azo-dye Orange II from aqueous solutions onto titania aerogels. Aerogels structure was confirmed by FTIR and N₂ adsorption revealed their specific surface area (500 m²/g), pore volume (2.86 cm³/g) and pore size (mean 13.9 nm). Adsorption tests were conducted in batch reactors under various conditions where the effect of pH, temperature, contact time, dye concentration, and adsorbent dose were studied. Experiments performed at pH 2 show the optimal adsorption due to the best surface charge interactions. The temperature shows a weak influence with a decrease in the adsorption uptake as the temperature increases. Adsorption kinetics is shown to be very fast and follows a pseudo second-order indicating the coexistence of chemisorption and physisorption with the intra-particle diffusion being the rate controlling step. The experimental data fit perfectly with Sips isotherms and reveal the ability of titania aerogel to adsorb 420 mg of Orange II per gram of adsorbent at the optimal conditions. The thermodynamic study reveals the activation energy (42.1 kJ mol⁻¹) and the changes in Gibbs free energy (1.2 kJ mol⁻¹), enthalpy (−16.4 kJ mol⁻¹), and entropy (−58 J mol⁻¹ K⁻¹). The entire regeneration of the titania aerogel adsorption sites at pH 11 and 30 °C shows a total recovery of the dye and the efficient reusability and the economic interest of these adsorbing materials for environmental purposes.     

Adulteration of anthocyanin- and betalain-based coloring foodstuffs with the textile dye ‘Reactive Red 195’ and its detection by spectrophotometric,chromatic and HPLC-PDA-MS/MS analyses

A wide range of natural food colorants and coloring foodstuffs is available for the food industry to meet current costumer trends. Most natural pigments are more sensitive towards heat, light, and pH changes compared to their synthetic counterparts. Additionally, high dosages are often required to attain desired color hues and intensities. In this research article, we report on the broad and worldwide incidence of a fraudulent practice to overcome these disadvantages by adding a non-approved azo-dye preparation originating from the textile dye Reactive Red 195 to natural pigment extracts. Since the respective products and their derivatives have been widely distributed, we present a rapid method allowing the differentiation of the fraudulent azo-dye from Hibiscus sabdariffa (roselle) flower and Beta vulgaris (red beet) root extracts, the two coloring foodstuffs that are most frequently adulterated. Furthermore, detailed HPLC-PDA-MS/MS data is presented for the unambiguous identification of Reactive Red 195 and its derivatives.     

Heterogeneous UV-Fenton catalytic degradation of dyestuff in water with hydroxyl-Fe pillared bentonite

In recent years, much attention has been focused on developing heterogeneous catalyst for Fenton or photo-Fenton process to reuse the catalyst and avoid the possible pollution caused by the metal ions in the solution. Through cation exchange reaction, hydroxyl-Fe pillared bentonite (H-Fe-P-B) was successfully prepared as a solid catalyst for UV-Fenton process. Compared with raw bentonite, the content of iron, interlamellar distance and external surface area of H-Fe-P-B increased remarkably. Heterogeneous UV-Fenton catalytic degradation of azo-dye Acid Light Yellow G (ALYG) was investigated in aqueous using UVA (365 nm) light as irradiation source. The effects of H₂O₂ concentration, catalyst dosage, initial pH and temperature on degradation of ALYG were studied in detail. The results demonstrated that the H-Fe-P-B had high catalytic activity. In optimal operation conditions, more than 98% discoloration and 65% TOC removal of 50 mg/L ALYG could be achieved after 120 min treatment. The iron leaching rates of H-Fe-P-B were all below 0.6% in multiple runs in the degradation of ALYG, which indicated that the heterogeneous catalyst had long-term stability and activity. Another advantage of this catalyst was its strong surface acidity, which made the range of pH for heterogeneous UV-Fenton system extended from 3.0 to 9.0. The results indicated that the H-Fe-P-B was a promising catalyst for heterogeneous UV-Fenton system.     

Preparation and Characterization of Polyimide Attached with Azo——dye Chromophore Side Chain

In order to improve the nonlinear optical property and stability of azo--dye chromophore, the nonlinear optical polyimide (NLOPI) attached with azo chromophore side chain is synthesized by diazo coupling reaction of 4-nitrobenzenediazonium tetrafloroborate. The designed chemical structure of production can be proved in the infrared spectrum and ultraviolet-visible absorption spectrum. The NLOPI exhibited UV--Vis absorption of the azobenzene chromophore in the vicinity of the wavelengths of 330 and 490 nm. The broad amorphous peak proved that the NLOPI was amorphous with a little periodical structure along the side chain. According to transmission electron microscope, the NLOPI film was homogeneous. NLOPI only displayed a decrease in mass of about 5% at the temperature of 400℃ through thermogravimetric analysis.     

Decolorizing textile wastewater with Fenton's reagent electrogenerated with a solar photovoltaic cell

In this work it is demonstrated that Fenton's reagent can be electroproduced with abundant and cheap feedstock: oxygen saturated wastewater and solar energy. Experiments were carried out in a divided electrochemical flow cell using two electrodes: a three dimensional reticulated vitreous carbon cathode and stainless steel anode. Fenton's reagent is produced by oxygen reduction on the cathode in the presence of 1 mM Fe²⁺. The influence of electrolyte nature and its concentration and potential difference on the current efficiency, as well as the rate of Fenton's reagent electroproduction is discussed and it is concluded that over this extended range of conditions the current efficiency, for Fenton's reagent production, fell within the range 50-70%. It is possible to electroproduce a stoichiometric amount of Fenton reagent for the oxidation of 0.061 mM Reactive Black 5 (in tap water + 0.05 M Na₂SO₄, ≈pH 2.8). Similar results were obtained for solutions containing 0.1 mM Acid Green 25. Some practical applications in the field of water treatment are included. The energy required for drive electrochemical reaction is supplied to the flow cell by means of a commercial solar panel.     

Enhancement of photoinduced hydrogen production from irradiated Pt/TiO2 suspensions with simultaneous degradation of azo-dyes

The production of hydrogen from aqueous Pt/TiO₂ suspensions illuminated with UV–vis light has been examined in the absence and in presence of azo-dyes in solution. The effects of operational variables, including dye concentration, solution pH and temperature, on the rate of hydrogen production were investigated. It has been found that deposition of Pt (0.5 wt.%) on the semiconductor surface results in an increase of the H₂ production rate, which goes through a maximum with time of irradiation and then drops to steady-state values comparable to those obtained over bare TiO₂. Both, maximum and steady-state rates obtained over Pt/TiO₂ suspensions were found to increase with increasing solution pH and temperature. Addition of small quantities of azo-dyes in solution results in significantly enhanced rates of H₂ production for a period which depends on dye concentration, solution pH and, to a lesser extent, solution temperature. It is proposed that the dye acts as a scavenger of photogenerated oxidizing species while it is degraded toward CO₂ and inorganic ions. When complete mineralization is achieved, oxygen can no longer be removed from the photocatalyst surface and the rate drops to steady-state values, comparable to those obtained in the absence of azo-dye in solution. The amount of additional H₂ produced is directly proportional to the amount of dye added in the solution. The rate increases with increasing solution pH, where dye degradation is faster, indicating that the process is limited by the rate of consumption of photogenerated oxygen. It is concluded that, under certain experimental conditions, it is possible to obtain significantly enhanced rates of photoinduced hydrogen production from Pt/TiO₂ suspensions with simultaneous mineralization of azo-dyes. The process could be used for combined production of fuel H₂ and degradation of organic pollutants present in water.     

A statistical experiment design approach for advanced oxidation of Direct Red azo-dye by photo-Fenton treatment

Advanced oxidation of an azo-dye, Direct Red 28 (DR 28) by photo-Fenton treatment was investigated in batch experiments using Box-Behnken statistical experiment design and the response surface analysis. Dyestuff (DR 28), H(2)O(2) and Fe(II) concentrations were selected as independent variables in Box-Behnken design while color and total organic carbon (TOC) removal (mineralization) were considered as the response functions. Color removal increased with increasing H(2)O(2) and Fe(II) concentrations up to a certain level. High concentrations of H(2)O(2) and Fe(II) adversely affected the color and TOC removals due to hydroxyl radical scavenging effects of high oxidant and catalyst concentrations. Both H(2)O(2) and Fe(II) concentration had profound effects on decolorization. Percent color removal was higher than TOC removal indicating formation of colorless organic intermediates. Complete color removal was achieved within 5min while complete mineralization took nearly 15min. The optimal reagent doses varied depending on the initial dyestuff dose. For the highest dyestuff concentration tested, the optimal H(2)O(2)/Fe(II)/dyestuff ratio resulting in the maximum color removal (100%) was predicted to be 715/71/250 (mgL(-1)), while this ratio was 1550/96.5/250 for maximum mineralization (97.5%).     

Photocatalytic decolorization of azo-dye with zinc oxide powder in an external UV light irradiation slurry photoreactor

Photocatalytic decolorization of azo-dye Orange II in water has been examined in an external UV light irradiation slurry photoreactor using zinc oxide (ZnO) as a semiconductor photocatalyst. The effects of process parameters such as light intensity, initial dye concentration, photocatalyst loading and initial solution pH on the decolorization rate of Orange II have been systematically investigated. A two-stage photocatalytic decolorization of Orange II, the first stage of fast decolorization rate and the subsequent second stage of rather slow decolorization rate, was found. The efficiency of decolorization of Orange II increased as initial Orange II concentration decreased and UV light intensity increased. There was the optimal ZnO concentration being around 1000 mg L(-1). The optimal pH was around 7.7, which was at the natural pH of the dye solution. The effect of aeration rate on the decolorization of Orange II has been also investigated and the enhancement of decolorization of Orange II with increasing aeration rate was found. By using a model for the light intensity profile in the external UV light irradiation slurry photoreactor, the simulation model for the decolorization of Orange II with ZnO photocatalyst has been developed. The proposed model in which the slow decolorization in the second stage as well as the initial fast decolorization is also taken into account could simulate the experimental results for UV light irradiation satisfactorily. The proposed simulation model in which the change of light intensity with time due to the decolorization of Orange II and the light scatter due to solid photocatalysts are considered will be very useful for practical engineering design of the slurry photoreactor of wastewater including textile dyes.