Decomposition Of Azo Dye Research Articles

Special traits of decomposition of azo dyes by anaerobic microbial communities

We present the results of an investigation into the special traits of conversion of azo dies golden yellow, acid orange, methyl orange, and methyl red under anaerobic conditions in comparison to aerobic conditions. In the presence of oxygen, only methyl red underwent decomposition, while under oxygen-free conditions, all remaining substances were fully discolored under the action of a methanogenous consortium of organisms. The products of reduction of the azo bond are determined in the case of each die. Introduction of additional acceptors of electrons (sulfate and nitrate) had a negative influence on the discoloration of azo dies. Addition of ethanol as an available organic cosubstrate accelerated decomposition of azo dies both under methanogenous and sulfate- and nitrate-reducing conditions. There is no direct correlation between the rates of conversion of azo dies under anaerobic conditions or their toxicity to acetoclastic methanogens. Changes in the morphological composition of the community discoloring an azo die depended on the duration of its impact on microorganisms. The mechanism of the reduction of the azo bond under the action of substances acting as mediators is explained. These substances are products of the metabolism of the microbial community in anaerobic conditions. It is shown that the supposed mediators NADH and sulfide efficiently discolor azo dies in a cell-free system, while riboflavin significantly increased the rate of conversion of substrates in recurrent cycles of discoloration only in the presence of an anaerobic microbial consortium.

Dye decomposition kinetics by UV/H 2O 2: Initial rate analysis by effective kinetic modelling methodology

The wastewater from textile industries containing non-biodegradable and toxic dye compounds is one important sources of environmental contamination. This study aims at investigating the decomposition of azo dye by UV/H 2O 2 process with varying H 2O 2 concentrations, dye concentrations, initial pHs, and UV irradiation powers. The results show that the initial rate increases with increase in initial H 2O 2 concentration, initial dye concentration to a certain point and then decreases with further increase in the above factors; the initial rate remains almost constant at lower pH and then decreases with increase in pH; the initial rate linearly increases with increase in UV irradiation power. A comprehensive kinetic model, based on reaction network analysis, was developed to predict the effects of H 2O 2 concentration, dye concentration, solution pH, and UV irradiation power on the initial dye reaction rate. The experimental data and the predicted results are in good agreement.

TiO2 modified by ammonia as a long lifetime photocatalyst for dyes decomposition

TiO2 modified by ammonia as a long lifetime photocatalyst for dyes decomposition Ammonia-modified TiO2 (TiO2/N), prepared in a pressure reactor was used as the well- active and longlife photocatalyst for the azo dye (Reactive Red 198) decomposition. The effect of aeration and the different value of the pH of the reaction medium on the photocatalytic degradation of Reactive Red 198 in water has been investigated. It has been reported that the degradation is greatly influenced by the reaction pH and the faster decomposition of azo dye took place at pH 3.5. When the solution was acidic, a larger amount of azo dye on the positively charged surface of TiO2 photocatalysts was adsorbed. From the obtained results it can be seen that the effectiveness of the decolourisation of the solution was faster by using the nitrogen-modified TiO2.

Analysis of electrochemical degradation products of sulphonated azo dyes using high‐performance liquid chromatography/tandem mass spectrometry

Electrochemical treatment of wastewaters containing azo dyes in the textile industry is a promising approach for their degradation. The monitoring of the course of the decomposition of azo dyes in wastewaters is essential due to the environmental impact of their degradation products. In this work, aqueous solutions of a simple azo dye with a low molecular weight (C.I. Acid Yellow 9) and more complex commercial dye (C.I. Reactive Black 5) were electrochemically treated in a laboratory-scale electrolytic cell in sodium chloride or ammonium acetate as supporting electrolytes. Ion-pairing reversed-phase high-performance liquid chromatography coupled with negative-ion electrospray ionization mass spectrometry is applied for the identification of electrochemical degradation products. In addition to simple inorganic salts, the formation of aromatic degradation products obtained due to the cleavage of azo bonds and further degradation reactions is shown, as well as chlorination where sodium chloride is the supporting electrolyte. Degradation mechanisms are suggested for the treatment with sodium chloride as the supporting electrolyte.

Oxidative decomposition of azo dye C.I. Acid Orange 7 (AO7) under microwave electrodeless lamp irradiation in the presence of H 2O 2

A novel microwave electrodeless lamp (MWL) rather than traditional electrode lamp (TEL) was used in a H 2O 2/MWL system as light source. This technique provided a new way to study the simultaneous effect of both UV–vis light and microwave irradiations. This study showed that H 2O 2/MWL process was 32% more effective than H 2O 2/TEL process in degrading azo dye Acid Orange 7 (AO7). Further study found that the degradation of AO7 by the H 2O 2/MWL process was initiated by the attack of HO radicals generated by the photolysis of H 2O 2. However, the direct photolysis of AO7 by MWL irradiation was not negligible. Effect of operation parameters, such as the initial concentrations of AO7 and H 2O 2 and pH, were investigated. A kinetic model of degradation of AO7 by H 2O 2/MWL process was found, in which not only the HO oxidation but also direct photolysis were considered. The kinetic model was consistent with the experiment results. The degradation of AO7 by H 2O 2/MWL corresponded to a pseudo-first order reaction. The apparent reaction constant ( k ap) was a function of initial concentrations of H 2O 2 and AO7 and pH of the solution.

Solar-light-induced photocatalytic decomposition of two azo dyes on new TiO2 photocatalyst containing nitrogen

The photocatalytic decolourisation of two azo dyes—Reactive Red 198 and Direct Green 99—in an aqueous solution by the artificial visible light radiation was investigated. The industrial metatitanic acid (H2TiO3) obtained directly from the sulphate technology installation was N-doped and used as photocatalyst. H2TiO3 was calcinated at different temperatures, ranging from 300 to 500°C, for 4 or 20h, respectively, in an ammonia atmosphere. The UV–vis/DR spectra of the modified catalysts exhibited an additional maximum in the vis region (λ≈476.8nm, EG=2.60eV for catalysts calcinated for 4h and λ≈479.5nm, EG=2.59eV for catalysts calcinated for 20h, which may be due to the presence of nitrogen in TiO2 particles. The chemical structure of the modified photocatalysts was investigated using FTIR/DRS spectroscopy and the presence of nitrogen was confirmed. A photocatalytic activity of the investigated catalysts was determined on the basis of a decomposition rate of azo dyes. The decomposition of Reactive Red 99 increased with increasing the calcination temperature of photocatalysts, whereas the activity of the prepared photocatalysts towards Direct Green 198 degradation was as follows: 300–20h<400–20h<500–20h<300–4h<400–4h<500–4h. Both, the calcination time and temperature had no influence on the amount of nitrogen-doped into TiO2 structure. The inversely proportional linear dependence between the decomposition rates of azo dyes and the intensity of the band attributed to the hydroxyl groups for both dissociated water and molecularly adsorbed water was observed. With increasing temperature of calcinations, the amount of the hydroxyl groups decreased, whereas the decomposition of azo dyes increased.

Degradation of Azo Dyes by Laccase and Ultrasound Treatment

The goal of this work was to investigate the decomposition of azo dyes by oxidative methods, such as laccase and ultrasound treatments. Each of these methods has strong and feeble sides. The laccase treatment showed high decolorization rates but cannot degrade all investigated dyes (reactive dyes), and high anionic strength led to enzyme deactivation. Ultrasound treatment can decolorize all tested dyes after 3 h at a high energy input, and prolonged sonication leads to nontoxic ionic species, which was demonstrated by ion chromatography and toxicity assays. For the first time, it was shown that a combination of laccase and ultrasound treatments can have synergistic effects, which was shown by higher degradation rates. Bulk light absorption and ion-pairing high-performance liquid chromatography (IP-HPLC) were used for process monitoring, while with reversed-phase HPLC, a lower number of intermediates than expected by IP-HPLC was found. Liquid chromatography-mass spectrometry indicated that both acid orange dyes lead to a common end product due to laccase treatment. Acid Orange 52 is demethylated by laccase and ultrasound treatment. Further results confirmed that the main effect of ultrasound is based on *OH attack on the dye molecules.

How does a Bleaching Agent Decompose Materials' Color? Decomposition of Azo Dyes by Sodium Hypochlorite

How does a Bleaching Agent Decompose Materials' Color? Decomposition of Azo Dyes by Sodium Hypochlorite

Sonochemical degradation of azo dyes in aqueous solution: a new heterogeneous kinetics model taking into account the local concentration of OH radicals and azo dyes

The sonochemical decolorization and decomposition of azo dyes, such as C. I. Reactive Red 22 and methyl orange, were performed from the viewpoints of wastewater treatment and to determine the reaction kinetics. A low concentration of the azo dye solution was irradiated with a 200 kHz and 1.25 W/cm 2 ultrasound in a homogeneous aqueous solution. The azo dye solutions were readily decolorized by the irradiation. The sonochemical decolorization was also depressed by the addition of the t-butyl alcohol radical scavenger. These results indicated that azo dye molecules were mainly decomposed by OH radicals formed from the water sonolysis. In this paper, we propose a new kinetics model taking into account the heterogeneous reaction kinetics similar to a Langmuir–Hinshelwood mechanism or an Eley–Rideal mechanism. The proposed kinetics model is based on the local reaction site at the interface region of the cavitation bubbles, where azo dye molecules are quickly decomposed because an extremely high concentration of OH radicals exists in this region. To confirm the proposed kinetics model, the effects of the initial concentration of azo dyes, irradiated atmosphere and pH on the decomposition rates were investigated. The obtained results were in good agreement with the proposed kinetics model.

Photocatalytic degradation of a cationic azo dye by TiO 2/bentonite nanocomposite

Titanium dioxide/bentonite clay nanocomposite prepared by acid-catalyzed sol–gel method was used as photocatalyst in the reaction of cationic azo dye decomposition in water. The incorporation of TiO 2 was confirmed by powder X-ray diffraction (XRD) and X-ray photoelectron spectrometer (XPS). The photocatalytic activity of those nanocomposite photocatalysts was much higher than that of the pure titanium dioxides. The nanocomposite created a kinetic synergy effect in Cationic Red GTL (GTL) disappearance with an increase of the rate constant by a factor of 2.57 for neat TiO 2 (P-25). The photo-activities were greatly dependent on the solution pH, and it was more effective for GTL to be degraded under alkaline condition. That was likely to contribute for the acid–base equilibria on the surface of the nanocomposite. Results also indicated that the proper addition of hydrogen peroxide could improve the decolorization rate, but the excess hydrogen peroxide could quench the formation of OH.