Azo Dye In Aqueous Solution Research Articles

Radiolysis of azo dyes in aqueous solution: Apollofix Red

The UV-Vis absorption spectra of azo dyes in aqueous solutions strongly overlap with the spectra of intermediates produced in the reaction of these dyes with the intermediates of water radiolysis. This overlap complicates the investigation of reaction mechanisms. The paper describes a method for the separation of the two spectra on the example of Apollofix Red, a triazine and H-acid containing dye. The reactivity of water radiolysis intermediates (e−aq, ˙OH, ˙H, ˙O−2/HO˙2) with the dye is also discussed. The most intensive discolouring was found in the reaction of e−aq and ˙H, which is due to the fast reaction of these intermediates with the azo group of the unreacted molecule, and their slow reaction with the transformed molecules.

Surface-induced hydrogelation

The first azo dye that gels from its aqueous solution was synthesized and its moist hydrogel was investigated with electron microscopy and atomic force microscopy; the anionic azo dye in aqueous solution forms a hydrogel on cationic surfaces even at concentrations 50 times below the minimal gelation concentration.

Comparison of several advanced oxidation processes for the decolorization of Reactive Red 120 azo dye in aqueous solution

In this study UV/TiO 2, electro-Fenton (EF), wet-air oxidation (WAO), and UV/electro-Fenton (UV/EF) advanced oxidation processes (AOPs) have been applied to degrade Reactive Red 120 (RR120) dye in aqueous solution. The most efficient method on decolorization and mineralization of RR120 was observed to be WAO process. Photocatalytic degradation of RR120 by UV/TiO 2 have been studied at different pH values. At pH 3 photocatalytic degradation kinetics of RR120 successfully fitted to Langmuir–Hinshelwood (L–H) kinetics model. The values of second order degradation rate ( k″) constant and adsorption constant ( K) were determined as 4.525 mg L −1 min −1 and 0.387 L mg −1, respectively. Decolorization efficiency observed in the order of WAO>UV/TiO 2=UV/EF>EF while WAO>UV/TiO 2>UV/EF>EF order was observed in TOC removal (mineralization). For all AOPs, it was found that degradation products in reaction mixture can be disposed safely to environment after 90 min treatment.

Comparison of several advanced oxidation processes for the decolorization of Reactive Red 120 azo dye in aqueous solution

In this study UV/TiO2, electro-Fenton (EF), wet-air oxidation (WAO), and UV/electro-Fenton (UV/EF) advanced oxidation processes (AOPs) have been applied to degrade Reactive Red 120 (RR120) dye in aqueous solution. The most efficient method on decolorization and mineralization of RR120 was observed to be WAO process. Photocatalytic degradation of RR120 by UV/TiO2 have been studied at different pH values. At pH 3 photocatalytic degradation kinetics of RR120 successfully fitted to Langmuir–Hinshelwood (L–H) kinetics model. The values of second order degradation rate (k″) constant and adsorption constant (K) were determined as 4.525 mg L−1 min−1 and 0.387 L mg−1, respectively. Decolorization efficiency observed in the order of WAO>UV/TiO2=UV/EF>EF while WAO>UV/TiO2>UV/EF>EF order was observed in TOC removal (mineralization). For all AOPs, it was found that degradation products in reaction mixture can be disposed safely to environment after 90 min treatment.

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.

Photochemical and photocatalytic degradation of an azo dye in aqueous solution by UV irradiation

The photochemical and photocatalytic degradation of aqueous solutions of Solophenyl Green (SG) BLE 155%, an azo dye preparation very persistent in heavy colored textile waters, has been investigated by means of ultraviolet (UV) irradiation. The pure photochemical process demonstrated to be very efficient for low initial concentrations of the dyestuff. For higher concentrations the photocatalyitic degradation was carried on using commercial titanium dioxide, and mixtures of this semiconductor with different activated carbons (AC) suspended in the solution. The kinetics of photocatalytic dyestuff degradation were found to follow a first-order rate law. It was observed that the presence of the activated carbon enhanced the photoefficiency of the titanium dioxide catalyst. Differently activated carbon materials induced different increases in the apparent first-order rate constant of the process. The effect was quantified in terms of a synergy factor ( R) already described in the literature. The kinetic behavior could be described in terms of a modified Langmuir–Hinshelwood model. The values of the adsorption equilibrium constants for the organic molecules, K C, and for the reaction rate constants, k C, were 0.0923 l mg −1 and 1.58 mg l −1 min −1 for the TiO 2/UV process and 0.0928 l mg −1 and 2.64 mg l −1 min −1 for the TiO 2+AC/UV system with highest synergy factor, respectively. The mechanism of degradation was discussed in terms of the titanium dioxide photosensitization by the activated carbon.

Kinetics of decolorization and mineralization of reactive azo dyes in aqueous solution by the UV/H 2O 2 oxidation

The photodegradation of three non hydrolysed reactive azo dyes (Reactive red 120, Reactive black 5, Reactive yellow 84) in aqueous solution was investigated in a laboratory-scale batch photoreactor equipped with an immersed low-pressure mercury lamp. Six different doses of hydrogen peroxide, at constant initial concentration of the substrate (100 mg/l) were used. The pseudo-first order rate constants have been calculated from the experimental kinetic curves, for the three azo dyes. These rate constants have extreme values of the order of 0.1 min −1 at a H 2O 2 dose of 24.5 mmol/l. The effectiveness of the UV/H 2O 2 process has been evaluated by the degree mineralization of the total organic carbon (TOC), as a complementary indicator of the treatment efficiencies. Our results confirm the suitability of the UV/H 2O 2 process as a textile wastewater pre-treatment step, once optimum operating conditions and cost effectiveness of the method are established.

Photocatalytic degradation of dye pollutants in the presence of acetone

The photodegradation of textile azo dyes in aqueous solution containing acetone (ACE) photosensitizer was investigated at 253.7 nm. In this study, a typical azo reactive dye (C I Reactive Red 2-RR2) is used as the probe compound. ACE is a powerful photosensitizer that possesses high triplet energy, and the presence of ACE significantly enhances the overall photodegradation reaction through simultaneous sensitization. In the UV/ACE system, at the optimum conditions, over 97% of RR2 can be successfully decomposed and decolored within 300 seconds of retention time. The photodegradation mechanisms of RR2 involve both photodechlorination and photoreduction, which follow pseudo first-order decay kinetics. The quantum yield of the photolysis system has been evaluated as a function of ACE concentration and the initial pH. RR2 contains the chlorotriazinyl group, which undergoes hydrolysis and results in the formation of hydrochloric acid, indicating that the photodechlorination process is the dominant reaction mechanism. The photo-product, H+, is likely to retard the quantum yield of dye decay, suggesting that the initial pH is a critical factor in changing the photodecolorization rates of dye. Generally, this system is more favorable at higher pH levels.

Pulse radiolysis and chemical analysis of azo dyes in aqueous solution I. p-phenylazoaniline

The spectroscopic and kinetic characteristics of transients produced by one electron reduced and by one electron oxidized p-phenylaniline (PAA) at various pHs are reported. In the presence of air at pH 4–10 the transient spectra are very similar to those observed by the OH-attack on PAA at pH=4. This indicates that in all cases the OH-radicals are the major reactive species towards PAA in addition to the specific e − aq reaction on the azo group. Steady-state radiolysis experiments were also performed under various conditions and the major radiolytic products were identified by HPLC.

Aggregation of Azo Dyes with Cationic Amphiphiles at Low Concentrations in Aqueous Solution

The aggregation of a series of n-alkyltrimethylammonium bromide (CnTAB, n = 10, 12, 14, 16, and 18) and 4-n-alkyl-1-methylpyridinium iodide amphiphiles (CmpyI, m = 8, 10, 12, and 14) induced by low concentrations of azo dyes in aqueous solution has been investigated by means of ultraviolet (UV) spectroscopy. It was observed that aggregation takes place at surfactant concentrations far below the cmc of C12TAB, C14TAB, C16TAB, and C18TAB with methyl orange (MO), ethyl orange (EO), and para-methyl red (pMR). Aggregation below the cmc of C10TAB was also induced by EO. In the case of MO and pMR, however, higher dye concentrations were necessary to induce aggregation. Interactions at low surfactant concentrations have also been observed in aqueous solutions of C10pyI, C12pyI, and C14pyI with MO. Binding of methyl red (MR), methyl yellow (MY), and azobenzene sulfonate (ABS) with cationic surfactants below their cmc did not occur. Aggregation was reflected by the appearance of a blue-shifted absorption band in the spectra of the dyes. Precipitates formed in aqueous solutions from the cationic surfactants and MO and pMR are CnTA−MO, CnTA−pMR, and Cmpy−MO salts and consist of an equimolar ratio of surfactant and dye. In similar experiments with EO, MR, MY, or ABS as the solvatochromic dye molecules, no precipitation occurred, although surfactant−EO salts precipitated at high EO concentration. Dye−surfactant salts formed from CnTAB and MO were found to form myelins in phase penetration experiments. Temperatures at which myelins start to form increase upon increasing alkyl chain length of the surfactant as revealed by optical microscopy. The formation of vesicles from C10TA−MO and from C12TA−MO crystals was indicated by electron microscopy. The presence and position of the ionic group in the dye molecule is important in determining the association. The importance of hydrophobic interactions is revealed by the chain length dependence on the aggregation process and the observation that interactions are absent in ethanol. Electrostatic interactions also play an important role, as shown by the effect of NaCl on the binding process.

Photocatalytic degradation of acid azo dyes in aqueous TiO 2 suspension I. The effect of substituents

The effect of substituents on the photocatalytic degradation of H/K acid based azo dyes in aqueous solution is investigated. The intramolecular chemical environment can easily change the charge transfer direction of the conjugated pair on both sides of the trans-azobenzene backbone in o-arylazonaphthols. The contribution from an intramolecular hydrogen bond or O–H⋯NH 2 hydrogen bond caused due to the pertinent substitution at the 1,8-positions in the naphthalene nucleus retards the attack of 1O 2, but the dyes could be destroyed by TiO 2 photoassisted catalysis. Compared with photosensitised degradation, homogeneous photocatalysis is a possible way of evaluating the light-fastness of azo dyes.

Decoloration and degradation of azo dye in aqueous solution supersaturated with oxygen by irradiation of high-energy electron beams

The electron beam-induced decoloration and degradation of an azo dye (Acid Red 265) in aqueous solution supersaturated with oxygen were studied. The solution, in which the dissolved oxygen concentration (DO) was increased by pressurizing with oxygen gas up to O.3 MPa, was fed through a nozzle to a water channel under atmospheric pressure and irradiated with high-energy electron beams. It was confirmed that with high DO concentration, cleavage of aromatic rings of the dye molecules and reduction of total organic carbon were induced effectively by irradiation. The DO concentration by pressurizing under 0.3 MPa of oxygen was found to be adequate for the electron beam-induced oxidation of organic substances in water in the range of 5–14 kGy.

Positional effects of a trifluoromethyl group on the aggregation of azo dyes in aqueous solutions

The aggregation behavior in aqueous solutions of monoazo sulfonic dyes containing a trifluoromethyl group at various positions to the azo linkage, and the corresponding dyes containing a methyl group, was investigated by means of 19 F NMR and visible absorption spectroscopy. The visible absorption spectra changed with dye concentration, exhibiting distinct isosbestic points. From this, the aggregation number was estimated as 2 for all the dyes in the concentration region used for the visible absorption measurements and the aggregation constants were calculated. Furthermore, the thermodynamic parameters were determined from the temperature dependence of the aggregation constants

Flash photolysis of azo dyes in aqueous solutions of biacetyl

Irradiation by microsecond flash of aqueous aerobic solutions of biacetyl (2, 3‐butanedione) and a number of different azo dyes resulted in oxidative fading of the dyes. The fading kinetics of all tautomeric dyes could only be described properly by assuming three oxidative species. The first one is believed to be singlet oxygen. Due to its short lifetime in aqueous systems, the dye fraction consumed by singlet oxygen was confined to a maximum of about 30%. Second order reaction rate constants for the second oxidator were in the range of 1.4–4.7 × 108 l/(mol s). A radical mechanism is proposed, in which the adduct of oxygen and triplet biacetyl is the second oxidising species. A third oxidator formed from the second was necessary to describe adequately the fading curves of four azo dyes with slow fading rates. This oxidator could be an acylperoxy‐radical. The non‐tautomeric dye Cl Acid Red 37 was recycled partially after very fast fading during the first 0.5 ms.

Effects of hydrating water molecules on the aggregation behavior of azo dyes in aqueous solutions

The aggregation behavior of three sulfonated monoazo dyes (C.I. Acid Red 88, C.I. Acid Red 13 and C.I. Acid Red 27) was investigated by means of visible absorption spectroscopy to elucidate the effects of the sulfonate groups. The aggregation numbers of the three dyes were estimated as two. The aggregation constant K Agg of the dye containing two sulfonate groups was the largest. This result is inconsistent with that expected from the electrostatic repulsion between the sulfonate groups in the dyes, suggesting that the other effects are dominant. The thermodynamic parameters determined from the temperature dependence of K Agg indicates that Hydrophobie interaction is involved in the aggregation reaction. From this, it is concluded that the hydrating water molecules around the dyes play an important role in the aggregation process. Furthermore, the effects of urea were investigated to clarify the influence of cosolutes on the aggregation behavior.

Relationship between aggregation and degradation of an azo dye in aqueous solutions

The degradation behaviour of sodium 1-(2-methylphenylazo)-2-hydroxy-3,6-naphthalenedisulphonate (o-TR) by sodium hypochlorite solution in the presence of ionenes was investigated by means of visible absorption spectrum measurements. The degradation rate of o-TR markedly changed with the ionene concentration. The visible absorption spectra of the aqueous dye solutions in the presence of the ionenes were measured to clarify the situation of o-TR in the ionene solutions. It was found that dye o-TR aggregated in a solution with a certain ionene concentration, this concentration being consistent with the concentration at which the degradation rate became the slowest. It is therefore concluded that the degradation rate of the dye aggregate is significantly slower than that of the dye monomer.

Oxidative fading reaction of azo dye in aqueous solution with sodium hypochlorite.

Oxidative fading reaction of azo dye in aqueous solution with sodium hypochlorite.

Effects of electrostatic repulsion on the aggregation of azo dyes in aqueous solution

The aggregation of an azo dye containing one trifluoromethyl and two sulphonate groups (m-FTR) in aqueous solution has been investigated by means of 19F n.m.r. and electronic absorption spectroscopy. The 19F n.m.r. signals shifted to lower magnetic field, indicating that the fluorine atoms are located outside the aromatic ring of an adjacent dye molecule in the aggregate. On the other hand, in the case of an azo dye carrying one trifluoromethyl and one sulphonate group (m-FTS), the fluorine atoms were oriented above the adjacent aromatic ring. This difference gives a different aggregate structure between m-FTR and m-FTS. The absorption spectra of m-FTR aqueous solution show a single monomer/dimer equilibrium. On the basis of the results, the aggregation constant K was determined. The value of K for m-FTR was half that for m-FTS, suggesting that the latter dye aggregates more easily than the former owing to a lower electrostatic repulsion.

Aggregation of an Azo Dye in Aqueous Solution

AbstractThe investigation of the aggregation of a simple monoazo dye carrying fluorine atoms was performed by means of 19F nuclear magnetic resonance Spectroscopy. — As the concentration of the dye increased, the signals of the fluorine showed progressive shifts to the higher field. From the changes in shift it is concluded that the fluorine atoms are oriented above an adjacent aromatic nucleus. The results of the visible absorption Spectroscopy indicate that the dye solutions are a polydispersed system. The equilibrium constant of the aggregation was estimated dn the basis of an isodesmic model. A molecular model of the aggregates was proposed.

Resonance Raman spectra and micellization of a surface-active azo dye in aqueous solutions

Resonance Raman spectra and micellization of a surface-active azo dye in aqueous solutions