Aromatic Azo Dyes Research Articles

Alkaline-thermal hydrolysate of waste activated sludge as a co-metabolic substrate enhances biodegradation of refractory dye reactive black 5

Aromatic azo dyes possess inherent resistance and are known to be carcinogenic, posing a significant threat to human and ecosystems. Enhancing the biodegradation of azo dyes usually requires the presence of co-metabolic substrates to optimize the process. In addressing the issue of excessive waste activated sludge (WAS) generation, this study explored the potential of utilizing alkaline-thermal hydrolysate of WAS as a co-metabolic substrate to boost the degradation of reactive black 5 (RB5) dyes. The acclimated microbial consortium, when supplemented with the WAS hydrolysate obtained at a hydrolysis temperature of 30 °C, achieved an impressive RB5 decolorization efficiency of 90.3% (pH = 7, 35 °C) with a corresponding COD removal efficiency of 45.0%. The addition of WAS hydrolysate as a co-substrate conferred the consortium with a remarkable tolerance to high dye concentration (1500 mg/L RB5) and salinity levels (4–5%), surpassing the performance of conventional co-metabolic sugars in RB5 degradation. 3D-EEM analysis revealed that protein-like substances rich in tyrosine and tryptophan, present in the WAS hydrolysate, played a crucial role in promoting RB5 biodegradation. Furthermore, the microbial consortium community exhibited an enrichment of dye-degrading species, including Acidovorax, Bordetella, Kerstersia, and Brevundimonas, which dominated the community. Notably, functional genes associated with dye degradation and intermediates were also enriched during the RB5 decolorization and biodegradation process. These findings present a practical strategy for the simultaneous treatment of dye-containing wastewater and recycling of WAS.

An intramolecular Mannich type reaction of ortho-amino aromatic azo dye and its detection effect for formaldehyde

A series of aromatic primary amine dyes were designed and applied for the modification of silk fibroin with Mannich-type reaction in the previous studies. Most aromatic primary amine dyes achieved the expected results with the participation of formaldehyde. However, those azo dyes with ortho-amino aromatic structure lost their colour and did not have any modification on silk fibroin under the same conditions of treatment. Therefore, the decolorization phenomenon of ortho-aniline aromatic azo dyes was analyzed using FT-IR, ESI-MS, NMR and Gaussian computation and the results indicated that an intramolecular Mannich reaction occurred between ortho-amino aromatic azo dyes and formaldehyde. In addition, a secondary effect of reduction of dyes by formaldehyde took place, in which the conjugated chromogenic system of the dye molecules was destroyed, producing benzimidazole, o-phenylenediamine and nitrogen-containing heterocyclic substances with polymethyl substitution. This decolorization of dye was studied as a detection or monitoring method for formaldehyde, and it showed advantages of sensitive response, clear visual indication, and no volatilization of organic solvent.

The Synthesis of a Novel Azo Dyes and Study of Photocatalytic Degradation

Six novel aromatic azo dyes were synthesized from 4-amino-2-nitrobenzoic acid with phenol, catechol, resorcinol, hydroquinone, salicylic acid and acetylsalicylic acid with very good yield. These azo dyes confirm by FTIR, CHNS and study the photo stability used TiO2 and ZnO. The photocatalytic degradation of novel aromatic azo dyes was investigated using TiO2 and ZnO as a catalyst under 125 watts UV lamp. A series of experiments was performed to reaching to the optimum condition of degradation. The photocatalytic degradation of azo dye follows the first order reaction. In all experiments photocatalytic degradation of the azo dye has been studied using different weight of TiO2 and ZnO suspended in an aqueous solution of azo dye irradiated by irradiated by 125–UV lamp in 100 cm3 a vessel reactor at room temperature with 10 cm3/min air bubble has been passed through the solution. In addition, all result was measured using UV-Visible spectrophotometer.

Green Synthesis of Novel Class of Azo Dyes Based on Naphthols, Coumarins, and Phenols with Molybdate Sulfuric Acid

ABSTRACTA new series of polycyclic aromatic azo dyes based on naphthols, coumarins, and phenols were efficiently synthesized by the diazotization of 7-amino coumarins in the presence of catalytic amounts of molybdate sulfuric acid (MSA) followed by coupling reactions. The diazotization and subsequent azo-coupling generated the related azo dyes at 0–5°C in short reaction times with a simple experimental procedure.

Effects of Surfactants on the Oxidation of Aromatic Azo Dyes

Effects of Surfactants on the Oxidation of Aromatic Azo Dyes

A highly selective colorimetric sensor to Fe3+ and Co2+ in aqueous solutions

Five aromatic azo dyes with hydroxyl groups (1–5) were designed and synthesized by coupling reactions. The relationships between structures of the compounds and the spectroscopic properties were investigated. The absorption spectra of these compounds upon titration with K+, Ca2+, Al3+, Mg2+, Ni2+, Mn2+, Cd2+, Cr3+, Fe3+, Cu2+, Zn2+, Co2+, Hg2+, and Pb2+ ions in neutral aqueous solutions were reported. The results are coincident with the calculation results using the density functional theory method. The high selectivity, excellent water solubility and simple synthetic process make 1-[(2-Hydroxyl)phenylazo]-2-naphthol (5) a potential sensor for sensing Fe3+ and Mn2+ with the naked eye. 1-[(2-hydroxyl)phenylazo]-2-naphthol-6-sulfonic acid (3) shows high selectivity for the colorimetric detection of Fe3+ and Co2+ among the tested metal ions. The detection limitations of 3 for determining Co2+ and Fe3+ were calculated to be 2.8 × 10−7 and 5.6 × 10−7 mol/L, respectively.

A DFT study on photoinduced surface catalytic coupling reactions on nanostructured silver: selective formation of azobenzene derivatives from para-substituted nitrobenzene and aniline

We propose that aromatic nitro and amine compounds undergo photochemical reductive and oxidative coupling, respectively, to specifically produce azobenzene derivatives which exhibit characteristic Raman signals related to the azo group. A photoinduced charge transfer model is presented to explain the transformations observed in para-substituted ArNO(2) and ArNH(2) on nanostructured silver due to the surface plasmon resonance effect. Theoretical calculations show that the initial reaction takes place through excitation of an electron from the filled level of silver to the lowest unoccupied molecular orbital (LUMO) of an adsorbed ArNO(2) molecule, and from the highest occupied molecular orbital (HOMO) of an adsorbed ArNH(2) molecule to the unoccupied level of silver, during irradiation with visible light. The para-substituted ArNO(2)(-)˙ and ArNH(2)(+)˙ surface species react further to produce the azobenzene derivatives. Our results may provide a new strategy for the syntheses of aromatic azo dyes from aromatic nitro and amine compounds based on the use of nanostructured silver as a catalyst.

Removing textile mill effluent recalcitrant COD and toxicity using the H2O2/UV system

The potential of the H2O2/UV process for improving quality of an industrial textile effluent before biological treatment was evaluated in the laboratory using a multivariate experimental design to determine the effects of pH, H2O2 dose and reaction time on colour, COD and toxicity removal efficiencies. Increasing reaction time (from 10 to 120 min) and H2O2 dose (from 0 to 5 mmol L(-1)) significantly improved removal efficiencies, while increasing pH (from 4 to 10) had a negative effect on colour and toxicity removals. Laboratory H2O2/UV treatment of the mill effluent under optimum conditions (pH 7, 5 mmol L(-1) H2O2, 120 min) resulted in decreases in colour (70%), COD (21%) and toxicity (67%), without lowering BOD. H2O2 was consumed within the first 30-60 min, while the effluent average oxidation state stabilized after 60 min. Decreasing reaction time to 60 min resulted in similar colour (63%) and COD (20%) removals but lower toxicity removal (44%). Spectrophotometric monitoring of the optimized reaction indicated partial destruction of residual aromatic azo dyes. H2O2 and residual peroxide and average oxidation state of the effluent Effluent biodegradability (BOD/COD) increased by 28% after the H2O2/UV treatment. Improvements observed in effluent quality are expected to enhance combined AOP-biological treatment efficiency of the mill effluent.

An insight into the mechanism of the cellulose dyeing process: Molecular modelling and simulations of cellulose and its interactions with water, urea, aromatic azo-dyes and aryl ammonium compounds

Potential cellulose-surface active aryl ammonium compounds that may also de-aggregate dye molecules in aqueous solution have been modelled using molecular mechanics methods and simulation methods, and compared with known additives such as amines and urea, as an extrapolation of modelling the interaction of water and urea molecules with cellulose microfibril surfaces. The results from these modelling studies have clearly elucidated the way in which polar molecules interact with cellulose surfaces, and have been used to provide insight into the dyeing process and to identify which new molecular systems might be predicted to act as molecular delivery agents for assisting dye processes.

Temperature dependent absorption spectroscopy of some tautomeric azo dyes and Schiff bases

The spectral properties of several aromatic azo dyes of fundamental importance (4-phenylazo-1-naphthol, 1-phenylazo-2-naphthol and 2-phenylazo-1-naphthol) and Schiff bases (N-(2-hydroxy-1-naphthylmethylidene)aniline and N-(1-hydroxy-2-naphthylmethylidene)aniline) are investigated at temperatures down to 100 K. The observed spectral changes are interpreted in terms of the existing tautomeric equilibrium and hydrogen-bonding (H-bonding) with the solvent. In non-polar solvents the decrease in temperature leads, in all compounds except 4-phenylazo-1-naphthol, to a full transformation of the enol tautomeric form (A) to the quinone form (H). The temperature dependence of the equilibrium A ⇌ H exhibits a shift around 240 K. In ethanol, due to intermolecular H-bonding, in the case of the azo dyes full transformation was not observed, while the behavior of the Schiff bases is the same as in non-polar solvents. The thermodynamic parameters of the equilibrium A ⇌ H were estimated in both non-polar solvent and ethanol for all investigated compounds.

Polarography of heterocyclic azo compounds and their metal complexes

Summary The polarographic behaviour of a wide range of pyridylazo and thiazolylazo dyes has been studied and several differences observed between the electrode reactions of these heterocyclic compounds and their benzene or naphthalene counterparts. The hydrazo derivatives of the heterocyclic dyes are more stable with respect to disproportionation, which is attributed to the strongly electron-attracting properties of the pyridyl and thiazolyl groups. In addition their disproportionation is base-catalyzed, whereas earlier studies showed that aromatic azo dyes undergo an acid-catalyzed reaction. Hammett substituent constants were calculated for a variety of heterocyclic groups. Half wave potential shifts were observed for several heterocyclic azo dyes in the presence of nickel and iron(III) ions, and the height of the metal-dye complex wave was proportional to metal concentration. Aluminium did not produce a shift with any of the dyes studied, which enables nickel or iron to be determined in the presence of an excess of aluminium.