Mixed Azo Dyes Research Articles

Photocatalytic degradation of mixed azo dyes in aqueous wastewater using mesoporous-assembled TiO 2 nanocrystal synthesized by a modified sol–gel process

In this work, several operational parameters affecting the photocatalytic degradation of mixtures of two azo dyes – Acid Yellow (AY) monoazo dye and Acid Black (AB) diazo dye – including types of dye, initial dye concentration, photocatalyst dosage, dissolved oxygen, initial solution pH, and water hardness concentration, were investigated by using a mesoporous-assembled TiO 2 nanocrystal photocatalyst. The experimental results showed that the initial concentration of both azo dyes in the dye mixture greatly affected the degradation efficiency. It was interestingly found that the degradation efficiency of one azo dye could be improved by the presence of the other with suitable concentrations. At AY and AB concentrations of 2.5 and 5 mg/l, the optimum conditions for the highest degradation efficiency of both azo dyes were a photocatalyst dosage of 10 g/l, a dissolved oxygen of 7.5 mg/l, and an initial solution pH of 4.5. Moreover, even though water hardness negatively affected the degradation efficiency, the pH adjustment could be applied for enhancing the degradation of the dyes present in the extremely hard solution.

Interaction in anaerobic biodecolorization of mixed azo dyes of Acid Red 1 and Reactive Black 5 under batch and continuous conditions

Anaerobic biodecolorization of mixed azo dyes of Acid Red 1 (AR1) and Reactive Black 5 (RB5) was investigated by both batch assays and a continuous process consisting of a photo-rotating biological contactor (PRBC) and an aerobic moving bed biofilm reactor (MBBR). Batch assays showed that the decolorization of RB5 in the mixed dye systems is in preference to AR1, and decolorization products of RB5 had acted as redox mediators to stimulate the decolorization of AR1. The addition of a final concentration of 720 mg/L RB5 increased the maximum decolorization rate of 420 mg/L of AR1 by 1.5-fold than RB5-free control. During the continuous treatment of AR1 with abundant cosubstrate, the addition of RB5 increased the biodecolorization efficiency of AR1 from 62.9% to 91.0%. The analysis using cyclic voltammetry (CV) and high performance liquid chromatography/mass spectrometry (HPLC–MS) indicates the mediating properties of the decolorization products from RB5.

Enzyme activities and decolourization of single and mixed azo dyes by the white-rot fungus Phanerochaete chrysosporium

Decolourization of two azo dyes, namely Direct Red–80 (DR–80) and Mordant Blue–9 (MB–9), by Phanerochaete chrysosporium was investigated both individually and in mixtures in batch shake flasks. Mixture experiments containing these dyes were performed at five different initial concentrations ranging from 10 to 200 mg l −1 each. While the results of dye decolourization in mixture indicated decolourization efficiencies of more than 92%, the efficiencies were more than 94% in the single dye system. During the experiments, enzyme activities of lignin peroxidase (LiP) and manganese peroxidase (MnP) were also analyzed. Maximum LiP and MnP activities of 136 U l −1 and 16 U l −1, respectively, were achieved after 24 h of the fungal culture for respective initial DR–80 concentrations of 10 mg l −1 and 150 mg l −1 in the single dye system. In case of MB–9, maximum enzyme activities were 118 U l −1 (LiP) and 34 U l −1 (MnP) at initial concentrations of 50 mg l −1 and 100 mg l −1, respectively. When the two dyes were added together to the culture, maximum LiP and MnP activities were found to be 139 U l −1 and 132 U l −1 respectively for an initial concentration combination of 50 mg l −1 DR–80 and 10 mg l −1 MB–9. These profiles of enzyme activities and dye decolourization by the fungus, in both single and mixed dye systems, suggest the fungal peroxidase enzymes play a strong role in dye decolourization.

Decolorization of sulfonated azo dyes with two photosynthetic bacterial strains and a genetically engineered Escherichia coli strain

Sulfonated azo dyes were decolorized by two wild type photosynthetic bacterial (PSB) strains (Rhodobacter sphaeroides AS1.1737 and Rhodopseudomonas palustris AS1.2352) and a recombinant strain (Escherichia coli YB). The effects of environmental factors (dissolved oxygen, pH and temperature) on decolorization were investigated. All the strains could decolorize azo dye up to 900 mg l−1, and the correlations between the specific decolorization rate and dye concentration could be described by Michaelis–Menten kinetics. Repeated batch operations were performed to study the persistence and stability of bacterial decolorization. Mixed azo dyes were also decolorized by the two PSB strains. Azoreductase was overexpressed in E. coli YB; however, the two PSB strains were better decolorizers for sulfonated azo dyes.

Synthesis, characterization and electrical conductivity properties of homo- and hetero-di and trimetallic complexes of mixed azo dyes

The synthesis of seven new complexes of mixed ligands and metals are reported. Their stoichiometries (metals:ligands) were found to be 1∶3, 2∶2 and 3∶2 corresponding to FeL12L2H, M2L1L2 and M′M2L1L2, respectively (where M′ = Cu2+, M = Cu2+, Co2+ or Ni2+; HL1 = Methyl Red; H2L2 = Alizarin Yellow R). The complexes were characterized by elemental analysis, infrared and Nujol mull electronic spectra and magnetic moment measurements. The results of the electrical conductivity studies for the prepared complexes in the solid state (using compressed tablets) indicated reasonable semiconducting properties. The magnitude of these values, logσ291 lay between −5.46 and −8.67, resulting from the structure and nature of the substituent of the two mixed ligands as well as the high metallic content of their complexes.