Azo Dye Molecules Research Articles

Effects of Additives on Sonolytic Degradation of Azo Dye Molecules Found in Industrial Wastewater

The growing number of industries is a threat to our environment, as they expose the polluted water directly into the natural water sources. Various processes have been expanded to evacuate these hazardous organic pollutants from water. Among them, advance oxidation process (AOP) is very popular, as the method is cost efficient and highly effective in the similar field. In this process ultrasound is exercised for the deterioration of these pollutants and occasionally some additives are also added to enhance the degradation. In this article, the author has reported the degradation of two azo dyes, named methyl orange (MO) and congo red (CR), in presence of some additives like, inorganic salts, charcoal, H<sub>2</sub>O<sub>2</sub>, CCl<sub>4</sub>, tert-butyl alcohol (TBA), glucose and sucrose. The total experiment was conducted at room temperature and the power of the sonication machine was fixed to 40 kHz-120W. For both of the dyes, it was found that charcoal was most effective additive, which highly enhanced the degradation rate, which was mainly due to its high adsorption capability. TBA found to be the least enhancer for MO, on the contrary, pure CR showed the lowest degradation rate. The effectiveness of additives for MO can be shown as 0.01g charcoal > 20 ml glucose > 20 ml NaCl > 100 μL CCl<sub>4</sub> > 10 ml Na<sub>2</sub>SO<sub>4</sub> > 400 μL H<sub>2</sub>O<sub>2</sub> > 10 ml sucrose > pure MO > TBA, while for CR is 0.01g charcoal > combined additives > TBA > 100 μL CCl<sub>4</sub> > pure CR, after sonication for 15 minutes in a sonicator.

Ceramic-supported graphene oxide membrane bioreactor for the anaerobic decolorization of azo dyes

A continuous compact membrane bioreactor consisted of ceramic-supported graphene oxide membrane (CSGoM) was implemented for the first time for anaerobic biodecolorization of monoazo Acid Orange 7 (AO7), diazo Reactive Black 5 (RB5), and triazo Direct Blue 71 (DB71) solutions, showing excellent decolorization potential. The membrane was prepared by vacuum filtration of various graphene oxide solutions using a UF ceramic flat element. The decolorization efficiency of the CSGoM bioreactor, made from 1 mg·mL−1 of GO solution (B-CSGoM-1), was investigated for several structurally distinct azo dyes, initial feed concentrations, and permeate fluxes. Maximum color removal was achieved under low feed concentration (50 mg·L−1) and permeate flux (0.05 L·m−2·h−1), reaching 99% for AO7, 96% RB5, and 92% for DB71. At this low permeate flux, the biodecolorization was stable for all azo dye solutions irrespective of the feed concentration. In a subsequent experiment under higher feed concentration and permeate flux (100 mg·L−1 and 0.10 L·m−2·h−1), the decolorization slightly fell to 93%, 85%, and 81% for monoazo, diazo, and triazo solutions, respectively. The existence of anaerobic bacteria (Geobacter and Pseudomonas guangdongensis) in the B-CSGoM-1 biofilm confirms that they could perform efficient biodegradation of azo dye molecules in association with the graphene oxide membrane.

Pure and cerium-doped ZnO nanorods grown on reticulated Al2O3 substrate for photocatalytic degradation of Acid Red 88 azo dye

Pure and Ce-doped ZnO photocatalyst nanorods were both grown on α-Al2O3 ceramic foams manufactured using a polymeric sponge replication technique. A three-dimensional network of α- Al2O3 struts which served as the substrate for the photocatalyst material was first seeded via dip coating. The seed-mediated synthesis of ZnO nanorods with controlled lengths and diameters was then carried out at low temperature (∼95 °C) by chemical bath deposition (CBD). Their morphologies and crystallographic orientations were verified using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The effect of Ce-doping on the optical properties of the ZnO nanorods was investigated by ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopies. There was a modification in the band-gap structure with the incorporation of cerium atoms in the ZnO matrix as observed by the partial redshift at the absorption edges and by the blue and green light emissions. Color removal efficiencies of the samples were evaluated under UVA and visible light irradiations over the photocatalytic degradation of Acid Red 88 (AR88) azo dye molecules dissolved in water. Enhanced degradation rates were achieved for the Ce-doped samples compared to those of the pure ones. Similarly, the extend of mineralization (i.e., total organic carbon (TOC) removal) reached the maximum value of 54% for the Ce-doped samples under UVA light. According to the scavenging experiment results, it was found that the most effective radical involved in the present photocatalytic degradation reactions was the superoxide anion (·O2−).

Cold Crystallization and Polymorphism Triggered by the Mobility of the Phenyl Group in Alkyl Azo Dye Molecules

The thermal behavior, including the cold crystallization, of alkyl-derivatized Sudan III (1-[4-(phenylazo)phenylazo]-2-naphthol), SD3-OCn, was investigated. Its structural flexibility due to the two azo groups caused the formation of plural crystal structures, which further resulted in complex cold crystallization. A metastable nonflat structure and a thermodynamically stable flat structure resulted in the two sets of crystallization and melting behavior during the heating process. Further, the change in the alkyl chain length caused variations in the crystallization rate and crystallinity, thus systematically changing the cold crystallization behavior. It was proven that the high mobility of the phenyl group triggered supercooling and cold crystallization and that the alkyl chain correspondingly controlled the thermal behavior.

A robust and inexpensive all optical switch with chiral nematic liquid crystal

A switchable photonic band gap with optical addressing is demonstrated. The switch can tune over a broad wavelength range (about 80 nm) without deformation and degradation with high reproducibility. The material is a mixture of reactive and nonreactive mesogens, azo dye molecules and chiral dopant. The mixture of reactive monomers and nonreactive mesogens leads to a robust polymer template filled with nano-droplets. Due to a photo-induced phase transition, the edges of the bandgap shift to shorter wavelengths after illumination. Three concentrations of reactive monomers are investigated. The features of the device are interesting for several emerging applications: all optical photonic switches, lab-on-a-chip devices, and switchable optical devices such as sensors, reflectors, diffraction gratings, polarizers, shutters, notch- and band-pass filters, reflective displays, mirror-less tunable lasers and modulators.

Nanostructured KxNa1-xNbO3 hollow spheres as potential materials for the photocatalytic treatment of polluted water

Potassium-sodium niobate-based hollows spheres were studied in the photocatalytic degradation of Basic Blue 41 dye in aqueous phase under UV irradiation. KxNa1-xNbO3 materials were prepared at 700 °C by the spray pyrolysis method. Photocatalysts were characterized by XRD, SEM, TEM, N2 adsorption/desorption isotherms and FTIR. Different kinetic models of adsorption, direct photolysis, and photocatalytic degradation of the azo-dye were performed as a function of the pH of solution. The increase in potassium content is responsible of the distortion and polarization of the niobate structure promoting a decrease in the energy band-gap down to 3.01 eV for K0.5Na0.5NbO3. The photocatalytic activity observed on K0.5Na0.5NbO3 was up to 23 times higher than that on TiO2 in terms of the surface concentration of the azo-dye molecules adsorbed. A mechanism for the degradation of Basic Blue 41 azo-dye based on the reactive oxygen species detected by scavenger’s tests and mass-spectroscopy analysis was proposed.

Highly efficient degradation of acid orange II on a defect-enriched Fe-based nanoporous electrode by the pulsed square-wave method

The degradation of acid orange II (AO II) by a nanoporous Fe-Si-B (NP-FeSiB) electrode under the pulsed square-wave potential has been investigated in this research. Defect-enriched NP-FeSiB electrode was fabricated through dealloying of annealed Fe76Si9B15 amorphous ribbons. The results of UV–vis spectra and FTIR indicated that AO II solution was degraded efficiently into unharmful molecules H2O and CO2 on NP-FeSiB electrode within 5 mins under the square-wave potential of ±1.5 V. The degradation efficiency of the NP-FeSiB electrode remains 98.9% even after 5-time recycling. The large amount of active surface area of the nanoporous FeSiB electrode with lattice disorders and stacking faults, and alternate electrochemical redox reactions were mainly responsible for the excellent degradation performance of the NP-FeSiB electrode. The electrochemical pulsed square-wave process accelerated the redox of Fe element in Fe-based nanoporous electrode and promoted the generation of hydroxyl radicals (·OH) with strong oxidizability as predominant oxidants for the degradation of azo dye molecules, which was not only beneficial to improving the catalytic degradation activity, but also beneficial to enhancing the reusability of the nanoporous electrode. This work provides a highly possibility to efficiently degrade azo dyes and broadens the application fields of nanoporous metals.

Modeling of Nonlinear Optical Phenomena in Host-Guest Systems Using Bond Fluctuation Monte Carlo Model: A Review.

We review the results of Monte Carlo studies of chosen nonlinear optical effects in host-guest systems, using methods based on the bond-fluctuation model (BFM) for a polymer matrix. In particular, we simulate the inscription of various types of diffraction gratings in degenerate two wave mixing (DTWM) experiments (surface relief gratings (SRG), gratings in polymers doped with azo-dye molecules and gratings in biopolymers), poling effects (electric field poling of dipolar molecules and all-optical poling) and photomechanical effect. All these processes are characterized in terms of parameters measured in experiments, such as diffraction efficiency, nonlinear susceptibilities, density profiles or loading parameters. Local free volume in the BFM matrix, characterized by probabilistic distributions and correlation functions, displays a complex mosaic-like structure of scale-free clusters, which are thought to be responsible for heterogeneous dynamics of nonlinear optical processes. The photoinduced dynamics of single azopolymer chains, studied in two and three dimensions, displays complex sub-diffusive, diffusive and super-diffusive dynamical regimes. A directly related mathematical model of SRG inscription, based on the continuous time random walk (CTRW) formalism, is formulated and studied. Theoretical part of the review is devoted to the justification of the a priori assumptions made in the BFM modeling of photoinduced motion of the azo-polymer chains.

Rational design of Z-scheme Bi12O17Cl2/plasmonic Ag/anoxic TiO2 composites for efficient visible light photocatalysis

An all-solid-state Z-scheme plasmonic Ag-Bi12O17Cl2/TiO2 heterojunction, for the first time, was constructed. The in-situ one-step preparation of Bi12O17Cl2 in the presence of Cl source on the surface of TiO2 fiber, which has not been previously reported, led to the successful coupling Bi12O17Cl2 and TiO2. The Ag particles were selectively anchored on the surface of Bi12O17Cl2 and the interface of Bi12O17Cl2/TiO2. The plasmonic effect and electron-hole bridge at the interfaces were thus separately realized. The Ag-Bi12O17Cl2/TiO2 exhibited greatly increased reaction rate in the removal of azo dye molecules under visible light irradiation, which was 5.4 and 1.4 times higher than that of TiO2 and Bi12O17Cl2, respectively. The enhanced photocatalytic performance was ascribed to the increased specific surface area, formed Z-scheme heterojunction, and the plasmonic effect of Ag nanoparticles. This work paves a new way for the rational design of recyclable, efficient Z-scheme photocatalyst for environmental remediation.

Patterned Photoalignment in Thin Films: Physics and Applications

Photoalignment of liquid crystals by using azo dye molecules is a commonly proposed alternative to traditional rubbing alignment methods. Photoalignment mechanism can be well described in terms of rotational diffusion of azo dye molecules exposed by ultraviolet polarized light. A specific feature of the irradiated light is the intensity dependent change of azimuthal anchoring of liquid crystals. While there are various mechanisms of azo dye photoalignment, photo-reorientation occurs when dye molecules orient themselves perpendicular to the polarization of incident light. In this review, we describe both recent achievements in applications of photoaligned liquid crystal cells and its simulation. A variety of display and photonic devices with azo dye aligned nematic and ferroelectric liquid crystals are presented: q-plates, optically rewritable flexible e-paper (monochromatic and color), and Dammann gratings. Some theoretical aspects of the alignment process and display simulation are also considered.

Prospects for the use of mixed micellar structures as a template in synthesis of MCM-41-type silicas

Formation of mixed micelles assisted by cetyltrimethylammonium bromide and methyl red was studied by means of conductometric and spectrophotometric methods. It follows from the analysis of conductometric dependences that the addition of azo dye leads to a decrease in critical micelle concentration of a long-chain quaternary ammonium salt. The respective thermodynamic parameters were calculated. The process of mixed micelles formation was stated to be spontaneous and the solubilization of azo dye by micelles of cetyltrimethylammonium bromide is profitable in terms of energy and accompanied by an increase in degrees of freedom of the system. Based on the data of spectrophotometric study of methyl red solutions in the presence of cetyltrimethylammonium bromide, the values of stability constant, partition coefficient and change in the standard free energy of methyl red distribution between aqueous and micellar medium were calculated. It was found that electrostatic and hydrophobic interactions arising between azo dye and cetyltrimethylammonium bromide molecules cause the orientation of methyl red from the shell towards the center of the micelles. It was shown that mixed micelles can be used as a template in sol-gel synthesis of mesoporous aminosilica of MSM-41 type. The results of low-temperature nitrogen adsorption-desorption and X-ray analysis revealed that the introduction of methyl red as a part of mixed micelles into the reaction medium of sol-gel synthesis causes substantial increase in specific surface area and total pore volume, noticeable reduction of pore diameter, thereby contributing to the formation of silica material with a pronounced long-range ordered mesoporous structure.

A Planar Fresnel Lens in Reflection Type Based on Azo-Dye-Doped Cholesteric Liquid Crystals Fabricated by Photo-Alignment.

This paper presents a focusing efficiency and focal length tunable planar Fresnel lens in reflection type based on azo-dye-doped cholesterol liquid crystal film. The Fresnel-like pattern of a pumping beam can be formed by a Sagnac interferometer. When the azo-dye molecules are irradiated by the pumping beam, the photoalignment effect will be induced in the bright (odd) zones due to the trans–cis photoisomerization of azo-dye molecules. Thus, the structures of cholesteric liquid crystals in the odd zones will reorient from the imperfectly planar textures to the perfectly planar textures. The different structures of cholesteric liquid crystals in two adjacent zones will give rise to phase difference for the reflected light and thus function as a Fresnel lens. The focusing efficiency of the proposed Fresnel lens can be controlled by the applied voltages and affected by the polarization state of incident light. Moreover, various focal lengths of the Fresnel lens can be achieved by rewriting a different center radius of the Fresnel-like pattern.

Синтез и исследование новых азокрасителей на основе функционально замещенных производных салициловой кислоты

Three chromatographically pure azo dyes based on salicylic acid and para-nitroaniline were isolated in 60-64% yields. The structure of the synthesized compounds was proved by IR spectroscopy. The spectra of the compounds contain characteristic absorption bands associated with the vibrations of O–H, N–H, C=O, and N=N groups. The products precipitated as orange-brown powders, which corresponds to compounds with a short system of conjugated double bonds. The predominant tautomeric form of existence of the synthesized azo compounds was determined – 5,5'-(diazen-1,2-diyl)bis(2-hydroxybenzoic acid), 2-hydroxy-5-((4-nitrophenyl)-diazenyl)benzoic acid, 5-amino-2-hydroxy-4-((4-nitrophenyl) diazenyl) benzoic acid. It was shown that they all exist as azo-tautomers. To determine the dyeing power of potential dyes, a test cold dyeing was carried out on samples of a multichannel consisting of six main types of fabrics used in the textile industry, under conditions corresponding to dyeing with acid and reactive dyes. The ability of the compounds to act as acid dyes was established, coloring woolen, polyamide and acetate fibers in yellow-orange and beige-brown colors. The introduction of an amino group into the salicylic acid fragment weakens the color properties of the azo dye molecule. The calculation of the toxicity of compounds with intravenous and oral routes of administration, carried out according to the GUSAR program, shows their low toxicity (4-5 toxicity class). The introduction of an amino group into the azo dye molecule is accompanied by an increase in its toxicity. All isolated compounds comply with Lipinski's rule, which indicates their bioavailability. Prediction of the biological activity of the compounds, carried out using the PASS program, shows that with a probability of more than 90%, the synthesized compounds exhibit antiseptic properties without irritating the skin and mucous membranes. This allows the isolated compounds to be considered promising for use as dyes in cosmetics.

Hierarchical porous induced competent removal of low concentration azo dye molecules by generating a leachy crystalline structure H-MIL-53(Fe)

The development in technology of synthetic azo dyes, has led to excessive water resources pollution. Even at lower concentration they can impart the quality of water and human life. Herein, we have developed a novel synthesis strategy via introducing salicylic acid (SA) for the synthesis of a leachy crystalline material H-MIL-53(Fe) with hierarchical pores (HP) and exposed coordination unsaturated sites (CUS), which had higher surface area and larger pore volume than the as synthesized MIL-53(Fe). Due to these characteristics, H-MIL-53(Fe) was competent removal of orange G (OG, one of the frequently used azo dyes) with equilibrium in 300 min and the maximum adsorption capacity of 163.9 mg/g. The adsorption mechanism of OG onto H-MIL-53(Fe) was mostly based on electrostatic attraction between CUS of H-MIL-53(Fe) along with HP as active species to OG diffusion and bind. By comparing H-MIL-53(Fe) with other adsorbents for OG adsorption, it is undoubtedly that H-MIL-53(Fe) can be used as a promising adsorbent for OG removal from aqueous solutions.

Facile Synthesis of Self-Assembled NiFe Layered Double Hydroxide-Based Azobenzene Composite Films with Photoisomerization and Chemical Gas Sensor Performances.

Two kinds of layered double hydroxide (LDH) Langmuir composite films containing azobenzene (Azo) groups were successfully prepared by Langmuir–Blodgett (LB) technology. Then, an X-ray diffractometer (XRD), a transmission electron microscope (TEM), and an atomic force microscope (AFM) were used to investigate the structures of NiFe-LDH and the uniform morphologies of the composite LB films. The photoisomerization and acid–base gas sensor performances of the obtained thin film samples were tested by infrared visible (FTIR) spectroscropy and ultraviolet visible (UV–vis) spectroscropy. It is proved that the Azo dye molecules in the composite film are relatively stable to photoisomerization. In addition, the prepared composite films have high sensing sensitivity and good recyclability for acid–base response gases. The present research proposes a new clue for designing thin film materials for chemical gas response with good stability and sensitivity.

Azo-dye degradation by Mn–Al powders

Manganese–Aluminum powders were recently reported to show high efficiency and fast reaction rates as decolorization materials for azo-dye aqueous solutions. This work presents a detailed study of different aspects of this material. Firstly, the influence of the crystalline phase and the microstructure was studied by comparing the efficiency of powders obtained by different production protocols. Secondly, the decolorization efficiency was investigated on various types of dyes, including real textile wastewater samples. The analysis of the treated water and the particles showed that the main reaction mechanism was the breaking of the azo-dye molecules, although important adsorption on the metallic surface was observed for some colorants. Finally, the reusability of the particles and the reduction of toxicity achieved during the treatments were assessed. The simple production and application methods, the high efficiency and the use of environmentally friendly metallic elements are the main advantages of Manganese–Aluminum powders compared to other high-efficient decolorizing metallic materials.

Anatase TiO2 powder immobilized on reticulated Al2O3 ceramics as a photocatalyst for degradation of RO16 azo dye

The three-dimensional network of open-celled Al2O3 ceramic supports were first fabricated using a polymeric sponge replication technique. The polyurethane foams soaked with the highly loaded Al2O3 ceramic slurry were drained, slowly dried and sintered at 950 °C to complete the burn out process and to construct the ceramic preforms. They were then carefully soaked again with the moderately loaded Al2O3 slurry and sintered at 1500 °C to increase their strength. Finally, the photocatalyst ceramic powder covering the outer surfaces was placed layer by layer through dipping the rigid Al2O3 supports repeatedly in the slurry of TiO2 powder. The dip-applied TiO2 was sintered eventually at relatively low temperature of 700 °C to prevent phase transformation. The efficiencies of the TiO2 coated Al2O3 samples were evaluated by the photocatalytic degradation of reactive orange 16 (RO16) azo dye molecules dissolved in water. Nearly complete color removals were achieved within 75 min under UVC irradiation.

Recording Polarization Holograms in Polymer Films with Azo Dyes and Azo Polymers

Based on polymers with the addition of azo dyes as chromophores and azopolymers with the same covalently linked chromophores, recording media for polarization holography are created and their properties are studied when recording holograms of a plane wave front with parallel and perpendicular polarization of recording rays. It is found that the diffraction efficiency and the storage time of holograms are much longer in recording media with films of azo polymers in comparison with polymeric solid solutions of azo dyes. In the latter case, the energy of light is spent only for the trans–cis isomerization of azo dye molecules during exposure of holograms and the polymer chains do not undergo deformation with the formation of a surface relief in the polymer film. Therefore, it is preferable to use recording media based on solid solutions of azo dyes in dynamic polarization holography.

Electrically Tunable Fresnel Lens in Twisted-Nematic Liquid Crystals Fabricated by a Sagnac Interferometer.

This paper presents an electrically tunable Fresnel lens in a twisted nematic liquid crystal cell fabricated by using a Sagnac interferometer. When the Fresnel-patterned green beam, formed by the Sagnac interferometer, is irradiated on the azo-dye doped liquid crystal mixture, the azo-dye molecules undergo trans–cis photoisomerization and then generate the photo-alignment effect in the bright (odd) zones. The director of the liquid crystal molecules in the odd zones reorients the direction perpendicular to the polarization direction of the linearly polarized green beam. The various structures of liquid crystals in the odd and even zones will result in a phase difference and thus, a Fresnel lens can be generated. The experimental results show that the proposed Fresnel lens has a high diffraction efficiency of 31.5% under an applied alternating-currents (AC) voltage. The focal length of the Fresnel lens can also be tuned by thermally erasing the photo-alignment effect of the azo dyes and rewriting by a different Fresnel-like pattern.

Azo dyes degradation and mutagenicity evaluation with a combination of microbiological and oxidative discoloration treatments

This work evaluated the degradation of the Acid Blue 161 and Procion Red MX-5B dyes in a binary solution by the filamentous fungus Aspergillus terreus and the yeast Saccharomyces cerevisiae in systems with and without electrochemical oxidation as the pretreatment process. UV–Vis spectrophotometry, high-performance liquid chromatography with (HPLC), Fourier transform infrared (FT-IR) spectroscopy and Salmonella/microsome assay (Ames test) were applied towards the degradation analysis of the dyes. Adsorption tests with white clay immobilized on alginate were also conducted after the discoloration treatments to remove intermediate metabolites formed during the degradation of the dye molecules. The discoloration treatments led to the complete color removal of the solutions in all the systems tested. The clay demonstrated affinity for the metabolites formed after discoloration treatments, the removal rates were variable, but the all systems has proved efficient. The Salmonella/microsome assay (Ames test) with strains TA98 and TA100 in the absence and presence of exogenous metabolism (S9 microsomal system, Moltox) revealed that the initial molecules and by-products of the metabolism of the dyes were direct mutagens. The electrochemical/A. terreus/clay system was able to discolor the solutions and transform the direct mutagens into non-mutagenic compounds in addition to reducing the mutagenic potency of the pro-mutagens to the Salmonella strain TA100/S9, which demonstrates the high efficiency of this system with regard to discoloring and degrading azo dye molecules and their by-products. Therefore, this study showed that although not having standard treatment system for this type of pollutant, the combination of treatments can be considered promising. The use of electrochemical oxidation along with microbiological treatment may lead to the degradation and mineralization of these compounds, reducing or eliminating the environmental impact caused by the improper disposal of these dyes in aquatic environments.