Decomposition Of Azo Dye Research Articles

Photocatalytic Decomposition of Azo Dyes and Phenols Using Polymer Composites Containing Nanostructured Poly(Titanium Oxide) Doped with Gold or Silver Nanoparticles under Light Irradiation in a Wide Wavelength Range

The photocatalytic properties of poly(titanium oxide) (PTO) dispersed in optically transparent polymeric matrices of different natures under the action of both UV and visible light on aqueous solutions of azo dyes and phenols were investigated. PTO in materials forms clusters of mixed polymorphic modification—anatase and rutile—with an average size ~12 nm. With a one-electron transition Ti4+ + e− → Ti3+ accompanied by a reversible break of the Ti-O bond, the formation of electron-hole pairs and, consequently, active oxygen species occurs in PTO under UV irradiation. The PTO band gap in nanocomposites is 3.11–3.35 eV. Its doping with gold and silver nanoparticles with sizes from ~10 to ~30 nm reduces the PTO band gap by up to 2.11 eV, which leads to the operating wavelength range extension of the materials. It provides the enhancement of nanocomposites’ photocatalytic properties under UV irradiation and is the reason for their high activity under visible light action. It was found that azo dyes decompose by ~90% in this case. A phenol and para-nitrophenol conversion of 80–90% was proven at ~60 min upon their aqueous solutions’ visible-light irradiation at the nanocomposite concentration in a solution of 0.5 g/L.

Refractory azo dye wastewater treatment by combined process of microbial electrolytic reactor and plant-microbial fuel cell

An innovative design of microbial electrolytic reactor (MER) coupled with Ipomoea aquaticaForsk. plant microbial fuel cell (IAF-PMFC) was developed for azo dye wastewater treatment and electricity generation. This study aims to assess the sequential degradation of azo dye and the feasibility of energy self-sufficiency in the MER/IAF-PMFC system. The decomposition of azo dye into aromatic amines and dye decolorization occurred in the MER at high hydraulic loading of 0.28 m3/(m2·d), while dye intermediates were mainly mineralized in the IAF-PMFC at low hydraulic loading of 0.06 m3/(m2·d). The final decolorization efficiency and COD removal of the combined system reached 99.64% and 92.06% respectively, even at influent dye concentration of 1000 mg/L. The effects of open/closed circuit conditions, presence/absence of aquatic plant and different cathode areas on the performance of the IAF-PMFC for treating the effluent of the MER were systematically tested, and the results showed that closed-circuit condition, plant involvement and larger cathode area were more beneficial to decolorization, detoxification and mineralization of dye wastewater, bioelectricity output, plant growth and photosynthetic rate. The power consumption by the MER was 0.0163 kWh/m3 of dye wastewater, while the highest power generation of the IAF-PMFC reached 0.0183 kWh/m3. The current efficiency of the MER for dye decolorization was as high as 942.83%, while the maximum coulombic efficiency of the IAF-PMFC for intermediates metabolism was only 6.30%, which still had much space of bioelectricity generation promotion. The MER/IAF-PMFC technology can simultaneously realize refractory wastewater treatment and balance of electricity production and consumption.

Promoting azo dye decomposition in natural molybdenite activated peroxymonosulfate process by low concentration of ferrous ions.

In this study, low concentration of ferrous ions (Fe2+) was added into natural molybdenite (MDN) activated peroxymonosulfate (PMS) process to degrade a typical azo dye, orange G (OG). It was found that the addition of Fe2+ promoted OG degradation and simultaneously reduced the leaching of toxic Mo ions significantly. Further, the utilization efficiency of MDN was improved immensely, which was estimated from reuse experiment. MDN mainly acted as the reductant to promote cycling of Fe3+/Fe2+ redox couple through reducible sulfur and Mo(IV) on its surface. Sulfate radicals (SO4•-), hydroxyl radical (•OH) and singlet oxygen (1O2) were verified as the main reactive oxygen species responsible for OG degradation by scavenging tests and electron paramagnetic resonance. Some experiment parameters, such as MDN dosage, Fe2+ concentration, PMS concentration, initial solution pH and coexisting anion, all affected OG degradation efficiency. In a word, this work provides a new method of enhancing PMS activation by MDN using low concentration of Fe2+ for degradation of organic pollutants in water.

Mixed imidazole ligand MIL-88A for enhanced photo-Fenton decomposition of azo dye

In this study, we fabricated MIL-88A metal–organic frameworks with excellent physicochemical properties using mixed organic ligands. In addition, we investigated the effects of different iron precursors on the physicochemical properties of the as-prepared MIL-88A samples. We determined that the difference between the dissociation rates of the metal ions of different iron precursors affected the crystallization rate of MIL-88A, which effectively decreased particle size, causing an increase in the adsorption capacity of MIL-88A and significantly improving its photocatalytic activity. Two organic ligands: 2-methylimidazole and fumaric acid, were mixed, and the formed dihydrate affected the crystallization rate of MIL-88A; moreover, the as-fabricated MIL-88A presented small particle size and high oxidation potential. The as-prepared mixed organic ligand MIL-88A removed 96.42% of AR1 dye from an AR1 dye solution with a concentration of 20 mg/L after 2 h of irradiation. Furthermore, an AR1 dye removal of 100% was achieved after only 45 min of irradiation using a 100 mg/L AR1 dye solution in the presence of trace H2O2. The decomposition efficiency of MIL-88A did not decrease after five removal cycles, and this was attributed to the excellent decomposition efficiency of MIL-88A with mixed organic ligands, which was ascribed to its remarkable adsorption capacity and high oxidation potential. Strong oxidizing hydroxyl radicals were generated via a photo-Fenton reaction to improve the oxidative power of MIL-88A, and pollutants were decomposed without generating residues. We believe that these findings can be used to significantly expand the application of MIL-88A in photocatalysis research.

Catalytic Decomposition of Azo Dye Using ZnO in Sunlight

The degradation of azo is a challenge for environmentalists. Catalytic decomposition of azo dyes by ZnO heterogeneous photocatalysis and the influence of operating parameters such as light intensity, temperature, amount of ZnO catalyst, solution pH and amount of pollutants. It has been observed that ZnO catalysts is quite capable of removing azo dyes in the presence of sunlight. We can use the same catalyst over and over, and it works well every time. We recovered 99% clear water within a few hours of exposure to sunlight.

Photocatalytic activity of oxide systems based on doped d-elements of titanium alloys

CO-, W-, MO- and Zn-containing hetero-oxide nanostructured coatings on titanium and its alloys formed by plasma-electrolyte oxidation in galvanostatic mode from alkaline electrolytes were investigated. The morphology of the surface of the formed coatings was studied by scanning microscopy on the Zeiss Evo 40XVP microscope. The phase composition of the obtained coatings was determined on the X-ray diffractometer Drone-2. Photocatalytic activity of ZnO-WO3/TiO2 films, ZnO-MOO3/TIO2, ZnO-Co3O4/TiO2, CoO-WO3/TiO2 tested in a model reaction of decomposition of an aqueous solution of azobye with a concentration of 12,2·10-5 mol/L (MО) at UV irradiation. It is shown that with plasma-electrolyte oxidation of titanium and its alloys in alkaline diphosphate electrolytes in the mode of «drop-down power» forming heterostructural composites with micro-globular surface morphology. The possibility of controlling the phase and elemental composition of oxide layers, as well as the topography of the surface by changing the composition of the electrolyte and the content of individual components, as well as the modes of formation is confirmed. Heteroxide coatings formed in PEO modes differ in composition and surface morphology, but all exhibit photocatalytic properties of varying degrees of activity. The study of the photocatalytic activity of the obtained coatings in the azo dye decomposition reaction by means of UV testing allowed to rank the heteroxide systems according to the specified parameter. Thus, the degree of decomposition of MF on ZnO-WO3/TiO2 films in 50 minutes was 23 %. Metal oxide systems ZnO-Co3O4/TiO2 had similar characteristics of the degree of decomposition – 21 %. The incorporation of CoO and WO3 oxides into the coating composition reduced the catalytic activity of the system to 19 %. The unstable mode of formation of ZnO-MoO3/TiO2 oxides and the low speed of the process have affected the quality of the catalytic coating activity, reduced the degree of decomposition of MO to values of titanium monoxide Ti/TiO2 without dopants. Comparison of quantitative characteristics of the properties of the obtained coatings allowed to determine the effects of dopants, incorporated into metal oxide systems, on their photocatalytic activity.

Fabrication of ZnO–TiO2 nanohybrids for rapid sunlight driven photodegradation of textile dyes and antibiotic residue molecules

Abstract Semiconductor nanohybrids garner huge interest among environmentalists for the various applications owing to their efficiency, cost-effectiveness and benignity. We report the fabrication of TiO2 nanoparticles (TNPs) functionalized ZnO nanoflakes (ZNFs) and their outstanding detoxification ability towards the methylene blue (MB), rhodamine 6G (R6G) and Oxytetracycline (OTC) molecules solution in water. TEM studies confirm the formation of 3D architecture of ZnO–TiO2 nanohybrids while high-resolution transmission electron microscopy assures the uniform functionalization of TNPs over ZNFs. Scanning electron microscopy studies reveal the modulation in the surface morphology with the tenability in volume ratios of Zn and Ti sources. Significant PL quenching in ZnO–TiO2 nanohybrids spectrum as compared to ZNFs confirms the improvement in the charge separation which is highly favorable for the enhancement in the photodegradation efficiency. The 3D architecture of ZnO–TiO2 with volume ratio (Zn: Ti: 4:1) showed superior photodegradation activity and decompose OTC, MB and R6G dye solution within 8 min, 6 min and 30 min respectively under natural solar light (~862 W/cm2). Most efficient ZnO–TiO2 nanohybrid exhibits extremely high rate constant values for MB, R6G and OTC molecules which are 7, 5 and 4.8 times of the rate constant value of pure ZNFs. Extremely superior photodegradation performance of 3D architecture of ZnO–TiO2 nanohybrid could be ascribed to the charge separation and synergistic effect between the TNPs and ZNFs which is responsible for the high density of electrons in the conduction band of ZnO–TiO2 nanohybrids. ZnO–TiO2 nanohybrids reveal the extremely high photodegradation rate for the decomposition of azo dyes and pharmaceutical residue which has not been reported till now.

Polysaccharide/Fe(III)-porphyrin hybrid film as catalyst for oxidative decolorization of toxic azo dyes: An approach for wastewater treatment

A hybrid film of chitosan/poly(vinyl alcohol)/cationic Fe(III)-porphyrin (Cht/PVA-FeTMPyP) was synthesized to act as a Fenton-like catalyst to decolorize methyl orange and methyl red azo dyes. The Cht/PVA-FeTMPyP film was characterized by different analytical and microscopy techniques, which indicated that the metalloporphyrin affects different properties of the hybrid film. Batch experiments revealed that the hybrid film exhibits enhanced catalytic activity towards dyes decolorization in the presence of H2O2 as compared to the “free” FeTMPyP. Fast decolorization rates as high as 90 min were observed for both azo dyes under mild conditions (pH 7 and room temperature), even at low concentrations of the catalyst in H2O2. After the decolorization, FTIR analysis showed that simple molecules are released as by-products. Moreover, the hybrid film performed well in cyclic runs without leaching out iron ions or losing its catalytic activity. All these features associated with its ease handling ranks the Cht/PVA-FeTMPyP hybrid film as a promising heterogeneous Fenton-like catalyst for the decomposition of azo dyes in water.

Long-Lived Polypyridyl Based Mononuclear Ruthenium Complexes: Synthesis, Structure, and Azo Dye Decomposition.

Two mononuclear ruthenium complexes [(bpy)2RuIIL1/L2](ClO4)2 ([1]2+/[2]2+) (bpy-2,2' bipyridine, L1 = 2,3-di(pyridin-2-yl)pyrazino[2,3-f][1,10]phenanthroline) and L2 = 2,3-di(thiophen-2-yl)pyrazino[2,3-f][1,10]phenanthroline have been synthesized. The complexes have been characterized using various analytical techniques. The complex [1]2+ has further been characterized by its single crystal X-ray structure suggesting ruthenium is coordinating through the N donors of phenanthroline end. Theoretical investigation suggests that the HOMOs of both complexes are composed of pyridine and pyrazine unit of ligands L1 and L2 whereas the LUMOs are formed by the contribution of bipyridine units. The low energy bands at ∼480 nm of the complexes can be assigned as MLCT with partial contribution from ligand transitions, whereas the rest are ligand centered. The complexes have shown RuII/RuIII oxidation couples at E1/2 at 1.26 (70 mV) V and 1.28 (62 mV) V for [1]2+ and [2]2+ vs Ag/AgCl, respectively, suggesting no significant role of distal thiophene or pyridine units of the ligands. The complexes are emissive and display solvent dependent emission properties. Both complexes have shown highest emission quantum yield and lifetime in DMSO (ϕ = 0.05 and τavg = 460 ns and λmaxem at 620 nm for [1]2+; ϕ = 0.043 and τavg = 425 ns and λmaxem at 635 nm for [2]2+). Further, the long luminescent lifetime of these complexes has been utilized to generate reactive oxygen species for efficient azo dye decomposition.

Unexpected high performance of Fe-based nanocrystallized ribbons for azo dye decomposition

Fe-based multiphase nanocrystallized ribbons (CR-II) prepared by annealing of metallic glasses show unexpected high performance for Orange II degradation.

An Unusual Electrochemical Reductive Cleavage of Azo Dye into Highly Redox Active Copolymeric Aniline Derivatives on a MWCNT Modified Electrode Surface at Neutral pH and Its Electroanalytical Features

Developments of new decomposition or degradation methods of environmentally hazardous azo dyes from textile industries are very important. Usually, strong acid-based chemical/electrochemical and neutral pH-based bacterial decomposition methods were widely used. Here, we report a mild, simple, and facile electrochemical method for decomposition of azo dye (Sudan yellow; SY) into a highly redox active copolymer of polyanilines via aniline derivatives as intermediates on a MWCNT modified glassy carbon electrode (GCE/MWCNT) surface unusually in a neutral pH using phosphate buffer solution (PBS) (GCE/MWCNT@SY-CoPANIpH7). One of the intermediate products, aniline (Mw = 93 mol g–1, calculated) was identified by an in situ cyclic voltammetry-electrochemical quartz crystal balance experiment. No such SY electrochemical reaction was observed on a naked GCE surface. Physico-chemical characterizations by TEM, Raman, IR, and UV–vis spectroscopic methods supported the formation of polymeric product on MWCNT surface (GCE/MWCNT@SY-CoPANIpH7). Electroanalytical performance of this new electrode was tested using ascorbic acid (AA) and Fe(CN)63–, as models. Interestingly, a dilute solution of Nafion (Nf) casted modified electrode system (GCE/MWCNT@SY-CoPANIpH7/Nf) showed improved electroanalytical performance, unlike the conventional Nafion modified system (GCE/MWCNT/Nf) with vanished peak current response due to the electrostatic repulsive interaction between the anionic AA (pKa = 4.10), Fe(CN)63– ion, and anionic sulfonic acid groups in Nafion. A zwitter ionic complex between a polaronic copolyaniline and sulfonic acid of Nafion is proposed as a possible structure for the newly developed hybrid system. Using the GCE/MWCNT@SY-CoPANIpH7/Nf, a selective flow injection analysis of AA has been demonstrated as an analytical application with good recovery values.

Efficient photocatalytic degradation of acid orange 7 on metal oxide p–n junction composites under visible light

MO(=CuO, Co3O4, NiO)/BiVO4 p–n junction composites were synthesized by urea-precipitation and wet impregnation method. The physicochemical and optical properties of the as-prepared materials were investigated by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–visible diffuse reflectance spectra. The photocatalytic performance of the as-prepared materials was investigated for decomposition of azo dye, acid orange 7. The CuO/BiVO4 and Co3O4/BiVO4 p–n junction composite photocatalysts exhibited the higher photocatalytic degradation of acid orange 7 than those of BiVO4 and NiO/BiVO4 as-prepared samples under visible light irradiation. We also discussed the mechanism of enhanced photocatalytic activity of p–n junctioned composites based on their energy band structures.

Fabrication, characterization, and photocatalytic activity of double-layer TiO2 nanosheet films

The double-layer TiO2 nanosheet films have been deposited on Si substrate by a liquid-phase deposition method using ZnO nanosheets as the template. The initial morphology of the ZnO nanosheet templates is maintained after the TiO2 deposition. The TiO2 nanosheets are uniformly distributed widely and grown perpendicularly to the substrate. The TiO2 nanosheets are of anatase phase with the outside thickness of ~220–380nm. The growth mechanism for the formation of TiO2 nanosheet films is investigated. Experimentally, it shows that the TiO2 nanosheet films have highly photocatalytic activities for the decomposition of azo dye C. I. reactive yellow 15.

Efficient Degradation of Azo Dyes over Sb2S3/TiO2 Heterojunction under Visible Light Irradiation

A cost- and time-saving coupling method was developed to prepare a novel Sb2S3/TiO2 heterostructure photocatalyst. The obtained sample was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectroscopy (DRS). UV–vis diffuse reflectance spectra showed a great shift to longer wavelengths and an extension of the absorption in the visible region for all of the samples compared to pure TiO2. The photocatalytic activity of the sample was investigated for the liquid-phase photocatalytic degradation of azo dyes under visible light irradiation. The influences of different mass ratios of Sb2S3 and sintered temperatures on the photocatalytic activity have also been investigated, and the highest efficiency is observed when calcined at 673 K with 60 wt % Sb2S3 content. Moreover, •OH has also been detected in the suspension of Sb2S3/TiO2 heterojunction under visible light irradiation, which leads to the decomposition of azo dyes.

Magnetic composite microspheres with exposed {001} faceted TiO2 shells: a highly active and selective visible-light photocatalyst

We have demonstrated a sandwich-structured Fe3O4/SiO2/Au/TiO2 photocatalyst, which shows magnetic separability, selective absorption and photocatalysis activity, and high efficiency, in catalyzing the decomposition of organic compounds under illumination of visible-light and simulated sunlight. The structural design of the photocatalyst takes advantage of the dense, homogeneous structure and the AuNPs content (ca. 4 nm, 1.63 wt%), which is prepared by a simple method. It possesses high efficiency visible-light photocatalytic activity due to the stable from nonmetal-doping and the plasmonic metal decoration, which enhances light harvesting and charge separation, and the small grain size of the anatase nanocrystals, which reduces the exciton recombination rate. More importantly, the catalyst is synthesized by a combination of plasmonic metal decoration of TiO2 nanocrystals with exposed {001} facets, and the selective adsorption and photocatalytic decomposition of azo dyes is accomplished by design of the surface chemistry. Additionally, these sandwich-structured photocatalysts can be applied to other catalytic system such as dye decoloration, water decomposition, hydrogen generation, and so on.

Photooxidation Contribution Study on the Decomposition of Azo Dyes in Aqueous Solutions by VUV-Based AOPs

The effects of pH value, VUV intensity, initial dye concentration, initial H2O2concentration, and TiO2loading dose on the degradation of three azo dyes: acid Orange 8, acid Blue 29, and acid Blue 113 were studied to explore and compare the treatment efficiencies among the adopted AOPs. It was found that pH played an important role in the degradation of dyes using VUV irradiation. For VUV/H2O2, VUV/TiO2, and VUV/TiO2/H2O2processes, the decoloration rates of the three azo dyes were more efficient under acidic conditions relative to alkaline conditions. The degradation rates of dyes increased with increasing concentrations of H2O2, but reaction rates were retarded at high concentrations of H2O2because the H2O2compound acted as a scavenger of the hydroxyl radical. In this paper, three azo dyes were decomposed efficiently by VUV irradiation only demonstrating the effectiveness of VUV direct photolysis.

Tunable photocatalytic selectivity of TiO2 films consisted of flower-like microspheres with exposed {001} facets

TiO(2) films composed of flower-like TiO(2) microspheres with exposed {001} facets were synthesized by a simple one-pot hydrothermal method and exhibited tunable photocatalytic selectivity towards decomposition of azo dyes in water by modifying the surface of TiO(2) microspheres as well as by varying the degree of etching of {001} facets.

Azo dye degradation kinetics in TiO 2 film-coated photoreactor

In this study, commercial nano-size TiO 2 suspension was used to coat on the inner surface of glass reactors and the immobilized TiO 2 film served as photocatalyst to decompose azo dye in aqueous solutions. A full factorial design approach using three factors, namely rotation time, rotation speed, and drying temperature was adopted to prepare TiO 2-coated reactors. The azo dye decomposition conversion under 8 W UV illumination for 4 h was measured as the response of the experimental design. The results showed that the three main effects were significant: increasing the rotation time from 10 to 50 min leaded to 11.4% increase in the dye conversion; increasing the rotation speed from 10 to 50 rpm leaded to 5.6% increase in the dye conversion; increasing the drying temperature from 150 to 250 °C leaded to 2.8% increase in the dye conversion. A series of dye degradation experiments with varying initial dye concentrations were conducted using the TiO 2-coated reactor. The dye degradation rate was found to be − r dye = k a C/(1 + k b C) with k = 0.0326 min −1 and k b = 0.764 L mg −1. The developed kinetic model was used to fit the experimental data satisfactorily.

Azo dye Acid Red 27 decomposition kinetics during ozone oxidation and adsorption processes

To elucidate the effects of ozone dosage, catalysts, and temperature on azo dye decomposition rate in treatment processes, the decomposition kinetics of Acid Red 27 by ozone was investigated. Acid Red 27 decomposition rate followed the first-order reaction with complete dye discoloration in 20 min of ozone reaction. The dye decay rate increases as ozone dosage increases. Using Mn, Zn and Ni as transition metal catalysts during the ozone oxidation process, Mn displayed the greatest catalytic effect with significant increase in the rate of decomposition. The rate of decomposition decreases with increase in temperature and beyond 40°C, increase in decomposition rate was followed by a corresponding increase in temperature. The FT-IR spectra in the range of 1000–1800 cm−1 revealed specific band variations after the ozone oxidation process, portraying structural changes traceable to cleavage of bonds in the benzene ring, the sulphite salt group, and the C-N located beside the -N = N- bond. From the 1H-NMR spectra, the breaking down of the benzene ring showed the disappearance of the 10 H peaks at 7-8 ppm, which later emerged with a new peak at 6.16 ppm. In a parallel batch test of azo dye Acid Red 27 adsorption onto activated carbon, a low adsorption capacity was observed in the adsorption test carried out after three minutes of ozone injection while the adsorption process without ozone injection yielded a high adsorption capacity.

Application of anatase-phase TiO 2 for decomposition of azo dye in a photocatalytic membrane reactor

The presented studies have focused on application of a new anatase-phase TiO 2 for decomposition of azo dye Acid Red 18 in a photocatalytic membrane reactor (PMR) combining photocatalysis and direct contact membrane distillation (DCMD). The catalyst used in this study (A-700-1h) was prepared from TiO 2 obtained directly from the production line (sulfate technology) at the Chemical Factory “Police” by calcination for 1 h at 973K in air. It was found that the effectiveness of the model dye degradation increased with increasing the value of all the parameters investigated, that is, feed flow rate, reaction temperature and catalyst loading. The addition of TiO 2 to a feed did not affect the permeate flux, regardless of the catalyst loading applied. The effectiveness of azo dye removal in the PMR was compared with the effectiveness obtained during photocatalysis alone conducted in the recirculation and batch modes. Taking into account both, the rate of azo dye degradation and the quality of the product, the most beneficial configuration seems to be the PMR.