Reducing degradation of azo dye by zero-valent iron in aqueous solution

Synthesis, magnetic properties, biotoxicity and potential mechanism of modified nano zero-valent iron for decolorization of dye wastewater

SiO2-coated nano zero-valent iron (nZVI) has emerged as a fine material for the treatment of dye wastewater due to its large specific surface area, high surface activity, and strong reducibility. However, the magnetic properties based on which SiO2-coated nZVI (SiO2-nZVI) could effectively separate and recover from treated wastewater, and the biotoxicity analysis of degradation products of the dye wastewater treated by SiO2-nZVI remain unclear. In this study, SiO2-nZVI was synthesized using a modified one-step synthesis method. The SiO2-nZVI nanoparticles were characterized using Transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Fully automatic specific surface and porosity analyzer, Vibrating sample magnetometer, and Zeta potential analyzer. The removal rate of methyl orange (MO) by SiO2-nZVI composite reached 98.35% when the degradation performance of SiO2-nZVI treating MO was optimized. Since SiO2-nZVI analysed by magnetic hysteresis loops had large saturation magnetization and strong magnetic properties, SiO2-nZVI exhibited excellent ferromagnetic behaviour. The analysis of the degradation products showed that the MO treated by SiO2-nZVI was converted into a series of intermediates, resulting in reducing the toxicity of MO. The potential mechanism of MO degradated by SiO2-nZVI was speculated through degradation process and degradation kinetics analysis. Overall, the SiO2-nZVI composite may be regarded as a promising catalyst for decolorization of dye wastewater.

Investigation of MO Adsorption Kinetics and Photocatalytic Degradation Utilizing Hollow Fibers of Cu-CuO/TiO2 Nanocomposite

This comprehensive study explores the kinetics of adsorption and its photocatalytic degradation of methyl orange (MO) using an advanced copper-decorated photocatalyst in the form of hollow fibers (HFs). Designed to boost both adsorption capacity and photocatalytic activity, the photocatalyst was tested in batch experiments to efficiently remove MO from aqueous solutions. Various isotherm models, including Langmuir, Freundlich, Sips, Temkin, and Dubinin-Radushkevich, along with kinetic models like pseudo-first and pseudo-second order, Elovich, Bangham, and Weber-Morris, were utilized to assess adsorption capacity and kinetics at varying initial concentrations. The results indicated a favorable MO physisorption on the nanocomposite photocatalyst under specific conditions. Further analysis of photocatalytic degradation under UV exposure revealed that the material maintained high degradation efficiency and stability across different MO concentrations. Through the facilitation of reactive oxygen species generation, oxygen played a crucial role in enhancing photocatalytic performance, while the degradation process following the Langmuir-Hinshelwood model. The study also confirmed the robustness and sustained activity of the nanocomposite photocatalyst, which could be regenerated and reused over five successive cycles, maintaining 92% of their initial performance at concentrations up to 15 mg/L. Overall, this effective nanocomposite photocatalyst structured in the form of HF shows great promise for effectively removing organic pollutants through combined adsorption and photocatalysis, offering valuable potential in wastewater treatment and environmental remediation.

UV light assisted degradation of acid orange azo dye by ZVI-ZnS and effluent toxicity effects

Azo dyes, the most common synthetic dyes used in the textile industry, are known xenobiotic compounds and recalcitrant to conventional degradation treatments. As consequence, such contaminants are often discharged into the effluents, treating aquatic ecosystems. Among several processes, the use of zero valent iron (ZVI) represents a suitable alternative to degrade organic molecules containing azo bonds. However, its applications are limited by corrosion and loss of reactivity over the time. To overcome these constraints, ZVI has been coupled to a suitable semiconductor (ZnS) to get a catalytic composite (ZVI-ZnS) active under UV light. The present work deals with the degradation of acid orange (AO7), used as model azo dye, by UV/ZVI-ZnS, as one step treatment and in combination with an adsorption process by biochar. The influence of ZVI-ZnS concentration (0.25, 0.5, 1 and 2 g/L) and reaction time (0-160 min) on degradation of AO7 were investigated. Intermediates formation was monitored by ESI-FT-ICR-MS analysis and the effluent toxicity was assessed by using Artemia franciscana. The experimental results showed that the UV/ZVI-ZnS process at 1 g/L of catalyst allowed to achieve a removal of AO7 up to 97% after 10 min. An increase of the dye relative concentrations as well as the toxicity related to intermediates formations has been observed for treatment time higher than 10 min. The total removal of AO7 together with effluent toxicity reduction was obtained only after the combined treatment (UV/ZVI-ZnS + biochar).

Reductive metabolism of azo dyes and drugs: Toxicological implications

Azo compounds are widely distributed synthetic chemicals in the modern world. Their most important applications are as dyes, but, in addition, several azo compounds are used as pharmaceuticals. Ingested azo compounds can be reduced by the action of bacteria in the gut, where the oxygen tension is low, and the development of microbiome science has allowed more precise delineation of the roles of specific bacteria in these processes. Reduction of the azo bond of an azo compound generates two distinct classes of aromatic amine metabolites: the starting material that was used in the synthesis of the azo compound and a product which is formed de novo by metabolism. Reductive metabolism of azo compounds can have toxic consequences, because many aromatic amines are toxic/genotoxic. In this review, we discuss aspects of the development and application of azo compounds in industry and medicine. Current understanding of the toxicology of azo compounds and their metabolites is illustrated with four specific examples - Disperse Dyes used for dyeing textiles; the drugs phenazopyridine and eltrombopag; and the ubiquitous food dye, tartrazine - and knowledge gaps are identified. SUBMISSION TO: FCT VSI: Toxicology of Dyes.

Electron induced efficient dechlorination of trichlorethylene with S doped Fe2B: The enhancement mechanism of S

In this work, S doped Fe₂B (Fe₂B-S) was synthesized by sintering method and applied for the enhanced dechlorination of trichlorethylene (TCE). The degradation ratio (D) of TCE was 99.8% with reaction rate constant (k_obs) of 0.956 h^-1 by 10.0at% S doped Fe₂B (corresponding to Fe₂B-S_10.0), compared to D and k_obs values 37.3% and 0.067 h^-1 by Fe₂B, respectively. The major dechlorination products of acetylene, ethene, ethane and C₃-C₆ hydrocarbon compounds were observed from a reductive β-elimination pathway. S doped and undoped Fe₂B could form the first-level in-situ galvanic cell, and the returned S provided a second-level galvanic cell to further enhance electron transfer. The doped S worked as electron donor to increase the density of localized unpaired electrons, and the electron enriched Fe atoms leading to stronger reducibility were verified by the density functional theory (DFT) calculation. This work provides a complete insight into the enhancement mechanism of S doped Fe₂B and guides the potential design of zero-valent iron (ZVI) with properties tailored for chlorinated hydrocarbons dechlorination.

Study on the catalytic degradation of Acid Orange 7 and the potential mechanism by ferrous-percarbonate

Factors affecting the degradation of Acid Orange 7 (AO7) were evaluated and optimized when ferrous was used to catalyze percarbonate in the present study. The optimized conditions included the initial pH values ranging from 3 to 11 for AO7 solution, the initial level of AO7, sodium percarbonate (SPC), and Fe²⁺ . Some ions and natural organic materials, which commonly exist in natural water, were also tested to evaluate their potential impacts on the degradation of AO7. The degradation efficiency of AO7 was up to 95% under the optimized test conditions, where the ferrous/percarbonate/AO7 molar ratio was 15/10/1 in the 0.285 mmol/l AO7 aqueous solution. The presence of Cl^- , SO₄ ^2- , NO₃ ^- , Na⁺ , and Mg²⁺ did not affect the removal of AO7. The addition of HCO₃ ^- significantly inhibited its removal, even when the concentration of HCO₃ ^- was low to 0.6 mmol/l. A slight inhibition effect was observed when the added concentration of humic acid ranged from 0.5 to 5 mg/l, whereas the residue of AO7 was significantly enhanced when the level of humic acid was continually increased from 50 to 100 mg/l. Hydroxyl radicals (•OH) were the main reactive intermediates controlling the oxidation of AO7 in the present Fe²⁺ /SPC system. The produced intermediates through the degradation of AO7 were identified to include 2-coumaranone, 2-naphthol, phthalic acid, phthalimide, N-methylnaphthylamine, and 2-methylphenol. The proposed degradation pathways are consistent with the radical formation and the identified intermediates. PRACTITIONER POINTS: The ferrous/percarbonate system can remove 95% of AO7 under the optimized conditions. AO7 removal was inhibited by adding HCO₃ ^- and humic acid, but not affected by Cl^- , SO₄ ^2- , NO₃ ^- , Na⁺ , and Mg²⁺ . Hydroxylation, ring opening, and mineralization driven by the generated hydroxyl radicals were derived as the major processes for degrading AO7.

A novel, direct-push approach for detecting sulfidated nanoparticulate zero valent iron (S-nZVI) in sediments using reactive and non-reactive fluorophores

Injection of microparticulate and nanoparticulate zero valent iron has become a regularly used method for groundwater remediation. Because of subsurface inhomogeneities, however, it is complicated to predict the ZVI transport in the subsurface, meaning that tools capable of determining its distribution after injection are highly useful. Here, we have developed a new direct-push based technique, which combines fluorescent and visible imaging, for detection of sulfidized nanoparticulate zero valent iron (S-nZVI) in the subsurface. Laboratory experiments show that the redox sensitive fluorophore riboflavin is rapidly reduced by S-nZVI within 200 s. Because the reduced riboflavin losses its green fluorescence, it can be used as S-nZVI sensitive indicator. Secondly, S-nZVI is black and tints light coloured sediment to a degree that allows detection in images. For quartz sand, 70 mg/kg of S-nZVI can be detected by visible imaging. Based on these results, a new direct-push probe (Dye-OIP) was designed based on Geoprobe's Optical Image Profiler (OIP), which was equipped with a fluorophore injection port below the OIP-unit. The injectant consisted of the redox active riboflavin mixed with the redox inactive fluorophore rhodamine WT, which fluoresces red and was used to verify that the mixture was indeed injected and detectable. Small scale experiments show that the fluorescence of this mixture in S-nZVI amended sand changes within 150 s from green with a hue of ~50 to red with a hue of ~30 when imaged with Dye-OIP. Tests of the Dye-OIP after a S-nZVI injection in a 1 m³ sized tank show that the tool could detect S-nZVI via fluorescence and visible imaging, when S-nZVI concentration was >0.2 mg per g dry sediment. Thus, these novel methods should be able to detect S-nZVI in the subsurface, without relying on infrastructure such as wells. Based on our results, the Dye-OIP could be further improved to make it suitable for regular use in the field.

Excellent dye degradation performance of FeSiBP amorphous alloys by Fenton-like process

Amorphous alloys are being newly applied in wastewater treatment because of their unique atomic packing structure. They possess excellent degradation efficiency, stability and reusability. In this work, Fe₈₀Si₁₀B₁₀ and Fe₈₃Si₅B₈P₄ amorphous ribbons exhibited advanced catalytic performance for the degradation of Methyl Blue (MB) and Rhodamine B (RhB) dyes, and the color removal reach nearly 100% within 11 min for both the dyes. Compared with the Fe₈₀Si₁₀B₁₀ amorphous ribbon, the Fe₈₃Si₅B₈P₄ ribbon showed higher degradation efficiency due to its lower reaction activation energy, higher electron transfer ability and higher Fe content, and the formation of the galvanic cell between the strong Fe-P bonds and the weak Fe-B bonds. It also exhibited high stability and reusability. The degradation efficiency was improved when the appropriate concentration of H₂O₂ is added. As regards the pH, high degradation efficiency was observed in acidic MB solution, but it decreased as the pH increased up to pH 7. The application of the electro-Fenton-like process is discussed, which can effectively improve the degradation performance in a nearly natural solution. This study presents a high efficiency low-cost catalyst for synthetic dye degradation and expands the functional applications of Fe-based amorphous alloys.

Complexation of an Azo Dye by Cyclodextrins: A Potential Strategy for Water Purification

The chemistry of the host-guest complex formation has received much attention as a highly efficient approach for use to develop economical adsorbents for water purification. In the present study, the synthesis of three β-cyclodextrin (β-CD) inclusion complexes with the oil orange SS (OOSS) azo dye as a guest molecule and their potential applications in water purification are described. The complexes were synthesized by the coprecipitation method and characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). FTIR and thermal analyses confirmed the encapsulation of OOSS dye within the hydrophobic cavity of β-CD. The encapsulation of hydrophobic dye inside the β-CD cavity was mainly due to the hydrophobic-hydrophobic interaction. The results showed that the stability of the OOSS dye had been improved after the complexation. The effect of three different compositions of the host-guest complexes was analyzed. The present study demonstrated that the hydrophobic dye could be removed from aqueous solution via inclusion complex formation. Thus, it can play a significant role in removing the highly toxic OOSS dye from the industrial effluent.

Effects of the Addition of Fe, Co on the Azo Dye Degradation Ability of Mn-Al Mechanically Alloyed Powders

Azo compounds are used in the textile and leather industry. A significant step during the azo dyes treatment of water is the degradation by breaking the N=N bonds. This break produces the decolorization of water. In this research work, 10% atomic of Fe or Co was added to produce ternary Mn-Al-rich, nanostructured, mechanically alloyed powders in order to improve the decolorization of Reactive Black 5 solutions and to check Fe and Co addition’s influence. The microstructure was followed by X-ray diffraction, the morphology and composition by electronic microscopy and energy-dispersive X-ray spectroscopy (EDS) microanalysis. The dye degradation was monitored with ultraviolet/visible absorption spectrophotometry. After degradation, the remaining organic compound was checked by high-performance liquid chromatography (HPLC) and the functional groups of the powdered alloys by infrared spectroscopy. Fe addition to Mn-Al displayed faster kinetics and a higher efficiency than the Co addition. The Mn-Al-Fe solution (0.25 g/100 mL) was fully decolorized in 5 min. On the other side, Mn-Al-Co powders were able to successfully decolorize the dyed solution in 10 min under the same conditions. Thus, nanocrystalline Fe-doped Mn-Al alloys are good candidates for use in the decolorization process, in comparison with Co-doped and other intermetallic particles.

Biological treatment of non-biodegradable azo-dye enhanced by zero-valent iron (ZVI) pre-treatment

Zero-valent iron (ZVI) pre-treatment in sequential strategy for removal of non-biodegradable azo-dye Orange II by activated-sludge was quantitatively examined. The decolorization and TOC (total organic carbon) removal of Orange II by ZVI pre-treatment were examined in the ranges of pH from 3 to 11 and ZVI dosage from 500 to 2000 mgL^-1. While the decolorization was enhanced with decreasing pH and the optimal pH for decolorization was found at pH 3, the TOC removal rate at pH 3 remained at 22.2% and the maximum TOC removal rate of 78.2% was obtained at pH 4. The decolorization and TOC removal of Orange II were monotonously increased with increasing ZVI dosage. To quantify the ZVI pre-treatment, the contributions of redox degradation, complexation/precipitation and adsorption to TOC removal by ZVI were defined. Novel kinetic models for the ZVI pre-treatment and activated-sludge post-treatment were developed. The proposed kinetic models satisfactorily predicted the transitional behaviors of the ZVI pre-treatment and activated-sludge post-treatment and the contributions of redox degradation, complexation/precipitation and adsorption to TOC removal by the ZVI pre-treatment. The complete removal of non-biodegradable azo-dye Orange II of 300 mgL^-1 was accomplished by 78.2% removal after 360 min ZVI pre-treatment with the ZVI dosage of 1000 mgL^-1 at pH 4 and subsequently 21.8% removal after 480 min activated-sludge post-treatment. The ZVI pre-treatment integrated with activated-sludge post-treatment was proved to be an effective strategy for treating non-biodegradable pollutants.

Synthesis of cost-effective magnetic nano-biocomposites mimicking peroxidase activity for remediation of dyes

The present study describes preparation of cellulose incorporated magnetic nano-biocomposites (CNPs) by using cellulose as base material. The prepared CNPs were characterised by SEM, EDAX, TEM, XRD, and FT-IR and found to exhibit an intrinsic peroxidase-like activity with a K_m and V_max of 550 μM and 3.8 μM/ml/min, respectively. The CNPs exhibited higher pH and thermal stability compared to commercial peroxidase. These nanocomposites were able to completely remove (i) a persistent azo dye, methyl orange at a concentration of 50 ppm, within 60 min under acidic conditions (pH 3.0) and also (ii) decolourize commercial textile dye mixture under acidic conditions within 30 min. CNP-mediated degradation of dyes into simple products was further confirmed by UV-Vis and AT-IR spectroscopy The added advantage of CNPs separation after decolourization by simple magnet due to their magnetic properties and consequent reusability makes them fairy attractive system for dye remediation from environmental samples or textile industries effluents.

Ecofriendly biodegradation of Reactive Black 5 by newly isolated Sterigmatomyces halophilus SSA1575, valued for textile azo dye wastewater processing and detoxification

A total of seven yeast strains from 18 xylanolytic and/or xylose-fermenting yeast species isolated from the wood-feeding termite Reticulitermes chinenesis could efficiently decolorize various azo dyes under high-salt conditions. Of these strains, a novel and unique azo-degrading and halotolerant yeast, Sterigmatomyces halophilus SSA1575, has been investigated in this study. This strain could significantly decolorize four combinations of a mixture of dyes. It showed a high capability for decolorizing Reactive Black 5 (RB5) even at 1,500 mg L⁻¹. The strain SSA1575 still showed a high capability for decolorizing a 50 mg L⁻¹ RB5 with a salt mixing at a NaCl concentration of up to 80 g L⁻¹. It also exhibited significant ability to decolorize repeated additions of dye aliquots, with a reduction in time of up to 18 h. Most of the tested carbon and nitrogen sources could significantly enhance a RB5 decolorization. However, this process was inhibited by the addition of sucrose and sodium nitrate. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase were determined as the key reductase and oxidase of S. halophilus SSA1575. Finally, strain SSA1575, can effectively detoxify RB5 into non-toxic products. Overall, S. halophilus SSA1575, might be a promising halotolerant yeast valued for the treatment of various textile effluents with high salinity.

Porous composite architecture bestows Fe-based glassy alloy with high and ultra-durable degradation activity in decomposing azo dye

Since the treatment of wastewater containing azo dye presents problems worldwide, it is important to seek effective materials and technology for the purification of wastewater containing azo dye. Fe-based metallic glasses have been identified as promising materials for the decomposition of dyeing wastewater due to their high chemical activity resulting from their amorphous structure. It is imperative to further improve their degradation performance, and especially their durability, for potential application in wastewater purification. Here, composite structures constructed of porous Ni and amorphous Fe₇₈Si₉B₁₃ powder with markedly enhanced degradation performance in Orange II solution were obtained by utilizing a magnet. Due to the favorable effects of structural electrocatalysis and high dispersity of the distinctive porous architecture in addition to its self-cleaning properties, the solid-liquid interface exhibited strong, continuous electrical and mass transport, and a compelling improvement in degradation performance was achieved. Based on degradation tests and spectrum analysis, the kinetic rate was improved over 11-fold. Moreover, ultra-high durability over 100 cycles was revealed in cycling tests. The results indicate that wastewater degradation performance can be greatly enhanced by properly combining Fe-based metallic glasses with porous material.

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.

Using scrap zero valent iron to replace dissolved iron in the Fenton process for textile wastewater treatment: Optimization and assessment of toxicity and biodegradability

A Fenton like advanced oxidation process (AOP) employing scrap zerovalent iron (SZVI) and hydrogen peroxide (H₂O₂) was studied for industrial textile wastewater treatment from a textile manufacturing plant located at Medellín, Colombia (South America). The wastewater effluent studied contains a mixture of organic compounds resistant to conventional treatments. The effect of initial pH and SZVI concentration and H₂O₂ concentration were studied by a response surface methodology (RSM) Box-Behnken design of experiment (BBD). The combined SZVI/H₂O₂ process led to reductions of 95% color, 76% of chemical oxygen demand (COD) and 71% of total organic carbon (TOC) at optimal operating conditions of pH = 3, SZVI = 2000 mg/L and [H₂O₂] = 24.5 mM. Molecular weight distribution measurement (MWD), ultraviolet-visible (UV-Vis) spectroscopy, HPLC, biodegradability and toxicity were used to characterize the pollutants after the treatment process finding that the resulting effluent was polluted mostly by low molecular weight carboxylic acids. A remarkable biodegradability enhancement of the effluent was evidenced by a BOD₅/COD ratio increase from 0.22 to 0.4; also, the SZVI/H₂O₂ process successfully reduced the toxicity from 60% to 20% of dead A. Salina crustaceans.

Removal of Acid Orange 51 by micro zero-valent iron under different operational conditions and evaluation of toxicity

The removal of Acid Orange 51 (AO 51) dye in aqueous solution by microscale zero-valent iron (m-ZVI) was investigated. The m-ZVI powder was characterized granulometrically by laser particle sizer and morphologically by transmission electron microscopy (TEM). The effects of pH, m-ZVI concentration, H₂O₂ addition, and dye concentration on the decolorization of AO 51 were experimentally investigated. Results indicate that the removal efficiency is independent from pH values, increases with increasing ZVI dosage, and decreases with dye concentration. With 1 g/L of m-ZVI, AO 51 was effectively removed without and with addition of 25 mM H₂O₂, yielding a decolorization efficiency of around 70% and 98%, respectively, at pH 3 within 60 min of reaction time. The involvement of ˙OH in oxidizing AO 51 was examined by measuring the removal rates based on ˙OH scavenging molecule. Finally, the disappearance of AO 51 was estimated by monitoring the UV-Vis spectral evolution after 120 min of treatment while the Fourier-Transform Infrared spectroscopy (FT-IR) was performed to verify the occurrence of organic sorption on m-ZVI surface. The scanning electron microscope (SEM) images before and after the reaction illustrated morphological changes on m-ZVI surface. The detoxification of the treated solution was demonstrated using phytotoxicity test.

Effective Dye Degradation by Graphene Oxide Supported Manganese Oxide

Graphene oxide (GO) was used as a support for manganese oxide (MnO2) for the preparation of a nanocomposite catalyst for the degradation of an azo dye, Reactive Black 5 (RB5). The nanocomposite was characterized for the structure by XRD, for the morphology with SEM, and for the surface chemistry with FTIR and potentiometric titration measurements. The GO-MnO2 nanocomposite presented a high catalytic activity for the degradation/oxidation of RB5 at ambient conditions, which was higher than that of the pure MnO2 and could be attributed to the beneficial contribution of the manganese oxide and the graphene oxide.

Soybean Peroxidase-Catalyzed Treatment of Azo Dyes with or without Fe° Pretreatment

  Representative azo dyes (Acid Blue 113 [AB113] and Direct Black 38 [DB38]) were treated in a single step with soybean peroxidase (SBP) and hydrogen peroxide (H2O2), or in two steps, zero-valent iron (Fe°) pretreatment followed SBP/H2O2. The purpose of this research was to compare both treatment processes and to determine which one was the optimal for degradation of each azo dye. For AB113, the preferred process was the single-step process, 1.0 mM AB113 required 2.5 mM H2O2, 1.5 U/mL SBP at pH 4.0 for ≥ 95% color and dye removal and 30% total organic carbon (TOC) removal. For DB38, due to the products formed after Fe° reduction, which are enzyme substrates (aniline and benzidine; two of four products) a two-step process was preferred, which allowed reduction in the required SBP and H2O2 concentrations by 5- and 2-fold, respectively, compared to a single-step treatment for ≥ 95% color, dye, and aniline/benzidine removal and 88% TOC removal.

Synthesis, Characterization and Reactivity of Nanostructured Zero-Valent Iron Particles for Degradation of Azo Dyes

Nanostructured zero-valent iron (NSZVI) particles were synthesized by the method of ferric ion reduction with sodium borohydride with subsequent drying and passivation at room temperature in technical grade nitrogen. The obtained sample was characterized by means of X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and dynamic light scattering studies. The prepared NSZVI particles represent 100–200[Formula: see text]nm aggregates, which consist of 20–30[Formula: see text]nm iron nanoparticles in zero-valent oxidation state covered by thin oxide shell. The reactivity of the NSZVI sample, as the removal efficiency of refractory azo dyes, was investigated in this study. Two azo dye compounds, namely, orange G and methyl orange, are commonly detected in waste water of textile production. Experimental variables such as NSZVI dosage, initial dye concentration and solution pH were investigated. The kinetic rates of degradation of both dyes by NSZVI increased with the decrease of solution pH from 10 to 3 and with the increase of NSZVI dosage, but decreased with the increase of initial dye concentration. The removal efficiencies achieved for both orange G and methyl orange were higher than 90% after 80[Formula: see text]min of treatment.

The decolorization and mineralization of orange II by microwave-assisted ball milling

This study proposed an integrated technique of reduction coupled with an oxidation process in order to acquire simultaneously both decolorization and mineralization of orange II under the condition of microwave-assisted milling. Experimental variables of initial dye concentration, iron dosage, microwave power, solution pH and initial H₂O₂ concentration were systematically studied. Under the optimal operational parameters (100 mg/L aqueous solution of pH 3 containing 400 mg/L H₂O₂ while controlling microwave power at 400 W), the results showed that the decolorization efficiency is up to 91% after reaction for 2 min and the total organic carbon removal efficiencies were 72.7% and 80.5% at a reaction time of 10 min and 60 min, respectively. It indicated that the decolorization and mineralization of orange II were largely enhanced by the reduction of zero-valent iron in the ball milling process and the oxidation of hydroxyl radicals generated by hydrogen peroxide. It suggested that microwave-assisted ball milling technology has potential application for degradation of azo dye in wastewater.

Degradation of azo dye with activated peroxygens: when zero-valent iron meets chloride

Selection of the most appropriate Fe-based peroxygen oxidation technology depends on the dye wastewater constituents and pH.

Rapid degradation of azo-dye using Mn–Al powders produced by ball-milling

This study was conducted on the reduction reaction of the azo dye Reactive Black 5 by means of the Mn₈₅Al₁₅ particles prepared by melt-spinning and ball-milling processes.

Effects of Sulfidation, Magnetization, and Oxygenation on Azo Dye Reduction by Zerovalent Iron

Applications of zerovalent iron (ZVI) for water treatment under aerobic conditions include sequestration of metals (e.g., in acid mine drainage) and decolorization of dyes (in wastewaters from textile manufacturing). The processes responsible for contaminant removal can be a complex mixture of reduction, oxidation, sorption, and coprecipitation processes, which are further complicated by the dynamics of oxygen intrusion, mixing, and oxide precipitation. To better understand such systems, the removal of an azo dye (Orange I) by micron-sized granular ZVI at neutral pH was studied in open (aerobic) stirred batch reactors, by measuring the kinetics of Orange I decolorization and changes in "geochemical" properties (DO, Fe(II), and Eh), with and without two treatments that might improve the long-term performance of this system: sulfidation by pretreatment with sulfide and magnetization by application of a weak magnetic field (WMF). The results show that the changes in solution chemistry are coupled to the dynamics of oxygen intrusion, which was modeled as analogous to dissolved oxygen sag curves. Both sulfidation and magnetization increased Orange I removal rates 2.4-71.8-fold, but there was little synergistic benefit to applying both enhancements together. Respike experiments showed that the enhancement from magnetization carries over from magnetization to sulfidation, but not the reverse.

Development of a novel high-entropy alloy with eminent efficiency of degrading azo dye solutions

In addition to its scientific importance, the degradation of azo dyes is of practical significance from the perspective of environmental protection. Although encouraging progress has been made on developing degradation approaches and materials, it is still challenging to fully resolve this long-standing problem. Herein, we report that high entropy alloys, which have been emerging as a new class of metallic materials in the last decade, have excellent performance in degradation of azo dyes. In particular, the newly developed AlCoCrTiZn high-entropy alloy synthesized by mechanical alloying exhibits a prominent efficiency in degradation of the azo dye (Direct Blue 6: DB6), as high as that of the best metallic glass reported so far. The newly developed AlCoCrTiZn HEA powder has low activation energy barrier, i.e., 30 kJ/mol, for the degrading reaction and thus make the occurrence of reaction easier as compared with other materials such as the glassy Fe-based powders. The excellent capability of our high-entropy alloys in degrading azo dye is attributed to their unique atomic structure with severe lattice distortion, chemical composition effect, residual stress and high specific surface area. Our findings have important implications in developing novel high-entropy alloys for functional applications as catalyst materials.

Sono-advanced Fenton decolorization of azo dye Orange G: Analysis of synergistic effect and mechanisms

In this study, a successful decolorization of Orange G was achieved by means of coupling zero valent iron (ZVI), H2O2 and ultrasound (US) under acidic pH conditions. The synergistic effect and characterization of potential roles of the factors including ZVI, tert-Butanol as radical scavenger, dissolved ferrous ions and H2O2 generated from sonication were evaluated in this sono-advanced Fenton process (SAFP) system. A clear synergy was evident in terms of decolorization rate and the TOC removal as the input of US enhanced the activity of the Fe(0)/H2O2 system. The results suggested that the ZVI was potential replacement for the Fe(2+) ion. This remarkable activity was attributed to the capacity of Fe(2+) formed and reduction of sonic-dissolved Fe(2+) concentration by the formation of {Fe·Fe(2+)}. The modification of the condition of H2O2 addition such as the dosage and input method showed significant variations in terms of decolorization rate. This result indicated that the optimal external addition of H2O2 and input method is a limited factor of decolorization rate due to its comparatively insufficient generated by ultrasound.

Genotoxic and carcinogenic products arising from reductive transformations of the azo dye, Disperse Yellow 7

Selected aromatic azo and benzidine based dyes are priority compounds under the Government of Canada's Chemical Management Plan (CMP) for environmental risk assessments. Organic compounds undergo chemical and biological transformations when they interact with environmental matrices and biotic species; identifying the transformation products is thus a critical component of the risk assessment process. Here, we used zero valent iron (ZVI) to initiate the reduction of the diazo compound dye Disperse Yellow 7 (DY 7). Using state-of-the-art accurate mass Liquid Chromatography-Quadrupole Time of Flight-Mass Spectroscopy (LC-QToF-MS), four transformation products were conclusively identified, while a fifth product was tentatively ascertained. The conclusively established transformation products included p-phenylenediamine (p-PDA, a known genotoxin), 4-aminoazobenzene (4-AAB, a category 2 carcinogen) and 4-aminobiphenyl (4-ABP, a category 1 human carcinogen). 4-ABP is thought to form via a benzidine rearrangement; this is the first report of DY 7 undergoing a benzidine rearrangement. Given the importance of reduction processes in the metabolism of organic contaminants by aquatic species, we used LC-MS/MS to analyze sediment samples that had been generated previously upon exposure of Western clawed frogs (Silurana tropicalis) to DY 7 (at exposure levels where cellular stress was observed in S. tropicalis). We found p-PDA, 4-AAB, and 4-ABP were present in all exposures, but not in any of the sediment controls, demonstrating that upon release of DY 7 to the aquatic environment, sediment dwelling organisms will metabolize DY 7 to generate known (and suspected) human carcinogens, including through a previously unreported in vivo benzidine rearrangement to produce 4-ABP.

One-step green synthesis of bimetallic Fe/Pd nanoparticles used to degrade Orange II

To reduce cost and enhance reactivity, bimetallic Fe/Pd nanoparticles (NPs) were firstly synthesized using grape leaf aqueous extract to remove Orange II. Green synthesized bimetallic Fe/Pd NPs (98.0%) demonstrated a far higher ability to remove Orange II in 12h compared to Fe NPs (16.0%). Meanwhile, all precursors, e.g., grape leaf extract, Fe(2+) and Pd(2+), had no obvious effect on removing Orange II since less than 2.0% was removed. Kinetics study revealed that the removal rate fitted well to the pseudo-first-order reduction and pseudo-second-order adsorption model, meaning that removing Orange II via Fe/Pd NPs involved both adsorption and catalytic reduction. The remarkable stability of Fe/Pd NPs showed the potential application for removing azo dyes. Furthermore, Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) confirmed the changes in Fe/Pd NPs before and after reaction with Orange II. High Performance Liquid Chromatography-Mass Spectrum (HPLC-MS) identified the degraded products in the removal of Orange II, and finally a removal mechanism was proposed. This one-step strategy using grape leaf aqueous extract to synthesize Fe/Pd NPs is simple, cost-effective and environmentally benign, making possible the large-scale production of Fe/Pd NPs for field remediation.

Rapid degradation of azo dye methyl orange using hollow cobalt nanoparticles

A rapid and efficient method for methyl orange degradation using hollow cobalt (Co) nanoparticles is reported. Hollow Co nanoparticles were fabricated by a galvanic replacement reaction using aluminum (Al) nanoparticles as the template material. The methyl orange degradation characteristics were investigated by measuring the time dependent UV-Vis absorption of the dye solution, which showed a very fast degradation rate under acidic conditions. At an initial methyl orange concentration of 100 mg/L (pH = 2.5) and Co nanoparticle dosage of 0.5 g/L, the azo dye degradation efficiency reached up to 99% within 4 min, and the degradation constant rate was up to 2.444 min(-1), which is the highest value among other studies. A comparison of the decolorization rates at similar conditions with several other azo dyes, including Congo red, Amaranth, and Orange G, showed that the dye with a simpler structure and lower molecular mass decolorized considerably faster than the ones having a more complicated structure (higher molecular mass). The methyl orange degradation was also conducted using hollow nickel (Ni) nanoparticles and commercially available solid spherical Co and Ni nanoparticles. The results showed that Co-based nanoparticles outperformed Ni-based nanoparticles, with the hollow Co nanoparticles exhibiting the fastest degradation rate. Using the hollow Co nanoparticles is a very promising approach for the remediation of methyl orange dye containing wastewater due to the fast degradation rate and high degradation efficiency. In addition, these hollow Co nanoparticles are easily recycled because of their magnetic property.

Decoloration of azo and triarylmethane dyes in the aqueous phase by catalytic hydrotreatment with Pd supported on pillared clays

Catalytic hydrotreatment of synthetic dyes as azo compounds and triarylmethanes has been carried out under ambient-like conditions (25–50 °C, 1 atm) with H₂using Pd supported on Al-pillared clays and Al₂O₃as catalysts.

Ultrafast degradation of azo dyes catalyzed by cobalt-based metallic glass

Reactivity and mass loss are considered mutually exclusive in conventional zero-valent metal (ZVM) technology to treat environmental contaminants. Here, we report the outstanding performance of Co-based metallic glass (MG) in degrading an aqueous solution of azo dye, thus eliminating this trade-off. Ball-milled Co-based MG powders completely degrade Acid Orange II at an ultrafast rate. The surface-area-normalized rate constant of Co-based MG powders was one order of magnitude higher than that of Co-based crystalline counterparts and three orders of magnitude higher than that of the widely studied Fe⁰ powders. The coordinatively unsaturated local structure in Co-based MG responds to the catalysis for degradation, resulting in very low mass loss. Wide applicability and good reusability were also present. Co-based MG is the most efficient material for azo dye degradation reported thus far, and will promote the practical application of MGs as functional materials.

The mechanism for degrading Orange II based on adsorption and reduction by ion-based nanoparticles synthesized by grape leaf extract

Biomolecules taken from plant extracts have often been used in the single-step synthesis of iron-based nanoparticles (Fe NPs) due to their low cost, environmental safety and sustainable properties. However, the composition of Fe NPs and the degradation mechanism of organic contaminants by them are limited because these are linked to the reactivity of Fe NPs. In this study, Fe NPs synthesized by grape leaf extract served to remove Orange II. Batch experiments showed that more than 92% of Orange II was removed by Fe NPs at high temperature based on adsorption and reduction and confirmed by kinetic studies. To understand the role of Fe NPs in the removal process of azo dye, surface analysis via X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were employed, showing that the Fe NPs were composed of biomolecules, hydrous iron oxides and Fe(0), thus providing evidence for the adsorption of Orange II onto hydrous iron oxides and its reduction by Fe(0). Degraded products such as 2-naphthol were identified using LC-MS analysis. A degradation mechanism based on asymmetrical azo bond cleavage for the removal of Orange II was proposed.

Effective removal of nemacide fosthiazate from an aqueous solution using zero-valent iron

In this study, the removal of fosthiazate in an aqueous solution using zero valent iron (ZVI) and the related removal reaction mechanism were investigated. The results indicate that the dissipation of fosthiazate adheres to a pseudo-first order reaction law. The apparent rate constant of fosthiazate removal could be improved by increasing the ZVI dosage, control temperature and initial pH. The observed pseudo-first-order degradation rate constants (Kobs) of fosthiazate removal using ZVI were varied in the different electrolyte solutions, and were determined as follows: Kobs (MgSO4) < Kobs (KCl) < Kobs (Control) <Kobs (NaCl) < Kobs (CaCl2) < Kobs (NaNO3) < Kobs (Na2SO4). In addition, the effects of Fe(2+) and Fe(3+) ions on the fosthiazate removal were also investigated, and the fosthiazate removal efficiencies were measured as 1.3% and 5.7% with Fe(2+) and Fe(3+), respectively. The characterizations of ZVI before/after the reaction were employed to gain insight into the reaction mechanism. Finally, the main degradation products were investigated by means of an Agilent 1100 LC/MSD Ion Trap.

Biochar Supported Nanoscale Iron Particles for the Efficient Removal of Methyl Orange Dye in Aqueous Solutions

The presence of organic contaminants in industrial effluents is an environmental concern of increasing global importance. One innovative technology for treating contaminated industrial effluents is nanoscale zero-valent iron supported on biochar (nZVI/BC). Based on Transmission Electron Microscopy, X-Ray Diffraction, and Brunauer-Emmett-Teller characterizations, the nZVI was well dispersed on the biochar and aggregation was dramatically reduced. Methyl orange (MO) served as the representative organic contaminant for verifying the effectiveness of the composite. Using decolorization efficiency as an indicator of treatment effectiveness, increasing doses of nZVI/BC yielded progressively better results with 98.51% of MO decolorized by 0.6 g/L of composite at an nZVI/BC mass ratio of 1:5. The superior decolorization efficiency of the nZVI/BC was attributed to the increase in the dispersion and reactivity of nZVI while biochar increasing the contact area with contaminant and the adsorption of composites. Additionally, the buffering function of acid-washed biochar could be in favor of maintaining the reactivity of nZVI. Furthermore, the aging nZVI/BC for 30 day was able to maintain the removal efficiency indicating that the oxidation of nZVI may be delayed in the presence of biochar. Therefore, the composite of nZVI/BC could represent an effective functional material for treating wastewater containing organic dyes in the future.

Kinetics of Solvent Blue and Reactive Yellow removal using microwave radiation in combination with nanoscale zero-valent iron

We investigated the efficiency and kinetics of the degradation of soluble dyes over the pH range 5.0-9.0 using a method employing microwave radiation in combination with nanoscale zero-valent iron (MW-nZVI). The nZVI particles (40-70 nm in diameter) were prepared by a liquid-phase chemical reduction method employing starch as a dispersant. Compared to the removal of Solvent Blue 36 and Reactive Yellow K-RN using only nZVI, more rapid and efficient dye removal and total organic carbon removal were achieved using MW-nZVI. The dye removal efficiency increased significantly with decreasing pH, but was negligibly affected by variation in the microwave power. The kinetics of dye removal by MW-nZVI followed both an empirical equation and the pseudo first-order model, while the kinetics of dye removal using nZVI could only be described by an empirical equation. It was also concluded that microwave heating of the dye solutions as well as acceleration of corrosion of nZVI and consumption of Fe(II) were possible reasons behind the enhanced dye degradation.

Rapid degradation of endosulfan by zero-valent zinc in water and soil

Endosulfan has been included in the list of persistent organic pollutants (POPs) in 2011. The degradation of endosulfan by zero-valent zinc in water and soil was first investigated. The results showed that >90% endosulfan could be degraded in 180 min. The degradation was accelerated under acidic conditions with the absence of dissolved oxygen, while the nature of the soil only exhibited a negligible effect. The half-life was decreased from 130.75 min to 41.75 min with the increment of Zn(0) from 0.1 g to 1 g in soil. The use of Zn(0) was more effective than Fe(0) for the degradation of endosulfan with a half-life of 110 min and 330 min. The cationic surfactant was more effective at enhancing the degradation of endosulfan than anionic and nonionic surfactant. The degradation pathway was speculated, and four chlorine of endosulfan were proposed to be reduced. The method exhibited obvious advantages over traditional endosulfan treatments, and the research results will lay a foundation for practical application of the method.

Can zero-valent iron nanoparticles remove waterborne estrogens?

Steroidal estrogens are one of the most challenging classes of hazardous contaminants as they can cause adverse effects to biota in extremely low concentrations. They emerge in both waste waters and surface waters serving as a source of drinking water. Environmental Quality Standards for 17β-estradiol (E2) and 17α-ethinylestradiol (EE2), promulgated within the EU Water Framework Directive, are 0.4 and 0.035 ng L(-1), respectively. Because nanoscale zero-valent iron (nZVI) particles have been previously used in numerous remediation technologies and have the advantage of possible magnetic separation, interaction of nZVI with E2 and EE2 in water was investigated to assess the potential role of nZVI in removing steroidal estrogens. A mixture of E2 and EE2 dissolved in water was shaken with varying doses of nZVI for 1-5 h. Concentration-dependent removal of the estrogens was observed but removal did not increase significantly with time. Concentrations of the estrogens were determined by HPLC/MS/MS and a biodetection reporter gene assay. Sorption and nonspecific oxygen-mediated oxidation of estrogens were identified as the most probable removal mechanisms. Two independent experiments confirmed that significant decrease of estrogens concentration is achieved when at least 2 g L(-1) of nZVI is applied. The presented study provides insights into the mechanisms of nZVI interaction with steroidal estrogens under aerobic conditions prevailing in currently applied water treatment technologies.

Enhanced decolorization of methyl orange using zero-valent copper nanoparticles under assistance of hydrodynamic cavitation

The rate of reduction reactions of zero-valent metal nanoparticles is restricted by their agglomeration. Hydrodynamic cavitation was used to overcome the disadvantage in this study. Experiments for decolorization of methyl orange azo dye by zero-valent copper nanoparticles were carried out in aqueous solution with and without hydrodynamic cavitation. The results showed that hydrodynamic cavitation greatly accelerated the decolorization rate of methyl orange. The size of nanoparticles was decreased after hydrodynamic cavitation treatment. The effects of important operating parameters such as discharge pressure, initial solution pH, and copper nanoparticle concentration on the degradation rates were studied. It was observed that there was an optimum discharge pressure to get best decolorization performance. Lower solution pH were favorable for the decolorization. The pseudo-first-order kinetic constant for the degradation of methyl orange increased linearly with the copper dose. UV-vis spectroscopic and Fourier transform infrared (FT-IR) analyses confirmed that many degradation intermediates were formed. The results indicated hydroxyl radicals played a key role in the decolorization process. Therefore, the enhancement of decolorization by hydrodynamic cavitation could due to the deagglomeration of nanoparticles as well as the oxidation by the in situ generated hydroxyl radicals. These findings greatly increase the potential of the Cu(0)/hydrodynamic cavitation technique for use in the field of treatment of wastewater containing hazardous materials.

Metal free access to amide compounds via peroxide-mediated NN double bond cleavage of azobenzenes

A direct amidation of aldehydes or benzylamines with azobenzenes through TBHP-mediated NN double bond cleavage of azobenzenes has been developed.