Azo Bond Research Articles

Integrated air cathode microbial fuel cell-aerobic bioreactor set-up for enhanced bioelectrodegradation of azo dye Acid Blue 29

In this study, an azo dye (Acid Blue 29 or AB29) was efficiently degraded with acetate as co-substrate into less contaminated biodegraded products using an integrated single chamber microbial fuel cell (SMFC)-aerobic bioreactor set-up. The decolorization efficiencies were varied from 91 ± 2% to 94 ± 1.9% and more than 85% of chemical oxygen demand (COD) removal was achieved for all dye concentrations after different operating time. The highest coulombic efficiency (CE) and cell potential were 3.18 ± 0.45% and 287.2 mV, respectively, for SMFC treating 100 mg L−1 of AB29. Electrochemical impedance spectroscopy (EIS) revealed that the anode resistance was 0.3 Ω representing an entirely grown biofilm on the anode surface resulted in higher electron transfer rate. Gas chromatography coupled mass spectrometry (GC–MS) investigation demonstrated that initially biodegradation of AB29 started with the cleavage of the azo bond (-N=N-), resulted the biotransformation into aromatic amines. In successive aerobic treatment stage, these amines were biodegraded into lower molecular weight compounds. The 16S rRNA microbial community analysis indicated that at phylum level, both inoculum and dye acclimated cultures were mainly consisting of Proteobacteria which was 27.9, 53.6 and 68.9% in inoculum, suspension and anodic biofilm, respectively. At genus level, both suspension and biofilm contained decolorization as well as electrochemically active bacteria. The outcomes exhibited that the AB29 decolorization would contest with electrogenic bacteria for electrons.

Recent Applications of Azo Dyes: A Paradigm Shift from Medicinal Chemistry to Biomedical Sciences.

Azo molecules possess the characteristic azo bond (-N=N-) and are considered fascinating motifs in organic chemistry. Since the last century, these brightly colored compounds have been widely employed as dyes across several industries in applications for printing, food, paper, cosmetics, lasers, electronics, optics, material sciences, etc. The discovery of Prontosil, an antibacterial drug, propelled azo compounds into the limelight in the field of medicinal chemistry. Subsequent discoveries including Phenazopyridine, Basalazide, and Sulfasalazine enabled azo compounds to occupy a significant role in the drug market. Furthermore, azo compounds have been employed as antibacterial, antimalarial, antifungal, antioxidant, as well as antiviral agents. The metabolic degradation of many azo dyes can induce liver problems if ingested, posing a safety concern and limiting their application as azo dyes in medicinal chemistry. However, azo dyes remain particularly significant for applications in cancer chemotherapy. Recently, a paradigm shift has been observed in the use of azo dyes: from medicinal chemistry to biomedical sciences. The latter benefits from azo dye application are related to imaging, drug delivery, photo-pharmacology and photo switching. Herein, we have compiled and discussed recent works on azo dye compounds obtained so far, focusing on their medicinal importance and future prospects.

Decolorization, degradation and detoxification of carcinogenic sulfonated azo dye methyl orange by newly developed biofilm consortia.

Metabolites of azo dyes are often carcinogenic, teratogenic, mutagenic and recalcitrant in nature. In this study, four biofilm consortia such as C1 (Vitreoscilla sp. ENSG301, Acinetobacter lwoffii ENSG302, Klebsiella pneumoniae ENSG303 and Pseudomonas fluorescens ENSG304), C2 (Escherichia coli ENSD101, Enterobacter asburiae ENSD102 and E. ludwigii ENSH201), C3 (E. asburiae ENSD102, Vitreoscilla sp. ENSG301 and Bacillus thuringiensis ENSW401), and C4 (E. coli ENSD101, E. ludwigii ENSH201 and B. thuringiensis ENSW401) were applied to degrade and detoxify methyl orange (MO), a carcinogenic, sulfonated mono azo dye, used in textile dyeing industry worldwide. The consortia of C1, C2, C3 and C4 showed 97.30, 98.75, 99.51 and 99.29% decolorization, respectively in yeast extract peptone (YEP) broth containing 200 mg L−1 MO within 60 h of incubation in static condition. The optimum pH and temperature for decolorization was 7.0 and 28 °C, respectively. Some divalent metal ions including Mg2+, Ca2+, Zn2+ and Mn2+ could stimulate MO decolorization. UV–Vis spectral analysis showed that the absorption peak at 465 nm originated from the azo (N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N) bond was completely disappeared within 60 h of incubation. Fourier transform infrared spectroscopy (FTIR) results also revealed that several major peaks including azo bond peak at 1602.6 cm−1 are completely or partly vanished, deformed or shifted. Activities of azoreductase, NADH-DCIP reductase and laccase were significantly increased in the bacterial cells within 60 h of incubation in comparison to that of control (0 h). The chemical oxygen demand was incredibly reduced by 85.37 to 91.44% by these consortia. Accordingly, plant (wheat seed germination) and microbial (growth of the plant probiotic bacteria such as Pseudomonas cedrina ESR12 and Bacillus cereus ESD3 on biodegraded products) toxicity studies showed that biodegraded products of MO are non-toxic. Thus, all these consortia can be utilized in bioremediation of MO from wastewater for safe disposal into environment. To our knowledge, this is the first report on degradation and detoxification of MO from wastewater by bacterial biofilm consortia.

A sensitive electrochemical method for indole based on the signal amplification strategy by gold/iron-oxide composite nanoparticles

Indole is a major metabolite of tryptophan, which plays an important role in the intestinal microecological balance and human physiological activities. The determination of indole becomes important for its researches. So, it is urgent to establish a sensitive and cost-effective method for indole detection. Herein, a sensitive electrochemical method was constructed to determine the concentration of indole using screen-printed carbon electrode (SPCE) with the signal amplification strategy by gold/iron-oxide composite nanoparticles (Au/Fe3O4). Au/Fe3O4 nanoparticles were successfully synthesized under the irradiation by high-energy electron beams. 4-aminothiophenol (4-ATP) was connected to Au/Fe3O4 via Au-S bond. And then NaNO2 reacted with 4-ATP to form the azo bond, which could form the final product of Au/Fe3O4@ATP-azo-indole by the coupling reaction. Thus, the concentration of indole was detected by the electrochemical signal produced by Au/Fe3O4@ATP-azo-indole indirectly. The detection sensitivity was greatly improved by the large specific surface area provided by Au/Fe3O4 after the modification. The linear range of indole was from 0.50 to 120.00 μg L−1 and the limit of detection (LOD) was as low as 0.10 μg L−1 (S/N = 3). Furthermore, the developed method exhibited acceptable intra-day and inter-day precisions with the coefficient of variations (CV) less than 4.9% and 8.2%, respectively. And the recoveries were from 97.2% to 105.4%. An innovative, sensitive, cost-effective method was established for indole determination in human plasma matrix in this manuscript, which provides a promising way for indole detection in conventional laboratories.

Turning Waste into Useful Products by Photocatalysis with Nanocrystalline TiO2 Thin Films: Reductive Cleavage of Azo Bond in the Presence of Aqueous Formate.

UV-photoexcitation of TiO2 in contact with aqueous solutions of azo dyes does not imply only its photocatalytic degradation, but the reaction fate of the dye depends on the experimental conditions. In fact, we demonstrate that the presence of sodium formate is the switch from a degradative pathway of the dye to its transformation into useful products. Laser flash photolysis experiments show that charge separation is extremely long lived in nanostructured TiO2 thin films, making them suitable to drive both oxidation and reduction reactions. ESR spin trapping and photoluminescence experiments demonstrate that formate anions are very efficient in intercepting holes, thereby inhibiting OH radicals formation. Under these conditions, electrons promoted in the conduction band of TiO2 and protons deriving from the oxidation of formate on photogenerated holes lead to the reductive cleavage of N=N bonds with formation and accumulation of reduced intermediates. Negative ion ESI–MS findings provide clear support to point out this new mechanism. This study provides a facile solution for realizing together wastewater purification and photocatalytic conversion of a waste (discharged dye) into useful products (such as sulfanilic acid used again for synthesis of new azo dyes). Moreover, the use of TiO2 deposited on an FTO (Fluorine Tin Oxide) glass circumvents all the difficulties related to the use of slurries. The obtained photocatalyst is easy to handle and to recover and shows an excellent stability allowing complete recyclability.

Novel bacterial biofilm consortia that degrade and detoxify the carcinogenic diazo dye Congo red.

Free-living planktonic single bacterial strain can decolorize Congo red (CR) but often produces the carcinogenic, mutagenic and genotoxic aromatic amines. Planktonic single and bacterial consortia are more susceptible to toxic pollutants than their biofilm counterparts. In the present study, four biofilm consortia (C1 = Vitreoscilla sp. ENSG301, Acinetobacter lwoffii ENSG302, Klebsiella pneumoniae ENSG303 and Pseudomonas fluorescens ENSG304, C2 = Escherichia coli ENSD101, Enterobacter asburiae ENSD102 and E. ludwigii ENSH201, C3 = E. asburiae ENSD102, Vitreoscilla sp. ENSG301 and Bacillus thuringiensis ENSW401, and C4 = E. coli ENSD101, E. ludwigii ENSH201 and B. thuringiensis ENSW401) were prepared and assessed for bioremediation of CR. All these biofilm consortia remarkably decolorized (96.9 to 99.5%) the CR (100mg/L) in static condition within 72h incubation at 28°C. These consortia also synthesized significantly more intracellular azoreductase and laccase enzyme than extracellular of these enzymes. UV-Vis spectral analysis revealed that the major peak at 478nm wavelength of CR was completely disappeared. FTIR analysis showed several major peaks along with azo bonds are completely or partly disappeared, deformed or widened. Chemical oxygen demand was reduced by 86.4, 85.5, 87.0 and 86.2% by C1, C2, C3 and C4, respectively. Accordingly, biodegraded metabolites of CR by different biofilm consortia did not inhibit the germination of wheat seeds and bacterial growth. Thus, these biofilm consortia can be applied in bioremediation of wastewater containing CR for safe disposal into the environment. To our knowledge, this is the first report on degradation and detoxification of aqueous solution containing CR by bacterial biofilm consortia.

Application of macroalgal biomass derived biochar and bioelectrochemical system with Shewanella for the adsorptive removal and biodegradation of toxic azo dye

The present study aimed towards adsorptive removal of the toxic azo dye onto biochar derived from Eucheuma spinosum biomass. Characterization of the produced biochar was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). Eucheuma spinosum biochar (ES-BC) produced at 600 °C revealed a maximum adsorption capacity of 331.97 mg/g towards reactive red 120 dye. The adsorption data fitted best to the pseudo-second order kinetics (R2 > 0.99) and Langmuir isotherm (R2 > 0.98) models. These adsorption models signified the chemisorption mechanism with monolayer coverage of the adsorbent surface with dye molecules. Furthermore, the adsorption process was mainly governed by electrostatic interaction, ion exchange, metal complexation, and hydrogen bonding as supported by the solution pH, FTIR, XPS, and XRD investigation. Nevertheless, alone adsorption technology could not offer a complete solution for eliminating the noxious dyes. Therefore, the bioelectrochemical system (BES) equipped with previously isolated marine Shewanella marisflavi BBL25 was intended for the complete remediation of azo dye. The BES II demonstrated highest dye decolorization (97.06%) within 48 h at biocathode where the reductive cleavage of the azo bond occurred. Cyclic voltammetry (CV) studies of the BES revealed perfect redox reactions taking place where the redox mediators shuttled the electrons to the dye molecule to accelerate the dye decolorization. Besides, the GC-MS analysis revealed biotransformation of the dye into less toxic metabolites as tested using a phyto and cytogenotoxicity.

A Polymorphic Azobenzene Cage for Energy‐Efficient and Highly Selective p‐Xylene Separation

AbstractDeveloping the competence of molecular sorbents for energy‐saving applications, such as C8 separations, requires efficient, stable, scalable, and easily recyclable materials that can readily transition to commercial implementation. Herein, we report an azobenzene‐based cage for the selective separation of p‐xylene isomer across a range of C8 isomers in both vapor and liquid states with selectivity that is higher than the reported all‐organic sorbents. The crystal structure shows non‐porous cages that are separated by p‐xylene molecules through selective CH–π interactions between the azo bonds and the methyl hydrogen atoms of the xylene molecules. This cage is stable in solution and can be regenerated directly under vacuum to be used in multiple cycles. We envisage that this work will promote the investigation of the azo bond as well as guest‐induced crystal‐to‐crystal phase transition in non‐porous organic solids for energy‐intensive separations.

A Polymorphic Azobenzene Cage for Energy-Efficient and Highly Selective p-Xylene Separation.

Developing the competence of molecular sorbents for energy-saving applications, such as C8 separations, requires efficient, stable, scalable, and easily recyclable materials that can readily transition to commercial implementation. Herein, we report an azobenzene-based cage for the selective separation of p-xylene isomer across a range of C8 isomers in both vapor and liquid states with selectivity that is higher than the reported all-organic sorbents. The crystal structure shows non-porous cages that are separated by p-xylene molecules through selective CH-π interactions between the azo bonds and the methyl hydrogen atoms of the xylene molecules. This cage is stable in solution and can be regenerated directly under vacuum to be used in multiple cycles. We envisage that this work will promote the investigation of the azo bond as well as guest-induced crystal-to-crystal phase transition in non-porous organic solids for energy-intensive separations.

Influence of number of azo bonds and mass transport limitations towards the elimination capacity of continuous electrochemical process for the removal of textile industrial dyes

This study focusses on the electrochemical decomposition of synthetic azo dyes (RO16, RR120 and DR80) using stainless steel electrodes, which is efficient, cost effective and industrially driven process. The experiments were carried out in a continuous electrochemical reactor and the effects of influencing parameters (initial concentration of dye, electrolyte concentration, pH) governing the process efficiency was studied. The interaction between the influencing parameters was investigated using Response Surface Methodology (RSM) and the regression value obtained for the generated model was above 0.9 for all the three dyes. The elimination capacity of electrochemical reactor was studied for the continuous removal of azo dyes with different ranges of concentration (100–400 mg L−1) and flow rate (0.1–0.5 L h−1). The maximum elimination capacity was obtained at a flow rate of 0.5 L h−1 for 300 mg L−1 of initial concentration of dye for RO16 and RR120 whereas it was 0.5 L h−1 for 400 mg L−1 of DR80. Further, a general dimensionless current density relation has been established for stirred tank reactor and allowed characterizing the relationship between kinetics and mass transport contributing to the overall reaction rate. The results quantitatively confirmed that the rate of electrochemical decolorization increased with the increasing initial dye concentration and flow rate due to the mass transport limitation. As newly established, the decolorization is also directly linked to the number of azo bonds.

Ethanol as an efficient cosubstrate for the biodegradation of azo dyes by Providencia rettgeri: Mechanistic analysis based on kinetics, pathways and genomics

Azo dyes pose hazards to ecosystems and human health and the cosubstrate strategy has become the focus for the bioremediation of azo dyes. Herein, Brilliant Crocein (BC), a model pollutant, was biodegraded by Providencia rettgeri domesticated from activated sludge. Additional ethanol, as a cosubstrate, could accelerate P. rettgeri growth and BC biodegradation, as reflected by the Gompertz models. This phenomenon was attributed to the smaller metabolites and greater number of potential pathways observed under the synergistic effect of ethanol. Genomic analysis of P. rettgeri showed that functional genes related to azo bond cleavage, redox reactions, ring opening and hydrolysis played crucial roles in azo dye biodegradation. Furthermore, the mechanism proposed was that ethanol might stimulate the production of additional reducing power via the expression of related genes, leading to the cleavage of azo bonds and aromatic rings. However, biodegradation without ethanol could only partly cleave the azo bonds.

Reduced graphene oxide@polydopamine decorated carbon cloth as an anode for a high-performance microbial fuel cell in Congo red/saline wastewater removal

A polydopamine decorated reduced oxide graphene (rGO@PDA) on carbon cloth (CC) as microbial fuel cell (MFC) anode was prepared by using dopamine polymerized reduction of oxide graphene. The anodes provided superhydrophilicity, high conductivity, good biocompatibility and long-term stability due to the combination of inorganic/organic components. These components and the resulting structure promoted enhancement of bacteria growth and enrichment, accelerated extracellular electron transfer between bacteria and anode surface, gained a high-performance rGO@PDA/CC MFC. The device achieved a short startup time of 18 h, maximum power density of 988.1 ± 5.2 mW·m−2 and Congo red decolorization efficiency of 89.7 ± 2.4% within 24 h. When Congo red and sodium acetate were continuously degraded, removal efficiency of chemical oxygen demand increased 77.8 ± 3.5% and 88.5 ± 5.8%, respectively. Thus, the synergistic effect of rGO and PDA effectively enhanced startup speed, power generation and pollutant degradation. The degradation products of Congo red were analyzed by mass spectrometry. Congo red was degraded to small organic molecules without azo bonds.

Evaluation of toxicity and mutagenicity of a synthetic effluent containing azo dye after Advanced Oxidation Process treatment

Approximately 20% industrial water pollution comes from textile dyeing process, with Azo dyes being a major problem in this scenario and requiring new forms of efficient treatment. Effluent treatments using the Advanced Oxidation Processes (AOP) are justified by the potential of application in the dyed effluent treatments once they can change the Azo dye chemical structure. Thus, this study aimed to evaluate the toxicity and mutagenic capacity of a synthetic effluent containing Amido Black 10B (AB10B) azo dye before treatment with AOP, named Gross Synthetic Effluent (GSE), and after the AOP, named Treated Synthetic Effluent (TSE). Daphnia magna and Allium cepa tests were used to evaluate acute toxicity effects and chromosomal mutagenesis, respectively. The Salmonella/microsome assay was performed to evaluate gene mutations. In silico assays were also performed aiming to identify the mutagenic and carcinogenic potential of the degradation byproducts of AB10B. There was 100% immobility to D. magna after 24 h and 48 h of treatments with TSE, showing EC50 values around 5%, whereas GSE did not show acute toxicity. However, GSE induced chromosomal mutations in A. cepa test. Both GSE and TSE were not able to induce gene mutations in S. typhimurium strains. These effects can be associated with two byproducts generated with the cleavage of the azo bonds of AB10B, 4-nitroaniline and -2-7-triamino-8-hydroxy-3-6-naphthalinedisulfate (TAHNDS). In conclusion, AOP is an efficient method to reduce the mutagenicity of synthetic effluent containing AB10B and additional methods should be applied aiming to reduce the toxicity.

Degradation and detoxification of azo dyes with recombinant ligninolytic enzymes from Aspergillus sp. with secretory overexpression in Pichia pastoris.

Ligninolytic enzymes, including laccase (Lac), manganese peroxidase (MnP) and lignin peroxidase (LiP), have attracted much attention in the degradation of contaminants. Genes of Lac (1827 bp), MnP (1134 bp) and LiP (1119 bp) were cloned from Aspergillus sp. TS-A, and the recombinant Lac (69 kDa), MnP (45 kDa) and LiP (35 kDa) were secretory expressed in Pichia pastoris GS115, with enzyme activities of 34, 135.12 and 103.13 U l−1, respectively. Dyes of different structures were treated via the recombinant ligninolytic enzymes under the optimal degradation conditions, and the result showed that the decolourization rate of Lac on Congo red (CR) in 5 s was 45.5%. Fourier-transform infrared spectroscopy, gas chromatography–mass spectrometry analysis and toxicity tests further proved that the ligninolytic enzymes could destroy the dyes, both those with one or more azo bonds, and the degradation products were non-toxic. Moreover, the combined ligninolytic enzymes could degrade CR more completely compared with the individual enzyme. Remarkably, besides azo dyes, ligninolytic enzymes could also degrade triphenylmethane and anthracene dyes. This suggests that ligninolytic enzymes from Aspergillus sp. TS-A have the potential for application in the treatment of contaminants.

Hypoxia-degradable and long-circulating zwitterionic phosphorylcholine-based nanogel for enhanced tumor drug delivery

Tumor microenvironment has been widely utilized for advanced drug delivery in recent years, among which hypoxia-responsive drug delivery systems have become the research hotspot. Although hypoxia-responsive micelles or polymersomes have been successfully developed, a type of hypoxia-degradable nanogel has rarely been reported and the advantages of hypoxia-degradable nanogel over other kinds of degradable nanogels in tumor drug delivery remain unclear. Herein, we reported the synthesis of a novel hypoxia-responsive crosslinker and the fabrication of a hypoxia-degradable zwitterionic poly(phosphorylcholine)-based (HPMPC) nanogel for tumor drug delivery. The obtained HPMPC nanogel showed ultra-long blood circulation and desirable immune compatibility, which leads to high and long-lasting accumulation in tumor tissue. Furthermore, HPMPC nanogel could rapidly degrade into oligomers of low molecule weight owing to the degradation of azo bond in hypoxic environment, which leads to the effective release of the loaded drug. Impressively, HPMPC nanogel showed superior tumor inhibition effect both in vitro and in vivo compared to the reduction-responsive phosphorylcholine-based nanogel, owing to the more complete drug release. Overall, the drug-loaded HPMPC nanogel exhibits a pronounced tumor inhibition effect in a humanized subcutaneous liver cancer model with negligible side effects, which showed great potential as nanocarrier for advanced tumor drug delivery.

Effect of Corncob Derived Biochar on Microbial Electroremediation of Dye Wastewater and Bioenergy Generation

AbstractThis paper describes the potential of waste biomass derived biochar for improvement in the dye wastewater treatment in a microbial fuel cell (MFC). The complete MFC, an energy generating unit, was made with the waste products in order to demonstrate that low cost alternatives are available to replicate the positive results. Waste corncob derived biochar produced after acid modification has been evaluated as a supplement in an MFC for treatment of real dye wastewater (RDW). The two doses of sulfuric acid modified corncob biochar (SA‐MCB), (0.5 g and 1 g) and a blank (without any dose) were assessed for the effect on MFC performance. The maximum power density (49.92 W/m2), current density (0.28 A/m2), COD removal efficiency (88.39%), decolorization efficiency (81.6%) and TDS reduction (84.4%) were obtained with 0.5 g biochar dose. The Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed the structural changes occurring on the SA‐MCB after use in the MFC. The SEM analysis revealed the better biofilm formation due to SA‐MCB deposition. Power density with 0.5 g of SA‐MCB dose improved to more than 24 times in comparison to the system without any such dose. The UV spectrophotometer analysis confirmed the azo bond deformation during treatment. The overall results suggest that the use of SA‐MCB biochar as anode material and as a supplement in the MFC system may provide an effective anode‐biofilm in MFCs for wastewater treatment.

Strong Activity Enhancement of the Photocatalytic Degradation of an Azo Dye on Au/TiO2 Doped with FeOx

The doping of Au/TiO2 with FeOx is shown to result in a strong enhancement of its photocatalytic activity in the degradation of the azo dye Orange II. In order to examine the source of this enhancement, Au-FeOx/TiO2 nanocomposites containing different molar ratios of Au:Fe were synthesized, and X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and high-resolution transmission electron microscope (HRTEM) analyses indicated that the TiO2-supported Au nanoparticles were partially covered with an amorphous layer of FeOx species, in which the iron was present as Fe2+ and Fe3+. The metal-semiconductor system, i.e., Au/TiO2, showed only a moderate degradation rate, whereas doping with FeOx strongly enhanced the degradation activity. The bandgap energy decreased gradually from Au/TiO2 (3.13 eV) to the catalyst with the highest FeOx loading Au-FeOx (1:2)/TiO2 (2.23 eV), and this decrease was accompanied by a steady increase in the degradation activity of the catalysts. XPS analyses revealed that compared to Au/TiO2, on Au-FeOx/TiO2 a much higher population density of chemisorbed and/or dissociated oxygen species was generated, which together with the decreased bandgap resulted in the highest photocatalytic activity observed with Au-FeOx (1:2)/TiO2. The processes occurring during reaction on the catalyst surface and in the bulk liquid phase were investigated using operando attenuated total reflection IR spectroscopy (ATR-IR) combined with modulation excitation spectroscopy (MES), which showed that the doping of Au/TiO2 with FeOx weakens the interaction of the dye with the catalyst surface and strongly enhances the cleavage of the azo bond.

Microbial fuel cell‐assisted Congo red dye decolorization using biowaste‐derived anode material

AbstractMicrobial fuel cell (MFC) is a promising technology for wastewater treatment coupled with electricity generation. Biowaste‐derived electrodes are used to improve the surface area, roughness, and hydrophilicity, which play pivotal role in the enhanced biofilm formation. In the present study, Ficus religiosa leaves (FRL) biowaste was used to develop the bioelectrode. In this study, Congo red (CR) dye decolorization was performed using MFC, wherein the effect of dye decolorization with respect to dye concentration, glucose concentration, and hydraulic retention time (HRT) was studied. The surface roughness and distribution of carbon powder on carbon cloth were confirmed using scanning electron microscope (SEM) analysis. Also, Bacillus subtilis adhesion and chain‐like structure formation on the electrode confirmed the biofilm formation on the electrode. The polarization curve was performed to assess the MFC performance. The maximum power density of 70.50 mW/m2 and current density of 251.79 mA/m2 at 2,224 Ω was achieved. The maximum decolorization of 80.95 ± 2.08% and COD reduction of 73.96 ± 1.76% were obtained, respectively, after complete treatment of MFC for 54 h. UV‐visible spectrometry analysis of dye contained samples during MFC treatment at various time intervals was confirmed the cleavage of azo bond (NN), and the corresponding peak intensity variation was noticed at 490 nm.

Green Synthesis of Kaolin-Supported Nanoscale Zero-Valent Iron Using Ruellia tuberosa Leaf Extract for Effective Decolorization of Azo Dye Reactive Black 5

Kaolin-supported nanoscale zero-valent iron (K-NZVI) was synthesized via a green synthesis method, in which leaf extract of Ruellia tuberosa was used as a reducing agent. The synthesized K-NZVI was used for decolorization of Reactive Black 5 (RB5), an azo dye widely used in textile industry. The XRD patterns of the K-NZVI particles show the characteristic peaks of Fe0, indicating that Fe0 nanoparticles (NZVI) were successfully synthesized on the kaolin surface. The SEM, TEM images and EDS elemental mapping show that the NZVI particles are well dispersed on the kaolin surface, thus, reducing the extent of NZVI aggregation. Batch experiments for decolorization of RB5 were carried out to investigate the effects of process parameters including solution pH, initial dye concentration and contact time. The results show that high decolorization efficiencies are obtained in acidic pH. Increasing initial dye concentration causes the decolorization efficiency to decrease, whereas increasing contact time results in higher efficiency. Furthermore, after five cycles of reuse of K-NZVI, the decolorization efficiency slightly decreases, indicating high reusability and stability of K-NZVI. The disappearance of the characteristic peaks of RB5 solution recorded by a UV–Vis spectrophotometer indicates cleavage of the azo bonds and, thus, the decomposition of RB5 in the solution. From a kinetic analysis performed at various RB5 concentrations, the decolorization process of RB5 by K-NZVI is well fit by the pseudo-first-order kinetic model.

Electrochemical process employing scrap metal waste as electrodes for dye removal

In the present study, efficiency of electro-coagulation-flotation (EC-F) process using waste metal scrap of Al and Fe collected from construction and demolition waste of Indian Institute of Technology Madras (IIT M) campus for the removal of double azo bond dye Acid Red 66 (AR66) was studied. The key operating parameters such as current density and electrical conductivity were optimized individually with an initial dye concentration of 50 mg/L, at pH 7. Different electrode combinations and connection modes (parallel MP-P, series (MP-S, BP-S)) were tested, at pre-optimized conditions, in order to achieve better removal of AR66 dye with minimum energy consumption. Series connection in bipolar electrode mode (BP–S) showed better COD reduction from 164 mg/L to 26.2 mg/L with complete decolourization (BDL). Hybrid electrode system of Fe–Al–Fe–Al–Fe–Al showed maximum reduction of COD from 164 mg/L to 11.3 mg/L along with 86.3% TSS reduction and complete decolourization. LC-MS analysis showed the formation of intermediates with m/z 195, m/z 210.6 and m/z 159.3 due to the destruction of AR66 dye during electrolysis. Highest current efficiency (CE φ = 107%) was observed in case of hybrid electrode system compared to Al (φ = 30.1%) and Fe (φ = 98.3%) electrode system at similar operating conditions. Compared to the same electrode material as anode and cathode, use of appropriate hybrid electrode combination can improve the removal efficiency and reduce the energy consumption (ENC). The influence of aeration on the performance of the system was also studied. Aeration significantly improved the COD removal efficiency (98.3%) along with complete decolourization (100%). The use of waste metal scrap as electrodes reduced the overall cost of the treatment process from 1.6 $/m3 to 0.06 $/m3. Using waste metal scrap as electrodes not only reduces the metal accumulation in the environment but also reduces the cost of EC-F process.