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A global water crisis is emerging due to increasing levels of contaminated water and decreasing clean water supply on Earth. This study aims to address the removal of azo dye from wastewater to enable its reuse. Recently, utilizing microorganisms has been proven to be a practical choice for the remediation of azo dyes in wastewater. Hence, in this study, we employed a preformed biofilm of Pseudomonas aeruginosa on a solid support (called substrate) to degrade azo dyes. This process offers several advantages, such as stability, substrate portability, more biofilm production in less time, and efficient utilization of enzymes for remediation. From 50 ppm of initial Congo Red concentration, 75.74% decolorization was achieved within ten h using a preformed biofilm on a coverslip. A maximum of 52.27% decolorization was achieved using biofilm during its formation after 72 h of incubation. The Fourier-transform infrared (FTIR) spectroscopic analysis of Congo Red dye before and after remediation revealed a significant change in peak intensity, indicating dye degradation. Phytotoxicity studies performed by seed germination with Vigna radiata revealed that, after 5-7 days, almost 40% more seeds with longer root and shoot lengths were germinated in the presence of treated dye compared to the untreated one. This data indicated that the harmful Congo Red was successfully degraded to a non-toxic product by Pseudomonas aeruginosa biofilm grown on a glass substrate.

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Azobenzene moieties can serve as active fragments in antimicrobials and exert trans/cis conversions of molecules. Herein, a series of novel nicotinamide derivatives (NTMs) were developed by employing a two-step strategy, including azo-incorporating and bioisosteric replacement. Azo-incorporation can conveniently provide compounds that can be easily optically interconverted between trans/cis isomers, enhancing the structural diversity of azo compounds. It is noteworthy that the replacement of the azo bond with a 1,2,4-oxadiazole motif through further bioisosteric replacement led to the discovery of a novel compound, NTM18, which made a breakthrough in preventing rice sheath blight disease. A control effect value of 94.44% against Rhizoctonia solani could be observed on NTM18, while only 11.11% was determined for boscalid at 200 mg·L-1. Further mechanism validations were conducted, and the molecular docking analysis demonstrated that compound NTM18 might have a tight binding with SDH via an extra π-π interaction between the oxadiazole ring and residue of D_Y586. This work sets up a typical case for the united applications of azo-incorporating and bioisosteric replacement in fungicide design, posing an innovative approach in structural diversity-based development of pesticides.

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Anaerobic digestion (AD) treatment of azo dyes wastewater often suffers from low decolorization efficiency and poor stability of anaerobic granular sludge (AnGS). In this study, iron and nitrogen co-modified biochar (FNC) was synthesized based on the secondary calcination method, and the feasibility of this material for enhanced AD treatment of azo dye wastewater and its mechanism were investigated. FNC not only formed richer conducting functional groups, but also generated Fe2+/Fe3+ redox pairs. The decolorization efficiency of Congo red and AD properties (e.g., methane production) were enhanced by FNC. After adding FNC, the content of extracellular polymeric substances (EPS) and the ratio of proteins remained stable under the impact of Congo red, which greatly protected the internal microbial community. This was mainly contributed to the excellent electrochemical properties of FNC, which strengthened the microbial extracellular electron transfer and realized the coupled mechanism of action: On the one hand, an electron transfer bridge between decolorizing bacteria and dyes was constructed to achieve rapid decolorization of azo dyes and mitigate the impact on methanogenic bacteria; On the other hand, the stability of AnGS was enhanced based on enhanced extracellular polymeric substances secretion, microbial community and direct interspecies electron transfer (DIET) process. This study provides a new idea for enhanced AD treatment of azo dyes wastewater.

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Graphitic carbon nitride is a semiconducting material of a graphite-like 2D layered structure. It is well known for its photocatalytic properties, which can be exploited for solar-light-driven water splitting and degradation of organic pollutants. Here, we report its capabilities of catalyzing the reduction of the azo bond by hydrazine to two amines under visible light. This photocatalytic reaction provides a novel, appealing way to reduce azo dye wastes as pollutants other than degradation. With this method, the azo dye wastes can be photochemically converted to amines, which can be used as precursors for new azo dyes.

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Background: Systematic studies on the biodiversity of bryophytes along elevational gradients have been conductuted within the native vegetation of the Azores, using the MOVECLIM framework. The primary objective of this study was to inventory the bryophytes present within preserved areas of native vegetation in Terceira Island (Azores). From 25 to 28 September 2012, an inventory of the bryoflora was carried out along an elevational gradient, starting near Serreta lighthouse (38.76658 Latitude; -27.37539 Longitude; 40 m a.s.l.) and culminating on the top of Santa Bárbara Mountain (38.73064 Latitude; -27.32164 Longitude; 1000 m a.s.l.). The study followed the adapted MOVECLIM standardised protocol, as follows: i) six sites were selected along an elevational transect, each site spaced at 200 m elevation intervals; ii) within each site, two 10 m x 10 m plots were established in close proximity from each other (10-15 m); iii) within these plots, three 2 m x 2 m quadrats were randomly selected and sampled for bryophytes. The following substrates were surveyed in each quadrat: rock, soil, humus, organic matter, tree bark at three different heights and leaves/fronds. For each available and bryophyte-colonised substrate, three replicate microplots of 10 cm x 5 cm were collected, resulting in a maximum of 24 microplots per quadrat. New information: Nearly three-quarters of the maximum expected number of microplots (636 out of 864; eventID) were found across the six sites on Terceira Island, resulting in a total of 3677 records (occurrenceID). A high proportion of the specimens could be identified to the species rank (n = 3661; 99.6%), representing 38 families, 60 genera and 92 species, including 58 species of liverworts (Marchantiophyta) and 34 species of mosses (Bryophyta). The inventory included several endemic species: two liverwort species endemic to the Azores, five species endemic to Macaronesia (three mosses and two liverworts) and 11 European endemic species (three mosses and eight liverworts). The elevations with the highest species richness, the highest number of endemic species and the highest number of conservation concern species, spanned between 600 and 1000 m a.s.l. above sea level, coinciding with the best preserved forest vegetation. Overall, tree-dwelling and ground-dwelling substrates showed similar levels of bryophyte occupation (75% vs. 72%). However, the 636 events were unevenly distributed across substrates: leaves and rocks had the fewest replicates (n = 54; 50.0%), while humus and the lowest tree height had the highest values (n = 106; 98.1% and n = 98; 90.7%, respectively).The study contributed to expanding knowledge about the diversity and distribution of the Azorean Bryoflora, both on a local and a regional scale.

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Synthesized SnO2 NPs demonstrate potential capacity to adsorb toxic azo dye. Powder X-ray diffraction and SEM imaging confirmed the rutile phase and spherical morphology of SnO2 NPs. Average particle size has been confirmed to be approximately 3 nm through TEM analysis. Adsorption capacity is attributed to the high surface and presence of oxygen vacancy confirmed through BET and XPS, respectively. To mitigate the leaching of NPs in treated water, the encapsulation of NPs in sodium alginate (SA) has been proposed as an environmentally friendly, biocompatible, and economic solution. This study specifically focuses on investigating the parameters for the encapsulation of NPs within a sodium alginate matrix using CaCl2 as cross-linker, including effect of physical shape of encapsulation, effect of sodium alginate and CaCl2 concentration on the encapsulation efficiency and overall adsorption efficiency. Experimental results indicated that the physical form of encapsulation, such as spherical, wire-like, or irregular shape maintained consistent adsorption efficiency, which indicates its versatility. For effective encapsulation of NPs and adsorption, SA and CaCl2 concentration are suggested to be within the range of 0.2-0.3 g and > 0.5 M, respectively..

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Monolithic electrocatalysts are desired for the electro-Fenton oxidation system. We used a hydrogel consisting of TEMPO-oxidized cellulose nanofibers (TOCN) and cationic guar gum (CGG) to disperse and support Fe-rich sludge and finally obtained a Fe-doped biochar (denoted as C-Sludge@TOCN/CGG) after the freeze-drying and carbonization. This C-Sludge@TOCN/CGG exhibited a porous structure with evenly-distributed Fe due to the inherently three-dimensional porous structure of TOCN/CGG hydrogel and the abundant carbon content. Importantly, Fe and FeO existed in C-Sludge@TOCN/CGG due to the presence of TOCN and CGG during the pyrolysis. The electrochemical properties of C-Sludge@TOCN/CGG demonstrated its good electrocatalytic activity and stability with few side reactions. It had good performance in the electrocatalytic degradation of various azo dyes, attributed to the synergistic integration of TOCN/CGG-derived carbon matrix and carbonized Fe-rich sludge particles. Specifically, two transient radicals (i.e. ·OH and ·O2-) primarily improved the electrocatalytic degradation performance of C-Sludge@TOCN/CGG. This C-Sludge@TOCN/CGG also efficiently degraded a papermill-sourced wastewater containing direct red 23, direct yellow 11, direct black 19 and toner, in which the COD value decreased from 365.12 to 179.13 mg/L within 9 h. This work provides an example of utilizing renewable materials and solid waste to design electrocatalysts to address the wastewater issue.

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This study explores a novel and sustainable approach to reusing textile wastewater for irrigation. This is investigated by degrading Evans blue dye, a model azo dye, in wastewater by combining iron oxide predecessor (IOP) catalyst with gaseous species generated by multi-electrode cylindrical plasma device (MCPD). Analysis of IOP-plasma gaseous species revealed the generation of different types of reactive oxygen species in solution which were responsible for degradation of model dye. Key factors influencing the degradation process were studied by performing optimization experiments that resulted in rates of up to 0.008 L mg-1 min-1, more than twice as fast as using plasma gas treatment alone. These studies included mechanistic response of MCPD generated gaseous species with the IOP. In particular, reusability testing of IOP affirmed the robustness and performance efficiency up to three cycles. Finally, toxicity analysis revealed not only reduced negative effects on plant growth by the treated wastewater, but also it can used as minerals to plants. These findings highlight the feasibility of the IOP-MCPD system as a sustainable and eco-friendly solution to reduce scarcity of water in irrigation by treating textile effluent.

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In this study, conducting polymers composed of polyaniline hydrochloric acid (PANI/HCl) with varying concentrations of a newly synthesized azo-azomethine dye (4-(((Z)-2-hydroxy-5-((Z)-(4-hydroxyphenyl)diazenyl)-3-methoxybenzylidene)amino)benzoic acid) were synthesized using a chemical oxidative polymerization technique. The synthesized azo-azomethine was characterized by FTIR, 1H-NMR, 13C-NMR, and HRMS. The effects of varying the concentration of the dopant azo-azomethine in PANI/HCl on its optical, structural, thermal, and electrical properties were examined using FTIR, UV-Vis, XRD, FESEM, TEM, cyclic voltammetry, and electrical impedance spectra. The results indicate that the optical, direct, and indirect band gaps of the doped polymers decreased from 4.48 and 3.96 eV to 3.91 and 2.49 eV, respectively. The crystalline structure and phase transitions in the doped polymers were examined using X-ray diffraction. Cyclic voltammetry demonstrated that the doped polymers exhibited higher electrochemical conductivity compared to the pure polymer, with the specific capacitance increasing from 161.17 to 816.9 F/g. The electrical impedance spectra revealed the bulk resistance and conductivity of the material. Among all the doped polymers, PANI/HCl with an azo-azomethine concentration of 5 × 10-5 M exhibited lower bulk resistance (10 Ω) and higher electrical conductivity (σ = 50.09 × 10-3 S cm-1).

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The crystal structures of two inter-mediates, 4-amino-3,5-di-fluoro-benzo-nitrile, C7H4F2N2 (I), and ethyl 4-amino-3,5-di-fluoro-benzoate, C9H9F2NO2 (II), along with a visible-light-responsive azo-benzene derivative, diethyl 4,4'-(diazene-1,2-di-yl)bis-(3,5-di-fluoro-benzoate), C18H14F4N2O4 (III), obtained by four-step synthetic procedure, were studied using single-crystal X-ray diffraction. The mol-ecules of I and II demonstrate the quinoid character of phenyl rings accompanied by the distortion of bond angles related to the presence of fluorine substituents in the 3 and 5 (ortho) positions. In the crystals of I and II, the mol-ecules are connected by N-H⋯N, N-H⋯F and N-H⋯O hydrogen bonds, C-H⋯F short contacts, and π-stacking inter-actions. In crystal of III, only stacking inter-actions between the mol-ecules are found.

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Tuning the physical and chemical interaction between metal-metal' (M-M') and metal-support is an ideal way to realize enhanced catalytic activity of metal nanoparticles (NPs). As a proof of concept, herein we report the fabrication of nickel-gold (Ni-Au) alloy nanoparticles attached to N-doped nanoporous carbon (NPC) intervened with MgO (Ni73Au27@MgO-NPC), achieved through the impregnation of metal precursors into Schiff-base network polymer (SNP) framework along with Mg(OH)2 and pyrolysis at 800 °C in N2 atmosphere. With high stability and heterogeneity, the nickel rich Ni73Au27@MgO-NPC exhibited higher catalytic activities with turnover frequencies of 29,272 h-1 (hydrogenation of p-nitrophenol), 93,843 h-1 (degradation of methyl orange), and 2,218 h-1 (epoxidation of stilbene). Enhanced catalytic activity is correlated to the synchronized electron density enhancement in Au, by Ni and MgO/N-rich nanoporous carbon heterostructures, as evident from detailed X-ray photoelectron spectroscopic studies.

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A simple method for purifying water using household items has been developed. The solution containing an environmental pollutant was added to the PET bottle. The lid of the PET bottle was closed, and the bottle was then placed with the lid down in a freezer for 9 h. The pourer of the PET bottle was surrounded by shredded paper scraps as a lagging material. Before the solution was completely frozen, the sample was removed from the freezer. The unfrozen portion (liquid) was sampled. The pollutant was concentrated in the liquid. The remaining frozen portion was completely thawed. As results, the concentration of the pollutant (Congo Red, Cr (VI), Pb (II), pentachlorophenol, fluoride, nitrate, or phosphate) in the thawed liquid was decreased by more than 90% compared with the initial concentration (0.10 mM). PRACTITIONER POINTS: A pollutant in a water sample can be removed by freezing a portion of the solution using a PET bottle, shredder scrap, and household freezer. Fluorine and hexavalent chromium can be removed from water to levels that meet water quality standards. The present method can efficiently remove a wide range of contaminants from water, including azo dyes, heavy metals, and pentachlorophenol.

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The brominated azo dye (BAD) Disperse Blue (DB79) is a widespread environmental pollutant. The long-term toxicological effects of DB79 and the mechanisms thereof must be understood to allow assessment of the risks of DB79 pollution. A dual-omics approach employing in silico analysis, bioinformatics, and in vitro bioassays was used to investigate the transgenerational (F0-F2) toxicity of DB79 in zebrafish at environmentally relevant concentrations and identify molecular initiating events and key events associated with DB79-induced fertility disorders. Exposure to 500 µg/L DB79 decreased fecundity in the F0 and F1 generations by > 30 % and increased the condition factor of the F1 generation 1.24-fold. PPARα/RXR and PXR ligand binding activation were found to be critical molecular initiating events associated with the decrease in fecundity. Several key events (changes in fatty acid oxidation and uptake, lipoprotein metabolism, and xenobiotic metabolism and transport) involved in lipid dysregulation and xenobiotic disposition were found to be induced by DB79 through bioinformatic annotation using dual-omics data. The biomolecular underpinnings of decreased transgenerational fertility in zebrafish attributable to BAD exposure were elucidated and novel biomolecular targets in the adverse outcome pathway framework were identified. These results will inform future studies and facilitate the development of mitigation strategies.

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In vitro plant cultures are able to remove and metabolise xenobiotics, making them promising tools for decontamination strategies. In this work, we evaluated Brassica napus hairy roots (HRs) to tolerate and remove high concentrations of the azo dye Naphthol Blue-Black (NBB). Experiments were performed using both growing and resting culture systems at different pHs. Reuse of HRs biomass was evaluated in successive decolourisation cycles. Proteomics was applied to understand the molecular responses likely to be involved in the tolerance and removal of NBB. The HRs tolerated up to 480 µg mL-1 NBB, and 100 % removal was achieved at 180 µg mL-1 NBB after 10 days using both culture systems. Interestingly, the HRs are robust enough to be reused, showing 55-60 % removal even after three reuse cycles. The highest dye removal rates were achieved during the first 2 days of incubation, as initial removal is mainly driven by passive processes. Active mechanisms are triggered later by regulating the expression of proteins with different biological functions, mainly those related to xenobiotic metabolism, such as hydrolytic and redox enzymes. These results suggest that B. napus HRs are a robust tool that could make a significant contribution to textile wastewater treatment.

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Azo dye-laden textile wastewater must be treated before release due to various health and environmental concerns. Bioremediation of textile wastewater, however, is a challenge owing to its alkaline and saline nature as mesophilic microbes, in general, are either not able to thrive or show less efficiency under such hostile environment. Thus, pre-treatment for neutralization or salinity removal becomes a prerequisite before applying microbes for treatment, causing extra economical and technical burden. Extremophilic bacteria can be the promising bioremediating tool because of their inherent ability to survive and show toxicants removal capability under such extreme conditions without need of pre-treatment. Among extremophiles, halophilic and alkaliphilic bacteria which are naturally adapted to high salt and pH are of special interest for the decolorization of saline-alkaline-rich textile wastewater. The current review article is an attempt to provide an overview of the bioremediation of azo dyes and azo dye-laden textile wastewater using these two classes of extremophilic bacteria. The harmful effects of azo dyes on human health and environment have been discussed herein. Halo-alkaliphilic bacteria circumvent the extreme conditions by various adaptations, e.g., production of certain enzymes, adjustment at the protein level, pH homeostasis, and other structural adaptations that have been highlighted in this review. The unique properties of alkaliphiles and halophiles, to not only sustain but also harboring high dye removal competence at high pH and salt concentration, make them a good candidate for designing future bioremediation strategies for the management of alkaline, salt, and azo dye-laden industrial wastewaters.

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Biomass-based adsorbent materials are characterized by their low cost, environmental friendliness, and ease of design and operation. In this study, biomass-based hydrogel microspheres erbium alginate (SA/Er) with high stability and adsorption properties were prepared by a one-step synthesis method. The prepared materials were characterized and analyzed by SEM-EDS, XRD, TGA, FT-IR, UV-Vis, BET-BJH and XPS, and the adsorption performance of SA/Er was investigated for high concentrations of azo dyes in water. The results showed that the adsorption performance of SA/Er on the azo dyes of direct violet N (DV 1) and direct dark green NB (DG 6) with concentrations of 850 mg/L and 1100 mg/L under the optimal conditions was very high, and the adsorption amount could be up to 692 mg/g and 864 mg/g, respectively. The adsorption process was in accordance with the quasi-secondary kinetic model, which was accomplished by physical and chemical adsorption; the Langmuir isothermal model was able to better respond to the adsorption equilibrium, and the adsorption was dominated by the adsorption of surface monolayers; after seven desorption cycles, the removal of both azo dyes by the adsorbent material could reach >79.7 %. Combined with the results of FT-IR, UV-vis and XPS analysis before and after the adsorption, it was revealed that the adsorption of SA/Er with the dye molecules mainly consisted of hydrogen bonding, electrostatic adsorption and surface complexation, which resulted in the significant adsorption effect on the two azo dyes, and the above results can provide a reference for the treatment of dye wastewater.

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Leveraging date palm spikelets (DPS) as a precursor, this study developed a DPS-derived composite (ZnO@DPS-AC) for water treatment, focusing on methyl orange (MO) removal. The composite was synthesized through ZnCl2 activation and pyrolysis at 600 °C. Comprehensive characterization was conducted using TGA, FTIR, XRD, SEM/EDS, and pHPZC. Characterization revealed a highly carbonaceous material (> 74% carbon) with significant porosity and surface functional groups. ZnO@DPS-AC demonstrated rapid MO removal, achieving over 45% reduction within 10 min and up to 99% efficiency under optimized conditions. The Langmuir model-calculated maximum adsorption capacity reached 226.81 mg/g at 20 °C. Adsorption mechanisms involved hydrogen bonding, π-π interactions, and pore filling. The composite showed effectiveness in treating real wastewater and removing other pollutants. This study highlights the potential of agricultural waste valorization in developing efficient, sustainable adsorbents for water remediation, contributing to circular bioeconomy principles.

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Synthetic dyes are the primary cause of water pollution in industrial regions. Azo dyes account for 60-70% of such dyes used in the textile sector due to their numerous beneficial characteristics. Nevertheless, there is a dearth of knowledge regarding the toxicity of Eriochrome Black T (EBT), a widely used azo dye in the textile industry. Therefore, the current study was designed to investigate the effect of EBT exposure on two catfish species, Heteropneustes fossilis and Clarias batrachus. Following 96 h exposure to 1, 10 and 20 mgL-1 of EBT, the MDA content and activities of SOD, CAT and GR exhibited a rising trend. However, as the concentration of EBT increased in both species, GPx showed decreased activity. EBT exposure also altered gut morphometry as well as the three main digestive enzymes activity (increase in lipase and trypsin activity, while decrease in amylase activity). In addition, the exposure of EBT had a significant impact on the gut microbiota of both species. C. batrachus demonstrated the suppression or absence of beneficial gut commensals (Bacillus and Cetobacterium), whereas H. fossilis revealed the proliferation and appearance of beneficial commensal microbes (Bacillus, Bacteroides, Prevotella, and Megashaera). Furthermore, the expansion or absence of these microbial communities indicated that the gut microbiota of both species was involved in dye digestion, immunity and detoxification. Overall, the percent change calculation of all the selected biomarkers, together with gut microbiota analysis, indicates that C. batrachus was more vulnerable to EBT exposure than H. fossilis. The present investigation effectively demonstrated the toxic impact of EBT on fish health by employing oxidative stress markers, digestive enzymes, and the fish gut microbiota as a promising tool for screening the impact of dye exposure on digestive physiology in toxicological research.

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PURPOSE: Food forensics is an emerging field and the initial part of this review showcases the toxic effects and the instrumental methods applied for the detection of the most commonly used azo dyes. Electrochemical detection has a lot of advantages and hence the significance of the most important techniques used in the electrochemical detection is discussed. The major part of this review highlights the surface modified electrodes, utilized for the detection of the most important azo dyes to achieve low detection limit (LOD). METHODS: A thorough literature study was conducted using scopus, science direct and other scientific databases using specific keywords such as toxic azo dyes, electrochemical detection, modified electrodes, LOD etc. The recent references in this field have been included. RESULTS: From the published literature, it is observed that with the growing interests in the field of electrochemical techniques, a lot of importance have been given in the area of modifying the working electrodes. The results unambiguously show that the modified electrodes outperform bare electrodes and offer a lower LOD value. CONCLUSION: According to the literature reports it can be concluded that, compared to other detection methods, electrochemical techniques are much dependable and reproducible. The fabrication of the electrode material with the appropriate modifications is the main factor that influences the sensitivity. Electrochemical sensors can be designed to be more sensitive, more reliable, and less expensive. These sensors can be effectively used by toxicologists to detect trace amounts of harmful dyes in food samples.

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In this work, the role of ascorbic acid in the process of azo dye degradation was explained. For this purpose, the kinetics of azo dye degradation under different conditions was studied. Among them, the influence of daylight protection/exposition, different concentrations of ascorbic acid (0.567-0.014 mol/dm3), and temperature (20 °C and 50 °C) on the rate of the dyes' degradation was considered. For this process, the kinetic equation was proposed, which indicates that the process of azo dye degradation using ascorbic acid is first order. Moreover, the observed rate constants were determined, and the mechanism of azo dye degradation was proposed. Spectrophotometry results, together with FTIR, fluorescence spectroscopy, and DFT calculations, explain the origin of the decolorization of the azo dyes and highlight the role of ascorbic acid in this process. Detailed analysis of the obtained products indicates that the process itself goes through several stages in which equally or more toxic compounds are formed. Obtained results from LCMS studies indicate that during tropaeolin OO degradation, 1,2-Diphenylhydrazine (m/z 185.1073) is formed. Thus, the process of azo dye degradation should be carried out in protective conditions. The proposed mechanism suggests that ascorbic acid at high content levels can be used for azo dye degradation from aqueous solution and can be an alternative method for their removal/neutralization from waste solution but with caution during the process.