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Anthraquinone dyes, which include an anthraquinone chromophore group, are the second-largest among dye classes, which is often employed in textile manufacturing. A significant number of anthraquinone dyes get into the environment, creating severe pollution since many of these dyes have intricate and stable structures. Currently, microbiological treatment of wastewater is an economically and feasibly viable solution for treating printing and dyeing wastewater, and there are growing reports of biodegradation of anthraquinone dyes. In this review, we outline the current advances in the biodegradation of anthraquinone dyes, summarizes dyes biodegradation by bacterial, fungal, and algae strains, factors influencing dyes biodegradation, current methods in enhancing dyes biodegradation, resuscitation of viable but non-culturable (VBNC) bacteria for better microbial performance, and potentials of VBNC bacteria in degrading dyes. Finally, future directions and important areas for study are given, and such efforts are anticipated to improve the anaerobic degradation process.

The biodegradation and detoxification potential of two azo disperse dyes and one anthraquinone disperse dye (commonly found in the wastewater effluent of a local textile industry) was investigated by using a consortium of six indigenously isolated bacteria from the wastewater stream in this study. It was found that consortium of bacteria can decolorize disperse red 167.1 dye at concentrations of 50, 150, and 250 mg/L more effectively and the other two dyes, disperse red 54 and disperse blue 60 dyes were decolorized more efficiently by individual bacteria. Bacterial strains namely Bacillus cereus AU50, Bacillus sphaericus, Paenibacillus pocheonensis sp. C-2, Paenochrobactrum glaciei, Bacillus subtilis and Brevibacillus panacihumi were isolated from a local textile industry wastewater stream (effluent) located in Ludhiana, Punjab, India and were used in this study to treat textile industry wastewater containing toxic dyes. The consortium (comprising of these six bacterial isolates) resulted in the maximum rate of decolorization (82.76 ± 0.255%) for disperse red 167.1 dye at three different concentrations within 24 h, with the increase in enzymatic activities whereas Bacillus cereus exhibited maximum rate of decolorization (84.17 ± 0.16%) for disperse red 54 and (76.29 ± 0.51%) for disperse blue 60 in 24 h.In addition, degradation pathways of selected dyes were investigated based on the intermediates identified by GC–MS and followed by phytotoxicity assay. Results of this study show the potential of naturally occurring bacteria in the treatment of wastewater by biodegrading textile dyes in the wastewater streams. The findings of this research will result in developing economically viable bio-filters where bacterial strains can be used to biodegrade textile industry pollutants before this wastewater enters local rivers and streams, and help improve water quality of rivers and aquatic ecology.

Dyes are among the main environmental pollutants, due to the high amount of discharge of wastewater, lost in the dyeing process, without any further treatment. Anthraquinone dyes are stable and resistant in the aquatic system. Among the methods that have been applied to remove these dyes from wastewaters, adsorption on activated carbon has been reported as a very effective technique, and its modification with oxides and hydroxides of metals have been used to increase its surface area. In the present study, the production of activated carbon was originated by coconut shells, and a mixture of metals and metalloids, such as magnesium, silicate, lanthanum, and aluminum (AC-Mg-Si-La-Al), was used for its subsequent modification and applied to Remazol Brilliant Blue R (RBBR) removal. AC-Mg-Si-La-Al surface morphology was studied by BET, FTIR, and SEM methods. For the evaluation of AC-Mg-Si-La-Al, several parameters, such as dosage, pH, contact time, and initial RBBR concentration were studied. According to the results, in pH 5.0 ± 0.1, the dye percentage rate reached 100% by applying 0.5 g/L. Therefore, the optimal dose of 0.4 g/L and pH 5.0 ± 0.1 are selected, which leads to 99% removal of RBBR. The experimental data found to better fit to Freundlich isotherm ( R 2  = 0.9189) and pseudo-second-order kinetic ( R 2  = 0.9291) models and 4 h were the sufficient time for adsorption. According to thermodynamics, a positive value of ∆H 0 (19.661 kJ/mol) suggests the endothermic nature of the process. The AC-Mg-Si-La-Al adsorbent was able to regenerate after 5 cycles of use, showing only a 17% decrease in its efficiency. Because of its effectiveness in full RBBR removal, AC-Mg-Si-La-Al could be further examined for the removal of several other dyes, even anionic or cationic. Graphical Abstract

By combining molecular dynamics (MD) simulations and density functional theory (DFT), the influence of dye structure on the optical modulation properties of negative-mode guest–host liquid crystal (GHLC) systems was systematically investigated. Firstly, the reliability of the simulation method was validated by comparing the performance parameters of the GHLC system obtained from simulations with those from experimental results. Subsequently, a series of guest dye molecules, along with their mixtures with negative dielectric anisotropy mesogens, were designed and analyzed. This exploration focused on how variations in dye terminal chain lengths, substitution positions, and substituent group properties affect dye molecular geometry, dye alignment within the host, transition dipole orientation, absorption spectra, and electronic excitation properties. Our findings suggest that dye molecules with a flexible terminal chain substitution of five carbon atoms, positioned at the 2 and 6 locations on the anthraquinone core, exhibit higher order parameters, favorable for enhancing dichroic performance. Moreover, introducing different α-substituents further influences the dye orientation and electronic behavior within the host. These results highlight that structural modifications of anthraquinone-based dyes allow for the design of high-dichroic-ratio materials with customized absorption properties. Overall, our results provide a beneficial understanding of the structure–property relation in GHLC systems, offering valuable guidance for designing high-performance dye molecules and advanced optoelectronic materials in future research.

The textile industry widely uses reactive anthraquinone dyes, which exhibit strong resistance to color removal and generate substantial volumes of wastewater containing significant quantities of residual dye requiring treatment prior to discharge. As part of a study aimed at reusing rather than discharging spent reactive anthraquinone dyebaths, Reactive Blue 4 (RB4) dye was used in dyeing cotton, and the generated spent dyebaths were biologically decolorized using a fluidized bed reactor (FBR) operated under hypersaline conditions at a salt concentration of 100 g NaCl/L, which is typically found in commercial spent reactive dyebaths. Across five consecutive runs, the FBR achieved a mean decolorization efficiency of 91.2 ± 2.8% within a 6 h incubation period. The quality of cotton dyed with the treated and reused spent dyebaths was evaluated through shade reproducibility and color consistency assessments. Five repetitive dyeings using the biologically decolorized dyebaths showed that the ΔEcmc fabric color difference values were 0.58~0.80, which were lower than the industry-accepted value of 1.0. This study demonstrates that biologically decolorized spent dyebaths can be effectively reused, offering substantial reductions in water and salt consumption and improving the economic and environmental sustainability of the reactive dyeing process.

A TiO2/ZnO oxide system was proposed as a support for the immobilization of laccase from Trametes versicolor (LTV). The obtained TiO2/ZnO/LTV biocatalytic system was then applied in the decolorization/degradation of C.I. Reactive Black 5 and C.I. Acid Green 25 dyes. The efficiency of immobilization was evaluated based on catalytic properties (Bradford method, oxidation reaction of 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and physicochemical (spectroscopic, porous, electrokinetic) analysis. The immobilization process was carried out with high performance (99.4%). Immobilized laccase retained about 40% of its activity in the whole analyzed temperature range and after 10 reaction cycles. Immobilization efficiency was also indirectly confirmed by the presence of characteristic functional groups (–C–H and –C–O), nitrogen and carbon on the TiO2/ZnO/LTV biocatalytic surface, identified by spectroscopic analyses. The increase in the surface area to 126 m2/g, change of isoelectric point (2.0) and zeta potential ranges (from +12.0 to −20.0 mV) after the immobilization process were also observed. The results show that the designed biocatalytic system enables the removal of acid dyes (C.I. Reactive Black 5 and C.I. Acid Green 25) with high efficiency (99% and 70%, respectively). Mass spectroscopy analysis indicated possible degradation products formed by the cleavage of N=N and C–N bonds.

Treatment of textile wastewater using heterogeneous photocatalysis began in the the last decade and attracted the attention of researchers due to its versatile application. The variety of applications of Ti[O.sub.2] as a photocatalyst was due toits numerous positive properties, such as low operating temperature, biologically inert nature, low energy consumption, water insolubility, availability and photoactivity, low toxicity, high chemical stability, suitable flat band potential, narrow bandgap and the fact that it is environmentally benign. Heterogeneous UV-Ti[O.sub.2] photocatalysis is capable of removing organic pollutants from textile wastewater; this has been widely studied, with the technology also having been commercialized in many developing countries. Decolorization of anthraquinone dye Reactive Blue 19 (RB 19) by heterogeneous advanced oxidation processes Ti[O.sub.2]/UV/[H.sub.2][O.sub.2], Ti[O.sub.2]/UV/KBr[O.sub.3] and Ti[O.sub.2]/UV/[(N[H.sub.4]).sub.2][S.sub.2][O.sub.8] was studied under different conditions and in the presence of electron acceptors such as hydrogen peroxide ([H.sub.2][O.sub.2]), potassium bromate (KBr[O.sub.3]) and ammonium persulphate ([(N[H.sub.4]).sub.2][S.sub.2][O.sub.8]). Decolorization was very fast for all three processes, and complete dye decolorization was achieved in 10 min. The effect of various ions ([Cl.sup.-], S[O.sub.4.sup.2-] and HC[O.sub.3.sup.-]) on RB 19 decolorization was also studied. The optimal condition for the decolorization of the dye were determined to be: Ti[O.sub.2] concentration 1 g-drrr (3), electron acceptor concentration 30.0 mmol*[dm.sup.-3], dye concentration 50.0 mg*[dm.sup.-3], UV intensity 1 950 [micro]W*[cm.sup.-2], at temperature 25 [+ or -] 0.5[degrees]C. In addition, experiments were performed and compared in three different matrices. In the surface water and dyebath effluent water, the removal efficiency for RB 19 was lower than that achieved in the deionized water because of the interference of complex constituents in the surface water and effluent. LC-MS analysis was carried out and the detected intermediates were compared with the previously published data for anthraquinone dyes. KEYWORDS anthraquinone dye electron acceptors photocatalysis Reactive Blue 19 titanium dioxide

The aim of this study was to investigate covalent immobilization of horseradish peroxidase (HRP) on magnetic nanoparticles (Mag) encapsulated in calcium alginate beads (MABs) for color degradation, combining easy and fast removal of biocatalyst from the reaction mixture due to its magnetic properties and strong binding due to surface alginate functional groups. MABs obtained by extrusion techniques were analyzed by optical microscopy, FEG-SEM and characterized regarding mechanical properties, magnetization and HRP binding. HRP with initial concentration of 10 mg/gcarrier was successfully covalently bonded on MABs (diameter ~1 mm, magnetite/alginate ratio 1:4), with protein loading of 8.9 mg/gcarrier, immobilization yield 96.9% and activity 32.8 U/g. Immobilized HRP on MABs (HRP-MABs) was then used to catalyze degradation of two anthraquinonic dyes, Acid Blue 225 (AB225) and Acid Violet 109 (AV109), as models for wastewater pollutants. HRP-MABs decolorized 77.3% and 76.1% of AV109 and AB225, respectively after 15 min under optimal conditions (0.097 mM H2O2, 200 mg of HRP-MABs (8.9 mg/gcarrier), 0.08 and 0.1 g/mg beads/dye ratio for AV109 and AB225, respectively). Biocatalyst was used for 7 repeated cycles retaining 75% and 51% of initial activity for AB225 and AV109, respectively, showing potential for use in large scale applications for colored wastewater treatment.

The generation and accumulation of environmental pollutant of industrial contaminations gave it a big challenge to develop many removal strategies of pollution. Textile dyes as dispersive blue 26 dye affected by several decolorization parameters like as temperature, initial pH and initial concentrations of dye. These variables parameter were studied on ZnO-dye suspension solution in dark and photoreaction conditions. In dark reaction, with using thermodynamic and kinetic parameters such as ΔH°, ΔS°, ΔG° and Ea, the type of adsorption was determined and found as a physical adsorption, exothermic and fast reaction. Moreover, the results demonstrated that the photoreaction process under UV-light-A would elevated the rate of reaction, percentage of decolorization and accelerated the half-time of decolorization reaction in 50 ppm of dye. The photoreaction of decolorization of this dye acts as pseudo first order kinetics with endothermic, less random less, non spontenous and fast reaction.

Decolorization of anthraquinone dye Reactive Blue 19 (RB19) with sulfate radicals generated in situ from persulfate and zero-valent iron (ZVI) was investigated. The effects of initial solution pH, initial concentration of RB19, ZVI and persulfate, reaction temperature and common dissolved anions were studied. 100% color removal efficiency and 54% TOC removal efficiency were achieved in 45 min with an initial RB19 concentration of 0.1 mM under typical conditions (pH 7.0, 0.8 g L−1 ZVI, 10 mM persulfate and 30 °C). The decolorization efficiency of RB19 increased with higher iron dosage, higher initial persulfate concentration, and higher reaction temperature. It is also an acid driven process. The decolorization process followed pseudo-first order kinetics and the activation energy was 98.1 kJ mol−1. RB19 decolorization was inhibited by common dissolved anions such as Cl−, NO3−, H2PO4− and HCO3− since they reacted with sulfate radicals that retarded the oxidation process. The experiment demonstrated that the combination of persulfate and ZVI was a promising technology for the decolorization of dye wastewater.