Search Results (861)

Synthetic dyes such as Methyl Orange (MO) and Congo Red (CR) are recalcitrant, toxic, mutagenic and resistant to conventional biodegradation, and their industrial discharge continues to contaminate aqueous ecosystems worldwide. This study reports the synthesis and characterization of a poly(MMA-co-2-AEMA) copolymer gel (Fe-Copolymergel-NH₂) treated with FeCl₃. It evaluates its adsorption performance from aqueous solution against the anionic azo dyes MO and CR. Extensive characterization using N₂ adsorption–desorption at 77 K, FTIR-ATR, XPS, SEM, and TEM revealed that Fe modification significantly improved the material’s textural properties, increasing its specific surface area from 8.11 m²/g to 12.55 m²/g and creating a highly irregular, interconnected, sponge-like morphology. Adsorption experiments showed that Fe-Copolymergel-NH₂ achieved competitive Langmuir maximum monolayer adsorption capacities of 3201.9 mg/g for CR and 1089.8 mg/g for MO. Kinetic modeling demonstrated that adsorption strictly followed the PSO model, primarily governed by chemisorption via electrostatic attractions and complexation within the internal structure at Fe³⁺ coordination centers. Thermodynamic analysis revealed that the dye removal process was spontaneous and exothermic. Consequently, the successful integration of Fe³⁺ coordination centers resolves the adsorption and structural limitations of pure polymer matrices, positioning Fe-Copolymergel-NH₂ as a highly promising and efficient adsorbent for the remediation of dye-contaminated industrial wastewater. Full article

This study focused on a comparative analysis of oxygen and hypochlorite ions as cathodic electron acceptors in microbial fuel cell (MFC) reactors treating wastewater containing methylene blue dye. One of the major factors influencing MFC performance is the choice of cathodic electron acceptor, which directly affects electrochemical efficiency and treatment performance. Based on the analysis, the hypochlorite ion-assisted MFC (MFC-H) performed better in its electrochemical properties, achieving a maximum power density of 115.2 mW m⁻², which was much higher than that of the oxygen-cathode MFC (29.44 mW m⁻²). The MFC-H system also exhibited higher coulombic efficiency, a more positive cathode potential, and greater decolorization efficiency (88%) compared to the oxygen-cathode configuration (79%). The enhanced performance of the hypochlorite-based system indicates more effective electron transfer and faster cathodic reaction kinetics, thereby improving energy recovery and dye removal. These results demonstrate that hypochlorite can serve as an effective alternative cathodic electron acceptor in MFCs for treating dye-containing wastewater. Full article

Betalains are water-soluble pigments containing nitrogen, and they exist naturally in the plants of the order Caryophyllales. They have gained increasing attention in recent years because of their intense colours, antioxidant activity, and safety, thus making them suitable replacements for artificial dyes. The increasing interest in natural pigments has led to intensified research on betalain biosynthesis and optimization of pigment production. Nonetheless, their application in industry faces limitations, such as their low natural occurrence, sensitivity to environmental conditions, and instability during manufacturing and storage. Unlike previous reviews that primarily focused on betalain chemistry, biosynthesis pathways, or biological activity, the present review highlights recent developments in the engineering of the biosynthesis pathways, synthetic biology, elicitation approaches, omics-based pathway identification, and nanobiotechnology for betalain pigments. Special attention is paid to the comparison of plant, plant cell, yeast, and bacterial production systems, as well as recent advancements towards industrial production of betalain pigments and bottlenecks in the commercialization of sustainable betalain bio-factories. Full article

Synthetic dyes released from industrial effluents represent an important environmental challenge due to their persistence and toxicity. In this study, for the first time, a crude extracellular laccase preparation from Bjerkandera adusta TMF1 produced by solid-state fermentation on a wheat/barley bran mixture was immobilized onto glutaraldehyde-activated alginate beads and applied for mediator-free Bromophenol Blue (BPB) decolorization. The produced laccase showed high activity (51.51 IU/mL; 128.77 IU/g dry substrate), while immobilization efficiency reached 98.84% with 88.39% residual activity under optimal immobilization conditions. FTIR and SEM analyses indicated successful enzyme immobilization and structural changes in the alginate matrix. Under optimal conditions (50 mg/L BPB, pH 5, 30 °C), free and immobilized crude extracellular laccase preparation achieved 73.02% and 78.12% decolorization within 1 h, respectively, without the addition of synthetic redox mediators. The immobilized preparation retained decolorization ability during repeated use, maintaining more than 50% decolorization efficiency after the third cycle. HPLC analysis indicated changes in the chromatographic profile of BPB after enzymatic treatment, while phytotoxicity and antimicrobial assays suggested reduced toxicity of the treated samples toward the tested organisms. These results demonstrate that a crude extracellular laccase preparation produced by B. adusta TMF1 can serve as an efficient immobilized biocatalyst for Bromophenol Blue decolorization while supporting the sustainable valorization of agro-industrial residues for low-cost enzyme production. Full article

Natural dyes are attracting increasing attention owing to their environmental compatibility and safety profile, particularly in contrast to synthetic dyes, which may contain hazardous compounds posing risks to human health and ecosystems. In this study, crude phycocyanin extract from the cyanobacterium Limnothrix planctonica (KU.B3) was evaluated as a natural blue color for textile screen printing. The investigation encompassed the optimization of curing temperatures and assessment of colorfastness under simulated-use conditions, including washfastness, lightfastness, and rubfastness. The results indicated that a curing temperature of 110 °C represented the practical upper limit for maintaining phycocyanin chromophore stability during the screen printing process. Among the additive compound evaluated, copper sulfate conferred the greatest resistance to UV-induced fading; the compound-treated fabric retained a K/S value of 0.83 ± 0.03 following 5 h of UV exposure, representing a decline of approximately 16% compared with approximately 25% in the untreated control. However, washfastness was poor across all treatment conditions (grey scale score 1), indicating that under the binder system investigated in this study phycocyanin may be more suitable for decorative rather than washable textile applications. Full article

This study evaluated the potential of biochar (BC) produced from olive mill solid waste (OMSW) for methylene blue (MB) removal from synthetic solutions. BC was prepared at pyrolysis temperatures of 400 °C, 500 °C, and 600 °C for residence times of 1, 3, and 5 h. The produced BCs were characterized using BET, SEM, FTIR, XRD, zeta potential, and elemental analysis, while adsorption performance was assessed through equilibrium, kinetic, and thermodynamic studies. The results demonstrated that increasing pyrolysis temperature improved the physicochemical properties of BC. The BET surface area increased from 1.34–1.9 m²/g at 400 °C to 135.23 m²/g at 600 °C, accompanied by enhanced pore volume and the development of a highly porous structure observed by SEM. FTIR analysis revealed progressive transformation of oxygen-containing functional groups, while XRD indicated increased structural ordering and carbonization at higher pyrolysis temperatures. BC produced at 600 °C exhibited the highest adsorption performance, achieving a maximum MB removal efficiency of 99.57% and an adsorption capacity of 17 mg/g. Adsorption kinetics were best described by the pseudo-second-order model (R² > 0.99), indicating strong adsorbate–adsorbent interactions. Equilibrium results were best fitted by the Langmuir isotherm with a maximum R² of 0.9963, suggesting predominantly monolayer adsorption, whereas the Freundlich model showed a maximum R² of 0.9788 under elevated temperature and prolonged contact conditions, indicating surface heterogeneity and multilayer adsorption. Thermodynamic analysis confirmed that MB adsorption was spontaneous (ΔG° = −38.61 to −47.57 kJ/mol), predominantly endothermic (ΔH° up to 4.11 kJ/mol), and associated with increased randomness at solid–solution interface (ΔS° > 0). Overall, BC produced at 600 °C for 3–5 h exhibited the most favorable structural characteristics and adsorption performance, highlighting its potential as a sustainable and low-cost adsorbent for wastewater treatment applications. Full article

Synthetic azo dyes may be fraudulently added to paprika powder to intensify color, creating a need for rapid, at-line screening before confirmatory chromatographic analysis. This study evaluated handheld laser-induced breakdown spectroscopy (LIBS) for the screening of sodium-salt azo dye adulteration represented by Allura Red (E129), Ponceau 4R (E124), and Orange II in paprika powder. Paprika was spiked at 17 levels (0–6% w/w) in three independent batches, mixed with Al₂O₃ binder, dried, pelletized, and measured with a portable SciAps Z-903 under argon in the broad 190–950 nm region. The calibration models were developed using SNV-pretreated spectra and partial least squares regression with test-set validation based on a 70/30 split by concentration level. The main concentration-related response was increased Na emission, consistent with the sodium-salt form of the dyes, while Al emission showed an inverse matrix-/plasma-coupled trend despite the constant binder fraction. Full-spectrum models gave R²_TSV values of 0.845–0.875 and RMSETSV values of 0.638–0.716% (w/w), using 4–5 latent variables. Outlier trimming improved prediction for Allura Red and Orange II, while regression coefficient-uncertainty variable selection reduced model complexity to 2–3 latent variables with dye-dependent effects. Since sodium-salt azo dyes are commonly used as adulterants in paprika powder, the Na-dominated LIBS response demonstrates good potential for rapid at-line screening. Nevertheless, as LIBS does not directly confirm dye identity, complementary confirmatory analysis using spectroscopic or chromatographic methods remains necessary. Full article

Industrial wastewater containing synthetic dyes is difficult to treat because many dyes are chemically stable, highly colored, and resistant to natural degradation. In this study, a Ag₂CO₃/montmorillonite (Ag₂CO₃/MMT) composite photocatalyst was synthesized by an in situ precipitation method using acid-activated MMT as a low-cost clay support. The prepared material was characterized by XRD, FTIR, SEM, BET, and UV–Vis diffuse reflectance spectroscopy to evaluate its structural, morphological, textural, and optical properties. XRD and FTIR confirmed the formation of crystalline Ag₂CO₃ on the MMT support, while SEM analysis showed dispersed Ag₂CO₃ surface particles/deposits on the clay sheets. BET analysis indicated that the composite retained mesoporosity after Ag₂CO₃ deposition, which is beneficial for dye adsorption and diffusion. The photocatalytic performance was evaluated using methylene blue (MB) and methyl orange (MO) under visible-light irradiation. The Ag₂CO₃/MMT composite showed efficient dye decolorization, with faster degradation of cationic MB than anionic MO, mainly due to stronger electrostatic interaction between MB and the negatively charged catalyst surface. Kinetic analysis followed a pseudo-first-order model, with apparent rate constants of 0.036 min⁻¹ for MB and 0.021 min⁻¹ for MO. Operational parameters, including solution pH, irradiation time, and catalyst dosage, strongly influenced photocatalytic efficiency. Reactive species trapping experiments indicated that superoxide radicals (•O₂⁻) and photogenerated holes (h⁺) were the dominant oxidative species. The catalyst retained more than 91% activity after four cycles, indicating good recyclability under the tested conditions. These results suggest that Ag₂CO₃/MMT is a promising visible-light-responsive photocatalyst for dye-contaminated wastewater treatment. Full article

In this study, olive mill leaves (OMLs), a waste generated during the olive cleaning at the mill, were used as an adsorbent for removing methylene blue (MB) from aqueous solution. An Olive Leaf-based Adsorbent (OLA) was prepared from OMLs with minimal processing. The maximum adsorption capacity experimentally measured for OLA was q_e = 12.8 mg∙g⁻¹. The adsorption of MB by OLA, primarily governed by electrostatic attraction, pore diffusion and weak interactions with functional groups of the leaves, is well described by the Koble–Corrigan isotherm model and pseudo-second-order kinetic model. The performance of OLA under practical environmental conditions, such as in synthetic wastewater, remained unchanged compared to tests carried out in ideal conditions. The possibility of regenerating OLA with methanol, HCl and NaCl solutions was demonstrated, allowing the material to be reused for at least three cycles with unchanged performance. A life cycle assessment was conducted to compare the impacts of OLA production with those of activated carbon, a benchmark for adsorbent materials. Overall, despite its moderate adsorptive performance, OLA stands out as a highly sustainable material for dye removal from polluted waters, owing to its exceptional cost-effectiveness, reusability, and minimal environmental impact. Full article

Synthetic dyes from textile effluents represent a major environmental concern due to their persistence and toxicity. Reactive Black 5 (RB5) is widely used in the textile industry and is commonly applied as a model azo compound in sorption studies. This study comparatively evaluates the sorption performance of raw and carbonized sorbents derived from industrial hemp (Cannabis sativa L.) biowaste using an integrated experimental and theoretical approach. The sorbents were prepared through washing, drying, and phosphoric acid-assisted carbonization followed by pyrolysis. Structural and physicochemical properties were characterized using elemental analysis, FTIR spectroscopy, and SEM microscopy. Sorption performance toward RB5 was investigated through batch kinetic and equilibrium experiments, supported by kinetic (pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models) and isotherm (Langmuir, Freundlich, and Temkin) modeling. Molecular docking simulations were performed to provide mechanistic insight into dye–sorbent interactions. Both materials exhibited rapid sorption kinetics, reaching equilibrium within approximately 45 min, with the pseudo-second-order model suggesting that surface-controlled interactions dominate the sorption rate. Molecular modeling, based on extensive conformational sampling, indicated a strong binding affinity between RB5 and cellulose-based structures, primarily associated with hydrogen bonding and other favorable noncovalent interactions. In contrast, graphene-based models revealed sorption governed by π–π interactions and confinement effects, supporting the experimentally observed differences between raw and carbonized sorbents. Full article

Wastewater contamination with synthetic organic dyes is a significant environmental challenge. Zinc oxide (ZnO) has attracted considerable attention as a non-toxic, multifunctional material for electronics, optics, piezoelectric devices, and photocatalysis, where its performance is strongly governed by morphology. In this work, we investigate the effect of hexamethylenetetramine (HMTA) on the formation and photocatalytic behavior of ZnO nanostructures synthesized from different zinc precursors, namely zinc acetate and zinc nitrate, via a one-step sol–gel process at low temperature without any post-treatment. All samples crystallize in the hexagonal wurtzite phase without detectable impurities, and the incorporation of HMTA leads to smaller, more uniform rod- and flake-like nanostructures. Although ZnO derived from zinc acetate without HMTA exhibits the highest specific surface area, ZnO synthesized in the presence of HMTA shows more favorable crystallinity, morphology, and pore connectivity, which together enhance charge separation and reactive oxygen species generation. As a result, ZnO samples synthesized with HMTA exhibit improved photocatalytic degradation of rhodamine B under UV irradiation. Full article

The increasing demand for cleaner coloration of synthetic textiles has renewed interest in plant-based dyes; however, limited dye–fiber affinity and shade durability remain major challenges in nylon dyeing. This study developed a mordant-free dyeing process for nylon fabric using Terminalia catappa leaf extract by optimizing extraction pH, dyebath pH, dyeing time, and temperature. Mature T. catappa leaves were aqueously extracted under acidic, neutral, and alkaline conditions, followed by systematic dyeing optimization. The dyed fabrics were evaluated using color strength (K/S), CIELAB color coordinates, standard fastness tests, FTIR spectroscopy, and FE-SEM analysis. Alkaline extraction followed by acidic dyeing produced the highest dye uptake. The optimum condition was extraction pH 11, dyebath pH 3, 120 °C, and 60 min, yielding a maximum K/S value of 21.94 with ΔL, Δa, and Δb values of −54.25, 8.03, and 24.92, respectively. FTIR and SEM results supported possible dye–fiber interaction through hydrogen bonding, electrostatic attraction, and surface/inter-filament dye deposition without obvious fiber damage. The optimized fabric showed very good washing, dry rubbing, perspiration, and saliva fastness, good light fastness, excellent ultraviolet protection, and slightly lower wet rubbing fastness. Overall, T. catappa leaf extract offers a promising mordant-free route for durable nylon coloration. Full article

The growing emphasis on sustainability in fashion and textile systems has renewed interest in natural dyes as both ecological colorants and expressive design tools. This study investigates a design-oriented approach to sustainable screen-printing by combining plant-based dyestuffs with conceptual pattern development and scientific performance analysis. It assumes that natural dyes can function not only as environmentally responsible alternatives to synthetic colorants but also as active design materials within contemporary textile printing. Accordingly, the study asks how dye type and fiber type influence color performance, fastness behavior, and fiber–dye interaction in screen-printed natural fabrics. Natural dyes derived from Rubia cordifolia (Rubia^®), Punica granatum peel (Mallow^®), and Morus alba leaves (Leafy Green^®) were applied to 100% cotton, linen, and silk fabrics through an environmentally responsible screen-printing process. A garlic-inspired motif was developed to support the study’s visual and conceptual framework by representing circularity, low-impact agriculture, and cultural sustainability. Colorimetric properties (L*, a*, b*, K/S, ΔE) were measured by spectrophotometric analysis, while washing and rubbing fastness were evaluated according to international standards. FTIR spectroscopy was used to examine fiber–dye interaction mechanisms, and statistical significance was tested through two-way ANOVA. The findings show that fabric type is the dominant factor affecting color performance, with cotton exhibiting the highest color strength due to its cellulose-rich and hydroxyl-dense structure. Rubia^® produced the darkest and most saturated tones, whereas Mallow^® yielded lighter pastel-like shades. FTIR results indicated that dye fixation occurred primarily through non-covalent interactions, explaining the balance between aesthetic richness and moderate fastness. The study offers a replicable model for environmentally responsible, design-oriented textile production that integrates material innovation with cultural and visual narratives. Full article

Synthetic textile dye solutions are commonly used as controlled model systems to evaluate adsorbent performance before application to real textile wastewater matrices. In this study, a magnetic adsorbent was developed by functionalizing pomegranate peel-derived biochar with iron oxide (Fe₃O₄) nanoparticles and was applied for chemical oxygen demand (COD) removal from synthetic aqueous solutions containing three individual acid dyes: Buracid Yellow BGL, Buracid Navy Blue RL, and Buracid Red FN. The effects of adsorbent loading, pH, contact time, and dye type on COD removal were systematically evaluated and optimized using Response Surface Methodology (RSM). The experimental results showed that adsorbent loading, pH, and contact time significantly influenced COD removal efficiency. The developed quadratic model showed good explanatory performance, with R² = 83.42% and adjusted R² = 79.28%, while the predicted R² value of 72.65% indicated moderate predictive capability. Under the identified optimum operating region (pH 7.4, contact time 35 min, and adsorbent loading 80 g/L), COD removal efficiency reached up to 84%, depending on dye type. These findings indicate that Fe₃O₄-modified pomegranate peel biochar is a promising adsorbent for COD reduction from synthetic textile dye solutions. However, further validation using real textile wastewater is required to evaluate matrix effects caused by salts, surfactants, suspended solids, mixed dyes, and other textile auxiliaries. Full article

Synthetic food dyes represent an important category of chemical contaminants with potential phytotoxic, genotoxic, and ecotoxic effects on living organisms and natural ecosystems. The present study aimed to evaluate the physiological effects induced by three commercial food dyes on the model organism Allium cepa, using the Allium test under hydroponic conditions. A total of 105 bulbs were exposed for 48 h to two different concentrations of each dye, for which gravimetric and physiological parameters, such as biomass, water content, mineral and organic composition, growth inhibition index, tolerance index, and relative growth rate, were subsequently analyzed. Statistical analyses revealed significant differences between batches for all evaluated parameters, indicating effects mainly dependent on the type of dye applied. The results suggest that exposure to synthetic food dyes causes disturbances in water balance, biomass accumulation and mineral homeostasis, confirming the phytotoxic potential of these compounds and the utility of the Allium test in the biomonitoring of chemical contaminants. Full article