Search Results (359)

Commercially available bismuth subcarbonate (Bi₂O₂CO₃) was treated with nitric acid and the surfactant cetyltrimethylammonium bromide. The treated catalysts exhibited enhanced photocatalytic activity compared to pure Bi₂O₂CO₃ in the decolorization of rhodamine B (RhB) under visible light irradiation. The absorbance at 554 nm gradually decreased over time and disappeared completely within 80 min. The crystal structure, morphology, and optical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The improved photocatalytic activity of the treated catalysts was attributed to partial carbonate removal and the formation of Bi⁵⁺ species. Scavenger experiments indicated that superoxide radicals (·O₂⁻) and photogenerated holes (h⁺) played significant roles in the photocatalytic decolorization of RhB. Full article

Synthetic dyes are highly recalcitrant and are discharged in large volumes in industrial wastewater, which represents a serious environmental pollution problem. Biological methods for dye degradation are a potentially effective option for these synthetic products. In this study, a strain of Pleurotus ostreatus was used to evaluate the decolorization of the Remazol Brilliant Blue R (RBBR) dye added to the culture medium in the exponential growth phase of the fungus. The dye removal capacity of live and inactivated pellets by biosorption, as well as the enzymatic degradation of the dye using a cell-free culture broth considered an extracellular extract (EE), were also evaluated. The activity of laccase and dye-decolorizing peroxidase was determined in both the EE and the intrapellet extract (IPE); their values increased in the presence of dye in the culture medium. A decolorization of 98.5% and 98.0% was obtained in the culture broth and by the EE, respectively; biosorption of the dye by the inactivated pellets was 17 mg/g. The results suggest that the decolorization of the dye is primarily enzymatic, although there are also bioadsorption and bioaccumulation of the dye, which is then enzymatically degraded, and could be used as a carbon source. Full article

This study investigates the influence of divalent metals—(Mg(II), Co(II), and Ni(II)) in layered double hydroxides (LDHs), with a constant trivalent Fe(III) component—on the decoloration of crystal violet and methyl blue dyes via a Fenton-type oxidation reaction. The catalysts, synthesized by co-precipitation and hydrothermal treatment, were tested in both hydroxide and oxide forms under varying agitation conditions (0 and 280 rpm). A 2² × 3 factorial design was used to analyze the effect of the divalent metal type, catalyst phase, and stirring. The Mg/Fe oxide, with the highest BET surface area (144 m²/g) and crystallite size (59.7 nm), showed superior performance—achieving up to 98% decoloration of crystal violet and 97% of methyl blue within 1 h. The kinetic analysis revealed pseudo-second-order and pseudo-first-order fits for crystal violet and methyl blue, respectively. These findings suggest that LDH-based catalysts provide a fast, low-cost, and effective option for dye removal in aqueous systems. Full article

Spent coffee grounds (SCG) are a widely available agro-industrial residue rich in carbon and phenolic compounds, presenting significant potential for biotechnological valorization. This study evaluated the use of SCG as a suitable substrate for fungal laccase production and the application of the resulting fermented biomass (RFB), a mixture of fermented SCG and fungal biomass as a biosorbent for textile dye removal. Two fungal strains, namely Lentinus crinitus UCP 1206 and Trametes sp. UCP 1244, were evaluated in both submerged (SmF) and solid-state fermentation (SSF) using SCG. L. crinitus showed superior performance in SSF, reaching 14.62 U/g of laccase activity. Factorial design revealed that a lower SCG amount (5 g) and higher moisture (80%) and temperature (30 °C ± 0.2) favored enzyme production. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analyses confirmed significant structural degradation of SCG after fermentation, especially in SSF. Furthermore, SCG and RFB were chemically activated and evaluated as biosorbents. The activated carbon from SCG (ACSCG) and RFB (ACRFB) exhibited high removal efficiencies for Remazol dyes, comparable to commercial activated carbon. These findings highlight the potential of SCG as a low-cost, sustainable resource for enzyme production and wastewater treatment, contributing to circular bioeconomy strategies. Full article

Iron–carbon micro-electrolysis and combined processes were used to treat simulated dyeing wastewater containing direct Big Red 4BE dye (concentration of 1500 mg/L, chromaticity of 80,000 times, and salt content of 20 g/L). Through single-factor experiments, the optimal reaction conditions were determined as follows: reaction time of 110 min, initial pH of 5, and iron and carbon mass ratio of 1:2. Under the optimal conditions, the concentration was reduced to 14.51 mg/L, the chromaticity was reduced to 3000 times, and the decolorization rate reached 99.03%. In order to further decrease the wastewater chromaticity, coagulation and Fenton oxidation were respectively employed for in-depth treatment after iron–carbon micro-electrolysis. The total decolorization rate of the dye wastewater exceeded 99.7%, with the treated effluent meeting the specified chromaticity discharge standard (80-fold). The integrated processes of iron–carbon micro-electrolysis combined with either coagulation sedimentation or Fenton oxidation demonstrated superior performance in treating direct Big Red 4BE dye wastewater. Full article

Covalent organic frameworks (COFs) are photocatalysts composed of covalent bonds of light elements and free of toxic metals. COFs are highly active against dyes. Furthermore, we aimed to improve the utility of COFs by making them into membranes. In this study, by utilizing the cross-linked structure of calcium alginate, we succeeded in forming the photocatalyst TpPa-COF-Cl₂ into a membrane without destroying its structure. This was confirmed by characterization such as FT-IR. In addition, methyl orange was decolorized at 450 nm, confirming the photocatalytic activity of the membrane. Full article

To overcome the low efficiency, high cost and less environmentally friendly limitations in existing textile wastewater disposal technology, an innovative approach of cation exchange membrane electrolysis coupled with magnesium salt precipitation (CEM-MSP) was implemented. This method simultaneously achieved the high-efficiency adsorption decolorization of dyes and the recovery of lye. The results indicated that cation exchange membrane electrolysis with MgSO₄ added to the anode chamber (CEM-EA) exhibited excellent decolorization performance on DB86 dye and achieved low residual Mg²⁺ concentration. Furthermore, the adsorption mechanism of Mg(OH)₂ on DB86 was systematically investigated. The adsorption process fitted with the first-order kinetic, where the adsorption of DB86 by Mg(OH)₂ was dominated by electrostatic attraction. Detailed comparison of the four systems demonstrated that CEM-EA was superior to the single magnesium addition method (85.24%) or the stand-alone membrane electrolysis method (10.36%), with 99% decolorization efficiency. In comparison to the cation exchange membrane electrolysis with MgSO₄ added to the cathode chamber (CEM-EC), the CEM-EA could diminish the Mg²⁺ concentration in the effluent to facilitate the lye recovery while guaranteeing the decolorization efficiency. In addition, the DB86 adsorption behavior during the formation of Mg(OH)₂ in the cathode chamber was investigated. The Mg(OH)₂ particles were relatively dense copper-blue agglomerates with a thin lamellar layer on the surface. Notably, only slight mass contamination was observed on the cation exchange membrane (CEM) surface after multiple cycles. Minor CEM contamination illustrated the stable treatment efficiency of the CEM-EA after several cycles. This study constructed a novel approach integrating membrane electrolysis with magnesium salt precipitation, delivering valuable technical solutions for textile wastewater disposal. Full article

The immobilization of a laccase from Pycnoporus sanguineus UEM-20 via the formation of cross-linked enzyme aggregates (CLEAs) was optimized through a central composite design (CCD) of response surface methodology (RSM). Both free and immobilized enzymes were investigated for their physico-chemical characteristics, and their adequacy in removing bisphenol A (BPA) and decolorizing malachite green dye in solution was evaluated. The immobilization caused only minor differences in thermostability. Upon immobilization, the enzyme experienced some changes in its kinetic properties. The V_max decreased by a factor of 1.1, and the K_M increased by a factor of 1.89. These kinetic changes did not modify in any remarkable way the capacity of the immobilized enzyme in degrading BPA and decolorizing malachite green dye. Its sensitivity to NaCl was also minimally affected by immobilization. However, its sensitivity to sodium sulfate was substantially decreased. After 1 month’s conservation, the activity of the free form had suffered a drastic drop. The immobilized form, by contrast, remained 100% active after 6 months. All these findings predict that the immobilized laccase from P. sanguineus UEM-20 may be useful in the enzymatic bioremediation of pollutants such as endocrine disruptors and synthetic dyes. Full article

This study investigates a sustainable approach to the photocatalytic degradation of Congo red (CR) dye using titanium dioxide (TiO₂) under simulated solar radiation, with a specific focus on the UV-A component of the radiation. The aim was to optimize reaction conditions to maximize dye removal efficiency while promoting environmentally friendly wastewater treatment practices. A central composite design (CCD) was implemented, and results were analyzed using analysis of variance (ANOVA). The key factors examined included TiO₂ concentration, UV-A radiation intensity, CR dye concentration, and suspension depth. The optimal conditions determined were 222.37 mg/L TiO₂, 20 W/m² UV-A irradiation, 25 µmol/L CR dye concentration, and a suspension depth of 29 mm. Under these conditions, decolorization was achieved with the lowest absorbance (0.367 at 498 nm) and total organic carbon (0.805 mg/L) values, indicating effective dye degradation. The findings confirm that TiO₂-assisted photocatalysis is a green and promising method for wastewater treatment. The potential use of natural solar radiation could reduce operational costs, making the process more sustainable. However, challenges such as photocatalyst recovery, aggregation, and the impact of the real wastewater matrices need further investigation. Full article

This study compares the effects of adding Mo, Cu, and Sn elements on the decolorization performance of Fe₇₇Si₁₃B₉M₁ (M = Mo, Cu, or Sn) amorphous alloys. After the addition of Cu and Sn elements, the Fe-Si-B amorphous alloys generate three-dimensional (3D) petal-like nanostructured corrosion products during the decolorization process. These petal-like nanostructures possess a high specific surface area and excellent adsorption capacity, thereby effectively promoting the decolorization of dyes. Furthermore, the influence of Fe content variation on the decolorization performance of Fe_77+xSi_13−xB₉Cu₁ (x = 0, 2, or 4) and Fe_77+xSi_13−xB₉Sn₁ (x = 0, 2, or 4) alloys was investigated. The glass-forming ability of Fe_77+xSi_13−xB₉Cu₁ alloys decreases with increasing Fe content, leading to the precipitation of α-Fe crystalline phases starting from Fe₇₉Si₁₁B₉Cu₁. As the crystallinity increases, the decolorization performance of the alloys gradually deteriorates. In contrast, the Fe_77+xSi_13−xB₉Sn₁ alloys maintain their amorphous structure even with increasing Fe content, and their decolorization performance for Orange II improves accordingly. The high decolorization efficiency of FeSiBSn amorphous alloys for Orange II can be attributed to their unique self-refreshing properties. Full article

The elimination of absorbance of excess dye by selective oxidation was first proposed for analytical methods using the formation of ion-association complexes (IAs). On this basis, a new sensitive and selective spectrophotometric method for the determination of phosphate in the form of the IA of 11-molybdovanadophosphate with diindodicarbocyanine (DIDC) was developed. Symmetric diindodicarbocyanine and diindotricarbocyanine dyes can be completely oxidized by sufficiently strong oxidizing agents such as permanganate, dichromate, cerium (IV), and vanadate. Of the three dyes investigated (DIDC, N,N’-dipropyldiindodicarbocyanine, and diindotricarbocyanine), the best results were obtained with DIDC. A mixture of molybdate, vanadate, and nitric acid was preferably used as an oxidizing agent. Selective decolorization of only free dye ions, as well as changes in the IA spectrum compared to the dye spectrum, were explained by the isolation of the dye due to the formation of poorly soluble IA nanoparticles and changes in the redox potential of the dye due to its aggregation. The following optimal conditions for phosphate determination were found: 0.3 M nitric acid, 0.43 mM sodium molybdate, 0.041 mM sodium vanadate, 0.015 mM DIDC, and 18 min for the reaction time. The molar absorptivity of the IA was 1.86 × 10⁵ mol⁻¹·L·cm⁻¹ at 600 nm, and the detection limit for phosphate was 0.013 µM. The developed method was applied to the determination of phosphate in natural water samples. Full article

The contamination of water bodies with toxic compounds from the agricultural, industrial, and domestic sectors is a serious environmental problem. Adsorption is one of the simplest, most functional, and economical methods for treating large volumes of water and removing its contaminant load. Thanks to its nanoporous structure, versatility, chemical inertness, and low-cost synthesis, anodic aluminum oxide (AAO) can be used as an adsorbent in a wide range of applications. In this work, nanostructured AAO coatings were successfully synthesized, and their performance as adsorbents was evaluated in decolorization tests of Eriochrome Black T (EBT) solutions. The adsorption process was found to be dependent on the initial dye concentration, agitation, temperature, and contact time. At 25 °C and 16 mg·L⁻¹ initial EBT concentration, a maximum removal efficiency (%R) of 78% was obtained after 4.5 h at 500 rpm and after 5.5 h at 100 rpm, while without agitation, after 8.3 h of treatment, the highest %R was 40%. Furthermore, the adsorption rate increased significantly with temperature, reaching a %R of 99% after 2.25 h at 60 °C and 500 rpm. Additionally, it was demonstrated that the adsorbent can be used up to four times with a removal efficiency greater than 50%. Full article

The effluent treatment from the packaging industry, particularly color removal, is strongly influenced by process interferences. High concentrations of dyes often make water reuse unfeasible. In this context, the present work aims to study the clarification of the dye used in the packaging industry by the photocatalytic process. Niobium was used as a catalyst, which was characterized by different techniques. Before verifying the catalytic activity in the industrial effluent, tests were performed with synthetic dye solutions. As a characterization result, it was possible to identify typical characteristics of the semiconductor. The results with the synthetic effluent indicated that the photocatalytic reaction was adequate for the decolorization of the solution. The optimized conditions indicated pH conditions without adjustments (4.2) and a catalyst concentration of 1.0 g L⁻¹, obtaining a decolorization of 98%. Tests with industrial effluent revealed that the optimum conditions were also obtained with an unadjusted pH (6.2) and catalyst concentration of 6.0 g L⁻¹, obtaining, however, 42% discoloration. This result highlights the influence of the organic load and other interfering factors such as additives. However, the process is promising in the clarification of the effluent, which possibly, with a 42% reduction in color, can be reused in the process generating water sustainability. A curve adjustment was proposed to determine the best conditions obtained for both synthetic and industrial effluents. Full article

Textile dyes pose a major environmental threat due to their toxicity, persistence in water bodies, and resistance to conventional wastewater treatment. To address this, researchers have explored biological and physicochemical degradation methods, focusing on microbial, photolytic, and nanoparticle-mediated approaches, among others. Microbial degradation depends on fungi, bacteria, yeasts, and algae, utilizing enzymatic pathways involving oxidoreductases like laccases, peroxidases, and azoreductases to breakdown or modify complex dye molecules. Photolytic degradation employs hydroxyl radical generation and electron-hole pair formation, while nanoparticle-mediated degradation utilizes titanium dioxide (TiO₂), zinc oxide (ZnO), and silver (Ag) nanoparticles to enhance dye removal. To improve efficiency, microbial consortia have been developed to enhance decolorization and mineralization, offering a cost-effective and eco-friendly alternative to physicochemical methods. Photocatalytic degradation, particularly using TiO₂, harnesses light energy for dye breakdown. Research advancements focus on shifting TiO₂ activation from UV to visible light through doping and composite materials, while optimizing surface area and mesoporosity for better adsorption. Nanoparticle-mediated approaches benefit from a high surface area and rapid adsorption, with ongoing improvements in synthesis, functionalization, and reusability, particularly through magnetic nanoparticle integration. These emerging technologies provide sustainable solutions for dye degradation. The primary aim of this review is to comprehensively evaluate and synthesize current research and advancements in the degradation of azo dyes through microbial methods, photolytic processes, and nanotechnology-based approaches. The review also provides detailed information on salient mechanistic aspects of these methods, efficiencies, advantages, challenges, and potential applications in industrial and environmental contexts. Full article

Removing high-concentration organic dye from wastewater is of great concern because the hazards can cause serious damage to the environment and human health. In this study, the hybrid dimensionally stable anode (DSA) with a Ce-doped and SnO₂-Sb₂O₅ intermediate layer was fabricated and used for the electro-catalytic oxidation of three kinds of ultra-high-concentration organic dyes. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the denser surface structure and morphology of the composite Ti/SnO₂-Sb₂O₅/Ce-PbO₂ electrode. Moreover, the electrode exhibited an excellent oxygen evolution potential of 1.58 V. The effect on the removal efficiencies of high concentrations of up to 1 g/L of methyl orange, methylene blue, and neutral red solutions with the above composite electrode was investigated. The research results illustrated that target molecules in the three different dye solutions were rapidly decolorized and decomposed by electro-catalytic oxidation in less than 35 min. Additionally, the degradation process still followed pseudo-first-order kinetics for high-concentration dye solutions. The removal efficiency of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD) for the three dye solutions was more than 98%, and the results of the gas chromatography–mass spectrometry (GC-MS) analysis showed that it had the best degradation effects for neutral red, which decomposed more thoroughly. More than 80 h of accelerated life also revealed excellent performance of the composite electrode in the face of high-concentration dye solution degradation. Considering these results, the Ti/SnO₂-Sb₂O₅/Ce-PbO₂ anode could be utilized to treat wastewater containing high-concentration dyes with high efficiency. Full article