Search Results (613)

Seminaphtofluorones (SNAFRs) are a family of benzannulated xanthene dyes that exhibit strong fluorescence in both neutral and anionic states and can reach emission wavelengths in the deep-red to near-infrared region. Their optical response is highly sensitive to regioisomerism and functionalization, making them attractive candidates for systematic structure–property investigations. Here, we computed the photophysical properties of six SNAFR regioisomers for both neutral and anionic species and correlate the calculated results with available experimental data. From the six dyes, we further chose two of them, SNAFR4 and SNAFR6, to further investigate how phenyl-ring functionalization modulates SNAFR properties by introducing methyl (–CH₃) and carboxyl (–COOH) substituents at the ortho (o), meta (m), and para (p) positions. The calculations indicate that substitution induces measurable changes in geometries, as well as in excitation and emission energies, with particularly pronounced effects for the anionic derivatives. Overall, these results provide a computational framework for the rational tuning of SNAFRs’ optical properties and the design of derivatives with tailored optical characteristics for fluorescence imaging and applications in photodynamic therapy. Full article

Heterogeneous catalytic degradation of organic dyes can effectively achieve the goals of reducing the chromaticity of aqueous solutions and completely removing pollutants. We here present a carbon-nitride-wrapped zero-valent Fe catalyst (CNFe), which can directly degrade Acid Red G (ARG) dye without additional oxidants. CNFe exhibited a nanotube-like morphology, wherein the zero-valent Fe (Fe⁰) was wrapped by a carbon layer to effectively enhance its dispersibility and prevent its oxidative deactivation. Meanwhile, the large specific surface area (169.19 m²/g), along with abundant active sites such as Fe and O, endowed CNFe with excellent activity. Under strongly acidic conditions, even in the presence of various anions, CNFe can still remove approximately 91.6% of ARG within 30 min. In a 10 h continuous flow column experiment, the removal efficiency of ARG consistently exceeded 67.6%, indicating that CNFe had great potential for treating actual dyeing wastewater. Catalytic mechanism studies showed that, under neutral conditions, CNFe mainly removed ARG through adsorption, whereas, under acidic conditions, the Fe⁰ in CNFe can not only activate molecular oxygen to generate HO· for the oxidative degradation of ARG but also remove ARG via reduction. Furthermore, CNFe can adsorb ARG through hydrogen bonding of surface hydroxyl groups. The developmental toxicity of the generated intermediates was effectively reduced, demonstrating lower environmental risks. Therefore, this study provided a simple, high-efficiency, and economical method for removing dyes from water, which can offer guidance for the treatment of practical dye wastewater. Full article

Poly(glycidyl methacrylate) (PGMA) is a polymer containing epoxy groups in its side chains, which makes it a suitable platform for the development of functional materials. In this study, crosslinked PGMA-based microspheres were synthesized by suspension polymerization using N,N′-methylenebisacrylamide as a crosslinker, and the effect of incorporating inorganic additives (InAds) (NaCl, CaCO₃, and MgO nanoparticles) during synthesis was evaluated. In all cases, solid microspheres were obtained, exhibiting variations in particle size, sphericity, and aggregation depending on the type and amount of InAds. Thermal stability was characteristic of crosslinked PGMA (i.e., a single broad thermal transition in ~80–110 °C), while water absorption remained within a narrow range (80–120% for t = 40 min). In addition, the number of epoxy groups per gram of sample was 4.83 ± 0.02 mmol g⁻¹. Selected microspheres were subsequently functionalized with polyethyleneimine (PEI) to obtain graft polymers (PGMA–PEI) and evaluated for the adsorption of three model contaminants: Acid Red 27 (AR-27), nitrites, and acetaminophen. PGMA–PEI showed high affinity toward AR-27 and nitrites, achieving high removal efficiencies at acidic and neutral pH, with rapid adsorption kinetics consistent with a pseudo-second-order model, attributed to electrostatic interactions between protonated amine groups and anions. At pH 11, anion desorption was promoted, enabling partial material regeneration. The results highlight the potential of PGMA–PEI microspheres for the removal of AR-27 (maximum retention ~0.25 mg of dye/g of polymer) and nitrites (maximum retention ~0.023 mg of ${NO}_2^{-}$/g of polymer), whereas acetaminophen removal was not evidenced. Full article

Hypochlorous acid (HClO) is widely used as a low-cost and effective disinfectant; however, its instability under heat and light necessitates simple and reliable monitoring methods. Herein, we report a morphology-evolving thin-film colorimetric sensor that enables intuitive visual detection of HClO through simultaneous color and pattern transitions. The sensor integrates two polymer films with distinct charge-state response behaviors, patterned in X-shaped and circular geometries on a single substrate. Upon exposure to HClO, chlorine-induced modification of amide and amine groups alters the surface charge states, thereby switching the adsorption preference for anionic and cationic dyes. This mechanism results in a pronounced transformation from a blue X-shaped motif to a red circular pattern, enabling direct visual discrimination between different HClO concentrations. Quantitative analysis of RGB values confirmed semi-quantitative detection in the sub-millimolar to millimolar range. The sensor exhibited a linear response in the range of 0–3 mM (R² > 0.979) with a limit of detection of 0.103 mM. The sensor further demonstrated practical applicability by tracking photodecomposition of a commercial disinfectant. This work demonstrates pattern-coupled colorimetric sensing as a straightforward, user-friendly approach for HClO monitoring. Full article

The secondary effluent from printing and dyeing wastewater contains recalcitrant organic pollutants, such as azo dye derivatives. Their persistence in aquatic environments not only creates ecological risks but also hampers the high-value reuse of reclaimed water. This study investigated the influence of typical binary anions on the degradation performance of low-concentration azo dye wastewater using a Ti/RuO₂-IrO₂ anode electrochemical oxidation system. The results demonstrated that maximum COD removal efficiency could reach 50.22%, and the controlling factors synergistically regulated the contribution and competition between Reactive Chlorine Species and free radicals. This led to a characteristic “rapid rise–decline–slow rebound” phenomenon in the COD removal rate, with the inflection points co-influenced by the current density, conductivity, and binary anion ratio of the electrochemical process. Furthermore, it alters the degradation pathway of the azo dye to “azo bond cleavage → demethylation/desulfonation → dehydroxylation/deamination oxidation → benzene ring opening”. Within a fixed duration of 60 min, the Response Surface Methodology model identified the optimal COD degradation conditions as follows: current density of 19.72 mA/cm², Cl⁻/SO₄²⁻ ratio of 5.40, and conductivity of 8.30 mS/cm. This research elucidates the differences between the electrochemical oxidation degradation pathway of low-concentration azo dye wastewater under the regulation of typical binary anions and the conventional pathway. It also reveals the regulatory effects of current density, conductivity, and binary anion ratio on the degradation patterns. Full article

The world’s water resources are being deteriorated by the continuous discharge of various contaminants, highlighting the problem of dyes. Many industrial activities (dyeing, food, and medicines) depend on the use of synthetic dyes. Due to their strong color, toxicity, and carcinogenic properties, dye effluents are detrimental to human health and the environment and their treatment is mandatory before discharge. The manuscript intends to present a comprehensive summary of the advantages and drawbacks of using different treatments on the removal of dyes, mainly those based on adsorption. Emphasis is placed on the use of adsorbents from biomass or biomass waste, which are used in their original form or after conversion into biochar or activated carbon (AC). In this review, the use of biomass-based feedstocks to produce biochar and ACs and their application on the removal of various types of dyes from liquid effluents are compiled and critically discussed. This approach positions waste and sub products not as a problem, but as a valuable raw material for producing high value-added materials. The performance of different adsorbents, for the removal of cationic and anionic dyes, is discussed and related to the textural, physical and chemical characteristics of adsorbents and adsorption. It differs from the other revision manuscripts in that it elucidates to the readers the points to ponder before choosing an adsorbent for the removal of a specific dye, mainly for large-scale uses. Full article

The biochars obtained by pyrolyzing tomato stems at temperatures of 400, 500, 600, and 700 °C were characterized, and their ability to absorb anionic (Direct Orange 26, DO26) and cationic (Rhodamine B, RhB) dyes from aqueous solutions was investigated. The effects of solution pH and ionic strength were studied. It was found that the adsorption process of both dyes was pH-dependent, but no effect of ionic strength was observed. The kinetics of dye adsorption on biochars were well described by the pseudo-second-order model. The equilibrium adsorption data were analyzed using the Freundlich, Langmuir, and Temkin isotherms. All three equations described dye adsorption on biochars quite well, although a slightly better fit was observed for the Freundlich model. The maximum adsorption capacities of BCs ranged from 54.44 mg/g (BC400) to 108.1 mg/g (BC700) for DO26 and from 4.483 mg/g (BC700) to 8.887 mg/g (BC400) for RhB. The study reveals that biochars derived from tomato stems can be used as efficient, low-cost adsorbents for the removal of anionic and cationic dyes from water. Full article

The existence of continually increasing refractory organic pollutants in water has always been a serious potential threat to human and environmental health due to their toxicity and persistence. Conventional water treatment technologies suffer from inherent limitations, including low degradation efficiency, secondary pollution issues, and high operational costs. Recently, molecular oxygen (O₂)-based advanced oxidation processes (O₂-AOPs) have attracted increasing attention as sustainable and efficient wastewater treatment technologies, as the abundant and environmentally benign oxidant in nature can be activated into reactive oxygen species (ROS), such as superoxide anions ($·{\mathrm{O}}_2^{-}$), hydroxyl radicals (·OH), and singlet oxygen (¹O₂), enabling the effective mineralization of refractory organic pollutants. This review presents a comprehensive summary of O₂-AOPs for water purification, specifically focusing on photocatalytic, electrocatalytic, thermocatalytic, and mechanocatalytic systems. Furthermore, we conduct a comprehensive analysis of the intrinsic reaction mechanisms associated with both free radical pathways and non-free radical pathways, which include processes involving singlet oxygen and high-valent metal-oxygen intermediates. Finally, we discuss the challenges and prospects associated with the degradation of typical organic pollutants, such as phenolic compounds, pharmaceuticals and personal care products (PPCPs), and organic dyes. Despite significant advancements in O₂-AOPs, several core challenges persist, including low efficiency in utilizing dissolved oxygen, insufficient catalyst stability, and unclear mechanisms of interfacial electron transfer. Future research should prioritize the precise regulation of material structures, a thorough analysis of reaction mechanisms, and the tailored development of reactors to facilitate the industrial application of this technology in water treatment. Overall, this review systematically outlines the current progress in technologies for removing organic pollutants using molecular oxygen, offering novel insights for mitigating organic pollution in water. Full article

The main objective of the work was to prepare a series of new activated biocarbons by chemical activation of black chokeberry seed and to assess their suitability for removing cationic and anionic dyes from an aqueous medium. Activation of the precursor was performed at 550 °C with orthophosphoric acid, using conventional or microwave-assisted heating. The activated biocarbons were characterized in terms of elemental composition, textural parameters, surface morphology, acid-base character of the surface, as well as electrokinetic properties. Adsorption tests were carried out against two organic compounds: methylene blue (thiazine dye of cationic character) and Congo red (azo dye of anionic character). The influence of the initial dye concentration (5–120 mg/L), temperature (20–40 °C), and solution pH (2–10) on dye removal efficiency from the liquid phase was investigated. Additionally, kinetic adsorption tests were carried out to determine the rate and mechanism of the dyes removal process. Microwave-assisted chemical activation with H₃PO₄ proved to be a very effective approach for generating a high specific surface area (884 m²/g) and a micro/mesoporous structure, which directly increases the adsorption capacity of activated biocarbons towards cationic and anionic synthetic dyes. The maximum adsorption capacities for methylene blue and Congo red were 194.5 and 68.6 mg/g, respectively. It was also confirmed that the choice of heating method at the activation stage plays a key role in determining the physicochemical properties and adsorption performance of the activated biocarbons prepared from waste biomass. In general, carbonaceous adsorbents derived from black chokeberry seeds exhibit high potential for the treatment of dye-contaminated wastewater. Full article

To develop low-cost and renewable materials for treating dye wastewater, an efficient biosorbent was prepared from Bambusa emeiensis bamboo powders (BPs) via a simple alkali pretreatment. Systematic investigation revealed that NaOH concentration was critical for enhancing adsorption performance. Under optimal conditions (NaOH ≥ 0.2 mol/L, dosage = 10.0 g/L), the BPs achieved over 96% removal of cationic Methylene Blue (MB, 20 mg/L) within 20 min, demonstrating rapid kinetics. The adsorption process followed the Langmuir isotherm model with a maximum adsorption capacity of 4.1 mg/g without adjusting the pH of the solution and complied with the pseudo-second-order kinetic model. Thermodynamic analysis confirmed the spontaneous (ΔG < 0) and exothermic (ΔH = −52.73 kJ/mol) nature of the adsorption. Notably, the alkali-treated BPs exhibited a pronounced preference for the cationic dye, achieving a high removal rate of 96.5% for MB, in contrast to a much lower removal of 23.6% for the anionic dye AO7 under identical single-dye conditions, attributed to the enhanced surface negative charge after alkali treatment. Furthermore, the BPs maintained a high removal efficiency of 91.2% after eight adsorption-desorption cycles using 0.1 mol/L HCl as eluent, demonstrating excellent reusability. This study presents a feasible and sustainable strategy for designing regenerative bamboo-based biosorbents with rapid and preferential adsorption capabilities for cationic dye wastewater. Full article

This study aims to develop a cost-effective and scalable modification strategy for valorizing lignin-rich biogas residue (BR) into high-performance adsorbents for anionic dye removal. To screen the optimal modification pathway, three distinct reagents, L-cysteine-based amino acid ionic liquids (AAILs, as green alternatives), conventional hydrochloric acid (HCl) and sodium hydroxide (NaOH, as traditional modification reagents), were compared in modifying non-carbonized BR for Congo Red (CR) adsorption. Comprehensive characterizations and adsorption tests revealed that each modifier exerted unique effects: NaOH only caused mild surface etching with limited performance improvement; AAILs achieved moderate adsorption capacity via a green, mild route; while HCl modification (BR-HCl) stood out with the most superior performance through a “selective dissolution-pore reconstruction” mechanism. Notably, despite a modest specific surface area increase to 12.05 m²/g, BR-HCl’s high CR adsorption capacity (120.21 mg/g at 45 °C) originated from the synergy of chemical bonding and enhanced electrostatic attraction—its isoelectric point (pH_PZC ≈ 9.02) was significantly higher than that of AAIL- and NaOH-modified samples, enabling strong affinity for anionic CR across a wide pH range. BR-HCl attained over 99% CR removal at a dosage of 0.4 g/L, fitted well with Langmuir isotherm and pseudo-second-order kinetic models (confirming monolayer chemisorption), and retained 82% of its initial capacity after five regeneration cycles. These results demonstrate that while AAILs show promise as green modifiers and NaOH serves as a baseline, the facile, low-cost HCl modification offers the most pragmatic pathway to unlock BR’s potential for sustainable wastewater treatment. Full article

Organophilic acidic magadiites were prepared after an acidic magadiite (A-Mgd) reaction with cetyltrimethylammonium solutions containing different anions, such as cetyltrimethylammonium bromide (C16TMABr), cetyltrimethylammonium chloride (C16TMACl), and cetyltrimethylammonium hydroxide (C16TMAOH). The resulting materials were studied as adsorbents for Eosin Y removal from artificially contaminated solution. Successful preparation of oganophilic A-Mgd was achieved using C16TMAOH solution with an increased basal spacing from 1.21 nm to 3.15 nm and uptake C16TMA amount of 1.16 mmol/g. Meanwhile, no variation in the basal spacing of 1.20 nm occurred using C16TMACl and C16TMA Br solutions with an uptake mount of 0.07 to 0.09 mmol/g, respectively. Other techniques supported the behavior of the counteranion of surfactant solution on the synthesis of organophilic A-Mgd samples. 13C CP/MAS NMR data revealed that C16TMA cations displayed all-trans conformation comparable to C16TMABr solid, and ²⁹Si MAS NMR confirmed the stability of the host silicate layers during the reaction. The specific surface area of A-Mgd was reduced after the intercalation of C16TMA cations from 38 m²/g to 11 m²/g. The removal properties of organophilic samples were investigated under different conditions, including the Eosin Y pH solution, initial concentration, dosage mass, and content of C16TMA cations. The maximum removal amount was 70 mg/g at acidic pH and using A-Mgd prepared from C16TMAOH solution, while the other organophilic A-Mgds exhibited low removal amounts of 3 to 5 mg/g. The regeneration tests indicated that the efficiency was maintained after four reuse tests with a drop of 30 to 50% from the initial value after seven cycles. The adsorber batch design was employed to estimate theoretically the required masses of used samples to treat an effluent volume of 10 L at a removal percentage of 95% at a fixed initial concentration of 200 mg/L. In total, 20 g of organophilic prepared from A-Mgd and C16TMAOH solution was needed, while 243 g of sample prepared from C16TMABr solution was required. This study proposes the development of a cost-effective, sustainable solution for dye-contaminated wastewater treatment. Full article

Dialdehyde crosslinked poly aspartate/alginate hydrogel beads were synthesized by covalently introducing poly aspartate into the alginate network via dialdehyde-mediated crosslinking, and the resulting effects on swelling and adsorption behavior were investigated. Alginate was partially oxidized to form dialdehyde alginate and crosslinked with poly aspartic acid via Schiff base formation, followed by ionic crosslinking with calcium ions. The chemical structure and morphology of the gel beads were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. Incorporation of PAsp significantly altered the swelling behavior of alginate-based gel beads. In saline solution, PAsp-modified gel beads exhibited a swelling ratio of approximately 112 g/g, which was higher than that of calcium alginate gel beads. This behavior is suggested to be associated with changes in the alginate–calcium network structure induced by polymer modification. PAsp-modified gel beads exhibited moderate but distinct adsorption behavior depending on the adsorbate. Removal efficiencies of approximately 40–50% were observed for copper and cobalt ions, while a removal efficiency of around 50% was obtained for the cationic dye crystal violet. In contrast, adsorption of the anionic dye Congo red decreased with increasing PAsp content, indicating charge-dependent adsorption behavior. Overall, this study demonstrates that PAsp modification via dialdehyde-mediated crosslinking influences both the swelling and adsorption properties of alginate-based hydrogel beads. The results provide fundamental insight into how network modification can be used to tune the behavior of alginate-based hydrogels in aqueous environments. Full article

A composite based on θ-Al₂O₃ microspheres coated with graphene oxide (GO) and reduced graphene oxide (RGO) was prepared and evaluated as a sorbent for the removal of synthetic dyes from aqueous solutions. GO was synthesized by a modified Hummers’ method and deposited onto alumina microspheres via ultrasound-assisted treatment under various conditions, followed by supercritical reduction to obtain the Al₂O₃_RGO composite. The structure, morphology, and composition of the materials were characterized by Raman spectroscopy, SEM, TGA/DSC, FTIR, and XRD, revealing the formation of mono- and few-layer GO/RGO coatings on the substrate surface. Adsorption tests for cationic methylene blue (MB) dye and anionic methyl orange (MO) dye demonstrated that the alumina substrate was inactive, whereas GO- and RGO-coated microspheres exhibited high adsorption efficiency for MB and partial uptake of MO from water solutions. In mixed-dye solutions, both Al₂O₃_GO and Al₂O₃_RGO composites showed selectivity toward MB, and the RGO-based composite demonstrated enhanced MB adsorption at low concentrations. The results highlight GO/RGO-coated θ-Al₂O₃ microspheres as convenient and selective composite sorbents for water purification processes. Full article

The aim of this study was to investigate the sorption efficiency of anionic dyes—Reactive Yellow 84 (RY84) and Reactive Black 5 (RB5)—and cationic dyes—Red 46 (BR46) and Basic Violet 10 (BV10)—onto potato peels (Solanum tuberosum L.). The research scope included characterization of the sorbent material (pH_PZC, FTIR), the effect of pH on dye sorption efficiency, kinetics (pseudo-first-order and pseudo-second-order models, intraparticle diffusion model), and studies on the sorbent’s maximum sorption capacity (Langmuir 1 and 2, and Freundlich isotherms). The point of zero charge (pH_PZC) for potato peels was determined to be pH_PZC = 6.43, indicating a slightly acidic character of the material. The sorption efficiency for RB5, RY84, and BV10 was highest at pH 2, while the efficiency for BR46 was highest at pH 6. The time required to reach sorption equilibrium on the tested sorbent increased with the initial dye concentration and ranged from 180 to 270 min for RB5, RY84, and BV10, and from 45 to 210 min for BR46. The maximum sorption capacity of this material was found to be 20.85 ± 0.33 mg/g and 21.63 ± 0.34 mg/g for RB5 and RY84, respectively, and 10.28 ± 0.24 mg/g and 27.15 ± 0.87 mg/g for BV10 and BR46, respectively. Full article