Search Results (155)

A hetero-disubstituted sugarcane bagasse (HDSB) was prepared by simultaneous one-pot chemical modification of sugarcane bagasse with succinic and phthalic anhydrides. HDSB was used in batch mode for the removal of the cationic dyes auramine-O (AO) and safranin-T (ST) from spiked aqueous solutions. Adsorption of the dyes in mono- and bicomponent systems was investigated as a function of HDSB dosage, pH, contact time, and initial dye concentration. Maximum adsorption capacities for AO and ST on HDSB, at pH 7.0, were 1.37 mmol g⁻¹ (367.7 mg g⁻¹) and 0.93 mmol g⁻¹ (293.3 mg g⁻¹), respectively. In the bicomponent system, ST was preferentially adsorbed on HDSB, revealing an antagonistic effect of ST on AO adsorption. Changes in the enthalpy of the adsorption as a function of HDSB surface coverage were determined by isothermal titration calorimetry, with Δ_adsH° values for AO and ST equal to −22.1 ± 0.3 kJ mol⁻¹ and −23.44 ± 0.01 kJ mol⁻¹, respectively. Under standard conditions, the adsorption of the dyes on HDSB was exergonic and enthalpically driven. Desorption removed ~50% of the adsorbed dyes, and subsequent re-adsorption showed that HDSB could be reused, with non-desorbed dye molecules acting as new binding sites. The interaction between AO and ST with HDSB was elucidated by molecular dynamics simulations with atomistic modeling. Full article

An outstanding adsorbent, such as the metal–organic framework (MOF) MIL-101 (Cr), was employed to study the adsorption of two dyes, namely reactive red 2 (RR2) and reactive blue 19 (RB19). Experimental adsorption data were retrieved at T = 25, 35 and 45 °C and analyzed to define the adsorption mechanism of these dyes. A modeling approach based on a double-layer model derived from statistical physics was used. The maximum adsorption capacity (MAC) was found to be 875, 954 and 1002 mg/g for RR2 and 971, 1093 and 1148 mg/g for RB19, at T = 25, 35 and 45 °C, respectively. These values indicate that MIL-101 (Cr) exhibits outstanding performance in removing potential water pollutants such as the RR2 and RB19 dyes. The possible orientations of the RR2 and RB19 dyes upon adsorption were determined by analyzing the number of dye molecules bound per MIL-101 (Cr) active sites during the adsorption process. It was found that the RR2 dye was removed via a mixed parallel and non-parallel orientation on MIL-101 (Cr), while RB19 was removed via an inclined orientation at higher temperatures. The adsorption mechanism suggested that MIL-101 (Cr) site density was reduced due to an exothermic effect, which decreases the number of active sites participating in dye adsorption, even though the reduction in water adsorption may be attributed to the overall endothermic behavior. From the adsorption energy (AE) and the chemical structure of MIL-101 (Cr) and both dyes, it was concluded that hydrogen bonds, Van der Waals forces and π-π stacking are involved in the dye removal process. This research provides new physical insights into the adsorption mechanism of two relevant dyes on an outstanding adsorbent such as the MIL-101 (Cr) MOF. Full article

The recovery of green waste and biomass presents a significant challenge in the 21st century. In this context, this study aims to valorize waste generated by the fruit juice processing industry at the N’Gaous unit (composed of the orange peel, fibers, pulp, and seeds) as an adsorbent to eliminate an anionic dye and to enhance its adsorption capacity through thermal activation at 200 °C and 400 °C. The aim is also to determine the parameters for the adsorption process including contact time (0–120 min), solution pH (2–10), initial dye concentration (50–700 mg/L), and adsorbent dosage (0.5–10 g/L). The adsorption tests showed that waste activated at 400 °C (AR400) demonstrated a higher efficiency for removing indigo carmine (IC) from an aqueous solution than waste activated at 200 °C (AR200) and unactivated waste (R). The experimental maximum adsorption capacities for IC were 70 mg/g for unactivated waste, 500 mg/g for waste activated at 200 °C, and 680 mg/g for waste activated at 400 °C. These tests were conducted under conditions of pH 2, an equilibrium time of 50 min, and an adsorbent concentration of 1 g/L. The analysis of the kinetic data revealed that the pseudo-second-order model provides the best fit for the experimental results, indicating that this mechanism predominates in the sorption of the pollutant onto the three adsorbents. In terms of adsorption isotherms, the Freundlich model was found to be the most appropriate for describing the adsorption of dye molecules on the R, AR200, and AR400 supports, owing to its high correlation coefficient. Before adsorption tests, the powder R, AR200 and AR400 were characterized by various analyses, including Fourier transform infrared (FTIR), pH zero charge points and laser granularity for structural evaluation. According to the results of these analyses, the specific surface area (SSA) of the prepared material increases with the increase in the activation temperature, which expresses the increase in the adsorption of material activated at 400 °C, compared with materials activated at 200 °C and the raw material. Full article

Dye wastewater poses significant risks to human health and aquatic ecosystems, necessitating efficient remediation strategies. This study developed a magnetic Fe₂O₃ nanocomposite (MNC) derived from phosphoric acid-treated walnut shell biomass carbon to remove Alizarin red S (AR) dye from polluted water. Characterization techniques confirmed the nanocomposite’s mesoporous structure, superparamagnetic properties (61.5 emu/g), and high crystallinity. Optimization using Response Surface Methodology (RSM) revealed a maximum adsorption efficiency of 94.04% under the following optimal conditions: A pH of 2, AR dye concentration of 85 mg/L, adsorbent dose of 1.5 g/L, and particle size of 448.1 nm. Adsorption followed pseudo-second-order (PSO) kinetics (R² = 0.9999) and Langmuir isotherm models (R² = 0.9983), with thermodynamic studies indicating spontaneous and endothermic chemisorption. The intra-particle diffusion model, Bangham, and Boyd plots describe the adsorption process, and external boundary layer diffusion of AR dye molecules in the aqueous phase limits the adsorbate removal rate. Regeneration tests demonstrated reusability over three cycles, with a desorption efficiency of 50.52% using 30 mM HCl. The MNC exhibited a maximum adsorption capacity (Q_max) of 115.35 mg/g, outperforming other adsorbents, making it an efficient and sustainable alternative solution for AR dye removal from water bodies. Full article

Adsorption of mononuclear tris(bipyridine) ruthenium(II) complexes and binuclear tris(bipyridine) ruthenium(II) complexes equipped with carboxyl groups (-COOH) on the (111) surface of TiO₂ crystal in anatase form was modeled using Monte Carlo simulations, applying the Universal force field. It was shown that the adsorption efficiency of the ruthenium-based dyes on the TiO₂ surface depends on the position of the anchoring -COOH group in the molecular structure. The increase in the number of possible anchor groups in the dyes increases their ability to deposit on the surface of semiconductors. The chemisorbed molecules, such as mononuclear tris(bipyridine) ruthenium(II) complexes with the -COOH group in para position (RuLp) and binuclear tris(bipyridine) ruthenium(II) complexes called B3 with two anchoring -COOH groups and phenyl in the spacer, interact with the adsorber and other neighboring dyes, changing their electron and optical properties. The obtained computational results help to explain the behavior of the dyes on the TiO₂ surface, giving impact on their DSSC applications. Full article

Graphene materials and their derivatives have shown promising capabilities in removing anionic and cationic dyes from wastewater. The present study aims at the synthesis of graphene-based material with a high specific surface area and evaluates its use as an adsorbent for removing toluidine blue and methyl violet from aqueous solutions. The physicochemical characterization of the adsorbent before and after dye adsorption is made by XRD, Raman spectroscopy, SEM, TEM, nitrogen physisorption, TG-DTA, and XPS. The influence of the solution’s pH, contact time, dye concentration, and temperature on the adsorption efficiency is investigated. The adsorbent demonstrated high adsorption capacity towards toluidine blue (265.2 mg.g⁻¹) and methyl violet (200.4 mg.g⁻¹) dyes from water. The adsorption process for both dyes follows the Langmuir model and involves physical rather than chemical interactions. Kinetic parameters were also determined. The adsorption of the studied cationic dyes can be attributed to a combination of mechanisms, including electrostatic interactions, hydrogen bonding, and π-π interactions between the dye molecules and the aromatic structure of reduced graphene oxide. The findings in the present work highlight the possibilities for enhancing graphene-based materials’ adsorption capabilities. Full article

Anatase-phase rod-shaped TiO₂ nanocrystals are prepared by the solvothermal method, the surface is metalated, and doped nanocrystals are achieved by thermal diffusion of surface metal ions. Incorporation of dopant ions into TiO₂ lattice enhances the visible light absorption of the material and in some cases can increase the rate of photocatalysis. Even though there are overflowing studies on the preparation of doped TiO₂ materials, there are no methods that enable the precise control of dopant concentration in TiO₂ nanocrystals. We have developed a method to load the surface of oleic acid stabilized anatase-phase rod-shaped TiO₂ nanocrystals (approx. 3 ± 1 nm diameter and 40 ± 10 nm long) with transition metal ions followed by ion diffusion to prepare metal-doped nanocrystals with exact control of the dopant concentration. Specifically, in this work, Cr³⁺ adsorbs TiO₂ nanorods to yield a green colloid, followed by ion diffusion at elevated temperature. After removal of any remaining surface Cr³⁺, tan-colored chromium-doped TiO₂ nanorods can be obtained. Electron microscopy and powder X-ray diffraction indicate no change in nanocrystal size and morphology throughout the process. The TiO₂ nanorods play an important role in photocatalysis owing to their excellent chemical and physical properties. Titanium dioxide is a low-cost, non-toxic, highly stable, chemically robust material. Doped TiO₂ materials have found application in photocatalysis (oxidative degradation of organic molecules, hydrogen evolution), photovoltaics, solar cells, lithium-ion batteries, supercapacitors, and sensors. TiO₂ photocatalysis is also the basis for clean energy technologies, such as dye-sensitized solar cells and photoelectrochemical cells. In photocatalysis applications, nanocrystalline TiO₂ presents advantages of a high surface area, ability to control the surface facet, and minimized bulk recombination. Full article

Dyes abundance in industrial wastewater exerts adverse effects on the environment and human health; adsorption represents a promising remediation strategy. Chitosan-based composites are interesting materials for dye adsorption. In this work, methyl orange (MO) adsorption using chitosan (CH) and chitosan–graphene oxide (CH-GO) aerogels produced by supercritical gel drying, performed at 200 bar/35 °C, was assessed by studying the effect of driving force (25–100 ppm) and adsorbent dosage (1–8 g/L). It was highlighted that the difference in the performance between the two adsorbents was non-negligible only at high concentrations: processing a 100 ppm MO solution, q_eq is 59 mg/g and 28 mg/g for CH-GO and CH, respectively. Starting from a 10 ppm MO solution, using a dosage of 8 g/L, it was possible to achieve adsorption efficiency of about 85%, meaning that small amounts of nanostructured devices can result in good process outcomes. Freundlich isotherm reliably describes the system behavior (R² = 0.99). The multi-linear IPD kinetic model confirms that in the case of nanostructured porous devices, there are different mass transfer phenomena that control molecule diffusion through the system. The research proposed in this work aims to explore, as a first assessment, the potential of nanostructured devices for adsorption purposes. Full article

This work aimed to investigate the adsorption of organic compounds (4-nitroaniline and 4-chlorophenoxyacetic acid) on activated carbon in the presence of selected dyes (uranine and Acid Red 88) and surfactants (sodium dodecyl sulfate and hexadecyltrimethylammonium bromide). The adsorbent, i.e., the activated carbon RIAA (experimental activated carbon, Norit NV, Amersfoort, The Netherlands), was fully characterised by nitrogen adsorption/desorption isotherms, potentiometric titration, small-angle X-ray scattering, X-ray photoelectron spectroscopy, and transmission electron microscopy. The measurements of the adsorption isotherms of individual adsorbates from aqueous solutions were performed, and the Generalised Freundlich equation (GF) was used for their analysis. The influence of the properties of the co-adsorbates and the adsorbent on the efficiency of removal of 4-nitroaniline and 4-chlorophenoxyacetic acid from the water phase was discussed. A sieving effect was found—large dye and surfactant molecules do not penetrate the micropores but only locate at their entrances, limiting the availability of carbon adsorption space for the nitro compound and the pesticide. A very clear influence of the co-adsorbates’ concentration on the adsorption efficiency of the organic pollutants from the mixture was also observed. When the CMC (critical micelle concentration) value was exceeded in the system with surfactant as the co-adsorbent, a decrease in the competition effect on the adsorption of 4-chlorophenoxyacetic acid was observed. This is due to the formation of large aggregates of the surfactant in the solution, which are poorly adsorbed on the activated carbon. Full article

This study explores the formation of functionalized carbon surfaces through shock compression of graphite in the presence of water, modeled using molecular dynamics and the ReaxFF reactive force field. The shock compression method produces activated carbon with surface functionalities, primarily hydroxyl groups, and varying morphological properties. Two approaches, unidirectional and isotropic compression, yield distinct surface structures: the former preserves a relatively flat surface, while the latter generates corrugated features with valleys and ridges. These features significantly impact the adsorption properties of methylene blue (MB), a commonly used dye. Simulations reveal that MB molecules are highly mobile on flat surfaces, aligning with a mobile adsorption model. However, on corrugated surfaces, MB exhibits localized adsorption, with the deepest valleys effectively immobilizing the dye molecules. Additionally, the study highlights the influence of surface hydroxyl groups, which, through interactions with water molecules, prevent MB from occupying these regions. The findings underscore that traditional adsorption models may not fully capture the dynamics of MB adsorption on activated carbons with complex morphologies. These insights are critical for advancing carbon-based adsorbents in water purification applications. Full article

A magnetic bio-based adsorbent derived from H₂O₂-activated zeolite and turmeric carbohydrate polymer was fabricated, characterized, and utilized in removing methylene blue (MB) dye at pH 8.0 and temperatures between 25 and 55 °C. To understand the molecular-scale adsorption mechanism, a range of advanced statistical physics models were employed in conjunction with conventional equilibrium models. The as-synthesized biosorbent presented high maximum capacities according to the Langmuir model, with values ranging from 268.67 to 307.73 mg/g. The double-layer equation yielded the best-fitting results to the MB experimental data among the applied statistical physics models. The number of MB molecules ranged from 1.14 to 1.97, suggesting a multi-molecular mechanism with a non-parallel orientation. The main factor affecting the effectiveness of this adsorbent was the density of its functional groups, which varied from 27.7 to 142.1 mg/g. Adsorption energies in the range of 19.22–21.69 kJ/mol were obtained, representing the existence of physical forces like hydrogen bonds and electrostatic interactions. To complete the macroscopic examination of the MB adsorption mechanism, thermodynamic parameters such as entropy, Gibbs free energy, and internal energy were considered. The adsorption/desorption outcomes up to five cycles displayed the stability of the magnetic biosorbent and its potential for decontaminating industrial effluents. Overall, this work increases our understanding of the MB adsorption mechanism onto the produced biosorbent at the molecular level. Full article

We developed dye-sensitized solar cells (DSSCs) using 1,5-carboxy-2-[[3-[(2,3-dihydro-1,1-dimethyl-3-ethyl-1H-benzo[e]indol-2-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-3,3-dimethyl-1-octyl-3H-indolium and 1,3,3-trimethyl indolino-6′-nitrobenzopyrylospiran. The DSSCs incorporate photochromic molecules to regulate photoelectric conversion properties. We irradiated photoelectrodes adsorbed with SQ2/SPNO₂ using both UV and visible light and observed the color changes in these photoelectrodes. Following UV irradiation, the transmittance at 540 nm decreased by 20%, while it increased by 15% after visible light irradiation. This indicates that SPNO₂ on the DSSCs is photoisomerized from the spiropyran form (SP) to the photomerocyanine (PMC) form under UV light. The photoelectric conversion efficiency (η) of the DSSCs increased by 0.15% following 5 min of UV irradiation and decreased by 0.07% after 5 min of visible light irradiation. However, direct electron injection from PMC seems challenging, suggesting that the mechanism for improved photoelectric conversion in these DSSCs is likely due to Förster resonance energy transfer (FRET) from PMC to the SQ2 dye. The findings suggest that the co-sensitization of DSSCs by PMC-SQ2 and SQ2 alone, facilitated by their respective photoabsorption, results in externally responsive and co-sensitized solar cells. This study provides valuable insights into the development of advanced DSSCs with externally controllable photoelectric conversion properties via the strategic use of photochromic molecules and energy transfer mechanisms, advancing future solar energy applications. Full article

According to environmental concerns related to water pollution, this study aims to develop a novel hydrogel bead as a biocompatible and efficient adsorbent by integrating bacterial cellulose-activated carbon (BCAC) and montmorillonite (MT) in alginate hydrogel (ALG). The ionotropic gelation method was applied to the fabrication of BCAC/MT/ALG hydrogel beads. The BCAC/MT/ALG hydrogel bead exhibited significantly higher tensile strength, Young’s modulus, and thermal stability, with ~1.4 times higher adsorption uptake of methylene blue (MB) from aqueous solution as compared to the pristine ALG bead. The textural properties, including specific surface area and porosity, were beneficial to accommodate the size of cationic MB as the target molecule. This resulted in a remarkable MB adsorption uptake of 678.2 mg/g at pH 7 and 30 °C. The adsorption isotherm showed the best fit for the nonlinear Redlich-Peterson isotherm model. Experimental adsorption data were well-described by the pseudo-second order kinetic model, with R² values reaching 0.997. In addition, the adsorbent bead demonstrated easy regeneration with high reusability with approximately 75% of MB removal after being used for six cycles. Therefore, BCAC/MT/ALG bead represents an eco-friendly, cost-effective, and highly efficient adsorbent for MB removal from water and could potentially be used for removal of a wide range of cationic dye pollutants from wastewater. Full article

This review embarks on a comprehensive journey, exploring the application of lignocellulosic biomass materials as highly effective adsorbents for the removal of textile dyes (cationic and anionic dyes) from wastewater. A literature review and analysis were conducted to identify existing gaps in previous research on the use of lignocellulosic biomass for dye removal. This study investigates the factors and challenges associated with dye removal methods and signifies their uses. The study delves into the pivotal role of several parameters influencing adsorption, such as contact time, pH, concentration, and temperature. It then critically examines the adsorption isotherms, unveiling the equilibrium relationship between adsorbent and dye and shedding light on the mechanisms of their interaction. The adsorption process kinetics are thoroughly investigated, and a detailed examination of the adsorbed rate of dye molecules onto lignocellulosic biomass materials is carried out. This includes a lively discussion of the pseudo-first, pseudo-second, and intra-particle diffusion models. The thermodynamic aspects of the adsorption process are also addressed, elucidating the feasibility and spontaneity of the removal process under various temperature conditions. The paper then dives into desorption studies, providing insights into the regeneration potential of lignocellulosic biomass materials for sustainable reusability. The environmental impact and cost-effectiveness of employing lignocellulosic biomass materials in textiles including Congo Red, Reactive Black 5, Direct Yellow 12, Crystal Violet, Malachite Green, Acid Yellow 99, and others dyes from wastewater treatment are discussed, emphasizing the significance of eco-friendly solutions. In summary, this review brings together a wealth of diverse studies and findings to present a comprehensive overview of lignocellulosic biomass materials as adsorbents for textile cationic and anionic dye removal, encompassing various aspects from influential parameters to kinetics, adsorption isotherms, desorption, and thermodynamics studies. Its scope and other considerations are also discussed along with its benefits. The collective knowledge synthesized in this paper is intended to contribute to the advancement of sustainable and efficient water treatment technologies in the textile industry. Full article

Polysaccharides have recently attracted growing attention as adsorbents for various pollutants, since they can be extracted from a variety of renewable sources at low cost. An interesting hydrophilic and biodegradable polysaccharide is dextran (Dx), which is well-known for its applications in the food industry and in medicine. To extend the application range of this biopolymer, in this study, we investigated the removal of crystal violet (CV) and methylene blue (MB) dyes from an aqueous solution by Dx-based cryogels using the batch technique. The cryogel adsorbents, consisting of cross-linked Dx embedding a polyphenolic (PF) extract of spruce bark, were prepared by the freeze-thawing approach. It was shown that the incorporation of PF into the Dx-based matrix induced a decrease in porosity, pore sizes and swelling ratio values. Moreover, the average pore sizes of the DxPF cryogels loaded with dyes further decreased from 42.30 ± 7.96 μm to 23.68 ± 2.69 μm, indicating a strong interaction between the functional groups of the cryogel matrix and those of the dye molecules. The sorption performances of the DxPF adsorbents were evaluated in comparison to those of the Dx cryogels and of the PF extract. The experimental sorption capacities of the DxPF cryogel adsorbents were higher in comparison to those of the Dx cryogels and the PF extract. The DxPF cryogels, particularly those with the highest PF contents (sample DxPF2), demonstrated sorption capacities of 1.2779 ± 0.0703 mmol·g⁻¹, for CV, and 0.3238 ± 0.0121 mmol·g⁻¹, for MB. The sorption mechanisms were analyzed using mathematical models, including Langmuir, Freundlich, Sips and Dubinin–Radushkevich isotherms, and kinetic models, like pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich and intra-particle diffusion (IPD). The sorption process was best described by the Sips isotherm and PSO kinetic models, indicating chemisorption as the dominant mechanism. This study outlines the importance of developing advanced renewable materials for environmental applications. Full article