Modification of chitin with high adsorption capacity for methylene blue removal

Chemical modifications and applications of chitin and chitosan

This letter emphasizes the potential of chemically modified chitin and chitosan in natural product research. Extracted from crustacean shells, these biopolymers are known for their biocompatibility, biodegradability and non-toxicity. Chemical modifications improve their solubility, adsorption capacity and antimicrobial properties, making them ideal for applications in drug delivery, wound healing and pollutant removal. Furthermore, combining natural products with modified chitosan creates novel therapeutic agents with increased efficacy and fewer side effects. This research highlights the significance of exploring the various applications of chitin and chitosan, aligning with the journal's focus on innovative natural product solutions.

Innovative chitin-glucan based material obtained from mycelium of wood decay fungal strains

Fungi are an alternative source to animal-based chitin. In fungi, chitin fibrils are strongly interconnected and bound with glucans that justify the unique matrix. The present study aimed to extract chitin and glucans from the mycelium of several wood decay fungal strains in order to obtain flexible materials and to check correlations between chitin content and the mechanical properties of these materials. Five strains were chosen in consideration of their different cell wall chemical composition (high content of α-glucans, β-glucans or chitin) to evaluate how these differences could influence the mechanical and chemical characteristics of the material. The fungal strains were cultivated in liquid-submerged dynamic fermentation (both flasks and bioreactor). Chitin and glucans were crosslinked with acetic acid and plasticized with glycerol to obtain flexible sheets. Abortiporus biennis, Fomitopsis iberica and Stereum hirsutum strains were found to adapt to produce material with adequate flexibility. The obtained materials were characterized by Thermogravimetric analysis (TGA) for the understanding of the material composition. The material obtained from each species was mechanically tested in terms of tear strength, elongation at break, and Young's modulus.

Removal of cationic dyes from aqueous solution using polyacrylic acid modified hemp stem

Water pollution caused by dyes is a pressing environmental challenge due to their persistence and difficulty in degradation. Herein, an anionic adsorbent (HS-PAANa) was synthesized by grafting polyacrylic acid (PAA) onto the agricultural waste-hemp stem (HS). The obtained HS-PAANa adsorbent exhibited rapid adsorption kinetics, high adsorption capacity, and a favorable preference for cationic dyes, such as methylene blue (MB) and crystal violet (CV). The experimental data fit well with the pseudo-second-order kinetic model and Langmuir isotherm, demonstrating the efficiency of HS-PAANa in dye removal. Notably, the optimal adsorption capacities of HS-PAANa for MB and CV were found to be 1296.65 mg/g and 1451.43 mg/g, respectively. In the cationic/anionic dyes (MB/MO) binary systems, HS-PAANa exhibited enhanced selective adsorption of cationic dyes (MB), indicating its potential for targeted removal of specific dyes from mixed solutions. Moreover, HS-PAANa adsorption shows an excellent recyclability, after five cycles, HS-PAANa still maintained MB and CV removal rates of 93.85% and 95.08%, respectively. Therefore, the bioadsorbent HS-PAANa exhibits high potential as a highly efficient adsorbent for the effective treatment of cationic pollutants in wastewater.

Surface modification of chitin nanofibers with dopamine as efficient nanosorbents for enhanced removal of dye pollution and metal ions

The development of environmentally friendly and low-cost adsorbents with high adsorption capacity remains a challenge. Herein, chitin nanofiber-polydopamine composite materials (CNDA) have been obtained by surface modification of chitin nanofiber using dopamine. According to the results of transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), and X-ray photoelectron spectrometer (XPS), polydopamine have been successfully coated on the surface of chitin nanofiber (ChNF). The ability to remove methylene blue (MB) has been analyzed via standard adsorption experiments, indicating that the maximum adsorption capacity (qmax) can reach 196.6 mg/g at MB initial concentration of 50 mg/L. Most importantly, the adsorption kinetics, isotherm, and thermodynamics were used to investigate the MB adsorption mechanism on composites. This indicated that the polydopamine on the surface of chitin nanofiber (ChNF) plays an important role in the MB dye adsorption. Moreover, the removal ability of CNDA to metal ions has also been investigated, indicating high capacities for Fe3+, Mn2+, Cu2+, and Ni2+. Based on their biodegradability and good adsorption capacity, the CNDA composite material can be considered a promising adsorbent for wastewater treatment.

Deep eutectic solvent-treated palm oil mill sludge adsorbents for methylene blue adsorption

This study evaluated the adsorptive properties of deep eutectic solvent (DES)-treated palm oil mill sludge adsorbents for methylene blue removal. The adsorbents were prepared at a ratio of 1:2 at 80°C to form P1:D2@80°C, at 25°C to form P1:D2@25°C and without DES to form dry sludge (DS). The adsorbent samples were characterized for surface functional groups, textural properties and surface morphology. The values of specific area were 534, 236 and 184 m2/g, respectively. Batch adsorption of methylene blue at varying concentration, adsorbent dosage, pH, contact time and temperature was performed. The maximum adsorption capacities by Sips model were recorded as 72.07, 56.18 and 48.33 mg/g for P1:D2@80°C, P1:D2@25°C and DS, respectively. P1:D2@80°C displayed the highest rate constant (Ks = 0.0037 g/mg.min). The adsorption data were well fitted into Sips isotherm and pseudo-second-order kinetic models, suggesting that the adsorption is a physical process onto heterogeneous adsorbent surface via pore filling and electrostatic attraction. The adsorption was spontaneous, feasible and exothermic with decreased disorderliness in the solid-bulk solution interface. The DES-treated palm oil mill sludge adsorbent is a promising alternative adsorbent for dye removal from wastewater.

Box-Behnken design with desirability function for methylene blue dye adsorption by microporous activated carbon from pomegranate peel using microwave assisted K2CO3 activation

This research aims to convert pomegranate peel (PP) into microporous activated carbon (PPAC) using a microwave assisted K2CO3 activation method. The optimum activation conditions were carried out with a 1:2 PP/K2CO3 impregnation ratio, radiation power 800 W, and 15 min irradiation time. The statistical Box-Behnken design (BBD) was employed as an effective tool for optimizing the factors that influence the adsorption performance and removal of methylene blue (MB) dye. The output data of BBD with a desirability function indicate a 94.8% removal of 100 mg/L MB at the following experimental conditions: PPAC dose of 0.08 g, solution pH of 7.45, process temperature of 32.1 °C, and a time of 30 min. The pseudo-second order (PSO) kinetic model accounted for the contact time for the adsorption of MB. At equilibrium conditions, the Freundlich adsorption isotherm describes the adsorption results, where the maximum adsorption capacity of PPAC for MB dye was 291.5 mg g-1. This study supports the utilization of biomass waste from pomegranate peels and conversion into renewable and sustainable adsorbent materials. As well, this work contributes to the management of waste biomass and water pollutant sequestration.

High-strength, antibacterial, antioxidant, hemostatic, and biocompatible chitin/PEGDE-tannic acid hydrogels for wound healing

Natural polymer hydrogels are widely used in various aspects of biomedical engineering, such as wound repair, owing to their abundance and biosafety. However, the low strength and the lack of function restricted their development and application scope. Herein, we fabricated novel multifunctional chitin/PEGDE-tannic acid (CPT) hydrogels through chemical- and physical-crosslinking strategies, using chitin as the base material, polyethylene glycol diglycidyl ether (PEGDE) and tannic acid (TA) as crosslinking agents, and 90 % ethanol as the regenerative bath. CPT hydrogels maintained a stable three-dimensional porous structure with suitable water contents and excellent biocompatibility. The mechanical properties of hydrogels were greatly improved (tensile stress up to 5.43 ± 1.14 MPa). Moreover, CPT hydrogels had good antibacterial, antioxidant, and hemostatic activities and could substantially promote wound healing in a rat model of full-thickness skin defect by regulating inflammatory responses and promoting collagen deposition and blood vessel formation. Therefore, this work provides a useful strategy to fabricate novel multifunctional CPT hydrogels with excellent mechanical, antibacterial, antioxidant, hemostatic, and biocompatible properties. CPT hydrogels could be promising candidates for wound healing.

Multifunctional Cross-Linked Shrimp Waste-Derived Chitosan/MgAl-LDH Composite for Removal of As(V) from Wastewater and Antibacterial Activity

This work synthesized a novel chitosan-loaded MgAl-LDH (LDH = layered double hyroxide) nanocomposite, which was physicochemically characterized, and its performance in As(V) removal and antimicrobial activity was evaluated. Chitosan-loaded MgAl-LDH nanocomposite (CsC@MgAl-LDH) was prepared using cross-linked natural chitosan from shrimp waste and modified by Mg-Al. The main mechanisms predominating the separation of As(V) were elucidated. The characteristic changes confirming MgAl-LDH modification with chitosan were analyzed through Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis-differential thermal analysis, and Brunauer-Emmett-Teller measurements. Porosity and the increased surface area play an important role in arsenic adsorption and microbial activity. Adsorption kinetics follows the general order statistically confirmed by Bayesian Information Criterion differences. To understand the adsorption process, Langmuir, Freundlich, and Liu isotherms were studied at three different temperatures. It was found that Liu's isotherm model was the best-fitted model. CsC@MgAl-LDH showed the maximum adsorption capacity of 69.29 mg g^-1 toward arsenic at 60 °C. It was observed that the adsorption capacity of the material rose with the increase in temperature. The spontaneous behavior and endothermic nature of adsorption was confirmed by the thermodynamic parameters study. Minimal change in percentage removal was observed with coexisting ions. The regeneration of material and adsorption-desorption cycles revealed that the adsorbent is economically efficient. The nanocomposite was very effective against Staphylococcus aureus and Bacillus subtilus.

One-Pot Synthesis of Cellulose/MXene/PVA Foam for Efficient Methylene Blue Removal

Ti₃C₂T_x MXene has attracted considerable interest as a new emerging two-dimensional material for environmental remediation due to its high adsorption capacity. However, its use is greatly limited by its poor mechanical properties, low processability and recyclability, and the low dispersity of such powder materials. In this work, a porous adsorbent (C–CMP) containing cellulose nanocrystals (CNC), Ti₃C₂T_x MXene and polyvinyl alcohol (PVA) was prepared by a simple and environmentally-friendly foaming method. Glutaraldehyde was used as crosslinker to improve the mechanical properties and boost the adsorption efficiency of methylene blue (MB) molecules. Fourier transform infrared (FT–IR), elemental analysis (EDX) and thermogravimetric analysis (TGA) further confirmed that the preparation of the C–CMP foam and cross-linking reaction were successful. Scanning electron microscope (SEM) indicated that the macropores were distributed homogeneously. The adsorption experiment showed that maximum adsorption capacity of MB can reach 239.92 mg·g⁻¹ which was much higher than anionic dye (methyl orange, 45.25 mg·g⁻¹). The adsorption behavior fitted well with the Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. Based on FT–IR, EDX and X-ray photoelectron spectroscopy (XPS) analysis, the adsorption mechanism between C–CMP and MB molecules was attributed to electrostatic interaction.

Applications of chitin and chitosan based biomaterials for the adsorptive removal of textile dyes from water - A comprehensive review

The presence of pollutants in the water bodies deteriorate the water quality and make it unfit for use. From an environmental perspective, it is essential to develop new technologies for the wastewater treatment and recycling of dye contaminated water. The surface modified chitin and chitosan biopolymeric composites based adsorbents, have an important role in the toxic organic dyes from removal wastewater. The surface modification of biopolymers with various organics and inorganics produces more active sites at the surface of the adsorbent, which enhances dye and adsorbent interaction more reliable. Herein, the work brought in the thought of the application of various chitin and chitosan composites in wastewater remediation and suggested the versatility in composites for the development of rapid, selective and effective removal processes for the detoxification of a variety of organic dyes. It further emphasizes the existing obstruction and impending prediction for the deprivation of dyes via adsorption techniques.

A detailed insight on fabricated porous chitosan in eliminating synthetic anionic dyes from single and multi-adsorptive systems with related studies

Chitosan was fabricated via gelation method using CaBr₂.xH₂O/methanol solution and was studied as a potential adsorbent (MCh) in adsorbing anionic synthetic dyes like Bromophenol blue (BB), Direct blue 6 (DB) and Congo red (CR) from single (one dye species at a time) and multi (having two dyes; binary and all three dyes; tertiary) adsorptive systems. Physico-chemical modifications of MCh surface prior and post modification and dye adsorption were evaluated using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, powder X-ray diffraction analysis, surface area analysis and Fourier-transformed infrared spectroscopy. Influential parameters influencing the adsorption process viz. initial pH of dye solution, MCh dosage, adsorption temperature and initial concentration of dye species were optimised. Adsorptive studies involving single adsorptive setups verified formation of sorbate's (dye species) monolayer over the sorbent's (MCh) surface via chemisorption; as established by Langmuir isotherm and pseudo-second order kinetics model analysis. Theoretical maximum adsorption capacities of MCh for BB, DB and CR was found to be 81.301 mg/g, 163.934 mg/g and 75.758 mg/g, respectively. Meanwhile, for all multi-adsorptive systems, competitive Langmuir isotherm model verified antagonistic behaviour of an individual dye over other dye adsorption over MCh surface in their respective adsorptive systems. Thermodynamics of the sorbate-sorbent interaction was exothermic, spontaneous, with elevated degree of disorderedness; concluding the interaction as thermodynamically favourable. Co-existing metal cations and anionic salts had minimal effect on MCh's adsorption efficiency. Phytotoxicity assay via germination of Vigna mungo seeds verified the efficacy of the adsorbent in eliminating the dye species from single and multi-adsorptive systems.

A State-of-the-Art Review on Biowaste Derived Chitosan Biomaterials for Biosorption of Organic Dyes: Parameter Studies, Kinetics, Isotherms and Thermodynamics

Chitosan is a second-most abundant biopolymer on earth after cellulose. Its unique properties have recently received particular attention from researchers to be used as a potential biosorbent for the removal of organic dyes. However, pure chitosan has some limitations that exhibit lower biosorption capacity, surface area and thermal stability than chitosan composites. The reinforcement materials used for the synthesis of chitosan composites were carbon-based materials, metal oxides and other biopolymers. This paper reviews the effects of several factors such as pH, biosorbent dosage, initial dye concentration, contact time and temperature when utilizing chitosan-based materials as biosorbent for removing of organic dyes from contaminated water. The behaviour of the biosorption process for various chitosan composites was compared and analysed through the kinetic models, isotherm models and thermodynamic parameters. The findings revealed that pseudo-second-order (PSO) and Langmuir isotherm models were best suited for describing most of the biosorption processes or organic dyes. This indicated that monolayer chemisorption of organic dyes occurred on the surface of chitosan composites. Most of the biosorption processes were endothermic, feasible and spontaneous at the low temperature range between 288 K and 320 K. Therefore, chitosan composites were proven to be a promising biosorbent for the removal of organic dyes.

Synthesis of a Lignin-Fe/Mn Binary Oxide Blend Nanocomposite and Its Adsorption Capacity for Methylene Blue

A high-performance modified lignin adsorbent was prepared through coprecipitation of ferrous, ferric, and permanganate with lignin in sodium hydroxide solution. The structural characteristics of the synthesized lignin-Fe/Mn binary oxide blend nanocomposite (L-F/M) and its performance on the methylene blue (MB) removal from aqueous solution were evaluated. Influence factors of adsorption effects were analyzed including pH, contact time, dye concentration, temperature, and thermodynamics. The pseudo-second-order kinetic model well described the adsorption kinetics, and the adsorption isotherms best fitted the Langmuir model with a maximum adsorption capacity of 252.05 mg g-1 at 298 K. The adsorption mechanism showed that the L-F/M introduced the metallic element and negative charges to the lignin surface, which improved the adherence of MB via hydrogen bonding, electrostatic interaction, and coordination. Moreover, the removal ratio of MB maintained 81.2% after being used in five adsorption-desorption cycles. Results indicated that the L-F/M obtained was an efficient candidate for dye wastewater treatment.

Adsorption and Desorption Properties of Polyethylenimine/Polyvinyl Chloride Cross-Linked Fiber for the Treatment of Azo Dye Reactive Yellow 2

In this study, the optimal conditions for the fabrication of polyethylenimine/polyvinyl chloride cross-linked fiber (PEI/PVC-CF) were determined by comparing the adsorption capacity of synthesized PEI/PVC-CFs for Reactive Yellow 2 (RY2). The PEI/PVC-CF prepared through the optimal conditions was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) analyses. Several batch adsorption and desorption experiments were carried out to evaluate the sorption performance and reusability of PEI/PVC-CF for RY2. As a result, the adsorption of RY2 by PEI/PVC-CF was most effective at pH 2.0. A pseudo-second-order model fit better with the kinetics adsorption data. The adsorption isotherm process was described well by the Langmuir model, and the maximum dye uptake was predicted to be 820.6 mg/g at pH 2.0 and 25 °C. Thermodynamic analysis showed that the adsorption process was spontaneous and endothermic. In addition, 1.0 M NaHCO₃ was an efficient eluent for the regeneration of RY2-loaded PEI/PVC-CF. Finally, the repeated adsorption–desorption experiments showed that the PEI/PVC-CF remained at high adsorption and desorption efficiencies for RY2, even in 17 cycles.

Fungal chitin-glucan nanopapers with heavy metal adsorption properties for ultrafiltration of organic solvents and water

Membranes and filters are essential devices, both in the laboratory for separation of media, solvent recovery, organic solvent and water filtration purposes, and in industrial scale applications, such as the removal of industrial pollutants, e.g. heavy metal ions, from water. Due to their solvent stability, biologically sourced and renewable membrane or filter materials, such as cellulose or chitin, provide a low-cost, sustainable alternative to synthetic materials for organic solvent filtration and water treatment. Here, we investigated the potential of fungal chitin nanopapers derived from A. bisporus (common white-button mushrooms) as ultrafiltration membranes for organic solvents and aqueous solutions and hybrid chitin-cellulose microfibril papers as high permeance adsorptive filters. Fungal chitin constitutes a renewable, easily isolated, and abundant alternative to crustacean chitin. It can be fashioned into solvent stable nanopapers with pore sizes of 10-12 nm, as determined by molecular weight cut-off and rejection of gold nanoparticles, that exhibit high organic solvent permeance, making them a valuable material for organic solvent filtration applications. Addition of cellulose fibres to produce chitin-cellulose hybrid papers extended membrane functionality to water treatment applications, with considerable static and dynamic copper ion adsorption capacities and high permeances that outperformed other biologically derived membranes, while being simpler to produce, naturally porous, and not requiring crosslinking. The simple nanopaper production process coupled with the remarkable filtration properties of the papers for both organic solvent filtration and water treatment applications designates them an environmentally benign alternative to traditional membrane and filter materials.

Mechanistic understanding of the adsorption and thermodynamic aspects of cationic methylene blue dye onto cellulosic olive stones biomass from wastewater

In the current study, the mechanistic understanding of the adsorption isotherm and thermodynamic aspects of cationic methylene blue (MB) dye adsorption onto cellulosic olive stones biomass from wastewater were investigated. The batch adsorption of MB onto the olive stones (black and green olive stones) was tested at a variety of pH, dye concentrations, temperatures, and biomass particle sizes. The adsorption thermodynamics such as Gibbs free energy, enthalpy, and entropy changes were also calculated. Moreover, the desorption studies of MB from the spent olive stones were studied to explore the re-usability of the biomasses. The results revealed that under the optimum pH of 10, the maximum MB uptake was achieved i.e. 80.2% for the green olive stones and 70.9% for the black olive stones. The green olive stones were found to be more efficient in remediating higher MB concentrations from water than the black olive stones. The highest MB removal of the green olive stones was achieved at 600 ppm of MB, while the highest MB removal of the black olive stones was observed at 50 ppm of MB. Furthermore, for almost all the concentrations studied (50-1000 ppm), the MB adsorption was the highest at the temperature of 45 °C (P value < 0.05). It was shown by the Fourier transform infrared that the electrostatic interaction and hydrogen bonding were proposed as dominant adsorption mechanisms at basic and acidic pH, respectively. While the hydrophobic-hydrophobic interaction was a dominant mechanism at neutral pH. The thermodynamic studies revealed that the adsorption process was endothermic, spontaneous, and favorable. Moreover, the real wastewater experiment and the desorption studies showed that the green and black olive stones were a cost-effective and promising adsorbents for MB remediation from wastewater on account of their high adsorption and desorption removal capacities.

Utilization of nano-olive stones in environmental remediation of methylene blue from water

BACKGROUND

The use of agricultural waste as a low-cost adsorbent for the removal of hazardous methylene blue (MB) from aqueous solution was investigated. In this research, the potentiality of using black nano olive stones (black NOS) and green nano olive stones (green NOS) for MB adsorption was conducted.

METHODS

Various remediation parameters such as initial MB concentration, pH, and temperature were investigated. Thermodynamic study was carried out to determine the homogeneity of the adsorbent and spontaneity of the adsorption process. Different physical and chemical characterizations were studied using scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Brunauer-Emmett-Teller (BET) surface area, pore radius and pore volume.

RESULTS

It was found that NOS exhibits an acidic nature, however the highest MB removal efficiency was recorded at pH 10; reaching up to 71%. The negative value of the heat of the adsorption process (∆H ° ) indicated the reaction followed an exothermic pathway while the negative value of Gibbs adsorption (∆G ° ) further suggested its spontaneous nature. The results indicated that the Freundlich model described well the adsorption process with 99.5% correlation coefficient for green NOS. FTIR was used to analyze functional groups on the adsorbents' surfaces that could play vital roles in the remediation process. SEM analysis revealed that the adsorbents comprised of abundant spherical deep cavities and porous nature.

CONCLUSION

The result obtained successfully demonstrated the potential of using black and green NOS as suitable adsorbents for the removal of MB from water.

Biohybrid Hydrogel and Aerogel from Self-Assembled Nanocellulose and Nanochitin as a High-Efficiency Adsorbent for Water Purification

A simple and novel method, self-assembly of nanocellulose and nanochitin, was developed to produce high-efficiency and versatile biohybrid hydrogel (BHH) and aerogel (BHA) for water purification. The self-assembly process was driven by the electrostatic force between one-dimensional (1D) negatively charged TEMPO-oxidized cellulose nanofiber (TOCNF) and positively charged partly deacetylated chitin nanofiber (PDChNF). The self-assembly process was performed at room temperature and without adding any cross-linking agents throughout the process. This results in the three-dimensional (3D) BHH that physically cross-linked via both electrostatic interactions and hydrogen bonding between TOCNF and PDChNF. The obtained BHA from lyophilized BHH exhibited a highly porous interconnected structure with a specific surface area of 54 m²·g^-1, which assures the availability of its internal active site for the adsorption of toxic metalloid ions and organic pollutants. Consequently, the BHA displayed super-high adsorption capacities of 217 mg·g^-1 for As(III) under the neutral pH conditions and 531 mg·g^-1 for methylene blue (MB) under an alkaline aqueous condition with rapid adsorption kinetics, in sharp contrast to conventional biobased adsorbents. Moreover, the BHA is reusable, which still exhibited a high MB adsorption capacity of 505 mg·g^-1 even after five successive adsorption-desorption cycles. This versatile BHA produced via a facile preparation strategy is proven to be a promising renewable adsorbent for water purification, offering simple and green alternatives to the conventional adsorbent from synthetic polymers.

Nigella sativa seed based nanohybrid composite-Fe2O3-SnO2/BC: A novel material for enhanced adsorptive removal of methylene blue from water

In this work, an advance approach is reported for the water treatment technology using nanohybrid composite Fe₂O₃-SnO₂/BC prepared by incorporation of iron-tin binary oxide into the cellulosic framework of medicinally active Nigella sativa (Black cumin) seed powder. The co-precipitation method was followed to prepare the nanohybrid composite which was subjected to investigate its physiochemical properties using spectroscopic and microscopic techniques. Fourier-transform infrared spectroscopy analysis confirmed the formation of highly functionalized nanocomposite through the hydrogen and electrostatic interactions between the functional groups of seeds and Fe₂O₃-SnO₂. X-ray and selected area electron diffraction pattern revealed the presence of cubic phase of γ-Fe₂O₃ and tetragonal phase of SnO₂ in the composite. The scanning electron microscopic images suggested the porous and relatively smooth surface of the composite, and transmittance electron microscopic images showed the trapping of nano-cubes of Fe₂O₃-SnO₂, having particles size in the range 95-185 nm, into the organic framework of Black cumin seeds, whose zero point charge was found at pH 7.2. The composite was investigated for adsorption of Methylene blue dye from water for which the results revealed that 2.0 gL^-1 amount of Fe₂O₃-SnO₂/BC was sufficient to remove more than 95% dye, within 15 min, at 6-9 pH, from its 10 mgL^-1 concentration. The thermodynamic studies established spontaneity, feasibility, and endothermic nature of the adsorption process. The adsorption data was satisfactorily described by the Freundlich isotherm which indicated inhomogeneous surface of the composite. Application of Temkin isotherm revealed the same extent of bonding probability and heat of adsorption at 27, 35, and 45 °C. The free energy change calculated from Dubinin-Radushkevich isotherm suggested weak interaction between Methylene blue and Fe₂O₃-SnO₂/BC. The process satisfactorily followed the pseudo-second order kinetics that was controlled by the film diffusion step which indicated interaction of Methylene blue with functional sites of the Fe₂O₃-SnO₂/BC. The Fourier-transform infrared spectroscopy analysis gave the confirmatory evidence for interaction of Methylene blue to Fe₂O₃-SnO₂/BC. The maximum Langmuir adsorption capacity of the Fe₂O₃-SnO₂/BC was found to be 58.82 mgg^-1 at 27 °C which is higher than the previously reported adsorbents, MnFe₂O₄/BC [J. Clean. Prod. 2018. 200, 996-1008], and Fe₂O₃-ZrO₂/BC [J. Clean. Prod. 2019. 223, 849-868]. Therefore, the study showed excellent results for water treatment and can be useful to develop advance water treatment technology.

Phosphate adsorption from wastewater using ZnAl-LDO-loaded modified banana straw biochar

ZnAl-layered double hydroxide-loaded banana straw biochar (ZnAl-LDH-BSB) was prepared via the hydrothermal method, and the efficient phosphorus removal agent ZnAl-LDO-BSB was obtained by calcination at 500 °C. Based on the ZnAl-LDO-BSB adsorption characteristics, the adsorption mechanism was evaluated via TG/DTA, FTIR, XRD, SEM, HRTEM, and other characterization methods. The results showed that the ZnAl-LDO-BSB assembled into microspheres with typical hexagonal lamellar structures and presented good thermal stability. The adsorption of total phosphate (TP) by ZnAl-LDO-BSB conforms to the Langmuir model, and the theoretical maximum adsorption capacity is 185.19 mg g^-1. The adsorption kinetics were in accordance with the second-order kinetic model, and the anion influence on TP adsorption followed the order CO₃^2- > SO₄^2- > NO₃^-. The combination of zeta potential measurements with the FTIR, XRD, SEM, HRTEM, and XPS results suggested that ZnAl-LDO-BSB adsorbs TP mainly by electrostatic adsorption, surface coordination, and anion intercalation. Graphical abstract.

Bioinspired catecholamine/starch composites as superadsorbent for the environmental remediation

Focusing on the encouraging properties of starch-based composite materials, starch‑g‑(acrylic acid‑co‑acrylamide) superabsorbent was synthesized using solution polymerization method, and then the catecholamine functional groups were introduced on to pore surface of the absorbent via oxidative polymerization of dopamine (DA). The adsorbent was optimized in terms of the monomers' mass ratio and synthesis conditions, and characterized by different characterization techniques. The polydopamine (PDA) coating thickness was estimated using transmission electron microscopy (TEM) image and it was found to be 83 nm. The bimodal mesoporous adsorbent with 5914.66% swelling ratio bearing micropores with a specific surface area of 2.8031 m² g^-1 was used for the adsorption of methylene blue (MB) as a model water pollutant dye. The maximum adsorption capacity was obtained 2276 mg g^-1 at pH 9 and within 100 min. The adsorbent with unprecedented super high adsorption capacity can be encouraging from different environmental remediation points of view.

Characteristics of nitrogen and phosphorus adsorption by Mg-loaded biochar from different feedstocks

Herein, biochars from 6 different feedstocks (taro straw, corn straw, cassava straw, Chinese fir straw, banana straw, and Camellia oleifera shell) were produced using magnesium chloride (MgCl₂) as a modifier due to their sorption behavior toward NH₄⁺-N and phosphorus in an aqueous solution. The biochar characteristics were evaluated, including pH, pH_PZC, biochar magnesium content, and total pore volume (PV_tot). The experimental results in terms of the kinetics and equilibrium isotherms showed that the cassava straw and banana straw biochars exhibited the theoretical maximum saturated adsorption capacities of 24.04 mg·g^-1 (NH₄⁺-N) and 31.15 mg·g^-1 (TP), respectively. Biochar produced from these feedstocks had higher magnesium contents and greater total pore volumes, reflecting the significant contributions from magnesium and steric effects. FTIR, XRD, and SEM/EDS analyses demonstrated that NH₄⁺-N and TP sorption mechanisms predominantly involved surface electrostatic attraction, Mg²⁺ precipitates and complexation with surface hydroxyl functional groups.

Response surface methodology for optimization of methylene blue adsorption onto carboxymethyl cellulose-based hydrogel beads: adsorption kinetics, isotherm, thermodynamics and reusability studies

Environment-friendly composite hydrogel beads based on carboxymethyl cellulose (CMC), alginate (Alg) and graphene oxide (GO) were synthesized by an ionotropic gelation technique and studied as an efficient adsorbent for methylene blue (MB). The chemical structure and surface morphology of the prepared hydrogel beads were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA) and point of zero charge (pH_pzc). A hybrid response surface methodology integrated Box–Behnken design (RSM-BBD) was successfully developed to model, simulate, and optimize the biosorption process. The synergistic effects between three critical independent variables including adsorbent dose (0.3–0.7 g), pH of the MB solution (6.5–9.5) and initial MB concentration (15–45 mg L⁻¹) on the MB adsorption capacity (mg g⁻¹) and removal efficiency (%) were statistically studied and optimized. The performance of the RSM-BBD method was found to be very impressive and efficient. Results proved that the adsorption process follows a polynomial quadratic model since high regression parameters were obtained (R²-value = 99.8% and adjusted R²-value = 99.3%). Analysis of variance (ANOVA) further confirms the validity of the suggested model. The optimal conditions for 96.22 ± 2.96% MB removal were predicted to be 0.6 g of CMC-Alg/GO hydrogel beads, MB concentration of 15 mg L⁻¹ and pH of 9.5 within 120 min. The adsorption equilibrium is better described by the Freundlich isotherm, indicating that physisorption is the rate controlling mechanism. The MB adsorption process was thermodynamically spontaneous and endothermic. A reusability study revealed that the prepared adsorbent is readily reusable. The adsorbent still maintains its ability to adsorb MB for up to four cycles. Results reported in this study demonstrated that CMC-Alg/GO hydrogel beads are an effective, promising and recyclable adsorbent for the removal of MB from aqueous solutions.

Environment-friendly composite hydrogel beads based on carboxymethyl cellulose (CMC), alginate (Alg) and graphene oxide (GO) were synthesized by an ionotropic gelation technique and studied as an efficient adsorbent for methylene blue (MB).

MOF–cation exchange resin composites and their use for water decontamination

Cation exchange resin–ZIF-8 composite beads were prepared and used for the decontamination of water from dye and medical pollutants.