Preparation, characterization, and adsorption kinetics of graphene oxide/chitosan/carboxymethyl cellulose composites for the removal of environmentally relevant toxic metals

Steric and energetic studies on adsorption of toxic arsenic ions by hematite nano-rods from laterite highlighting the impact of modification periods

This study presents a facile, cost-effective hydrothermal transformation of natural lateritic iron ore into hematite nanorods, offering significant economic and technical benefits for the remediation of toxic arsenic ions. Lateritic iron ore was subjected to alkaline modification for different durations (12 h (HM12), 24 h (HM24), 36 h (HM36), and 48 h (HM48)), leading to morphological evolution into nanorod structures (2D) with variations in surface area, crystallinity, and adsorption efficacy for arsenate (As(V)) ions. Comprehensive characterization confirmed significant structural and physicochemical modifications. X-ray diffraction (XRD) analysis revealed a shift in peak positions and intensity reduction, indicative of lattice strain and increased surface defects. Fourier-transform infrared spectroscopy (FT-IR) confirmed modifications in the Fe-O coordination, and Brunauer-Emmett-Teller (BET) surface area analysis demonstrated a notable increase in surface area, with HM36 exhibiting the highest value (154.7 m2/g). Adsorption experiments indicated that HM36 achieved the highest As(V) removal capacity (151.4 mg/g), followed by HM48 (138.2 mg/g), HM24 (125.4 mg/g), and HM12 (113.8 mg/g). Advanced equilibrium modeling revealed steric and energetic parameters governing the adsorption mechanism, with HM36 exhibiting the highest density of active sites (Nm = 67.9 mg/g). Each active site accommodated up to three As(V) ions, emphasizing the significance of multi-ionic interactions and vertical stacking at the adsorption interface. The adsorption energy, evaluated using both classic models (< 4 kJ/mol) and advanced statistical physics models (< 9 kJ/mol), confirmed a predominantly physical and exothermic adsorption mechanism. Thermodynamic evaluations further supported the spontaneous and favorable nature of As(V) adsorption across all modified hematite derivatives. The ease of synthesis, low-cost natural precursor, improved adsorption efficiency, and recyclability highlight the potential application of these hematite nanorods in real-world wastewater remediation. The findings suggest that HM36 is a highly efficient and scalable adsorbent for arsenic removal, offering sustainable solutions for industrial and agricultural wastewater treatment.

Dibenzo-18-Crown-6 modified lignin as a sustainable adsorbent for removal of Lead and cadmium ions from aqueous solutions

A novel adsorbent was synthesized by integrating lignin extracted from walnut shells with dibenzo[18]crown-6 (DB18C6), and its potential for eliminating lead and cadmium ions from aqueous solutions was evaluated. Both lignin (LGN) and DB18C6 can individually adsorb heavy metals. However, the adsorption capacity of the composite was significantly and synergistically enhanced by adding DB18C6 to LGN. The removal percentages for Cd2+ and Pb2+ by the [LGN + DB18C6] composites were much higher than those of the individual LGN and DB18C6 composites. Lignin is tagged with dibenzo[18]crown-6 to introduce crown ether functionalities, which enhance its ability to bind metal ions. The synthesized adsorbent was characterized using various advanced physicochemical techniques, including FTIR, FESEM, BET, and EDX. The optimal conditions for achieving the highest removal rate in this study were determined to be a contact time of 10 to 20 min, a pH of 5.0, an adsorbent dosage of 0.011 g, and ion concentrations in the range of 5.0-30 mg/L for lead and cadmium ions, respectively. The sorption behavior of lead and cadmium ions was modeled using pseudo-second-order kinetics and Langmuir isotherm equations. The highest removal capacities of the modified lignin for Cd2+ and Pb2+ ions were determined to be 400 mg/g and 227.3 mg/g, respectively. Key variables influencing the adsorption process, such as temperature, mixing time, adsorbent amount, pH, and initial ion concentration, were systematically analyzed. Importantly, the adsorbent demonstrated excellent reusability, as it could be efficiently regenerated using 0.1 M hydrochloric acid.

Utilization of a constructed nanohydroxyapatite/Arabic gum/alginate composite based on cuttlefish bone for the removal of cadmium ions

The purpose of this work is to explore the efficacy of cadmium ions (Cd2+) removal employing adsorption onto manufactured solid nanomaterials. This study synthesized three nanosolid adsorbents: nanohydroxyapatite based on cuttlefish bone (NHAPs), nanohydroxyapatite/alginate beads (HC), and nanohydroxyapatite/Arabic gum/alginate as triple biocomposite (HGC) beads. Various physicochemical techniques were used to study the morphological, physical, and chemical characteristics of solid nanoadsorbents. The fabricated triple composite (HGC) showed a higher surface area (564.9 m2/g), acceptable pHPZC (7.3), and average TEM particle size of 150 nm. These manufactured materials were used as solid adsorbents to eliminate cadmium ions from wastewater under various test conditions such as shaking time, sample dose, pH, starting Cd2+ concentration, and temperature. The data revealed that HGC had a greater adsorption capacity (246.10 mg/g) at 16 °C. The adsorption of Cd2+ was well applied by nonlinear pseudo-first order and Elovich as kinetic investigations, besides Langmuir and Temkin models according to adsorption isotherm investigations onto all the samples. Based on the values of reduced chi-square value (ꭓ2), the pseudo-first order and Langmuir models are more accepted models for Cd2+ adsorption. The thermodynamic study revealed that the adsorption process of Cd2+ is endothermic and spontaneous. After eight adsorption and desorption operations, the highest batch adsorption capacity was reduced by 1.45 % for NHAPs, 5.49 % for HC, and 5.24 % for HGC. Our findings demonstrated that HGC has outstanding adsorption capacity, quick kinetics, and high effectiveness promising composite in water treatment applications.

Co-precipitation fabrication of cellulose/chitosan-aniline grafted composites for efficient removal of Pb2+ ions from aqueous solution

Heavy metal ions, are non-biodegradable, high toxic tendency, and have serious hazardous effects on the health of humans. Then, removing them from the environment using different techniques is necessary. Several routes are expensive, low-efficient, and require a long time to achieve adsorption equilibrium. In this paper, novel chitosan-based composites CS/CL@An-1 and CS/CL@An-2 were synthesized, characterized by FT-IR, DSC, XRD, and SEM, and applied as new adsorbents in batch experiments for the removal of Pb2+ ions from aqueous solution. The effect of important parameters such as initial pH solution (2-7), adsorbent dose (0.005, 0.01, and 0.02 g), adsorption contact time (0-240 min), initial Pb2+ metal ion (25-200 mg/L) and ionic strength on their adsorption behavior was investigated. The adsorption results at best conditions (pH solution = 6, adsorbent dose = 0.02 g, contact time = 180 min and initial ion concentration = 100 mg/L) predicted that the maximum removal percentage (adsorption capacity) of Pb2+ metal ion using CS/CL@An-1 and CS/CL@An-2 is 95.6 % (239 mg/g) and 98.8 % (247 mg/g), respectively, much higher than other chitosan-based adsorbents. The absorption kinetic results confirmed that the adsorption of Pb2+ showed the best fit with the pseudo-second-order (PSO) model as a chemisorption process. The absorption mechanism was regulated by the coordination and n-π attractions of Pb2+ ions with the active sites on the surface of adsorbents. The adsorption of Pb2+ was well-fitted by a homogeneous monolayer Langmuir isotherm model. Finally, the reusability of adsorbents was examined after five adsorption-desorption cycles, and the results show that the adsorption efficiency still reaches >90 %. Therefore, the compounds were potentially new adsorbents for removing Pb2+ ions from aqueous solution.

Manufacturing sulfated cellulose nanofibers using a unique combined DES-based pretreatment-functionalization protocol for metal ion decontamination through porous adsorbents

This study confirms the efficacy of a unique combined pretreatment-functionalization protocol based on the use of deep eutectic solvent (DES) to obtain sulfated lignocellulose and cellulose nanofibers (SLNF or SNF) hydrogels, which have been successfully shaped as sponge-based adsorbents and fruitfully assessed for the removal of heavy metals from water. A comprehensive characterization study was conducted, demonstrating an excellent degree of sulfation (0.62) in DES-treated wheat straw-derived nanofibers. The direct use of SLNF or SNF hydrogels and their application as porous sponges exhibited highly favorable characteristics for successful ion decontamination. Cu2+ removal was up to 70 % higher using DES-sulfated nanocellulose hydrogels compared to conventional treated-nanocellulose. Various isotherm models were studied, and the analysis of the kinetic and diffusion studies confirmed the influence of the sample format in the removal behavior. SLNF and SNF-sponges proved to be the most effective in adsorption, achieving Cu2+ removal rates of up to 60 %. More profitable decontamination processes with lower run times could be guessed when the application of nanocellulose is led through the processing of advanced formats. The easy handling of sponges would avoid the extra costs of the downstream unit operations which are sometimes needed to separate the hydrogel of the decontaminated media.

Amino acid functionalized carboxymethyl cellulose-based crosslinked aerogels for efficient removal of dye and metal ion from aqueous solution

In order to protect water resources and maintain sustainable development of society, it is crucial to design the adsorption materials with high adsorption capacity and environmental friendliness to effectively remove the pollutants in wastewater. In this study, amino acid functionalized carboxymethyl cellulose-based aerogels were successfully prepared by combining grafting, blending, freeze-drying and crosslinking technologies. The aerogels exhibited outstanding adsorption properties for methylene blue (MB) and lead ions (Pb (II)) with adsorption capacities of 461.68 and 304.60 mg/g, respectively. The adsorption experiment showed that the adsorption process of aerogels for MB conformed to Freundlich adsorption isotherm model and quasi-second-order kinetics model, and the adsorption process for Pb (II) conformed to Langmuir model and quasi-second-order kinetics model. Furthermore, the aerogels displayed excellent recyclability, with the removal efficiency of over 90.0 % for MB and only 14.0 % reduction for Pb (II) after 6 cycles. It is evident that the aerogels hold great potential for application in wastewater treatment, which has important practical significance for environmental protection and high-value utilization of natural polymers.

Facile preparation of NiFe2O4 decorated chitosan-graphene oxide for efficient remediation of Co(II) and adsorption mechanism

In the background of severe water pollution, adsorption is a charming technique for heavy metal remediation. In this work, NiFe2O4 decorated chitosan-graphene oxide (NFCG) was prepared by simple hydrothermal method for Co(II) remediation application. Adsorption mechanism was elaborately elucidated based on multiple evidences extracted from adsorption fitting (isotherms, thermodynamics and kinetics), spectroscopic test (XPS, UV-Vis absorption, fluorescent emission and Raman spectra) and the hard-soft acid-base (HSAB) theory inspection. Result shows, for Co(II) with initial concentration 200 mg·L-1, NFCG with dosage 500 mg·L-1 reaches adsorption equilibrium in 24 min, rendering removal percentage and adsorption amount 96.87 % and 387.48 mg·g-1, respectively. Owing to the efficient recovery enabled by paramagnetism, NFCG keeps adsorption amount 311.01 mg·g-1 for Co(II) after six consecutive cycles. Moreover, NFCG exhibits selectivity towards Co(II) under the coexistence of common interfering substances. Adsorption fitting suggests chemical adsorption based on heterogeneous affinity. Spectroscopic analysis discloses, CO, CO, -C(=O)NH-, OH and aromatic part contribute to Co(II) adsorption via electron donation, forming CoO bond. This atomic scale adsorption mechanism was substantiated by HSAB theory calculation. In brief, this work provides basic knowledge and technical support for fabricating high efficiency magnetic bio adsorbent.

Eco-Friendly Carbon Nanotubes Reinforced with Sodium Alginate/Polyacrylic Acid for Enhanced Adsorption of Copper Ions: Kinetics, Isotherm, and Mechanism Adsorption Studies

This study investigates the removal efficiency of Cu2+ from wastewater using a composite hydrogel made of carbon nanotubes (CNTs), sodium alginate (SA), and polyacrylic acid (PAA) prepared by free radical polymerization. The CNTs@SA/PAA hydrogel's structure and properties were characterized using SEM, TEM, FTIR, XRD, rheology, DSC, EDS, elemental mapping analysis, and swelling. The adsorption performance for Cu2+ was tested in batch adsorption experiments, considering the pH, dosage, initial concentration, and contact time. The optimal conditions for Cu2+ removal were pH 5.0, an adsorbent dosage of 500 mg/L, and a contact time of 360 min. The adsorption followed pseudo-second order kinetics. Isotherm analyses (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Sips, Toth, and Khan) revealed that the Freundlich isotherm best described the adsorption, with a maximum capacity of 358.52 mg/g. A thermodynamic analysis indicated that physical adsorption was the main interaction, with the spontaneity of the process also demonstrated. This study highlights the high efficiency and environmental friendliness of CNT@SA/PAA composites for Cu2+ removal from wastewater, offering a promising approach for water treatment.

Mucoadhesive phenylboronic acid-grafted carboxymethyl cellulose hydrogels containing glutathione for treatment of corneal epithelial cells exposed to benzalkonium chloride

Benzalkonium chloride (BAK) is the most commonly-used preservative in topical ophthalmic medications that may cause ocular surface inflammation associated with oxidative stress and dry eye syndrome. Glutathione (GSH) is an antioxidant in human tears and able to decrease the proinflammatory cytokine release from cells and reactive oxygen species (ROS) formation. Carboxymethyl cellulose (CMC), a hydrophilic polymer, is one of most commonly used artificial tears and can promote the corneal epithelial cell adhesion, migration and re-epithelialization. However, most of commercial artificial tears provide only temporary relief of irritation symptoms and show the short-term treatment effects. In the study, 3-aminophenylboronic acid was grafted to CMC for increase of mucoadhesive properties that might increase the precorneal retention time and maintain the effective therapeutic concentration on the ocular surface. CMC was modified with different degree of substitution (DS) and characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. Phenylboronic acid (PBA)-grafted CMC hydrogels have interconnected porous structure and shear thinning behavior. Modification of CMC with high DS (H-PBA-CMC) shows the strong bioadhesive force. The optimal concentration of GSH to treat corneal epithelial cells (CECs) was evaluated by cell viability assay. H-PBA-CMC hydrogels could sustained release GSH and decrease the ROS level. H-PBA-CMC hydrogels containing GSH shows the therapeutic effects in BAK-damaged CECs via improvement of inflammation, apoptosis and cell viability. After topical administration of developed hydrogels, there was no ocular irritation in rabbits. These results suggested that PBA-grafted CMC hydrogels containing GSH might have potential applications for treatment of dry eye disease.

Fabrication of melamine formaldehyde/graphene oxide composite for efficient static and dynamic adsorption of lead ions from aqueous medium

The present work discusses the synthesis, characterization, and environmental applications of graphene oxide (GO), melamine formaldehyde resin (MF), and melamine formaldehyde/graphene oxide composite (MGO) for the efficient removal of Pb2+ from aqueous medium via batch and column procedures. TGA, XRD, TEM, zeta potential, nitrogen adsorption/desorption, ATR-FTIR, and other characterization techniques revealed that MGO is characterized by a greater surface area (609 m2/g), total pore volume (1.0106 cm3/g), pHPZC (6.5), and the presence of various surface chemical functional groups. The synthesized solid adsorbents were used in both static and dynamic adsorption processes to remove Pb2+, with varying application parameters such as pH, starting concentration, adsorbent dosage, and shaking time in the case of static adsorption method. While through the column adsorption process the effects of column bed height, flow rate, and starting Pb2+ were taken into consideration. Results of the batch adsorption demonstrated that MGO had the highest Langmuir adsorption capacity (201.5 mg/g), and the adsorption fit the nonlinear Langmuir adsorption model and Elovich kinetic models. The adsorption of Pb2+ onto all prepared solid materials is endothermic, spontaneous, and physical in nature, as demonstrated by thermodynamic studies. Column adsorption of Pb2+ well fitted by Thomas and Yoon Nelson nonlinear adsorption models. MGO showed a maximum column adsorption capacity of 168 mg/g when applying 4 cm, 15 mL/min, and 150 mg/L as bed height, flow rate, and initial Pb2+, respectively. With only a 12.6% reduction in its adsorption capacity, column regeneration showed that MGO exhibited a high degree of reusability even after five cycles of adsorption/desorption studies.

Insights into adsorption performance and mechanism of chitosan-bentonite biocomposites for removal of imazethapyr and imazamox

In the present study, chitosan-bentonite biocomposites were synthesised by ultrasonication, characterized using spectral techniques and assessed for their effectiveness in removing imazethapyr and imazamox from aqueous solution. The response surface methodology based box behnken design was utilized to generate optimum conditions viz. pH (1 to 9), adsorbent dose (0.01 to 1.0 g), contact time (0.5 to 48 h) and temperature (15 to 55 °C) for adsorption of herbicides on biocomposites. Based on model predictions, 60.4 to 91.5 % of imazethapyr and 31.7 to 46.4 % of imazamox was efficiently removed under optimal conditions. Adsorption data exhibited a strong fit to pseudo-second-order kinetic (R2 > 0.987) and Freundlich isotherm (R2 > 0.979). The adsorption capacity ranged from 3.88 to 112 μg1-ng-1mLn and order of adsorption was: low molecular weight chitosan-bentonite> medium molecular weight chitosan-bentonite> high molecular weight chitosan-bentonite> bentonite. Thermodynamic experiments suggested a spontaneous, exothermic process, reducing the system randomness during adsorption. Desorption experiments revealed successful desorption ranging from 91.5 to 97.0 % using 0.1 M NaOH. The adsorption mechanism was dominated by synergistic electrostatic interactions and hydrogen bonding. These results collectively indicated the potential environmental remediation application of chitosan-bentonite biocomposites to adsorb imazethapyr and imazamox from wastewaters.