Removal of methylene blue from wastewater using ternary nanocomposite aerogel systems: Carboxymethyl cellulose grafted by polyacrylic acid and decorated with graphene oxide

Hydrogel-based nonwoven with persistent porosity for whole-stage hypertonic wound healing by regulating of water vaporization enthalpy

Moisture induced by wound exudate is crucial throughout the wound repair process. The dressing directly affects the absorption, permeation, and evaporation of the wound exudate. However, most dressings in clinical often result in excessive dryness or moisture of wound due to their monotonous structure and function, leading to ineffective thermodynamic control of evaporation enthalpy. Herein, a hydrogel-based nonwoven dressing (Gel-Fabric) with asymmetric amphiphilic surface and persistent microscopic porous structure is constructed by integrating intrinsic hydrophilic absorbent hydrogel fibers and hydrophobic ultrafine PET fibers. The novel Gel-Fabric facilitates rapid vertical drainage of wound exudate through the capillary effect and Laplace pressure synergy. Additionally, dynamic stepwise moisture management is also achieved by regulating the vaporization enthalpy of exudate. In vivo experiments confirm that Gel-Fabric significantly promotes wound healing, vascularization, and endothelialization, achieving a higher healing rate than ordinary dressings. Furthermore, compared to the clinical dressings, Gel-Fabric significantly reduces the frequency of dressing changes, offering improved outcomes for patients and more efficient wound management for healthcare providers.

Dual cross-linked magnetic gelatin/carboxymethyl cellulose cryogels for enhanced Congo red adsorption: Experimental studies and machine learning modelling

To achieve highly efficient and environmentally degradable adsorbents for Congo red (CR) removal, we synthesized a dual-network nanocomposite cryogel composed of gelatin/carboxymethyl cellulose, loaded with Fe3O4 nanoparticles. Gelatin and sodium carboxymethylcellulose were cross-linked using transglutaminase and calcium chloride, respectively. The cross-linking process enhanced the thermal stability of the composite cryogels. The CR adsorption process exhibited a better fit to the pseudo-second-order model and Langmuir model, with maximum adsorption capacity of 698.19 mg/g at pH of 7, temperature of 318 K, and initial CR concentration of 500 mg/L. Thermodynamic results indicated that the CR adsorption process was both spontaneous and endothermic. The performance of machine learning model showed that the Extreme Gradient Boosting model had the highest test determination coefficient (R2 = 0.9862) and the lowest root mean square error (RMSE = 10.3901 mg/g) among the 6 models. Feature importance analysis using SHapley Additive exPlanations (SHAP) revealed that the initial concentration had the greatest influence on the model's prediction of adsorption capacity. Density functional theory calculations indicated that there were active sites on the CR molecule that can undergo electrostatic interactions with the adsorbent. Thus, the synthesized cryogels demonstrate promising potential as adsorbents for dye removal from wastewater.

Biobased amphoteric aerogel with core-shell structure for the hierarchically efficient adsorption of anionic and cationic dyes

Efficient and simultaneous removal of anionic and cationic dyes from wastewater using low-cost and environmentally-friendly adsorbent is highly required. Herein, the carboxylated cellulose (carboxyl content: 2.97 mmol/g) derived from pomelo peel was extracted by a one-step H2O2/H2SO4-mediated oxidation method. Subsequently, a novel pomelo-peel cellulose/chitosan/sodium alginate (PCS) amphoteric aerogel with a specific core-shell structure was synthesized by multiple physical cross-linking strategies. The shell layer and core layer of the optimized P3CS0.75 aerogel can selectively adsorb cationic dyes and anionic dyes, in which, the theoretical maximum adsorption capacities were 888.27 mg/g and 1816.87 mg/g towards methylene blue (MB) and Congo red (CR), respectively. Especially, the aerogel's core/shell layer exhibited hierarchical adsorption behavior without overlapping sites even in the binary dye systems. The adsorption performance of obtained amphoteric aerogel remained effective in a wide pH range and under different practical water systems. Moreover, the removal efficiencies for MB and CR were slightly reduced from 90.76 % and 99.66 % to 88.08 % and 91.39 %, respectively, after 5 adsorption-desorption cycles, and the aerogel's structural integrity was also maintained due to its good compressive strength (487.16 KPa). In addition, the adsorption mechanism of PCS aerogel was investigated using adsorption kinetics, isotherm, thermodynamics, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. It was proved that the adsorption process was endothermic spontaneous-monolayer adsorption driven by electrostatic attraction and hydrogen bonding. Therefore, the prepared biobased aerogel was expected to be a prospective material for removing mixed dyes from wastewater.

Green preparation of polydopamine-modified multiwalled carbon nanotube/calcium alginate composite aerogels for effective adsorption of methylene blue

Polydopamine-modified multiwalled carbon nanotube/calcium alginate (P-CNTs/CA) aerogel was greenly prepared. The synthesis method of the P-CNTs/CA aerogel was evaluated for its environmental friendliness. SEM, FT-IR, Raman, TGA, BET, XPS, and Zeta potential characterized the P-CNTs/CA aerogel. Batch adsorption experiments were conducted to assess the adsorption efficacy of the P-CNTs/CA aerogel on methylene blue (MB). The results demonstrated that the maximum theoretical adsorption capacity of the P-CNTs/CA aerogel for MB was 506.12 mg‧g-1. The adsorption kinetics analysis indicated that the adsorption of MB by the P-CNTs/CA aerogel was more consistent with the pseudo-second-order model. The adsorption isotherm analysis demonstrated that the Sips model exhibited the most accurate fit to the experimental data. The adsorption thermodynamics showed that the adsorption process was spontaneous and heat-absorbing. The adsorption mechanism of MB adsorption by P-CNTs/CA aerogel was analyzed graphically by the density functional theory (DFT) and independent gradient model (IGM), which revealed the involvement of hydrogen bonding, electrostatic, and dispersive interactions. In parallel, the distribution of adsorption forces was analyzed using isosurfaces. Adsorption desorption experiment showed that the P-CNTs/CA aerogel maintained 79 % removal capacity after six adsorption cycles.

Biosynthesis of TiO2/CuO and Its Application for the Photocatalytic Removal of the Methylene Blue Dye

In this study, we successfully synthesized a TiO2/CuO nanocomposite using the aqueous extract of Impatiens tinctoria A.rich. leaf extract as a capping, reducing, and stabilizing agent for the first time in an environmentally friendly, low-cost, straightforward, and sustainable technique. Numerous characterization techniques such as ultraviolet-visible diffuse reflectance spectroscopy (UV-vis-DRS), photoluminescence (PL), Raman spectroscopy, Fourier-transform infrared (FTIR), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and high resolution TEM (HRTEM) were used to characterize the obtained TiO2/CuO nanocomposite. XRD verified that the TiO2/CuO nanocomposite has an average crystallite size of about 21 nm. The TEM result revealed an average particle size of 29 nm for the biosynthesized TiO2/CuO NC. The HRTEM analysis showed the presence of polycrystalline structures with the predominant lattice fringes 0.352 and 0.19 which were attributed to anatase phase TiO2 in the crystal plane of (101) and (200), respectively. The lattice fringes for monoclinic CuO were observed with values of 0.213 and 0.252 for the lattice planes of (111) and (111̅), respectively. The photoluminescence spectroscopic analysis revealed that the TiO2/CuO NC showed the lowest intensity compared to the pristine TiO2 and CuO indicating the reduction of exciton recombination in the case of the TiO2/CuO NC. The BET analysis showcased the formation of mesoporous materials with a surface area of 87.5 m2/g. The photocatalytic degradation performance of the biosynthesized TiO2, CuO, and TiO2/CuO nanomaterials against the potentially harmful MB dye was tested using the light source of a 150 tungsten-halogen lamp with a wavelength range of 360-2800 nm. The factors affecting photodegradation efficiencies like catalyst dose (20 mg), dye concentration(15 ppm), pH (9), and reaction time (90 min) were optimized for the degradation of the MB dye. The TiO2/CuO catalyst showed the highest degradation efficiency of 99% under the optimized conditions. The degradation rate of the MB dye in the presence of the TiO2/CuO NC was evaluated and found to be fitted to the pseudo-first-order kinetics with a rate constant of 0.03 min-1. The reusability test of the TiO2/CuO catalyst showed its good stability.

Enhancing leachate management with antibacterial nanocomposites incorporating plant-based carbon dots and Satureja Khuzestanica essential oils

Landfill leachate, a complex mixture of pollutants, poses a significant environmental hazard. This study reports the synthesis and characterization of superabsorbent nanocomposites (SANs) designed for enhanced performance in waste management applications. SANs were prepared using carboxymethyl cellulose (CMC) and sodium polyacrylate (SPA) as the main components, carbon dots (CDs) to improve absorption, and Satureja Khuzestanica essential oil (SEO) for antibacterial performance. The results demonstrated that the addition of CDs significantly increased the absorption capacity and liquid retention of the samples, with a water absorption capacity reaching up to 8621 %. Furthermore, the samples exhibited high mechanical strength, with tensile strength improving by over 100 % in the presence of CDs. The inclusion of SEO provided strong antibacterial activity against Escherichia coli and Staphylococcus aureus, with inhibition zones measuring up to 26 mm. These SANs, with their high absorption capacity, mechanical robustness, and antibacterial properties, show great potential for improving waste management practices, particularly in leachate absorption strategies.

Poly(methyl methacrylate) functionalized graphene oxide/CuO as nanocomposite for efficient removal of dye pollutants

In this research, the use of a three-component nanocomposite of graphene oxide-methyl methacrylate and copper(II) oxide (PMMA-GO-CuO) was investigated. The aim of synthesizing this nanocomposite is to removal dye pollutants, specifically methylene blue (MB) and methyl orange (MO), which are commonly used in dyeing industries, through adsorption. The study focuses on creating GO-CuO and PMMA-GO-CuO nanocomposites as effective adsorbents. A simple and quick method led to the development of the PMMA-GO-CuO nanocomposite, which shows enhanced physical and chemical properties. Key materials include graphene oxide, methyl methacrylate, and copper(II) oxide nanoparticles. Characterization techniques such as FT-IR, XRD, SEM, and TGA were used to analyze the nanocomposite. Results indicate that dye adsorption is more effective at lower pH levels, suggesting that the PMMA-GO-CuO nanocomposite can efficiently remove dyes from industrial wastewater. The experimental data showed that the Langmuir isotherm model accurately represented the equilibrium adsorption, with maximum capacities of 285.71 mg g-1 for methylene blue and 256.41 mg g-1 for methyl orange, indicating a single layer of adsorption. The kinetics followed a pseudo-second order model, suggesting that the adsorption process involves chemical bonding. Additionally, thermodynamic parameters (ΔG°, ΔH°, and ΔS°) indicated that the adsorption is spontaneous. The adsorption mechanism involves hydrogen bonding, π-π interactions, and electrostatic interactions. This study investigates how factors like pH, temperature, contact time, and dye concentration affect the adsorption of methyl orange and methylene blue dyes. A PMMA-GO-CuO nanocomposite was used, achieving 84% removal of MB and 35% removal of MO from industrial wastewater. This study highlights the promising potential of PMMA-GO-CuO nanocomposite as an effective material for the removal of dye pollutants from industrial wastewater. The results showed that the graphene oxide in the composite is effective for removing cationic dyes due to its negative charge. Further research will focus on the optimization of the synthesis process with the aim of achieving competitive performance of this nanocomposite on a large scale. These findings not only advance the field of nanocomposite materials but also provide a practical solution to an important environmental issue, demonstrating the innovation of the present study in the literature.

One stone, two birds: An eco-friendly aerogel based on waste pomelo peel cellulose for the efficient adsorption of dyes and heavy metal ions

To achieve the objective of "waste control by waste", in this study, a green aerogel adsorbent comprised of pomelo-peel cellulose and sodium alginate (PCC/SA) was prepared through dual-network crosslinking. The resulting 3D hierarchical porous structured PCC/SA aerogel exhibited good structural stability, and kept the morphological integrity during 10 days in a wide pH range (2-10), suggesting its potential for recycling in diverse complex environments. Besides, the superior adsorption capacities for methylene blue (MB) and Cu(II) were observed, with the qm values and adsorption equilibrium times were recorded to be 1299.59 mg/g (300 min) and 287.55 mg/g (120 min), correspondingly. Furthermore, the favorable reusability of the PCC/SA aerogel was also demonstrated, with the removal efficiency for MB remaining almost unchanged (about 94 %) after 10 adsorption-desorption cycles, while there was a slight reduction for Cu(II) from 85.28 % to 72.47 %. XPS and FTIR analysis revealed that electrostatic attraction, hydrogen bonding, cation exchange and coordination were the major adsorption mechanisms. Importantly, the PCC/SA aerogel can be naturally degraded in soil within 10 weeks. Therefore, the as-prepared aerogel bead derived from pomelo peel shows great promise as an adsorbent for wastewater treatment containing dye and heavy metal ions.

Synthesis of carboxymethyl starch co (polyacrylamide/ polyacrylic acid) hydrogel for removing methylene blue dye from aqueous solution

Natural polysaccharides, notably starch, have garnered attention for their accessibility, cost-effectiveness, and biodegradability. Modifying starch to carboxymethyl starch enhances its solubility, swelling capacity, and adsorption efficiency. This research examines the synthesis of an effective hydrogel adsorbent based on carboxymethyl starch for the elimination of methylene blue from aqueous solutions. The hydrogel was synthesized using polyacrylamide and polyacrylic acid as monomers, ammonium persulfate as the initiator, and N,N'-methylenebisacrylamide as the cross-linker. Through FESEM, swelling morphology was evaluated in both distilled water and methylene blue dye. The adsorption data elucidated that the adsorption capacity of the hydrogel significantly depends on the dosage of the adsorbent, pH, and concentration of the MB dye. At a pH of 7 and a dye concentration of 250 mg/L, the hydrogel exhibited an impressive 95 % removal rate for methylene blue. The results indicate that the adsorption process follows pseudo-second-order kinetics and conforms well to the Langmuir adsorption isotherm, indicating a maximum adsorption capacity of 1700 mg/g. According to the pseudo-second-order kinetic model and FTIR analysis, methylene blue chemisorbs to the adsorbent material. Hydrogel absorbents regulate adsorption through both intra-particle diffusion and liquid film diffusion. These results highlight the potential of the new hydrogel absorber for water purification.

β-Lactoglobulin-based aerogels: Facile preparation and sustainable removal of organic contaminants from water

Economically and efficiently removing organic pollutants from water is still a challenge in wastewater treatment. Utilizing environmentally friendly and readily available protein-based natural polymers to develop aerogels with effective removal performance and sustainable regeneration capability is a promising strategy for adsorbent design. Here, a robust and cost-effective method using inexpensive β-lactoglobulin (BLG) as raw material was proposed to fabricate BLG-based aerogels. Firstly, photocurable BLG-based polymers were synthesized by grafting glycidyl methacrylate. Then, a cross-linking reaction, including photo-crosslinking and salting-out treatment, was applied to prepared BLG-based hydrogels. Finally, the BLG-based aerogels with high porosity and ultralight weight were obtained after freeze-drying. The outcomes revealed that the biocompatible BLG-based aerogels exhibited effective removal performance for a variety of organic pollutants under perfectly quiescent conditions, and could be regenerated and reused many times via a simple and rapid process of acid washing and centrifugation. Overall, this work not only demonstrates that BLG-based aerogels are promising adsorbents for water purification but also provides a potential way for the sustainable utilization of BLG.

The dual-configured hydrogen bonds induced by polymerized deep eutectic solvents-modified magnetic biochar enhanced the selectivity for 3,4-methylenedioxymethamphetamine

The accurate discovering and monitoring of 3,4-methylenedioxymethamphetamine (MDMA) are especially important because of its substantial toxicity and potential harm to human and the ecological systems. Three types of polymerized deep eutectic solvents functionalized magnetic biochar (MBC@poly (AA/AAC/AAm-ChCl)) were successfully synthesized to adsorb MDMA. The isotherm and kinetic data confirmed that MBC@poly (AAm-ChCl) had the strongest adsorption capacity, and the order of adsorption capacity is as follow: MBC@poly(AAm-ChCl) > MBC@poly(AA-ChCl) > MBC@poly(MAA-ChCl), which also revealed that the adsorption was heterogeneous multi-layer chemisorption. The findings of the characterizations manifested that MBC@poly(AAm-ChCl) was the optimal adsorbent owning to its higher nitrogen content, resulting in the formation of a greater number of hydrogen bonds. Due to the strong hydrogen bonding effect of CO and -NH2 functional groups, MBC@poly(AAm-ChCl) exhibited the high selectivity towards MDMA under the coexistence of multiple chemical substances, and excellent adsorption performance over the pH range of 4-11. Urea as a hydrogen bond inhibitor further confirmed MBC@poly(AAm-ChCl) had high-density active hydrogen bonding sites. Furthermore, utilizing density functional theory (DFT) for simulating adsorption both before and after the process verified that the high selectivity of MBC@poly(AAm-ChCl) attributed to the formation of the dual-configured hydrogen bonds. This study provides support for the production of highly selective biochar for use in pretreatment during drug detection.

Integrating DFT and machine learning for the design and optimization of sodium alginate-based hydrogel adsorbents: Efficient removal of pollutants from wastewater

This study presents a novel approach to design and optimize a sodium alginate-based hydrogel (SAH) for efficient adsorption of the model water pollutant methylene blue (MB) dye. Utilizing density functional theory (DFT) calculations, sodium alginate-g-poly (acrylamide-co-itaconic acid) was identified with the lowest adsorption energy (Eads) for MB dye among 14 different clusters. SAHs were prepared using selected monomers and sodium alginate combinations through graft co-polymerization, and swelling studies were conducted to optimize grafting conditions. Advanced characterization techniques, including FTIR, XRD, XPS, SEM, EDS, and TGA, were employed, and the process was optimized using statistical and machine learning tools. Screening tests demonstrated that Eads serves as an effective predicting indicator for adsorption capacity (qe) and MB removal efficiency (RRMB,%), with reasonable agreement between Eads and both responses under given conditions. Process modeling and optimization revealed that 5 mg of selected SAH achieves a maximum qe of 3244 mg g-1 at 84.4% RRMB under pH 8.05, 98.8 min, and MB concentration of 383.3 mg L-1, as identified by the desirability function approach. Moreover, SAH effectively eliminated various contaminants from aqueous solutions, including sulfasalazine (SFZ) and dibenzothiophene (DBT). MB adsorption onto selected SAH was exothermic, spontaneous, and followed the pseudo-first-order and Langmuir-Freundlich isotherm models. The remarkable ability of SAH to adsorb MB is attributed to its well-designed structure predicted through DFT and optimal operational conditions achieved by AI-based parametric optimization. By integrating DFT-based computations and machine-learning tools, this study contributes to the efficient design of adsorbent materials and optimization of adsorption processes, also showcasing the potential of SAH as an efficient adsorbent for the abatement of aqueous pollution.

Efficient removal of ciprofloxacin and ofloxacin from aqueous solutions using a novel nano-scale adsorbent: Modeling, optimization, and characterization

In the fascinating realm of water purification, our study unveils the remarkable potential of a cutting-edge nano-scale adsorbent-combining graphene oxide (GO), chitosan (CS), and polydopamine (PDA)-in efficiently remove ciprofloxacin (CPF) and ofloxacin (OFL) from aqueous solutions. Our exploration delves deep into the adsorbent's character, utilizing a range of analytical techniques including SEM, RAMAN, FTIR, TGA, BET, XRD, and Zeta potential analyses provided insights into the adsorbent's properties. Modeling the adsorption process with Response Surface Methodology (RSM), Artificial Neural Network (ANN) and General Regression Neural Network (GRNN) indicated excellent predictions by GRNN, with RMSE = 0.0200 and 0.0166, MAE = 0.0082 and 0.0092, as well as AAD = 0.0002 and 0.0006, highlighting its modeling power. Optimization using genetic algorithm (GA) revealed maximum CPF removal efficiency of approximately 95.20% under pH = 6.3, sonication time = 9.0 min, adsorbent dosage = 2.10 g L⁻1, temperature = 45 °C and initial CPF concentration = 90.0 mg L⁻1. Similarly, OFL removal reached about 95.50% under pH = 6.30, sonication time = 8.0 min, adsorbent dosage = 2.0 g L⁻1, temperature = 45 °C and OFL concentration = 115.0 mg L⁻1. RSM optimization closely aligned with GA results. Pseudo-second-order (PSO) kinetic model and Langmuir isotherm model best fitted the experimental data for both antibiotics. Thermodynamic analysis indicated a favorable and spontaneous adsorption process for CPF and OFL. The study concludes that the proposed adsorbents show effectiveness in removing CPF and OFL at lower doses and shorter sonication times compared to various reported adsorbents.

Curdlan/sodium carboxymethylcellulose composite adsorbents: A biodegradable solution for organic dye removal from water

Composite adsorbent comprised of curdlan (CURD) and sodium carboxymethylcellulose (CMC) were fabricated through a single-step heating process, targeting the removal of methylene blue (MB) from wastewater. The CURD/CMC composite adsorbents had a honeycomb porous structure. The integration of CMC not only increased the storage modulus of the CURD/CMC composite hydrogels but also affected the thermal stability and swelling behavior of the composite adsorbents in different pH solutions. Specifically, the addition of 1.2 % CMC increased the peak temperature (184.73 °C) of CURD/CMC composite adsorbent melting by 5.99 °C compared to CURD adsorbent. The addition of CMC improved the swelling ratio of the composite adsorbent at pH 3,7, and 12 with swelling ratio up to 918.07 %. The synergistic interaction between CURD and CMC led to an enhanced adsorption capacity of the aerogel for MB, achieving a maximum adsorption capability of 385.85 mg/g. Adsorption isotherm assessments further demonstrated that the Langmuir isotherm model well fitted the adsorption data of the composite adsorbent on MB. Collectively, these findings underscore the potential of the developed biodegradable adsorbents as promising adsorbents for efficiently eliminating organic dyes from water.

Electrochemical Regeneration of Highly Stable and Sustainable Cellulose/Graphene Adsorbent Saturated with Dissolved Organic Dye

Electrochemical regeneration of adsorbents presents a cost-effective and environmentally friendly approach. Yet, its application to 3D structured adsorbents such as cellulose/graphene-based aerogels remains largely unexplored. This study introduces a method for producing these aerogels, highlighting their significant adsorption capacity for dissolved organic pollutants and resilience during electrochemical regeneration. By adjusting the ratio of hydrophobized cellulose nanofibers to graphene, the aerogels demonstrate a tunable adsorption capacity, ranging from 56 to 228 mg/g. Hydrophobization using oleic acid is vital for maintaining the aerogels' structural stability in water. Notably, the aerogels maintain structural integrity and efficiency over at least 18 electrochemical regeneration cycles, underscoring their potential for long-term environmental applications. The increase in adsorption capacity observed after regeneration cycles, approximately 10-20% by the fifth cycle, is attributed to electrochemical surface roughening and the creation of new adsorption sites. The tunability and durability of these aerogels offer a sustainable solution for adsorption with electrochemical regeneration technology.

Tailored ultra-tough, antimicrobial and recyclable hydrogels based on chitosan and ionic liquid modified montmorillonite with different chain lengths for efficient adsorption of organic dyes in wastewater

Water pollution had exacerbated the global water crisis. Dye effluents posed a serious threat to the environment and human health, so there was an urgent need to develop sustainable methods to mitigate water pollution. In this work, sodium-based montmorillonite (MMT) was stripped using ionic liquids (ILs) with different chain lengths, and a pAAM/pAA/LMA/MMT@ILs-CS hydrogel adsorbent (MICHA) was prepared. The gel-based adsorbent was used to adsorb typical cationic (methylene blue: MB, rhodamine B: RhB) and anionic (methyl orange: MO, indigo carmine: IC) dyes from wastewater. The maximum adsorption capacities of MI16CHA for MB, MO, IC and RhB were 349.6817, 325.415, 316.0142 and 339.8154 mg/g, respectively. The adsorption kinetics and equilibrium data of MI16CHA for dyes were in accordance with the pseudo-first order and Langmuir isotherm models. The adsorption mechanism of MI16CHA on dyes were based on hydrogen bonding, electrostatic and π-π interaction. Thermodynamic studies showed that the adsorption of dyes on MI16CHA was spontaneous and heat-absorbing. The selective experiments demonstrated that MI16CHA has a promising application in real industrial conditions. Cyclic adsorption tests demonstrated the excellent recyclability of MI16CHA. In addition, MI16CHA had excellent antimicrobial and mechanical properties, which endowed the gel adsorbent with anti-pollution and durability.

Recent advances in cellulose- and alginate-based hydrogels for water and wastewater treatment: A review

From the environmental perspective, it is essential to develop cheap, eco-friendly, and highly efficient materials for water and wastewater treatment. In this regard, hydrogels and hydrogel-based composites have been widely employed to mitigate global water pollution as this methodology is simple and free from harmful by-products. Notably, alginate and cellulose, which are natural carbohydrate polymers, have gained great attention for their availability, price competitiveness, excellent biodegradability, biocompatibility, hydrophilicity, and superior physicochemical performance in water treatment. This review outlined the recent progress in developing and applying alginate- and cellulose-based hydrogels to remove various pollutants such as dyes, heavy metals, oils, pharmaceutical contaminants, and pesticides from wastewater streams. This review also highlighted the effects of various physical or chemical methods, such as crosslinking, grafting, the addition of fillers, nanoparticle incorporation, and polymer blending, on the physiochemical and adsorption properties of hydrogels. In addition, this review covered the alginate- and cellulose-based hydrogels' current limitations such as low mechanical performance and poor stability, while presenting strategies to improve the drawbacks of the hydrogels. Lastly, we discussed the prospects and future directions of alginate- and cellulose-based hydrogels. We hope this review provides valuable insights into the efficient preparations and applications of hydrogels.

Recent advances and future perspective on lignocellulose-based materials as adsorbents in diverse water treatment applications

The growing shortage of non-renewable resources and the burden of toxic pollutants in water have gradually become stumbling blocks in the path of sustainable human development. To this end, there has been great interest in finding renewable and environmentally friendly materials to promote environmental sustainability and combat harmful pollutants in wastewater. Of the many options, lignocellulose, as an abundant, biocompatible and renewable material, is the most attractive candidate for water remediation due to the unique physical and chemical properties of its constituents. Herein, we review the latest research advances in lignocellulose-based adsorbents, focusing on lignocellulosic composition, material modification, application of adsorbents. The modification and preparation methods of lignin, cellulose and hemicellulose and their applications in the treatment of diverse contaminated water are systematically and comprehensively presented. Also, the detailed description of the adsorption model, the adsorption mechanism and the adsorbent regeneration technique provides an excellent reference for understanding the underlying adsorption mechanism and the adsorbent recycling. Finally, the challenges and limitations of lignocellulosic adsorbents are evaluated from a practical application perspective, and future developments in the related field are discussed. In summary, this review offers rational insights to develop lignocellulose-based environmentally-friendly reactive materials for the removal of hazardous aquatic contaminants.

The Effect of Silver Nanoparticles/Titanium Dioxide in Poly(acrylic acid-co-acrylamide)-Modified, Deproteinized, Natural Rubber Composites on Dye Removal

This work aims to enhance the dye-removal performance of prepared poly(acrylic acid-co-acrylamide)-modified, deproteinized, natural rubber ((PAA-co-PAM)-DPNR) through incorporation with silver nanoparticles/titanium dioxide. The (PAA-co-PAM)-DPNR was prepared by emulsion-graft copolymerization with a grafting efficiency of 10.20 ± 2.33 to 54.26 ± 1.55%. The composites based on (PAA-co-PAM)-DPNR comprising silver nanoparticles and titanium dioxide ((PAA-co-PAM)-DPNR/Ag-TiO2) were then prepared by latex compounding using the fixed concentration of AgNO3 (0.5 phr) and varying concentrations of TiO2 at 1.0, 2.5, and 5.0 phr. The formation of silver nanoparticles was obtained by heat and applied pressure. The composites had a porous morphology as they allowed water to diffuse in their structure, allowing the high specific area to interact with dye molecules. The incorporation of silver nanoparticles/titanium dioxide improved the compressive modulus from 1.015 ± 0.062 to 2.283 ± 0.043 KPa. The (PAA-co-PAM)-DPNR/Ag-TiO2 composite with 5.0 phr of TiO2 had a maximum adsorption capacity of 206.42 mg/g, which increased by 2.02-fold compared to (PAA-co-PAM)-DPNR. The behavior of dye removal was assessed with the pseudo-second-order kinetic model and Langmuir isotherm adsorption model. These composites can maintain their removal efficiency above 90% for up to five cycles. Thus, these composites could have the potential for dye-removal applications.

Construction and demolition waste as a high-efficiency advanced process for organic pollutant degradation in Fenton-like reaction to approach circular economy

The Fenton-like reaction is a promising organic wastewater treatment reaction among advanced oxidation processes (AOP), which has emerged to replace the conventional Fenton reaction. Recycled construction and demolition waste (CDW), which is porous and rich in iron, manganese, and magnesium, can be reused as a Fenton-like catalyst. This study proposes an AOP wastewater treatment strategy using recycled porous CDW mixed with hydrogen peroxide (H2O2) to decompose methylene blue (MB) wastewater. According to the apparent first-order rate (Kapp) of 10 ppm MB adsorption, CDW-3, having the highest specific surface area, also has the highest Kapp of 0.23 min-1 g-1. The optimized conditions recommended by the Taguchi method include a 0.3 g mL-1 CDW-3 concentration, a 0.254 g mL-1 H2O2 concentration, and 10 ppm MB, resulting in an about 2.01 min-1Kapp value. In addition, MB concentration is observed as the most influential factor for Kapp, which decreases with increasing MB concentration and is about 0.62 min-1 at 1000 ppm MB. Repeating the Fenton-like reaction five times at 100 p.m. MB using the same CDW-3, the Kapp is about 0.64 min-1, which is 86% of the initial run. The synergistic effect index (ξ) is defined to quantify the level of interaction between CDW and H2O2, which produces free radicals during the Fenton-like process. The ξ of CDW-3 is about 2.16. Overall, it is demonstrated that CDW is a promising catalyst for Fenton-like reactions, and the synergistic effect index (ξ) can be used as a reference index to evaluate the catalytic generation of free radicals between the catalyst and H2O2.

Selective adsorption of organic dyes from aqueous environment using fermented maize extract-enhanced graphene oxide-durian shell derived activated carbon composite

A secure aquatic environment is essential for both aquatic and terrestrial life. However, rising populations and the industrial revolution have had a significant impact on the quality of the water environment. Despite the implementation of strong and adapted environmental policies for water treatment worldwide, the issue of organic dyes in wastewater remains challenging. Thus, this study aimed to develop an efficient, cost-effective, and sustainable material to treat methylene blue (MB) in an aqueous environment. In this research, maize extract solution (MES) was utilized as a green cross-linker to induce precipitation, conjugation, and enhance the adsorption performance of graphene oxide (GO) cross-linked with durian shell activated carbon (DSAC), resulting in the formation of a GO@DSAC composite. The composite was investigated for its adsorptive performance toward MB in aqueous media. The physicochemical characterization demonstrated that the cross-linking method significantly influenced the porous structure and surface chemistry of GO@DSAC. BET analysis revealed that the GO@DSAC exhibited dominant mesopores with a surface area of 803.67 m2/g. EDX and XPS measurements confirmed the successful cross-linking of GO with DSAC. The adsorption experiments were well described by the Harkin-Jura model and they followed pseudo-second order kinetics. The maximum adsorption capacity reached 666.67 mg/g at 318 K. Thermodynamic evaluation indicated a spontaneous, feasible, and endothermic in nature. Regenerability and reusability investigations demonstrated that the GO@DSAC composite could be reused for up to 10 desorption-adsorption cycles with a removal efficiency of 81.78%. The selective adsorptive performance of GO@DSAC was examined in a binary system containing Rhodamine B (RhB) and methylene orange (MO). The results showed a separation efficiency (α) of 98.89% for MB/MO and 93.66% for MB/RhB mixtures, underscoring outstanding separation capabilities of the GO@DSAC composite. Overall, the GO@DSAC composite displayed promising potential for the effective removal of cationic dyes from wastewater.

Cellulose nanocrystal/halloysite nanotube composite aerogels for water purification

The quest for advanced water purification technologies has been vigorous over recent decades, motivated by the promise of ever more efficient, greener, and affordable tools. Halloysite nanotubes (HNTs) are naturally-occurring materials that have shown potential as dye sorbents. Unfortunately, these nanoclays suffer from low permeation during water treatment, which limits their widespread application. Here, we use cellulose nanocrystals (CNCs) as structural scaffolds to support HNTs and fabricate permeable aerogel sorbent materials with mechanical stability. Aerogels containing 40 wt% HNTs showed a maximum dye adsorption capacity of 60 mg g-1 towards methylene blue, with only 15% decay in efficiency after 5 cycles. The good mechanical properties of these materials allowed for their incorporation into free-flowing purification columns that displayed excellent dye removal ability. Overall, this work provides a new strategy to fabricate green, renewable, and low-cost sorbent materials for the removal of dyes and shows potential for the sorption of other ionic pollutants.

Bacterial Cellulose Aerogels Derived from Pineapple Peel Waste for the Adsorption of Dyes

Valorization of pineapple peel waste is an attractive research topic because of the huge quantities of this byproduct generated from pineapple processing industries. In this study, the extract from pineapple waste was collected to produce a hydrogel-like form containing bacterial cellulose fibers with a three-dimensional structure and nanoscale diameter by the Acetobacter xylinum fermentation process. The bacterial cellulose suspension was subsequently activated by freeze-drying, affording lightweight aerogels as potential adsorbents in wastewater treatment, in particular the adsorptive removal of organic dyes. Intensive tests were carried out with the adsorption of methylene blue, a typical cationic dye, to investigate the influence of adsorption conditions (temperature, pH, initial dye concentration, time, and experiment scale) and aerogel-preparation parameters (grinding time and bacterial cellulose concentration). The bacterial cellulose-based aerogels exhibited high adsorption capacity not only for methylene blue but also for other cationic dyes, including malachite green, rhodamine B, and crystal violet (28-49 mg/g). However, its activity was limited for most of the anionic dyes, such as methyl orange, sunset yellow, and quinoline yellow, due to the repulsion of these anionic dyes with the aerogel surface, except for the case of congo red. It is also an anionic dye but has two amine groups providing a strong interaction with the hydroxyl group of the aerogel via hydrogen bonding. Indeed, the aerogel has a substantially large congo red-trapping capacity of 101 mg/g. Notably, the adsorption process exhibited similar performances, upscaling the solution volume to 50 times. The utilization of abundant agricultural waste in the simple aerogel preparation to produce a highly efficient and biodegradable adsorbent is the highlight of this work.

Development of carboxymethyl cellulose-graphene oxide biobased composite for the removal of methylene blue cationic dye model contaminate from wastewater

Utilizing Glutaraldehyde crosslinked sodium carboxymethyl cellulose (CMC-GA) hydrogel and its nanographene oxide composite (CMC-GA-GOx), an effective carboxymethyl cellulose-graphene oxide biobased composites adsorbent was developed for the adsorption removal of methylene blue (MB) cationic dye contaminate from industrial wastewater. The CMC-GA-GOx composites developed were characterized using FTIR, RAMAN, TGA, SEM, and EDX analysis instruments. Through batch experiments, several variables affecting the removal of MB dye, including the biocomposites GO:CMC composition, adsorption time, pH and temperature, initial MB concentration, adsorbent dosage, and NaCl concentration, were investigated under different conditions. The maximum dye removal percentages ranged between 93 and 98%. They were obtained using biocomposites CMC-GA-GO102 with 20% GO weight percent, adsorption time 25 min, adsorption temperature 25 °C, MB concentrations 10-30 ppm, adsorption pH 7.0, and 0.2 g adsorbent dose. The experimental data of the adsorption process suit the Langmuir isotherm more closely with a maximal monolayer adsorption capacity of 76.92 mg/g. The adsorption process followed the kinetic model of pseudo-second order. The removal of MB was exothermic and spontaneous from a thermodynamic standpoint. In addition, thermodynamic results demonstrated that adsorption operates most effectively at low temperatures. Finally, the reusability of the developed CMC-GA-GO102 has been proved through 10 successive cycles where only 14% of the MB dye removal percentage was lost. These results suggest that the developed CMC-GA-GO102 composite may be an inexpensive and reusable adsorbent for removing organic cationic dyes from industrial wastewater.

Preparation of poly (methacrylic acid)/graphene oxide aerogel as solid-phase extraction adsorbent for extraction and determination of dopamine and tyrosine in urine of patients with depression

Dopamine (DA) and l-tyrosine (l-Tyr) are neurotransmitters involved in various neuropsychiatric disorders. Therefore, it is important to monitor their levels for diagnosis and treatment. In this study, we synthesized poly (methacrylic acid)/graphene oxide aerogels (p(MAA)/GOA) by in situ polymerization and freeze-drying using graphene oxide and methacrylic acid as substrates. Then, the p(MAA)/GOA were applied as solid-phase extraction adsorbents to extract DA and l-Tyr from urine samples, followed by quantification using high performance liquid chromatography (HPLC). The p(MAA)/GOA showed better adsorption performance for DA and l-Tyr than commercial adsorbents, likely as a result of the strong adsorption of the target analytes via π-π and hydrogen bonding interactions. Further, the developed method had good linearity (r > 0.9990) at concentrations of DA and l-Tyr of 0.075-2.0 and 0.75-20.0 μg mL^-1, respectively, as well as a limit of detection of 0.018-0.048 μg mL^-1, limit of quantitation of 0.059-0.161 μg mL^-1, spiked recovery of 91.1-104.0%, and interday precision of 3.58-7.30%.The method was successfully applied to determine DA and l-Tyr in the urine samples of patients suffering from depression, demonstrating its potential for clinical applications.

Polymeric hydrogels-based materials for wastewater treatment

Low-cost and reliable wastewater treatment is a relevant issue worldwide to reduce the concentration of environmental pollutants. Industrial effluents containing dyes, heavy metals, and other inorganic and organic compounds can pollute water resources; therefore, novel technologies are required to mitigate and control their release into the environment. Adsorption is one of the simplest methods for treating contaminated water in which a wide spectrum of adsorbents can be used to remove emerging compounds. Hydrogels are interesting materials with high adsorption capacities that can be synthesized via green routes. These adsorbents are promising for large-scale industrial wastewater treatment applications; however, gaps still exist in achieving sustainable commercial implementation. This review focuses on the discussion and analysis of preparation, characterization, and adsorption properties of hydrogels for water purification. The advantages of these polymeric materials for water treatment were analyzed, including their performance in the removal of different organic and inorganic contaminants. Recent advances in the functionalization of hydrogels and the synthesis of novel composites have also been described. The adsorption capacities of hydrogel-based adsorbents are higher than 500 mg/g for different organic and inorganic pollutants, and can reach values of up to >2000 mg/g for organic compounds, significantly outperforming other materials reported for water cleaning. The main interactions involved in the adsorption of water pollutants using hydrogel-based adsorbents were described and explained to allow the interpretation of their removal mechanisms. The current challenges in the implementation of hydrogels for water purification in real-life operations are also highlighted. This review provides an updated picture of hydrogels as interesting materials to address water depollution worldwide.

Deep insight into selective adsorption behavior and mechanism of novel deep eutectic solvent functionalized bio-sorbent towards methcathinone: Experiments and DFT calculation

This work designed and synthesized novelly selective, highly efficient and friendly environmental biochar nanomaterial (ZMBC@ChCl-EG) by screening suitable deep eutectic solvent (DES) as the functional monomer via Density Functional Theory (DFT). The prepared ZMBC@ChCl-EG achieved the highly efficient adsorption of methcathinone (MC) and exhibited excellent selectivity as well as good reusability. Selectivity analysis concluded that the distribution coefficient value (K_D) of ZMBC@ChCl-EG towards MC was 3.247 L/g, which was about 3 times higher than that of ZMBC, corresponding to stronger selective adsorption capacity. The studies of isothermal and kinetics indicated that ZMBC@ChCl-EG had an excellent adsorption capacity towards MC and the adsorption was mainly chemically controlled. In addition, DFT was used to calculate the binding energies between MC and each component. The binding energies were -10.57 kcal/mol for ChCl-EG/MC, -3.15∼-9.51 kcal/mol for BCs/MC, -2.33 kcal/mol for ZIF-8/MC, respectively, suggesting that DES played a major role in enhancing methcathinone adsorption. Lastly, the adsorption mechanisms were revealed by variables experiment combined with characterizations and DFT calculation. The main mechanisms were hydrogen bonding and π-π interaction.

Multifunctional fully biobased aerogels for water remediation: Applications for dye and heavy metal adsorption and oil/water separation

Water ecosystem contamination from industrial pollutants is an emerging threat to both humans and native species, making it a point of global concern. In this work, fully biobased aerogels (FBAs) were developed by using low-cost cellulose filament (CF), chitosan (CS), citric acid (CA), and a simple and scalable approach, for water remediation applications. The FBAs displayed superior mechanical properties (up to ∼65 kPa m³ kg^-1 specific Young's modulus and ∼111 kJ/m³ energy absorption) due to CA acting as a covalent crosslinker in addition to the natural hydrogen bonding and electrostatic interactions between CF and CS. The addition of CS and CA increased the variety of functional groups (carboxylic acid, hydroxyl and amines) on the materials' surface, resulting in super-high dye and heavy metal adsorption capacities (619 mg/g and 206 mg/g for methylene blue and copper, respectively). Further modification of FBAs with a simple approach using methyltrimethoxysilane endowed aerogel oleophilic and hydrophobic properties. The developed FBAs showed a fast performance in water and oil/organic solvents separation with more than 96% efficiency. Besides, the FBA sorbents could be regenerated and reused for multiple cycles without any significant impact on their performance. Moreover, thanks to the presence of amine groups by addition of CS, FBAs also displayed antibacterial properties by preventing the growth of Escherichia coli on their surface. This work demonstrates the preparation of FBAs from abundant, sustainable, and inexpensive natural resources for applications in wastewater purification.

Production of single-component cellulose-based hydrogel and its utilization as adsorbent for aqueous contaminants

The growing concern for the environment has resulted in renewed interest in bio-based resources. This study aims to produce a hydrogel adsorbent from cellulose and examine its adsorption performance. In pursuit of this goal, we report a simple one-pot synthesis of cellulose acetate sulfate (CAS), followed by the formation of CAS hydrogels and their subsequent adsorption performances. The CAS includes both hydrophilic and hydrophobic functional groups, enable the formation of a single-component hydrogel through intermolecular interactions in deionized water. The thermal reversibility of CAS hydrogels makes them easily processable into various shapes. The durability of the CAS hydrogel adsorbents can be improved by introducing divalent cations (e.g., Ca²⁺), which create ionically crosslinked hydrogels. The ionically a crosslinked CAS hydrogel adsorbent exhibits a maximum adsorption capacity of 245 mg/g for methylene blue (MB) at 23 °C and a pH of 7. The adsorption behavior of MB on the CAS hydrogel follows both the pseudo-second-order model and the Langmuir adsorption isotherm model. Furthermore, the CAS hydrogel adsorbent maintains a 70 % removal ratio after five cycles. The simplicity of synthesis and hydrogel formation opens up new possibilities for producing and utilizing cellulose-based hydrogels as adsorbents for aqueous contaminants.

Magnetite carboxymethylcellulose as biological macromolecule-based absorbent for cationic dyes removal from environmental samples

In this study, magnetite carboxymethylcellulose (CMC@Fe₃O₄) composite as magnetic biological molecules were synthetized for the use as adsorbent to remove four types of cationic dyes, namely Methylene Blue, Rhodamine B, Malachite Green, and Methyl Violet from aqueous solution. The characteristic of the adsorbent was achieved by Fourier Transform Infrared Spectroscopy, Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction, Vibrating Sample Magnetometer and Thermal Gravimetric Analysis techniques. Besides, essential influencing parameters of dye adsorption; the solution pH, solution temperature, contact time, adsorbent concentration and initial dye dosage were studied. FESEM analysis showed the magnetic Fe₃O₄-TB, Fe₃O₄@SiO₂, Fe₃O₄@SiO₂-NH₂ and CMC@Fe₃O₄ composites were in spherical shape, with average size of 43.0 nm, 92.5 nm, 134.0 nm and 207.5 nm, respectively. On the saturation magnetization (Ms), the results obtained were 55.931 emu/g, 34.557 emu/g, 33.236 emu/g and 11.884 emu/g. From the sorption modelling of Isotherms, Kinetics, and Thermodynamics, the adsorption capacity of dyes is (MB = 103.33 mg/g), (RB = 109.60 mg/g), (MG = 100.08 mg/g) and (MV = 107.78 mg/g). With all the adsorption processes exhibited as exothermic reactions. The regeneration and reusability of the synthetized biological molecules-based adsorbent was also assessed.

Adsorption-enhanced catalytic oxidation for long-lasting dynamic degradation of organic dyes by porous manganese-based biopolymeric catalyst

Improving the adsorption kinetics of metal-oxide catalysts is critical for the enhancement of catalytic performance in heterogeneous catalytic oxidation reactions. Herein, based on the biopolymer pomelo peels (PP) and metal-oxide catalyst manganese oxide (MnO_x), an adsorption-enhanced catalyst (MnO_x-PP) was constructed for catalytic organic dyes oxidative-degradation. MnO_x-PP shows excellent methylene blue (MB) and total carbon content (TOC) removal efficiency of 99.5 % and 66.31 % respectively, and keeps the long-lasting stable dynamic degradation efficiency during 72 h based on the self-built continuous single-pass MB purification device. The chemical structure similarity and negative-charge polarity sites of the biopolymer PP improve the adsorption kinetics of organic macromolecule MB, and construct the adsorption-enhanced catalytic oxidation microenvironment. Meanwhile, the adsorption-enhanced catalyst MnO_x-PP obtains lower ionization potential and O₂ adsorption energy to promote the continuous generation of active substance (O₂*, OH*) for the further catalytic oxidation of adsorbed MB molecules. This work explored the adsorption-enhanced catalytic oxidation mechanism for the degradation of organic pollutants, and provided a feasible technical idea for designing adsorption-enhanced catalysts for the long-lasting efficient removal of organic dyes.

Green Synthesis and Characteristics of Cellulose Nanocrystal/Poly Acrylic Acid Nanocomposite Thin Film for Organic Dye Adsorption during Water Treatment

Nanocellulose shows potential as an effective natural adsorbent for removing harmful contaminants from wastewater. This paper describes the development of innovative nanocellulose thin films made of cellulose nanocrystals (CNCs), polyacrylic acid (PAA), and active carbon (AC) as adsorbent materials for absorbing azo dyes from wastewater. The CNCs were recovered from sugarcane bagasse using alkali treatment and acid hydrolysis. The composition and processing parameters of the thin films were optimized, and their adsorption capacity was determined using thermodynamic isotherms and adsorption kinetics. Adsorption characteristics such as the methylene blue (MB) dye concentration, contact time, temperature, and pH were investigated to determine how they affected adsorption. The results show that the adsorption process follows pseudo-second-order kinetics. At an adsorbent mass of 50 mg, dye concentration of 50 ppm in 50 mL, and contact period of 120 min at 25 °C, the thin film comprising 64 wt% CNC, 16 wt% PAA, and 20 wt% AC showed high dye removal efficiency (86.3%) and adsorption capacity (43.15 mg/g). The MB removal efficiency increased to 95.56% and the adsorption capacity to 47.78 mg/g when the medium's pH was gradually increased from neutral to alkaline. The nontoxicity, low production cost, water stability, easy recovery, and high adsorption capacity of these membranes make them suitable for water treatment systems.

Adsorption mechanism and removal efficiency of magnetic graphene oxide-chitosan hybrid on aqueous Zn(II)

Magnetic architecture incorporating graphene-chitosan has demonstrated encouraging application in wastewater purification. Herein, a ternary hybrid based on Fe₃O₄-graphene oxide-chitosan (MGOCS) was fabricated and employed as adsorbent to remove aqueous Zn(II). The adsorption mechanism was intensively inspected based on the hard and soft acid base (HSAB) theory. Results present, MGOCS removes 96.73 % of Zn(II) in 38 min, with adsorption quantity 386.92 mg·g^-1. Electron transfer and energy lowering determined by the HSAB theory illuminate the plausible adsorption sites in each component of MGOCS: O₂^- in Fe₃O₄, -C(=O)NH-, -NH₂ in chitosan and -OH in graphene oxide. The exploration was upheld by spectroscopic analyses. Thereby, following adsorption mechanism was proposed. (1) ZnO bond was formed featured by electron donation. (2) The -C(=O)NH- group formed via amidation between graphene oxide and chitosan contributes to Zn(Π) uptake. This work may inspire the development of efficient adsorbent based on magnetic graphene-chitosan for wastewater remediation.

Magnetic Ionotropic Hydrogels Based on Carboxymethyl Cellulose for Aqueous Pollution Mitigation

In this work, stabilized ionotropic hydrogels were designed using sodium carboxymethyl cellulose (CMC) and assessed as inexpensive sorbents for hazardous chemicals (e.g., Methylene Blue, MB) from contaminated wastewaters. In order to increase the adsorption capacity of the hydrogelated matrix and facilitate its magnetic separation from aqueous solutions, sodium dodecyl sulfate (SDS) and manganese ferrite (MnFe₂O₄) were introduced into the polymer framework. The morphological, structural, elemental, and magnetic properties of the adsorbents (in the form of beads) were assessed using scanning electron microscopy (SEM), energy-dispersive X-ray analysis, Fourier-transform infrared spectroscopy (FTIR), and a vibrating-sample magnetometer (VSM). The magnetic beads with the best adsorption performance were subjected to kinetic and isotherm studies. The PFO model best describes the adsorption kinetics. A homogeneous monolayer adsorption system was predicted by the Langmuir isotherm model, registering a maximum adsorption capacity of 234 mg/g at 300 K. The calculated thermodynamic parameter values indicated that the investigated adsorption processes were both spontaneous (ΔG < 0) and exothermic (ΔH < 0). The used sorbent can be recovered after immersion in acetone (93% desorption efficiency) and re-used for MB adsorption. In addition, the molecular docking simulations disclosed aspects of the mechanism of intermolecular interaction between CMC and MB by detailing the contributions of the van der Waals (physical) and Coulomb (electrostatic) forces.

Enhanced adsorption of 3,4-methylenedioxymethamphetamine by magnetic graphene oxide-polydopamine nanohybrid modified zeolitic imidazolate framework-67 and its micro-mechanism: Experiments and calculations

Exploring the structure-dependent adsorption mechanism of contaminants in wastewater is beneficial to high-efficiency adsorbents design and environmental remediation. In this study, emerging porous material of zeolitic imidazolate framework-67 (ZIF-67) has been modified by the magnetic graphene oxide-polydopamine nanohybrid (mGOP) to obtain three-dimensional ZIF-67/mGOP through an in-situ growth strategy, which was applied to adsorb 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") in wastewater. A combination of characterizations, experiments (pH, humic acid and ion strength effect) and quantum chemical calculations revealed the microscopic adsorption mechanism involves each single component, of which the hydrogen bond (O/N…HO) and π-π electron donor acceptor (π-π EDA) interactions of mGOP endowed favourable adsorption of ZIF-67/mGOP, and mechanisms of the pore filling and Co-O chelation of ZIF-67 played synergistic effect. Such nanocomposite as a ZIFs-based adsorbent exhibited ultra-high porosity (total pore volume = 0.4033 cm³/g) and specific surface area (995.22 m²/g), revealed the heterogeneity and multilayer adsorption properties, and obtained a theoretical maximum adsorption capacity of 159.845 μg/g which higher than that of mZIF-67 alone. Overall, this work provided an effective strategy for rationally modulate ZIFs-based composites and exploration of adsorption mechanism.

Removal of anionic and cationic dyes using porous chitosan/carboxymethyl cellulose-PEG hydrogels: Optimization, adsorption kinetics, isotherm and thermodynamics studies

Chitosan (CS)/carboxymethyl cellulose (CMC) porous hydrogels chemically crosslinked by epichlorohydrin were synthesized using polyethylene glycol (PEG) as a pore-forming agent for anionic (Congo red, CR) and cationic (methylene blue, MB) dyes removal from aqueous solutions. The swelling ratio of hydrogels prepared with 2 % CS and 2 % CMC (CS₂/CMC₂) exhibited optimal performance at different pHs. The addition of PEG into hydrogels (denoted as CS₂/CMC₂-PEG_1.25) exhibited a significantly higher adsorption for CR and MB, increasing from 117.83 to 159.12 mg/g and 110.2 to 136 mg/g, respectively. The comprehensive analyses of Fourier transform infrared spectroscopy, thermalgravimetric study and scanning electron microscopy showed that CS₂/CMC₂-PEG_1.25 hydrogels became more porous with no significant changes in intermolecular and intramolecular interactions, compared with CS₂/CMC₂ hydrogels. The adsorption process for CR and MB conformed to the pseudo-second-order and pseudo-first-order kinetics models, respectively. The results of adsorption isotherm for CR followed both Freundlich and Langmuir models with the maximum adsorption capacities of 1053.88 mg/g, whereas the isotherm for MB fitted the Langmuir model better with the maximum adsorption capacities of 331.72 mg/g. The thermodynamic study results proved that the CR and MB adsorption by hydrogels was spontaneous, but the CR adsorption was endothermic and the MB adsorption was exothermic.

Combination mechanism of the ternary composite based on Fe3O4-chitosan-graphene oxide prepared by solvothermal method

Magnetic nanohybrid combining chitosan and graphene have demonstrated promising application in environmental remediation. Herein, ternary composite MCG based on Fe₃O₄, chitosan (CS) and graphene oxide (GO) was facilely prepared via solvothermal method. The as prepared composite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman, Brunauer/Emmett/Teller-Barret/Joyner/Halenda (BET-BJH) and thermo gravimetric-differential thermal analysis (TG-DTA). The combination mechanism of MCG was unveiled via employing the hard-soft acid-base (HSAB) theory and spectroscopic investigations including X-ray photoelectron spectroscopy (XPS), Ultraviolet-visible (UV-Vis) and fluorescent emission spectra. Particularly, combination mechanism of MCG was elucidated by the probable site to site interaction of the couplet components in MCG, as follows. (1) CS-Fe₃O₄. The primary interaction is N(NH₂)-Fe(III), electron donates from N to Fe, transforming one half of the amino groups of chitosan into positive N⁺. (2) GO-CS. Amidation reaction is the primary interaction form, converting the other half of the amino groups of chitosan into -C(O)NH-. (3) GO-Fe₃O₄. Dominant interactions are those of epoxy, hydroxyl and aromatic ring with Fe(III). Moreover, MCG exhibits fair adsorption performance on divalent heavy metals in six consecutive cycles. These explorations may shed light on the design of efficient adsorbent based on Fe₃O₄-chitosan-graphene architecture.

Recoverable cellulose composite adsorbents for anionic/cationic dyes removal

GO/HEC/PGDE/Fe₃O₄ materials were successfully fabricated using environmentally-friendly hydroxyethyl cellulose (HEC), poly(ethylene glycol) diglycidyl ether (PGDE), graphene oxide (GO) and magnetic Fe₃O₄. Systematic investigations were completed to explore the influences of GO content in GO/HEC/PGDE/Fe₃O₄ and adsorption conditions on the adsorptions of cationic dyes (methylene blue (MB), crystal violet (CV)) and anionic dye acid blue 25 (AB-25). The increase of GO content can remarkably improve the adsorption capacity of GO/HEC/PGDE/Fe₃O₄ for the dyes. The three kinetic, four isothermic and three thermodynamic models were investigated to reveal the adsorption behaviors of the dyes. The formation of HEC/PGDE/Fe₃O₄ and adsorption mechanisms of the dyes by GO/HEC/PGDE/Fe₃O₄ were suggested. The GO/HEC/PGDE/Fe₃O₄ endowed with easy-fabrication, eco-friendly feature, efficient adsorption capacity of anionic/cationic dyes, convenient separation and reusability has potential applications in wastewater purification industry.

Mapping 3D Printability of Ionically Cross-Linked Cellulose Nanocrystal Inks: Architecting from Nano- to Macroscale Structures

Engineering the rheological properties of colloidal inks is one of the main challenges in achieving high-fidelity 3D printing. Herein, we provide a comprehensive study on the rheological behavior of inks based on cellulose nanocrystals (CNCs) in the presence of given salts to enable high-quality 3D printing. The rheological properties of the CNC suspensions are tailored by considering the nature of the electrolyte (i.e., 10 types of salts featuring different ion sizes, charge numbers, and inter- and intra-molecular interactions) at various concentrations (25-100 mM). A high printing fidelity is achieved in a narrow CNC and salt concentration range, significantly depending on the salt type. The structure-property relationship is explored in a "3D-printing" space (2D map), introducing a guideline for researchers active in this field. To further unravel the effect of salt type on morphological properties, CNC aerogels are developed by freeze-drying the printed structures. The results illustrate that enhancing viscoelastic properties render a denser structure featuring smaller pores.

Chemically activated carbon preparation from natural rubber biosludge for the study of characterization, kinetics and isotherms, thermodynamics, reusability during Cr(VI) and methylene blue adsorption

Alkaline leachate, dust generation, and foul smell during the stacking process of natural rubber biosludge (NRBS) can pollute surrounding water, soil, and air. In this study, natural rubber chemically activated carbon (NRCAC) has been synthesized for the first time from NRBS by pyrolysis using ZnCl₂ at 700 °C for adsorptive removal of Cr(VI) and methylene blue (MB) from aqueous solutions. Both NRBS and NRCAC were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Brunauer-Emmett-Teller (BET), and thermogravimetric analyzer (TGA). FTIR and SEM-EDS suggested significant functional and morphological transformations in NRCAC. Experimental investigations of different process parameters, such as pH, concentration, contact time, salt concentration, etc., were conducted to study their influences on adsorption. Adsorption and desorption kinetics followed a pseudo-second-order model, while adsorption equilibrium followed Liu isotherm. Maximum uptake calculated from the Liu model was 81.28 and 211.90 mg/g for Cr(VI) and MB, respectively. Thermodynamic analysis established spontaneous and endothermic adsorption. Up to five adsorption/desorption cycles were conducted using eluents such as 1 M NaOH and water for Cr(VI) and MB, respectively. Electrostatic attraction and ion-exchange favored Cr(VI)/MB adsorption, while hydrogen bonding and π-π stacking were significant in MB uptake. Overall findings suggest that NRBS (a renewable agro-industrial, abundant, and freely available) could be employed to synthesize biochar for adsorptive removal of wastewater containing Cr(VI)/MB.

Performance Evaluation of Gum Gellan-Based Hydrogel as a Novel Adsorbent for the Removal of Cationic Dyes: Linear Regression Models

In this work, the suitability and efficacy of the previously reported biodegradable gellan gum (GG)-based hydrogel have been thoroughly investigated with respect to the adsorption mechanisms of malachite green (MG) and methylene blue (MB) dyes. The dyes' removal from aqueous solutions using GG-cl-poly(AA) as an adsorbent material has been studied in a discontinuous system with respect to contact time, dose, pH, and temperature. The synthesized hydrogel was characterized by FT-IR, TGA, XRD, ¹H NMR, and FE-SEM. The adsorption capacity of GG-cl-poly(AA) hydrogel was investigated at different pH solutions (3, 7, and 10), and it was found that neutralized charge plays a crucial role in the enhancement of dye removal. To better understand the behavior of the GG-cl-poly(AA) hydrogel in adsorbing model dyes, adsorption kinetics, isotherms, and thermodynamics were also investigated. The values of qmax for MG and MB were obtained to be 552.48 and 531.9 mg g^-1. In addition, the influence of NaCl concentration on adsorption efficiency was investigated, and it was found that as the ion concentration increased, the effectiveness of the adsorption process dropped. Moreover, the synthesized hydrogel's potential application in the adsorption and separation of dyes from wastewater is enhanced by the reusability investigations conducted in convenient conditions. As a result, it is possible to conclude that reusing GG-cl-poly(AA) hydrogel as a low-cost, easy-to-handle, nontoxic material in an industrial wastewater treatment plant's adsorption process can provide a number of advantages, including high efficiency for MG and MB removal and cost savings on overall treatment plant operations.

FeOCl-confined activated carbon for improving intraparticle Fenton-like oxidation regeneration

Highly efficient oxidation, as non-thermal regeneration technology, is a promising method to solve the regeneration problem of spent activated carbon (AC) in wastewater treatment. In this study, FeOCl was confined into activated carbon (FeOCl/AC) for catalytic oxidation of contaminants on AC during the regeneration process. The characterization results of FeOCl/AC showed that amorphous FeOCl was distributed in micropores, mesopores and macropores of AC. The methylene blue (MB)-adsorbed FeOCl/AC had a regeneration efficiency of 93.7 % at neutral pH in the presence of H₂O₂, much higher than 46.9 % by Fenton oxidation and 33.7 % by H₂O₂ oxidation. Meanwhile, the spent FeOCl/AC after the adsorption of atrazine, 2,4-dichlorophenol, and ofloxacin had the regeneration efficiencies of 71.5 %, 86.4 %, and 100 %, respectively. Moreover, the regeneration efficiency still reached 87 % in the fifth adsorption-regeneration cycle, and was linearly decreased with the increase of adsorbed amounts of MB. During 6 h regeneration of spent FeOCl/AC, 97 % of adsorbed MB was degraded. Electron paramagnetic resonance and radical trapping experiments indicated that both superoxide and hydroxyl radicals were involved in MB oxidation during the regeneration process.

Enhanced performance of hydroxyl and cyano group functionalized graphitic carbon nitride for efficient removal of crystal violet and methylene blue from wastewater

This work reports the synthesis of an innovative multifunctional carbon nitride based adsorbent and its successful application for the removal of crystal violet (CV) and methylene blue (MB) from wastewater. The functionalized graphitic carbon nitride (f/g-CN) adsorbent was produced by the pyrolysis of melamine followed by thermal alkali treatment to introduce OH, NH x , and CN groups onto the graphitic carbon nitride (g-CN) surface. Experimental data obtained from batch tests revealed that the maximum adsorption capacities of g-CN and f/g-CN were found to be 28.9 and 239.0 mg g-1 for MB, and 163.0 and 532.0 mg g-1 for CV, respectively, at pH 8, 25 °C and after 90 min. This increase in adsorption capacity of f/g-CN can be explained by the presence of multiple functional groups in its structure. f/g-CN showed 100% removal for MB and CV with concentrations lower than 100 ppm and the equilibrium time required for the 100% removal of 500 ppb dye is 60 seconds. Additionally, the experimental data fitted well with the Langmuir isotherm model (R 2 = 0.992) and pseudo second order kinetic model (R 2 = 0.999) suggesting that the mechanism of adsorption is based on π-π stacking and electrostatic interactions between the NH x and OH groups of f/g-CN and dye molecules with monolayer formation. Moreover, a reusability test showed that the adsorption capacity remained at around 90% after 7 cycles. This work highlights the merits of the prepared adsorbent f/g-CN which is an eco-friendly, stable, efficient, and reusable adsorbent for removing cationic dyes from wastewater.

A study on the uptake of methylene blue by biodegradable and eco-friendly carboxylated starch grafted polyvinyl pyrrolidone

This study is based on the removal of methylene blue (MB) from aqueous solution by cost effective and biodegradable adsorbent carboxymethyl starch grafted polyvinyl pyrolidone (Car-St-g-PVP). The Car-St-g-PVP was synthesized by grafting vinyl pyrolidone onto carboxymethyl starch by free radical polymerization reaction. The structure and different properties of Car-St-g-PVP were determined by ¹H NMR, FT-IR, XRD, TGA and SEM. A series of batch experiments were conducted for the removal of MB, The adsorption affecting factors such as temperature, contact time, initial concentration of MB dye, dose of Car-St-g-PVP and pH were studied in detail. The other parameters like the thermodynamic study, kinetics and isothermal models were fitted to the experimental data. The results showed that pseudo 2^nd order kinetics and Langmuir's adsorption isotherms were best fitted to experimental data with regression coefficient R² viz. 0.99 and 0.97. The kinetic study showed that the adsorption mechanism favored chemisorption. The Gibbs free energy (ΔG°) for the adsorption process was found to be -7.31 kJ/mol, -8.23 kJ/mol, -9.00 kJ/mol and -10.10 kJ/mol at 25 °C, 35 °C, 45 °C and 55 °C respectively. The negative values of ΔG° suggested the spontaneous nature of the adsorption process. Similarly, the positive values of entropy (ΔS°) and enthalpy (ΔH°) 91.27 J/k.mol and 19.90 kJ/mol showed the increasing randomness and endothermic nature of the adsorption process. The value of separation factor (R_L) was found to be less than one (RL < 1), which supported the feasibility of the adsorption process. The maximum MB removal percentage (% R) was found to be 98.6%. So, these findings show that Car-St-g-PVP can be meritoriously used for the treatment of MB from wastewater.