Adsorption behavior of cationic dye on mesoporous silica SBA-15 carried by calcium alginate beads: Experimental and molecular dynamics study

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.

Molecular simulation-based insights into dye pollutant adsorption: A perspective review

Growing concerns about environmental pollution have highlighted the need for efficient and sustainable methods to remove dye contamination from various ecosystems. In this context, computational methods such as molecular dynamics (MD), Monte Carlo (MC) simulations, quantum mechanics (QM) calculations, and machine learning (ML) methods are powerful tools used to study and predict the adsorption processes of dyes on various adsorbents. These methods provide detailed insights into the molecular interactions and mechanisms involved, which can be crucial for designing efficient adsorption systems. MD simulations, detailing molecular arrangements, predict dyes' adsorption behaviour and interaction energies with adsorbents. They simulate the entire adsorption process, including surface diffusion, solvent layer penetration, and physisorption. QM calculations, especially density functional theory (DFT), determine molecular structures and reactivity descriptors, aiding in understanding adsorption mechanisms. They identify stable adsorption configurations and interactions like hydrogen bonding and electrostatic forces. MC simulations predict equilibrium properties and adsorption energies by sampling molecular configurations. ML methods have proven highly effective in predicting and optimizing dye adsorption processes. These models offer significant advantages over traditional methods, including higher accuracy and the ability to handle complex datasets. These methods optimize adsorption conditions, clarify adsorbent functionalization roles, and predict dye removal efficiency under various conditions. This research explores MD, MC, QM, and ML approaches to connect molecular interactions with macroscopic adsorption phenomena. Probing these techniques provides insights into the dynamics and energetics of dye pollutants on adsorption surfaces. The findings will aid in developing and optimizing new materials for dye removal. This review has significant implications for environmental remediation, offering a comprehensive understanding of adsorption at various scales. Merging microscopic data with macroscopic observations enhances knowledge of dye pollutant adsorption, laying the groundwork for efficient, sustainable removal technologies. Addressing the growing challenges of ecosystem protection, this study contributes to a cleaner, more sustainable future.

Fabrication of silica/calcium alginate nanocomposite based on rice husk ash for efficient adsorption of phenol from water

The current work discusses the synthesis of three different solid adsorbents: silica nanoparticles derived from rice husk (RS), calcium alginate beads (AG), and silica/alginate nanocomposite (RSG). The fabricated solid adsorbents were characterized by using different physicochemical techniques such as TGA, XRD, nitrogen adsorption/desorption analysis, ATR-FTIR, pHPZC, SEM, and TEM. The adsorption efficiencies of the prepared solid adsorbents were considered for the removal of phenol as a selected hazardous pollutant. Because of its improved adsorption capacity and environmentally friendly character, a composite made of biosilica nanoparticles and naturally occurring alginate biopolymer by click chemistry is significant in environmental treatment. Adding silica nanoparticles to the alginate biopolymer hydrogel has many advantages, including increased surface area, easier recovery of the solid adsorbent, and additional surface chemical functional groups. The silica/alginate nanocomposite showed surface heterogeneity with many chemical functional groups present, whereas silica nanoparticles had the highest surface area (893.1 m2 g-1). It has been found that the average TEM particle size of RS, AG, and RSG was between 18 and 82 nm. RSG displayed the maximum adsorption capacity of phenol (100.55 mg g-1) at pH 7 and 120 min as equilibrium adsorption time. Adsorption of phenol onto the solid adsorbents fit well with a nonlinear Langmuir isotherm with favorable adsorption. Kinetic and thermodynamic studies prove that the adsorption process follows a pseudo-second-order kinetic model, endothermic process, physical, and spontaneous adsorption. Sodium hydroxide is effective in desorbing 94% of the loaded phenols, according to desorption investigations. Solid reusability tests showed that, after seven cycles of phenol adsorption/desorption, RSG lost only 8.8% of its adsorption activity.

Synthesis of Ordered Mesoporous Silica with Nonionic Surfactant/Anionic Polyelectrolyte as Template under Near-Neutral pH Conditions

Ordered mesoporous silica is widely used in catalysis, adsorption, and biomedicine, among which SBA-15 (Santa Barbara Amorphous-15) is one of the most widely studied. However, the synthesis of SBA-15 often requires strong acid (hydrochloric acid or sulfuric acid), which will not only corrode industrial equipment but also pollute the environment with the wastewater containing strong acid and halogen (sulfur). Here, we demonstrate a green synthetic strategy for SBA-15 under weakly acidic conditions through an anionic assembly route. With the assistance of poly(acrylic acid) (PAA) and 3-aminopropyltrimethoxysilane (APMS), the pH value of the synthesis system can be increased to 4-5, which is a mild near-neutral condition. In addition, halogen-free synthesis using organic acids is also achieved. The powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 sorption characterizations show that the obtained SBA-15 has good texture properties, with a specific surface area of 430-500 m2/g and ordered 6-8 nm mesopores, which is similar to SBA-15 synthesized in traditional strong acid. This strategy provides a facile and environmentally friendly route for the large-scale production of ordered mesoporous materials.

New insights on the decolorization of waste flows by Saccharomyces cerevisiae strain - A systematic review

One of the common causes of water pollution is the presence of toxic dye-based effluents, which can pose a serious threat to the ecosystem and human health. The application of Saccharomyces cerevisiae (S. cerevisiae) for wastewater decolorization has been widely investigated due to their efficient removal and eco-friendly treatments. This review attempts to create an awareness of different forms and methods of using Saccharomyces cerevisiae (S. cerevisiae) for wastewater decolorization through a systematic approach. Overall, some suggestions on classification of dyes and related environmental/health problems, and treatment methods are discussed. Besides, the mechanisms of dye removal by S. cerevisiae including biosorption, bioaccumulation, and biodegradation and cell immobilization methods such as adsorption, covalent binding, encapsulation, entrapment, and self-aggregation are discussed. This review would help to inspire the exploration of more creative methods for applications and modification of S. cerevisiae and its further practical applications.

Gemini Quaternary Ammonium Surfactants with Different Counterions-modified Montmorillonite for Efficient Removal of Methyl Orange

Organic Na-montmorillonite (OMt-12-2-12·2Y - , Y=CH 3 CO 3 - , C 6 H 5 COO - and Br - ) modified by a series of Gemini quaternary ammonium surfactants with different counterions was prepared for enhancing the adsorption capacity of methyl orange. Compared with the initial adsorption capacity of 5.251 mg/g of Na-Mt, the adsorption effect of OMts under the optimal conditions increased by about 31~34 times. The adsorption isotherms and kinetics of all adsorption processes were respectively described by Langmuir and pseudo-second-order models. The structure, hydrophobicity and hydration of the counterions, as well as the affinity of the counterions with the long aliphatic chains, had a certain influence on the adsorption performance of OMts for methyl orange.

Removal of crystal violet dye using a three-dimensional network of date pits powder/sodium alginate hydrogel beads: Experimental optimization and DFT calculation

Biodegradable and very low-cost adsorbent beads were prepared from date pits powder (DP) and sodium alginate (SA). DP to SA ratios was varied (1/2, 1/4 and 1/6) and used to eliminate Crystal violet (CV) a cationic dye. Adsorbents were characterized by FTIR, SEM-EDS, UV-vis DR, TGA and the point of zero charge (pHPZC). The optimal composite beads SA@6DP show high adsorption capacities of 83.565 mg/g toward CV than SA@2DP and SA@4DP. The kinetics investigation showed that the adsorption is well described by the pseudo-second-order kinetic (R2 = 0.998). The thermodynamics and isotherms studies exhibit that the adsorption phenomenon for SA@6DP adsorbent is endothermic and significantly fitted with the Redlich-Peterson model. The experimental adsorption tests were optimized by the Box-Behnken design (BBD) which led to conclude the maximal CV removal efficiency achieved by SA@6DP was 99.873 % using [CV] = 50 mg/L, adsorbent mass = 20 mg and 48 h of contact time. The theoretical calculation proved that the CV molecules favor the mode of attack due to their electrophilic character and can accept the SA@6DP adsorbent electrons more easily to form an anti-bonding orbital. SA@6DP hydrogel beads are therefore an exceptional bio-adsorbent that offers excellent adsorption performance.

Efficient removal of Cu2+ and methylene blue pollutants from an aqueous solution by applying a new hybrid adsorbent based on alginate-chitosan and HAP derived from Moroccan rock phosphate

Alginate-chitosan/hydroxyapatite (Alg-Cs/HAP) beads were prepared as adsorbent to remove methylene blue (MB) and copper ions from an aqueous solution using a batch system. FTIR, TGA, point of zero charge (pHpzc), SEM, XRD, and BET analysis were used to characterize the elaborated material. The effect of several parameters such as initial pH value, adsorbent dose, temperature, contact time, and initial pollutant concentration were also investigated. The obtained results showed that Alg-Cs/HAP exhibit excellent adsorption properties for Cu (II) and MB removal, with high adsorption capacities of copper ions (208.34 mg/g) and methylene blue (454.54 mg/g). The kinetic of the adsorption process is correlated with the pseudo-first-order for methylene blue and the pseudo-second-order for copper ions. The equilibrium data for MB dye fitted the Freundlich isotherm model, thus implying that the adsorption process consists of multilayer adsorption as well as interactions between the adsorbate and the adsorbent. The equilibrium data for copper ions corresponds closely with the Langmuir model which suggests that the adsorbed molecules occur over a monolayer. Various thermodynamic parameters such as the standard Gibbs energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were calculated. All results indicated that Alg-Cs/HAP material has a good potential for the treatment of wastewater.

Decoration of sodium carboxymethylcellulose gel microspheres with modified lignin to enhanced methylene blue removal

The introduction of active groups from biomass is currently the most promising alternative method for increasing the adsorption effect of dyes. In this study, modified aminated lignin (MAL) rich in phenolic hydroxyl and amine groups was prepared by amination and catalytic grafting. The factors influencing the modification conditions of the content of amine and phenolic hydroxyl groups were explored. Chemical structural analysis results confirmed that MAL was successfully prepared using a two-step method. The content of phenolic hydroxyl groups in MAL significantly increased to 1.46 mmol/g. MAL/sodium carboxymethylcellulose (NaCMC) gel microspheres (MCGM) with enhanced methylene blue (MB) adsorption capacity owing to the formation of a composite with MAL were synthesized by a sol-gel process followed by freeze-drying and using multivalent cations Al³⁺ as cross-linking agents. In addition, the effects of the MAL to NaCMC mass ratio, time, concentration, and pH on the adsorption of MB were explored. Benefiting from a sufficient number of active sites, MCGM exhibited an ultrahigh adsorption capacity for MB removal, and the maximum adsorption capacity was 118.30 mg/g. These results demonstrated the potential of MCGM for wastewater treatment applications.

Effective adsorption of Orange G dye using chitosan cross-linked by glutaraldehyde and reinforced with quartz sand

In this study, quartz sand (QS) incorporated into a crosslinked chitosan-glutaraldehyde matrix (QS@Ch-Glu) was prepared and employed as an efficient adsorbent for the elimination of Orange G (OG) dye from water. The sorption process is adequately described by the pseudo-second order kinetic model and the Langmuir isotherm model with maximum adsorption capacities of 172.65, 188.18, and 206.65mg/g at 25, 35, and 45 °C, respectively. A statistical physics model was adopted to elucidate the adsorption mechanism of OG on QS@Ch-Glu. Calculated thermodynamic factors revealed that the adsorption of OG is endothermic, spontaneous, and occurs via physical interactions. Overall, the proposed adsorption mechanism was based on electrostatic attractions, n-π stacking interaction, hydrogen bonding interaction, and Yoshida hydrogen bonding. The adsorption rate of QS@Ch-Glu was still above 95 % even after 6 cycles of adsorption and desorption. Furthermore, QS@Ch-Glu demonstrated high efficiency in real water samples. All these findings demonstrate that QS@Ch-Glu is qualified for practical applications.

A review on remediation of dye adulterated system by ecologically innocuous "biopolymers/natural gums-based composites"

The mitigation of wastewater exploiting biopolymers/natural gums-based composites is an appealing research theme in today's scenario. The following review presents a comprehensive description of the polysaccharides derived from biopolymers (chitosan, collagen, cellulose, starch, pectin, lignin, and alginate) and natural gums (guar, gellan, carrageenan, karaya, moringa oliefera, tragacanth, and xanthan gum). These biopolymers/natural gums-based composites depicted excellent surface functionality, non-toxicity, economic and environmental viability, which corroborated them as potential candidates in the decontamination process. The presence of -OH, -COOH, and -NH functional groups in their backbone rendered them tailorable for modification/functionalization, and anchor an array of pollutants via electrostatic interaction, hydrogen bonding, and Van der Waals forces. Further, due to these functional moieties, these bio-based composites revealed an excellent adsorption capacity than conventional adsorbents. This review provides an overview of the classification of biopolymers/natural gums based on their origin, different ways of their modification, and the remediation of dye-contaminated aqueous environments employing diverse bio-based adsorbents. The isotherm, kinetic modelling along with thermodynamics of the adsorption process is discussed. Additionally, the reusable efficacy of these bio-adsorbents is reviewed.

Interlayer adsorption of cationic dye on cationic surfactant-modified and unmodified montmorillonite

Water pollution by toxic organic dyes is one of the most critical health and environmental problems worldwide. By means of molecular dynamics method, the present work aims to evaluate the applicability of montmorillonite (Mt) modified by hexadecyltrimethylammonium cations (HDTMA⁺) compared to unmodified Na-Mt for the adsorption of cationic methylene blue (MB) dye. The results showed that the adsorption energy of MB on both HDTMA-Mt and Na-Mt absorbent ranged from - 100 to - 250 kJ/mol, indicating the effectiveness of two types of adsorbents in dye water treatment. The highest adsorption energy was found at w = 50% in each adsorbent system. Adsorption mechanisms of MB depend on molecular orientations, which is influenced by the surfactant and water content. The adsorption mechanism of MB is chemisorption dominated by strong electrostatic interaction between CH₃ groups of MB and oxygen atoms of Mt surfaces. Besides, physisorption also plays a minor role in MB orientations. It is found that the existence of cationic surfactants can slightly improve the adsorption capacity of MB only at higher water content through enlarging the interlayer space of Mt and reducing mobility of MB. However, there will be a negative impact on the reduction of adsorption sites for dyes especially at low water content. Our results provide a possible application for swelling clay minerals being a promising adsorbent for dyes-surfactants co-existing wastewater treatment.

Carbon-based nanocomposite materials with multifunctional attributes for environmental remediation of emerging pollutants

Carbon-based materials are among the most biosynthesized nanocomposites with excellent tunability and multifunctionality features, that other materials fail to demonstrate. Naturally occurring materials, such as alginate (Alg), can be combined and modified by linking the active moieties of various carbon-based materials of interest, such as graphene oxide (GO), carbon nanotubes (CNTs), and mesoporous silica nanocomposite (MSN), among others. Thus, several types of robust nanocomposites have been fabricated and deployed for environmental remediation of emerging pollutants, such as pharmaceutical compounds, toxic dyes, and other environmentally hazardous contaminants of emerging concern. Considering the above critiques and added features of carbon-based nanocomposites, herein, an effort has been made to spotlight the synergies of GO, CNTs, and MSN with Alg and their role in mitigating emerging pollutants. From the information presented in this work, it can be concluded that Alg is a material that has excellent potential. However, its use still requires further tests in different areas and other materials to carry out a holistic investigation that exploits its versatility for environmental remediation purposes.

New alginic acid derivatives ester for methylene blue dye adsorption: kinetic, isotherm, thermodynamic, and mechanism study

In this paper, the application of ester materials prepared by grafting different carbon chain lengths of diols in alginic acid (AA) by a simple, fast and efficient method for the adsorption of methylene blue (MB) is studied. The AA ester derivatives are characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Zeta potential before and after MB adsorption. This study shows a significant improvement in the adsorption capacity of MB by AA after its esterification with a Q_max value up to 454.545 mg/g for the best adsorbent "Poly(AA-g-EG)". The experimental data are studied according to two isothermal models (Langmuir and Freundlich) and two kinetic models (pseudo-second order and intra-particle diffusion). The adsorption of MB is also evaluated thermodynamically. An adsorption mechanism of MB is established.

Synthesis and characterization of a new meso-tetrakis (2,4,6-trimethylphenyl) porphyrinto) zinc(II) supported sodium alginate gel beads for improved adsorption of methylene blue dye

Chemical modification of a biopolymer offers a simple strategy to realize new materials with added benefits. In this paper, meso-tetrakis(2,4,6-trimethylphenyl) porphyrinto) zinc(II) supported sodium alginate gel beads were successfully prepared, characterized, and used for the removal of a cationic dye from aqueous solution. The chemical structure of the prepared composite beads was confirmed by FT-IR, SEM, XRD and TGA/DTG techniques. Analytical data suggested that the sodium alginate beads and meso-tetrakis(2,4,6-trimethylphenyl) porphyrinto) zinc(II) complex interacted via non-covalent interaction (H-bonding) mode. The morphological micrographs showed spherical and smooth composite beads. The crosslinking of hydroxyl and carboxylate groups of the biopolymer with calcium ions and the incorporation of meso-tetrakis(2,4,6-trimethylphenyl) porphyrinto) zinc(II) into alginate matrix resulted in a small decrease of residual mass. The maximum adsorption capacities of methylene blue, at 20 °C, were found to be 52.3 mg/g and 34.8 mg/g for sodium alginate composite beads (3%) and plain sodium alginate beads, respectively. The adsorption process followed Freundlich isotherm and pseudo second order kinetics. The thermodynamic study displayed an exothermic and non-spontaneous process.

Catalytic behavior and antibacterial/antifungal activities of new MNPs/zeolite@alginate composite beads

In this paper, a new family of composite materials was prepared based on calcium alginate and metal nanoparticle-loaded zeolite omega. Different types of metal nanoparticles (MNPs), namely Cu, Co and Fe, were loaded onto zeolite omega to test the performance of the resulting metal/zeolite@alginate composites towards the catalytic reduction of methylene blue dye. To examine their application field as broadly as possible, these composite beads were also tested as antibacterial and antifungal agents against several types of bacteria. Several techniques such as XRD, XRF, FTIR, XPS, SEM and TGA were used to characterize the samples. The obtained results showed that all the composite bead samples were effective in the reduction of MB dye. The composite Co/Zeolite@ALG with relatively low Co nanoparticle (NP) content was selected as the best performing catalyst due to its reduction of MB dye being completely achieved in 3 min with a rate constant of 1.4 min-1, which was attributed to its highly porous structure. The reuse tests conducted on the best-performing catalyst showed good results which persisted through five successive cycles. For antibacterial and antifungal activities, the Cu/Zeolite@ALG and Fe/Zeolite@ALG composites showed good activity with significant inhibition zones.

Alginate-based nano-adsorbent materials - Bioinspired solution to mitigate hazardous environmental pollutants

Population growth and industrialization is associated with the elevation of hazardous pollutants, including heavy metals, biomedical wastes, personal-care products, endocrine-disrupters, pharmaceutically active compounds, and colorants in the environment. The scientific focus has been devoted to developing novel adsorbents to mitigate hazardous pollutants by constructing hybrids of different polymers and nano-structured materials for improved workability and physicochemical attributes. Recently, much attention has been devoted to nanomaterials in environmental remediation, owning to their exceptional characteristics including novel electrical/chemical features, quantum size effects, tunable functionalization, high scalability, and surface-area-to-volume ratio. Target-specific designing of nanocomposites impart high functionality. The cost-effective and eco-friendly synthesis of bioadsorbent materials is increasing for the removal of hazardous pollutants. Due to biocompatible, biodegradable, and eco-friendly nature, sodium alginate has been widely reported for the preparation of bioadsorbent materials to remove different inorganic/organic pollutants. In this review, the potentialities of alginate-based nanocomposites have been described for environmental remediation purposes. Different nanomaterials, including silica, metallic oxide, graphene oxide, hybrid inorganic-organic, non-magnetic-magnetic, carbon nanorods, nanotubes, polymeric nanocarriers, and several other materials have been described in combination with alginate biopolymer for environmental remediation.

Silk Sericin Enrichment through Electrodeposition and Carbonous Materials for the Removal of Methylene Blue from Aqueous Solution

The recycling and reuse of biomass waste for the preparation of carbon-based adsorbents is a sustainable development strategy that has a positive environmental impact. It is well known that a large amount of silk sericin (SS) is dissolved in the wastewater from the silk industry. Utilizing the SS instead of discharging it into the environment without further treatment would reduce environmental and ecological problems. However, effective enrichment of the SS from the aqueous solution is a challenge. Here, with the help of carboxymethyl chitosan (CMCS), which can form a gel structure under low voltage, an SS/CMCS hydrogel with SS as the major component was prepared via electrodeposition at a 3 V direct-current (DC) voltage for five minutes. Following a carbonization process, an SS-based adsorbent with good performance for the removal of methylene blue (MB) from an aqueous solution was prepared. Our results reveal that the SS/CMCS hydrogel maintains a porous architecture before and after carbonization. Such structure provides abundant adsorption sites facilitating the adsorption of MB molecules, with a maximum adsorptive capacity of 231.79 mg/g. In addition, it suggests that the adsorption is an exothermic process, has a good fit with the Langmuir model, and follows the intra-particle diffusion model. The presented work provides an economical and feasible path for the treatment of wastewater from dyeing and printing.