Gellan gum/bacterial cellulose hydrogel crosslinked with citric acid as an eco-friendly green adsorbent for safranin and crystal violet dye removal

The effective treatment of dye-containing simulated wastewater by using the cement kiln dust as an industrial waste adsorbent

This study compares the adsorption behavior of both Methylene Blue (MB) and Congo Red (CR) dyes on the surfaces of cement kiln dust (CKD) powder from the experimentally simulated wastewater solution. The cement kiln dust powder was characterized using X-ray Fluorescence (XRF), X-ray diffraction (XRD), N2 adsorption-desorption Brunauer-Emmett-Teller (BET), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) tests. The adsorption for such dyes was studied under varying mixing contact times, temperatures, and pH as well as various initial concentrations of both dyes and adsorbent using the batch mode experiments. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were applied, and the results revealed that the pseudo-second-order fitted well to the kinetic data. Thermodynamic parameters stated that the adsorption process was endothermic. Studying Linear and nonlinear forms of Langmuir and Freundlich's adsorption isotherms revealed that the adsorption process was followed by both homogeneous mono-layer and heterogeneous multilayer coverage on the active sites of cement kiln dust particles. The data showed that the adsorption capacities of the methylene blue and Congo red dyes were 58.43 and 123.42 mg/g, respectively and cement kiln dust is an adsorbent with little cost for the treatment of wastewater.

Effectiveness of polyacrylamide-g-gelatin/ACL/Mg-Fe LDH composite hydrogel as an eliminator of crystal violet dye

Cationic synthetic dyes are one of the hazards in aqueous solutions that can affect the health of humans and living organisms. In the current work, polyacrylamide (PAM)-g-gelatin hydrogel and modified PAM-g-gelatin hydrogel using activated carbon of Luffa cylindrica (ACL) and ACL/Mg-Fe LDH were applied to eliminate crystal violet (CV), a cationic dye, from water media. The hydrogels were synthesized using free radical polymerization approach, and the hydrogels were characterized using FTIR, XRD, TGA-DTG, BET, SEM, and EDX-Map. The surface area of ACL, ACL/Mg-Fe LDH, PAM-g-gelatin, PAM-g-gelatin/ACL, and PAM-g-gelatin/ACL/Mg-Fe LDH were 99.71, 141.99, 0.74, 1.47, and 1.65 m2/g, respectively, which shows that the presence of ACL and ACL/Mg-Fe LDH improved the area of the hydrogels. The maximum abatement of CV using PAM-g-gelatin (92.81%), PAM-g-gelatin/ACL (95.71%), and PAM-g-gelatin/ACL/Mg-Fe LDH (98.25%) was obtained at pH=9, temperature 25 °C, 10 mg/L CV, 60 min time, and adsorber dose of 2 g/L (for PAM-g-gelatin) and 1.5 g/L (other samples). The value of thermodynamic factors confirmed that the abatement process is exothermic and spontaneous. The kinetics data followed the pseudo-second kinetic (PSO) model. The Langmuir isotherm model had a more remarkable ability to describe the equilibrium data. The maximum adsorption capacity for PAM-g-gelatin, PAM-g-gelatin/ACL, and PAM-g-gelatin/ACL/Mg-Fe LDH was determined 35.45, 39.865, and 44.952 mg/g, respectively. Generally, the studied hydrogels can eliminate dyes from wastewater and be used as effective adsorbers.

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.

Effect of polyethylene glycol on polysaccharides: From molecular modification, composite matrixes, synergetic properties to embeddable application in food fields

Polyethylene glycol (PEG) is a flexible, water-soluble, non-immunogenic, as well as biocompatible polymer, and it could synergize with polysaccharides for food applications. The molecular modification strategies, including covalent bond interactions (amino groups, carboxyl groups, aldehyde groups, tosylate groups, etc.), and non-covalent bond interactions (hydrogen bonding, electrostatic interactions, etc.) on PEG molecular chains are discussed. Its versatile structure, group modifiability, and amphiphilic block buildability could improve the functions of polysaccharides (e.g., chitosan, cellulose, starch, alginate, etc.) and adjust the properties of combined PEG/polysaccharides with outstanding chain tunability and matrix processability owing to plasticizing effects, compatibilizing effects, steric stabilizing effects and excluded volume effects by PEG, for achieving the diverse performance targets. The synergetic properties of PEG/polysaccharides with remarkable architecture were summarized, including mechanical properties, antibacterial activity, antioxidant performance, self-healing properties, carrier and delivery characteristics. The PEG/polysaccharides with excellent combined properties and embeddable merits illustrate potential applications including food packaging, food intelligent indication/detection, food 3D printing and nutraceutical food absorption. Additionally, prospects (like food innovation and preferable nutrient utilization) and key challenges (like structure-effectiveness-applicability relationship) for PEG/polysaccharides are proposed and addressed for food fields.

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.

Sponge-like biodegradable polypyrrole-modified biopolymers for selective adsorption of basic red 46 and crystal violet dyes from single and binary component systems

Recently, several researchers have been trying to reduce the ecological effects of water pollution by considering the use of biodegradable materials that prevent the generation of secondary pollution in our environment and enable water reuse. Here, new biodegradable hydrogels based on alginate (Alg), gelatin (Gel) and polypyrrole (PPy) were successfully implemented to remove two known highly toxic cationic dyes from wastewater. The design process was performed in two steps: in-situ polymerization of polypyrrole within the Alg/Gel mixture, followed by hydrogel formation. Biocomposites showed promising efficacy for the removal of both basic red 46 (BR46) and crystal violet (CV) dyes from real and demineralized water samples. However, Alg-Gel-PPy hydrogel showed better selectivity for BR46 than for CV as compared to the pristine Alg-Gel hydrogel. Adsorption of both pollutants on biocomposite hydrogel beads followed the Langmuir isotherm and pseudo-second order kinetic models. Besides, the highest adsorption capacities (125 mg g-1 for BR46 and 88.5 mg g-1 for CV) were obtained for the Alg-Gel-PPy hydrogel, compared with those determined for PPy-free hydrogel (103.09 mg g-1 for BR46 and 86.96 mg g-1 for CV) and remained at a satisfactory level for five adsorption-desorption cycles. Finally, the obtained hydrogels showed excellent biodegradability by natural soil microorganisms, with 91 % decomposition.

Advances in gum-based hydrogels and their environmental applications

Gum-based hydrogels (GBHs) have been widely employed in diverse water purification processes due to their environmental properties, and high absorption capacity. More desired properties of GBHs such as biodegradability, biocompatibility, material cost, simplicity of manufacture, and wide range of uses have converted them into promising materials in water treatment processes. In this review, we explored the application of GBHs to remove pollutants from contaminated waters. Water resources are constantly being contaminated by a variety of harmful effluents such as heavy metals, dyes, and other dangerous substances. A practical way to remove chemical waste from water as a vital component is surface adsorption. Currently, hydrogels, three-dimensional polymeric networks, are quite popular for adsorption. They have more extensive uses in several industries, including biomedicine, water purification, agriculture, sanitary products, and biosensors. This review will help the researcher to understand the research gaps and drawbacks in this field, which will lead to further developments in the future.

Adsorptive exclusion of crystal violet dye using barium encapsulated alginate/carbon composites: characterization and adsorption modeling studies

The present study is devoted to the removal of crystal violet dye using the synthesized barium alginate/carbon composites abbreviated as BA (barium alginate), BAAC (barium alginate/activated carbon), BASC (barium alginate/starch carbon), and BASSC (barium alginate/starch carbon modified with CTAB). The adsorptive removal of crystal violet as a function of contact time, pH of solution, composite dose, initial dye concentration, and temperature was studied. The uptake of crystal violet (CV) dye for the composites was recorded in the range of 36 mg g-1 to 50 mg g-1 at pH 8.03 ± 0.03 for an equilibrium time of 120 min. The adsorption kinetics and isotherms in compliance with the CV sorption onto BA/carbon composites corroborated the utmost fit of pseudo-second-order and Freundlich isotherm models, respectively. The recycling process was achieved using the barium alginate-treated bead carbons for different initial CV dye concentrations of 10-30 mg L-1 with a scope of zero disposal. The practicability of BA/carbon composites in a groundwater sample spiked with 30 mg L-1 of CV was successfully achieved with a removal efficiency of about 65-74%. Characterization studies for the composites using FTIR, SEM (with EDS), XRD, TGA, and BET were carried out and discussed in the paper.

Chitosan/carboxymethylcellulose polyelectrolyte complexes (PECs) are an effective material for dye and heavy metal adsorption from water

Granular macroscopic chitosan/carboxymethylcellulose polyelectrolytic complexes (CHS/CMC macro-PECs) were produced and tested as adsorbents for six pollutants often present in wastewaters: sunset yellow (YS), methylene blue (MB), Congo red (CR) and safranin (S), cadmium (Cd²⁺) and lead (Pb²⁺). The optimum adsorption pH values at 25 °C were 3.0, 11.0, 2.0, 9.0, 10.0, and 9.0 for YS, MB, CR, S, Cd²⁺, and Pb²⁺, respectively. Kinetic studies indicated that the pseudos-econd order model best represented the adsorption kinetics of YS, MB, CR, and Cd²⁺, whereas the pseudo-first order model was the most suitable for S and Pb²⁺ adsorption. The Langmuir, Freundlich, and Redlich-Peterson isotherms were fitted to experimental adsorption data, with the Langmuir model providing the best fit. The maximum adsorption capacity (q_máx) of CHS/CMC macro-PECs for the removal of YS, MB, CR, S, Cd²⁺, and Pb²⁺ was 37.81, 36.44, 70.86, 72.50, 75.43, and 74.42 mg/g, respectively (corresponding to 98.91 %, 94.71 %, 85.73 %, 94.66 %, 98.46 %, and 97.14 %). Desorption assays showed that CHS/CMC macro-PECs can be regenerated after adsorbing any of the six pollutants studied, with possibility of reuse. These results provide an accurate quantitative characterization of the adsorption of organic and inorganic pollutants on CHS/CMC macro-PECs, indicating a novel technological applicability of these two inexpensive, easy-to-obtain polysaccharides for water decontamination.

Novel hydrogel poly (GG-co-acrylic acid) for the sorptive removal of the color Rhodamine-B from contaminated water

Textile effluent's treatment is highly desired due to the presence of hazardous, water-soluble and non-biodegradable dyes that not only have harmful effect on the environment but on living beings as well. Treatment of these pollutants by sorption through biosorbents is considered to be a best method of choice due to greener nature of the processes. In this connection hydrogel sorbents might be an intriguing option due to its straightforward application, great efficacy, easy synthesis, rapid turnaround, and potential of recycling. Herein, novel hydrogel was prepared using Gellan Gum and acrylic acid (GG-co-AAc) which were then characterized by instrumental techniques like UV/visible and FTIR spectroscopy, SEM, EDX and XRD. The anionic hydrogel's adsorption capacity, swelling behavior, and sorption potential were determined using Rhodamine-B as potential environmental pollutant. The hydrogel exhibited an impressive adsorption capacity of 1250 mg/g. Swelling experiments were performed in Milli-Q distilled water at different pH levels, reaching maximum swelling of 3230% after 23 h as determined through Fickian diffusion. At pH 7, the anionic hydrogel's sorption potential was thoroughly studied in the subsequent experiments. The adsorption process was found to follow the Langmuir isotherm, indicating a monolayer adsorption mechanism supported by higher R2 values compared to the Freundlich isotherm. Thermodynamic analysis revealed the exothermic nature of the adsorption process, with a negative enthalpy value of -11371 KJmol-1 and negative entropy value of -26.39 Jmol-1K-1, suggesting a less ordered system. These findings provide valuable insights into the adsorption characteristics and potential applications of the synthesized anionic hydrogel.

Development and optimization of geopolymer adsorbent for water treatment: Application of mixture design approach

The current paper refers to the study of a new approach to optimizing the adsorptive properties of geopolymers by varying the aluminosilicate precursors from kaolin (K), metakaolin (MK), and coal fly ash (CFA) as internal synthesis factors. The simplex-augmented-centroid mixture design was applied to identify the optimal formulation from the three aluminosilicate precursors to develop a geopolymer (GP) with a distinctive structure that positively affects its dye adsorption efficiency. The variously formulated GP samples were tested for the removal of both methylene blue (MB-dye) and crystal violet dye (CV-dye) from an aqueous solution. The mathematical-statistical analysis of the experimental readings suggested that the generated special cubic models were significant, and thus the chosen approach was adequate for determining the optimum blending proportion. The optimization tools indicated that the optimal mixture from the three aluminosilicate precursors for developing a GP with high adsorption efficiency was 58% MK, 42% K, and 0% CFA. The optimized geopolymer (GP_O) was synthesized and then analyzed using a variety of physicochemical techniques, which revealed the presence of an amorphous N-A-S-H gel-rich porous structure as an influencing property on the geopolymer's organic dye adsorption efficiency. The dependence of the adsorption mechanism of both MB-dye and CV-dye by GP_O on the adsorbent dosage, contact time, initial dye concentration, temperature, and solution pH was evaluated. The isothermic and kinetic experimental readings for MB and CV-dyes adsorption by GP_O were well fitted to the pseudo-second-order and Freundlich models, with an exothermic, favorable, and spontaneous adsorption reaction thermodynamically. The experimental studies in the lab scale on GP_O produce comparable results. From these results, it has been concluded that the accuracy and feasibility of the mixture design simulation succeeded in optimizing and developing a geopolymeric sorbent material with great potential as an excellent economical agent for removing cationic dyes from aqueous media. This point represents an added value compared to traditional non-optimized geopolymer absorbents. Besides, this geopolymer material represents a significant application possibility for water treatment and remediation of hazardous dye pollutants.

An Eco-Friendly Adsorbent Based on Bacterial Cellulose and Vermiculite Composite for Efficient Removal of Methylene Blue and Sulfanilamide

In this work, a novel composite of bacterial cellulose (BC) and expanded vermiculite (EVMT) composite was used to adsorb dyes and antibiotics. The pure BC and BC/EVMT composite were characterized using SEM, FTIR, XRD, XPS and TGA. The BC/EVMT composite exhibited a microporous structure, providing abundant adsorption sites for target pollutants. The adsorption performance of the BC/EVMT composite was investigated for the removal of methylene blue (MB) and sulfanilamide (SA) from an aqueous solution. The adsorption capacity of BC/ENVMT for MB increased with increasing pH, while the adsorption capacity for SA decreased with increasing pH. The equilibrium data were analyzed using the Langmuir and Freundlich isotherms. As a result, the adsorption of MB and SA by the BC/EVMT composite was found to follow the Langmuir isotherm well, indicating a monolayer adsorption process on a homogeneous surface. The maximum adsorption capacity of the BC/EVMT composite was found to be 92.16 mg/g for MB and 71.53 mg/g for SA, respectively. The adsorption kinetics of both MB and SA on the BC/EVMT composite showed significant characteristics of a pseudo-second-order model. Considering the low cost and high efficiency of BC/EVMT, it is expected to be a promising adsorbent for the removal of dyes and antibiotics from wastewater. Thus, it can serve as a valuable tool in sewage treatment to improve water quality and reduce environmental pollution.

Highly compressible and macro-porous hydrogels via the synergy of cryogelation and double-network for efficient removal of Cr(VI)

Mechanically robust and macro-porous hydrogels are urgently required for the dynamic removal of heavy metals in wastewater purification field. Herein, a novel microfibrillated cellulose/polyethyleneimine hydrogel (MFC/PEI-CD) with high compressibility and macro-porous structures was fabricated via the synergy of cryogelation and double-network for Cr(VI) adsorption from wastewater. MFCs were pre-cross-linked by bis(vinyl sulfonyl)methane (BVSM) and then formed double-network hydrogels with PEIs and glutaraldehyde below freezing. The SEM showed that the MFC/PEI-CD possessed interconnected macropores with an average pore diameter of 52 μm. Mechanical tests indicated a high compressive stress of 116.4 kPa at 80 % strain, which was 4 times higher than the corresponding MFC/PEI with a single-network. The Cr(VI) adsorption performance of MFC/PEI-CDs was systematically investigated under different parameters. Kinetic studies indicated that the adsorption process was well described by the pseudo-second-order model. Isothermal adsorption behaviors accorded well with Langmuir model with the maximum adsorption capacity of 545.1 mg/g, which was superior to most adsorption materials. More importantly, the MFC/PEI-CD was applied to dynamically adsorb Cr(VI) with the treatment volume of 2070 mL/g. Therefore, this work demonstrates that the synergy of cryogelation and double-network is a novel method for preparing macro-porous and robust materials with promising heavy metal removal from wastewater.

Chitosan-based composite hydrogel with a rigid-in-flexible network structure for pH-universal ultra-efficient removal of dye

Polysaccharide-based hydrogel adsorbents become popular because of their high adsorption capacity and fast adsorption rate, but their low removal rate and poor pH resistance have always been fatal shortcomings. Herein, a feasible strategy was proposed to strengthen the ability of hydrogel adsorbent to remove organic pollutants (i.e., dye) by incorporating natural rectorite (REC) into chitosan-g-poly (2-acrylamido-2-methyl-propane-sulfonic-acid) hydrogel network to form a rectorite-in-polymer network structure. The introduction of less dosage of REC (1.2 wt%) into the hydrogel facilitates to improve its adsorption capacities toward methylene blue (MB) in deionized water, tap water, seawater, Yangtze River water, and Yellow River water (1083.39-1303.49 mg/g); while incorporating higher content of REC (15.8 wt% REC) helps to improve the removal rate (99.6 % for MB in real waters), which are greatly superior to commercial activated carbons. The adsorbent keeps high adsorption efficiency in a broad pH range (2-11), and can be reused for >4 times.

Lignin/sodium alginate hydrogel for efficient removal of methylene blue

In this work, a class of bio-based hydrogels (LN-NH-SA hydrogel) were prepared from aminated lignin and sodium alginate. The physical and chemical properties of the LN-NH-SA hydrogel were fully characterized using field emission scanning electron microscopy, thermogravimetric analysis, fourier transform infrared spectroscopy, N₂ adsorption-desorption isotherms, and other techniques. LN-NH-SA hydrogels were tested for the adsorption of dyes (methyl orange and methylene blue). The LN-NH-SA@3 hydrogel showed better adsorption efficiency for MB with a maximum adsorption capacity of 388.81 mg·g^-1, a bio-based adsorbent with a high adsorption capacity. The adsorption process followed the pseudo-second-order model and fitted to the Freundlich isotherm equation. More importantly, LN-NH-SA@3 hydrogel maintained 87.64 % adsorption efficiency after 5 cycles. Overall, the proposed hydrogel with environmentally friendly and low cost is promising for the absorption of dye contamination.

Synthesis and Characterization of Terbium-Based Metal Organic Framework for Environmental Remediation Application

In the present study, terbium-based metal-organic frameworks (MOFs) based on fcu topology, fcu-Tb- FTZB-MOF, was synthesized using 2-fluoro-4-(1H-tetrazol-5-yl)benzoic acid (FTZB) as a linear ligand, and then was characterized using powder X-ray diffraction (PXRD) and Brunauer-Emmett-Teller (BET) analysis and to study the texture properties of the Tb-FTZB-MOF. The characterization results confirmed the successful synthesis of the high surface area Tb-FTZB-MOF (1220 m2/g). The synthesized Tb-FTZB-MOF was then applied as a catalytic adsorbent to remove direct violet 31 (DV31) dye as an example of organic pollutants, from a model and real solution. The effect of various operational parameters such as adsorbent loading, contact time, initial DV31 dye concentration, initial solution pH, different water matrix, temperature, and ionic strength have also been evaluated. Solution pH and temperature significantly influenced the adsorption of DV31 dye using Tb-FTZB-MOF, and the results should efficiently remove the DV31 dye at ambient temperature, and at pH value of 8.0 using 35 mg Tb-FTZB-MOF, within few minutes. The process was studied kinetically and found to follow the pseudo-second-order kinetic model, and thermodynamically the process was spontaneous, endothermic, with a positive entropy. Finally, the result showed that Tb-FTZB-MOF was able to adsorb a high percentage of DV31 dye and maintained reasonable efficiency even after five cycles, indicating that Tb-FTZB-MOF could be a promising adsorbent in wastewater remediation.

Green and Superior Adsorbents Derived from Natural Plant Gums for Removal of Contaminants: A Review

The ubiquitous presence of contaminants in water poses a major threat to the safety of ecosystems and human health, and so more materials or technologies are urgently needed to eliminate pollutants. Polymer materials have shown significant advantages over most other adsorption materials in the decontamination of wastewater by virtue of their relatively high adsorption capacity and fast adsorption rate. In recent years, "green development" has become the focus of global attention, and the environmental friendliness of materials themselves has been concerned. Therefore, natural polymers-derived materials are favored in the purification of wastewater due to their unique advantages of being renewable, low cost and environmentally friendly. Among them, natural plant gums show great potential in the synthesis of environmentally friendly polymer adsorption materials due to their rich sources, diverse structures and properties, as well as their renewable, non-toxic and biocompatible advantages. Natural plant gums can be easily modified by facile derivatization or a graft polymerization reaction to enhance the inherent properties or introduce new functions, thus obtaining new adsorption materials for the efficient purification of wastewater. This paper summarized the research progress on the fabrication of various gums-based adsorbents and their application in the decontamination of different types of pollutants. The general synthesis mechanism of gums-based adsorbents, and the adsorption mechanism of the adsorbent for different types of pollutants were also discussed. This paper was aimed at providing a reference for the design and development of more cost-effective and environmentally friendly water purification materials.