Adsorption properties of cellulose/guar gum/biochar composite hydrogel for Cu2+, Co2+ and methylene blue

Acid-induced hydrogels of edible Chlorella pyrenoidosa protein with composite biopolymers network

This study aimed to prepare Glucono-δ-lactone (GDL)-induced Chlorella pyrenoidosa protein (CPP) hydrogel and further investigate the effect of polysaccharides on the mechanical properties and stability enhancement of the composite hydrogels. Polysaccharides composed of different ratios of low acyl gellan gum (GE) and guar gum (GU) imparted dense honeycomb-like networks and adjustable textural properties to the composite hydrogels induced by CaCl2. In particular, the hardness of hydrogels increased significantly from 14 to 833 g. Scanning electron microscopy results revealed that CPP-GE/GU composite hydrogels had better stable spatial porous structures. Moreover, fourier transform infrared spectroscopy (FTIR) indicated hydrogen bonding interaction between CPP and GE/GU. The composite network showed improved viscoelasticity, increased thermal stability, and self-healing ability of hydrogels. The composite hydrogels also showed high water holding (89-98%) and swelling (747-862%) properties compared to the pure CPP hydrogel. These findings further expand CPP hydrogel products and broaden application in plant protein-based food.

Strong, tough, conductive and transparent nanocellulose hydrogel based on Ca2+-induced cross-linked double-networks and its adsorption of methylene blue dye

A novel multi-performance SHNC/SA/CaCl2 hydrogel with multi-performance was prepared via ultra-low-temperature freeze-thaw cycling and Ca2+ cross-linking for the removal of methylene blue (MB) from industrial wastewater. Various methods were used to characterize the structure and properties of hydrogel, and the internal structure of hydrogel showed a three-dimensional network with hydrogen and ester bonds. The SHNC/SA/CaCl2-15 hydrogel exhibited the highest tensile properties (elongation = 800 %), viscoelasticity (90 kPa), compressive strength (0.45 MPa), tensile strength (0.47 MPa) and ionic conductivity (4.34 S/cm). The maximum adsorption capacity of 2 g SHNC/SA/CaCl2-15 hydrogel was 608.49 mg/g at 40 °C, pH = 8 and adsorption 24 h. The adsorption process of hydrogel toward MB was more consistent with the second-order kinetic model and Langmuir isothermal adsorption model. According to the Langmuir isotherm model, the maximum monolayer adsorption capacity of SHNC/SA/CaCl2-15 hydrogel toward MB can reach 613.88 mg/g. Finally, it was found that the removal rate of SHNC/SA/CaCl2-15 hydrogel for MB was still as high as 90 % after five cycles of the adsorption-desorption test, and it could be reused. The hydrogel can be used as cheap and reusable adsorption material for cationic dyes. Our study provides a new perspective for the development of multifunctional cellulose hydrogel adsorbent materials.

Functional Bio-Based Polymeric Hydrogels for Wastewater Treatment: From Remediation to Sensing Applications

In recent years, many researchers have focused on designing hydrogels with specific functional groups that exhibit high affinity for various contaminants, such as heavy metals, organic pollutants, pathogens, or nutrients, or environmental parameters. Novel approaches, including cross-linking strategies and the use of nanomaterials, have been employed to enhance the structural integrity and performance of the desired hydrogels. The evolution of these hydrogels is further highlighted, with an emphasis on fine-tuning features, including water absorption capacity, environmental pollutant/factor sensing and selectivity, and recyclability. Furthermore, this review investigates the emerging topic of stimuli-responsive smart hydrogels, underscoring their potential in both sorption and detection of water pollutants. By critically assessing a wide range of studies, this review not only synthesizes existing knowledge, but also identifies advantages and limitations, and describes future research directions in the field of chemically engineered hydrogels for water purification and monitoring with a low environmental impact as an important resource for chemists and multidisciplinary researchers, leading to improvements in sustainable water management technology.

Removal of Mo(VI), Pb(II), and Cu(II) from wastewater using electrospun cellulose acetate/chitosan biopolymer fibers

Environmentally friendly polymers such as cellulose acetate (CA) and chitosan (CS) were used to obtain electrospun fibers for Cu2+, Pb2+, and Mo6+ capture. The solvents dichloromethane (DCM) and dimethylformamide (DMF) allowed the development of a surface area of 148 m2 g-1 for CA fibers and 113 m2 g-1 for cellulose acetate/chitosan (CA/CS) fibers. The fibers were characterized by IR-DRIFT, SEM, TEM, CO2 sorption isotherms at 273 K, Hg porosimetry, TGA, stress-strain tests, and XPS. The CA/CS fibers had a higher adsorption capacity than CA fibers without affecting their physicochemical properties. The capture capacity reached 102 mg g-1 for Cu2+, 49.3 mg g-1 for Pb2+, and 13.1 mg g-1 for Mo6+. Furthermore, optimal pH, adsorption times qt, and C0 were studied for the evaluation of kinetic models and adsorption isotherms. Finally, a proposal for adsorbate-adsorbent interactions is presented as a possible capture mechanism where, in the case of Mo6+, a computational study is presented. The results demonstrate the potential to evaluate the fibers in tailings wastewater from copper mining.

Environmental applications of lignin-based hydrogels for Cu remediation in water and soil: adsorption mechanisms and passivation effects

Heavy metal pollution, particularly the excessive release of copper (Cu), is an urgent environmental concern. In this study, sodium lignosulfonate/carboxymethyl sa-son seed gum (SL-Cg-g-PAA) designed for remediation of Cu-contaminated water and soil was successfully synthesized through a free radical polymerization method using lignin as a raw material. This hydrogel exhibits remarkable Cu adsorption capability when applied to water, with a maximum adsorption capacity reaching 172.41 mg/g. Important adsorption mechanisms include surface complexation and electrostatic attraction between Cu(Ⅱ) and oxygen-containing functional groups (-OH, -COOH), as well as cation exchange involving -COONa and -SO3Na. Furthermore, SL/Cg-g-PAA effectively mitigated the bioavailability of heavy metals within soil matrices, as evidenced by a notable 14.1% reduction in DTPA extracted state Cu (DTPA-Cu) content in the S4 treatment (0.7% SL/Cg-g-PAA) compared to the control group. Concurrently, the Cu content in both the leaves and roots of pakchoi exhibited substantial decreases of 55.19% and 36.49%, respectively. These effects can be attributed to the precipitation and complexation reactions facilitated by the hydrogel. In summary, this composite hydrogel is highly promising for effective remediation of heavy metal pollution in water and soil, with a particular capability for the immobilization of Cu(Ⅱ) and reduction of its adverse effects on ecosystems.

Biofilm hydrogel derived from physical crosslinking (self-assembly) of xanthan gum and chitosan for removing Cd2+, Ni2+, and Cu2+ from aqueous solution

This study aimed to fabricate a series of biodegradable hydrogel films by gelating/physically crosslinking a blend of xanthan gum (XG) and chitosan (CS) in various combinations using a facile, green, and low cost solution casting technique. The adsorption of Cd2+, Cu2+ and Ni2+ by the XG/CS biofilm in aqueous solution was studied in batch experiments to determine how the pH of the solution, contact time, dosage of adsorbent, initial metal ion concentration and ionic strength affect its adsorption. A highly pH-dependent adsorption process was observed for three metal ions. A maximum amount of Cd2+, Ni2+, and Cu2+ ions was adsorbable with 50 mg of the adsorbent at pH 6.0 for an initial metal concentration of 50 mg.L-1. An empirical pseudo-second-order model seems to fit the kinetic experimental data reasonably well. It was found that the Langmuir model correlated better with equilibrium isotherm when compared with the Freundlich model. For Cd2+, Ni2+, and Cu2+ ions at 25 °C, the maximum monolayer adsorption capacity was 152.33, 144.79, and 139.71 mg.g-1, respectively. Furthermore, the biofilm was capable of regenerating, allowing metal ions to adsorb and desorb for five consecutive cycles. Therefore, the developed biodegradable film offers the potential for remediation of specified metal ions.

Enhanced dye sequestration with natural polysaccharides-based hydrogels: A review

Due to the expansion of industrial activities, the concentration of dyes in water has been increasing. The dire need to remove these pollutants from water has been heavily discussed. This study focuses on the reproducible and sustainable solution for wastewater treatment and dye annihilation challenges. Adsorption has been rated the most practical way of the several decolorization procedures due to its minimal initial investment, convenient utility, and high-performance caliber. Hydrogels, which are three-dimensional polymer networks, are notable because of their potential to regenerate, biodegrade, absorb bulky amounts of water, respond to stimuli, and have unique morphologies. Natural polysaccharide hydrogels are chosen over synthetic ones because they are robust, bioresorbable, non-toxic, and cheaply accessible. This study has covered six biopolymers, including chitosan, cellulose, pectin, sodium alginate, guar gum, and starch, consisting of their chemical architecture, origins, characteristics, and uses. The next part describes these polysaccharide-based hydrogels, including their manufacturing techniques, chemical alterations, and adsorption effectiveness. It is deeply evaluated how size and shape affect the adsorption rate, which has not been addressed in any prior research. To assist the readers in identifying areas for further research in this subject, limitations of these hydrogels and future views are provided in the conclusion.

Adsorbents prepared from epoxy-based porous materials of microcrystalline cellulose for excellent adsorption of anionic and cationic dyes

It reported a porous material prepared from microcrystalline cellulose (MCC), to achieve rapid preparation of adsorbents. The porous material was characterized by several tools including 1H NMR, FTIR, XPS, and SEM. Two adsorbents were prepared and subjected to adsorption experiments. Dye adsorption experiments show that the adsorption driving is electrostatic interactions and the process is chemisorption. The maximum capacity of Microcrystalline cellulose-g-Poly (glycidyl methacrylate)-Tannins (MPT) reached 191.3 (Methylene blue), 123.7 mg g-1 (Rhodamine B), and Microcrystalline cellulose-g-Poly (glycidyl methacrylate)-Lysine (MPL) attained 425.8 (Methylene blue), 480.7 mg g-1 (Methyl orange). The results were followed the pseudo-second-order (PSO) and agreed with the Langmuir fit model. Adsorption-desorption cycling experiments further indicate that the adsorbent possesses outstanding reproducibility. At last, epoxidized bio-porous materials are positive in the preparation of dye adsorbents with critical adsorption properties.

Chitosan-based adsorptive membrane modified by carboxymethyl cellulose for heavy metal ion adsorption: Experimental and density functional theory investigations

Low adsorption capacity and weak mechanical stability are the main drawbacks of chitosan (CS)-based adsorptive membranes for heavy metal ion removal. Polyvinyl alcohol (PVA) has been used to improve the mechanical stability of CS membranes, but adsorption capacity is disregarded. In the current study, the surface of the chitosan/polyvinyl alcohol (CP) membrane was modified using carboxymethyl cellulose (CMC) to increase its heavy metal ion adsorption capacity. Experimental and density functional theory (DFT) calculations were used to evaluate the heavy metal ion (As3+ and Cr3+) adsorption capabilities of CP and carboxymethyl cellulose-functionalized CP (CMC-CP) membranes. The batch adsorption process presented a higher heavy metal adsorption capacity of the CMC-CP membrane (As3+/CMC-CP = 234.78 mg/g and Cr3+/CMC-CP = 230.12 mg/g) compared to the CP membrane (As3+/CP = 89.02 mg/g and Cr3+/CP = 75.61 mg/g). The heavy metal/CMC-CP complexes confirmed higher adsorption energies (As3+/CMC-CP = -23.62 kcal/mol and Cr3+/CMC-CP = -23.21 kcal/mol) than the heavy metal/CP complexes (As3+/CP = -3.47 kcal/mol and Cr3+/CP = -2.92 kcal/mol). The electronic band structure was higher for CMC-CP (5.42 eV) compared to CP (4.43 eV). Experimental and theoretical findings were close, implying that the CMC-CP membrane has superior heavy metal adsorption capability than the CP membrane.

Robust functionalized cellulose-based porous composite for efficient capture and ultra-fast desorption of aqueous heavy metal pollution

The heavy metal pollution control industry requires convenient and cost-effective solutions to address complex aqueous environment. Adsorption method can be an effective strategy to realize these goals. Considering the importance of environmental and sustainable development strategies, there is an urgent need to develop efficient, green and non-toxic heavy metal adsorbents. In this work, a robust aminated cellulose-based porous adsorbent (PGPW) was developed from delignified wood and amino-rich polymer using a solvent-free, mild, simple and efficient preparation method. Such adsorbent exhibited excellent adsorption capacity (188.68 mg g-1) for Cu(II), and its adsorption behavior was consistent with pseudo-second order kinetic and Langmuir isotherm models. Notably, PGPW with superior compressibility could be squeezed to achieve rapid desorption and reach equilibrium within 5 min, while still retaining 87 % adsorption efficiency after 50 cycles. In addition, PGPW showed remarkable selectivity towards various coexisting ionic systems and demonstrated a considerable adsorption capacity in natural water applications. The adsorption mechanism of heavy metal ions on porous adsorption material was elucidated. This approach provides a simple, gentle and sustainable strategy for preparing functionalized wood-based composites with efficient adsorption and ultra-fast desorption of heavy metal ions.

Chitosan-grafted hydrogels for heavy metal ion adsorption and catalytic reduction of nitroaromatic pollutants and dyes

Chitosan-grafted-poly(acrylic acid) (CS-g-PAA) and chitosan-grafted- poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (CS-g-P(AA-co-AMPS)) hydrogels were synthesized and then employed as adsorbents for the effective removal of Cu2+ and other heavy metal ions. The effect of hydrogel's composition on the Cu2+ adsorption was explored. The CS-g-PAA hydrogel demonstrated a superior adsorption capacity compared to pristine CS, PAA hydrogel, and CS-g-P(AA-co-AMPS) hydrogels. The adsorption followed the Langmuir isotherm model, and the pseudo-second order kinetic model. Additionally, the CS-g-PAA hydrogel exhibited relatively high adsorption performances toward Cr3+, Co2+, Ni2+, Pb2+, and Zn2+. Metal ions adsorbed within CS-g-PAA hydrogels underwent reduction to their corresponding metallic states and were reutilized as catalysts for the reduction of 4-nitrophenol. The comparative catalytic performances of the metal species in the hydrogel were in the order of Cu > Ni > Co > Zn. The reduction efficiency of Cu-CS-g-PAA increased with increased catalyst dosage, NaBH4 concentration, and temperature. A very low activation energy of 3.7 kJ/mol was observed. The catalyst maintained high catalytic performance even when subjected to real water samples and proved its reusability for up to three cycles. Moreover, the catalyst could effectively reduce 2-nitrophenol and methyl orange.