Polysaccharide-based cationic hydrogels for dye adsorption

Efficient removal of anionic dye congo red by Chitosan/Poly (dimethyl diallyl ammonium chloride-co-acrylamide) composite hydrogel

Chitosan, as a natural and environmentally friendly material, has attracted significant attention in the field of water treatment. In this study, a Chitosan/poly (dimethyl diallyl ammonium chloride-co-acrylamide) composite hydrogel (CPDA hydrogel) featuring a semi-interpenetrating network structure was synthesized via free radical copolymerization for the removal of the anionic dye Congo Red (CR) from wastewater. SEM-EDS, FTIR, XPS, TG, Zeta potential, and mercury intrusion porosimetry (MIP) were employed to analyze the physical and chemical changes in the hydrogel before and after adsorption. The results revealed that the CPDA hydrogel can selectively adsorb anionic dyes through electrostatic interactions. The study on the adsorption performance of the CPDA hydrogel demonstrated its excellent swelling capacity and stable adsorption of Congo Red over a broad pH range of 4 to 10. Subsequently, the adsorption process of Congo Red followed the Pseudo-Second-Order kinetic model and the Hill isotherm model, suggesting that Congo Red may self-assemble into ribbon-like micelles for cooperative adsorption and achieving a maximum adsorption capacity of 1803.507 mg/g. Furthermore, the CPDA hydrogel exhibited outstanding reusability over six adsorption-desorption cycles. Thus, the prepared CPDA hydrogel shows great potential as a material for the selective removal of Congo Red from mixed dye solutions.

Epichlorohydrin/triethylamine modified psyllium as a highly efficient adsorbent for selective adsorption of anionic dyes

To develop new green sustainable adsorbents, herein, psyllium, a polysaccharide, was transformed into a cationic material by introducing a quaternary ammonium group in its structure through a two-step process. Psyllium was epoxidized with epichlorohydrin to epoxy propyl form (EPsy) and the resulting material was reacted with triethylamine to obtain a quaternized psyllium, TPsy. TPsy demonstrates selective elimination of anionic dyes (CR and MO). The maximum % adsorption (Pr) of 93.94 %, and 94.44 % were reported for MO and CR (anionic dyes) respectively within 70 min. The strong adsorption of MO and CR can be attributed to electrostatic attraction and hydrogen bonding. The adsorption process adhered to the pseudo-second-order kinetics indicating chemisorption and Langmuir isotherm suggesting monolayer adsorption, exhibiting a maximum adsorption capacity (qm) of 223.71 mg/g for MO and 260.41 mg/g for CR. TPsy is regenerable even after twelve adsorption-desorption cycles with cumulative q of 903.97 mg/g and 932.83 mg/g for MO and CR respectively. Our study introduces a novel approach by reversing the surface charge of psyllium (anionic, PZC = 2.25) through quaternization to TPsy (cationic, PZC = 6.23), which significantly enhances its efficiency as an anionic dye adsorbent.

Functionalized Cyclodextrin/Carboxymethyl Cellulose Composite Hydrogel with Double Network Structure for Adsorption of Heavy Metal Ions in Wastewater

Heavy metal ions in industrial wastewater pose significant environmental and ecological threats. In this work, a hydrogel featuring a double network structure was synthesized via radical polymerization and cross-linking of β-cyclodextrin (CD) and carboxymethylcellulose (CMC) with acrylic acid (AA). The hydrogel's functional groups and microstructure were characterized using Fourier transform infrared spectroscopy (FTIR-ATR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Mechanical properties were evaluated through rheological and compression tests. The study examined the impact of initial metal ion concentration, adsorbent-ion contact time, and solution pH on adsorption capacity. The maximum adsorption capacities of the functionalized CD/CMC-PAA-MBA hydrogel for Cu2+, Pb2+, and Cd2+ ions were 158.12, 393.56, and 290.12 mg/g, respectively. Notably, the hydrogel exhibited the highest selectivity for Pb2+ in mixed solutions. The adsorption kinetics of the metal ions were modeled using the pseudo-second-order rate equation and the Langmuir adsorption isotherm.

Preparation of dandelion flower extract-based polyvinyl alcohol-chitosan-dandelion-CuNPs composite gel for efficient bacteriostatic and dye adsorption

A multifunctional composite gel with efficient bacteriostatic and dye adsorption properties was prepared using polyvinyl alcohol, chitosan, and soybean isolate protein as carriers, CuNPs prepared by green reduction of dandelion extract as bacteriostatic agent, and glutaraldehyde as cross-linking agent. The composite gel showed good inhibition capacity of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa with the diameter of inhibition zone of 27.0-28.3 mm by agar diffusion method. The composite gel antibacterial rate remained above 90 % after 14 days of preparation. After 6 times reuse of composite gel in water, the antibacterial rate remained above 90 %, proving its good stability and reusability. Adding dandelion extract and CuNPs greatly improved the gel antioxidant property, acquiring free radical scavenging rate at 95.6 %. This composite gel had good biocompatibility and adsorption performance, and the maximum adsorption amount of methylene blue and methyl orange was 40.36 mg/g and 41.81 mg/g, respectively. To sum up, the green composition of composite gel has good antimicrobial performance and high dye adsorption, which holds significant promising for treating the water body pollution and protecting the environment. To build cost-effective antibacterial and dye adsorption process on a large-scale, in-depth exploration about this topic is still needed to develop.

Regulating natural galactomannan into composite hydrogels for improved adhesion, anti-swelling capability and efficient dye pollution removal

Constructing bio-based composite hydrogel materials are receiving much interest, while regulating the interactions of the hydrogel components and integrating functions for multi-application meet various challenges. Herein, composite hydrogels were prepared by cross-linking of poly-acrylamide (PAM) and poly-N-[3-(Dimethylamino) propyl] acrylamide (PDMAPAA), assisted by natural galactomannan (GM) regulation. Even distribution and compatibility of GM in the three-dimensional materials were proved by a series of chemical and morphological characterizations, which favored the improvement of mechanical properties (~80 kPa) and flexibility. Besides, the hydrogels were well-connected with double networks of noncovalent intermolecular hydrogen bonding interactions and hydrophobic interactions, in addition to covalent-linked polymers. Due to great amount of inner hydrogen bond linkages, the hydrogels present satisfying anti-swelling capabilities (<15 %), exhibiting high potential for application in water treatment. Meanwhile, abundant surface functional groups provided possibilities to form interactive layer with the various substrates surface, exhibiting highly adhesive properties. Significant dyes adsorption capabilities were revealed on the hydrogels according to the electrostatic attraction with Congo red and hydrogen bond interactions with Brilliant green respectively. Thus, the proposed composite hydrogels integrated multi-functions due to the tuning the surface groups and cross-linking interactions, which provided deeper understanding on bio-based materials on fields of water treatment and environmental protection.

Adsorption of methyl orange and methylene blue from aqueous solutions on pure bentonite: statistical physical modeling provides an analytical interpretation

This study investigates the adsorption of methylene blue (MB) and methyl orange (MO) dyes from aqueous solutions using purified Moroccan bentonite, being mainly composed of silica and alumina, in the form of quartz and cristobalite. The temperature controls the adsorption capacity for the kinetics, increasing 5.08% (from 295.1 to 310.1 mg/g) for the MB and 55.47% (from 86.8 to 134.9 mg/g) for the MO. It was discovered that the pseudo-second-order model, with a low Bayesian criterion indicator of 12.72 and R2adj > 0.996, was the best suitable for explaining both systems. The adsorption isotherm, experimental data indicate that both systems follow the Langmuir isotherm. At lower temperatures, 298.15 K 1.22 molecules are adsorbed per site. However, at a higher temperature of 328.15 K, the number of molecules is less than a unit of 0.68. As for MO, the number of molecules remains above 1.4 per site for all the temperatures studied. The endothermic nature of the system is indicated by the observation that the adsorption energy tends to grow for both systems: for the MB, it increases from 18.85 to 21.26 kJ/mol, and for the MO, it increases from 14.83 to 19.01 kJ/mol. Last, thermodynamic functions indicate that maximum entropy is reached around the half-concentration saturation at 25 and 124 mg/L, which is the maximum energetic concentration of the system. The same results were obtained for Gibbs free energy, where the maximum energy found was - 5.39 × 10-18 kJ/mol for the MB and - 1.99 × 10-18 kJ/mol for the MO at 328.15 K.

Highly effective removal of basic fuchsin dye using carboxymethyl konjac glucomannan grafted acrylic acid-acrylamide/montmorillonite composite hydrogel

This study developed a nanocomposite hydrogel, CAM4-MMT, for efficiently removing basic fuchsin dye from water. The hydrogel was prepared by grafting a copolymer of acrylic acid (AA) and acrylamide (AM) onto carboxymethyl konjac glucomannan (CMKGM), and doped with montmorillonite (MMT), exhibited excellent thermal stability, a porous inner structure, large specific surface area (1.407 m2/g), and high swelling capacity (107.3 g/g). The hydrogel achieved a maximum adsorption capacity of 694.1 mg/g and a removal rate of 99.5 %. The Langmuir isotherm and pseudo-second-order kinetic model best described the adsorption process. Regeneration and reuse tests confirmed that the hydrogel has excellent recyclability. In conclusion, the CAM4-MMT composite hydrogel efficiently removed basic fuchsin from water solutions, offering a new scheme for eliminating basic fuchsin using natural polysaccharides with promising applications.

Semi-IPN polysaccharide-based hydrogels for effective removal of heavy metal ions and dyes from wastewater: a comprehensive investigation of performance and adsorption mechanism

The escalating issue of environmental pollutants necessitates efficient, sustainable, and innovative wastewater treatment technologies. This review comprehensively analyzes the mechanisms and isotherms underlying the adsorption processes of semi-interpenetrating polymer network (semi-IPN) polysaccharide-based hydrogels to remove heavy metal ions and dyes from wastewater. Polysaccharides are extensively utilized in hydrogel synthesis due to their biocompatibility, cost-effectiveness, and non-toxic nature. The synthesis of these hydrogels as semi-IPNs enhances their mechanical and structural robustness and adsorption capacity. This review explores the key parameters affecting adsorption performance, including pH, temperature, contact time, and adsorbent dosage. Findings highlight that semi-IPN polysaccharide-based hydrogels exhibit remarkable adsorption capabilities through electrostatic interactions, ion exchange, and surface complexation. Furthermore, this review highlights the distinct advantages of semi-IPNs over other polymer networks. Semi-IPNs offer improved mechanical stability, higher adsorption efficiencies, and better reusability, making them a promising solution for wastewater treatment. Detailed isotherm models, including Langmuir and Freundlich isotherms, were studied to understand these hydrogels' adsorption behavior and capacity for different pollutants. This study highlights the potential of semi-IPN polysaccharide-based hydrogels as effective adsorbents for heavy metals and dyes and as a promising solution for mitigating environmental pollution. The insights provided herein contribute to developing advanced materials for environmental remediation, aligning with global sustainability goals, and advancing wastewater treatment technology.

Unveiling the rheological and thermal behavior of a novel Salecan and whey protein isolate composite gel

The burgeoning interest in the versatile hydrogel matrix, with its multifarious applications, has spurred extensive research in recent years. However, the implementation of chemically crosslinked gels on a large-scale has been hindered by their poor biosafety and excessive energy consumption. To address these challenges, this study focuses on harnessing physical methods to engineer novel composite hydrogels utilizing natural polysaccharides Salecan and whey protein isolate, obviating the need for structural modification or chemical crosslinking. The aim was to explore the rheological properties to understand their multiple behaviors. Various models, including Power-Law, Herschel-Bulkley, and Arrhenius, were also employed to compare and analyze rheological parameters. This study holds significance as it is the pioneering report on the hydrogels fabricated from Salecan/Whey protein isolate. These gels possess favorable attributes encompassing optimized elasticity, thermal-stability, enhanced injectability, and self-recovery, rendering them suitable for a multitude of applications in the realms of food and biomedicine.

An eco-friendly porous hydrogel adsorbent based on dextran/phosphate/amino for efficient removal of Be(II) from aqueous solution

A novel environmentally-friendly porous hydrogel adsorbent (GHPN) is firstly designed and prepared using dextran, phosphate, and calcium hydroxide for the adsorption of Be(II). GHPN shows good adsorption selectivity for Be(II) (Kd = 1.53 × 104 mL/g). According the adsorption kinetics and thermodynamics, the theoretical adsorption capacity of GHPN to Be(II) is 43.75 mg/g (35 °C, pH = 6.5), indicating a spontaneous exothermic reaction. After being reused for 5 cycles, the adsorption and desorption efficiencies of Be(II) with GHPN are obtained to be more than 80 %, showing acceptable recycling performance. Both of the characterizations and theoretical calculations indicate that the phosphate group, hydroxyl group, and amino group own the affinity to form stable complexes with Be(II). Benefiting from the introduction of phosphate and amino, the adsorption effect of the hydrogel adsorbent on Be(II) can be greatly improved, and surface precipitation, complexation, and ligand exchange are the dominant mechanisms of beryllium adsorption. The results suggest that GHPN has great potential to be utilized as an eco-friendly and useful adsorbent of Be(II) from aqueous solution.

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.

Recent developments in chitosan based microgels and their hybrids

Chitosan based microgels have gained great attention because of their chemical stability, biocompatibility, easy functionalization and potential uses in numerous fields. Production, properties, characterization and applications of chitosan based microgels have been systematically reviewed in this article. Some of these systems exhibit responsive behavior towards external stimuli like pH, light, temperature, glucose, etc. in terms of swelling/deswelling in an aqueous medium depending upon the functionalities present in the network which makes them a potential candidate for various applications in the fields of biomedicine, agriculture, catalysis, sensing and nanotechnology. Current research development and critical overview in this field accompanying by future possibilities is presented. The discussion is concluded with recommended possible future works for further progress in this field.

Gum acacia based hydrogels and their composite for waste water treatment: A review

The non-toxic nature of natural polysaccharides and their biodegradability makes them the first choice of researchers. Various natural polysaccharides are available nowadays, like cellulose, starch, chitosan, gum acacia, guar gum etc. Among these, gum acacia is a common natural polysaccharide presently used in research and technology. It is highly biodegradable, pH stable and shows appropriate water solubility. It is used in research to synthesize hydrogels and hydrogel nanocomposites for various applications because of its antimicrobial, anti-inflammatory and excellent absorption properties. The major fields of applications include the stabilization of metal nanoparticles in the form of nanocomposites, wound dressing materials, delivery systems of various drugs and pharmaceutical agents, bioengineering, tissue engineering, purification of water, synthesis of antibacterial and antifungal composites for agricultural improvements, and many others. Due to the increasing problem of water pollution, the major focus is on research helping to reduce this problem. Gum acacia-based hydrogel and hydrogel composites were synthesized and tested for pollutant removal efficiency from wastewater by different researchers. The research on gum acacia hydrogel and their hydrogel composite applications for water purification, as well as their synthesis processes and properties, are summarized in this review article.

Recent progress in magnetic polydopamine composites for pollutant removal in wastewater treatment

Various water pollution issues pose a significant threat to human water safety. Magnetic polydopamine composites (MPCs), which can be separated by magnetic fields after the adsorption process, exhibit outstanding adsorption capacity and heterogeneous catalytic properties, making them promising materials for water treatment applications. In particular, by modifying the polydopamine (PDA) coating, MPCs can acquire enhanced high reactivity, antibacterial properties, and biocompatibility. This also provides an attractive platform for further fabrication of hybrid materials with specific adsorption, catalytic, antibacterial, and water-oil separation capabilities. To systematically provide the background knowledge and recent research advances in MPCs, this paper presents a critical review of MPCs for water treatment in terms of both structure and mechanisms of effect in applications. Firstly, the impact of different PDA positions within the composite structure is investigated to summarize the optimization of properties contributed by PDA when acting as the shell, core, or bridge. The roles of various secondary modifications of magnetic materials by PDA in addressing water pollution problems are explored. It is anticipated that this work will be a stimulus for further research and development of magnetic composite materials with real-world application potential.

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.

High strength chitin/chitosan-based aerogel with 3D hierarchically macro-meso-microporous structure for high-efficiency adsorption of Cu(II) ions and Congo red

A high-strength aerogel with a 3D hierarchically macro-meso-microporous structure (HPS-aerogel) was designed based on biological macromolecules of chitin and chitosan. The macropores can be created within HPS-aerogel after CaCO₃ removal, and meso-micropores resulting from water sublimation during freeze-drying. The macro-meso-microporous structure endowed HPS-aerogel with high porosity, good mechanical properties, and excellent compression strength (1472 kPa at strain of 80 %). The HPS-aerogel exposed many adsorption sites and was used as an adsorbent to simultaneously remove Cu(II) and Congo red (CR) from water for the first time. The adsorption capability for Cu(II) and CR was 59.21 mg/g and 2074 mg/g at 303 K, respectively, and the adsorption processes matched Pseudo-second-order and Langmuir models with spontaneous and endothermic nature. Additionally, HPS-aerogel showed good anti-interference ability for coexisting pollutant. Importantly, HPS-aerogel exhibited an effective fixed-bed column adsorption performance for dynamic Cu(II) and CR with superior reusability and stability. Furthermore, HPS-aerogel showed outstanding adsorption efficiencies for Cu(II) and CR in real samples. The main adsorption mechanism for Cu(II) was attributed to the electrostatic attraction and chelation, and which was electrostatic attraction, Schiff base, and hydrogen bonding for CR. Therefore, HPS-aerogel should to be a promising adsorbent for removing both heavy-metal ions and dyes from wastewater.

Adsorptive removal of crystal violet from wastewater using sodium alginate-gelatin-montmorillonite ternary composite microbeads

In this study, the performance of the montmorillonite-filled sodium alginate/gelatin (SA-GEL-MMT) ternary biocomposite microbeads on the adsorptive removal of crystal violet (CV) dye was investigated. Firstly, the composites containing different weight ratios of MMT such as 10 %, 15 %, and 20 % were prepared. The composite beads were cross-linked using a calcium chloride (3%wt/v) solution. To determine the optimum sorption conditions the studies were performed at different parameters namely temperature, pH, contact time, sorbent dose, and dye concentration. From the sorption studies, the maximum capacity of the microbeads was found as 1000.0 mg/g whereas the maximum removal of the dye was 92.1 % at pH = 7 and a temperature of 25 °C. Additionally, the kinetic studies showed that the sorption of the dye followed the pseudo-second-order kinetics. Moreover, the adsorptive removal of the dye occurs spontaneously. This study suggests that the use of SA-GEL-MMT can be highly effective and reusable for the treatment of wastewater.

Research Advances in Mechanical Properties and Applications of Dual Network Hydrogels

Hydrogels with a three-dimensional network structure are particularly outstanding in water absorption and water retention because water exists stably in the interior, making the gel appear elastic and solid. Although traditional hydrogels have good water absorption and high water content, they have poor mechanical properties and are not strong enough to be applied in some scenarios today. The proposal of double-network hydrogels has dramatically improved the toughness and mechanical strength of hydrogels that can adapt to different environments. Based on ensuring the properties of hydrogels, they themselves will not be damaged by excessive pressure and tension. This review introduces preparation methods for double-network hydrogels and ways to improve the mechanical properties of three typical gels. In addition to improving the mechanical properties, the biocompatibility and swelling properties of hydrogels enable them to be applied in the fields of biomedicine, intelligent sensors, and ion adsorption.

Biosorption Characteristic and Cytoprotective Effect of Pb2+, Cu2+ and Cd2+ by a Novel Polysaccharide from Zingiber strioatum

The pollution of heavy metal ions can cause damage to the human body through food, so developing a new biocompatible material that can remove the damage of heavy metal ions has a good application prospect. In this study, we obtained a new homogeneous polysaccharide composed of seven monosaccharides from Zingiber strioatum by using the method of separation and purification of polysaccharide. The results of adsorption behavior showed that the concentration, temperature and pH value could affect the adsorption effect of Zingiber strioatum polysaccharide (ZSP). Through model fitting of the data of adsorption time and metal concentration, the pseudo second-order kinetic model can well describe the kinetics of the adsorption process, and the adsorption isotherm data fit well with the Langmuir model. In the preliminary research results of adsorption mechanism, SEM showed the appearance of ZSP as flake and porous surface; EDX analysis confirmed the metal adsorption capacity of ZSP. Meanwhile, XPS and FT-IR further clarified the adsorption based on functional groups composed of C and O. The cells preprotected by ZSP can resist heavy metal ions. The above results show that ZSP can be used as a new macromolecule to bind heavy metal ions, which can broaden the research scope of polysaccharides in contaminated food systems.

Exploring the Rheological and Structural Characteristics of Novel Pectin-Salecan Gels

The hydrogels based on natural polysaccharide offers high hydrophilicity and excellent biocompatibility while exhibiting soft physical properties related to texture and tissues, making them ideal candidates for food and biomedical applications. Herein, a new gel system composed of pectin and salecan (PS) was designed and prepared, and its structural and functional characteristics were further explored by scanning electron microscopy and rheological testing. Data fitting based on Herschel–Bulkley (HB) and Power-Law models enable in-depth comparisons and elucidations of the PS gels’ flow behavior. The cyclic strain time scanning test gave an interesting maximum strain recovery rate of about 70%; meanwhile, the creep data reported an adjustable creep compliance of 0.0146 to 0.1802. The comprehensive analysis of the structure and rheological exploration of the novel pectin-salecan hydrogels demonstrated their potential advantages over pectin and broader applicability in different food or biomedical fields.

Microwave-Assisted Extraction of Polyphenols from Blackcurrant By-Products and Possible Uses of the Extracts in Active Packaging

The design of experiment (DoE) approach was used to optimize the extraction of polyphenols from blackcurrant by-products with microwave-assisted extraction and deionized water as a green solvent. Three factors (microwave power, extraction time, and solvent/matrix ratio) were evauated, and a central composite orthogonal design (CCO) was applied in order to reduce experimental runs. Empirical models relating the response and process parameters were developed. The validity of the models was tested using an analysis of variance (ANOVA). The optimal extraction conditions were found using the highest value of microwave power (780–800 W) and the lowest extraction time (60 min) and solvent/matrix ratio (10 m/g). Compared with conventional solvent extraction, the polyphenol yield increased by 25% after applying the optimized MAE process. The obtained extract was used to realize a sustainable active maltodextrin (Glucidex 2) pad using an electrospinning technique. The antimicrobial and antioxidant activities of the pads were tested on the post-harvest storage of raspberries. Two set of experiments were carried out. The recorded results showed that the pad had antimicrobial activity on the tested fruit samples and implied the possibility of using it to extend the shelf-life of the fruits.

Algal Polysaccharides-Based Hydrogels: Extraction, Synthesis, Characterization, and Applications

Hydrogels are three-dimensional crosslinked hydrophilic polymer networks with great potential in drug delivery, tissue engineering, wound dressing, agrochemicals application, food packaging, and cosmetics. However, conventional synthetic polymer hydrogels may be hazardous and have poor biocompatibility and biodegradability. Algal polysaccharides are abundant natural products with biocompatible and biodegradable properties. Polysaccharides and their derivatives also possess unique features such as physicochemical properties, hydrophilicity, mechanical strength, and tunable functionality. As such, algal polysaccharides have been widely exploited as building blocks in the fabrication of polysaccharide-based hydrogels through physical and/or chemical crosslinking. In this review, we discuss the extraction and characterization of polysaccharides derived from algae. This review focuses on recent advances in synthesis and applications of algal polysaccharides-based hydrogels. Additionally, we discuss the techno-economic analyses of chitosan and acrylic acid-based hydrogels, drawing attention to the importance of such analyses for hydrogels. Finally, the future prospects of algal polysaccharides-based hydrogels are outlined.

Synthesis of Sodium Carboxymethyl Cellulose/Poly(acrylic acid) Microgels via Visible-Light-Triggered Polymerization as a Self-Sedimentary Cationic Basic Dye Adsorbent

In this study, sodium carboxymethyl cellulose/poly(acrylic acid) (CMC/PAA) microgels were successfully synthesized via visible-light-triggered free-radical polymerization to remove methylene blue (MB) from water. The microgels had a loose and porous 3-D network structure, exhibiting excellent adsorption performance. The equilibrium adsorption capacity and the removal efficiency of the microgels reached approximately 1479 mg/g and 97%, respectively, when the initial concentration of MB was 300 mg/L. The adsorption kinetics was well described by the pseudo-second-order model, and the adsorption isotherms followed the Langmuir isothermal model. Notably, CMC/PAA microgels could naturally settle and be separated from the MB solution. Furthermore, the recovery efficiency of the regenerated CMC/PAA microgels reached approximately 94% after five adsorption-desorption cycles. Therefore, the microgels could be used as promising adsorbents due to the advantages of high adsorption capacity, fast removal rate, and reusability.

Removal of inhibitory furan aldehydes in lignocellulosic hydrolysates via chitosan-chitin nanofiber hybrid hydrogel beads

To obtain fermentable sugars from lignocellulose, various inhibitors, especially furan aldehydes, are usually generated during the pretreatment process. These inhibitors are harmful to subsequent microbial growth and fermentation. In this study, a novel detoxification strategy was proposed to remove 5-hydroxymethylfurfural (HMF) and furfural while retaining glucose and xylose using self-prepared chitosan-chitin nanofiber hybrid hydrogel beads (C-CNBs). After C-CNBs treatment, the removal rates of HMF and furfural from sugarcane bagasse hydrolysates reached 63.1% and 68.4%, while the loss rates of glucose and xylose were only 6.3% and 8.2%, respectively. Two typical industrial strains grew well in monosaccharide-rich detoxified hydrolysates, with a specific growth rate at least 4.1 times that of undetoxified hydrolysates. Furthermore, adsorption mechanism analysis revealed that the Schiff base reaction and mesopore filling were involved in furan aldehyde adsorption. In total, C-CNBs provide an efficient and practical approach for the removal of furan aldehydes from lignocellulosic hydrolysates.

Sustainable production of curable maltodextrin-based electrospun microfibers

Maltodextrins are inexpensive, water-soluble starch hydrolysis products composed of high molecular weight polysaccharide molecules. This feature allows their water solutions to be processed by electrospinning to produce bio-based microfibrous mats. Also, the presence of hydroxyl functions along the maltodextrin's backbone enables cross-linking reactions to be performed, necessary to overcome the intrinsic solubility of the starting material, by exploiting suitable functional molecules. In this work, the electrospinning process to obtain fibre deposition from water solutions of five different commercial maltodextrins was firstly optimized. Well-defined fibres with diameters ranging between 1.1 μm and 1.5 μm were successfully obtained using water as the unique solvent. Subsequently, the same maltodextrin-containing water solutions with citric acid added were then processed again. The presence of citric acid did not hinder the spinnability of the studied systems, while the possibility to achieve a one-step thermal curing of the obtained fibres was proved via solubility tests, TGA, and FTIR-ATR analyses. Eventually, bio-based cross-linked mats with fibre diameters ranging from 0.7 μm to 1.4 μm were obtained from the electrospinning of commercial maltodextrins and citric acid, employing water as the unique solvent and environmentally friendly curing processes. This approach enables the reported mats to be further studied for environmental, pharmaceutical, and medical applications.

Environmentally Friendly Polyvinyl Alcohol-Alginate/Bentonite Semi-Interpenetrating Polymer Network Nanocomposite Hydrogel Beads as an Efficient Adsorbent for the Removal of Methylene Blue from Aqueous Solution

Hazardous chemicals like toxic organic dyes are very harmful to the environment and their removal is quite challenging. Therefore there is a necessity to develop techniques, which are environment friendly, cost-effective and easily available in nature for water purification and remediation. The present research work is focused on the development` and characterization of the ecofriendly semi-interpenetrating polymer network (semi-IPN) nanocomposite hydrogels composed of polyvinyl alcohol (PVA) and alginate (Alg) hydrogel beads incorporating natural bentonite (Bent) clay as a beneficial adsorbent for the removal of toxic methylene blue (MB) from aqueous solution. PVA-Alg/Bent nanocomposite hydrogel beads with different Bent content (0, 10, 20, and 30 wt%) were synthesized via external ionic gelation method. The designed porous and steady structure beads were characterized by the use of Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM). The performance of the beads as MB adsorbents was investigated by treating aqueous solutions in batch mode. The experimental results indicated that the incorporation of Bent (30 wt%) in the nanocomposite formulation sustained the porous structure, preserved water uptake, and increased MB removal efficiency by 230% compared to empty beads. Designed beads possessed higher affinity to MB at high pH 8, 30 °C, and fitted well to pseudo-second-order kinetic model with a high correlation coefficient. Moreover, the designed beads had good stability and reusability as they exhibited excellent removal efficiency (90%) after six consecutive adsorption-desorption cycles. The adsorption process was found be combination of both monolayer adsorption on homogeneous surface and multilayer adsorption on heterogeneous surface. The maximum adsorption capacity of the designed beads system as calculated by Langmuir isotherm was found to be 51.34 mg/g, which is in good agreement with the reported clay-related adsorbents. The designed semi-IPN PVA-Alg/Bent nanocomposite hydrogel beads demonstrated good adsorbent properties and could be potentially used for MB removal from polluted water.

In Situ Synthesis of Magnetic Poly(DMAEAB-co-NIPAm)@Fe3O4 Composite Hydrogel for Removal of Dye from Water

Water pollution by toxic substances, such as dye molecules, remains a major environmental problem that needs to be solved. In the present work, the magnetic composite hydrogel based on the poly(2-(methacryloyloxy)-N-(2-hydroxyethyl)-N,N-dimethylethan-1-aminium bromide-co-N-isopropylacrylamide) copolymer with incorporated Fe3O4 particles ((poly(DMAEAB-co-NIPAm)@Fe3O4)) was prepared by an in situ synthesis technique for the efficient removal of dye molecules from water. The successfully synthesized magnetic hydrogel was characterized by FTIR, XRD, TGA, and TEM. The removal efficiency of the anionic dye bromophenol blue (BPB) and the cationic dye rhodamine B (RDM) by the prepared hydrogel adsorbents was evaluated. Various adsorption parameters, including the concentration of adsorbents and adsorption time, were also investigated. The results showed that the synthesized magnetic hydrogel had excellent BPB removal performance compared to the removal of RDM. The optimum adsorbent concentration for 0.5 mM BPB solution was approximately 0.5 g/L, and the removal efficiency was more than 99%. The kinetics data of BPB removal fitted well into the pseudo-2nd-order model, indicating that BPB dye adsorption involves chemical adsorption and physical adsorption. In addition, recycling studies were conducted to examine the reusability of the magnetic hydrogel for BPB removal for up to five cycles and the hydrogel could be reused without losing its high removal efficiency. The magnetic hydrogel poly(DMAEAB-co-NIPAm)@Fe3O4 with high removal efficiency, good selectivity, and reusability shows great potential for the removal of anionic dyes in wastewater treatment.

Green Synthesis of pH-Responsive, Self-Assembled, Novel Polysaccharide Composite Hydrogel and Its Application in Selective Capture of Cationic/Anionic Dyes

Dyes are one of the most hazardous chemicals causing significant environmental pollution and affecting water quality. Majority of the existing methods for dye removal and degradation involve synthetic membranes and use of hazardous chemicals, further resulting in secondary pollution. The present study reports polysaccharide based novel composite hydrogel as biodegradable matrix for pH-responsive selective adsorption of cationic/anionic dyes. This membrane showed pH-responsive adsorption of methyl green (MG) and methyl orange (MO) with similar adsorption equilibrium, i.e., 315 and 276 mg g-1, respectively. Interestingly, selective adsorption at different pH has allowed separation of dye mixtures that holds incredible industrial importance for dyes recovery. The hydrogel matrix was able to completely separate MG, a model cationic dye at neutral pH from the dye mixture whereas, it was possible to remove 60% MO, a model anionic dye at acidic pH. Furthermore, comprehensive isothermal and kinetic studies of adsorption revealed that Freundlich isotherm describing the multilayer coverage and pseudo-second-order kinetics were followed. Thermodynamic studies indicated that the adsorption process was spontaneous and endothermic. In fact, the membrane was reusable for at least ten cycles and exhibited desorption efficiency of 80 and 60% for MO and MG, respectively, which may be further recycled to make the process environmentally sustainable. Overall, this study proposes an inexpensive, simple, biologically safe, and efficient adsorbent material for dye effluent treatment.

Preparation of cationic cotton through reaction with different polyelectrolytes

Cationization of cotton fabrics was performed by exhaustion procedure utilizing four different reagents provided with quaternary ammonium groups: poly diallyldimethylammonium chloride (PDDACl), poly acrylamide-co-diallyldimethylammonium chloride (PAcD), poly[bis(2-chloroethyl) ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] quaternized (P42) and 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC). Pretreated samples were dyed using Reactive Red 195 dye. The cationic fabrics were analyzed by colorimetric and fastness properties, zeta potential, SEM, FTIR and an estimate of the bactericidal effect. Cationic cotton treated with PDDACl and CHPTAC showed a higher affinity for the reactive dye, with color strength (K/S) values varying from 41 to 48, against 32 for conventional dyeing. P42 presented competitive results with K/S of 27-28. The cationic dyeing considerably reduced the amount of effluent, especially for the CHPTAC samples, which requires a single washing bath for complete removal of unfixed dye. The PDDACl and P42 samples presented bactericidal activity.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-021-04260-4.

Enhanced Cu(II) adsorption using sodium trimetaphosphate-modified cellulose beads: equilibrium, kinetics, adsorption mechanisms, and reusability

The current study is focused on the simple synthesis of two novel biosorbent beads: BASB/STMP and CNFB/STMP, derived respectively from bleached almond shell (BAS) and cellulose nanofiber from almond shell (CNF) by means of chemical crosslinking with sodium trimetaphosphate (STMP). These biosorbents were thoroughly characterized in terms of structure (FTIR), texture (N₂ adsorption-desorption), thermal behavior (TGA/DTG), morphology (SEM), and surface properties (XPS). The adsorption kinetics of Cu(II) ions onto BASB/STMP and CNFB/STMP materials proved the chemisorption interaction between Cu(II) ions and the STMP functionalized beads. The BASB/STMP equilibrium data were successfully described by the Redlich-Peterson model and the CNFB/STMP data by the Sips model which disclosed maximum adsorption capacities of 141.44 mg g^-1 and 147.90 mg g^-1, respectively. Furthermore, the BASB/STMP bioadsorbent offers easy regeneration and better reusability with high efficiency (> 83%). This study sheds light on the preparation of low-cost adsorbents for wastewater treatment in order to improve the competitiveness and eco-friendliness of agrowaste-based processes.

A Water-Soluble Schiff Base Turn-on Fluorescent Chemosensor for the Detection of Al3+ and Zn2+ Ions at the Nanomolar Level: Application in Live-Cell Imaging

A water-soluble Schiff base, 2,3-bis((E)-(2-hydroxy-3-methoxybenzylidene)amino) propanoic acid (ODA) prepared by condensing o-vanillin and DL-2,3-diaminopropionic acid was evaluated as an efficient "turn on" fluorescent chemosensor for the selective recognition of Al3+ and Zn2+ ions in presence of several interfering metal ions (detection limit; for Al3+ = 1.82 nM, Zn2+ = 7.06 nM). The probe also shows a selective chromogenic behavior towards Al3+ and Zn2+ ions that the naked eye can view. The binding stoichiometry was determined using 1H-NMR titration and ESI-MS spectrometry. The sensing mechanism is due to the inhibition of ESIPT and isomerization of -C=N of ODA on complexation with Al3+/Zn2+. The intramolecular hydrogen bonding energy and the critical bond energy in ODA-Al3+/Zn2+ were calculated using QTAIM analysis. The Thin Layer Chromatography (TLC) plates and strip papers loaded with ODA were used to test the practical applications for sensing Al3+ and Zn2+ ions. Moreover, the probe has been used for live-cell imaging to detect Al3+ and Zn2+ ions in hepatoma C3A and human glioblastoma U87 cells.

The Use of Megamolecular Polysaccharide Sacran in Food and Biomedical Applications

Natural polymer is a frequently used polymer in various food applications and pharmaceutical formulations due to its benefits and its biocompatibility compared to synthetic polymers. One of the natural polymer groups (i.e., polysaccharide) does not only function as an additive in pharmaceutical preparations, but also as an active ingredient with pharmacological effects. In addition, several natural polymers offer potential distinct applications in gene delivery and genetic engineering. However, some of these polymers have drawbacks, such as their lack of water retention and elasticity. Sacran, one of the high-molecular-weight natural polysaccharides (megamolecular polysaccharides) derived from Aphanothece sacrum (A. sacrum), has good water retention and elasticity. Historically, sacran has been used as a dietary food. Moreover, sacran can be applied in biomedical fields as an active material, excipient, and genetic engineering material. This article discusses the characteristics, extraction, isolation procedures, and the use of sacran in food and biomedical applications.

Villi-like poly(acrylic acid) based hydrogel adsorbent with fast and highly efficient methylene blue removing ability

Organic dye-containing wastewater has become an increasingly serious environmental problem due to the rapid development of the printing and dyeing industry. Hydrogel is a promising adsorbent for organic dyes because of its unique three-dimension network structure and versatile functional groups. Though many efforts have been made in hydrogel adsorbents recently, there is still a critical challenge to fabricate hydrogel adsorbent with high adsorption capacity and high efficiency at the same time. To address this concern, we developed a calcium hydroxide nano-spherulites/poly(acrylic acid -[2-(Methacryloxy)ethyl]trimethyl ammonium chloride) hydrogel adsorbent with novel villi-like structure. The hydrogels were prepared through a simple free radical copolymerization method using calcium hydroxide nano-spherulites as crosslinker. The resultant hydrogel adsorbents showed a maximum adsorption capacity of 2249 mg/g in a 400 mg/L methylene blue solution and a high removal ratio of 98% in 1 h for a 50 mg/L methylene blue solution. In addition, the adsorption behaviors of our hydrogel adsorbents could be well described by pseudo-second-order kinetic model and Langmuir adsorption isotherm model. Furthermore, this kind of hydrogel adsorbent showed selective adsorption behavior for methylene blue. Altogether, the hydrogel adsorbent developed in this work has a high capacity and high efficiency in organic dye removing and promised a great potential in wastewater treatment application.

Water-soluble poly(ethylene glycol) methyl ether-grafted chitosan/alginate polyelectrolyte complex hydrogels

This study aimed to fabricate polyelectrolyte complexes from water-soluble poly(ethylene glycol) methyl ether-grafted chitosan (mPEG-g-CTS) and alginate (ALG) in the absence of acetic acid. The complexes formed fibrous network macrogels when mPEG-g-CTS with short mPEG chains (mPEG750-g-CTS and mPEG2000-g-CTS) and mPEG-g-CTS:ALG weight ratios in the range from 1:0.14 to 1:1 were used. The macrogels at a weight ratio of mPEG-g-CTS:ALG of 1:1 possessed the highest elasticity with electrophoretic mobility close to 0 m²·V^-1·s^-1. Water uptake of the sponge-like lyophilized macrogels decreased with increasing ALG content, mPEG chain length, and degree of substitution of mPEG-g-CTS. In contrast, the polyelectrolyte complexes prepared using long mPEG chains of mPEG-g-CTS (mPEG5000-g-CTS) formed spherical nanoparticles (70-90 nm) and showed highly negative electrophoretic mobility (< -3.20 × 10⁸ m²·V^-1·s^-1). The obtained mPEG-g-CTS/ALG polyelectrolyte complex hydrogels and nanoparticles have the potential to be applied as carriers for functional food additives, drugs, and bioactive compounds.

Efficient removal of selenate in water by cationic poly(allyltrimethylammonium) grafted chitosan and biochar composite

The discovery of cheap and eco-friendly functional materials for the removal of anionic heavy metal ions is still challenging in the treatment of heavy metal-contaminated water. Herein, a new poly(allyltrimethylammonium) grafted chitosan and biochar composite (PATMAC-CTS-BC) was introduced for the removal of selenate (SeO₄^2-) in water. Results suggest that the PATMAC-CTS-BC showed a rapid removal of SeO₄^2- with efficiency of >97% within 10 min and it followed a pseudo-second-order model. High capacity of SeO₄^2- adsorption by the composite was achieved, with maximum value of 98.99 mg g^-1 based on Langmuir model, considerably higher than most of reported adsorbents. The thermodynamic results reflected the spontaneous and exothermic nature of SeO₄^2- adsorption onto the composite. The composite could be applied at a wide initial pH range (2-10) with high removal efficiency of SeO₄^2- because of permanent positive charges of quaternary ammonium groups (=N⁺-). The removal mechanisms of SeO₄^2- were mainly attributed to electrostatic interactions with =N⁺- and protonated -NH₃⁺ groups, and redox-complexation interactions with -NH₂, -NH-, and -OH groups. Besides SeO₄^2-, the hexavalent chromium (Cr₂O₇^2-) was considered as example to further demonstrate the anion removal capability of cationic hydrogel-BC composite. The study outcomes open up new opportunities to efficiently remove anionic heavy metal ions (e.g., SeO₄^2- and Cr₂O₇^2-) in water using these materials.

One-step sustainable synthesis of cationic high-swelling polymers obtained from starch-derived maltodextrins

The good water solubility displayed by most starch-derived maltodextrins has limited their use when specific mechanical properties are required, particularly when working in aqueous media. As a result, numerous attempts to cross-link such polysaccharides to obtain cross-linked polymers have been reported; in this context, non-toxic and biocompatible water-soluble diglycidyl ethers have performed well. Besides, amines are commonly used as curing agents in combination with diglycidyl ethers for the production of epoxy resins. For this reason, amine-mediated epoxy ring-opening reactions of 1,4-butanediol diglycidyl ether have been studied as approaches to obtain sustainable cross-linked polymers suitable for eco-friendly scaling-up, based upon commercial starch-derived maltodextrins, using water as a unique solvent.

Polydopamine/montmorillonite-embedded pullulan hydrogels as efficient adsorbents for removing crystal violet

Both secondary pollution and the low mechanical strength of adsorbents have severely impeded the practical application of adsorption methods in the dye wastewater treatment. In this work, we innovatively synthesized a composite hydrogel adsorbent by incorporating polydopamine (PDA) and montmorillonite (MMT) into the pullulan hydrogel matrix for dye adsorption. First, the successful formation of the resultant adsorbents was verified by Fourier-transform infrared spectroscopy and scanning electron microscope elemental mapping analysis. Then, several physicochemical properties (such as thermal and swelling properties, microarchitecture, and mechanical strength) of the five prepared adsorbents (PM1-PM5) were investigated. These results demonstrated the adsorbents had tunable properties, which can be achieved by adjusting the PDA/MMT mass ratio. Next, the dye adsorption performance was systematically explored. The resultant adsorbent (PM3) had a maximum adsorption capacity of 112.45 mg/g and its adsorption data was best described by a Langmuir isotherm and pseudo-second-order kinetic. Finally, the adsorption mechanisms and potential commercial practicability of the adsorbent were studied. Altogether, the designed adsorbent could effectively avoid generating the secondary pollution typical of adsorbents and it displayed excellent mechanical strength, thus opening up a new horizon in mitigating environmental pollution from textile industries.