Structure Of Hydrogels Research Articles

Effects of different salt ions on the structure and rheological behavior of sulfated cellulose nanocrystal hydrogel

Cellulose nanocrystal (CNC) hydrogels are increasingly used in various applications. Here, CNC hydrogels were formed by adding four salt ions (NaCl, KCl, MgCl2, and CaCl2) to sulfated CNC suspensions. NaCl and KCl are monovalent salt ions and MgCl2 and CaCl2 are divalent salt ions; each pair has similar cation charges but different cation radii. This study compared the effects of four salt ions on the structure and rheological behavior of CNC hydrogels. At the same ion concentration, compared with NaCl and KCl, the addition of MgCl2 and CaCl2 significantly reduced the distance between the CNC particles, forming pronounced aggregates and denser network structures. Furthermore, the G′ and G″ of the CNC hydrogels with salt ions followed the order NaCl < KCl < MgCl2 < CaCl2 in the small-amplitude oscillatory shear (SAOS) test, and more viscoelastic hydrogels exhibited relatively lower deformability in the creep-recovery test. Under large-amplitude oscillatory shear (LAOS) conditions, the CNC hydrogels with salt ions exhibited LAOS type III behavior, and the change in yield stress followed the same order as the SAOS results. Among them, CNC hydrogel with CaCl2 exhibited stronger nonlinear response and enhanced strain-stiffening behavior (higher I3/I1 and e3/e1) to resist deformation before 20% strain, as well as an enhanced softening effect (higher |v3/v1|) as the structure was destroyed and rearranged at strains ranging from 20% to 100%. Such CNC hydrogels with different salt ions, which can regulate structural and rheological properties, provide basis for designing hydrogels and meet potential requirements in food and biomedicine fields.

The Application of Three-Dimensional-Printed Hydrogels in Bone Tissue Engineering.

Bone defects are a prevalent clinical issue that presents a serious medical challenge. Bone tissue engineering (BTE) has emerged as an effective approach for treating large bone defects. Hydrogels, as hydrophilic three-dimensional polymers, are recognized as suitable material for BTE due to their excellent biocompatibility and degradability. However, the submicron and nanoporous structure of hydrogels limits the survival of osteoblasts, hindering bone tissue regeneration. In recent years, 3D printing technology has attracted appreciable attention. The use of hydrogels as 3D-printed ink facilitates the printing of hydrogels in any desired shape, enabling personalized or more complex requirements. This article provides a systematic review of the latest applications of 3D-printed hydrogels in BTE. These hydrogels serve as a multifunctional platform for the next generation technology in treating bone defects. The advantages and limitations of 3D-printed hydrogels in BTE are discussed, and future research directions are explored. This review can form the basis for future hydrogel design.

Polyethylene glycol-impregnated carbon quantum dots-phenolic phase change composites for highly efficient thermal energy storage

The development of stable smart thermal energy storage systems is the key to reaching breakthroughs in thermal management technologies based on phase change composites (PCC). In this study, high-performance PCC is developed by impregnating polyethylene glycol (PEG), as a polymeric phase change material (PCM), into the porous structure of modified resorcinol-formaldehyde (RF) hydrogels. Carbon quantum dots (CQDs) and 3-chlorophenol are introduced into the RF structure during the synthesis process to increase energy storage properties and impregnation efficiency. A sol-gel polymerization method is used to synthesize the hydrogels, followed by the impregnation of liquid PEG600 into the hydrogel structure. The low PEG leakage of optimal PCC consisting of 3-chlorophenol and 0.2 wt% CQDs is related to the presence of surface functional groups in the structure of the modified RF hydrogels resulting in the formation of hydrogen bonding and electrostatic forces. The melting enthalpy of the optimal PCC is 67 % higher than the unmodified RF-based PCC, while the encapsulation efficiency is 92.5 %. Our results confirm that thermal energy storage performance can be improved by 40 % through the addition of CQDs and 3-chlorophenol into the polymeric material. These PCC systems show long-term stability in terms of storage/release cycles and have the potential to be used as thermal regulator systems.

Photopolymerized multifunctional sodium alginate-based hydrogel for antibacterial and coagulation dressings

Trauma caused by tissue damage in clinical applications has posed a serious threat to public safety. Dressings with a single function cannot meet the needs of wound healing, but multifunctional dressings are difficult to achieve and obtain. To address this issue, this research designed a facile one-pot photo-crosslinking method to prepare multifunctional sodium alginate-based hydrogel dressings for effective wound healing. According to irregular wounds, sodium alginate-based hydrogel dressings can be quickly prepared anytime and anywhere. The structure and physicochemical properties of hydrogels are regulated by modulating the proportion of main components sodium alginate and acrylamide. The results showed the sodium alginate-based composite hydrogel as a candidate multifunctional dressing that exhibits excellent stretchability and compressibility, viscoelasticity, and suitable tissue-like adhesion. In vitro drug release and antibacterial experiments indicated that the hydrogel has effective antibacterial properties against S. aureus and P. aeruginosa. Furthermore, the haemostatic behaviour of the hydrogel was demonstrated using the coagulation activation test, whole blood-clotting test, and blood cell and platelet adhesion experiments. All these results demonstrated that the sodium alginate-based hydrogel had high application potential as a multifunctional medical dressing for wound healing.

Inorganic Hydrogel Based on Low-Dimensional Nanomaterials.

Composed of three-dimensional (3D) nanoscale inorganic bones and up to 99% water, inorganic hydrogels have attracted much attention and undergone significant growth in recent years. The basic units of inorganic hydrogels could be metal nanoparticles, metal nanowires, SiO2 nanowires, graphene nanosheets, and MXene nanosheets, which are then assembled into the special porous structures by the sol-gel process or gelation via either covalent or noncovalent interactions. The high electrical and thermal conductivity, resistance to corrosion, stability across various temperatures, and high surface area make them promising candidates for diverse applications, such as energy storage, catalysis, adsorption, sensing, and solar steam generation. Besides, some interesting derivatives, such as inorganic aerogels and xerogels, can be produced through further processing, diversifying their functionalities and application domains greatly. In this context, we primarily provide a comprehensive overview of the current status of inorganic hydrogels and their derivatives, including the structures of inorganic hydrogels with various compositions, their gelation mechanisms, and their exceptional practical performance in fields related to energy and environmental applications.

Chemically bound hydrophobic modification in hydrogel surface layer using poly(N-vinylamide)s

The novel hydrophobic surface modification of hydrogel structure, referred to as organohydrogel, was firstly achieved through the utilization of poly(N-vinylamide)s hydrogels, taking advantage of the property of polycation precursor. Following the shrinkage of poly(N-acetamide-co-N-vinylformamide), only the surface moiety was subjected to hydrolysis. Subsequently, a radical initiator was chemically tethered to the amino groups on the hydrogel surface to facilitate atom transfer radical polymerization (ATRP) of hydrophobic monomer, phenylethylacrylate. Hydrophobic layer characteristics were differentiated by varying hydrolysis time (xt) and ATRP time (yt), resulting in the creation of hydrophobic surface-modified gel (HSMgel). All HSMgels resulted in stable swelling ratio (S.R.) regardless of yt. The contact angle of water droplets increased gradually with both increasing xt and yt, from 17.6° to 91.9°, while maintaining a relatively constant S.R. The drying process of hydrophobic surface-modified HSMgels was accelerated, while that of precursor hydrophilic gels was delayed. These unique properties stemmed from the chemical structure of poly(N-vinylamide)s, which led to the formation of a chemically bound hydrophobic layer within the hydrogels.

Waste to value: Enhancing xanthan gum hydrogel with wine lees extract for optimal performance

The current study investigated the potential of utilizing wine lees extract (WLE) from red wine to enhance the sustainability and cost-effectiveness of xanthan gum (XG). A novel hydrogel system was successfully generated by cross-linking WLE and XG. Response surface methodology (RSM) was used to thoroughly analyze the characteristics of this novel hydrogel to understand its behavior and possible applications. Consistency index (K), flow behavior index (n), water holding capacity (%), and oil binding capacity (%) of the cross-linked hydrogels were optimized, and the best formulation was determined to be 0.81 % XG + 0.67 % WLE and crosslink temperature of 47 °C. The addition of WLE (0–1 % w/v) to different concentrations of XG (0–1 % w/v) was found to have a notable impact on the rheological properties, but changes in cross-link temperature (45–65 °C) did not have a significant effect. The activation energy was increased by incorporating WLE at XG concentration above 0.5 %, indicating a more robust and stable structure. FTIR and SEM analyses confirmed the chemical bonding structure of the optimum hydrogel. Incorporating WLE could significantly improve the functional properties of XG hydrogels, allowing the development of healthier product formulations.

Influence of conductive carbon and MnCo2O4 on morphological and electrical properties of hydrogels for electrochemical energy conversion.

In this work, a strategy for one-stage synthesis of polymer composites based on PNIPAAm hydrogel was presented. Both conductive particles in the form of conductive carbon black (cCB) and MnCo2O4 (MCO) spinel particles were suspended in the three-dimensional structure of the hydrogel. The MCO particles in the resulting hydrogel composite acted as an electrocatalyst in the oxygen evolution reaction. Morphological studies confirmed that the added particles were incorporated and, in the case of a higher concentration of cCB particles, also bound to the surface of the structure of the hydrogel matrix. The produced composite materials were tested in terms of their electrical properties, showing that an increase in the concentration of conductive particles in the hydrogel structure translates into a lowering of the impedance modulus and an increase in the double-layer capacitance of the electrode. This, in turn, resulted in a higher catalytic activity of the electrode in the oxygen evolution reaction. The use of a hydrogel as a matrix to suspend the catalyst particles, and thus increase their availability through the electrolyte, seems to be an interesting and promising application approach.

Using embossing ice particulate method to prepare polyvinyl alcohol/pullulan hydrogels with surface open pores loaded with microspheres for breast cancer treatment

In the post-operative treatment of breast cancer, early prevention of locoregional recurrence is crucial to avoid metastasis of cells from leftover microtumor tissues. The limitations in conventional drug delivery systems show a growing clinical demand for disease-specific drug-releasing systems. This study explores a novel poly(vinyl alcohol)/pullulan (PVA/PUL) hydrogel system for local drug delivery in post-operative breast cancer treatment. Hydrogel was produced by combination of lyophilization and embossing ice particulate techniques to create microspheres loaded open pores on the hydrogel surface for localized release of doxorubicin-loaded polycaprolactone microspheres (DOX-PCL-MSs). PVA/PUL hydrogel was successfully crosslinked with glutaraldehyde and stabilized hydrogel structure has possessed slow degradation rate and increasing water retention through 12 days. Release of DOX after 7 and 16 days from DOX-PCL-MSs loaded hydrogels were slower with a 6.2 ± 8.9 % and 56.6 ± 4.5 % release compared to 60.9 ± 14.6 % and 76.8 ± 19.7 % release from free DOX loaded hydrogel since DOX release was controlled by PCL microspheres. When interacted with human breast cancer cell line (MCF-7), DOX-PCL-MSs were able to disrupt cell and spheroid morphology after 7 days at concentrations as low as 12 μg/mL loaded DOX. In vitro cytotoxicity study has showed that, DOX-PCL-MSs loaded hydrogel was able to decrease MCF-7 viability after 7 days of incubation with controlled release of DOX. While free DOX releasing hydrogel has lost cytotoxic activity even after 4 days of incubation. Furthermore, ability of PVA/PUL hydrogel to support L929 cell attachment was shown in the study, suggesting hydrogels potential for promoting tissue regeneration after anti-cancer treatment. The study reveals that PVA/PUL hybrid hydrogels loaded with DOX-PCL-MSs has impactful potential in post-surgical treatment of breast cancer.

Rational Design of Dynamically Super-Tough and Super-Stretchable Hydrogels for Deformable Energy Storage Devices.

Hydrogels possess unique polymer networks that offer flexibility/stretchability, high ionic conductivity, and resistance to electrolyte leakage, making them suitable for deformable energy storage devices. Endowing the mechanical functionality of the hydrogel electrolytes focus on either enhancing the stretchability or the toughness. However, the stretchability and the toughness are generally a trade-off that the stretchable gels are intrinsically prone to damage and sensitive to notches and cracks. Here, the regulating strategies on the hydrogel's mechanical properties are provided to develop the designated hydrogel electrolyte, where different polymeric network structures are constructed, including single network structures, semi-interpenetrating network structures, and interpenetrating dual-network structures. A comprehensive comparison of these polymer network structures is conducted to evaluate their mechanical stretchability and toughness. Designing super-tough and super-stretchable hydrogels based on specific application requirements can be realized by striking a balance by regulating the hydrogel structure. In specific, incorporating semi-interpenetrating networks significantly can enhance stretchability to achieve a break elongation up to 1300%, while the interpenetrating dual-networks can largely improve the toughness to realize the extraordinary fracture toughness of 6.843kJm-2. These findings offer valuable designing guidance for designated hydrogel electrolytes and the deformable zinc-silver battery is demonstrated with high mechanical stability and electrochemical performance.

Modeling calcium diffusion and crosslinking dynamics in a thermogelling Alginate-Gelatin-Hyaluronic acid ink: 3D bioprinting applications

Alginate-based inks are widely used in 3D bioprinting. Its crosslinking by Ca2+ ions is extremely important to achieve scaffolds with optimal mechanical properties. Notably, despite previous studies on calcium diffusion in alginate systems, there have been no reported data regarding the effect of temperature on the diffusion and crosslinking dynamics of thermogelling alginate-based hydrogels. This study focuses on investigating the kinetics of the crosslinking front and Ca2+ diffusion within a matrix of Alginate-Gelatin-Hyaluronic acid ink, exploring the impact of temperature and Ca2+ concentration. The Ca2+ diffusion rate or ink crosslinking rate increase as the crosslinker concentration and ink temperature increase. Additionally, the mechanical properties of the scaffolds, assessed through compression, tension, and dynamic tests, were correlated with the crosslinking time.The innovative aspect of this study lies in the development of a code that simulates the diffusion of Ca2+ ions from the exterior to the interior of a hydrogel structure. Specifically, the code facilitates the calculation of the crosslinking time for a cylindrical structure up to a specified thickness, providing valuable insights for the production of airways or blood vessels. Furthermore, the Python script, incorporating the numerical model, manages to simulate the crosslinking dynamics of scaffolds of any shape, and properly fits the rheological measurements of dynamic moduli during the crosslinking process. This represents a significant advance for the precise and controlled scaffold fabrication process using 3D bioprinting.

Effects of charge state of nano-chitin on the properties of polyvinyl alcohol composite hydrogel

The present work investigates the effects of nano-chitin with different charge, obtained by acid hydrolysis and TEMPO oxidation, on the structure and properties of borax crosslinked polyvinyl alcohol (PVA) hydrogels. In detail, nano-chitin prepared by acid hydrolysis (ACh) is positively charged (+28.8 mV). The electrostatic attraction between ACh and borax ions leads to a maximum tensile stress of composite hydrogel (ACh/PB), 54.25 KPa, 17 times of the borax crosslinked PVA (PB). In contrast, nano-chitin prepared by TEMPO-oxidation (TCh) shows negative charge (−59.0 mV). Due to the electrostatic repulsion with borax ions, the maximum tensile stress of composite hydrogel (TCh/PB) is only 9.25 KPa, a very limit reinforcing effect. However, TCh/PB showed better self-healing efficiency (96.0 %) as well as ionic conductivity (1.25 × 10−5 S/m). The present work shows that the charge state of the nano-chitin exerts great influence on the interaction with the crosslinking agent borax, therefore, affects the structure and properties of the final PVA composite hydrogels. The results could provide important information about making full use of nano-chitin as a reinforcement by adjusting its surface charge state.

Temperature-responsive microcapsule hydrogel fabricated by pickering emulsion polymerization for pheromones application

Insect pheromone is a natural effective biological pesticide. To improve the utilization efficiency of pheromone pesticides and reduce labor costs, a sustained and controlled release preparation coordinating with the circadian rhythm of insects has been proposed by our previous report. However, that preparation has some deficiencies, such as the loading capacity of pheromone and sustained time. In order to overcome the existent shortcomings, a temperature-responsive release microcapsule hydrogel loaded with myrcene (as a pheromone model) was fabricated by Pickering emulsion polymerization using modified SiO2 nanoparticles as a stabilizer of microcapsule wall, octadecane and Poly(N-isopropylacrylamide) (PNIPAM) separately as temperature responders of microcapsule core and wall in the present study. The morphological structure and thermal performance of the microcapsule hydrogel were characterized. The release behaviors of myrcene at different environmental temperatures and alternating temperature cycles were also tested. The results indicated that myrcene was successfully loaded in the Myrcene/Octadecane@SiO2-PNIPAM (MOSP) microcapsule hydrogel with encapsulation efficiency and loading capacity of 80.3 % and 13.3 %, respectively. The results of the myrcene release under simulated diurnal temperature cycles revealed that the cumulative release amount was only about 43 % during 15 cycles and release rates respectively were about 0.79 μg/h at 35 °C and 0.058 μg/h at 25 °C, which demonstrated the persistent temperature sensitivity and good temperature rhythm remained after 15 cycles. These results suggested that the MOSP microcapsule hydrogel had a good controlled release effect on myrcene and could adapt well to the circadian rhythm activity of some insects. Therefore, this study provided a promising strategy to improve the utilization efficiency of pheromones through the combination of octadecane and PNIPAM as pheromones release controllers.

A stable and efficient hydrogel/sponge solar evaporator with splendid water supply

Solar-driven interfacial evaporation is an effective and realizable way of water purification. However, a short supply of water limits the evaporation performance of evaporator greatly. Here, an integrated photothermal evaporator owning double-layer structure of hydrogel and sponge with strong water transport ability is successfully prepared by cross-linking and dopamine modification. Abundant pores and hydrophilic functional groups in hydrogel and modified sponge benefit to enhance water transport of the whole evaporator and further relieve salt accumulation. Carbon black having the advantages of low cost and full spectrum absorption is dispersed into hydrogel networks to improve the capacity of photothermal conversion. Under the illumination of 1 kW m−2, the evaporator exhibits an excellent evaporation rate of 1.71 kg m-2h−1, corresponding to an evaporation efficiency of 93.8 %. Furthermore, the evaporator shows excellent stability during 8 cycles of solar evaporation. And the evaporator demonstrates superior salt tolerance in 3.5 wt% NaCl solution during the continuous evaporation of 8 h and has an outstanding efficiency of 99.8 % in 4-NP wastewater purification. The outdoor experiment proves that the evaporator of 1 m2 can produce 7.28 L of fresh water per day, which meet the drinking water demand of two adults. The hydrogel/sponge integrated photothermal evaporator has great application potential in seawater desalination and wastewater purification.

A Perfusable Multi‐Hydrogel Vasculature On‐Chip Engineered by 2‐Photon 3D Printing and Scaffold Molding to Improve Microfabrication Fidelity in Hydrogels

AbstractEngineering vasculature networks in physiologically relevant hydrogels represents a challenge in terms of both fabrication, due to the cell–bioink interactions, as well as the subsequent hydrogel‐device interfacing. Here, a new cell‐friendly fabrication strategy is presented to realize perfusable multi‐hydrogel vasculature models supporting co‐culture integrated in a microfluidic chip. The system comprises two different hydrogels to specifically support the growth and proliferation of two different cell types selected for the vessel model. First, the channels are printed in a gelatin‐based ink by two‐photon polymerization (2PP) inside the microfluidic device. Then, a human lung fibroblast‐laden fibrin hydrogel is injected to surround the printed network. Finally, human endothelial cells are seeded inside the printed channels. The printing parameters and fibrin composition are optimized to reduce hydrogel swelling and ensure a stable model that can be perfused with cell media. Fabricating the hydrogel structure in two steps ensures that no cells are exposed to cytotoxic fabrication processes, while still obtaining high fidelity printing. In this work, the possibility to guide the endothelial cell invasion through the 3D printed scaffold and perfusion of the co‐culture model for 10 days is successfully demonstrated on a custom‐made perfusion system.

Magnetic fibrin nanofiber hydrogel delivering iron oxide magnetic nanoparticles promotes peripheral nerve regeneration.

Peripheral nerve injury is a debilitating condition that have a profound impact on the overall quality of an individual's life. The repair of peripheral nerve defects continues to present significant challenges in the field. Iron oxide magnetic nanoparticles (IONPs) have been recognized as potent nanotools for promoting the regeneration of peripheral nerves due to their capability as biological carriers and their ability to template the hydrogel structure under an external magnetic field. This research used a fibrin nanofiber hydrogel loaded with IONPs (IONPs/fibrin) to promote the regeneration of peripheral nerves in rats. In vitro examination of PC12 cells on various concentrations of IONPs/fibrin hydrogels revealed a remarkable increase in NGF and VEGF expression at 2% IONPs concentration. The biocompatibility and degradation of 2% IONPs/fibrin hydrogel were assessed using the in vivo imaging system, demonstrating subcutaneous degradation within a week without immediate inflammation. Bridging a 10-mm sciatic nerve gap in Sprague Dawley rats with 2% IONPs/fibrin hydrogel led to satisfactory morphological recovery of myelinated nerve fibers. And motor functional recovery in the 2% IONPs/fibrin group was comparable to autografts at 6, 9 and 12 weeks postoperatively. Hence, the composite fibrin hydrogel incorporating 2% IONPs exhibits potential for peripheral nerve regeneration.

A 3D printable gelatin methacryloyl/chitosan hydrogel assembled with conductive PEDOT for neural tissue engineering

In neural tissue engineering, biomaterial scaffolds that have high conductivity and customized structures are crucial in promoting nerve regeneration. Poly(3,4-ethylenedioxythiophene) (PEDOT) has emerged as a promising conductive polymer with excellent chemical stability and biocompatibility. However, traditional three-dimensional (3D) printing of PEDOT-based conductive scaffolds faces challenges in limited printing resolution, poor solubility, and brittleness of conductive materials. Herein, digital light processing (DLP) printing was used to fabricate complex hydrogel structures using gelatin methacryloyl (GelMA) and chitosan (CS) while incorporating PEDOT nanoparticles through interfacial polymerization to create conducting pathways within a hydrogel structure. The integration of PEDOT significantly enhanced the electrical conductivity and mechanical properties of the GelMA/CS hydrogel while preserving printed details. The GelMA/CS-PEDOT hydrogel promoted cell proliferation and facilitated axon outgrowth of PC12 cells and Schwann cells during in vitro culture. Moreover, in vitro direct current electrical stimulation promoted axon elongation of PC12 cells cultured on a conductive substrate. In vivo studies used a conductive nerve conduit to repair a 10-mm rat sciatic nerve defect, validating the efficacy of GelMA/CS-PEDOT scaffold in peripheral nerve injury repair. These findings highlight the significant potential of conductive GelMA/CS-PEDOT hydrogel in the field of neural tissue engineering.

Correlating structural changes in thermoresponsive hydrogels to the optical response of embedded plasmonic nanoparticles.

Stimuli-responsive microgels, composed of small beads with soft, deformable polymer networks swollen through a combination of synthetic control over the polymer and its interaction with water, form a versatile platform for development of multifunctional and biocompatible sensors. The interfacial structural variation of such materials at a nanometer length scale is essential to their function, but not yet fully comprehended. Here, we take advantage of the plasmonic response of a gold nanorod embedded in a thermoresponsive microgel (AuNR@PNIPMAm) to monitor structural changes in the hydrogel directly near the nanorod surface. By direct comparison of the plasmon response against measurements of the hydrogel structure from dynamic light scattering and nuclear magnetic resonance, we find that the microgel shell of batch-polymerized AuNR@PNIPMAm exhibits a heterogeneous volume phase transition reflected by different onset temperatures for changes in the hydrodyanmic radius (RH) and plasmon resonance, respectively. The new approach of contrasting plasmonic response (a measure of local surface hydrogel structure) with RH and relaxation times paves a new path to gain valuable insight for the design of plasmonic sensors based on stimuli-responsive hydrogels.

H-PVA Cross-Linking Mechanism Prepared By Freeze-Thaw And Annealing: Optimizing Gel Fraction And Swelling

PVA has attracted attention as a material in the formation of hydrogels for drug release media. Crosslinking is one of the keys to hydrogel formation. Gel fraction, swelling ratio, and degree of crystallinity are parameters used to determine the enhancement of crosslinking and the formation of mechanical properties of hydrogels. H-PVA was synthesized through freeze-thaw and annealing processes and optimized by Box-Behnken design. Analysis of the degree of crystallinity revealed that the freeze-thaw and annealing processes formed and increased crosslinking. This is supported by data from the gel fraction analysis, which indicates that the number of crosslinks increases and the swelling ratio decreases, indicating that the hydrogel structure is strong enough to withstand water absorption. The results of the design of the experiment (DOE) showed that simultaneously the model was able to explain the presence of crosslinks formed in H-PVA, as seen from the p-value &gt;0.0001 and the statistical test results R2 = 0.99 (close to 1). Optimal conditions were found at a PVA concentration of 18.972 (%w/v), a freeze-thaw cycle of three times, and an annealing temperature of 92 °C.

Removal of methylene blue dye from water with Fe3O4/poly(HEMA-co-AMPS) magnetic hydrogels

In this research, a novel magnetic hydrogel (MHG) adsorbent based on Fe3O4/poly(2-hydroxyethylmethacrylate-co-2-acrylamido-2-methylpropanesulfonic acid) Fe3O4/poly(HEMA-co-AMPS) was synthesized by in situ co-precipitation of Fe3O4 magnetic particles inside poly(HEMA-co-AMPS) hydrogels. This adsorbent was used to adsorb the organic cationic dye methylene blue (MB) from aqueous solutions. The properties of the adsorbent were characterized by FT-IR, TGA, XRD, VSM, and EDX-SEM techniques. The degree of swelling was recorded in water, acidic medium (HCl 0.01 M), and basic medium (NaOH 0.01 M). The results confirmed that Fe3O4 particles were successfully synthesized within the poly(HEMA-co-AMPS) hydrogel structure. Magnetic hydrogels have higher swelling and reach equilibrium faster than hydrogels. The magnetic hydrogel prepared with 3 % crosslinker and 10 % AMPS (MHG3(10)) showed better potential to remove MB dye, adsorption capacity Qmax = 445.35 mg/g, this was obtained under the best conditions at pH 6.5, dose of 1 g/L, and contact time of 10 min. Over the test pHpzc, the surface of the MHG3(10) is predominantly negative at pH values higher than 2.47. The adsorption process of MHG3(10) for MB removal follows the Langmuir model and obeys pseudo-second-order kinetics. In addition, thermodynamic studies performed show that the adsorption process is endothermic (ΔH0 = 75.946 kJ/mol) and spontaneous with a positive value of entropy (ΔS0 = 263.562 J/mol·K). Regeneration experiments showed that MHG3(10) can be reused several times as its removal efficiency is still 94 % after 10 adsorption–desorption cycles. Therefore, the magnetic hydrogel MHG3(10) proved to be a promising adsorbent for the removal of the pollutant MB dye from aqueous media.