Chemical Cross-linking Research Articles

Unlocking Auxetic Behavior in Recyclable Thermosetting Foams Enabled by Dynamic Disulfide Cross‐linking Strategy

AbstractAuxetic foams with a negative Poisson's ratio (NPR) have attracted considerable attention in material engineering due to their outstanding performance in seismic and energy absorption. Nevertheless, thermoplastic auxetic foams are compromised by weak non‐covalent crosslinking that diminishes the mechanical strength and durability of foams. Conversely, thermosetting foams with chemical crosslinking, although mechanically robust, face challenges in elaborating auxetic structure and in achieving recyclability. Herein, an alternative approach is proposed to tackle this dilemma by incorporating dynamic disulfide bonds into the polymer network for preparing a thermosetting polyurethane foam with covalent adaptable network. By leveraging the unidirectional multi‐effect compression technique, the topological network reorganization of foam is induced, transforming the initial circular open‐cell structure into a re‐entrant cell structure. This structural transformation endows the foam with stable NPR capability, achieving a minimum Poisson's ratio value of −0.4 within 30% compressive strain. Benefiting from its reinforced network structure, the foam also demonstrates high compressive strength (6.47 MPa) and tensile strength (1.67 MPa). Furthermore, it is recyclable and can be recompressed into thermosetting films. This work offers a straightforward approach to making auxetic thermosetting foams with good mechanical and recyclable properties, which is interesting for the development of high‐performance auxetic materials.

Development of two-dimensional amyloid fibril/carboxymethyl cellulose hybrid membranes for effective adsorption of hexavalent chromium

Amyloid fibrils (AFs) are protein aggregates with highly ordered fibrillar structures and can be formed via self-assembly of proteins under appropriate conditions. Owing to the unique properties of AFs, e.g., high surface-to-volume ratio and versatile functional groups, they offer abundant binding sites for the efficient adsorption of hexavalent chromium (Cr(VI)). This study was aimed at examining the performance of two-dimensional AF-based hybrid membranes for adsorbing Cr(VI). First, AF/carboxymethyl cellulose (AF/CMC) hybrid membranes were synthesized via chemical crosslinking coupled with phase inversion, followed by investigating the synthesis mechanism using Fourier transform infrared spectroscopy. Our results revealed that the surface microstructures and mechanical properties of the hybrid membranes could be affected by the AF:CMC mass ratio of the membrane. The porosity and ζ-potential of hybrid membranes were found to be dependent on both pH value and membrane composition. Analyses of the kinetics and thermodynamic behavior of Cr(VI) adsorption on the AF/CMC hybrid membranes revealed that the initial adsorption rate and maximum adsorption capacity were determined to be ∼149.20 mg g–1 h–1 and ∼311.11 mg g–1, respectively. The Cr(VI) removal percentage of hybrid membrane with high CMC content was found to remain at >75 % after five successive adsorption-desorption cycles. Finally, the mechanism and interactions involved in the adsorption of Cr(VI) on the hybrid membrane were further investigated via thermodynamic analysis and X-ray photoelectron spectroscopy. This study provides an excellent example of harnessing AF-based membranes in water remediation, highlighting the potential of AF-based hybrid materials for wastewater treatment applications.

Synthesis of a novel biomass-based flame retardant featuring vinyl-terminated chemical cross-linking and application in flame retardancy, smoke suppression, toxicity reduction and mechanical enhancement of PAN composite fibers

To develop green and efficient polyacrylonitrile (PAN) fibers with excellent fire safety properties, a new biomass-based flame retardant (PPC@VA) with vinyl-terminated groups was prepared based on the reaction of hexachlorocyclotriphosphonitrile, teat polyphenols, ethylenediamine and vinylphosphonic acid. Subsequently, it was mixed with spinning solution to obtain PPC@VA/PAN through wet spinning, which were then chemically cross-linked via thermal initiation to achieve CC-PPC@VA/PAN fibers. CC-PPC@VA/PAN showed a significant improvement in flame retardancy with a limiting oxygen index value of 32.5 %. The peak of smoke production rate, total smoke production and CO production rate were lowered by 81.9 %, 77.8 % and 91.3 %. Besides, the hazardous gas HCN was greatly suppressed. Owing to the macromolecular entanglement, hydrogen bonding and covalent cross-linking, CC-PPC@VA/PAN improved elongation at break and tensile strength by 19.2 % and 72.1 %. Also, chemical cross-linking contributed to decrease the migration of P/N-based flame retardants, lower the potential risk of water eutrophication and increased the service life of the fibers.

Facile fabrication of ultradurable flame-retardant and hydrophobic cotton fabric with P/N-rich maltodextrin derivative and octadecyltrimethoxysilane

Flame-retardant and hydrophobic cotton fabric provides protections from fire, stain and bacteria in daily life. However, it is still a great challenge to achieve ultrahigh durability via a green and facile technology. Herein, we synthesized a reactive P/N-rich maltodextrin derivative (PM), and reported a facile dipping-baking strategy to fabricate ultradurable flame-retardant and hydrophobic cotton fabric with PM and octadecyltrimethoxysilane (OTMS). The acids released from PM not only reacted with cellulose during baking, but also catalyzed the hydrolysis-polycondensation of OTMS and silylation reaction of cellulose. Thanks to the P/N/Si synergy and the existence of polyalkylsiloxane coating, treated fabric exhibited outstanding flame retardancy and hydrophobicity with a limiting oxygen index (LOI) of 34.7% and a water contact angle (WCA) of 143.3°. The chemical crosslinkings in PM-cellulose and OTMS-cellulose imparted ultrahigh durability to treated fabric. The LOI and WCA of treated fabric still reached 27.2% and 127.9° after 50 harsh washing cycles, respectively. Moreover, the WCA still maintained above 125° after 3000 intense friction cycles or soaked in strongly acidic/alkaline solution for 3 days. This work not only provides a new idea to synthesize biobased reactive flame retardant, but also a feasible and sustainable strategy for fabricating ultradurable hydrophobic and flame-retardant cotton fabric.

Green and energy-saving tread rubber by constructing chemical cross-linking interface between graphene oxide and natural rubber

The dispersibility of fillers and interfacial interaction are crucial for polymer nanocomposites. Developing a simple, efficient and green method to simultaneously reduce and functionalize graphene oxide (GO) for preparing graphene/rubber composites with excellent dispersibility and enhanced interfacial interactions remains one of the main trends in developing and expanding the application of graphene in the rubber industry. In this work, VOC (volatile organic compound) -free and environmentally friendly L-methionine (L-Met) was selected as the functional modifier of GO. Then, L-Met-modified GO (MGO) was blended with natural rubber (NR) in an aqueous phase to prepare MGO/NR composites. The amphiphilic property of L-Met not only reduced GO but also endowed it with less agglomeration and excellent water dispersibility, which was a prerequisite for achieving uniform dispersion of GO in the NR matrix. In addition, the amino acids on the surface of MGO enhanced the compatibility between GO and the protein-phospholipid layer on the outer layer of NR latex particles. Meanwhile, L-Met containing sulfur bonds promoted rubber vulcanization, resulting in the formation of a cross-linked network between the modified GO and NR molecular chains. Compared to unmodified GO/NR composites, MGO/NR composites exhibited excellent mechanical properties and low heat build-up. More importantly, the solid tire prepared by using L-Met as the interface modifier for GO filled rubber showed lower rolling resistance and temperature rise, and the energy saving efficiency was improved. This strategy is expected to provide a new insight into the green production of organically modified graphene and the preparation of low-energy-consumption green graphene tires.

Diverse Strategies to Develop Poly(ethylene glycol)-Polyester Thermogels for Modulating the Release of Antibodies.

In this work, we present basic research on developing thermogel carriers containing high amounts of model antibody immunoglobulin G (IgG) with potential use as injectable molecules. The quantities of IgG loaded into the gel were varied to evaluate the possibility of tuning the dose release. The gel materials were based on blends of thermoresponsive and degradable ABA-type block copolymers composed of poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) or poly(lactide-co-caprolactone)-b-poly(ethylene glycol)-b-(lactide-co-caprolactone) (PLCL-PEG-PLCL). Primarily, the gels with various amounts of IgG were obtained via thermogelation, where the only factor inducing gel formation was the change in temperature. Next, to control the gels' mechanical properties, degradation rate, and the extent of antibody release, we have tested two approaches. The first one involved the synergistic physical and chemical crosslinking of the copolymers. To achieve this, the hydroxyl groups located at the ends of the PLGA-PEG-PLGA chain were modified into acrylate groups. In this case, the thermogelation was accompanied by chemical crosslinking through the Michael addition reaction. Such an approach increased the dynamic mechanical properties of the gels and simultaneously prolonged their decomposition time. An alternative solution was to suspend crosslinked PEG-polyester nanoparticles loaded with IgG in a PLGA-PEG-PLGA gelling copolymer. We observed that loading IgG into thermogels lowered the gelation temperature (TGEL) value and increased the storage modulus of the gels, as compared with gels without IgG. The prepared gel materials were able to release the IgG from 8 up to 80 days, depending on the gel formulation and on the amount of loaded IgG. The results revealed that additional, chemical crosslinking of the thermogels and also suspension of particles in the polymer matrix substantially extended the duration of IgG release. With proper matching of the gel composition, environmental conditions, and the type and amount of active substances, antibody-containing thermogels can serve as effective IgG delivery materials.

High internal phase emulsions stabilized by fluorescent phycocyanin for improved stability and bioaccessibility of β-carotene.

High internal phase emulsions (HIPE) are distinguished from ordinary emulsions by higher oil-phase percentage and better storage stability. Recently, HIPE stabilized with protein-based particles has received more attention. However, organic precipitation, chemical cross-linking and thermal denaturation are often needed to stabilize emulsions with natural proteins, and there is an urgent need to reduce the pollution of organic reagents. HIPE loaded with β-carotene stabilized by phycocyanin was prepared under mild conditions. It demonstrated strong stability in terms of temperature and storage, as evidenced by its 94.17% retention rate and 81.06% bioavailability. This stability was ascribed to the efficient defense against heat and UV rays, which was probably associated with the oil-droplet environment and interfacial protection of phycocyanin. It is speculated that the possible main interaction site between phycocyaninand sorbitol exists near amino acids 110 to 120 of the B chain. The hydrogen bond and hydrophobic interaction between them make the phycocyanin fully adsorbed on the oil-water interface when sorbitol is stable, forming a strong oil-water structure, which increases the stability of the emulsion. The outstanding fluorescence characteristics provide a feasible alternative for fluorescent emulsions to distribute and trace active compounds in vitro. HIPE loaded with β-carotene might have potential as a 3D printing material for edible functional foods. © 2024 Society of Chemical Industry.

Synthetic Extracellular Matrix of Polyvinyl Alcohol Nanofibers for Three-Dimensional Cell Culture.

An ideal extracellular matrix (ECM) replacement scaffold in a three-dimensional cell (3D) culture should induce in vivo-like interactions between the ECM and cultured cells. Highly hydrophilic polyvinyl alcohol (PVA) nanofibers disintegrate upon contact with water, resulting in the loss of their fibrous morphology in cell cultures. This can be resolved by using chemical crosslinkers and post-crosslinking. A crosslinked, water-stable, porous, and optically transparent PVA nanofibrous membrane (NM) supports the 3D growth of various cell types. The binding of cells attached to the porous PVA NM is low, resulting in the aggregation of cultured cells in prolonged cultures. PVA NMs containing integrin-binding peptides of fibronectin and laminin were produced to retain the blended peptides as cell-binding substrates. These peptide-blended PVA NMs promote peptide-specific cell adherence and growth. Various cells, including epithelial cells, cultured on these PVA NMs form layers instead of cell aggregates and spheroids, and their growth patterns are similar to those of the cells cultured on an ECM-coated PVA NM. The peptide-retained PVA NMs are non-stimulatory to dendritic cells cultured on the membranes. These peptide-retaining PVA NMs can be used as an ECM replacement matrix by providing in vivo-like interactions between the matrix and cultured cells.

Gelatin-Sodium Alginate Hydrogels Cross-Linked by Squaric Acid and Dialdehyde Starch as a Potential Bio-Ink.

Hydrogels as biomaterials possess appropriate physicochemical and mechanical properties that enable the formation of a three-dimensional, stable structure used in tissue engineering and 3D printing. The integrity of the hydrogel composition is due to the presence of covalent or noncovalent cross-linking bonds. Using various cross-linking methods and agents is crucial for adjusting the properties of the hydrogel to specific biomedical applications, e.g., for direct bioprinting. The research subject was mixtures of gel-forming polymers: sodium alginate and gelatin. The polymers were cross-linked ionically with the addition of CaCl2 solutions of various concentrations (10%, 5%, 2.5%, and 1%) and covalently using squaric acid (SQ) and dialdehyde starch (DAS). Initially, the polymer mixture's composition and the hydrogel cross-linking procedure were determined. The obtained materials were characterized by mechanical property tests, swelling degree, FTIR, SEM, thermal analysis, and biological research. It was found that the tensile strength of hydrogels cross-linked with 1% and 2.5% CaCl2 solutions was higher than after using a 10% solution (130 kPa and 80 kPa, respectively), and at the same time, the elongation at break increased (to 75%), and the stiffness decreased (Young Modulus is 169 kPa and 104 kPa, respectively). Moreover, lowering the concentration of the CaCl2 solution from 10% to 1% reduced the final material's toxicity. The hydrogels cross-linked with 1% CaCl2 showed lower degradation temperatures and higher weight losses than those cross-linked with 2.5% CaCl2 and therefore were less thermally stable. Additional cross-linking using SQ and DAS had only a minor effect on the strength of the hydrogels, but especially the use of 1% DAS increased the material's elasticity. All tested hydrogels possess a 3D porous structure, with pores of irregular shape and heterogenic size, and their swelling degree initially increased sharply to the value of approx. 1000% during the first 6 h, and finally, it stabilized at a level of 1200-1600% after 24 h. The viscosity of 6% gelatin and 2% alginate solutions with and without cross-linking agents was similar, and they were only slightly shear-thinning. It was concluded that a mixture containing 2% sodium alginate and 6% gelatin presented optimal properties after gel formation and lowering the concentration of the CaCl2 solution to 1% improved the hydrogel's biocompatibility and positively influenced the cross-linking efficiency. Moreover, chemical cross-linking by DAS or SQ additionally improved the final hydrogel's properties and the mixture's printability. In conclusion, among the tested systems, the cross-linking of 6% gelatin-2% alginate mixtures by 1% DAS addition and 1% CaCl2 solution is optimal for tissue engineering applications and potentially suitable for 3D printing.

Highly biocompatible, antioxidant and antibacterial gelatin methacrylate/alginate - Tannin hydrogels for wound healing

Gelatin (Gel) hydrogels are widely utilized in various aspects of tissue engineering, such as wound repair, due to their abundance and biocompatibility. However, their low strength and limited functionality have constrained their development and scope of application. Tannic acid (TA), a naturally occurring polyphenol found in plants and fruits, has recently garnered interest as a crosslinking, anti-inflammatory, and antioxidant agent. In this study, we fabricated novel multifunctional gelatin methacrylate/alginate-tannin (GelMA/Alg-TA) hydrogels using chemical and physical crosslinking strategies with gelatin methacrylate (GelMA), alginate (Alg), and TA as the base materials. The GelMA/Alg-TA hydrogels maintained a stable three-dimensional porous structure with appropriate water content and exhibited excellent biocompatibility. Additionally, these hydrogels demonstrated significant antioxidant and antibacterial properties and substantially promoted wound healing in a mouse model of full-thickness skin defects by modulating inflammatory responses and enhancing granulation formation. Therefore, our study offers valuable insights into the design principles of novel multifunctional GelMA/Alg-TA hydrogels, highlighting their exceptional biocompatibility, antioxidant, and antibacterial properties. GelMA/Alg-TA hydrogels are promising candidates for wound healing applications.

Improving the curing reactivity, interfacial strength, thermal and mechanical properties of phthalonitrile resin/basalt fiber composites by reactive organic coating

Phthalonitrile (PN) resin is a thermosetting resin with excellent properties, but its poor processability hinders its wide application. Meanwhile, as a high-performance green fiber, basalt fiber (BF) shows good overall properties, but the chemical inertness and smooth surface limits its application as well. In this work, a highly reactive organic coating polydopamine (PDA) was used to promote the curing of PN resin and enhance the interfacial interaction between the polymer matrix and the fiber cloth. The successful coating of PDA was verified by SEM observation, FTIR and XPS spectra. It was found that PDA could not only increase the polarity of BF, aid the infiltration of PN resin into the fiber cloth, enhance the interfacial strength, but also promote the consumption of cyano groups and increase the chemical crosslinking density. Consequently, the overall performance of the composites was enhanced. Specifically, the laminate 0.4DABF/BAPh showed flexural strength of 447 MPa and flexural modulus of 23.3 GPa, which was 131 MPa and 4.5 GPa higher than those of BF/BAPh. The glass transition temperature of 0.4DABF/BAPh was also 77 °C higher than that of BF/BAPh.

Super-strain, high sensitivity, and multi-responsive flexible sensor based on nanocellulose hydrogels

The application of flexible sensors based on conductive hydrogels in human motion monitoring has been widely studied. Here, a facile one-pot method is proposed to prepare nanocellulose/polyacrylamide/sodium alginate hydrogel (CNWs/SA/PAM). The resulting CNWs/SA/PAM hydrogel has exceptional mechanical properties (7850 %, 1.3 MPa) and high sensitivity (14200 %, GF=3.6, 68 ms). The nanocellulose crystals (CNWs) are bent and entangled with the backbone of the polyacrylamide/sodium alginate (PAM/SA) hydrogel network, effectively transferring external mechanical forces to the entire physical and chemical cross-linking domains. This feature considerably improves the tensile strength, strain sensing range, and sensitivity of the hydrogel. The CNWs/SA/PAM hydrogel exhibits a sensitive response to water molecules and temperature-stimulated shape memory behaviour and can act as a programmable deformation actuator. The hydrogel sensor can detect and monitor subtle human motion signals in a timely and accurate manner. It is designed as a single-electrode friction nanogenerator insole (insole-TENG) that can monitor the large motion states of the human body in real time and can be efficiently used for small self-powered electronic devices. This study will shed some light on developing cellulose hydrogels in multifunctional human motion health detection sensors, soft-actuated robots, and self-powered applications for small electronic devices.

Enhancing mechanical performance of boronic ester based vitrimers via intermolecular boron–nitrogen coordination

Malleability and reprocessability of cross-linked polymers can be achieved via exchange reactions of the boronic ester crosslinking. Herein, we report a facile strategy to fabricate and modulate vitrimers by introducing intermolecular boron-nitrogen coordinated boronic ester crosslinking. Using a one-pot reaction, a series of boronic ester vitrimers based on polybutyl acrylate (PBA) was synthesized. The nitrogen containing monomer dimethylaminoethyl methacrylate (DMAEMA) was successfully copolymerized in the backbone to generate intermolecular boron-nitrogen (B–N) coordination. The presence of B–N coordination increases intermolecular interactions, leading to a denser crosslinked network structure and an elevated glass transition temperature. With the formation of B–N coordination, PBA-xB-yN samples at the same crosslinking density exhibit higher elongation at break and tensile strength. These samples dissipate more energy at the same strain and show a more pronounced strain rate dependency, highlighting the sacrificial role of the B–N coordination bonds. Stress relaxation experiments reveal that the intermolecular B–N coordination promotes faster relaxation of PBA-xB-yN compared to PBA-xB due to accelerated exchange dynamics of boronic ester. Mechanical reinforcement after recycling is observed in PBA-1B–2N, indicating that structural optimization of chemical and physical crosslinking occurs during thermal reprocessing. This study will provide a new strategy to fabricate boronic ester based vitrimeric materials with mechanical reinforcement and toughness enhancement.

Unlocking the electrochemical performance of glassy carbon electrodes by surface engineered, sustainable chitosan membranes

Chitosan coatings, derived from crustacean shell waste, possess inherent biocompatibility and biodegradability, rendering them suitable for various biomedical and environmental applications, including electrochemical biosensing. Its amine and hydroxyl functional groups offer abundant sites for chemical modifications to boost the charge transfer kinetics and provide excellent adhesion, enabling the construction of robust electrode-coating interfaces for electroanalysis. This study explores the role of electrostatically-driven chemical interactions and crosslinking density originating from different chitosan (Cs) and glutaraldehyde (Ga) concentrations in this aspect. Studying anionic ([Fe(CN)6]3−/4−), neutral (FcDM0/+), and cationic ([Ru(NH3)6]2+/3+) redox probes highlights the influence of Coulombic interactions with chitosan chains containing positively-charged pathways, calculated by DFT analysis. Our study reveals how a proper Ch-to-Ga ratio has a superior influence on the cross-linking efficacy and resultant charge transfer kinetics, which is primarily boosted by up to 20× analyte preconcentration increase, due to electrostatically-driven migration of negatively charged ferrocyanide ions toward positively charged chitosan hydrogel. Notably the surface engineering approach allows for a two-orders of magnitude enhancement in [Fe(CN)6]4− limit of detection, from 0.1 µM for bare GCE down to even 0.2 nM upon an adequate hydrogel modification.

Synthesis and characterization of novel water hyacinth (Eichhornia Crassipes) biodegradable mulch films

In this paper, carboxymethyl cellulose (CMC) and hemicellulose derived from water hyacinth were used to prepare hemicellulose-based biodegradable mulch film by covalent cross-linking and ionic cross-linking in order to expand its application in agricultural production practice. The esterification reaction between hemicellulose, CMC and citric acid resulted in an increase in tensile strength and elongation at break of the membranes. When citric acid was not used as cross-linking agent and the pH was lowered, the sodium carboxylate group was protonated into carboxylic acid group, which provided abundant active sites for chemical cross-linking of hydroxyl group on hemicellulose and hydroxyl group on CMC. Furthermore Zn2+ could cross-link with carboxylic acid group through hydrogen bonding, and when the DS of carboxymethyl group was high, the cross-linking of Zn2+ with Zn2+ was higher, and the conversion into nano ZnO was lower, which was conducive to the uniform distribution and reduction of agglomeration phenomenon in the films. It is favorable for its uniform distribution in the film and reduces the agglomeration phenomenon. The mulch films made from water hyacinth has excellent mechanical properties, light transmittance, water absorption, soil moisture retention and heat preservation, and is biodegradable. This study will provide new ideas for water pollution control and farmland pollution for sustainable agricultural production.

Self-assembling chitosan based injectable and expandable sponge with antimicrobial property for hemostasis and wound healing

Chitosan and chitosan derivative are widely used in hemostasis, antibiosis and wound repair for its good biocompatibility and unique effect. However, the preparation of chitosan based hemostatic materials or wound dressings generally involves chemical crosslinking agent introduction, acid residue or complicated preparation process, which limits its clinical application. In this study, an injectable and expandable chitosan sponge was constructed by chitosan (CS) and quaternized chitosan (QCS) self-assembly without acid retention and chemical crosslinker introduction. In the neutral condition, the hydrogen bond of CS molecules can act as the driving force to form cross-linking network, and the QCS was introduced to regulate the hydrogen bond of CS to avoid the excessive aggregation. The porous QCS/CS sponge was obtained by freeze-drying of the self-assembly QCS/CS hydrogel. The sponge exhibited high expansibility, injectability and water/blood triggered shape memory property. Due to the introduction of QCS, the sponge showed good antibacterial properties, which can protect the wound from bacterial invasion. The convenient and green preparation method of injectable and expandable QCS/CS sponge is a potential method for the treatment of hemostasis and wound healing.

Ultra-high stretchability and shape fixation rate shape memory polyurethanes based on cyclic polytetrahydrofuran molecular rings

Chemical cross-linking is commonly used to prevent slippage between molecular chains in shape memory polymers (SMPs) to improve shape return. However, chemical cross-linking makes SMPs less stretchable, and the disordered network structure reduces the ability of SMPs to maintain temporary shapes. To obtain ultra-high stretchability and better shape memory properties, a cyclic polymer (C-PTHF-OH) was introduced into the shape memory polyurethane (PUCX) network, and the PUCX network topology was controlled by adjusting the content of C-PTHF-OH molecular rings. PUC0.5 exhibited the highest shape fixation (99.9 %) and shape recovery (98.4 %), and the higher the content of the C-PTHF-OH molecular ring, the higher the elongation at break of the prepared PUCX, with a slight decrease in tensile strength. Compared to PUC0 (2000 % elongation at break and 32 MPa tensile strength) prepared from the linear polymer, PUC0.5 showed up to 2150 % elongation at break and 31 MPa tensile strength. This study provides new ideas for the design of network structures for SMPs and is a new paradigm introduced into the SMPs network by cyclic topological polymers.

Adsorption of haem by magnetic chitosan microspheres: Optimal conditions, adsorption mechanisms and density functional theory analyses

Magnetic chitosan microspheres (Al@CTS@Fe3O4) were prepared for haem separation via chemical cross-linking of chitosan, Fe3O4 and AlCl3·6H2O. The properties of the Al@CTS@Fe3O4 microspheres were investigated through techniques including XRD, TEM, FTIR, BET analysis, SEM, TG, VSM, XPS and pHpzc analysis. The haem adsorption of Al@CTS@Fe3O4 was optimized via a Box–Behnken design (BBD) with three operating factors: Fe3O4 dose (0.5–1.3 g), AlCl3·6H2O concentration (0.25–1.25 mol/L) and glutaraldehyde dose (2–6 mL). The optimal haem adsorption effect was achieved with 1.1 g of Fe3O4, 0.75 mol/L AlCl3·6H2O, and 3 mL of glutaraldehyde. The adsorption kinetics and isotherms demonstrated that haem adsorption by the Al@CTS@Fe3O4 microspheres was best described by the pseudo-second-order model. The maximum adsorption capacity is 33.875 mg/g at pH 6. After six adsorption–desorption cycles, the removal of haem still reached 53.83 %. The surface adsorption mechanism of haem on Al@CTS@Fe3O4 can be attributed to electrostatic, hydrogen bonding, and n-π interactions. Thermodynamic calculations indicated that the adsorption process is spontaneous, with the microspheres preferentially accepting electrons and haem preferentially providing electrons. Consequently, the Al@CTS@Fe3O4 microspheres exhibit considerable potential as adsorbents for haem separation.

Enhancing micro-scale SiOx anode durability: Electro-mechanical strengthening of binder networks via anchoring carbon nanotubes with carboxymethyl cellulose

With the increasing prevalence of lithium-ion batteries (LIBs) applications, the demand for high-capacity next-generation materials has also increased. SiOx is currently considered a promising anode material due to its exceptionally high capacity for LIBs. However, the significant volumetric changes of SiOx during cycling and its initial Coulombic efficiency (ICE) complicate its use, whether alone or in combination with graphite materials. In this study, a three-dimensional conductive binder network with high electronic conductivity and robust elasticity for graphite/SiOx blended anodes was proposed by chemically anchoring carbon nanotubes and carboxymethyl cellulose binders using tannic acid as a chemical cross-linker. In addition, a dehydrogenation-based prelithiation strategy employing lithium hydride was utilized to enhance the ICE of SiOx. The combination of these two strategies increased the CE of SiOx from 74% to 87% and effectively mitigated its volume expansion in the graphite/SiOx blended electrode, resulting in an efficient electron-conductive binder network. This led to a remarkable capacity retention of 94% after 30 cycles, even under challenging conditions, with a high capacity of 550 mA h g−1 and a current density of 4 mA cm−2. Furthermore, to validate the feasibility of utilizing prelithiated SiOx anode materials and the conductive binder network in LIBs, a full cell incorporating these materials and a single-crystalline Ni-rich cathode was used. This cell demonstrated a ∼27.3% increase in discharge capacity of the first cycle (∼185.7 mA h g−1) and exhibited a cycling stability of 300 cycles. Thus, this study reports a simple, feasible, and insightful method for designing high-performance LIB electrodes.

Recent Advances in Superabsorbent Hydrogels Derived from Agro Waste Materials for Sustainable Agriculture: A Review.

Superabsorbent hydrogels made from agro waste materials have the potential to promote sustainable agriculture and environmental sustainability. These hydrogels not only help reduce water consumption and increase crop yields but also contribute to minimizing waste and lowering greenhouse gas emissions. Recent research on superabsorbent hydrogels derived from agro wastes has focused on the preparation of hydrogels based on natural polymers isolated from agro wastes, such as cellulose, hemicellulose, and lignin. This review provides an in-depth examination of hydrogels developed from raw agro waste materials and natural polymers extracted from agro wastes, highlighting that these studies start with raw wastes as the main materials. The utilization strategies for specific types of agro wastes are comprehensively described. This review outlines different methods utilized in the production of these hydrogels, including physical cross-linking techniques such as dissolution-regeneration and freeze-thawing, as well as chemical cross-linking methods involving various cross-linking agents and graft polymerization techniques such as free radical polymerization, microwave-assisted polymerization, and γ radiation graft polymerization. Specifically, this review explores the applications of agro waste-based superabsorbent hydrogels in enhancing soil properties such as water retention and slow-release of fertilizers for sustainable agriculture.