Sol-gel Transition Method Research Articles

Photopolymerized PAM/CTS/SA/Ca2+/TiO2 hydrogel for sustainable passive cooling

Evaporative cooling and radiative cooling are considered to be energy-saving and environmentally friendly cooling technologies. However, the evaporative cooling system requires complex external water supply equipment, and the radiative cooling is susceptible to weather, which hinder the practical application. Herein, TiO2 was used as the photo-initiator and spectral regulator, and a hydrogel integrating radiative cooling and evaporative cooling was prepared by combining photopolymerization with semi-acidification sol–gel transition method. The obtained hydrogel shows good mechanical strength (elongation at break > 600 %, and fracture stress > 200 kPa), high visible reflectance (>80.0 %) and emissivity in atmospheric window band (>90.0 %). At the same time, due to the introduction of hygroscopic agent CaCl2, it can replenish water itself at night. In outdoor experiment, the hydrogel showed a cooling effect of up to 12.5 °C, showing a significant potential for reducing energy consumption in cooling applications. In addition, the synthesis process of hydrogel is green, which aligns with environmental safety and sustainability goals. This study provides a new strategy for developing efficient, environmentally friendly, and low-cost passive coolers to reduce the global energy burden.

Polyelectrolyte composite hydrogels based on a derivative of functional dietary fiber for long-term gastric retention and drug delivery

Gastric retention drug delivery is experiencing significant demand for hydrogels that exhibit in situ controllable forming in the stomach, resistance against severe gastric degradation, and exceptional biocompatibility. However, current studies lack comprehensive investigations on these requirements. In this study, resistant starch is chosen as a kind of novel dietary fiber with remarkable gastric retention effects compared to conventional natural polymers. To address its limited solubility, resistant starch was modified by carboxymethyl groups. Moreover, a semi-dissolution acidification sol–gel transition method was employed to enable in situ gelation under gastric acid conditions and fabricate physically crosslinked polyelectrolyte composite hydrogels (CMRS/CTS) based on carboxymethylated resistant starch and chitosan. This method obviates the need for toxic chemical crosslinkers and initiators, ensuring favorable biocompatibility. The influence of carboxymethyl substitution degree and the anion-to-cation ratio of the composite hydrogels on the mechanical, rheological, and swelling properties was thoroughly investigated. Compared to conventional carboxymethyl starch-based hydrogels, CMRS/CTS maintained a relatively intact structure even after immersion in simulated gastric fluid for 30 days owing to the enzymatic stability of the hydrogel. Upon drug loading, CMRS/CTS exhibited sustained and controlled drug release, facilitating prolonged therapeutic effects. Simultaneously achieving in situ gastric drug release, biocompatibility, resistance to degradation, and sustained release, CMRS/CTS represents a promising avenue for the development of long-term gastric retention hydrogels.

Self-Assembled Chitosan/Dialdehyde Carboxymethyl Cellulose Hydrogels: Preparation and Application in the Removal of Complex Fungicide Formulations from Aqueous Media.

Environmental contamination with pesticides occurs at a global scale as a result of prolonged usage and, therefore, their removal by low-cost and environmentally friendly systems is actively demanded. In this context, our study was directed to investigate the feasibility of using some self-assembled hydrogels, comprising chitosan (CS) and carboxymethylcellulose (CMC) or dialdehyde (DA)-CMC, for the removal of four complex fungicide formulations, namely Melody Compact (MC), Dithane (Dt), Curzate Manox (CM), and Cabrio®Top (CT). Porous CS/CMC and CS/DA-CMC hydrogels were prepared as discs by combining the semi-dissolution acidification sol-gel transition method with a freeze-drying approach. The obtained CS/CMC and CS/DA-CMC hydrogels were characterized by gel fraction yield, FTIR, SEM, swelling kinetics, and uniaxial compression tests. The batch-sorption studies indicated that the fungicides' removal efficiency (RE%) by the CS/CMC hydrogels was increased significantly with increasing sorbent doses reaching 94%, 93%, 66% and 48% for MC, Dt, CM and CT, respectively, at 0.2 g sorbent dose. The RE values were higher for the hydrogels prepared using DA-CMC than for those prepared using non-oxidized CMC when initial fungicide concentrations of 300 mg/L or 400 mg/L were used. Our results indicated that CS/DA-CMC hydrogels could be promising biosorbents for mitigating pesticide contamination of aqueous environments.

Hyperbranched polyamidoamine-chitosan polyelectrolyte gels crosslinking by polyacrylic acid and alginate for removal of anionic dyes

Difficult-to-treat wastewater discharged from printing and dyeing industries has posed an environmental risk. Three-dimensional porous structures exhibit excellent dye adsorption properties. In this study, chitosan (CTS) was introduced in situ on polyamidoamine (PAMAM). Then, the composite gels containing sodium alginate (SA)/CTS in situ grown on PAMAM/polyacrylic acid (SCPP-Gn (n = 0,1,2,3)) were prepared with a controllable structure using a semi-dissolution acidification sol-gel transition method (SD-A-SGT). Owing to the stronger mechanical strength and larger specific surface area, the SCPP-G2 composite gel has the higher stability and the greater adsorption capacity for dyes, with maximum adsorption capacities of 325.21 mg/g for rose bengal (RB) and 222.40 mg/g for sunset yellow (SY). The mechanism study showed that the adsorption toward RB and SY was dominated by chemical adsorption. After five adsorption-desorption cycles, it was found that 70 % of the initial adsorption capacity could be retained. Our study demonstrates the great potential of the SCPP-G2 composite gel as an adsorbent in water treatment.

Preparation of CTS/PAMAM/SA/Ca2+ hydrogel and its adsorption performance for heavy metal ions

As a new functional polymer material with three-dimensional polymer network structure, hydrogel is widely used in the removel of heavy metal ions pollutants in sewage. In this work, semi-dissolution acidification sol–gel transition method was used to prepare the hydrogel with chitosan/sodium alginate/calcium ion (CTS/SA/Ca2+) physical cross-linked double network structure without adding chemical cross-linking agent. Meanwhile, hyperbranched polyamide-amine with different generations which was rich in amino groups were introduced to improve the adsorption capacity of hydrogel, and the CTS/PAMAM/SA/Ca2+ hydrogel adsorbent with no secondary pollution, environmental protection and high adsorption capacity was obtained. Experimental results show that the hydrogel with third-generation hyperbranched polyamide-amine have the best comprehensive performance. Its maximum adsorption capacities for copper ions and cadmium ions could reach 174.82 mg/g and 157.72 mg/g respectively. Furthermore, it was found that the adsorption behaviors of copper ions and cadmium ions on the hydrogel conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm model by studying the factors affecting the adsorption process. The CTS/PAMAM/SA/Ca2+ hydrogel has the advantages of high heavy metal ion adsorption capacity, uniform structure, and recyclability. As a functional material with simple preparation and excellent performance, it has good application potential and research value.

Injectable, self-healable and adhesive hydrogels using oxidized Succinoglycan/chitosan for pH-responsive drug delivery

We prepared chitosan (CS) based multifunctional hydrogels using oxidized succinoglycan (OSG) with a semi-dissolving acidified sol-gel transition method. OSG cross-linked CS hydrogels (OSG/CS) was prepared by aldehyde-amine Schiff-base reaction. OSG/CS increased not only thermal stability but also improved mechanical strength by 5.75 times. Through the tensile and strain sweep test, OSG/CS showed excellent self-healing properties by 98.82% and 99.89%, respectively. It showed the high compressive stress of 173 kPa at 60% strain, the adhesive strength of 2763 kPa, and the antibacterial effect of 90%. Furthermore, OSG/CS showed a pH-controlled drug release pattern, where a change of pH from 7.4 to 2.0 accelerated for 5-fluorouracil release from 60% to 90%. WST-8 assay demonstrated that OSG/CS maintained 97.30% cell viability and 98.84% cell proliferation after 7 days, indicating the potential as biocompatible hydrogel materials such as wound healing, tissue engineering and drug release systems.

Preparation of chitosan/sodium alginate conductive hydrogels with high salt contents and their application in flexible supercapacitors

Conductive hydrogels (CHs) are a potential material for flexible electronics. However, most of CHs display disadvantages of low ionic conductivities and intolerance to low temperatures. Herein, a novel physical CHs with salt contents as high as 30 wt% was prepared with chitosan (CTS) and sodium alginate (SA) by combining the anti-polyelectrolyte effect and semi-dissolution acidification sol-gel transition (SD-A-SGT) method. The obtained hydrogels show extremely high ionic conductivities up to 2.96 × 10−1 S·cm−1 at room temperature and 4.9 × 10−2 S·cm−1 at −20 °C. The effects of different salts on the ion mobility and electrochemical properties of CTS/SA CHs were predicted and analyzed. The flexible supercapacitor assembled using CTS/SA CHs as the electrolyte exhibits the specific capacitance as high as 405 F·g−1 at the current density of 0.25 A·g−1 and satisfying electrochemical stability with 74.91% capacitance retention in 1000 cycles. Our work has provided a new strategy for constructing green CHs with high ionic conductivities.

Fabrication and characterization of antibacterial epsilon-poly-L-lysine anchored dicarboxyl cellulose beads

Pathogens in the food and environment pose a great threat to human health. To solve this problem, we described a novel route to synthesize antibacterial epsilon-poly-L-lysine (EPL) anchored dicarboxyl cellulose beads. Cellulose beads were prepared via a sol-gel transition method and oxidized by sodium periodate and sodium chlorite to form carboxyl groups. EPL was anchored on the beads using carbodiimide mediated amidation. The structure and morphology of beads were characterized by FTIR, XPS, XRD, SEM, and TGA. After dissolution and regeneration, the crystalline form of cellulose is transformed from cellulose I to cellulose II. The thermal degradation temperature of the beads is 200∼300 °C.The samples displayed excellent antimicrobial activity against Staphylococcus aureus, Alicyclobacillus acidoterrestris and Escherichia coli within 12 h. The beads could be biodegraded in soil after 20 days. The biodegradable beads exhibited great potential in food and environmental applications.

Chain end-termination of p-polybenzimidazole by bulk segment for efficient electrochemical power generation and hydrogen separation

We investigated the effects of hydrogen separation using high-temperature anhydrous proton-exchange membrane fuel-cell technology. Various acid-doped para-polybenzimidazole (p-PBI)-chain end-tethered amine-polyhedral oligomeric silsesquioxane (NH2-POSS) membranes were prepared via a unique sol–gel transition method termed as the poly(phosphoric acid) process. The resulting NH2-POSS-capped p-PBI membranes exhibited a higher phosphoric acid-doping level (128–223.5%) and proton conductivity (0.23–0.29Scm−1 at 160°C and 0% relative humidity) than the parent p-PBI membrane. The chemical chain end-termination of p-PBI with cage-like NH2-POSS significantly enhanced the electrochemical H2/CO2 and H2/CO separation at 160°C. The hydrogen separation of the NH2-POSS-capped p-PBI system required a relatively small amount of energy, and the system exhibited a good dynamic response. The favorable interfacial interaction between the NH2-POSS and the p-PBI host, high thermomechanical stability, and good fuel-cell and hydrogen-separation performance at high temperatures up to 160°C indicate the applicability of the NH2-POSS-capped p-PBI membranes to electrochemical power generation and hydrogen pumps for practical industrial applications in harsh and extreme environments.

In Situ Synthesis of Ag–Fe3O4 Nanoparticles Immobilized on Pure Cellulose Microspheres as Recyclable and Biodegradable Catalysts

The preparation of reusable and eco-friendly materials from renewable biomass resources such as cellulose is an inevitable choice for sustainable development. In this work, cellulose was dissolved in 7 wt % NaOH/12 wt % urea aqueous solution at −12 °C with rapid stirring. Cellulose microspheres (Cels) were fabricated by a sol–gel transition method. Subsequently, novel magnetic Ag–Fe3O4 nanoparticles (NPs) supported on cellulose microspheres were successfully constructed by an in situ one-pot synthesis. The magnetic cellulose microspheres (MCels) displayed a spherical shape with mesoporous structure and had a narrow particle size distribution (10–20 μm). Many nanopores with a pore diameter of 5–40 nm were observed in MCels. The Ag–Fe3O4 NPs were immobilized by anchoring with the hydroxyl groups on the surface of Cels. MCels were applied as a microreactor to evaluate their catalytic activities. 4-Nitrophenol (4-NP) could be reduced to 4-aminophenol (4-AP) in 5 min, catalyzed by MCels. Moreover, the magnetic microspheres exhibited a small hysteresis loop and low coercivity. Thus, MCels could be quickly gathered in water under a magnetic field in 10 s, as well as almost 9 cycle times, maintaining relatively high catalytic activity. In this work, cellulose matrix as the catalyst support could be biodegraded completely in the environment. It provided a green process for the utilization of biomass in nanocatalytic applications.

Construction of physically crosslinked chitosan/sodium alginate/calcium ion double-network hydrogel and its application to heavy metal ions removal

Abstract Chemical hydrogels have been extensively applied to the removal of heavy metal pollutants. However, most of chemical hydrogels inevitably contain toxic chemical crosslinker residues, which impose serious threats on the environment. Herein, a novel eco-friendly physically-crosslinked double-network hydrogel of chitosan/sodium alginate/calcium ion (CTS/SA/Ca2+ PCDNH) was prepared by the combination of the semi-dissolution acidification sol–gel transition method with the internal gelation method. The PCDNH is formed via the physical crosslinking of sustainable biopolymers, which avoids the excessive use of toxic chemical reagents. In addition, the PCDNH exhibits significantly better mechanical properties than the single-network physical hydrogel crosslinked via electrostatic interactions, which overcomes the weak mechanical properties of physical hydrogels. The formation mechanism and structure of the hydrogel were determined by Fourier-transform infrared spectroscopy (FTIR), 13C solid state nuclear magnetic resonance spectroscopy (13C-SSNMR) and scanning electron microscopy (SEM). The heavy metal ions adsorption mechanism was explored by X-ray photoelectron spectroscopy (XPS) analysis. The adsorption kinetics, isotherms and thermodynamics were further studied to understand the adsorption mechanism. Our work has provided a new method for the fabrication of natural polymers-based eco-friendly, low-cost and robust physical hydrogels for the heavy metal ions removal.

Preparation, characterization and long-term antibacterial activity of nisin anchored magnetic cellulose beads

Along with the concerns for food safety and environment, the demand of cost-effective and biodegradable materials in food treatment is increasing. In order to solve the problem of certain spoilage microorganisms, nisin anchored cellulose beads were prepared by a sol–gel transition method. By mixing γ-Fe2O3 nanoparticles with cellulose in 8% LiOH·H2O/15% urea aqueous solution precooled at − 20 °C, regenerated cellulose beads mixed with γ-Fe2O3 nanoparticles (RC) were fabricated via a dropping technology. Subsequently, cellulose beads were oxidized by sodium periodate in dark room and nisin was anchored on the beads (NCs) through Schiff base reaction. The oxidization process and grafting reaction between the amino groups of nisin and the aldehyde groups of oxidized cellulose were confirmed via Fourier transform infrared spectra, field emission scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction. The beads containing γ-Fe2O3 nanoparticles exhibits the sensitive magnetic response and excellent thermal stability with decomposition temperature over 200 °C. A long-term antimicrobial activity against Alicyclobacillus acidoterrestris DSM 3922 were investigated. To the best of our knowledge, this is the first report of such nisin-anchored beads. The biodegradable nisin-anchored beads are novel antimicrobial materials with great potential in food industry.

Cellulose microspheres-filled pipet tips for purification and enrichment of glycans and glycopeptides

The pretreatment of low-abundance glycans/glycopeptides prior to mass spectrometry (MS) analysis is of great significance for glycosylation identification of proteins. Herein, a simple one-step purification and enrichment procedure of glycans and glycopeptides was achieved using cellulose microspheres-filled pipet tips (CM-PTs). CM-PTs were fabricated by conveniently filling cellulose microspheres synthesized by sol-gel transition method into 100 μL pipet tips. The whole enrichment and purification process were completed within two minutes by pipetting up and down for dozens of times (30–40), followed by the direct analysis of MALDI TOF-MS. Upon the assessment of model glycoproteins, including human immunoglobulin G (IgG) and horse radish peroxidase (HRP), the CM-PT method exhibited good selectivity (IgG/BSA = 1:100), high sensitivity (1 ng μL−1 of IgG), large binding capacity (125 mg g−1, IgG/cellulose microspheres) and excellent reproducibility in glycopeptide enrichment. The capability for purifying glycans of CM-PTs was also investigated, presenting high binding capacity (8 mg g−1, maltoheptaose/cellulose microspheres) and good recoveries (81.3–89.8%). The developed in-pipet-tip system shows a great potential in efficient and high-throughput analysis of protein glycosylation.

Preparation of the polyelectrolyte complex hydrogel of biopolymers via a semi-dissolution acidification sol-gel transition method and its application in solid-state supercapacitors

Hydrogels have drawn many attentions as the solid-state electrolytes in flexible solid-state supercapacitors (SCs) recently. Among them, the polyelectrolyte complex hydrogel (PECH) electrolytes of natural polymers are more competitive because of their environmentally friendly property and low cost. However, while mixing two biopolymer solutions with opposite charges, the strong electrostatic interactions between the cationic and anionic biopolymers may result in precipitates instead of hydrogels. Here we report a novel method, semi-dissolution acidification sol-gel transition (SD-A-SGT), for the preparation of the PECH of chitosan (CTS) and sodium alginate (SA), with the controllable sol-gel transition and uniform composition and successfully apply it as the hydrogel electrolyte of solid-state supercapacitors (SCs). The CTS-SA PECH exhibits an extremely high ionic conductivity of 0.051 S·cm−1 and reasonable mechanical properties with a tensile strength of 0.29 MPa and elongation at break of 109.5%. The solid-state SC fabricated with the CTS-SA PECH and conventional polyaniline (PANI) nanowire electrodes provided a high specific capacitance of 234.6 F·g−1 at 5 mV·s−1 and exhibited excellent cycling stability with 95.3% capacitance retention after 1000 cycles. Our work may pave a novel avenue to the preparation of biodegradable PECHs of full natural polymers, and promote the development of environmentally friendly electronic devices.

Agar/gelatin bilayer gel matrix fabricated by simple thermo-responsive sol-gel transition method

We present a simple and environmentally-friendly method to generate an agar/gelatin bilayer gel matrix for further biomedical applications. In this method, the thermally responsive sol-gel transitions of agar and gelatin combined with the different transition temperatures are exquisitely employed to fabricate the agar/gelatin bilayer gel matrix and achieve separate loading for various materials (e.g., drugs, fluorescent materials, and nanoparticles). Importantly, the resulting bilayer gel matrix provides two different biopolymer environments (a polysaccharide environment vs a protein environment) with a well-defined border, which allows the loaded materials in different layers to retain their original properties (e.g., magnetism and fluorescence) and reduce mutual interference. In addition, the loaded materials in the bilayer gel matrix exhibit an interesting release behavior under the control of thermal stimuli. Consequently, the resulting agar/gelatin bilayer gel matrix is a promising candidate for biomedical applications in drug delivery, controlled release, fluorescence labeling, and bio-imaging.

Probiotics in cellulose houses: Enhanced viability and targeted delivery of Lactobacillus plantarum

Cellulose-based microgels, prepared by the sol-gel transition method, were evaluated to extent the loading capacity and make more controlled release of probiotics. Granules of calcium carbonate as porogenic agents made the cellulose microgels with different porosity, and the SBET of modified cellulose microgels was increased to 197 m2/g. The microgels were constituted by the interconnected network of the cellulose nanofibrils, which was house-like. The house-liked microgels had the ability for the accommodation of Lactobacillus plantarum (L. plantarum) as high as 1010 cfu/g, and the released viable cells was up to 3.10 × 1010 cfu/g. Furthermore, the Ca-alginate shell protection of the cellulose houses kept the loaded L. plantarum cells from liberating into stomach but released the cells at intestinal tracts due to the effect of pH-responsibility. From the cross-sectional fluorescence image, L. plantarum cells mainly focused on the cellulose microgels houses instead of Ca-alginate shell. It indicated that the surface modification of the cellulose microgels houses by using alginate based hydrogel exhibited more controlled release of L. plantarum cells, which could be increased to 5.80 × 108 cfu/mL at 360 min. Prolonged duration in simulated intestine fluid contributed to making sure that cells reached the desired region of intestine tracts. The designed composite system advances in affording better shelter for probiotic residence or other bioactive nutrients.

Porous Cellulose Microgel Particle: A Fascinating Host for the Encapsulation, Protection, and Delivery of Lactobacillus plantarum.

Advances in probiotic markets are always restrained by a low viable loading capacity and poor viability. Herein, cellulose microgels (CMs) with high porosity of 95.83 ± 0.38%, prepared by the sol-gel transition method, turned out to be a hospitable host that accommodated a large number of viable Lactobacillus plantarum higher than 10(9) colony-forming units (cfu)/g. The unique porous structure fascinated probiotics to penetrate into the core of microgels. The conjugation with alginate helped for better acid resistance and bacterial survival of the probiotics. In comparison to Ca-alginate gels, core-shell gels showed sustainable release of L. plantarum cells without damage of viability, lasting for 360 min in simulated intestine fluid. The cellulose host helped to sustain the viable cell release for a longer duration and afford better shelter for L. plantarum cells as a result of the porous structure and rigid supporting property. The core-shell gels are promising for constructing targeted delivery vehicles of bioactive nutrients.

Preparation and properties of Sr2Si5N8:Eu2+–cellulose hybrid films for sunlight conversion

Sr2Si5N8:Eu2+–cellulose hybrid films were successfully prepared, by use of a green sol–gel transition method, from cellulose and a sunlight-conversion agent. Cellulose quickly dissolved in 7 wt% NaOH–12 wt% urea aqueous solution at low temperature, as a result of a fast dynamic self-assembly process. The Sr2Si5N8:Eu2+ particles were embedded firmly in the cellulose matrix, as a consequence of a strong interaction between the cellulose and the particles. Results from scanning electron microscopy, absorption spectroscopy, fluorescence spectroscopy, and tensile testing confirmed the hybrid films had a homogenous structure, wide absorption, strong fluorescence emission, and good tensile properties. Moreover, fluorescence spectroscopy confirmed that the excitation and the emission intensity of films were related to the concentration of the Sr2Si5N8:Eu2+. The mechanical properties could be improved by adjustment of the concentration of Sr2Si5N8:Eu2+. This work has provided a new method for preparation of sunlight-conversion films; the process has potential for large-scale application and is expected to be used in greenhouse planting.

Fabrication of chitin microspheres and their multipurpose application as catalyst support and adsorbent.

In this study, novel chitin microspheres (CM) with diameters of 1010 μm, 750 μm, 490 μm, 280 μm were fabricated by employing the sol-gel transition method. Then the chitin microspheres served as the enabling platform for a range of applications including recyclable catalyst support and adsorbent. First, the freeze dried porous chitin microspheres were coated with dopamine to enhance the loading efficiency of a model biomacromolecule, α-amylase. The immobilized enzyme (49.6 mg/g) retained more than 95% of relative activity after 10 repeated cycles and exhibited easy recovery ability. Then porous magnetic chitin microspheres could be prepared, and the swollen porous polymer successfully controlled the growth of gold nanoparticles. The chitin/Au nanocomposite microspheres were a good recyclable catalyst due to the porous structure and a reduced dimension of the metal particles (r ≤ 5 nm). Finally, the magnetic chitin microspheres were modified into an adsorbent for enhanced removal of a typical cationic compound, methylene blue from aqueous solution.

Synthesis of novel magnetic cellulose-chitosan composite microspheres and their application in laccase immobilization.

Novel magnetic cellulose-chitosan composite microspheres were prepared by sol-gel transition method using ionic liquids as solvent for dissolution and regeneration. Subsequently, the composite microspheres activated by glutaradehyde to immobilize enzyme. Which of their structure, properties and morphology were studied by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating-sample magnetometer showed Fe3O4 nanoparticles with mean size of -10 nm were successfully embedded in the composite microspheres. The microshpheres were examined to be with the mean size of 20 μm and good magnetic property with saturation magnetization of 30.1 emu g(-1). The effect of pH and temperature on the immobilization of laccase was also investigated. Compared with free laccase, the pH, thermal and operational stabilities of the immobilized laccase were improved and the activity recovery of immobilized laccase reached 80.6%. Immobilized laccase retained 88.9% activity after 12 reaction cycles. Therefore, the cellulose-chitosan composite microspheres were expected to be a novel support for enzyme immobilization.