Novel approach of silica-PVA hybrid aerogel synthesis by simultaneous sol-gel process and phase separation

Adsorption and immobilization of phosphorus in eutrophic lake water and sediments by a novel red soil based porous aerogel

To effectively mitigate global eutrophication in lakes, regulating sedimentary phosphorus release remains a primary strategy. Enhancing the adsorption and stabilization performance of passivating agents is integral to addressing endogenous phosphorus pollution in aquatic systems. This study presents a novel aerogel with a high specific surface area (663.06 m²/g) and a mean pore size of 2.78 nm, synthesized from cost-effective and abundant red soil. Batch experiments demonstrated that the red soil aerogel (RSA) achieved a maximum phosphorus adsorption capacity of 23.29 mg P/g, surpassing lanthanum-modified bentonite (LMB) by 1.5 times. The RSA exhibited phosphorus removal efficiencies between 82 % and 97 % across a pH range of 4 to 9. Moreover, RSA retained a removal rate exceeding 95 % in the presence of common ions (SO42-, Cl-, and NO3-) at concentrations of 100 mg/L, showing minimal performance reduction even under high HCO32- concentrations. The comprehensive analysis identifies electrostatic attraction, ligand exchange, and Lewis acid-base interactions as the primary mechanisms driving phosphate adsorption onto the RSA surface. RSA exhibited a strong capacity to immobilize phosphorus within sediments, achieving an 83.0 % to 97.5 % reduction in endogenous phosphorus release into the overlying lake water and promoting the conversion of mobile phosphorus into NaOH-P. After 38 days of hypoxic incubation, active phosphorus levels in surface sediments were reduced by over 60 % compared to the control group. The findings highlight RSA's potential as an effective passivating agent for mitigating internal pollution. This study presents a cost-efficient porous silicon-aluminum aerogel with high phosphorus adsorption efficiency, synthesized using the readily available red soil from southern China, offering a viable strategy to address endogenous phosphorus release in eutrophic lake environments.

Foamy Melamine Resin-Silica Aerogel Composite-Derived Thermal Insulation Coating

A novel class of SiO2 aerogel-based resin composite with a self-formed foamy structure and an extremely low thermal conductivity, as well as excellent fire resistance, was fabricated via a room temperature and atmospheric pressure route. The self-formed foamy structure was achieved by utilizing SiO2 aerogel particles not only as a thermal insulative functional additive filler but also as nano-sized solid particles in a Picking emulsion system, adjusting the surface tension as a stabilizer at the interface between the two immiscible phases (liquid and air in this case). The results of foamy structure analyses via scanning electron microscopy, micro-CT, and N2 adsorption-desorption isotherms validate the successful generation of a micro-scale porous structure with the enhancement of the aerogel nano-scale solid particles at the wall as a stabilizer. A combination of multiscale pores imbues the aerogel-based foamy coating with a low thermal conductivity, as well as a high cohesive strength. For the foamy coating studied, with variable emulsion/foaming agent/aerogel ratios of 1/2/x, the thermal conductivity decreases from 0.141 to 0.031 W/m·K, and the cohesive strength increases from being non-detectable to 0.41 MPa. The temperature difference, which is a direct indicator of the thermal insulation behavior of the foamy coating, can increase from 12.1 °C to 48.6 °C under an 80 °C hot plate.

Strength enhanced expandable polyvinyl alcohol/chitosan cryogel for non-compressible hemostasis

For penetrating and deep non-compressible bleeding, hemostatic materials need to meet the demand of easy filling and rapid expansion to close the wound. However, developing an expandable material with sufficient mechanical strength remains a challenge. This study proposed an improved non-solvent induced phase separation (NIPS) method to prepare polyvinyl alcohol/chitosan (PVA/CS) cryogel with large pore structure (70-75 um) and enhanced mechanical properties. The pore structure on the surface enables blood to quickly enter the dry and shape-fixed PVA/CS cryogel, triggering volume expansion. By regulating the hydrogen bond of PVA molecules by CS, the hydrophilia of cryogel was enhanced and the full volume recovery time of PVA/CS15% was shortened (27 ± 3 s). The aggregation of PVA molecular in solution enhances the crosslinking, endowing the prepared PVA/CS cryogel with good mechanical properties. The tensile strength of PVA/CS cryogel is up to 0.694 ± 0.044 MPa, and the compressive strength reach to 0.32 ± 0.04 MPa with 75 % compression. The good mechanical properties are beneficial for providing physical support. The preparation method does not require the introduction of toxic chemical cross-linking agents and complicated operation process, which has potential applications in non-compressible hemostasis.

Sol-Gel Synthesis of Silica-Poly (Vinylpyrrolidone) Hybrids with Prooxidant Activity and Antibacterial Properties

The present work deals with the sol-gel synthesis of silica-poly (vinylpyrrolidone) hybrid materials. The nanohybrids (Si-PVP) have been prepared using an acidic catalyst at ambient temperature. Tetramethyl ortosilane (TMOS) was used as a silica precursor. Poly (vinylpyrrolidone) (PVP) was introduced into the reaction mixture as a solution in ethanol with a concentration of 20%. The XRD established that the as-prepared material is amorphous. The IR and 29Si MAS NMR spectra proved the formation of a polymerized silica network as well as the hydrogen bonding interactions between the silica matrix and OH hydrogens of the silanol groups. The TEM showed spherical particle formation along with increased agglomeration tendency. The efficacy of SiO2/PVP nanoparticles as a potential antimicrobial agent against a wide range of bacteria was evaluated as bacteriostatic, using agar diffusion and spot tests. Combined effects of hybrid nanomaterial and antibiotics could significantly reduce the bactericidal concentrations of both the antibiotic and the particles, and they could also eliminate the antibiotic resistance of the pathogen. The registered prooxidant activity of the newly synthesized material was confirmative and explicatory for the antibacterial properties of the tested substance and its synergetic combination with antibiotics. The effect of new hybrid material on Crustacea Daphnia magna was also estimated as harmless under concentration of 0.1 mg/mL.

Non-crosslinked systems modulate the gel behavior and structural properties of chitosan/silica composite aerogels

The aim of this study was to achieve rapid gelation of chitosan (CS) and silica (SA) without crosslinking agent, the relationship between process parameters and the composite aerogels properties were also explored. By varying the composition ratio of the system (from SA:CS = 1:1 to 5:1), the system gelation time was reduced by >12 times, and the drying shrinkage of the composite aerogel reached a minimum of 7.6 %. During the two recombination processes, chitosan rapidly formed aqueous colloid secondary structure under the influence of ethanol. This phenomenon reduced the stability of the system and allowed silica to form a two-phase composite hydrogel. Because the network gap between the fibers was used as a limiting medium for gel growth. In addition, the chitosan/silica composite aerogels exhibited a mesoporous structure with low density (0.1144 g/cm3), and the thermal conductivity was 0.028 W/(m·K) at 30 °C. The trimethylchlorosilane made the composite aerogel have good hydrophobicity with water contact angle as 134.7°, and the adsorption capacity of carbon tetrachloride could reach >10 times of its own weight. This study provides an eco-friendly and high-efficiency method for preparing aerogels, which has potential applications in the fields of thermal insulation, oil-water separation, etc.

Promoting microbial fermentation in lignocellulosic hydrolysates by removal of inhibitors using MTES and PEI-modified chitosan-chitin nanofiber hybrid aerogel

To further enhance the removal efficiency for furanic and phenolic compounds in lignocellulosic hydrolysates, a new detoxification strategy was proposed, which retained fermentable sugars and promoted the growth and metabolism of subsequent bacteria. The best adsorbent (P/M-CCA) was prepared by hybrid chitosan-chitin nanofiber, graft modification with polyethylenimine, and silanization with methyl triethoxylsilane in order. Taken corn cob hydrolysate as object, the removal rates of HMF and furfural were 85.1 % and 99.0 %, respectively. The removal rates of six out of nine phenolic inhibitors were 100 %, and the other three were more than 65 %. Even better, the retention rates of glucose and xylose were both 100 %. In contrast to no growth in undetoxified hydrolysates, Bacillus coagulans grew normally in detoxified hydrolysates, and lactic acid reached 19.1 g/L after 12 h fermentation. P/M-CCA achieves both removal of multiple inhibitors and retain sugars, which would promote the valorization of highly toxic lignocellulosic hydrolysates.

Emerging Trends in Nanotechnology: Aerogel-Based Materials for Biomedical Applications

At present, aerogel is one of the most interesting materials globally. The network of aerogel consists of pores with nanometer widths, which leads to a variety of functional properties and broad applications. Aerogel is categorized as inorganic, organic, carbon, and biopolymers, and can be modified by the addition of advanced materials and nanofillers. Herein, this review critically discusses the basic preparation of aerogel from the sol-gel reaction with derivation and modification of a standard method to produce various aerogels for diverse functionalities. In addition, the biocompatibility of various types of aerogels were elaborated. Then, biomedical applications of aerogel were focused on this review as a drug delivery carrier, wound healing agent, antioxidant, anti-toxicity, bone regenerative, cartilage tissue activities and in dental fields. The clinical status of aerogel in the biomedical sector is shown to be similarly far from adequate. Moreover, due to their remarkable properties, aerogels are found to be preferably used as tissue scaffolds and drug delivery systems. The advanced studies in areas including self-healing, additive manufacturing (AM) technology, toxicity, and fluorescent-based aerogel are crucially important and are further addressed.

Diffusion/Reaction Limited Aggregation Approach for Microstructure Evolution and Condensation Kinetics during Synthesis of Silica-Based Alcogels

A base-catalysed methyltrimethoxysilane (MTMS) colloidal gel formation was implemented as a cellular automaton (CA) system, specifically diffusion and/or reaction-limited aggregation. The initial characteristic model parameters were determined based on experimental synthesis of MTMS-based, ambient-pressure-dried aerogels. The applicability of the numerical approach to the prediction of gels' condensation kinetics and their structure was evaluated. The developed model reflects the kinetics properly within the investigated chemical composition range (in strongly reaction-limited aggregation conditions) and, to a slightly lesser extent, the structural properties of aggregates. Ultimately, a relatively simple numerical model reflecting silica-based gel formation was obtained and verified experimentally. The CA simulations have proved valid for understanding the relation between the initial chemical composition and kinetics constants of MTMS-based synthesis and their impact on secondary particle aggregation process kinetics.

Understanding the mechanism and kinetics of the formation and breaking of ring structures during silica polymerization: a computational study

Ring structures are ubiquitous in porous materials and play a crucial role in the functioning of these materials. Understanding the ring formation and breaking mechanism is essential for designing and controlling the porosity, framework density, channels, and cage formation in porous materials. The current work attempts to understand the formation, breaking, and survival of rings using a computational approach. We have used the reaction ensemble Monte Carlo simulation technique and studied silica polymerization starting from monomers to inter-connected large silica clusters in dilute and concentrated silica systems. We calculated various properties of representative smaller and bigger rings at different stages of polymerization. We found that smaller rings form in the initial polymerization stages and larger ring sizes appear at later stages. The smaller rings have a larger residence time than the bigger rings in the silica system, and the residence time changes with the polymerization stage. Both smaller and bigger rings have a shorter residence time in the dilute system than the concentrated silica system. As a result, ring formation and breaking kinetics are faster in the dilute silica system, which causes reorganization within the silica cluster leading to a dense cluster. A slow reorganization of rings in the concentrated silica system is observed, due to which clusters retain their random, branched configuration and porous region within the cluster. We also investigated a series of ring formation and breaking steps to understand the formation mechanism of isolated and grouped rings in the studied silica systems. We found that rings form and break by all possible reactions during ring-formation and cluster-aggregation stages. In contrast, only one reaction is dominant in the initial and aging stages of polymerization. The concentration of silica affects the formation of isolated rings, whereas the kinetics of a grouped ring is not significantly altered. Detailed insights into the reaction dynamics of rings at various stages of polymerization would be helpful in the rational design of porous silica polymorphs.

Ambient-Dried Silica Aerogel Powders Derived from Coal Gangue by Using One-Pot Method

In this paper, we report a new and convenient method for the synthesis of insulating aerogel by recycling solid waste coal gangue, which can reduce the industrial production cost of silica aerogels and realize high value-added utilization of solid waste. Sodium silicate was prepared from a cheap industrial waste coal gangue as the precursor for silica aerogels, which was used for silica wet gel preparation by a one pot method; this method of solvent exchange/surface modification was carried out quickly by mechanical stirring process, and the wet gels derived from coal gangue were dried under ambient pressure condition. A high surface area (~748 m²/g) nanostructured aerogel with a 3D open porous microstructure was synthesized, which exhibits a low density (~0.18 g/cm³) and a superior thermal insulation performance (~0.033 W·m^-1·K^-1). More significantly, the synthetic yield of silica aerogel powder by recycling coal gangue can reach 92%.

Adsorption desulfurization performance of PdO/SiO2@graphene oxide hybrid aerogel: Influence of graphene oxide

Preparation of PdO/SiO₂@graphene oxide (GO) hybrid aerogels were carried out sol-gel method combined with atmospheric drying technology to study their adsorption performance for thiophenics and compared with PdO/SiO₂. Scanning electron microscope (SEM), N₂ adsorption-desorption isotherms, X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and fourier transformation infrared spectroscopy (FT-IR) for samples were performed. The adsorption performance of PdO/SiO₂@GO for thiophene were better than that of PdO/SiO₂, attributed to that incorporation of GO increased the specific surface area and the Pd incorporation rate, where Pd²⁺ ions acted as the π-complexation and sulfur-metal (SM) bond adsorption active centers, as well as GO adsorbed thiophene by the π-π stacking effect. The adsorption capacities of PdO/SiO₂@GO-1.0 for thiophene (TH), benzothiophene (BT) and dibenzothiophene (DBT) were 8.89, 9.3 and 12.6 mg-S/g_ads, respectively. The addition of GO in aerogels could improve the inhibition effect of toluene, cyclohexene and pyridine while decreased the inhibition effect of MTBE and H₂O for the adsorption of thiophene, due to the π-π stacking effect and the hydrophobicity of GO, respectively. The adsorption process was spontaneous and exothermic, be well fitted by the apparent second-order kinetic model and dominated by chemical interaction. Pd/SiO₂@GO-1.0 had a good solvent elution regeneration performance.

Impact of hydrophilic polymers in organosilica matrices on structure, stability, and biocatalytic activity of immobilized methylotrophic yeast used as biofilter bed

The impact of hydrophilic polymers in an organosilica matrix on the features and performance of immobilized methylotrophic yeast cells used as biocatalysts was investigated and described. Yeast cells were immobilized in a matrix made of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) by one-step sol-gel route of synthesis in the presence of polyethylene glycol (PEG) or polyvinyl alcohol (PVA). Organosilica shells were spontaneously built around cells as a result of yeast immobilization at a TEOS to MTES ratio of 85/15 vol% and hydrophilic polymer (PEG or PVA). As a structure-directing agent, PVA produces organosilica films. Stable high-performance biocatalysts active for one year, if stored at -18 °C, have been obtained by entrapment of methylotrophic yeast cells. A trickling biofilter with and without active aeration was designed using entrapped yeast cells to treat methanol polluted wastewater. A biofilter model with active aeration could halve methanol input thus demonstrating better performance compared to treatment without active aeration.

Application of organosilicate matrix based on methyltriethoxysilane, PVA and bacteria Paracoccus yeei to create a highly sensitive BOD

We have studied immobilization of Paracoccus yeei VKM B-3302 cells in an organosilica sol-gel matrix consisting of tetraethoxysilane, methyltriethoxysilane and polyvinyl alcohol as a structure-modifying agent. Optical microscopy showed that higher amounts of methyltriethoxysilane make the solid material structure softer. In addition, formation of structures, probably, with bacterial cells inside was spotted. We have analyzed the catalytic power of the immobilized bacteria and discovered that the material's catalytic potential is the highest at 50% of methyltriethoxysilane. Therefore, this seems to be the best ratio of precursors in a material for bacteria to become effectively encapsulated. Analysis of the material structure by low-temperature nitrogen absorption and scanning electron microscopy revealed that in the given conditions the material got crack-like mesopores and spherical particles of about 25 µm in diameter with immobilized bacterial cells on their surface. The study found that the fabricated organosilica material can effectively protect bacterial cells against UV radiation, pH change, high salinity and high heavy metal ion concentration.