Stages Of Sol Research Articles

Valorizing brewery industry waste in nanocellulose cryogel-PEG composites for cold chain packaging

Global concerns about food and energy waste call for new sustainable solutions. Phase changing materials (PCM) are promising thermal storage and management materials which have potential to mitigate food waste, yet they often suffer from leakage and non-shape stability. Here, a green shape-stabilized polyethylene glycol 300 (PEG) nanocellulose-based composite was developed using readily available and cost-effective side streams from the brewery industry. Two different routes were examined for the incorporation of PEG into the cellulose nanofiber (CNF) cryogel including adding different dry mass ratios of PEG in the sol stage, with or without physical crosslinking, or adding the PEG after CNF gelation. FTIR and TGA analysis revealed the improved thermal stability of PEG after incorporation into the CNF cryogel. The PEG/CNF composite produced by adding PEG in the gel stage outperformed the other material formulations by demonstrating the highest enthalpy value (93.2 J/g) and the best mechanical properties (Young's modulus of 140 kPa). The package containing the PEG/CNF composite could maintain the meat temperature below 0 °C around 4 times longer than the control package when the cold system was interrupted. Furthermore, the PEG/CNF composite showed a positive effect on the color and drip loss values of frozen meat.

Non-hydrolytic sol-gel synthesis of BaTiO3 nano-powder: Effect of calcination temperature and modified titanium source on particles

In this study, BaTiO3 nanopowders were prepared by non-hydrolytic sol-gel (NHSG) method using barium acetate and tetrabutyl titanate (TBT) as precursors and acetylacetone (Hacac) as additive. The effects of acetylacetone modification and calcination temperature on nanoparticle size and crystalline phase were evaluated. The products were analysed by SEM, TEM, DSC/TG, FTIR, XRD, Raman. FTIR analysis showed the formation of Ba-O-Ti bond at the sol stage of the NHSG method. DSC/TG and XRD analyses showed that BaTiO3 was produced at 500 ℃. According to SEM/TEM, the particle size of the powder becomes larger as the temperature increases, meanwhile the addition of acetylacetone can make the final product particle size decrease. Raman analysis showed that BaTiO3 has the presence of tetragonal phase, so the crystalline phases of the product and impurities were analysed by XRD refinement, and the results showed that the relative content of tetragonal phase of BaTiO3 was linearly correlated with the calcination temperature.

Bone Formation on Murine Cranial Bone by Injectable Cross-Linked Hyaluronic Acid Containing Nano-Hydroxyapatite and Bone Morphogenetic Protein.

New injection-type bone-forming materials are desired in dental implantology. In this study, we added nano-hydroxyapatite (nHAp) and bone morphogenetic protein (BMP) to cross-linkable thiol-modified hyaluronic acid (tHyA) and evaluated its usefulness as an osteoinductive injectable material using an animal model. The sol (ux-tHyA) was changed to a gel (x-tHyA) by mixing with a cross-linker. We prepared two sol-gel (SG) material series, that is, x-tHyA + BMP with and without nHAp (SG I) and x-tHyA + nHAp with and without BMP (SG II). SG I materials in the sol stage were injected into the cranial subcutaneous connective tissues of mice, followed by in vivo gelation, while SG II materials gelled in Teflon rings were surgically placed directly on the cranial bones of rats. The animals were sacrificed 8 weeks after implantation, followed by X-ray analysis and histological examination. The results revealed that bone formation occurred at a high rate (>70%), mainly as ectopic bone in the SG I tests in mouse cranial connective tissues, and largely as bone augmentation in rat cranial bones in the SG II experiments when x-tHyA contained both nHAp and BMP. The prepared x-tHyA + nHAp + BMP SG material can be used as an injection-type osteoinductive bone-forming material. Sub-periosteum injection was expected.

Effect of Ag Content on Photocatalytic Activity of Ag@TiO2/rGO Hybrid Photocatalysts

In this study, silver (Ag)-doped titanium dioxide/reduced graphene oxide (Ag@TiO2/rGO, TGA) hybrid photocatalysts were synthesized for enhanced photocatalytic properties. TGA hybrid photocatalysts were synthesized through a facile sol–gel method. Synthesis of graphene oxide (GO) nanoparticles were obtained by Hummer’s method followed by chemical reduction to obtain rGO nanoparticles. Ag doping was carried out at the sol stage of the sol–gel synthesis. Increasing amounts of Ag nanoparticles from 0.5 wt.% to 4 wt.% were added to increase the degradation effect of methylene blue (MB) under UV light irradiation. X-ray diffractometry (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), UV-vis spectrophotometry, photoluminescence spectroscopy (PL), and diffuse reflectance spectroscopy (DRS) were used to investigate the crystal structure, topography, morphology, chemical and optical properties of the samples, respectively. Samples were calcined in order to obtain the anatase phase at 500°C with a heating rate of 10°C/min for 2 h in air atmosphere. The effect of Ag content on the photocatalytic properties of TiO2 based nanocomposite material was observed by keeping the weight ratio of rGO constant at 4 wt.%. Ag addition into the TiO2/rGO matrix exposed an excellent photocatalytic activity under UV light irradiation than that of undoped TiO2/rGO photocatalyst. The absorbance value of MB was degraded from 0.683 to 0.011 at 664 nm by TGA1 sample for 240 min. This demonstrated that the TGA1 hybrid photocatalyst containing 1 wt.% of Ag exhibited the highest degradation efficiency of 98.4%. This paper indicates the potential photocatalytic application of Ag-doped TiO2/rGO photocatalysts on the removal of dissolved organic pollutants in water.

Characterization of Multimodal Silicas Using TG/DTG/DTA, Q-TG, and DSC Methods

The formation of hierarchical, multimodal porosity materials with controlled shape and size of pores is the essential challenge in materials science. Properties of silica materials depend largely on different features: crystal structure, dispersity, surface composition, and porosity as well as the method of preparation and possible modification. In this paper, multimodal silicas obtained using different additives are presented. A-50 and A-380 aerosils and wide-porous SiO2 milled at 300 rpm were used as the additives in the sol stage at 20 °C, the sol–gel stage followed by hydrothermal modification (HTT) at 200 °C, or in the mechanochemical treatment (MChT) process. The characterizations were made by application of N2 adsorption/desorption, SEM imaging, quasi-isothermal thermogravimetry (Q-TG), dynamic thermogravimetry/derivative thermogravimetry/differential thermal analysis (TG/DTG/DTA), and cryoporometry differential scanning calorimetry (DSC) methods. Results showed that such a one-step preparation method is convenient and makes it possible to obtain multimodal silicas of differentiated porous structures and surface chemistry.

Synthesis and characterization of composite materials “aerogel-MWCNT”

Composite materials “aerogel—multi-walled carbon nanotubes” were prepared and characteristics of these materials were investigated. Multi-walled carbon nanotubes were embedded into silica and alginate aerogels at stage of sol. Effects of the multi-walled carbon nanotubes embedding on porosity, specific surface area and pore size distribution were analyzed. Multi-walled carbon nanotubes concentration ranged from 0 to 4.5 wt% for silica aerogel and from 0 to 30 wt% for alginate aerogel. It was observed that multi-walled carbon nanotubes occupy pores with diameter of 30–40 nm that correspond to the carbon nanotube diameter. BET analysis using nitrogen adsorption revealed the specific surface areas within 737–780 m2/g range for the composite “silica aerogel—multi-walled carbon nanotubes” and 317–459 m2/g range for the composite “alginate aerogel—multi-walled carbon nanotubes”.

Modified sol–gel processed silica matrix for gel electrophoresis applications

Modified sol–gel processed silica matrices were prepared to explore the possibilities of using these matrices for electrophoresis applications. The sol–gel was prepared at room temperature using tetraethyl orthosilicate as a precursor at different molar ratios (R = 4, 16, 32 and 64) in the presence of sodium phosphate buffer. The sol–gel derived from R = 32 formed smooth and transparent gel, and showed high transmittance value (97%) compared to other molar ratios. Transmission electron microscopy and scanning electron microscopy studies of gel matrix (R-32) confirmed randomly distributed interstitial space of variable size (30–60 nm) with slit like openings on the gel surface. The R = 32-based matrix internal and surface characteristics were suitable for gel electrophoresis. Therefore, sol–gel electrophoresis was carried out using gel matrix (R = 32) on molecular markers and pre-stained proteins (08–220 kDa). The silica gel matrix allowed migration as well as separation of proteins based on their molecular weights. The results were compared with standard gels (agarose and polyacrylamde). The aim of the work to prepare a silica matrix suitable for gel electrophoresis which could be utilised to develop electrophoresis-based point-of-care technologies for clinical diagnostics. Schematic illustration of sol–gel electrophoresis (SoGE), showing different stages of sol–gel preparation and its utilisation for separation of proteins 8–220 kDa.

‘U-spectrum’ type of Gd(III) EPR spectra recorded at various stages of TEOS-based sol–gel process

The various stages of the tetraethyl orthosilicate-based sol–gel process were studied using Gd(III) cations as a spin probe, using EPR spectroscopy at ambient and liquid nitrogen temperatures. The Gd(III) EPR spectra (being of the ‘U-spectrum’ type) were very similar, as recorded at 77 K, at the various defined stages of the sol–gel process. The analysis of the experimental EPR spectra showed that as the sol–gel process proceeded, the spin Hamiltonian parameters remained unchanged, but the relative amplitude of the α-line (at g ~ 2.8) and β-line (at g ~ 2.0) changed significantly, such that the α/β-ratio decreased progressively. This is the first report that the silica sol-to-gel transition from the low viscosity, starting reaction mixture, to the high viscosity, colloid suspension, up to the viscoelastic gel and finally to the dry gel, can be successfully monitored using Gd(III) EPR spectroscopy.

Wollastonite ceramics with bimodal porous structures prepared by sol–gel and SPS techniques

In this work, we suggest a novel synthetic route combining sol–gel and SPS for the fabrication of porous ceramics based on wollastonite with bimodal pore size distributions (100–500 nm and 1–500 μm) and high mechanical strength (Young's modulus from 72.5 to 172 MPa). We studied peculiarities in the formation of the biporous silicate framework using two types of pore forming additives (templates) of various natures, shapes and sizes, introduced during different stages of sol–gel and SPS synthesis: organo-nonorganic (polymer latex of “core–shell” type) and nonorganic (carbonaceous filler). The influence of carbonaceous template content (5% or 25%) on the structural and mechanical properties of ceramics synthesized by spark plasma current was described. The original approach presented here provides formation of wollastonite ceramics with high mechanical strength and a biporous structure that is similar to the texture of bone tissue and is capable of executing its main functions. The obtained ceramics meet all the requirements of the bioceramics class demanded by modern medicine.

Structural Change of Methyltrimethoxysilane in the Early Stage of Sol–Gel Coating via Silsesquioxane

Abstract Structural change of methyltrimethoxysilane (MTMS), which can form sol–gel coating films via silsesquioxane, was investigated to elucidate the mechanism of coating at the early stage. Although films that can be used for sol–gel coating can be formed only after heating at about 100 °C for an hour, growth of nanoparticles was detected in the MTMS solutions at room temperature by static and dynamic light scattering. The existence and growth of nanoparticles were also confirmed by other measurements.

Monitoring the Tetraethyl Orthosilicate (TEOS)-Based Sol–Gel Process with Cu(II) Ions as a Spin Probe

The various stages of the tetraethyl orthosilicate-based sol–gel process were investigated using electron paramagnetic resonance (EPR) spectroscopy with Cu(II) cations as a spin probe. The latter were introduced to the starting reaction mixture in the form of various copper(II) salts containing anions of different basicity (CuCl2, Cu(ac)2, or CuSO4). At the various defined stages of the sol–gel process, the experimental EPR spectra, recorded at both ambient and liquid nitrogen temperature, were found to be a superimposition of three main types of individual subspectra (Γ 1, Γ 2, and Φ), which reflect the different local environment in which the Cu(II) ions were located. The spin Hamiltonian parameters of each individual subspectrum remained identical, within experimental error, throughout the various stages of the sol–gel process. In contrast, the relative proportion of the individual subspectra varied significantly as the sol–gel process proceeded, from which the liquid-state to solid-state transition could be monitored as it occurred in the sol–gel reaction medium. Identical results were obtained, irrespective of the nature of the copper(II) salt employed. The results demonstrate that the EPR method provides an effective means with which to monitor the sol-to-gel transition from the viscous, colloid suspension to the final viscoelastic gel.

Non-VOC Water-Based Nanocomposite Sol-Gel Thin Films for Corrosion Protection of Commercial Magnesium Alloys

Novel non-VOC and non-chromate water-based organic-inorganic hybrid thin films doped with ZrO2 nanoparticles have been successfully prepared for corrosion protection of AZ31 and AZ61 magnesium alloys. These nanocomposite thin films were synthesized by sol-gel process. The organosiloxane sols were obtained by mixing of 3-glycidoxypropyltrimethoxysilane (GPTMS) and methyltriethoxysilane (MTEOS). Additionally these hybrid sols were doped with ZrO2 nanoparticles prepared from hydrolyzed zirconium tetra-tert-butoxide (ZTB). Different concentrations ZrO2 have been tested in order to obtain several experimental materials. For properly preparing the organosilane coating, hexamethoxymethylmelamine (HMMM) has been added to the solution during the sol stage. Small aliquots of p-toluenesulphonic (p-TSA) were also added to coating formulation just before coating. HMMM acts as a crosslinking agent and p-TSA as a blocked acid catalyst. In a second stage of the study a set of these ZrO2 nanocomposite thin films has been modified by adding to the sols variable amounts of corrosion inhibitors (benzotriazole, L-cysteine). The thermal stability of the prepared hybrids was investigated by using thermal analysis (TG/DTG). Attenuated total reflectance Fourier transformer infrared spectroscopy (FTIR-ATR) has been used to determine which functional groups are present in coatings. The hydrophobic behaviour of coatings was evaluated by contact angle measurements. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) microanalysis have been applied to study the surface morphology and composition of coated samples. Thickness of the sol-gel coatings was determined using cross-section SEM images. Atomic-force microscope (AFM) has been used for obtaining 3D topography images and for calculating the root-mean-squared roughness (RMS roughness) of both bare and sol–gel coated surfaces. The corrosion behaviour of the resulting metal/coating systems was studied by immersion tests in NaCl aqueous solutions at different concentrations and variable exposure time. The obtained results show that the combination of XPS, SEM/EDX and AFM with global and local electrochemical impedance spectroscopies (EIS and LEIS) allow not only to assess the protective ability of these new water-based sol-gel thin films but also the influence of inhibitors added to the films on the kinetics and mechanisms of corrosion of the metal substrates. The ZrO2 nanoparticles act as active nanoreservoirs providing a prolonged and smart release of corrosion inhibitors during contact of the sol-gel thin film with NaCl aqueous solutions. The organic inhibitors provide self-healing properties to the protective system suppressing the corrosion processes as expected. This self-healing mechanism can be ascribed to sealing or absorption phenomena which take place on the bare metal surface into the micropores and defects developed on the sol-gel coatings during the immersion tests in the NaCl aqueous solutions. The water-based sol-gel films modified with benzotriazole were the most effective but controlling appropriately the formulation of films, L-cysteine could be used as an environmentally friendly inhibitor for potential replacement to benzotriazole.

Tetraethyl orthosilicate (TEOS)-based sol–gel process monitored by EPR spectroscopy with VO(II) cations as a spin-probe

The various stages of the TEOS-based sol–gel process were studied by EPR spectroscopy using a VO(II) spin-probe. A detailed analysis of the multicomponent VO(II) EPR spectra recorded at 77 K showed that three main types of individual signals appeared superimposed at the various stages of the sol–gel process, which corresponds to different environments of the paramagnetic VO(II) cations. The spin Hamiltonian parameters of each individual subspectrum remain unchanged throughout the various stages of the sol–gel process. However, the relative contribution of individual signals changed significantly as the sol–gel process proceeded. The results show that the VO(II) cations are not directly incorporated into the siloxane network, but are trapped relatively freely as [VO(H2O)5]2+ complexes in a solution-like environment during the evolution of the sol–gel process. It was amply demonstrated that the sol-to-gel transformation from the viscous, colloid suspension to the viscoelastic gel can be successfully monitored by EPR spectroscopy with VO(II) as a spin-probe.

Retraction Note to: Microenvironment characterization for a novel biocompatible hybrid carbon-silicon material

The compatible carbon-silicon complex materials originated from precursor diglycerylsilane (DGS) and sugar-modified silane N-(3-triethoxysilylpropyl)gluconamide (GLS) have gained substantial popularity by demonstrating admirable properties to stabilize entrapped biomolecules. The microenvironment inside these materials, especially the distribution of sugar moieties inside the matrix, which is likely the most critical factor determining compatibility of these materials, still remains unclear. To deeply investigate the biocompatibility mechanism of these materials, we have adopted two different preparation routes for these materials by introducing GLS into the starting DGS sol stage, but things are different after the DGS gel is formed. A fluorescence probe rhodamine 6G is introduced herein in the DGS sol to monitor the distribution of GLS moieties, as well as the evolution of the microenvironment inside resulting materials. All in all, the findings demonstrated that the timing of GLS addition plays a critical role in controlling the evolution of the inner structure of materials, suggesting that this factor provides a promising route to tune the properties of the resulting materials.

Nucleation and fractal growth of zirconium oxo-alkoxy nanoparticles at the induction stage of sol–gel process

Monodispersed zirconium oxo-alkoxy nanoparticles are synthesized via a sol–gel method in a rapid micromixing reactor with in situ particle size measurements. The nucleated nanoparticles of 4.7 nm diameter are free from impurities and conserve high chemical activity. They can be associated in 1D fractals. These nanoparticles can form high optical-quality coatings on hydrophilic substrates.

Multifunctional polymethylsilsesquioxane (PMSQ) surfaces prepared by electrospinning at the sol–gel transition: Superhydrophobicity, excellent solvent resistance, thermal stability and enhanced sound absorption property

Multifunctional superhydrophobic polymethylsilsesquioxane (PMSQ) surfaces with excellent solvent resistance, thermal stability and enhanced sound absorption property were manufactured by electrospinning. The surfaces with various hierarchical morphologies and hydrophobicity were obtained by electrospinning at the different stages of sol–gel transition of PMSQ prepolymer solution. At the stage with a proper viscosity the superhydrophobic PMSQ surface with a contact angle as high as 151° and a sliding angle as low as 8° was prepared. Due to the excellent thermal stability and solvent resistance properties of the cured PMSQ, the resultant surfaces remain superhydrophobicity after thermal treatment at 300°C and immersion into many solvents. Additionally, an enhanced acoustical performance and ultra water repellency were obtained simultaneously when the traditional acoustical sponge was decorated with the electrospun PMSQ superhydrophobic surface. The robust superhydrophobic PMSQ surfaces may promise practical applications in many fields.

RETRACTED ARTICLE: Microenvironment characterization for a novel biocompatible hybrid carbon-silicon material

The compatible carbon-silicon complex materials originated from precursor diglycerylsilane (DGS) and sugar-modified silane N-(3-triethoxysilylpropyl)gluconamide (GLS) have gained substantial popularity by demonstrating admirable properties to stabilize entrapped biomolecules. The microenvironment inside these materials, especially the distribution of sugar moieties inside the matrix, which is likely the most critical factor determining compatibility of these materials, still remains unclear. To deeply investigate the biocompatibility mechanism of these materials, we have adopted two different preparation routes for these materials by introducing GLS into the starting DGS sol stage, but things are different after the DGS gel is formed. A fluorescence probe rhodamine 6G is introduced herein in the DGS sol to monitor the distribution of GLS moieties, as well as the evolution of the microenvironment inside resulting materials. All in all, the findings demonstrated that the timing of GLS addition plays a critical role in controlling the evolution of the inner structure of materials, suggesting that this factor provides a promising route to tune the properties of the resulting materials.

Silica gel-glasses doped with Cr-containing nanoparticles

Transparent silica glasses doped with heat-resistant luminescent nanoparticles with Cr3+ ions in the “strong” octahedral crystal field at the sol stage have been synthesized through the direct sol-gel-glass transition. Their electron microscopy and luminescence spectral studies have been performed. It has been found that the nanoparticles incorporated in these glasses are subject to the isotropic compression by the matrix and to slight dissolution (due to the absence of the melt stage) when the optical Cr n+ centers (n = 3–6) are formed.

Elastic instability of the nano-structured state as an intrinsic probe to study the early formation stages of sol–gel derived (Pb1-xCax)TiO3 thin films

A novel method to investigate the early formation stages of polycrystalline (Pb1-xCax)TiO3 (PCT) perovskite films by means of traditional Brillouin and micro-Brillouin spectroscopy (BS, mBS) is described in the present work. The films were prepared by chemical solution deposition (CSD) onto oxidized (100)Si substrates and treated at temperatures between 350–650 °C by rapid thermal processing (RTP). The elastic instability observed by Brillouin spectroscopy at the nano-structured state of the PCT films was used here to determine their crystallization temperatures. Coexistence of different nanocrystalline phases (e.g., pyrochlore, perovskite) in the films could also be detected by this technique. The reliability of these results is demonstrated by complementary information obtained by X-ray diffraction (XRD) and scanning force microscopy (SFM). The effects of the annealing temperature and of the Ca2+ content on the crystallization process of these films are also discussed.

Effect of polyvinylpyrrolidone on the ammonia-catalyzed sol–gel process of TEOS: Study by in situ 29Si NMR, scattering, and rheology

Ammonia-catalyzed sol–gel process of polyvinylpyrrolidone/tetraethoxysilane (PVP/TEOS) system in methanol was studied by in situ liquid 29Si nuclear magnetic resonance (NMR), dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and rheology. A scientific connection was established between the reaction composition and the microstructures of sol particles. It was found that the concentration of PVP played an important role in the hydrolysis kinetics of TEOS and the SiO 2 sol–gel process. The results of in situ 29Si NMR showed that PVP addition reduced both hydrolysis rate and condensation rate of TEOS, and the condensation rate decreased more seriously than the hydrolysis rate. The particle size distributions obtained from DLS and SAXS indicated that PVP held back the growth of SiO 2 clusters by hydrogen-bonding the silanol groups on particle surface with the electronegative inner amide of PVP side chain. Thus, gelation was retarded and the rheology of sol was largely modified by PVP. Rheology study showed typical Newtonian fluid behavior before gelation and shear thinning fluid behavior after gelation point, respectively. The changes in fractal dimensions of PVP/SiO 2 sols, obtained by SAXS, explained the different microstructures of SiO 2 sol particles in the presence of PVP. The changes of microstructure and macroscopic properties should be pre-determined by the very early stages of sol–gel process.