Sol Formation Research Articles

Influence of the substitution of CaO by SrO on the structure, degradation and in vitro apatite formation of sol–gel derived SiO2–CaO–SrO–P2O5system bioactive glasses

The present study investigates the influence of the substitution of CaO by SrO on the structure, degradation and in vitro apatite formation of sol–gel-derived bioactive glasses with composition of 58SiO2–(38-x)CaO–xSrO–4P2O5, where x varies between 0 and 10 mol.%. The IV-type nitrogen adsorption/desorption isotherms and pore size values (ranging from 5.41 to 12.56 nm) confirmed the mesoporous structure of the synthesized glasses. The detailed structural analysis was carried out by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). As network modifiers, the addition of Ca and Sr oxides disrupted the bonds of bridging oxygens (BOs) and resulted in the formation of non-bridging oxygens (NBOs), where the substitution of Ca with Sr led to an increase in Q1 units and a decrease in Q3 units. The effects of the addition of Sr on sample degradation and apatite formation were assessed using an assay in tris-(hydroxymethyl)-aminomethane and hydrochloric acid (Tris–HCl) and simulated body fluid (SBF). The results demonstrated that the substitution of CaO by SrO in the CaO–SiO2–P2O5 bioglass system altered the glass structure, resulting in reduced sample degradation and delayed apatite formation. This suggests that the incorporation of Sr into bioactive glasses may serve as a promising strategy to regulate the structure, dissolution behavior and apatite formation of silicate-based glasses, particularly concerning their long-term applications within the human body.

The Sol-Gel Process, a Green Method Used to Obtain Hybrid Materials Containing Phosphorus and Zirconium.

The sol-gel process is a green method used in the last few decades to synthesize new organic-inorganic phosphorus-containing hybrid materials. The sol-gel synthesis is a green method because it takes place in mild conditions, mostly by using water or alcohol as solvents, at room temperature. Therefore, the sol-gel method is, among others, a promising route for obtaining metal-phosphonate networks. In addition to phosphorus, the obtained hybrid materials could also contain titanium, zirconium, boron, and other elements, which influence their properties. The sol-gel process has two steps: first, the sol formation, and second, the transition to the gel phase. In other words, the sol-gel process converts the precursors into a colloidal solution (sol), followed by obtaining a network (gel). By using the sol-gel method, different organic moieties could be introduced into an inorganic matrix, resulting in organic-inorganic hybrid structures (sometimes they are also referred as organic-inorganic copolymers).

Synthesis and study of organo-modified silica based hydrogels: Rheological properties and drug release kinetics.

The method of synthesis of unmodified and organo-modified silica hydrogels and their composites with orotic acid as a model drug was developed. The hydrogels had a pH of 6.5-7.8. The particulate nature and highly porous structures of the hydrogel materials were revealed using scanning electron and optical microscopy methods. The content of aqueous phase in the hydrogels was 99% or more. In order to evaluate the possibility of their application as a basis for development of novel soft drug formulations and cosmetic compositions, rheological properties of the hydrogels and in vitro release kinetics of the drug were studied. The effects of synthesis conditions (increasing concentration of catalyst of silica sol formation, drug loading) and the silica matrix modification with various organic groups on the indicated properties were investigated. It was found that all synthesized hydrogels exhibited pseudoplasticity, thixotropy and controlled release of the drug, which are important for their potential application. However, in general, the indicated effects led to worsening the properties of the hydrogel materials in comparison with the unmodified silica hydrogels.

Amino Acid‐Mediated Formation of Zirconia Nanoparticles and their Transparent Dispersions

AbstractWe present a straightforward one‐pot hydrothermal method for the synthesis of zirconia nanodispersions, leading to the formation of stable sols. By simply varying the nature of the stabilizer used, one can obtain a large variety of objects with different sizes, shapes and crystallinities. Our results demonstrate the crucial role played by aliphatic amino acids both during the formation of the objects and after, since their interaction with the surface of the inorganic crystals influences strongly the optical properties and colloidal stability of the latter. Importantly, the versatility of this method allows for the introduction of different dopants, increasing substantially the scope of applications that can be achieved with such nanoscale oxides. The high transparencies and the easy dispersibility of nanoparticles in different liquid matrixes ensure the formation of zirconia‐based nanocomposites and ceramics with outstanding optical features for the orthopedic, dental, photonics and chemical sectors. This method can be easily scaled up, being already available for the production of high‐quality zirconia nanodispersions at the industrial level.

In English

Currently, textile and food industries produce a significant volume of sewages containing azo dyes and other organic pollutants. These effluents are serious environmental threats, so new methods for their treatment and the degradation of azo dyes are attracting much attention. Composite materials based on TiO2 modified by noble metals and nanoceria show high activity in the photodegradation of organic contaminates and are proposed for hydrogen synthesis as well. To optimize the treatment of contaminants, different processes can combine including the strategies of adsorption, photoluminescence, photocatalysis, etc. The synthesized TiO2-based nanomaterials (sols, powders) will be exploited for bioremediation due to their small size and surface plasmon resonance from noble metals. Binary nanocomposites based on TiO2 were obtained by the chemical co-precipitation method from solutions of titanium tetraisopropoxide (TTIP) and inorganic salts of cerium, silver, and palladium. It has been stated that TiO2 is represented by anatase with primary particle size (CSR) from 8.5 to 16.8 nm, depending on the nature and concentration of the dopant. It is shown that Ag is reduced on the surface of anatase particles and blocks their growth, while Pd and Ce penetrate the titanium dioxide matrix in the form of small clusters with the deformation of the anatase crystal lattice. Nanocomposite particles formed loose and fragile aggregates, which spontaneously dispersed in solutions of dyes with the formation of colloid-stable sols, required the use of a centrifugal field for their sedimentation. Nanoparticles of TiO2&Pd were electronegative and others were electropositive according to the values 4.1÷9.6 of ZPC (zero point of charge). It was shown that the particles of all composites sorbed Methylene Blue (MB) without photocatalytic activity under the visible light to any dye. Moreover, anionic dyes such as Orange-G (Or-G) and Methyl Orange (MO) were excellently discolorated in the presence of TiO2&Pd system; cationic dyes of MB and Rhodamine B (RhB) discolorated too with the TiO2, TiO2&CeO2, and TiO2&Ag systems under UV light action. As such, photocatalysis tests showed that Orange-G’s and MO’s discoloration was higher for TiO2&Pd (2 wt. %) and TiO2 systems with the correlation coefficient R2 0.999.

Towards a biomimetic cellular structure and physical morphology with liposome-encapsulated agarose sol systems

The cytoplasm, serving as the primary hub of cellular metabolism, stands as a pivotal cornerstone for the harmonious progression of life. The ideal artificial cell should not only have a biomembrane structure system similar to that of a cell and the function of carrying genetic information, but also should have an intracellular environment. In this pursuit, we employed a method involving the incorporation of glycerol into agarose, resulting in the formation of agarose-glycerol mixed sol (AGs). This dynamic sol exhibited fluidic properties at ambient temperature, closely mimicking the viscosity of authentic cytoplasm. Harnessing the electroformation technique, AGs was encapsulated within liposomes, enabling the efficient creation of artificial cells that closely resembled native cellular dimensions through meticulous parameter adjustments of the alternating current (AC) field. Subsequently, artificial cells harboring AGs were subjected to diverse electrolyte and non-electrolyte solutions, enabling a comprehensive exploration of their deformation phenomena, encompassing both inward and outward budding. This study represents a significant stride forward in addressing one of the most fundamental challenges in the construction of artificial cytoplasm. It is our fervent aspiration that this work shall offer invaluable insights and guidance for future endeavors in the realm of artificial cell construction.

Contact time dependence of adhesion force studied at low, moderate, and high relative humidities on AFM: Influence of surface hydrophilicity

Contact time dependence of adhesion force remains insufficiently comprehended and demands further clarification. Adhesion forces between cantilevers and various substrates were measured with atomic force microscopy to study the dependence at low, moderate, and high relative humidities (RH). Results indicate a strong correlation between the dependence and surface hydrophilicity. In some situations, the adhesion force exhibits a dependence on contact time: it experiences a rapid increase, followed by a gradual rise and eventual saturation with a saturation time of 20 ∼ 200 s. On hydrophilic surfaces, the force is dependent only at some RHs. On most partially hydrophobic surfaces, the dependent behaviors are observed under all levels of RH. However, the force on hydrophobic surfaces is independent under all levels of RH. With the dominant capillary force, the dependent behavior was attributed to the slow flow of thin films caused by the high viscosity of interfacial water. The high viscosity at low and moderate RHs was due to its configuration and film thickness, while that at high RH was due to contaminants and the formation of silica sols and gels. The findings have the potential to enrich the comprehension of adhesion and provide remedies for stiction-related problems in miniature devices.

Direct Synthesis of Metal-Organic Framework Sols: Advances and Perspectives.

The intrinsic lack of processability in the conventional nano/microcrystalline powder form of metal-organic frameworks (MOFs) greatly limits their application in various fields. Synthesis of MOFs with certain flowability make them promising for multitudinous applications. The direct synthesis strategy represents one of the simplest and efficient method for synthesizing solution processable MOF sols/suspensions, compared with other approaches, for instance, the post-synthesis surface modification, the direct dispersion of MOFs in hindered ionic liquids, as well as the calcination method toward a few MOFs with melting behavior. This article reviews the recent direct synthesis strategies of solution processable MOF sols and their typical applications in different fields. The direct synthesis strategies of MOF sols can be classified into two categories: particle size reduction strategy, and selective coordination strategy. The synthesis mechanism of different strategies and the factors affecting the formation of sols are summarized. The application of solution processable MOF sols in different fields are introduced, showing great application potentials. Furthermore, the challenges faced by the direct synthesis of MOF sols and the main methods to deal with the challenges are emphasized, and the future development trend is prospected.

Lightweight, robust hierarchically porous ceramics from cost-effective powders for dye removal

A facile and cost-effective approach for hierarchically porous ceramics has been proposed firstly, using coal fly ash as the main powder while secondary aluminum dross (SAD) as curing and foaming agents. Benefited from the hydrolysis of AlN and Al in SAD, gas and lamellar aluminum hydroxide sol attached to the surface of unreacted particles were produced, meanwhile pH value and viscosity increased, realizing foaming and coagulation casting simultaneously to fabricate porous green body. The increase of SAD amount could contribute to more intensive formation of flaky aluminum hydroxide sol, enhancing mechanical strength of green body, which has high compressive strength of 1.03 MPa at a bulk density of 0.68 g/cm3. Porous mullite-based ceramics could be sintered at a relatively low temperature of 1200–1250 °C owing to alkali metal oxide and amorphous SiO2 in the solid wastes, which also help to form micropores on the pore wall due to partially sintering. Porous mullite-based ceramics possess hierarchical pores, bulk density of 1.00 g/cm3, open porosity of 66.15%, specific surface area of 2.24 m2/g and compressive strength of 9.14 MPa. Their removal rate of malachite green solution reaches 99.1% at a concentration of 100 mg/L and an adsorbent dosage of 100 g/L.

In situ infrared spectroscopic ellipsometry as a tool to probe the formation of sol–gel based mesoporous films

In situ infrared spectroscopic ellipsometry as a tool to probe the formation of sol–gel based mesoporous films

Effects of anionic and cationic surfactants on the surface Plasmon resonance intensity of biogenic silver nanoparticles: Stability, and position of optical band

Fabrication of noble metal nanoparticles by using green plant extract as reducing agent have been the subject of various investigators due to their enhanced plasmonic properties for various applications. This paper describes the effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) on the nucleation of silver sols formation by using coriander seeds extract and silver nitrate redox reaction. The wavelength maxima (λmax) were blue shifted from 433 nm to 425, 423, and 420 nm, respectively, with 0.0, 0.4, 1.0, and 1.6 mM CTAB. The blue and red shifts were also observed from 433 nm to 421, 421, 418, and 438 with 0.0, 0.4, 1.0, 1.6 and 2.0 mM SDS, respectively. The pre-micellar inhibition, and post-micellar catalytic effects were observed on the formation of silver sols with cationic CTAB surfactant. SDS exhibits inhibitory effect on the nucleation rate for an entire range of concentration. Additionally, antioxidant activity in vitro revealed that the percentage scavenging with 2,2-diphenyl-1-picrylhydrazyl (DPPH•) were depended on the dose of AgNPs.

Effect of Glymo on the Morphological and Optical Properties of Eu3+-Doped Lu2SiO5 Films

Eu3+-(5% mol)-doped Lu2SiO5 optical quality films were prepared using the sol–gel method and dip-coating technique from lutetium and europium salts as the lanthanide precursors and tetraethyl orthosilicate (TEOS) as the silicon source. To increase the thickness of the films, 3-Glycidyloxypropyl trimethoxysilane (Glymo) was added as the rheological agent during sol formation. Structural, morphological, and luminescent properties were investigated for Lu2SiO5, Eu3+:Lu2SiO5, and Eu3+:Lu2SiO5/Glymo in order to obtain high quality in luminescent films. X-ray diffraction (XRD) results show that the incorporation of the Eu3+ ions do not affect the A-Type and B-Type monoclinic crystalline phase typical of Lu2SiO5, even after five dipping cycles on quartz substrates and a final annealing process at 1100 °C. The morphology and topography of the films were studied by SEM and AFM. These techniques revealed films without surfactant that were uniform with low rugosity while the film with surfactant presented porous hills and valleys with uneven high values of roughness. The photoluminescence spectrum of Eu3+:Lu2SiO5 films showed 2 broad emission peaks centered at 589 nm and 612 nm. The presence of Glymo in the system promoted the formation of residual Lu2Si2O7 compounds with the highest lifetime values compared with films without surfactant. The results of the films are promising for luminescent applications.

Topical Cream Carrying Drug-Loaded Nanogels for Melanoma Treatment.

In this study, nanogel creams carrying paclitaxel (PTX) and temozolomide (TMZ) were prepared for thetopical treatment of melanoma. PTX and TMZ were first loaded in poly-(D,L-lactide-co-glycolide)-block-poly(ethylene glycol)-block-poly-(D,L-lactide-co-glycolide) (PLAG-b-PEG-b-PLGA)thermosensitive nanogels, which made a transition from a free-flowing sol (formation of micellar network) at 25°C with the z-average particle size of c.a. 96nm to a gel (aggregation of micelles) at 33°C with the z-average particle size of c.a. 427nm. An anhydrous absorption ointment base, aquaphor, was then added to drug-loaded nanogels to form nanogel creams carrying PTX and TMZ. Nanogel creams permitted controlled release of the payloads and improved the penetration of the payloads through the rodent skin compared to drug(s)-loaded nanogels. PTX and TMZ in a combination were synergistically effective in inhibiting SK-MEL28, A375, and B16-F10 melanoma cancer cells in vitro. Topically applied nanogel creams carrying TMZ/PTX (4mg/1.5mg/dose) showed a trend of tumor volume inhibition on B16-F10-bearing xenograft mice in vivo.

Kinetic Improvement of the Gel-sol Transition of Thermoresponsive Hydrogels Utilizing a High Surface Area Host

Rapid reversible phase transitions of biocompatible thermoresponsive sealants (TRS) upon cooling are required for their practical application in many sectors. The gel–sol transition rate of the TRS studied here [poly(N-isopropylacrylamide-co-butyl acrylate 95:5, number-averaged molecular weight = 7–64 kg mol–1] after being heated to 50 °C is slowed dramatically. The unheated materials return to a free-flowing sol form in a matter of minutes, while the heated materials remain in a gel or solid form for hours. The gel–sol transition of these polymers is enhanced in the presence of a high surface area host in the form of open-cell foams such as polyurethane (PUR), polyimide (PIM), hydrophilic polyurethane Aquazone (AQZ), and neoprene (NEO). An enhanced rate of sol formation on cooling and high TRS recovery (74–99%) were observed across a range of foam types and pore sizes when compared to samples stored without a host (9% recovery). Polyurethane demonstrates the greatest increase in TRS recovery (∼10-fold) after storing the TRS solution at 50 °C followed by cooling for 10 min at 0 °C, maintaining the thermally reversible gelation and mechanical strength of the TRS. Crucially, rheological measurements demonstrate that the viscosity, storage modulus, and loss modulus are not significantly affected by storage in a foam host. This work may be potentially extended to other injectable in situ forming hydrogels, which have suitable mechanical strength but less ideal phase transition times.

Removal of hydroxyl groups and its influence on the microstructures evolution of alumina-mullite fibers fabricated by sol-gel process

Hydroxyl groups are essential groups in the preparation of alumina-mullite fibers by the sol-gel process, which contributes to the formation of spinnable precursor sol. In this work, the removal of hydroxyl groups during pyrolysis and sintering, and its effect on fibers phase transition and microstructural evolution were systematically studied. Five pyrolyzed alumina-mullite fibers samples with different hydroxyl groups content were obtained by adjusting the pyrolysis temperature or introducing water vapor. It was revealed that the removal of hydroxyl groups existed throughout the sintering process, mainly concentrated before 800 °C. The mullitization temperature of the pyrolyzed fibers with more hydroxyl groups was about 1300 °C, while that of pyrolyzed fibers with fewer hydroxyl groups was 700 °C. In addition, an appropriate amount of residual hydroxyl groups (13.3 wt%) was beneficial to obtain a dense fine-grained microstructure of the pyrolyzed fibers after sintering, and the tensile strength of the fibers was increased to 1.6 ± 0.22 GPa. Finally, the influence mechanism of different hydroxyl content on the alumina-mullite fibers was discussed.

Influence of Gelling in Natural Esters Under Open Beaker Accelerated Thermal Aging

The present work is focused on the oxidation aspects (focused on gelling) of natural esters and its influence on the performance of transformer insulation systems. Even though natural esters are not suitable for breathing units, the scenario considered simulates a defect in the sealing system and thus bringing the liquid in direct contact with atmospheric air. Commercially available natural ester liquids are thermally degraded under open beaker conditions in the presence of cellulose with a controlled aging history. The accelerated aging conditions are maintained until the formation of sol and gel is evident in the bulk of the liquid. Later, the insulating liquids and insulating papers are analyzed to understand the behavioral impact of sol and gel on the insulation. The discussions in this article are supported by the physicochemical and electrical characterizations of the degraded liquids and papers. The characterizations include Fourier transform infrared spectroscopy (FTIR), ac breakdown voltage (BDV) failure probability rate, X-ray diffraction (XRD), degree of polymerization (DP), and viscosity. It is found that before the formation of gelling, sol is witnessed in the bulk of the liquid. The presence of the sol highly influences the viscosity of the liquid and aids in rapid acceleration of the oxidation process. It is understood that that the gelling phenomena in natural esters do not have a noticeable impact on the liquid BDV failure rate and paper degradation.

An optimization study for preventing silica gelation and improving filtration effectiveness during pH reduction of high concentration silica solutions

AbstractThe steam generation processes at the steam‐assisted gravity drainage facilities result in huge quantities of wastewater streams, which are characterized by high pH and high silica levels. These concentrated streams need to be neutralized before their disposal via down‐hole injection. The neutralization of these high‐pH brines results in the formation of a gel‐like substance, which makes it difficult to filter the amorphous silica gel. The wastewater used in this study was synthetically prepared using sodium metasilicate to mimic high‐concentration silica solutions. Our experiments did not show any advantage of a two‐step pH‐neutralization process over the single‐step process for suppressing silica gelation. A systematic experimental campaign was undertaken to investigate the effects of SiO2 concentration, NaCl:SiO2 ratio, and pH on the residual silica concentration, percent silica removal, filtration rate, and filtration effectiveness. For NaCl:SiO2 ratios higher than 4.5, silica precipitation during pH reduction did not lead to the formation of gel or sol. The response surface methodology (RSM), based on the Doehlert design of experiments, was implemented to optimize the responses and provide high efficacy with fewer experiments. The results from the analysis of variance (ANOVA) analyses of the experimental data were used to evaluate the significance of each term in the quadratic model. 3D response surfaces and 2D contour plots were generated for determining the optimal ranges of independent factors for achieving the maximum silica removal, the highest filtration rate, the best filtration effectiveness, and the minimum residual silica concentration. An optimum operating region was established from the RSM analysis and overlay plot.

Investigation of processes of obtaining cerium dioxide sol with polyvinyl alcohol having bioactive properties

Cerium dioxide sols are widely used in photocatalysis, catalysis, medicine and cosmetics. It is believed that sols with a CeO2 size of up to 10 nm have the most active biological properties. The method of sols preparation affects their functional properties. They are usually obtained through the stage of separating the oxide in the solid phase from the solution, which can lead to particle agglomeration, and then transferring the oxide to a colloidal solution under the action of various stabilizers. In this study, we propose the method of CeO2 sol obtaining without step of solid phase oxide separation. The stabilizer (polyvinyl alcohol (PVA)) is present at the stage of formation of weakly aggregated CeO2 nanoparticles from cerium(III) salt with an ammonia and hydrogen peroxide solution. Using IR, UV spectroscopy, viscometry and titration it was found that H2O2 eventually oxidizes Ce(III) in solution to Ce(IV) and does not oxidize PVA. The intermediate formed after the addition of ammonia solution to cerium(IV) salt has the composition Ce(ООН)3OН⋅nH2O, which is confirmed by the data of proton magnetic resonance, weight and thermal analyses. The process of CeO2 sol formation stabilized by PVA goes through the stages of Ce(ООН)3ОН dissolution accompanying with an endothermic effect, followed by decomposition. Peroxide compounds in the solid phase are stable in air up to 90–100 °C. The prepared sol has the composition CeO2–PVA–ammonium nitrate, exhibit antioxidant properties, is not a nutrient medium for E. Coli and S. Aureus and is capable to form a calcium-phosphate layer on its surface from a model solution of SBF.

The Influence of Aminoalcohols on ZnO Films' Structure.

Preparing structures with the sol-gel method often requires control of the basal plane of crystallites, crystallite structures, or the appearance of the voids. One of the critical factors in the formation of a layer are additives, such as aminoalcohols, which increase the control of the sol formation reaction. Since aminoalcohols differ in boiling points and alkalinity, their selection may play a significant role in the dynamics of structure formation. The main aim of this work is to examine the properties of ZnO layers grown using different aminoalcohols at different concentration rates. The layers were grown on various substrates, which would provide additional information on the behavior of the layers on a specific substrate, and the mixture was annealed at a relatively low temperature (400 °C). The research was conducted using monoethanolamine (MEA) and diethanolamine (DEA). The aminoalcohols were added to the solutions in equal concentrations. The microscopic image of the structure and the size of the crystallites were determined using micrographs. X-ray diffractometry and Raman spectroscopy were used for structural studies, phase analysis and to establish the purity of the obtained films. UV-vis absorption and photoluminescence were used to evaluate structural defects. This paper shows the influence of the stabilizer on the morphology of samples and the influence of the morphology and structure on the optical properties. The above comparison may allow the preparation of ZnO samples for specific applications.

Aqueous sol-gel synthesis, structural, thermoanalytical studies, and conductivity properties of lithium lanthanum titanate

Newly developed aqueous sol-gel preparation technique was applied for the synthesis of lithium lanthanum titanate with the initial composition of Li0.35La0.55TiO3. The influence of hydrochloric acid, which plays a crucial role in the formation of Li–La–Ti–O tartrate gel precursor, was also investigated. The dissolution mechanism of titanium in the concentrated hydrochloric acid and its relation with the corresponding lithium and lanthanum salts was proposed. Besides, the effect of the tartaric acid as a ligand to the formation of transparent sol and homogeneous gel precursor was discussed. X-ray diffraction revealed that below the temperature of 800 °C starts the crystallization of the final tetragonal crystal phase for Li0.3La0.567TiO3 ceramic. Rietveld refinement of the crystalline samples showed the tendency of crystallites growing with the increase of heat-treatment temperature. Besides, the single crystalline ceramic compounds heat-treated at 1000 °C and 1250 °C of temperatures were obtained only for the initial composition of Li0.35La0.55TiO3. The calculated values of the tolerance factor and structural distortion parameters in octahedral coordination of TiO6 octahedral network for tetragonal and orthorhombic crystal structures confirmed the phase transition tendency by the increase of heat treatment temperature. The scanning electron microscopy proved the formation of the dense structure of the sample for Li0.35La55TiO3 ceramic after the additional heat treatment at the temperature of 1,250 °C. In addition, the quality of synthesized ceramic was confirmed by the impedance spectroscopical measurements, which revealed that the conductivity value for bulk at the temperature of 27 °C (300 K) is equal to 0.123 S m–1.