Tetramethoxysilane Research Articles

Synthesis of chiral mesoporous silica nanoparticles for the adsorptive removal of the chiral insecticide sulfoxaflor from water.

Mesoporous materials have garnered significant interest because of their porous structure, large surface area and ease of surface functionalization to incorporate the functional groups of choice. Herein, chiral mesoporous silica nanoparticles (CMSNPs) were prepared using quaternary amino silane as the template, tetramethyl orthosilicate as the silica source and proline and cellulose as chiral selector. The developed CMSNPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental analysis, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction analysis, BET surface area analysis and BJH pore size/volume analysis. It was observed that the CMSNPs have high specific surface area and narrow particle size and pore size distribution. These CMSNPs were used as adsorbents for separation of the chiral insecticide sulfoxaflor. The effects of various parameters that affect adsorption, such as initial concentration of the analyte, adsorbent dose, time and pH, were evaluated, and the optimum values were determined. At optimum conditions, the removal efficiency and adsorption capacity were 98.5% and 435.45 mg g-1, respectively. Further, adsorption isothermal study was carried out using Freundlich and Langmuir models. Results showed that mesoporous silica nanoparticles functionalized with amide-bonded cellulose are promising and cost-effective adsorbents for the removal of chiral pesticides from water and wastewater.

PREPARATION OF ORGANIC-INORGANIC COMPOSITE MATERIALS USING SOL-GEL TECHNOLOGY

This article reviews the principles of hydrolytic polycondensation of tetramethoxysilane (TMOS) in alkaline media. Depending on the concentration of tetramethoxysilane, both nanoscale mono-disperse SiO2 particles and monolithic samples of xerogels were synthesized. Pyridine derivatives, representatives of several chemically and thermally stable aromatics, which perform the function of catalysts, were selected for the work. During the sol-gel process of hydrolysis of tetramethox-ysilane and the polycondensation of the compounds formed with the presence of 4-(dimethylamino)-pyridine as a catalyst, a linear increase in the pKa of the conjugate acid to 9.70 was observed. Since the particles formed in an alkaline environment are negatively charged and repel each other, their growth occurs by the condensation mechanism due to the dissolution of smaller particles. Heating the sol-gel system for 30 minutes does not increase the particle size, but brings the gela-tion point closer. Thus, a small amount of catalyst leads to the formation of a group of particles with a small diameter and a tendency to polycondensate, but a larger amount of catalyst concen-trationcausing the formation of very large particles. The physico-chemical properties of the synthe-sized particles were determined. The dimensions of the processed samples were recorded using a scanning electron microscope (SEM). Keywords: Sol-gel, hydrolysis, polycondensation, tetramethoxysilane, xerogel, pKa, catalyst, SEM.

Bionanocomposite Thin Films Based on Eco-Friendly Carbon-Clay Materials for Corrosion Protection of Light Alloys

This study aims to develop new environmentally compliant coatings as surface pretreatments for the protection of light alloys. To achieve this goal, chitosan and zein biopolymers were combined with eco-friendly carbon-clay fillers to produce bionanocomposite thin films. Chitosan- and zein-based suspensions were prepared for the synthesis of the bionanocomposite thin films. For the chitosan-based suspension, carbon-sepiolite fillers and/or caffeic acid were dispersed in an acetic acid solution [1]. For the zein suspension, the carbon-sepiolite and/or caffeic acid additives were dispersed in an ethanol/water mixture. The carbon-clay fillers were prepared by impregnating natural sepiolite clay with liquid caramel, followed by thermal treatment under N2 flow at 550ºC for graphitization [2,3]. The resulting suspensions were then deposited on AA2024-T3 aluminium alloy and AZ61 magnesium alloy samples using the dip-coating technique. A post-treatment involving the application of an organic-inorganic hybrid top-coat on a series of bionanocomposite thin films. The purpose was to seal the inherent pores within these layers and enhance their corrosion resistance. The hybrid matrix was prepared by co-hydrolysis and polycondensation of a mixture of γ-methacryloxypropyltrimethoxysilane and tetramethyl orthosilicate by using the sol-gel process. The resulting coatings were characterized using field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). The corrosion protection of these coatings was evaluated by open circuit potential (OCP) measurements and electrochemical impedance spectroscopy (EIS) during immersion tests in a 0.06 M NaCl solution. FESEM images acquired on the corrosion test areas confirmed the corrosion protection offered by the bionanocomposite thin films. Electrochemical studies showed that the degradation process of these coatings goes through two stages. Initially, a barrier effect exerted by the sol-gel top-coat predominates. Once this layer has failed, an active protection mechanism against corrosion engaged by the bionanocomposite thin film is activated. As a remarkable conclusion of the study, it should be noted that these bionanocomposite thin films exhibit relevant properties that make them promising green candidates for applications in the automotive and aeronautical industries. Acknowledgements: This work was developed within the scope of the projects CICECO UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC) as well as MCIN/AEI/10.13039/501100011033 - PID2019-105479RB-I00 and PID2022-139920OB-I00 projects, Spain. AB and PF are thankful to FCT for grant SFRH/BD/148856/2019 and the Investigator FCT (IF/00300/2015), respectively. CN is grateful to Portuguese national funds (DL 57/2016/CP1482/CT0031).

Development of Green Conversion Sol-Gel Coatings for Corrosion Protection of AZ61 Magnesium Alloy

The urgent need to address the challenges posed by climate change has led to increased research and development efforts aimed at creating lightweight materials to reduce greenhouse gas emissions. This study focuses on corrosion protection of the commercial magnesium alloy AZ61, valued for its wide-ranging applications in engineering and industry, including automotive, aeronautics, and biomedical engineering. Despite its interesting mechanical properties, the AZ61 alloy exhibits poor corrosion resistance in saline aqueous environments, prompting significant research into coatings to enhance its durability.This research aims to design and prepare organic-inorganic hybrid sol-gel coatings for corrosion protection of the AZ61 alloy. The inorganic phase, mainly based on tetramethyl orthosilicate (TMOS), serves as a cross-linking agent, while four organofunctionalized silanes containing hydrolysable methoxy groups and functional organic groups into the same molecule are used as precursors for the organic component of these hybrid coatings. Specifically, the organofunctionalized silanes selected are γ-methacryloxypropyltrimethoxysilane (MAPTMS), γ -glycidoxypropyltrimethoxysilane (GPTMS), γ -aminopropyltrimethoxysilane (AMPTMS), and γ -mercaptopropyltrimethoxysilane (MPTMS). These silanes are chosen for their ability to create organopolysiloxane coatings with sufficient chemical compatibility and flexibility to accommodate other species without phase segregation or cracking. These properties are essential to create a suitable structural environment to encapsulate the selected ecofriendly corrosion inhibitors that are added in later stages of the study, thereby yielding a processable system that serves as a functional phase of active corrosion protection coatings for magnesium alloys.Physicochemical characterization techniques are employed to understand the chemical environment within the hybrid networks and confirm the successful formation of organopolysiloxane networks. Thermogravimetry and differential thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state 13C and 29Si nuclear magnetic resonance spectroscopies are used for these purposes.The performance of coated AZ61 samples is analysed using the aforementioned organic-inorganic hybrid gels. These sol-gel coatings are applied using immersion techniques (dip-coating) on unpolished (as-received) and polished AZ61 samples, to determine the influence of surface conditions on their behaviour during immersion tests in 0.6, 0.06 and 0.006 M NaCl aqueous solutions. Open circuit potential (OCP) measurements and global and localized electrochemical impedance spectroscopies (EIS, LEIS) are applied with this purpose. The microstructure and texture of the coatings, both before and after the corrosion tests, are observed by optical microscopy (OM) and scanning electron microscopy (SEM). Moreover, Energy dispersive X-ray (EDX) microanalyses are performed on several areas of the coated samples after the corrosion tests.In the last phase of the study, modifications to the sol-gel formulations are explored by incorporating environmentally friendly corrosion inhibitors such as cysteine (L-Cys) and benzotriazole (BTA), as well as cross-linking agents like hexamethoxymethylmelamine (HMMM) in presence of an acid catalysts, specifically p-toluenesulfonic acid (p-TSA), to facilitate the cross-linking reaction within the organosilicon network. These modifications aim to enhance the protective properties of the sol-gel coatings. EIS and LEIS are used to assess their effectiveness. Films formulated with HMMM demonstrate robust passive protection against corrosion, while those doped with L-Cys and BTA exhibit self-healing and active protection properties, offering a promising alternative to traditional chemical conversion pretreatments based on hexavalent chromium. Funding Sources This work has been supported by the Project PID2022-139920OB-I00 (Ministry of Science, Innovation and Universities, MICINN, Spain).

Degradation of Chlorothalonil by Catalytic Biomaterials

Chlorothalonil (2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile, TPN, CAS: 1897-45-6) is a halogenated fungicide currently widely applied to a large variety of crops. Its carcinogenicity, embryo lethality, and high chronic oral toxicity in mammals, among other effects on a variety of organisms, has made its biodegradation of great interest. Chlorothalonil dehalogenase (Chd) from the bacterium Pseudomonas sp. CTN-3 offers a potential solution by catalyzing the first step in the degradation of chlorothalonil. Reported herein are active biomaterials of Chd when encapsulated in tetramethylorthosilicate (TMOS) gels using the sol–gel method (Chd/sol), alginate beads (Chd/alginate), and chitosan-coated alginate beads (Chd/chitosan). Both Chd/sol and Chd/chitosan increased protection from the endopeptidase trypsin as well as imparted stability over a pH range from 5 to 9. Chd/sol outperformed Chd/alginate and Chd/chitosan in long-term storage and reuse experiments, retaining similar activity to soluble Chd stored under similar conditions. All three materials showed a level of increased thermostability, with Chd/sol retaining >60% activity up to 70 °C. All materials showed activity in 40% methanol, suggesting the possibility for organic solvents to improve TPN solubility. Overall, Chd/sol offers the best potential for bioremediation of TPN using Chd.

In Situ CALB Immobilization in Xerogel and Sonogel Employing TMOS as Silica Precursor and Polyethylene Glycol as Additive

The immobilization of enzymes, especially lipases, presents a significant challenge in contemporary biotechnology due to their wide-ranging application in industrial processes. Given the array of available techniques for enzyme immobilization, this study aimed to immobilize Candida antarctica B (CALB) lipase within silica xerogel and sonogel matrices obtained through the sol–gel technique. Polyethylene glycol (PEG) was incorporated as an additive, with tetramethylorthosilicate (TMOS) serving as the silica precursor. This study assessed the operational stability, storage stability, and thermal properties of the resulting supports. Results revealed that both sonogel and xerogel supports, supplemented with PEG, maintained storage stability above 50% throughout a 365-day period. Moreover, operational stability tests demonstrated that the xerogel support could be reused up to 21 times, while the sonogel support exhibited 10 reuses. Thermal analysis further highlighted a reduction in the deactivation constant and an elongation of the half-life time for both supports. These observations suggest that the supports effectively shield the enzyme from thermal inactivation. Overall, these findings underscore the potential utility of PEG-enhanced sonogel and xerogel supports in various industrial enzyme applications, providing valuable insights into their operational, storage, and thermal stability.

Impact of Pre-Silica-Coating on the Luminescence Properties of Silica-Coated Indium Phosphide Nanoparticles

This study examined the impact of silica-coating on the luminescence characteristics of indium phosphide (InP) nanoparticles. Silica-coated InP nanoparticles were prepared using three different techniques. The first method utilized tetraethoxysilane (TEOS) as the silica source, resulting in the encapsulation of multiple InP nanoparticles within silica spheres. This approach caused a red-shift in the luminescence peak wavelength of the InP colloidal solution post-TEOS coating, compared to the original InP colloidal solution. Conversely, the second method employed tetramethoxysilane (TMOS), resulting in the formation of irregularly shaped silica-coatings on multiple InP nanoparticles, which reduced the red-shift in the luminescence peak wavelength of the silica-coated InP colloidal solution. The third method involved pre-coating InP nanoparticles with TMOS, followed by thickening the silica shells using TEOS. This technique successfully encapsulated multiple InP nanoparticles within silica spheres, maintaining the luminescence peak wavelength of the InP colloid solution post-coating with TMOS and TEOS nearly identical to that of the original solution. This method merged the advantageous outcomes of the first two methods. Additionally, silica spheres containing InP nanoparticles synthesized using both TMOS and TEOS exhibited the highest luminescence intensity. In summary, this study introduces a novel approach in nanoparticle engineering, enhancing the functional properties of InP nanoparticles and expanding their potential applications in optoelectronic devices.

Preparation of monolithic silica HPLC columns with truss-structured skeletons and embedded surfactant-templated mesopores

Monolithic macro/mesoporous silica gels have been prepared via a sol-gel process using triblock copolymer Pluronic P123 (EO20PO70EO20) as a structure-directing agent. In this synthesis, P123 not only induces phase separation to form macroporous structure but also acts as a supramolecular template to form mesopores with precisely controlled shape and size. Obtained was a monolithic silica composed of continuous truss-like columnar skeletons in which cylindrical mesopores are arranged in a 2D-hexagonal symmetry. These monolithic silica gels have extremely high porosity approaching 90% and exhibited high specific surface area and sharp pore size distribution as revealed by N2 sorption measurements. Combinations of the initial composition and the post-gelation treatment on wet gels allowed the control of physical properties of meso- and macropore structures. The monolithic HPLC columns prepared using these silica gels surface-modified by ODS (octadecylsilyl) ligands gave as many as 140,000 theoretical plates/m for the separation of alkylbenzenes in a reversed-phase mode. Very weak dependence of height equivalent to theoretical plate, H, on the mobile phase velocity was also recognized in comparison with conventional particle-packed columns.Graphical SEM images of monolithic silica prepared with tetramethoxysilane (TMOS) and P123 composed of truss-structured continuous skeletons. The performance for HPLC separation medium was examined.

First Example of Single‐Crystal Nanodiamonds Immobilized in Porous SiO2‐Aerogel Matrix: Synthesis and Characterization

AbstractA first composite material containing uniformly dispersed disaggregated detonation nanocrystalline diamonds (DNDs) in SiO2 aerogel matrix was prepared. The synthetic protocol included hydrolysis of tetramethyl orthosilicate (Si(OMe)4, TMOS) by hydrosol of surface carboxylated DNDs with a typical size of 4–5 nm with DMSO serving as a cosolvent and a stabilizer of DND single crystals. Composite samples containing DNDs in silica aerogel matrix in concentration 1.0, 0.1 and 0.01 % w/w were prepared at ambient temperature. HRTEM data revealed that DNDs nanocrystals were uniformly distributed in aerogel and did not form aggregates. Textural and optical composites’ properties were determined.

Silica infiltration as a strategy to overcome zirconia degradation

The excellent clinical performance of yttria-partially stabilized zirconias (Y-SZs) makes them promising materials for indirect restorations. However, the Y-SZ phase stability is a concern, and infiltrating Y-SZs with a silica nanofilm may delay their degradation processes. In this study, we analyzed stabilities of silica-infiltrated zirconia surfaces after exposure to artificial aging (AA).Four zirconia materials with different translucencies (n = 40) were used, including low translucency 3 mol% Y-SZ (3Y-LT, Ceramill ZI, Amann Girrbach); high translucency 4 mol% Y-SZ (4Y-HT, Ceramill Zolid); and two high translucency 5 mol% Y-SZs (5Y-HT, Lava Esthetic, 3M and 5Y-SHT, Ceramill Zolid, FX white). Sintered specimens were exposed to 40 cycles of silica (SiO2) through room temperature atomic layer deposition (RT-ALD) using tetramethoxysilane (TMOS) and ammonium hydroxide (NH4OH). AA was applied for 15 h in an autoclave (134°C, 2 bar pressure). Stabilities of zirconia-silica surfaces were characterized in terms of hardness and Young's modulus using nanoindentation techniques and crystalline contents using x-ray diffraction (XRD) analyses. Silica deposition was also characterized by X-ray photoelectron spectroscopy (XPS).There was a significant effect of the interaction of materials and surface treatments on the hardness and Young's modulus values of zirconia-silica surfaces (p < 0.001). Silica deposition on zirconia surfaces improved the material resistance to degradation by AA.

Development of water vapor recovery membrane for efficient recycling system

Abstract In wastewater treatment at semiconductor plants separation operations are currently conducted mainly by distillation. Membrane distillation using ceramic surface-treated membranes is expected to provide more efficient separation. In this study, we investigated the improvement of acid resistance of surface-treated ceramic membranes by using four silicon alkoxides, Hexamethyldisiloxane(HMDS), Dimethyldimethoxysilane(DMDMOS), 3,3,3-Trifluoropropyltrimethoxysilane (TFPrTMOS), Tetramethoxysilane(TMOS) were used as surface treatment and it was performed in the gas phase. The water vapor permeance of the TFPrTMOS surface treated membrane was 2.35✕10−6 [mol m−2 s−1 Pa−1], and it maintained its functionality after immersion in a 10 wt% sulfuric acid solution under 60°C for 170 h. The membrane with multiple surface treatments with TFPrTMOS showed an increase in acid resistance to 491h, indicating that unreacted alkoxide affected the degradation. The water vapor permeance of the TFPrTMOS-DMDMOS treated membrane combined silicon alkoxides was 2.85✕10−6[mol m−2 s−1 Pa−1] and the acid resistance was 687 h. It is possible that DMDMOS acted as a cross-linker in modifying the unreacted alkoxide portion of the membrane, leading to improved resistance.

Silicon-infused bacterial cellulose: in situ bioprocessing for tailored strength and surface characteristics

In this study we investigate the use of in situ bioprocessing for the production and surface modification of bacterial cellulose (BC) with silicon additives. The surface properties and tensile strength of the BC were studied and compared with plain BC. The effect the modification exhibited on the survivability of the bacteria was assessed by optical density measurements and found that the addition of the modification marginally slowed growth in the case of Tetramethyl orthosilicate (TMOS) and did not affect the growth in the case of Tetraethyl orthosilicate (TEOS). Characterisation of the modified BC was carried out using FTIR, EDX and confirmed the presence of silicon in the material. The width of fibres in the microstructure of BC was measured using SEM. Two different silicon modifications were used to modify the BC, it was shown that the TMOS modification decreased the tensile strength but that the TEOS increased the tensile strength of the BC fibres compared to plain BC. In addition, we found that the washing conditions of 1% NaOH (w/v), industrial methylated spirit (IMS), and deionised water (DI) showed some impact on the properties of the samples, particularly the IMS produced a reduced contact angle in the modified samples. However, the contact angle increased in the case of TEOS modification with the NaOH wash. In conclusion this study shows a novel method of modifying BC materials in-situ using silicon additives for increased tensile strength and the potential for tuneable hydro interactions.

Dual-emission CPB@SMSO@SiO2 composites with tunable afterglow through energy transfer

Afterglow materials face limitations in color variety, low luminosity, and stability. Thus, developing materials with adjustable afterglow color, increased photoluminescence (PL) intensity, and enhanced stability is crucial. This paper reports the fabrication of a series of core–shell composites, CPB@SMSO@SiO2, which combine Sr2MgSi2O7: Eu2+, Dy3+ (SMSO) and lead halide perovskite quantum dots (CsPbBr3/CPB PeQDs) through a process involving in-situ growth and hydrolytic coating. The SMSO in the composite can absorb 365 nm UV light and then emit 470 nm light, which can be absorbed by the CsPbBr3 PeQDs, resulting in an overall increase in the PL intensity of the composite. The afterglow color can be turned from green to blue by adjusting the ratio of SMSO and CsPbBr3. Furthermore, the stability of the composites is improved by the SiO2 shell layer formed by hydrolysis of tetramethyl orthosilicate (TMOS). This study presents an opportunity to develop innovative afterglow materials.

Transition metal salt catalysed green synthesis of mesoporous silica nanoparticles

Conventionally, mesoporous silica nanoparticles are prepared by catalysing silicon alkoxides using acids or bases and are highly important in storage, delivery, and catalysis. Here, for the first time, we demonstrate that a transition metal ion (such as Ni(II), Co(II), and Mn(II)) also catalyses the hydrolysis and condensation reactions of silicon alkoxides in aqueous media without any additional acid or base to synthesize mesostructured and micro/mesostructured silica nanoparticles. An aqueous solution of a transition metal salt (specifically, nitrate salts of Ni(II), Co(II), or Mn(II), or chloride and sulphate salts of Ni(II)), 10-Lauryl ether (C12H25(OCH2CH2)10OH, C12E10) and cetyltrimethylammonium bromide (C16H33N(CH3)3Br, CTAB), and tetramethyl orthosilicate (TMOS) undergoes a precipitation reaction at room temperature, yielding ultra-small ordered mesostructured silica nanoparticles. These nanoparticles are subsequently calcined to produce mesoporous silica (meso-SiO2) with a high surface area (680–871 m2/g), large pore-volume (2.2–3.71 cm3/g), and small pore-size (1.2–3.0 nm). Moreover, the counter anions of the salts play an important role in the assembly process to obtain nanoparticles with an additional well-defined secondary pore (7.5–33.4 nm or larger). Coordinated water of the metal ion and methoxy group of the silica source react to produce a complex in which two hydroxy sides are in close vicinity to speed up the condensation reaction. We propose a hydrolysis and condensation reaction mechanism for TMOS to highlight the role of the metal ion as a catalyst.

Cosolvent-free sol–gel synthesis of macroporous silica gels from tetramethoxysilane–tetraethoxysilane mixtures

Tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and their mixtures were used for the cosolvent-free synthesis of macroporous silica gels as precursors for monolithic silica glasses. The liquid-state 29Si nuclear magnetic resonance (NMR) spectroscopy of precursor solutions indicated that cross-transesterification between TMOS and TEOS was completed in a few hours at 20 °C in the presence of an acid catalyst, whereas it was negligible when the catalyst was absent. In the precursor solutions prepared from TMOS, phase separation occurred after gelation, resulting in translucent gels. In contrast, in the solutions prepared from TEOS or a mixture of TMOS and TEOS at a TMOS mole fraction of 0.8, the phase separation can be induced before gelation, and opaque xerogels were easily obtained without fracture. The average size of macroscopic particles and macroporous structures were uniform over opaque xerogels prepared from TEOS. In contrast, in opaque xerogels prepared from the TMOS-rich mixture of TMOS and TEOS, the average particle size and macroscopic porosity inside them were notably smaller than those of the subsurface, probably because of a large exotherm upon gelation and the resulting temperature gradient in the gelling solutions. Such spatial morphology distribution made the sintering of the opaque gels into clear silica glasses difficult. Opaque gels prepared from TEOS and translucent gels prepared from solutions containing TMOS were transformed to clear silica glasses in high yields of ~99% by sintering in a helium atmosphere at 1050–1350 °C.Graphical abstractPhotographs of xerogels prepared from (left) TEOS or (right) a mixture of TMOS and TEOS with a TMOS molar fraction of 0.8, their SEM images taken at the inside (central) and subsurface (edge) parts, and silica glasses derived from these xerogels. The former xerogel was sintered into a clear glass because of the high uniformity of average particle size and macroscopic porosity, whereas the spatial unevenness of macroscopic morphology made the sintering of the latter one difficult.

SELECTION OF SUITABLE CATALYSTS FOR PRODUCTION OF NEW NANOCOMPOSITE MATERIALS

The article is devoted to the principles of hydrolytic polycondensation of tetramethoxysilane (TMOS) in an alkaline environment. Monolithic samples of SiO2 particles and xerogels were synthesized as a result of hydrolytic polycondensation of tetramethoxysilane in alkaline medium. Amine catalysts - pyridine derivatives were used to carry out the process. As a result, samples of different sizes were synthesized depending on the concentration of substances taken as catalysts. Smaller diameter particles were obtained at lower amine concentrations and larger diameter particles at higher concentrations. As the pKa value of the catalysts used in the synthesis of xerogels increases, certain increases and decreases in the properties of the resulting particles have been observed. Thus, with an increase in the pKa value, the density and hardness of the samples decreased, the percentage of SiO2 increased, and at the same time, the gelation time in the sol-gel system decreased. Images of the synthesized particles were obtained using a scanning electron microscope (SEM). Keywords: sol-gel, hydrolysis, polycondensation, tetramethoxysilane, xerogel, pKa, catalyst, SEM.

Facile room temperature synthesis of size-controlled spherical silica from silicon metal via simple sonochemical process

The waterglass or St o¨ ber method is commonly used to synthesize spherical colloidal silica; however, these methods have some disadvantages, such as complicated processes for the removal of sodium ions and expensive and energy-consuming raw materials such as tetraethoxysilane (TEOS). In this study, size-controlled spherical colloidal silica was synthesized from silicon metal at room temperature using an ultrasound process with hydrazine monohydrate as the solvent. Silicon metal dissolves easily in hydrazine monohydrate under ultrasound irradiation, and spherical colloidal silica can be synthesized by adding alcohol to this precursor solution. By changing the concentration or type of alcohol, size-controlled colloidal silica 20–200 nm in size could be easily obtained. In addition, finer and more monodisperse particles were produced by low-frequency ultrasound irradiation, which had a higher stirring effect at the particle formation stage. The present method is effective because size-controlled colloidal silica can be synthesized at room temperature using only silicon metal, hydrazine, and alcohol as raw materials, without complicated processes or expensive and energy-consuming raw materials such as TEOS or tetramethoxysilane (TMOS).

Silica Biomineralization with Lignin Involves Si-O-C Bonds That Stabilize Radicals.

Plants undergo substantial biomineralization of silicon, which is deposited primarily in cell walls as amorphous silica. The mineral formation could be moderated by the structure and chemistry of lignin, a polyphenol polymer that is a major constituent of the secondary cell wall. However, the reactions between lignin and silica have not yet been well elucidated. Here, we investigate silica deposition onto a lignin model compound. Polyphenyl propanoid was synthesized from coniferyl alcohol by oxidative coupling with peroxidase in the presence of acidic tetramethyl orthosilicate, a silicic acid precursor. Raman, Fourier transform infrared, and X-ray photoelectron spectroscopies detected changes in lignin formation in the presence of silicic acid. Bonds between the Si-O/Si-OH residues and phenoxyl radicals and lignin functional groups formed during the first 3 h of the reaction, while silica continued to form over 3 days. Thermal gravimetric analysis indicated that lignin yields increased in the presence of silicic acid, possibly via the stabilization of phenolic radicals. This, in turn, resulted in shorter stretches of the lignin polymer. Silica deposition initiated within a lignin matrix via the formation of covalent Si-O-C bonds. The silica nucleants grew into 2-5 nm particles, as observed via scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. Additional silica precipitated into an extended gel. Collectively, our results demonstrate a reciprocal relation by which lignin polymerization catalyzes the formation of silica, and at the same time silicic acid enhances lignin polymerization and yield.

Deposition of thin films on basalt fibers surface by atmospheric pressure plasma with different siloxane precursors

In this study, surface modification of basalt fibers (BFs) utilizing atmospheric pressure plasma deposition was carried out. Using this one-step deposition approach, three siloxane precursors with different structures including methyltrimethoxysilane (MTMS), hexamethyldisiloxane (HMDSO), and tetramethoxysilane (TMOS) were deposited on BFs surface, respectively. The physicochemical properties of the thin films from three different siloxane compounds are elucidated. In comparison with MTMS-coated sample, HMDSO-coated and TMOS-coated BFs surfaces feature an improved thermal insulation performance. The results demonstrate that atmospheric pressure plasma deposition is an efficient approach to modify flexible materials surface with improved thermal insulation. Moreover, it provides a reference to decide which precursor type is preferred for certain applications.

Phase Behavior of the Mixtures of 2- and 3-Components for Poly(styrene-co-octafluoropentyl methacrylate) by Dispersion Polymerization under CO2.

The dispersed-phase polymerization of poly(styrene-co-2,2,3,4,4,4-octafluoropentyl methacrylate), also known as p(styrene-co-OFPMA), took place in supercritical carbon dioxide (sc-CO2). The chemical and physical properties of p(styrene-co-OFPMA) were studied by varying the styrene-to-OFPMA ratios (40:1, 30:1, and 20:1) and 2,2'-azobis(isobutyronitrile) (AIBN) initiator amounts (wt %: 1.0, 2.0, 3.0). The cloud-point data were obtained for various systems, including the binary mixtures of p(styrene-co-OFPMA) (30:1 ratio, AIBN wt %: 1.0, 2.0, 3.0) with supercritical solvents such as sc-CO2, sc-CH3OCH3, sc-C3H6, sc-C4H8, and sc-CHClF2. Phase behavior (i.e., mixtures) was studied at temperatures of 324-455 K and pressure below 201 MPa. In the binary system of p(styrene-co-OFPMA) + sc-CH3OCH3, a lower critical solution temperature (LCST)-type curve was observed, characterized by a positive slope. Conversely, the binary systems of p(styrene-co-OFPMA) + (sc-C3H6, sc-C4H8, sc-CHClF2) exhibited an upper critical solution temperature (UCST) behavior with a decreasing slope. The phase equilibrium curves were obtained for p(styrene-co-OFPMA) [30:1; 1.0% (Mw = 42,400), 2.0% (Mw = 33,800), and 4.0% (Mw = 24,100); AIBN: 1.0 wt %] + sc-C3H6, sc-C4H8, and sc-CHClF2 mixtures. These curves exhibited an increasing slope for p(styrene-co-OFPMA) + sc-CH3OCH3 and a negative slope for p(styrene-co-OFPMA) + (sc-C3H6, sc-C4H8, sc-CHClF2) systems, indicating distinct phase behavior. Tetramethyl orthosilicate (TMOS) addition (0.0-68.9 wt %) to P(styrene-co-OFPMA) (30:1; AIBN wt %: 1.0) + solvents altered the phase equilibrium, switching from UCST to LCST, as evidenced by changes in the pressure-temperature slope.