Optimization of Parameters for Synthesis of MFI Nanoparticles by Taguchi Robust Design

MFI‐type zeolite was successfully synthesized by hydrothermal crystallization of clear synthesis mixtures. A statistical experimental design method (the Taguchi method with an L8 orthogonal array) was implemented to optimize the experimental conditions for the preparation of MFI nanocrystals with respect to particle size and distribution as the desirable properties. In the Taguchi experimental design, crystallization temperature, water content, template/silica molar ratio, aluminum content, as well as the presence of alkaline cations were chosen as significant parameters affecting the properties. It was shown that water and aluminum content of the synthesis solution were the most important parameters affecting particle size and distribution. The MFI nanocrystals with an average particle size of 95 nm and the narrow particle size distribution of ± 8.5 nm were synthesized under optimum conditions.     

Determination of Heat Treatment Temperature for Completing Polycondensation of Vinyl Substituted Silica Particles Prepared by Sol‐Gel Method

The completion of the polycondensation of sol‐gel derived organic‐inorganic hybrid silica by heat treatment was studied for powder samples prepared from vinyltrimethoxysilane and vinyltriethoxysilane. The appropriate temperature for the completion of the prepared submicron powdery samples from both starting compounds was determined through thermogravimetric analysis. The completion or incompletion of the polycondensation was elucidated by means of several instrumental methods in addition to a light scattering test. The lowest heat treatment conditions for the particles from vinyltrimethoxysilane and vinyltriethoxysilane are 170 °C and 180 °C, respectively, for 24 h. The morphologies of the heat treated samples were found to be slightly different depending on the starting material used.     

Optimization of Effective Sol‐Gel Parameters for the Synthesis of Mesoporous γ‐Al2O3 Using Experimental Design

Mesoporous nanocrystalline γ‐alumina was prepared by a template‐free sol‐gel method using aluminum ethoxide as precursor. Significant parameters, such as the water/aluminum ethoxide molar ratio, the pH of the solution, and the time and temperature of aging, were optimized by the Taguchi method to obtain γ‐alumina with a high surface area and pore volume. The influences of the main parameters on the catalytic performance of the prepared catalysts were investigated via dehydration of methanol to dimethyl ether in a fixed‐bed reactor. The catalysts were characterized by X‐ray diffraction, N₂ adsorption‐desorption, ammonia temperature‐programmed desorption, and scanning electron microscopy techniques. The results show that the aging temperature had a significant influence on the catalyst performance.     

Water‐Resistant Poly(vinyl alcohol)‐Silica Hybrids through Sol‐Gel Processing

Poly(vinyl alcohol) (PVA)‐silica hybrids with exceptionally reduced solubility in water were synthesized. The hybrid xerogels were fabricated through sol‐gel processing of a mixture of PVA and the acid‐catalyzed silica precursor tetraethoxysilane. The effects of varying ratios of PVA and silica precursor on the surface structure, thermal properties, crystallinity, and solubility of the hybrids were investigated. Unlike the highly water‐soluble nature of PVA, all the hybrids displayed considerably reduced solubility in water. This anomalous behavior of PVA in the hybrids can be attributed to the unavailability of its pendant –OH groups. Water‐resistant PVA‐silica hybrids can find applications in various technologies requiring biocompatible systems that are stable in aqueous environments.     

Preparation and Properties of an AP/RDX/SiO2 Nanocomposite Energetic Material by the Sol‐Gel Method

A nanocomposite energetic material was prepared using sol‐gel processing. It was incorporated into the nano or submicrometer‐sized pores of the gel skeleton with a content up to 95 %. AP, RDX, and silica were chosen as the energetic crystal and gel skeleton, respectively. The structure and its properties were characterized by SEM, BET methods, XRD, TG/DSC, and impact sensitivity measurements. The structure of the AP/RDX/SiO₂ cryogel is of micrometer scale powder with numerous pores of nanometer scale and the mean crystal size of AP and RDX is approx. 200 nm. The specific surface area of the AP/RDX/SiO₂ cryogel is 36.6 m² g⁻¹. TG/DSC analyses indicate that SiO₂ cryogel can boost the decomposition of AP and enhance the interaction between AP and RDX. By comparison of the decomposition heats of AP/RDX/SiO₂ at different mass ratios, the optimal mass ratio was estimated to be 6.5/10/1 with a maximum decomposition heat of 2160.8 J g⁻¹. According to impact sensitivity tests, the sensitivity of the AP/RDX/SiO₂ cryogel is lower than that of the pure energetic ingredients and their mixture.     

Bioactive Sol‐Gel Coatings

Recent sol‐gel techniques enable bioactive composite layers to be prepared by the embedding of bioactive compounds, biomolecules (BMs) and cellular systems within inorganic layers. These novel bioactive layers offer interesting new applications, e.g. biocompatible coatings on implants and medical products, the preparation of biosensors and biocatalysts, and coatings that can release biocides in a controlled manner.     

Effects of Solution History on Sol‐Gel Processed Tin‐Oxide Thin‐Film Transistors

Antimony‐doped tin‐oxide (SbTO) thin films deposited by solution processing methods represent a promising avenue toward low‐cost transparent and flexible electronics, but reproducibility and performance homogeneity of devices prepared from these thin films have been seldom investigated. In this study, the role of sol‐gel precursor aging is investigated by comparing SbTO thin‐film transistors (TFT) fabricated from two different sol‐gel solutions: the first one was aged for 4 years, whereas the second was prepared freshly. For each of the solutions, a set of TFT was assembled on the same chip, to investigate the distinct roles of aging and sample inhomogeneity on the electronic and transport properties of SbTO. Higher electron mobility, but lower on/off ratios, was found in TFTs assembled from freshly prepared solution, an effect that may be assigned to larger size of SbTO grains. This study demonstrates the critical role of the solution “history” in determining the properties and reproducibility of SbTO TFTs, over other factors, including local film inhomogeneity and local fluctuations of the annealing temperature.     

High‐Temperature Capture of CO2 on Lithium‐Based Sorbents Prepared by a Water‐Based Sol‐Gel Technique

A convenient water‐based sol‐gel technique was used to prepare a highly efficient lithium orthosilicate‐based sorbent (Li₄SiO₄‐G) for CO₂ capture at high temperature. The Li₄SiO₄‐G sorbent was systematically studied and compared with the Li₄SiO₄‐S sorbent prepared by solid‐state reaction. Both sorbents were characterized by X‐ray diffraction, scanning electron microscopy, nitrogen adsorption, and thermogravimetry. The CO₂ sorption stability was investigated in a dual fixed‐bed reactor. Li₄SiO₄‐G exhibited a special Li₄SiO₄ structure with smaller crystalline nanoparticles, larger surface area, and higher CO₂ adsorption properties as compared with Li₄SiO₄‐S. The Li₄SiO₄‐G sorbent also maintained higher capacities during multiple cycles.     

Synthesis,Characterization, and In Vitro Bioactivity of Sol‐Gel‐Derived Zn,Mg, and Zn‐Mg Co‐Doped Bioactive Glasses

Bioactive glasses in the systems CaO‐SiO₂‐P₂O₅‐ZnO, CaO‐SiO₂‐P₂O₅‐MgO, and CaO‐SiO₂‐P₂O₅‐MgO‐ZnO were prepared and characterized. Bioactive glass powders were produced by the sol‐gel method. The prepared bioactive glass powders were immersed in a simulated body fluid (SBF) for periods of up to 28 days at 310 K to investigate the bioactivity of the produced samples. Inductively coupled plasma (ICP) and ultraviolet (UV) spectroscopic techniques were used to detect changes in the SBF composition. X‐Ray diffraction (XRD) was utilized to recognize and confirm the formation of a hydroxyapatite (HA) layer on the bioactive glass powders. Microstructural characterizations of the bioactive glass samples were investigated by scanning electron microscopy (SEM) techniques. Density, porosity, and surface area values of bioactive glass powders were also determined in order to characterize the textural properties of the samples. The results revealed the growth of an HA layer on the surface of the bioactive glass samples. MgO in the glass sample increases the rate of formation of an HA layer while ZnO in the glass slows it down.     

Solvent-Free Enzymatic Synthesis of 1-o-Galloylglycerol Optimized by the Taguchi Method

Gallic acid (GA) and its lipophilic forms, alkyl gallates, have been widely used in several industrial fields as antioxidants. However, the potential harmful effects of alkyl gallates, such as estrogenic effects, limit their application and raise safety concerns. The glycerol ester of GA, 1-o-galloylglycerol (GG), has not been reported to cause adverse health effects. Owing to the steric and electron-donating effects of GA, lipase-catalyzed synthesis of GG has not been successfully achieved. In this work, glycerol ester of GA, GG, was successfully synthesized for the first time by the enzymatic transesterification of glycerol and n-propyl gallate (PG). GG was synthesized with an immobilized and commercially available food-grade lipase (Lipozyme® 435) under solvent-free (no extra solvent) conditions at atmospheric pressure and nitrogen flow. The effects of the reaction conditions, including the reaction temperature, substrate molar ratio, reaction time, and enzyme load, were optimized using the Taguchi method and regression analysis. The structure of the product was elucidated using Fourier-transform infrared spectroscopy (FT-IR), electrospray ionization high-resolution accurate-mass tandem mass spectrometry (ESI-HRAM-MS/MS), and 1D and 2D nuclear magnetic resonance spectroscopy (NMR). Under the optimal conditions, GG was synthesized in 67.1 ± 1.9% yield at 50°C, 25:1 (glycerol:PG) substrate molar ratio, 120 hours, and 23.8% enzyme load relative to the total weight of the substrates.     

Catalysis with Doped Sol‐Gel Silicates

Silicates doped with catalytic species have only been slowly adopted by the fine chemicals and pharmaceutical industries, in spite of their remarkable and unique properties such as pronounced physical and chemical stability; high (enantio)selective activity and ease of materials production and application. This is now changing thanks to stricter safety regulations and to concomitant success of the first commercial catalysts. In this account we tell the story of these materials and identify some deficiencies in the innovation process that may serve as lesson in guiding the future management of innovation in these relevant industries.     

A Simple Method for the Reinforcement of UV‐Cured Coatings via Sol‐Gel Photopolymerization

A difunctional methacrylate oligomer was mixed with a variable amount of a MAPTMS precursor in the presence of both a radical and a cationic photoinitiator. The simultaneous photolysis of both photosensitive molecules upon UV irradiation allowed the single‐step generation of a type‐II polymethacrylate/polysiloxane nanocomposite film. Methacrylate and methoxysilyl conversions during irradiation were efficiently monitored by FTIR spectroscopy. The inorganic structure of the resulting silica‐based hybrid films was characterized using ²⁹Si solid‐state NMR. Finally, the reinforcement ability of the resulting hybrid films was also assessed by using a unique range of characterization techniques: DMA, scratch test, and nanoindentation.

     

Preparation of Nano‐Structured RDX in a Silica Xerogel Matrix

RDX is preferred as explosive in munitions due to its balance of power and sensitivity that is known to be dependent on its particle size and size distribution. In this study, we prepared nano‐sized RDX in a silica xerogel matrix using a sol‐gel method and investigated its sensitivity for explosive properties. The presence of RDX in composite xerogel was confirmed by TG‐DSC and FTIR techniques. Microstructure and porosity were characterized by transmission electron microscopy (TEM), small angle X‐ray scattering, and N₂‐physisorption techniques. TEM results showed that the size of RDX particles in the RDX‐silica composites is in the range of 10–30 nm. The sensitivity to impact and friction was found to be higher for the composites compared to raw RDX. It was also found to be significantly dependent on the acetone/TMOS ratio used in the preparation.     

Colloidal Sol–Gel Synthesis and Photocatalytic Activity of Nanoparticulate Nb2O5 Sols

A detailed study of a novel synthesis via colloidal sol–gel route for obtaining nanoparticulate Nb₂O₅ was performed. Parameters such as temperature and H⁺:Nb⁵⁺ and Nb⁵⁺:H₂O molar ratios were controlled in order to determine the best conditions of synthesis. Moreover, particle size distribution, zeta potential, structure by X‐ray diffraction, and the photocatalytic activity of the particulate sols were also evaluated. The obtained results indicate that the colloidal sol–gel synthesis is a good alternative for obtaining Nb₂O₅ either as stable nanoparticulate sol or as a nanosized powder. Nb₂O₅ amorphous nanoparticles with an average size of 20 nm were obtained by controlling the synthesis variables. The heat‐treatment process allowed the formation of Nb₂O₅ with orthorhombic structure that transforms at higher temperatures to monoclinic phase. The highest photocatalytic activity was observed under λ = 365 nm, the smallest UV energy used in the experimental tests.     

Alumina‐Catalyzed Epoxidation with Hydrogen Peroxide: Recycling Experiments and Activity of Sol‐Gel Alumina

Commercial alumina looses some activity after the first epoxidation reaction of (S)‐limonene with hydrogen peroxide, but maintains a good activity and a very high selectivity in the subsequent three reactions. After this its activity is strongly reduced, probably due to structural modifications. Aluminas obtained by sol‐gel methods are normally less active than the commercial alumina. However, the use of monomeric aluminum sec‐butoxide and of oxalic acid to form stable alumina mesophases allows a very active alumina to be obtained, which catalyses the epoxidation of the less reactive cyclohexene with hydrogen peroxide in 98% yield. Close to 50% of the active oxygen is used up in the formation of molecular oxygen.     

Sol‐Gel‐Derived Sb‐Doped SnO2 Nanoparticles Controlled in Size by Nb2O5

Nanocrystalline Sb‐doped SnO₂ particles were prepared by sol‐gel and their particle growth was controlled by niobium oxide. In the present synthesis, SnCl₄ and SbCl₃, as precursors, were dissolved and hydrolyzed in ethylene glycol at 80–120 °C, and further 0.1 mol.‐% Nb₂O₅ through its precursor NbCl₅ was mixed to the above solution. The mixture was then dried at 120–150 °C and calcinated at 600 °C for 2 hours. By XRD and TEM, Sb‐doped SnO₂ nanoparticles were highly crystalline and their mean crystal size was ca.10–20 nm with narrow particle size distribution. As the addition of antimony increased, the crystallinity and particle size distribution of SnO₂ particles had the trend to decrease.     

Synthesis of Organic Dye-Impregnated Silica Shell-Coated Iron Oxide Nanoparticles by a New Method

A new method for preparing magnetic iron oxide nanoparticles coated by organic dye-doped silica shell was developed in this article. Iron oxide nanoparticles were first coated with dye-impregnated silica shell by the hydrolysis of hexadecyltrimethoxysilane (HTMOS) which produced a hydrophobic core for the entrapment of organic dye molecules. Then, the particles were coated with a hydrophilic shell by the hydrolysis of tetraethylorthosilicate (TEOS), which enabled water dispersal of the resulting nanoparticles. The final product was characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, photoluminescence spectroscopy, and vibration sample magnetometer. All the characterization results proved the final samples possessed magnetic and fluorescent properties simultaneously. And this new multifunctional nanomaterial possessed high photostability and minimal dye leakage.     

Application of Taguchi Method for Characterization of Corrosion Behavior of TiO2 Coating Prepared by Sol‐Gel Dipping Technique

Titanium oxide (TiO₂) nanoparticle coatings were deposited on the 316L stainless steel substrates by sol‐gel method. The morphology, structure, and corrosion resistance of the coating were analyzed using SEM, AFM, X‐ray diffraction, and electrochemical techniques. The deposition parameters employed to realize the anticorrosion performance including calcinations temperature, polyethylene glycol (PEG) content, pH value, and number of dipping cycles were investigated. Taguchi statistical experiments were carried out to determine the influence of the deposition variables on anticorrosion properties and optimal conditions. The results indicated that a higher anticorrosion performance of TiO₂ films could be achieved using 1 g of PEG in a sol with pH in range of 7–9, six cycles of dipping, and calcination temperature at 400°C. The Tafel polarization measurements indicate that i_corr value decreases about 200 times and the R_corr value increases around 57 times compared with uncoated 316L stainless steel.