Precursor Tetraethyl Orthosilicate Research Articles

Synthesis of silica-encapsulated myristic acid phase-change-assisted nanocapsules for thermal management applications

AbstractMyristic acid-based silica (MA/SiO2) nano-encapsulated phase change materials (NePCMs) were synthesized by the sol–gel process. Five different samples of the MA/SiO2 nanocapsules were prepared by varying the mass of the myristic acid. The nanocapsules were characterized by Fourier transform infrared spectrophotometer (FTIR), X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX), and dynamic light scattering (DLS). These characterization techniques confirmed the successful encapsulation of the myristic acid inside the silica shell. The maximum latent heat was found to be 114.46 J/g for the sample which was prepared with 25 g myristic acid and 20 ml tetraethyl orthosilicate precursor material. The highest encapsulation ratio of approximately 62% was obtained in the same sample and the mean size of the nanocapsules was 597 nm. The thermal stability of these nanocapsules was assessed using the thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC) results exhibited that the thermophysical properties remained consistent after 50 heating/cooling thermal cycles indicating excellent durability of the NePCMs.

A promising method for promoting interfacial adhesion of aramid/rubber composite using atmospheric pressure plasma surface modification

AbstractToday, aramid fibers are well known as a high‐performance and ideal material for reinforcement purposes in rubber product manufacturing including hoses, tires, cables, and conveyors composites. However, surface modification of aramid fiber is necessary to solve poor interfacial adhesion between aramid fibers and the rubber matrix. Accordingly, in the present study, the effect of the surface modification of aramid fibers using atmospheric pressure plasma treatment with different precursors on adhesion to the rubber matrix was investigated. For that, the plasma coating was conducted using argon as the main working gas, and toluene, acetonitrile, tetraethyl orthosilicate (TEOS), and hexamethyldisiloxane (HMDSO) as liquid precursors. The physical–chemical characterization of the layer confirmed the successful deposition of amorphous carbon, amorphous nitride‐carbon, SiO2, and Polydimethylsiloxane (PDMS)‐like coating layers on the surface of aramid fibers by using toluene, acetonitrile, TEOS, and HMDSO as precursors, respectively. Overall, the result showed that the plasma surface modifications with acetonitrile precursor leads to the increase in interfacial adhesion of aramid/rubber composite, while retaining the tensile strength, and flame resistance properties of aramid as original fibers. Notably, the results of this study confirm the potential use of atmospheric pressure plasma for surface modification of aramid yarn to produce functional aramid for use in rubber composites.Highlights The plasma‐coated aramid using HMDSO, TEOS, toluene, and acetonitrile precursors was prepared; and its effect on the tensile properties of aramid fiber as well as interfacial adhesion between aramid/rubber composite was investigated. The positive effect of atmospheric pressure plasma coating using HMDSO precursor on the tensile properties of aramid fiber was revealed. The positive effect of atmospheric pressure plasma coating using toluene and acetonitrile on the interfacial adhesion between aramid/rubber composite was revealed. The positive effect of atmospheric pressure plasma coating using TEOS precursor on the flam resistance property of aramid fiber was revealed. This study provides valuable insights into the effect of the different plasma‐coated organosilicon and hydrocarbon precursors on the interfacial adhesion between aramid/rubber composite.

Low-frequency noise in InSnZnO thin film transistors with high-quality SiO2 gate oxide stacks

Low-frequency noise (LFN) in InSnZnO (ITZO) thin-film-transistors (TFT) with high-quality SiO2 gate oxide (GO) stacks is studied. This stack is fabricated by the plasma enhanced chemical vapor deposition (PECVD) and comprises two single layers. One layer is deposited by a SiH4 source (SiH4–SiO2), and the other uses a tetraethyl-orthosilicate precursor (TEOS-SiO2). The drain current noise power spectral densities follow the typical 1/f rule, and the main origin of LFN changes with the variation of drain current intensities. At low drain current intensities, LFN is affected by grain boundaries in the channel. As the drain current intensities increase, LFN originates from the carrier number fluctuations in devices with single TEOS-SiO2 GOs and from the carrier number with correlated mobility fluctuations in devices with SiO2 stacks GOs. At extremely high drain current intensities, the contact noise acts as a significant source of LFN in devices with SiO2 GO stacks. According to the carrier number with correlated mobility fluctuation (ΔN−Δμ) model, the devices with optimal stacks GOs exhibit a relatively low trap density near the ITZO/SiO2 interface. Additionally, these devices have a lower border trap density in GOs compared to those with single compositions. It demonstrates that high-quality SiO2 stacks reduce traps near the SiO2/ITZO interface, leading to enhanced devices performance. This work provides a precise and efficient method to evaluate the quality of GOs in metal oxide TFTs.

Silica Nanofibers with Enhanced Wettability and Mechanical Strength for Bone Tissue Engineering: Electrospinning without Polymer Carrier and Subsequent Heat Treatment

AbstractThe unique properties of silica, such as biocompatibility and the ability to promote cell growth, demonstrate favorable results in different applications such as drug delivery, biomedical applications, and tissue engineering (TE). Electrospinning has emerged as a method for creating a substrate with a high surface area and structural resemblance to natural extracellular matrices. A common method of fabricating silica nanofibers (SNFs) for TE involves hybrid silica/ polymer nanofibers, which require calcination to remove the polymer and obtain pure silica. This study aimed to use the sol‐gel precursor tetraethyl orthosilicate (TEOS) to fabricate pure SNFs through electrospinning and investigate calcination's effect on their morphology, thermal behavior, mechanical properties, wettability, and porosity. The findings indicated that the calcination process reduced Young's modulus, wettability, and porosity, which may influence the applications of SNFs in TE. Nanofibrous mats with high Young's modulus can play a crucial role in providing mechanical support for tissue repair. Additionally, high porosity and wettability can facilitate cell attachment and growth by improving nutrient and oxygen transport to the cells. This study provides valuable insights into the potential use of pure SNFs and highlighted the effects of heat treatment on their properties.

Silica-magnetite nanoparticles: Synthesis, characterization and nucleic acid separation potential

Silica-coated magnetic nanoparticles can be utilized for the magnetic separation of nucleic acids, which is an important step in many clinical procedures. A series of silica-functionalized superparamagnetic iron oxide nanoparticles (SiO2@MNPs) was synthesized to efficiently separate nucleic acids for the sensitive detection of viral infections. Magnetite nanoparticles (MNPs) coated with different thicknesses of silica layer resulting from different ratios of tetraethylorthosilicate (TEOS) precursor to magnetite (TEOS/MNPs = 0.4, 1.0, 2.0, 3.0, 4.0, 5.0 ml/g) have been selected for characterization of their physico-chemical properties and biological activities. The SiO2@MNPs' morphology, size, magnetic and surface properties, cytotoxicity and nucleic acid binding propensity were determined to select the ones with the highest RNA separation potential. Our results showed that RNA-binding properties and magnetic separation efficiency are nanoparticle size-dependent. The highest binding and separation efficiencies were detected for the smaller SiO2@MNPs with TEOS/MNPs (v/w) ratios equal to 1.0 and 2.0. These nanoparticles are promising candidates for clinical application relevant to RNA viruses.

Synthesis and Characterization of Zirconia-Silica PMMA Nanocomposite for Endodontic Implants.

This study aimed to enhance the mechanical properties of PMMA composites by introducing various types of fillers, including ZrO2, SiO2, and a mixture of ZrO2-SiO2 nanoparticles, which were prepared as prototypes for an endodontic implant. The ZrO2, SiO2, and mixed ZrO2-SiO2 nanoparticles were synthesized using the sol-gel method and the precursors Tetraethyl Orthosilicate, Zirconium Oxychloride, and a mixture of both precursors, respectively. Before polymerization, the as-synthesized powders were subjected to the bead milling process to obtain a well-dispersed suspension. Two scenarios for the fillers were implemented in the preparation of the PMMA composite: a mixture of ZrO2/SiO2 and ZrO2-SiO2 mixed with two different types of silane: (3-Mercaptopropyl) trimethoxysilane (MPTS) and 3-(Trimethoxysilyl) Propyl Methacrylate (TMSPMA). The observation of the characteristics of all of the investigated fillers included the use of a particle-size analyzer (PSA), a Zeta-potential analyzer, FTIR, XRF, XRD, and SEM. The mechanical properties of the MMA composites, as prepared under various scenarios, were observed in terms of their flexural strength, diametrical tensile strength (DTS), and modulus of elasticity (ME). These levels of performance were compared with a PMMA-only polymer. Each sample was measured five times for flexural strength, DTS, and ME. The results showed that the best PMMA composite was SiO2/ZrO2/TMSPMA, as revealed by measurements of the flexural strength, DTS, and ME corresponding to 152.7 ± 13.0 MPa, 51.2 ± 0.6 MPa, and 9272.8 ± 2481.4 MPa, which are close to the mechanical properties of dentin. The viability of these PMMA composites, as measured up to day 7, was 93.61%, indicating that they are nontoxic biomaterials. Therefore, it was concluded that the PMMA composite created with SiO2/ZrO2/TMSPMA can be considered to be an acceptable endodontic implant.

Controlled synthesis and superior UV-visible photocatalytic activity of carbon quantum dots encapsulated with silica

• Synthesis of C-QDs was performed from dehydration of Glucose-D in concentrated sulphuric acid at room temperature. • Silica encapsulated C-QDs were carried out in situ, followed by high temperature calcination. In this work, we report a facile one-step approach to prepare carbon quantum dots doped silica. Carbon quantum dots (C-QDs) were synthesized using Glucose as precursor and sulfuric acid (98%) as carbonating agent in aqueous medium. The encapsulation of C-QCDs was then achieved by in situ hydrolysis of precursor Tetraethyl orthosilicate (TEOS) through Solgel method. The structural studies of C-QDs doped silica was done by powdered X-ray diffraction ( p -XRD). The optical characterization of the prepared C-QDs was performed by Ultraviolet-visible (UV-vis) spectroscopy. Consequently, the as-prepared C-QCDs were found to be highly fluorescent with little crystallinity. The morphological investigation of as-made silica and C-QCDs doped silica was studied by field emission scanning electron (FSEM). In order to study photodegradation studies methylene blue was used as model compound. C-QCDs doped silica showed higher degradation (98.5%) in comparison to the pristine C-QDs (38%) and silica (76%) in neutral media.

A simple and green self-conversion method to construct silicon hollow spheres for high-performance Li-ion battery anodes

Silicon (Si) anode has garnered attention as a potential replacement for high energy density lithium-ion battery anodes. Its commercial application, however, is still hindered by the issues of rapid capacity attenuation due to large volume change during (de)lithiation process, complex preparation process, and high cost. In this work, a simple and green strategy was proposed to fabricate carbon-coated hollow porous silicon spheres (Hp-Si@C) by a self-conversion method and subsequent magnesiothermic reduction. The synthesis of Hp-Si@C by this method used inexpensive tetraethyl orthosilicate precursors and did not involve the use of additional sacrificial template, complicated CVD and toxic hydrofluoric acid, which was simple, inexpensive, green and scalable. NaCl was introduced as a heat scavenger to avoid the formation of SiC and maintain the hollow morphology of the precursor. The electrochemical behaviors of Hp-Si@C were investigated by in situ electrochemical characterization. The structure of Hp-Si@C defined fast ion transport routes and provided expansion space during lithiation process, endowing it with stable cycling performance and fast electrochemical reaction kinetics. Hp-Si@C had a delithiation capacity of 1228 mAh g−1 with a capacity retention of 69% at 2 A g−1, and a rate capacity of 865 mAh g−1 at 10 A g−1.

A Hybrid Molecularly Imprinted Polymer for Selective Adsorption of Urinary S-Phenylmercapturic Acid

A hybrid molecular imprinted polymer (HMIP) obtained by the organic monomer 4-vinylpyridine (4-VP) and the inorganic precursor tetraethyl orthosilicate (TEOS) was synthesized for the selective extraction of urinary S-phenylmercapturic acid (u-SPMA), a biomarker of benzene exposure. The chemical and structural characterization of the synthetic adsorbent was performed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and textural analysis employing N2 adsorption-desorption isotherms. Selective and adsorptive performance of the imprinted polymers were evaluated by kinetic, isothermal, thermodynamic, and selectivity studies. The kinetic data were well adjusted to pseudo-second order and intraparticle diffusion models, leading to selectivity coefficient (K) value of 0.03 g mg-1 min-1 for HMIP. In addition, the adsorption isotherms were better described by the Sip model achieving a maximum adsorption capacity of 284.81 μg g-1 (at 288.15 K).

Effect of pH on the Synthesis of Silica Sol-Gel Tetraethylorthosilicate-Trimethylchlorosilan (TEOS-TMCS)

Sol-gel synthesis of silica employing the co-precursor trimethylchlorosilane (TMCS) and the precursor tetraethylorthosilicate (TEOS) was accomplished. The purpose of this investigation was to ascertain how pH affected the properties of synthetic silica. The synthesized hydrophobic silica was characterized using FTIR, TGA, and GSA to determine the effect of pH adjustment on the functional group characters, thermal properties, and pore morphology. The ratio between TEOS/TMCS was fixed at 75:25 and varied the pH (4, 6, 7, 8, and 10) and the calcination temperature (without calcination, 300℃ and 500℃). FTIR analysis showed that the number of C-H and Si-OH groups in the xerogel decreased with increasing calcination temperature. Xerogel formed at pH 6 provides the highest thermal stability among other pHs. The results from the BET analysis revealed that changes in pH directly affect the physical characteristics of the surface, making the resulting gel network less rigid and more susceptible to shrinkage of pore volume and diameter in the atmosphere. Meanwhile, in an alkaline medium, continuous condensation will occur so that the pore diameter and volume decrease. The high pore diameter and volume imply that pH 7 is ideal for preparing xerogels.

Removal of Penicillin G from aqueous medium by PPI@SBA-15/ZIF-8 super adsorbent: Adsorption isotherm, thermodynamic, and kinetic studies

In the present paper, synthesis of SBA-15 nanoparticles was carried out from tetraethyl orthosilicate (TEOS) precursor using the sol-gel process. After being combined with Poly propylene imine, and ZIF-8 they were employed for the removal of Penicillin G. The synthesized combination morphology was assessed using nitrogen adsorption and desorption (BET), Fourier transform infrared (FTIR) spectroscopy, and X-ray powder diffraction (XRD). The parameters affecting Penicillin G removal, including pH, amount of adsorbent, time of contact, temperature, and concentration, were optimized, and the optimum levels of the mentioned variables were reported to be pH = 3, 0.03 g, 90 min, 25 °C, and 100 ppm, respectively. In addition, application of Freundlich, Langmuir, Dubinin–Radushkevhch, and Tempkin models and pseudo-first-order and pseudo-second-order adsorption synthetic equations aimed at determining the type of adsorbent isotherm. The results showed that the best fitting of Langmuir (R2 = 0.9944, qm = 400 mg/g) for adsorption isotherm and pseudo-second-order model (R2 = 0.9905) for kinetics studies. Furthermore, data of Gibbs free energy and enthalpy demonstrated an exothermic and spontaneous process in the research.

A Sol-gel Membrane Utilized Cellulose Paper Doped with α-furil Dioxime for Colorimetric Determination of Nickel.

A simple and sensitive colorimetric sensor for nickel(II) ions has been successfully prepared by immobilizing α-furil dioxime reagent in the sol-gel matrix with a solid supporting filter paper medium. The sensor was developed using tetraethyl orthosilicate (TEOS) precursors with 4 days aging time, the mole ratio of water: precursor was 4:1, and reagent concentration at 0.10%. The sensor was quantified by utilizing the Red (R), Green (G), and Blue (B) values ​​of the colors that were successfully displayed after the detection process. The RGB value is confirmed by the Euclidean Distance (ED) equation to determine the optimum conditions. There was no observed degree of leaching in plain sight, and the result of leaching investigation by the double dyeing method did not show any significant change. The linear range was ​​0.10 to 2.8 ppm with an R2 of 0.9964. The values of LOD and LOQ were 0.1 ppm and 0.4 ppm, respectively. In addition, the sensor was free from interfering species and had a percent recovery around 90 to 110%.

Exploring the Effect of Glycerol and Hydrochloric Acid on Mesoporous Silica Synthesis: Application in Insulin Loading.

Mesoporous silica (MPS), a carrier for active pharmaceutical ingredients, has a wide range of particle and pore morphology. A thorough understanding of ingredients used in MPS synthesis is an important prerequisite for optimizing its physicochemical characteristics. The present study aimed to evaluate the effect of glycerol and hydrochloric acid on the characteristics of synthesized MPS. Ordered MPS materials were synthesized using the pluronic P123 template and tetraethyl orthosilicate (TEOS) precursor. A three-level factorial design was employed to study the interaction between glycerol and hydrochloric acid. The optimized MPS particles were reasonably uniform in shape (short and rod-shaped) and < 1 μm in size with a smooth surface morphology. The nitrogen adsorption–desorption analysis revealed that the uniform cylindrical pores of the prepared MPS had a diameter > 5 nm and a total surface area > 500 m2/g. With increasing acid and glycerol concentrations, the particle size of MPS decreased. However, while the glycerol increased the heterogeneity of the synthesized particles, the acid decreased it. The developed MPS was successfully loaded with a biological drug (insulin) with a 21.94% encapsulation efficiency. The MPS prepared in this study exhibits potential applications as a drug delivery carrier for drugs with a large molecular weight.

Synthesis, characterization and application of new adsorbent composites based on sol-gel/chitosan for the removal of soluble substance in water

In this work, new adsorbent composites from the silica precursor tetraethyl orthosilicate (TEOS) and chitosan have been successfully synthesized, denominated 20%Chi, 30%Chi and 40%Chi. The composites presented enhanced chemical and physical characteristics, with emphasis on the high surface areas between 374.94 m2/g to 886.31 m2/g. The application of the composites in the model system (TY - Tartrazine yellow dye), presented adsorption capacities dependent on the amount of chitosan in the composite (40%Chi > 30%Chi > 20%Chi). However, from the experimental data of the constituent materials, 30%Chi provided the greatest increase in the adsorption capacity in the monolayer, with values of 36%. This demonstrates that the amount of chitosan in the compound alters the arrangement of adsorption sites. The 30%Chi composite presented life cycle superior to 10 reuse cycles.

Synthesis, characterization and photocatalytic efficiency of Fe3O4/SiO2/TiO2, SrFe12O19/SiO2/TiO2 and Fe3O4/SiO2/ZnO core/shell/shell nanostructures

In this research, three magnetically separable photocatalysts, Fe3O4/SiO2/TiO2, SrFe12O19/SiO2/TiO2 and Fe3O4/SiO2/ZnO, with core/shell/shell structures were successfully prepared. In the first step, soft magnetic and hard magnetic Fe3O4 and SrFe12O19 powders were synthesized using carbon reduction and co-precipitation routes, respectively. In the second step, silica coating was performed by controlling the hydrolysis and con- densation of tetraethyl orthosilicate (TEOS) precursor on the magnetic cores. In the third step, a layer of TiO2 or ZnO photocatalytic shells was made on the as-prepared composites using titanium n-butoxide (TNBT) or zinc nitrate hexahydrate, respectively. The formation of the core/shell/shell structures was confirmed by FESEM and TEM analyses. The saturation magnetizations of the Fe3O4/SiO2/TiO2, SrFe12O19/SiO2/TiO2 and Fe3O4/SiO2/ZnO photocatalytic materials were 41.5, 33 and 49 emu/g, respectively. Photocatalytic activity was evaluated by degradation percentages of methylene blue (MB) under UV illumination, which were 88%, 83% and 62%, for the Fe3O4/SiO2/TiO2, SrFe12O19//TiO2 and Fe3O4/SiO2/ZnO composites, respectively. The first-, and second-order reaction kinetics were used to find out the suitable MB removal kinetics.

Electric field enhanced in situ silica nanoparticles grafted activated carbon cloth electrodes for capacitive deionization

Activated carbon clothes (ACCs) were modified by in situ deposition of silica nanoparticles (SiO2 NPs) to enhance the dielectric property of ACC surface and used as electrodes in the capacitive deionization (CDI) system. Four different concentrations of tetraethyl orthosilicate precursors were used as silica source and the effect of concentration on the CDI performance was investigated. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis revealed the presence of Si-O bonds on the ACC surface and Raman analysis confirmed the graphitic structure of the ACC was intact after grafting with SiO2 NPs. SiO2 NPs coated ACC electrodes revealed better desalination efficiency and average salt removal rate (ASRR) than pristine ACC. Specifically, ACC electrodes coated with 45 mM silica (SiO2-III) exhibited the highest specific capacitance of 97.4 ± 0.1F/g, average desalination efficiency of 70 % with ASRR of 0.075 ± 0.008 mg/cm2/min using 200 ppm NaCl. Moreover, CDI Ragone’s plot verified the highest desalination rate was achieved with 45 mM SiO2 coated ACC electrodes. Furthermore, different salt concentrations and applied potentials upon desalination performances were also investigated. Moreover, post characterization of used pristine ACC and SiO2-III electrodes exhibited the sign of substantial electrode oxidation for pristine ACC but less on SiO2 NPs coated ACC electrodes. SiO2 NPs decorated ACC electrodes were not only enhanced localized electric field around dielectric coating of SiO2 NPs but also prevented the surface oxidation of the electrodes.

Hydrolysis and Condensation of Tetraethyl Orthosilicate at the Air–Aqueous Interface: Implications for Silica Nanoparticle Formation

The silica (SiO2) nanoparticles of a well-known silica precursor tetraethyl orthosilicate (TEOS) are generally synthesized via a promising solution-gelation inorganic polymerization process. The monodisperse silica nanoparticles have potential applications ranging from the formation of dental nanocomposites to antireflective coatings. In the present study, we have systematically investigated the in situ interfacial molecular structure of TEOS and its impact on the interfacial water structure during the processes of hydrolysis and condensation at the air–aqueous interface using sum-frequency generation (SFG) vibrational spectroscopy. With the presence of water, a gradual decrease in the SFG intensity in the CH-stretch region for each concentration of TEOS with time reflects the elimination of ethoxy groups, which is a signature of the hydrolysis process. Further, the impact of the hydrolysis process is revealed from the significant enhancement in the SFG signal in the OH-stretch region. The hydrolysis of TEOS is then followed by condensation in which the ≡Si─O– charged species are replaced by forming the ≡Si─O─Si≡ bridging network. The signature of the condensation process is reflected with the gradual decrease in the observed enhanced SFG signal in the OH-stretch region. The formation of monodispersed silica nanoparticles as an end product of size variation from 1.75 to 4.67 nm with the increase in TEOS concentration is confirmed with the DLS measurements. We have also probed the pH-dependent SFG studies at three different pH values (2.0, 5.8, and 9.0). The dominant pH-dependent hydrolysis process is revealed from the observed molecular structure of TEOS at the air–aqueous interface.

Electrochemical detection of food preservative SO2 in red wine using SiO2 coated CdS nanomaterials

Cadmium sulfide is an important chalcogenide semiconductor nanoparticle prepared by reverse micelle method using cetyltrimethylammonium bromide (CTAB), surfactant. Toxic CdS is coated with silica using tetraethyl orthosilicate (TEOS) precursor and are well characterized. SiO2 provides a sufficient contrast to show the core homogeneously surrounded by the silica shell. The coating can be made thicker by the addition of TEOS resulting in monodispersed silica spheres with CdS core. SO2 is the most important chemical (as preservative and antioxidant) used to prevent wine oxidation. CdS@SiO2 is serving as adsorbent for the detection of SO2 in wine. The detection mechanism and the sensitivity of the method were validated using limit of detection and the limit of quantification values which are determined from differential pulse voltammetric technique. This electrochemical sensing is found to be simple and reliable to detect the free SO2 present in the wine sample.

Ambient-temperature porogen-free method for preparation of silica-based macroporous materials

The presented work focuses on the synthesis of silica-based macroporous aggregates composed of silica nanoparticles using a template-free method. To improve the mechanical strength of the prepared fractal-like aggregates, the silica precursor tetraethyl orthosilicate (TEOS) is used during nanoparticle aggregation. The obtained results confirm the possibility to tailor the pore size distribution (PSD) simply by using primary particles of various sizes. The prepared porous materials have a porosity ranging from 60% to 74% with a specific surface area between 10 and 200 m2/g and an average pore diameter from 30 to 1300 nm. Functionalization of the aggregate surface was done by replacing part of TEOS with a silica precursor that contained desired functional groups. This was demonstrated by preparing macroporous aggregates with carboxyl, amine and epoxy functional groups. The application of prepared aggregates was demonstrated by immobilization of urease from Canavalia ensiformis resulting in high enzyme activity compare to free enzymes.

Morphological Studies of Composite Spin Crossover@SiO2 Nanoparticles.

Spin crossover (SCO) iron (II) 1,2,4-triazole-based coordination compounds in the form of composite SCO@SiO2 nanoparticles were prepared using a reverse microemulsion technique. The thickness of the silica shell and the morphology of the as obtained core@shell nanoparticles were studied by modifying the polar phase/surfactant ratio (ω), as well as the quantity and the insertion phase (organic, aqueous and micellar phases) of the tetraethylorthosilicate (TEOS) precursor, the quantity of ammonia and the reaction temperature. The morphology of the nanoparticles was monitored by transmission electron microscopy (TEM/HRTEM) while their composition probed by combined elemental analyses, thermogravimetry and EDX analyses. We report that not only the particle size can be controlled but also the size of the silica shell, allowing for interesting perspectives in post-synthetic modification of the shell. The evolution of the spin crossover properties associated with the change in morphology was investigated by variable temperature optical and magnetic measurements.