Mesoporous Silicon Dioxide Research Articles

Facile and Direct Preparation of Ultrastable Mesoporous Silica with Silver Nanoclusters: High Surface Area.

We report the successful direct synthesis of an ultrastable mesoporous silicon dioxide framework containing silver nanoclusters using a modified true liquid crystal templating method. Our modification produced an extraordinary material with a high average Brunauer‐Emmett‐Teller specific surface area of 1785 m2 g−1 – the highest reported surface area to date – and an ultrastable mesoporous structure, which has been stable for nine years so far. This method eliminates the need for reduction of silver oxide into metallic silver and restricts the growth of silver clusters. The silver nanoclusters, with an average size of 1 nm, occupy the pores and walls of the framework. Analysis of the material using nitrogen adsorption/desorption method, high‐resolution transmission electron microscopy, X‐ray diffractometry, energy‐dispersive X‐ray diffractometry, X‐ray photoelectron spectroscopy, and scanning electron microscopy is discussed herein.

Hydrophobic mesoporous silicon dioxide for improving foam stability.

In this study, mesoporous SiO2 nanoparticles (MSNs) were synthesized via a sol–gel method and modified with (3-chloropropyl) trimethoxysilane to make them hydrophobic (MMSNs). The material was characterized via SEM, TEM, FT-IR, DLS, BET and contact angle measurements. The MMSNs have good foam stability, so that the foam properties of the added particles have been increased by 38.4% in an oil/SDS solution. Simultaneously, it becomes a promising material for foam stabilization in order to enhance the oil recovery because it is bio-compatibile and environment friendly. Also, it provides a novel application-stable foam for mesoporous materials.

Self-healing performance and corrosion resistance of graphene oxide–mesoporous silicon layer–nanosphere structure coating under marine alternating hydrostatic pressure

Alternating hydrostatic pressure (AHP) is the main cause of the marine coating failure of deep-sea tools and equipment. Herein, we synthesized a novel nanostructure, namely, graphene oxide–mesoporous silicon dioxide layer–nanosphere structure loaded with tannic acid (GSLNTA), as a self-healing coating additive. The anti-corrosion and anti-AHP performance and the self-healing capability of GSLNTA coating were evaluated through electrochemical impedance spectroscopy, field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, and alternating current scanning electrochemical microscopy (AC-SECM). Results showed that the nanolayer structure of GSLNTA effectively inhibited corrosion mass transmission under simulated deep-sea AHP. The nanospheres of GSLNTA released inhibitors to form a ferric tannate film on the exposed metal surface under AHP. The nanolayer and nanosphere of GSLNTA self-healing coating exerted a synergistic effect on anti-corrosion and anti-AHP performance and blocked corrosion factor transmission and coating failure in deep-sea applications. AC-SECM revealed the advantages of local impedance complementation of different electrochemical parameters (|Z| and –phase) to monitor the self-healing of coatings with GSLNTA. This work also investigated the self-healing performance of alkyd varnish coating embedded with synthetic GSLNTA in protecting steel surfaces. Self-healing materials have an “active healing” capability to prolong the life of organic coatings after unwanted external damage in deep-sea environments.

Mesoporous silica prepared by modified true liquid crystal templating method with high thermal stability and 10-year shelf life

We prepared mesoporous silicon dioxide with high thermal stability via modified true liquid crystal templating (TLCT). The structure of this material could withstand multiple calcination processes at 570 °C for 104 h. The material is sturdy, and it has maintained the mesoporous structure for 10 years so far. Further, it has a high Brunauer–Emmett–Teller (BET) surface area (1280 m2 g−1), exceeding 1000 m2 g−1, which was the maximum surface area produced by the original TLCT method. The material was characterized by employing the N2 sorption method, X-ray diffraction analysis, high-resolution transmission electron microscopy, X-ray photoelectron spectrometry, and 29Si magic angle spinning-nuclear magnetic resonance analysis. The 29Si MAS-NMR of the solid sample revealed that the Q4 value [Si(SiO)4] increased in direct proportion to the heat treatment duration, indicating that the condensation process continued even after multiple heat treatments. This also means that our material not only is thermally stable but also continues to improve with multiple heat treatments. Therefore, our mesoporous material is promising for use as a host in nanoparticle/cluster gusset synthesis that requires heat treatments and as an absorbent of sulfur compounds in oil products.

Structural and magnetic properties of the nanocomposite materials based on a mesoporous silicon dioxide matrix

The structural and magnetic properties of the mesoporous systems based on silicon dioxide with a regular hexagonal arrangement of pores several microns in length and several nanometers in diameter, which are filled with iron compound nanofilaments in various chemical states, are studied in detail. The studies are performed using the following mutually complementary methods: transmission electron microscopy, SQUID magnetometry, electron spin resonance, Mossbauer spectroscopy, polarized neutron small-angle diffraction, and synchrotron radiation diffraction. It is shown that the iron nanoparticles in pores are mainly in the γ phase of Fe2O3 with a small addition of the α phase and atomic iron clusters. The effective magnetic field acting on a nanofilament from other nanofilaments is 11 mT and has a dipole nature, the ferromagnetic–paramagnetic transition temperature is in the range 76–94 K depending on the annealing temperature of the samples, and the temperature that corresponds to the change in the magnetic state of the iron oxide nanofilaments is T ≈ 50–60 K at H = 0 and T ≈ 80 K at H = 300 mT. It is also shown that the magnetization reversal of an array of nanofilaments is caused by the magnetostatic interaction between nanofilaments at the fields that are lower than the saturation field.

Synthesis of Particular Symmetrical Mesoporous Silicon Dioxide Sphere

In this study, two particle sizes of mesoporous silicon dioxide spheres (sample A and B) were synthesized with didecytrimethylammonium bromide as template, and tetraethyl orthosilicate (TEOS) as the silica source. The particles of the samples were extraordinarily uniform and regular. The diameters of the spheres were 439 ± 5 and 485 ± 5 nm. The samples were stable up to 1000°C. The samples revealed only one stage of the weight loss, and the slightly endothermic weight loss was 7.3% for sample A and 9.1% for sample B. It showed that the prepared samples had the higher thermal stability.

Multifunctional electrospinning composite fibers for orthotopic cancer treatment in vivo

A multifunctional, dual-drug carrier platform was successfully constructed. Core-shell structured NaGdF4:Yb/Er@NaGdF4:Yb@mSiO2-polyethylene glycol (abbreviated as UCNPS) nanoparticles loaded with the antitumor drug, doxorubicin (DOX) were incorporated into poly(ɛ-caprolactone) (PCL) and gelatin loaded with antiphlogistic drug, indomethacin (MC) to form nanofibrous fabrics (labeled as MC/UCNPS/DOX) via electrospinning process. The resultant multifunctional spinning pieces can be surgically implanted directly at the tumor site of mice as an orthotopic chemotherapy by controlled-release DOX from mesoporous silicon dioxide (SiO2) and upconversion fluorescence/magnetic resonance dual-model imaging through NaGdF4:Yb/Er@NaGdF4:Yb embedded in MC/UCNPS/DOX in vivo.

Synthesis and properties of a new generation of carbon materials from the Sibunit family modified with silicon compounds

The latest advances in the synthesis of granulated carbon-carbon materials based on nanodispersed globular and pyrolytic carbons modified with silicon or its compounds at the Institute of Hydrocarbons Processing, Siberian Branch, Russian Academy of Sciences are considered. The methods and main regularities of the synthesis and the physicochemical properties of silicon-containing composite materials like C/SiO2, C/SiO2/C, and SiO2/C are discussed. It is shown that the synthesis of modified nanocomposites with the use of polyorganosiloxanes is a promising line in the development of silicon-containing carbon-carbon materials. In this work, a nontraditional approach to the production of mesoporous silicon dioxide based on nanodispersed globular carbon and polyorganosiloxanes is proposed.

Magnetic cylindrical ordered mesoporous nanocarriers for targeted drug delivery

An MCM-41 type magnetic cylindrical ordered mesoporous silicon dioxide (M-COMSD) nanocarrier for targeted drug delivery has been synthesised. Pharmaceutical drug molecules have been loaded into the mesoporous framework of the M-COMSD. In vitro (Hale cells) and in vivo (mice) drug storage and release experiments of the nanocarrier have been performed. The results of the M-COMSD system demonstrate that this material could play a significant role in developing a new generation of controlled-release nanocarriers.

Obtaining antireflecting coatings from mesoporous silicon dioxide on silicate glass at lowered temperatures of baking of gel

Silicon dioxide sol with oligoethers can be used to obtain antireflecting coatings on silicate glass at various baking temperatures of the coating: 400, 300, and 200°C. At an optimal concentration of 4.0 mass % of oligoether based on PPG-725 in a sol, the maximum light transmission of 99.7%, and the refractive index of the nanoporous coating of 1.23 do not depend on the baking temperature in the range from 200 to 400°C. Silicon dioxide sol with a 4.0 mass % of ALM-10 give a maximum light transmission of 99.7% and a refractive index of the nanoporous coating of 1.23 at a baking temperature of 300–400°C. A maximum light transmission of the glass with a coating of 98.7% and the refractive index of 1.27 at an optimal concentration of 8.0 mass % of oligoether based on PEG-200 were obtained at baking temperatures of 300–400°C.

White-light photoluminescence and photoactivation in cadmium sulfide embedded in mesoporous silicon dioxide templates studied by confocal laser scanning microscopy

SBA-15 and SBA-16 silica templates have been infiltrated with CdS by means of nanocasting using a hybrid precursor. The morphology and structure of both the SiO2@CdS nanocomposites and the silica-free CdS replicas have been characterized. The three-dimensional nanocrystalline CdS networks embedded in SBA-15 and SBA-16 silica templates exhibit broad photoluminescence (PL) spectra over the entire visible range, together with enhanced PL intensity compared to silica-free CdS replicas. These effects result from the role silica plays in passivating the surface of the CdS mesostructures. Furthermore, photoactivation is eventually observed during continuous illumination because of both structural and chemical surface modifications. Owing to this combination of properties, these materials could be appealing for solid-state lighting, where ultra-bright near-white PL emission is indispensable.

Study on Hemostatic Materials of Mesoporous Silicon Dioxide Doped Ca and Ag with Antibacterial Properties

An antibacterial hemostatic material of mesoporous silicon oxide gel doped with Ca and Ag (m-SCA) gel was fabricated by using cetyltrimethylammonium bromide(CTAB) as templates and Sol-Gel process. The results showed that m-SCA with mesoporous structure had the surface area of 416 m 2 /g and pore size of around 2 nm. The m-SCA with high surface area and good clotting function could significantly shorten the prothrombin time (PT) and activated partial thromboplastin time (APTT). The m-SCA containing a small quantity of Ag had no obvious effects on its clotting properties while Ca in m-SCA could promote clotting. The m-SCA doped 0.02wt% Ag without cyto- toxicity had good antibacterial properties against E.coli. Animal experimental results showed that the m-SCA could control hemorrhage and shorten the bleeding time of rabbit ear wound, showing good hemostatic properties. It sug- gestes that the m-SCA is a good hemostatic material with antibacterial properties.

Spontaneous Crystalline-to-Amorphous Phase Transformation of Organic or Medicinal Compounds in the Presence of Porous Media, Part 3: Effect of Moisture

Amorphization of crystalline compounds using mesoporous media is a promising technique to improve the solubility and drug release of poorly-soluble compounds. The objective of this paper is to understand the effect of moisture on the capacity and performance of vapor-phase mediated amorphization. Mesoporous silicon dioxide (SiO(2)) and crystalline naphthalene were used as the model system. The effect of moisture on the amorphization capacity of naphthalene was determined using adsorption chambers with various levels of relative humidity. Enthalpy and capacity of water vapor adsorption on SiO(2) were measured using isothermal microcalorimetry and thermogravimetry. Moisture not only suppressed the amorphization capacity of naphthalene, but reversed an already-amorphized formulation as well. On the other hand, through the same competitive interaction, improved drug release and enhanced solubility were obtained. The initial supersaturation was followed by an entropy-driven crystallization. In addition, moisture-induced siloxane bond fracture was found at normal processing conditions, which led to the changes in silica surface chemistry. However, the implication in amorphization has not reached a definitive conclusion. Humidity during processing and storage must be carefully controlled for this type of amorphous formulation. Further investigation is needed to better understand the moisture-induced changes of silica.

Deposition of antireflection coatings onto silicate glass from a silicon dioxide sol containing a nonionogenic surfactant and oligoester based on propylene oxide

Possibility of obtaining low-refractive-index antireflection coatings composed of mesoporous silicon dioxide by simultaneous introduction of two organic compounds, oligoester based on propylene oxide and a nonionogenic surfactant, into a silicon dioxide sol was studied.

Spontaneous crystalline‐to‐amorphous phase transformation of organic or medicinal compounds in the presence of porous media, part 2: Amorphization capacity and mechanisms of interaction

Amorphization of crystalline compounds using mesoporous media is a promising technique to improve the solubility and dissolution rate of poorly soluble compounds. The objective of this paper is to determine the capacity of amorphization and understand the mechanisms of phase transformation. Commercial grades of mesoporous silicon dioxide (SiO2) samples (5‐ to 30‐nm mean pore diameters) with either constant surface area or constant pore volume were used. The amorphization capacity of naphthalene was not proportional to either the surface area or the pore volume measured using adsorption chambers. Instead, the amorphization capacity correlated with surface curvature, that is, the smaller the pore diameter and the higher the surface curvature, the greater the amorphization capacity. The change in surface chemistry due to a highly curved surface may be responsible for the enhanced amorphization capacity as well. The amorphization of crystalline compounds was facilitated through capillary condensation, with the decrease in pore volume as the direct experimental evidence. The amorphization capacity was also enhanced by the dipole–dipole or dipole‐induced dipole interaction, promoted by the hydroxyl groups on the surface of SiO2. The enthalpy of vapor–solid condensation of crystalline compounds was a useful indicator to predict the rank order of amorphization capacity. © 2011 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:4674–4686, 2011

Adsorption Behavior of Environmental Hormone Bisphenol A onto Mesoporous Silicon Dioxide

Mesoporous silicon dioxide (meso-SiO2) was prepared using cetyltrimethylammonium bromide as the structure-directing reagent and tetraethyl orthosicate as the silicon source. The influence of pH value on the adsorption behavior of bisphenol A (BPA) was investigated. The adsorption capacity of BPA onto meso-SiO2 increases slightly with pH value from 2 to 6, and then gradually decreases as further improving pH value. The effect of temperature was also studied, and the adsorption capacity of BPA gradually declines with increasing temperature. The adsorption kinetics and thermodynamics of BPA were examined. It is found that the adsorption of BPA onto meso-SiO2 is in good agreement with Langmuir adsorption model. The rate constant of adsorption is 5.17 × 10 �3 g mg �1 min �1 , and the maximum adsorption capacity is as high as 353.4 mg g �1 at 20 o C.

Synthesis of titanium oxide structures on mesoporous silicon dioxide surface by molecular layering

The formation of titanium oxide structures through the repeated successive treatment of SBA-15 mesoporous silicon dioxide with vapors of TiCl4 and H2O at 200°C is investigated. The influence of the number of synthesis cycles on the character of the buildup of the surface titanium oxide structures and changes in the adsorption and structural characteristics of modified silica is shown.

Spontaneous Crystalline-to-Amorphous Phase Transformation of Organic or Medicinal Compounds in the Presence of Porous Media, Part 1: Thermodynamics of Spontaneous Amorphization

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal molecules in the presence of mesoporous materials has been observed, for which pathway was suggested to be via the vapor phase, that is, sublimation of the crystalline molecules followed by adsorption on the porous media. The objective of this paper is to rigorously evaluate this amorphization pathway and to study the thermodynamics of spontaneous amorphization. Mesoporous silicon dioxide (SiO(2)) was used as a model system. Physical mixtures of SiO(2) and crystalline compounds were prepared and stored at 0% relative humidity (RH) and 40 °C. Loss of crystallinity of the model compounds was confirmed using powder X-ray diffraction and polarized light microscopy. Adsorption chamber was set up, in which naphthalene and SiO(2) were stored, without physical contact, under reduced pressure at 0% RH and 40 °C. Data confirmed that the rate and extent of sublimation and adsorption of naphthalene were significant for amorphization to occur on a pharmaceutically relevant timescale. Furthermore, a thermodynamic model has been developed to explain spontaneous amorphization. This unique phase transformation phenomenon can be a simple and effective method to improve the aqueous solubility and bioavailability of poorly soluble drug molecules.

Preparation of antireflection coatings from silicon dioxide on glass and quartz by the sol-gel method with oligoethers

Antireflection coatings with a low refractive index (1.18–1.23) have been prepared on silicate glass and optical quartz from mesoporous silicon dioxide synthesized by the sol-gel method in the presence of oligoethers. The optimum concentration of the oligoester in the sol is equal to 1.5–2.5 wt %. For the single-layer double-sided coating, the maximum transmission is equal to 99.0% for the silicate glass and 99.9% for quartz.

Influence of the temperature-time conditions on the textural and structural properties of mesoporous silicon dioxide synthesized in an ammonia-alcohol medium

The conditions for the formation of mesostructural silica materials (MSMs) in the ammonia-alcohol media were determined. Mesoporous silicon dioxide was synthesized by the template liquid-phase condensation method at high concentrations of the surfactant. The effect exerted by temperature and time of the synthesis, autoclaving, and by organosilane additive [(trimethylsiloxy)silane] used in synthesis on the structural and textural properties of the mesoporous material was determined. The temperature-time conditions for the preparation of mesostructured silicon dioxide were optimized.