Gelatin-assisted porous expansion of mesoporous silica

In this study, we report the pore expansion effect of gelatin, a common amphoteric biological protein, on the hexagonal mesoporous silica materials. Tetraethyl orthosilicate (TEOS) was used as silica source and the nonionic surfactant P123 (EO₂₀PO₇₀EO₂₀) as template. The microstructure characters of products were investigated by low-angle X-ray diffraction (LAXRD), transmission electron microscope (TEM), and N₂ adsorption–desorption measurements. The results show that the products prepared with gelatin have the mild expansion ratios of 29–39% and 5–22% in pore diameter and pore volume, respectively. The specific surface area of products ranges from 445 to 590 m² g⁻¹. Moreover, it is revealed that the presence of gelatin did not change the intact 2D-hexagonal mesoporous structure of materials. The ultraviolet–visible absorption spectroscopy (UV–Vis) analysis indicates that there is an interaction between the oxygen atoms of P123 and gelatin molecules. The pore expansion may be because the gelatin can interact with the hydrophilic sides of P123 micelles via hydrogen bonds interaction, which is different from the reported pore expansion mechanisms for other systems.     

Synthesis of 3-dimensional mesoporous silica using a di-block copolymer template

Exploring polymeric surfactants as templates for synthesizing ordered mesoporous silicas has become increasingly important for both academic interests and industrial applications. In this work, we employed C₁₆EO₄₀, a di-block copolymer polyethylene-poly(ethylene oxide), as template in an attempt to synthesize a modified 3-dimensional wormhole mesoporous silicas (WMS-39). In addition, various synthesizing conditions were investigated, including pre-hydrolysis time of TEOS, reaction temperatures and the ratios of TEOS to template. The products were characterized using powder XRD, TEM, ²⁹Si MAS NMR and nitrogen adsorption measurements. The characteristics of as-synthesized mesoporous silica were compared with SBA-15, a highly ordered mesoporous silica, prepared using non-ionic tri-block copolymers of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) as templates. The WMS-39 materials have a BET surface area of 600–970 m²/g and narrowly distributed pore diameter around 3.9 nm. The morphology of WMS-39 was found to be wormhole framework as indicated in TEM diagrams. Thermal transformation of the as-synthesized mesoporous materials were carefully analyzed with TGA/DTA. Findings obtained from this work enable us to propose a modified assembly mechanism of mesoporous silicas.     

Synthesis and characterization of TiO<Subscript>2</Subscript>-incorporated silica foams

Titania-incorporated silica (TiO₂–SiO₂) porous materials have great applications in diverse areas. In this work, TiO₂–SiO₂ porous materials with tunable Si/Ti molar ratio (R) have been successfully prepared through a one-pot method under a near-neutral condition. With decreasing Si/Ti R, a phase transition from a macroporous foam-like structure to mesostructure is observed. The resultant TiO₂–SiO₂ porous materials possess large surface areas and high pore volumes. In addition, the titania species are homogenously dispersed in silica matrix when Si/Ti R ≥ 10. Our contribution provides a convenient method to synthesize TiO₂/SiO₂ porous materials with very large pore size, high pore volume, and relatively high titania content well dispersed in the silica wall framework.     

Surfactant/co-polymer template hydrothermal synthesis of thermally stable, mesoporous TiO2 from TiOSO4

Industrial TiOSO₄ solution was used as inorganic precursor to prepare mesoporous titania via composite template route, using cetyl-trimethylammonium bromide (CTAB) and tri-block copolymer EO₂₀PO₇₀EO₂₀ (P-123) as structure-directing agents (SDA) under high acidic conditions. Mesoporous TiO₂ with high thermal stability was obtained via controlling the hydrolysis and condensation rate of industrial TiOSO₄ solution by adjusting the pH value and post hydrothermal treating. The as-prepared materials were characterized by XRD, nitrogen adsorption-desorption, SEM and HRTEM. The powder calcined at 723 K for 2 h showed higher thermal stability, with BET specific surface area of 218.7 m²/g and an average pore diameter of 3.63 nm.     

Synthesis of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> mesoporous bioactive glasses with high P<Subscript>2</Subscript>O<Subscript>5</Subscript> content by evaporation induced self assembly process

Mesoporous bioactive glasses (MBGs) of the CaO–SiO₂–P₂O₅ system containing relatively high P₂O₅ contents (10–30 mol%) were prepared from a sol–gel. An evaporation-induced self-assembly (EISA) technique was used with poly(ethylene oxide)-block–poly(propylene oxide)-block–poly(ethylene oxide) (EO₂₀–PO₇₀–EO₂₀, P123) acting as a template. The structural, morphological and textural properties of MBGs were investigated by small-angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and a N₂ sorption/desorption technique. SAXRD and TEM results display the reduced long-range ordering of mesopores with increasing P₂O₅ content. N₂ sorption/desorption analysis shows that all three samples exhibit a type IV isotherm with type H1 hysteresis loops, characteristic of independent cylindrical slim pore channels and this material has a Barret–Joyner–Halenda (BJH) model pore size of ~4 nm and BET specific surface area ~430 m²/g. NMR results indicate a more condensed framework for samples with 30 mol% P₂O₅ than samples with 10 mol% P₂O₅. For in vitro bioactivity tests where samples were soaked in simulated body fluid (SBF), samples with 30 mol% P₂O₅ showed higher crystallinity than those with lower P₂O₅ contents Silicon concentration increased in SBF solution during the soaking period, which indicates MBGs can be degradable in SBF solution.     

Synthesis and characterization of Ti-SBA-16 ordered mesoporous silica composite

Ti-SBA-16 mesoporous silica with a cubic Im3m structure has been successfully synthesized through prehydrolysis of a silica precursor in the presence of a tri-block copolymer F127 under acidic condition. X-ray diffraction (XRD) shows that the highly ordered mesostructure was maintained even at the high loading of titanium up to 5.5 (bulk molar ratio SiO₂/TiO₂). UV–vis and Raman spectroscopy reveal that the titanium species was highly dispersed in the silica framework with tetrahedral coordinate and octahedral coordinate, respectively. N₂-adsorption data exhibit that the BET surface, pore size and pore volume were maintained with an increase of titanium species loading for this cubic Im3m mesoporous composite. SEM image shows its amorphous morphology. The synthesis of mesoporous TiO₂-containing SBA-16 composite with a cubic Im3m structure will open new applications for catalysts.     

PE6400 templated monolithic mesoporous silica with orientated block structure

Novel monolithic mesoporous silica was synthesized with a new SDA (Structure-Directing Agent) of PE6400 (EO₁₃PO₃₀EO₁₃). The monolithic silica was found possessing special “oriented block” structure at nano-scale where pore channels' orientations were the same in a single block but not always the same in different blocks. Pore channels of a single oriented block were well ordered hexagonally oriented. Moreover, the average pore diameter, the average wall thickness, the specific surface area and the pore volume of the obtained monolithic silica were 3.5 nm, 3.3 nm, 777.5 m²/g and 0.44 m³/g, respectively.     

Infrared spectroscopic study of water in mesoporous silica under supercritical conditions

The structure of water under high temperature–pressure conditions in mesospace was investigated by measuring the infrared spectra of water in mesoporous silica. Absorption peaks attributed to OH-stretching vibration of water in mesoporous silica were detected at lower wavenumbers as compared with bulk water, and the absorption peak positions were dependent on pore diameter. For small pore diameters (3–20 nm), absorption peak positions of water were detected at lower wavenumbers (ca. 3,300 cm⁻¹) at 400 °C, while for larger pore diameters (30–50 nm) the peaks were detected at higher wavenumbers (ca. 3,500 cm⁻¹). We attribute these features to the effects of mesoporous silica surface structure on the structural and vibrational modes of water. Furthermore, absorption peak positions changed significantly at different pore sizes (20 and 30 nm), indicating that the structure of water in small pores approaches a more ice-like structure. Based on our experimental results, the structured water layer in mesoporous silica is estimated to be at least 10 nm thick, which is thicker than that previously documented in molecular dynamic simulation studies where the thickness of structured water was found to be two or three layers from the surface.     

Effect of Cr doping on the structure,optical and magnetic properties of multiferroic BiFeO<Subscript>3</Subscript> thin films

Multiferroic BiCr _x Fe_1−x O₃ (BCFO) (0 ≤ x ≤ 0.12) thin films were fabricated on silicon substrates by sol–gel technique. The microstructure and properties of the films are characterized using X-ray diffraction, spectroscopic ellipsometry, micro-Raman spectrometry and a Modular Control system. The BCFO films are the rhombohedral structure with the Cr content up to 7%. Raman scattering spectra of the BCFO films demonstrate the transformation of structure with the Cr content exceeding 10%. The band gap of the BCFO films is from 2.53 to 2.82 eV with the Cr content being from 0 to 12%. The magnetization of the BCFO films is significantly enhanced with the increasing of the Cr content.     

Synthesis of mesoporous structured hydroxyapatite particles using yeast cells as the template

In this study, hydroxyapatite (HAp) particles with mesoporous structure have been synthesized from calcium hydroxide and di-ammonium hydrogen phosphate using yeast cells as the template. The characterization methods such as X-ray diffraction (XRD), Fourier transform infrared spectrograph (FTIR), N₂ adsorption–desorption isotherms (NADI), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) were used for determination of the particles structure (particle size, structural evolution and morphology). The results show that HAp particles with mesoporous structure could be produced. The size of HAp particles was approximately hundreds of nanometer. The pore width of HAp particles was in the range of 2.0–40 nm and the maximum centered around 4.5 nm.     

Electron spin resonance study of Mo(V) ion species incorporated into aluminosilicate nanospheres with solid core/mesoporous shell structure

Silica spheres with sub-micrometer sized solid core and mesoporous shell (SCMS) structure were synthesized, and aluminum was incorporated into the mesoporous shell framework by impregnation method to generate SCMS aluminosilicate (AlSCMS) nanospheres. The impregnation of aluminum into the SCMS spheres generates the acid sites on the framework due to the presence of Al³⁺ ions. The AlSCMS was then used to support molybdenum ion species on the mesoporous shell framework. A solid-state reaction of MoO₃ with AlSCMS followed by thermal reduction generated paramagnetic Mo(V) species. The dehydration produced a Mo(V) species that is characterized by electron spin resonance with g _e > g _⊥ > g _||. The structural properties of active sites in the AlSCMS were characterized by means of XRD, UV–Vis, ²⁷Al MAS NMR, FT-IR, and energy dispersive X-ray spectrometric measurements. Upon O₂ adsorption, the Mo(V) ESR signal intensity decreased, and a new O₂ ⁻ radical was generated. The Mo species in the dehydrated Mo-AlSCMS is found to exist as oxo-molybdenum species, (MoO₂)⁺ or (MoO)³⁺. Since the AlSCMS has a low framework negative charge, the MoO₂ ⁺ with a low positive charge can be easily stabilized and thus seems to be more probable in the AlSCMS framework.     

Microstructures and high temperature oxidation resistance of alloys from Nb–Cr–Si system

Oxidation behavior of Nb–30Si–(10,20)Cr alloys have been evaluated in air from 700 to 1400 °C by heating for 24 h and furnace cooling them. The lower weight gain per unit area has been observed for 20Cr alloy at 1200, 1300, and 1400 °C. Pesting has been observed at lower temperatures (700, 800, 900 °C). Analysis indicates that the powder formation at 900, 100, 1100 °C may be associated with β form of Nb₂O₅ (base centered monoclinic form). However the m-monoclinic form of Nb₂O₅ evolves at temperatures above 900 °C while o-orthorhombic Nb₂O₅ forms at below this temperature. The phases in the alloys have been calculated using the Pandat^TM software program at different temperatures using calculated Nb–Cr–Si phase diagrams.     

A cellular level biocompatibility and biosafety evaluation of mesoporous SiO<Subscript>2</Subscript>-based nanocomposite with lanthanum species

The risk assessment of SiO₂ nanoparticles has attracted extensive attention due to their great potential for various commercial purposes. However, the toxicity of mesoporous SiO₂-based nanocomposite is still unclear. Herein SiO₂-based hexagonal mesoporous nanosphere doping La³⁺ ions with diameter of 40–50 nm (SLa-HMS) and micronsized SiO₂-based hexagonal mesoporous solid inlaid with nanowires, 80–250 nm in length and 4–5 nm in diameter, of La species (WLa-HMS) were synthesized via self-assembly method. The specimens were characterized by small angle XRD, TEM, EDS, FT-IR, and N₂ ad–desorption. HeLa, fibroblast, and HBMSC cells were exposed to 0.1–100 μg/mL of SLa-HMS and WLa-HMS colloids for 12, 24, 48, and 72 h. Our data demonstrated that exposure of SLa-HMS in the dose range tested had no hazardous effect on all three cell lines, which was greatly different from previous reports. However, the WLa-HMS with average particle size of 10–19 μm was proven to be very toxic to the growth of all three cell lines. These interesting findings strongly suggest that doping heteroatom could be a way to improve the cytotoxicity of nanomaterials, as well as to oncotherapy on the basis of the hazardous effect of nanomaterials.     

Preparation and photocatalytic activity of highly ordered mesoporous TiO2–SBA-15

TiO₂–SBA-15 complex materials with highly ordered mesostructures have been prepared by a one-step hydrothermal synthesis method of titanium tetraisopropoxide (TTIP) and tetraethoxysilane (TEOS) in an acidic solution using surfactant P123 (EO₂₀PO₇₀EO₂₀) as structure-directing reagent. The prepared materials were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction patterns (SAXRD), Fourier transformed infrared spectroscopy (FT-IR) and N₂ adsorption–desorption experiments. The resulting TiO₂–SBA-15 complex materials showed highly ordered mesoporous structure with uniform pore sizes of 5.95 and 8.24 nm, high specific surface areas S_BET of 689 m² g^? 1 and 347 m² g^? 1 at different hydrothermal temperatures (100 °C and 130 °C). The photocatalytic activity of these TiO₂–SBA-15 mesoporous materials has been studied by 4-chlorophenol decomposition under UV light irradiation. The TiO₂–SBA-15 mesoporous materials prepared at the TiO₂:SiO₂ mass ratios of 25:75, 40:60 and 50:50 showed higher photocatalytic activity than that prepared at the TiO₂:SiO₂ mass ratio of 75:25.     

Synthesis and characterization of ordered and cubic mesoporous silica crystals under a moderately acidic condition

Ordered and cubic mesoporous silica materials were synthesized by using poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymer as template under a moderately acidic condition of 0.5 mol/l HCl solution. These mesoporous materials were characterized by Fourier transform (FT) IR spectroscopy, thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption–desorption measurements. The three-dimensional cage-like microporosity of the prepared mesoporous silica having ordered hexagonal mesoporous structure was evidenced by the well-defined XRD patterns combined with TEM photographs. SEM observation shows a highly regular cubic crystal structure for the prepared mesoporous silica. The size of these crystallites was maintained within the range between 4 and 6 μm, which is fairly important for the application to the stationary phase for separation. The nitrogen adsorption–desorption analysis reveals that the prepared mesoporous silica possesses a small pore diameter of 3.68 nm, a total surface area of 363.648 m²/g, a total pore volume of 0.379 cm³/g, and a pore-wall thickness of 6.63 nm. These features may lead to higher thermal and hydrothermal stability, excellent microporosity, and good connectivity. The mesoporous silica prepared in this study exhibits potential applications to catalysis, sensoring, and separation.     

Synthesis and characterization of bimodal rod-like mesoporous carbons from raffinose by SBA-15 templates

Mesoporous carbons with bimodal rod-like pore structures and tunable pore sizes from 3.66 to 5.42 nm were for the first time obtained by employing SBA-15 as templates and raffinose as carbon precursors. Small angle X-ray diffraction, transmission electron microscopy, scanning electron microscopy, N₂ sorption analysis, and Raman spectroscopy were used to determine the textural properties of the resulting materials. Bimodal frameworks with mesopores (4–5 nm) as well as macropores (125–130 nm) were achieved. The mesoporous carbons lost its ordered structure from the templates due to mesostructural shrinkage and collapse of mesopores, which resulted in partial duplicate of the template and pore-widening effect (meso to macropores). With the increasing of carbonization temperature from 500, 700 to 900 °C, the textural parameters such as specific surface areas, pore volumes, and mean pore diameters all increased significantly. In the temperature range studied, higher carbonization temperature would generate much more abundant porosity. The ratio of I _D to I _G (I _D/I _G) indicated a rather low crystallinity with the varying of aging temperature and the carbonization temperatures. The advantage of the procedure was that no acid or other chemical catalysts were involved during the infiltration and carbon formation process.     

H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> supported on mesoporous MCM-41 and Al–MCM-41 materials: preparation and characterisation

MCM-41 and Al–MCM-41 has been synthesized using cetyl-trimethylammonium bromide (CTAB) surfactant as template and adding the silica precursor to aqueous solutions containing CTAB. The obtained solids were calcined at 600 °C for 4 h. HPW heteropolyacid supported on the mesoporous were prepared using the incipient wetness method. The characterization of materials was performed by X-ray diffraction, Transmission Electron Microscopy, N₂ adsorption, ²⁹Si Cross Polarization–Magic Angle Spinning and ²⁷Al MAS NMR. Results showed that the hexagonal structure is obtained in both cases. The Aluminium species are located inside an extra-framework. The impregnation reduces the surface area of the mesoporous materials especially of the Al–MCM-41 suggesting a participation of aluminium during the impregnation. HPW is well dispersed in the mesoporous materials and is located inside the pores interacting with the silanol group of the pores wall. ²⁷Al MAS NMR measurements have showed that the impregnation causes the removal of the non-framework aluminium.     

Si-incorporated alumina phases formed out of diphasic mullite gels

The diphasic mullite gel forms o-mullite on heating via intermediate spinel phase. Characterization of the latter phase with various physico-chemical techniques is concisely reviewed. It is noticeable that XRD intensity of both the amorphous scattering band and the diffraction peak of Al–Si spinel phase changes during each step of transformation processes of diphasic gel. Accordingly, the integrated area of the intensity peak of amorphous band and that of Al–Si spinel phase generated during heating diphasic gels were measured by XRD technique with the help of X’Pert Graphics and Profit softwares. The amount of free SiO₂ (A) content present at various stages of heating diphasic gels was estimated by classical alkali leaching study standardized earlier. The results show that diphasic gel which forms an aluminosilicate (A) phase initially by dehydration and dehydroxylation, subsequently crystallizes to Al–Si spinel phase. In consequence, the ratio of XRD peak of spinal phase to that of amorphous band increases in the temperature range of 600–1000 °C. This study confirms the earlier view of incorporation of silica into the alumina structure with formation of Al–Si spinal phase. Complementary alkali leaching study indicates the existence of non-crystalline silica-rich aluminous phase other than free non-crystalline silica during heating diphasic gel at ~1000 °C.

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Liquid–liquid phase equilibria,density difference,and interfacial tension in the Al–Bi–Si monotectic system

We have performed thermodynamic calculation of the phase equilibria in the ternary monotectic system Al–Bi–Si. The liquid–liquid miscibility gap in the Al–Bi–Si system extends over almost the entire concentration triangle. The thermal analysis data for (Al_0.345Bi_0.655)_100−x Si _x alloys (x = 2.5, 5, 7.5, and 10 wt%) excellently agree with the calculated phase diagram. The experimental density difference of the coexisting liquid phases shows a good agreement with the density difference calculated in the approximation of ideal solution using the densities of pure elements and the compositions of L′ and L′′ from the thermodynamic calculation. The liquid–liquid interfacial tension in the (Al_0.345Bi_0.655)_100−x Si _x liquid alloys increases with Si content. The experimental temperature dependence of the interfacial tension is well described by the power low in reduced temperature (T _C–T) at approach of the critical temperature with the exponent μ = 1.3, which is close to the value predicted by the renormalization group theory of critical behavior.     

Negative temperature coefficient thermistor based on BaFe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3−ε</Subscript> solid solutions

A negative temperature coefficient (NTC) thermistors based on BaFe _x Sn_1−x O_3−ε were fabricated by conventional solid-state reaction method. The microstructure and electrical properties of the NTC thermistors were characterized by X-ray diffraction (XRD), electric (R(T)), and impedance measurements. The XRD analysis shows that the BaFe _x Sn_1−x O_3−ε still remains cubic perovskite structure and the crystal growth orientation changes at higher Fe content. Similarly, the electric measurements indicates that all the samples show typical NTCR behavior; with increasing Fe content, the room temperature resistivity, activation energy, and thermistor constant decrease, are in the range of 2.52–217 KΩ cm, 0.343–0.43 eV, and 3900–4896 K, respectively. The impedance spectroscopy confirms that the observed ac resistance, consisting of the grain bulks, grain boundaries, and electrode–ceramic interface, mainly attributes to the grain boundaries and grain bulks; with the rise in temperature the grain boundary resistance shows more rapid change than the grain resistance; moreover, the Fe concentration can greatly affect the grain and grain boundary resistance.