Optimal synthesis of mesostructured hollow titania nanotubes templated on CaCO3 nanoparticles

Approximate 10 µm length of mesostructured hollow titania nanotubes with intact configuration was successfully prepared by using needle-like calcium carbonate and octadecylamine as double templates at room temperature in nonaqueous system. During the whole preparation, two parameters i.e. tetrabutoxytitanium/calcium carbonate molar ratio and annealing temperature, were optimized to obtain titania nanotubes with well-defined tubular morphology and mesoporous structure in tube walls. The as-prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, broad-angle X-ray diffraction, pore size distribution and Brunauer-Emmett-Teller. The results showed that under optimal experimental conditions i.e. tetrabutoxytitanium/calcium carbonate molar ratio (50 wt.%) and annealing temperature (773 K), the tube materials exhibited uniform tubular structure with a length of 8-15 µm and an inner diameter of ∼ 400 nm, a wall thickness of ∼ 40 nm, a surface area of 112.2 m²/g and a pore volume of 0.18 cm³/g. The optimized titania nanotubes were utilized as a carrier for the immobilized of ibuprofen via a simple adsorption method. It was found that the loaded drug presented good sustained release property in three release media, i.e. simulated body fluid, normal saline and pure water.     

Controlled‐release drug carriers based hierarchical silica microtubes templated from cellulose acetate nanofibers

We report a facile method to synthesize hollow silica microtubes (SMTs) from electrospun cellulose acetate fiber precursors. Specific surface areas of up to 765 m²/g (Brunauer–Emmett–Teller) were measured for the SMTs, which had a typical wall thickness of ～100 nm and submicron inner diameters. An average pore size of 4.6 nm and pore volume of 0.41 cm³/g were derived from Barrett–Joyner–Halenda fitting, whereas Horvath–Kawazoe pore size distribution analysis revealed microporous median pore size and maximum pore volume of 0.7 nm and 0.18 cm³/g, respectively. The as‐prepared SMTs featuring micro‐ and mesoporous structures in the walls where amino‐functionalized to facilitate a very high drug loading (15% by weight). Drug release profile revealed sustained release rates (79% of acetylsalicylic acid was released after 6 h). It is concluded that the high drug loading and sustained release resulted from the advantageous integration of SMTs' hollow structure and wall mesoporosity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42562.     

Preparation of mesoporous silica nanoparticles with controlled pore size,particle diameter,morphology, and structure by two-step process of chlorosilane residue

In this study, mesoporous silica nanoparticles (MSNs) were successfully prepared in two steps using chlorosilane residue. First, chlorosilane residue was subjected to alcoholysis with n-propanol to synthesize tetrapropoxysilane (TPOS), followed by the synthesis of MSNs using TPOS as silicon source. Alcoholysis experiment was designed and optimized using orthogonal experimental method. In addition, effects of four factors (i.e., molar ratio of n-propanol to chlorosilane residue; feed rate of n-propanol; reaction temperature; and molar ratio of n-hexane to chlorosilane residue) on the yield of TPOS were investigated. The optimum alcoholysis conditions were determined. Yield of TPOS was 56% under the optimum alcoholysis conditions. Results obtained from single factor analysis of variance revealed that molar ratio of n-propanol to chlorosilane residue was the most significant factor affecting TPOS yield. Next, a series of spherical MSNs with dendritic structure and irregular mesoporous/microporous silica nanoparticles with non-dendritic structure were successfully synthesized via precise regulation of various experimental parameters in emulsion systems. In this regard, the adjustment of n-hexanol/1,3,5-triisopropylbenzene (TIPB) molar ratio or n-octane/n-hexanol/TIPB molar ratio was found to be effective for achieving controllable regulation of morphology (spherical or irregular); structure (dendritic or non-dendritic); pore size (mesoporous (4.6–9.2?nm) or microporous (1.6–1.7?nm)); and particle diameter (60–134?nm) of silica nanoparticles. However, the adjustment of n-octane/TIPB molar ratio marginally affected spherical morphology, dendritic structure, and pore size (4.0–4.6?nm) of synthesized MSNs, with considerable effect on particle diameter (61–151?nm). In addition, as-synthesized MSNs exhibited large specific surface area (708–857?m²/g) and large pore volume (1.5–3.6 cm³/g).     

Preparation of phenolic resin derived 3-D ordered macroporous carbon

Three-dimensionally ordered long-range macroporous carbon structures were prepared using commercially available phenolic resin by utilizing sacrificial colloidal silica crystalline arrays as templates that were subsequently removed by HF etching after pyrolysis in an argon atmosphere. SEM, TEM, and BET were employed to characterize the morphology and the surface area of the porous carbon structures. The pore size (150–1000 nm) and BET surface area, which reflect pore volume (298.6 m²/g (1.32 cm³/g) ∼ 93.7 m²/g (0.12 cm³/g)), of the macroporous carbon structures produced were approximately proportional to the size (150–1000 nm) of the sacrificial silica sphere templates used (annealing temp. 550°C). The achieved 550 nm porous carbon structures were examined to function as potential catalyst carriers and were successfully impregnated with Ag or Pt-Ru on their inner walls after borohydride reduction at room temperature. In addition, porous carbon patterns were fabricated using the ‘micromolding in capillary’ technique, which has potential applications in the microreaction technology.     

Influence of template on the structure of mesoporous carbon prepared with novalac resin as carbon precursor

Mesoporous carbons with different mesostructures were prepared with amphiphilic triblock copolymer PlurionicF127, Pluronic P123 and blends of F127/P123 as templates, and hexamethyltetramine cured novolac as precursors. When the mass ratio of template/novolac changed from 1/1 to 1/2, the ordering of mesoporous carbons reduced, and mesoporous carbons prepared with F127 as templates exhibited more excellent ordering compared to those prepared with P123 as templates. Increasing the content of P123 in the blends of F127/P123 induced the changes of mesophase and texture properties of resulting products. When the mass ratio of F127/P123 decreased from 0.67/0.33 to 0.33/0.67, the mesoporous carbons changed from two dimensional (2D) hexagonal to wormhole framework. Meanwhile, the mesoporous carbons exhibited similar surface area (about 574 cm²/g), and decreasing pore size (from 3.4 to 3.0 nm), total pore volume (0.37–0.32 cm³/g), d-spacing (8.3–7.7 nm) and wall thickness (5.5–3.9 nm). The 2D hexagonal mesoporous carbons prepared with F127 as templates exhibited larger specific surface area (670 m²/g), pore size (3.5 nm) and total pore volume (0.40 cm³/g), and slightly lower d-spacing (7.4 nm) and wall thickness (5.0 nm) compared to those prepared with blends of F127/P123 as templates.     

High-temperature resistant ambient pressure-dried aluminum doped silica aerogel from inorganic silicon and aluminum sources

Aluminum doped silica aerogel (ASA) exhibiting improved high-temperature resistance is usually prepared via supercritical drying from organic silicon and/or aluminum precursors, which propels the production cost significantly. Herein we demonstrate a simple and effective method to prepare highly thermal resistant ASA via the sol-gel and ambient pressure drying route by using water glass and aluminum chloride as precursors. Effects of the Al/Si molar ratio in precursor, the calcination temperature and the modifier type on the crystallinity, morphology, pore structure of ASA are investigated. Results show that the Al/Si molar ratio and the calcination temperature have significant effects on the structure and heat resistance performance of ASA at temperature of 600–1000 °C. The sample with Al/Si molar ratio of 0.15 shows the highest specific surface area of 805.9 m²/g and pore volume of 5.038 cm³/g after heated to 600 °C, and retains 179.5 m²/g and 1.295 cm³/g respectively after heated to 1000 °C. Mechanism analysis indicates that, though the actual aluminum content is extremely low (0.18%, wt%), the high-temperature resistance of ASA is greatly improved owing to the effective doping of aluminum in the lattice of SiO₂ and the corresponding electrostatic repulsion between neighboring nanoparticles induced by the replacement of Si⁴⁺ by Al³⁺ ions.     

Synthesis of 3D porous ceramic scaffolds obtained by the sol-gel method with surface morphology modified by hollow spheres for bone tissue engineering applications

In the present work, we modified the surface morphology of 3D porous ceramic scaffolds by incorporating strontium phosphate (SrP) hollow nano-/microspheres with potential application as delivery system for the local release of therapeutic substances. SrP hollow spheres were synthesized by a template-free hydrothermal method. The influence of the reaction temperature, time and concentration of reactants on precipitates' morphology and size were investigated. To obtain a larger number of open hollow spheres, a new methodology was developed consisting of applying a second hydrothermal treatment to spheres by heating them at 120 °C for 24 h. The X-ray diffraction (XRD) analysis indicated that spheres consisted of a main magnesium-substituted strontium phosphate phase ((Sr_0.86Mg_0.14)₃(PO₄)₂). The scanning electron microscopy (SEM) micrographs confirmed that spheres had hollow interiors (～350 nm size) and an average diameter of 850 nm. Spheres had a specific surface area of 30.5 m²/g, a mesoporous shell with an average pore size of 3.8 nm, and a pore volume of 0.14 cm³/g. These characteristics make them promising candidates for drug, cell and protein delivery. For the attachment of spheres to scaffolds’ surface, ceramic structures were immersed in an ethanol solution containing 0.1 g of hollow spheres and kept at 37 °C for 4 h. The scaffolds with incorporated spheres were bioactive after being immersed in simulated body fluid (SBF) for 7 days and spheres were still adhered to their surface after 14 days.     

Preparation of hollow submicrocapsules with a mesoporous carbon shell

The preparation of carbon submicrocapsules with size up to 800 nm and a mesoporous shell by hard silica templating is reported. Washing and template synthesis conditions were varied to promote porosity and avoid deformation of the microcapsules. The silica template synthesis conditions analyzed were: silica nucleus formation time (0.25–6 h), octadecyltrimethoxysilane/tetraethylorthosilicate volume ratio for silica shell formation (0.2–0.6) and silica shell formation time (1–24 h). The samples were characterized by 77 K nitrogen adsorption/desorption, mercury porosimetry and electron microscopy. Under all the washing conditions tested the carbon submicrocapsules were deformed due to the large size of the hollow core and the thickness of the shell. Changes in the silica template synthesis conditions did not result in substantial improvement of the strength of the microcapsules. The synthesis of a silica template with a double shell allowed us to obtain thick shell carbon submicrocapsules without significant deflation and with higher porosity. The characterization of these microcapsules showed that they have a BET surface area of 1541 m²/g and a pore size distribution with peaks centered at 0.75, 0.86, 1.0 nm in the micropore range and 3.5 nm in the mesopore range. The pore volume in the 2–80 nm range was 1.7 cm³/g.     

Synthesis of highly ordered supermicroporous silica using short-chain cationic trimeric surfactant as structure-directing agent

Highly ordered supermicroporous silica was synthesized by short chains cationic trimeric surfactant [C₁₀H₂₁N⁺(CH₃)₂(CH₂)₂N⁺(CH₃)(C₁₀H₂₁) (CH₂)₂N⁺(CH₃)₂C₁₀H₂₁] · 3Br⁻ (denoted C_10-2-10-2-10) with a short spacer group (s = 2) as the structure-directing agent and tetraethyl orthosilicate as the precursor. The obtained samples were characterized by small-angle X-ray diffraction, high resolution transmission electron microscopy, and N₂ adsorption–desorption. The results showed that the pore structure of the resulting samples belonged to the two-dimensional hexagonal structure (space group 2D-p6mm) with a pore size from 1.92 to 2.16 nm, which was within the supermicroporous range. The high-quality supermicroporous silica was formed at a low molar ratio of C_10-2-10-2-10 to tetraethyl orthosilicate (0.08:1), which indicated that the self-assembly ability of C_10-2-10-2-10 was stronger than that of corresponding monovalent surfactants. We strictly compared the methods of calculating surface area and pore size of supermicroporous materials, and the surface area was found to be in the range of 910–1,135 m² g⁻¹ by the α_s plot method. With the increase of hydrothermal temperature, the ordering of the supermicroporous structure increased first then decreased, at the same time the pore size was enlarged.     

Ordered mesoporous carbide-derived carbons prepared by soft templating

Free-standing films of ordered mesoporous silicon and titanium carbide-derived carbons have been synthesized using a novel soft templating approach without employing hydrofluoric acid. Tetraethyl orthosilicate or titanium citrate, alternatively, and a phenolic resin underwent an evaporation induced self-assembly yielding ordered mesoporous silicon carbide/carbon or titanium carbide/carbon composites. High temperature chlorine treatment transformed these materials conformally into carbide-derived carbons (CDC) while the ordered arrangement of mesopores was maintained. The corresponding hierarchical pore structures consist of narrowly distributed micro- and mesopores (distribution maxima at 1 and 5 nm, respectively) with a high surface area and pore volume of up to 1538 m²/g and 2.53 cm³/g, respectively.     

Methane sorption on ordered mesoporous carbon in the presence of water

An ordered mesoporous carbon was synthesized using SBA-15 as the template. The sorption isotherms of methane on the synthesized carbon material were collected. Its ordered structure was confirmed by the XRD, SEM and TEM examinations. The BET surface area is 1100-1200 m²/g, the total pore volume is 1.24-1.30 cm³/g, and the pore size distribution is very narrow and centered at 2-5 nm. As high as 41.2 wt.% of methane was stored per unit mass of carbon at 275 K and pressures less than 7 MPa in the presence of 3.86 times more water. This sorption amount is 31% higher than the largest sorption capacity reached by activated carbon in the presence of water, which was equal to or higher than the storage capacity of compression till 20 MPa. The enthalpy change corresponding to the sudden change of isotherms was equal to the enthalpy change of methane hydrate formation; therefore, the mechanism of the enhanced methane storage was considered due to the formation of methane hydrate in the porous carbon material.     

Synthesis of Al-MCM-41 and FCC diesel hydrorefining study

Mesostructured aluminosilicates (MCM-41) with ordered 2-dimensional hexagonal structure were successfully synthesized via the alkali-treatment step and nanocrystal aluminosilicates assembly in the basic and hydrothermal synthesis conditions by sol?Cgel approach. Highly hydrothermally stable MCM-41 coupled with large surface area and pore volume is desirable. To find out the optimum conditions, An orthogonal experiment L₁₆(4³) with three factors and four levels was adopted and the effects were also discussed. Various techniques including X-ray diffraction (XRD), N₂ adsorption-desorption, temperature program desorption and fourier transform infrared spectroscopy were used to monitor the physical?Cchemical properties of MCM-41. When the synthesis was operated under 80?°C lasting 1?h with C_NaOH 0.5?mol/L and molar ratio of CTAB to ZSM-5 0.15, the synthesized MCM-41 possessed high specific surface area 1,150?m²/g, large pore volume 1.23?cm³/g with appropriate acid distribution as well as highly hydrothermal stability. In addition, the results reveal that the as-synthesized samples have a uniform phase without MFI structure. Samples have a 5-membered ring in the framework and have a better hydrothermal stability than the conventional Al-MCM-41. Performance evaluation was carried out on a 20?mL fixed-bed hydrorefining unit with the Daqing FCC diesel as feedstock. The sulfur and nitrogen removal is 99.3% and 99.6%, respectively, while the cetane number was increased by 5.4.     

Synthesis of a ferrocene-containing ordered mesoporous organosilica and its catalytic activity

A new ordered mesoporous organosilica has been synthesized through co-condensation of 1,1′-bis[2-(triethoxylsilyl)ethyl]ferrocene and tetraethyl orthosilicate under basic conditions using supramolecular templates of cetyltrimethylammonium bromide as structure directing agents. The templates were removed through solvent extraction to yield the ferrocene-containing ordered mesoporous organosilicas. The pore diameter, BET surface area, and pore volume of the extracted material were 2.2 nm, 1,085 m²/g and 0.67 cm³/g, respectively. The material also has been characterized by XRD, TEM, FT-IR, UV–Vis DRS, solid state ²⁹Si MAS NMR and ¹³C CP-MAS NMR etc. In the reaction of benzene hydroxylation to phenol, the ferrocene-containing ordered mesoporous materials show a comparable activity with the homogeneous ferrocene catalyst, giving 20.2% of yield and 65.3% of selectivity for phenol.     

Effects of templating surfactant concentrations on the mesostructure of ordered mesoporous anatase TiO2 by an evaporation-induced self-assembly method

We prepared ordered hexagonal mesoporous TiO₂ by an evaporation-induced self-assembly (EISA) method using Pluronic P123 and tetrabutyl orthotitanate (Ti(OBuⁿ)₄, TBOT) as the templating agent and the titanium source, respectively. The main purpose of this study was to elucidate the effects of surfactant concentrations on the pore arrangement, pore size, specific surface area and structure of mesoporous TiO₂ by the EISA method. The mesostructures of mesoporous TiO₂ were characterized with X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms, and transmission electron microscopy (TEM). By varying the concentration of the block copolymer, mesoporous TiO₂ of various pore sizes and pore ordering were prepared. Because the mesostructure is governed by the concentration of P123 surfactant at gelation of the solution, a higher P123/TBOT mole ratio favored the formation of highly ordered mesoporous TiO₂ with a maximum pore volume of 0.26 cm³/g, a high specific surface area of 244 m²/g, and a BJH average pore size of 4.7 nm.     

Fabrication and nano-structure control of carbon aerogels via a microemulsion-templated sol-gel polymerization method

Carbon aerogels were successfully fabricated by a microemulsion-templated sol-gel polymerization method. When a suitable molar ratio of surfactant to resorcinol (S/R) and an appropriate resorcinol-formaldehyde concentration were selected, the organic gels thus obtained could be dried with little shrinkage by heating at ambient pressure. The size of carbon nano-particles and the pore size of carbon aerogels thus produced decrease with an increase of S/R. The highest specific surface area and specific mesopore volume of the carbon aerogels prepared by our method were 620 m² g⁻¹ and 1.14 cm³/g, respectively.     

A simplified synthesis of N-doped zeolite-templated carbons, the control of the level of zeolite-like ordering and its effect on hydrogen storage properties

Nitrogen-doped, microporous carbon materials have been prepared using zeolite EMC-2 as a hard template and acetonitrile as the carbon source via chemical vapour deposition (CVD) in the temperature range 700–950 °C. The carbon products exhibited high surface areas (up to 3360 m²/g), high pore volumes (up to 1.71 cm³/g) and had zeolite-like structural ordering derived from the template. The carbons had XRD patterns that exhibited two well resolved peaks and TEM images that showed well ordered pore channels. A high proportion of porosity (up to 85% of surface area and 73% of pore volume) for the best ordered carbon arose from micropores that exhibited narrow size distribution in the range 5–15 Å. The carbons generally retained the morphology of the template with solid-core particles at CVD temperatures up to 900 °C and hollow shells at 950 °C. The carbons had total hydrogen storage capacities up to 6.0 wt.% at −196 °C and 20 bar. The hydrogen uptake was found to be dependent on the level of zeolite-like ordering and the resulting textural properties. Particularly, high levels of zeolite-like ordering favoured micropores of size <15 Å which are favourable for higher hydrogen uptake capacities.     

The synthesis of Al-MCM-41 from volclay — A low-cost Al and Si source

The alkaline fusion of volclay (a low-cost sodium exchanged smectite) was used as source to generate the Si and Al components which were effectively transformed into mesoporous Al-MCM-41 depending on hydrothermal condition. The Al-MCM-41 materials were investigated by powder X-ray diffraction (XRD), N₂ adsorption–desorption measurements and both scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM). The volclay which converted into a silicon and an aluminium source allowed the formation of well ordered mesoporous Al-MCM-41 materials with high aluminium content (roughly 4 times higher than a Al-MCM-41 produced by a standard method), a high specific surface area (1060 m²/g), a pore volume of 0.8 cm³/g (for pore width < 7.1 nm) with an mono-modal pore distribution with a maximum in the mesoporous pore size of 3.8 nm in pore width.     

A low-temperature autoclaving route to synthesize monolithic carbon materials with an ordered mesostructure

Low-temperature autoclaving has been demonstrated to synthesize monolithic carbon materials with an ordered mesostructure by using triblock copolymer F127 as template, and resorcinol/formaldehyde resol as carbon precursor under acidic conditions. Transmission electron microscopy, small angle X-ray scattering, Fourier transform infrared spectroscopy and nitrogen adsorption measurements show that the crack-free carbon monoliths have a 2-D hexagonal pore system, a uniform pore size of ∼5.0 nm and a high surface area of ∼675 m² g⁻¹. The macroscopic morphology can be tuned by changing the diameter of the autoclave. The influence of the synthesis conditions including the autoclaving treatment time and the molar ratio of formaldehyde (F) to resorcinol (R) are discussed. It is found that while the F/R molar ratio ?2 and the autoclaving treatment time ?2 d, highly ordered mesoporous carbon monoliths can be obtained. In comparison, monolithic mesoporous carbon materials prepared through an evaporation-induced self-assembly strategy are partly cracked with a disordered wormhole-like mesostructure, suggesting that low-temperature autoclaving is an efficient way to prepare crack-free monolithic carbon materials with an ordered mesostructure.     

Assembling Colloidal Silica into Porous Hollow Microspheres

A non-surfactant-based synthesis approach to mesoporous hollow spheres through the use of colloidal silica is presented. Based on nanoparticle assembly chemistry developed previously for silica/polymer hybrid microcapsules, the room-temperature preparation follows a two-step sequence: (1) the electrostatic reaction of cationic polymer with an anionic salt solution, resulting in a suspension of salt-bridged polymer aggregates; and (2) the electrostatic reaction between this suspension and an aqueous suspension of nanoparticles (NPs). As a specific example, 13-nm silica particles, combined with polyallylamine and sodium citrate, gave silica/polymer hollow spheres with a mean diameter of 2.1 μm and a BET surface area of 4 m²/g. After calcination at 600 °C, the resulting silica-only microcapsules had a BET surface area of 259 m²/g, a modal pore size of 4.0 nm, and a pore volume of 0.38 cc/g, values that exceeded those of calcined silica NPs. This colloidal silica-based material is an example of the simultaneous control of pore size (at the nanometer scale) and particle morphology (at the micrometer scale) that is possible through charge-driven NP assembly.     

Preparation of controlled porosity carbon aerogels for energy storage in rechargeable lithium oxygen batteries

Porous carbon aerogels are prepared by polycondensation of resorcinol and formaldehyde catalyzed by sodium carbonate followed by carbonization of the resultant aerogels in an inert atmosphere. Pore structure of carbon aerogels is adjusted by changing the molar ratio of resorcinol to catalyst during gel preparation and also pyrolysis under Ar and activation under CO₂ atmosphere at different temperatures. The prepared carbons are used as active materials in fabrication of composite carbon electrodes. The electrochemical performance of the electrodes has been tested in a Li/O₂ cell. Through the galvanostatic charge/discharge measurements, it is found that the cell performance (i.e. discharge capacity and discharge voltage) depends on the morphology of carbon and a combined effect of pore volume, pore size and surface area of carbon affects the storage capacity. A Li/O₂ cell using the carbon with the largest pore volume (2.195 cm³/g) and a wide pore size (14.23 nm) showed a specific capacity of 1290 mA h g⁻¹.