Adsorption studies of thermal stability of SBA-16 mesoporous silicas

Cage-like ordered mesoporous silicas, SBA-16, and ethane-silicas with cubic (Im3m) and (Fm3m) symmetry groups were synthesized with addition of sodium chloride by using tetraethyl orthosilicate (TEOS) as silica precursor, 1,2-bis(triethoxysilyl)ethane (BTESE) as bridged silsesquioxane and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymer Pluronic F127 (EO₁₀₆PO₇₀EO₁₀₆) as template at low acid concentrations. The resulting samples were subjected to extraction in order to remove the polymeric template. The as-synthesized and extracted materials were calcined in the range of 350-900 °C to determine their thermal stability. Based on the XRD analysis and nitrogen adsorption data such as the BET specific surface area, volume of primary mesopores, pore wall thickness and pore size distributions, the SBA-16 silicas exhibit relatively high thermal stability because their mesostructural ordering was retained even up to 900 °C. However, an increase in the calcination temperature tended to decrease significantly the BET surface area, volumes of primary and complementary pores, and to less extent the pore size and pore wall thickness due to the structural shrinkage. Furthermore, the as synthesized samples subjected to a short extraction with acidic ethanol solution possessed even better thermal stability. On the other hand, calcination at 550 °C of ethane-silicas caused a complete removal of the ethane bridging groups from the periodic mesoporous organosilicas and their calcination above 800 °C led to the partial collapse of the structure.     

Preparation of highly ordered mesoporous AlSBA-15-SO3H hybrid material for the catalytic synthesis of chalcone under solvent-free condition

Single-step preparation of SBA-15 materials functionalized with both propylsulfonic acid groups and aluminum species (AlSBA-15-SO₃H) was carried out by hydrothermal treatment of a mixture of aluminum isopropoxide, 3-mercaptopropyltriethoxysilane, tetraethoxysilane, and triblock copolymer surfactant. At Si/Al molar ratio of 11-96, the materials exhibited well-ordered hexagonally arranged mesopores with pore diameter of ca. 9 nm, BET surface area of 546.9-666.0 m² g⁻¹, and pore volume of 0.82-1.03 cm³ g⁻¹. As-prepared AlSBA-15-SO₃H was successfully used in the Claisen-Schmidt condensation reaction of benzaldehyde with acetophenone to produce chalcone under solvent-free condition, and the influence of the reaction parameters including temperatures, molar ratios of BZD to APN, and aluminum loadings were considered during the chalcone synthesis procedure. It showed that AlSBA-15-SO₃H exhibited significantly high catalytic activity and selectivity, outperforming the reference catalysts such as sulfuric acid, ZSM-5, and acidic MCM-49. In addition, the catalytic stability and regeneration of AlSBA-15-SO₃H was studied.     

Polymer-templated mesoporous carbons synthesized in the presence of nickel nanoparticles, nickel oxide nanoparticles, and nickel nitrate

Mesoporous carbon composites, containing nickel and nickel oxide nanoparticles, were obtained by soft-templating method. Samples were synthesized under acidic conditions using resorcinol and formaldehyde as carbon precursors, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock co-polymer Lutrol F127 as a soft template and nickel and nickel oxide nanoparticles, and nickel nitrate as metal precursors. In addition, a one set of samples was obtained by impregnation of mesoporous carbons with a nickel nitrate solution followed by further annealing at 400 °C. Wide angle X-ray powder diffraction along with thermogravimetric analysis proved the presence of nickel nanoparticles in the final composites obtained using nickel and nickel oxide nanoparticles, and Ni(NO₃)₂ solution. Whereas, the impregnation of carbons with a nickel nitrate solution followed by annealing at 400 °C resulted in needle-like nickel oxide nanoparticles present inside the composites’ pores. Low-temperature (−196 °C) nitrogen physisorption, X-ray powder diffraction, and thermogravimetric analysis confirmed good adsorption and structural properties of the synthesized nickel-carbon composites, in particular, the samples possessed high surface areas (>600 m²/g), large total pore volumes (>0.50 cm³/g), and maxima of pore size distribution functions at circa 7 nm. It was found that the composites were partially graphitized during carbonization process at 850 °C. The samples are stable in an air environment below temperature of 500 °C. All these features make the synthesized nickel-carbon composites attractive materials for adsorption, catalysis, energy storage, and environmental applications.     

Evolution of pores in mesoporous silica films: Porogen loading effect

Mesoporous silica films were synthesized via a sol-gel process under an acidic condition. Various amounts of triblock copolymer F38 were loaded to precursor sols as the pore generator. The evolution of the pores generated by porogen decomposition was investigated as a function of F38 loading by positron annihilation gamma-ray energy spectroscopy and positron annihilation lifetime spectroscopy based on slow positron beams. The threshold of pore percolation is found to be around 10 wt% of F38 loading by positron annihilation gamma-ray energy spectroscopy. Positron annihilation lifetime spectroscopy in the films show that the pore size increases from 1 nm to 3 nm with increasing F38 loading from 5 wt% to 30 wt%.     

A metal-ion-assisted assembly approach to synthesize disulfide-bridged periodical mesoporous organosilicas with high sulfide contents and efficient adsorption

Well-ordered two-dimensional (2D) hexagonal periodic mesoporous organosilicas (PMOs) with a high content of disulfide groups have been prepared by a simple metal-ions-assisted amphiphilic surfactant templating process under a strong acidic condition. Long-chain organic bridge silane, bis(triethoxysilylpropyl)disulfide (BTSPDS) was used as a precursor which can be co-condensed with tetraethoxysilane (TEOS) to assemble with the triblock copolymer Pluronic P123 template and to construct the mesostructured organic-inorganic frameworks. The content of disulfide functional groups is up to 20% (BTSPDS molar content in the initial silane mixture) incorporated into the framework. The obtained ordered mesoporous DS-PMO materials have relatively high BET surface area (∼580 m²/g), large uniform pore size (up to 6.3 nm) and thick pore walls (thickness up to 7.1 nm), because of the long-chain disulfide bridges. The metal ions such as Zn²⁺ formed the four-coordination complex with two sulfides of BTSPDS and ethylene oxide moieties of P123 template, which could enhance the interaction between the “soft” long disulfide groups and P123 template, thus improving the mesostructural regularity correspondingly. The disulfide-bridged PMO materials exhibit excellent hydrothermal stability in boiling water for 5 days, probably due to the thick pore walls. SEM images show that after the hydrothermal treatment, the morphology of the ordered disulfide-bridged PMO materials is retained, as that of the wheat-like SBA-15. Excellent adsorption efficiency (∼716 mg/g) for Hg²⁺ ions is observed, suggesting a potential application in removal of heavy metal ions in wastewater.     

Mesostructures and properties of transparent block copolymer/silica nanocomposite monoliths

In this work, three different block copolymer/silica hybrid nanocomposite monoliths that possess mesostructured domains (hexagonal, cubic, and disordered) were prepared through the micellization of the block copolymer during the sol-gel process of a silica precursor. Transparent block copolymer/silica nanocomposite monoliths were obtained from the amphiphilic triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (EO₁₀₆PO₇₀EO₁₀₆, Pluronic F127), which we used to organize the polymerizing silica networks; the ratio between the block copolymer and silica was fixed at 60:40 (wt%). Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to observe the mesostructural ordering. Temperature-dependent SAXS patterns of the cubic structured nanocomposites showed that the calcination process takes place at 210°C. The transmittances of the nanocomposite monoliths over the range of wavelengths from 400 to 800 nm was >85%. From rheological measurements at low frequency, it was found that the hexagonally structured monoliths had higher storage and loss moduli relative to the monoliths possessing cubic and disordered structures.     

Fabrication and application of highly ordered mesoporous Co3O4, NiO, and their metals

Highly ordered mesoporous Co₃O₄, NiO, and their metals were synthesized by nanocasting method using there corresponding mesoporous SBA-15 silica as a template. The obtained porous metal oxides have high surface areas, large pore volume, and a narrow pore size distribution. The N₂-adsorption data for mesoporous metal oxides have provided the BET area of 257.7 m² g⁻¹ and the total pore volume of 0.46 cm³ g⁻¹. The mesoporous metals were employed as a catalyst in the synthesis of (S)-3-pyrrolidinol from chiral (S)-4-chloro-3-hydroxybutyronitrile, and a high yield to (S)-3-pyrrolidinol-salt was obtained on the mesoporous Co metal catalyst.     

Depth profiling of taxol-loaded poly(styrene-b-isobutylene-b-styrene) using Ga and C60 ion beams

The surface of a triblock copolymer, containing a solid-phase drug, was investigated using 15 keV Ga⁺ and 20 keV C₆₀⁺ ion beams. Overall, the results illustrate the successful use of a cluster ion beam for greatly enhancing the molecular ion and high-mass fragment ion intensities from the surface and bulk of the polymer system. The use of C₆₀⁺ also established the ability to see through common overlayers like poly(dimethyl siloxane) which was not possible using atomic ion sources. Moreover, the use of C₆₀⁺ allowed depth profiles to be obtained using primary ion dose densities in excess of 6 × 10¹⁴ C₆₀⁺/cm². Resulting sputter craters possess relatively flat bottoms without the need for sample rotation and reached depths of ca. 2 μm. AFM results illustrate the more gentile removal of surface species using cluster ions. Specifically, phase contrast and topographic images suggest the relatively high ion doses do not significantly alter the phase distribution or surface topography of the polymer. However, a slight increase in rms roughness was noticed.     

Iron–cobalt nanocrystalline alloy supported on a cubic mesostructured silica matrix: FeCo/SBA-16 porous nanocomposites

A series of novel nanocomposites constituted of FeCo nanoparticles dispersed in an ordered cubic Im3m mesoporous silica matrix (SBA-16) have been successfully synthesized using the wet impregnation method. SBA-16, prepared using the non-ionic Pluronic 127 triblock copolymer as a structure-directing agent, is an excellent support for catalytic nanoparticles because of its peculiar three-dimensional cage-like structure, high surface area, thick walls, and high thermal stability. Low-angle X-ray diffraction, N₂ physisorption, and transmission electron microscopy analyses show that after metal loading, calcination at 500 °C, and reduction in H₂ flux at 800 °C, the nanocomposites retain the well-ordered structure of the matrix with cubic symmetry of pores. FeCo alloy nanoparticles with spherical shape and narrow size distribution (4–8 nm) are homogeneoulsy distributed throughout the matrix and they seem in a large extent to be allocated inside the pores.     

The influence of temperature on magnetic and microwave absorption properties of Fe/graphite oxide nanocomposites

Fe/graphite oxide nanocomposites were prepared by inserting Fe³⁺ into layers of graphite oxide and then reducing Fe³⁺/graphite oxide compound at different reduced reaction temperatures in H₂. The composition, crystal structure, magnetic and microwave absorption properties of Fe/graphite oxide nanocomposites were investigated using elemental analysis, transmission electron microscope (TEM), X-ray diffraction (XRD), magnetic hysteresis curve and electromagnetic parameter analysis. The results show that the densities of samples are 2.43–2.47 g/cm³ and the nanocomposites are soft magnetic materials. The optimum reduced reaction temperature for preparing Fe/graphite oxide nanocomposites is 600 °C. With the increase of the thickness of the sample, the matching frequency tends to shift to the lower frequency region, and theoretical reflection loss becomes less at the matching frequency. Microwave absorption property of Fe/graphite oxide nanocomposites prepared at 600  °C (FeGO600) is the best. When the thickness is 1 mm, the maximum theoretical reflection loss of FeGO600 is −9 dB and the frequency region in which the maximum reflection loss is more than −6.0 dB is 11–18 GHz. In conclusion, FeGO600 is a good candidate for microwave absorbent due to its low density, wide frequency region for microwave absorption and large reflection loss.