Nanochannels Of SBA-15 Research Articles

Novel Hybrid Thioamide Ligand Supported Copper Nanoparticles on SBA-15: A Copper Rich Robust Nanoreactor for Green Synthesis of Triazoles and Tetrazoles in Water Medium

In this work, a new thioamide based ligand with reductive nature was designed for modification of mesoporous SBA-15. For this purpose, the channels of SBA-15 were modified with Tris(2-aminoethyl)amine (TAEA) groups and then reacted with S8 and phenyl acetylene to form thioamide groups via Willgerodt-Kindler reaction. This porous material proved to be an effective host for the immobilization of inexpensive Cu(II) ions. The catalytically active Cu(I) species were generated automatically due to the reductive nature of thioamide modified surface of catalyst without use of any toxic reducing agents. The well stabilized Cu(I) species into the nano-channels of SBA-15 were used for synthesis of various triazoles from sodium azide, phenyl acetylene and alkyl/benzyl halides or alkyl epoxides and various tetrazoles from sodium azide and aryl/alkyl nitriles under green mild aqueous reaction conditions. This catalytic system was used for 9 and 11 consecutive runs for synthesis of triazoles and tetrazoles, respectively.

Encapsulation of Homogeneous Catalysts in Mesoporous Materials Using Diffusion-Limited Atomic Layer Deposition.

The heterogenization of homogeneous metal complex catalysts has attracted great attention. The encapsulation of metal complexes into nanochannels of mesoporous materials is achieved by coating metal oxides at/near the pore entrance by diffusion-limited atomic layer deposition (ALD) to produce a hollow plug. The pore size of the hollow plug is precisely controlled on the sub-nanometer scale by the number of ALD cycles to fit various metal complexes with different molecular sizes. Typically, Co or Ti complexes are successfully encapsulated into the nanochannels of SBA-15, SBA-16, and MCM-41. The encapsulated Co and Ti catalysts show excellent catalytic activity and reusability in the hydrolytic kinetic resolution of epoxides and asymmetric cyanosilylation of carbonyl compounds, respectively. This ALD-assisted encapsulation method can be extended to the encapsulation of other homogeneous catalysts into different mesoporous materials for various heterogeneous reactions.

Solvent-free direct formulation of poorly-soluble drugs to amorphous solid dispersion via melt-absorption

To improve the dissolution properties of poorly water soluble active pharmaceutical ingredients (APIs), a solvent-free melt-absorption process was applied to directly load the APIs into mesoporous SBA-15 silica powder as an amorphous solid dispersion. Two model compounds, poorly aqueous soluble ibuprofen (IBU) and fenofibrate (FEN), were individually mixed with SBA-15 powder and heated above their respective melting points. Upon cooling, the physicochemical and solid-state properties of the solid dispersions were investigated by N2 adsorption, DSC, XRD, SEM and solid-state NMR. The molten API was found to be absorbed into the pores, confined within the nano-channels of SBA-15, and re-solidified to an amorphous solid dispersion. Due to the amorphous properties, the APIs showed a significant enhancement in dissolution rate as compared with the untreated crystalline APIs. Although the amorphous forms were not at thermodynamic equilibrium, the APIs exhibited excellent solid-state physical stability even under accelerated stress conditions. In comparison with APIs loaded using a co-spray drying process (previous work), the melt-absorption process required no organic solvent, produced powders with a coarser size distribution and more desirable flow properties. This solvent-free direct melt-absorption process can be used to formulate a wide range of poorly soluble drugs to be amorphous solid dispersions.

Electromagnetic wave absorbing properties of SiC/SiO2 composites with ordered inter-filled structure

Silicon carbide/silica (SiC/SiO2) monoliths with ordered inter-filled structure were prepared via nanocasting and cold-pressing, using polycarbosilane as precursor and ordered mesoporous silica SBA-15 as template. The SiC grains were incorporated, in form of ordered rodlike arrays, into nanochannels of SBA-15. Their electromagnetic (EM) wave absorbing properties were investigated in X-band, in which SiC acted as EM wave absorber and SiO2 as transparent matrix. The results indicated that the composites had good EM absorbing properties due to the enhanced dielectric loss resulting from their intrinsic physical properties and special structures. The optimal absorbing properties were determined by impedance match and quarter-wavelength law.

Preparation of Superhighly Dispersed Co3O4@SBA-15 with Different Morphologies in Supercritical CO2 with the Assistance of Dilute Acids

In previous reports, organic solvents have usually been used as cosolvents in supercritical fluid applications. In this study, dilute acids were introduced into supercritical CO2 as cosolvents for the first time to improve the adsorption and dispersion of metal precursors on the substrate. Superhighly dispersed Co3O4 nanoparticles were confined in the nanochannels of SBA-15 after deposition and calcination when a small amount of nitric acid was added as the cosolvent. As the concentration of nitric acid increased, more individual small nanoparticles aggregated in adjacent nanochannels through the micropores in the walls of the substrates, which favored the formation of large nanoparticles. Furthermore, only Co3O4 nanoparticles were obtained when nitric acid was added to supercritical CO2–ethanol solution, whereas nanowires were found instead when hydrochloric acid was used. This indicates that H+ favors the adsorption and dispersion of precursors on the substrates and Cl– plays a key role in dictating the nanowire morphology.

A novel Fe3+ ions chemosensor by covalent coupling fluorene onto the mono, di- and tri-ammonium functionalized nanoporous silica type SBA-15

Fluorene functionalized mesoporous silica (FM-SBA-15, FD-SBA-15 and FT-SBA-15) were prepared the post synthesis grafting method of SBA-15. The grafting of fluorene in nanochannels of SBA-15 was performed in two steps: (i) attachment of the 3-aminopropyltriethoxysilane, [1-(2-aminoethyl)-3-aminopropyl]trimethoxysilane and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane on SBA-15, then (ii) covalent linkage of fluorene. The obtained material was characterized by SAXS, N2 adsorption–desorption, FT-IR spectroscopy, Raman spectroscopy and thermogravimetric analysis that indicate the successful immobilization of fluorene on the surface of mesoporous silica. The sensing ability of FM-SBA-15, FD-SBA-15 and FT-SBA-15 was studied by addition of the cations Fe3+, Mg2+, Cr3+, Co2+, Ni2+ Cu2+, Hg2+ and Zn2+ to water suspensions of the assayed solid. Of all the cations tested addition of Fe3+ ion to a suspension of these materials resulted in the largest decrease in the fluorescence intensity but addition of Mg2+, Cr3+, Co2+, Ni2+, Cu2+, Hg2+ and Zn2+ did not quench the fluorescence of FM-SBA-15, FD-SBA-15 and FT-SBA-15. A good linearity between the fluorescence intensity of the prepared materials and the concentration of Fe3+ ion is constructed, which enables these materials as a fluorescence chemo sensor for detecting the Fe3+ ion with a suitable detection limit.

Self-Assembly and Diffusion of Block Copolymer Templates in SBA-15 Nanochannels

Molecular dynamics of triblock copolymers under confinement by the nanochannels of SBA-15 was investigated using pulsed field gradient (PFG) NMR spectroscopy with high-intensity field gradient pulses. The mesoporous material SBA-15 was synthesized using the surfactant Pluronic P123 (EO(20)-PO(70)-EO(20)). The diffusion of P123 in mixtures with water was studied both in bulk and under the condition of confinement by the mesoporous channels of SBA-15. As a result, at room temperature the diffusion of P123 in SBA-15 is more than a factor three smaller than that of the same polymer in the bulk mixture with water. A pronounced atypical temperature dependence of the measured diffusivities was observed both in the confined and in the bulk systems. This atypical temperature dependence was attributed to the transition from the aggregated state to the molecular solution and gave an evidence for a qualitative similarity of the supermolecular organization of the Pluronic/water mixtures under confinements and in the bulk. Confinements were shown to produce significant effects on diffusion properties of Pluronic molecules. The diffusivity of self-associates forming up at room temperature was considerably diminished in comparison to the bulk systems. In contrast, at low temperatures diffusion of the individually dissolved molecules was comparably fast, but subjected to anisotropy induced by channels.

Preparation, Characterization and Catalysis Properties of Ag/SBA-15 Nanocomposite by Supercritical Fluid Deposition

Ag/SBA-15 nanocomposite was prepared by supercritical fluid deposition(SCFD) method,with AgNO3 as the precursor and ethanol or glycol as the cosolvent.AgNO3 was firstly deposited onto the SBA-15 support at 50℃,23-25MPa,and reacted for 3-24h.The resultant composite was then subjected to calcination and reduction treatment for obtaining Ag/SBA-15 nanocomposite.Characterizations with XRD and TEM show that Ag nanoparticles(with sizes of 3-7nm) or nanowires(5-9nm in width and tens of nanometers to several micrometers in length) are formed in the nanochannels of SBA-15 support.It is demonstrated that SCFD is a green and effective method for preparation of nanocomposite.With the aid of cosolvent,the supercritical carbon dioxide can dissolve the inorganic metallic salts.Moreover,the morphologies of the nanocomposite can be controlled to some extent by selecting the deposition conditions.A catalytic test on the Ag/SBA-15 nanocomposite shows that the sample has a moderate activity,with the complete conversion of CO at 300℃.

Photooxidation of Olefins under Oxygen in Platinum(II) Complex-Loaded Mesoporous Molecular Sieves

Cyclometalated platinum(II) complex has been successfully incorporated into the (3-aminopropyl) triethoxysilane-modified channels of ordered mesoporous silica SBA-15 that has large pore hexagonal channels. Studies on the (1)O(2) generation conclusively demonstrates that the olefins in the nano-channels of SBA-15 can be enriched 8 times higher than those in the homogeneous solution as the diffusion quantum yield of singlet oxygen ((1)O(2)) is assumed to be unit. The platinum(II) complex loaded in the channel of SBA-15 is stable, and the photosensitized oxidation occurs efficiently. No obvious degradation and leaching of photosensitizers is observed even after 10 runs. Only a simple filtration is needed for the recycled use of the expensive noble metal catalysts. This versatile system is a good example of photochemical reactions occurring in the mesoporous silica molecular sieve. SBA-15 not only provides a support for the photosensitizer, but also acts as a nano-reactor to facilitate the photooxidation.