Periodic mesoporous organosilicas with multiple bridging groups and spherical morphology

Bi- and trifunctional periodic mesoporous organosilicas (PMOs) with phenylene, thiophene, and ethane bridging groups were synthesized using 1,2-bis(triethoxysilyl)ethane (BTEE), 1,4-bis(triethoxysilyl)benzene (BTEB), and 2,5-bis(triethoxysilyl)thiophene (BTET) organosilica precursors and a poly(ethylene oxide)-poly(D,L-lactic acid-co-glycolic acid)-poly(ethylene oxide) (PEO-PLGA-PEO) triblock copolymer template under low acidic conditions. The PMO samples with different concentrations of organic bridging groups were obtained in the form of spherical particles having average diameters of 2-3 mum and 2D hexagonal (p6m) mesostructure with pore diameters of 7.3-8.4 nm. The particle morphology and chemistry of pore walls were tailored using different mixtures of organosilica precursors. Adsorption and structural properties of the aforementioned PMOs have been studied by nitrogen adsorption and small-angle X-ray scattering, whereas their framework chemistry was quantitatively analyzed by solid-state 13C and 29Si MAS NMR.     

Periodic mesoporous organosilica with large heterocyclic bridging groups

Periodic mesoporous organosilica with a heterocyclic bridging group of large molecular weight, tris[3-(trimethoxysilyl)propyl]isocyanurate, is reported. Incorporation of an organic moiety into the silica framework afforded material attractive for adsorption of mercury and related heavy metal ions from aqueous solutions.     

Face-centered-cubic large-pore periodic mesoporous organosilicas with unsaturated and aromatic bridging groups

Large-pore ethenylene-bridged (-CH═CH-) and phenylene-bridged (-C(6)H(4)-) periodic mesoporous organosilicas (PMOs) with face-centered-cubic structure (Fm3m symmetry) of spherical mesopores were synthesized at 7 °C at low acid concentration (0.1 M HCl) using Pluronic F127 triblock copolymer surfactant in the presence of aromatic swelling agents (1,3,5-trimethylbenzene, xylenes-isomer mixture, and toluene). In particular, this work reports an unprecedented block-copolymer-templated well-ordered ethenylene-bridged PMO with cubic structure of spherical mesopores and an unprecedented block-copolymer-templated face-centered cubic phenylene-bridged PMO, which also has an exceptionally large unit-cell size and pore diameter. The unit-cell parameters of 30 and 25 nm and the mesopore diameters of 14 and 11 nm (nominal BJH-KJS pore diameters of 12-13 and 9 nm) were obtained for ethenylene-bridged and phenylene-bridged PMOs, respectively. Under the considered reaction conditions, the unit-cell parameters and pore diameters were found to be similar when the three different methyl-substituted benzene swelling agents were employed, although the degree of structural ordering appeared to improve for phenylene-bridged PMOs in the sequence of decreased number of methyl groups on the benzene ring.     

Highly ordered three-dimensional large-pore periodic mesoporous organosilica with Im3m symmetry

Highly ordered three-dimensional Im3m-type periodic mesoporous organosilica with a cavity size of 9.8 nm has been synthesized under strongly acidic media in the presence of inorganic salts using triblock copolymer F127 as the template and 1,2-bis(trimethoxysilyl)ethane as the organically bridged silica source.     

PMO[KIT-5]-n: synthesis of highly ordered three-dimensional periodic mesoporous organosilicas with Fm3m symmetry

Divalent surfactant [CH3(CH2)15N(CH3)2(CH2)3N(CH3)3]2+ - 2Br- (C16-3-1) was used as a structure directing agent (SDA) for the synthesis of highly ordered periodic mesoporous organosilicas (PMOs) with cubic Fm3m symmetry from 1,2-bis(triethoxylsilyl)ethane (BTEE) under basic conditions.     

Synthesis of diamine functionalized mesoporous organosilicas with large pores

Hybrid mesoporous silicas functionalized with ethylenediamine groups have been synthesized via sol–gel process under different conditions. The best textural properties, with pore diameters up to 170 Å, have been obtained using carboxylic acids as catalysts in propanol as solvent without the need for any surfactant. The presence of the diamine moiety has been demonstrated by different characterization techniques, and the materials have been used in the adsorption of copper cations. The adsorption capacity of all the solids is high (up to 1.87 mmol/g and up to 2.47 Cu atoms/nm²), with important variations in the properties of the silica surface, besides the role of the immobilized diamine moieties as ligand for copper. In general the surface area seems to be the most important feature controlling the adsorption.     

An ordered cubic Im3m mesoporous Cr-TiO2 visible light photocatalyst

An ordered and well-crystallized cubic Im3m mesoporous Cr-TiO2 photocatalyst with superb performance under visible light has been fabricated.     

Periodic mesoporous organosilicas with co-existence of diurea and sulfanilamide as an effective drug delivery carrier

In this article we report the synthesis of new periodic mesoporous organosilicas (PMOs) with the co-existence of diurea and sulfanilamide-bridged organosilica that are potentially useful for controlled drug release system. The materials possess hexagonal pores with a high degree of uniformity and show long-range order as confirmed by the measurements of small-angle X-ray scattering (SAXS), N₂ adsorption isotherms, and transmission electron microscopy(TEM). FT-IR and solid state ²⁹Si MAS and ¹³C CP MAS NMR spectroscopic analyses proved that the bridging groups in the framework are not cleaved and covalently attached in the walls of the PMOs. It was found that the organic functionality could be introduced in a maximum of 10 mol% with respect to the total silicon content and be thermally stable up to 230 °C. The synthesized materials were shown to be particularly suitable for adsorption and desorption of hydrophilic/hydrophobic drugs from a phosphate buffer solution at pH 7.4.     

Triblock copolymer assisted synthesis of periodic mesoporous organosilicas (PMOs) with large pores

Periodic mesoporous organosilicas (PMOs) with unusually large pores and high BET surface areas have been synthesized using triblock PEO-PPO-PEO copolymer P123 as the structure-directing agent and 1,2-bis(trimethoxysilyl)ethane (BTME) as the organically bridged silica source.     

Direct evidence for interactions between acidic functional groups and silanols in cubic mesoporous organosilicas

A facile one-pot synthesis route for preparation of a well-ordered cubic mesoporous silica SBA-1 functionalized with -COOH functional groups is reported for the first time. The results of 29Si{1H} HETCOR NMR provide direct evidence for the interactions between the carboxylic acid and silanol groups in carboxylic acid functionalized SBA-1. Density functional theory calculations indicate that the T3-Q4-Q3 motif is the favorable framework composition in the material and the carboxylic protons in the T3 species can form hydrogen bonds with the spatially proximate oxygen atom in the Q3 Si-OH species.     

Functionalized periodic mesoporous organosilicas: Hierarchical and chiral materials

The integration of organic and inorganic fragments within the pore walls of the periodic mesoporous organosilicas (PMOs) represents one of the recent breakthroughs in material science. The resulting PMOs are promising materials for applications in such areas as catalysis, adsorption, separation and drug-delivery. We summarize here the recent progress made in the synthesis of PMOs with hierarchical structures and large functional groups, with special emphasis on the chiral mesoporous organosilicas and their ...     

Synthesis of large-pore methylene-bridged periodic mesoporous organosilicas and its implications

In this article, we report the synthesis of methylene-bridged periodic mesoporous organosilicas (PMOs) of the SBA-15 type. The materials were characterized by SAXS, BET, NMR, FESEM, and TEM. It was found that the synthesis of methylene-bridged SBA-15 PMOs requires more rigorous conditions than that of SBA-15 PMOs bearing organic bridges other than methylene. A mild acidic environment, which slows down the hydrolysis and condensation rates of the precursor, with the assistance of a salt, which enhances precursor-template interaction, should be used to synthesize high-quality large-pore methylene-bridged PMOs. We attributed this to the fast hydrolysis and condensation rates and the rigid backbone of precursor 1,2-bis(triethoxysilyl)methylene. By examining and comparing the synthesis of three large-pore PMOs with different bridges, we concluded that the inductive, bridging, and conformation effects of the organic bridging group play an important role in the synthesis of large-pore PMO materials.     

Synthesis and characterization of chiral benzylic ether-bridged periodic mesoporous organosilicas

The first synthesis of a chiral periodic mesoporous organosilica (PMO) carrying benzylic ether bridging groups is reported. By hydrolysis and condensation of the new designed chiral organosilica precursor 1,4-bis(triethoxysilyl)-2-(1-methoxyethyl)benzene (BTEMEB) in the presence of the non-ionic oligomeric surfactant Brij 76 as supramolecular structure-directing agent under acidic conditions, an ordered mesoporous chiral benzylic ether-bridged hybrid material with a high specific surface area was obtained. The chiral PMO precursor was synthesized in a four-step reaction from 1,4-dibromobenzene as the starting compound. The evidence for the presence of the chiral units in the organosilica precursor as well as inside the PMO material is provided by optical activity measurements.     

Three-dimensional mesoporous gallosilicate with Pm3n symmetry and its unusual catalytic performances

Three-dimensional, mesoporous-cage-type, GaSBA-1 materials with different n(Si)/n(Ga) ratios have been successfully prepared for the first time by using a low hydrochloric acid to silicon (n(HCl)/n(Si)) molar ratio in the synthesis gel by templating with cetyltriethylammonium bromide as the structure-directing agent in a highly acidic medium. The obtained materials have been unambiguously characterized in detail by several sophisticated techniques including X-ray diffraction (XRD), N(2) adsorption, high-resolution transmission electron microscopy, high-resolution scanning electron microscopy, energy dispersive spectroscopy, elemental mapping, and (29)Si magic-angle-spinning NMR spectroscopy. XRD and nitrogen adsorption results reveal that the structures of the GaSBA-1 materials resemble that of SBA-1, which possesses a cubic, three-dimensional, cage-type structure with open windows. In addition, the specific surface area and the specific pore volume of the GaSBA-1 materials are much higher than those of the SBA-1 silica, which are very important for the catalytic applications. The amount of Ga cation in the SBA-1 silica framework has been found to play a critical role in controlling the morphology and the pore diameter of the materials. Finally, the catalytic activity in the tert-butylation of phenol with tert-butanol as the alkylating agent has been investigated and the results are compared with those of other mesoporous catalysts such as AlMCM-41, FeMCM-41, FeAl-MCM-41, and FeSBA-1. Moreover, the effect of various reaction parameters such as the reaction temperature, reactant feed ratio, and time-on-stream on the phenol conversion in the tert-butylation of phenol over GaSBA-1 catalysts has been demonstrated. Among the catalysts examined, GaSBA-1(17), in which the number in the parenthesis denotes the n(Si)/n(Ga) ratio, showed remarkable activity with a high conversion of phenol and selectivity to 4-tert-butylphenol; it was found to be superior over other mesoporous catalysts used in the study.     

Transformation of highly ordered large pore silica mesophases (Fm3m, Im3m and p6mm) in a ternary triblock copolymer-butanol-water system

Exceptional control of the phase behavior of highly ordered large pore mesostructured silica (with the choice of Fm3m, Im3m or p6mm symmetry) is achieved using a triblock copolymer (EO(106)PO(70)EO(106)) and butanol at low acid concentrations.     

Structural relation properties of hydrothermally stable functionalized mesoporous organosilicas and catalysis

The surfactant assistant syntheses of sulfonic acid functionalized periodic mesoporous organosilicas with large pores are reported. A one-step condensation of tetramethoxysilane (TMOS) with 1,2-bis(trimethoxysilyl)ethane (BTME) and 3-mercaptopropyltrimethoxysilane (MPTMS) in highly acidic medium was performed in the presence of triblock copolymer Pluronic P123 and inorganic salt as additive. During the condensation process, thiol (-SH) group was in situ oxidized to sulfonic acid (-SO(3)H) by hydrogen peroxide (30 wt % H(2)O(2)). X-ray diffraction studies along with nitrogen and water sorption analyses reveal the formation of stable, highly hydrophobic, and well-ordered hexagonal mesoscopic structures in a wide range of -CH(2)CH(2)- concentrations in the mesoporous framework. The resultant materials were also investigated by (29)Si MAS and (13)C CP MAS NMR, thermogravimetric analyses, UV-Raman spectroscopy, and FT-IR spectroscopy. The role of the bridged organic group on the hydrothermal stability of the mesoporous materials was established, which revealed an enhancement in hydrothermal stability of the materials with incorporation of the bridged organic groups in the network. The catalytic performance of -SO(3)H functionalized mesoporous materials was investigated in the esterification of ethanol with acetic acid, and the results demonstrate that the ethane groups incorporated in the mesoporous framework have a positive influence on the catalytic behavior of the materials.