Adsorption–desorption isotherms of aromatic (mesitylene and toluene) and aliphatic (methylcyclohexane, neopentane and n-pentane) hydrocarbons were measured on ordered mesoporous materials, including MCM-41, MCM-48, SBA-15, SBA-16 and MCF silicas, a periodic mesoporous organosilica and a CMK-3 carbon, in order to evaluate the effect of the adsorbent characteristics on the organic compounds adsorption behaviour. A clear separation between aliphatic and aromatic hydrocarbons is observed at low p/po for the materials having pores accessible by narrow openings. The presence of narrow pore openings causes an increase in the volume adsorbed of mesitylene, toluene, methylcyclohexane and n-pentane prior to capillary condensation that does not occur for neopentane. The increase of the hydrophobicity and change of the surface structure, resulting from the incorporation of chloromethyl groups on the silica walls, causes the p/po at which the aromatic hydrocarbons condense to increase while the introduction of aromatic rings into the pore walls has a less significant effect on the condensation pressures. However, at low p/po, all the hydrocarbons have higher affinity for the periodic mesoporous organosilica surface than for the pure silica or silica with chloromethyl groups surfaces...
One-dimensional periodic mesoporous organosilica (PMO) nanoparticles with tunable aspect ratios are obtained from a chain-type molecular precursor octaethoxy-1,3,5-trisilapentane. The aspect ratio can be tuned from 2:1 to >20:1 simply by variation in the precursor concentration in acidic aqueous solutions containing constant amounts of triblock copolymer Pluronic P123. The mesochannels are highly ordered and are oriented parallel to the longitudinal axis of the PMO particles. No significant Si–C bond cleavage occurs during the synthesis according to29Si MAS NMR. The materials exhibit surface areas between 181 and 936 m2 g−1.
A periodic mesoporous organosilica (PMO) with nanorice morphology was successfully synthesized by a template assisted sol–gel method using a chain-type precursor. The PMO is composed of D and T sites in the ratio 1:2. The obtained mesoporous nanorice has a surface area of 753 m2 g−1, one-dimensional channels, and a narrow pore size distribution centered at 4.3 nm. The nanorice particles have a length of ca. 600 nm and width of ca. 200 nm.
Periodic mesoporous materials of the type (R′O)3Si-R-Si(OR′)3 with benzene as an organic bridge and a crystal-like periodicity within the pore walls were functionalized with SO3H or SO3
− groups and investigated by small-angle neutron scattering (SANS) with in situ nitrogen adsorption at 77 K. If N2 is adsorbed in the pores the SANS measurements show a complete matching of all of the diffraction signals that are caused by the long-range ordering of the mesopores in the benzene-PMO, due to the fact that the benzene-PMO walls possess a neutron scattering length density (SLD) similar to that of nitrogen in the condensed state. However, signals at higher q-values (>1 1/Å) are not affected with respect to their SANS intensity, even after complete pore filling, confirming the assumption of a crystal-like periodicity within the PMO material walls due to π–π interactions between the organic bridges. The SLD of pristine benzene-PMO was altered by functionalizing the surface with different amounts of SO3H-groups, using the grafting method. For a low degree of functionalization (0.81 mmol SO3H·g−1) and/or an inhomogeneous distribution of the SO3H-groups, the SLD changes only negligibly, and thus, complete contrast matching is still found. However...
A photocatalytic system for CO2 reduction exhibiting visible-light harvesting was developed by preparing a hybrid consisting of a supramolecular metal complex as photocatalyst and periodic mesoporous organosilica (PMO) as light harvester. A RuII–ReI binuclear complex (Ru–Re) with methylphosphonic acid anchor groups was adsorbed on acridone or methylacridone embedded in the walls of PMO mesochannels to yield the hybrid structure. The embedded organic groups absorbed visible light, and the excitation energy was funneled to the Ru units. The energy accumulation was followed by electron transfer and catalytic reduction of CO2 to CO on the Re unit. The light harvesting of these hybrids enhanced the photocatalytic CO evolution rate by a factor of up to ten compared with that of Ru–Re adsorbed on mesoporous silica without a light harvester.
Highly ordered rods of large-pore periodic mesoporous organosilica (PMO) were successfully synthesized at low acid concentrations and in the presence of inorganic salt using triblock copolymer P123 as template. The roles of inorganic salt, acidity and temperature in the production of highly ordered mesostructure and the morphology control of PMOs were examined and elucidated. It was found that the addition of inorganic salt can dramatically widen the range of the synthesis parameters to produce highly ordered 2D hexagonal pore structure of p6mm symmetry. However, the uniform rods of PMOs can only be synthesized in a narrow range of acid and salt concentrations, which was sensitive to induction time. The results also showed that the optimized salt concentration (1 M) and low acidity (0.167 M) at 40 oC were beneficial to not only the production of highly ordered mesostucture but also the control of rod-like morphology. Highly ordered rods can also be produced at low temperature (35 oC) with high salt amount (1.5 M) or high temperature (45 oC) with low salt concentration (0.5 M).; Shizhang Qiao, Lianzhou Wang, Qiuhong Hu, Zhonghua Zhu, G. Q. Lu
This contribution describes the preparation of multifunctional yolk–shell nanoparticles (YSNs) consisting of a core of silica spheres and an outer shell based on periodic mesoporous organosilica (PMO) with perpendicularly aligned mesoporous channels. The new yolk–shell hybrid materials were synthesised through a dual mesophase and vesicle soft templating method. The mesostructure of the shell, the dimension of the hollow space (4∼52 nm), and the shell thickness (16∼34 nm) could be adjusted by precise tuning of the synthesis parameters, as evidenced by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen sorption investigations. Various metal nanoparticles (e.g., Au, Pt, and Pd) were encapsulated and confined in the void space between the core and the shell using impregnation and reduction of adequate metal precursors. The selective oxidation of various alcohol substrates was then carried out to illustrate the benefits of such an architecture in catalysis. High conversion (∼100%) and excellent selectivity (∼99%) were obtained over Pd nanoparticles encapsulated in the hybrid PMO yolk–shell structures.; Jian Liu, Heng Quan Yang, Freddy Kleitz, Zhi Gang Chen, Tianyu Yang...
There is currently a great interest in the field of porous organosilica
materials because of the high surface areas (> 1000 m²/g) and narrow pore size
distributions which are beneficial for applications such as chromatography, chiral
catalysis, sensing or selective adsorption. Periodic mesoporous organosilicas
(PMOs) represent an interesting class of hybrid silica materials because of the
wide variety of bridging organic groups which can be incorporated within the
precursors [(OR)3Si-R-Si(OR)3] giving rise to materials with exceptional
We have synthesized and characterized various aromatic PMOs
composed of supporting structural monomers (phenylene- or biphenylenebridged)
and functional stilbene monomers (cis and trans) (1, 2). The effect of
the different synthetic procedures and varying amounts of functional stilbene
monomer on the properties of the materials was examined. The functional transstilbene
component was determined to be well distributed in a phenylene-bridged
PMO using P123 as a pore template from TEM techniques with Os staining. The
trans-stilbene linkers were completely transformed to aryl aldehydes through
ozonolysis with dimethylsulfide workup. Further transformation of the carbonyl
functionality to an aryl imine showed a moderate level of success.
Enantiomeric forms of a novel...
Surfactant-templated, sol-gel based methodologies for the synthesis of tailored, nanostructured, hybrid inorganic–organic materials are incredibly powerful and versatile. Although growth in this field has been explosive in recent decades, a lot of room remains to contribute to the design and synthesis of new materials, as well as the development of advanced applications.
In the work described herein, we firstly explored the synthesis of thick, mesoporous organosilica films and their application as functional coatings for solution-based, fibre-optic heavy metal sensors. Notably, sub-ppm level detection was observed for the detection of Pb(II) in mixed aqueous–organic media in short timeframes, and progress has been made toward synthesizing organotitania films that would allow for heavy metal sensing in purely aqueous solution. Furthermore, the utility of these types of surfactant-templated, organically-functionalized, mesostructured coatings has been preliminarily extended to other types of optical devices for heavy metal sensing.
We have also explored the use of designer amphiphilic, alkyl oligosiloxane precursors for the tightly-controlled formation of thin, self-templated, hybrid nanostructured films. Moreover, films bearing uniaxial 2D hexagonal alignment over macroscopic length scales were obtained using polymer-treated substrates to control the interfacial interactions between the film precursors and the substrate surface. In addition...
Chapter 1 constitutes a review of current methods of aromatic substitution focusing on Directed ortho Metalation (DoM) and Directed remote Metalation (DreM). The field of mesoporous silica is reviewed in Chapter 2, focusing on the preparation, characterization, and application of mesoporous silicates.
Chapter 3 presents an introduction of phosphorus based Directed Metalation Groups (DMGs). The development of the directed ortho metalation (DoM) reaction of the tetraethyl phosphorodiamidate DMG is described. In addition to being one of the most powerful DMGs, migration of the OPO(NEt2)2 group to the ortho and remote positions is demonstrated, constituting new reactions as well as affording new organophosphorus compounds.
Attempts to improve the synthetic utility of the DMG led to the discovery and optimization of a two new nickel-catalyzed cross coupling reactions, which is described in Chapter 4. Both the OPO(NEt2)2 and OCONEt2 DMGs are demonstrated to undergo cross coupling reactions with aryl boronic acids.
By means of DoM and cross coupling tactics, the concise synthesis of a chiral binaphthol bridged silasesquioxane is described. Chapter 5 explores new methods to prepare chiral periodic mesoporous organosilica (PMO) materials using this monomer. PMOs are prepared by the co-condensation of a relatively small amount of chiral binaphthyl dopant which acts to twist the bulk prochiral biphenylene framework.; Thesis (Master...
Lattice Monte Carlo simulations are used to study the phase behavior of
self-assembling ordered mesoporous materials formed by an organic template with
amphiphilic properties and an inorganic precursor in a model solvent. Three
classes of inorganic precursors have been modeled: terminal (R-Si-(OEt)3) and
bridging ((EtO)3-Si-R-Si-(OEt)3)) organosilica precursors (OSPs), along with
pure silica precursors (Si-(OEt)4). Each class has been studied by analyzing
its solubility in the solvent and the solvophobicity of the inorganic group. At
high surfactant concentrations, periodic ordered structures, such as
hexagonally-ordered cylinders or lamellas, can be obtained depending on the
OSPs used. Ordered structures were obtained in a wider range of conditions when
bridging hydrophilic OSPs have been used, because a higher surfactant
concentration was reached in the phase where the material was formed. Terminal
and bridging OSPs produced ordered structures only when the organic group is
solvophilic. In this case, a partial solubility between the precursor and the
solvent or a lower temperature favored the formation of ordered phases. With
particular interest, we have analyzed the range of conditions leaving to the
formation of cylindrical structures...
Effective and controlled drug delivery systems with on-demand release
abilities and biocompatible properties receive enormous attention for
biomedical applications. Here, we describe a novel inorganic-organic hybrid
material with a strikingly high organic content of almost 50 wt%. The colloidal
periodic mesoporous organosilica (PMO) nanoparticles synthesized in this work
consist entirely of curcumin and ethane derivatives serving as constituents
that are crosslinked by siloxane bridges, without any added silica. These
mesoporous curcumin nanoparticles (MCNs) exhibit very high surface areas (over
1000 m2/g), narrow particle size distribution (around 200 nm) and a strikingly
high stability in simulated biological media. Additionally, the MCNs are used
as a cargo delivery system in live-cell experiments. A supported lipid bilayer
(SLB) efficiently seals the pores and releases Rhodamin B as model cargo in
HeLa cells. This novel nanocarrier concept provides a promising platform for
the development of controllable and highly biocompatible theranostic systems.; Comment: 10 pages, 12 figures