Periodic Mesoporous Silica Research Articles

Functionalized Periodic Mesoporous Silica Nanoparticles for Inhibiting the Progression of Atherosclerosis by Targeting Low-Density Lipoprotein Cholesterol.

Atherosclerotic disease is a substantial global burden, and existing treatments, such as statins, are recommended to lower low-density lipoprotein cholesterol (LDL-C) levels and inhibit the progression of atherosclerosis. However, side effects, including gastrointestinal unease, potential harm to the liver, and discomfort in the muscles, might be observed. In this study, we propose a novel method using periodic mesoporous silica nanoparticles (PMS) to create heparin-modified PMS (PMS-HP) with excellent biocompatibility, enabling selective removal of LDL-C from the blood. In vitro, through the introduction of PMS-HP into the plasma of mice, we observed that, compared to PMS alone, PMS-HP could selectively adsorb LDL-C while avoiding interference with valuable components such as plasma proteins and high-density lipoprotein cholesterol (HDL-C). Notably, further investigations revealed that the adsorption of LDL-C by PMS-HP could be well-fitted to quasi-first-order (R2 = 0.993) and quasi-second-order adsorption models (R2 = 0.998). Likewise, in vivo, intravenous injection of PMS-HP enabled targeted LDL-C adsorption (6.5 ± 0.73 vs. 8.6 ± 0.76 mM, p < 0.001) without affecting other plasma constituents, contributing to reducing intravascular plaque formation (3.66% ± 1.06% vs. 1.87% ± 0.79%, p < 0.05) on the aortic wall and inhibiting vascular remodeling (27.2% ± 6.55% vs. 38.3% ± 1.99%, p < 0.05). Compared to existing lipid adsorption techniques, PMS-HP exhibited superior biocompatibility and recyclability, rendering it valuable for both in vivo and in vitro applications.

Photocatalytic H2O2 production with perylene(bis-imide)-doped periodic mesoporous silica using micropollutants as sacrificial donors

A perylene-doped mesoporous silica material is used as a photocatalyst to produce H2O2 from aerated polluted water samples under light soaking.

Samarium- and Ytterbium-Grafted Periodic Mesoporous Silica for Carbon Dioxide Capture and Conversion.

Immobilized coordination compounds of Lewis acidic metals are powerful catalytic components of systems for the cycloaddition of CO2 to epoxides that do not require sophisticated coordination frameworks to harness the metal center and modulate its activity. Surface organometallic chemistry (SOMC) is a valuable methodology to prepare well-defined and site-isolated surface complexes and coordination compounds on metal oxides, with ligand environments easily adjustable to a targeted catalytic reaction. In this work, the SOMC methodology is applied to prepare SmII, YbII, and SmIII alkoxide surface complexes on periodic mesoporous (organo)silica of distinct pore symmetry/size for application in the CO2 cycloaddition reaction. The surface complexes are readily accessible by the grafting of the bis(trimethylsilyl)amide precursors LnII[N(SiMe3)2]2(THF)2 (Ln = Sm, Yb) and SmIII[N(SiMe3)2]3, followed by ligand exchange with alcohols (ethanol and neopentanol). The use of periodic mesoporous supports led to hybrid materials with relatively high surface areas and pore sizes, affording good performance in CO2 capture and in the cycloaddition of CO2 to epoxides under mild conditions (60-80 °C, 1-10 bar). In terms of catalytic performance, recyclability, and low amount of added nucleophile TBAX (X = Br, I), the most active materials prepared in this work compare well to a variety of previously reported SOMC-derived surface complexes and to other heterogeneous Lewis acids displaying more elaborate ligand environments.

Hierarchically structured and highly active palladium-loaded Al-MIL-53-linked hybrid periodic mesoporous silica catalysts for Suzuki-Miyaura cross-coupling reaction

The rational design and precise preparation of hierarchically structured catalysts (HSCs) with an enhanced catalytic activity and reusability are still enormous challenges in material science and catalysis. Herein, a HSC Pd/Al-MIL-53@HOOC-SBA-15 was successfully prepared by the oriented growth of metal-organic framework Al-MIL-53 into/onto HOOC-SBA-15 via a hydrothermal technique and in-situ deposition of Pd nanoparticles reduced by NaBH4. Such a heterogeneous catalyst was applied to Suzuki-Miyaura cross-coupling reaction (CCR) of various aryl halides and phenylboronic acid. The results showed a highly catalytic performance over 99% conversion/yield, thanks to the crucial role of functional group, the synergistic effect of microporous-mesoporous structure, mesoporous confinement effect and microporous confinement effect. As a comparison, Pd/HOOC-SBA-15 and Pd/SBA-15 were also fabricated for C-C CCR, showing characteristic functional group-protected effect ensuring the stability and redeposition of Pd during catalysis. Based on experimental results, an order on catalytic activity and recyclability is Pd/Al-MIL-53@HOOC-SBA-15 > Pd/HOOC-SBA-15 > Pd/SBA-15 > Pd/Al2O3-C@SBA-15, revealing an excellent catalytic activity and high reusability of Pd/Al-MIL-53@HOOC-SBA-15. Combining with structure and composition of all catalysts, the leaching-redeposition mechanism can well explain highly catalytic performance and deactivation behavior in C-C CCR. This study provides an efficient strategy to prepare large-scale multi-composite HSCs for multi-functionalized catalytic applications.

Benzene bridged hybrid organosilicate films with improved stiffness and small pore size

Critical properties of porous periodic mesoporous silica (PMO) low-k dielectric with a different ratio of benzene bridges and methyl terminal groups are studied by using various advanced instrumentations such as Ellipsometric Porosimetry (EP), Surface Acoustic Wave Spectroscopy (SAWS), Specular X-ray reflectivity and others. It is shown that the pore size and surface roughness of the films decrease with an increase in the concentration of the benzene bridge, although at a concentration of benzene bridges >25 mol %, the pore size sharply decreases and changes little with a further increase in the concentration of bridges. The concentration of the benzene bridge also increases dielectric constant and improves the mechanical properties. The increase in Young's modulus with the benzene bridge concentration has percolation type behavior and sharply increases at a concentration of the benzene bridge close to 50 mol %. It has also been found that introducing 30 wt % porosity into benzene-bridged films without methyl terminal groups increases the Young's modulus. It is assumed that this unusual behavior is associated with the formation of crystal-like structure on the film framework. The increase of dielectric constant is associated with the higher polarizability of the benzene bridges in comparison with methyl terminal groups, as well as with their higher hydrophilicity and presence of adsorbed water.

Janus phenol–formaldehyde resin and periodic mesoporous organic silica nanoadsorbent for the removal of heavy metal ions and organic dyes from polluted water

Janus phenol–formaldehyde resin and periodic mesoporous organic silica nanoadsorbent for the removal of heavy metal ions and organic dyes from polluted water

Structure of Water at Hydrophilic and Hydrophobic Interfaces: Raman Spectroscopy of Water Confined in Periodic Mesoporous (Organo)Silicas

The temperature dependence of the structure of water confined in hydrophilic mesostructured porous silica (MCM-41) and hydrophobic benzene-bridged periodic mesoporous organosilicas (PMOs) is studied by Raman vibrational spectroscopy. For capillary filled pores (75% relative humidity, RH), the OH stretching region is dominated by the contribution from liquid water situated in the core part of the pore. It adopts a bulklike structure that is modestly disrupted by confinement and surface hydrophobicity. For partially filled pores (33% RH), the structure of the nonfreezable adsorbed film radically differs from that found in capillary filled pores. A first remarkable feature is the absence of the Raman spectral fingerprint of low-density amorphous ice, even at a low temperature (−120 °C). Second, additional bands reveal water hydroxyl groups pointing toward the different water/solid and water/vapor interfaces. For MCM-41, they correspond to water molecules acting as weak H-bond donors with silica and dangling hydroxyl groups oriented toward the empty center of the pore. For benzene-bridged PMO, we found an additional type of dangling hydroxyl groups, which we attribute to water at the hydrophobic solid interface.

Hierarchically Structured and Highly Active Palladium-Loaded Al-Mil-53-Linked Hybrid Periodic Mesoporous Silica Catalysts for Suzuki-Miyaura Cross-Coupling Reaction

Hierarchically Structured and Highly Active Palladium-Loaded Al-Mil-53-Linked Hybrid Periodic Mesoporous Silica Catalysts for Suzuki-Miyaura Cross-Coupling Reaction

Omeg@Silica: Entrapment and Stabilization of Sustainably Sourced Fish Oil.

Fish oil rich in long‐chain polyunsaturated fatty acids, vitamin D3 and carotenoid pigments have been sustainably extracted from anchovy fillet leftovers using biobased limonene. The oil is conveniently stabilized by adsorption on periodic mesoporous silicas. The simplicity of the process, the high load of fish oil, and the biocompatible nature of mesoporous silica support numerous forthcoming applications of this new class of “Omeg@Silica” materials.

Recent advances in preparation and application of sulfonic acid derivatives bonded to inorganic supports

Heterogeneous acid-catalyzed organic transformations can be classified as one of the most important aspects of catalysis mostly due to its ability in recycling. This review deals with general discussion on the preparation of sulfonic acid derivatives immobilized on inorganic supports such as silica, periodic mesoporous silica, magnetic nanoparticles, metal organic frameworks, KIT-6, ZSM-5, MCM-41, bentonite, boehmite, clay, and other inorganic supports via organic linker. In addition, application of these inorganic supports in the acceleration of organic transformation is discussed one by one. This review aims to provide an overview of the recent developments in the field of heterogenizing homogeneous catalysts with a particular emphasis on the reaction scope and advantages of heterogeneous solid acid catalysts.

Thiol-Functionalized Ethylene Periodic Mesoporous Organosilica as an Efficient Scavenger for Palladium: Confirming the Homogeneous Character of the Suzuki Reaction

This work describes the synthesis of thiol-functionalized periodic mesoporous organosilicas (PMOs) prepared using the precursor 1-thiol-1,2-bis(triethoxysilyl)ethane, alone or mixed with 1,2-bis(triethoxysilyl)ethane. The thiol groups incorporated into the structure were found to be efficient for palladium binding. This has allowed these materials to be used as catalysts in the Suzuki cross-coupling reaction of bromobenzene and phenylboronic acid. Their performance has been compared to palladium-supported periodic mesoporous (organo)silicas and important differences have been observed between them. The use of different heterogeneity tests, such as hot filtration test and poisoning experiments, has provided a deep insight into the reaction mechanism and has confirmed that the reaction occurs in the homogeneous phase following a “release and catch” mechanism. Furthermore, the thiol-functionalized periodic mesoporous organosilica, synthesized using only 1-thiol-1,2-bis(triethoxysilyl)ethane as a precursor, has proven to be an efficient palladium scavenger.

Pd-chelated 1,3,5-triazine organosilica as an active catalyst for Suzuki and Heck reactions

Design of novel functional periodic mesoporous organosilica with molecular level control finds applications in several fields of energy and environmental research including adsorption, catalysis, nanotechnology, and energy harvesting. Herein we present a melamine (1,3,5-triazine) functionalized periodic mesoporous silica (MPMO) by self-assembly of N2,N4,N6-tris(3-(triethoxysilyl)propyl)-1,3,5-triazine-2,4,6-triamine (TTET) with tetraethylorthosilicate (TEOS) via cocondensation strategy. The TTET silsesquioxane precursor was synthesized by the condensation reaction between cyanuric chloride and 3-aminopropyl triethoxysilane. The resultant MPMO material serves as an effective solid chelating agent through amine and triazine functionalities for Pd(II) to provide Pd-MPMO. The Pd-MPMO material was thoroughly characterized by a small-angle XRD, HRTEM, N2 sorption, 13C CP-MAS NMR, 29Si CP-MAS NMR, and ICP analyses. The Pd-MPMO serves as an active catalyst for CC bond formation reactions by Suzuki- and Heck cross-coupling methodologies under ligand- and cocatalyst-free conditions. Notably, the present catalytic protocol demonstrates a wide spectrum of substrate scope towards Suzuki coupling between aryl halides (I−, Br−, Cl−) and aryl boronic acids with high turn-over-number (TON) in aqueous phase under air ambience. Whereas for Heck-coupling reaction, the phenyl iodides furnished high TON than the other aryl halides. Investigation of Pd-leaching by a hot filtration test as well as reusability experiments confirms the true heterogeneous nature of present Pd-MPMO and its robustness in terms of substrate scope, catalyst stability, and durability.

Titanium(IV) Catecholate‐Grafted Mesoporous Silica KIT‐6: Probing Sequential and Convergent Immobilization Approaches

Molecular TiIV catecholates were obtained as dimeric complexes from protonolysis reactions of Ti(NMe2)4 with pyrocatechol (H2CAT), 4‐tert‐butylcatechol (H2CATtBu‐4), 3,5‐di‐tert‐butylcatechol (H2CATtBu2–3,5), 2,3‐dihydroxynaphthalene (H2DHN) and 3,6‐di‐tert‐butylcatechol (H2CATtBu2–3,6). The heteroleptic monocatecholate amide complexes were characterized by X‐ray structure analysis but only [Ti(CAT)(NMe2)2]2 and [Ti(DHN)(NMe2)2]2 were obtained as pure compounds. The solid‐state structures revealed TiIV centers bridged by two catecholato ligands adopting a [κ2(O,µ‐O′)] coordination mode except for complex [Ti(CATtBu2–3,6)(NMe2)2] featuring one bridging catecholato and one bridging amido ligand. Heteroleptic complex [Ti(DHN)(NMe2)2]2 was grafted onto large‐pore periodic mesoporous silica KIT‐6 (convergent approach) and the resulting TiIV surface species compared with the established sequential approach, i.e., grafting of Ti(NMe2)4 onto the KIT‐6 material and subsequent ligand exchange with H2DHN. Dimeric complex [Ti(DHN)(NMe2)2]2 proved to be sufficiently reactive for a direct grafting yielding the same dominant surface species as obtained according to the sequential approach, as revealed by nitrogen physisorption, elemental analysis, and DRIFT/13C CP MAS spectroscopy.

Immobilization of titanium dioxide in mesoporous silicas: Structural design and characterization

The hybridization of titanium dioxide with periodic mesoporous silicas has been investigated so far to construct heterogeneous catalysts. In the present review article, the studies on the complexation of titanium dioxide with periodic mesoporous silicas are summarized from the viewpoints of the preparation and the structural characteristics (the size and the content of titanium dioxide, their location in periodic mesoporous silicas, the porosity of the hybrids) in order to highlight the present status of the titanium dioxide-mesoporous silica hybrids. The structure has been varied depending on the syntheses, which will be correlated to the materials’ performances.

A highly organic functionalized three-connected periodic mesoporous silica by Co-condensation with hydridosilica

Organic functionalization of periodic mesoporous silicas (PMSs) is an imperative and effective measure to advance their preeminent properties and widespread application due to their structural superiority. In this study, we reported a novel synthesis of organic functionalized PMSs by co-condensing (R’O)3Si-H and (R’O)3Si-R type terminal trialkoxyorganosilanes based on periodic mesoporous hydridosilica, which is stable but pore walls are comprised of a three-connected three-dimensional network. The synthesis extended the “co-condensation” strategy and broke the incorporation limitation of organic groups by HSiO3 units in the framework to form hydrogen bonds, which provided a more effective way to obtain PMSs with high degree of organic functionalization.

Silica‐Grafted Neodymium Catalysts for the Production of Ultrahigh‐Molecular‐Weight cis‐1,4‐Polyisoprene

AbstractSupported neodymium‐based Ziegler‐type catalysts are obtained by grafting homoleptic methylaluminate Nd(AlMe4)3 onto high‐surface silica materials including periodic mesoporous silicas MCM‐41, SBA‐15, and KIT‐6. Low [Et2AlCl]‐cocatalyst contents allow for the fabrication of polyisoprenes with ultrahigh molecular weight (UHMWPI). The synthetic rubbers display molecular weights as high as 3×106 g mol−1, polydispersity indices as low as 1.2, and microstructures with 99 % cis‐stereospecificity. Combined analysis of the organolanthanide/silica hybrid materials by nitrogen physisorption, FTIR and magic angle spinning NMR spectroscopies, and elemental (metal) analysis assist in elucidating the intrapore surface organometallic chemistry and suggest the formation of unprecedented organolanthanide species.

Modelling the self-assembly of silica-based mesoporous materials

Periodic Mesoporous Silicas (PMS) are one of the prime examples of templated porous materials – there is a clear connection between the porous network structure and the supramolecular assemblies formed by surfactant templates. This opens the door for a high degree of control over the material properties by tuning the synthesis conditions, and has led to their application in a wide range of fields, from gas separation and catalysis to drug delivery. However, such control has not yet come to full fruition, largely because a detailed understanding of the synthesis mechanism of these materials remains elusive. In this context, molecular modelling studies of the self-assembly of silica/surfactant mesophases have arisen at the turn of the century. In this paper, we present a comprehensive review of simulation studies devoted to the synthesis of PMS materials and their hybrid organic–inorganic counterparts. As those studies span a wide range of time and length scales, a holistic view of the field affords some interesting new insight into the synthesis mechanisms. We expect simulation studies of this complex but fascinating topic to increase significantly as computer architectures become increasingly powerful, and we present our view to the future of this field of research.

Graphene Nanocomposites: Sandwich‐Type Nanocomposite of Reduced Graphene Oxide and Periodic Mesoporous Silica with Vertically Aligned Mesochannels of Tunable Pore Depth and Size (Adv. Funct. Mater. 47/2017)

Graphene Nanocomposites: Sandwich‐Type Nanocomposite of Reduced Graphene Oxide and Periodic Mesoporous Silica with Vertically Aligned Mesochannels of Tunable Pore Depth and Size (Adv. Funct. Mater. 47/2017)

Sandwich‐Type Nanocomposite of Reduced Graphene Oxide and Periodic Mesoporous Silica with Vertically Aligned Mesochannels of Tunable Pore Depth and Size

AbstractSandwich‐type nanocomposites of graphene oxide (GO) and periodic mesoporous silica (PMS) with vertically aligned mesochannels of different pore depth and size are synthesized and characterized, and their formation modes are examined. The existence of mesoscale ordered structure in the mixture of GO and surfactant solutions is confirmed for the first time by in situ small angle X‐ray scattering measurement using synchrotron radiation. The mesochannel depth and pore wall ripening of PMS in the nanocomposites are controlled by the reaction time of the hydrolysis of tetraethyl orthosilicate. The pore size of PMS in the nanocomposites can be varied in the range of 1–5 nm by varying the chain length of alkyltrimethylammonium (CnTA+) template and high specific surface area (≈1000 m2 g−1) is achieved for all samples. Nanocomposites with vertically aligned PMS mesochannels can be synthesized by applying CnTA+ templates of n ≥ 12, whereas with CnTA+ of n ≤ 10, either PMS nanoparticle deposited GO structure or the structure with incomplete coverage of GO surface with imperfect PMS is found. The aggregation behaviors of surfactant molecules on GO depend on surfactant concentration relative to critical micelle concentration and reaction temperature, and result in the peculiar nanocomposites of different structural styles.

Cytosine-functionalized SBA-15 mesoporous nanomaterials: Synthesis, characterization and catalytic applications

Periodic mesoporous silica functionalized by cytosine (Cyt@SBA-15) was prepared from Cytosine-chloropropyltriethoxysilane and tetraethoxysilane as precursors by a sol-gel method. The surface area and pore volume of Cyt@SBA-15 were 490 m2/g and 0.77 cm3/g. Due to their porous structure and active functional groups of cytosine on the pore of the hybrid material (Cyt@SBA-15), its catalytic performance was studied in the Knoevenagel condensation of aldehydes and ketones with malononitrile to α, β-unsaturated dicyanides in the presence of ethanol as solvent. The catalyst exhibited an excellent activity and selectivity toward the final condensation product under mild reaction conditions. Furthermore, the catalyst could be recovered and reused several times without any significant loss in either activity or product selectivity.