Well-ordered Mesoporous Silica Research Articles

NondemandingIn SituEncapsulation Route to Ultrastable Perovskite Nanocrystals for White Light-Emitting Diodes

Although tremendous advancement regarding the highly stable metal halide perovskite nanocrystals (PNCs) has been achieved, previous studies were primarily focused on green light-emitting PNCs (i.e., bromine-based PNCs). The stability of chlorine-based PNCs with a violet or blue emission property was still lagging behind that of their bromine-based counterparts. Herein, a nondemanding and versatile strategy for in situ encapsulating all-inorganic chlorine-based PNCs with multifold exceptionally high stabilities was presented. Well-ordered mesoporous silica enabled the confined growth of PNCs in its pores followed by the porosity sealing by tetramethyl orthosilicate hydrolysis, thereby rendering full encapsulation of chlorine-based PNCs in dense silica that originated from high-temperature calcination. This judiciously designed structure imparted enclosed violet/blue emitting PNCs impart with outstanding long-term stability (>1.5 year) with high photoluminescence quantum yield (i.e., 30.4%) in pure water as the result of complete isolation of PNCs from detrimental stimuli, eventually leading to the application in the white light-emitting diode device.

Formation of a super-dense hydrogen monolayer on mesoporous silica

Adsorption on various adsorbents of hydrogen and helium at temperatures close to their boiling points shows, in some cases, unusually high monolayer capacities. The microscopic nature of these adsorbate phases at low temperatures has, however, remained challenging to characterize. Here, using high-resolution cryo-adsorption studies together with characterization by inelastic neutron scattering vibration spectroscopy, we show that, near its boiling point (~20 K), H2 adsorbed on a well-ordered mesoporous silica forms a two-dimensional monolayer with a density more than twice that of bulk-solid H2, rather than a bilayer. Theoretical studies, based on thorough first-principles calculations, rationalize the formation of such a super-dense phase. The strong compression of the hydrogen surface layer is due to the excess of surface–hydrogen attraction over intermolecular hydrogen repulsion. Use of this super-dense hydrogen monolayer on an adsorbent might be a feasible option for the storage of hydrogen near its boiling point, compared with adsorption at 77 K.

Amphiphilic-triblock-copolymer-derived protective layer for stable-cycling lithium metal anodes

Lithium metal batteries have shown great potential for the development of efficient energy storage devices. However, the uncontrollable growth of lithium metal dendrites results in poor cycling efficiency and severe safety concerns. In this study, amphiphilic triblock copolymers (P123) were used for the direct polymerization of silica precursors, resulting in a well-ordered mesoporous silica structure SBA-15 with a large surface area and excellent absorbent properties for the protective layer. The protective layer consisting of SBA-15 stores Li ions in a large number of pores as an electrolyte reservoir, which exhibits sufficient ionic conductivity. Furthermore, it ensures a spatially uniform Li-ion flux on the anode surface and plays an important role in the physical blocking of dendrite growth. As proof of concept, the SAB-15 protective layer anode demonstrates a high average Coulomb efficiency, rate capability, and cycle stability at 1 mA h cm−2 over 1200 cycles. Moreover, SAB-15 can be cycled stably for more than 750 cycles in symmetric cells. The results provide insights for implementing stable lithium metal anodes in next-generation batteries.

Ordered Mesoporous Silica Pyrolyzed from Single-Source Self-Assembled Organic-Inorganic Giant Surfactants.

We report the preparation of hexagonal mesoporous silica from single-source giant surfactants constructed via dihydroxyl-functionlized polyhedral oligomeric silsesquioxane (DPOSS) heads and a polystyrene (PS) tail. After thermal annealing, the obtained well-ordered hexagonal hybrid was pyrolyzed to afford well-ordered mesoporous silica. A high porosity (e.g., 581 m2/g) and a uniform and narrow pore size distribution (e.g., 3.3 nm) were achieved. Mesoporous silica in diverse shapes and morphologies were achieved by processing the precursor. When the PS tail length was increased, the pore size expanded accordingly. Moreover, such pyrolyzed, ordered mesoporous silica can help to increase both efficiency and stability of nanocatalysts.

Rapid synthesis of solid amine composites based on short mesochannel SBA-15 for CO2 capture

Hydrothermal is common process for synthesizing well-ordered mesoporous silica, however, it costs time and energy simultaneously. To improve the efficiency of synthesis process, it is necessary to propose a facile synthesis strategy with less time and energy requirement. In this study, an innovative non-hydrothermal method using NH3∙H2O as catalyst after ripening step is developed to prepare SBA-15 with short mesochannels (SSBA-15) for the first time. The synthesis period of SSBA-15 framework was extremely shortened within 40 min under the optimized conditions (30 min of ripening step and 25% of NH3∙H2O concentration), while obtained material exhibits well-ordered hexagonal pore structure and fine particle morphology of SSBA-15 (pore length of 250 ± 50 nm and mesopore size of 9.8 nm). This method can also be employed to synthesize conventional SBA-15 successfully. Moreover, the application of SSBA-15 as support of solid amine adsorbents on CO2 adsorption and well-fitting of experimental CO2 adsorption data with Avrami and intraparticle diffusion models reveal that the adsorbents combine the advantages of micro-mesoporous structure, short mesochannel and amine reagents (high affinity of CO2), resulting in enhanced molecular diffusion, fast adsorption kinetics and high CO2 adsorption capacity. Notably, the solid amine adsorbents exhibited excellent regeneration ability during ten adsorption-desorption cycles. This work opens up new opportunities in efficient preparation of materials that require hydrothermal process.

Supersaturable organic-inorganic hybrid matrix based on well-ordered mesoporous silica to improve the bioavailability of water insoluble drugs

Mesoporous silica with uniform 2-D hexagonal pores has been newly employed as facile reservoir to impove the dissolution rate of water insoluble drugs. However, rapid drug release from mesoporous silica is usually accompanied by the generation of supersaturated solution, which leads to the drug precipitation and compromised absorption. To address this issue, a supersaturated ternary hybrid system was constructed in this study by utilizing inorganic mesoporous silica and organic precipitation inhibitor. Vinylprrolidone-vinylacetate copolymer (PVP VA64) with similar solubility parameter to model drug fenofibrate (FNB) was expected to well inhibit the precipitation. Mesoporous silica Santa Barbara amorphous-15 (SBA-15) was synthesized in acidic media and hybrid matrix was produced by hot melt extrusion technique. The results of in vitro supersaturation dissolution test obviously revealed that the presence of PVP VA64 could effectively sustain a higher apparent concentration. PVP VA64 was suggested to simultaneously reduce the rate of nucleation and crystal growth and subsequently maintain a metastable supersaturated state. The absorption of FNB delivered by the organic-inorganic hybrid matrix was remarkably enhanced in beagle dogs, and its AUC value was 1.92-fold higher than that of FNB loaded mesoporous silica without PVP VA 64. In conclusion, the supersaturated organic-inorganic hybrid matrix can serve as a modular strategy to enhance the oral availability of water insoluble drugs.

VOHPO4.5H2O/KIT-6 composites: Preparation and their application in extractive and catalytic oxidation desulfurization of benzothiophene and dibenzothiphene

Abstract The catalytic activity of vanadyl hydrogen phosphate hemihydrate (VPO) for deep desulfurization of a model fuel was explored. For this purpose, a series of composites containing different amounts of vanadyl hydrogen phosphate and well-ordered mesoporous silica (KIT-6) were prepared and their structural and textural characterizations were carried out using SEM, TEM, ICP-AES, FT-IR, N2 adsorption-desorption, XPS and XRD techniques. It was found that the catalyst with maximum vanadium phosphate loading (VPKA) shows the highest catalytic activity in dibenzothiophene (DBT) removal through oxidative desulfurization (ODS) process. Different reaction conditions such as temperature, the mole ratio of H2O2:DBT, and catalyst loading were investigated in the catalytic system.

Well-ordered mesoporous silica and bioactive glasses: promise for improved hemostasis.

Immediate control of uncontrolled bleeding and infection are essential for saving lives in both combat and civilian arenas. Inorganic well-ordered mesoporous silica and bioactive glasses have recently shown great promise for accelerating hemostasis and infection control. However, to date, there has been no comprehensive report assessing their specific mechanism of action in accelerating the hemostasis process and exerting an antibacterial effect. After providing a brief overview of the hemostasis process, this review presents a critical overview of the recently developed inorganic mesoporous silica and bioactive glass-based materials proposed for hemostatic clinical applications and specifically investigates their unique characteristics that render them applicable for hemostatic applications and preventing infections. This article also identifies promising new research directions that should be undertaken to ascertain the effectiveness of these materials for hemostatic applications.

Synthesis of ordered mesoporous carbonaceous materials and their highly efficient capture of uranium from solutions

An extremely effortless method was applied for successful synthesis of mesoporous carbonaceous materials (MCMs) using well-ordered mesoporous silica as template. Various characterizations (scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman, X-ray photoelectron spectroscopy (XPS), Brunner-Emmet-Teller (BET) and Zeta potential) confirmed that MCMs had large surface area, uniform pore size distribution, and abundant oxygen-containing functional groups. The batch techniques were employed to study U(VI) adsorption on MCMs under a wide range of experiment conditions. The adsorption kinetics of U(VI) onto MCMs were well-fitted by pseudo-second-order kinetic model, indicating a chemisorption process. The excellent adsorption capacity of MCMs calculated from the Langmuir model was 293.95 mg g−1 at pH 4.0. The FT-IR and XPS analyses further evidenced that the binding of U(VI) onto MCMs was ascribed to the plentiful adsorption sites (–OH and –COOH groups) in the internal mesoporous structure, which could efficiently trap guest U(VI) ions. The results presented herein revealed that MCMs were ideal adsorbents in the efficient elimination of uranium or other lanthanides/actinides from aqueous solutions, which would play an important role in environmental pollution management application.

Sustained-release study on Exenatide loaded into mesoporous silica nanoparticles: in vitro characterization and in vivo evaluation

BackgroundExenatide (EXT), the first glucagon-like peptide-1 receptor agonist, has been approved as an adjunctive therapy for patients with type 2 diabetes. Due to EXT’s short half-life, EXT must be administrated by continuous subcutaneous (s.c.) injection twice daily. In previous studies, many studies on EXT loaded into polymer materials carriers for sustained release had been reported. However, these carriers have some defects, such as hydrophobicity, low surface energy, low mechanical strength, and poor chemical stability. Therefore, this study aims to develop a novel drug delivery system, which is EXT loaded into well-ordered hexagonal mesoporous silica structures (EXT-SBA-15), to control the sustainability of EXT.MethodsSBA-15 was prepared by hydrothermal method with uniform size. Morphology of SBA-15 was employed by transmission electron microscopy. The pore size of SBA-15 was characterized by N2 adsorption–desorption isotherms. The in vitro drug release behavior and pharmacokinetics of EXT-SBA-15 were investigated. Furthermore, the blood glucose levels of diabetic mice were monitored after subcutaneous injection of EXT-Sol and EXT-SBA-15 to evaluate further the stable hypoglycemic effect of EXT-SBA-15.ResultsEXT-SBA-15 showed a higher drug loading efficiency (15.2 ± 2.0%) and sustained-release features in vitro. In addition, pharmacokinetic studies revealed that the EXT-SBA-15 treatment group extended the half-life t1/2(β) to 14.53 ± 0.70 h compared with that of the EXT solution (EXT-Sol) treatment group (0.60 ± 0.08 h) in vivo. Results of the pharmacodynamics study show that the EXT-SBA-15 treatment group had inhibited blood glucose levels below 20 mmol/L for 25 days, and the lowest blood glucose level was 13 mmol/L on the 10th day.ConclusionsThis study demonstrates that the EXT-SBA-15 delivery system can control the sustainability of EXT and contribute to improve EXT clinical use.Graphical abstract

Co and Ni catalysts loaded on typical well-ordered micro- and mesoporous supports for acetic acid reduction

The consecutive reduction of acetic acid was studied over two monometallic (nickel and cobalt) catalysts compared to indium doped bimetallic composites. A fixed bed flow-through reactor was applied with hydrogen stream at 21 bar at 240–380 °C. Efficient catalysts containing finely dispersed metal particles were obtained by in situ pretreatment with H2 at 450 °C. It was shown that cobalt, opposite to nickel, can direct the consecutive catalytic reduction to ethanol formation inhibiting hydrodecarbonylation. Resulting in higher activity, the well-ordered mesoporous silica, SBA-15 seems to be more efficient support than a crystalline microporous aluminosilicate, FAU.

Facilitated Diffusion of Methane in Pores with a Higher Aromaticity

Shale gas, which was recently discovered with a large reserve, has invoked wide interest as an alternative energy resource of natural gas. However, little is known about the molecular properties of shale gas (mainly methane) confined in the nanopores of shale, such as their diffusivity, which is essential for its exploitation and utilization. We study here the diffusivity of methane using 1H pulsed field gradient (PFG) NMR and theoretical modeling. Following analysis of the physicochemical properties of shale, a well-ordered mesoporous silica material (SBA-15) modified with organic functional groups is employed to model the mesopores observed in the shale and to study the fundamental behavior of shale gas. The results demonstrate that methane moves faster in the pores modified with the aromatic phenyl groups than those with nonaromatic cyclohexyl groups, suggesting a higher diffusivity of methane with increasing maturity of shale.

Effect of withdrawal speed on film thickness and hexagonal pore-array dimensions of SBA-15 mesoporous silica thin film.

Two-dimensional hexagonal mesoporous silica thin films of SBA-15 were synthesized on Si substrates via dip-coating using an evaporation-induced self-assembly process. The effect of the withdrawal speed on the thicknesses, one-dimensional pore alignments, and two-dimensional hexagonal pore arrays of the films was elucidated. Detailed analyses of FE-SEM and TEM images and XRD and XRR patterns of the synthesized thin films clarified that the pore sizes, interplanar spacings, and film thicknesses depend on the withdrawal speed. Furthermore, the same films were synthesized on Si substrates with microtrenches. The local flow of coating solutions around microtrenches affects the pore direction as well as the film thickness. In order to form well-ordered mesoporous silica thin films with large surface areas, it is important to control the synthetic conditions such as the local flow of the coating solutions as well as the physicochemical properties of the silica precursor solutions or template molecules.

Structure and Morphology of SBA-15 Thin Films on Different Substrates

Well-ordered hexagonal mesoporous silica thin films, SBA-15 type, were synthesized with Pluronic P123 and tetraethyl orthosilicate in a diluted ethanol-hydrochloric acid solution. Films deposited on a broad range of distinct substrates by a sol-gel dip-coating method resulted in transparent and adherent samples. Transmission electron microscopy images revealed, predominantly, well-ordered regions of hexagonal arrays of cylindrical mesopores parallel to the substrate. X-ray reflectivity showed similar lattice parameters for all analyzed films, with a (h00) preferred orientation. The films presented diverse shrinkage susceptibilities, which were tested after different polymer removal procedures. Calcined films have 342 m2/g surface area, 0.130 cm3/g pore volume, and 6.8 nm pore diameter. The wetting characteristics of the substrates in water and alcoholic solutions were evaluated. The films showed different structural properties, mostly related to the mean surface roughness of the substrates and to the drying process.

Preparation of Silicon-Carbon Composite via Magnesiothermic Reduction Method and Its Application to the Anode Material for Lithium Ion Battery

Silicon-carbon composite was prepared by the magnesiothermic reduction of mesoporous silica and subsequent impregnation with a carbon precursor. This was applied for use as an anode material for high-performance lithium-ion batteries. Well-ordered mesoporous silica(SBA-15) was employed as a starting material for the mesoporous silicon, and sucrose was used as a carbon source. It was found that complete removal of by-products (Mg2Si and Mg2SiO4) formed by side reactions of silica and magnesium during the magnesiothermic reduction, was a crucial factor for successful formation of mesoporous silicon. Successful formation of the silicon-carbon composite was well confirmed by appropriate characterization tools (e.g., N2 adsorption-desorption, small-angle X-ray scattering, X-ray diffraction, and thermogravimetric analyses). A lithium-ion battery was fabricated using the prepared silicon-carbon composite as the anode, and lithium foil as the counter-electrode. Electrochemical analysis revealed that the silicon-carbon composite showed better cycling stability than graphite, when used as the anode in the lithium-ion battery. This improvement could be due to the fact that carbon efficiently suppressed the change in volume of the silicon material caused by the charge-discharge cycle. This indicates that silicon-carbon composite, prepared via the magnesiothermic reduction and impregnation methods, could be an efficient anode material for lithium ion batteries.

Magnetic solid-phase extraction based on mesoporous silica-coated magnetic nanoparticles for analysis of oral antidiabetic drugs in human plasma

In the present work, magnetic nanoparticles embedded into mesoporous silica were prepared in two steps: first, magnetite was synthesized by oxidation–precipitation method, and next, the magnetic nanoparticles were coated with mesoporous silica by using nonionic block copolymer surfactants as structure-directing agents. The mesoporous SiO2-coated Fe3O4 samples were functionalized using octadecyltrimethoxysilane as silanizing agent. The pure and functionalized silica nanoparticles were physicochemically and morphologically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The resultant magnetic silica nanoparticles were applied as sorbents for magnetic solid-phase extraction (MSPE) of oral antidiabetic drugs in human plasma. Our results revealed that the magnetite nanoparticles were completely coated by well-ordered mesoporous silica with free pores and stable pore walls, and that the structural and magnetic properties of the Fe3O4 nanoparticles were preserved in the applied synthesis route. Indeed, the sorbent material was capable of extracting the antidiabetic drugs from human plasma, being useful for the sample preparation in biological matrices.

Porous Silicon/Carbon Nanocomposites As Anode Materials for Lithium-Ion Batteries

A series of porous silicon/carbon composites were successfully synthesized by employing mesoporous silica (SBA-15 and MCM-48) and diatomite as silicon precursor, followed by low temperature magnesiothermic reduction, impregnation and carbonization of phenolic resin. The structure and morphology of the porous composites were characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscope and nitrogen absorption and desorption. Electrochemical performance of the porous composite electrodes were investigated. The obtained Si/C composites present an interweaved porous structure composed of Si, inactive SiOx and conductive carbon. The ordered pore structure is retained after the magnesiothermic reduction of well-ordered mesoporous silica. The resulting porous Si/C composites exhibit high reversible capacity and excellent cycling performance. These improvements could be attributed to the introduction of carbon in the porous Si/C composites, which effectively improve the electrical conductivity. Moreover, the porous structure can accommodate the volume expansion and improve cycling stability of the electrode materials during lithium ion insertion and extraction.

Well-Ordered Mesoporous Silica Nanoparticles as a Recoverable Catalyst for One-Pot Multicomponent Synthesis of 4H-Chromene Derivatives

A simple, efficient, and environmentally benign protocol for the synthesis of 4 H -chromene derivatives was developed using bio-compatible, neutral, and recoverable mesoporous silica nanoparticles as a catalyst. The 4 H -chromene derivatives were obtained in excellent yields by three component reaction of an aldehyde or isatin, malononitrile, and cyclic 1,3-diketones in ethanol at 60 °C. Synthesis of 4 H- chromenes by three component condensation of aldehydes or isatines, malononitrile, and cyclic 1,3-diketones was performed using mesoporous silica nanoparticles as a reusable catalyst.

A Stand‐Alone Mesoporous Crystal Structure Model from in situ X‐ray Diffraction: Nitrogen Adsorption on 3 D Cagelike Mesoporous Silica SBA‐16

We present a modeling scheme to analyze cagelike silica mesoporous crystals based on in situ X-ray diffraction (XRD) data collected during gas adsorption-desorption (physisorption) processes. Nitrogen physisorption on a silica mesoporous crystal of SBA-16 was directly monitored by using synchrotron in situ powder XRD measurements conducted at SPring-8. SBA-16 is a well-ordered mesoporous silica in which three-dimensional interconnected cagelike primary mesopores are located at the body-centered cubic lattice points. In addition, the surrounding silica matrix contains random microporous and mesoporous intrawall porosities that are significantly influential to the diffusion properties, and thus important to be quantified for this media. The in situ XRD data exhibits seven Bragg reflections throughout the measurements, and the present method allows one to obtain the maximal and stand-alone information about the pore structure (for example, the mesopore size, the matrix density, the intrawall porosity, and pore surface roughness) together with the nitrogen film evolution in the primary mesopores and the intrawall pore-filling in the silica matrix. We furthermore observe a macroscopic amount of nitrogen adsorbed assuming the density of the fluid, and confirm that the XRD "isotherm" recalculated from the analysis result is consistent with the conventional nitrogen isotherm on a semi-quantitative level; however, these results suggest that the intrawall pores would have a greater contribution to the adsorption than considered based on the conventional isotherm analyses. The present method is readily extendable to any ordered mesopores wrapped by the wall matrix containing a certain intrawall porosity.

Interweaved Si@SiOx/C nanoporous spheres as anode materials for Li-ion batteries

Si@SiOx/C nanoporous spheres as anode materials for high-performance lithium ion batteries were fabricated through a facile magnesiothermic reduction of well-ordered mesoporous silica and subsequent impregnating of carbon precursor into the Si@SiOx nanoporous spheres followed by carbonization at 800°C. The obtained nanoporous spheres present an interweaved porous structure composed of high-capacity Si, inactive SiOx and conductive carbon, which can effectively enhance the electrochemical performance of the composite materials. The resulting Si@SiOx/C nanoporous spheres display a reversible specific capacity of 913mAhg−1 at the first cycle and the capacity retention ratio is 97% after 60cycles at a current density of 100mAg−1. The nanoporous structure of Si, SiOx and C can effectively accommodate the volume change for Si-based materials' expansion, release the mechanical stress and improve the electronic conductivity. The Si@SiOx/C nanoporous spheres exhibit a great potential as anode materials for lithium ion batteries.