Pore Structure Of Mesoporous Silica Research Articles

Tribological behavior of 3D printed nanofluid reinforced photosensitive self-lubricating polymer materials

Oil-loaded polymer composites have become a research focus in tribology due to the good environmental stability and excellent performance. Usually, it is necessary to endow the polymer with a porous structure to facilitate lubricating oil storage. However, most methods require complex operating steps, making it difficult to control the complex shape of materials, and excessive pores often lead to an imbalance between the oil storage and retention rates. At the same time, the mechanical properties of the material can also be negatively affected. Developing a simple synthesis method to obtain oil-loaded polymer composite materials with good self-lubricating and mechanical properties still faces challenges. Herein, a one-pot synthesis method for oil-loaded self-lubricating polymers was proposed, which embeds the porous silica nanoparticles loaded with lubricating oil into the polymer and uses vat photopolymerization-based technologies to construct the polymer with various complex and delicate structures. After a series of treatments, such as photocuring and cleaning, an oil-loaded polymer-based composite material with good self-lubricating performance was prepared. Benefiting from the rich mesoporous pore structure of mesoporous silica, high specific surface area of 467 m2g−1, and pore volume of 1.06 cm3g−1, the oil content and retention rate of the composite materials are at a high level. In addition, by combining oil-loaded mesoporous silica nanoparticles with 3D printing, controllable preparation of complex shapes of self-lubricating composite materials has been achieved. During the friction performance testing process, the oil-loaded particles in the polymer composite can continuously provide lubricating oil on the friction surface, thus making the friction coefficient and wear rate reduced by 85.7% and 97.7%.

Mesoporous silica-supported Pt catalysts in enantioselective hydrogenation of ethyl pyruvate

Catalytic properties of Pt catalysts supported on mesoporous silica (Pt/m-SiO2) have been studied in enantioselective hydrogenation of ethyl pyruvate. The influences of pore structure of mesoporous silica (m-SiO2), type of chiral modifier, and H2 pressure on the catalytic performance have been investigated by using various m-SiO2 supports and cinchona alkaloids and by varying H2 pressure. The use of MCM-41, SBA-15, KIT-6, and MCF reveals that characteristic pore structure and size of m-SiO2 supports significantly affect both activity and enantioselectivity. A facile diffusion of chiral modifier through large mesopores of MCF support enables Pt/MCF to exhibit excellent performance. A comparison of the efficiency of cinchona alkaloids-modified Pt catalysts shows that QN and QD lead to higher performance than CD and CN at ambient H2 pressure. The influence of cinchona alkaloids on enantioselectivity noticeably depends on H2 pressure. Cinchona alkaloid-modified Pt/m-SiO2 exhibit superior enantioselectivity to the corresponding Pt/Al2O3 under various H2 pressures. These results imply that m-SiO2 is a promising support and that fine control of pore structure can further improve catalytic performance of Pt/m-SiO2 in heterogeneous enantioselective hydrogenation.

Relationship Between the Pore Structure of Mesoporous Silica Supports and the Activity of Nickel Nanocatalysts in the CO2 Reforming of Methane

The question remains over the role of the pore structure of the support material on the catalytic behaviour of Ni catalysts during the CO2/dry reforming of methane (DRM). For this reason, a series of mesoporous materials with different pore structures, namely MCM-41, KIT-6, tri-modal porous silica (TMS), SBA-15 and mesostructured cellular foams (MCFs) were synthesised via hydrothermal synthesis methods and further impregnated with 15 wt.% NiO (11.8 wt.% Ni). It was observed that synthesised TMS is a promising catalyst support for DRM as Ni/TMS gave the highest activity and stability among these materials as well as the Ni catalysts supported on classic ordered mesoporous silicates support reported in the literature at the relatively low temperature (700 °C). On the other hand, Ni supported on CMC-41 exhibited the lowest activity among them. To understand the reason for this difference, the physicochemical properties of these materials were characterised in detail. The results show that the thickness of the silica wall and the pore size of the support material play a critical role in the catalytic activity of Ni catalysts in the CO2 reforming of methane.

Outside-in synthesis of mesoporous silica/molybdenum disulfide nanoparticles for antitumor application

Very different from traditional inside-out method, which used guest material as the inside core and then surface-coated outer layer, herein, we propose a facile and unique outside-in approach for the synthesis of high dispersive mesoporous silica nanoparticle (MSN)/MoS2-PEG nanoparticles (SMPs) based on the differences of precursor solubility in different solvents, for the first time. The prepared SMPs exhibit both higher drug loading efficiency of 64.7% owing to the pore structure of mesoporous silica, and excellent photothermal performance with photothermal efficiency of 41.5% due to the inside decorated MoS2 nanosheets, which could be used for the combination of tumor hyperthermia and chemotherapy. The in vivo results indicate that SMPs show great synergistic effect, i.e., the heat produced during PTT can increase the chemotherapy sensitivity of DOX and synergistically improve its therapeutic effect. Such a facile strategy provides a new facile way to construct a novel theranostic agent by integrating different functions into one dosage, and shows a promising approach for the construction of nanomaterials using MSN as a template.

Pore structure of mesoporous silica (KIT-6) synthesized at different temperatures using positron as a nondestructive probe

Ordered mesoporous SiO2 (KIT-6) was synthesized using triblock copolymer P123 as the structure template and tetraethyl orthosilicate (TEOS, C8H20O4Si) as silica source. Small-angle X-ray scattering and high resolution electron microscope measurements indicate the 3d cubic Ia3d symmetry of the pore structure of KIT-6 synthesized at 30–120 °C. When the synthesis temperature increases to 180 °C, the order of pores was deteriorated. The pore size was estimated by nitrogen adsorption/desorption measurements, which increases from 3.8 nm to 18.5 nm as the synthesis temperature increases from 30 °C to 180 °C. With the increase of mesopore size, the pore wall thickness shows continuous decrease. Positron annihilation lifetime spectra was measured for the synthesized KIT-6. The lifetime spectra can be resolved to two short and two long lifetime components. The two long lifetimes τ3 and τ4 correspond to o-Ps lifetime in micropore and mesopores, respectively. The size of mesopores was estimated from the o-Ps lifetime by using Goworeck’s model for cylindrical pores, which shows continuous increase with synthesis temperature, and is consistent with the N2 adsorption/desorption measurements. The size of micropore has no change with increasing synthesis temperature. However due to the decrease in wall thickness, the number of micropores in the wall shows subsequent decrease. In addition, the second lifetime component τ2 is also found to be a sensitive parameter for the pore size, which shows the same trend as lifetime τ4 with increasing synthesis temperature.

The surface modification by carboxyl ionic liquid for mesoporous silica and the preparation of composite polymer electrolyte with the modified mesoporous silica

A modified mesoporous silica was prepared by esterification reaction of the hydroxyl group on the surface of mesoporous silica with 1‐carboxymethyl‐3‐methyl imidazolium bis(trifluoromethylsulfonate)imine ([(HOOC)C1C1Im][NTf2]). The esterification reaction and structure of the modified mesoporous silica were investigated using the X‐ray photoelectron spectroscopy, Nitrogen adsorption–desorption analysis, Transmission electronic microscopy, Field emission scanning electronic microscopy, Energy dispersive X‐ray spectroscopy, and Thermogravimetric analysis.The analysis results indicated that the carboxyl group of [(HOOC) C1C1Im] [NTf2] can occur the catalytic esterification reaction with the hydroxyl group on the surface of mesoporous silica and the introduction of ILs did not affect the long range ordered pore structure of mesoporous silica, and the modified mesoporous silica contains 8.14% (wt.) of [(HOOC)C1C1Im][NTf2]. In addition, a composite polymer electrolyte (CPE) was prepared through introducing the modified mesoporous silica and bis (trifluoromethanesulfon) imide lithium salt (LiTFSI) into the carboxylate butadiene‐acrylonitrile rubber (XNBR) matrix and the ionic conductivity and mechanical properties of the CPE were studied. The results showed that the mechanical properties and ionic conductivity of the CPE were obviously improved by filling the modified mesoporous silica. When loading 20 phr modified mesoporous silica, the tensile strength was increased to 6.2 MPa from 2.4 MPa, and that the ionic conductivity at room temperature was increased to 1.5 × 10−5 S/cm from 2.0 × 10−6 S/cm. POLYM. COMPOS., 39:3586–3593, 2018. © 2017 Society of Plastics Engineers

Mesoporous Silica Supported Pd-MnOx Catalysts with Excellent Catalytic Activity in Room-Temperature Formic Acid Decomposition.

For the application of formic acid as a liquid organic hydrogen carrier, development of efficient catalysts for dehydrogenation of formic acid is a challenging topic, and most studies have so far focused on the composition of metals and supports, the size effect of metal nanoparticles, and surface chemistry of supports. Another influential factor is highly desired to overcome the current limitation of heterogeneous catalysis for formic acid decomposition. Here, we first investigated the effect of support pore structure on formic acid decomposition performance at room temperature by using mesoporous silica materials with different pore structures such as KIE-6, MCM-41, and SBA-15, and achieved the excellent catalytic activity (TOF: 593 h−1) by only controlling the pore structure of mesoporous silica supports. In addition, we demonstrated that 3D interconnected pore structure of mesoporous silica supports is more favorable to the mass transfer than 2D cylindrical mesopore structure, and the better mass transfer provides higher catalytic activity in formic acid decomposition. If the pore morphology of catalytic supports such as 3D wormhole or 2D cylinder is identical, large pore size combined with high pore volume is a crucial factor to achieve high catalytic performance.

The size-controllable synthesis of nanometer-sized mesoporous silica in extremely dilute surfactant solution

10–60 nm-sized mesoporous silica particles with ordered or worm-like pore structures were controllably synthesized in extremely dilute surfactant solution, and the lowest concentrations of TEOS and CTAB were 12.45 mM, 1.52 mM, respectively. The synthesis of nanometer-sized Al-incorporated mesoporous silica particles (Al-MS) was also performed under the similar conditions. Compared to the mesoporous silica without doping of aluminum, those Al-incorporated silica particles have a certain textural mesoporosity. The results indicate that the size and pore structure of mesoporous silica can be adjusted by changing the concentration of reactants. The mesoporous silica nanoparticles, including Al-MS, were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction (SAXRD), as well as nitrogen adsorption/desorption techniques. It was suggested that the formation of the mesoporous silica nanoparticles could be attributed to the deposition of self-assembled silicate micelles.

Effect of drying on the mesoporous structure of sol–gel derived silica with PPO–PEO–PPO template block copolymer

The effects of drying method on the pore structure of mesoporous silica were studied from the viewpoint of enhancing closed porosity in mesoporous silica. The mesoporous silica was prepared via a sol–gel process using polyethyleneoxide–polypropyleneoxide–polyethyleneoxide (PEO–PPO–PEO) triblock copolymer (Pluronic P123) as the structure-directing template. The closed porosity was evaluated from the apparent mass density of the sample measured by a helium pycnometer. These mesoporous silicas were also characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and nitrogen adsorption. The drying method was shown to be responsible for the finally templated mesoporous structure of the silica. More rapid drying is more preferable for enhancing the closed porosity of the mesoporous silica. The closed pores were formed by immediate immobilization of copolymer molecular assemblies in the silica matrix due to the instant removal of the solvent and solidification at higher temperatures. The drying method, mainly affecting the drying rate, is highly influential on the finally replicated mesoporous structure in silica.

Determination of size and ordering of pores in mesoporous silica using small angle neutron scattering

Small angle neutron scattering (SANS) has been used to study the size and ordering of the pore structure of mesoporous silica. Mesoporous silica was synthesised in the presence of a 16 carbon chain surfactant, cetyl-trimethyl ammonium bromide (CTAB) using the sol–gel method. The SANS patterns of the mesoporous silica were measured on samples before and after calcination. Calcination at 600°C for 2 h results in removal of the surfactant template. The SANS study revealed the presence of an ordered pore structure with pore spacing of approximately 3.5 nm. After calcination the pore spacing decreased. Using the SANS technique it was possible to quantify the pore sizes and pore spacing and then determine the wall thickness.

Synthesis of hollow spherical silica with MCM-41 mesoporous structure

Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm−3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N2 gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N2 adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased

Effect of Pentanol on Morphologies and Pore Structure of Mesoporous Silica

Using wormlike micelles of cetyltrimethylammonium bromide (CTAB) and nitric acid as templates, fibrous mesoporous silica was synthesized and the effects of pentanol on the morphologies and ordered pore structure of mesoporous silica were studied. The resulting mesoporous silica was characterized by small-angle X-ray diffraction, nitrogen adsorption−desorption measurements, and scanning electron microscopy. Results showed that the amount of mesoporous silica with fibrous shapes decreased with the decrease of the molar ratio of CTAB to pentanol and that mesoporous silica with a spherical appearance only was obtained at a molar ratio of 1:3 (CTAB to pentanol). The pore structure of mesoporous silica was more ordered when the molar ratio of CTAB to pentanol was between 1:1 and 1:2, and distances between centers of two adjacent pores increased with the decrease of the molar ratio of CTAB to pentanol. There existed a type IV adsorption isotherm and an H1 hysteresis loop in N2 adsorption−desorption curves; total...