Showing papers on "Mesoporous silicate published in 2016"

Mixed alcohol dehydration over Brønsted and Lewis acidic catalysts

Abstract: Mixed alcohols are attractive oxygenated products of biomass-derived syngas because they may be catalytically converted to a range of hydrocarbon products, including liquid hydrocarbon fuels. Catalytic dehydration to form olefins is a potential first step in the conversion of C2–C4 alcohols into longer-chain hydrocarbons. We describe here the physical and chemical characterization along with catalytic activity and selectivity of 4 Bronsted and Lewis acidic catalysts for the dehydration of two mixed alcohol feed streams that are representative of products from syngas conversion over K-CoMoS type catalysts (i.e., ethanol, 1-propanol, 1-butanol and 2-methyl-1-propanol). Specifically, a Lewis acidic Zr-incorporated mesoporous silicate (Zr-KIT-6), a commercial Al-containing mesoporous silicate (Al-MCM-41), a commercial microporous aluminosilicate (HZSM-5), and a commercial microporous silicoaluminophosphate (SAPO-34) were tested for mixed alcohol dehydration at 250, 300 and 350 °C. The zeolite materials exhibited high activity (>98% ethanol conversion) at all temperatures while the mesoporous materials only displayed significant activity (>10% ethanol conversion) at or above 300 °C. The turnover frequencies for ethanol dehydration at 300 °C decreased in the following order: HZSM-5 > SAPO-34 > Al-MCM-41 > Zr-KIT-6, suggesting that Bronsted acidic sites are more active than Lewis acidic sites for alcohol dehydration. At 300 °C, SAPO-34 produced the highest yield of olefin products from both a water-free ethanol rich feed stream and a C3+-alcohol rich feed stream containing water. Post-reaction characterization indicated changes in the Bronsted-to-Lewis acidic site ratios for Zr-KIT-6, Al-MCM-41 and HZSM-5. Ammonia temperature programmed desorption indicated that the acid sites of post-reaction samples could be regenerated following treatment in air. The post-reaction SAPO-34 catalyst contained more aromatic, methylated aromatic and polyaromatic compounds than its zeolite counterpart HZSM-5, while no aromatic compounds were observed on post-reaction Al-MCM-41 or Zr-KIT-6 catalysts. Olefin yield at 300 °C over SAPO-34 (>95%) was comparable to published values for the methanol-to-olefins process, indicating the potential industrial application of mixed alcohol dehydration. Furthermore, the olefin product distribution over SAPO-34 was tunable by the composition of the alcohol feed mixture.

All-into-one strategy to synthesize mesoporous hybrid silicate microspheres from naturally rich red palygorskite clay as high-efficient adsorbents.

Abstract: A mesoporous hybrid silicate microsphere with superior adsorption performance has been successfully synthesized by employing an “all-into-one” strategy and a simple one-pot hydrothermal process using naturally abundant low-grade red palygorskite (PAL) clay as raw material in the presence of non-toxic SiO32− and Mg2+ ions. As is expected, both the PAL and associated minerals transformed into a new amorphous mesoporous hybrid silicate microsphere without using any additional pore-forming template. The mesoporous silicate microsphere shows a large pore size of 37.74 nm, high specific surface area of 489.81 m2/g (only 54.67 m2/g for raw PAL) and negative surface potential of −43.3 mV, and its maximum adsorption capabilities for Methylene bule (MB) and Crystal violet (CV) reach 407.95 mg/g and 397.22 mg/g, respectively. Meanwhile, 99.8% of MB (only 53% for raw PAL) and 99.7% of CV (only 43% for raw PAL) were sucessfully removed from 200 mg/L of initial dye solution by only using 1 g/L of the adsorbent. In addition, the spent adsorbent can be easily regenerated and repeatly reused for muptiple cycles. The study on adsorption mechanism revealed that electrostatic attraction, hydrogen bonding and chemical complexing interactions are the main factors contributed to the high dye adsorption.

Synthesis of oak gall tannin-immobilized hexagonal mesoporous silicate (OGT-HMS) as a new super adsorbent for the removal of anionic dye from aqueous solution

Abstract: Tannin as a natural biomass has been extracted from oak gall and was immobilized on hexagonal mesoporous silicate (HMS) in order to remove direct yellow 86 (DY86) from aqueous solution. The characteristics of the oak gall tannin-HMS adsorbent were substantiated by different techniques such as FTIR, TEM, TGA, BET, and XRD. From the BET analysis, a decline of 75.61% for the surface area of HMS nanoparticles was observed and indicates the proper coating through tannin. In order to analyze the adsorption data, five different isotherms were utilized and nonlinear regression scheme was employed using MATLAB software. It was concluded from the Langmuir isotherm that the maximum monolayer adsorption capacity was 435.5 mg g−1. The thermodynamic analysis of this study also revealed that the adsorption was feasible, since the process was spontaneous and endothermic. The findings also indicate that the adsorption of DY86 follows the pseudo-second-order kinetic model.

Efficient Loading and Encapsulation of Anti-Tuberculosis Drugs using Multifunctional Mesoporous Silicate Nanoparticles

Abstract: Objectives: Development of a novel method for loading drugs into spherical mesoporous silicate nanoparticles (MSNs), and further modification for the loaded MSNs to produce smart drug delivery system. Methods: MSNs have been prepared and loaded using rotary evaporation as a novel method for drug loading. The highly loaded MSNs were further modified as a smart drug delivery system designed for endosomal escape, and sustained release of its cargo into the cytosol. MSNs loaded with anti-tuberculosis front line drugs such as isoniazid, pyrazinamide, pyrazonic acid, and ethambutol, in addition to fluorescein, have been coated with polyethyleneimine followed by mannose labeling for selective targeting of macrophage cells, the loading efficiency was compared to the conventional impregnation loading method. The selected drugs exhibit differences size, charge, and polarity. The developed delivery system has been characterized to indicate the surface are, loading efficiency, morphology, and release behavior at different pH. Results: The loading process is independent of the nature of the drug molecule used and achieves loading efficiencies reaching one order of magnitude higher than those reported for conventional impregnation loading method. Characterization of the modified system indicated unique high surface area as high as 875.8 m2/g, pore size of 3.86 nm, and total pore volume of 1.029 cm3/g. In-vitro release experiments confirmed the pH-controlled release of the cargo molecules from the nanoparticles. Conclusion: We have concomitantly employed previously reported components such as mesoporous silicate, polyethyleneimine coating and mannose labeling, in addition to a novel encapsulation method combined together to develop a smart drug delivery system making use of the advantages of each component. The developed system may be used as a potential novel drug delivery system for combating tuberculosis and/or alike clinical disorders.

Layer‐by‐Layer Gold–Ceramic Nanoparticulate Electrodes for Electrocatalysis

Abstract: Film electrodes prepared from oppositely charged silicate sub-microparticles and gold nanoparticles were applied for electrocatalysis. Mesoporous silicate sub-microparticles with sulfonate functionalities were prepared by the sol–gel method. They were immobilized on an indium tin oxide film surface together with imidazolium-functionalized gold nanoparticles by the layer-by-layer method, that is, alternating immersion into their suspensions. As shown by scanning electron microscopy, the deposited silicate sub-microparticles were covered by gold nanoparticles. The nanoparticulate film was found to be stable, and its electroactive surface was determined to be significantly larger than that of the electrode substrate. It exhibited some cation accumulation behavior. After activation, a gold–ceramic nanoparticulate electrode exhibited catalytic properties towards the reduction dioxygen and the oxidation of hydrazine, SO32−, and NO2−.

Evaluation of mesoporous silicate nanoparticles for the sustained release of the anticancer drugs: 5-fluorouracil and 7-hydroxycoumarin

Abstract: In this study, effects of chemical structure and molecular size of the anticancer drugs 5-fluorouracil and 7-hydroxycoumarin on their release from MCM-48 nanoparticles were investigated. Nanoparticles of the mesoporous silicate material, MCM-48, were prepared and characterized by XRD, SEM and FTIR. Loading of 5-fluorouracil and 7-hydroxycoumarin onto the nanoparticles was confirmed by FTIR and TGA measurements, and loading capacities of about 24 and 14 % were achieved, respectively. Release experiments for 5-fluorouracil were conducted in buffer solutions at pH = 7.4 and 5.2. However, due to the instability of 7-hydroxycoumarin in basic media, release experiments were conducted only in acidic buffer solution at pH = 5.2. The release of 5-fluorouracil was slightly affected by the pH of the release medium, and it was almost complete in about 2 h. However, the release of 7-hydroxycoumarin which has a larger size and higher acidity followed a prolonged release mode over a period of 12 h. The prolonged release of 7-hydroxycoumarin from MCM-48 nanoparticles points out to the potential use of this system as sustained release delivery carrier.

Synthesize and characterization of Aminosilane functionalized MCM-41 for removal of anionic dye: Kinetic and thermodynamic study

Abstract: In this study, removal of Acid blue 62 from aqueous solution by mesoporous silicate MCM-41 modified by Aminopropyltriethoxysilane (APTES) composite was studied. Properties of synthesized composite were analyzed and confirmed by SEM, EDX and FTIR. Results show that Langmuir adsorption isotherm has the best compatibility with the results of experiments. Kinetic analysis using pseudo-first-order model, pseudo-second-order and the intra-particle diffusion model was carried out. Results also confirmed that adsorption process is compatible with the pseudo-second-order kinetic model. Thermodynamic parameters such as Gibbs free energy changes (ΔGo), Enthalpy changes (ΔHo) and Entropy changes (ΔSo) were calculated. Negative value of ΔGo and positive value of ΔHo show that adsorption of Acid blue 62 on aminated nanocomposite is a spontaneous process also endothermic.

Unique characteristics of MnO x -incorporated mesoporous silicate, Mn-FDU-5, prepared via evaporation induced self assembly

Abstract: Mn containing 3D mesostructured FDU-5 (Ia3d) silicates with varying Si/Mn ratios were synthesized for the first time via evaporation induced self assembly (EISA) technique under acidic conditions at room temperature, employing Pl23 triblock copolymer as a structure directing agent. This method facilitates complete incorporation of higher amounts of Mn in the framework and extraframework locations of FDU-5 even under highly acidic synthesis conditions. The Mn-FDU-5 samples possessed surface areas of 300–500 m2/g, pore volumes of 0.42–0.55 cm3/g and narrow pore size distributions of 4.1–4.9 nm. Homogeneous dispersion of Mn species and aggregated Mn oxide clusters were evidenced from FIB-SEM micrographs. Complementary analytical techniques such as diffuse reflectance UV–Vis, FTIR, TPR and EPR analyses provide insights into the nature of the different types of Mn species (Mn2+, Mn3+ and Mn3O4 nanoparticles) that co-exist in FDU-5. The Mn-FDU-5 material is shown to be active for the epoxidation of trans-stilbene (TS, ~60 % conversion) to trans-stilbene epoxide (~64 % selectivity) with TBHP as oxidant. Although the activity of Mn-FDU-5 (~45 % TS conversion) is similar to those observed with MCM-41 and MCM-48 supports containing similar amounts of Mn (1 wt%), higher epoxide selectivity (~64 %) was observed with Mn-FDU-5. The mixed oxidation states of Mn (Mn2+, Mn3+) along with the extraframework Mn3O4 are found to be beneficial in catalyzing TS epoxidation.

Mesoporous silica reinforced polybutadiene rubber hybrid composite

Abstract: Polybutadiene rubber (BR) hybrid composites reinforced with mesoporous silica (MPS)/nanoclays, silica and MPS/carbon black were prepared. The primary focus of this research was to incorporate the mesoporous silicate (MPS), e.g., mobil composition of matter (MCM-41) as reinforcing filler in the BR matrix. The textural properties of the mesoporous materials were characterized by powder X-ray diffraction (XRD), transmission electron microscopy and N2 isothermal adsorption measurements. The quantity of MCM-41 in the BR matrix was first optimized and the similar optimized quantity of different MPS was compared in terms of tensile strength. The composites were characterized by XRD and scanning electron microscopy. The composite containing 10 phr-loaded MCM-41 showed 250 % improvement in tensile strength compared to the matrix devoid of nanomaterial. The effects of co-incorporation of two different kinds of nanomaterials having different nanostructures, e.g., layered montmorillonite and particulate MCM-41 were also studied. MCM-41 enhanced the mechanical strength of BR almost double the value compared to precipitated silica at the same filler loading. The morphological features of the composites were well corroborated with the mechanical properties.

Determination of the surface area of mesoporous silicates by X-ray diffraction patterns using partial least squares and multiple linear regressions

Abstract: Surface area of modified mesoporous silicates have been quantitatively determined using x-ray diffraction patterns and chemometric methods. The modified mesoporous silicate samples with varying surface area (223–1164 m2/g) were synthesized and their effective surface areas were calculated by the Brunauer–Emmett–Teller (BET) method using their nitrogen adsorption isotherms. The x-ray diffraction patterns of the samples were measured. The chemometric techniques were used to model the diffraction patterns as a function of the calculated surface area. The prediction results of the multiple linear regression (MLR) model was better than the partial least squares (PLS) model and both of the methods can be used for predicting the surface area of new mesoporous samples.

Quantum effects in the sorption kinetics of 4He by mesoporous materials

Abstract: Sorption and desorption of 4He by a mesoporous silicate material MCM-41 was studied in the temperature range of 1.5–290 K. It was shown that for T = 25–290 K the thermal activation mechanism is dominant in the sorption kinetics of 4He atoms by an MCM-41 sample. Its activation energy was estimated as Ea ≈ 164.8 K. For T = 12–23 K, the diffusion of 4He atoms in the MCM-41 was practically independent of temperature, which typically occurs when the tunnelling mechanism of diffusion dominates over the thermally activated one. A change in the mobility of 4He atoms in MCM-41 channels was observed at T = 6–12 K, which may be indicative of the formation upon cooling (or decay upon heating) of a 4He monolayer and subsequent multilayers on the inner surfaces of the channels. Below 6 K, the diffusion coefficients of 4He are only weakly temperature dependent, which may be attributed to the behavior of quantum 4He liquid in the MCM-41 channels covered with several layers of 4He atoms.

Synthesis of KIT-1 Mesoporous Silicates Showing Two Different Macrosporous Strucrtues; Inverse-opal or Hollow Structures

Abstract: We report a facile method for preparing KIT-1 mesoporous silicates with two different macroporous structures by dual templating. As a template for macropores, polystyrene (PS) beads are assembled into uniform three dimensional arrays by ice templating, i.e., by growing ice crystals during the freezing process of the particle suspension. Then, the polymeric templates are directly introduced into the precursor-gel solution with cationic surfactants for templating the mesopores, which is followed by hydrothermal crystallization and calcination. Later, by burning out the PS beads and the surfactants, KIT-1 mesoporous silicates with macropores are produced in a powder form. The macroporous structures of the silicates can be controlled by changing the amount of EDTANa4 salt under the same templating conditions using the PS beads and inverse-opal or hollow structures can be obtained. This strategy to prepare mesoporous powders with controllable macrostructures is potentially useful for various applications especially those dealing with bulky molecules such as, catalysis, separation, drug carriers and environmental adsorbents.