Small-angle X-ray Powder Diffraction Research Articles

ChemInform Abstract: The High Catalytic Activity and Reusability of the Proline Functionalized Cage‐Like Mesoporous Material SBA‐16 for the Asymmetric Aldol Reaction Proceeding in Methanol—Water Mixed Solvent.

The cage-like mesoporous material SBA-16 has been successfully functionalized with L-4-hydroxyproline and characterized by Fourier transform infrared (FT-IR) spectroscopy, Small-angle X-ray powder diffraction (XRD), N2 sorption detection, transmission electron microscopy (TEM), elemental analysis and thermo gravimetric analysis (TGA). This chiral non-metallic catalyst avoided heavy metal pollution during the preparing and using process, and demonstrated high catalytic activity (up to 91%), diastereoselectivity (up to 97:3) and enantioselectivity (up to 83%) in the asymmetric aldol reaction between aldehyde acceptors and ketone donors with methanol–H2O as solvent. Moreover, the synthesized catalyst could be easily separated from the reaction mixture by filtration and reused for up to five runs without any obvious loss of activity, indicating its excellent recyclability.

Synthesis of Straight Rod-Shaped Mesoporous Silica Templated with Polyvinylpyrrolidone and P123 for Controlled Ibuprofen Release

Straight rod-shaped mesoporous silica materials (SRMS) were successfully prepared using polyvinylpyrrolidone and triblock copolymer as dual template, which would be further functionalized with (3-aminopropyl) triethoxysilane. SRMS and functionalized SRMS (NH-SRMS) were characterized by means of small-angle X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, N2adsorptiondesorption. The results indicated that SRMS was straight rod-shaped mesoporous silica with a hexagonal symmetry structure (p6mm) and the structure did not change after functionalization. A comparative study of the loading and release of ibuprofen on the carriers of SRMS and NH-SRMS were carried out in phosphate buffered saline. NH-SRMS exhibited a lower release rate than SRMS, suggesting that NH-SRMS was a promising carrier for achieving prolonged drug release.

Lanthanide (Eu3+, Tb3+) functionalized SBA-15 through modified hexafluoroacetylacetone linkage: Covalently bonding construction, physical characterization, and luminescent properties

Abstract

Open-system nanocasting synthesis of nanoscale α-Fe2O3 porous structure with enhanced acetone-sensing properties

Nanoscale α-Fe2O3 with porous structure was synthesized via an open-system nanocasting method. Characterization of the crystal structures, morphologies, surface areas, and pore size distributions of the as-synthesized α-Fe2O3 by wide-angle and small-angle X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen physisorption analysis demonstrated that the nanoscale α-Fe2O3 synthesized in open system had a less crystallinity with average diameter of ∼6.0nm, higher BET specific surface area of 205.4m2g−1, and wider pore size distribution from ∼2.2nm to 15.7nm compared with that of the mesoporous α-Fe2O3 synthesized in closed system. The gas-sensing measurement results revealed that the nanoscale α-Fe2O3 based gas sensor had a much better response to acetone than that of the device prepared from the mesoporous α-Fe2O3. A possible gas-sensing mechanism based on the α-Fe2O3 samples synthesized with different nanocasting systems was discussed in detail. Wide porous distribution of the nanoscale α-Fe2O3, as well as small particle size and high surface area are effective for gas molecules diffusion and formation of sufficient electron depletion area and result the enhanced sensor response, which suggests that it has great potential for practical applications in diabetes diagnosis.

The high catalytic activity and reusability of the proline functionalized cage-like mesoporous material SBA-16 for the asymmetric aldol reaction proceeding in methanol–water mixed solvent

The cage-like mesoporous material SBA-16 has been successfully functionalized with L-4-hydroxyproline and characterized by Fourier transform infrared (FT-IR) spectroscopy, Small-angle X-ray powder diffraction (XRD), N2 sorption detection, transmission electron microscopy (TEM), elemental analysis and thermo gravimetric analysis (TGA). This chiral non-metallic catalyst avoided heavy metal pollution during the preparing and using process, and demonstrated high catalytic activity (up to 91%), diastereoselectivity (up to 97:3) and enantioselectivity (up to 83%) in the asymmetric aldol reaction between aldehyde acceptors and ketone donors with methanol–H2O as solvent. Moreover, the synthesized catalyst could be easily separated from the reaction mixture by filtration and reused for up to five runs without any obvious loss of activity, indicating its excellent recyclability.

Synthesis, characterization and heterogeneous catalytic application of copper integrated mesoporous matrices

Ordered copper integrated mesoporous silicate catalysts (CuMSC) have been synthesized by the utilization of the amphiphilic tri-block copolymer pluronic F127 as a structure directing agent (SDA) under acidic aqueous conditions. The mesophase of the materials was investigated using small-angle powder X-ray diffraction and transmission electron microscopic (TEM) image analysis. N2 adsorption-desorption studies show that the BET surface area of CuMSC (214-407 m(2) g(-1)) is lower than that of pure silica (611 m(2) g(-1)) and has smaller average pore dimensions (4.0-5.0 nm), both prepared following the same synthetic route. The reduction of pore size and surface area points to incorporation of copper within the silicate network. FEG-SEM results suggest that the materials have a plate-like morphology and are composed of very tiny nanoparticles. EDS surface chemical analysis was utilized for the detection of the distribution of Si, O and Cu in the matrix. The FT IR spectral study suggests the complete removal of the surfactants from the calcined materials and the presence of Si-O-Cu bonds for high nominal contents. X-ray photoelectron spectroscopy (XPS) and UV-vis reflectance spectra show the oxidation state of copper and coordination mode, respectively. These mesoporous materials display a good catalytic activity in the oxidation of cyclohexane to cyclohexanone and cyclohexanol in the presence of the green oxidant hydrogen peroxide. The maximum yield (cyclohexanone and cyclohexanol) was ca. 29% and the TON (turnover number) was 276 under optimal reaction conditions. The good catalytic activity could be attributed to the large surface area and the presence of a high number of active sites located at the surface of the material, as well as to its stability. The catalysts showed negligible loss of activity after five cycles.

Enhancement of CO2 adsorption on phenolic resin-based mesoporous carbons by KOH activation

Carbons with high surface area and large volume of ultramicropores were synthesized for CO2 adsorption. First, mesoporous carbons were produced by soft-templating method using triblock copolymer Pluronic F127 as a structure directing agent and formaldehyde and either phloroglucinol or resorcinol as carbon precursors. The resulting carbons were mainly mesoporous with well-developed surface area, large total pore volume, and only moderate CO2 uptake. To improve CO2 adsorption, these carbons were subjected to KOH activation to enhance their microporosity. Activated carbons showed 2–3-fold increase in the specific surface area, resulting from substantial development of microporosity (3–5-fold increase in the micropore volume). KOH activation resulted in enhanced CO2 adsorption at 760mmHg pressure: 4.4mmolg−1 at 25°C, and 7mmolg−1 at 0°C. This substantial increase in the CO2 uptake was achieved due to the development of ultramicroporosity, which was shown to be beneficial for CO2 physisorption at low pressures. The resulting materials were investigated using low-temperature nitrogen physisorption, CO2 sorption, and small-angle powder X-ray diffraction. High CO2 uptake and good cyclability (without noticeable loss in CO2 uptake after five runs) render ultramicroporous carbons as efficient CO2 adsorbents at ambient conditions.

One-pot morphology-controlled synthesis of various shaped mesoporous silica nanoparticles

A simple synthetic method has been developed for synthesis of mesoporous silica nanoparticles with versatile morphologies by adopting CTAB and C12–OH as dual soft templates. In such a simple method, only by regulating the dose of C12–OH and temperature, we can well-realize the silica nanoparticle morphological transformation from sphere to shell-like, rugby-like, peanut-like, hollow, and complex yolk–shell structures. These as-fabricated silica nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller (BET), and small-angle powder X-ray diffraction. The as-prepared mesoporous silica nanoparticles with versatile morphologies possessing varying BET surface areas, pore diameter, and pore distributions have some potential applications in separation, sensing, and heterogeneous catalysis.

Anionic surfactant templated chiral nanospheres and their enantioselective adsorption

Monodispersed chiral mesoporous spheres of nanometer size with high specific area and good thermal stability were synthesized using the chiral anionic surfactant (N-palmitoyl-L-phenylalanine) as a template according to the co-structure directing agent (CSDA) method. The resulting mesoporous nanospheres were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), small angle X-ray powder diffraction (XRD) and nitrogen sorption experiments. The particle distribution was 190–210 nm with pore diameters of 3–4 nm. The enantioselective ability of this chiral mesoporous silica, after extraction of the chiral surfactant, was investigated by the selective adsorption of enantiomers and racemic solutions of alanine. The chiral selective adsorbability of this material type was shown by the asymmetric preferential adsorption of alanine as observed using circular dichroism (CD) spectroscopy and was further verified in a racemic mixture of valine. It was found that the adsorption of L-alanine was higher than that of D-alanine on as-prepared chiral mesoporous materials with a chiral selectivity factor of 3.15, which generates new possibilities for enantiomeric separation and other enantioselective applications.

Tungstic acid functionalized mesoporous SBA-15: A novel heterogeneous catalyst for facile one-pot synthesis of 2-amino-4H-chromenes in aqueous medium

A new highly ordered mesoporous tungstic acid functionalized SBA-15, TAFMC-1 has been synthesized via post-synthesis modification of mesoporous SBA-15 with (3-chloropropyl) triethoxysilane followed by substitution reaction of chlorine atom of the 3-chloropropyl group by tungstic acid group under refluxing conditions in n-hexane. The tungstic acid functionalized mesoporous silica material has been characterized by using small angle powder X-ray diffraction, N2 sorption, HR-TEM, FE-SEM, FT-IR and solid state MAS NMR studies. TAFMC-1 catalyzes the facile one-pot catalytic three-component condensation reaction of resorcinol, aromatic aldehyde and malononitrile for the synthesis of a diverse range of 2-amino-4H-chromenes in aqueous medium. This heterogeneous catalyst can be recycled very efficiently for six consecutive reaction cycles without significant loss of catalytic activity.

Enhancing the catalytic properties of porcine pancreatic lipase by immobilization on SBA-15 modified by functionalized ionic liquid

The mesoporous silica SBA-15 was modified by carboxyl-functionalized ionic liquid (COOH-IL-SBA). The prepared support was used to immobilize porcine pancreatic lipase (PPL) by physical adsorption (PPL-COOH-IL-SBA) and covalent attachment (PPL-CON-IL-SBA). Enzymatic properties of the immobilized PPL were investigated in the triacetin hydrolysis reaction. It was found that carboxyl functionalized ionic liquid modification of the support surface was an effective method to improve the properties of immobilized PPL. Incorporating into the functionalized SBA-15 made PPL more resistant to temperature and pH changes, compared with PPL immobilized on parent SBA-15 (PPL-SBA). Especially, after the covalent attachment to a functionalized support, the stability of PPL was improved obviously, which retained 81.25% and 52.50% of the original activity after incubation for 20days and four times recycling, respectively, whereas PPL-SBA exhibited only 58.80% and 27.78% of the original activity under the same conditions. In addition, physical and chemical properties of the supports and immobilized PPL were characterized by small-angle X-ray powder diffraction (SAXRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), nitrogen adsorption, nuclear magnetic resonance (NMR) and thermogravimetry (TG). The images and data confirmed chemical modification in SBA-15 and PPL immobilization on the tested support.

DSM as a probe for the characterization of modified mesoporous silicas

Two methods were applied for the functionalization of mesoporous silica materials (MCM-41 and SBA-15). For the acidic functionalization with sulfonicpropyl groups a direct synthesis method was used. For the basic functionalization with aminopropyl groups a post-synthesis methodology was used. Sample characterization was performed by small angle X-ray powder diffraction, nitrogen adsorption and desorption and transmission electron microscopy. Direct functionalization has a high impact on the structural characteristics, decreasing BET surface area and changing its pore size distribution. Trans-4-[(4-dimethylamino)styryl]-1-methylpyridinium iodide (DSM+) was used for the acid base characterization of the synthesized materials. Ground state absorption spectra and laser induced time resolved emission spectra have shown the existence of two forms of the probe: DSM+ and the protonated, DSMH2+. Lifetime distribution analysis confirmed the presence of these two species in all materials, but with different relative amounts depending on the surface characteristics. All these findings clearly show that DSM+ is an excellent probe capable of providing important information regarding the internal surfaces of these materials, with channels of nanometer dimensions, namely the different acid properties of the active sites of these silica based hosts.

Biocatalytic esterification of caprylic acid with caprylic alcohol by immobilized lipase on amino-functionalized mesoporous silica

Ordered mesoporous silica (MS) materials were prepared using Pluronic P123 (triblock copolymer poly(ethylene glycol)–block–poly(propylene glycol)–block–poly(ethylene glycol)) and poly(ethylene glycol) as dual templates, and functionalized with (3-aminopropyl)triethoxysilane using the postsynthesis-grafting method. Fourier-transform infrared spectroscopy, 29Si and 13C cross-polarization and magic angle spinning nuclear magnetic resonance, elemental analysis, small-angle X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption–desorption were used to monitor the effect of surface functionalization on the structural and textural features of MS. MS was found to possess a short rod-shaped macrostructure and a two-dimensional hexagonal P6mm mesoscopic structure. After functionalization, the mesoscopic structure was retained and the interplanar spacing d (100) increased, whereas the pore diameters, pore volumes, and surface areas decreased. MS and functionalized MS were used as carriers to immobilize porcine pancreatic lipase (PPL). The immobilized PPL on both kinds of carriers were then employed to catalyze the hydrolysis of triacetin and esterification of caprylic acid with caprylic alcohol. All observed biocatalytic characteristics of PPL immobilized on functionalized MS were compared with those of PPL immobilized on MS. The hydrolysis activity of lipase immobilized on functionalized MS was almost twice that on MS. Functionalized MS immobilized PPL showed greater reusability, and its hydrolysis conversion was still retained at 24%, which was 15% higher than that of lipase immobilized on MS after the fifth reuse. The synthetic activity and effect of several parameters on caprylic caprylate production for immobilized PPL were investigated. Immobilized PPL exhibited significantly higher activity, with a caprylic acid conversion ratio of 67.47% when the reaction was catalyzed by PPL immobilized on functionalized MS. The corresponding value was 58.75% using PPL immobilized on MS at 50°C.

Improving the controlled release of water-insoluble emodin from amino-functionalized mesoporous silica

Several types of amino-functionalized mesoporous silica, including F5-SBA-15, F10-SBA-15, and F15-SBA-15 were prepared through co-condensation of tetraethoxysilane (TEOS) and (3-aminopropyl)triethoxysilane (APTES) in varying molar ratios (5mol%, 10mol%, and 15mol%) via a hydrothermal process. The materials obtained were characterized by means of small-angle X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption–desorption, Fourier transformed infrared spectra, and X-ray photoelectron spectroscopy. Increasing APTES molar ratios decreased the degree of orderliness of the functionalized mesoporous silica. Pure and amino-functionalized SBA-15 samples were employed as supports for the controlled release of water-insoluble drug emodin. Loading experiments showed that drug loading capacities mainly depended on the surface areas and pore diameters of the carriers. Controlled release profiles of emodin-loaded samples were studied in phosphate buffered saline (PBS, pH 7.4), and results indicated that the emodin release rate could be controlled by surface amino-functionalized carriers. Emodin loaded on functionalized mesoporous supports exhibited a lower release rate than that of loaded on pure SBA-15, emodin loaded on F10-SBA-15 showed the smallest release amount (71.74wt%) after stirring in PBS for 60h. Findings suggest that functionalized mesoporous SBA-15 is a promising carrier for achieving prolonged release time periods.

Microwave synthesis, characterization and transesterification activities of Ti-MCM-41

A series of Ti-MCM-41 mesoporous materials with different titanium content (Si/Ti ratio varying from 100 to 5) were prepared using a microwave irradiation method. Physicochemical and structural properties of the materials were investigated using small angle X-ray powder diffraction (SAXRD), N2 adsorption–desorption, Fourier transform infrared (FT-IR) spectroscopy, transmission electron micrograph (TEM), inductively coupled plasma optical emission spectrometry (ICP-OES), diffuse reflectance UV–visible (DRUV–vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), FT-IR measure of adsorbed pyridine and ammonia temperature programmed desorption (NH3-TPD) techniques. Merging results of those characterizations mentioned above, it indicates that, with the decrease of Si/Ti ratio from 100 to 5, Ti-MCM-41 samples exhibit typical long-range order of hexagonal structure with a certain decrease of structure ordering; titanium species incorporate into the framework entirely and are mainly in tetrahedral coordination. As the titanium content increases gradually, the amount of framework Ti(IV) sites, which could result in the formation of weak Lewis acid sites on the surface, also rises correspondingly. The rich weak Lewis acid sites and mesoporous structure with large pore diameter are significant factors affecting the catalytic properties of Ti-MCM-41 materials for transesterification of dimethyl oxalate and phenol.

Solvothermal synthesis of mesoporous aluminophosphate for polluted water remediation

Tiny nanoparticles of mesoporous aluminophosphate have been synthesized through solvothermal method in presence of a long chain fatty acid as template. The mesophase of the material was investigated by using small-angle powder X-ray diffraction and transmission electron microscopy (TEM) image analysis. N2 adsorption–desorption studies show high surface area (235m2g−1) and broad pore size distribution (∼6.0nm). FE SEM results suggest the material is composed of very tiny nanoparticles and pores are generated due to the inter particles voids of dimension ∼6.0nm. EDS surface chemical analysis was utilized for the detection of the distribution of Al and P in the matrix. FT IR spectral study suggests almost complete removal of the surfactants from the calcined material. This mesoporous material showed excellent adsorption capacity for the pollutant heavy metal cations and can be utilized as a potential candidate for the remediation of contaminated ground water.

Luminescent hybrid materials of lanthanide β-diketonate and mesoporous host through covalent and ionic bonding with anion metathesis

Luminescent mesoporous materials were prepared by performing an anion metathesis reaction on ionic liquid modified SBA15, which has imidazolium chloride bridging units. The lanthanide β-diketonate complex anion was successfully anchored onto the SBA15 framework after the anion metathesis reaction. The resulting materials were characterized by FTIR, TEM, TGA, small-angle X-ray powder diffraction (SAXRD) and nitrogen adsorption-desorption isotherms. The photoluminescent properties of these materials were investigated in detail, and the results reveal that these hybrid mesoporous SBA15, prepared through this preparation approach, present favorable photoluminescent behavior such as high luminescent quantum efficiencies and long luminescent lifetimes.

Improving adsorption and activation of the lipase immobilized in amino-functionalized ordered mesoporous SBA-15

Ordered mesoporous SBA-15 was prepared by hydrothermal process and was functionalized with(3-aminopropyl) triethoxysilane (APTES) by post-synthesis-grafting method. The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS), small-angle X-ray powder diffraction (SAXRD), N 2 adsorption-desorption and Fourier transform infrared spectroscopy (FT-IR). The results indicated that SBA-15 had a 2-dimensional hexagonal p6 mm mesoscopic structure and the mesoscopic structure was remained after the functionalization procedure. The activities of porcine pancreatic lipase (PPL) immobilized in SBA-15 by physical adsorption and in APTES functionalized SBA-15 by chemical adsorption were studied by hydrolysis of triacetin. Chemically adsorbed PPL showed higher loading amount and catalytic activity comparing with physically adsorbed PPL. The stability of immobilized PPL against thermal and pH of reaction medium was significantly improved. Recycling experiments showed that chemically adsorbed PPL exhibited better reusability than physically adsorbed PPL.

Physical Stability Studies of Miscible Amorphous Solid Dispersions

Physical stability of 12 amorphous solid dispersions was evaluated over 9-22 months under ambient conditions using X-ray powder diffraction. The nine dispersions initially characterized as miscible drug-polymer systems all remained X-ray amorphous for the duration of their respective studies. In contrast, the three phase-separated systems all crystallized in 1-2 months, while the pure amorphous active pharmaceutical ingredients used in this study all crystallized within a few days, under the conditions of this study. Changes in the local order of dispersions that included polyvinylpyrrolidone were observed and appeared to correlate to periods of higher relative humidity (RH), reverting back to the original local order as the RH decreased. Phase-separation in the miscible dispersions as a result of ambient RH conditions did not appear to take place. Finally, formation of pores (voids) was observed through small-angle X-ray powder diffraction during crystallization of one model drug (felodipine).

Trimming Nanostructured Walls While Fluorinating their Surfaces: A Route to Making and Widening Pores of Nanoporous Materials and Efficient Catalysts

We report on the synthesis and characterization of highly ordered mesoporous fluorosilicas (OMFs) and nanoporous and corrugated fluorosilica nanospheres which contain 2.4−7.0 wt % F, corresponding to a loading of 1.3−3.7 mmol/g. Synthesis of these materials is carried out from parent mesoporous silicas (MCM-41 and SBA-15) and silica nanospheres under ambient conditions using dilute nonaqueous solutions of triethyloxonium tetrafluoroborate (Et3OBF4). As evidenced by nitrogen physisorption measurements, small angle powder X-ray diffraction (XRD), and transmission electron microscopy (TEM), fluorination of the mesostructures is accomplished with only minor alteration of the materials’ overall order. Detailed compositional analyses before and after fluorination are carried out with the aid of FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS) as well as elemental analysis proving the existence of silicon oxyfluoride species. FTIR studies show the appearance of new absorptions (730−750 cm−1) upon fluorination corresponding to [F6−nSi(OH)n]2−, O4/2SiF species or Si−O−Si stretches altered by the presence of nearby Si−F species as well as general broadening of the Si−O−Si asymmetric stretching region (1000−1200 cm−1). XPS analyses exhibit two distinct F species observed at 690.5 and 687.6 eV corresponding to silicon oxyfluoride (SiOF) and silicon fluoride (SiF), respectively. Surface silanol content is evaluated by 29Si HP-MAS NMR spectroscopy, which shows significant reductions in (Q2+Q3)/Q4 ratios from 1.26, 0.61, and 1.07 to 0.22, 0.38, and 0.61 for SBA-15, trimethylsilyl-capped SBA-15, and MCM-41 mesoporous silicas, respectively, because of the formation of (SiO3)SiF or pentacoordinated (SiO4)SiF species. The as-described synthetic procedure is also applied to sulfonic acid (−SO3H)-functionalized SBA-15. Enhancement of the acid-catalyzed ring opening of styrene oxide by aniline to produce the corresponding β-aminoalcohol by the fluorinated materials is presented. Ring opening of styrene oxide by aniline at room temperature after 4 h using −SO3H functionalized SBA-15 result in 77% conversion, whereas the as-synthesized OMF and OMF-SO3H materials exhibit 79% and 87% conversions, respectively. Fluorination of silica nanospheres with Et3OBF4 under similar conditions also produces etched nanoporous fluorosilica nanospheres with different degrees of exfoliation depending on the fluorination temperature.