Functionalized SBA-15 materials for bilirubin adsorption

To investigate the driving force for bilirubin adsorption on mesoporous materials, a comparative study was carried out between pure siliceous SBA-15 and three functionalized SBA-15 mesoporous materials: CH₃-SBA-15 (MS), NH₂-SBA-15 (AS), and CH₃/NH₂-SBA-15 (AMS) that were synthesized by one-pot method. The obtained materials exhibited large surface areas (553-810 m²/g) and pore size (6.6-7.1 nm) demonstrated by XRD and N₂-ad/desorption analysis. The SEM images showed that the materials had similar fiberlike morphology. The functionalization extent was calculated according to ²⁹Si MAS NMR spectra and it was close to the designed value (10%). The synthesized mesoporous materials were used as bilirubin adsorbents and showed higher bilirubin adsorption capacities than the commercial active carbon. The adsorption capacities of amine functionalized samples AMS and AS were larger than those of pure siliceous SBA-15 and MS, indicating that electrostatic interaction was the dominant driving force for bilirubin adsorption on mesoporous materials. Increasing the ionic strength of bilirubin solution by adding NaCl would decrease the bilirubin adsorption capacity of mesoporous material, which further demonstrated that the electrostatic interaction was the dominant driving force for bilirubin adsorption. In addition, the hydrophobic interaction provided by methyl groups could promote the bilirubin adsorption.     

Layer by layer growth of silver chloride nanoparticle within the pore channels of SBA-15/SO3H mesoporous silica (AgClNP/SBA-15/SO3K): Synthesis,characterization and antibacterial properties

The growth of silver chloride nanoparticles within the pore channels of functionalized SBA-15 mesoporous was achieved by sequential dipping steps in alternating bath of potassium chloride and silver nitrate under ultrasound irradiation at pH=9. The effects of sequential dipping steps in growth of the AgCl nanoparticles have been studied. The growth and formation of AgCl nanoparticles inside the sulfonated SBA-15 were characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Antibacterial activity of the synthesized materials was investigated against Escherichia coli (E.coli) using the conventional diffusion-disc method. The materials showed high antibacterial activity.     

CO2 adsorption on branched polyethyleneimine-impregnated mesoporous silica SBA-15

Adsorption of pure CO₂ on SBA-15 impregnated with branched polyethyleneimine (PEI) has been studied. Materials were prepared by impregnating the pore surface of SBA-15 mesoporous silica with different amounts of branched PEI (10, 30, 50 and 70 wt%). Textural properties, elemental analysis and low angle XRD measurements of the prepared samples showed a progressive pore filling of SBA-15 as PEI loading was increased. Pure CO₂ adsorption isotherms on these modified SBA-15 materials were obtained at 45 °C, showing high adsorption efficiency for CO₂ removal at 1 bar. Chemisorption of CO₂ on amino sites of the modified SBA-15 seems to be the main adsorption mechanism. PEI content of impregnated SBA-15 influences the adsorption capacity of the material, being a relevant variable for CO₂ removal by adsorption. Temperature effect on adsorption was also studied in the range 25-75 °C, showing that temperature strongly influences CO₂ adsorption capacity. Adsorption capacity was also tested after regeneration of the PEI-impregnated SBA-15 materials. Our results show that these branched PEI-impregnated materials are very efficient even at low pressure and after several adsorption-regeneration cycles.     

Green approaches via nanocatalysis with nanoporous materials: Functionalization of mesoporous materials for single site catalysis

Among the various green keys, catalysis, especially using heterogeneous catalysts, has been powerfully applied to achieve greener chemical processes. Here are presented nanoporous materials which have mesoporosity with the functional groups on the inner pore walls. The materials were synthesized via a rather greener process, such as microwave synthesis, and over these nanocatalysts some of the green chemical reactions were carried out with high activities and selectivities. Cobalt species has been successfully functionalized and stabilized as a Co(III) complex onto SBA-15 support and proven to be an active catalyst in alkylaromatic oxidation with molecular oxygen, styrene epoxidation with tert-butyl hydroperoxide (TBHP), and allylic oxidation of cycloolefins with H₂O₂. Short-channeled amino-functionalized SBA-15 catalyst with hexagonal plate morphology was synthesized directly by using microwave synthesis from the co-condensation of aminopropyl triethoxysilane (APTES) and sodium metasilicate under a strong acidic condition. The catalyst showed high catalytic activity in liquid-phase Knoevenagel condensation reactions, due to easy diffusion and mass transfer of substrates into the short mesopore channel. The HO₃S–SBA-15 was prepared by grafting of mercaptopropyl trimethoxysilane onto the calcined mesoporous silica surface and subsequently oxidized with H₂O₂. The resulting catalyst was applied as a Bronsted solid-acid catalyst for the esterification of oleic acid with methanol.     

A novel method for preparation of 8-hydroxyquinoline functionalized mesoporous silica: Aluminum complexes and photoluminescence studies

8-Hydroxyquinoline (8-HQ) was attached to mesoporous silica by sulfonamide bond formation between 8-hydroxyquinoline-5-sulfonyl chloride (8-HQ-SO₂Cl) and aminopropyl functionalized SBA-15 (designated as SBA-SPS-Q) and then aluminum complexes of 8-HQ was covalently bonded to SBA-SPS-Q using coordinating ability of grafted 8-HQ.The prepared materials were characterized by powder X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier transform infrared (FT-IR), thermal analysis (TGA-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental analysis and fluorescence spectra. The environmental effects on the emission spectra of grafted 8-HQ and its complexes were studied and discussed in details.     

Optical oxygen sensing materials based on a novel dirhenium(I) complex assembled in mesoporous silica

A new dirhenium(I) complex fac-[{Re(CO)₃(4,7-dinonadecyl-1,10-phenanthro -line)}₂ (4,4′-bipyridyl)] (trifluoromethanesulfonate)₂ (denoted as D-Re(I) ) is assembled in MCM-41 and SBA-15 type mesoporous silica support. The emission peaks of D-Re(I) in D-Re(I)/MCM-41 and D-Re(I)/SBA-15 are observed at 522 and 517 nm, respectively. Their long excited lifetimes, which are of the order of microseconds, indicate the presence of phosphorescence emission arising from the metal to ligand charge-transfer (MLCT) transition. The luminescence intensities of D-Re(I)/MCM-41 and D-Re(I)/SBA-15 decrease remarkably with increase in the oxygen concentration, meaning that they can be used as optical oxygen sensing materials based on luminescence quenching. The ratios I₀/I₁₀₀ of D-Re(I)/MCM-41 and D-Re(I)/SBA-15 are estimated to be 5.6 and 20.1, respectively. The obtained Stern-Volmer oxygen quenching plots of the mesoporous sensing materials could be fitted well to the two-site Demas model and Lehrer model.     

Studies on ordered mesoporous materials for potential environmental and clean energy applications

Two series of ordered mesoporous materials, SBA-15 silica and CMK-3 carbon were synthesized. The ordered nanostructure of these materials was confirmed by TEM and XRD analysis. Structural parameters including the specific surface area, pore volume and pore size distribution were determined on the basis of nitrogen adsorption data at 77 K. Potential applications of these materials were explored in relation to the CO₂ sequestering, methane storage and fuel desulfurization. Initial studies of both materials showed their usefulness for environmental and clean energy applications. SBA-15 modified with triethanolamine showed a very good adsorption selectivity for CO₂ while its adsorption reversibility was retained. Also, this material after CuCl deposition was useful for removal of fuel thiophenes. However, CMK-3 was shown to be promising material for storage of natural gas. As high as 41 wt.% of methane was stored in this material in the presence of appropriate amount of water.     

The instant-direct-templating synthesis of phenyl-functionalized HOM-type mesoporous silica materials

Two kinds of novel phenyl-functionalized mesoporous silica materials have fabricated for the first time by an instant-direct-templating method using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and tetraethyl orthosilicate as surfactant template and precursor, respectively. Samples were characterized by Fourier transform infrared spectroscopy, small-angle X-ray diffraction, thermogravimetric analysis, N₂ adsorption-desorption, scanning electron micrography and transmission electron micrography. The results show that phenyl groups are attached covalently to the pore wall of mesoporous materials after modification. The functionalized materials still preserve a desirable ordered hexagonal P6mm and cubic Ia3d mesophase structure, respectively, have high specific surface area, large pore volume and narrow pore size distribution.     

Facile synthesis and characterization of acid-base bifunctionalized mesoporous silica

A simple acid-base bifunctionalized approach has been developed through grinding the precursors, magnesium and aluminium nitrates, with the as-prepared SBA-15, and then the generation of acid-base active sites and removal of host template were combined into a single step in the subsequent calcination procedure. A series of acid-base bifunctional mesoporous materials MgO-Al₂O₃-SBA-15 (MA-SBA-15) have been successfully synthesized by means of this approach. X-ray diffraction (XRD), high-resolution transmission electron microscopes (HRTEMs), N₂ adsorption, FT-IR spectra, ²⁷Al and ²⁹Si magic-angle-spinning (MAS) NMR, NH₃- and CO₂-temperature programmed desorption (TPD), pyridine adsorption were employed to characterize the resultant mesoporous materials. The results indicate that the guests can be well dispersed in the channel of SBA-15, and the resultant materials exhibit excellent acid-basic properties with well mesoporous backbone, which make it possessing high activity for the synthesis of ethyl methyl carbonate, an important asymmetric carbonate ester compound.     

An experimental study on the effect of mesoporous silica addition on ion conductivity of poly(ethylene oxide) electrolytes

Solid polymer electrolyte (SPE) composites, which are composed of poly(ethylene oxide) (PEO), mesoporous silica (SBA-15), and lithium salt were prepared in order to investigate the influence of SBA-15 content on the ionic conductivity of the composites. The ionic conductivity of the SPE composites was monitored by frequency response analyzer (FRA), and the crystallinity of the SPE composites was evaluated by using XRD. As a result, the addition of SBA-15 to the polymer mixture inhibited the growth of PEO crystalline domain, due to the mesoporous structure of the SBA-15. Also, the PEO₁₆LiClO₄/SBA-15 composite electrolytes show an increased ion conductivity as a function of SBA-15 content up to 15 wt.%. These ion conductivity characteristics are dependent on crystallinity with SBA-15 content.     

Adsorption studies of thermal stability of SBA-16 mesoporous silicas

Cage-like ordered mesoporous silicas, SBA-16, and ethane-silicas with cubic (Im3m) and (Fm3m) symmetry groups were synthesized with addition of sodium chloride by using tetraethyl orthosilicate (TEOS) as silica precursor, 1,2-bis(triethoxysilyl)ethane (BTESE) as bridged silsesquioxane and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymer Pluronic F127 (EO₁₀₆PO₇₀EO₁₀₆) as template at low acid concentrations. The resulting samples were subjected to extraction in order to remove the polymeric template. The as-synthesized and extracted materials were calcined in the range of 350-900 °C to determine their thermal stability. Based on the XRD analysis and nitrogen adsorption data such as the BET specific surface area, volume of primary mesopores, pore wall thickness and pore size distributions, the SBA-16 silicas exhibit relatively high thermal stability because their mesostructural ordering was retained even up to 900 °C. However, an increase in the calcination temperature tended to decrease significantly the BET surface area, volumes of primary and complementary pores, and to less extent the pore size and pore wall thickness due to the structural shrinkage. Furthermore, the as synthesized samples subjected to a short extraction with acidic ethanol solution possessed even better thermal stability. On the other hand, calcination at 550 °C of ethane-silicas caused a complete removal of the ethane bridging groups from the periodic mesoporous organosilicas and their calcination above 800 °C led to the partial collapse of the structure.     

Synthesis and characterization of MnWO4 nanoparticles encapsulated in mesoporous silica SBA-15 by fast microwave-assisted method

The MnWO₄ nanoparticles encapsulated in mesoporous silica (MnWO₄/SBA-15) was successfully synthesized by a fast microwave-assisted method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption–desorption isotherm, and Fourier transform infrared spectroscopy (FTIR). Our results showed that the MnWO₄/SBA-15 nanocomposites have the ordered hexagonal meso-structure of SBA-15, indicating MnWO₄ nanoparticles were successfully distributed into the channels of SBA-15. The size of MnWO₄ nanoparticles in SBA-15 is significantly smaller than the size of MnWO₄ nanoparticles prepared without SBA-15, indicating that the MnWO₄/SBA15 nanocomposites would be very promising for improving photocatalytic activity of MnWO₄ nanoparticles.     

Facile post-synthesis and photocatalytic activity of N-doped ZnO–SBA-15

N-doped ZnO–SBA-15 materials (denoted as nN–xZnO–SBA-15, where n is number of urea treatments and x is the weight ratio of ZnO/(ZnO+SBA-15)) were successfully synthesized by a two-step procedure. First, xZnO–SBA-15 was prepared by impregnating SBA-15 with Zn(NO₃)₂, followed by calcinating at 550 °C. In the second step, xZnO–SBA-15 was modified n times by doping nitrogen with the assistance of urea. The resulting nN–xZnO–SBA-15 materials prepared with various numbers of urea treatments were characterized by XRD, TEM, SEM, EDS, N₂ adsorption/desorption at 77 K, diffuse reflectance UV–vis, and XPS. The results show that the nN–xZnO–SBA-15 maintains its ordered hexagonal mesostructure and exhibits light absorbance in the visible region. The nN–xZnO–SBA-15 samples were investigated with the photodegradation of methylene blue under visible light, and exhibited significant photocatalytic activity. The kinetics of the reaction obeyed the Langmuir–Hinshelwood model.     

Preparation and characterization of L-Leucine-modified amphiprotic bifunctional mesoporous SBA-15 molecular sieve as a drug carrier for ribavirin

In this study, an amphiphilic bifunctional mesoporous SBA-15 material (AMPBIF-SBA-15) was synthesized through post-synthesis method as a drug carrier. Ribavirin was selected as the model drug and whose release from both unmodified and functionalized SBA-15 was evaluated in four media solutions with different pH or ionic strength. The release process indicated that AMPBIF-SBA-15 was a pH-sensitive drug carrier, which showed a phased low-release effect to ribavirin in the simulated body fluid (PBS, pH 7.4) solution. The materials were further characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption measurements and elemental analysis. This study provided a novel drug carrier for ribavirin to improve curative effect of ribavirin.     

Template occluded SBA-15: An effective dissolution enhancer for poorly water-soluble drug

The aim of the present work was to improve the dissolution rate of piroxicam by inclusion into template occluded SBA-15. Our strategy involves directly introducing piroxicam into as-prepared SBA-15 occluded with P123 (EO₂₀PO₇₀EO₂₀) by self assembling method in acetonitrile/methylene chloride mixture solution. Ultraviolet spectrometry experiment and thermogravimetric analysis-differential scanning calorimetry (TG-DSC) profiles show that the piroxicam and P123 contents in the inclusion compound are 12 wt% and 28 wt%, respectively. X-ray powder diffraction and DSC analysis reveal that the included piroxicam is arranged in amorphous form. N₂ adsorption-desorption experiment indicates that the piroxicam has been introduced to the mesopores instead of precipitating at the outside of the silica material. The inclusion compound was submitted to in vitro dissolution tests, the results show that the piroxicam dissolve from template occluded inclusion compound more rapidly, than these from the piroxicam crystalline and template removed samples in all tested conditions. Thus a facile method to improve the dissolution rate of poorly water-soluble drug was established, and this discovery opens a new avenue for the utilization of templates used for the synthesis of mesoporous materials.     

Crystallization of mesoporous silica SBA-15 in a high pressure hydrothermal environment

Mesoporous silica SBA-15 (with ～6?nm pore size and ～6?nm wall thickness) was exposed to a hydrothermal environment at 2 and 5?GPa. The p,T quenched products were investigated by powder X-ray diffraction and transmission electron microscopy. Infrared spectroscopy and thermogravimetric analysis of a sample subjected to 5?GPa at room temperature suggests functionalization of both inner and outer pore surface by silanol. Partial transformation to nano-sized (20–50?nm) coesite crystals with nonfaceted morphology was observed during short equilibration times of 2?h at 125°C, which is significantly below the melting point of water (～250°C). Untransformed SBA-15 maintained intact pore structure. At 175°C and during 8?h, SBA-15 transformed completely into faceted coesite crystals with dimensions 100–300?nm, suggesting Ostwald ripening and thus significant mass transport in the solid water environment. At 2?GPa the melting point of water is near 70°C. Partial transformation to nano-sized α-quartz was observed at 65°C and during 2?h. Untransformed SBA-15 partially pore collapsed. The reduced pore stability of SBA-15 at 2?GPa is attributed to the presence of liquid water in the pores due to melting point depression of confined water.     

Development of TREN dendrimers over mesoporous SBA-15 for CO2 adsorption

Mesoporous SBA-15 was synthesized using rice husk ash (RHA) as the silica source and their defective Si-OH groups were grafted with tris(2-aminoethyl) amine (TREN) dendrimers generation through step-wise growth technique. The X-ray diffraction (XRD) and nitrogen adsorption/desorption results of parent SBA-15 obtained from RHA, suggests its resemblance with SBA-15 synthesized using conventional silica sources. Furthermore, the nitrogen adsorption/desorption results of SBA-15/TREN dendrimer generations (G1-G3) illustrates the growth of dendrimer inside the mesopores of SBA-15 and their CO₂ adsorption capacity was determined at 25 °C. The maximum CO₂ adsorption capacity of 5-6 and 7-8 wt% over second and third dendrimer generation was observed which is discernibly higher than the reported melamine and PAMAM dendrimers. The experimental CO₂ adsorption capacity was found to be less than theoretically calculated CO₂ adsorption capacity due to inter and intra molecular amidation as result of steric hindrance during the dendrimer growth. These SBA-15/TREN dendrimer generations also exhibit thermal stability up to 350 °C and CO₂ adsorption capacity remains unaltered upon seven consecutive runs.     

Properties of SBA-15 modified by iron nanoparticles as potential hydrogen adsorbents and sensors

SBA-15-Fe was synthesized via the incorporation of Fe⁰ nanoparticles (Fe(0)-Nps) in the mesoporous channels. Electron microscopy and X-ray diffraction showed that dispersion of fine iron NPs occurs mainly inside the channels of SBA-15, producing a slight structure compaction. This was accompanied by a significant improvement of both the affinity towards hydrogen and electrical conductivity, as supported by hydrogen adsorption tests and impedance measurements. CO₂ thermal programmed desorption measurements revealed an attenuation of the acid character of the solid surface. This was explained in terms of strong iron interaction with the lattice oxygen atoms that reduces the SiO–H bond polarity. The close vicinity of fine Fe(0)-Nps combined with the large pore size of SBA-15 appear to contribute to a synergistic improvement of the electrical conductivity. The results reported herein open new prospects for SBA-15 as potential adsorbents for hydrogen storage and carriers for hydrogen sensors. The use of iron in lieu of noble metals for designing such materials is a novelty, because such applications of iron-loaded silica have not been envisaged so far due to the high reactivity of iron towards air and water. The development of such technologies, if any, should address this issue.     

Synthesis and characterization of molybdenum incorporated mesoporous aluminophosphate

A synthesis of molybdenum incorporated mesoporous aluminophosphate with long-chain n-alkylamine as template material had been prepared under non-aqueous condition. These materials were extensively characterized by using X-ray diffraction (XRD), nitrogen sorption isotherms, nuclear magnetic resonance of ²⁷Al and ³¹P (NMR), inductive coupled plasma (ICP), electron spin resonance (ESR), Fourier transform infrared (FTIR) and thermogravimetric-differential thermal analysis (TG-DTA). Morphology of the materials had been observed by using transmission electron microscope (TEM) that revealed the mesoporous materials possessed wormhole-like structures. Alkaline solvent extraction using n-butylamine/ethanol had been efficiently removed the n-alkylamine from the mesoporous samples which yielded BET surface areas around 550-730 m²/g. BJH analysis showed a narrow pore size distribution which increased with increasing of the carbon chain length of alkylamine (template). Valence state and coordination of the molybdenum in the obtained samples were investigated by using ESR and FTIR where it was found that Mo⁴⁺ and Mo⁶⁺ molybdenum species existed in the molybdenum incorporated mesoporous aluminophosphate in tetrahedral coordination.     

Structure and acid-base properties of surface-modified mesoporous silica

A series of surface-modified mesoporous silica endowing with acid-base properties have been successfully synthesized in one pot by in situ introduction of zirconium and magnesium salts into the initial mixture of synthesizing mesoporous silica (SBA-15) and this method combines into a single step to form a novel material with a periodically ordered mesoporous backbone and specific chemical reactivity of the acid-basic sites. X-ray diffraction, high-resolution transmission electron microscopes (HRTEM), N₂ adsorption, FT-IR transmission spectra, ²⁹Si MAS NMR spectra, NH₃- and CO₂-temperature programmed desorption (TPD) are employed to characterize the titled mesoporous materials. The results indicate that the product possesses excellent acid-basic properties with well mesoporous structure, which make it promising for their application in heterogeneous catalysis and adsorption-separation processes.