Mono- and quaternary-ammonium functionalized mesoporous silica materials for nitrate adsorptive removal from water and wastewaters

Mesostructured porous silica SBA-15 materials functionalized with either primary or quaternary ammonium groups have been prepared by co-condensation and post-synthesis grafting using either aminopropyltriethoxysilane or N-((trimethoxysilyl)propyl)-N,N,N-trimethylammonium chloride as functional groups precursors. The materials functionalized with aminopropyl groups were further treated in acid solutions to convert the amine groups into charged propyl-ammonium groups. The physicochemical characteristics of the resulting adsorbent materials have been investigated using various techniques and discussed with respect to the nature of organo-functional groups in the materials. The adsorption performances were evaluated from batch experiments for the removal of nitrate anions from aqueous solutions. Results showed that adsorption capacity was influenced by the organic functional group nature and the functionalization strategy. In the case of propyl-ammonium functional groups, the adsorption capacity reached 46 and 55 mg NO₃ ^?/g for the materials synthesized via co-condensation and grafting, respectively. Similar tendency was observed in the case of propyl-trimethyl-ammonium organic functional groups where the grafted material registered a remarkably high capacity of 63 mg NO₃ ^?/g under the experimental conditions investigated.     

Synthesis and characterization of tungsten-incorporated mesoporous molecular sieve MCM-48 by one step

Tungsten-substituted mesoporous MCM-48 materials are successfully synthesized at 393 K by a one-step co-condensation sol–gel method. The prepared samples with different Si/W ratios are characterized by X-ray diffraction (XRD), nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), diffuse reflectance UV–visible spectroscopy and FT-IR, and the results indicate the presence and good dispersion of tungsten species inside the silica pores, the Si/W ratio is controlled above 28. When the Si/W ratio is less than 28, though no bulk tungsten is detected outside the MCM-48 mesoporous silica, the pore structure order becomes worse.     

Octadecyl grafted MCM-41 silica spheres using trifunctionalsilane precursors – preparation and characterization

MCM-41 silica spheres were prepared via the pseudomorphic route. Subsequent surface modification of the mesoporous silica spheres was achieved by two silylating agents, n-octadecyltrihydridosilane and n-octadecyltrimethoxysilane, which provided different surface coverages. The MCM-41 pore structure, surface properties and morphological features were examined by small angle X-ray scattering, nitrogen adsorption–desorption and scanning electron microscopy. The investigations revealed an influence of the silica source on the mesoporous structure, as reflected by a higher long-range order for the pores in MCM-41 spheres prepared from Kromasil silica. Surface modification is accompanied by a reduction of the surface area, pore diameter and pore volume of the MCM-41 materials, whereas the spherical morphology of the spheres is retained. The degree of grafting and cross-linking of the alkylsilanes was determined by ²⁹Si NMR spectroscopy. A higher degree of alkyl chain grafting was observed for the solvent extracted MCM-41 spheres and for samples prepared via surface polymerization.FTIR and ¹³C NMR spectroscopies were employed to study the conformational behaviour and mobility of the grafted octadecyl chains. The conformational order was found to strongly depend on the history of the MCM-41 supports (calcination, solvent extraction) and on the actual surface modification procedure. In general, a lower conformational order was observed for the present mesoporous alkyl modified silica spheres as compared to conventional C₁₈ modified silica gels which is mainly attributed to the lower surface coverage.     

Fe(III)-salim anchored MCM-41: synthesis,characterization and catalytic activity towards liquid phase cyclohexane oxidation

Abstract  

A novel organic–inorganic hybrid catalyst [MCM-41-Fe^III(salim)] was synthesized by covalently anchoring Fe^III(salim) complex into the pore channels of MCM-41. The material was synthesized by the co-condensation of tetraethyl orthosilicate (TEOS) and the precursor of salicylaldehyde modified with 3-aminopropyl triethoxysilane in the presence of cetyltrimethyl ammonium bromide (CTAB). The Fe(III)-salicylideneimine MCM-41 mesoporous silica was generated (in situ) by taking MCM-41-salimH (I) and FeCl₃ in ethanol solution. The immobilization of the complex on the functionalized silica was confirmed by small angle X-ray diffraction (XRD), N₂ adsorption–desorption, electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance UV–vis spectroscopy. Solid state CP-MAS NMR spectroscopy of ²⁹Si (²⁹Si CP-MAS NMR) showed a highly condensed siloxane network. Catalytic activity of the supported catalyst was examined by the oxidation of cyclohexane. Cyclohexane was successfully oxidized in good conversion (68%) to cyclohexanone, as a major product with 72% selectivity using tert. butylhydroperoxide as oxidant and acetonitrile as solvent. The catalysts can be reused up to three cycles without losing much of its activity.     

Selective removal of sulfur compounds in city-gas by adsorbents

Silver nitrate impregnated on beta zeolite (BEA), mesoporous silica MCM-41 and SBA-15 (AgNO₃/BEA, AgNO₃/MCM-41, AgNO₃/SBA-15) were prepared to remove sulfur compounds selectively in city-gas, which contains tetrahydrothiophene and tert-butylmercaptane. Sulfur adsorption capacity was determined when the sulfur concentration of effluent gas in breakthrough test reached 0.1 ppm, which is acceptable sulfur concentration for hydrogen production in a reformer for fuel cells. As the AgNO₃ concentration in AgNO₃/BEA, AgNO₃/MCM-41, and AgNO₃/SBA-15 increased, their sulfur adsorption capacities also increased. Although microporous zeolite BEA has smaller pore volume and lower surface area than those of mesoporous silica MCM-41 and SBA-15, the sulfur adsorption capacity of AgNO₃/BEA was higher than those of AgNO₃/MCM-41 and AgNO₃/SBA-15. Adsorbed sulfur molecules per impregnated silver nitrate and the shape change of breakthrough curves depending on the adsorption temperature showed that not only chemisorption but also physisorption was involved in sulfur compounds adsorption on AgNO₃ impregnated adsorbent. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Synthesis of chloropropylamine grafted mesoporous MCM-41, MCM-48 and SBA-15 from rice husk ash: their application to CO<Subscript>2</Subscript> chemisorption

Mesoporous siliceous MCM-41, MCM-48 and SBA-15 were synthesized using Rice Husk Ash (RHA) as the silica source. Their defective –OH sites were then grafted with 3-chloropropyl amine hydrochloride (3-CPA) and characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and BET techniques. Those results portrayed their resemblance with that synthesized from conventional silica sources. 3-CPA grafted mesoporous silicas were tested for CO₂ chemisorption over fixed bed reactor at different temperatures. The maximum adsorption of 1.7 mmol/g of CO₂ was observed on 3-CPA grafted SBA-15 (SBA-15/CPA) at 25°C. The chemisorbed CO₂ on amine grafted mesoporous silica was stabilized by weak hydrogen bonds formed during the nucleophilic attack between lone pair of electrons in amine groups and quadrupolar CO₂ with more degree of positive charge to form carbamates. The rapid steep slope which arises due to CO₂ adsorption illustrated a minimal mass transfer effect and extreme fast kinetics. Performance tests such as reproducibility, stability and selectivity towards CO₂ adsorption were also carried out over 3-CPA grafted mesoporous silica and the results were in line with that of well established CO₂ sorbent.     

Catalytic applications of sulfonic acid functionalized mesoporous organosilicas with different fraction of organic groups in the pore wall

Organosulfonic acid functionalized mesoporous organosilicas with different fraction of organic groups in the pore wall was synthesized in the presence of P123 (EO₂₀PO₇₀EO₂₀) by controlling the molar ratio of tetramethoxysilane (TMOS) to 1,2-bis(trimethoxysilyl)ethane (BTME) in the initial mixture during the co-condensation process of silane precursors in acidic medium. Structural characterizations (X-ray diffraction, nitrogen sorption analysis, and transmission electron microscopy) show that all materials have ordered hexagonal mesoporous structure with large pore diameter (7–9 nm). The existence of ethane and sulfonic acid groups in the material was verified by ²⁹Si MAS and ¹³C CP MAS NMR and X-ray photoelectron spectroscopy (XPS). The mesoporous solid acids can adsorb both water and hexane (the adsorption capacity for water and hexane is 240 and 600 mg/g, respectively) due to the existence of surface hydroxyl groups, propyl sulfonic acid group, and the ethane moiety. These mesoporous solid acids are efficient catalysts for the dehydration of 1-butanol and the hydration of propylene oxide (PO).     

Cubic Mesoporous Silica with Tailored Large Pores

MCM-48 silica was synthesized using GEMINI surfactant and its pore size was enlarged via a post-synthesis procedure in the presence of dimethyldecylamine (DMDA) as swelling agent. The effects of the amount of DMDA as well as the post-synthesis temperature on the pore size of the MCM-48 material were investigated. It was found that pore sizes up to 11.2 nm could be obtained. Generally, the pore size distributions were reasonably narrow and the pore volumes quite high (up to 2.6 cm³/g). The present work demonstrated the possibility to tailor the pore sizes of the MCM-48 silica.     

Factors affecting Hg(II) adsorption on hybrid nanostructured silicas: influence of the synthesis conditions

This paper reports the synthesis, characterization and mercury adsorption behaviour of new organic–inorganic hybrid nanostructured silicas obtained by co-condensation, molecular imprinting and post-synthesis routes. N₂ adsorption–desorption measurements, XRD, FT-IR, MAS NMR, SEM, TEM and elemental analysis were used to characterize the physico-chemical properties of the hybrid nanostructured materials. The materials were studied for Hg(II) adsorption in aqueous medium at pH 3 and compared with unmodified nanostructured silica. Mercury adsorption was higher in the hybrid material prepared by the co-condensation method that reached a mercury uptake of 134 mg Hg/g. The best mercury adsorption efficiency was observed for the hybrid material prepared by molecular imprinting route. The synthetic route employed clearly affects the textural properties of the silica, the amount of organic ligand attached onto the support and mercury adsorption behaviour.     

Adsorption of toluene on mesoporous materials from waste solar panel as silica source

The adsorption of toluene was tested with MCM-41 and mesoporous silica materials (S-MCM) synthesized from waste solar panel. X-ray powder diffraction (XRD), nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) were applied to characterize the prepared samples. In addition, the adsorption capacities of MCM-41 and S-MCM were almost the same which was observed according to the breakthrough experiments. The adsorption capacity of toluene in S-MCM was 57, 104, 200 and 277 mg g^− 1 for initial toluene concentrations of 250 to 1500 ppm respectively. The effects of the operation parameters, such as contact time and initial concentration on adsorption performance, were also tested in this study.     

Synthesis,characterization and catalytic properties of mesoporous MCM-48 containing zeolite secondary building units

Mesoporous aluminosilicate MCM-48 containing zeolite secondary building units in the pore wall has been synthesized in alkaline media with a two-step procedure. The aluminosilicate precursors comprising zeolite secondary building units were first synthesized by carefully controlling reaction conditions and then were assembled using co-templates of gemini surfactant [C₁₈H₃₇N(CH₃)₂(CH₂)₃-N(CH₃)₂C₁₈H₃₇]²⁺ (18-3-18) and triethanolamine (TEA). X-ray Diffraction (XRD) patterns of the as-made samples indicated that highly ordered mesostructured MCM-48 was formed. Transmission Electron Microscopy (TEM) images further verified the formation of MCM-48 with uniform cubic pore channel system having the pore opening diameter of about 25 ?. Compared with the conventionally synthesized MCM-48, the as-synthesized MCM-48 sample showed an adsorption band at 520–600 cm⁻¹ in its FT-IR spectrum, which was assigned to five-membered ring vibration from zeolite structure. This suggested the presence of zeolite building units in the pore wall. N₂ adsorption data showed that the material had a much higher specific surface area (1 200 m²/g) than the conventional MCM-48(1 100 m²/g). Finally, the catalytic performance of the as-made MCM-48 was evaluated by hydrogenation dealkylation reaction of heavy aromatic hydrocarbons. Catalytic results showed that the as-made MCM-48 catalyst exhibited higher conversion than the conventional MCM-48 catalyst. The as-made mesostructured MCM-48 may have a potential catalytic application in the conversion of bulky molecules. Translated from Journal of Fuel Chemistry and Technology, 2006, 34(1): 105–108 [译自: 燃料化学学报]     

Effects of poly (vinyl alcohol) (PVA) content on preparation of novel thiol-functionalized mesoporous PVA/SiO2 composite nanofiber membranes and their application for adsorption of heavy metal ions from aqueous solution

Thiol-functionalized mesoporous poly (vinyl alcohol)/SiO₂ composite nanofiber membranes and pure PVA nanofiber membranes were synthesized by electrospinning. The results of Fourier transform infrared (FTIR) indicated that the PVA/SiO₂ composite nanofibers were functionalized by mercapto groups via the hydrolysis polycondensation. The surface areas of the PVA/SiO₂ composite nanofiber membranes were >290 m²/g. The surface areas, pore diameters and pore volumes of PVA/SiO₂ composite nanofibers decreased as the PVA content increased. The adsorption capacities of the thiol-functionalized mesoporous PVA/SiO₂ composite nanofiber membranes were greater than the pure PVA nanofiber membranes. The largest adsorption capacity was 489.12 mg/g at 303 K. The mesoporous PVA/SiO₂ composite nanofiber membranes exhibited higher Cu²⁺ ion adsorption capacity than other reported nanofiber membranes. Furthermore, the adsorption capacity of the PVA/SiO₂ composite nanofiber membranes was maintained through six recycling processes. Consequently, these membranes can be promising materials for removing, and recovering, heavy metal ions in water.     

Simple one-pot synthesis of a mesoporous superacidic catalyst for the dehydration of glycerol to acrolein

Mesoporous silica containing a ZrO₂/SO₄²⁻ superacid catalyst (SZS) was synthesized via a simple one-pot process. ZrO₂/SO₄²⁻ (SZ) was introduced during the synthesis of the SBA-15. When the molar ratio of Zr to Si was less than 0.37 : 1, a 2D-hexagonal pore structure was maintained. The superacidic SZ was successfully supported on mesoporous silica resulting in superacidity. The prepared SZS catalysts were applied to the conversion of glycerol to acrolein by dehydration and had considerable catalytic activity. The present study describes the first attempt to utilize mesoporous silica-supported superacid catalysts in the dehydration of glycerol to produce acrolein.     

Design and synthesis of near-IR luminescent mesoporous materials covalently linked with tris(8-hydroxyquinolinate)lanthanide(III) complexes

By using the bifunctional ligand, 8-hydroxyquinoline-functionalized organosilane (Q-Si), the new mesoporous material Q–MCM-41 covalently bonded with 8-hydroxyquinoline was synthesized. Through the ligand exchange reaction, the new near-infrared (NIR) luminescent mesoporous LnQ₃–MCM-41 (Ln = Er, Nd, Yb) materials were prepared by linking the lanthanide quinolinate complexes to the ordered mesoporous Q–MCM-41 material. The LnQ₃–MCM-41 materials were characterized by powder X-ray diffraction and N₂ adsorption/desorption, and they all show the characteristic mesoporous structure of MCM-41 with highly uniform pore size distributions. Fluorescence spectra of these LnQ₃–MCM-41 materials were recorded and the corresponding luminescence decay analyses were measured. After ligand-mediated excitation, all the emission spectra of the LnQ₃–MCM-41 materials show the characteristic NIR-luminescence of the corresponding lanthanide ions via the intramolecular energy transfer from the ligands to the lanthanide ions. The good luminescent performances enable these NIR-luminescent mesoporous materials to have potential applications in optical amplification (operating at 1.3 or 1.5 μm) and laser systems, etc.     

Direct fabrication of mesoporous carbons using in-situ polymerized silica gel networks as a template

Mesoporous carbons were synthesized by in-situ polymerized silica gel networks as a template. The co-condensation of carbon precursor (sucrose) and silica precursor (sodium silicate) followed by heat treatment generated a carbon/silica nanocomposite. After etching the silica template, mesoporous carbons were obtained. Under optimum synthesis conditions a mesoporous carbon with a high surface area of >800 m²/g and a narrow pore size distribution centered at 3 nm was produced. The three-dimensionally interconnected silica structures effectively functioned as the template for the porous carbon materials.     

The relationship between the hydrophobic capacity and extraction efficiency of organic–inorganic hybrid mesoporous silicas for the determination of dibutyl phthalate by SPME–HPLC

Three kinds of organofunctionalized mesoporous silicas, including methyl-MCM-41, propyl-MCM-41 and octyl-MCM-41, were synthesized via one-step co-condensation and for the first time employed as the coatings of solid-phase microextraction fibers coupled with HPLC to extract dibutyl phthalate (DBP). The samples were characterized by fourier transform infrared, small-angle X-ray diffractometer, transmission electron microscope, thermogravimetry analysis and N₂ adsorption–desorption. The results showed that the organofunctionalized mesoporous silicas still preserve a desirable two-dimensional P6mm hexagonal structure with large pore volume, good thermal stability and strong hydrophobicity after introducing alkyl groups of various carbon chains to the framework of MCM-41. When the concentration of DBP in standard solution is 1.0 × 10^?9 mol L^?1, the extraction efficiency of octyl-MCM-41, propyl-MCM-41 and methyl-MCM-41 is 5.7, 4.6 and 4.1 times higher than that of the pure MCM-41, respectively.     

Ternary rare earth sulfoxide-functionalized mesoporous hybrids Phen-RE (OBDS(BSAB))3-SBA-15 (RE = Eu, Tb): Coordination bonding assembly, characterization, and photoluminescence

Novel mesoporous SBA-15 type of hybrid materials (OBDS-SBA-15 and BSAB-SBA-15) are synthesized by co-condensation of tetraethoxysilane (TEOS) and the modified sulfoxide (OBDSSi and BSABSi, OBDS = oxobenzyldimethyl sulphoxide, BSAB = benzylsulfingl acetylbenzene) in the presence of Pluronic P123 surfactant as a template. The preservation of the organic ligand structure during the hydrothermal synthesis and the surfactant extraction process is confirmed by Fourier transform infrared FTIR, TGA and XRD measurements. Novel luminescent organic-inorganic mesoporous hybrids containing RE³⁺ (Eu³⁺, Tb³⁺) complexes and functionalized mesoporous silica matrix SBA-15 (OBDS-SBA-15 and BSAB-SBA-15) have been assembled with chemical bonding, which are designated as Phen-RE(OBDS)₃-SBA-15 and Phen-RE(PPS)₃-SBA-15, are obtained by introducing the RE(NO₃)₃ and 1,10-phenanthroline (Phen) complexes into the hybrid materials via the coordination reaction. The mesostructure of hybrid materials (OBDS-SBA-15 and BSAB-SBA-15) is characterized by TEM, XRD and N₂ adsorption measurements. The luminescence properties of these resulting materials are characterized in details, which reveals that the Phen-RE(OBDS)₃-SBA-15 mesoporous hybrids exhibit stronger luminescent intensities, longer lifetimes and higher luminescent quantum efficiencies than those of Phen-RE(BSAB)₃-SBA-15 hybrids.     

Ordered thiol-functionalized mesoporous silica with macrostructure by true liquid crystal templating route

Ordered thiol-functionalized mesoporous silica has successfully been synthesized via co-condensation of tetramethyl orthosilicate (TMOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) in lyotropic liquid crystalline phase of Brij 56 surfactact (C₁₆EO₁₀). In contrast to the common synthesis in micellar solution, true liquid crystal templating synthesis can easily fabricate organic-functionalized mesoporous silica with desirable macro-morphology and the loading amount of organic moieties can also be controlled well. The resultant materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), nitrogen sorption, polarized optical microscopy, Fourier transform infrared (FT-IR) spectra, differential scanning calorimetry and thermogravimetric analysis (DSC–TGA), and elemental analyses (EA). Direct evidence of the presence of chemically attached thiol groups was provided by FT-IR, DSC–TGA and EA. Adsorption measurement indicates that the materials are effective for the removal of heavy metal ions from aqueous solutions. The Hg²⁺ adsorption isotherm fits Langmuir behavior, but the Type-IV adsorption isotherm for Cd²⁺ was unexpectedly observed, which is probably attributed to significantly different Cd²⁺ affinity ability for the thiol groups on the external surface and those lining the framework pore channels of the nanoporous adsorbent.     

Colloidal templating synthesis and adsorption characteristics of microporous–mesoporous carbons from Kraft lignin

Microporous–mesoporous carbons were synthesized via colloidal silica templating using Kraft lignin as a carbon precursor, which is a waste byproduct from paper industry. A unique feature of these carbons are uniform spherical mesopores achieved after dissolving colloidal silica used as a hard template, while micropores were created by post-synthesis CO₂ activation. The resulting activated lignin-based carbons possessed high specific surface area (up to 2000 m²/g) and microporosity and mesoporosity easily tunable by adjusting activation conditions and optimizing the amount and particle size of the colloidal silica used. The total pore volumes of activated carbons obtained by using 20 and 13 nm silica colloids as a hard template exceeded 1 and 2 cm³/g, respectively.     

Utilization of mesoporous molecular sieves synthesized from natural source rice husk silica to Chlorinated Volatile Organic Compounds (CVOCs) adsorption

The adsorption of trichloroethylene (TCE), tetrachloroethylene (PCE), and carbon tetrachloride was studied over our synthesized mesoporous material, MCM-41, from rice husk silica source, abbreviated as RH-MCM-41. More than 99% silica for RH-MCM-41 synthesis was extracted from rice husk under refluxing in HBr solution and then calcined at 873 K for 4 hours. RH-MCM-41 possessed surface area around 750-1,100 m²/g with a uniform pore size with an average diameter of 2.95 nm, narrow range of pore distribution and somewhat hexagonal structure, similar to properties of parent MCM-41. The adsorption of CC1₄ to RH-MCM-41 was stronger than that of TCE and PCE. The adsorption capacity of RH-MCM-41 for CVOCs (chlorinated volatile organic compounds) was higher than commercial mordenite and activated carbons.