CO2 adsorption on amine-modified mesoporous silicas

Mesoporous silicas with enhanced pore structures were synthesized and polyethylenimine (PEI) was immobilized in them to produce adsorbents for CO₂. The prepared samples were characterized by N₂ adsorption–desorption isotherms and small angle X-ray diffraction, and their CO₂ adsorption performance were evaluated. CO₂ adsorption capacity increased with operating temperature initially and then decreased. Besides, CO₂ adsorption capacity increased due to the PEI loading with more amine sites. The results showed that the structure of support played an important role in the CO₂ adsorption capacity. High surface area and large pore volume also favored the CO₂ adsorption capacity.     

Template synthesis of mesoporous silicas containing phosphonic groups

Mesoporous silicas containing the functional group ≡Si(CH₂)₂P(O)(OC₂H₅)₂ in the surface layer have been obtained using the template method (template—P123). Their treatment by a concentrated hydrochloric acid results in the formation of functional groups of the composition ≡Si(CH₂)₂P(O)(OH)₂ that is in agreement with the IR spectroscopy data. It has been shown that the above treatment causes an increase of the sample specific surface area (up to 605 m²/g), sorption capacity, and pore diameter. As established by means of the CP/MAS NMR spectroscopy on ³¹P nuclei, the sample drying in vacuum at 110°C results in the formation of fragments ≡Si(CH₂)₂P(O)(OH)—OSi≡ with the content of 10–15 wt %. However, according to the TEM data, the sample mesoporous structure is retained.     

有机-无机杂化介孔二氧化硅的合成及应用

有机-无机杂化介孔材料因其具有显著的活性中心、较高的机械和水热稳定性等特点,成为国内外学者广泛关注的热点研究材料。综述了有机-无机杂化介孔二氧化硅材料的主要合成方法,包括后合成法、共缩聚法和有序介孔有机硅法,并对3种方法存在的优缺点进行了比较。同时详细介绍了有机-无机杂化介孔二氧化硅材料在催化、环境保护、生物医药和光学领域的应用。并展望了有机-无机杂化介孔二氧化硅材料的发展及应用前景。     

有机-无机杂化介孔二氧化硅的合成及应用

有机-无机杂化介孔材料因其具有显著的活性中心、较高的机械和水热稳定性等特点,成为国内外学者广泛关注的热点研究材料。综述了有机-无机杂化介孔二氧化硅材料的主要合成方法,包括后合成法、共缩聚法和有序介孔有机硅法,并对3种方法存在的优缺点进行了比较。同时详细介绍了有机-无机杂化介孔二氧化硅材料在催化、环境保护、生物医药和光学领域的应用。并展望了有机-无机杂化介孔二氧化硅材料的发展及应用前景。     

Removal of reactive dyes using organofunctionalized mesoporous silicas

Mesoporous inorganic–organic hybrids with mono- or bifunctional pendant chains anchored onto the silica backbones were investigated for reactive dye removal. The organofunctionalized silicas obtained from silylating agents contain the functional groups: 3-aminopropyl, octadecyldimethyl(silylpropyl)ammonium and 3-mercaptopropyl. The pendant electrophilic chains attached on the new porous silicas interact with the negative charge of industrial textile reactive dyes: yellow GR, red RB and blue RN. The best maximum sorption results were obtained for both mercapto and amino groups, to give 351, 388 and 203 mg g^?1 for GR, RN and RB dyes. These silicas also have the advantage of undergoing sorption without initial pH adjustment and surface saturation in short times. The high sorption capacity is due to the combination of properties associated with higher pore volume, surface area, smaller particle and the presence of two different functional groups, also emphasizing the presence of one mercapto group in the hybrid. These silicas, mainly the structurally bifunctional arrangement, with available disposition of pendant chains, are promising for textile effluent removal.     

Hydrolysis of sugars catalyzed by water-tolerant sulfonated mesoporous silicas

Mesoporous silicas are modified with sulfonic acid groups either by one-pot or by grafting method. In the hydrolysis of sucrose and starch, the sulfonated mesoporous silicas work as water-tolerant recyclable solid acid catalysts, showing higher conversion and turnover frequency than conventional Amberlyst-15, Nafion-silica and HZSM-5 catalysts.     

介孔分子筛改性及在吸附脱硫中的应用

介孔分子筛由于具有较大的比表面积、孔容、孔径等优点使得其在吸附分离等领域得到了广泛的应用。本文综述了介孔分子筛改性的不同方法,包括嵌入法、负载法,以及有机-无机杂化介孔材料的制备等。对介孔分子筛在吸附脱硫方面的最新研究进展进行了总结,包括对燃料油、天然气、煤气中硫化物的吸附脱除,以及H2S、SO2等大气污染物的吸附脱除。同时对介孔分子筛的改性及发展前景进行了展望,合成新型有机-无机杂化介孔材料并将其应用于吸附等领域是未来发展的主要趋势。     

新型介孔硅胶材料对西维因吸附性能的研究

以两种表面活性剂十六烷基三甲基溴化铵、溴代十六烷基吡啶和N-1-萘基乙二胺盐酸盐为模板,合成了3种介孔硅胶前驱体材料;以荧光为检测手段,分别考察了它们对氨基甲酸酯类农药西维因的吸附性能,结果显示,以N-1-萘基乙二胺盐酸盐为模板合成的新型介孔硅胶对西维因的吸附性最强,吸附率为99.7%;研究了西维因的光谱特性;结合3种模板分子和西维因的结构特点,对吸附机理进行了探讨.     

Design of multifunctionalized mesoporous silicas for esterification of fatty acid

Organosulfonic acid mesoporous silicas further functionalized with hydrophobic organic groups were synthesized via postsynthesis grafting and one-step co-condensation methods. The resulting materials were tested in the esterification of fatty acid with methanol to produce methyl esters as a pretreatment step in the production of biodiesel. Incorporation of the hydrophobic group into the organic–inorganic hybrid acid catalyst was found to improve the performance of the resulting catalyst. However, the performance of the multifunctionalized mesoporous materials demonstrated a strong dependence on the incorporation method and on the size of the hydrophobic organic groups. Solution effects within the reaction mixture appeared to influence the catalytic activity of the catalysts. The results indicate the potential for intentional design of the catalytic environment at a molecular level with the use of organic–inorganic mesoporous materials.     

Synthesis, characterization and phenol adsorption of carbonyl-functionalized mesoporous silicas

Carbonyl-functionalized mesoporous silicas have been synthesized by co-condensation of tetraethoxysilane and varying contents of 3-(trimethoxysilyl)propyl methacrylate in acidic medium with the block copolymer Pluronic 123 as a structure directing agent. The functionalized materials were characterized by PXRD, TEM, SEM, IR, and N₂ adsorption?Cdesorption at 77?K. Adsorption of phenol in aqueous solution on the materials has been investigated. The experimental results showed that carbonyl-functionalized mesoporous silicas possess strong adsorption ability for phenol with interaction of O-H??O?=?C hydrogen bond. The adsorption data are fitted to Langmuir Isotherms and a maximum adsorption capacity calculated from the Langmuir equation can reach 0.87?mmol of phenol/g. The effect of the pH on phenol adsorption has been studied.     

Adsorption of phosphate and nitrate anions on ammonium-functionnalized mesoporous silicas

Surface modified mesostructured silica materials represent potential adsorbents offering an opportunity to remediate several important water pollutants. In the present work, ammonium-functionnalized MCM-41, MCM-48 and SBA-15 mesoporous silica materials were synthesized via post-synthesis grafting and co-condensation. Their efficiency to remove nitrate and phosphate anions in aqueous solutions was investigated. The adsorbent materials showed high adsorption capacities reaching 46.5 mg NO₃⁻/g and 55.9 mg H₂PO₄⁻/g under the operating conditions explored. The mesoporous silica materials functionalized via post-synthesis grafting method exhibited higher performances in terms of percentage pollutant removal and adsorption capacities if compared to their analogs synthesized according to the co-condensation strategy.     

Catalytic behavior of vanadium-containing mesoporous silicas in the oxidative dehydrogenation of propane

Three series of vanadium-containing silica catalysts (2–7.6 wt% V) have been prepared by varying the synthesis method. In all cases, conversion values in the oxidative dehydrogenation of propane increase with the temperature, vanadium loading and reducibility. For impregnated and anchored catalysts, a relationship between the selectivity towards propene and the effective acidity, as determined in the dehydration of 2-propanol, can be established. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gold and iron nanoparticles in mesoporous silicas: Preparation and characterization

Gold and iron oxide nanoparticles in mesoporous silicas are prepared and characterized by N₂-physisorption, XRD, TEM-EDAX, UV–Vis and Moessbauer spectroscopies. Their reductive behaviour and catalytic properties in ethylacetate combustion are also tested. The dispersion and intimate contact between the obtained gold and iron particles are affected not only by the preparation method and pretreatment temperature used, but could be successfully regulated by the pore accessibility of the host matrix.     

Macro–mesoporous silicas complex and the carbon replica

Novel macroporous silicas with ordered mesoporous wall structures (15 nm in pore size) have been synthesized by finely balancing the emulsification of the oil phase with the self-assembly of the amphiphilic block copolymers. The nanocasting method was used to produce hierarchically ordered macro–mesoporous carbon materials. These porous materials have potential applications in catalysis, sorption, separation, etc.     

Application of the Indium-containing mesoporous silicas catalysts in the alkylation of aromatics reaction

The benzylation of benzene and substituted benzenes reaction employing benzyl chloride as the alkylating agent over a series of Indium-containing mesoporous silicas with different In contents has been investigated. These materials (In-HMS-n) have been characterized by chemical analysis, N₂ adsorption/desorption isotherm, X-ray diffraction (XRD) and FTIR spectroscopy. The mesoporous Indium-containing materials showed both high activity and high selectivity for benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > anisole. More interesting is the observation that these catalysts are always active and selective for large molecules like naphthenic compounds such as methoxynaphthalene. Kinetics of the benzene benzylation over these catalysts have also been investigated.     

Pd/Ce-HMS介孔材料的结构和表面化学态

为了制备新型负载型Pd催化剂,采用合成后组装法和浸渍法室温合成了Pd/Ce-HMS介孔材料,产物用XRD、N2吸附、FTIR及XPS谱等手段进行表征。结果表明,Ce、Pd引入后六方介孔结构仍保持完好。产物的BET表面积为742.9 m2·g-1,孔容0.803 cm3·g-1,表面Pd、Ce物种主要以PdO2和CeO2形式存在。研究表明,Ce前驱体通过与孔表面富集的Si—OH基团作用而嵌入骨架或键合于孔表面,Pd担载时由于模板剂仍留在孔道中,因而没有造成孔道堵塞。     

The radical species and impurities present in mesoporous silicas as oxidation active centres

Three kinds of mesoporous silicas with hexagonal arrangement of mesopores, i.e. MCM-41, SBA-3 and SBA-15, were synthesised and characterised by XRD, N₂ adsorption, FTIR, UV–vis and ESR techniques. A choice of these silicas was determined by the use of various siliceous precursors, templates and synthesis conditions. Their catalytic activity was estimated in the oxidation of methanol (gas phase) and cyclohexene (liquid phase) as well as in acid-basic test reactions (propanol–2 decomposition and acetonylacetone (AcAc) cyclisation). It was evidenced that the sources of siliceous, nature of templates and the preparation conditions (pH) play a crucial role in the formation of active species. The E′ and NBOHC (Si–O) and iron and chloride impurities were estimated as active centres for both oxidation reactions.     

Hexagonal mesoporous silicas with and without Zr as supports for HDS catalysts

Hexagonal mesoporous materials (HMS) with and without zirconium were used as supports for preparation of HDS catalysts. The catalysts prepared by modification of the supports with 12-phosphomolybdic acid (HPMo) were characterised by nitrogen adsorption, IR spectroscopy, TPD of ammonia, TPR and catalytic activity in thiophene hydrodesulphurisation. Parent silicas showed mesoporous structure with BET surface area between 1200 and 800 m² g⁻¹, pore size diameter around 3.3 nm and acidity around 0.3 mmol NH₃ g⁻¹. Molybdenum catalysts possess stronger acidity than the supports used. The catalytic activities in hydrodesulphurisation of thiophene of the molybdenum containing catalysts prepared with HMS were higher than the activity of the catalyst prepared with amorphous silica. Higher acidity of Zr–HMS supports lead to lower stability in the thiophene conversion.     

Effect of the crystallinity of kaolinite precursors on the properties of mesoporous silicas

Mesoporous silicas (MesoPSs) were hydrothermally synthesized from calcined and selectively acid-leached kaolinites with a range of crystallinity, using cetyltrimethyl ammonium bromide (CTABr), to investigate the effect of the kaolinite crystallinity on the porous properties of the resulting MesoPSs. Four kaolinites were used, with Hinckley indices ranging from 0.51 to 1.20 and (001) crystallite sizes ranging from 20 to 37 nm. After calcination at 600 °C for 24 h they were selectively leached with 2.5 M H₂SO₄ at 90 °C for 2 h to prepare microporous silica (MicroPSs). The Si/Al ratios of these MicroPSs varied from 21 to 82 and their specific surface areas (S_BET) ranged from 169 to 370 m²/g, these parameters tending to increase with decreasing Hinckley index of the kaolinite. MesoPSs were synthesized by reacting the resulting MicroPSs with CTABr in NaOH solution under hydrothermal conditions. The MicroPS was mixed with CTABr, NaOH and water in the molar ratio (MicroPS):CTABr:NaOH:H₂O = 1:0.1:0.3:150. The synthesis was carried out by stirring the suspension at room temperature for 24 h, aging for 24 h, hydrothermal treatment at 110 °C for 24 h and calcination at 560 °C for 6 h to remove the surfactants. The S_BET values of the resulting MesoPSs ranged from 932 to 1240 m²/g, correlating with the S_BET values of the precursor MicroPS and the crystallinity of the kaolinite starting materials.     

Amine-functionalized ordered mesoporous silicas as model materials for liquid phase acid capture

Uptake of dilute aqueous acetic acid was compared using primary, secondary, tertiary amines, and quaternary ammonium grafted ordered mesoporous silica. Primary amine and quaternary ammonium grafted samples showed the highest uptake, 0.21 mmol acetic acid/g SBA-15, with secondary and tertiary amines showing nominally lower, 0.18 mmol/g, at 0.5 mmol aminosilane loaded per gram SBA-15. Solution conditions during uptake were varied to conclude that only associated acetic acid could be bound and that the mechanism relied heavily on electrostatic interactions. The aminosilane packing density was found to be crucial to performance with variation depending on the ligand bulk as well as the silica support's pore size. Relevant solution conditions for cellulose depolymerization were also explored by comparing uptake of multiple organic acids and with dextrose added. Here, it was shown that the most hydrophobic organic acid was preferentially extracted, and the uptake was enhanced in the presence of dextrose.