Effect of pH in preparation and properties of mesoporous sieve from montmorillonite

Mesoporous material with dual mesoporous size distribution had been synthesized with montmorillonite as precursor. The materials exhibited two kinds of mesopores: one is mesopore in interlayers of montmorillonite with mean sizes of 2.9 nm, the other is mesopore out of layers of montmorillonite with mean sizes of 3.9 nm. With the increasing of pH values (8.0–11.0), the specific surface area and pore volume of two kinds of mesopores changed regularly. The samples were characterized by XRD, TEM and Nitrogen adsorption/desorption isotherms. The results indicated that higher pH benefits the synthesis of mesoporous montmorillonite with smaller pore and the TOT of montmorillonite had been present as porous wall.     

Preparation of structured meso–macroporous silica materials: influence of composition variables on material characteristics

Meso–macroporous silica materials with a well-ordered array of mesopores were prepared from oil-in-water emulsions. The influence of the following three composition variables on material characteristics was studied: the dispersed phase fraction of the emulsion, the concentration of silica used and the concentration of surfactant. The obtained materials were characterized via small-angle X-ray diffraction scattering, scanning electron microscopy, transmission electron microscopy, Hg intrusion porosimetry and nitrogen adsorption–desorption isotherms. A network of structured mesopores was obtained even when using a highly concentrated emulsion (volume of the disperse phase, ? ≥ 0.75). The mesopores network presented a hexagonal arrangement, with mesopore diameters between 4 and 7 nm. Non-ordered macropores, with diameters between 50 nm and 10–15 μm were also present, depending on composition variables. The isotherms were of type IV, typical of mesoporous materials, but at high p/p₀ they were the usual shape for the macroporous materials. The possibility of tailoring mesopore and macropore structures by altering in composition variables could extend the application of these materials.     

Determination of Both Mesopores and Macropores in Three-Dimensional Ordered Porous Materials by Nitrogen Adsorption

Three-dimensionally ordered silica structures containing both mesopores and macropores are created using polystyrene coacervate spheres with a diameter of ca. 146 nm. The close-packed polystyrene coacervate spheres are intercalated with tetraethyl orthosilicate. The spheres are removed by calcination leaving an inverse silica replica with a spherical macropore cavity diameter of 110 nm. Due to the nature of these porous structures, pores leading into the macropore cavity are in the mesopore regime, 40 nm in diameter. The nitrogen adsorption data described in the following paper gives a pore size for both the macropore cavity and the mesopore openings leading into the cavity. The pore sizes as determined by nitrogen sorption are in good agreement with the pore sizes observed by scanning electron microscopy. Mercury intrusion porosimetry results confirm the size of the mesopore openings leading into the macropore cavity, however due to destruction of the sample upon intrusion, extrusion results can not be obtained to determine main cavity diameters. As a result, nitrogen sorption may be a viable option for determining pore sizes with these three-dimensionally ordered materials containing both mesopores and macropores.     

具有介孔结构丝光沸石的合成与表征

基于丝光沸石骨架结构固有的晶体缺陷特征,提出诱导晶体结构缺陷和由结构缺陷衍生晶内介孔的研究方案。采用三元有机超分子胶束模板剂和两段变温晶化水热法,制备出丝光沸石基多级介孔材料。通过粉末X射线衍射、77K氮吸附–脱附、场发射透射电子显微镜、氨程序升温脱附对合成的介孔材料的晶相、形貌、介孔特征和水热稳定性进行了表征。结果表明：所合成的典型丝光沸石具有较高的相对结晶度,介孔比表面积和介孔体积分别为152.7m2/g和0.163 cm3/g;晶体内介孔在3～50 nm区间呈多级分布;其酸性质与微孔丝光沸石相匹配;水热稳定性较有序介孔材料MCM-41有显著提高。与聚集态纳米沸石组装介孔材料不同,合成的介孔丝光沸石晶体表面上介孔排布密度和尺寸分布缺乏均一性,故而由体相结构缺陷诱导形成的附加介孔呈显著无序状态。     

A boric acid-assisted hydrothermal process for preparation of mesoporous silica nanoparticles with ultra-large mesopores and tunable particle sizes

This work reports that monodispersed ultra-large mesopore mesoporous silica nanoparticles (LP-MSNs) can be facilely prepared by a simple and highly effective boric-assisted hydrothermal (BAH) process. This BAH process provides an easy and mild way to prepare LP-MSNs with tunable porous structure and mesopore size. Such BAH process enables the transformation from conventionally prepared MSNs with small mesopores (∼2.3 nm) into LP-MSNs with ultra-large mesopore size over 15 nm. This BAH process also enables reliable control over particle sizes (98 nm–278 nm) by varying synthesis conditions. The effect of different synthesis conditions on mesopore enlargement was investigated, including the amounts of initial ethanol, boric acid, and ethanol in mixtures during hydrothermal treatment (HT) and HT temperatures. It is newly found that the ethanol added in synthesis step (1st ethanol), boric acid and ethanol added in mixture during HT process (2nd ethanol) and HT conditions play synergistic roles in the preparation of LP-MSNs with variable mesopore sizes and particle sizes. The underlying principle of such mesopore enlargement by such experimental setup was also analyzed. The BET surface area, pore size, and total pore volume of typical LP-MSNs reach 238 m²/g, 15.3 nm, and 0.67 cm³/g, respectively. Such LP-MSNs can find different applications in various fields.     

Synthesis of well-dispersed layered double hydroxide core@ordered mesoporous silica shell nanostructure (LDH@mSiO₂) and its application in drug delivery

We demonstrate an efficient synthesis of novel layered double hydroxide mesoporous silica core-shell nanostructures (LDH@mSiO(2)) that have a hexagonal MgAl-LDH nanoplate core and an ordered mesoporous silica shell with perpendicularly oriented channels via a surfactant-templating method. Transmission electron microscopy, X-ray diffraction and N(2) sorption analyses confirmed that the obtained nanostructures have uniform accessible mesopores (～2.2 nm), high surface area (～430 m(2) g(-1)), and large pore volume (～0.22 cm(3) g(-1)). Investigations of drug release and bio-imaging showed that this material has a slow release effect of ibuprofen and good biocompatibility. This work provides an economical approach to fabricate LDH@mSiO(2) core-shell nanostructures, which may have great potential in broad drug delivery and hyperthermia therapy applications.     

Synthesis of mesoporous MOR materials by varying temperature crystallizations and combining ternary organic templates

An approach, which involved perturbations of synthesis conditions in crystallization temperature and organic template composition, has been proposed for derivation of mesopores from bulk structural defects formed in mordenite (MOR) phases, based on the character of intrinsic crystal defects and tensional distortions of two compressed 8-membered rings in MOR framework. Consequently, hierarchically porous materials with MOR structures were prepared by varying temperature synthesis and using ternary organic micelles templates. The synthesized materials were characterized by powder X-ray diffraction, nitrogen adsorption at 77 K and transmission electron microscopy. These crystalline materials combined the advantages of both mordenites with the micropore system and mesoporous materials by featuring an additional intracrystalline mesopore system in MOR single crystals, resulting in a hierarchical pore distribution in range of 1.7-80.0 nm together with the significant specific surface areas. In particular, individual crystal morphologies of typical mesoporous MOR materials showed the defect-rich structures responding essentially to the mesoporosity; the mesoporous materials were substantiated matchable well to normal mordenites in acid capacity and acid strength distribution. Furthermore, several factors acting on intracrystalline mesopore formation were elucidated for explicating the perturbation synthesis approach, and whole reaction routes for synthesizing different solid products under related crystallization conditions were summarized coupling with a demonstration of part TEM micrographs. The overall results suggested that the investigative approach of perturbation imposed on crystal growth provides an alternative route for direct hydrothermal synthesis of mesoporous zeolite materials and implied that bulk structural defects within single crystals lead to the formation of intracrystalline mesopores in various sizes.     

Preparation of mesoporous activated carbon fibers by catalytic gasification

A commercial activated carbon fiber with micropores, CH700-20 (Kuraray), was reformed to a mesoporous one by catalytic gasification. The catalytic gasification was composed of two steps: CO₂ pretreatment and air oxidation. Cobalt was used as the catalyst and gasification was performed in the temperature range of 500–700 °C. BET surface area and pore volume of catalytically modified carbon fiber were analyzed by N₂ adsorption. BET surface area of the original CH700-20 was 1,711 m²/g, and the mesopore volume percentage was 11.9%. After catalytic gasification, BET surface area was similar to the original CH700-20, while mesopore volume percentage increased up to 56%. The average pore size of mesopores was 3–4 nm in diameter. The average size of mesopores could be controlled with nanometer resolution by varying the temperature and time of activation.     

Characteristics of Ti-MCM-41 and its Catalytic Properties in Oxidation of Benzene

A series of mesoporous titanosilicate Ti-MCM-41 molecular sieves with various Si/Ti ratios have been hydrothermally synthesized using hexadecyl-trimethylammonium bromide as the organic surfactant. These materials were characterized with powder X-ray diffraction (XRD), framework FTIR, diffuse reflectance UV-visible spectroscopy, nitrogen sorption measurements, differential thermal analysis (DTA), and transmission electron microscopy (TEM). The crystallinity of Ti-MCM-41 after calcination was almost two-fold higher than that of the as-synthesized one. The crystallinity and surface area of Ti-MCM-41 both decrease with an increase of titanium content. The results of XRD and FTIR show that the solid products have the MCM-41 structure and contained only atomically dispersed titanium, consistent with framework titanium in Ti-MCM-41. All of the materials had a uniform pore size distribution with pore size of around 3.0 nm. The hexagonal array structure of uniform pore size was observed by TEM. It proved that the pores were highly aligned. The catalytic activities of Ti-MCM-41 were tested in the partial oxidation of benzene by diluted hydrogen peroxide in a batch reactor. Ti-MCM-41 had a higher activity than TiO₂ and Ti/NaY. The activity of Ti-MCM-41 increased with titanium content. The activity of Ti-MCM-41 prepared with hydrothermal synthesis was higher than that of the sample prepared with impregnation. The high activity in Ti-MCM-41 can be attributed to its hydrohobicity and large pore size. Phenol was the only liquid phase product on all of the samples.     

In-situ generation of large microporous skeleton in mesoporous silica framework using different dicarboxylic acids

Mesoporous Santa Barbara Amorphous-15 is known to possess a small fraction of micropores, in the walls of mesopores. The ratio of micropore to mesopore area can have a profound influence on the application of this highly ordered material in various fields. The present work aims to investigate the influence of dicarboxylic acids as organic structure interrupting agents on the micropore to mesopore ratio. The physiochemical characterization of the synthesized samples including electron microscopy, nitrogen adsorption–desorption isotherms, MAS ²⁹Si-NMR, FT-IR demonstrate a distinct change in the morphology and micropore area due to the different dicarboxylic acids used during synthesis. Our results show that the decrease in chain length of the dicarboxylic acid has a direct relation to the increase in micropore area which has a significant role in the adsorption properties of mesoporous silica. Thus the dicarboxylic acid mediated tuning of the micropores area of mesoporous silica can be used for various applications.     

KOH activation of ordered mesoporous carbons prepared by a soft-templating method and their enhanced electrochemical properties

Ordered mesoporous carbon (COU-2) was synthesized by a soft-templating method. The COU-2 mesoporous carbon was activated by using KOH to improve its porosity. The mesopore size of COU-2 was 5.5 nm and did not change by the KOH activation. But, the BET surface area of COU-2 largely increased from 694 to 1685 m²/g and total pore volume was increased from 0.54 to 0.94 cm³/g after the KOH activation. The large increase of micropore volume is due to the increase of the surface area. Electrochemical cyclic voltammetry measurements were conducted in aqueous (1 M sulfuric acid) and organic (1 M tetraethyl ammonium tetrafluoroborate/polypropylene carbonate) electrolyte solutions. The KOH-activated COU-2 carbon shows superior capacitances over the COU-2 carbon and a commercial microporous carbon both in aqueous and organic electrolyte solutions. These results suggest that the carbons having regularly-interconnected uniform mesopores and micropores in thin pore walls are desirable for the electrodes in electrochemical double-layer capacitors.     

Superior electric double layer capacitors using ordered mesoporous carbons

This paper reports for the first time superior electric double layer capacitive properties of ordered mesoporous carbon (OMCs) with varying ordered pore symmetries and mesopore structure. Compared to commercially used activated carbon electrode, Maxsorb, these OMC carbons have superior capacitive behavior, power output and high-frequency performance in EDLCs due to the unique structure of their mesopore network, which is more favorable for fast ionic transport than the pore networks in disordered microporous carbons. As evidenced by N₂ sorption, cyclic voltammetry and frequency response measurements, OMC carbons with large mesopores, and especially with 2-D pore symmetry, show superior capacitive behaviors (exhibiting a high capacitance of over 180 F/g even at very high sweep rate of 50 mV/s, as compared to much reduced capacitance of 73 F/g for Maxsorb at the same sweep rate). OMC carbons can provide much higher power density while still maintaining good energy density. OMC carbons demonstrate excellent high-frequency performances due to its higher surface area in pores larger than 3 nm. Such ordered mesoporous carbons (OMCs) offer a great potential in EDLC capacitors, particularly for applications where high power output and good high-frequency capacitive performances are required.     

Exploring suitable ZSM-5/MCM-41 zeolites for catalytic cracking of n-dodecane: Effect of initial particle size and Si/Al ratio

In this study, various ZSM-5/MCM-41 micro/mesoporous zeolite composites have been prepared by alkalidesilication and surfactant-directed recrystallization of ZSM-5. The effects of particle size and Si/Al ratio of initial ZSM-5 zeolites on the structure and catalytic performance of ZSM-5/MCM-41 composites are studied. The results of XRD, TEM N₂-adsorption-desorption, NH₃-TPD and in situ FT-IR revealed that ordered hexagonal MCM-41 mesopores with 3-4 nm pore size were formed around ZSM-5 crystals, and the specific surface area and mesopore volume of composites increased with increasing the Si/Al ratio of initial ZSM-5. Catalytic cracking of n-dodecane (550 ℃, 4 MPa) showed that the ZSM-5/MCM-41 composites obtained from the high Si/Al ratio and nano-sized initial ZSM-5 zeolites exhibited superior catalytic performance, with the improvement higher than 87% in the catalytic activities and 21% in the deactivation rate compared with untreated zeolites. This could be ascribed to their suitable pore structure, which enhanced the diffusion of reactant molecules in pores of catalysts.     

The synthesis of Al-MCM-41 from volclay — A low-cost Al and Si source

The alkaline fusion of volclay (a low-cost sodium exchanged smectite) was used as source to generate the Si and Al components which were effectively transformed into mesoporous Al-MCM-41 depending on hydrothermal condition. The Al-MCM-41 materials were investigated by powder X-ray diffraction (XRD), N₂ adsorption–desorption measurements and both scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM). The volclay which converted into a silicon and an aluminium source allowed the formation of well ordered mesoporous Al-MCM-41 materials with high aluminium content (roughly 4 times higher than a Al-MCM-41 produced by a standard method), a high specific surface area (1060 m²/g), a pore volume of 0.8 cm³/g (for pore width < 7.1 nm) with an mono-modal pore distribution with a maximum in the mesoporous pore size of 3.8 nm in pore width.     

A biomimetic mesoporous silica–polymer composite scaffold for bone tissue engineering

A biomimetic organic–inorganic composite system comprising of microspheres fabricated from combination of a biodegradable polymer poly(lactide-co-glycolide) (PLGA) and bioactive mesoporous silica (SBA-15) has been developed through sintering technique for bone regeneration applications. The morphological and structural properties of the SBA-15/PLGA composite scaffold were evaluated using electron microscopy and fourier transform infrared spectroscopy and the results showed spherical morphology and composite nature. The presence of mesopores in the silica was confirmed through nitrogen adsorption–desorption isotherms. The surface area and pore size of mesoporous silica were found to be 792 m² g^?1 and 3.7 nm, respectively. The thermal characteristics of the SBA-15/PLGA composites studied using thermogravimetry analysis shows a weight loss of around 80% with the degradation occurring at 324?°C. The prepared scaffold is also found to support the adhesion and proliferation of osteoblast cells. The expression of specific bone markers is significantly enhanced in the SBA-15/PLGA composite scaffold when compared with the pristine polymeric scaffold indicating the positive effect of mesoporous silica. Hence, these SBA-15/PLGA composite scaffolds can be explored further for bone regeneration applications.     

Y分子筛/介孔Al-SBA-15复合材料与脱铝Y分子筛的表征和重油加氢裂化性能

采用两步法和水热-化学方法制备了具有高水热稳定性的Y分子筛/介孔Al-SBA-15复合材料和含有介孔的脱铝Y分子筛,用浸渍法制备了加氢裂化催化剂,并利用XRD、N2 吸附、SEM、XRF和TEM等分析手段对Y分子筛/介孔Al-SBA-15复合材料、含有介孔的脱铝Y分子筛及其催化剂的物化性质进行了对比分析。相同条件下催化剂的重油加氢裂化性能对比评价结果表明,以Y分子筛/介孔Al-SBA-15复合材料为载体的加氢裂化催化剂的中间馏分油收率和中油选择性高达66.21%和84.5%,比以脱铝Y分子筛为载体的催化剂分别提高了5.68%和5.7%。     

Hierarchical Porosity Components by Infiltration of a Ceramic Foam

A ceramic body with hierarchical meso–macro-porosity was prepared by depositing a mesoporous silica coating on the walls of a macroporous silicon oxycarbide (SiOC) foam. Scanning electron microscopy, transmission electron microscopy, and small-angle X-ray scattering revealed that a uniform mesoporous coating was deposited on the walls of the macropores, with the mesopores arranged in a highly ordered cubic lattice. Nitrogen adsorption measurements showed a bimodal pore size distribution and revealed that the specific surface area is one order of magnitude higher than in macroporous SiOC foams. Therefore, interesting applications in adsorption and catalysis can be devised.     

Volumetric distribution of Pt nanoparticles supported on mesoporous carbon substrates studied by X-ray photoelectron spectroscopy depth profiling

We present an X-ray photoelectron spectroscopy depth profiling study of the size and volumetric distributions of Pt nanoparticles supported on two mesoporous carbons. Based on the analysis of the chemical shift of the Pt4f peaks, we found the one with a mesopore diameter of ∼5 nm has a uniform distribution of crystalline Pt nanoparticles throughout the porous body. In contrast, the other with a mesopore diameter of ∼3 nm has a distinct distribution of crystalline Pt nanoparticles on the outermost surfaces of the porous material and extremely small (<1 nm) Pt nanoparticles in the interior region. The small Pt particle size in the interior represents the effect of pore entrance blockage of those mesopore channels with diameter less than 3 nm. Such blockage gives rise to the encapsulation of very small amounts of Pt precursors inside the nanospace of the porous matrix, with the result that the particles grown in the interior region of the support are less than 1 nm in size.     

Worm-hole structured mesoporous carbon monoliths synthesized with amphiphilic triblock copolymer

In the present work, mesoporous carbon monoliths with worm-hole structure had been synthesized through hydrothermal reaction by using amphiphilic triblock copolymer F127 and P123 as templates and resole as carbon precursor. Synthesis conditions, carbonization temperature and pore structure were studied by Fourier transform infrared, thermogravimetric analysis, transmission electron microscopy and N₂ adsorption–desorption. The results indicated that the ideal pyrolysis temperature of the template is 450 °C. The organic ingredients were almost removed after further carbonized at 600 °C and the mesoporous carbon monoliths with worm-hole structure were obtained. The mesoporous carbon synthesized with P123 as single template exhibited larger pore size (6.6 nm), higher specific surface area (747 m² g^?1), lower pore ratio (45.9 %) in comparison with the mesoporous carbon synthesized with F127 as single template (with the corresponding value of 4.9 nm, 681 m² g^?1, 49.6 %, respectively), and also exhibited wider pore size distribution and lower structure regularity. Moreover, the higher mass ratio of template P123/resole induced similar pore size, larger specific surface area and lower pore ratio at the same synthesizing condition. It was also found that the textural structure of mesoporous carbon was affect by calcination atmosphere.     

Confined growth of iron cobalt nanocrystals in mesoporous silica thin films: FeCo–SiO2 nanocomposites

Mesoporous silica films with controlled porosity were utilized as the host matrices to prepare FeCo–SiO₂ nanocomposites through an impregnation process. The mesoporous silica films were first impregnated with a solution containing Co(II) and Fe(III) ions and then submitted to a reduction treatment under H₂ flow. FeCo nanocrystals growth took place inside the mesopores, and their monodisperse size was dictated only by the size of the mesopores. We illustrate this process by the use of two different silica film matrices having different pore size and mesophase symmetry as the templates for the growth of FeCo alloy nanocrystals. The films and the nanocomposite samples were investigated by grazing-incidence small-angle X-ray scattering, X-ray diffraction and transmission electron microscopy. Unimpregnated mesoporous silica samples before and after the same thermal reduction treatment were also studied in order to investigate the mesopore structure variation upon the reduction treatment.