In Situ and Post Reaction Cobalt-Incorporation into Periodic Mesoporous Ethanesilica Materials

Cobalt incorporated periodic mesoporous organosilica materials were synthesized in situ by condensation of 1,2-bistrimethoxysilylethane (BTME) in the presence of cetyltrimethylammonium bromide (CTAB) and cobalt nitrate and by incipient wetness addition of Co to BTME mesoporous silica. BET and pore measurements as well as DTA and TGA analysis of the materials revealed that the mesoporous structure is retained under the synthetic conditions used, after solvent extraction and importantly to temperatures of ca. 400°C under N₂. Raman spectroscopy also revealed the presence of the ethane moiety in the Co materials and that the surfactant was removed by solvent extraction. BET and pore measurement studies revealed that the surface area and pore volume of the materials decreased with increasing cobalt loading. The studies indicate that the new Co materials have potential as Fischer-Tropsch catalysts.     

Effects of Template Contents on the Physicochemical Sorption Properties of Zr—Incorporated Mesoporous Titania Materials

Zr-Incorporated mesoporous titania materials were prepared via nonsurfactant templated sol-gel process of zirconium(IV) butoxide(ZBT) and titanium(IV) butoxide(TBT) in the presence of urea molecules as template or pore forming agent.The effcets of template contents on the pore parameters of the materials synthesized with fixed Zr incorporation contents were investigated by mitrogen adsorption-desrption measurements,powder X-ray diffraction(XRD) study and transmission electron microscopy(TEM).The changes of template contents play significant roles on the pore parameters at low incorporsation content of Zr.The pore diameters display a clear increase tendency with the increase of template contents.When high Zr incorporation content is used,the template contents have less effect on the pore diameters that almost keep unchanged with the increase of template contents.All the materials possess type IV isotherms with H2 hysteresis loops suggesting the formation of mesophase.The materials with low Zr incorporation content have anatase structures；however,it can not be found in the materials with high Zr incorporation content.TEM images show that some accumulated inter-particulate pores and welldistributed worm-like pores are present in the Zr-incorporated materials.     

Die Hysterese der Adsorptions- und Desorptionsisothermen an porösen Silicagelen und Aluminiumoxiden

In selected groups of amorphous silica gels and finely crystalline aluminium oxides, hysteresis loops between the adsorption- and desorption isotherms of water were determined. The total volumes of the pore systems were analysed with the aid of the differential quotients of the hysteresis loops. In the group of silica gels relationships will be demonstrated between the precipitation of polysilicid acids and the distribution of the pore volume in the xerogels. In the group of aluminium oxides the influence of sintering at high temperatures on the distribution of the pore volume will be described. The hysteresis loops and especially the differential quotients distinctly differentiate specific properties of the used materials with their variables pore systems. An apparatus was used which recorded weights of water (= volumes and volume differences) with high sensitivity over the entire range p/po = 0 to 0,95. The appearance of hysteresis according to the fundamental theory was a sign that in this range adsorption and desorption of the liquid phase water took place in mesopores.     

Study of the Pm3n space group of cubic mesoporous silica.

By using a Gemini surfactant, [C14H25N+(CH3)2-(CH2)2-N+(CH3)2C14H25]2 Br-(C(14-2-14)), with a short spacer group (s = 2) as structure-directing agent and sodium silicate as precursor, high-quality, ordered cubic mesoporous silica with space group Pm3n was prepared by the S+I-route (S = surfactants, I = precursor). The samples were characterized by small-angle X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption. The results showed that the pore structure of the resulting mesoporous silica belonged to the cubic system (space group Pm3n). The unit-cell parameter of the cubic system was in the range of 8.81-9.14 nm. The high-quality cubic mesoporous structure was formed at molar ratios of C(14-2-14) to sodium silicate of 0.33:1 to 0.16:1 and a molar ratio of ethyl acetate to sodium silicate of 2:1. N2 adsorption-desorption curves revealed type IV isotherms and H1 hysteresis loops. The primary pore volume, and the most probable pore size according to the Barrett-Joyner-Halenda (BJH) model, increased with increasing molar ratio of C(14-2-14) to sodium silicate.     

Characterization of the pore structure of three-dimensionally ordered mesoporous carbons using high resolution gas sorption

The use of colloidal crystals with various primary particle sizes as templates leads to the formation of three-dimensionally ordered mesoporous (3DOm) carbons containing spherical pores with tailorable pore size and extremely high pore volumes. We present a comprehensive structural characterization of these novel carbons by using nitrogen (77.4 K) and argon (87.3 K) adsorption coupled with the application of novel, dedicated quenched solid density functional theory (QSDFT) methods which assume correctly the underlying spherical pore geometry and also the underlying adsorption mechanism. The observed adsorption isotherms are of Type IV with Type H1-like hysteresis, despite the fact that pore blocking affects the position of the desorption branch. This follows also from detailed, advanced scanning hysteresis experiments which not only allow one to identify the underlying mechanisms of hysteresis, but also provide complementary information about the texture of these unique porous materials. This work addresses the problem of pore size analysis of novel, ordered porous carbons and highlights the importance of hysteresis scanning experiments for textural analysis of the pore network.     

Adsorption properties of ordered mesoporous silicas synthesized in the presence of block copolymer Pluronic F127 under microwave irradiation

Ordered mesoporous silicas (OMSs) were prepared at different temperatures by using tetraethyl orthosilicate (TEOS) as a silica source, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (Pluronic F127) as a structure directing agent and sodium chloride as an additive under acidic conditions and microwave irradiation. The small angle X-ray diffraction patterns of these samples indicate the presence of ordered mesopores, while adsorption studies show that they possess high volumes of pores, bimodal pore size distributions and large pore sizes. There is an interesting change in the hysteresis loop of nitrogen adsorption isotherms with increasing temperature of hydrothermal treatment; a delayed desorption characteristic for cage-like mesostructures is observed for the OMS samples treated at 100 and 120?°C, while the hydrothermal treatment at 140 and 160?°C leads to the samples having hysteresis loops characteristic for channel-like materials.     

Adsorption of Carbon Tetrachloride by 3.4 nm Pore Diameter Siliceous MCM-41: Isotherms and Neutron Diffraction

Adsorption isotherms of carbon tetrachloride at temperatures between 273 and 323 K have been determined on the pure silica form of MCM-41 of pore diameter ca. 3.4 nm. All isotherms were of Type V, the isotherms at 273, 288 and 303 K showing hysteresis loops, whereas the isotherm at 323 K was completely reversible. Despite the questionable validity of the Kelvin equation when applied to narrow mesopores, changes in the relative pressure positions of capillary condensation and evaporation as a function of the temperature appear to be well described. Neutron diffraction measurements at 200 and 273 K show significant changes in the physical properties of the adsorbed CCl4 in the MCM-41 from those of bulk adsorbate. The results also suggest a highly heterogeneous surface and appear to show some flexibility in the pore walls upon pore filling. The conditions required for first order reversible capillary condensation are discussed.     

Fabrication of MCM-41 mesoporous silica through the self-assembly supermolecule of β-CD and CTAB

Using the self-assembly β-cyclodextrin (β-CD) and cetyltrimethylammonium bromide (CTAB) as structure-directing agents, high-quality ordered MCM-41 silicas have been prepared. Small-angle X-ray diffraction (SXRD), N₂ adsorption-desorption and scanning electron microscope (SEM) techniques were used to characterize the calcined samples. Results showed that the pore structure of the resulting mesoporous silica belonged to the two-dimensional hexagonal structure (space group p6mm). The high-quality hexagonal structure was formed as n?1 (n denotes molar ratio of β-CD to CTAB). N₂ adsorption-desorption curves revealed type IV isotherms, H4 hysteresis loops, for all samples, and H1 hysteresis loops for samples at n=0, 0.1, 1 and 2, respectively. The pore size and the pore wall thickness of the samples increased with the increase in n values, respectively.     

Effects of functionalization, catenation, and variation of the metal oxide and organic linking units on the low-pressure hydrogen adsorption properties of metal-organic frameworks

The dihydrogen adsorption isotherms of eight metal-organic frameworks (MOFs), measured at 77 K up to a pressure of 1 atm, have been examined for correlations with their structural features. All materials display approximately Type I isotherms with no hysteresis, and saturation was not reached for any of the materials under these conditions. Among the six isoreticular MOFs (IRMOFs) studied, the catenated materials exhibit the largest capacities on a molar basis, up to 9.8 H(2) per formula unit. The addition of functional groups (-Br, -NH(2), -C(2)H(4)-) to the phenylene links of IRMOF-1 (MOF-5), or their replacement with thieno[3,2-b]thiophene moieties in IRMOF-20, altered the adsorption behavior by a minor amount despite large variations in the pore volumes of the resulting materials. In contrast, replacement of the metal oxide units with those containing coordinatively unsaturated metal sites resulted in greater H(2) uptake. The enhanced affinities of these materials, MOF-74 and HKUST-1, were further demonstrated by calculation of the isosteric heats of adsorption, which were larger across much of the range of coverage examined, compared to those of representative IRMOFs. The results suggest that under low-loading conditions, the H(2) adsorption behavior of MOFs can be improved by imparting larger charge gradients on the metal oxide units and adjusting the link metrics to constrict the pore dimensions; however, a large pore volume is still a prerequisite feature.     

Morphology and surface properties of fumed silicas

Several series of fumed silicas and mixed fumed oxides produced and treated under different conditions were studied in gaseous and liquid media using nitrogen and water adsorption-desorption, mass spectrometry, FTIR, NMR, thermally stimulated depolarization current (TSDC), photon correlation spectroscopy (PCS), zeta potential, potentiometric titration, and Auger electron spectroscopy methods. Aggregation of primary particles and adsorption capacity (Vp) decrease and hysteresis loops of nitrogen adsorption-desorption isotherms becomes shorter with decreasing specific surface area (S(BET)). However, the shape of nitrogen adsorption-desorption isotherms can be assigned to the same type independent of S(BET) value. The main maximum of pore size distribution (gaps between primary nonporous particles in aggregates and agglomerates) shifts toward larger pore size and its intensity decreases with decreasing S(BET) value. The water adsorption increases with increasing S(BET) value; however, the opposite effect is observed for the content of surface hydroxyls (in mmol/m2). Associative desorption of water (2(SiOH)-->SiOSi+H2O) depends on both the morphology and synthesis conditions of fumed silica. The silica dissolution rate increases with increasing S(BET) and pH values. However, surface charge density and the modulus of zeta-potential increase with decreasing S(BET) value. The PCS, 1H NMR, and TSDC spectra demonstrate rearrangement of the fumed silica dispersion depending on the S(BET) value and the silica concentration (C(SiO2)) in the aqueous suspensions. A specific state of the dispersion is observed at the C(SiO2) values corresponding to the bulk density of the initial silica powder.     

Synthesis of hollow spherical silica with MCM-41 mesoporous structure

Hollow spherical mesoporous silica was synthesized by using sodium silicate as a precursor and a low concentration of cetyltrimethylammonium bromide (CTAB) (0.154 mol dm^–3). The resulting hollow spherical particles were characterized with scanning electron microcopy (SEM), small-angle X-ray diffraction (SXRD), transmission electron microscopy (TEM), and N₂ gas adsorption and desorption techniques. The results showed that regular spherical mesoporous silica could be obtained only if the molar ratio of propanol to CTAB was in the range of approximately 8:1–9:1. The spherical particles were hollow (inside), and the shell consisted of smaller particles with a pore structure of hexagonal symmetry. With an increase of the molar ratio of propanol to CTAB, the distance (a value) between centers of two adjacent pores increased, and the pore structure of mesoporous silica became less ordered. N₂ adsorption–desorption curves revealed type IV isotherms and H1 hysteresis loops; with an increase of the molar ratio of propanol to CTAB, the pore size with Barrett–Joyner–Halenda (BJH) diameter of the most probable distribution decreased, but the half peak width of the pore size distribution peak increased     

Pore formation during the pyrolysis of C-Nb2O5 and C-Ta2O5 xerogels

Binary organic-inorganic gels have been prepared by mixing a carbonaceous hydrosol and a Nb₂O₅ or Ta₂O₅ sol derived by hydrolysis of the alkoxides. The gels are pyrolyzed under an inert atmosphere into precursors in which carbon and the metal oxides are mixed very intimately. High temperature treatment converts the precursors into the cubic face centered carbides. The precursors as well as the carbides have been shown to be micro- and mesoporous materials. Measurements of nitrogen adsorption reveal a characteristic change of the shapes of the isotherms (Type I Type IV) and of the hysteresis loops (H4H2H1) during the thermal processes. Pore widening has been observed with rising temperature. The phenomena of crystallization, carbothermal reduction and sintering were found to control the pore shape and size. The results of the adsorption measurement correlate well with those of the thermoanalytical and X-ray diffraction studies.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Preliminary Synthesis and Characterization of Mesoporous Nanocrystalline Zirconia

A novel method to prepare mesoporous nano-zirconia was developed. The synthesis was carried out in the presence of PEO surfactants via a solid-state reaction. The materials exhibit a strong diffraction peak at low 28 angle and their nitrogen adsorption/desorption isotherms are typical of type IV with H1 hysteresis loops. The pore structure imaged by TEM can be described as wormhole domains. The tetragonal zirconia nanocrystals are uniform in size (around 1.5 nm) and their mesopores focus on around 4.6 nm. The zirconia nanocrystal growth is tentatively postulated to be the result of an aggregation mechanism. This study also reveals that the PEO surfactants can interact with the Zr-O-Zr framework to reinforce the thermal stability of zirconia. The ratio of NaOH to ZrOC12, crystallization and calcination temperature play an important role in the synthesis of mesoporous nano-zirconia.     

Porosity and surface properites of SBA-15 with grafted PNIPAAM: a water sorption calorimetry study

Mesoporous silica SBA-15 was modified in a three-step process to obtain a material with poly-N-isopropylacrylamide (PNIPAAM) grafted onto the inner pore surface. Water sorption calorimetry was implemented to characterize the materials obtained after each step regarding the porosity and surface properties. The modification process was carried out by (i) increasing the number of surface silanol groups, (ii) grafting 1-(trichlorosilyl)-2-(m-/p-(chloromethylphenyl) ethane, acting as an anchor for (iii) the polymerization of N-isopropylacrylamide. Water sorption isotherms and the enthalpy of hydration are presented. Pore size distributions were calculated on the basis of the water sorption isotherms by applying the BJH model. Complementary measurements with nitrogen sorption and small-angle X-ray diffraction are presented. The increase in the number of surface silanol groups occurs mainly in the intrawall pores, the anchor is mainly located in the intrawall pores, and the intrawall pore volume is absent after the surface grafting of PNIPAAM. Hence, PNIPAAM seals off the intrawall pores. Water sorption isotherms directly detect the presence of intrawall porosity. Pore size distributions can be calculated from the isotherms. Furthermore, the technique provides information regarding the hydration capability (i.e., wettability of different chemical surfaces) and thermodynamic information.     

Nano-fibriform production of silica from natural chrysotile

Nano-fibriform silica was extracted from chrysotile by the acid-leaching method. The acid-leached residue of chrysotile has been studied by TEM, XRD, FT-IR, and thermal analysis techniques, etc. When the magnesium leaching degree (MLD) is over 90%, the nano-fibriform silica consists of hydrous silicon dioxide (above 90%) with small amount of magnesium trapped inside the SiO network. The amount of hydroxyl on surface of nano-fibriform silica is 6 unit nm(-2). This value is between the values of fumed and precipitated silica. This study shows that nano-fibriform silica is a kind of amorphous matter with a high special surface area (368 m2/g), a high adsorption (330 cm3/g), and a larger pore volume (0.51 cm3/g). The diameter of a single silica fiber is 20-30 nm. The nitrogen adsorption isotherm is similar to Type IV curve. The nano-fibriform silica is one of mesopores materials.     

多喷嘴对置式水煤浆气化炉内固体颗粒微观特性研究

气化炉内固体颗粒微观结构特性对气流床气化过程中熔渣、粗渣和细渣的形成具有重要影响。基于多喷嘴对置式水煤浆气化实验,对典型工况(O/C原子比为1.0)下气化炉轴向不同位置的固体颗粒进行取样,利用氮气等温吸附法和扫描电子显微镜对颗粒孔隙结构和微观形态进行研究。结果表明,气化炉内固体颗粒典型形态为不规则多孔状和规则球状,喷嘴平面有少量致密性不规则颗粒和中空颗粒。从喷嘴平面沿气化炉轴向向下,随着气化反应的进行,颗粒表面愈加粗糙,孔隙结构愈加发达。颗粒吸附曲线属于II型等温线,迟滞回线属于H3型回线,表明颗粒具有大量裂缝形孔和较连续的完整孔系统。比表面积和孔容积均随着与喷嘴平面距离的增加而增大,而平均孔径逐渐减小,在喷嘴平面附近变化幅度较大。孔结构以孔径小于10 nm的孔为主,随着气化反应的进行颗粒中小于10 nm的孔逐渐增多,而大于10 nm的孔分布状态变化不大。     

Sorption behaviour of nanocrystalline MOR type zeolite for Th(IV) and Eu(III) removal from aqueous waste by batch treatment

The nanocrystalline mordenite (MOR) type zeolite materials with initial chemical composition Na(2)O:Al(2)O(3):10SiO(2):48H(2)O have been synthesized under hydrothermal conditions. MOR1 and MOR2 are spherically shaped nanocrystals, whereas MOR3 and MOR4 have rod-like morphology. This paper reports the sorption characteristics of MOR analogues for Th(IV) and Eu(III) removal from aqueous nuclear waste. Sorption of Th(IV) and Eu(III) on MOR1, MOR2, MOR3 and MOR4 in a single component system with varying initial metal ion concentration, solution pH, contact times, sorbent dose and temperatures has also been investigated. Further, the Langmuir and Freundlich sorption models have been applied to describe equilibrium isotherms at different temperatures. The adsorption capacity increases largely with increasing solution pH and temperature of the system. Specific surface area and pore volume have been investigated by Brunauer-Emmett-Teller (BET) method. The N(2) adsorption isotherm presents a type IV isotherm with narrow hysteresis loop which indicates the presence of mesopores related to inter-particle voids. Thermodynamic results indicate that the sorption follows an endothermic physisorption process. It has been found that these exchangers have good sorption capacity and out of which MOR4 has highest sorption capacity. Thus, nanocrystalline MOR4 is proved to be good sorbent for both Th(IV) and Eu(III).     

Synthesis and characterization of nanocast silica NCS-1 with CMK-3 as a template

Nanocast silica (NCS-1) was synthesized by a casting process by employing the mesoporous carbon CMK-3 (the replica of SBA-15) as a template, tetraethoxysilane (TEOS) as the silica source, and hydrochloric acid (HCl) as the catalyst. The ordered carbon template was removed by employing different methods, such as calcination, thermal treatment followed by calcination, and controlled combustion. According to XRD and TEM characterization, NCS-1 exhibits an ordered structure with hexagonal symmetry and retains the morphology of the original SBA-15 used for the synthesis of CMK-3 over two replication steps on the nanometer scale. This demonstrates the well-connected porosity in CMK-3 type carbon, which can be used as a mold to synthesize mesostructured materials. The nitrogen adsorption isotherms generally show type IV shape, indicating mesoporous characteristics. The structure of NCS-1 is strongly influenced by variables of the nanocasting process, such as the loading amount of silica, hydrolysis temperature, and carbon removal methods. The surface area, pore size, and pore volume of NCS-1 can be tuned to a certain range by varying these parameters.     

Porous Texture and Surface Character of Dehydroxylated and Rehydroxylated MCM-41 Mesoporous Silicas-Analysis of Adsorption Isotherms of Nitrogen Gas and Water Vapor

Four samples of MCM-41 mesoporous silicas whose average pore diameters are 2.4, 2.8, 3.2, and 3.6 nm were prepared using sodium orthosilicate and cationic surfactants of [CH(3)(CH(2))(n)N(CH(3))(3)]X (n=11, 13, 15, 17). These four samples were calcined at 1123 K in vacuo to obtain the dehydroxylated samples, which were further rehydroxylated at 298 K to obtain the rehydroxylated samples. The adsorption isotherms of nitrogen gas (77 K) for the 12 MCM-41 mesoporous silicas are of Type IVc, giving no adsorption hysteresis. On the other hand, the first adsorption isotherms of water vapor (298 K) for the dehydroxylated MCM-41 samples are quite different from those of nitrogen gas, giving the remarkable adsorption hysteresis. The second water isotherms for the rehydroxylated MCM-41 samples are of Type IV, showing slight hysteresis. Using the nitrogen isotherms, the relation between the pore size and carbon chain length of the surfactant has been determined, and the effect of dehydroxylation and rehydroxylation on the porous texture has been examined. Using the first and second water isotherms, the adsorption model of physisorbed waters adsorbed on the surface silanol groups has been proposed. From the pore size distribution curves of nitrogen and water, the presence of constrictions in the cylindrical pores has been predicted. Copyright 2000 Academic Press.     

Preparation of adsorbents from sugarcane manufacturing by-product filter-mud by thermal activation

A series of experiments with thermal activation were carried out on filter-mud waste from the sugarcane refining process in a rotary reactor. The influence of activation parameters on the agro-industrial waste by varying the operation temperature of 600–800 °C was determined. The variations of pore properties as well as the change of chemical characteristics in the resulting solids (FM series) were also studied. The results show that the resulting samples are type IV with hysteresis loops corresponding to type H3 from nitrogen adsorption–desorption isotherms, indicating slit-shaped mesoporous characteristics (BET surface areas of 57–132 m² g⁻¹). The results also show that the surface areas of the unwashed products and water-washed products are lower than those of the washed products because of residues left in the crude products. The adsorption of paraquat on FM sample was preliminarily evaluated. The isotherm showed that the FM adsorbent had a high affinity for this herbicide and can be well fitted by Freundlich model. Thus, the agro-industrial waste is one resource for producing the mesoporous materials, and it may be applied to the water treatment for the removal of organic contaminants.