Showing papers in "Journal of Porous Materials in 2008"

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

Abstract: 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 NO 3 − /g and 55.9 mg H2PO 4 − /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.

Adsorption removal of thiophene and dibenzothiophene from oils with activated carbon as adsorbent: effect of surface chemistry

Abstract: Commercial coconut-based activated carbons (AC), before and after being treated using 65 wt% HNO3 at different temperatures (termed as AC–Hs), were used as adsorbents to remove thiophene (T) or dibenzothiophene (DBT) from model oils. The fresh AC sample and all of the AC–Hs samples were characterized by Boehm titration, Fourier-transform infrared spectroscopy, and thermal analysis, which yield the information of the surface chemistry properties of the carbon materials. The results show that in comparison to the fresh AC sample, the quantity of oxygen-containing functional groups on the surface of AC–Hs samples increases as the pretreatment temperature of the fresh AC sample increases. The adsorption capabilities of the AC samples for removal of T and DBT from model oils were evaluated in a batch-type reactor. It has been found that the refractory DBT can be removed easily over the untreated commercial AC with the removal efficiency even being higher than that of T. In the case of acid modified AC–Hs samples, the efficiency for removal of T has been greatly improved, but this is not the case for the removal of DBT. The possible mechanism for adsorption removal of T and DBT over activated carbons is discussed in terms of the quantity of surface oxygen-containing functional groups of adsorbents and the chemical structure of sulfur compounds. The effect of olefin (1-octene) and aromatic hydrocarbons (benzene) in the model oils on the selective adsorption DBT over AC is also evaluated, revealing that in the case of DBT, the competitive adsorption is involved in the process, and the removal efficiency levels off at a level over 80%.

Characterization of highly selective microporous carbon hollow fiber membranes prepared from a commercial co-polyimide precursor

Abstract: In this work, the preparation of gas separating carbon hollow fiber membranes based on a 3,3′4,4′- benzophenone tetracarboxylic dianhydride and 80% methylphenylene-diamine + 20% methylene diamine co-polyimide precursor (BTDA-TDI/MDI, Ρ84 Lenzing GmbH), their permselectivity properties as well as details of the carbon nanostructure are reported. Hollow fibers were initially prepared by the dry/wet phase inversion process in a spinning set-up, while the spinning dope consisted of P84 as polymer and NMP as solvent. The developed polymer hollow fibers were further carbonized in nitrogen at temperatures up to 1173 K. Thermogravimetric analysis was used to investigate the weight loss during the carbonization process. The nitrogen, methane and carbon dioxide adsorption capacity of the prepared materials was determined gravimetrically at 273 and 298 K and hydrogen adsorption experiments were performed at 77 K up to 1 bar. Scanning electron microscopy was used to elucidate the morphological characteristics and the nanostructure while H2 sorption at 77 K was applied to evaluate the microporosity of the developed carbon hollow fiber membranes. In all cases, the permeability (Barrer) of He, H2, CH4, CO2, O2 and N2 were measured at atmospheric pressure and temperatures 313, 333 and 373 K and were found higher than those of the precursor. Moreover, the calculated permselectivity values were significantly improved. The developed carbon fibers exhibit rather low H2 permeance values (8.2 GPU or 2.74 × 10−9 mol/m2·s·Pa) with a highest H2/CH4 selectivity coefficient of 843 at 373 K.

Acid activated montmorillonite: an efficient immobilization support for improving reusability, storage stability and operational stability of enzymes

Abstract: Three enzymes, a-amylase, glucoamylase and invertase, were immobilized on acid activated montmorillonite K 10 via two independent techniques, adsorption and covalent binding. The immobilized enzymes were characterized by XRD, N2 adsorption measurements and 27 Al MAS-NMR spectroscopy. The XRD patterns showed that all enzymes were interca- lated into the clay inter-layer space. The entire protein backbone was situated at the periphery of the clay matrix. Intercalation occurred through the side chains of the amino acid residues. A decrease in surface area and pore volume upon immobilization supported this observation. The extent of intercalation was greater for the covalently bound systems. NMR data showed that tetrahedral Al species were involved during enzyme adsorption whereas octahedral Al was involved during covalent binding. The immobilized enzymes demon- strated enhanced storage stability. While the free en- zymes lost all activity within a period of 10 days, the immobilized forms retained appreciable activity even after 30 days of storage. Reusability also improved upon immobilization. Here again, covalently bound enzymes exhibited better characteristics than their adsorbed counterparts. The immobilized enzymes could be successfully used continuously in the packed bed reactor for about 96 hours without much loss in activity. Immobilized glucoamylase demonstrated the best results.

The influence of manufacturing parameters on the properties of macroporous Zirfon ® separators

Abstract: The manufacturing of the macroporous Zirfon® separator is based on the film casting technique. This film casting technique allows different manufacturing steps to be varied in order to adapt both the composition and the structure of the separator to the specific requirements of the application. The Zirfon® separators can be used in alkaline electrochemical cells as a replacement of asbestos. At a temperature of 30 °C the ionic resistance of the separator is as low as about 0.01 Ω. Bubble-Point (BP) pressures as high as 1 MPa could be obtained.

The influence of carbon source on the wall structure of ordered mesoporous carbons

Abstract: A series of ordered mesoporous carbons (OMCs) have been synthesized by filling the pores of siliceous SBA-15 hard template with various carbon precursors including sucrose, furfuryl alcohol, naphthalene and anthracene, followed by carbonization and silica dissolution. The carbon replicas have been characterized by powder XRD, TEM and N2 adsorption techniques. Their electrochemical performance used as electric double-layer capacitors (EDLCs) were also conducted with cyclic voltammetry and charge-discharge cycling tests. The results show that highly ordered 2D hexagonal mesostructures were replicated by using all these four carbon sources under the optimal operation conditions. Physical properties such as mesoscopic ordering, surface areas, pore volumes, graphitic degrees, and functional groups are related to the precursors, but pore sizes are shown minor relationship with them. The sources, which display high yields to carbons, for example, furfuryl alcohol and anthracene are favorable to construct highly ordered mesostructures even at high temperatures (1300 °C). OMCs prepared from non-graphitizable sources such as sucrose and furfuryl alcohol display amorphous pore walls, and large surface areas and pore volumes. The functional groups in the precursors like sucrose and furfuryl alcohol can be preserved on carbon surfaces after the carbonization at low temperatures but would be removed at high temperatures. The graphitizable precursors with nearly parallel blocks and weak cross-linkage between them like anthracene are suitable for deriving the OMCs with graphitic walls. Therefore, the OMCs originated from sucrose and furfuryl alcohol behave the highest capacitances at a carbonization of 700 °C among the four carbons due to the high surface areas and plenty of functional groups, and a declination at high temperatures possibly attribute to the depletion of functional groups. Anthracene derived OMCs has the lowest capacitance carbonized at 700 °C, and a steady enhancement when heated at high temperatures, which is attributed to the graphitization. The OMCs derived from naphthalene have the stable properties such as relatively high surface areas, few electroactive groups and limited graphitizable properties, and in turn medium but almost constant capacitances.

Synthesis of Fe, Co, and Mn substituted AlPO-5 molecular sieves and their catalytic activities in the selective oxidation of cyclohexane

Abstract: Fe, Co, and Mn substituted AlPO-5 molecular sieves, including FeAPO-5, CoAPO-5, MnAPO-5, FeCoAPO-5, FeMnAPO-5, and CoMnAPO-5 were synthesized by hydrothermal method and characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), nitrogen adsorption, and Fourier transform infrared (FT-IR) spectroscopy. The lattice expansions were observed with Fe, Co, and/or Mn substitution of Al atom in AlPO-5. The selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (K/A oil) with molecular oxygen was studied over these catalysts at the reaction temperature of 403 K. The higher activities of the multi-metal substituted AlPO-5, compared to that of single metal substituted AlPO-5, were observed. The underlying reason for the superior activity of the multi-metal substituted AlPO-5 was analyzed.

Design and fabrication of hybrid bi-modal wick structure for heat pipe application

Abstract: A new hybrid bi-modal wick structure was designed and fabricated in this study with the objective to simultaneously enhance performance in capillary pumping, permeability and evaporative heat transfer. Utilizing substrates with large pores and sintered powders, a highly integrated bi-modal wick structure was created with small pores lining the walls of the large pores. This unique structure can be tailored to a number of different configurations, including uniform, radial and axially varied pore morphologies. Tests of heat pipes containing the bi-modal wick structure in various configurations revealed increases in effective thermal conductivity by as much as 400% as compared to baseline heat pipes containing monolithic wick materials such as copper mesh.

Mesoporous silica supported cobalt oxide catalysts for catalytic removal of benzene

Abstract: Two types of mesoporous silica SBA-15 with different pore diameter were synthesized with an ageing temperature of 373 K and an ageing temperature of 308 K, respectively; in addition, mesoporous silica with amorphous structure was synthesized by adding organosiloxane as part of the silica source during the synthesis procedure. Mesoporous silica and conventional alumina supported cobalt oxide catalysts were prepared by incipient wetness impregnation method. These materials were characterized by FT-IR, nitrogen adsorption-desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and Temperature programmed reduction (TPR) techniques, and the activity of the supported cobalt oxide catalysts for deep oxidation of benzene were evaluated in a fixed-bed reactor. It seems that the pore diameter of the silica increase with the elevation of the ageing temperature. Mesoporous silica supported cobalt oxide catalysts are more active than conventional alumina supported ones. Cobalt oxide can be relatively better dispersed on the surface of mesoporous silica which has larger pore diameter and surface areas. Meanwhile, more silanol groups exist on the surface of amorphous silica, which could induce a strong interaction with the supported cobalt oxide species, leading to poor activity for benzene oxidation.

Development of porous ultra high molecular weight polyethylene scaffolds for the fabrication of orbital implant

Abstract: Porous implants having interconnecting channels allow ingrowth of host connective tissue. Complete implant vascularization reduces the risk of infection, extrusion, and other complications associated with nonintegrated implants. Attempts were made to develop 60% and 70% porous ultra high molecular weight polyethylene (UHMWPE) scaffolds and blocks using sodium chloride as channeling agent, which when dissolved in boiling water leaves behind the interconnecting channels. The average diameter of the pores of 60% and 70% porous scaffolds was found to be approx. 170 µm and 210 µm, respectively. Mechanical characterizations of the scaffolds indicated sufficient strength to be used for orbital implant fabracation. Surface roughness of the scaffolds indicated increase in surface roughness with the increase in porosity. The scaffolds developed were found to be hemocompatible with the human blood. Subsequently, the 70% porous scaffold was dip coated with a solution mixture of sodium carboxy methyl cellulose (SCMC)/polyvinyl alcohol (PVA)/hydroxyapatite (HA) which also showed hemocompatibility. Ciprofloxacin release pattern from the membrane was determined. Finally an orbital implant was fabricated from the 70% porous scaffold.

Fabrication of bioceramic scaffolds with pre-designed internal architecture by gel casting and indirect stereolithography techniques

Abstract: A new technique of combining the gel casting and indirect rapid prototyping methods was utilized to fabricate macroporous β-tricalcium phosphate (β-TCP) scaffolds, which provided an excellent control over the internal architecture of scaffolds and enhanced their mechanical properties. A stereolithography apparatus was used to produce resin molds for ceramic gel casting. These molds were filled with a water based thermosetting ceramic slurry which solidifies inside the mold. After burning the resin mold and sintering, the β-TCP scaffolds with designed pore architecture were obtained. The pore morphology, size, and distribution of the resulting scaffolds were characterized using a scanning electron microscope. X-ray diffraction was used to determine the crystal structure and chemical composition of scaffolds. The mechanical measurements showed that the average compressive strength was 16.1 ± 0.8 MPa.

Effect of protic solvents on the physical properties of the ambient pressure dried hydrophobic silica aerogels using sodium silicate precursor

Abstract: Considering the importance of the highly porous, low density, transparent and nanostructured hydrophobic silica aerogels in the scientific and industrial applications, the experiments have been carried out to prepare the low density silica aerogels using the 1.12 specific gravity water glass (sodium silicate, Na2SiO3) precursor, ammonium hydroxide (NH4OH) catalyst, trimethylchlorosilane (TMCS) silylating agent, various first exchanging protic solvents and hexane as a second exchanging aprotic solvent. The first exchanging solvents used were: methanol, ethanol, propanol, isopropanol, butanol, isobutanol and hexanol. The molar ratio of the Na2SiO3:H2O:NH4OH:TMCS was kept constant at 1:56:0.02:0.4 respectively. The ambient pressure dried method was used for the preparation of hydrophobic silica aerogels. The effect of the exchanging protic solvents on the physical properties of the aerogels such as density, % of volume shrinkage, % of porosity, % of optical transmission, thermal conductivity, thermal stability and contact angle of the aerogels with water, were studied. FTIR studies were carried out to confirm the silylation of the aerogel samples. It was found that the exchanging protic solvents have profound effect on the physical and hydrophobic properties of the aerogels. Low density (0.07 g/cm3), high porosity (96.6 %), low thermal conductivity (0.091 W/mK), high contact angle (166°) silica aerogels could be prepared by using the isopropanol first exchanging solvent followed by the hexane as the second exchanging solvent along with the TMCS silylating agent with sodium silicate precursor.

Review on the key controls of designer copolymer-silica mesophase monoliths (HOM-type) with large particle morphology, ordered geometry and uniform pore dimension

Abstract: This review introduces the extensive key factors of the design of mesostructured monoliths with two- and three-dimensional (2D and 3D) geometries and large particle morphologies. Simple strategy in terms of fabrication time (within 10 min) and composition phase domains was achieved by using an instant direct-templating method of lyotropic and microemulsion phases of a variety of triblock copolymer (EOm-POn-EOm) surfactants, as we recently reported in [33] and [34]. The synthetic strategy provides realistic control over a wide range of mesophase geometries, yet maintains the long-range structural ordering, and thus improved the simplicity, significant periodicity, and high uniformity of the resultant silica monoliths. Cubic mesophases, in particular, exhibit a wide variety of mesostructured geometries when the block copolymers were used as a structure-directing agent under acidic synthesis conditions. For example, triblock copolymer (P123, EO20PO70EO20) was used to fabricate 2D hexagonal (P6mm). Our synthesis protocol revealed that ordered 3D cubic (Fd3m), (Im3m), and (Ia3d) silica monoliths were also fabricated in large domain sizes by templating P123 copolymers. In general, key factors such as the degree of solubilization of the hydrocarbons (co-solvent), the copolymer concentrations used in the phase domains, and the copolymer molecular nature, such as EO/PO ratio, significantly affect the formation of mesostructured phases and their extended long-range ordering in the final replicas of the silica monolith frameworks. The remarkable structural findings of 2D and 3D frameworks, transparent monoliths, and micropores combined with large cage- and cylindrical-like mesopores might show their desirability in many applications.

Comparative study on iodide and bromide isotopic exchange reactions by application of radioactive tracer technique

Abstract: In the present investigation, a short lived radioactive tracer isotopes 131I and 82Br were used to study the kinetics of isotopic exchange reactions. For bromide isotopic exchange reaction, the calculated values of specific reaction rate (min−1), and amount of bromide ions exchanged (mmol) were obtained higher than that for iodide isotopic exchange reaction under identical experimental conditions. For both the exchange reactions it was observed that when the concentration of ionic solution was increased twice, the␣percentage of ions exchanged increases sharply at nearly same specific reaction rate, indicating that concentration greatly influences the exchange reactions.

Characterization of the porous structure of biodegradable scaffolds obtained with supercritical CO2 as foaming agent

Abstract: Poly(e-caprolactone) foams were prepared, via a batch process, by using supercritical CO2 as foaming agent. Their porous structure was characterized through mercury porosimetry, helium and mercury pycnometry, scanning electron microscopy (SEM) and X-ray microtomography observations coupled with image analysis. The pore size distributions obtained by these two latter techniques show that the pore structure is more homogeneous when the foaming process is performed under a high CO2 saturation pressure (higher than 250 bars).

Silver modified porous silica from rice husk and its catalytic potential

Abstract: Rice husk silica modified with Ag (RH-Ag) and its calcined form, RH-Ag(C) are heterogeneous catalysts prepared from rice husk. The sodium silicate was extracted from rice husk using a simple solvent extraction technique. Silver was added during the precipitation of the gel to form RH-Ag. Calcination of RH-Ag yielded RH-Ag(C). RH-Ag and RH-Ag(C) was found to have a well defined amorphous phase and a crystalline phase. TEM analysis showed that silver was encapsulated into the silica matrix. Well defined mesoporous channels were found in RH-Ag(C). The EDX analysis showed that silver was indeed incorporated in the matrix of RH-Ag but it was not homogenously distributed. The specific surface area of RH-Ag and RH-Ag(C) was found to be 447 and 419 m2 g−1 respectively. The cation exchange capacity (CEC) for RH-Ag was found to be 0.470 mmol g−1 which was higher than that of RH-Ag(C) with 0.273 mmol g−1. Both the CEC and the BET values for RH-Ag(C) was consistent with the calcination process. Catalysis of benzyl alcohol using RH-Ag and RH-Ag(C) gave two products which were identified as benzaldehyde and dibenzyl ether. Percentage conversion was higher when the reaction was conducted with pure oxygen (14.0%) than in open air (0.60%). Overall, RH-Ag(C) was found to be a better catalyst for the formation of dibenzyl ether. The optimum weight and time of reaction for the oxidation was found to be 0.3 g and 3 h respectively for both catalysts. It was found that even in an inert atmosphere, 13% of benzaldehyde was obtained with RH-Ag(C) as catalyst. Mechanisms for the formation of benzaldehyde under oxygen and inert atmosphere and the condensation mechanism assisted by the presence of the Ag on the surface of the catalyst have been suggested.

Effects of carbonization conditions on the properties of coal-based microfiltration carbon membranes

Abstract: Carbon membranes, a novel porous inorganic membrane, have considerable potential applications in many industrial fields owing to their better stability in aggressive and adverse environments. However, the high cost of precursor materials has hampered their wide applications on commercial scale. In this study, coal, a cheap material, is used to prepare the tubular microfiltration carbon membranes. The effects of carbonization conditions on the properties of coal-based carbon membrane were investigated by the variation of the weight loss, shrinkage ratio of tube size and pore structure characteristics during carbonization. The results show that carbonization conditions greatly affect the properties of coal-based carbon membranes. The carbon membranes carbonized in the inert gases have more “open” porous structure and high gas flux compared to those carbonized in vacuum which makes the carbon membrane possess smaller pores and low gas flux. The carbonization temperature plays an important role in the determination of the pore structure and densification of carbon matrix. At the temperature below 600°C, the pore structure and carbon matrix of carbon membrane are formed with more than 95% of the total weight loss and only 48% of the total size shrinkage ratio. The matrix of carbon membrane gets more compact with the temperature increasing from 600°C to 900°C, in which the size shrinkage ratio is up to 52% with only 5% of the total weight loss. The low heating rate should favor the preparation of the carbon membranes with small average pore size and narrow pore size distribution, and the high gas flow rate can produce the carbon membranes with large average pore size and high porosity.

Synthesis and characterization of MCM-41-type composite materials prepared from ZSM-5 zeolite

Abstract: Micro/mesoporous composite materials with microporous and mesoporous double pores-size distribution were hydrothermally synthesized by using slurry or filtrate of alkali-treated ZSM-5 zeolite and were characterized by XRD, N2 adsorption, FT-IR, TEM and so on. The XRD and TEM patterns indicate the composite materials possess ordered hexagonal structure. The sample MZ-B using filtrate of alkali-treated ZSM-5 zeolite hardly contains raw ZSM-5 particles. However, sample MZ-A originated from the slurry of alkali-treated ZSM-5 zeolite may contain some ZSM-5 crystallites, owing to the differences in concentration and time of alkaline treatment for ZSM-5 zeolite.

Preparation of activated carbons by utilizing solid wastes from palm oil processing mills

Abstract: Feasibility of producing activated carbons by utilizing solid wastes (extracted flesh fibre and seed shell) from palm oil processing mills was investigated. The effects of activation conditions (CO2 flow rate, activation temperature and retention time) on the characteristics of the activated carbons, i.e. density, porosity, BET surface area, pore size distribution and surface chemistry were studied. In this study, the optimum conditions for activation were an activation temperature of 800 °C and a retention time of 30 min for fiber or 50 min for shell, which gave the maximum BET surface area. Pore size distribution revealed that the shell-based activated carbons were predominantly microporous whilst fiber activated carbon had predominant mesopores and macropores, suggesting the application of shell and fiber activated carbon as adsorbents for gas-phase and liquid-phase adsorption, respectively. This was confirmed by further gas- and liquid-phase adsorption tests.

A simple room temperature synthesis of MCM-41 with enhanced thermal and hydrothermal stability

Abstract: Highly ordered mesoporous silica samples were synthesized in less than 3 h using a simple synthesis methodology at room temperature with surfactant to silica ratio 0.1, using sodium silicate as a source of silica and cetyltrimethylammonium bromide (CTAB) as structure directing agent. Powder X-ray diffraction and N2 adsorption studies exemplified addition rate of sodium silicate solution is critical on the final properties of the materials. Remarkable thermal and hydrothermal stabilities of the samples prepared through this route were seen in contrast with the conventional methodology. Optimization of conditions surmised HCl as neutralizing agent and silicate addition time of 10 min is appropriate for obtaining a well crystalline and stable material. Slower rate of silicate addition might have facilitated better condensation of oligomeric silica on the preformed silica-surfactant aggregates responsible for such high thermal and hydrothermal stabilities. Development of such simple and easily expandable methodologies for these mesoporous materials will pave ways for their practical applications.

Effect of process parameters on the synthesis of mesoporous nanocrystalline zirconia with triblock copolymer as template

Abstract: Nanocrystalline zirconia powders with high surface area, mesoporous structure and tetragonal crystallite phase have been prepared by the surfactant-assisted route by using of Pluronic P123 block copolymer surfactant. The effect of several process parameters such as the type of zirconium precursor, pH value, refluxing time, refluxing temperature and surfactant to zirconium molar ratio on the structural properties of the powders have been investigated.

The formation mechanisms of multi-wall carbon nanotubes over the Ni modified MCM-41 catalysts

Abstract: Multi-wall carbon nanotubes (MWCNTs) were grown by thermal chemical vapor deposition (thermal CVD) of CH4 by using Ni-MCM-41 as the catalyst. Methane pyrolysis has been performed in a quartz tube reactor over the catalyst surface to form carbon atoms via dehydrogenation process. The migration and rearrangement of the surface carbon atoms result in the formation of MWCNTs. Transmission electron microscope (TEM) and scanning electron microscope (SEM) were used to determine the morphologies and structures of CNTs, and Raman spectroscopy was exploited to analyze their purity with the relative intensity between the D-band (Disorder band) in the vicinity of 1,350 cm−1 which is characteristic of the sp3 structure and G-band (Graphitic band) in vicinity of 1,580 cm−1 which is characteristic of the sp2 structure. In addition, the controlling factors of methane pyrolysis such as the catalyst composition; the reaction temperature, and the methane flow rate on the formation of MWCNTs were investigated to optimize the structure and yield of MWCNTs. SEM/TEM results indicate that the yield of the CNTs increases with increasing Ni concentration in the catalyst. The optimized reaction temperature to grow CNT is located between 640 and 670 °C. The uniform and narrow diameter MWCNTs form at lower flow rate of methane (∼30 sccm), and non-uniform in diameter and disorder structure of MWCNTs are observed at higher flow rate of methane. This is consistent with Raman analysis that the relative intensity of I D/I G increases with increasing methane flow rate. The formation mechanisms of the MWCNTs on the Ni-MCM-41 catalyst have been determined to be a Tip-Growth mode with a nanoscale catalyst particle capsulated in the tip of the CNT.

Hydrocracking of heavy oil using zeolites Y/Al-SBA-15 composites as catalyst supports

Abstract: A series of Y/Al-SBA-15 composites were prepared by a two-step synthesis procedure in mild acidic medium. The materials were characterized by powder X-ray diffraction (XRD), N2 sorption isotherms and TEM techniques. Catalytic cracking of cumene and 1,3,5-tri-isopropylbenzene was carried out as the probing reactions on these composites. The XRD results showed that these materials are composites of Al-SBA-15 and Y zeolite. N2 sorption isotherms and TEM displayed that these composites were abundant in micropores and mesopores. At the same time, the mesopores may communicate with the␣micropores in some domains, which may result in the high catalytic activities of Y/Al-SBA-15 composites for the␣cracking of both small-molecule (cumene) and large-molecule (1,3,5-tri-isopropylbenzene) hydrocarbons. The existence of mesopores may also make the acid sites easily accessible for reactants. Catalysts of W–Ni supported on Y/Al-SBA-15 and modified Y zeolites with mesopores were prepared by impregnation method, and the hydrocracking of heavy oil was performed on these catalysts. The catalyst using zeolite Y/mesoporous Al-SBA-15 composites as support gave higher yield of diesel compared to the catalysts using modified zeolite Y as support. In addition, the higher aromatics potential of heavy naphtha and the significantly lower BMCI (U.S. Bureau of Correlation Index) of tail oil revealed Y/Al-SBA-15 composite catalyst possessed integrated performance in the hydrocracking of heavy oil. These results proved that the combination of Y zeolites and mesoporous Al-SBA-15 plays a great role in improving the performance of catalysts for hydrocracking heavy oils.

Thiouracil modified activated carbon as a sorbent for some precious and heavy metal ions

Abstract: A new sorbent is prepared by modifying activated carbon obtained from apricot stones with 2-hydroxy-2-mercaptopyrimidine (2-thiouracil). The products have been characterized as to their surface area, pore volumes, content of the functional groups with basic and acidic properties, IR spectra, sulfur content. Their sorption properties with respect to some precious (Au(III), Ag(I), Pt(II)) and heavy (Cu(II), Mn(II), Ni(II), Hg(II)) metals are investigated. The sorption is studied as a function of pH (in the interval 1÷8) and stirring time (1÷24 h). The static sorption capacities towards the metal ions are determined under optimum conditions at room temperature. The new sorbent containing thiouracil is appropriate for simultaneous preconcentration of the precious and heavy metal ions within a wide pH range. It shows a significantly higher capacity for the investigated metal ions than the original carbon.

Zeolite beta monoliths with hierarchical porosity by the transformation of bimodal pore silica gel

Abstract: Zeolite beta monoliths with hierarchical porosity were prepared by the steam-assisted conversion of pre-seeded bimodal pore silica gel using the Layer-by-Layer process. The bimodal pore silica gel acts as both macrotemplates and silica source. The zeolite beta monoliths were characterized by X-ray diffraction, scanning electron microscopy, IR absorption spectra and nitrogen adsorption measurements. This zeolite beta monolith had hierarchical porosity: the unique micropores within the zeolite, the small macropores generated by aggregation of crystallites and three dimensionally interconnected macropores formed by template of silica gel. It is believed that the hierarchical structured zeolite monoliths will show good properties and potential applications the fields of catalyst, ion exchange, and adsorption.

Catalytic cracking of isobutane over HZSM-5, FeHZSM-5 and CrHZSM-5 catalysts with different SiO2/Al2O3 ratios

Abstract: Several systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with different ratios of SiO2/Al2O3 (25,38,50,80, and 150) were prepared and they were characterized by means of X-ray diffraction (XRD), UV–Vis, NH3-TPD and BET techniques. The results indicated that, compared with uncalcined HZSM-5 zeolites, the total acid amounts, acidic site density and acidic strength of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts obviously decreased, while those of weak acid amounts obviously enhanced with the decrease of SiO2/Al2O3 molar ratio. When the ratio of SiO2/Al2O3 is less than 50, the three systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with same ratio of SiO2/Al2O3 gave similar and high isobutane conversions. However, when the ratio of SiO2/Al2O3 was equal to or greater than 80, these three systems of catalysts possessed different altering tendencies of isobutane conversions, thus their isobutene conversions were different. High yields of light olefins were obtained over the FeHZSM-5 and CrHZSM-5 zeolite catalysts with high ratio of SiO2/Al2O3 (≥80). The ratio of SiO2/Al2O3 has large effects on the surface area, and acidic characteristics of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolites catalysts, and thus further affect their catalytic performances for isobutane cracking. That is the nature of SiO2/Al2O3 ratio effect on the catalytic performances.

Requirements of organic gels for a successful ambient pressure drying preparation of carbon aerogels

Abstract: In this paper, we investigated the requirements of organic gels for a successful ambient pressure drying by analyzing the role of the strength, the pore size and the surfactant of organic gels in decreasing the drying shrinkage of organic aerogels. Experimental results showed the effect of the decrease of the surface tension, resulting from the surfactant, on the drying shrinkage was very small and negligible. The drying shrinkage depended strongly on the strength and the pore size. Subsequently, the respective role of the strength and the pore size was evaluated. It can be found that the strength plays a greater role than the pore size.

Development and characterization of silica-based membranes for hydrogen separation

Abstract: The method of chemical vapor deposition (CVD) in the counter current configuration was employed in the present study for the development of composite silica membranes. The experiments were carried out in a horizontal CVD reactor under controlled temperature conditions and at various reaction times and differential pressures across the substrate sides. Tetraethylorthosilicate (TEOS) and ozone were used as deposition precursors. Two types of substrates were employed: a porous Vycor tube and an alumina (γ-Al2O3) nanofiltration (NF) tube. Measurements with a novel mercury intrusion technique showed that significant reduction of the initial pore size of the γ-Al2O3 substrates was achieved, which reached 76% in the cases of extended silica deposition. Additionally, by appropriately interpreting the Knudsen type O2 permeance results, acquired during the CVD treatment of Vycor tubes, a pore radius reduction even down to the 30% of the initial value was concluded. The permeance of Η2 and other gases (Ηe, Ν2, Αr, CO2) on the developed membranes was measured in a home-made apparatus. The separation capability of the composite membranes was determined by calculating the selectivity of hydrogen over helium, nitrogen, argon and carbon dioxide.

The origins of photocatalysis

Abstract: The study of photocatalytic reactions was initiated in 1970's. The definitions of photocatalysis, photosynthesis and photodegradation (photo-ageing) are given. For photocatalysis the wavelength of UV irradiation and the nature of the photocatalyst are discussed. The experimental conditions and the mechanism of the photo-partial-oxidation of alkanes and olefinic hydrocarbons into aldehydes and ketones, at R.T., are presented. Conditions for the ``photo-splitting'' of water are discussed.

Effect of supercritical drying conditions in ethanol on the structural and textural properties of silica aerogels

Abstract: Research on the preparation and characterization of silica aerogels has focused mainly on transparency and monolithicity. In this paper, we address the effect of supercritical drying conditions in ethanol on the shrinkage and porous texture of aerogels. The variables studied included the initial amount of ethanol added to the reactor, initial pressure of N2, heating rate and stabilization time above supercritical conditions. The starting material was an alcogel obtained by the sol–gel process in acidic media. All aerogels were amorphous. In general, skeletal density increased when the initial amount of ethanol added into the body of the autoclave was decreased and the volume fraction of porosity was above 91%. According to infrared spectra, skeletal SiO2 network was independent of supercritical drying conditions. N2 adsorption isotherms identify the macroporous character of aerogels, which was confirmed by SEM and TEM. Specific surface area significantly increased when the initial volume of ethanol added to the reactor was increased and the stabilization time above supercritical conditions decreased, whereas surface area decreased when autoclave pre-pressurization was increased.