Showing papers on "BET theory published in 2002"

Enhanced photocatalytic activity of mesoporous and ordinary TiO2 thin films by sulfuric acid treatment

Abstract: Transparent anatase mesoporous TiO2 (MTiO2) and TiO2 nanometer thin films were prepared on soda-lime glass and fused quartz via the reverse micellar method and sol–gel method, respectively. The as-prepared MTiO2 and TiO2 films were then treated by dipping them in a H2SO4 solution. The MTiO2 and TiO2 films before and after surface acid treatment were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), BET surface area and UV–VIS spectrophotometry. The photocatalytic activity of the samples was evaluated by photocatalytic oxidation of acetone in air. It was found that MTiO2 thin films showed higher photocatalytic activity than that of the TiO2 thin films. This was attributed to the fact that MTiO2 thin films were composed of smaller monodisperse spherical particles about 15 nm and had higher specific surface areas. Furthermore, the monodispersity of TiO2 particles was beneficial to transfer and separation of photo-generated electrons and holes in the inner of and on the surface of TiO2 particle and reduced the recombination of photo-generated electrons and holes. The films deposited on quartz showed the highest photocatalytic activity because films deposited on quartz exhibited a better crystallization and had no sodium contaminant. The photocatalytic activity of MTiO2 and TiO2 thin films deposited on different substrates after treated with H2SO4 solution was significantly enhanced. Acid treatment was particularly effective for MTiO2/glass and TiO2/glass, which showed activity enhancement of four and over two times, respectively. This increase in activity has been correlated with the reduction of sodium ions and the increase in the adsorbed hydroxyl content on the surface of TiO2 films.

Synthesis of Nanorattles Composed of Gold Nanoparticles Encapsulated in Mesoporous Carbon and Polymer Shells

Abstract: In this study, we fabricated new spherical silica templates with submicrometer sized solid cores containing an encapsulated Au nanoparticle surrounded by a mesoporous shell structure. Hollow spherical carbon and polymer capsules, containing gold nanoparticles, were synthesized using these silica templates. The resulting carbon capsules inversely replicated the structure of the silica template and contained uniform pores with a narrow pore size distribution centered at 3.8 nm. These carbon capsules exhibited a BET surface area of >1000 m2 g-1 and a total pore volume of >1.0 cm3 g-1. In addition, hollow polymer capsules having a well-defined pore size were fabricated using a similar synthetic procedure.

Effects of calcination temperature on the photocatalytic activity and photo-induced super-hydrophilicity of mesoporous TiO2 thin films

Abstract: Mesoporous TiO2 nanometer thin films were prepared on fused quartz by the dip-coating sol–gel method from a system containing a triblock copolymer as a template (or pore-forming agent), and then calcined at different temperatures. These films were characterized by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, BET surface area and UV-visible spectrophotometry. The photocatalytic activity and photo-induced super-hydrophilicity of the films were evaluated by the photocatalytic degradation of acetone and water contact angle measurement in air, respectively. It was found that the thin films calcined at 700 °C not only show the highest photocatalytic activity, but also possess the greatest light-induced hydrophilicity and the slowest conversion rate from the hydrophilic to a hydrophobic state. The former is attributed to the fact that the films calcined at 700 °C are composed of anatase and rutile, which is beneficial in enhancing the transfer of photo-generated electrons from the anatase to the rutile phase, reducing the electron–hole combination rate in anatase and enhancing its activity. The high light-induced hydrophilicity and slow hydrophilic to hydrophobic conversion rate are due to the synergetic effect of good photocatalytic activity, sufficient surface hydroxyl content and a degree of surface roughness. Because of their high specific surface areas and mesoporous structures, the photocatalytic activity of mesoporous TiO2 thin films is higher than that of conventional TiO2 thin films.

Preparation of Wormhole-like Mesoporous TiO2 with an Extremely Large Surface Area and Stabilization of Its Surface by Chemical Vapor Deposition

Abstract: Mesoporous titania with BET surface area over 1200 m2/g-1 was synthesized by primary amine templating. Dodecyl-, tetradecyl-, and hexadecylamines gave intense XRD patterns with narrow pore-size distributions in which the most probable diameter changed according to the carbon chain length. Thermal treatment was necessary for the formation of a stable structure, which strongly depends on the vapor pressure during the process. No diffraction patterns were observed above 2θ = 10°, suggesting the amorphous nature of the mesoporous titania. UV−vis and XANES spectroscopies demonstrated that the local structure of titanium was mainly 5-coordinated and Oh (6-coordinated) Ti. Chemical vapor deposition (CVD) of titanium isopropoxide followed by its decomposition with water vapor was carried out to improve the thermal stability of template-extracted titania. Although this CVD treatment resulted in a decrease in the BET surface area by 20%, the treated TiO2 showed high thermal stability; surface areas higher than 500 ...

Sonochemical Synthesis of Mesoporous Iron Oxide and Accounts of Its Magnetic and Catalytic Properties

Abstract: Synthesis of mesoporous iron oxides has been reported using a sonochemical technique. Iron(III) ethoxide was used as an inorganic precursor and CTAB as an organic structure directing agent. After sonication the surfactant was removed by calcination and solvent extraction methods. FTIR spectra demonstrated the removal of the surfactant from the pores of the mesoporous iron oxide. The calcinated material was characterized by XRD, TEM, TGA, and BET surface area measurements. The surface area after solvent extraction is found to be 274 m2/g. The magnetic and catalytic properties of the materials have been studied. The as-prepared amorphous Fe2O3 has shown a paramagnetic behavior, while after calcination at 350 °C it changes to γ-Fe2O3 with good magnetic properties. The catalytic activity of mesoporous iron oxide was studied in the reaction of cyclohexane oxidation under mild conditions. The mesoporous Fe2O3 catalyst has shown high conversion of cyclohexane into cyclohexanone and cyclohexanol, with a high sele...

Light-induced super-hydrophilicity and photocatalytic activity of mesoporous TiO2 thin films

Abstract: Transparent mesoporous TiO2 (MTiO2) and TiO2 nanometer thin films were prepared on fused quartz via the modified reverse micellar and sol–gel methods. The MTiO2 and TiO2 films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD), BET surface area and UV–Vis spectrophotometry. The photoinduced super-hydrophilicity and photocatalytic activity of the films were evaluated by the water contact angle measurement and photocatalytic oxidation of acetone in air, respectively. It was found that MTiO2 thin films at 500 °C showed higher photocatalytic activity and better light-induced hydrophilicity than the TiO2 thin films. This is attributed to the following reasons: (1) MTiO2 thin films are composed of smaller monodisperse spherical particles about 15 nm diameter, and possess more mesopores between spherical particles and higher surface areas and surface roughness, (2) the monodispersity of MTiO2 particles was beneficial to the transfer and separation of photo-generated electrons and holes inside of and on the surface of TiO2 particles, and reduced the recombination of photo-generated electrons and holes. At 900 °C, the MTiO2 and TiO2 films appeared to be in the rutile phase, but showed photoinduced hydrophilicity and no photocatalytic activity. This confirmed that the mechanism of photoinduced super-hydrophilicity of the films is different from that of photocatalytic oxidation.

Influence of the silica based matrix on the formation of iron oxide nanoparticles in the Fe2O3–SiO2 system, obtained by sol–gel method

Abstract: Composite iron oxide–SiO2 materials were prepared by a sol–gel method starting with two types of precursors, tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS), as the SiO2 source. As the iron source a soluble Fe2+ salt, mainly Fe(SO4)2·7H2O, was used, the iron oxides were generated during the sol–gel process. The amorphous gels obtained were thermally treated up to 1000 °C in order to obtain iron oxides with different structures and grain size. The initial gels and the thermally treated samples were characterised by DTA/TGA analysis, DR-UV–VIS and IR-spectroscopy, EPR measurements, transmission electron microscopy (TEM) and BET surface area methods. The matrices obtained from the precursors play a major role in the evolution of the process. In both cases the initial gels are amorphous. In the non-porous matrix obtained by thermal treatment using methyltriethoxysilane (MTEOS), the tendency for crystallisation increases, and the iron oxide particle size is increased.

The kinetics and mechanism of SO2 oxidation by O3 on mineral dust

Abstract: The oxidation of SO2 by O3 on mineral dust was studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Formation of sulfate was observed on the surface. A two-step mechanism that involves physisorbed SO2 followed by oxidation is presented. The formation rate was determined to be first order with respect to SO2 and zero order in O3. The reactive uptake coefficient, γ, was determined from the infrared absorbance, that was calibrated by ion chromatography, and from the geometric or the BET surface area. γSO2 was independent of the SO2 concentration and was determined to be in the order of 10−3 using the geometric surface area, or 10−7 using the BET surface area for [SO2] = 2.2 × 1012 to 2.0 × 1013 and [O3] = 5.6 × 1012 (in units of molecule cm−3). γO3 depended linearly on the O3 concentration and varied from 10−2 to 10−4 using the geometric area or 10−6 to 10−8 using the BET area for [O3] = 1.9 × 1012 to 5.5 × 1013 and [SO2] = 5.4 × 1012 (in units of molecule cm−3). In all experiments surface saturation was observed with an amount of 2 × 1019 sulfate ions g−1 on the mineral dust sample. In the presence of water vapor regeneration of active sites was observed. After several exposures to water vapor corresponding to 80% relative humidity and successive SO2 and O3 treatments the amount of formed sulfate covering the surface was increased by 47% compared to the dry experiments.

Hydrophobic particulate inorganic oxides and polymeric compositions containing same

Abstract: Described are hydrophobic particulate inorganic oxides useful for reinforcing polymeric composition, e.g., rubber. The materials are characterized by: (a) the substantial absence of functional groups capable of chemical reaction with rubber; (b) a BET surface area of in the range of from 40 to 350 m2/g; (c) a hydroxyl content in the range of 2 to 15 OH/nm2; (d) a carbon content in the range of from 0.1 to 6 percent by weight that is substantially non-extractable; (e) a pH in the range of from 3 to 10; (f) an M1 Standard White Area less than 0.4 percent and (g) a methanol wettability of from 15 to 45 percent. Compositions such as polymers, cured organic rubber articles, master batches and slurries containing the hydrophobic fillers are also described.

Hybrid organic-inorganic derivatives of layered double hydroxides and dodecylbenzenesulfonate: Preparation and adsorption characteristics

Abstract: Layered double hydroxides (LDHs) are anionic clays that can be synthesized under laboratory conditions. In this study, different LDHs were synthesized by a coprecipitation method, with the parent products and calcined derivatives evaluated for their ability to adsorb the anionic surfactant, dodecylbenzenesulfonate (DBS). Adsorption isotherms for DBS retention on LDHs were typical L-type curves, with adsorption data conforming to a simple Langmuir equation. Langmuir maximum adsorption of DBS on calcined-LDH was significantly higher than that on uncalcined-LDHs. Organo-LDHs were also synthesized by incorporating DBS into LDHs via ion-exchange, reconstruction of calcined-LDH and in-situ synthesis methods. X-ray diffraction analysis of organo-LDHs revealed that DBS was intercalated into LDHs with the mono-layer DBS molecules oriented perpendicularly to LDH surfaces. Intercalation of DBS into LDHs decreased surface area according to BET analysis. The adsorption capacities of organo-LDHs for trichloroethylene (TCE) and tetrachloroethylene (PCE) were substantially greater than the original LDH materials. Adsorption of organic compounds by organo-LDHs was due to a partitioning mechanism.

Effect of pH on Competitive Adsorption of Cu(II), Ni(II), and Zn(II) from Water onto Chitosan Beads

Abstract: The amounts of adsorption of Cu 2+ ,N i 2+ , and Zn 2+ from single, binary, and tertiary nitrate solutions onto glutaraldehyde cross-linked chitosan beads were measured. The beads had an average particle size and pore volume of 2 mm and 0.06 cm 3 /g, respectively, and had a BET surface area of 60 m 2 /g. All experiments were performed at 298 K as a function of initial pH (2.0-5.0), total metal concentration (0.77-17.0 mol/m 3 ), and molar concentration ratio (0.25-4) in the aqueous phase. It was shown that the amount of metal adsorption generally increased with increasing solution pH. Competitive adsorption was significant in binary and tertiary systems when Cu 2+ was present. The selectivity factor reached maximum in an equilibrium pH range of 5.1-5.3 and 4.5-4.9 for the Cu-Ni and Cu-Zn binary systems, respectively. This adsorbent provided a possibility for selective separation of Cu 2+ from such multi-component solutions.

Cadmium uptake by hydroxyapatite synthesized in different conditions and submitted to thermal treatment.

Abstract: This paper intends to evaluate the uptake of cadmium ions from aqueous solution by 21 hydroxyapatite samples which have been synthesized in different conditions. It has been determined thatthe variation on the hydroxyapatite sorption capacity is neither related to sample solubility nor to hydroxyapatite Ca/P molar ratio. Cd2+ sorption is controlled by sample BET surface area, which shows a direct dependence on the hydroxyapatite crystallite dimensions. The hydroxyapatite pore distribution presented modes at 1000 and 60,000 A, corresponding to intracrystallite voids and voids between the agglomerate of these crystallites, respectively. Pores belonging to the former mode immobilize the major part of Cd2+. The influence of sample thermal treatment on Cd2+ sorption efficiency has been studied using hydroxyapatite samples calcined at temperatures ranging from 500 to 1140 degrees C. Similarly to nonthermally treat samples, the Cd2+ sorption on calcined hydroxyapatite could be described by Langmuir isotherms. The results showed that the maximum sorption capacity decreased from 0.631 mmol g(-1) for the noncalcined sample to 0.150 mmol g(-1) for the one calcined at 900 degrees C. This drop in the sorption capacity could also be explained by a reduction in its specific surface area, which is induced bythe increase of the crystal size.

Wet air oxidation of p-coumaric acid over promoted ceria catalysts

Abstract: The catalytic wet air oxidation (WAO) of p -coumaric acid (PCA) has been investigated over Fe- and Zn-promoted ceria catalysts. The catalysts have been prepared by the coprecipitation method and have been characterized by X-ray diffraction (XRD), BET surface area, SEM–EDX and temperature programmed reduction (TPR). The oxidation reaction was carried out in a batch reactor under an air pressure of 2 MPa and in the temperature range 353–403 K. Fe-CeO 2 catalysts, with 20–50 mol% of iron, were found more effective than the unpromoted and Zn-promoted ceria catalysts. On the basis of characterization data, it has been suggested that the higher activity of the Fe-promoted catalysts is related to the modification of the structural and redox properties of the ceria oxide catalyst on addition of iron.

Preparation of nanosized nickel aluminate spinel by a sonochemical method

Abstract: Nanosized nickel aluminate spinel particles have been synthesized with the aid of ultrasound radiation by a precursor approach. Sonicating an aqueous solution of nickel nitrate, aluminium nitrate and urea yields a precursor which on heating at 950 °C for 14 h yields nanosized NiAl 2 O 4 particles with a size of ca. 13 nm and with a surface area of about 108 m 2 g −1 . The nanosized nickel aluminate particles as well as the precursor have been characterized by elemental analysis, powder X-ray diffraction, Transmission electron microscopy, Thermogravimetric analysis, DSC, FT-IR, Diffuse reflectance spectroscopy and BET surface area measurements.

Preparation, characterization and activity testing of vanadia catalysts deposited onto silica and alumina supports by atomic layer deposition

Abstract: A gas phase preparation technique, atomic layer deposition (ALD), was applied to synthesize supported vanadium oxide catalysts. The growth of vanadia on silica and alumina was achieved by chemisorption of the volatilized vanadium precursor onto surface hydroxyl groups of the support, followed by oxidative treatment in air. The influence of the preparative method on surface structure, redox and acidic properties and catalytic activity was demonstrated by examining also the corresponding conventionally impregnated catalysts. The catalysts were characterized by chemical analysis, BET surface area measurements, X-ray diffraction (XRD), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and 51 V solid state nuclear magnetic resonance ( 51 V NMR). Tetracoordinated surface vanadia species were detected as the principal vanadium species in all the catalysts studied. The ALD catalysts, compared to the analogous impregnated ones, were found to be highly dispersed and more easily reduced, as revealed by temperature programmed reduction (TPR). The results from measurements using ammonia adsorption microcalorimetry and pyridine adsorption infrared (IR) spectroscopy indicated that the number, strength and strength distribution of the surface acid sites were affected by the preparative mode and the support. The same Lewis and Bronsted acid sites were detected for all impregnated and ALD catalysts, but those prepared in the gas phase showed slightly stronger acidic characteristics. In propane dehydrogenation (DH), the rate of propene formation by the ALD catalysts was higher than that achieved by the conventionally impregnated catalysts.

Quantifying surface areas of clays by atomic force microscopy

Abstract: Rapid and accurate determination of the surface area of three kaolinite clay standards, taking into account the complex microtopography of the particles, was achieved using atomic force microscopy images and computerized image analysis. All surface areas were determined to within 3%. Edge surface area is 18.2–30.0% of the total surface area depending on the particular kaolinite standard. Specific surface areas agree to within 4% of published values determined by the BET method. The approach can be applied to clay and nanoparticle samples too small in quantity for BET analysis, since it requires ~11 orders of magnitude less material.

Water vapor sorption behavior of smectite-kaolinite mixtures

Abstract: An experimental program was conducted to investigate the water-vapor sorption characteristics of smectite and kaolinite mixtures. End-member smectite and kaolinite were slurry-mixed together at mass-controlled ratios corresponding to 0%, 20%, 50%, 70%, 80%, 90% and 100% smectite. Vapor desorption isotherms for the mixtures were measured at 24°C for relative humidity (RH) ranging from ∼95% to 0%. Results show that the amount of water adsorbed by the clay mixtures at a given RH increases systematically with increasing smectite content. Derivative analysis of the sorption isotherms shows evidence of transitions between the two-, one- and zero-layer hydrate-states for the smectite-rich mixtures. The transitions become less apparent as the smectite content decreases. Monolayer coverage, specific surface area, and heat of adsorption were estimated from the isotherms using BET theory. It is shown that monolayer coverage and specific surface for the clay mixtures can be reasonably approximated by weighted averaging of the end-member clay properties. General methodologies are presented for predicting the sorption behavior (i.e. soil-water characteristics) and effective specific surface area from measurements of the end-member sorption isotherms.

Unburned Carbon from Fly Ash for Mercury Adsorption: I. Separation and Characterization of Unburned Carbon

Abstract: In searching for a low cost adsorbent for mercury removal from flue gas, this study focuses on the utilization of unburned carbons from fly ash as the substitute material for the costly activated carbons In this first paper of the series, various separation technologies are introduced for the extraction of unburned carbon from different sources of fly ash The unburned carbons have been efficiently separated from clean ash, which is a value-added product for the concrete industry, with the separation technologies such as gravity separation, electrostatic separation, and froth flotation Carbon concentrate with a LOI (Loss On Ignition) value of 67~80% has been generated from the processes Characterization of the carbon products has been performed to determine the physical and chemical properties of the material It has been found that the unburned carbon particles had a porous structure, which is similar to the activated carbon The BET surface area of these materials was in a range of 25~58m2/g The majority of the pores are in the range of macropore, and some parts of the surface were embedded with glass spheres There is a linear relationship between the LOI value and the carbon and sulfur content in the carbon concentrate Chemical analysis indicated that the mercury content in unburned carbon was much higher than the other separation products, which suggests that the carbon has certain ability to capture mercury from flue gas