Showing papers on "BET theory published in 2003"

Photocatalytic degradation of various dyes by combustion synthesized nano anatase TiO2

Abstract: The 8–10 nm pure anatase phase titania with $156 m^2/g$ BET surface area was prepared by solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and BET surface area. This catalyst was used for the photocatalytic degradation of various dyes such as heteropolyaromatic dye (Methylene blue), anthraquinonic dye (Alizarin S), and azoic dyes (Methyl red, Congo red, and Orange G). The effect of catalyst loading, initial concentrations of the dyes, pH, and transition metal doping on $TiO_2$ was investigated. Substitution of $TiO_2$ with transition metal had a detrimental effect on the photocatalytic activity. However, this inhibition effect was not observed with Pt impregnated $TiO_2$. This was attributed to the metals being in ionic state in metal substituted $TiO_2$ synthesized by combustion method, and zero state of metal in impregnated catalysts as evidenced by XPS study. The degradation of dyes was also investigated in solar exposure. The photoactivity of the combustion synthesized titania was higher than commercial $TiO_2$(Degussa P-25) for both UV and solar exposure. The experimental data followed Langmuir–Hinshelwood (L–H) rate form and the kinetic parameters were obtained.

Application of TiO2-mounted activated carbon to the removal of phenol from water

Abstract: TiO 2 -mounted activated carbon was prepared through hydrolytic precipitation of TiO 2 from teraisopropyl orthotitanate and following heat treatment at 650–900 °C for 1 h under a flow of nitrogen The removal of phenol from its aqueous solution under UV irradiation was measured on TiO 2 -mounted activated carbons thus prepared Although BET surface area of TiO 2 -mounted activated carbons decreased drastically in comparison with the original activated carbon, the efficiency of phenol removal under UV irradiation was high The sample heated at 900 °C, which consisted mainly of rutile phase, showed the highest total removal of phenol Efficiency of phenol degradation is reduced because of phenol adsorption on the catalyst

Synthesis and Characterization of Hydroxyapatite Nanopowders by Emulsion Technique

Abstract: Nanocrystalline HAp powder was synthesized using surfactant template systems. Composition of the microemulsion and synthesis parameters had significant effect on the formation of HAp nanopowder and their surface area and morphology. Powders were prepared with a surface area of 130 m2/g and particle size between 30 and 50 nm with needle shape and spherical morphology. Nanocrystalline hydroxyapatite (HAp) powder was synthesized using the reverse micelle-processing route. Cyclohexane was used as the oil phase, mixed poly(oxyethylene)5 nonylphenol ether (NP-5) and poly(oxyethylene)12 nonylphenol ether (NP-12) as the surfactant phase, and a solution of Ca(NO3)2 and H3PO4 was used as the aqueous phase. The powders were characterized by BET surface area analyzer, powder X-ray diffraction, and transmission electron microscopy. It was found that experimental conditions such as aqueous/organic phase volume ratio, pH, aging time, aging temperature, and metal ion concentration in the aqueous phase affected the crysta...

Physicochemical characterization and adsorption behavior of calcined Zn/Al hydrotalcite-like compound (HTlc) towards removal of fluoride from aqueous solution.

Abstract: A Zn/Al hydrotalcite-like compound (HTlc) was prepared by co-precipitation (at constant pH) method and was characterized by XRD, TG/DTA, FTIR, and BET surface area The ability of Zn/Al oxide to remove F− from aqueous solution was investigated All the adsorption experiments were carried out as a function of time, pH, concentration of adsorbate, adsorbent dose, temperature etc It was found that the maximum adsorption takes place within 4 h at pH 60 The percentage of adsorption increases with increase in the adsorbent dose, but decreases with increase in the adsorbate concentration From the temperature variation it was found that the percentage of adsorption decreases with increase in temperature, which shows that the adsorption process is exothermic in nature The adsorption data fitted well into the linearly transformed Langmuir equation Sulfate and phosphate were found to have profound effects on fluoride removal Thermodynamic parameters such as ΔG0, ΔH0, and ΔS0 were calculated The negative value of ΔH0 indicates that the adsorption process is exothermic The apparent equilibrium constants (Ka) are also calculated and found to decrease with increase in temperature With 001 M NaOH the adsorbed F− could be completely desorbed from Zn/Al oxide in 6 h

Carbon capacious Ni-Cu-Al2O3 catalysts for high-temperature methane decomposition

Abstract: Steady and efficient decomposition of methane can be achieved at 625–675 °C over copper-promoted (8–15 wt.% of copper) nickel catalysts prepared from a Feitknecht compound precursor. Such catalysts permit one to increase the yield of catalytic filamentous carbon (CFC) and control both microstructural and textural properties of CFC by varying the copper concentration in the catalyst. The maximal conversion of methane into hydrogen and carbon reaches 40% at 675 °C at the carbon capacity not lower than 700 g/g Ni under optimal conditions. The BET surface area of the CFC is 285.9 m 2 /g. The influence of promotion of nickel-containing catalysts with copper on the catalytic activity is discussed.

Direct preparation of nanoporous carbon by nanocasting.

Abstract: Nanoporous carbon with narrow pore size distribution was prepared via a nanocasting technique by direct carbonization of cyclodextrin-silica organic−inorganic hybrid composite. The obtained carbon exhibited very high BET surface area and high pore volume.

A nanoporous network polymer derived from hexaazatrinaphthylene with potential as an adsorbent and catalyst support

Abstract: The synthesis and properties of a nanoporous network polymer incorporating 5,6,11,12,17,18-hexaazatrinapthylene (Hatn) as the rigid functional unit is described. This material is readily prepared from the efficient dibenzodioxane forming reaction between 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene and 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane and exhibits a high BET surface area (775 m2 g−1) similar to that obtained from related nanoporous networks based on phthalocyanine and porphyrin macrocycles. The ability of the Hatn unit to bind to metal ions was shown by the sequential binding of three palladium(II) dichloride moieties to a soluble model Hatn compound using a 1H NMR titration experiment. When exposed to an excess of palladium(II) dichloride in chloroform solution, the Hatn nanoporous network is shown to adsorb 3.9 mmol g−1 of the metal complex. The resulting material retains porosity (BET surface area = 347 m2 g−1) and should be useful as a heterogeneous catalyst. The Hatn network polymer is also shown to be effective for the adsorption of phenol from aqueous solution with a maximum adsorption of 5 mmol g−1, which is a significant improvement over the performance of activated carbon reported in similar studies.

Effects of Alkali Metal and Ammonium Cation Templates on Nanofibrous Cryptomelane-type Manganese Oxide Octahedral Molecular Sieves (OMS-2)

Abstract: Four alkali cations (Li+, Na+, K+, and Rb+) and ammonium (NH4+), have been successfully used as templates for the synthesis of cryptomelane-type manganese oxide octahedral molecular sieves (A−OMS-2, A = the template cation). H−OMS-2 material has been prepared by the calcination of NH4−OMS-2. These A−OMS-2 materials have been characterized by X-ray diffraction, transmission electron microscopy, high-resolution scanning electron microscopy, thermogravimetric analysis, temperature-programmed desorption, inductively coupled plasma analysis, and BET surface area pore size distribution measurements. Catalytic evaluation of these A−OMS-2 materials has been done with the aerobic oxidation of cyclohexanol to cyclohexanone. All of these A−OMS-2 materials have cryptomelane tunnel structures with different degrees of crystallinity and nanofibrous morphology. The nature of the cation templates affects the formation and microstructures of the A−OMS-2 materials. The physical and chemical properties, such as the thermal ...

Formation of Silicalite-1 Hollow Spheres by the Self-assembly of Nanocrystals

Abstract: A simple approach is reported for the preparation of hollow spheres with a 10−20-nm-thick shell of silicalite-1 nanocrystals. The nanocrystals were produced by the steaming of silicalite-1 nanoprecursors (NPs), collected with the help of surfactant from a clear synthesis solution immediately following the induction period. The nanocrystals produced were ≈10−20 nm with a BET surface area of 440−470 m2/g and an external surface area >112 m2/g. A water adsorption isotherm confirmed that the nanocrystals were hydrophobic in nature. These nanocrystals self-assembled into hollow spheres of 100−300-nm diameter when ultrasonicated in ammoniac ethanol.

Sonochemical Deposition of Air-Stable Iron Nanoparticles on Monodispersed Carbon Spherules

Abstract: A novel route was used to prepare “perfect spherical” monodispersed carbon with a smooth surface, which has a surface area of 8 m2/g. Air-stable iron nanoparticles with an average size of ∼10 nm were deposited on the surface of preformed carbon spherules with the aid of power ultrasound. This coating was achieved by ultrasonic irradiation of a slurry of carbon spherules and Fe(CO)5 in diphenylmethane for 90 min under an argon atmosphere. The as-prepared amorphous material was annealed in argon at 700 °C, forming air-stable iron deposited on carbon spherules. The product was characterized by XRD, TEM, EDAX, BET surface area, HR-SEM, TGA, DSC, magnetic measurements, electron paramagnetic resonance, and Raman spectroscopy.

Water gas shift reaction of reformed fuel over supported Ru catalysts

Abstract: Precious metal catalysts (Ir, Pd, Pt, Rh and Ru) supported on Al2O3 and Ru catalysts on CeO2, La2O3, MgO, Nb2O5, Ta2O5, TiO2, V2O5 and ZrO2 were investigated for water gas shift reaction of reformed gas. Ru/V2O3 catalyst reduced at 400 °C in H2 demonstrated the highest activity for the shift reaction without producing methane. The activities for the shift reaction over Ru catalysts supported on different oxides were not correlated with BET surface area or Ru dispersion, but the activity depended on the chemical character of oxide supports. The catalyst supported on a strongly basic or acid oxide is not effective for the shift reaction. In the same series of catalysts like Ru/V2O3, the activity systematically changed with BET surface area and Ru dispersion.

Synthesis and characterization of nano-biomaterials with potential osteological applications.

Abstract: The manufacture of high-surface area, un-agglomerated nano-sized (1–100 nm) bioceramic particles are of interest for many applications including injectable/controlled setting bone cements, high strength porous/non-porous synthetic bone grafts, and the reinforcing phase in nano-composites that attempt to mimic the complex structure and superior mechanical properties of bone. In the present study, we report on the manufacture of nano-particle hydroxyapatite powders by several wet chemical methods, which incorporate a freeze-drying step. In particular, it was found that the emulsion-based syntheses yielded powders with high surface areas and small primary particle sizes. Freeze drying rather than oven drying of powders prepared by conventional wet chemical synthesis yielded a nano-sized powder with a comparatively higher surface area of 113 m2/g. All powders were calcined in air in a furnace at 900 °C to investigate the effects of synthesis method on phase purity and surface area. The materials were characterized by a range of analytical methods including Fourier-transform infrared spectroscopy employing the photo acoustic (PAS-FTIR) sampling technique, BET surface area analysis, X-ray powder diffraction (XRD), and the particles were examined using a transmission electron microscope (TEM).

Highly stable Pd/CeO2 catalyst for hydrodechlorination of chlorobenzene

Abstract: Catalysts containing 1 wt.% Pd supported on CeO2 were prepared by the deposition–precipitation (DP) and conventional impregnation (IMP) methods. The effect of the nature of precursor was also investigated using the chloride and nitrate salts of Pd. The catalysts were characterized by nitrogen adsorption (for BET surface area), CO chemisorption, temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). Their activity and stability was evaluated in the vapor phase hydrodechlorination (HDC) of chlorobenzene, using molecular hydrogen. The catalyst prepared by the DP method using the chloride precursor exhibited the highest stability during the reaction. Contrary to the general observation that the low dispersed catalysts are preferred for the HDC, by adopting the DP method of catalyst preparation, the present investigation demonstrates that high dispersed catalysts also offer better stability. This is a significant observation in terms of considerable reduction in Pd content of the catalyst. The higher stability is ascribed to the formation of cationic Pd species which resist deactivation. On the contrary, the IMP catalysts are susceptible for transformation into inactive palladium chloride, thus loosing stability.

Modelling arsenic(III) adsorption from water by sulfate-modified iron oxide-coated sand (SMIOCS)

Abstract: A medium developed by coating BaSO4 and Fe on quartz sand known as sulfate-modified iron oxide-coated sand (SMIOCS) was evaluated for the removal of arsenic(III) from simulated water with an ionic strength of 0.01 M NaNO3 during batch studies. The medium was characterised for BET surface area, alkali-resistance, acid-resistance and the presence of iron and barium on the coated surface. Two simplified kinetic models, ie active available site (AAS) and chemical reaction rate models, were tested to investigate the adsorption mechanisms. The values of rate constants for both the models were found to decrease with increasing As(III) concentrations in the solute. The inverse relationship of rate constants of the reaction rate model with BET surface area showed that As(III) adsorption on SMIOCS was not due to physisorption but to chemisorption. A study of the effect of solute temperature showed that the adsorption of As(III) on SMIOCS media was due to chemisorption. The results of isothermal studies conducted at different pH values showed that adsorption data satisfied both the Langmuir and the Freundlich isotherm models. The adsorption of As(III) on the medium was pH dependent and maximum removal was observed in the pH range of 7–9. © 2002 Society of Chemical Industry