Showing papers on "BET theory published in 2004"

Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density

Abstract: 1 Theoretical- 1 Introduction- 11 Real Surfaces- 12 Factors Affecting Surface area- 13 Surface Area from Particle Size Distributions- 14 References- 2 Gas Adsorption- 21 Introduction- 22 Physical and Chemical Adsorption- 23 Physical Adsorption Forces- 24 Physical Adsorption on a Planar Surface- 25 References- 3 Adsorption Isotherms- 31 Pore Size and Adsorption Potential- 32 Classification of Adsorption Isotherms- 33 References- 4 Adsorption Mechanism- 41 Langmuir and BET Theories (Kinetic Isotherms)- 411 The Langmuir Isotherm- 412 The Brunauer, Emmett, and Teller (BET) Theory- 42 The Frenkel-Halsey-Hill (FHH) Theory of Multilayer Adsorption- 43 Adsorption in Microporous Materials- 431 Introduction- 432 Aspects of Classical, Thermodynamic Theories for Adsorption in Micropores: Extension of Polanyi's Theory- 433 Aspects of Modern, Microscopic Theories for Adsorption in Micropores: Density Functional Theory and Molecular Simulation- 4331 Density Functional Theory (DFT)- 4332 Computer Simulation Studies: Monte Carlo Simulation and Molecular Dynamics- 4333 NLDFT and Monte Carlo Simulation for Pore Size Analysis- 44 Adsorption in Mesopores- 441 Introduction- 442 Multilayer Adsorption, Pore Condensation and Hysteresis- 443 Pore Condensation: Macroscopic, Thermodynamic Approaches- 4431 Classical Kelvin Equation- 4432 Modified Kelvin Equation- 444 Adsorption Hysteresis- 4441 Classification of Hysteresis Loops- 4442 Origin of Hysteresis- 445 Effects of Temperature and Pore Size: Experiments and Predictions of Modern, Microscopic Theories- 45 References- 5 Surface Area from the Langmuir and BET Theories- 51 Specific Surface Area from the Langmuir Equation- 52 Specific Surface Area from the BET Equation- 521 BET-Plot and Calculation of the Specific Surface Area- 522 The Meaning of Monolayer Coverage- 523 The BET Constant and Site Occupancy- 524 The Single Point BET Method- 525 Comparison of the Single Point and Multipoint Methods- 526 Applicability of the BET Theory- 527 Importance of the Cross-Sectional Area- 528 Nitrogen as the Standard Adsorptive for Surface Area Measurements- 529 Low Surface Area Analysis- 53 References- 6 Other Surface Area Methods- 61 Introduction- 62 Gas Adsorption: Harkins and Jura Relative Method- 63 Immersion Calorimetry: Harkins and Jura Absolute Method- 64 Permeametry- 65 References- 7 Evaluation of the Fractal Dimension by Gas Adsorption- 71 Introduction- 72 Method of Molecular Tiling- 73 The Frenkel-Halsey-Hill Method- 74 The Thermodynamic Method- 75 Comments About Fractal Dimensions Obtained from Gas Adsorption- 76 References- 8 Mesopore Analysis- 81 Introduction- 82 Methods based on the Kelvin equation- 83 Modelless Pore Size Analysis- 84 Total Pore Volume and Average Pore Size- 85 Classical, Macroscopic Thermodynamic Methods versus Modern, Microscopic Models for Pore Size Analysis- 86 Mesopore Analysis and Hysteresis- 861 Use of Adsorption or Desorption Branch for Pore Size Calculation?- 862 Lower Limit of the Hysteresis Loop- Tensile Strength Hypothesis- 87 Adsorptives other than Nitrogen for Mesopore Analysis- 88 References- 9 Micropore Analysis- 91 Introduction- 92 Micropore Analysis by Isotherm Comparison- 921 Concept of V-t curves- 922 The t- Method- 923 The ?s method- 93 The Micropore Analysis (MP) Method)- 94 Total Micropore Volume and Surface Area- 95 The Dubinin-Radushkevich (DR) Method- 96 The Horvath-Kawazoe (HK) Approach and Related Methods- 97 Application of NLDFT: Combined Micro/Mesopore Analysis With a Single Method- 98 Adsorptives other than Nitrogen for Super- and Ultramicroporosimetry- 99 References- 10 Mercury Porosimetry: Non-Wetting Liquid Penetration- 101 Introduction- 102 Young-Laplace Equation- 103 Contact Angles and Wetting- 104 Capillarity- 105 The Washburn Equation- 106 Intrusion - Extrusion Curves- 107 Common Features of Porosimetry Curves- 108 Hysteresis, Entrapment and Contact Angle- 109 Contact Angle Changes- 1010 Porosimetric Work- 1012 Theory of Porosimetry Hysteresis- 1013 Pore Potential- 1014 Other Hysteresis Theories (Throat-Pore Ratio Network Model)- 1015 Equivalency of Mercury Porosimetry and Gas Sorption- 1016 References- 11 Pore Size and Surface Characteristics of Porous Solids by Mercury Porosimetry- 111 Application of The Washburn Equation- 112 Pore Size and Pore Size Distribution from Mercury Porosimetry- 1121 Linear Pore Volume Distribution- 1122 Logarithmic Pore Volume Distribution- 1123 Pore Number Distributions- 1124 Pore Length Distribution- 1125 Pore Population (Number Distribution)- 1126 Surface Area and Surface Area Distribution from Intrusion Curves- 1127 Pore Area Distributions- 113 Pore Shape from Hysteresis- 114 Fractal Dimension- 115 Permeability- 116 Tortuosity- 117 Particle Size Distribution- 1171 Mayer & Stowe Approach- 1172 Smith & Stermer Approach- 118 Comparison of Porosimetry and Gas Sorption- 119 Solid Compressibility- 1110 References- 12 Chemisorption: Site Specific Gas Adsorption- 121 Chemical Adsorption- 122 Quantitative Measurements- 123 Stoichiometry- 124 Monolayer Coverage- 1241 Extrapolation- 1242 Irreversible Isotherm and Bracketing- 1243 Langmuir Theory- 1244 Temperature Dependent Models- 1245 Temkin Method- 1246 Freundlich Method- 1247 Isotherm Subtraction - Accessing Spillover- 1248 Surface Titration- 125 Active Metal Area- 126 Dispersion- 127 Crystallite (Nanoparticle) Size- 128 Heats of Adsorption and Activation Energy- 1281 Differential Heats of Adsorption- 1282 Integral Heat of Adsorption- 1283 Activation Energy- 129 References- 2 Experimental- 13 Physical Adsorption Measurements - Preliminaries- 131 Experimental Techniques for Physical Adsorption Measurements- 132 Reference Standards- 133 Representative Samples- 134 Sample Conditioning: Outgassing of the Adsorbent- 135 Elutriation and Its Prevention- 136 References- 14 Vacuum Volumetric Measurements (Manometry)- 141 Basics of Volumetric Adsorption Measurement- 142 Deviations from Ideality- 143 Void Volume Determination- 144 Coolant Level and Temperature Control- 145 Saturation Vapor Pressure, P0 and Temperature of the Sample Cell- 146 Sample Cells- 147 Low Surface Area- 148 Micro- and Mesopore Analysis- 1481 Experimental Requirements- 1482 Micropore Analysis and Void Volume Determination- 1483 Thermal Transpiration Correction- 1484 Adsorptives other than Nitrogen for Micro- and Mesopore Analysis - Experimental Aspects- 149 Automated Instrumentation- 1491 Multistation Sorption Analyzer- 1492 The NOVA Concept- 1410 References- 15 Dynamic Flow Method- 151 Nelson and Eggertsen Continuous Flow Method- 152 Carrier Gas (Helium) and Detector Sensitivity- 153 Design Parameters for Continuous Flow Apparatus- 154 Signals and Signal Calibration- 155 Adsorption and Desorption Isotherms by Continuous Flow- 156 Low Surface Areas Measurement- 157 Data Reduction - Continuous Flow Method- 158 Single Point Method- 159 References- 16 Volumetric Chemisorption: Catalyst Characterization by Static Methods- 161 Applications- 162 Sample Requirements- 163 General Description of Equipment- 164 Measuring System- 1641 Pressure Measurement- 1642 Valves- 1643 Vacuum- 1644 Sample Cell- 1645 Heating System- 1646 Gases and Chemical Compatibilities- 165 Pretreatment- 1651 Heating- 1652 Atmosphere- 166 Isotherms- 1661 Reactive Gas- 1662 The Combined Isotherm- 1663 The Weak Isotherm- 1664 The Strong Isotherm- 1665 Multiple Isotherms- 167 References- 17 Dynamic Chemisorption: Catalyst Characterization By Flow Techniques- 171 Applications- 172 Sample Requirements- 173 General Description of Equipment- 1731 Flow Path- 1732 Sample Cell- 1733 Gases- 1734 Heating- 1735 Pulse Injection- 1736 Detector- 174 Pretreatment- 175 Pulse Titration- 176 Additional Requirements for Temperature Programmed Methods- 1761 Programmed Heating- 1762 Sample Temperature- 177 Temperature Programmed Reduction- 178 Temperature Programmed Oxidation- 179 Temperature Programmed Desorption- 1791 Some Specific Applications- 17811 Acid/Base- 17812 Oxidizers- 17813 Reducers- 1710 Mass Spectrometry- 1711 Metal Parameters- 1711 References- 18 Mercury Porosimetry: Intra and Inter- Particle Characterization- 181 Applications- 182 Working with Mercury- 183 Experimental Requirements- 184 Sample Cell- 185 Volume Measurement- 186 Contact Angle- 1861 Dynamic Contact Angle- 1862 Static Contact Angle- 187 A Modern Porosimeter- 188 Low Pressure Measurements- 1881 Sample Cell Evacuation- 1882 Filling with Mercury- 1883 Low Pressure Intrusion-Extrusion- 189 High Pressure Measurements- 1810 Scanning Method- 1811 Stepwise Method- 1812 Mercury Entrapment- 1813 Working with Powders- 1814 Inter/Intra Particle Porosity- 1815 Isostatic Crush Strength- 1816 References- 19 Density Measurement- 191 Introduction- 192 True Density- 193 Apparent Density- 194 Open-Closed Porosity- 195 Bulk Density- 196 Tap Density- 197 Envelope or Geometric Density- 198 Effective Density- 199 Density by Mercury Porosimetry- 1910 Standard Methods- 1911 References

Adsorption of arsenate and arsenite on titanium dioxide suspensions

Abstract: Adsorption of arsenate (As(V)) and arsenite (As(III)) to two commercially available titanium dioxide (TiO2) suspensions, Hombikat UV100 and Degussa P25, was investigated as a function of pH and initial concentration of adsorbate ions. The BET surface area and zeta potential values of TiO2 were also measured to understand the difference in adsorption behavior of two suspensions. Both As(V) and As(III) adsorb more onto Hombikat UV100 particles than Degussa P25 particles. Adsorption of As(V) onto TiO2 suspensions was more than As(III) at pH 4 while the adsorption capacity of As(III) was more at pH 9. The electrostatic factors between surface charge of TiO2 particles and arsenic species were used to explain adsorption behavior of As(V) and As(III) at different pH. The Langmuir and Freundlich isotherm equations were used to interpret the nature of adsorption of arsenic onto TiO2 suspensions. The usefulness of adsorption data in removing arsenic in water is briefly discussed.

Zeolite from fly ash: synthesis and characterization

Abstract: Coal fly ash was used to synthesize X-type zeolite by alkali fusion followed by hydrothermal treatment. The synthesized zeolite was characterized using various techniques such as X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, BET method for surface area measurement etc. The synthesis conditions were optimized to obtain highly crystalline zeolite with maximum BET surface area. The maximum surface area of the product was found to be 383 m2/g with high purity. The crystallinity of the prepared zeolite was found to change with fusion temperature and a maximum value was obtained at 823 K. The cost of synthesized zeolite was estimated to be almost one-fifth of that of commercial 13X zeolite available in the market.

Determination of adsorptive properties of clay/water system: methylene blue sorption.

Abstract: In this study, adsorption of methylene blue onto clay was investigated. The effect of adsorption time and temperature on the adsorption process was studied. To reveal the adsorptive characteristics of the clay studied, porosity and BET surface area measurements were made. It was observed that the adsorption capacity decreases with increasing temperature, and adsorption equilibrium was attained within 1 h. It was found that the data fit well to Langmuir, Halsey, Henderson, and Harkins-Jura models but experimental data deviate significantly from BET and Freundlich models at especially high concentrations. Furthermore, isosteric adsorption enthalpy and entropy are calculated as -7.99 kJ mol(-1) and 25.41 JK(-1)mol(-1), respectively.

Adsorption of basic dyes onto montmorillonite.

Abstract: Ca-montmorillonite (Ca-Mont) was exchanged with titanium cations and the adsorption equilibrium and kinetics of Basic Green 5 (BG5) and Basic Violet 10 (BV10) on these montmorillonites were measured to examine the ion-exchange effects on the basic dyes adsorption. The relationship between the dye adsorption and the alteration of pore structures of montmorillonite induced by ion-exchange processes was discussed. Moreover, the changes in the surface and pore structure of montmorillonites during adsorption were characterized based on classical and fractal analyses of the nitrogen adsorption isotherms as well as the XRD patterns. The decrease in BET surface area of montmorillonites after adsorption of dyes was interpreted in terms of both the coverage of some surface roughness (surface screening effect) and the inhibition of the movement of nitrogen molecule into some pores (pore blocking effect). The surface fractal dimension D was used to examine whether or not the surface screening effect exists and the pore blocking effect was examined with the changes of mean pore size before and after adsorbing basic dyes.

New Heterogeneous Polyoxometalate Based Mesoporous Catalysts for Hydrogen Peroxide Mediated Oxidation Reactions

Abstract: Inorganic−organic hybrid mesoporous materials were prepared by cocrystallization of a “sandwich” type polyoxometalate, [ZnWZn2(H2O)2(ZnW9O34)2]12-, and branched tripodal organic polyammonium salts, tris[2-(trimethylammonium)ethyl]-1,3,5-benzenetricarboxylate or 1,3,5-tris[4-(N,N,N-trimethylammoniumethylcarboxyl)phenyl]benzene trications. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed formation of three-dimensional perforated coral-shaped amorphous materials with the organic cations surrounding polyoxometalate anions. N2 sorption analysis showed that the hybrid materials have a BET surface area of ∼30−50 m2 g-1 and an average pore diameter of 36 A leading to the classification of these materials as mesoporous materials with moderate surface areas. These hybrid materials behaved as very effective and selective heterogeneous catalysts for the epoxidation of allylic alcohols and oxidation of secondary alcohols to ketones with hydrogen peroxide as oxidant. The activity and...

Production of activated carbon from rubber wood sawdust

Abstract: The present work comprehensively addresses various experimental methods reported in the literature and substantiates the use of two-stage activation process with semi-carbonization stage up to 200°C as first stage followed by an activation stage at a desired temperature, for production of activated carbon from carbonaceous precursors using phosphoric acid. Efforts are made towards developing a high surface area activated carbon from rubber wood sawdust by a two-stage activation process with phosphoric acid as the activating agent. Experiments are conducted in a lab scale muffle furnace under static conditions in a self-generated atmosphere covering process parameters such as impregnation ratio, carbonization time and temperature. The precursor material with impregnation agent is exposed straightaway to semi-carbonization and activation temperature unlike following the specific temperature progression as reported in the literature. The process parameters are optimized based on product yield and iodine number. Semi-carbonization at 200°C for 15 min followed by activation at 500°C for 45 min with impregnation ratio of 1.5 yielded a product with iodine number 1096 which corresponds to a BET surface area of 1496 m 2 / g with the product yield of 35% and activation agent recovery of 90%.

Preparation of activated carbon fibers supported TiO2 photocatalyst and evaluation of its photocatalytic reactivity

Abstract: Activated carbon fibers (ACFs) supported TiO2 Photocatalyst was successfully prepared by a molecular adsorption-deposition (MAD) method followed by calcination in a stream of Ar gas. The photocatalyst developed was characterized by SEM, XRD, XPS, BET surface area and UV-vis adsorption spectroscopy. SEM observation showed TiO2 was deposited on almost each carbon fiber with a coating thickness of about 100 nm, and the space between adjacent fibers was remained unfilled to allow UV light to penetrate into the felt-form photocatalyst to a certain depth. Anatase-form TiO2 was uniquely developed even as calcination temperatures rose up to 900degreesC. Tight contact of thin TiO2 coating to carbon fibers surfaces was supposed to suppress phase transformation of TiO2 from anatase to rutile, and to keep high crystallinity of anatase. As confirmed by XRD and XPS examinations, the micrographic structure and surface properties of ACFs had not been damaged by the deposition process and calcination at high temperatures. The present photocatalyst showed high photocatalytic reactivity in photodegradation of highly concentrated methylene blue (MB) solutions. The comparative experiments indicated the photocatalyst produced had a combined effect of photocatalytic reactivity of anatase-type TiO2 with adsorptive property of activated carbon fibers. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed. (C) 2004 Elsevier B.V. All rights reserved.

Carbon dioxide reforming of methane over Ni incorporated into Ce–ZrO2 catalysts

Abstract: A co-precipitation/digestion method was employed in a single step to prepare Ni–Ce–ZrO 2 catalysts useful for carbon dioxide reforming of methane. The loading amount of Ni and the ratio of CeO 2 to ZrO 2 were systematically varied to optimize the co-precipitated Ni–Ce–ZrO 2 catalysts. The prepared catalysts were characterized by various physico-chemical characterization techniques such as XRD, BET surface area, hydrogen chemisorption, SEM, TPR and XPS. It was found that 15% Ni (w/w) co-precipitated with Ce 0.8 Zr 0.2 O 2 having cubic phase gave synthesis gas with CH 4 conversion more than 97% at 800 ° C and such activity was maintained without significant loss during the reaction for 100 h. On the contrary, Ni–Ce–ZrO 2 having tetragonal phase (Ce 0.2 Zr 0.8 O 2 ) or mixed phase (Ce 0.5 Zr 0.5 O 2 ) deactivated during the reaction due to carbon formation. The enhanced catalytic activity and stability of the co-precipitated Ni–Ce 0.8 Zr 0.2 O 2 catalyst is attributed to a combination of the nano-crystalline nature of cubic Ce 0.8 Zr 0.2 O 2 support and the finely dispersed nano-sized NiO x crystallites, resulting in the intimate contact between Ni and Ce 0.8 Zr 0.2 O 2 particles.

A condensable amphiphile with a cleavable tail as a "Lizard" template for the sol-gel synthesis of functionalized mesoporous silica.

Abstract: Use of a dialkoxysilane-containing, condensable alanine amphiphile with a cleavable hexadecyl ester tail (1) as a “lizard” template for sol−gel synthesis results in the formation of a mesoporous silicate (2) whose channels are filled with an organic group of the template. Treatment of 2 with aqueous HCl allows selective cleavage of the ester moiety to leave nanochannels (3) whose surface is densely covered with alanine−CO2H. According to XRD and TEM, 2, on conversion into 3, can preserve its regular hexagonal structure. 3 displays a clear N2 adsorption/desorption isotherm with a BET surface area of 536 m2 g-1. 3 can also adsorb a basic guest such as NH3 up to 0.7 mmol g-1, which is 7 times greater than that observed for mesoporous silica obtained by calcination of 2.

Physical and photocatalytic properties of zinc ferrite doped titania under visible light irradiation

Abstract: Visible light responsive zinc ferrite doped titania photocatalyst (TiO2(ZnFe2O4)) was prepared by sol–gel method and was calcined at different temperatures. Diffuse reflectance spectroscopy (DRS) results show that the absorption edge of TiO2(ZnFe2O4) has moved to the visible spectrum range in comparison with the undoped titania. The photocatalytic experimental result demonstrates that TiO2(ZnFe2O4) powder can effectively photodegrade methyl orange (MO) under visible light irradiation. Effect of calcination temperature on the photocatalytic activity of TiO2(ZnFe2O4) was also investigated. Zeta potential measurements indicate that the isoelectric point (IEP) of the TiO2(ZnFe2O4) powder shifts to lower pH units with the increase of calcination temperature. Brunauer–Emmett–Teller (BET) surface area decreases with the rise of calcination temperature. It is concluded that the surface charge and BET surface area are the key factors for the higher photoactivity of zinc ferrite doped titania photocatalyst calcined at 400 °C.

Thermally stable hematite hollow nanowires.

Abstract: Thermally stable hematite (alpha-Fe(2)O(3)) hollow nanowires were synthesized by a vacuum-pyrolysis route from beta-FeOOH nanowires for the first time. The products can catalyze the oxidation of almost 100% carbon monoxide at 320 degrees C, exhibiting excellent catalytic performances despite their small BET surface area.

Ta3N5 nanoparticles with enhanced photocatalytic efficiency under visible light irradiation.

Abstract: Nanocrystalline Ta3N5 particles with a surface area of more than 33 m2/g were synthesized by nitridation of nanosized Ta2O5 particles using NH3 as the reactant gas. It was found that nanocrystalline Ta2O5 was converted into Ta3N5 completely (by X-ray diffraction, XRD) at 700 °C within 5.0 h, which was much lower than the temperature 900 °C for the complete nitridation of micrometer-sized Ta2O5 powder. The oxide precursor and the resulting nitride were characterized by XRD analysis, transmission electron microscopy, UV−vis diffuse reflectance spectra, and BET surface area techniques. The nitrogen contents in the prepared Ta3N5 powders were quantitatively determined with a CHN elemental analyzer. Nanocrystalline Ta3N5 showed an absorption edge of around 600 nm, and Ta3N5 in the size of about 26 nm exhibited a blue shift of 15 nm in the adsorption edge. The photocatalytic activity of the prepared Ta3N5 under UV−vis and visible light irradiation was compared to that of nanocrystalline TiO2-xNx using the photo...

The adsorption of palmytic acid on rice husk ash chemically modified with Al(III) ion using the sol-gel technique.

Abstract: Silica-incorporated aluminum (RHA-Al) was synthesized from rice husk ash (RHA) using the sol-gel technique. RHA-Al was calcined at 500 degrees C for 5 h to yield RHA-Al(C). The ratio of silica to alumina was found to be 4:1. The BET analysis of RHA-Al(C) showed an increase in total pore volume and specific surface area compared to RHA-Al. SEM and XRD showed that RHA-Al and RHA-Al(C) were composed of microcrystals and the surface of both samples had a porous structure. Adsorption studies of palmytic acid on RHA-Al and RHA-Al(C) at 30, 40, and 50 degrees C conformed to the Langmuir isotherm. The equilibrium parameter, R, revealed that both are good adsorbents for palmytic acid. The Gibbs free energy of adsorption, DeltaG(ads)(0), was determined to be between -21.0 and -26.0 kJ mol(-1). DeltaH(ads)(0) and DeltaS(ads)(0) for RHA-Al were found to be 26.2 kJ mol(-1) and 158 J mol(-1), respectively. Corresponding values for RHA-Al(C) were 31.7 kJ mol(-1) and 178 J mol(-1). The adsorption of fatty acid on RHA-Al and RHA-Al(C) was an endothermic process, which occurred spontaneously. An FTIR study on the adsorbed material was used to determine the possible adsorbed complex on the surface of the adsorbent.