The Experts below are selected from a list of 20682 Experts worldwide ranked by ideXlab platform
Jia Guo - One of the best experts on this subject based on the ideXlab platform.
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microporous oil palm shell activated carbon prepared by physical activation for Gas Phase Adsorption
Langmuir, 2001Co-Authors: Aik Chong Lua And, Jia GuoAbstract:Preparation, characterization, and evaluation of activated carbon from oil-palm shell, an abundant agricultural byproduct in some tropical countries, were carried out. The effects of CO2 activation conditions (i.e., activation temperature and hold time) on the characteristics of the activated carbon, namely, composition, porosity, hardness, and internal pore surface area, were investigated in order to optimize preparation parameters. To analyze the reaction kinetics, a random pore model was developed to determine pore development during the carbon−CO2 reaction process. Adsorption tests showed that the activated carbons prepared from oil-palm shells were more suitable for Gas-Phase rather than liquid-Phase applications. When SO2 Gas was used as the adsorbate, a linear relationship between the specific pore surface area and the adsorptive capacity of the adsorbent was observed. This could be elucidated by the neutral (or slightly acidic) nature of the surface functional groups, as detected by Fourier transf...
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preparation and characterization of activated carbons from oil palm stones for Gas Phase Adsorption
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001Co-Authors: Aik Chong Lua, Jia GuoAbstract:Abstract Preparation and characterization of activated carbons from oil-palm stones by carbon dioxide activation were studied in this paper. These oil-palm stones are agricultural by-products from palm-oil mills in several tropical countries. Ultimate and proximate analyses, pycnometry, mercury porosimetry, surface area and porosimetry as well as transmission electron microscopy were carried out for evaluating the textural properties of the activated carbons. It was found that the activation temperature and hold time had significant influences on the surface area and pore size distribution of the activated carbon. The optimum conditions for preparing these activated carbons from chars pyrolyzed at 600°C to derive the highest specific surface areas were found to be an activation temperature of 900°C and a hold time of 30 min. For chemical characterization, an X-ray diffractometer and a Fourier transform infrared (FTIR) spectroscope were used to identify the inorganic components and surface organic functional groups of the activated carbons, respectively. The activation temperature and hold time had significant effects on the surface functional groups. For the determination of the adsorptive capacity of the activated carbons, Adsorption of sulphur dioxide was carried out using thermogravimetric analyses. Experimental results showed that sulphur dioxide could be adsorbed effectively by the oil-palm stone-activated carbons. The adsorptive capacity of these activated carbons was comparable with those of some commercial activated carbons.
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effect of surface chemistry on Gas Phase Adsorption by activated carbon prepared from oil palm stone with pre impregnation
Separation and Purification Technology, 1999Co-Authors: Jia Guo, Aik Chong LuaAbstract:Effects of surface chemistry (acidity or basicity) on Gas-Phase Adsorption (NO2 or NH3) by activated carbons prepared from oil-palm stones pre-impregnated with various solutions (ZnCl2, H3PO4 and KOH) were studied in this paper. Textural and chemical characterizations of these activated carbons were carried out. High solid density and hardness, fairly high BET surface area and predominant microporosity (as shown in the pore size distributions) of the oil-palm-stone activated carbons suggested their potential applications in Gas-adsorbing processes. Chemical characterization showed that impregnation affected significantly the surface chemistry, i.e. surface functional group. The samples pre-treated with H3PO4 presented acidic groups such as phenols and carboxylic acids, whereas those with KOH impregnation showed basic groups likely to be pyrones (cyclic ketone) and other keto-derivatives of pyran. From Adsorption tests of NO2 and NH3, it was found that the activated carbons pre-treated with KOH could adsorb more NO2 but less NH3 than those pre-treated with H3PO4, even though they had almost identical BET surface areas. This indicated that the adsorptive capacity of the activated carbon was not only determined by its textural characteristics, but also related to the surface chemistry, which was relevant to the type of impregnating agent, concentration of impregnation solution and activation temperature. In general, the activated carbons prepared from oil-palm stones impregnated with H3PO4 and KOH are suitable for adsorbing basic (NH3) and acidic (NO2) Gases, respectively.
D Nicholson - One of the best experts on this subject based on the ideXlab platform.
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monte carlo simulation of the Gas Phase volumetric Adsorption system effects of dosing volume size incremental dosing amount pore shape and size and temperature
Journal of Physical Chemistry B, 2011Co-Authors: Van T Nguyen, D D Do, D NicholsonAbstract:We model the volumetric method commonly used in the measurement of Gas-Phase Adsorption isotherms by using Monte Carlo (MC) simulation to study slit pore Adsorption in a finite volume. Although the method has been used for a very long time, modeling of the operation by a Monte Carlo scheme to account properly for the exchange of mass between the solid and the finite dosing volume has not been widely studied in the literature. This paper presents the MC simulation of the system composed of the solid subsystem and the Gas Phase surrounding it. We show that not only the size of the dosing volume and the incremental dosing amount but also the pore shape, pore size, and temperature have significant effects on the unstable region of the Phase diagram, especially when the system is going through a first-order transition. This study extends and augments the recent work of Puibasset et al.(1) by showing that the shape of the adsorbent walls and the incremental dosing amount can affect the chemical potential in the...
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molecular simulation of excess isotherm and excess enthalpy change in Gas Phase Adsorption
Journal of Physical Chemistry B, 2009Co-Authors: D NicholsonAbstract:We present a new approach to calculating excess isotherm and differential enthalpy of Adsorption on surfaces or in confined spaces by the Monte Carlo molecular simulation method. The approach is very general and, most importantly, is unambiguous in its application to any configuration of solid structure (crystalline, graphite layer or disordered porous glass), to any type of fluid (simple or complex molecule), and to any operating conditions (subcritical or supercritical). The behavior of the adsorbed Phase is studied using the partial molar energy of the simulation box. However, to characterize Adsorption for comparison with experimental data, the isotherm is best described by the excess amount, and the enthalpy of Adsorption is defined as the change in the total enthalpy of the simulation box with the change in the excess amount, keeping the total number (Gas + adsorbed Phases) constant. The excess quantities (capacity and energy) require a choice of a reference Gaseous Phase, which is defined as the adsorptive Gas Phase occupying the accessible volume and having a density equal to the bulk Gas density. The accessible volume is defined as the mean volume space accessible to the center of mass of the adsorbate under consideration. With this choice, the excess isotherm passes through a maximum but always remains positive. This is in stark contrast to the literature where helium void volume is used (which is always greater than the accessible volume) and the resulting excess can be negative. Our definition of enthalpy change is equivalent to the difference between the partial molar enthalpy of the Gas Phase and the partial molar enthalpy of the adsorbed Phase. There is no need to assume ideal Gas or negligible molar volume of the adsorbed Phase as is traditionally done in the literature. We illustrate this new approach with Adsorption of argon, nitrogen, and carbon dioxide under subcritical and supercritical conditions.
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on the henry constant and isosteric heat at zero loading in Gas Phase Adsorption
Journal of Colloid and Interface Science, 2008Co-Authors: D NicholsonAbstract:The Henry constant and the isosteric heat of Adsorption at zero loading are commonly used as indicators of the strength of the affinity of an adsorbate for a solid adsorbent. It is assumed that (i) they are observable in practice, (ii) the Van Hoff's plot of the logarithm of the Henry constant versus the inverse of temperature is always linear and the slope is equal to the heat of Adsorption, and (iii) the isosteric heat of Adsorption at zero loading is either constant or weakly dependent on temperature. We show in this paper that none of these three points is necessarily correct, first because these variables might not be observable since they are outside the range of measurability; second that the linearity of the Van Hoff plot breaks down at very high temperature, and third that the isosteric heat versus loading is a strong function of temperature. We demonstrate these points using Monte Carlo integration and Monte Carlo simulation of Adsorption of various Gases on a graphite surface. Another issue concerning the Henry constant is related to the way the Adsorption excess is defined. The most commonly used equation is the one that assumes that the void volume is the volume extended all the way to a boundary passing through the centres of the outermost solid atoms. With this definition the Henry constant can become negative at high temperatures. Although Adsorption at these temperatures may not be practical because of the very low value of the Henry constant, it is more useful to define the Henry constant in such a way that it is always positive at all temperatures. Here we propose the use of the accessible volume; the volume probed by the adsorbate when it is in nonpositive regions of the potential, to calculate the Henry constant.
Aik Chong Lua - One of the best experts on this subject based on the ideXlab platform.
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preparation and characterization of activated carbons from oil palm stones for Gas Phase Adsorption
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001Co-Authors: Aik Chong Lua, Jia GuoAbstract:Abstract Preparation and characterization of activated carbons from oil-palm stones by carbon dioxide activation were studied in this paper. These oil-palm stones are agricultural by-products from palm-oil mills in several tropical countries. Ultimate and proximate analyses, pycnometry, mercury porosimetry, surface area and porosimetry as well as transmission electron microscopy were carried out for evaluating the textural properties of the activated carbons. It was found that the activation temperature and hold time had significant influences on the surface area and pore size distribution of the activated carbon. The optimum conditions for preparing these activated carbons from chars pyrolyzed at 600°C to derive the highest specific surface areas were found to be an activation temperature of 900°C and a hold time of 30 min. For chemical characterization, an X-ray diffractometer and a Fourier transform infrared (FTIR) spectroscope were used to identify the inorganic components and surface organic functional groups of the activated carbons, respectively. The activation temperature and hold time had significant effects on the surface functional groups. For the determination of the adsorptive capacity of the activated carbons, Adsorption of sulphur dioxide was carried out using thermogravimetric analyses. Experimental results showed that sulphur dioxide could be adsorbed effectively by the oil-palm stone-activated carbons. The adsorptive capacity of these activated carbons was comparable with those of some commercial activated carbons.
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effect of surface chemistry on Gas Phase Adsorption by activated carbon prepared from oil palm stone with pre impregnation
Separation and Purification Technology, 1999Co-Authors: Jia Guo, Aik Chong LuaAbstract:Effects of surface chemistry (acidity or basicity) on Gas-Phase Adsorption (NO2 or NH3) by activated carbons prepared from oil-palm stones pre-impregnated with various solutions (ZnCl2, H3PO4 and KOH) were studied in this paper. Textural and chemical characterizations of these activated carbons were carried out. High solid density and hardness, fairly high BET surface area and predominant microporosity (as shown in the pore size distributions) of the oil-palm-stone activated carbons suggested their potential applications in Gas-adsorbing processes. Chemical characterization showed that impregnation affected significantly the surface chemistry, i.e. surface functional group. The samples pre-treated with H3PO4 presented acidic groups such as phenols and carboxylic acids, whereas those with KOH impregnation showed basic groups likely to be pyrones (cyclic ketone) and other keto-derivatives of pyran. From Adsorption tests of NO2 and NH3, it was found that the activated carbons pre-treated with KOH could adsorb more NO2 but less NH3 than those pre-treated with H3PO4, even though they had almost identical BET surface areas. This indicated that the adsorptive capacity of the activated carbon was not only determined by its textural characteristics, but also related to the surface chemistry, which was relevant to the type of impregnating agent, concentration of impregnation solution and activation temperature. In general, the activated carbons prepared from oil-palm stones impregnated with H3PO4 and KOH are suitable for adsorbing basic (NH3) and acidic (NO2) Gases, respectively.
Sebastijan Peljhan - One of the best experts on this subject based on the ideXlab platform.
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dft study of Gas Phase Adsorption of benzotriazole on cu 111 cu 100 cu 110 and low coordinated defects thereon
Physical Chemistry Chemical Physics, 2011Co-Authors: Sebastijan Peljhan, Anton KokaljAbstract:The Adsorption of benzotriazole--an outstanding corrosion inhibitor for copper--on Cu(111), Cu(100), Cu(110), and low coordinated defects thereon has been studied and characterized using density functional theory (DFT) calculations. We find that benzotriazole can either chemisorb in an upright geometry or physisorb with the molecular plane being nearly parallel to the surface. While the magnitude of chemisorption energy increases as passing from densely packed Cu(111) to more open surfaces and low coordinated defects, the physisorption energy is instead rather similar on all three low Miller index surfaces. It is pointed out that due to a large dipole moment of benzotriazole the dipole-dipole interactions are rather important. For perpendicular chemisorption modes the lateral repulsion is very long ranged, extending up to the nearest-neighbor distance of about 60 bohrs, whereas for parallel Adsorption modes the lateral interactions are far less pronounced and the molecules experience a weak attraction at distances ≲25 bohrs. The chemisorption energies were therefore extrapolated to zero coverage by a recently developed scheme and the resulting values are -0.60, -0.73, and -0.92 eV for Cu(111), Cu(100), and Cu(110), respectively, whereas the zero-coverage physisorption energy is about -0.7 eV irrespective of the surface plane. While the more densely packed surfaces are not reactive enough to interact with the molecular π-system, the reactivity of Cu(110) appears to be at the onset of such interaction, resulting in a very stable parallel Adsorption structure with an Adsorption energy of -1.3 eV that is ascribed as an apparent chemisorption+physisorption mode.
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density functional theory study of ata btah and btaoh as copper corrosion inhibitors Adsorption onto cu 111 from Gas Phase
Langmuir, 2010Co-Authors: Anton Kokalj, Sebastijan PeljhanAbstract:A low-coverage Gas-Phase Adsorption of three corrosion inhibitors-3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH)-on perfect Cu(111) surface has been studied and characterized using density functional theory calculations. We find that the molecules in neutral form chemisorb weakly to the perfect surface in an upright geometry. The strength of the chemisorption increases in the order BTAH < BTAOH < ATA with Adsorption energies of -0.40, -0.53, and -0.60 eV, respectively. The molecules bond to the surface with triazole nitrogen atoms and also through X-H···Metal hydrogen bonds (X = N or O). In addition to chemisorption, BTAH and BTAOH can also physisorb with the molecular plane being nearly parallel to the surface and the energies of the physisorption are -0.72 and -0.97 eV, respectively, hence being more exothermic than the corresponding chemisorption energies. On the other hand, the molecules in dehydrogenated form chemisorb strongly to the surface and the strength of the chemisorption increases in the order BTAO· < ATA· < BTA· with the Adsorption energies of -1.65, -2.22, and -2.78 eV, respectively. This order is compatible with the trend of experimentally observed corrosion inhibition effectiveness on copper in near-neutral chloride solutions. Although the calculations are performed at the metal/vacuum interface, they provide enough insight to rationalize why in some experiments the BTAH was observed to be adsorbed with an upright geometry and in the others with parallel geometry.
Anton Kokalj - One of the best experts on this subject based on the ideXlab platform.
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dft study of Gas Phase Adsorption of benzotriazole on cu 111 cu 100 cu 110 and low coordinated defects thereon
Physical Chemistry Chemical Physics, 2011Co-Authors: Sebastijan Peljhan, Anton KokaljAbstract:The Adsorption of benzotriazole--an outstanding corrosion inhibitor for copper--on Cu(111), Cu(100), Cu(110), and low coordinated defects thereon has been studied and characterized using density functional theory (DFT) calculations. We find that benzotriazole can either chemisorb in an upright geometry or physisorb with the molecular plane being nearly parallel to the surface. While the magnitude of chemisorption energy increases as passing from densely packed Cu(111) to more open surfaces and low coordinated defects, the physisorption energy is instead rather similar on all three low Miller index surfaces. It is pointed out that due to a large dipole moment of benzotriazole the dipole-dipole interactions are rather important. For perpendicular chemisorption modes the lateral repulsion is very long ranged, extending up to the nearest-neighbor distance of about 60 bohrs, whereas for parallel Adsorption modes the lateral interactions are far less pronounced and the molecules experience a weak attraction at distances ≲25 bohrs. The chemisorption energies were therefore extrapolated to zero coverage by a recently developed scheme and the resulting values are -0.60, -0.73, and -0.92 eV for Cu(111), Cu(100), and Cu(110), respectively, whereas the zero-coverage physisorption energy is about -0.7 eV irrespective of the surface plane. While the more densely packed surfaces are not reactive enough to interact with the molecular π-system, the reactivity of Cu(110) appears to be at the onset of such interaction, resulting in a very stable parallel Adsorption structure with an Adsorption energy of -1.3 eV that is ascribed as an apparent chemisorption+physisorption mode.
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density functional theory study of ata btah and btaoh as copper corrosion inhibitors Adsorption onto cu 111 from Gas Phase
Langmuir, 2010Co-Authors: Anton Kokalj, Sebastijan PeljhanAbstract:A low-coverage Gas-Phase Adsorption of three corrosion inhibitors-3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH)-on perfect Cu(111) surface has been studied and characterized using density functional theory calculations. We find that the molecules in neutral form chemisorb weakly to the perfect surface in an upright geometry. The strength of the chemisorption increases in the order BTAH < BTAOH < ATA with Adsorption energies of -0.40, -0.53, and -0.60 eV, respectively. The molecules bond to the surface with triazole nitrogen atoms and also through X-H···Metal hydrogen bonds (X = N or O). In addition to chemisorption, BTAH and BTAOH can also physisorb with the molecular plane being nearly parallel to the surface and the energies of the physisorption are -0.72 and -0.97 eV, respectively, hence being more exothermic than the corresponding chemisorption energies. On the other hand, the molecules in dehydrogenated form chemisorb strongly to the surface and the strength of the chemisorption increases in the order BTAO· < ATA· < BTA· with the Adsorption energies of -1.65, -2.22, and -2.78 eV, respectively. This order is compatible with the trend of experimentally observed corrosion inhibition effectiveness on copper in near-neutral chloride solutions. Although the calculations are performed at the metal/vacuum interface, they provide enough insight to rationalize why in some experiments the BTAH was observed to be adsorbed with an upright geometry and in the others with parallel geometry.
