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Adsorption: Journal of the International Adsorption Society (v.15, #2)
Heating effects on morphological and textural characteristics of individual and composite nanooxides by V. M. Gun’ko; R. Leboda; J. Skubiszewska-Zięba (pp. 89-98).
Morphological, structural and adsorption characteristics of nanooxides (fumed individual silica, alumina and titania, and composite silica/alumina, silica/titania and alumina/silica/titania) were compared after different treatments (wetting/drying, ball-milling, suspending/drying, heating) at different temperatures (373–1173 K) using low-temperature nitrogen adsorption data. The structural characteristics such as specific surface area (S BET), pore volume (V p), pore (PSD) and particle (PaSD) size distributions (calculated using self-consisting regularization procedure with respect to both PSD and PaSD), fractality, adsorption energy distributions depend differently on heating temperature because desorption of water molecularly and dissociatively adsorbed at a surface and in bulk of primary nanoparticles occurs over a wide temperature range at different rates. These processes affect both structural and energetic characteristics of nanooxides.
Keywords: Nanooxides; Morphology; Structural characteristics; Adsorption characteristics; Temperature effects
Adsorption potential distributions for carbons having defined pore structure—GCMC simulations of the effect of heterogeneity by Piotr A. Gauden; Artur P. Terzyk; Sylwester Furmaniak; Piotr Kowalczyk (pp. 99-113).
Adsorption Potential Distribution (APD) is one of the most important and widely propagated by Jaroniec and co-workers method since it is modeless. Using the GCMC simulation of Ar adsorption in pores with well defined geometry (slit-like, cylindrical, hexagonal and quadratic) we study the effect of heterogeneity on the APDs. The heterogeneity is introduced by controlled removal of carbon atoms from the first internal layer of an adsorbent. Since defects are introduced for pores having different initial geometries it is possible to study the systematic changes in the APD curves.
Keywords: Adsorption; GCMC; Adsorption potential distribution; Activated carbon; Carbon nanotubes; Slit-like pores; Heterogeneity
Fine pore mouth structure of molecular sieve carbon with GCMC-assisted supercritical gas adsorption analysis by Ryoji Kobori; Tomonori Ohba; Takaomi Suzuki; Taku Iiyama; Sumio Ozeki; Michio Inagaki; Akihiro Nakamura; Masato Kawai; Hirofumi Kanoh; Katsumi Kaneko (pp. 114-122).
N2 adsorption isotherms of molecular sieve carbon were measured at 77 K and 303 K. The Ar adsorption isotherms of molecular sieve carbon samples were also measured at 303 K. The grand canonical Monte Carlo (GCMC) simulation technique was applied to calculate the N2 and Ar adsorption isotherms at 303 K using the ultramicropore volume determined by H2O adsorption. The comparative method of experimental and simulated isotherms of supercritical N2 and Ar at 303 K gave the width of the micropore mouth of the molecular sieve carbon, which can be applied to the ultramicropore width determination for other noncrystalline porous solids.
Keywords: Molecular sieve carbon; Characterization; Supercritical gas adsorption; GCMC simulation
Adsorption of xylene isomers on ordered hexagonal mesoporous FDU-15 polymer and carbon materials by Zhangxiong Wu; Yunxia Yang; Bo Tu; Paul A. Webley; Dongyuan Zhao (pp. 123-132).
The oil industry has been facing the challenges of separation of xylene isomers, o-xylene, m-xylene and p-xylene or removing them from the environment. In our present work, we investigated the adsorption of the three isomers on two mesoporous materials, FDU-15-350 polymer and FDU-15-900 carbon materials. The isomer adsorption capacities are well correlated with their physical pore properties. It is found that the micropores are very crucial for the adsorption of these three isomers. The more micropore volume the adsorbent has, the better the adsorption capacity is. Henry’s constants were also calculated for the three isomers on the two adsorbents. Both on FDU-15-350 polymer and FDU-15-900, the Henry’s constants for the three isomers show the same trend o>m>p xylene which is coincidently in accordance with their polarity trend, indicating more polar adsorbate is preferred for adsorption on the two adsorbents. The isosteric heats of adsorption are correlated with the microporosity and the size of the adsorbate molecule. More microporosity and smaller molecules give higher heats of adsorption. Extracted information on pore properties of adsorbents by using the three isomers has very similar results as that resolved from nitrogen adsorption, indicating the feasibility of using the three isomers as adsorbates to extract pore information.
Keywords: Mesoporous materials; FDU-15; Adsorption; Xylene; Carbon
Principles of methane adsorption and natural gas storage by Yan Sun; Congmin Liu; Wei Su; Yaping Zhou; Li Zhou (pp. 133-137).
The adsorption amount of methane on 16 different kinds of materials at 3.5 MPa and 298 K holds a linear relation with the specific surface area. The linear relationship implies that gases are adsorbed monolayerly on the surface of adsorbents at above-critical temperatures. Determination of surface area and calculation of storage capacity of a material are explicitly discussed. It is indicated that methane storage is different from natural gas storage and the difference affects the development of storage material. Natural gas is a mixture and all components other than methane cannot be desorbed when the tank pressure released to atmospheric at ambient temperature, therefore, a storage mechanism other than adsorption might be more suitable.
Keywords: Principle; Adsorption; Storage; Methane; Natural gas
A simple method to ordered mesoporous carbons containing nickel nanoparticles by Xiqing Wang; Sheng Dai (pp. 138-144).
A series of ordered mesoporous carbons containing magnetic Ni nanoparticles (Ni-OMCs) with a variety of Ni loadings was made by a simple one-pot synthetic procedure through carbonization of phenolic resin-Pluronic block copolymer composites containing various amount of nickel nitrate. Such composite materials were characterized by N2 sorption, XRD, and STEM. Ni-OMCs exhibited high BET surface area, uniform pore size, and large pore volume without obvious pore blockage with a Ni loading as high as 15 wt%. Ni nanoparticles were crystalline with a face-center-cubic phase and observed mainly in the carbon matrix and on the outer surface as well. The average particle size of Ni nanoparticles was dependent on the preparation (carbonization) temperature and Ni loading; the higher the temperature was used and the more the Ni was incorporated, the larger the Ni nanoparticles were observed. One of the applications of Ni-OMCs was demonstrated as magnetically separable adsorbents.
Keywords: Ordered mesoporous carbon; Magnetic; Adsorbent; Nickel; Synthesis
Gold-vanadium-niobium catalysts in environmental protection—adsorption and interaction of NO, C3H6 and O2—FT-IR study by Izabela Sobczak; Maria Ziolek; Natalia Kieronczyk (pp. 145-155).
FT-IR study of NO and C3H6 adsorption, co-adsorption and interaction in the presence of oxygen were performed in order to estimate the catalytic behaviour of Au and V-containing MCM-41 materials in NO-SCR with propene. MCM-41 were modified with gold, vanadium and niobium by their introduction during the synthesis (co-precipitation) carried out with the use of HCl or H2SO4 as pH adjustment agent. The texture/structure properties of the prepared samples were investigated by N2 adsorption, XRD, XPS and TEM techniques. It has been found that the nature of acid used for the pH adjustment during the synthesis determines the gold particles size and dispersion and influences the interaction of NO+O2+C3H6 with the catalyst surfaces. In both types of AuVMCM-41 catalysts, the SCR reaction route occurs via NO2 formation. In the case of AuVMCM-41(HCl) and AuVNbMCM-41(HCl) nitrites are formed and stored, and upon heating NO2 is released. These kinds of nitrites are not formed on AuVMCM-41(H2SO4) and AuVNbMCM-41(H2SO4). Instead of that NO2 is chemisorbed on metallic gold, niobium and vanadium species and reacts with propene and/or oxygenates.
Keywords: AuVMCM-41; AuVNbMCM-41; FT-IR co-adsorption of NO, C3H6, O2
Synthesis of large-pore SBA-15 silica using poly(ethylene oxide)-poly(methyl acrylate) diblock copolymers by Liang Cao; Hongchen Dong; Liang Huang; Krzysztof Matyjaszewski; Michal Kruk (pp. 156-166).
Poly(ethylene oxide)-poly(methyl acrylate) diblock copolymers with narrow molecular weight distributions were synthesized using atom transfer radical polymerization. The copolymers were used as micellar templates for the synthesis of mesoporous silicas. The products were characterized using small-angle X-ray scattering, transmission electron microscopy (TEM) and nitrogen adsorption. The obtained silicas exhibited two-dimensional hexagonal structures of cylindrical mesopores, and thus can be classified as SBA-15 silicas. In some cases, the size of ordered domains was very small. The (100) interplanar spacings were 13–17 nm, depending on the size of the diblock copolymer used and on the synthesis conditions. Nitrogen adsorption showed that the silicas exhibited specific surface areas of 350–800 m2 g−1, pore volumes ∼1 cm3 g−1, and narrow pore size distributions. The BJH (nominal) pore diameters were up to ∼20 nm, but actual diameters of cylindrical pores are expected to be somewhat smaller. In many cases, the mesopores exhibited constrictions.
Keywords: Nitrogen adsorption; SBA-15; Micelle-templated material; Cylindrical pore
Synthesis and adsorption properties of colloid-imprinted mesoporous carbons using poly(vinylidene chloride-co-vinyl chloride) as a carbon precursor by Jerzy Choma; Aleksandra Zawiślak; Joanna Górka (pp. 167-171).
A facile synthesis of micro- and mesoporous carbons has been proposed using colloidal silica nanoparticles with diameter of ∼24 nm and poly(vinylidene chloride-co-vinyl chloride) (Saran) as a carbon precursor. The resulting carbons possessed large specific surface area, ∼800 m2/g, and approximately the same volume of micro- and mesopores, each about 50% of the total pore volume. While the size of micropores was around 1 nm, the large and uniform spherical mesopores (about 24 nm) resemble the diameters of silica colloids used. Nitrogen adsorption measurements proved that these mesopores were interconnected and accessible. The well-developed microporosity was created mainly by decomposition of Saran copolymer during carbonization.
Keywords: Colloidal imprinting method; Micro- and mesoporous carbons; Adsorption properties
Quantitative assessment of hysteresis in voltammetric curves of electrochemical capacitors by Marek Kosmulski; Piotr Próchniak; Czesław Saneluta (pp. 172-180).
A family of coefficients for quantitative assessment of hysteresis in cyclic voltammetric (CV) curves of electrochemical capacitors and of electrodes for electrochemical capacitors has been defined. Hysteresis index 1 (HI1) is based on the maximum in the difference in current measured at the same potential in ascending and descending branch of CV curve, and HI2 is based on the average difference in current measured at the same potential in ascending and descending branch of CV curve. The values of HI1 and HI2 range from 0 (no hysteresis) to 1 for an ideal capacitor. CV curves of two commercially available electrochemical capacitors over a potential range 0–1500 mV at scan rate of 5 mV/s showed HI1 of 0.94 and 0.97 and HI2 of 0.77 and 0.83, respectively. At the same experimental conditions, a series of 52 home made electrochemical capacitors showed HI1 up to 0.7 and HI2 up to 0.55. HI1 and HI2 measured at constant scan rate (5, 20 or 50 mV/s) in that series of capacitors showed a correlation coefficient >0.98 while HI1 and HI2 measured at different scan rates showed limited correlation. 98 CV curves of electrochemical capacitors and of electrodes for electrochemical capacitors from literature, obtained at various conditions show HI1 from 0.42 to 1, HI2 from 0.27 to 0.97, and a correlation coefficient of 0.90 between HI1 and HI2.
Keywords: Cyclic voltammetry; Electrochemical capacitor; Electrode materials; Low temperature ionic liquids
On the applicability of the pseudo-second order equation to represent the kinetics of adsorption at solid/solution interfaces: a theoretical analysis based on the statistical rate theory by Władysław Rudzinski; Wojciech Plazinski (pp. 181-192).
It is shown that the empirical pseudo-second order kinetic equation is a very efficient formula to correlate the kinetic data generated by applying theoretical expressions developed from the fundamental SRT (Statistical Rate Theory) approach to the interfacial transport. This is especially true when the most popular linear representation is used in which time/adsorbed amount is plotted vs. time. However, the commonly observed goodness of such linear plots does not necessarily speak for the applicability of the pseudo-second order kinetic equation. A reliable estimation, for instance, of the equilibrium adsorbed amount is possible only when a substantial part of a kinetic isotherms corresponds to the conditions close to equilibrium. Energetic surface heterogeneity increases the goodness of these linear regressions. Then, experimental errors have only little effect on the pseudo-second linear plots.
Keywords: Statistical rate theory; Adsorption; Kinetics; Pseudo-second order equation; Estimating the equilibrium adsorbed amount
Porous graphitic carbon sorbents in biomedical and environmental applications by Monika Michel; Bogusław Buszewski (pp. 193-202).
This review is written as a privilege of the work of Professor Mietek Jaroniec on surface phenomena, adsorption, chromatographic separations, chemistry of conventional and ordered nanoporous materials.The problems of the porous graphitic carbon (PGC) application in analytical field are presented. Special attention is paid on possibilities of use PGC as a specific sorbent and packing material for selective isolation and analytes enrichment from complex matrices by means of liquid-solid extraction techniques (SPE, SPME, MSPD) and as particular stationary phase in analytical chromatographic columns. Surface and adsorption properties as well as a unique mechanism of retention on porous graphitized carbon sorbents are described. As supplement the examples of application in biomedical and environmental area are added.
Keywords: Porous graphitic carbon; HPLC; Stationary phase; Environmental and biomedical application
Adsorption of CO2 as a method for the characterisation of the structure of alumina-pillared clay catalysts by A. Gil; A. G. Dachary; S. A. Korili (pp. 203-210).
The aim of this work was to study the effect of the metal loading on the structure of two series of cobalt and manganese pillared clay-supported catalysts. For this purpose, equilibrium data for CO2 adsorption at 273 K were analysed using Freundlich, Langmuir and Toth isotherm models, in order to estimate the adsorption parameters and to relate them with the metal loading of the catalysts. The metal distributions on the porous structure of the catalysts were studied using the temperature programmed reduction results combined with information from the nitrogen physisorption data. Comparison of all results reveals that up to a certain metal loading, about 0.5 wt% of Co and 2 wt% of Mn, the metal oxide is well dispersed into the porous structure of the pillared clay. At higher metal loadings, bulk-metal oxide particles are formed on the external surface.
Keywords: Alumina-pillared clays; Gas adsorption; Structure characterization; Manganese; Cobalt
Zeta potential and surface free energy changes of solid-supported phospholipid (DPPC) layers caused by the enzyme phospholipase A2 (PLA2) by Malgorzata Jurak; Emil Chibowski (pp. 211-219).
Stability and wetting properties changes of systems formed of phospholipid DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) layers covering silica particles or glass slides due to the phospholipase A2 (PLA2) action were determined by zeta potential measurements and the surface free energy evaluation, respectively. The comparison of the zeta potential and surface free energy, which was evaluated from advancing and receding contact angles via applying models of interfacial interactions, i.e. van Oss et al. (LWAB) and contact angle hysteresis (CAH), was found to be helpful for better understanding the mechanism of PLA2 action on the lipid layers, what is discussed in the paper.
Keywords: Phospholipase A2 ; DPPC; Zeta potential; Surface free energy