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1.
G. W. Chądzyński P. Staszczuk D. Sternik M. Błachnio 《Journal of Thermal Analysis and Calorimetry》2008,94(3):623-626
Properties relating to porosity of solids (fractal dimensions, surface roughness parameters) were evaluated from atomic force
microscopy (AFM) and nitrogen adsorption-desorption isotherms measured at 77 K for selected high-temperature [(RE) Ba2Cu3O7−x, RE=Y, Sm] superconductors. Adsorption capacity, specific surface area, fractal dimensions were determined from adsorption-desorption
isotherms. The adsorption isotherms of all samples were S-shaped and belong to type II according to the IUPAC classification.
A linear relationship was demonstrated between the fractal coefficients calculated by using the two methods and values of
adsorption capacity of monolayer. 相似文献
2.
P. Staszczuk D. Sternik G. W. Chądzyński E. Robens M. Błachnio 《Journal of Thermal Analysis and Calorimetry》2006,86(1):133-136
Nitrogen
adsorption measured at 77 K was used to characterize the surface heterogeneity
of high-temperature superconductor surfaces. Properties relating to adsorption
and porosity of the solids (adsorption capacity, specific surface area, radii
and volume of the pores, pore-size distribution function) were determined
from nitrogen adsorption–desorption isotherms and atomic force microscopy
(AFM) for a series of oxide superconductors. It is shown that the adsorption
isotherms of all samples are S-shaped and belong to type II according to the
IUPAC classification. On the basis of the nitrogen adsorption isotherms and
AFM data, fractal dimensions were determined and correlations found with adsorption
and porosity parameters. 相似文献
3.
The porous structure of TEOS derived silica gels was studied using nitrogen adsorption at 77 K. Silica gels were prepared using TEOS, H2O and ethanol for different molar ratios. No catalyst was used in this study. Silica gels were also heat treated up to 1000°C. The nitrogen sorption isotherms were analyzed by two models: Fractal and Percolation Theories. Using the fractal analysis approach, the surface roughness of the porous structure of silica gels was determined. The surface fractal dimension depends on the hydrolysis conditions and heat treatment. The surface fractal dimension decreases with increasing H2O/TEOS molar ratio or heating temperature. For the silica gels studied, the surface fractal dimension changed from 2.6 to 2.5 after heating the gels, and from 2.4 to 2.6 with decreasing H2O/TEOS ratio.Using the Percolation theory, we have determined the connectivity of the porous structure of silica gels. The extent of sorption hysteresis of the nitrogen isotherms reflects the connectivity of the pore network. The mean coordination number (connectivity) Z, and the linear dimension of the network, L, have been calculated from the hysteresis of the isotherms. For the as-prepared silica gels, Z was about 8 and L close to 2. On heating the gels, Z decreases to 4 and L increases to 7, results which are in accordance with the collapse of the porous network. 相似文献
4.
Y. S. Lipatov V. N. Bliznyuk T. T. Todosiychuk V. N. Chornaya R. K. Katumenu V. D. Konovalyuk 《Colloid and polymer science》2006,284(8):893-899
The thickness of nanolayers formed by adsorption from dilute and semi-dilute solutions on a solid SiO2 surface has been estimated from adsorption isotherms and atomic force microscopy (AFM) measurements for polystyrene, poly(butyl methacrylate), and their mixtures. The thickness of the adsorption layers depends strongly on the adsorption conditions and is controlled by several features of the adsorbing entities. In a low-concentration regime of adsorption, the length of polymer chains and the nature of their interaction with the substrate are the most important factors controlling the adsorption process. Above the critical concentration C*, macromolecular clusters (aggregates of several overlapping chains) are formed in a solution as a result of polymer chains self-assembly. Therefore, the final adsorption layer thickness is determined mainly by the size of the clusters in this concentrated regime of adsorption. We also demonstrate that in the case of polymer mixtures, the adsorption leads to formation of mosaic structures with alternation of the polymeric components in plane of the substrate and a characteristic domain size of approximately 200 nm for each of the components. AFM study reveals that the adsorbed layers are fractal structures whose fractal dimensions depend on the type of the polymer and the adsorption process. We demonstrate therefore that the structure of nanolayers of polymers and their mixtures on the solid surface can be regulated by variation of the adsorption conditions. 相似文献
5.
Guihua Chen Yong Wang Fumin Zhang Huading Liang Fang Wang Liquan Li 《Journal of Sol-Gel Science and Technology》2012,64(3):564-570
Nd3+ doped mesoporous TiO2 samples with different molar ratio of Nd/Ti were synthesized by a sol?Cgel method. The textural and optical properties of the samples were systematical characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption?Cdesorption isotherms, Fourier transform infrared spectroscopy and UV?CVisible absorbance spectroscopy. It was revealed that Nd3+ doping inhibited the phase transformation from anatase to rutile after calcination, and the mesoporous structure of doped samples was still retained with the increase of Nd/Ti molar ratio. The surface area of the samples varied from 137 to 210 m2g?1 and the average pore size of them ranged between 5.7 and 8.2?nm. The photocatalytic activities of all the samples were evaluated by degradation methyl orange (MO) in aqueous solution as a model reaction under UV light irradiation. The results showed that the doped samples demonstrated a higher photocatalytic activity than the mesoporous TiO2, and the 3?mol% Nd3+ doped mesoporous TiO2 exhibited the best photocatalytic performance. Meanwhile, a promotion effect of the H2O2 added was verified in the degradation of MO. 相似文献
6.
《Annales de Chimie Science des Materiaux》2001,26(2):79-85
The sorption of 2.4-dichloro phenoxyacetic acid (2.4-D) on two different activated carbons was determined using the batch equilibration technique. The calculated slopes of the Freundlich sorption isotherms were significantly less than 1. The (K) values were higher for the activated carbon which has the higher specific surface, and increased with NaCl concentration. The rate of attaining equilibrium of 2.4-D increased with a decrease in absorbent concentration. Dynamic modelling of the adsorption showed that a first order reversible kinetic model was followed for the adsorption process. The overall rate constant K′, the adsorption rate K1, the desorption rate constant K2, and the equilibrium constant Kc for the adsorption process were calculated. 相似文献
7.
–SO3H modified mesoporous silica adsorbent with water sorption capacity and fast desorption kinetics for water sorption was synthesized and studied via a combined experimental and numerical approach. Mesoporous silica was synthesized using sol–gel method in H2SO4 medium. The water adsorption isotherms and kinetics over the silica were evaluated by a dynamic water vapor sorption analyzer. Mesoporous silica was modeled using annealing simulation with CVFF forcefield. –SO3H modified mesoporous silica was modeled by the attachment of –SO3H to the surface hydroxyl groups and validated. Simulation results show water sorption capacity at low relative humidity (RH) increases with –SO3H loading on mesoporous silica. Energy distribution of intermolecular interaction and micro-view of water sorption over –SO3H modified mesoporous silica reveal that although strong interaction (intermolecular interaction of ?40 to ?20 kcal/mol) between hydrophilic groups (–SO3H) with water can increase water sorption capacity at low RH, weak H2O–H2O interaction (intermolecular interaction of ?20 to ?10 kcal/mol) dominated water sorption capacity at both low and high RH. 相似文献
8.
E. R. Oskotskaya E. N. Gribanov N. N. Basargin O. I. Markov Yu. V. Khripunov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(10):1804-1809
Studies of the surface of polymer complexing sorbents (PCSes) with an o, o′-dioxy-(1-azo-1′) functional analytic group were conducted by means of atomic force spectroscopy (AFM). The characteristic
linear dimensions of surface relief objects and their fractal dimensions were determined. The PCS roughness parameters (the
mean-root-square profile roughness and average arithmetic roughness) were established and the quantitative dependence between
them and the scanning scale was found. The effect of temperature on the sorbents’ structural organization was demonstrated.
The obtained data enable us to solve the problem of sorption process intensification through the targeted impact of the class
of compounds under examination on the supramolecular structure and polymer substrate morphology in creating the optimum conditions
of sorption with PCS participation. 相似文献
9.
P. Staszczuk J. C. Bazan M. Błachnio D. Sternik N. J. Garcia 《Journal of Thermal Analysis and Calorimetry》2006,86(1):57-68
This paper presents possible applications of thermal analysis, sorptometry
and porosimetry to study physico-chemical properties of Na- and La-montmorillonite
samples, especially for determination of total surface heterogeneity. The
quasi-isothermal thermogravimetric (Q-TG) mass loss and its first derivative
(Q-DTG) curves with respect to temperature and time obtained during programmed
liquid thermodesorption under quasi-isothermal conditions have been used to
study adsorbed layers and heterogeneous properties of the Na- and La-montmorillonites.
Calculations of the desorption energy distribution functions by analytical
procedure using mass loss Q-TG and differential mass loss Q-DTG curves of
thermodesorption under quasi-isothermal conditions of polar and non-polar
liquid vapours preadsorbed on a material surface are presented. Parameters
relating to porosity of samples were determined by sorptometry, mercury porosimetry
and atomic force microscopy (AFM). From nitrogen sorption isotherms from sorptometry
and porosimetry methods, the fractal dimensions of montmorillonites have been
calculated. Moreover, a new approach is proposed to calculate fractal dimensions
of materials obtained from Q-TG curve; this is compared with values obtained
by the above methods. The total heterogeneous properties (energy distribution
function and pore-size distribution functions) of samples studied were estimated.
The radius and pore volume of the tested samples calculated on the basis of
thermogravimetry, sorptometry and porosimetry techniques were compared and
good correlations obtained. 相似文献
10.
D. Sternik P. Staszczuk M. Majdan A. Gładysz-Płaska E. Dąbrowska K. Bigda 《Journal of Thermal Analysis and Calorimetry》2006,86(1):69-75
The paper presents physico-chemical properties
of mixed adsorbents in the clinoptylolite (mordenite)/SiO2
system containing 30, 50, 80 mass% zeolite. Adsorption capacity towards polar
(water, butanol) and non-polar (n-octane)
substances as well as total surface heterogeneity (energetic and geometrical)
were determined. Desorption energy distribution functions as well as fractal
dimensions were also determined and compared with the low-temperature nitrogen
adsorption data. Irregular shapes of the curves q=f(E
d)
as well as large values of volumetric fractal dimensions (D
f~2.6)
revealed heterogeneous properties of the zeolite/SiO2 system surfaces. Addition
of zeolite increases total heterogeneity of the material. 相似文献
11.
Oxygen Sorption and Desorption Properties of Selected Lanthanum Manganites and Lanthanum Ferrite Manganites 下载免费PDF全文
Temperature‐programmed desorption (TPD) with a carrier gas was used to study the oxygen sorption and desorption properties of oxidation catalysts and solid‐oxide fuel cell (SOFC) cathode materials (La0.85Sr0.15)0.95MnO3+δ (LSM) and La0.60Sr0.40Fe0.80Mn0.20O3‐δ (LSFM). The powders were characterized by X‐ray diffractometry, atomic force microscopy (AFM), and BET surface adsorption. Sorbed oxygen could be distinguished from oxygen originating from stoichiometry changes. The results indicated that there is one main site for oxygen sorption/desorption. The amount of sorbed oxygen was monitored over time at different temperatures. Furthermore, through data analysis it was shown that the desorption peak associated with oxygen sorption is described well by second‐order desorption kinetics. This indicates that oxygen molecules dissociate upon adsorption and that the rate‐determining step for the desorption reaction is a recombination of monatomic oxygen. Typical problems with re‐adsorption in this kind of TPD setup were revealed to be insignificant by using simulations. Finally, different key parameters of sorption and desorption were determined, such as desorption activation energies, density of sorption sites, and adsorption and desorption reaction order. 相似文献
12.
Willian Kopp Hernane S. Barud Marcelo F. Paz Luciano A. Bueno Raquel L. C. Giordano Sidney J. L. Ribeiro 《Journal of Sol-Gel Science and Technology》2012,63(2):219-223
The addition of calcium chloride eletrolyte to sodium polyphosphate solutions lead to Calcium polyphosphate coacervates. The effects of a thermal treatment were investigated with the objective to increase the relative stability of the obtained material. Thermogravimetry analysis indicates that coacervates became less hydrophilic and more thermally stable after the thermal treatment. Crystallization was identified through differential scanning calorimetry and X-ray diffraction. Morphological changes were observed after the thermal treatment by scanning electron microscopy. N2 adsorption?Cdesorption isotherms suggest that both materials, thermally treated or not, display type IV isotherms, low superficial area and mesoporous structure. Stability experiments in solutions at different pH values show that the thermally treated calcium polyphosphate is relatively more stable than the non-treated coacervate. 相似文献
13.
Layered double hydroxide (LDH) with a Mg/Al molar ratio of 1 : 1 was synthesized by using a co-precipitation method and its calcined product (CLDH) was obtained by calcination of the MgAl-LDH at 500 ℃. The sorption removal of Pb^2+ from solution was investigated, finding that both LDH and CLDH show good sorption ability and they could be used as a new type of environmental sorbent for the removal of Pb^2+ from water. The sorption kinetics and the sorption isotherms of Pb^2+ on both LDH and CLDH can be described by the pseudo-second order kinetics and Freundlich isotherm, respectively, under the studied conditions. The sorption amounts of Pb^2+ on LDH and CLDH are independent of pH in a pH range of about 3-10. The presence of NaNO3 may inhibit the sorption of Pb^2+ on LDH while hardly affect that on CLDH. The sorption mechanism of Pb^2+ on LDH and CLDH may be attributed to the surface precipitation and the surface complex adsorption. The surface complex adsorption may be further distinguished to the chemical binding adsorption forming the inner-sphere surface complexes and the electrostatic binding adsorption forming the outer-sphere surface complexes. The sorption mechanism of Pb^2+ on LDH may be attributed to the surface precipitation and the electrostatic binding adsorption, while that on CLDH may be attributed to the surface precipitation and the chemical binding adsorption. 相似文献
14.
Yu-hua Shen An-jian Xie Xue-rong Yu Gang Wu Ling-guang Qiu Shi-kuo Li Xiang-yun Kong Cheng-xiang Han 《Colloid Journal》2007,69(3):348-354
The properties of octadecanoic acid-otctadecylamine monolayers and growth of calcium carbonate (CaCO3) induced by the monolayers on the surface of supersaturated CaCO3 solution with N,O-carboxymethyl chitosan (CMC) are studied. The results suggest that CMC is either adsorbed on or inserted into the monolayers,
as is confirmed by π-A, dπ/dA-A, and π-t isotherms. The adsorption of CMC changes the properties of the monolayers, a process that results in the transformation of
the shape of CaCO3 particles from crystal-like into the fractal pattern beneath the monolayers. Different fractal morphologies, such as butterfly
and wicker branches consisting of hollow ellipsoidal, solid ellipsoidal, and spherical particles, correspondingly, are observed;
these morphologies depend on the CMC concentration in the subphase. The dimensions of fractal patterns are determined. The
mechanisms of the formation of CaCO3 crystals and fractal structures are discussed.
The text was submitted by the authors in English. 相似文献
15.
N. A. Mamleeva V. V. Lunin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(3):658-663
Adsorption of phenol on aspen and pine wood is investigated. It is shown that adsorption isotherms are described by the Langmuir model. The woods’ specific surface areas and adsorption interaction constants are determined. It is found that the sorption of phenol on surfaces of aspen and pine is due to Van der Waals interactions (Ssp = 45 m2/godw for aspen and 85 m2/godw for pine). The difference between the adsorption characteristics is explained by properties of the wood samples’ microstructures. 相似文献
16.
E. Chmielewská-Horváthová J. Lesný 《Journal of Radioanalytical and Nuclear Chemistry》1995,200(4):351-363
The possibility to use the monoionic Ag+-form (eventually Hg+- and Hg2+- forms) of clinoptilolite of domestic origin for radioactive iodide elimination from waters has been studied. The capacity of the monoforms of clinoptilolite towards iodide exceeds many times that of the capacity of clinoptilolite in natural form. Due to the low solubility product of AgI, Hg2I2 and HgI2 iodides generate precipitates on the zeolite surface. Rtg analyses of the silver form of clinoptilolite after sorption of iodide demonstrate the formation of new crystals on the zeolite surface. The influence of interfering anions on the adsorption capacity of silver clinoptilolite towards iodide was investigated, too. Kinetic curves of iodide desorption from the surface of silver and mercury clinoptilolite were compared. Simultaneously, adsorption isotherms for the systems aqueous iodide solution/Ag–, Hg-clinoptilolite were determined. 相似文献
17.
Surface structure of CTMA modified bentonite and their sorptive characteristics towards organic compounds 总被引:1,自引:0,他引:1
Lifang Zhu Runliang Zhu 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,320(1-3):19-24
This work was to examine the correlation between surface structure and sorptive characteristics of cetyltrimethylammonium cations (CTMA+) modified bentonite, which will provide novel information for exploring the sorptive mechanisms of organoclays. Various amounts of CTMA+ (0.21–1.98 mmol/g) were intercalated into bentonite to prepare a series of organobentonites with different structures. N2 adsorption–desorption isotherms were plotted for the organobentonites to obtain the surface structure information, and sorption capacities of these organobentonites toward phenol, aniline, nitrobenzene and naphthalene were examined. It was shown that surface areas, pore volumes and surface fractal dimension of the organobentonites decreased with increasing CTMA+ loading amount. Sorption capacities of the organobentonites towards the four organic compounds have no evident correlation with their surface structures, and Koc values of the organic compounds were shown to first increase until the maximum and then decrease as CTMA+ loading amount further increased. Combining with the surface structure and sorption capacities of the organobentonites, we proposed that the solute molecules were penetrated into the CTMA+ aggregates, and partition rather than adsorption mechanism dominated the sorption processes. The CTMA+ aggregates formed optimal partition phases in the intermediate surfactant loading range. 相似文献
18.
Hui Liu Hongliang Li Zhaolong Ding Aiping Fu Hongyan wang Peizhi Guo Jianqiang Yu Cunguo Wang Xiu Song Zhao 《Journal of Cluster Science》2012,23(2):273-285
Using the surface charged and acid dissolvable melamine formaldehyde (MF) microspheres as sacrificial hard templates, silica coated MF core?Cshell composite microspheres, denoted as MF@SiO2, were synthesized via a surfactant-assisted sol?Cgel process by using tetraethyl orthosilicate (TEOS) as silica source. Hollow SiO2 spheres with mesoporous shells were then obtained after selective removal of the MF cores and the pore directing surfactant by hydrochloric acid etching or calcinations in air. Interesting shrinkage phenomena were observed in both the hollow products derived from hydrochloric acid etching and calcinations. The influence of the ratio of MF sphere to TEOS and the removal method of the MF core on the size of the hollow spheres, the shell thickness and the shell surface roughness have been studied. The composition, the thermal stability, the morphology, the surface area and pore size distribution, the wall thickness and adsorption properties of the hollow spheres derived from hydrochloric acid etching and calcinations were also investigated and compared based on the FTIR, SEM, TEM, TGA, Nitrogen adsorption?Cdesorption and spectrophotometer techniques or measurements. 相似文献
19.
D. B. Hernández-Uresti A. Martínez-de la Cruz Leticia M. Torres-Martínez 《Research on Chemical Intermediates》2012,38(3-5):817-828
PbMoO4 molybdate with scheelite structure was synthesized by a simple co-precipitation method. The material was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and adsorption?Cdesorption N2 isotherms (BET). The photocatalytic activity of PbMoO4 molybdate was evaluated with the degradation reactions of rhodamine B (rhB), indigo carmine (IC), orange G (OG), and methyl orange (MO) under UV irradiation. In order to elucidate aspects of the degradation mechanism of the organic dyes, some experimental variables were modified such as pH and O2 level in solution. The total organic carbon (TOC) analysis of samples irradiated revealed that mineralization of organic dyes by the action of PbMoO4 was feasible in rhB (60%), IC (80%), and OG (65%) after 96?h of irradiation. For the same time of irradiation, a recalcitrant behavior to the mineralization was observed in MO reaching only a 10% of mineralization degree. 相似文献
20.
Adsorption of cetyltrimethylammonium bromide (CTAB) onto bituminous coal (BC) and a clay mineral, montmorillonite (MMT), was
studied. Simultaneous measurements of the CTAB adsorption and zeta potential determination of the adsorption suspensions were
carried out. The adsorption isotherms were found to be of the typical Langmuir type; values of the CTAB adsorption capacities
were calculated (a
m = 0.65 mmol g−1 for coal and a
m = 3.24 mmol g−1 for MMT). The shape of the adsorption isotherms was correlated with zeta potential values at the adsorption equilibrium.
The adsorption properties of both sorbents were studied by voltammetry on carbon paste electrodes (CPE) modified with coal-CTAB
and MMT-CTAB system, respectively. Open circuit sorption with differential pulse voltammetry was performed in order to compare
the sorption properties of the systems with the unmodified sorbents. The Cu2+ adsorption on BC and MMT decreased to approximately 50 % and 40 %, respectively. The surface adsorption mechanism of CTAB
on coal based on hydrophilic interactions was proposed. In the case of montmorillonite, the CTAB intercalation is expected
via ion exchange into the inter-layer space forming a double- or triple-layer arrangement. 相似文献