A model of the two-stage condensation mechanism of water adsorption on nonporous carbon adsorbents

The mechanism of adsorption of water molecules on nonporous carbon adsorbents has been suggested in terms of two different states of adsorbed water; stretched liquid water and water that occupies an intermediate state between the liquid and vapor. Two stages of adsorption were distinguished: condensation and pre-condensation that assumes the formation of molecular associates. The BET model was used to describe the pre-condensation stage. The equations of the adsorption isotherm for water vapor in the region of condensation process and the expression for the determination of the specific hydrophilic surface of adsorbents were found. Examination of the experimental data on adsorption of water vapor on nongraphitized samples of carbon adsorbents shows that in the region of polymolecular adsorption, all isotherms fall into a common curve determined by the equation of the stretched liquid film and can be calculated regardless of the properties of individual liquid water. The equation for adsorption of water vapor on the hydrophobic surface was obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1933–1939, October, 1998.     

Hydration of calixarene-containing polymers

The hydration of cross-linked polymers containing tetramethylcalix[4]resorcinarene and tetraphenylcalix[4]resorcinarene was studied using the isopiestic, calorimetric, and MNDO/PM3 method. Adsorption of water vapor by calixarene-containing polymers leads to type II isotherms according to the Brunauer—Deming—Deming—Teller classification. In the framework of the Aranovich model of polymolecular adsorption, the monolayer capacity and pure heat of adsorption were calculated. The first monolayer is formed from 3—4 water molecules adsorbed due to hydrogen bonding with OH groups of calixarenes. The integral thermodynamic functions of hydration of the calixarene-containing polymers in water at 298 K were determined.     

Density Functional Theory Study of Infrared and Ultraviolet Spectra of Urea L-Malic Acid

During the measurement of atmospheric nitrate radical by long-path differential optical absorption spectroscopy, water vapor strong absorption could affect the measurement of nitrate radical and detection limits of system. Under the tropospheric condition, the optical density of water vapor absorption is non-linearly dependent on column density. An effective method was developed to eliminate the effect of water vapor absorption. Reference spectra of water vapor based on the daytime atmospheric absorption spectra, when fitted together with change of cross section with water vapor column densities, gave a more accurate fitting of water vapor absorptions, thus its effect on the measurements of nitrate radical could be restricted to a minimum and detection limits of system reached 3.6 ppt. The modified method was applied during an intensive field campaign in the Pearl River Delta, China. The NO3 concentration in polluted air masses varied from 3.6 ppt to 82.5 ppt with an average level of 23.6±1.8 ppt.     

Effect of Water Vapor Absorption on Measurements of Atmospheric Nitrate Radical by LP-DOAS

During the measurement of atmospheric nitrate radical by long-path differential optical absorption spectroscopy, water vapor strong absorption could affect the measurement of nitrate radical and detection limits of system. Under the tropospheric condition, the optical density of water vapor absorption is non-linearly dependent on column density. An effective method was developed to eliminate the effect of water vapor absorption. Reference spectra of water vapor based on the daytime atmospheric absorption spectra, when fitted together with change of cross section with water vapor column densities, gave a more accurate fitting of water vapor absorptions, thus its effect on the measurements of nitrate radical could be restricted to a minimum and detection limits of system reached 3.6 ppt. The modified method was applied during an intensive field campaign in the Pearl River Delta, China. The NO3 concentration in polluted air masses varied from 3.6 ppt to 82.5 ppt with an average level of 23.6±1.8 ppt.     

Transference numbers of potassium picrate in water at 25°C and the dimerization of picrate ions

The cation- and anion-constituent transference numbers of aqueous 0.02M potassium picrate have been measured at 25°C by the moving-boundary method. The large difference (0.014) between the results and the predictions of the Debye-Hückel-Onsager theory, and similar anomalies in the literature, are consistent with the existence of picrate ion dimers (Pi ₂ ^2– ) with a formation constant of 4(±2) liter-mole^–1.This work was carried out at Imperial College while P. G. N. Moseley was on leave of absence from the University of Khartoum.     

Color Centers in Irradiated Potassium Picrate

The kinetics of the formation of color centers in solid potassium picrate in a -radiation field was studied. Optical spectra in potassium picrate were studied for the first time. The transmission spectra of irradiated crystals of potassium picrate displayed peaks at 515 (2,6-dinitro-para-quinone) and 630 nm (a picric acid-derived radical containing the nitrite group), with the intensity increasing with an increase in the absorbed dose. The potassium picrate radiolysis scheme is discussed.     

Evaluation of selectivity-determining factors for membrane electrodes based on naphtho-15-crown-5 by liquid-liquid extraction

Liquid-liquid extractions of sodium and potassium picrates with naphtho-15-crown-5 (N15C5) into 1,2-dichloroethane are studied, in order to clarify the factors governing the high potassium ion selectivity of the N15C5-based membrane electrode. The distribution coefficient of N15C5 between water and 1,2-dichloroethane was 1800 at 15°C. The formation constants of the complexes of N15C5 with the sodium ion and the potassium ion in the aqueous phase were less than unity and there was no remarkable difference between their values. Potassium picrate was mainly extracted into 1,2-dichloroethane by forming the 2:1 N15C5-potassium complex, while sodium picrate was extracted by forming the 1:1 complex. The extraction constants for sodium picrate and potassium picrate were 10^3.86 and 10^7.61, respectively, The high potassium selectivity is concluded to be due to the high extractability of the 2:1 potassium complex.     

Adsorption–desorption phenomena of water vapor on a superabsorbent polymer partially crosslinked with potassium

The objective of this article is to study an amorphous superabsorbent polymer, which is able to absorb up to 300 times its weight of water. Adsorption–desorption phenomena of water vapor on the polymer as a function of temperature showed a reversibility of the adsorption–desorption phenomena. The thermal stability of the polymer at atmospheric pressure was also studied. The kinetic study of the desorption phenomena of water vapor on the polymer according to certain physicochemical parameters was discussed. The results showed that the kinetic regime governing the desorption phenomena of water vapor on the polymer is a process limited by a mono-dimensional diffusion for low masses and by a three-dimensional diffusion for high masses.     

Adsorption on nonporous and supermicroporous adsorbents

The mean values of the characteristic energy of C₆H₆ adsorption in large micropores were calculated from the adsorption isotherms of benzene vapor on carbon blacks. The supermicropores are characterized by the significant dispersion of the adsorption potential resulted from the pore-size distribution, which imparts the polymolecular character to adsorption. The effect of enhancement of the characteristic energy of adsorption was analyzed, which was caused by the overlap of the force fields of the opposite pore walls and the reduction of the adsorption film surface with micropore volume filling. The both factors are comparable by magnitude and depend on the micropore sizes.     

Modeling of water vapor adsorption isotherms onto polyacrylic polymer

The adsorbed amounts of water vapor onto polyacrylic polymer (polymer ×10) were measured using a thermogravimetry method as a function of pressure at 298 and 313 K. The adsorption isotherms are categorized to type II isotherms by IUPAC classification leading to a hysteresis loop between adsorption and desorption branches. The current study was completed by the measurement of the adsorption heats at 298 K using a differential scanning calorimetry. The calorimetric curves showed two adsorption heats domains. These domains have been attributed to the adsorption of “equivalent monolayer” and the condensation of water between polymeric chains. The correlation of experimental data to some chosen theoretical models shows that the GAB model is the most adequate to describe water vapor sorption isotherms.     

Adsorption of carbon dioxide on microporous carbon adsorbents

Adsorption isotherms of carbon dioxide on microporous carbon adsorbents prepared by activation with potassium sulfide in water vapor were measured. The measurements were carried out in the pressure interval from 1 Pa to 0.1 MPa at temperatures from 216.2 to 293.15 K. Based on the theory of volumetric filling of micropores, the main structural and energetic parameters of the microporous carbon adsorbents were calculated. The adsorption isosters of carbon dioxide were calculated from the adsorption isotherms in the same pressure and temperature ranges and approximated by linear dependences. The plots of the differential mole isosteric heats of adsorption vs amount adsorbed were constructed by using the adsorption isosters.     

引入三氟甲基侧基对对苯醚型聚酰亚胺薄膜吸水性及水蒸汽透过性的影响

合成了3种含三氟甲基的芳香二胺,进而与3,3′,4,4′-联苯四甲酸二酐(BPDA)缩聚,得到3种对苯醚型含氟聚酰亚胺薄膜,并由4,4′-二氨基二苯醚（4,4′-ODA）与BPDA缩聚得到聚酰亚胺薄膜。 对4种聚酰亚胺薄膜的水蒸汽透过率、吸水性和热学性能的测试结果表明,其中聚合物PI-1（2,2′-BTF-4,4′-BADE+BPDA;BTF：双三氟甲基;BADE：二氨基二苯醚）的水蒸汽透过率为7.70 g/（h·m2）,吸水率为0.67%,玻璃化转变温度为259.74 ℃,质量损失5%的温度为521.40 ℃,具有良好的水蒸汽透过性和低吸水性。     

The effect of component partitioning on potassium picrate transport across multicomponent supported liquid membranes

Supported liquid membrane experiments were performed with systematically varied liquid membrane compositions including dicyclohexyl-18-crown-6 ether as the carrier and various ratios of methylene chloride and a 35 carbon aliphatic oil. The partitioning of the crown ether species toward the membrane phase increased markedly with methylene chloride addition to the aliphatic oil. p]The unanticipated unsteady state transport of potassium picrate across the liquidfilled microporous membranes resulted from evaporation of methylene chloride from the aqueous reservoirs and subsequent depletion from the membrane phase. The depletion of methylene chloride from the liquid membrane caused progressively reduced partitioning of the carrier and carrier complexes to the membrane relative to the contiguous aqueous phases. The reduction in carrier concentration in the membrane phase resulted in progressively decreased concentration gradients of the carrier complex. The rate of potassium picrate transport decreased during the course of the experiments even though the upstream potassium concentration was insignificantly decreased and the downstream concentration of potassium picrate remained small compared with the upstream concentration. p]These experimental results focus attention upon the important practical problem of non-infinite partitioning of carrier and key solvent components between the membrane phase and the contiguous aqueous phases. Subtle changes in the carrier distribution coefficient markedly compromise process efficacy since the volume ratio of the aqueous and membrane phases is enormous.     

Dynamics of joint adsorption of mutually soluble substances by activated carbons

A model for the dynamics of isothermal absorption of a binary mixture of an organic substance, soluble in water, and water vapor in a fixed bed of activated carbon was proposed. It includes the equations of material balance and the Myers—Prausnitz model for equilibrium adsorption. The possibility of formation of the condensed phase during the adsorption of an organic substance on moist activated carbon was shown. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1491–1495, August, 1998.     

Surface Forces in Wetting Films

Reviewed are theoretical and experimental results of Russian and foreign researchers of the surface forces acting in asymmetric system, wetting films contacting with the condensed phase on the one side and with the gaseous phase or own vapor on the other side. Wetting films play an important role in such phenomena as wetting and spreading, flotation, polymolecular adsorption, evaporation of liquids from porous bodies, and capillary condensation. Disjoining pressure isotherms of wetting films determine the wetting conditions and the values of forming contact angles. The mechanisms of film stability, rupture, and coalescence are discussed based on the theory of surface forces. The properties of the films of nonpolar liquids and liquid mixtures; polymolecular adsorption films of polar liquids; as well as wetting films of aqueous electrolyte solutions, surfactants and polymers are analyzed systematically.     

Alkane films on water: stability and wetting transitions

Types of surface forces determining the disjoining pressure isotherms of wetting films of low-molecular-weight alkanes on water surface are discussed. The van der Waals forces in alkane interlayers at different temperatures were calculated using a combination of exact equations of the Dzyaloshinsky—Lifshitz—Pitaevsky macroscopic theory and the multi-oscillator model for representation of the dielectric permittivity spectra of contacting bodies. Taking account of competitive action of the van der Waals and image forces allows one not only to reproduce specific features of wetting in the systems studied at different temperatures, but also to describe quantitatively the contact angles and the experimentally observed isotherms of polymolecular adsorption. The experimentally detected wetting transition in the water—pentane—vapor system was rationalized using the results of calculations mentioned above and the Derjaguin—Frumkin theory of wetting. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 256–266, February, 2008.     

Adsorption of univalent and bivalent metal nitrates on hydrous lead dioxide Adsorption behaviour of potassium, cupric, zinc, cadmium and nitrate ions

The individual adsorption behaviour of potassium, cupric, zinc, cadmium and nitrate ions on hydrous lead dioxide (HLD) was investigated. HLD was found to be an amphoteric ion-exchanger with an equi-adsorption point in the vicinity of pH 4.6. For bivalent metal ions, the amount of adsorption increased with pH (at pH > 3) and there was almost 100% adsorption at pH > 6. Both the adsorption capacity and the adsorption affinity on HLD were in the order copper(II) > zinc(II) > cadmium(II).     

Component activities in the system thorium nitrate-nitric acid-water at 25°C

The equilibrium composition of the vapor above thorium nitrate-nitric acid-water mixtures has been studied as a function of the concentrations of thorium nitrate and nitric acid using a transpiration technique. At 25°C, the thorium nitrate concentrations m _T ranged from 0.1 to 2.5 molal and the nitric acid concentrations m _N from 0.3 to 25 modal. The vapor pressure of the nitric acid was found to increase with increasing thorium nitrate concentration for a constant molality of nitric acid in aqueous solution. At constant m _T , the nitric acid vapor pressure was particularly enhanced at low nitric acid concentrations. The water vapor pressures decreased regularly with increasing concentrations of both nitric acid and thorium nitrate. The experimental data were fitted to Scatchard's ion-component model, and to empirical multiparameter functions. From the fitting parameters, and available literature data for the nitric acid-water and thorium nitrate-water systems at 25°C, expressions were calculated for the variation of water and thorium nitrate activities, as functions of the nitric acid and thorium nitrate concentrations, using the Gibbs-Duhem equation. Calculated values for the thorium nitrate activities were strongly dependent on the form of the function originally used to fit the vapor pressure data.Issued as AECL-7461.     

Saturated Vapor Pressure Over Melts of the Binary System NaNO2-KNO3

The partial pressures of sodium nitrite and potassium nitrate over melts of the binary system NaNO₂-KNO₃ were measured at 798, 823, and 848 K. Negative deviations of the vapor pressure from Raoult's law, which decrease with increasing temperature, are established. Coefficients A and B of the Clausius-Clapeyron equation, partial molar heats of vaporization, activity and activity coefficient are calculated as functions of composition for potassium nitrate.     

Fourier transform infrared study on the sorption of water to various kinds of polymer thin films

The state of sorbed water and the sorbing processes of water to various polymer thin films were studied with Fourier transform infrared (FTIR) spectroscopy. To prepare the polymer films, we used poly(ethylene glycol)s of different molecular weights and various kinds of vinyl polymers, such as poly(2‐methoxyethyl acrylate). The O? H stretching band of water sorbed in the films increased gradually on contact with water vapor at 50% relative humidity and leveled off. When O? H stretching bands of water sorbed to polymer films were compared, the peak positions and profiles of water sorbed to the polymeric materials with the same hydrogen‐bonding site were similar. A hybrid density‐functional method supported the assignment of the peaks. Furthermore, the diffusion coefficient (D) of water vapor in the polymer films was estimated by time‐resolved measurements of the sorbed water at the very initial stage (0–830 s). It was clearly shown that the D values of water vapor in the polymer materials with a strong hydrogen‐bonding site were smaller than those in hydrophobic polymers. The usefulness of the FTIR technique to investigate water sorption to polymer materials was definitely demonstrated. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2175–2182, 2001