Sorption and catalytic effects upon the dehydration of methanol on perfluorinated copolymer-containing sulfo groups

The peculiarities of methanol transformation on the surface of perfluorinated copolymer, fluoroplastic, containing sulfo groups were studied. At temperatures of 70–120°C, the polymer was established to have high initial activity during the conversion of methanol into dimethyl ether; this reaction was, however, accompanied by strong water sorption that leads to a rapid drop in the activity. The sorption/desorption processes were characterized by temperature effects such as heating during sorption and cooling during desorption. The structure of the polymer in the salt (sodium cations) and acid (hydrolyzed polymer) forms was studied by IR spectroscopy. H₃O⁺SO₃⁻ ionic pairs were found to be present in the acid form.     

Role and effect of dopant ion on sorption-induced motion of polypyrrole films

The sorption-induced bending and recovery motion of PPy films containing different dopant ions have been investigated, and the interaction between water vapor and PPy was studied from sorption isotherms and kinetics. It was found that the PPy/BF₄ film exhibited the most rapid motion, and the initial speeds of bending and recovery motion were 7.9 and 5.9 mm s⁻¹, respectively. The linear expansion coefficient of the film increased in order of PPy/DBS, PPy/TsO, PPy/ClO₄, and PPy/BF₄, which is consistent with the packing density of the PPy chains (ϕ_PPy). The dual-mode sorption model applied to the isothermal sorption of water vapor to the PPy demonstrated that the Langmuir's capacity constant increased in the same order with the ϕ_PPy, while the Henry's law constant was nearly constant. The sorption kinetics obeyed Fickian despite the dimensional change of the films, and the PPy/BF₄ film had the largest diffusion coefficient of 3.13 × 10⁻⁸ cm² s⁻¹. The experimental results indicated that the kind of dopant ion was crucial to the thermodynamics and kinetics of sorption, and the quick and intensive bending motion of PPy/BF₄ films was attributed to the fast diffusion of water vapor, which caused the large dimensional change of the film.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2635–2642, 1998     

Mutual selective exclusion of unlike polymers in dilute solution and its measurement by light scattering

The interaction of unlike polymer molecules (components 2 and 4) in a ternary solution can be regarded as selective exclusion or desorption of one polymer by another. A relation is derived between the coefficient of selective sorption and the interaction parameters A₂₄ and A₂₄₄ which are analogs of the second and third virial coefficients. The ratio between the apparent light-scattering molecular weight and the true value for a polymer solute in a ternary system with one component of a binary solvent polymeric is more involved than in a ternary system in which both solvent components are of low molecular weight. Under certain conditions, the introduction of polymer component 2 into a dilute solution of polymer component 4 may lead to a decrease in the total intensity of scattered light.     

Ion exchange and solvent extraction of the thiourea complex cation of technetium-99 from mineral acid solutions

Sorption of macroamounts of the technetium thiourea complex cation by a cation exchange resin was studied in HNO₃ and HClO₄ solutions as a function of the concentration and reaction time for pertechnetate with thiourea. The distribution ratio reaches the value of 10³ and may be even higher (>10⁴) when sorption proceeds from a solution of the solid complex in dilute perchloric acid. The complex cation is extracted from 0.25–1M HNO₃ with solutions of the bis(1,2-dicarbollyl)cobalt(III) anion in nitrobenzene—chloroform (1:1), log D=2.75−2.95 being obtained. The preconcentration and separation of technetium on cation exchangers from dilute mineral acids would seem to be one field of application.     

Effects of humidity,imidization history,and thickness on water sorption behavior of poly(p-phenylene biphenyltetracarboximide) films

Poly(p-phenylene biphenyltetracarboximide) films with various thicknesses were prepared from the poly(amic acid) precursor by thermal imidization at 230–400°C for 1–10 h under a nitrogen atmosphere. The water sorption in the films was measured at 25°C over 22–100% relative humidity using a Cahn microbalance as a function of film thickness and thermal imidization history. The water diffusion in all the films followed nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. The diffusion coefficient and water uptake varied in 0.85 × 10^?10 ? 7.50 × 10^?10 cm²/s and 0.12–2.4 wt %, respectively, depending upon humidity, film thickness, and imidization history. Both diffusion coefficient and water uptake increased with increasing humidity, but decreased as imidization temperature and time increased. With increasing film thickness, the diffusion coefficient increased whereas the water uptake decreased. The water sorption behavior was interpreted with the consideration of morphological variations, such as polymer chain order, in-plane orientation, and intermolecular packing order due to the film thickness and imidization history. © 1995 John Wiley & Sons, Inc.     

Effect of absorption of low-molecular-weight compounds by some polymer flocculants

The sorption properties of the intramolecular complex - poly(acrylamide) to poly(vinyl alcohol) grafted copolymer (PVA-PAA_N) in block state were investigated with respect to a number of compounds. The relatively small molecules of phenol, phenylalanine in water solution as well as nitrobenzene in hexane are strongly absorbed by PVA-PAA_N films. The large humine acid molecules (sizes are larger by more than ≈ 10 times) are absorbed by PVA-PAA_N very weakly. It was determined the absorption influence on the character of polymer film solution. In a number of cases the oscillation of the dilution and sorption were observed when determining the critical concentrations of guest molecules in the upper layer of polymer films were achieved. The possible mechanisms of absorption were discussed.     

Fluorination of polyhydrofluoroethylenes. II. Formation of perfluoroalkyl carboxylic acids on the surface region of poly(vinylidene fluoride) film by oxyfluorination,fluorination, and hydrolysis

Oxyfluorination and postfluorination behaviors of poly(vinylidene fluoride) films, as well as hydrolysis of the films treated so far, have been studied by infrared (IR) spectrometry. By exposing the polymer film to a mixture of oxygen and fluorine at about 90°C acyl fluoride groups attendant on the scission of the polymer chains were formed. The oxyfluorinated molecules could be further perfluorinated with fluorine alone at about 90°C, leaving many of the acyl fluoride groups. When the properly oxyfluorinated and postfluorinated film was further treated with a hot 6M sodium hydroxide solution the opaque layer of perfluoroalkyl sodium carboxylate of high molecular weight was formed on the surface of the film, to about 3 μm in thickness, which behaved as a cation exchanger. This new type of cation exchanger of perfluoroalkyl carboxylic acid was significantly more acidic than the usual methacrylic acid exchanger. It was able to adsorb the sodium ions from a neutral sodium chloride solution up to about 70% of the exchange capacity and to keep the ions stable while washing them with water, though it could be regenerated to the hydrogen form with a dilute acetic acid solution. The nature of the new ion exchanger has been examined in some detail by IR spectrometry with Li⁺, Na⁺, and Cs⁺ ions.     

Contribution to the study of the sorption of radionuclides on hydrated oxides

The mechanism of¹⁰⁶Ru(III),¹⁰⁶RuNO(II),¹⁴⁴Ce(III),¹⁴⁷Pm(III),⁸⁵Sr(II),¹³¹I⁻,³⁵SO ₄ ²⁻ , and H₂ ³²PO ₄ ²⁻ radionuclide sorption on hydrated ferrous, ferric, aluminium and chromic hydrated oxides was studied. The dependence of sorption on the pH has shown that in a certain range of pH values it is the ion exchange of the radionuclide for a proton or a hydroxyl group of the oxide that probably plays a decisive role in the sorption process. The sorption depends considerably on the pH in the whole range of studied, but its decrease with cations in alkaline media and its increase with I⁻ ion in acidic media does not agree with the above sorption mechanism. Similarly, the course of the dependence of sorption on the sorbent concentration does not indicate ion exchange to be the only mechanis, but it indicates a more complicated sorption process. Probably the sorption of colloidal forms of the radionuclides proceeds, too.     

Large breathing effect induced by water sorption in a remarkably stable nonporous cyanide-bridged coordination polymer

While metal–organic frameworks (MOFs) are at the forefront of cutting-edge porous materials, extraordinary sorption properties can also be observed in Prussian Blue Analogs (PBAs) and related materials comprising extremely short bridging ligands. Herein, we present a bimetallic nonporous cyanide-bridged coordination polymer (CP) {[Mn(imH)]₂[Mo(CN)₈]}_n (1Mn; imH = imidazole) that can efficiently and reversibly capture and release water molecules over tens of cycles without any fatigue despite being based on one of the shortest bridging ligands known – the cyanide. The sorption performance of {[Mn(imH)]₂[Mo(CN)₈]}_n matches or even outperforms MOFs that are typically selected for water harvesting applications with perfect sorption reversibility and very low desorption temperatures. Water sorption in 1Mn is possible due to the breathing effect (accompanied by a dramatic cyanide-framework transformation) occurring in three well-defined steps between four different crystal phases studied structurally by X-ray diffraction structural analysis. Moreover, the capture of H₂O by 1Mn switches the EPR signal intensity of the Mn^II centres, which has been demonstrated by in situ EPR measurements and enables monitoring of the hydration level of 1Mn by EPR. The sorption of water in 1Mn controls also its photomagnetic behavior at the cryogenic regime, thanks to the presence of the [Mo^IV(CN)₈]⁴⁻ photomagnetic chromophore in the structure. These observations demonstrate the extraordinary sorption potential of cyanide-bridged CPs and the possibility to merge it with the unique physical properties of this class of compounds arising from their bimetallic character (e.g. photomagnetism and long-range magnetic ordering).

A cyanide-bridged coordination polymer {[Mn(imH)]₂[Mo(CN)₈]}_n shows exceptional water sorption properties, very large breathing effect and outstanding stability – properties that are unique for this class of compounds – Prussian blue analogs.     

Sorption of hafnium on hydrous titanium oxide using radiotracer technique

The sorption of hafnium on hydrous titanium oxide (TiO₂·1.94 H₂O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk _d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g^–1·min^–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK=6.33·10^–2 min^–1 and of the rate constant for sorptionk ₁=6.32·10^–2 min^–1 and desorptionk ₂=2.28·10^–5 min^–1 have been evaluated using linear regression analysis. The value of correlation factor() is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10^–5 to 9.01·10^–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g^–1 and of a constant related to sorption energy have been estimated to be 2917 dm³·mole^–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.     

Hydration mechanism of polysaccharides: A comparative study

Water sorption was studied at 20 °C on films composed of different natural polymers. Three polysaccharides were investigated: chitosan, cellulose, and alginate. The major differences between these polymers, from a structural point of view, lay in the substitution of an OH group by an NH₂ function for chitosan and by an ionic COO^?Na⁺ group for alginate. An analysis of the experimental water sorption isotherms, expressed as the number of water molecules sorbed per repeating unit in the amorphous phase, associated with an analysis of the enthalpy profile related to the water sorption allowed us to propose a water sorption mechanism in two steps for all the polymers: water sorption on polymer‐specific sites in the first step and water clustering around the first sorbed water molecules in the second step. It was determined that two water molecules interacted with the polymer chains for cellulose and chitosan, whereas four water molecules were bonded to alginate chains. The specific sorption sites were identified as OH groups for cellulose, OH and NH₂ groups for chitosan, and ionic and OH groups for alginate. A systematic reduction of the half‐sorption time was observed in the activity range corresponding to this first sorption step, and it was explained by a water plasticization effect. On the other hand, an increase in the half‐sorption time was observed in the second sorption step, at a high activity (>0.8), for chitosan and alginate. A modelization associating the Guggenheim–Anderson–de Boer model and the clustering theory, applied to our systems, allowed us to relate the occurrence of this last phenomenon to the formation of water clusters containing more than two water molecules. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 48–58, 2005     

Poly(ionic liquid)s as new materials for CO2 absorption

A series of imidazolium‐based ionic liquid monomers and their corresponding polymers (poly(ionic liquid)s) were synthesized, and their CO₂ sorption was studied. The poly(ionic liquid)s had enhanced CO₂ sorption capacities and fast sorption/desorption rates compared with room temperature ionic liquids. The effects of the chemical structures, including the types of anion, cation, and backbone of the poly(ionic liquid)s on their CO₂ sorption have been discussed. In contrast to room temperature ionic liquids, the polymer with PF anions had the highest CO₂‐sorption capacity, while those with BF or Tf₂N^? anions had the same capacities. The CO₂ sorption and desorption of the polymers were fast and reversible, and the sorption was selective over H₂, N_2, and O₂. The measured Henry's constants of P[VBBI][BF₄] and P[MABI][BF₄] were 26.0 bar and 37.7 bar, which were lower than those of similar room temperature ionic liquids. The preliminary study of the mechanism indicated that the CO₂ sorption of the polymer particles was more absorption (the bulk) but less adsorption (the surface). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5477–5489, 2005     

Effect of pH and washing on calcium and magnesium distribution between pulp and filtrate

The impact of pH and washing procedure on calcium and magnesium distribution between pulp and filtrate in pulp processing was investigated. Depending on media pH, the elements are present in the form of ions (Ca²⁺, Mg²⁺) and hydrated oxides (Ca(OH)₂, Mg(OH)₂). Distribution was monitored using binary systems of CaCl₂ and MgCl₂ dissolved in deionized water or Ca²⁺ and Mg²⁺ ions present in filtrates from an industrial pulp mill. Complying with the relevant standards in force, Ca and Mg contents are expressed as CaO and MgO. The study was aimed at obtaining mathematic relations between pH and calcium and magnesium, as two important non-process elements, sorption on pulp. Distribution of the elements between pulp and liquid (filtrate or water) was determined with analytical procedures and simulation of pulp washing. It was found that both pH and filtrate composition influenced sorption/desorption of the elements on/from pulp. Filtrate from a pulp mill, mainly content of organic substances in liquid phase, affects their sorption on pulp and desorption to liquid. The higher the pH value the more efficient the sorption of the elements, magnesium being sorbed on pulp in higher amounts than calcium. Prevalence of the sorbed magnesium is preserved even at lower concentrations of both elements. Distribution of the elements between pulp and solution is expressed through mathematic relations which, in turn, can be employed to purposefully modify or optimize the distribution between the solid (pulp) and liquid (filtrate) media. Moreover, rationalized exploitation of mathematical relations enables balancing the elements within a cellulose manufacture, regulating media recycling, and predicting an eventual impact on technological processes.     

Theoretical analysis of sorption of a binary solvent in a polymer phase. II. Occurrence of maxima and minima in the curve of total sorption

It has been shown that sorption equilibrium in the system polymer–mixed solvent and the total sorption as one of its manifestations can be derived from osmotic equilibrium. The equilibrium relation for the dependence of the osmotic pressure II (as the potential for total sorption) on the composition of the ternary polymer-containing phase also includes the preferential sorption ε. This complication leads to difficulties in the analysis of the dependence of II on composition: for this reason, analysis has been limited to the case of a very dilute polymer phase. If preferential sorption is neglected, the occurrence of an extremum on the curve representing the dependence of the total sorption on the composition of the mixed solvent is affected by the Flory-Huggins parameters as in the occurrence of an inversion in preferential sorption, with the exception that in the former case the difference in the molar volumes of the solvent components contributes a term smaller by a factor of two. In the general case, however, the contribution of preferential sorption to the osmotic pressure (which has always a negative sign) also plays its role. Consequently, while total sorption, at a low preferential sorption and at a large positive value of the solvent–solvent interaction parameter χ₁₂, can exhibit a maximum, a larger preferential sorption can overcompensate the effect of the parameter χ₁₂, so that a minimum appears. The coexistence of a minimum with a maximum on the same curve is possible in some cases with positive χ₁₂. The latter theoretical predictions have not yet been confirmed experimentally. At a negative χ₁₂ the extremum is always a minimum.     

Monitoring formation of poly(neutral red) film by EQCM

An electrochemical quartz crystal microbalance (EQCM) is employed for monitoring the growth of poly(neutral red) films on platinum in the electrolytic solution containing 5.0 mmol dm⁻³ neutral red, 0.3 mol dm⁻³ H₂SO₄, and 0.5 mol dm⁻³ Na₂SO₄. The in situ measurement of the frequency changes of the EQCM reveals that both the adsorption/desorption of neutral red and the formation of poly(neutral red) film can be observed together with anion sorption/desorption during the redox transformation of the polymer, and that the polymerization rate of neutral red increases slowly before the 11th cycle and then increases quickly with increasing number of potential cycles. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 3, pp. 284–289. The text was submitted by the authors in English.     

Trifluoroborate-substituted polythiophene as a novel conjugated polymer promising for sensing and solid-state reactions

The anodic oxidation of trifluoroborate-substituted thiophene 1 in CH₃CN without added electrolyte yielded at ca. 1.0 V (vs. Ag⁺|Ag) a conjugated polymer film showing electroactivity both in water and organic media. The electrochemical and UV–visible spectroscopic responses of such a material were found to be dependent on the nature of cation.     

Sorption of plutonium from low level liquid waste using nano MnO2

Nano-crystalline MnO₂ has been synthesized by the method of alcoholic hydrolysis of KMnO₄ and its potential as a sorbent for plutonium present in the low level liquid waste (LLW) solutions was investigated. The kinetic studies on the sorption of Pu by MnO₂ reveal the attainment of equilibrium sorption in 15 h, however 90 % of sorption could be achieved within an hour. In the studies on optimization of the solution conditions for sorption, it was observed that the sorption increases with the pH of the aqueous solution, attains the maximum value of 100 % at pH = 3 and remains constant thereafter. The sorption was found to be nearly independent of the ionic strength (0.01–1.0 M) of the aqueous solutions maintained using NaClO₄, indicating the inner sphere complexation between the Pu⁴⁺ ions and the surface sites on MnO₂. Interference studies with different fission products, viz., Cs⁺, Sr²⁺ and Nd³⁺, revealed decrease in the percentage sorption with increasing pH of the suspension indicating the competition between the metal ions. However, at the metal ion concentrations prevalent in the low level liquid waste solutions, the decrease in the Pu sorption was only marginally decreased to 90 % at pH = 3, the decrease being more in the case of Nd³⁺ than that in the case of Cs⁺. This study, therefore, shows nano-crystalline MnO₂ can be used as a sorbent for separation of Pu from LLW solutions.     

Sorption of neptunyl(V) cations on suspended silicate: Effects of pH, ionic strength, complexing anions, humic acid, and metal ions

Sorption of NpO₂ ⁺ on silicate (10.00 g/l) particles dispersed in sodium perchlorate media was studied as a function of pcH and ionic strength at 298 K. The sorption increased with increased pcH in the range of ∼6.5 to 9.2, above which saturation was observed. An increase in ionic strength from 0.20M to 1.00M (NaClO₄), increased the NpO₂ ⁺ sorption, which then decreased at 1.50M (NaClO₄) for 7<pcH<8.5. The effects of different types of ligands on the sorption of NpO₂ ⁺ to suspended silicate were investigated. The types of ligands included: (i) inorganic anions (fluoride, carbonate, phosphate (ii) N-donors (ethylenediamine, 1,10 phenanthroline (iii) carboxylic acids (oxalic acid, citric acid, iminodiacetic acid, ethylenediaminetetraacetic acid) and (iv) humic acid. A synergistic enhancement in sorption to the suspended silicate was observed for phosphate, oxalate, ethylenediaminetetraacetic acid, ethylenediamine, 1,10 phenanthroline (5<pcH<8) and humic acid (6.5<pcH<8.8). This behavior was attributed to the formation of ternary NpO₂ ⁺/silicate/ligand complexes. The effects of Ca(II) (1.00·10⁻³M) and Eu(III) (1.00·10⁻⁴ and 1.00·10⁻³M) ions on NpO₂ ⁺ sorption to suspended silicate were also investigated. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.     

Magnetic molecularly imprinted composite for the selective solid‐phase extraction of p‐aminosalicylic acid followed by high‐performance liquid chromatography with ultraviolet detection

A new method for the selective extraction of p‐aminosalicylic acid from aqueous and urine samples has been developed using magnetic molecularly imprinted polymer nanoparticles before determination by high‐performance liquid chromatography. The Fe₃O₄ nanoparticles were first prepared through the chemical coprecipitation of Fe²⁺ and Fe³⁺ and then coated with a vinyl shell. Subsequently, a layer of molecularly imprinted polymers was grafted onto the vinyl‐modified magnetic nanoparticles by precipitation polymerization. FTIR spectroscopy, scanning electron microscopy, vibrating sample magnetometry, and thermogravimetric analysis were applied to characterize the sorbent properties. Moreover, the predominant parameters affecting the magnetic solid phase extraction such as sample pH, sorption and elution times, the amount of sorbent, and composition and volume of eluent were investigated thoroughly. The maximum sorption capacity of the imprinted polymer toward p‐aminosalicylic acid was 70.9 mg/g, which is 4.5 times higher than that of the magnetic nonimprinted polymer. The magnetic molecularly imprinted polymer nanoparticles were applied for the selective extraction of p‐aminosalicylic acid from aqueous and urine samples and satisfactory results were achieved. The results illustrate that magnetic molecularly imprinted polymer nanoparticles have a great potential in the extraction of p‐aminosalicylic acid from environmental and biological matrices.     

Kinetics of electron transfer reactions of metal complexes at impermeable redox active polymeric films on electrode surfaces and charge transport within the polymer film

At rotated Pt disk electrodes coated with thin films of the redox polymer poly-[Ru(vbpy)₃]²⁺, ruthenium and iron bipyridine complexes dissolved in acetonitrile can become oxidized by two pathways. The first is diffusion of the solute complex through the polymeric film to react at its normal potential E_sub⁰, at the Pt/polymer interface. The second is a mediated electron transfer cross-reaction between the solute complex and poly-[Ru(vbpy) ₃]²⁺ sites generated in the film at adequately positive potentials. The mediated reaction, as judged from the lack of variation of its rate k_crsΓ with the quantity of polymer mediator sites present in the multimolecular layer film, and from other evidence, is confined to the outer few (one?) monolayers of ruthenium polymer film sites. The mediated reaction becomes the dominant pathway for films with Γ_T ～2×10^?9 mol/cm² of ruthenium polymer sites, owing to the low permeability (measured independently) of the solutecomplexes into the film. The rate k_crsΓ could be measured when the solute complex oxidation potential is more positive than that of the redox film, and is too fast to measure when E_sub⁰, is more negative than the redox film E_cal?⁰, New theory is presented and evaluated to describe the rising portions of the voitammetric waves for the nine solute complexes studied. The rate of charge transport through the poly-[Ru(vbpy)₃]²⁺ film becomes controlling under certain conditions and can be thereby measured as well.