Types Of Acidic Groups Research Articles

Synthesis of the new ion exchangers based on polyacrylonitrile fiber Nitron C

New ion exchangers based on polyacrylonitrile fiber were obtained by catalytic amination of nitrile groups with tetraethylenepentaamine and pentaethylenehexaamine. Chelating ion exchangers with aminodiacetic functional groups were obtained on the base of these materials. The acid-base parameters of the functional groups of obtained ion exchangers were determined by potentiometric titration: initial polyampholytes have a high anion exchange capacity (E b = 4.5–5.5 m-eq/g) distributed between three types of groups with pK a equal to 3.3, 6.2 and 9.2, and a cation exchange capacity with E a ≈ 1 m-eq/g and pK a ≈ 10.7; chelating ion exchangers on their base contain three types of acid groups with pK a approximately equal to 3.5, 6.0, 10.5 and two types of anion-exchange groups with pK a equal to 2.0 and 6.0. Initial polyampholytes have a high efficiency in the processes of air purification from acidic impurities (experimental data for sulfur dioxide), chelating ion exchangers – in the processes of water purification from heavy metal ions.

The enhanced removal of cationic dyes in binary system using novel copolymers with two kinds of acidic groups

Abstract In this study novel copolymer hydrogels based on methacrylic acid (MAA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) were synthesized by free-radical aqueous copolymerization and characterized. Derived P(MAA- co -AMPS) hydrogels, joining well the affection of numerous anionic groups toward cations and the accessibility of active sites in the swollen network were recognized as potential sorbents for removal of cationic species. The effect of various initial parameters on sorption of two cationic dyes onto P(MAA- co -AMPS) hydrogels was investigated in both, single and binary, systems. Results showed that the copolymerization of MAA and AMPS significantly increased sorption capability of copolymers compared to both pure-component hydrogels—PMAA and PAMPS hydrogels. The main advantage of novel copolymer hydrogels is enhanced sorption of dyes in binary systems, reaching maximal values of 98.8% (Basic Yellow 28) and 96.4 (Basic Red 46), onto hydrogel P (MAA- co -AMPS) 50/50. The desorption rate of BY28 and BR46 in both, single and in binary, systems increased with the increase in AMPS content in hydrogels. This investigation showed that copolymerization of two acidic monomers, bearing different types of acid groups, could significantly improve the sorption thus decreasing the price and the amount of material needed for successful removal of pollutants.

Physicochemical study of the nanodiamond surface

Suspensions of five types of ultrafine diamond of a detonation synthesis in distilled water and 0.9 mol/l NaCl solution were found to have pHs in the range of 3–6, which results from the intrinsic acidity of their surfaces. The possibility of quantitatively determining the protogenic groups of a surface is found using the pH-potentiometric method. The data on the kinetics of the varying pH of suspensions in water and 0.9 mol/l NaCl solution and the data on the curves of the alkali titration of the suspensions of nanodiamond in the indicated systems make it possible to infer the presence of one or two types of acid groups on the surface of a diamond. The constants of dissociation (pK 1) of these groups on the assumption of their single-base nature are estimated. From 1 × 10−3−5 × 10−2 mol/l chloride solutions of H[AuCl4] and RhCl3 on the surface of diamond, gold(III) and rhodium(III) are found to be adsorbed; the adsorption of methylene blue from its 2.5 × 10−4−5 × 10−4 mol/l solutions reaches more than 90% (upon adsorption from 5 ml of the initial solution by a 0.05-g nanodiamond).

Synthesis of chemically active polymeric fibers bearing sulfo and carboxy groups

A chemically active material bearing two types of acid groups, strongly acidic sulfo groups and weakly acidic carboxy groups, was prepared by radiation-induced graft copolymerization of two kinds of monomers, acrylic acid and sodium styrenesulfonate, onto polypropylene fibers. The main parameters affecting the graft copolymerization are considered.

Adsorption of Heavy Metal Ions onto Insolubilized Humic Acid

A fundamental study of the application of humic acid (HA) to the recovery of cadmium and lead from dilute solutions was carried out. HA, which has an excellent complexing ability with heavy metals, was insolubilized by heating at 330°C for 1 h and was used as an adsorbent. A metal-complexation model was used to compare the adsorption characteristics of insolubilized humic acid (IHA) with those of HA. The results showed that two different types of acidic groups were present on HA and the insolubilization process scarcely influenced the metal-complexation constant of acidic groups; however, the number of available metal binding sites on IHA was decreased to some extent.

Potentiometric titration of unbleached kraft cellulose fibre surfaces

The surface properties of unbleached kraft cellulose fibres in the pH range 2–8 have been investigated using a high precision potentiometric titration method. The pulps were digested in various ways, varying both digestion time (level of residual lignin) and the amount of excess alkali. Titrations were made at constant ionic strength (0.1 M NaCl). The results were evaluated by assuming the existence of different types of acidic groups in the surface and adjusting their intrinsic stability constants and the capacitance of the electrical double layer to obtain the best possible fit to experimental data. Fitting was done using the error square sum minimising program fiteql, version 2.0. Distribution diagrams were calculated with the program solgaswater. It was found that the amount of acidic groups decreases with increasing digestion time, while the amount of excess alkali is not important. The pulps contain two types of acidic groups that dissociate in the pH range 2.5–7.5 (intrinsic stability constants p K≈3.4 and p K≈5.5). The p K value of the stronger acid agrees with what could be expected for uronic acids in hemicellulose (xylan), while the amount of the weaker acid correlates directly with the amount of lignin in the pulps.

Influence of pH and Ionic Strength on Equilibrium Sorption of Cationic Dyes by Acrylic Fibers

We have investigated the equilibrium sorption of two cationic dyes by acrylic fibers at different pH levels and sodium chloride concentrations. To interpret the data, we used the simple Donnan approach with the assumption that the acrylic fibers contained two different types of acidic groups. The distribution coefficients of the dyes are dis cussed in relation to the structures of the dyes and the fibers and the effect of sodium chloride. The equilibrium sorption at different pH levels gives some indication of the strength of the strongly and weakly acidic groups of the acrylic fibers not directly accessible by experiments.

Donnan Approach to Equilibrium Sorption: Interactions of Cationic Dyes with Acrylic Fibers

The equilibrium sorption of ten cationic dyes by porous and regular acrylic fibers has been investigated. The data have been interpreted by a simple Donnan approach, based on the assumption that there are two different types of acidic groups in these fibers. The ionic distribution coefficients KD for the dyes and the fibers were calculated. These coefficients provide an indirect measure of the “affinity” of the dyes for the fibers. The values of KD have been discussed in relation to the structures of the dyes and fibers, and in relation to the effects of salts, pH, and temperature.

The role in CaCO3 crystallization of an acid Ca2+-binding polysaccharide associated with coccoliths of Emiliania huxleyi.

Coccoliths of the unicellular marine alga Emiliania huxleyi are formed intracellularly in a specialized vesicle. Closely associated with the CaCO3 crystals of the coccoliths is an acid Ca2+‐binding polysaccharide. The latter is considered to fulfil a regulatory function in CaCO3 crystallization. In this study it is demonstrated that the coccolith polysaccharide is able to inhibit CaCO3 precipitation in vitro. The degree of inhibition is dependent on the nature of the cations bound to the acid groups of the polysaccharide. After substitution of Na+ by Ca2+ ions the polysaccharide is far less effective in inhibiting CaCO3 precipitation.The coccolith polysaccharide contains two types of acid groups: uronic acids and sulphate esters. Only the uronic acids are responsible for the inhibition of CaCO3 precipitation. Desulphated polysaccharide inhibits precipitation to the same extent as the native molecule whereas the carboxyl‐reduced polysaccharide is unable to block CaCO3 crystallization.Inhibition of CaCO3 precipitation can be suppressed by the presence of ethanol. Presumably the conformation of the molecule is altered under these conditions.Alginic acid [poly(mannuronic‐iduronic acid)] and poly(galacturonic acid) also inhibit CaCO3 precipitation. Inhibition of precipitation is effected by the coccolith polysaccharide and alginic acid at comparable concentrations. The concentration of poly(galacturonic acid) needed to obtain the same result is about 20‐times higher. Contrary to the coccolith polysaccharide, both poly(uronic acid)s inhibit CaCO3 precipitation in the absence as well as in the presence of ethanol. These results suggest that conformational changes of the coccolith polysaccharide may play a role in CaCO3 crystallization in vivo.

Study of acid groups of lignocarbohydrate complex, isolated from spruce wood by mechanical grinding method

1. The main types of acid groups in the lignocarbohydrate complex and its low-molecular fraction are phenolic hydroxyls, the carboxyl groups of aromatic structures, and glucuronic acid residues. 2. From the results of the acid and alkaline hydrolysis, and also the nitrobenzene oxidation, of the lignocarbohydrate complex it follows that its lignin portion is closely similar to Bjorkman lignin both as regards the molecular weight and the structure. 3. From the established structural characteristics of the low-molecular fraction of the lignocarbohydrate complex, in particular the high amount of vanillic acid in it, it follows that this fraction is the portion of the lignocarbohydrate complex that is most amenable to the oxidative-destructive action of grinding. 4. The most probable types of lignocarbohydrate linkages mainly present in the lignocarbohydrate complex and its low-molecular fraction are acetal linkages, and also alkali-stable phenylglycoside and alkylglycoside linkages.