Number Of Acid Groups Research Articles

Two-dimensional tools for analyzing polymer microstructure; coupling non-aqueous ion-exchange chromatography to size-exclusion chromatography

Traditional liquid-chromatographic techniques, such as size-exclusion chromatography, (critical) interaction chromatography, and hydrodynamic chromatography, can all reveal certain aspects of polymers and the underlying distributions. The distribution of incorporated acid groups present in polyacrylates can be determined by non-aqueous ion-exchange chromatography, independent of other distributions present. The microstructural details on how this number of acid groups is incorporated in the polymer remains unknown. A low-molar mass polymer molecule with high acid content and a high-molar mass polymer with a low acid content may have the exact same number of acid groups. To take a next step towards understanding the polymer microstructure of water-borne resins, the distribution of incorporated acid groups over the molar-mass distribution has been investigated.For this purpose, an on-line coupling of non-aqueous ion-exchange chromatography (NAIEX) to size-exclusion chromatography (SEC) was established. Practical considerations regarding the system setup with respect to chromatography modes and column- and valve switching dimensionality are discussed. The orthogonality of NAIEX and SEC is demonstrated. Both liquid chromatography modes may be calibrated using polymer standards, yielding a calibrated separation plane. Cross-sectional data on either the molar mass distribution or the acid group distribution at a certain point of the separation plane is obtained. The value of the designed setup was demonstrated by the detailed characterization of the combined acid-group and molar-mass distribution in polymers with a low acid content, in the order of a few mass-%. Several stages of the emulsion polymerization process could be identified using the combined power of NAIEX and SEC.

Equilibrium data, kinetics and process design for the adsorptive removal of safranin-o by activated carbons

The impact of pH, contact time and temperature of solution on the adsorptive removal of Safranin-O by activated carbons with variable number of carbon–oxygen functional groups and unlike surface characteristics have been studied. The experimental adsorption data have been studied with Langmuir and Freundlich isotherms. The data fit the Langmuir equation better. The adsorption is much affected by the number of acidic groups. It increases on increasing the acidic functional groups by oxidation and decreases slowly on the removal of surface groups during degassing. The adsorption obeys the first-order rate law. In single batch adsorber design, the prediction has been done that the required amount of oxidized activated carbon is 56% less than that of the unoxidized activated carbon for 95% removal of Safranin-O from its solution.

Solvation Enhances the Distinction between Carboxylated Armchair and Zigzag Single-Wall Carbon Nanotubes (SWNT-COOH)

The effect of various solvents on the structures and properties of carboxylated SWNTs has been explored using the same level different basis set approach (SLDB), where B3LYP functional of density functional theory (DFT) was applied. Armchair (4,4) and zigzag (8,0) and (9,0) tubes were considered as the testbed. In order to simulate varying concentration of −COOH groups, one to five acids groups were placed at one end of these tubes. These samples were placed in different solvents (namely, CS2, THF, and water) with varying polarity and results were compared with gas-phase properties. Similar to the gas-phase, zigzag tubes also exhibit both regular (r-COOH, ν(C═O) above 1700 cm–1) and low-frequency (lf-COOH, ν(C═O) below 1700 cm–1) acid groups. Characteristics of the r-COOH group are not affected much in solvents, but lf-COOH of the zigzag tube is the one that makes these tubes distinguishable from its armchair cousin. Stability and charge distribution of SWNT-COOH strongly depend on the number of acid groups in different solvents which may help controlling further functionalization. Vibrational analyses reveal certain features in the 1400–1600 cm–1 range that are characteristic of lf-COOH and in different solvents, which may help in the assignment of experimental spectra of oxidized SWNT in solvents.

Hyperbranched polyester polyacids and their binary systems with surfactants for doxorubicin encapsulation

Doxorubicin fixation by hyperbranched polyester polyol Boltorn H acid derivatives and their binary systems in the presence of a surfactant (Brij-35, Triton X-100) was investigated. Doxorubicin fixation degree nonlinearly depends on the number of acid groups in the polyester polyacid. Polyacid/surfactant binary systems fix up to 60% of doxorubicin from the solution.

A Novel Microbial Biofilm for Bioremoval of Nickel from Aqueous Media

ABSTRACTThis study evaluated the efficacy of a microbial biofilm in removing Ni ions in aqueous media. The biofilm was developed incorporating a garden soil fungus with a bacterium isolated from Ni-rich serpentinite soil. The biofilm was characterized using microscopy, scanning electron microscopy, Fourier transform infrared (FTIR) investigations, and Boehm and potentiometric titrations. Ni removal was determined using batch experiments as a function of pH, Ni concentration, and time. The adsorption isotherm assay was conducted with varying Ni concentrations from 25 to 500 mg/L for 4 days. Isotherm and kinetic modeling were applied to the experimental data to understand the mechanisms of Ni removal. The zero point charge at pH 4.5 indicated the pH values greater than 4.5 is favorable for Ni adsorption. Acidic nature of the biofilm was reflected from Boehm titration data showing higher number of acidic groups than basic groups. With the increase in initial Ni concentration, the uptake increased from 3.43 to 38.16 mg/g. Hill, the best-fitted isotherm model, indicated a maximum adsorption capacity of 165.37 mg/g. After 4 days, the adsorption rate reached an equilibrium with a maximum sorption of ∼30 mg/g for an initial concentration of 100 mg/L. Kinetic model fitting with Power function further demonstrated the chemisorptive interaction of Ni with the biofilm surface. A clear involvement of functional groups of the biofilm in Ni bonding was observed from the attenuated total reflection (ATR)-FTIR spectrum. The microbial biofilm showed an efficient but slow removal of Ni from aqueous media.

MECHANICAL OXIDATION OF MULTI-WALLED CARBON NANOTUBES AS A REPLACEMENT OF ACID OXIDATION METHOD

In the present study, a candid approach using mechanical oxidation, for modification of multi-walled carbon nanotubes (CNTs) has been utilized, and its advantages over conventional acid oxidation methods have been established. Higher concentration of acidic groups was found in case of mechanically oxidized CNTs (i.e., McCNT) as compared to acid oxidized CNT (i.e., ACNT). Raman spectrum exhibited greater degree of transformation of sp2 carbon into sp3 carbon. X-ray diffraction (XRD) analysis revealed maintained crystalline organization in McCNT. The major finding of the study was that, the mechanical oxidation method can be used easily to replace the conventional acid treatment method. This is because in the mechanical oxidation crystalline organization of CNTs can be maintained, relatively higher number of acid groups can be incorporated, no loss to the mass of CNTs is allowed etc.

Preparation of Enteromorpha prolifera-based cetyl trimethyl ammonium bromide-doped activated carbon and its application for nickel(II) removal

Activated carbon was prepared from Enteromorpha prolifera (EP) by H3PO4 activation in the presence of doped cetyl trimethyl ammonium bromide (CTAB), producing EPAC–CTAB. The thermal decomposition process of the activated carbon substrate was identified by thermo-gravimetric analysis. Scanning electron microscope (SEM), N2 adsorption/desorption, Fourier transform infrared spectroscopy (FTIR), Boehm titration, and X-ray Photoelectron Spectroscopy (XPS) were employed to characterize the physicochemical properties of native EPAC and EPAC–CTAB. EPAC–CTAB exhibited smaller surface area (689.0m2/g) and lower total pore volume (0.361cm3/g) than those of EPAC (1045.8m2/g and 1.048cm3/g), while the number of acidic groups, oxygen and nitrogen groups on the surface of EPAC–CTAB increased through CTAB doping. The batch kinetics and isotherm adsorption studies of nickel(II) onto the adsorbents were examined and agreed well with the pseudo-second-order model and the Langmuir model. The maximum adsorption capacity determined from the Langmuir model was 16.9mg/g for EPAC and 49.8mg/g for EPAC–CTAB. Under acidic condition, the adsorption of nickel(II) onto EPAC and EPAC–CTAB was hindered due to ion competition and electrostatic repulsion. The results indicated that using CTAB as a dopant for EPAC modification could markedly enhance the nickel(II) removal.

Determination of surface functional groups on mechanochemically activated carbon cloth by Boehm method

In order to improve sorption properties of activated carbon cloth that can be used for wastewater purification, mechanochemical activation was performed in both inert and air atmosphere. Boehm method was used to follow the changes in the number and types of surface groups induced by mechanical milling. The number of the base groups of 0,2493 mmol/g is significantly smaller than the total amount of acidic functional groups, 2,5093 mmol/g. Among the acidic groups present on the surface, the most represented are phenolic groups (2.3846 mmol/g ), ie . > 95 % , the carboxylic groups are present far less (0.1173 mmol /g), ie. 4.5 %, while the presence of the lactone group on the surface of ACC is negligible (0.0074 mmol/g) ie. under 0.3 %. Mechanochemical activation lead to an increase in the number of acidic and basic groups on the surface of the ACC. The milling in inert atmosphere has dominant effect with respect to the changes in the total number of basic functional groups (compared to milling in an air atmosphere): the number of basic groups of the ACC was 0.8153 mmol/g milled under argon, 0.7933 mmol/g in the air; the number of acidic groups is 2.9807 mmol/g for a sample milled under argon and 3.5313 mmol/g for one milled in the air.

Gas Phase Acidity Measurement of Local Acidic Groups in Multifunctional Species: Controlling the Binding Sites in Hydroxycinnamic Acids

The applicability of the extended kinetic method (EKM) to determine the gas phase acidities (GA) of different deprotonable groups within the same molecule was tested by measuring the acidities of cinnamic, coumaric, and caffeic acids. These molecules differ not only in the number of acidic groups but in their nature, intramolecular distances, and calculated GAs. In order to determine independently the GA of groups within the same molecule using the EKM, it is necessary to selectively prepare pure forms of the hydrogen-bound heterodimer. In this work, the selectivity was achieved by the use of solvents of different vapor pressure (water and acetonitrile), as well as by variation of the drying temperature in the ESI source, which affected the production of heterodimers with different solvation energies and gas-phase dissociation energies. A particularly surprising finding is that the calculated solvation enthalpies of water and the aprotic acetonitrile are essentially identical, and that the different gas-phase products generated are apparently the result of their different vapor pressures, which affects the drying mechanism. This approach for the selective preparation of heterodimers, which is based on the energetics, appears to be quite general and should prove useful for other studies that require the selective production of heterodimers in ESI sources. The experimental results were supported by density functional theory (DFT) calculations of both gas-phase and solvated species. The experimental thermochemical parameters (deprotonation ΔG, ΔH, and ΔS) are in good agreement with the calculated values for the monofunctional cinnamic acid, as well as the multifunctional coumaric and caffeic acids. The measured GA for cinnamic acid is 334.5 ± 2.0 kcal/mol. The measured acidities for the COOH and OH groups of coumaric and caffeic acids are 332.7 ± 2.0, 318.7 ± 2.1, 332.2 ± 2.0, and 317.3 ± 2.2 kcal/mol, respectively.

Interaction of pyrene fluoroprobe with natural and synthetic humic substances: Examining the local molecular organization from photophysical and interfacial processes

The direct and indirect interaction mechanisms of pyrene with: (i) various molecular weight fractions of a synthetic humic-like substance (SyHA) and (ii) extracts of natural humic acids (NHA) from Moselle River suspended matter were investigated using quenching fluorescence and surface tension measurements. Humic materials were characterized in a previous study. The Stern–Volmer associative constants were determined from the quenching technique. Surface tension measurements revealed an increase in surface activity as a function of concentration for each humic fraction independently of the pyrene presence in solution, even during the formation of humic micelles. The results obtained suggest the possibility of specific intermolecular interactions occurring during pyrene entrapment within humic acids. In addition, we show that molecular weight, aliphatic chains (especially those containing nitrogen groups) and number of acidic groups are determinant characteristics for pollutant entrapment capacity at concentrations below the critical micellar concentration (CMC) of humic substances.

Síntesis y caracterización de espumas flexibles de poliuretano obtenidas a partir de aceite de castor maleinizado

En este trabajo se realiza la síntesis de espumas flexibles de poliuretano empleando un diseño experimental Taguchi, utilizando aceite de castor con y sin maleinización, se estudia la cinética de la reacción de esterificación del aceite por cuantificación de los grupos ácido (ASTM D4662 - 03) y se evalúan las propiedades mecánicas de las espumas (densidad, resistencia tensil, % elongación, resiliencia y dureza. Norma NTC 2019 Icontec) obtenidas en función de las variables de síntesis (cantidad y tipo de catalizador, relación molar aceite castor (CO) - aceite maleinizado (MACO), cantidad de agua y surfactante empleado). Se realizan análisis de FTIR y SEM para las espumas. Los resultados mostraron una cinética de primer orden con respecto al anhídrido. El aceite maleinizado (MACO) incrementa la resistencia mecánica de las espumas, debido al mayor entrecruzamiento por la incorporación de grupos ácido.

Temperature dependence of the point of zero charge of oxidized and non-oxidized activated carbons

Three activated carbons in the form of grains, fibers and pellets were oxidized with ammonium peroxidisulfate. The oxidized and non-oxidized activated carbons were characterized by: N 2 adsorption at 77 K, temperature programmed desorption up to 1273 K, and potentiometric titrations in the temperature range between 288 and 318 K. The point of zero charge (PZC) of the oxidized activated carbons decreased with increasing temperature and this decrease was in the same direction as the change in 1/2p K w, the neutral point of water. The non-oxidized activated carbons behaved in a similar manner, but the PZC decreased by more than the corresponding change in 1/2p K w. Variation of surface charge of the three oxidized activated carbons was fitted to a single second-order function with respect to pH and temperature. However, a single equation could not be found for the three non-oxidized activated carbons. Standard thermodynamic functions at the PZC were obtained from potentiometric curves. Acidity constant distributions were obtained and showed an increase in the number of acidic groups when the temperature increased. The number of carboxylic and phenolic groups obtained from these distributions was compared with that obtained from the deconvolution of temperature programmed desorption spectra.

The zirconium sulfate microcrystal structure in relation to their activity in the esterification

Zirconium sulfate (ZS) varying in crystalline phase from hydrate to anhydrous was prepared at different treatment temperature. The relationship between microcrystal structure at different treatment temperature and activity in esterification was evaluated. The number of acid groups was found to increase with increased of pretreatment temperature, except for the samples treated above 330 °C. For that sample, it is observed that hydration of crystalline water to anhydrous phase is significant at temperature of 330–420 °C, reducing the surface acidity. The reaction was poisoned by the exchange of surface protons on ZS with Cs +. Thus, the major effective active sites must be the protons acidity. It was demonstrated that the microcrystal structure and catalytic activity of ZS was affected by thermal treatment due to changes in crystalline water.

Effects of functional groups on the fragmentation of dyes in electrospray and atmospheric pressure chemical ionization mass spectra

Electrospray ionization (ESI) is most suitable for dyes with an ionic or very polar character, while atmospheric pressure chemical ionization (APCI) suits better those dyes and pigments with low to medium polarity. The negative-ion mode of ESI is used for anionic dyes such as (poly)sulfonated and/or (poly)sulfated variants, where the series of deprotonated molecules enables an easy determination of molecular weights and the number of acid groups. The positive-ion APCI or ESI mass spectra of non-ionic and cationic dyes and pigments provide typical molecular adducts [M + H] +, [M + Na] + and [M + K] + used for the molecular assignment. The first-order mass spectra often suffer from the lack of fragment ions, which can be solved by using multistage tandem mass spectra (MS n ) measured with an ion trap analyzer. The effects of various functional groups on the fragmentation behavior are described herein. The detailed understanding of fragmentation paths enables the correlation among particular functional groups and the fragmentation patterns. The presented approach is applicable for the structural analysis of complex mixtures using HPLC/MS/MS techniques with volatile ion-pairing agents.

A simple approach to the prediction of electrophoretic mobilities of diverse organic acids

Based on the principle of separation by capillary electrophoresis, three simple molecular structural descriptors, the number of acid groups (NG), number of atoms (NA) and molecular weight (MW) were employed to model the molecular structure–electrophoretic mobility relationship with the general form of μ 0 = aNG/( bNA k + cMW k ), where the value of k ranges from 1/3 to 2/3 depending on the magnitude of molecular weight. The absolute electrophoretic mobilities ( μ 0) of three diverse data sets including carboxylic acids, sulfonic acids and peptides were investigated. Each data set was randomly divided into a training set for model generation and a test set for prediction test. The absolute average relative deviations (AARD and AARD P) of the training set and the test set are 7.21% and 7.53% for data set 1, 1.99% and 1.96% for data set 2, 3.25% and 3.95% for data set 3, respectively. Compared to the quantitative structure–mobility relationship (QSMR) models reported in the literature, the approach proposed in this study is much simpler in terms of the calculation of structural descriptors and the interpretation of the physicochemical meaning of the models.

The influence of oxidation on the texture and the number of oxygen-containing surface groups of carbon nanofibers

The effect of liquid-phase oxidation on the texture and surface properties of carbon nanofibers has been studied using XRD, TEM, SEM, N 2-physisorption, TGA-MS, XPS and acid–base titrations. Oxidation was performed by refluxing the nanofibers in HNO 3 and mixtures of HNO 3/H 2SO 4 for different times. The graphite-like structure of the treated fibers remained intact, however, the specific surface area and the pore volume increased with the severity of oxidation treatment. For the first time it is shown that the most predominant effect that gives rise to these textural modifications is the opening of the inner tubes of the fibers. Moreover, it is demonstrated that both the total oxygen content (O/C=0.02–0.07 at/at) as well as the number of acidic groups (1–3 nm −2) are a function of the type of oxidizing agent used and the treatment time. The total oxygen content of the oxidized samples turns out to be substantially higher than can be accommodated in the form of oxygen-containing groups at the exterior surface.

Adhesive and anticorrosive properties of poly(vinylidene fluoride) powders blended with phosphonated copolymers on galvanized steel plates

AbstractFluoropolymers with adhesive and anticorrosive properties were investigated by blending statistical phosphonated copolymers with poly(vinylidene fluoride) (PVDF). In a first part, methacrylic monomers bearing dialkyl phosphonate and phosphonic acid groups were synthesized. Dimethyl(2‐methacryloyloxyethyl)phosphonate was obtained by carrying out a one‐step methacrylation of a commercial phosphonated alcohol. Then, a chemical conversion of the dimethyl phosphonate group to phosphonic acid groups was accomplished by two routes, including on the one hand a trimethylhalosilane and on the other hand an inorganic halide as dealkylation reagents. The resulting monomers were analyzed by nuclear magnetic resonance (NMR) spectroscopy and results were discussed. In a second part, the phosphonated monomers were copolymerized with methyl methacrylate in the presence of 2,2'‐azobis(isobutyronitrile) (AIBN) to give statistical copolymers in high yields. In a third and last part, copolymers were introduced into PVDF as adhesion promoters and anticorrosion inhibitors. Good dry and wet adhesion properties onto galvanized steel plates were obtained with blends containing mainly phosphonic acid groups. Results of corrosion tests show that the phosphonic acid groups maintain some level of adhesion, thereby preventing the spread of corrosion. However, the number of acid groups and their neighbors influence the adhesive and anticorrosive properties of the PVDF coatings. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2277–2287, 2002

Morphology of Neutralized Low Molecular Weight Maleated Ethylene−Propylene Copolymers (MAn-g-EPM) As Investigated by Small-Angle X-ray Scattering

The thermoreversible nature of the ionic associations in aggregates makes ionomers with a low glass transition temperature interesting candidates for thermoplastic elastomers. In this paper, a low-Tg ionomer based on low molecular weight ethylene−propylene copolymers modified by maleic anhydride (MAn-g-EPM) is introduced, and the morphology of a series of ionomers, neutralized with Cs+, Na+, K+, Li+, Zn2+, Ba2+, and Mg2+, was investigated with small-angle X-ray scattering (SAXS). To determine the size and composition of the ionic aggregates, the observed SAXS peak was interpreted with the help of the Yarusso−Cooper model, which describes the ionomer morphology by spherical aggregates of the ionic species with a high electron density surrounded by a layer with a restricted mobility. The results from the ionomer precursors suggest that there is a critical concentration above which aggregation of the polar groups in the apolar matrix occurs. Upon increasing degree of neutralization, the average dimension of the aggregate remains almost constant, while the restricted mobility layer increases. The size of the aggregates is much larger in comparison to other ionomer systems, and as a consequence, the number of acid groups within an aggregate is much larger. For low degrees of neutralization, it was shown that the aggregates contain a large fraction of EPM fragments of at least 60 vol %. For the ionomers neutralized with divalent cations, it was observed that the morphology changes drastically beyond degrees of neutralization of 50%; the number of the aggregates decreases, and the size increases. This was explained with the help of the coordination mechanism.

PH of activated carbon surface as an indication of its suitability for H 2S removal from moist air streams

Samples of activated carbons of different origins were tested as removers of hydrogen sulfide at room temperature. The breakthrough capacity was evaluated using a lab designed test. The surface properties of the carbons were studied using Boehm titration, nitrogen sorption and thermal analysis. The results obtained indicate that the choice of unimpregnated carbon for hydrogen sulfide removal should be based on the parameters describing surface acidity such as pH, number of acidic groups, or weight loss during thermal treatment associated with the presence of acidic functional groups. There are certain threshold ranges of these quantities which, when exceeded, have a dramatic effect on the H 2S breakthrough capacity.

STUDY OF TWO-PHASE BEHAVIOR OF NITRILE POLYMERS BY IN SITU HOT-STAGE IR SPECTROSCOPY

The temperature behavior of polyacrylonitrile with a small number of acidic groups incorporated in its chains was studied by in situ hot-stage IR spectroscopy. It has been shown that acidic groups trigger the hydrolysis of nitrile groups at temperatures below the first glass point of polyacrylonitrile. At higher temperatures, the acidic groups separate from the hydrophobic polymer and aggregate to form clusters. This leads to the appearance of a second phase characterized by its own higher temperature glass transition at 140°C. It is also shown that acidic groups do not trigger the cyclization reaction, and that their availability reduces of the reaction rate.