Concentration Of Carboxylic Acid Groups Research Articles

Fourier Transform Infrared Spectroscopic Analysis of Fruit Peels before and after the Adsorption of Heavy Metal Ions from Aqueous Solution

For orange peel (OP), lemon peel (LP), and banana peel (BP) as adsorbents for removal of heavy metal ions such as Cu2+, Ni2+, Cd2+, Pb2+, and Zn2+ from aqueous solution, a simple FT-IR technique was used and discussed to study the variation in functional groups upon modification. Metal−carbon bond formation was witnessed by FT-IR during metal ion adsorption. All of these adsorbents were characterized by FT-IR, BET, and SEM. The presence of carboxylic and hydroxyl groups was confirmed by FT-IR. The FT-IR spectrum of lemon peel cellulose (LPC) showed well resolved peaks for carboxylic acid and hydroxyl groups compared to LP indicating the appreciable contents of carboxylic acid and hydroxyl groups in LPC. The widely used Langmuir adsorption isotherms were used to describe the adsorption equilibrium process. The adsorption capacity of the metal ions such as Cu2+ and Ni2+ was found to be more than those of other metal ions. Upon comparison of the adsorbents, surface modified LPC (LPCACS) was found to show enh...

Characterization and Complexing Capacity of Humic Acid Extracted from Yakouren Soil with Heavy Metals by Conductimetry and Quenching of Fluorescence

New humic acid isolated from forest soil of Yakouren (YHA), Algeria, and purified commercial humic acid (PCHA) were analyzed and characterized. Elemental analyses, electronic microscopy, UV-Vis absorbance E465/E665 ratio and molecular spectroscopy investigation using CP-MAS 13C-NMR of YHA indicated the presence of a high content of aliphatic and carboxylic acid groups. The higher O/C, H/C and N/C ratios of YHA can be assigned to the low aromatization degree. A study of interaction between Ni(II), Zn(II), Cd(II) and humic acids (HAs) at different metal-ligand ratios has been made by conductimetric and fluorescence techniques. The results obtained by the conductimetry method are interpreted using an excess function (Δk), which related the conductivity of the mixture and of the separated components. A positive value of this function is obtained. It indicates the complexation of HAs with metallic ions. The association degree of the heavy metals (M) with both HAs was in the following order: Ni > Zn > Cd and the binding capacity of PCHA is smaller than that of YHA. A fluorescence titration method and a single site model were used for determining metal ion complexing capacities (CCM) and stability constants (log KM) of YHA and PCHA complexes. Titration of HAs with metal ions at pH 7 and ionic strength 0.1 mol/L resulted in a marked decrease of fluorescence intensities of untreated HAs. The quenching constants (KSV) between HAs and M are obtained in terms of Stern–Volmer analysis. KSV show that the YHA binds the higher amount metals than PCHA. CCM of YHA calculated by MATLAB program were higher than those of PCHA and other natural HAs found in the literature at pH 7. Based on these results, YHA may play the role of a biocaptor of polluting metals.

Surface properties of ionomers based on styrene-b-acrylic acid copolymers obtained by copolymerization in emulsion

Surface properties of styrene-b-acrylic acid copolymers obtained in emulsion and suitable ionomers before and after UV-irradiation were studied by measurements of contact angles and FTIR-ATR spectroscopy. The research focused on the influence of different content of carboxylic acid groups in copolymers, of various types and contents of alkali metal salts in ionomers and of cesium acrylate or methacrylate in ionomers on hydrophilicity of the surfaces of these samples and the course of photodegradation in them. Hydrophilicity of initial copolymer surfaces was higher than this of polystyrene as a result of presence of carboxylic acid groups, which also made the surfaces of these copolymers more sensitive to UV-irradiation. Hydrophilicity of the surfaces of ionomers containing cesium acrylates depended on the content of cesium salt in the samples. The course of ionomer photooxidation was also dependent on the content of this salt. The surface of ionomer containing cesium methacrylate was more polar than this of ionomer containing cesium acrylate. Styrene-based ionomers containing 3.7 mol% of various alkali metal acrylates had less polar surfaces than initial copolymer and they were also more resistant to UV-irradiation in comparison to the initial copolymer. Copolymers obtained in emulsion and suitable ionomers had more polar surfaces and they were more sensitive to UV-light compared to copolymers obtained in bulk and their ionomers.

Carbonyl Groups in Sulfonated Styrene−Divinylbenzene Macroporous Resins

The generation of carbonyl groups during sulfonation of porous styrene−divinylbenzene copolymers is reported. The carbonyl groups and sulfonic acid groups were verified by infrared spectroscopy and quantified by acid−base titrations. A gradual change in sulfonation reaction conditions from 70 °C/30 min to 98 °C/60 min resulted in a gradual increase in sulfonic acid group concentration from ∼1.85 to ∼3.13 mol/kg and in the carboxylic acid group concentration from ∼0 to ∼0.34 mol/kg. Data on the swelling coefficients in water indicate a slight increase in cross-linking during sulfonation. Conversion of ethyl or residual vinyl groups to carboxylic acid groups, followed by conversion of some of the acid groups to cross-links through an acid-catalyzed acylation reaction, is proposed. The proposed reactions also explain the pH-dependent color change of the resins. Sulfonation of copolymers with varied cross-linkages further supports our assertion that, as the concentrations of ethyl and residual vinyl groups increase, the concentration of —COOH groups also increases and the resin color becomes darker.

Large Deformable Multiwalled Carbon Nanotube Core–Shell Structure on Polystyrene Beads

Multiwalled carbon nanotube (MWCNT)-coated polystyrene (PS) beads have been prepared by dispersion polymerization followed by a layer-by-layer self-assembly method. The concentration of carboxylic acid groups on the MWCNTs increased from 1.81 × 10(21) to 3.43 × 10(22) COO(-) per g as the treatment time was increased from 3 to 9 h. The sulfonated polystyrene (SPS) beads changed from being negatively charged to positively charged when the cationic polyelectrolyte was self-assembled on their surface. The surface morphology of the adsorbed polyelectrolyte was smooth without any aggregation and the thickness of the polyelectrolyte coating on the SPS beads was ≈0.6 µm. The electrical conductivity and resistance of the MWCNT-coated SPS beads were measured to be 4.0 × 10(-2) S · cm(-1) and 12.8 Ω at a volume fraction of 91%, respectively.

Promoting the adhesion of high‐performance polymer fibers using functional plasma polymer coatings

AbstractPlasma‐copolymerized functional coatings of acrylic acid and 1,7‐octadiene were deposited onto high strength, high modulus, poly‐p‐phenylene benzobisoxazole (PBO) fibers. X‐ray photoelectron spectroscopy (XPS) with trifluoroethanol derivatization confirmed that the PBO fibers were covered completely with the plasma copolymer and that the coating contained a quantitative concentration of carboxylic acid groups. Microdebond single filament adhesion and interlaminar shear strength (ILSS) tests were used to evaluate the interfacial strength of epoxy resin composites containing these functionalized PBO fibers. Both the interfacial shear strength (IFSS) obtained from single filament tests, and the ILSS of high volume fraction composites were a function of the surface functionality of the fibers so that there was a good correlation between ILSS and IFSS data. The tensile strengths of single fibers with or without coating were comparable, demonstrating that the fiber surface was not damaged in the plasma‐coating procedure. Indeed, the statistical analysis showed that Weibull modulus was increased. Therefore, plasma‐polymerized coatings can be used to control the interfacial bond between PBO fibers and matrix resins and act as a protective size for preserving the mechanical properties of the fibers. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Characterization of the surface chemistry of carbon materials by potentiometric titrations and temperature-programmed desorption

Two methods currently used to characterize oxygen-containing functional groups on the surface of carbon materials are compared, namely potentiometric titration (PT) and temperature-programmed desorption (TPD). Two materials were used, activated carbon and multi-walled carbon nanotubes, which were subsequently modified by oxidative treatments in order to produce samples with different amounts of surface groups. The concentrations of carboxylic acid groups determined by both techniques are in good agreement, but the quantitative result obtained by TPD is closer to the analytical concentration of the species obtained by elemental analysis. Discrepancies between the quantitative results are more pronounced at higher p K a values (weak acids), where the concentrations determined by PT are lower than those obtained by TPD. This directly reflects the effects of neglecting the electrostatic interaction parameter. The TPD method was particularly suited for the characterization of samples modified with ethylenediamine, which is anchored to specific oxygenated groups. PT results are useful to describe the material behaviour in aqueous solutions, where the activity of the surface groups depends not only on their concentrations, but also on their environment.

Chemical Response of Hardwood Oligosaccharides as a Statistical Function of Isolation Protocol

Hardwoods contain a substantial amount of hemicellulose-type oligosaccharides, the chemical structures of which are typically categorized in the xylan saccharide class. The efficient and selective isolation of these hemicelluloses is regarded as one of the most critical obstacles to overcome for their eventual biomaterial and bioenergy utilization. Therefore, the objective of the current work was to perform a fundamental exploration of the function of extraction pH, temperature, and time on the final chemical properties of the extracted hemicelluloses. The extraction chemistries employed varied pH and showed that acidic conditions provided a higher extractive yield versus alkaline conditions. An alkaline environment gave higher yields than an acidic environment and also resulted in much higher lignin removal from wood, especially at high temperature. In general, control of the pH chemistry leads to a change in the carboxylic acid groups present in the extracts. When the extraction pH changed from acidic to alkaline, the total carboxylic acid group content in the hemicelluloses removed significantly increased due to more acetic acid group hydrolysis and increased lignin degradation.

Wet air oxidation of nitro-aromatic compounds: Reactivity on single- and multi-component systems and surface chemistry studies with a carbon xerogel

The treatment of dinitrophenol (DNP) and trinitrophenol (TNP), typically found in the effluents from the process of mononitrobenzene (MNB) synthesis, was investigated by wet air oxidation in both non-catalytic (WAO) and catalytic (CWAO) conditions, operating as two phase and three phase reactors, respectively. In the first case, the effect of treating DNP and TNP separately (single-component system) or using mixtures of these compounds (multi-component systems) was assessed by analysing the decrease of the individual pollutant concentration, the total organic carbon (TOC) evolution and the reaction by-products. Of the various systems screened, it was possible to conclude that the presence of DNP enhances the overall oxidation in multi-component systems. TNP is not oxidized individually but totally degraded in the presence of DNP. The observed reactivities were correlated with the number and type of functional groups attached to the aromatic ring and the HO induced denitration may be considered as the main reaction mechanism.Concerning the CWAO experiments, two catalysts were synthesized in this study, a carbon xerogel (CX) and a nanosized cerium oxide (CeO2), using sol–gel and solvothermal methodologies, respectively, and tested for the degradation of the multi-component system. The CX catalyst operating in slurry conditions was found to be highly active and led to practically complete removal of DNP and TNP, total bleaching of color and 83% mineralization after 120min of reaction. The best catalyst was thoroughly characterized. An increase in the concentration of carboxylic acid groups at the catalyst surface was observed by TPD analysis of the catalyst after the reaction, followed by a decrease in the concentration of phenolic and quinone functional groups. The catalyst surface modification was a consequence of the large amounts of nitrates produced from the model compounds. Nitrites were not detected and, therefore, CWAO seems to be a potential treatment which can be coupled with a biological process to remove the nitrates formed during the reaction.

Effect of diacid stabilizers on kinetics of hydrolytic polymerization of ε-caprolactam in industrial reactors

The rate constants in hydrolytic polymerization of ε-caprolactam are dependent on the concentration of carboxylic acid groups in the reaction medium. Therefore, the use of diacid stabilizers for regulating molecular weight are likely to have favorable effect on the kinetics of polymerization compared to monoacid stabilizers, which are traditionally used in such polymerizations. To understand the kinetics of polymerization in the presence of diacid stabilizer compared to monoacid stabilizer, mathematical kinetic models were developed using the end group approach. These models were used to quantify the effect of both stabilizers on nylon-6 synthesis in a closed isothermal batch reactor at different temperatures in the range of 245–265°C. The kinetic model for the diacid-stabilized system was then extended to an industrial VK tube reactor using the process model developed earlier for the monoacid stabilized system. Both the mathematical modeling and experimental results showed that the presence of diacid stabilizer could significantly enhance the overall kinetics of the reaction compared to the monoacid stabilized system and in turn, resulted in reduction of the polymerization time by about 20–25%. The study suggests that diacid stabilizers may be used preferably over monoacid stabilizers in synthesis of nylon-6 to reduce the cost of polymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effect of wet chemical treatments on the distribution of surface oxides on carbonaceous materials

The properties of carbonaceous materials are often modified using wet chemical treatments; however, the detailed changes in the oxide distribution that accompany different chemical treatments have not been clearly elucidated. To illustrate how this information can be obtained, we have employed chemical derivatization in conjunction with X-ray photoelectron spectroscopy (XPS) to quantify changes in the concentration of hydroxyl, carbonyl, and carboxylic acid groups on the surface of a modified wood char following several different wet chemical treatments (H 2O 2, HNO 3, ammonium persulfate, O 3, and NaBH 4). Results from the present investigation highlight the fact that changes in surface oxide distributions are sensitive to the chemical treatment. For example, ammonium persulfate selectively increases the carboxylic acid group concentration. In contrast, O 3 increases the concentrations of hydroxyl, carbonyl, and carboxylic acid groups with roughly equal propensity. These oxide distributions were further modified by reduction with NaBH 4, which generally converts carbonyl and carboxylic acid groups to hydroxyl groups. A comparison of results obtained from XPS and chemical analysis reveal that the oxidative effects of wet chemical treatments are restricted to the char’s surface.

Influence of Kraft Pulping on Carboxylate Content of Softwood Kraft Pulps

This study characterizes changes in fiber charge, which is the carboxylate content of fibers, for two sets of kraft pulps: (1) conventional laboratory cooked loblolly pine kraft pulps and (2) conventional pulping (CK) versus low solids pulping (LS) pulps. Laboratory kraft pulping of loblolly pine was carried out to study the influence of pulping conditions, including effective alkali (EA), sulfidity, and pulping temperature, on fiber charge. The results indicated that, when pulping to the same H-factor, low EA charge and low pulping temperature are favorable for increasing bulk carboxylic acid group content of fibers. Sulfidity did not have an obvious effect on bulk or surface carboxylic acid group content of fibers. Surface charge was not significantly affected by pulping temperature. Bulk fiber charge has a linear relationship with water retention value. Roughnesses of holocellulose fiber handsheets were determined by atomic force microscopy (AFM). No apparent relationship between roughness and surface...

Hydrogels with Acid Groups for Removal of Copper(II) and Lead(II) Ions

Acrylamide-maleic acid (AAM-MA) hydrogels having high acid group content prepared with different maleic acid ratios were used for the removal of Cu(II) and Pb(II) ions from aqueous solutions in competitive and noncompetitive conditions. The effects of pH, time, and initial metal ion concentration on the metal ion adsorption capacity were investigated. The adsorption isotherm models were applied on experimental data and it is shown that the Freundlich equation was the best model for Cu(II) ion while the Langmuir isotherm model was the best one for Pb(II) ion. The stability constants of acrylamide-maleic acid hydrogel-Cu(II) and Pb(II) complexes were also determined by van den Berg/Ruzic transformation, and K values obtained were 1.60 × 103 and 1.81 × 103 for Cu(II) and Pb(II) ions, respectively. The experiments under competitive conditions showed that the hydrogels prefered Pb(II) ion and this preference increased with increasing of carboxylic acid group content (AGC) of polymers. It is stated that these hydrogels can be regenerated efficiently (>95%) and used repeatedly.

Aminofunctionalized acrylamide–maleic acid hydrogels: Adsorption of indigo carmine

Aminofunctionalized acrylamide–maleic acid hydrogels having both amine and acid groups were prepared by transamidation reaction of acrylamide–maleic acid (AAM–MA) hydrogels using ethylenediamine in non-aqueous media. Modified polymers were characterized by determination of amine value (AV), carboxylic acid group content (AGC) and FTIR spectra. The modified hydrogels obtained have the amine value of 2.81 mmol/g. Their swelling properties were changed depending upon the pH value of external medium. The modified hydrogels were used as a new sorbent for removal of indigo carmine from aqueous solution. The effects of pH, time, NaCl concentration and initial dye concentration on the adsorption capacity were investigated. Almost 70–80% of capacity was saturated within approximately 30 min and quite high adsorption capacity was observed. The adsorption capacity increased at acidic pH and also in presence of NaCl in dye solution. The adsorption isotherm models were applied to the experimental data and it was seen that the Langmuir isotherm model was the best fit for these modified AAM–MA hydrogels–indigo carmine system.

Functionalized multiwall carbon nanotube/gold nanoparticle composites.

Multiwall carbon nanotubes (MWCNTs) were chemically oxidized in a mixture of sulfuric acid and nitric acid (3:1) while being ultrasonicated. The effect of oxidative ultrasonication at room temperature on development of functional groups on the carbon nanotubes was investigated. The dispersability and the carboxylic acid group concentration of functionalized MWCNTs (fMWNTs) varied with reaction time. The concentration of carboxylic acid groups on fMWNTs increased from 4 x 10(-4) mol/g of fMWNTs to 1.1 x 10(-3) mol/g by doubling the treatment period from 4 to 8 h. The colloidal stability of aqueous fMWCNTs dispersions was enhanced through elongated oxidation. fMWCNTs that were reacted longer than 4 h did not precipitate in aqueous media for at least 24 h. The layer-by-layer self-assembly of polyelectrolytes on fMWCNTs was characterized by zeta potential measurements. The zeta potential of fMWCNTs changed from negative charge to positive charge when cationic polyelectrolytes were self-assembled on their surface. With addition of anionic polyelectrolytes, cationic polyelectrolyte coated fMWCNTs showed the expected charge reversal as expected for multilayer self-assembly. Complex formation of positively charged gold nanoparticles and negatively charged fMWCNTs was achieved with and without polyelectrolyte coatings by electrostatic interaction. The complex formation was characterized by high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The here found complex formation of positively charged colloidal gold and defect sites on fMWNTs indicates the location of functional groups on carbon nanotubes. It is suggested that positively charged colloids such as gold nanoparticles could be used for detection of defect sites on carbon nanotubes.

Relationship between dissolution of fiber materials and development of pulp strength in alkaline peroxide bleaching of mechanical pulp

Abstract This study elucidates the relationship between the dissolution of pulp components and the development of fiber bonding properties in alkaline peroxide bleaching of aspen mechanical pulp. In general, bleaching reactions cause the removal of pulp substances from the fibers, which in turn improves pulp strength properties. Nonetheless, alkaline hydrolysis is particularly important to the development of strength because this reaction mechanism plays a key role in imparting additional carboxylic acid groups onto the fibers. The strong correlation between fiber carboxylic acid group concentration and the amount of anionic dissolved substances makes it possible for us to predict the strength properties of bleached pulps by estimating the anionicity of bleaching filtrates using analytical methods such as cationic demand. The paper also provides insights into the importance of the alkalinity in peroxide bleaching to the dissolution of pulp materials and the strength development.

The gas separation properties of carbon molecular sieve membranes derived from polyimides having carboxylic acid groups

Carbon molecular sieve (CMS) membranes were prepared by pyrolysis of polyimides containing carboxylic acid groups, in order to investigate their permeation properties for He, CO 2, O 2 and N 2. The polyimides were synthesized with a varying number of carboxylic acid groups in the diamine. Wide-angle X-ray diffraction and nitrogen gas sorption isotherms were employed to characterize the carbon structures. From pure gas permeation experiments, it was found that the removal of carboxylic acid pendent side groups during the pyrolysis resulted in a large pore volume in the carbon matrix, which significantly affected the gas separation performance of the final CMS membranes. The gas permeabilities of the CMS membranes pyrolyzed at 700 °C improved with increasing carboxylic acid group content. The CMS membranes derived from polyimide containing 50 mol% diamines showed maximum gas permeability for O 2 of 707 Barrers (1×10 −10 cm 3 (STP) cm/cm 2 s cmHg) and an O 2/N 2 selectivity of 9 at 25 °C.

Biobleaching chemistry of laccase-mediator systems on high-lignin-content kraft pulps

A high-lignin-content softwood kraft pulp was reacted with laccase in the presence of 1-hydroxybenzotriazole (HBT), N-acetyl-N-phenylhydroxylamine (NHA), and violuric acid (VA). The biodelignification response with violuric acid was superior to both 1-hydroxybenzotriazole and N-acetyl-N-phenylhydroxylamine. NMR analysis of residual lignins isolated before and after the biobleaching treatments revealed that the latter material was highly oxidized and that the magnitude of structural changes was most pronounced with the laccase – violuric acid biobleaching system. An increase in the content of carboxylic acid groups and a decrease in methoxyl groups were noted with all three laccase-mediator systems. The oxidation biobleaching pathway is directed primarily towards noncondensed C5 phenolic lignin functional structures for all three laccase-mediated systems. The laccase – violuric acid system was also reactive towards C5-condensed phenolic lignin structures.Key words: laccase, mediator, lignin, pulp, biobleaching, phenolics.

Development of novel substrates for tumor immunotherapy

Acid-terminated polyglycolide microparticles (PG-MP) were prepared as a versatile substrate that could be surface-modified for either immobilization of anti-cd3 and anti-cd28 mAb to activate T cells or sustained release of granulocyte-macrophage colony stimulating factor (GM-CSF) for dendritic cell (DC) recruitment and maturation. PG-MP were prepared with a volume-weighted mean diameter of 56 or 57 μm. Accessible carboxylic acid group concentration was determined by potentiometric titration to be 0.3 mmole/g and corresponded to a zeta potential of −21.87 mV. PG-MP immobilized with either anti-human CD3/CD28 or anti-mouse cd3/cd28 induced significant proliferation of T cells. Intracellular flow cytometry in activated mouse T cells was significant for IFN-γ, but not IL-4. Microparticles surface-modified for GM-CSF release were prepared from either PG-MP or PG pre-treated with poly- l-lysine (PG-Lys) to manipulate surface charge. GM-CSF released from PG-Lys-MP was observed for up to 26 days. The biologic activity of released GM-CSF was confirmed by using a h-GM-CSF-dependent cell line. The efficacy of the α-cd3/cd28-MP and GMCSF-MP was studied in a syngeneic mouse tumor prevention and regression model. Co-injection of Meth A fibrosarcoma cells with α-cd3/cd28-MP and GMCSF-MP completely prevented tumor implantation (0/24). The regression model showed complete tumor regression in four of seven animals and stable disease in three of seven. In the latter study, a dramatic level of DC infiltration was observed compared to controls.

Oxidized cellulose esters: I. Preparation and characterization of oxidized cellulose acetates — a new class of biodegradable polymers

Oxidized cellulose acetates (OCA), with a degree of substitution (DS) value ranging between 1.1 and 2.3 and a free carboxylic acid group content of 20% (w/w), have been prepared by reacting oxidized cellulose (OC, COOH content 20% w/w) with a mixture of acetic acid and acetic anhydride in the presence of sulfuric acid as a catalyst. The DS of OCA, in general, increased with increasing reaction temperature, reaction time, and concentration of acetic anhydride in the reaction mixture. The yield of OCA, in contrast, increased with increasing concentration of acetic anhydride and decreased with increasing reaction time and temperature. The intrinsic viscosity of OCA varied between 0.100 and 0.275, depending on the reaction conditions used during its preparation. In general, an increase in reaction temperature and the use of a prolonged reaction time decreased the intrinsic viscosity of OCA. No correlation was found between DS and intrinsic viscosity of OCA. The apparent pKa of OCA is 3.7-3.9. The new OCA polymers are practically insoluble in water and slowly dissolve in pH 7.4 phosphate buffer solution. They are, however, soluble in a range of organic solvents (e.g. ethyl acetate, acetone, acetone/water, chloroform/methylene chloride, dimethylsulfoxide, dimethylformamide, and/or chloroform/methanol).