Weak Acid Groups Research Articles

Physicochemical studies of cadmium(II) biosorption by the invasive alga in Europe, Sargassum muticum.

In recent years, there has been a significant increase in the studies concerning brown seaweed as biosorbents for metal removal owing to their high binding ability and low cost. This work reports the results of a study regarding the cadmium binding equilibria of dead biomass from the seaweed Sargassum muticum; this alga is a pest fouling organism that competes with the local fucalean species and may also interfere with the "sea industry"; therefore, it would constitute an ideal material to be used as biosorbent. Seven different treatments were tested in order to obtain a stable biomass that could be suitable for industrial use under a broad range of operational conditions. The treatments employed were protonation, chemical cross-linking with formaldehyde, KOH, Ca(OH)(2) and CaCl(2) or physical treatments with acetone and methanol. The equilibrium adsorption isotherms of Langmuir, Freundlich, and Langmuir-Freundlich were obtained for the quantitative description of the cadmium uptake. The effect of pH on biosorption equilibrium was studied at values ranging from 1 to 6, demonstrating the importance of this parameter for an accurate evaluation of the biosorption process. Maximum biosorption was found pH higher than 4.5. The maximum biosorption uptake for the raw biomass was 65 mg g(-1), while for formaldehyde cross-linking biomass the uptake increases to 99 mg g(-1) and for protonated biomass to 95 mg g(-1). Potentiometric titrations were carried out to estimate the total number of weak acid groups and to obtain their apparent pK value, 3.85, using the Katchalsky model. Kinetic studies varying cadmium concentration, algal dose, and ionic strength were carried out. Over 95% of the maximum cadmium uptake was achieved within 45 min, so the process can be considered relatively fast. A pseudo-second-order model, for the kinetics of cadmium biosorption, was shown to be able to reproduce experimental data points with accuracy.

Immobilization of lipase in a mesoporous reactor based on MCM-41

An immobilized enzyme has been prepared by incorporation of porcine pancreatic lipase (PPL) in the channels of MCM-41 by virtue of the hydrogen bonding interactions between the abundant weakly acidic hydroxyl groups of the support and the enzyme. The activity of the immobilized enzyme falls off rapidly when reused, however, because the weakly held enzyme is leached out from the pores. When the immobilized enzyme is treated with vinyltrimethoxysilane, the N 2 adsorption–desorption plot of the product shows a type I isotherm with a steep region in the desorption branch of the hysteresis loop, suggesting that most of the organic groups have been coupled to the walls at the pore openings, which partly shrink the pore opening. The 29 Si MAS-NMR spectrum shows three peaks between −60 and −80 ppm consistent with the presence of siloxane groups grafted at the pore openings, resulting in a decrease in their size. After the grafting process is complete, pores with narrow necks and wide bodies (so-called ‘ink bottle’ pores) are formed. When the modified immobilized enzyme was used to hydrolyze triacetylglycerol in a batch process, the activity remained constant over five cycles of reuse. This confirms that reaction with vinyltrimethoxysilane has led to the enzyme being immobilized inside a ‘mesoporous reactor’ from which leaching of the enzyme is prevented without inhibiting access to the substrate and release of the products.

Effect of acidic treatment on metal adsorptions of pitch-based activated carbon fibers

In this work, the pitch-based activated carbon fibers (ACFs) were prepared by nitric acid to investigate the multi-metal adsorption in interfacial and textural points of view. N 2 /77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were studied by BET specific surface area and t -plot methods, respectively. As a result, the specific surface area of the almost neutral ACFs in nature significantly decreased with nitric acid treatment, probably due to the widening of micropores. However the total acidity, including the carboxyl groups, on carbon surfaces was extremely induced during the acidic surface treatment. From the adsorptions of Cu 2+ and Ni 2+ , it was revealed that the adsorption capacity of metal ions was mainly influenced by the weakly acidic functional groups such as lactones on the carbon surfaces at pH<p I (isoelectric point), and by the strongly acidic functional groups such as carboxyl groups at pH>p I .

A novel support of MCM-48 molecular sieve for immobilization of penicillin G acylase

As a novel support of immobilizing penicillin G acylase (PGA), MCM-48 and Co-MCM-48 molecular sieves were synthesized and characterized by XRD, N 2 adsorption, NH 3-TPD, FT-IR and so on. The studies show that MCM-48 and Co-MCM-48 has well ordered long-range structure, narrow pore size distribution, larger surface area and higher concentration of the weakly acidic silanol groups on their surface. Penicillin G acylase was immobilized on MCM-48 or Co-MCM-48 by interacting silanol groups on the surface. The presence of cobalt in the framework of MCM-48 increases the amount of the weak acid sites. For the hydrolysis of penicillin G catalyzed by PGA/Co-MCM-48 (Co/Si=0.01), its specific activity reaches 1682 U/g. After used for six cycles, PGA/MCM-48(0.01) can keep 1375 U/g of the specific activity. If MCM-41 was used as the support, the activity of immobilized PGA is only 402 U/g.

Synthesis and polymerization of tail-type cationic polymerizable surfactants and hydrophobic counter-anion induced association of polyelectrolytes

A series of tail-type cationic surface-active monomers with the cationic charge at the ω-end (1; ST-C m -AB, m=5, 7, and 9, where ST is a styrenic group, C m the alkylene chain at the 4-position of styrene, and AB is alkyltrimethylammonium bromide) have been synthesized as a novel cationic polymerizable surfactant. Their fundamental physicochemical properties such as critical micelle concentration (cmc) and weight-average aggregation number of the micelle (N w(agg)) have been characterized in water at 25 °C by static light-scattering measurements. The cmc values determined for the tail-type surfactant monomers are two-orders of magnitude smaller than those of the corresponding head-type cationic surfactant monomers (2; ST-C1-AC-C m ). The N w(agg) of ST-C m -AB is 68 for m=5, 156 for m=7, and 413 for m=9. Free-radical homopolymerization of ST-C7-AB proceeds very rapidly in water as a result of organization in the micelle to afford the corresponding amphiphilic cationic polyelectrolyte with M w=3.63×106 and 23 nm hydrodynamic radius at 25 °C. Emulsion copolymerization of styrene with ST-C m -AB also proceeds rapidly to afford very stable cationic polystyrene latex particles of 30–60 nm diameter. The amphiphilic cationic polyelectrolyte of poly(ST-C7-AB) is likely to assume a compact conformation with high segment density in 0.1 mol L−1 NaCl in water. Addition of hydrophobic aromatic counter-anions with an weak acid group, for example potassium hydrogen phthalate (PHK) and sodium salicylate, to a salt-free aqueous solution of poly(ST-C7-AB) induces intermolecular aggregation and increases the solution viscosity substantially, often producing gels and precipitation at high polymer concentration.

Effect of acidic treatment on metal adsorptions of pitch-based activated carbon fibers

In this work, the pitch-based activated carbon fibers (ACFs) were prepared by nitric acid to investigate the multi-metal adsorption in interfacial and textural points of view. N 2/77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were studied by BET specific surface area and t-plot methods, respectively. As a result, the specific surface area of the almost neutral ACFs in nature significantly decreased with nitric acid treatment, probably due to the widening of micropores. However the total acidity, including the carboxyl groups, on carbon surfaces was extremely induced during the acidic surface treatment. From the adsorptions of Cu 2+ and Ni 2+, it was revealed that the adsorption capacity of metal ions was mainly influenced by the weakly acidic functional groups such as lactones on the carbon surfaces at pH<p I (isoelectric point), and by the strongly acidic functional groups such as carboxyl groups at pH>p I.

Titration of Surface Modified Pigment Particles

Surface modified pigments are playing an increasingly important role in high performance inkjet inks. Titration has been developed as a quantitative tool to evaluate pigment particles bearing weak acid or base functional groups. The value of total titratable groups in mmol/g pigment indicates the level of surface modification. The dissociation constants (pKa or pKb), which can be derived from the mathematical treatment of the titration curve, provide an insight into the colloidal stability as a function of pH. Titration studies of pigment particles have been reported before; however, due to poorly determined functional groups, data interpretation has been difficult. Cabot's surface modification technology, which introduces specific functional groups to the pigment surface, provides a unique opportunity for a systematic investigation. In this paper, a range of surface modified pigment particles has been investigated. The impact of ionic strength (Im), inkjet ink components, and the nature of the surface functional groups have been studied and related to the pigment stability. The discrepancy between apparent pK (as measured experimentally) and the functional group pK is explained using a diffuse double layer (DDL) correction term. Using this method, the stability of the pigment dispersions can be better understood and the ability to destabilize these systems in a controlled manner through pH, ionic strength, or other environmental changes can be anticipated.

Cation‐exchange fabric prepared by electron beam‐induced graft copolymerization of binary monomer mixture

AbstractApplying the electron‐beam preirradiation method in air the cation ‐ exchange fabric (CEF) containing sulfonic acid (R‐SO3H) groups was prepared by graft copolymerization of sodium styrenesulfonate with acrylic acid onto non woven polypropylene fabric. The effect of reaction conditions on the grafting yield and reaction mechanism was examined.The ion‐exchange properties towards Cu(II) and Co(II) ions of the CEF were investigated depending on the form of the CEF and a pH of the solution. It was found that the synthesized CEF contains both strong acid groups (R‐SO3H) and weak acid (R‐COOH) groups in almost equal proportion. The utilization of the CEF in Na+ form allows to make the best use of its ion‐exchange capacity.

Immobilized Proton Sponge on Inorganic CarriersThe Synergic Effect of the Support on Catalytic Activity

Abstract 1,8-bis(dimethylaminonaphthalene) (DMAN), a proton sponge, was grafted onto amorphous and pure-silica MCM-41. The results show that DMAN supported on MCM-41 is an excellent base catalyst for the Knoevenagel condensation between benzaldehyde and different active methylene compounds as well as for the Claisen–Schmidt condensation of benzaldehyde and 2'-hydroxyacetophenone to chalcones and flavanones. The influence of the solvent and the polarity of the support on the activity of the catalysts was studied. It was found that the activity of the supported catalyst is directly related to the polarity of the inorganic support. Moreover, the support can also preactivate the reagents by interaction of the carbonyl groups with the weakly acidic silanol groups of the MCM-41. This preactivation step enables DMAN, anchored onto MCM-41, to abstract protons with a higher p K a than that of the DMAN. Finally, the study of the deactivation and recycling of the DMAN anchored onto MCM-41 catalysts showed that it is a stable material with respect to deactivation and leaching and results in comparable rates in successive batch reactions.

Immobilized Proton Sponge on Inorganic Carriers: The Synergic Effect of the Support on Catalytic Activity

1,8-bis(dimethylaminonaphthalene) (DMAN), a proton sponge, was grafted onto amorphous and pure-silica MCM-41. The results show that DMAN supported on MCM-41 is an excellent base catalyst for the Knoevenagel condensation between benzaldehyde and different active methylene compounds as well as for the Claisen–Schmidt condensation of benzaldehyde and 2'-hydroxyacetophenone to chalcones and flavanones. The influence of the solvent and the polarity of the support on the activity of the catalysts was studied. It was found that the activity of the supported catalyst is directly related to the polarity of the inorganic support. Moreover, the support can also preactivate the reagents by interaction of the carbonyl groups with the weakly acidic silanol groups of the MCM-41. This preactivation step enables DMAN, anchored onto MCM-41, to abstract protons with a higher p K a than that of the DMAN. Finally, the study of the deactivation and recycling of the DMAN anchored onto MCM-41 catalysts showed that it is a stable material with respect to deactivation and leaching and results in comparable rates in successive batch reactions.

Towards waste minimisation in WWTP: activated carbon from biological sludge and its application in liquid phase adsorption

AbstractSurplus sludge produced during the biological treatment of wastewater requires costly disposal procedures. With increasing environmental and legislative constraints, increasing sludge production and more limited disposal options, new recycling alternatives have to be found. The possibility of obtaining activated carbons from surplus biological sludge by chemical activation with H2SO4 has been investigated. Operational parameters such as the amount of H2SO4 added, the temperature, and activation time were modified to ascertain their influence on the quality of the activated carbon obtained. The quality of the sludge‐based activated carbons was evaluated by established characterisation parameters for adsorption from solution such as phenol value, iodine number, methylene blue number and tannin value and compared with commercial activated carbons. Activation at 700 °C for 30 min in the presence of 0.5 cm3 H2SO4 g−1 dry solids in the sludge led to an activated carbon with a good capacity for iodine and tannic acid. The sludge‐derived activated carbon obtained is mesoporous in nature with a high presence of large macropores. Weak and moderate acidic surface functional groups were detected on the surface, which impart a hydrophilic nature to the solid. When compared with a commercial activated carbon, the sludge‐derived activated carbon performed better when removing dyes with a high presence of anionic solubilising groups and heavy metals. The results indicate that COD adsorption from a biologically‐treated effluent may also be an area for application.© 2002 Society of Chemical Industry

Characterisation of novel modified active carbons and marine algal biomass for the selective adsorption of lead

This paper discusses the sorption performance of novel materials for the removal of lead(II) and copper(II) from near-neutral aqueous solutions. Active carbons with surface heteroatoms of oxygen and phosphorus have been prepared. The surface functional groups display weakly acidic ion exchange characteristics. The optimum solution pH for maximum metal sorption is related to the pK values of the surface functional groups. In oxygenated active carbons, pK values are not distinct but can be obtained by describing proton binding to the heterogeneous adsorbent surface as a continuous proton affinity distribution. Information derived from zeta-potential measurements combined with knowledge of the pK distribution function and concentration of surface functional groups has been used to explain the selectivity of oxidised active carbons towards lead(II) in the presence of copper(II) from multi-metal bearing solutions. Marine algal-based biosorbents have been challenged with lead(II) and copper(II)-bearing wastewater. The weakly acidic carboxyl groups of structural polysaccharides present within the algal matrix display high sorption capacity for both metals. The negative surface charge of algal particles results in electrostatic interactions as well as coordination between metal species and the adsorbent surface. Proton affinity for the algal surface lowers the negative surface potential at pH values around 2. The surface functional groups in algae unlike those in oxidised active carbons may be represented by discrete acid-dissociation constant values. The influence of conformational differences in uronic-acid segments upon metal ion selectivity is discussed.

Role of Aromatic Side Chains in the Binding of Volatile General Anesthetics to a Four-α-Helix Bundle

Currently, the mechanism by which anesthesia occurs is thought to involve the direct binding of inhaled anesthetics to ligand-gated ion channels. This hypothesis is being studied using four-alpha-helix bundles as model systems for the transmembrane domains of the natural "receptor" proteins. This study concerns the role in anesthetic binding played by aromatic side chains in the binding cavity of a four-alpha-helix bundle designed to assume a Rop-like fold. Specifically, the effect of the substitution W15Y on bundle structure, stability, and anesthetic binding energetics was investigated. No appreciable effect of substituting W for Y on the secondary structure or the thermodynamic stability of the four-alpha-helix bundle was identified. However, the substitution W15Y resulted in about 6- and 3-fold decreases in halothane and chloroform binding affinities, respectively. This effect may reflect weaker dipole-aromatic quadrupole interactions between the aromatic side chain and the anesthetic in the tyrosine-containing species, which possesses the smaller aromatic ring system. For these anesthetic binding proteins, this class of interaction occurs when the permanent nonspherical distribution of electrons in the aromatic ring systems interact with the weakly acidic CH group of the anesthetics.

Characterisation of the surface of oxidised carbon adsorbents

The surface reactivity and functional group content of a series of oxidised active carbons has been assessed by elemental analysis, electrophoretic mobility measurements and potentiometric titrations. Oxidation of carbons with hot air resulted in a greater proportion of relatively weak acidic surface functional groups (i.e., phenolic), whereas nitric acid modification produced a greater amount of carboxylic groups. Electrophoretic mobility measurements suggest that the carbon surface is negatively charged within the range of the pH values studied. pH titration results indicate that the surface acidity of active carbons is stronger than that of a commercial polymeric carboxylic acid ion exchange resin. Possible mechanisms of carbon surface oxidation are discussed.

Methylacetylene and tert-butylacetylene as IR-probe molecules for the characterisation of basicity

Methylacetylene (MA) and tert-butylacetylene (TA) were used as probe molecules in infra-red spectroscopy for characterisation of the basicity of MgO. Reference experiments with SiO 2 showed the formation of a π-complex via the CC bond of MA or TA with the weakly acidic silanol groups. The adsorption model proposed for MA and TA on MgO involves a H-bonding adsorption interaction of the probe molecule via the acidic CH end with the basic O 2− sites with a possible simultaneous interaction of the CC bond with OH groups which are preferentially located at corners on the MgO surface.

High-resolution determination of H+ by ion chromatography. Application to the simultaneous determination of H+, Na+, NH4+ and K+ in acid rain.

An ion chromatographic (IC) method was developed for the high-resolution determination of a sample's free hydrogen ion concentration (H+). Highly purified lithium dodecyl sulfate was used as the stationary phase, a slightly acidified aqueous LiCl solution was used as the mobile phase and conductivity was used for analyte detection. An electrical double layer (EDL) containing H+ was established on the stationary phase by using a slightly acidified electrolyte solution as the eluent. H+ in the EDL protonated any weak acid groups (i.e., silanols) on the stationary phase so that H+ from the sample could be retained/separated purely by dodecyl sulfate. The optimum molar ratio of H+:Li+ in the EDL for this IC system was obtained by using an aqueous solution containing 40.0 mM LiCl and 0.07 mM H2SO4 as the eluent. After separation, H+ was detected by direct conductimetric measurement. An H+ detection limit of better than 8.2 x 10(-6) M was obtained from the analysis of standard aqueous H2SO4 solutions. Other monovalent cations could also be separated with this method, giving detection limits of 7.4 x 10(-5), 4.3 x 10(-5) and 4.2 x 10(-5) M for Na+, NH4+ and K+, respectively. The method was applied to the simultaneous determination of H+, Na+, NH4+ and K+ in acid rain. The results obtained showed a significant improvement in reproducibility when compared with those from a conventional pH-meter. Acid rain samples with a pH < 5 could be analyzed with this IC system.

Influence of pH, temperature, culture age and cations on adsorption and uptake of Ni by Chlorella vulgaris

Nickel accumulation by C. vulgaris was studied distinguishing adsorption and intracellular accumulation. The surface adsorption contributed maximally (<80%) to total Ni accumulation by the test alga. It was maximal and of equal magnitude at pH 3.5 and 5.5 accordingly suggesting the participation of strong and weak acidic functional groups of C. vulgaris with relatively low and high affinity for Ni adsorption. Nickel uptake was greatly reduced at acidic pH. The cultures in the decline phase of growth showed highest adsorption of Ni but the rate of Ni uptake was greatly reduced when cultures were in the decline or stationary phase of growth. A better exposure of Ni binding sites, or generation of new sites was perhaps responsible for greater Ni adsorption by old cultures of C. vulgaris. Sodium and K caused mixed inhibition whereas Ca and Mg caused noncompetitive inhibition of adsorption and uptake of Ni. Chromium was not able to competitively inhibit adsorption and uptake of Ni by the test alga. The competitive inhibition of Ni adsorption by Cu and Zn seems to be related to their similar ionic properties. Cu stimulated Ni uptake due possibly to increased permeability of the plasma membrane. The present study disagrees with the general conception that cations are competitive inhibitors of metal adsorption and uptake by algae.

Surface Forces between Hydrophilic Self-Assembled Monolayers in Aqueous Electrolytes

In this paper we present an atomic force microscopy (AFM) study on electrostatic and acid−base interactions between hydrophilic self-assembled monolayers (SAMs) with monoprotic ionizable acid functional groups (−COOH). As expected for surfaces composed of weak acid groups the surface potential and strength of interaction are sensitive to pH and ionic strength. Repulsive forces grow with the degree of ionization. At low fractional ionization, the surfaces experience attractions with a range larger than that expected for van der Waals interactions and the strength of adhesion is large. The strength of adhesion and extent of attractions diminish with increasing pH. As the surface groups ionize, at intermediate pH values, jump-in distances and adhesion grow with ionic strength and at high pH they saturate with increasing electrolyte concentration at values close to those expected for van der Waals interactions. However, the maximum charge is around 5% of the total expected for the surfaces. Thus, allowing sodium ions to bind, with a binding constant of pKNa = 3.7 and pKa = 6.3, ionic strength and pH dependencies of the surface charge can be described.

Modeling Adsorption of Copper(II), Cadmium(II) and Lead(II) on Purified Humic Acid

In this study, a system consisting of Pb, Cu and Cd as typical heavy metal pollutants, and purified Aldrich humic acid as a representative of natural organic materials were selected as prototypes to model the environmental system. The effect of environmental factors such as pH, salinity, and concentration on the interaction between metals and humic acid were investigated in detail. The experimental results show that pH and ionic strength are the most important variables in controlling metal adsorption on humic acid. The results also show a high complexation capacity of humic acid for the metals, especially Cu and Pb. The strength of binding of the three metals is in the sequence of Pb > Cu > Cd. A theoretical model featured by surface complexation reactions and double layer theory combined with the Poisson−Boltzmann equation was applied to simulate the experimental data. Titration data of humic acid with NaOH and Ba(OH)2 were used as concentrations of strong and weak acid groups on HA and the input data for the model calculations. Intrinsic adsorption constants and capacitance are estimated based on literature values and optimized to obtain the best agreement between the experimental and the model results. The model was also used to predict surface properties such as the speciation of the metals adsorbed on humic acid. Good agreement between theoretical modeling results and experimental data suggests the applicability of the theoretical model to this system. Given these parameters, theoretical calculations obtained using the model proposed in this study can give a detailed picture of the actual environmental conditions. Also, the model calculations will help in the evaluation of the actual toxicity of heavy metal pollutants in the aquasystem.

Removal of Cadmium Using Electrochemically Oxidized Activated Carbon

A wood-based activated carbon, AUG WHK, was oxidized electrochemically to enhance its metal binding capacity and subsequently studied for the removal of cadmium ions from aqueous solution. Treated adsorbents were characterized by N2 adsorption at 77K before and after oxidation, and a quantitative determination of weak-acid surface groups was carried out by direct titration. The BET surface area decreased considerably after oxidation ; however, the total amount of oxygen-containing surface groups was 3.36 times higher compared to the untreated adsorbent. Batch equilibrium tests indicated that the oxidized material has 16.5 times higher sorption capacity for cadmium than conventional activated carbon. Equilibrium isotherms were determined at pH4, 5 and 6 and showed that there was a slight increase in cadmium uptake with increase in pH. The experimental data were fitted by Langmuir and Freundlich isotherms and it was found that the Freundlich isotherm fitted better in all the cases. Overall, the results indicated a rapid adsorption rate with over 96% fractional uptake of metal occurring in the first 12 minutes. Small-scale mini-column experiments were performed and indicated that breakthrough occurred after about 140 bed volumes (BV) of feed solution, containing 1mM Cd at pH6, was passed at 10BV h-1 for oxidized WHK, whereas breakthrough was instantaneous for the unoxidized sample.