Journal of Colloid And Interface Science (v.295, #1)
Editorial Board (CO1).
Modeling of copper(II) and lead(II) adsorption on kaolinite-based clay minerals individually and in the presence of humic acid by Jülide Hizal; Resat Apak (1-13).
The aim of this study is to explain how clay minerals adsorb heavy metals individually and in the presence of humic acid, and to model heavy metal adsorption specifically based on surface–metal binary and surface–metal–ligand ternary complexation. The adsorption of Cu(II) and Pb(II) on kaolinite-based clay minerals has been modeled by the aid of the FITEQL3.2 computer program using single- and double-site binding models of the Langmuir approach. Potentiometric titrations and adsorption capacity experiments were carried out in solutions containing different concentrations of the inert electrolyte NaClO4; however, the modeling of binary and ternary surface complexation was deliberately done at high ionic strength (0.1 M electrolyte) for eliminating adsorption onto the permanent negatively charged sites of kaolinite. A “two-site, two p K a ” model was adapted, and as for the two surface sites responsible for adsorption, it may be arbitrarily assigned that S1OH sites represent silanol and organic functional groups such as carboxyl having p K a values close to that of silanol, and S2OH sites represent aluminol and organic functional groups such as phenolics whose p K a values are close to that of aluminol, as all the studied clays contained organic carbon. Copper(II) showed a higher adsorption capacity and higher binding constants, while lead(II), being a softer cation (in respect to HSAB theory) preferred the softer basic sites with aluminol–phenol functional groups. Heavy metal cations are assumed to bind to the clay surface as the sole (unhydrolyzed) M(II) ion and form monodentate surface complexes. Cu(II) and Pb(II) adsorption in the presence of humic acid was modeled using a double-site binding model by the aid of FITEQL3.2, and then the whole system including binary surface–metal and surface–ligand and ternary surface–metal–ligand complexes was resolved with respect to species distributions and relevant stability constants. Electrostatic effects were accounted for using a diffuse layer model (DLM) requiring minimum number of adjustable parameters. Metal adsorption onto clay at low pH increased in the presence of humic acid, and the metal adsorption vs pH curves of metal–kaolinite–humic acid suspensions were much steeper (and distinctly S shaped) compared to the wider pH-gradient curves observed in binary clay–metal systems. The clay mineral in the presence of humic acid probably behaved more like a chelating ion-exchanger sorbent for heavy metals rather than being a simple inorganic ion exchanger.The figure was drawn as a result of modeling of Cu(II) and humic acid adsorption on kaolinite-based clay by the aid of FITEQL program. It describes metal adsorption (as experimental and model curves) in the ternary Cu(II)–humic acid–clay system as mol adsorbed/L liquid solution vs pH (for 50 g/L solid-to-liquid ratio, 0.004% humic acid, 10 ppm metal nitrate in 0.1 M NaClO4 solution). Various surface species are symbolized.
Keywords: Copper(II); Lead(II); Clay minerals; Kaolinite; Humic acid; Adsorption; Modeling; FITEQL;
Effect of background electrolytes and pH on the adsorption of Cu(II)/EDTA onto TiO2 by Jae-Kyu Yang; Seung-Mok Lee; Allen P. Davis (14-20).
Cu(II)/EDTA adsorption onto TiO2 has been studied with a variation of pH, ionic strength, and type of background electrolytes. Cu(II) adsorption onto TiO2 increased as ionic strength increased when NaClO4 was used as a background electrolyte. This can be explained by the increase of exp ( − F Ψ / R T ) as a part of the electrostatic correction within a surface complexation model. Model predictions described experimental adsorption trends. Types of background anions (ClO4, Cl, NO2, NO3, SO3, and PO4) did not affect adsorption trends and adsorption amounts of Cu(II) onto TiO2. However, different trends were observed with various types of background ions used as ionic strength in EDTA and Cu(II)–EDTA adsorption. EDTA adsorption was decreased by using Na2SO3 and Na3PO4 as background ions, while NaClO4, NaCl, NaNO2, and NaNO3 showed negligible interference on the EDTA adsorption, which matched well with model predictions. The presence Na2SO3 and Na3PO4 also interfered with Cu(II)–EDTA adsorption, to a somewhat greater extent compared to EDTA adsorption, especially at lower pH. This interference was also noted in Cu(II)–EDTA adsorption with a variation of Cu(II)–EDTA concentration at constant ionic strength ( 3 × 10 −3 M ) by using Na2SO3 and Na3PO4, especially at lower ratios of Cu(II)–EDTA to Na2SO3 and Na3PO4. These results suggest that the ratio of Cu(II)–EDTA to Na2SO3 and Na3PO4 is an important factor for the controlling of competition between these background ions and Cu(II)–EDTA onto TiO2. Model prediction generally matched well with experimental adsorption using NaClO4, NaCl, NaNO2, and NaNO3 as backgrounds ions, while a severe deviation was observed in the presence of Na2SO3 and Na3PO4. These results suggest that the mobility of copper ions as Cu(II)–EDTA can be increased from polluted area in the presence of multivalent background ions, especially as the ratio of adsorbates/background ions decreased.The mobility of copper ions as Cu(II)–EDTA can be increased from polluted area in the presence of multivalent background ions, especially as the ratio of adsorbates/background ions decreased.
Keywords: Adsorption; Cu(II); Cu(II)–EDTA; EDTA; Ionic strength; TiO2;
Adsorption of Ni(II) on clays by Susmita Sen Gupta; Krishna G. Bhattacharyya (21-32).
The present work investigates the adsorptive interactions of Ni(II) ions with kaolinite, montmorillonite, and their poly(oxo zirconium) and tetrabutylammonium derivatives in aqueous medium. Batch adsorption studies were carried out with various Ni(II) concentrations, amount of clay adsorbents, pH, agitation time and temperature. The adsorption is strongly dependent on pH of the medium with enhanced adsorption as the pH turns from acidic to alkaline side till precipitation sets in. The process was very fast initially and maximum adsorption was observed within 180 min of agitation. The kinetics of the interactions, tested with pseudo first order Lagergren equation, second order kinetics, Elovich equation, liquid film diffusion model and intra-particle diffusion mechanism, showed better agreement with second order kinetics ( k 2 = 1.3 × 10 −2 to 5.3 × 10 −2 g / ( mg min ) ). The adsorption data gave good fits with Langmuir and Freundlich isotherms and yielded Langmuir monolayer capacity of 2.75 to 21.14 mg/g and Freundlich adsorption capacity of 0.70 to 3.40 mg(1−1/n) l1/n /g for the clay adsorbents. The adsorption process was exothermic with ΔH in the range of −24.0 to −45.1 kJ/mol accompanied by decrease in entropy (ΔS: −118.2 to −160.5 J/(mol K)) and Gibbs energy (ΔG: −34.6 to −49.5 kJ/mol). The results have shown that montmorillonite has the largest adsorption capacity followed by ZrO-montmorillonite, TBA-montmorillonite, kaolinite, ZrO-kaolinite and TBA-kaolinite. Introduction of ZrO- and TBA- groups into the clays reduced their adsorption capacity by blocking the available adsorption sites.In this work, two clay minerals, kaolinite and montmorillonite, and their poly(oxo zirconium) and tetrabutylammonium derivatives have been shown to be very effective in removing Ni(II) from aqueous medium by adsorption.
Keywords: Kaolinite; Montmorillonite; Poly(oxo zirconium) clay; Tetrabutylammonium clay; Adsorption; Adsorption kinetics; Adsorption isotherm; Temperature; Enthalpy;
Adsorption of zwitterionic drugs onto oxidized cellulose by Dmitry S. Zimnitsky; Tatiana L. Yurkshtovich; Pavel M. Bychkovsky (33-40).
Adsorption of zwitterionic drugs (β-lactam antibiotics and amino acids) onto samples of oxidized cellulose (OC) with various carboxyl contents and structural characteristics from aqueous and water/alcohol solutions was investigated. The adsorption process can be described according to the theory of localized stoichiometric adsorption and represented by Langmuir isotherms. It was established that the constants of interfacial distribution mainly increase with increased relative sorbate hydrophobicity. The dependencies of adsorption on pH of equilibrium drug solution have a maximum at pH 3–3.5, which is caused by peculiarities of dissociation of OC and sorbates. The drug uptake is shown to increase with an increase of alcohol mole fraction in the solution and transfer to the binary water/isopropanol from water/ethanol solutions. The dominant contribution to the increase of uptake is the desolvation of ionic groups of zwitterions in the solution, which increases with increased alcohol content. The degree of crystallinity of the sorbent has no considerable effect on drug adsorption from aqueous solutions. In water/alcohol solutions the adsorption of drugs by OC samples with similar exchange capacity increases with reducted uniformity of carboxylic group distribution in the volume of the polymer, which is connected with increased accessibility of carboxylic groups for sorbate molecules.The scheme of adsorption of zwitterions onto oxidized cellulose.
Keywords: Adsorption; Langmuir isotherm; β-Lactam antibiotics; Amino acids; Oxidized cellulose; Degree of crystallinity;
A new route to the formation of biomimetic phosphate assemblies on gold: Synthesis and characterization by Annika Borgh; Johan Ekeroth; Rodrigo M. Petoral; Kajsa Uvdal; Peter Konradsson; Bo Liedberg (41-49).
A biomimetic model system based on long-chain alkanethiols tailored with serine, threonine and tyrosine side-chain groups is created as a platform for the study of phosphorylated amino acids. The phosphorylated analogues are synthesized with protective tert-butyl groups that after assembly on thin polycrystalline gold films are removed in an acidic deprotection solution to form the corresponding phosphate self-assembled monolayers (SAMs). The SAMs are thoroughly characterized with null ellipsometry, contact angle goniometry, infrared reflection–absorption spectroscopy and X-ray photoelectron spectroscopy. The assembly and the subsequent deprotection process are optimized with respect to molecular orientation and chain conformation by varying the incubation time and the exposure time to the deprotection solution. The high quality of the generated SAMs suggests that the present assembly/deprotection approach is an attractive alternative when traditional synthetic routes become demanding because of solubility problems.A biomimetic model system based on long-chain alkanethiols tailored with serine, threonine and tyrosine side-chain groups is created as a platform for the study of phosphorylated amino acids. The phosphorylated analogues are synthesized with protective groups that after assembly on thin gold films are removed in an acidic deprotection solution.
Keywords: SAM; Thiols; Gold; Phosphorylated amino acids; Surface deprotection scheme;
Zn2+ and Sr2+ adsorption at the TiO2 (110)–electrolyte interface: Influence of ionic strength, coverage, and anions by Z. Zhang; P. Fenter; L. Cheng; N.C. Sturchio; M.J. Bedzyk; M.L. Machesky; L.M. Anovitz; D.J. Wesolowski (50-64).
The X-ray standing wave technique was used to probe the sensitivity of Zn2+ and Sr2+ ion adsorption to changes in both the adsorbed ion coverage and the background electrolyte species and concentrations at the rutile (α-TiO2) (110)–aqueous interface. Measurements were made with various background electrolytes (NaCl, NaTr, RbCl, NaBr) at concentrations as high as 1 m. The results demonstrate that Zn2+ and Sr2+ reside primarily in the condensed layer and that the ion heights above the Ti–O surface plane are insensitive to ionic strength and the choice of background electrolyte (with <0.1 Å changes over the full compositional range). The lack of any specific anion coadsorption upon probing with Br−, coupled with the insensitivity of Zn2+ and Sr2+ cation heights to changes in the background electrolyte, implies that anions do not play a significant role in the adsorption of these divalent metal ions to the rutile (110) surface. Absolute ion coverage measurements for Zn2+ and Sr2+ show a maximum Stern-layer coverage of ∼0.5 monolayer, with no significant variation in height as a function of Stern-layer coverage. These observations are discussed in the context of Gouy–Chapman–Stern models of the electrical double layer developed from macroscopic sorption and pH-titration studies of rutile powder suspensions. Direct comparison between these experimental observations and the MUltiSIte Complexation (MUSIC) model predictions of cation surface coverage as a function of ionic strength revealed good agreement between measured and predicted surface coverages with no adjustable parameters.The X-ray standing wave measurements probe the height sensitivity of divalent metals (Sr2+ and Zn2+) adsorbed at the rutile TiO2 (110)–aqueous interface to changes of background electrolytes.
Keywords: Electrical double layer; Rutile; Adsorption; Oxide–aqueous interface; X-ray standing wave; Multisite complexation; Ionic strength;
Retention of phosphorus by iron and aluminum-oxides-coated quartz particles by M. Arias; J. Da Silva-Carballal; L. García-Río; J. Mejuto; A. Núñez (65-70).
The capacity of adsorption of P on Fe and Al-oxides-coated quartz sand has been studied. The adsorption process has been described as Freundlich and Langmuir isotherms. In all cases Langmuir equation yields better fits than Freundlich equation. The covering quartz particles with Fe and Al oxides provide a high capacity adsorption and immobilization of P from natural and waste waters. The values obtained for adsorption, desorption and adsorption/desorption cycles show that Al oxides particles provide an excellent material for construction of a P removal system for waste waters. The characteristics of this material would allow the design of a complementary filtration system to reduce P levels in the effluent, reducing contamination risks and combating eutrophication of nearby watercourses.The adsorption of P on Fe and Al-oxides-coated quartz sand was described as Freundlich and Langmuir isotherms. The cover of quartz particles provides a high capacity adsorption and immobilization.
Keywords: Wastewater treatment; P retention; Aluminum oxides; Iron oxides; Quartz;
Application of zeolite MCM-22 for basic dye removal from wastewater by Shaobin Wang; Huiting Li; Longya Xu (71-78).
MCM-22 was employed as an effective adsorbent for removal of basic dyes including methylene blue, crystal violet, and rhodamine B from aqueous solution. The adsorption kinetics and isotherms were investigated. The adsorption capacity of MCM-22 for three dyes follows an order of MB > CV ∼ RB. Kinetic studies indicate that the adsorption follows the pseudo second-order kinetics and the adsorption is a two-step diffusion process with film diffusion dominating the process. The adsorption isotherm can be well fitted by both the Langmuir and the Freundlich models. Thermodynamic calculations suggest that the adsorption of basic dyes on MCM-22 is an endothermic reaction.MCM-22, a novel nanoporous material, has been tested as a new adsorbent for dye removal from aqueous solution. It has been shown that MCM-22 exhibits a comparable adsorption capacity to activated carbon.
Keywords: MCM-22; Adsorption kinetics; Isotherm; Basic dyes; Wastewater treatment;
Surface esterification of cellulose fibers: Characterization by DRIFT and contact angle measurements by Daniel Pasquini; Mohamed Naceur Belgacem; Alessandro Gandini; Antonio Aprigio da Silva Curvelo (79-83).
The surface chemical modification of microcrystalline cellulose and cellulose fibers obtained from different sugar cane bagasse pulping processes, viz. Kraft, organosolv ethanol/water and organosolv/supercritical carbon dioxide, were studied in heterogeneous conditions using modest amounts of octadecanoyl and dodecanoyl chloride. The ensuing surfaces acquired a non-polar character, suitable for incorporating these fibers as reinforcing agents in composite materials based on polymeric matrices. The success of these chemical modifications was assessed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, elemental analysis, scanning electron microscopy (SEM) and contact angle measurements. In particular, the dynamic and equilibrium contact angle measurements, before and after the treatments, revealed that the value of the polar component ( γ s p ) of the surface energy had decreased very considerably following the modification.
Keywords: Surface modification; Cellulose; Octadecanoyl chloride; Dodecanoyl chloride; Surface energy; Hydrophobisation;
Competitive adsorption of fibrinogen and dipalmitoylphosphatidylcholine at the air/aqueous interface by Sook Heun Kim; Elias I. Franses (84-92).
The competitive adsorption of fibrinogen (FB) and DPPC at the air/aqueous interface, in phosphate buffer saline at 25 °C, was studied with tensiometry, infrared reflection absorption spectroscopy (IRRAS), and ellipsometry. For FB/DPPC mixtures with 750 ppm (0.075 wt%) FB and 1000 ppm (0.10 wt%) DPPC, the tension behavior was found to be similar to that of FB when alone, even with DPPC and FB being at the interface. Thus, FB interferes with adsorption of DPPC and inhibits its surface tension lowering ability. When FB protein is introduced in the solution after a DPPC monolayer has formed, the adsorption of FB is inhibited by the DPPC monolayer. When a DPPC monolayer is spread onto a solution with a preadsorbed FB layer, the DPPC monolayer excludes FB from the surface and controls the tension behavior with little inhibition by FB. When a DPPC dispersion is introduced with the Trurnit method, or sprayed dropwise, onto an aqueous FB/DPPC surfaces, the DPPC layer formed on the surface prevents the adsorption of FB and dominates the surface tension behavior. These results have implications in controlling the inhibition of lung surfactant tension behavior by serum proteins, when they leak at the alveolar lining layer, and in developing surfactant replacement therapies for alveolar respiratory diseases.In a fibrinogen–dipalmitoylphosphatidylcholine (DPPC) mixture in aqueous saline buffer, the protein adsorbs first and inhibits the surface-tension-lowering ability of DPPC vesicles, which form an incomplete monolayer.
Keywords: Competitive adsorption; Dipalmitoylphosphatidylcholine; Lipid inhibition by fibrinogen; Air/aqueous interface; Dynamic surface tension; IRRAS spectroscopy;
Microstructuring of phospholipid bilayers on gold surfaces by micromolding in capillaries by Steffen Schuy; Andreas Janshoff (93-99).
Microstructuring of lipid bilayers on gold surfaces was achieved by micromolding in capillaries employing chemically modified polydimethylsiloxane (PDMS). Microfluidic networks of PDMS were prepared by micromolding and functionalized with thiol end-groups using 3-mercaptopropyltrimethoxysilane. The PDMS stamps were firmly attached to the gold substrate via quasi-covalent linkage providing a tight seal, a prerequisite for establishing individual addressable capillaries. Bilayers composed of POPC/POPG were subsequently prepared on microstructured self assembly monolayers of 11-amino-1-undecanethiol via strong electrostatic interactions. This way it is possible to generate individually addressable lipid bilayers on gold surfaces, a procedure, which is of widespread interest for investigating protein lipid interactions with microscopic techniques.Microstructuring of lipid bilayers on gold surfaces was achieved by micromolding in capillaries employing chemically modified polydimethylsiloxane (PDMS). The PDMS stamp was therefore functionalized with thiol end-groups and the bilayers were prepared on a microstructured SAM.
Keywords: Soft lithography; PDMS; Scanning force microscopy; Solid supported lipid bilayers; Self assembly;
Comparative analysis of the structure of sterically stabilized ferrofluids on polar carriers by small-angle neutron scattering by M.V. Avdeev; V.L. Aksenov; M. Balasoiu; V.M. Garamus; A. Schreyer; Gy. Török; L. Rosta; D. Bica; L. Vékás (100-107).
Results of experiments on small-angle neutron scattering from ferrofluids on polar carriers (pentanol, water, methyl-ethyl-ketone), with double-layer sterical stabilization of magnetic nanoparticles, are reported. Several types of spatial structural organization are observed. The structure of highly stable pentanol-based samples is similar to that of stable ferrofluids based on organic non-polar carriers (e.g., benzene) with mono-layer covered magnetic nanoparticles. At the same time, the effect of the interparticle interaction on the scattering is stronger in polar ferrofluids because of the structural difference in the surfactant shell. The structure of the studied methyl-ethyl-ketone- and water-based ferrofluids essentially different from the previous case. The formation of large (>100 nm in size) elongated or fractal aggregates, respectively, is detected even in the absence of external magnetic field, which corresponds to weaker stability of these types of ferrofluids. The structure of the fractal aggregates in water-based ferrofluids does not depend on the particle concentration, but it is sensitive to temperature. A temperature increase results in a decrease in their fractal dimension reflecting destruction of the aggregates. In addition, in water-based ferrofluids these aggregates consist of small (radius ∼10 nm) and temperature-stable primary aggregates.Small-angle neutron scattering is applied to study particle structure and interaction in ferrofluids on polar carriers such as pentanol (figure), water and methyl-ethyl-ketone.
Keywords: Ferrofluids; Magnetic fluids; Sterical stabilization; Small-angle neutron scattering; Aggregation;
Mono-layer of Ni100−x Fe x nanoparticles fabricated on a polyimide film under different curing atmospheres by Sung K. Lim; Ik S. Chun; Ki S. Ban; Chong S. Yoon; Chang K. Kim; Young H. Kim (108-114).
A mono-layer of nano-sized metal particles was prepared on the surface of a polyimide film by simply depositing a thin film of Ni80Fe20 on top of the polyamic acid that was spin coated onto a Si wafer. During thermal imidization of the polyamic acid film, Fe was selectively etched by reacting with the carbonyl group of the polyamic acid to leave behind uniformly distributed Ni-rich metallic particles. The average diameter of the particles was 4 nm and the particles were confined into a single layer on top of the polymer film. Moreover, it was also shown that the morphology of the nanoparticles can be substantially altered by curing the precursor film in a hydrogen atmosphere, without significantly damaging the polymer film. Thus produced nanoparticles lay exposed on top of the electrically insulating and chemically stable polymer film so that it is possible that the nanoparticles can be directly used for fabricating a nonvolatile flash memory device or as a template for building functional nano-structures.A mono-layer of nano-sized metal particles was prepared on the surface of a polyimide film by simply depositing a thin film of Ni80Fe20 on top of the polyamic acid.
Keywords: Metallic nanoparticle; Polyimide; Ni rich nanoparticle; Selective reaction; XPS; H2 atmosphere;
The effect of humic acid adsorption on pH-dependent surface charging and aggregation of magnetite nanoparticles by E. Illés; E. Tombácz (115-123).
The pH-dependent adsorption of humic acid (HA) on magnetite and its effect on the surface charging and the aggregation of oxide particles were investigated. HA was extracted from brown coal. Synthetic magnetite was prepared by alkaline hydrolysis of iron(II) and iron(III) salts. The pH-dependent particle charge and aggregation, and coagulation kinetics at pH ∼ 4 were measured by laser Doppler electrophoresis and dynamic light scattering. The charge of pure magnetite reverses from positive to negative at pH ∼ 8 , which may consider as isoelectric point (IEP). Near this pH, large aggregates form, while stable sols exist further from it. In the presence of increasing HA loading, the IEP shifts to lower pH, then at higher loading, magnetite becomes negatively charged even at low pHs, which indicate the neutralization and gradual recharging positive charges on surface. In acidic region, the trace HA amounts are adsorbed on magnetite surface as oppositely charged patches, systems become highly unstable due to heterocoagulation. Above the adsorption saturation, however, the nanoparticles are stabilized in a way of combined steric and electrostatic effects. The HA coated magnetite particles form stable colloidal dispersion, particle aggregation does not occur in a wide range of pH and salt tolerance is enhanced.Magnetic separation of magnetite nanoparticles is hindered as shown in vials (Nd–Fe–B magnet between them) containing large (left) and trace (right) amount of humic acid in salty medium.
Keywords: Iron oxide; Magnetite; Humic acid; Adsorption; Surface modification; Colloidal stability; Heterocoagulation; Aggregation; Magnetic separation;
The effects of unequal ionic sizes for an electrolyte in a charged slit by Jiang Yu; Gabriel E. Aguilar-Pineda; A. Antillón; Shi-Hai Dong; M. Lozada-Cassou (124-134).
The modified Gouy–Chapman (MGC) theory has been used to study the electrical double layer near two charged plates immersed in a model electrolyte. The effects of assigning to the cations and anions different distances of closest approach to the charged surfaces are examined. The dependence of overcharging and charge reversal on the system parameters such as concentration, ion size and valence, is investigated both inside and outside the charged slit.
Keywords: Electrical double layer; Unequal ionic sizes; Overcharging; Charge reversal;
Sequestered carbon on clay mineral probed by electron paramagnetic resonance and X-ray photoelectron spectroscopy by Kátia Cylene Lombardi; Antonio Salvio Mangrich; Fernando Wypych; Ubirajara Pereira Rodrigues-Filho; José L. Guimarães; Wido H. Schreiner (135-140).
This paper describes the interaction among soil organic matter components with kaolinite, an important clay mineral present in tropical soils, especially in Brazil. XPS data show that the soil organic matter adsorbed on kaolinite has aromatic and aliphatic structures, with phenolic and/or alcoholic functions and carbonyl carbons (C＝O) of amide and/or carboxylic groups. The N1s spectrum of the kaolinite shows an asymmetric peak that is assigned to amide and protonated ammines probably from humin. The interaction between them is strong enough to resist chemical oxidative or reductive attack besides loose amide functionalities. EPR data show that reductive treatment reduces some Fe3+ of the kaolinite structure, loosing organic components. A schematic representation of the reduction of structural Fe3+ in the concentrated domains and consequently increased concentration of Fe3+ ions in diluted domains of the spectrum is presented. This reinforces the hypothesis that humin is a stable carbon sink in soils when adsorbed to clays.This paper describes the interaction among soil organic matter components with kaolinite, an important clay mineral present in tropical soils, especially in Brazil. XPS data show that the soil organic matter adsorbed on kaolinite has aromatic and aliphatic structures, with phenolic and/or alcoholic functions and carbonyl carbons (C＝O) of amide and/or carboxylic groups. The N1s spectrum of the kaolinite shows an asymmetric peak that is assigned to amide and protonated ammines probably from humin. The interaction between them is strong enough to resist chemical oxidative or reductive attack besides loose amide functionalities. EPR data show that reductive treatment reduces some Fe3+ of the kaolinite structure, loosing organic components. A schematic representation of the reduction of structural Fe3+ in the concentrated domains and consequently increased concentration of Fe3+ ions in diluted domains of the spectrum is presented. This reinforces the hypothesis that humin is a stable carbon sink in soils when adsorbed to clays.
Keywords: Kaolinite; Humin; EPR; XPS;
Preparation of alkaline earth phosphates with sol containing sodium alginate and sodium diphosphate by Shigeru Sugiyama; Minako Fujii; Kazuya Fukuta; Kazunori Seyama; Ken-Ichiro Sotowa; Naoya Shigemoto (141-147).
Magnesium hydrogen phosphate, calcium hydroxyapatite, and strontium hydroxyapatite were successfully prepared from sol consisting of sodium alginate and Na4P2O7 with Mg2+, Ca2+, and Sr2+ in the corresponding nitrates, respectively. It is revealed that the order of the addition of those substrates and the role of sodium alginate are important factors for the preparation of desired phosphate compounds. According to the previous paper on the preparation of calcium hydroxyapatite, sodium alginate was mixed with aqueous Na4P2O7, followed by the addition of the aqueous divalent cations, resulting in the poor formation of the target phosphates. However, as a revised sol–gel technique, sodium alginate was added to the mixture of Na4P2O7 and aqueous Mg2+ and Sr2+, resulting in a rather favorable formation of MgHPO4 and strontium hydroxyapatite, respectively, while the sol thus obtained was stable within a few days. However for aqueous Ca2+, calcium hydroxyapatite could not be obtained through the revised sol–gel technique. In the preparation of magnesium hydrogen phosphate, sodium alginate contributes mainly to the sol formation of the precursor. The ion exchange between Na+ in sodium alginate and aqueous Ca2+ was important for the preparation of calcium hydroxyapatite. In contrast, the reaction of sodium alginate with the mixture of Na4P2O7 and aqueous Sr2+ afforded strontium hydroxyapatite at the specific ratio of those three substrates. The structure of calcium and strontium phosphates prepared from the revised sol–gel process evidently depended on the amount of sodium alginate introduced into the mixture of Na4P2O7 and the corresponding divalent cations.
Keywords: Sol–gel; Sodium alginate; Alkaline earth phosphates; Apatites;
Solid-state storage of Ag nanoparticles in anion exchange resin beads and their recovery by S. Manikandan; G. Majumdar; D. Chowdhury; A. Paul; Arun Chattopadhyay (148-154).
This paper reports the idea and describes a method of reversible storage and recovery of silver nanoparticles (NPs) in anion exchange resin beads based on the principle of ion exchange. We also report that similar exchange of NPs was not possible with cation exchange resins. The Ag NPs were stored by simple exchange of anions of the resins, which were activated with OH− and NO− 3 ions. FTIR spectroscopic measurements support that the Ag NPs were exchanged with NO− 3 ions in the resins. The so-stored NPs could be regenerated by addition of NaBH4 solution to the resins. These NPs were recovered and subsequently utilized for catalytic reduction of an organic dye (eosin). Powder X-ray diffraction (XRD) pattern indicated storage of the NPs in the form of various oxides of silver in the resin, with the peak value of intensity corresponding to XRD of the NPs not changing with time. Scanning electron microscopic measurements show that the NPs in the beads were stable for over a month without the formation of any apparent agglomeration.Ag nanoparticles (NPs) could be stored in anion exchange resin beads in the form of their oxides and then again recovered back into Ag NPs using sodium borohydride.
Keywords: Anion exchange resins; Ag nanoparticles; Catalysis; Nanomaterials; Storage; UV–vis spectroscopic methods;
Potentiometric behavior of ion-selective electrodes to large cationic species modulated by decyl alcohol by Walton J. Cabrera; Marianne A. Kaempfe; Marcela D. Urzúa; Hernán E. Ríos (155-158).
The effect of 1-decanol on the potentiometric response of three ion-selective electrodes to large cationic species is analyzed. The electrodes were constructed with plasticized PVC membranes. The results suggest that 1-decanol alters the ionic transport through the membrane/water interface to an extent that depends on the strength of the active ion pair. The water solubility of the cation, its molecular weight, and the size of the ion pair seem to be relevant factors in this type of behavior. The potentiometric selectivity coefficients are also dependent on the presence of 1-decanol in the membrane. These results are similar to those already described in ion-selective electrodes with membranes capable of sensing anionic benzene sulfonate-type systems. Thus, the effect of the alcohol appears to be general by affecting mainly the membrane surface polarity.
Keywords: Ion-selective electrodes; Papaverine; Procaine; Lidocaine; 1-Decanol; Doping agent;
Kinetics of heterogeneous photocatalytic degradation of reactive dyes in an immobilized TiO2 photocatalytic reactor by Niyaz Mohammad Mahmoodi; Mokhtar Arami; Nargess Yousefi Limaee; Nooshin Salman Tabrizi (159-164).
The photocatalytic degradation of two reactive dyes has been investigated by UV/TiO2/H2O2 using an immobilized TiO2 photocatalytic reactor. Reactive Blue 8 (RB 8) and Reactive Blue 220 (RB 220) textile dyes were used as model compounds. Photocatalytic degradation processes were performed using a 5-L solution containing dyes. The initial concentrations of dyes were 50 mg/L. The radiation source was two 15 W UV-C lamps. A batch mode immersion photocatalytic reactor was utilized. UV–vis and ion chromatography (IC) analyses were employed to obtain the details of the photodegradation of the selected dyes. Colored synthetic waters were completely decolorized in relatively short time after UV irradiation in the presence of various concentrations of hydrogen peroxide. Formate, acetate, oxalate, and glyoxylate anions were detected as dominant aliphatic intermediates where they were further oxidized slowly to CO2. The UV/TiO2/H2O2 process was able to oxidize the dyes with partial mineralization of carbon, nitrogen, and sulfur heteroatoms into CO2, NO− 3, and SO2− 4, respectively. Kinetics analysis indicates that the photocatalytic decolorization rates of the dye can be approximated by a pseudo-first-order model. The UV/TiO2/H2O2 process proved to be capable of decolorization and mineralization of the reactive dyes (RB 8 and RB 220).This paper deals with the photocatalytic degradation of two reactive dyes (Reactive Blue 8 (RB 8) and Reactive Blue 220 (RB 220)) using immobilized TiO2 photocatalytic reactor.
Keywords: Reactive dyes; Decolorization; Mineralization; Kinetics; Photocatalysis;
The influence of the preparation method and the Co loading on the structure and activity of cobalt oxide/γ-alumina catalysts for NO reduction by propene by Athanasios Sarellas; Dimitrios Niakolas; Kyriakos Bourikas; John Vakros; Christos Kordulis (165-172).
In the present work we studied the influence of the preparation method and the Co loading on the physicochemical properties and the catalytic activity of the cobalt oxide/γ-alumina catalysts for the reduction of NO by propene under net oxidizing conditions. Two series of catalysts containing 1 and 5% w/w Co, respectively, were prepared using three preparation methods, namely, the equilibrium deposition filtration (EDF), the conventional incipient wetness impregnation (IWI) and the IWI adding nitrilotriacetic acid (nta) in the impregnating solution (IWInta). The catalysts were tested at various temperatures in the range 300–550 °C using a fixed-bed microreactor for the NO reduction by propene under lean burn conditions. The evolution of the Co species on the alumina surface was followed after each preparation step by diffuse reflectance spectroscopy (DRS). It was found that the catalysts of the first series were more active for the title reaction than those of the second one. The EDF sample of the first series was proved to be the most active and selective one followed by the IWI and then the IWInta sample of the same series. The DRS results indicated that the enhanced activity and selectivity of the EDF sample could be attributed to the increased concentration of isolated Co(II) inner sphere complexes of octahedral coordination, which are formed on the support surface by adsorption of the corresponding aqueous complexes, [Co(H2O)6]2+, being in the impregnating solution. These inner sphere complexes are transformed upon thermal treatment into a CoAl2O4 like phase with high dispersion. On the other hand, the [Co(H2O)6]2+(NO3)2− and [ Co - nta ] − ⋅ NH 4 + (or H+) and/or [ Co - 2nta ] 4 + ⋅ 4 NH 4 + (or 4H+) complex salts, precipitated on the alumina surface upon drying in the cases of the IWI and IWInta samples, are transformed upon calcination into CoAl2O4 like phases with lower dispersion. All the samples of the second series promoted the propene combustion as well as the oxidation of NO and N2, used as carrier gas, to NO2. DRS results revealed that in all these samples cobalt(III) oxo species are formed in addition to the CoAl2O4 phase. These species are considered to be responsible for the enhancement of the rates of the oxidation reactions mentioned above.1% w/w Co/Al2O3 catalysts prepared with equilibrium deposition filtration (EDF) (a), incipient wetness impregnation (IWI) (b), IWI in the presence of nitrilotriacetic acid (c), and γ-Al2O3 support (d) for the HC-SCR of NO. F ( R ) EDF < F ( R ) IWI < F ( R ) IWInta . Dispersion of CoAl2O4: EDF > IWI >IWInta. Activity for the HC-SCR of NO: EDF > IWI > IWInta.
Keywords: Cobalt oxide catalysts; Preparation method; Equilibrium adsorption; Lean burn; SCR; NO reduction; DRS;
Acid–base properties of bentonite rocks with different origins by Noémi M. Nagy; József Kónya (173-180).
Five bentonite samples (35–47% montmorillonite) from a Sarmatian sediment series with bentonite sites around Sajóbábony (Hungary) is studied. Some of these samples were tuffogenic bentonite (sedimentary), the others were bentonitized tuff with volcano sedimentary origin. The acid–base properties of the edge sites were studied by potentiometric titrations and surface complexation modeling. It was found that the number and the ratio of silanol and aluminol sites as well as the intrinsic stability constants are different for the sedimentary bentonite and bentonitized tuff. The characteristic properties of the edges sites depend on the origins. The acid–base properties are compared to other commercial and standard bentonites.
Keywords: Acid–base properties; Bentonite; Montmorillonite; Surface complexation;
Design and interfacial behavior of two series of gemini amphiphiles with different charge positions based on imidazole moiety by Xiaodong Zhai; Minghua Liu (181-187).
Two series of gemini amphiphiles based on 2-heptadecylimidazole were designed. One is exo-BisImC17Cn ( n = 2 , 4, 6, 8, 10), in which the positive charges are positioned on the outsides of the headgroups. The other is endo-BisImC17Cn ( n = 2 , 4, 6, 8, 10), whose positive charges are localized on the insides of the headgroups. The interfacial behavior at the air/water interface of these gemini amphiphiles was investigated in relation to the effect of the charge position and the spacer length. Monolayers of exo-BisImC17Cn show small differences in interfacial behavior when spread on water and aqueous Na2SO4 subphases. In contrast, significant distinctions were observed for molecules of endo-BisImC17Cn. The limiting areas of endo-BisImC17Cn monolayers on water are obviously larger than those on the aqueous Na2SO4 solution. While the limiting areas of the exo-BisImC17Cn monolayers increased monotonically with the spacer length, those of the endo-BisImC17C10 monolayer on Na2SO4 solution is obviously smaller than those of endo-BisImC17C6 and endo-BisImC17C8 monolayers, suggesting the wicket conformation of the alkyl chain in endo-BisImC17C10. On the other hand, both of the gemini amphiphiles could form complex monolayers with negatively charged TPPS at the air/water interface. The transferred complex multilayer films of the gemini amphiphiles/TPPS showed supramolecular chirality, although both of the gemini amphiphiles and TPPS are achiral. The exciton couplet was observed for the endo-BisImC17Cn/TPPS films, while no couplet was detected for the exo-BisImC17Cn/TPPS films. A reasonable comparison between the two series of geminis in relation to the effect of charge positions and the spacer lengths on the interfacial behavior and the supramolecular chirality was performed.Two series of gemini amphiphiles with positive charges localized in the exo and endo positions were designed and obvious different interfacial behaviors were found.
Keywords: Gemini amphiphile; Monolayer; Langmuir–Blodgett film; Supramolecular chirality;
Nuclear magnetic resonance diffusion with surface relaxation in porous media by A. Valfouskaya; P.M. Adler; J.-F. Thovert; M. Fleury (188-201).
Nuclear magnetic resonance (NMR) diffusion simulations with surface relaxation were performed numerically in unconsolidated and consolidated porous media by a random walk technique. Two uniform and nonuniform models of surface relaxation were proposed and compared. The apparent diffusion coefficient and extinction function were determined and studied in the fast, slow and intermediate diffusion regimes of relaxation. According to theoretical predictions, it was observed that the extinction function does not depend on surface relaxivity parameter ρ 2 in the slow diffusion regime. The apparent diffusion coefficients are independent of ρ 2 in the fast diffusion regime and tend to be superposed onto a single curve in the slow one. The evolution of the apparent diffusion coefficients is gathered by a reduced representation in the fast diffusion regime.Diffusion simulations with surface relaxation were performed numerically in unconsolidated (a) and consolidated porous media (b) by random walks resulting in apparent diffusion coefficients (c).
Keywords: Porous media; NMR; Diffusion;
Influence of cationic surfactant removal on the thermal stability of organoclays by Hongping He; Jannick Duchet; Jocelyne Galy; Jean-François Gérard (202-208).
The microstructure, thermal stability, surface energy, and swelling characteristics of two kinds of commercial organoclays, before and after washing treatment with a mixture of H2O/ethanol, were investigated using X-ray diffraction (XRD), thermogravimetric analysis (TG/DTG), wettability measurement, and swelling measurement. This study demonstrates that the external-surface physically adsorbed surfactant can be removed after washing treatment, resulting in an increase in thermal stability and a decrease in surface energy of the resultant organoclays. Organoclays are difficult to be introduced into a solvent when their surface energies are lower than that of the solvent. On the other hand, the organoclay with γ organoclay < γ solvent is easier to be swollen and expandable by the solvent. The swelling and basal spacing measurements of the organoclays introduced into organic media indicate that the swelling factor and the interlayer swelling are two independent parameters. Both the polar character of the solvent and the swelling capacity of clay have a prominent effect on the interlayer swelling of the organoclays.The thermal stability and swelling characteristics of two commercial organoclays, before and after washing with a mixture of H2O/ethanol, were investigated using XRD, TG/DTG, wettability and swelling measurements. The external-surface physically adsorbed surfactant can be removed after washing treatment, resulting in an increase in thermal stability. The swelling and basal spacing measurements of the organoclays introduced into organic media indicate that the swelling factor and the interlayer swelling are two independent parameters. Both the polar character of the solvent and the swelling capacity of clay have a prominent effect on the interlayer swelling of the organoclays.
Keywords: Organoclay; Organic solvent; Surface energy; Swelling factor; Interlayer swelling; X-ray diffraction; Thermogravimetric analysis;
Adsorption and phase transition of alkanol and fluoroalkanol at electrified mercury/aqueous solution interface by Ryo Murakami; Hiroyasu Sakamoto; Yoshiteru Hayami; Hiroki Matsubara; Takanori Takiue; Makoto Aratono (209-217).
The adsorption behavior and the phase transition of alkanol and fluoroalkanol at the electrified mercury/aqueous solution interface were investigated by the interfacial tension measurements and the thermodynamic analysis. In the alkanol system, it is found that the phase transitions in low interfacial densities occur: the ones from the zero adsorption to the gaseous or the expanded state and the gaseous to the expanded state at the electrified interface depending on the electrostatic nature as well as the concentration in the bulk phase. These phase transitions were verified by the thermodynamic equations derived by the assumption of coexistence of two phases at the electrified interface. Furthermore the distribution of ionic species in the interfacial region is discussed on the basis of dependence of the interfacial charge density of solution phase on an applied potential. Fluoroalkanol, on the other hand, was practically not adsorbed at the electrified interface within this experimental condition. The zero adsorption of fluoroalkanol molecules suggests the driving force of the adsorption may be the interaction hydrophobic group of alcohol molecule and mercury.
Keywords: Alkanol; Fluoroalkanol; Adsorption; Phase transition; Thermodynamics; Electrocapillary curve; Electrified interface; Distribution of ions;
A model for foam formation, stability, and breakdown in glass-melting furnaces by John van der Schaaf; Ruud G.C. Beerkens (218-229).
A dynamic model for describing the build-up and breakdown of a glass-melt foam is presented. The foam height is determined by the gas flux to the glass-melt surface and the drainage rate of the liquid lamellae between the gas bubbles. The drainage rate is determined by the average gas bubble radius and the physical properties of the glass melt: density, viscosity, surface tension, and interfacial mobility. Neither the assumption of a fully mobile nor the assumption of a fully immobile glass-melt interface describe the observed foam formation on glass melts adequately. The glass-melt interface appears partially mobile due to the presence of surface active species, e.g., sodium sulfate and silanol groups. The partial mobility can be represented by a single, glass-melt composition specific parameter ψ. The value of ψ can be estimated from gas bubble lifetime experiments under furnace conditions. With this parameter, laboratory experiments of foam build-up and breakdown in a glass melt are adequately described, qualitatively and quantitatively by a set of ordinary differential equations. An approximate explicit relationship for the prediction of the steady-state foam height is derived from the fundamental model.
Keywords: Foam; Model; Glass; Viscous; Dynamic; Surface; Mobility;
Percolation phenomenon in mixed reverse micelles: The effect of additives by Bidyut K. Paul; Rajib K. Mitra (230-242).
The conductivity of AOT/IPM/water reverse micellar systems as a function of temperature, has been found to be non-percolating at three different concentrations (100, 175 and 250 mM), while the addition of nonionic surfactants [polyoxyethylene(10) cetyl ether (Brij-56) and polyoxyethylene(20) cetyl ether (Brij-58)] to these systems exhibits temperature-induced percolation in conductance in non-percolating AOT/isopropyl myristate (IPM)/water system at constant compositions (i.e., at fixed total surfactant concentration, ω and X nonionic ). The influence of total surfactant concentration (micellar concentration) on the temperature-induced percolation behaviors of these systems has been investigated. The effect of Brij-58 is more pronounced than that of Brij-56 in inducing percolation. The threshold percolation temperature, T p has been determined for these systems in presence of additives of different molecular structures, physical parameters and/or interfacial properties. The additives have shown both assisting and resisting effects on the percolation threshold. The additives, bile salt (sodium cholate), urea, formamide, cholesteryl acetate, cholesteryl benzoate, toluene, a triblock copolymer [(EO)13(PO)30(EO)13, Pluronic, PL64], polybutadiene, sucrose esters (sucrose dodecanoates, L-1695 and sucrose monostearate S-1670), formamide distinctively fall in the former category, whereas sodium chloride, cholesteryl palmitate, crown ether, ethylene glycol constitute the latter for both systems. Sucrose dodecanoates (L-595) had almost marginal effect on the process. The observed behavior of these additives on the percolation phenomenon has been explained in terms of critical packing parameter and/or other factors, which influence the texture of the interface and solution properties of the mixed reverse micellar systems. The activation energy, E p for the percolation process has been evaluated. E p values for the AOT/Brij-56 systems have been found to be lower than those of AOT/Brij-58 systems. The concentration of additives influence the parameters T p and E p for both systems. A preliminary report for the first time on the percolation phenomenon in mixed reverse micelles in presence of additives has been suggested on the basis of these parameters ( T p and E p ).
Keywords: Mixed reverse micelles; Threshold percolation temperature; Activation energy; Additive effects; AOT; Isopropyl myristate;
Interactions between zwitterionic and conventional anionic and cationic surfactants by Aleisha A. McLachlan; D. Gerrard Marangoni (243-248).
Critical micelle concentration (cmc) values have been determined for the mixed zwitterionic/anionic surfactant systems of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12)/sodium dodecyl sulfate (SDS), N-dodecyl-N,N-(dimethylammonio)butyrate (DDMAB)/SDS, N-octyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-08)/sodium octyl sulfate (SOS), and the zwitterionic/cationic systems of ZW3-12/dodecyltrimethylammonium bromide (DTAB), DDMAB/DTAB. Conductivity studies and nuclear magnetic resonance (NMR) spectroscopy were the methods employed for cmc determinations. The degree of nonideality of the interaction in the micelle ( β m ), for each system, was determined according to Rubingh's nonideal solution theory. Evidence was found for the existence of strong interactions between zwitterionic and anionic surfactants in each of the zwitterionic/anionic systems. The ZW3-08/SOS and DDMAB/SDS systems behaved synergistically at all mole fractions studied while the ZW3-12/SDS system exhibited synergistic behavior above mole fractions of 0.30. Greater negative deviations from ideal behavior were demonstrated in the DDMAB/SDS system than in the other two zwitterionic/anionic systems. The zwitterionic/cationic systems of ZW3-12/DTAB and ZW3-08/OTAB displayed only slight deviations from ideal behavior, therefore indicating near ideal mixing.
Keywords: Mixed micelles; Surfactants; Critical micelle concentration; Synergistic effects;
Adsorption behaviour of lactoferrin in oil-in-water emulsions as influenced by interactions with β-lactoglobulin by Aiqian Ye; Harjinder Singh (249-254).
Oil-in-water emulsions (pH 7.0 or pH 3.0) containing 30 wt% soya oil and various concentrations of lactoferrin were made in a two-stage valve homogenizer. The average droplet size ( d 32 ), the surface protein coverage (mg/m2) and composition, and the ζ-potential of the emulsions were determined. The value of d 32 decreased with increasing lactoferrin concentration up to 1%, and then was almost independent of lactoferrin concentration beyond 1% at both pH 7.0 and pH 3.0. The surface protein coverage of the emulsions made at pH 7.0 increased almost linearly with increasing lactoferrin concentration from 0.3 to 3%, but increased only slightly in emulsions made at pH 3.0 at lactoferrin concentrations >1%. The surface protein coverage of the emulsions made at pH 3.0 was lower than that of the emulsions made at pH 7.0 at a given protein concentration. The emulsion droplets had a strong positive charge at both pH 7.0 and pH 3.0, indicating that stable cationic emulsion droplets could be formed by lactoferrin alone. When emulsions were formed with a mixture of lactoferrin and β-lactoglobulin (β-lg) (1:1 by weight), the charge of the emulsion droplets was neutralized at pH 7.0 suggesting the formation of electrostatic complexes between the two proteins. The composition of the droplet surface layer showed that both proteins were adsorbed, presumably as complexes, from the aqueous phase at pH 7.0 in equal proportions, whereas competitive adsorption occurred between lactoferrin and β-lg at pH 3.0. At this pH, β-lg was adsorbed in preference to lactoferrin at low protein concentrations (⩽1%), whereas lactoferrin appeared to be adsorbed in preference to β-lg at high protein concentrations.Formation of electrostatic complexes between β-lactoglobulin and lactoferrin affects their adsorption behavior in oil–water emulsions which in turn determines the ζ-potential of oil droplets. The ζ-potential of emulsion droplets made with 30 wt% soya oil and a mixture of lactoferrin and β-lg (1:1 by weight) at pH 7.0 (●) and 3.0 (○), as well as β-lg alone (▴) at pH 7.0, as a function of the total protein concentration.
Keywords: Cationic emulsion; Lactoferrin; β-Lactoglobulin; Adsorption; Positive charge;
Different sources of 4-aminophthalimide solvation dynamics retardation inside micellar systems by Andrzej Maciejewski; Jacek Kubicki; Krzysztof Dobek (255-263).
The solvation dynamics of 4-aminophthalimide (4-AP) in two micellar systems (cetyltrimethylammonium bromide (M-CTAB) and Triton X-100 (M-TX-100)) has been studied. The results presented are in agreement with our earlier findings in sodium dodecyl sulfate (M-SDS) micelle (J. Phys. Chem. B 107 (2003) 13,986, J. Phys. Chem. B 109 (2005) 9422). They have confirmed that the main reason for the observed shape and position of the time changes in 4-AP time-resolved emission spectra (TRES) is the process of establishing a new equilibrium between two emissive species present in micellar systems, the excited 4-AP in the intramolecular charge transfer state (S1-ICT) and the exciplex formed between 4-AP in the S1-ICT state and water molecules dissolved inside micelles. In M-TX-100 and in M-CTAB this process has been found to be slower than in the earlier studied M-SDS. The presence of two emitting species has been concluded on the basis of observation of the isoemissive point in the time-resolved area-normalized emission spectra (TRANES) of 4-AP in micellar systems studied. It has been shown that the distance between the 4-AP molecule and the water molecules present inside the micelles can be one of the parameters responsible for the long-time duration of the exciplex formation and solvation process in the micelles.Sources of changes of 4-AP TRANES in M-CTAB and M-TX-100 micelles.
Keywords: Micelles; Time resolved emission spectra; Solvation dynamics; 4-Aminophthalimide;
Spectroscopic techniques applied to the study of laminin fragments inserted into model membranes by E. Crosas; M.A. Egea; F. Reig (264-269).
The influence of four laminin-derived peptides on bilayer organization is studied. Spectroscopic methods applied were based on pyrene fluorescence properties (quenching, I1/I3, and monomer/excimer equilibrium), asymmetric membrane fluorescence (NBD-PE/dithionite), and polarization fluorescence (TMA-DPH). Also, the ability of these peptides to release carboxyfluorescein entrapped in vesicles was determined. Results suggest that these peptides do not noticeably modify the packing and motion of lipids (in the gel state), but coat its surface, preventing penetration of quenchers and chemical reactants. Nevertheless, their presence promotes a soft release of entrapped CF after incubation at 37 °C.
Keywords: Laminin; Peptides; Liposomes; Fluorescence; Quenching;
Electrorheological properties of polyaniline suspensions: Field-induced liquid to solid transition and residual gel structure by Piyanoot Hiamtup; Anuvat Sirivat; Alexander M. Jamieson (270-278).
Polyaniline (PANI) was synthesized via oxidative coupling polymerization in acid conditions and de-doped in solution of ammonia. The electrorheological (ER) properties of the PANI/silicone oil suspensions were investigated in oscillatory shear as functions of electric field strength, particle concentration, and host fluid viscosity. Consistent with literature, the PANI ER fluid exhibits viscoelastic behavior under the applied electric field and the ER response is strongly enhanced with increasing electric field strength and particle concentration. The dynamic moduli, G ′ and G ″ increase dramatically, by 5 orders of magnitude, as the electric field strength is increased to 2 kV/mm. A viscoelastic liquid to solid transition occurs at a critical electric field strength, in the range E c = 50 – 200 V / mm , whose value depends on particle concentration and host fluid viscosity. The fibrillar structure formed in the presence of the applied field has a static yield strength τ y , whose value scales with electric field strength as τ y ∼ E 1.88 . When the field is switched off a residual structure remains, whose yield stress increases with the strength of the applied field and particle concentration. When the applied stress exceeds the yield stress of the residual structure, fast, fully reversible switching of the ER response is obtained.Under action of electric field, the fibrillar structures are formed within polyaniline suspension which will remain when the field is switched off unless shear stress exceeding the yield stress of the residual structure is applied.
Keywords: Electrorheological fluid; Conductive polymer; Polyaniline; Sol to gel transition;
Sedimentation of a concentrated dispersion of composite colloidal particles by Eric Lee; Kuang-Ting Chou; Jyh-Ping Hsu (279-290).
The sedimentation of a concentrated spherical dispersion of composite particles, where a particle comprises a rigid core and a membrane layer containing fixed charge, is investigated theoretically. The dispersion is simulated by a unit cell model, and a pseudo-spectral method based on Chebyshev polynomials is adopted to solve the problem numerically. The influences of the thickness of double layer, the concentration of particles, the surface potential of the rigid core of a particle, and the amount of fixed charge in the membrane layer on both the sedimentation potential and the sedimentation velocity are discussed. Several interesting results are observed; for example, depending upon the charged conditions on the rigid core and in the membrane layer of a particle, the sedimentation potential might have both a local maximum and a local minimum and the sedimentation velocity can have a local minimum as the thickness of double layer varies. Also, the sedimentation velocity can have a local maximum as the surface potential varies. We show that the sedimentation potential increases with the concentration of particles. The relation between the sedimentation velocity and the concentration of particles, however, depends upon the thickness of double layer.Sedimentation of a concentrated dispersion of composite colloidal particles, cell model.
Keywords: Sedimentation; Concentrated spherical dispersion; Composite particle; Double-layer polarization; Double-layer overlapping;
Comment on “Preparation and electrorheological property of rare earth modified amorphous Ba x Sr1−x TiO3 gel electrorheological fluid” by H.J. Choi; I.S. Lee; J.H. Sung; B.J. Park; M.S. Jhon (291-293).
The comments on the recent results on electrorheological (ER) property of rare earth modified amorphous barium strontium titanate gel based ER fluid are given via analysis of its dynamic yield stress data as a function of applied electric field strengths. Using our previously reported universal yield stress equation, we obtained the critical electric field strength and collapsed their data onto a single curve.
Keywords: Electrorheological fluid; Yield stress; Rare earth; Polarization model;
A simple FTIR technique for estimating the surface area of silica powders and films by Ben McCool; Lawrence Murphy; Carl P. Tripp (294-298).
A simple technique using FTIR spectroscopy to estimate the surface area of porous and non-porous silica powders is presented. The surface area is estimated by comparing the integrated area of the band due to isolated silanol groups on different silicas. We have found that by using a fumed silica as a calibrant, an accuracy of about 7% in the surface area of several silica materials is obtained when compared to the surface area computed by BET nitrogen adsorption techniques. The FTIR technique for computing surface area is simple and takes very little time to complete the analysis. The principle advantage of this method is that it enables surface area measurements of silica films on porous supports. To the best of our knowledge, there are no other methods that provide this information.
Keywords: Surface area; Silica; Infrared spectroscopy;
Surface functionalization of mesoporous and microporous activated carbons by immobilization of diamine by Hisashi Tamai; Katsumi Shiraki; Takeshi Shiono; Hajime Yasuda (299-302).
The introduction of amino groups on HNO3-treated microporous (ACmicro-At) and mesoporous (ACmeso-At) activated carbon, which was followed by thionyl chloride (SOCl2) treatment, by immobilization of diamine compounds was investigated in terms of change in pore characteristics. The immobilization was improved by treatment with SOCl2. The BET surface area of ACmicro-At largely decreased by immobilization of ethylenediamine (EDA) and hexamethylenediamine (HMDA). Decreases in BET surface area and pore volume of ACmeso-At by immobilization of EDA and HMDA were scarcely observed. These results suggest that amino groups introduced to mesoporous activated carbon are effective as functional groups for additional reactions.
Keywords: Activated carbon; Chemical treatment; Diamine immobilization;