Journal of Colloid And Interface Science (v.307, #1)
Selective adsorption of refractory sulfur species on active carbons and carbon based CoMo catalyst
by Hamdy Farag (pp. 1-8).
Adsorption technique could be a reliable alternative in removing to a certain remarkable extent the sulfur species from the feedstock of petroleum oil. The performance of various carbons on adsorption of model sulfur compounds in a simulated feed solution and the sulfur containing compounds in the real gas oil was evaluated. The adsorption experiments have been carried out in a batch scale at ambient temperature and under the atmospheric pressure. In general, the most refractory sulfur compounds in the hydrotreatment reactions were selectively removed and adsorbed. It was found that the adsorbents affinities to dibenzothiophene and 4,6-dimethyldibenzothiophene were much more favored and pronounced than the aromatic matrices like fluorene, 1-methylnaphthalene and 9-methylanthracene. Among the sulfur species, 4,6-dimethyldibenzothiophene was the highest to be removed in terms of both selectivity and capacity over all the present adsorbents. The studied adsorbents showed significant capacities for the polyaromatic thiophenes. The electronic characteristics seem to play a certain role in such behavior. Regeneration of the used adsorbent was successfully attained either by washing it with toluene or by the release of the adsorbates through heat treatment. A suggested adsorptive removal process of sulfur compounds from petroleum distillate over carbon supported CoMo catalyst was discussed.Simultaneous combination of both adsorption and hydrodesulfurization could be a promise process for obtaining ultra low sulfur fuel. Bi-functional catalyst is necessary in applying such approach.
Keywords: Adsorption; Dibenzothiophene; 4,6-Dimethyldibenzothiophene; Gas oil; Hydrodesulfurization; Process
Removal of basic dyes from aqueous solutions with a treated spent bleaching earth
by Mohamed Mana; Mohand-Said Ouali; L.C. de Menorval (pp. 9-16).
A spent bleaching earth from an edible oil refinery was treated by impregnation with a normal sodium hydroxide solution followed by mild thermal treatment (100 °C). The obtained material (TSBE) was washed, dried, and characterized by X-ray diffraction, FTIR, SEM, BET, and thermal analysis. The clay structure was not apparently affected by the treatment and the impregnated organic matter was quantitatively removed. We have investigated the comparative sorption of safranine and methylene blue on this material, the spent bleaching earth (SBE), and the virgin bleaching earth (VBE). The kinetic results fit the pseudo-second-order kinetic model and the Weber and Morris intraparticle diffusion model. The pH had no effect on the sorption efficiency. The sorption isotherms followed the Langmuir model for various sorbent concentrations with good values of the determination coefficient. A linear relationship was found between the calculated maximum removal capacity and the solid/solution ratio. A comparison between the results obtained with this material and those of the literature highlighted the low cost and the good removal capacity of treated spent bleaching earth.Sorption of methylene blue (▴) and safranine (■) on treated spent bleaching earth. The Langmuir maximal sorption capacities increase with the solid/solution ratio.
Keywords: Spent bleaching earth; Sorption; Basic dyes; Isotherms
Monte Carlo simulations of surface energy of the open tetrahedral surface of 2:1-type phyllosilicate
by Xiandong Liu; Xiancai Lu; Kan Yang; T.C.T. Hubble; Qingfeng Hou (pp. 17-23).
Monte Carlo simulations were employed to investigate the surface energy of the open tetrahedral surface of 2:1-type phyllosilicate. Argon was selected as the probe molecule. The adsorption isotherm was simulated and the adsorption potential map was calculated. Both the density and energy distributions of adsorbed atoms were derived at different pressures to explore the adsorption mechanism. It is found that there exist two kinds of energetic sites: minima (−15.5 kJ/mol) corresponding to the centers of six-membered rings and platform points (−8.0 kJ/mol) corresponding to the edges and vertexes of hexagons. They are primary and secondary adsorption sites, respectively. The implications for experiments and future studies are discussed. Current results are applicable for understanding surface energy properties of other clay minerals, since they have very similar basal surfaces.We simulated argon adsorption on the model basal surface of 2:1-type phyllosilicate using Monte Carlo. The potential map discloses two kinds of energetic sites corresponding to centers and vertexes of six-membered rings of the substrate surface, respectively.
Keywords: Surface energy; Phyllosilicate; Adsorption isotherm; Monte Carlo; Tetrahedral surface
Kinetic modeling of adsorption of di-2-pyridylketone salicyloylhydrazone on silica gel
by P. Antonio; K. Iha; M.E.V. Suárez-Iha (pp. 24-28).
The kinetics of DPKSH (di-2-pyridylketone salicyloylhydrazone) adsorption onto silica gel has been investigated at(25±1)°C and pH 1 and 4.7. The kinetics of adsorption of DPKSH is discussed using three kinetic models, the first-order Lagergren model, the pseudo-second-order model, and the intraparticle diffusion model. The adsorption of DPKSH, at pH 1 and 4.7, onto silica gel proceeds according to the pseudo-second-order model and the correlation coefficients were very close to 1. The intraparticle diffusion of DPKSH molecules within the silica gel particles was identified as the rate-limiting step. The parameters of the pseudo-second-order model areqmax,calc=1.02×10−4 and1.5×10−4g DPKSH/g silica;k2=3.01×104 and9.67×104h−1g silica/g DPKSH, respectively, for pH 1 and 4.7.The rates and mechanism of DPKSH adsorption onto silica gel were investigated. Kinetic models including pseudo-first- and -second-order equations and the intraparticle diffusion model were used to describe the adsorption processes.
Keywords: Adsorption; DPKSH; Silica gel; Kinetic models
Thermodynamic aspects of sorption of Fe2+ onto unbleached kraft fibres
by C.H. Chia; Tuan D. Duong; Kien L. Nguyen; S. Zakaria (pp. 29-33).
The sorption of Fe2+ onto unbleached kraft fibre was investigated at different conditions such as pH, temperature, and concentrations. The sorption, which increased with concentration and temperature, followed the Langmuir isotherm. Thermodynamically, the process was spontaneous and endothermic. It was found that the precipitation of Fe2+ was highly dependent on pH and reached 100% when pH exceeded ∼8.The sorption of Fe2+ increased when pH >3 due to the increased degree of ionization of the cellulosic components in the fibres. When pH exceeded 8, 100% of Fe2+ precipitated in the solution.
Keywords: Sorption; Kraft pulp; Langmuir isotherms; Precipitation
Liquid–vapor density profiles from equilibrium limit of diffusion equation for interacting particles
by Y. Chen; G.L. Aranovich; M.D. Donohue (pp. 34-39).
Liquid–vapor density profiles are derived from the equilibrium limit of diffusion equation for interacting particles. These profiles are in good agreement with classical hyperbolic tangent relation. For simple Lennard-Jones fluids, predicted density distributions agree with computer simulation data, but have a slightly sharper transition zone. For alkali metals with Lennard-Jones-like potentials, the new equations predict a very good average distribution with quite satisfactory agreement with Monte Carlo simulation results. For liquid metals and water surfaces, accurate interfacial profile predictions also can be achieved by using effective two-body potential data instead of Lennard-Jones parameters.Analytical extension to one-dimensional diffusion equation for interacting particles is derived to predict monotonic density profile across the gas–liquid interface. The resulting density profiles are in good agreement with classical hyperbolic tangent relation.
Keywords: Liquid–vapor density profile; Diffusion equation
Sorption of Cu(II) onto vineyard soils: Macroscopic and spectroscopic investigations
by Stéphanie Boudesocque; Emmanuel Guillon; Michel Aplincourt; Eric Marceau; Lorenzo Stievano (pp. 40-49).
The sorption of Cu on five vineyard soils was examined via macroscopic and spectroscopic investigations. The composition of the soils was previously determined using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy (XAS) was employed to determine the metal environment with regard to the identity and interaction of the nearest atomic neighbors, the bond distances, and the coordination numbers. The five soils present similar sorption properties and there is no XAS evidence that the nature of the soil samples affects the local chemical environment of Cu(II). The kinetics of the Cu sorption reactions is rapid, with the equilibrium loading of Cu on the surface achieving approximately 200 μmol g−1, i.e., 12.7 mg g−1. The XAS data indicate that Cu is adsorbed in the form of inner-sphere complexes with first shell CuO parameters of four equatorial CuO bonds equal to 1.93 Å and two axial CuO bonds at 2.43 Å. This is in accordance with a Jahn–Teller distorted octahedron environment around copper. Our results provide evidence of the complexation of Cu(II) onto soil organic matter coated with an inorganic surface (quartz, clay, and goethite).A study of the sorption of copper(II) onto vineyard soils was conducted at macroscopic and molecular scales.
Keywords: Copper; Sorption; Soil; DRX; EXAFS; XANES
Changes in the surfaces of adsorbed para-nitrophenol on HDTMA organoclay—The XRD and TG study
by Qin Zhou; Ray L. Frost; Hongping He; Yunfei Xi (pp. 50-55).
Surfactant modified montmorillonitic clays synthesized by ion exchange using the hydrothermal reaction method have been compared using XRD and thermal analysis. X-ray diffraction (XRD) shows the changes in the surface properties of organoclays through expansion with surfactant loading. A polynomial relationship exists between the basal spacing and the CEC loading described by the equationy=0.3232x2+0.2052x+1.2834 withR2=0.9955. Different arrangements of the surfactant molecules in the organoclays are inferred from the changes in basal spacings. para-Nitrophenol also causes the expansion of the montmorillonite clay and affects the arrangements of the surfactant molecules within the clay layers. Changes in the surfactant molecular arrangements were analyzed by thermogravimetry. Additional thermal decomposition steps were observed when para-nitrophenol is adsorbed on the organoclay.Surfaces of a sodium montmorillonite from Neimeng, China were modified through intercalation with the cationic surfactant hexadecyltrimethylammonium bromide labeled HDTMAB (CH3(CH2)15(CH3)3N+Br−). Different configurations of surfactants within montmorillonite interlayer are proposed based on d(001) basal spacings. Changes in these configurations are enforced when para-nitrophenol is adsorbed.
Keywords: Montmorillonite; Organoclay; Surfactant; High resolution thermogravimetric analysis; X-ray diffraction
Probing particle structure in waterborne pressure-sensitive adhesives with atomic force microscopy
by C.H. Lei; K. Ouzineb; O. Dupont; J.L. Keddie (pp. 56-63).
There is a need to know the nanostructure of pressure-sensitive adhesive (PSA) films obtained from waterborne polymer colloids so that it can be correlated with properties. Intermittent-contact atomic force microscopy (AFM) of an acrylic waterborne PSA film identifies two components, which can be attributed to the polymer and the solids in the serum (mainly surfactant). It is found that when the average AFM tapping force,Fav, is relatively low, the polymer particles appear to be concave. But whenFav is higher, the particles appear to have a convex shape. This observation is explained by a height artefact caused by differences in the indentation depths into the two components that vary with the tapping amplitude andFav. To achieve the maximum contrast between the polymer and serum components,Fav should be set such that the indentation depths are as different as possible. Unlike what is found for the height images, the phase contrast images of the PSA do not show a reversal in contrast over the range of tapping conditions applied. The phase images are thus reliable in distinguishing the two components of the PSA according to their viscoelastic properties. At the surface of films dried at room temperature, the serum component is found in localized regions within permanent depression into the film.Whether particles in an adhesive latex film appear convex or concave in atomic force microscopy depends on the differences in indentation depths between the polymer and serum phases, which are shown to vary with the tapping force. The corresponding phase contrast images (not shown) do not undergo a reversal in contrast.
Keywords: Latex; Surfactant; Atomic force microscopy; Indentation; Adhesive; Nanostructure; Film formation; Height artefacts
Isosteric heats of sorption of 1-naphthol and phenol from aqueous solutions by β-cyclodextrin polymers
by Íñigo X. García-Zubiri; Gustavo González-Gaitano; José Ramón Isasi (pp. 64-70).
The sorption of phenol and 1-naphthol from aqueous solutions by β-cyclodextrin polymers has been analyzed using the isosteric heat approach. This has proven to be a useful tool for comparing the interactions between the sorbents and the sorbates. With the purpose of ascertaining the role of the cyclodextrin cavities and the crosslinking network in the sorption process, analogous sucrose polymers have been prepared using the same crosslinking reagents (epichlorohydrin, succinyl chloride, 1,6-hexamethylene diisocyanate, and toluene-2,4-diisocyanate). The two studied sorbates, phenol and 1-naphthol, also show important differences in their affinities for the cyclodextrin cavities and the crosslinking networks.Two different mechanisms of sorption (inclusion complexation within cyclodextrin cavities and interaction with the polymeric networks) can be analyzed using the isosteric heat approach.
Keywords: Sorption; Cyclodextrin polymers; Host–guest systems; Isosteric heat
Why inhaling salt water changes what we exhale
by Wiwik Watanabe; Matthew Thomas; Robert Clarke; Alexander M. Klibanov; Robert Langer; Jeffrey Katstra; Gerald G. Fuller; Lester C. Griel; Jennifer Fiegel; David Edwards (pp. 71-78).
We find that inhaling salt water diminishes subsequently exhaled biomaterial in man and animals due to reversible stabilization of the airway lining fluid (ALF)/air interface as a novel potential means for control of the spread of airborne infectious disease. The mechanism of this phenomenon relates to charge shielding of mucin or mucin-like macromolecules that consequently undergo gelation; this gelation alters the physical properties of the ALF surface and reduces its breakup. Cations in the nebulized solution and apparent surface viscoelasticity of the ALF (more than any other ALF intrinsic physical property) appear to be responsible for the reduced tendency of the ALF to disintegrate into very small droplets. We confirm these effects in vivo and show their reversibility through nebulization of saline solutions to anesthetized bull calves.In vitro and in vivo experiments indicate that the delivery of salt water onto airway lining fluid (ALF) stabilizes the interface through a surface gelation of the mucus. Apparent surface viscoelasticity of the ALF, more than any other intrinsic ALF physical property, appears responsible for the reduced propensity of the ALF to disintegrate into very small droplets.
Keywords: Bioaerosol; Airway lining fluid; Surface interface; Cation; Mucin; Gelation; Airborne infectious disease
Hydrothermal synthesis of ZnO nanobundles controlled by PEO–PPO–PEO block copolymers
by Zhiqing Zhang; Jin Mu (pp. 79-82).
Homocentric ZnO nanobundles with pyramidlike and hexagonal prism shapes were synthesized in colloidal systems formed by PEO–PPO–PEO amphiphilic block copolymers. The prism- and pyramidlike ZnO crystals were produced by L64 and F68, respectively, which may be attributed to the different growth rates of various crystal facets. It was proposed that the two processes for crystallization, including nucleation and crystal growth, happened in the macromolecular micelles under hydrothermal conditions. The room-temperature photoluminescence spectra of the ZnO products showed sharp ultraviolet emission located around 390 nm originating from the radiative recombination of free excitons. The sharp emission, with a half-maximum of about 8 nm, gave a powerful attestation that the sample was of high crystal quality, which was consistent with the SEM and TEM observations. The single ultraviolet emission is important for the application of ZnO-based materials in the electronic and photonic realms.The supersaturated Zn(OH)2−4 solution enwrapped in macromolecular micelles first nucleated under hydrothermal conditions. Many tiny ZnO crystal nuclei were restricted in the hydrophobic core. The epitaxial growth of these ZnO nuclei along (0001) direction resulted in the formation of ZnO homocentrical bundle structures.
Keywords: ZnO; Block copolymer; Nanobundles; Hydrothermal synthesis; Photoluminescence
Spontaneous association of hydrophobized dextran and poly- β-cyclodextrin into nanoassemblies.
by S. Daoud-Mahammed; C. Ringard-Lefebvre; N. Razzouq; V. Rosilio; B. Gillet; P. Couvreur; C. Amiel; R. Gref (pp. 83-93).
New nanoassemblies were instantaneously prepared by mixing two aqueous solutions, one containing a β-cyclodextrin polymer (p βCD), and the other a hydrophobically modified by alkyl chains dextran (MD). The formation mechanism and the inner structure of these nanoassemblies were analysed using surface tension measurements and1H NMR spectroscopy. The effect of a hydrophobic guest molecule, such as benzophenone (BZ), on the formation and stability of the nanoassemblies was also evaluated. MD exhibited the typical behaviour of a soluble amphiphilic molecule and adsorbed at the air/water interface. Whereas the injection of native β-CDs in the solution beneath the adsorbed MD monolayer did not produce any change in the surface tension, that of the p βCD resulted in an increase in the surface tension, indicating the desorption of the polymer from the interface. This result accounts for a cooperative effect of β-CDs linked together in the p βCD polymer on dextran desorption. The presence of benzophenone in the system hindered the sequestration of dextran alkyl moieties by β-CD in the polymer without impeding the formation of associative nanoassemblies of 100–200 nm.1H NMR investigations demonstrated that, in the BZ-loaded nanoassemblies, the hydrophobic molecule was mainly located into the cyclodextrin cavities.The formation mechanism and the structure of cyclodextrin based nanoassemblies were investigated. A cooperative effect between several cyclodextrins linked together was essential to sequestrate MD polymer from the air/water interface.
Keywords: Nanoassemblies; Self-assembly; Hydrophobically modified polymer; Cyclodextrins; Surface tension; 1; H NMR
A novel cetyltrimethyl ammonium silver bromide complex and silver bromide nanoparticles obtained by the surfactant counterion
by Xian-Hao Liu; Xiao-Hong Luo; Shu-Xia Lu; Jing-Chang Zhang; Wei-Liang Cao (pp. 94-100).
A novel cetyltrimethyl ammonium silver bromide (CTASB) complex has been prepared simply through the reaction of silver nitrate with cetyltrimethyl ammonium bromide (CTAB) in aqueous solution at room temperature by controlling the concentration of CTAB and the molar ratio of CTAB to silver nitrate in the reaction solution, in which halogen in CTAB is used as surfactant counterion. The structure and thermal behavior of cetyltrimethyl ammonium silver bromide have been investigated by using X-ray diffraction (XRD), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), UV/vis spectroscopy, thermal analysis (TG–DTA), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results show that the complex possesses a metastable layered structure. Upon heating the CTASB aqueous dispersion to above 80 °C, the structure change of the complex took place and CTAB-capped nanosized silver bromide particles further formed.The CTAB-capped silver bromide nanoparticles were obtained by the thermal decomposition of AgBr/CTAB complex at above 80 °C.
Keywords: Complex; Layer structure; Thermal behavior; Silver bromide; Nanoparticle
Surface properties of kaolin and illite suspensions in concentrated calcium hydroxide medium
by Koffi Léon Konan; Claire Peyratout; Jean-Pierre Bonnet; Agnès Smith; Alain Jacquet; Patrick Magnoux; Philippe Ayrault (pp. 101-108).
The adsorption behaviour of calcium hydroxide onto illite and kaolin clay minerals was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clay minerals to calcium hydroxide solutions of various concentrations. Both clay minerals can adsorb calcium and hydroxyl ions. Rather than just considering proton exchanges at the clay mineral surfaces, the adsorption is explained by an approach based on Lewis description of molecules. With this approach, a mechanism for calcium hydroxide adsorption not only at the edges of the clay particles but also onto the faces is proposed. In order to gain a better insight onto the active groups at the surface of the studied clay minerals, adsorption of pyridine and ammonia on illite and kaolin was followed by FTIR spectroscopy. These measurements gave the signature of edges, which are marginally involved in interactions with calcium ions.The adsorption behaviour of calcium hydroxide onto illite and kaolin clay minerals was explained by an approach based on Lewis' description of molecules. We give a qualitative description of the binding mechanism of calcium hydroxide onto clay minerals surfaces.
Keywords: Brönsted and Lewis active sites; pH; Clay minerals
A novel method for preparing and characterizing alcoholic EPD suspensions
by M.F. De Riccardis; D. Carbone; A. Rizzo (pp. 109-115).
Ceramic suspensions composed of alumina and mixtures of alumina and zirconia powders in ethyl alcohol were prepared. A solution of citric acid and triethylamine was used as dispersant. The citric acid, which usually is used as dispersant in water alumina suspensions, gave excellent results in ethyl alcohol also if it was used in conjunction with triethylamine. A novel method consisting of combined measurements of grain size, zeta potential, and transmittance was optimized to study the dispersion and stability properties of the ceramic suspensions; by using this method the optimal dispersant amount was determined. The suspensions based on alumina and alumina–zirconia powders were used to coat stainless steel plates by electrophoretic deposition (EPD); the optimal composition of suspensions and the used EPD parameters made it possible to obtain coatings with uniform thickness and composition.A novel method consisting of combined measurements of grain size, zeta potential, and transmittance was optimized to study the dispersion and stability properties of the ceramic suspensions for electrophoretic deposition.
Keywords: Alumina; Zirconia; EPD; Suspension; Dispersant
AFM interaction study of α-alumina particle and c-sapphire surfaces at high-ionic-strength electrolyte solutions
by Huseyin Yilmaz; Kimiyasu Sato; Koji Watari (pp. 116-123).
Ionic strength dependence of interaction and friction forces between hydrophilic α-alumina particles and c-sapphire surfaces (0001) were investigated under basic pH conditions using the colloidal probe method. The compression of the double layer could be seen from force–distance curves as the ionic strength of the solution increased. The forces were repulsive at all ionic strengths measured, even though the interaction distance changed drastically. No jump to contact occurred. The interaction distance decreased from about 20 nm in 10−3 M KCl solution to about 7 nm in the 1 M KCl case. The lubricating effect of hydrated cations on the lateral friction force was demonstrated at high electrolyte concentrations. This was attributed to more hydrated cations being present in the solution. The friction behavior was closely related to the short-range repulsive forces between the α-alumina surfaces at pH 11.
Keywords: SPM; AFM; Colloid probe method; Alumina
Surface complexes of phthalic acid at the hematite/water interface
by Yu Sik Hwang; Jin Liu; John J. Lenhart; Christopher M. Hadad (pp. 124-134).
The adsorption of o-phthalic acid at the hematite/water interface was investigated experimentally using batch adsorption experiments and attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy over a wide range of solution pH, surface loading, and ionic strength conditions. Molecular orbital calculations for several possible surface complexes were also performed to assign atomistic structures to the features observed in the ATR-FTIR spectra. The results of the batch adsorption experiments exhibit typical anionic characteristics with high adsorption at low pH and low adsorption at high pH. The adsorption of phthalic acid also exhibits a strong dependence on ionic strength, which suggests the presence of outer-sphere complexes. ATR-FTIR spectra provide evidence of three fully deprotonated phthalate surface complexes (an outer-sphere complex and two inner-sphere complexes) under variable chemical conditions. A fully deprotonated outer-sphere complex appears to dominate adsorption in the circumneutral pH region, while two fully deprotonated inner-sphere complexes that shift in relative importance with surface coverage increase in importance at low pH. Comparison of experimental and theoretical calculations suggests the two inner-sphere complexes are best described as a mononuclear bidentate (chelating) complex and a binuclear bidentate (bridging) complex. The mononuclear bidentate inner-sphere complex was favored at relatively low surface coverage. With increasing surface coverage, the relative contribution of the binuclear bidentate inner-sphere complex increased in importance.Three fully deprotonated phthalate surface complexes (an outer-sphere complex and two bidentate inner-sphere complexes) were observed to be present on hematite under the studied conditions.
Keywords: Adsorption; Phthalic acid; Hematite; ATR-FTIR spectroscopy; Molecular orbital calculations; Inner-sphere complex; Outer-sphere complex
Size-controlled synthesis and electrochemical characterization of spherical CeO2 crystallites
by Fu Zhou; Xiaomin Ni; Yongfeng Zhang; Huagui Zheng (pp. 135-138).
Spherical ceria (CeO2) crystallites assembled by nanoparticles were synthesized by hydrothermal treatment of Ce(NO3)3⋅6H2O using poly( N-vinyl-2-pyrrolidone) (PVP) as surfactant. It was found that these spheres were developed from the gradual aggregation of small nanoparticles and size of the spheres could be tailored by adjusting the reagent concentrations. Electrochemical tests indicated that thus-prepared CeO2 spheres exhibited size-dependent discharge capacities and good cyclability in the Li/CeO2 couple, showing their promising usages as anode materials in the lithium ion battery.Spherical CeO2 crystallites were synthesized by hydrothermal treatment of Ce(NO3)3⋅6H2O using poly ( N-vinyl-2-pyrrolidone) (PVP) as surfactant.
Keywords: Ceria; Size control; Electrochemical properties; Lithium insertion
Preparation and electrocatalytic properties of Pt–SiO2 nanocatalysts for ethanol electrooxidation
by B. Liu; J.H. Chen; X.X. Zhong; K.Z. Cui; H.H. Zhou; Y.F. Kuang (pp. 139-144).
Due to their high stability in general acidic solutions, SiO2 nanoparticles were selected as the second catalyst for ethanol oxidation in sulfuric acid aqueous solution. Pt–SiO2 nanocatalysts were prepared in this paper. The micrography and elemental composition of Pt–SiO2 nanoparticles were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The electrocatalytic properties of Pt–SiO2 nanocatalysts for ethanol oxidation were investigated by cyclic voltammetry. Under the same Pt loading mass and experimental conditions for ethanol oxidation, Pt–SiO2 nanocatalysts show higher activity than PtRu/C (E-Tek), Pt/C (E-Tek), and Pt catalysts. Additionally, Pt–SiO2 nanocatalysts possess good anti-poisoning ability. The results indicate that Pt–SiO2 nanocatalysts may have good potential applications in direct ethanol fuel cells.Due to good stability in general acidic solution, SiO2 nanoparticles were selected as the second catalyst for ethanol oxidation in sulfuric acid aqueous solution. Pt–SiO2 nanocatalysts with 1–2 nm show higher electrocatalytic activity than PtRu/C (E-Tek), Pt/C (E-Tek), and Pt catalysts.
Keywords: Ethanol; Electrocatalyst; Pt–SiO; 2; nanoparticles; Fuel cells
Nanostructured Cu xCe1− xO2− y mixed oxide catalysts: Characterization and WGS activity tests
by Albin Pintar; Jurka Batista; Stanko Hočevar (pp. 145-157).
Cu xCe1− xO2− y mixed oxide catalysts were prepared by different preparation procedures: co-precipitation, the sol–gel peroxide route, and the sol–gel citric acid-assisted route. The resulting solids were investigated by means of XRD, BET, H2 and CO temperature-programmed reduction (TPR), oxidation (TPO) and desorption (TPD) analyses, and N2O pulse selective reaction. It was confirmed that H2 (CO) consumed for complete reduction of well-dispersed and bulk-like CuO phases to Cu0, reduction of surface ceria and H2 (CO) adsorption on the catalyst surface contribute to the total H2 (CO) consumption. Among catalysts examined, the Cu0.15Ce0.85O2− y mixed oxide sample prepared by means of co-precipitation method exhibits the highest activity and stability for water–gas shift (WGS) pulse reaction in the range of employed operating conditions. WGS activity of copper–ceria mixed oxide catalysts is determined by the extent of surface ceria reduction and dispersion of copper species.Nanostructured Cu–Ce mixed oxide catalysts prepared by co-precipitation method exhibit promising activity and stability for water–gas shift (WGS) reaction.
Keywords: Catalytic activity; Cu; x; Ce; 1−; x; O; 2−; y; Heterogeneous catalysis; Synthesis; TPR; TPO; TPD; Water–gas shift reaction
A two-step route to synthesis of small-pored and thick-walled SBA-16-type mesoporous silica under mildly acidic conditions
by Zhengwei Jin; Xiaodong Wang; Xiuguo Cui (pp. 158-165).
Highly ordered SBA-16-type mesoporous silica materials were synthesized by using poly(ethylene oxide– b–propylene oxide– b–ethylene oxide) triblock copolymer (EO132–PO50–EO132, Pluronic F108) as template through a two-step pathway under mildly acidic conditions (pH 2.15–4.50). The highly ordered cage-like mesoporosity of the prepared SBA-16-type mesoporous silica materials having Im3m cubic mesostructure was proved by the well-defined X-ray diffraction patterns combined with transmission electron microscopy. Scanning electron microscopy shows a variation from the spherical agglomerations to the randomly shaped ones with an increase of pH value. The nitrogen adsorption–desorption analysis reveals that the prepared SBA-16-type mesoporous silica materials have a uniform small-sized pore diameter (3.37–4.24 nm) and very thick pore wall (8.84–10.2 nm). These features may make the SBA-16-type mesoporous silica materials synthesized in this study favor the incorporation of catalytically active heteroatoms in silica frameworks, and the functionalization of organic groups for applications in catalysis, sensor and separation. The two-step synthetic method under the mildly acidic conditions can also be extended to the production in the industrial scale as an environmentally friendly way.Small-pored and thick-walled SBA-16-type mesoporous silica materials were synthesized by templating with an amphiphilic triblock copolymer through a two-step pathway under mildly acidic conditions. This new synthetic method is friendly to the environment, and is possible to be extended to preparation of a wide family of the mesoporous silica materials as well as their industrial products.
Keywords: SBA-16-type mesoporous silica; Mildly acidic conditions; Two-step pathway; Synthesis; Characterization
Mass transfer of weak acid in nanometer-sized pores of octadecylsilyl-silica gel
by Hiroshi Kakizaki; Chiaki Aonuma; Kiyoharu Nakatani (pp. 166-171).
The sorption of bromophenol blue or anthracene-9-carboxylic acid as a weak acid into single octadecylsilyl (ODS)-silica gel microparticles in a solution was analyzed by microcapillary injection-manipulation and absorption microspectroscopy. The distribution ratio and the sorption rate were highly dependent on the pH of the solution. These results are discussed in terms of the acid dissociation/association, distribution between the ODS and solution phases, and intraparticle diffusion of the weak acid in the nanometer-sized pores of the ODS-silica gel.
Keywords: Octadecylsilyl-silica gel; Diffusion; Sorption; Acid dissociation; Microspectroscopy
Synthesis and characterization of mesoporous ceria/alumina nanocomposite materials via mixing of the corresponding ceria and alumina gel precursors
by Kamal M.S. Khalil (pp. 172-180).
Mesoporous ceria/alumina, CeO2/Al2O3, composites containing 10, 20 and 30% (w/w) ceria were prepared by a novel gel mixing method. In the method, ceria gel (formed via hydrolysis of ammonium cerium(IV) nitrate by aqueous ammonium carbonate solution) and alumina gel (formed via controlled hydrolysis of aluminum tri-isopropoxide) were mixed together. The mixed gel was subjected to subsequent drying and calcination for 3 h at 400, 600, 800 and 1000 °C. The uncalcined (dried at 110 °C) and the calcined composites were investigated by different techniques including TGA, DSC, FTIR, XRD, SEM and nitrogen adsorption/desorption isotherms. Results indicated that composites calcined for 3 h at ⩽800 °C mainly kept amorphous alumina structure and γ-alumina formed only upon calcinations at 1000 °C. On the other hand, CeO2 was found to crystallize in the common ceria, cerinite, phase and it kept this structure over the entire calcination range (400–1000 °C). Therefore, high surface areas, stable surface textures, and non-aggregated nano-sized ceria dispersions were obtained. A systematic texture change based on ceria ratio was observed, however in all cases mesoporous composite materials exposing thermally stable texture and structure were obtained. The presented method produces composite ceria/alumina materials that suit different applications in the field of catalysis and membranes technology, and throw some light on physicochemical factors that determine textural morphology and thermal stability of such important composite.
Keywords: Ceria/alumina; CeO; 2; /Al; 2; O; 3; Mesoporous; Composite; Thermal stability
Visualization of fluid occupancy in a rough fracture using micro-tomography
by Z.T. Karpyn; A.S. Grader; P.M. Halleck (pp. 181-187).
The purpose of this work is to study the effects of fracture morphology on the distribution and transport of immiscible fluid phases, such as oil and water, through a vertical fracture. An experimental approach, using micro-computed tomography (MCT), was selected to characterize the internal fracture structure and to monitor two immiscible phases. The experiment was performed in Berea sandstone cores with a single longitudinal fracture. The artificially created fracture was oriented parallel to the natural bedding of the rock. The sample was initially vacuum-saturated with water, and oil was later injected through the longitudinal crack. Fluid occupancy in the fracture was mapped under four different flowing conditions: continuous oil injection, continuous water injection, simultaneous injection of oil and water, and a static pseudo-segregated state. Some of the mechanisms observed in this experiment include fluid trapping, preferential flow paths, snapping-off of non-wetting fluid globules, and coalescence and redistribution of globules between dynamic and static conditions. Experimental results indicate that distribution was mainly determined by fracture geometry, saturations, and wetting characteristics of the rock. A strong correspondence between fluid distribution and fracture apertures was found through direct comparison of two- and three-dimensional fracture structures.Non-wetting globules of oil are mapped inside a rough fracture. Experimental results indicate trapping and preferential flow paths in agreement with local fracture apertures.
Keywords: Open fractures; Oil–water interface; Asperities; Computed tomography; Interfacial tension
Linear stability of a draining film squeezed between two approaching droplets
by Fabio Baldessari; G.M. Homsy; L. Gary Leal (pp. 188-202).
In the present paper we analyze the effect of infinitesimal non-axisymmetric perturbations in determining the critical gap thickness at which a draining, finite radius thin-film becomes unstable. The film is part of the suspending fluid trapped between two approaching deformable drops under the action of a flow field. We carry out a linear stability analysis in the context of a quasi-static approximation where the rate of growth of the disturbances is assumed to be much faster than the rate of film drainage. An analytical solution is derived for the model in the special case of a uniformly thick film, for two types of perturbation: fixed-end and free-end. It is shown, for this special case, when the hydrodynamic force pushing the drops together from the external flow is constant, that the four most unstable disturbances are of the free-end kind, associated with the lowest frequency modes of azimuthal variation in the film thickness. Higher modes are stabilized by surface tension. Our analysis also shows that adopting the unretarded form of the van der Waals disjoining pressure yields results similar to the analysis when electromagnetic retardation effects are included in the calculation. A second case is analyzed where the film is also of uniform thickness but its lateral extent and the gap thickness are both time-dependent. This case was included to extend the predictions to glancing drop-collisions where the external hydrodynamic force is time-dependent. We find that there is a maximum capillary number below which the film becomes unstable, and that there is range of angles in the trajectory where the film becomes unstable, but that outside this range the film is stable.Effect of 3D perturbations on the stability of a bounded thin-fluid layer trapped between two approaching droplets.
Keywords: Thin film stability; Coalescence
Instability of a two-layer thin liquid film with surfactants: Dewetting waves
by L.S. Fisher; A.A. Golovin (pp. 203-214).
Dewetting dynamics of a liquid film composed of two superposed ultra-thin layers of immiscible liquids resting on a solid substrate is investigated in the case when surfactants are present at the liquid–liquid interface. Two cases are considered: insoluble surfactant and surfactant soluble in the lower liquid. The dependence of Hamaker constants on the surfactant concentration is taken into account. A system of three strongly nonlinear evolution equations describing large (comparable to the layer thicknesses), long-wave perturbations of the liquid–liquid and liquid–gas interfaces, as well as the surfactant concentration, is derived for each case in the lubrication approximation. The linear stability analysis shows that in the presence of surfactants, oscillatory dewetting instability can occur. Numerical simulations of this system of nonlinear evolution equations are performed. It is found that in the case of oscillatory instabilities, the system exhibits either standing or traveling “dewetting waves.” The weakly nonlinear analysis explains this phenomenon.
Keywords: Thin liquid films; Van der Waals interactions; Dewetting; Insoluble and soluble surfactants; Dewetting waves
Molecular behavior and synergistic effects between sodium dodecylbenzene sulfonate and Triton X-100 at oil/water interface
by Ying Li; Xiujuan He; Xulong Cao; Guoqing Zhao; Xiaoxue Tian; Xiaohong Cui (pp. 215-220).
Significant synergistic effects between sodium dodecylbenzene sulfonate (SDBS) and nonionic nonylphenol polyethylene oxyether, Triton X-100 (TX-100), at the oil/water interface have been investigated by experimental methods and computer simulation. The influences of surfactant concentration, salinity, and the ratio of the two surfactants on the interfacial tension were investigated by conventional interfacial tension methods. A dissipative particle dynamics (DPD) method was used to simulate the adsorption properties of SDBS and TX-100 at the oil/water interface. The experiment and simulation results indicate that ultralow (lower than 10−3 mN m−1) interfacial tension can be obtained at high salinity and very low surfactant concentration. Different distributions of surfactants in the interface and the bulk solution corresponding to the change of salinity have been demonstrated by simulation. Also by computer simulation, we have observed that either SDBS or TX-100 is not distributed uniformly over the interface. Rather, the interfacial layer contains large cavities between SDBS clusters filled with TX-100 clusters. This inhomogeneous distribution helps to enhancing our understanding of the synergistic interaction of the different surfactants. The simulation conclusions are consistent with the experimental results.Effect of salt on the distribution of SDBS and TX-100 on the O/W interface and in bulk solution.aHH decreases andaWE increases while salt concentration increases. Cyan and green beads represent head groups of SDBS and TX-100, respectively, and magenta and red beads represent tail chains of theirs. Water and oil beads are removed.
Keywords: Synergism effect; Computer simulation; Dissipative particle dynamics; Oil/water interface; Ultralow interfacial tension
Effect of ionic strength on the rheological behavior of aqueous cetyltrimethylammonium p-toluene sulfonate solutions
by Miguel F. Torres; Juan M. González; Mario R. Rojas; Alejandro J. Müller; A. Eduardo Sáez; David Löf; Karin Schillén (pp. 221-228).
The influence of ionic environment on the rheological properties of aqueous cetyltrimethylammonium p-toluene sulfonate (CTAT) solutions has been studied under three different flow fields: simple shear, opposed-jets flow and porous media flow. Emphasis was placed in the experiments on a range of CTAT concentration in which wormlike micelles were formed. It is known that these solutions exhibit shear thickening in the semi-dilute regime, which has been explained in terms of the formation of shear-induced, cooperative structures involving wormlike micelles. In simple shear flow, the zero shear viscosity exhibits first an increase with salt addition followed by a decrease, while the critical shear rate for shear thickening increases sharply at low salt contents and tends to saturate at relatively high ionic strengths. The results are explained in terms of a competition between micellar growth induced by salt addition and changes in micellar flexibility caused by ionic screening effects. Dynamic light scattering results indicate that micelles grow rapidly upon salt addition but eventually achieve a constant size under static conditions. These observations suggest that the wormlike micelles continuously grow with salt addition, but, as they become more flexible due to electrostatic screening, the wormlike coils tend to adopt a more compact conformation. The trends observed in the apparent viscosities measured in porous media flows seem to confirm these hypotheses—but viscosity increases in the shear thickening region—and are magnified by micelle deformation induced by the elongational nature of the local flow in the pores. In opposed-jets flow, the solutions have a behavior that is close to Newtonian, which suggests that the range of strain rates employed makes the flow strong enough to destroy or prevent the formation of cooperative micellar structures.
Keywords: CTAT; Shear-thickening; Extensional flow; Porous media flow
Effect of hydrogen-bonding interactions on the self-assembly formation of sodium N-(11-acrylamidoundecanoyl)-l-serinate,l-asparaginate, andl-glutaminate in aqueous solution
by Sumita Roy; Joykrishna Dey (pp. 229-234).
Aggregation behavior of three N-acyl amino acid surfactants, sodium N-(11-acrylamidoundecanoyl)-l-serinate (SAUS), sodium N-(11-acrylamidoundecanoyl)-l-asparaginate (SAUAS), and sodium N-(11-acrylamidoundecanoyl)-l-glutaminate (SAUGL), was studied in aqueous solution by use of surface tension, fluorescence, dynamic light scattering, and transmission electron microscopic techniques. The amphiphiles have been shown to initially form flexible bilayer structures, which upon increase of surfactant concentration transform into closed spherical vesicles. The transmission electron micrographs of the aqueous solutions of the surfactants confirmed the existence of spherical vesicles. Dynamic light scattering measurements were performed to obtain hydrodynamic radii of the vesicles. Circular dichroism spectra of the amphiphiles indicated formation of chiral helical aggregates in the case of SAUS. The self-assembly formation of the amphiphiles has been discussed in light of the intermolecular hydrogen bonding interaction of the amide groups.
Keywords: N; -acyl amino acids; Vesicle; Fluorescence; Light scattering; Circular dichroism; Microscopy
Effect of added ionic liquid on aqueous Triton X-100 micelles
by Kamalakanta Behera; Parmila Dahiya; Siddharth Pandey (pp. 235-245).
Addition of ionic liquids to aqueous surfactant solutions can alter/modify physicochemical properties of such systems in favorable manner. Changes in the properties of aqueous solutions of a useful nonionic surfactant Triton X-100 (TX-100) are assessed upon addition of 2.1 wt% of a common and popular ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). It is shown that the solubility of ‘hydrophobic’ bmimPF6 in aqueous TX-100 increases with TX-100 concentration. This observation combined with the conductivity data strongly indicates partitioning of bmimPF6 into TX-100 micellar phase. Behavior of a variety of molecular absorbance [methyl orange, phenol blue, and N, N-diethyl-4-nitroaniline] and fluorescence [phenyl on the TX-100, pyrene, pyrene-1-carboxaldehyde, 2-( p-toluidino)naphthalene-6-sulfonate, and 1,3- bis-(1-pyrenyl)propane] probes further confirm this observation. Statistically insignificant increase in critical micelle concentration (cmc) and decrease in aggregation number (Nagg) of TX-100 micelles are observed upon addition of 2.1 wt% bmimPF6. Based on the overall data, it is inferred that ionic liquid bmimPF6 partitions into the TX-100 micellar phase; presence of bmimPF6 both close to the core as well as in the palisade layer of TX-100 micelles is suggested. Presence of favorable interactions (e.g., H-bonding, dipole-induced dipole, among others) between bmimPF6 and TX-100 is proposed to be the reason for these observations.
Keywords: Ionic liquids; TX-100; Nonionic surfactants; bmimPF; 6; Fluorescence probes
Aggregation behaviour of a dirhamnolipid biosurfactant secreted by Pseudomonas aeruginosa in aqueous media
by Marina Sánchez; Francisco J. Aranda; María J. Espuny; Ana Marqués; José A. Teruel; Ángeles Manresa; Antonio Ortiz (pp. 246-253).
The process of micelle formation, along with the formation of higher order aggregates, is described for a dirhamnolipid extracellular biosurfactant secreted by Pseudomonas aeruginosa. As determined by surface tension measurements, at pH 7.4 the CMC of dirhamnolipid is 0.110 mM, whereas at pH 4.0 it falls to 0.010 mM, indicating that the negatively charged diRL has a much higher CMC value than the neutral species. Centrifugation and dynamic light scattering measurements show formation of larger aggregates at concentrations above the CMC. These aggregates have been shown by electron microscopy to be mainly multilamellar vesicles of heterogeneous size. X-ray scattering gave a value of 32 Å for the interlamellar repeat distance of these vesicles. Taking into account the experimental data, a molecular modelling of the dirhamnolipid moiety has been carried out, which details the size of the hydrophilic and hydrophobic portions, and suggests the possible intermolecular interactions responsible for the stabilisation of dirhamnolipid aggregates. The relevance of this aggregation behaviour is discussed with respect to the molecular basis of its activities.Molecular modelling of dirhamnolipid and intermolecular interactions. By stablishing a high number of hydrogen bonds, dirhamnolipids are able to selfaggregate and form lamellar vesicles.
Keywords: Rhamnolipids; Bacterial glycolipids; Biosurfactants; CMC; Aggregation behaviour
Thermodynamics of ions and water transport in porous media
by A. Revil (pp. 254-264).
The thermodynamic framework of Prigogine, de Groot, and Mazur is extended to study the transport of ions and water in thermoporoelastic materials assuming infinitesimal deformations. New expressions are developed for the first and second principles of nonequilibrium thermodynamics of multicomponent systems and a generalized power balance equation is derived. For porous materials, all the components cannot be treated on a symmetric basis. A Lagrangian framework associated with deformation of the solid phase is introduced and, in this framework, Curie's principle is used to set up the form of the linear constitutive equations describing the transport of ions, water, and heat through the pore network. The material properties entering these equations were recently obtained by Revil and Linde [J. Colloid Interface Science 302 (2006) 682–694] using a volume-averaging approach based in the Nernst–Planck and Stokes equations. This provides a way to relate the material properties entering the constitutive equations to two textural parameters characterizing the topology of the pore space of the material (namely the tortuosity of the pore space and the permeability). The generalized power balance equation is used to derive the linear poroelastic constitutive equations (including the osmotic pressure) to describe the reversible contribution of deformation of the medium in response to ions and water transport through the connected porosity.A thermodynamic model is developed for a multicomponent system and applied to the study of the transport of ions and water in a deformable porous medium saturated by a multicomponent electrolyte.
Keywords: Self-potential; Nonequilibrium thermodynamics; Porous material; Thermoporoelasticity; Dissipation
Residence time distribution for electrokinetic flow through a microchannel comprising a bundle of cylinders
by Jyh-Ping Hsu; Chung-Chieh Ting; Duu-Jong Lee; Shiojenn Tseng; Chur-Jen Chen; Ay Su (pp. 265-271).
The electrokinetic flow of an electrolyte solution through a microchannel that comprises a bundle of cylinders is investigated for the case of constant surface potential. The system under consideration is simulated by a unit cell model, and analytical expressions for the flow field and the corresponding residence time distribution under various conditions are derived. These results are readily applicable to the assessment of the performance of a microreactor such as that which comprises a bundle of optical fibers. Numerical simulations are conducted to investigate the influences of the key parameters, including the thickness of the double layer, the strength of the applied electric field, the magnitude of the applied pressure gradient, and the characteristic sizes of a microchannel, on the residence time distribution. We show that the following could result in a shorter residence time: thin double layer, strong applied electric field, large applied pressure gradient, and small number of cylinders. Based on the thickness of the double layer, criteria are proposed for whether the flow field can be treated as a laminar flow or as a plug flow, two basic limiting cases in reactor design.
Keywords: Residence time distribution; Microchannel; Bundle of cylinders; Electrokinetic flow; Cell model
Self-assembly of acridine orange dye at a mica/solution interface: Formation of nanostripe supramolecular architectures
by Hiroshi Yao; Shogo Kobayashi; Keisaku Kimura (pp. 272-279).
Optical waveguide spectroscopy and atomic force microscopy (AFM) have been used to characterize the supramolecular architectures of acridine orange (AO) dye self-assembled at a mica/aqueous solution interface. Under the saturated adsorption conditions, optical waveguide spectroscopy revealed that the dye formed H-type aggregates at the interface. In situ AFM visualized interesting morphology of the dye aggregates showing nanosized meandering stripes with the width of∼1.5nm (or brightness periodicity of∼3nm). Electrostatic adsorption of the dye cations onto a mica surface as well as the intermolecularπ–π stacking brought about the ordered nanostructures. We propose an interfacial aggregation model that shows a meandering staircase structure with the intermolecular slip angle of 60°. According to the model, the AO molecule occupies a surface area of about 1.0 nm2.Meandering nanostripe morphology of self-assembled AO dye at a mica/solution interface.
Keywords: Interface; Dye self-assembly; Optical waveguide spectroscopy; AFM
Formation of supramolecular hydrogels with controlled microstructures and stability via molecular assembling in a two-component system
by Jiwei Wu; Liming Tang; Kai Chen; Liang Yan; Fei Li; Yujiang Wang (pp. 280-287).
Two isomeric building units, 4-oxo-4-(2-pyridinylamino) butanoic acid (defined as G1) and 4-oxo-4-(3-pyridinylamino) butanoic acid (defined as G2) formed fiber- and tree-like crystals in aqueous solutions, respectively. The crystal formation process of G1 was suggested based on the layered cross section of an individual crystal and the single crystal structure. Through cooling the aqueous solutions of their mixtures under G1/G2 molar ratios ranged from 7/1 to 1/3, a series of supramolecular hydrogels were formed based on hydrogen bonds as the main driving force. As decreasing G1/G2 ratios, the first observed aggregates in solution changed from fiber to particle form, while the gelating time became longer and longer. At the collapsing temperature, the gels formed at G1/G2 ratio ⩾3/1 kept the original gel shape but released water, while at G1/G2 ratio ⩽2/1 they broke into pieces without releasing water. The “dropping ball” experiment indicated that the highest gel-to-sol dissociation temperature (Tgel) is obtained at G1/G2 ratio of 2/1. As measured by UV–vis spectroscopy, the two building units distributed uniformly within the gel formed at G1/G2 ratio of 1/1, indicating they assembled together in forming hydrogel. The scanning electron microscope (SEM) and infrared spectrometer (FT-IR) analysis of the dried samples indicated that the backbone shape changed from fiber to sheet and the content of free carboxyl groups increased with decreasing G1/G2 ratios, therefore resulting in hydrogels with different stability. The simple gelator structures and the possibility in controlling gel structure and stability make the hydrogels suitable for various uses.Supramolecular hydrogels with controlled structure and stability were formed via self-assembling 4-oxo-4-(2-pyridinylamino) butanoic acid and 4-oxo-4-(3-pyridinylamino) butanoic acid in water under various ratios.
Keywords: Supramolecular hydrogel; Hydrogen bonding; Molecular assembling; Gel structure and stability
Polymer-mediated chain-like self-assembly of functionalized gold nanoparticles
by Rama Ranjan Bhattacharjee; Tarun K. Mandal (pp. 288-295).
We report an easy solution phase template-based method to assemble mercaptoundecanoic acid-functionalized gold nanoparticles (MUA-GNPs) along poly(ethylene oxide) (PEO) chains. Transmission electron microscopy (TEM) images show one-dimensional and two-dimensional chain-like sequences of GNPs resembling PEO chains. The progress of the assembly was monitored by the evaluation of surface plasmon resonance band of MUA-GNPs with time by UV–vis spectroscopy. The assembly process is a result of hydrogen bonding interaction between the ethereal oxygen of PEO and carboxylic acid group of MUA attached to GNPs surface, which was confirmed through FTIR spectroscopy. The interaction between PEO and MUA-GNPs was further confirmed by thermal analysis using differential scanning calorimetry.One- and two-dimensional structures of mercaptoundecanoic acid (MUA)-coated gold nanoparticles have been prepared using poly(ethylene oxide) (PEO) as a template through hydrogen bonding interaction between theCOOH groups of surface-adsorbed MUA and the COC groups of PEO.
Keywords: Gold nanoparticle; Polymer; Self-assembly; Chain-like
Relocation of active acetylcholinesterase to liposome–gel conjugate
by Yukihisa Okumura; Hiroki Mizushima; Junzo Sunamoto (pp. 296-299).
Relocation of a glycosylphosphatidylinositol (GPI)-anchored protein acetylcholinesterase (AChE) in its enzymatically active form from proteovesicles containing human erythrocyte ghost membrane proteins onto a liposome–gel conjugate was examined. Liposomes of 1,2-dimyristoylphosphatidylcholine (DMPC) were immobilized on Sephacryl S-1000 gel that was chemically modified to bear hydrophobic octyl moieties. Upon coincubation of the liposome–gel conjugate with freely suspended proteovesicles prepared from erythrocyte ghosts, 50% of the AChE left the proteovesicles and immobilized onto the liposome–gel conjugate in 18 h. When the proteovesicles were immobilized and interacted with freely suspended plain liposomes, approximately 2% of the AChE appeared in the liposome fraction. The relocation of AChE apparently possesses strong preference for the liposome–gel conjugate, suggesting that the hydrophobic moieties on the gel could assist the relocation.Relocation of a glycosylphosphatidylinositol-anchored protein, acetylcholinesterase (AChE), in its enzymatically active form from proteovesicles onto a liposome–gel conjugate was examined.
Keywords: Liposome; Proteovesicle; Acetylcholinesterase; Liposome immobilization; Protein transfer; Glycosylphosphatidylinositol-anchored protein; Cross-linked polymer gel; Protein painting; Protein reconstitution
Copper- and ligand-free Sonogashira reaction catalyzed by palladium in microemulsion
by Jian-Zhong Jiang; Chun Cai (pp. 300-303).
An oil-in-water microemulsion containing PdCl2 and NaOH can be used as an effective catalyst system for rapid copper- and ligand-free Sonogashira reaction of aryl halides and phenylacetylene. Excellent yield of the Sonogashira reaction catalyzed by 0.5 mol% palladium could be achieved within 5 min. The types of base have an intense influence on the reaction. The reaction rate was increased with increased aqueous content in the microemulsions, and dispersed palladium nanoparticles can be in situ formed without other reductants.An oil-in-water microemulsion containing PdCl2 and NaOH can be used as an effective catalyst system for rapid copper- and ligand-free Sonogashira reaction of aryl halides and phenylacetylene. Excellent yield of the Sonogashira reaction catalyzed by 0.5 mol% palladium could be achieved within 5 min.
Keywords: Microemulsion; Palladium; Sonogashira reaction
Formation of 2D colloidal crystals by the Langmuir–Blodgett technique monitored in situ by Brewster angle microscopy
by Alvaro Gil; Francisco Guitián (pp. 304-307).
We report a method that combines Brewster angle microscopy and Langmuir–Blodgett films technique to obtain highly ordered 2D colloidal crystals of nanospheres. The deposition of Langmuir–Blodgett films of silica spheres monitored by Brewster angle microscopy allows to determine with accuracy the best physical conditions to transfer highly ordered monolayers of nanoparticles.A novel, easy and practical method that combines Brewster angle microscopy and Langmuir–Blodgett films to obtain highly ordered colloidal crystals templates of nanospheres is reported.
Keywords: Colloidal crystals; Langmuir–Blodgett; Nanospheres; Photonic crystals