Journal of Colloid And Interface Science (v.334, #2)

Motion of deformable drops through granular media and other confined geometries by Robert H. Davis; Alexander Z. Zinchenko (113-123).
An emulsion of deformable drops flowing through a random loose packed array of solid spheres is simulated using a boundaryintegral method combined with multipole acceleration in a periodic box.This article features recent simulation studies of the flow of emulsions containing deformable drops through pores, constrictions, and granular media. The flow is assumed to be at low Reynolds number, so that viscous forces dominate, and boundary-integral methods are used to determine interfacial velocities and, hence, track the drop motion and shapes. A single drop in a flat channel migrates to the channel centerplane due to deformation-induced drift, which increases its steady-state velocity along the channel. A drop moving towards a smaller interparticle constriction squeezes through the constriction if the capillary number (ratio of viscous deforming forces and interfacial tension forces) is large enough, but it becomes trapped when the capillary number is below a critical value. These concepts then influence the flow of an emulsion through a granular medium, for which the drop phase moves faster than the suspending liquid at large capillary numbers but slower than the suspending liquid at smaller capillary numbers. The permeabilities of the granular medium to both phases increase with increasing capillary number, due to the reduced resistance to squeezing of easily deformed drops, though drop breakup must also be considered at large capillary numbers.
Keywords: Multiphase flow; Drops; Emulsions; Porous media;

Simultaneous adsorption of Cd2+ and phenol on modified N-doped carbon nanotubes: Experimental and DFT studies by Paola E. Diaz-Flores; Florentino López-Urı´as; Mauricio Terrones; J. Rene Rangel-Mendez (124-131).
Optimized geometries for nitrogen-doped single-walled carbon nanotubes (CNx). (a) corresponds to CNx and (b) to CNx with a phenol molecule and charged Cd+2 atom attached to the tube surface.Carbon nanotubes are novel materials that have been investigated for diverse applications, but only a few studies have been focused on environmental issues. In this work, we report on the efficient adsorption of phenol and cadmium ions on N-doped carbon nanotubes (CNx), which have been modified in air at different temperatures. The pristine and modified CNx nanotubes were characterized by SEM, TGA, elemental analysis and their surface areas were also determined. The adsorption experiments of toxic pollutants were carried out in batch reactors at 25 °C. The characterization of modified CNx by these techniques showed an increase in oxygen content and surface area in comparison with the pristine CNx tubes. The individual adsorption capacity was 0.10 and 0.07 mmol/g for phenol and Cd2+, respectively. The experimental data of the competitive adsorption of phenol and Cd2+ revealed that the cadmium removal was favored as the phenol concentration increased, whereas the phenol adsorption capacity was slightly affected at any cadmium concentration. These results suggest that modified CNx tubes have a great potential in environmental applications as adsorbents of organic and inorganic compounds in aqueous phases. In addition, first-principles calculations were carried out in order to elucidate the mechanism of Cd2+ adsorption on CNx.
Keywords: Adsorption; Toxic pollutants; Nitrogen-doped; Carbon nanotubes;

Experimental study and modelling of selenite sorption onto illite and smectite clays by T. Missana; U. Alonso; M. García-Gutiérrez (132-138).
Sorption edges of selenite onto Na-smectite: experimental data at different ionic strengths in NaClO4 and modelling.This study provides a large set of experimental selenite sorption data for pure smectite and illite. Similar sorption behavior existed in both clays: linear within a large range of the Se concentrations investigated (from 1 × 10−10 to 1 × 10−3 M); and independent of ionic strength. Selenite sorption was also analysed in the illite/smectite system with the clays mixed in two different proportions, as follows: (a) 30% illite–70% smectite and (b) 43% illite–57% smectite.The objective of the study was to provide the simplest model possible to fit the experimental data, a model also capable of describing selenite sorption in binary illite/smectite clay systems.Selenite sorption data, separately obtained in the single mineral systems, were modeled using both a one- and a two-site non-electrostatic model that took into account the formation of two complexes at the edge sites of the clay. Although the use of a two-site model slightly improved the fit of data at a pH below 4, the simpler one-site model reproduced satisfactorily all the sorption data from pH 3 to 8.The complexation constants obtained by fitting sorption data of the individual minerals were incorporated into a model to predict the adsorption of selenium in the illite/smectite mixtures; the model’s predictions were consistent with the experimental adsorption data.
Keywords: Adsorption; Selenium; Clays; Radioactive waste;

Supported lipid membranes: how do vesicles fuse to a hydrophobic substrate?We investigated the process of phospholipid vesicle fusion to a hydrophobic surface using electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). The kinetics of the fusion of dimyristoyl phosphatidylcholine (DMPC) vesicles to an octadecanethiol (ODT) self-assembled monolayer (SAM) was followed with EIS and found to be slower than previously reported observations by surface plasmon resonance. AFM images of the DMPC layer taken at various stages of completion show they are uniform with topography similar to that of the bare ODT SAM. The AFM was used in contact mode to scrape away a portion of a completed DMPC monolayer and the hole was stable for several hours. Surprisingly, the hole remained stable even after the temperature of the system was raised to 38 °C, well above the gel transition temperature for DMPC of 23 °C. We were unable to scrape holes in the partially completed monolayers. We conclude that in the early stages of monolayer growth the DMPC molecules spread across the ODT surface after vesicle fusion rather than remaining in dense islands. However, when the DMPC monolayer is complete this mobility is lost and the DMPC will not spread into a vacant area.
Keywords: Adsorption kinetics; AFM; Atomic force microscope; Electrochemical impedance spectroscopy; Supported membrane;

Free energies of PAA adsorption on the Al2O3 surface as a function of temperature.Free energies of polyacrylic acid (PAA) adsorption (ΔG) on an alumina (Al2O3) surface in the temperature range 15–35 °C were estimated on the basis of adsorption–desorption measurements of the inorganic radioactive ions 36Cl, 45Ca, and 55Fe. Adsorbing polymer macromolecules caused the desorption process of previously adsorbed radioactive ions. The free energy of Ca-PAA surface complex formation (ΔG) was estimated to be close to the free energy of Ca2+ ions adsorption (polymer causes about 50% desorption of these ions). Moreover, a free energy of polymer molecule adsorption increase with the increasing temperature was observed. The obtained values of ΔG were compared with those calculated from the adsorption data. Additionally, the amount of polymer adsorbed and the thicknesses of polymer adsorption layers were determined in the temperature range 15–35 °C. The changes of polymer chain conformation with the temperature increase are responsible for the increase of PAA adsorption as well as thickness of polymer adsorption layers in the studied temperature range.
Keywords: Polyacrylic acid; Alumina; Polyelectrolyte adsorption; Adsorption free energy; Polymer adsorption layer thickness;

Intelligent core-shell nanoparticles and hollow spheres based on gelatin and PAA via template polymerization by Yansong Wang; Youwei Zhang; Weiping Du; Chengxun Wu; Jiongxin Zhao (153-160).
Core-shell nanoparticles are prepared by polymerization of AA in a gelatin aqueous solution, followed by successive selective cross-linking and core cavitation to obtain hollow spheres.PAA/gelatin nanoparticles, with interpolymer complexes of gelatin and polyacrylic acid (PAA) as the cores and gelatin as the shells, were prepared via facile polymerization of AA on gelatin template. The morphology change of the nanoparticles during the reaction was traced by a combined use of dynamic light scattering (DLS) and atomic force microscopy (AFM) techniques, which revealed a discrepancy among the structure of the nanoparticles formed at different stages of the reaction: as the reaction proceeds, nanoparticles with larger compact cores and thinner shells are produced. The resultant nanoparticles are multi-responsive. Especially, they exhibit a significant temperature-dependent size change: upon raising the temperature from 25 °C, the nanoparticle size decreases monotonically until reaching equilibrium at about 40 °C. This temperature-dependence of the nanoparticle size was found to be reversible provided the nanoparticle solution was cooled at a low temperature (4 °C). The thermo-sensitivity of the nanoparticles is attributed to the thermo-induced sol–gel transition of the gelatin shells. In addition, the nanoparticles were further converted to hollow spheres via successive locking the shell structure by the reaction of gelatin with cross-linker glutaraldehyde, and cavitation of the cross-linked nanoparticles by switching the medium from acidic to neutral. The cavitation process was monitored by DLS, which indicated a mass decrease and size shrinkage. AFM and transmission electron microscopy (TEM) were used to trace the morphology change of the nanoparticles during the cavitation. The hollow structure was confirmed by TEM observation.
Keywords: Polymerization; Intelligent nanoparticles; Cavitation; Hollow spheres;

Selective immobilization of proteins on gold dot arrays and characterization using chemical force microscopy by Hyunsook Kim; Jun Hyung Park; Il-Hoon Cho; Sung-Kyoung Kim; Se-Hwan Paek; Haiwon Lee (161-166).
The proteins were selectively immobilized on desired sites of a gold nanostructure fabricated by nanosphere lithography. Selective immobilization of antibodies was characterized by imaging the substrate with an atomic force microscope and measuring the interaction force between biomaterials by chemical force microscopy.Streptavidin that has four binding sites arranged in two opposing pairs is known as one of the most important linker proteins for binding the second biotinylated protein. To efficiently locate streptavidins to selective positions without nonspecific binding, we prepared well-controlled arrays of biotins on a gold surface by using a mixed self-assembly process. Two thiol derivatives (11-mercapto-1-undecanol and 11-mercaptoundecanoic-(8-biotinylamido-3,6-dioxaoctyl)amide) were used for preparing the mixed self-assembled monolayers. Fragment antibodies modified with biotin were immobilized on a gold surface covered with streptavidin. This system was applied to gold dot arrays formed by nanosphere lithography. The gold dot arrays were used as the mother structure to construct the array of proteins at the nanometer scale. Selective immobilization of antibodies was characterized by imaging the substrate with an atomic force microscope and measuring the interaction force between biomaterials by chemical force microscopy. Also, the interaction force between antibodies was compared with the force predicted using the Johnson–Kendall–Roberts theory.
Keywords: Mixed self-assembled monolayers (mixed SAMs); Streptavidin; Biotinylated antibody; Nanosphere lithography (NSL); Atomic force microscopy (AFM); Chemical force microscopy (CFM);

Cloud point extraction by using a Schiff base ligand named N,N′-bis(2-hydroxyacetophenone)-1,2-propanediimine is proposed as a pre-concentration step prior to flame atomic absorption spectrometry determination of trace amounts of copper in water samples.Cloud point extraction was used with lipophilic Schiff base N,N′-bis(2-hydroxyacetophenone)-1,2-propanediimine (L) as a pre-concentration step prior to flame atomic absorption spectrometry determination of trace amounts of copper in water samples. The process is based upon the formation of Cu(II)/L complexes soluble in a micellar phase composed by the non-ionic surfactant Triton X-114. These complexes are then extracted into the surfactant-rich phase, at above its cloud point temperature. The parameters affecting the extraction efficiency, i.e. pH of aqueous solution, concentration of the Schiff base, amount of the surfactant, incubation temperature, and time were investigated. Under the optimum experimental conditions, the calibration graph was linear in the range 0.1–1300 ng ml−1 with a limit of detection of 0.06 ng ml−1. The proposed method was successfully applied for the determination of copper in various water samples.
Keywords: Cloud point extraction; Pre-concentration; Copper(II); Schiff base; Water samples;

Drastically enhanced photocatalytic activity in nitrogen doped mesoporous TiO2 with abundant surface states by Gang Liu; Xuewen Wang; Lianzhou Wang; Zhigang Chen; Feng Li; Gao Qing (Max) Lu; Hui-Ming Cheng (171-175).
In contrast to undoped mesoporous TiO2, nitrogen doped mesoporous TiO2 exhibited drastically remarkable UV- and visible photocatalytic activities due to its abundant surface states.Nitrogen doped mesoporous TiO2 was prepared via a modified two-step hydrothermal route. In contrast to undoped mesoporous TiO2, nitrogen doped mesoporous TiO2 has superior photocatalytic activity under both UV and visible light irradiation. Photoluminescence spectra reveal that nitrogen doped mesoporous TiO2 possesses abundant surface states, which can play a vital role in trapping photoinduced carriers as evidenced by photoelectrochemical process and prolonging the lifetime of the carriers. The remarkably enhanced photocatalytic activity in nitrogen doped mesoporous TiO2 is attributed to the generated abundant surface states.
Keywords: TiO2; Mesoporous; Surface states; Nitrogen doping; Photoluminescence;

Hollow Ni–B amorphous alloy with enhanced catalytic efficiency prepared in emulsion system by Hui Li; Ye Xu; Jun Liu; Qingfei Zhao; Hexing Li (176-182).
Hollow Ni–B amorphous alloy nanospheres are fabricated in emulsion system, which exhibits enhanced catalytic performances relative to the dense counterpart, due to the special curved surface with higher Ni dispersion.Ni–B nanospheres were synthesized through chemical reduction of nickel ions with borohydride in an emulsion system comprised of cyclohexylamine, polyethylene glycol, and water. With the characterization of X-ray diffraction, selective area electronic diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, the resulting hollow Ni–B nanospheres were identified to be amorphous alloys with a hollow chamber. Cyclohexylamine played a significant role in fabricating hollow Ni–B nanospheres, because only solid nanoparticles were obtained in the absence of cyclohexylamine. Polyethylene glycol also had a significant influence on the formation of hollow Ni–B nanospheres, because low yield of hollow nanospheres were achieved without this polymer. During liquid-phase chloronitrobenzene hydrogenation, the as-synthesized Ni–B catalyst exhibited a much higher activity and even better selectivity than the dense Ni–B nanoparticles prepared by direct reduction of nickel ions with borohydride.
Keywords: Ni–B amorphous alloy; Hollow nanospheres; Emulsion system; Chloronitrobenzene; Hydrogenation; Chloroaniline;

Zinc oxide nanoparticles/glucose oxidase photoelectrochemical system for the fabrication of biosensor by Xiangling Ren; Dong Chen; Xianwei Meng; Fangqiong Tang; Xianquan Hou; Dong Han; Lin Zhang (183-187).
ZnO nanoparticles could significantly enhance the current response of the enzyme electrodes and the current response of these modified electrodes could be further increased under illumination.Nanosized semiconductor crystals can increase efficiency of photochemical reactions and greatly improve the catalytic activity of enzymes to generate novel photoelectrochemical systems. In this work, glucose oxidase (GOx)/zinc oxide (ZnO) is selected as a model system to assess the photovoltaic effect of semiconductor nanoparticles on the enzyme electrode. UV-spectrum and circular dichroism (CD) results show that the structure of GOx is preserved after conjugation with ZnO nanoparticles. The current response of the enzyme electrode containing ZnO nanoparticles increases from 0.82 to 21 μA cm−2 in the solution of 10 mM β-d-glucose. Furthermore, after irradiating the enzyme electrode with UV light for 2 h, the current response can be increased nearly 30% and the detection limit can be lowered about two orders compared with the catalytic reactions in the dark, which indicate that a technique to fabricate a novel photocontrolled enzyme-based biosensor may be developed.
Keywords: Zinc oxide nanoparticles; Photoelectrochemical system; Glucose oxidase; Biosensor;

Synthesis of highly-monodisperse spherical titania particles with diameters in the submicron range by Shunsuke Tanaka; Daisuke Nogami; Natsuki Tsuda; Yoshikazu Miyake (188-194).
Highly-monodisperse titania particles prepared using dodecylamine had mesopores near the surface of the spheres, providing high pore accessibility to the sphere from the surface–air interface.Monodisperse titania spheres with particle diameters in the range 380–960 nm were successfully synthesized by hydrolysis and condensation of titanium tetraisopropoxide. The preparation was performed using ammonia or dodecylamine (DDA) as a catalyst in methanol/acetonitrile co-solvent at room temperature. The samples were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and nitrogen sorption measurement. The use of DDA was effective for the synthesis of monodisperse titania spheres with low coefficient of variation. When the titania spherical particles with coefficient of variation less than 4% were obtained, the colloidal crystallization easily occurred simply by centrifugation. The monodispersity was maintained even after crystallization of the particles by high temperature annealing. The titania particles prepared using DDA had mesopores near the surface of the spheres, providing high pore accessibility to the sphere from the surface–air interface. The particle size uniformity and photocatalytic reactivity of the titania prepared using DDA were higher than those of the titania prepared using ammonia.
Keywords: Titania; Monodisperse particles; Primary amine; Mesoporous; Pore accessibility;

Functionalization of ceramic tile surface by sol–gel technique by F. Bondioli; R. Taurino; A.M. Ferrari (195-201).
Sol–gel SiO2–TiO2 mixed films have been prepared and deposited onto grés substrate by air-brushing to improve its cleanability keeping good mechanical performances. TiO2 rich films treated at 600 °C exhibit photo-induced hydrophilicity and good scratch resistance.The aim of this investigation was the surface functionalization of industrial ceramic tiles by sol–gel technique to improve at the same time the cleanability of unglazed surfaces. This objective was pursued through the design and preparation of nanostructured coating that was deposited on polished unglazed tiles by air-brushing. In particular TiO2–SiO2 binary film with 1, 2 or 5 wt% of titania were prepared by using tetraethoxysilane and titania nanoparticles as precursors. The obtained films were characterized by scratch tests to verify the adhesion of the coatings to the polished tiles. To mainly evaluate the effect of the thermal treatment (temperature range 100–600 °C) on the photocatalicity of the coatings, the films were studied under UV exposure by contact angle measurements and cleanability test. Particular attention has been paid to preserve the aesthetical aspect of the final product and the obtained hue variation was evaluated by means of UV–visible spectroscopy and colorimetric analysis.
Keywords: Functionalization; Tile; Titania; Photocatalicity; Sol–gel; Contact angle; Scratch resistance; Self-cleaning;

Room temperature fabrication of single crystal nanotubes of CaSn(OH)6 through sonochemical precipitation by Zhiyong Jia; Yiwen Tang; Lijuan Luo; Bihui Li; Zhenghua Chen; Jianbo Wang; He Zheng (202-207).
CaSn(OH)6 nanotubes were fabricated by sonochemical precipitation method at room temperature. A direct rolling process from nanosheets to nanotubes was expected for the synthesis of CaSn(OH)6 nanotubes. The transient CaSn(OH)6 nanosheets are formed as intermediates produced by the spontaneous self-assembly and transformation of amorphous colloid clusters. During the crystallization process of intermediate nanosheets, the relaxation of surface strain in the nanosheet interfaces can induce the nanosheets to roll up to form nanotubes under ultrasonic conditions. In this synthesis, the addition of Na2CO3 seems to play an important role in the formation, size, and shape control of the nanotubes. Investigations into the stability performance of the nanotubes indicate that the morphologies are very sensitive to pH and temperature. The method suggests a general strategy for the design and fabrication of functional single-crystalline nanotubes through an intermediate nanosheet rolling process. The in vitro fabrication of such single crystal nanotubes could shed light on fundamental mechanisms for closed hollow nanostructures. Furthermore, nanotubes produced in high yield and at low cost are envisioned to have applications in areas ranging from medicine to pharmaceuticals through to materials science.
Keywords: Room temperature; Nanotubes; Single crystal; Sonochemical; Precipitation;

The simple and facile methods to improve dispersion stability of nanoparticles: Different chain length alkylcarboxylate mixtures by Longhai Piao; Kyung Hoon Lee; Won Jong Kwon; Sang-Ho Kim; Sungho Yoon (208-211).
The dispersion stability of a Ag nanoparticle with a mixed surfactant of different chain length alkylcarboxylates showed improved dispersion stability compared with those with normal alkylcarboxylates.The dispersion stability of the Ag nanoparticles with a mixed surfactant of alkylcarboxylates was quantitatively examined, compared with those of the Ag nanoparticles with a single molecule surfactant of alkylcarboxylates. The nanoparticles with a mixed surfactants have far-improved dispersion stability compared with those with normal alkylcarboxylates. The surface roughness of the surfactant layer might be responsible for the improved dispersion stability through the enhanced solvent–surfactant interaction and the decrease in inter-particle surfactant interactions.
Keywords: Mixed surfactant; Carboxylic acids; Silver nanoparticle; Colloids; Dispersion stability;

Single-walled carbon nanotubes can be reversibly switched between aggregated and well-exfoliated states by altering pH or temperature in the aqueous solution of poly(N-isopropylacrylamide-co-acrylic acid).Single-walled carbon nanotubes (SWNTs) were homogeneously dispersed in the aqueous solution of poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAm-co-AA)) with the assistance of sonification as evidenced by UV–vis absorption spectroscopy, transmission electron microscopy, field emission scanning electron microscopy and atomic force microscopy, etc. In addition, the SWNTs were endowed with pH- and thermo-sensitivity at the same time. The SWNTs switched reversibly between the aggregated and the well-exfoliated states by using pH or temperature as a stimulus. Moreover, the factors including solvent composition while preparing P(NIPAm-co-AA), concentration and composition of P(NIPAm-co-AA) showed evident influence on the dispersing stability of SWNTs. The introduction of a tiny amount of acrylic acid to copolymerize with N-isopropylacrylamide could greatly enhance dispersing ability of SWNTs.
Keywords: pH-responsive; Thermo-responsive; Single-walled carbon nanotubes; Poly(N-isopropylacrylamide-co-acrylic acid);

by Arthur Hubbard (217).