Journal of Colloid And Interface Science (v.292, #2)


Adsolubilization of toluene and acetophenone as a function of surfactant adsorption by Potjanee Asvapathanagul; Pomthong Malakul; John O'Haver (305-311).
Adsolubilization, solubilization of organic compounds into adsorbed surfactant aggregates, has attracted much attention in the past few years. It is being explored for a variety of new commercial applications including the formation of engineered surfaces, pharmaceutical applications, and nanotechnology. Adsolubilization is strongly influenced by the amount of adsorbed surfactant, which in turn depends upon pH, ionic strength, and surfactant type and concentration. In this study, the adsorption of a cationic surfactant, cetyltrimethylammonium bromide (CTAB) on precipitated silica and the adsolubilization of organic solutes (toluene and acetophenone) into the adsorbed surfactant aggregates were examined as a function of surfactant adsorption at two pH values (5 and 8). Three levels of surfactant adsorption, corresponding to equilibrium concentration low in region II, high in region II, and low in region III of the adsorption isotherm, and the adsolubilization of toluene and acetophenone were investigated both in single- and mixed-solute systems. The results showed that the adsorption of CTAB depended strongly on pH and for each pH the adsolubilization increased with increasing surface adsorption. However, the adsolubilization behaviors of the adsorbed CTAB aggregates in different adsorption regions were quite distinct, suggesting that the structural arrangement of the surfactant aggregates may play an important part in addition to the amount of adsorbed surfactant. This phenomenon was more noticeable at low surfactant adsorption than at higher surface adsorption. In mixed-solute systems, the presence of acetophenone had little effect on the toluene adsolubilization. In contrast, a synergetic effect was observed in the adsolubilization of acetophenone in the presence of toluene.
Keywords: Adsolubilization; Cetyltrimethylammonium bromide; Adsorption; Toluene; Acetophenone; Admicelles;

The dependency of adsorption energy (E) and affinity coefficient (β) of Dubinin equations (Dubinin–Radushkevich (DR) or Dubinin–Astakhov (DA)) on surface chemistry and porosity of activated carbons was investigated by analyzing adsorption of nitrogen, benzene, trichloroethylene (TCE), and water vapor by several surface-modified activated carbons and carbon fibers. For all studied nonpolar adsorbates, carbons with smaller average micropores showed higher adsorption energies independent of their surface chemistry. For water vapor, carbons with higher surface polarities showed higher adsorption energies due to specific adsorbate–adsorbent interactions. Adsorption energies increased with decreasing average micropore widths. β N 2 , DR for different carbons were observed to vary in the 0.292–0.539 range. Carbons with higher degrees of mesoporosity had higher β N 2 , DR values, while no dependency was observed between β N 2 , DR and surface chemistry. A comparison of DR and DA cases indicates that: (1) the average value of β N 2 , DA is considerably above the classical value of this parameter; and (2) the range of β N 2 , DA values were smaller compared to β N 2 , DR , despite a wide range of mesoporosity of carbons examined. Obtained β TCE , DR values varied in the 0.952–1.243 range, with an average value of 1.085 ± 0.083 , independent of surface chemistry or porosity of activated carbons. A similar result was observed for β TCE , DA . β H 2 O , DR values of different granular and fibrous activated carbons changed in the range of 0.081–0.271. They depended more on the carbon surface chemistry and less on the porosity. A similar result was obtained when DA equation was considered.The dependency of adsorption energy and affinity coefficient of Dubinin equations on characteristics of activated carbons was investigated. Adsorption energies increased with decreasing average micropore widths. For nitrogen, carbons with higher degrees of mesoporosity had higher affinity coefficients. For water vapor, carbons with higher surface polarities showed higher adsorption energies.
Keywords: Activated carbon; Carbon fiber; Adsorption; Dubinin equation; Adsorption energy; Affinity coefficient; Carbon fibers; Nitrogen; Benzene; Trichloroethylene; Water vapor;

Thermodynamic aspects of the adsorption of hexametaphosphate on kaolinite by Elena Castellini; Gigliola Lusvardi; Gianluca Malavasi; Ledi Menabue (322-329).
The adsorption of hexametaphosphate ion, an important deflocculant used in the ceramic industry, from aqueous solutions onto kaolinite has been studied at different temperatures. The adsorption isotherm follows the Langmuir model: the thermodynamic parameters Δ G ads 0 , Δ H ads 0 , and Δ S ads 0 were calculated and found to be consistent with an interaction model involving the formation of an inner-sphere complex between HMP and aluminol groups. Also, the dependence of the adsorption behavior on the kaolinite volume fraction has been studied and discussed in term of association processes between the clay particles.The adsorption of hexametaphosphate onto kaolinite was investigated and the related thermodynamic parameters were found coherent with the formation of an inner-sphere complex with the aluminol groups. The arrangement of hexametaphosphate on kaolinite surface was also discussed.
Keywords: Adsorption isotherm; Hexametaphosphate; Kaolinite; Thermodynamic parameters; Adsorption geometries; Volume fraction;

Modeling of adsorption and ultrasonic desorption of cadmium(II) and zinc(II) on local bentonite by Oral Lacin; Bahar Bayrak; Ozlem Korkut; Enes Sayan (330-335).
The adsorption and ultrasonic desorption of toxic heavy metal cations (i.e., Cd(II) and Zn(II)) on natural bentonite have been modeled with the aid of a factorial design approach. The ability of untreated bentonite to remove Cd(II) and Zn(II) from aqueous and acidic solutions at different pH values has been studied for different metal concentrations by varying the amount of adsorbent, temperature, stirring speed, and contact time. The same factors, except stirring speed and metal concentration, were applied in desorption study. Ultrasound power was used for desorption instead of stirring speed. A flame atomic absorption spectrometer was used to measure the cadmium and zinc concentration before and after both experimental study. The highest adsorption for Zn and Cd was 99.85 and 96.84%, respectively, and the highest desorption for Zn and Cd obtained was 66.57 and 51.37%, respectively. It is believed that the models obtained for adsorption and desorption may provide a background for detailed mechanism searches and pilot and industrial scale applications.The statistical analysis shows that solid/liquid ratio (X1), contact time (X2), pH (X3) and temperature (X6) have positive effects, whereas metal concentration (X4), stirring speed (X5) have negative effects on Cd(II) adsorption by untreated bentonite.
Keywords: Adsorption; Desorption; Heavy metals; Ultrasound; Bentonite;

Fly ash, natural zeolite, and unburned carbon separated from fly ash have been employed as low-cost adsorbents for dye adsorption in methylene blue-containing wastewater. It is found that the unburned carbon exhibits a much higher adsorption capacity than raw fly ash and natural zeolite. The adsorption capacities of fly ash, natural zeolite, and unburned carbon for methylene blue are 2 × 10 −5 , 5 × 10 −5 , and 2.5 × 10 −4  mol / g , respectively. Investigation also indicates that adsorption is influenced by initial dye concentration, particle size, dye solution pH, and adsorption temperature. Adsorption on unburned carbon increases with the initial dye concentration, solution pH, and temperature, but reduces with the increasing particle size. Kinetic studies show that adsorption of methylene blue on fly ash, natural zeolite, and unburned carbon can be best described by the pseudo-second-order adsorption model and that adsorption is a two-step diffusion process. The apparent activation energies for methylene blue adsorption on unburned carbon in the first and second diffusion processes are 12.4 and 39.3 kJ/mol, respectively.Unburned carbon in fly ash exhibits a highly porous structure and shows higher capacity for dye adsorption from aqueous solution.
Keywords: Unburned carbon; Fly ash; Natural zeolite; Dye adsorption; Wastewater; Methylene blue;

Biosorbent for tungsten species removal from water: Effects of co-occurring inorganic species by Hatice Gecol; Erdogan Ergican; Parfait Miakatsindila (344-353).
The effect of co-occurring inorganic species on the removal of tungsten from water was investigated using biosorbent (i.e., chitosan coated montmorillonite clay). Simulated natural water and well water from Fallon, NV were used for this study. The concentrations of tungsten (21–541 mg/L) and inorganic species ([H2CO3] = 0–4.2 mg/L, [H4SiO4] = 0–90 mg/L, and [SO2− 4] = 0–400 mg/L) in simulated feed water were varied. The concentration of tungsten in the well water was 26 μg/L. The pH level of simulated feed water and well water was adjusted to 4 since this pH was found to be the most effective pH for the tungsten removal using chitosan coated clay. Tungsten removal without the existence of co-occurring inorganic species decreases from 99.8 to 87.1% with an increase in initial tungsten concentration from 21 to 541 mg/L. It reduces further as the co-occurring inorganic species concentration increases. The percentage of the tungsten removal ranges between 68.2–93.8%, 66.7–94.2%, and 53.6–93.7% for simulated natural water containing varied amount of H2CO3, H4SiO4, and SO2− 4, respectively. The adsorption kinetic data could be best described by the pseudo second order expression. The adsorption equilibrium data was modeled with the Langmuir, Temkin, and Freundlich equations and was found to be represented well by the Langmuir equation. The essential characteristics of the Langmuir isotherm indicate that the adsorption of tungsten on chitosan coated clay is favorable regardless of the presence of interfering species. Compared to natural clay, chitosan coated clay has about 116 times larger adsorption capacity per gram of chitosan, which makes it a superior adsorbent. However, the maximum tungsten adsorption capacity decreases in the presence of co-occurring species since the co-occurring species suppress the adsorption. For the well water treated with biosorbent, the tungsten concentration in the product water was found to be lower than the detection limit (1 μg/L) of the inductively coupled plasma mass spectrometer (ICP-MS). The repeatable results obtained from the treatment of both simulated and well water suggest that using chitosan coated clay can be an efficient adsorbent for tungsten removal from contaminated sites.
Keywords: Tungsten; Biosorbent; Chitosan; Clay; Water treatment; Adsorption kinetics; Adsorption dynamics;

Kinetic and isotherm studies of Cu(II) adsorption onto H3PO4-activated rubber wood sawdust by M. Helen Kalavathy; T. Karthikeyan; S. Rajgopal; Lima Rose Miranda (354-362).
Adsorption of Cu(II) from aqueous solution onto H3PO4-activated carbon using rubber wood sawdust (RSAC) was investigated in a batch system. Kinetic and isotherm studies were carried out by considering the effects of various parameters, such as initial concentration, contact time, pH, and temperature. The optimal pH value for Cu(II) adsorption onto RSAC was found to be 6.0. Thermodynamic parameters such as standard Gibbs free energy ( Δ G 0 ), standard enthalpy ( Δ H 0 ), and standard entropy ( Δ S 0 ) were evaluated by applying the Van't Hoff equation. The thermodynamics of Cu(II) adsorption onto RSAC indicates its spontaneous and exothermic nature. Langmuir, Freundlich, and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The Langmuir isotherm fits the experimental data significantly better than the other isotherms. Adsorption kinetics data were tested using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The initial sorption rate, pseudo-first-order, pseudo-second-order, and intraparticle diffusion rate constants for different initial concentrations were evaluated and discussed. Adsorption mechanism studies revealed that the process was complex and followed both surface adsorption and particle diffusion. The rate-controlling parameter and effective diffusion coefficient were determined using the Reichenberg plot. It was found that the adsorption occurs through film diffusion at low concentrations and at higher concentration the particle diffusion becomes the rate-determining step.
Keywords: Adsorption; Rubber wood sawdust; Activated carbon; Copper; Isotherms; Diffusion; Kinetics;

Multistep adsorption of anionic dyes on silica/chitosan hybrid by Antonio R. Cestari; Eunice F.S. Vieira; Alane A. Pinto; Elaine C.N. Lopes (363-372).
In this work, a hybrid silica/chitosan was synthesized and characterized by nitrogen elemental analysis and thermal analysis (TG, DTG, DTA, and DSC) and BET surface area. The hybrid was used in adsorption studies of two anionic dyes from aqueous solutions. A rise of temperature accelerates mass transfer of dyes into the hybrid. However, the maximum adsorption capacities reach similar values from 25 to 55 °C. The kinetic data were first evaluated in relation to the decrease of the time-related residual concentration of the dyes in solution, where the second-order model has presented the best fitting. The solid-phase interaction of dye data presents a rough fitting to the traditional first-order Lagergren kinetic model. However, a modified Avrami kinetic equation was successfully fitted to the kinetic quantities, where from five to seven kinetic regions were found. A pore-diffusion model has also demonstrated that the diffusion is the rate-controlling interaction mechanism. However, the experimental–calculated comparative values are the best way to evaluate a specific aqueous- or solid-phase kinetic model.
Keywords: Silica gel; Chitosan; Anionic dyes; Adsorption kinetics;

A new model to describe the sorption of surfactants on solids in non-aqueous media by P. Somasundaran; S. Krishnakumar; Somil C. Mehta (373-380).
A new phenomenological model is developed to describe the sorption of surfactants on solids in non-aqueous media. This is based on the use of interaction parameters (δ) among solid, solute and solvent to assess the degree of the various interactions and computing an effective interaction parameter for the entire system represented by δ eff = abs { A | δ solid − δ solvent | + B | δ solute − δ solvent | − C | δ solid − δ solute | } . The effective interaction parameter determines the extent of adsorption that can occur in a given system. Interaction parameters typically account for dispersive interactions between the different components. This new model is used to describe the sorption behavior of a number of surfactant/solvent/solid systems.
Keywords: Effective interaction parameter; Solubility product; Hydrophobic interaction; Sorption model;

The sorption characteristics of insolubilized humic acid (IHA) were investigated for Ni (II) in a column arrangement. The sodium form of the IHA (INaA) was used as a solid phase. Column operations were performed with five steps and all of them were monitored continuously by a flowthrough cell-adapted UV-Vis spectrophotometer. Thus, all solid-phase extraction (SPE) steps were visualized by breakthrough curves and analyses progress were evaluated. However, all calculations and evaluations were focused on the atomic absorption spectrophotometric (AAS) analyses of the solutions collected during the stripping steps. There was a high correlation ( r 2 , 0.972) between peak area and AAS data of stripping steps. The effect of concentration and pH of the loading solution onto sorption of Ni (II) by INaA was investigated. Sorption characteristics were evaluated by using Freundlich, Langmuir, and Dubinin–Radushkevich (D-R) adsorption isotherms, as well as by Scatchard plot analysis. Multilayer sorption was found to be agreeable for Ni (II). From the D-R isotherm the mean free energy of sorption (E) was calculated (6.65 kJ mol−1) and attributed to the multilayer sorption. Finally, the sorption characteristic of the INaA-Ni (II) system was compared with that of the INaA-Cu (II) system, and possible separation of two ions in a binary mixture system is discussed.
Keywords: Insolubilized humic acid; Solid-phase extraction; Breakthrough curve; Nickel; Copper; Adsorption; Ion exchange; Complexation; Stripping; Dubinin–Radushkevich;

Molecular-scale observation of the surface of polystyrene particles by AFM by Tetsuya Yamamoto; Tomohiro Fukushima; Yoichi Kanda; Ko Higashitani (392-396).
The surface morphology of polystyrene particles prepared by soap-free emulsion polymerization was observed in situ using the tapping mode of an atomic force microscope (AFM). Here, the use of a cationic initiator enabled us to synthesize positively charged polystyrene, which then adsorbed electrostatically onto the negatively charged mica plate with molecular-scale smoothness. The following was found from AFM measurements in water. The surface of polystyrene particles changed from smooth to rough as the polymerization proceeded in the experimental condition, where the bulk generated tiny particles continuously, because of the heterocoagulation in the growth process between the newborn and tiny particles and the existing particles. However, it is easy to prepare the particles with smooth surfaces on the condition of rich monomers because the monomers in the bulk dissolve the polymers which form the surface morphology to be deformable and reduce the interfacial area.
Keywords: Polystyrene particles; AFM; Growth mechanism; Soap-free emulsion polymerization; Surface morphology;

In this work a comparative study of different molecular-weight fractions of the amphiphilic polymer poly(tetrahydropyranyl-2-methyl methacrylate) (PTHPMM) in solution and at the air/water interface is reported. The synthesis of the polymer was carried out in solution by radical polymerization. The polymer was fractionated and five fractions were studied in solution and at the air/water interface. The weight-average molecular weight M ¯ w , the second virial coefficient A 2 , and the radius of gyration R g were determined in toluene by static light scattering. Intrinsic viscosities [η] of the polymer fractions in three solvents were obtained. The Kuhn–Mark–Houwink–Sakurada relationships were established. The Langmuir isotherms for different polymer fractions were obtained at the air/water interface by monolayer compression at constant temperature. The overlap surface concentrations were determined, and from these results the radius of gyration in two dimensions was calculated. The thermodynamic power of the toluene and the air/water interface for PTHPMM were estimated from the empirical relationship between the radius of gyration in two and three dimensions and the weight-average molecular weight.
Keywords: Amphiphilic polymer; Air/water interface; Monolayer; Theta condition;

Nanosized hexagonal gibbsite seeds are grown from a mixture of dissolved alumina alkoxides at 85 °C. Centrifugation reduces the polydispersity by 30%. The seeds can be grown further by adding them to a fresh alkoxide mixture and heating it. This procedure was repeated several times to obtain particles of 570 nm ± 11% diameter and a thickness of 47 ± 23%. No indications of a size limit were observed. The thus obtained particles may form easily a columnar phase. Individual gibbsite particles in solution can be seen by confocal microscope.
Keywords: Colloidal platelets; Monodisperse; Gibbsite; Seeded growth; Confocal microscopy;

Surfactant-controlled synthesis of Fe nanorods in solution by Dongen Zhang; Xiaomin Ni; Huagui Zheng (410-412).
Rodlike Fe particles were prepared by reduction of iron salts with hydrazine hydrate in the presence of CTAB. The as-prepared powders were characterized in detail by conventional techniques such as X-ray diffraction, and scanning electron microscopy, and their magnetic properties were evaluated on a vibrating sample magnetometer.
Keywords: Iron; Nanocrystalline materials; Rodlike; X-ray diffraction; Coercivity;

This study focuses on the relation among hydrodynamics, physicochemical conditions, and floc size. During ortho-kinetic flocculation, the floc size is controlled by a balance between hydrodynamic stress and aggregate strength. Special attention was paid to the influence of a hydrodynamic sequencing on both the aggregate strength and the flocculation processes. Experimental research was conducted in a 1-L jar for two different pH values. The hydrodynamic sequencing was made up of successive slow and rapid mixing periods, and different slow mixing intensities were studied. First, the large floc size was shown to decrease with increasing velocity gradient (G), with an expected trend ( d ∝ ɛ − 1 4 ). Then, the aggregate strength was shown to depend on two main factors: the flocculation history and the physicochemical conditions, which control the cohesion forces between primary particles. Finally, flocculation processes are discussed in terms of aggregation and breakup phenomena, with relation to local hydrodynamics and physicochemical conditions.
Keywords: Floc size distribution; Hydrodynamic sequencing; Dissipation rate of kinetic energy; Image processing; Aggregate strength;

Influence of synthetic parameters on the size, structure, and stability of dodecanethiol-stabilized silver nanoparticles by Marcela M. Oliveira; Daniel Ugarte; Daniela Zanchet; Aldo J.G. Zarbin (429-435).
Metal nanoparticles (NP) are very attractive because of their size- and shape-dependent properties. A widely used preparation of ligand-stabilized metal NP is the two-phase liquid–liquid method using dodecanethiol (DT) as ligand. This work presents various procedures to synthesize dodecanethiol-capped silver NPs, all of them based on a two-phase liquid–liquid method. Small alterations in the synthetic parameters lead to dramatic modifications in the nanoparticles' average size, size distribution width, stability, and structure, as well as in their ability to self-assemble.This work shows the influence of synthetic parameters on the size, size distribution, stability and structure of dodecanethiol-capped silver nanoparticles. High homogeneous samples can be obtained through a deeper control of these parameters.
Keywords: Silver nanoparticles; Colloid materials; Nanochemistry;

In order to improve the rheological behavior of the nanosilica composite no-flow underfill, filler surface treatment using silane coupling agents was investigated to reduce the filler–filler interaction and to achieve the mono-dispersity of the nanosilica in the underfill resin. The experimental conditions of the surface treatment were investigated in a design of experiment (DOE) in terms of the pre-treatment methods, coupling agent types, concentrations, and treatment durations. The particle dispersion after treatment was evaluated by the laser particle analyzer and the transmission electron microscopy (TEM). A mono-dispersed nanosilica solution in the polar medium was achieved using optimal experimental condition. The surface chemistry of the nanosilica was studied using Fourier transformed infrared spectroscopy (FTIR). The wettability of underfill resin and water on the silane treated glass slides was studied using a goniometer. Based on the investigations, the silane-treated nanosilica fillers were incorporated into an underfill resin to formulate a nanocomposite no-flow underfill. It was found that the proper filler treatment could significantly reduce the viscosity of the nanocomposite.The viscosity of nanosilica/epoxy underfill is significantly influenced by the surface chemistry of filler. The nanosilica modified by amine-type coupling agent is even worse than the unmodified nanosilica in terms of compatibility with epoxy underfill and viscosity.
Keywords: Nanocomposite; Underfill; Particle dispersion; Surface modification; Rheology;

We have designed a simple synthetic procedure to encapsulate colloidal gold nanoparticles by electrostatic adsorption with water-soluble poly(aniline-2-carboxylic acid). The composite nanoparticles are stable in aqueous buffer and retain the respective optical reactivity of the gold colloid to refractive index increases, and of the conductive polymer to pH changes and oxidoreduction. The new composite displays, however, significant enhancements in photonic performance when compared to the individual components, which seem to result from electronic interplay between the two materials in the hybrid structure. The enhanced photonic reactivity of the composite structure offers new opportunities for biosensing application.
Keywords: Gold colloid; Conductive polymer; Composite; Encapsulation; Photonic reactivity; Surface plasmon resonance; pH; Oxidoreduction;

A new SERS-active silver film prepared by directly depositing silver nanoparticles on glass is reported. The spontaneous reduction of Ag+ ions in N , N -dimethylformamide (DMF) (in the absence of a protecting agent) leads to the deposition of silver nanoparticles on clean glass surfaces in contact with the solution. The observed optical micrographs and AFM images show that the arrangement of the nanoparticles is inhomogeneous and the particles appear to be closely packed. These films are shown to be excellent substrates for SERS measurements, demonstrating significant enhancement, good stability, and trace detection capability. The SERS enhancement of the silver films with different deposition times was compared and found that the 8-h film gives the largest enhancement ability with an enhancement factor estimated at about 109. It is also found that the silver films stored for 80 days in air show no significant degradation in their sensitivity.A SERS-active substrate based on deposition of silver nanoparticles on clean glass surfaces was reported. This film shows significant enhancement, good stability, and trace detection capability for SERS measurements.
Keywords: SERS; Silver nanoparticles; Substrate;

The interlayer swelling and molecular packing in organoclays by D.R. Paul; Q.H. Zeng; A.B. Yu; G.Q. Lu (462-468).
Understanding the interlayer swelling and molecular packing in organoclays is important to the formation and design of polymer nanocomposites. This paper presents recent experimental and molecular simulation studies on a variety of organoclays that show a linear relationship between the increase of d-spacing and the mass ratio between organic and clay. A denser molecular packing is observed in organoclays containing surfactants with hydroxyl–ethyl units. Moreover, our simulation results show that the head (nitrogen) groups are essentially tethered to the clay surface while the long hydrocarbon chains tend to adopt a layering structure with disordered conformation, which contrasts with the previous assumptions of either the chains lying parallel to the clay surface or being tilted at rather precise angles.Molecular simulations show that the alkyl chains of organoclay surfactants pack in a disordered conformation but with a tendency for layering. The measured and calculated gallery spacings increase in proportion to the mass of the surfactant consistent with a given mass density of the confined organic material with good agreement between experiment and simulation.
Keywords: Organoclay; Interlayer swelling; Molecular packing; Nanocomposite;

A roughened silver electrode modified with silver nanoparticles is used as a substrate, on which high-quality surface-enhanced Raman spectroscopy (SERS) of isonicotinic acid (INA) are obtained, indicating that the silver-modified silver electrode is a highly SERS-active substrate. It is difficult to separate the contributions of the electromagnetic and chemical mechanisms to the great enhancement of the Raman signal. The shift by 5–20 cm−1 of the surface-enhanced Raman spectroscopy (SERS) bands and the change in their relative intensity compared with the ordinary Raman spectrum indicate the chemisorption of the sample molecules on the silver-modified silver surface. Furthermore, the silver nanoparticles modified on the roughened silver surface play the important role of magnifying the surface local electric field near the silver surface through resonant surface plasmon excitation. From the rich information on the silver-modified silver electrode obtained from high-quality potential-dependent SERS, we may deduce the adsorption behavior of INA and the probable SERS mechanism in the process. The probable reasons are given.A new SERS-active substrate—roughened silver electrode modified with silver nanoparticles shows highly SERS activity which is much superior to that of the silver aqueous colloid and the roughened silver electrode.
Keywords: Surface-enhanced Raman spectroscopy (SERS); Isonicotinic acid (INA); Silver nanoparticles; Silver electrode; Silver-modified silver electrode; Adsorption behavior;

Zirconia having high thermal stability and high surface area (up to 160 m2/g at 700 °C) has been prepared by a colloidal “digesting” process. This material having demonstrated high surface areas at elevated temperatures was then applied as a catalyst support. A Pd colloid with diameter of ≈12 nm has been successfully deposited on the high surface area zirconia material. All systems have been well characterized by TEM, X-ray diffraction, N2 adsorption isotherms, FTIR, elemental analysis and dynamic light scattering techniques. The colloidal Pd particles have been found homogeneously well dispersed in the hydrous zirconia matrix without aggregation. The Pd/ZrO2 catalysts have been screened for cyclohexene and 1-hexene hydrogenation activity and it was found that the catalyst is extremely active.A colloid “digesting” route has been employed to synthesize high surface area Pd/ZrO2 catalyst. This catalyst was found to be very active toward cyclohexene and 1-hexene hydrogenation reactions.
Keywords: Heterogeneous; Catalyst; Palladium; Zirconia; Hydrogenation; Colloid;

The Wells–Dawson tungsten heteropolyacid, H6P2W18O62 supported on sol–gel and non-sol–gel alumina has been investigated by infrared spectroscopy (IR), thermal analysis (TGA/DSC), and X-ray diffraction (XRD). X-ray diffraction indicates that the heteropolyacid primary structure in bulk form holds up to 350 °C and by supporting it on the sol–gel alumina the thermal stability rose to 650 °C. UV–vis spectroscopy showed that the sol–gel alumina has a higher tendency to adsorb Wells–Dawson tungsten heteropolyacid than the non-sol–gel alumina. The heteropolyacid showed higher interaction with the sol–gel alumina than with the non-sol–gel. Esterification of propanoic acid with hexanol in the presence of alumina-supported heteropolyacid revealed that the acidic character of the heteropolyacid remains active to some extent.UV–vis spectroscopy shows that the sol–gel alumina has a higher tendency to adsorb Wells–Dawson tungsten heteropolyacid than the non-sol–gel alumina.
Keywords: Heteropolyacid; Wells–Dawson; Sol–gel; Alumina; Adsorption;

The reduction of nitric oxide (NO) over Cu/ACFs, prepared by copper electroplating, has been studied. It is found that copper content on the ACFs increases with increasing plating time (up to 45 wt%), while the textural properties including specific surface areas and total pore volumes decrease. As an experimental result, the NO reduction efficiency is increased in all of the Cu/ACFs, and it is confirmed that NO is converted into nitrogen and oxygen on the Cu/ACF surfaces (at 500 °C). Especially, the Cu metals on the ACF surfaces scavenge oxygen by oxidizing themselves into Cu2O and finally CuO as a reductant. It is indicated that copper metals on the Cu/ACFs play a major role in the NO removal in this system.The reduction of nitric oxide (NO) over Cu/ACFs, prepared by copper electroplating, has been studied. It is found that copper content on the ACFs increases with increasing plating time (up to 45 wt%), while the textural properties including specific surface areas and total pore volumes decrease. As an experimental result, the NO reduction efficiency is increased in all of the Cu/ACFs, and it is confirmed that NO is converted into nitrogen and oxygen on the Cu/ACF surfaces (at 500 °C). Especially, the Cu metals on the ACF surfaces scavenge oxygen by oxidizing themselves into Cu2O and finally CuO as a reductant. It is indicated that copper metals on the Cu/ACFs play a major role in the NO removal in this system.
Keywords: Activated carbon fibers; Electroplating; NO reduction; Metallic copper particles;

The competitive transport of Fe(III) and Ti(IV) ions and the effect of chelating agents on separation from binary mixture solutions through charged polysulfone cation-exchange membrane (SA3S) has been studied under Donnan dialysis conditions. The amount of chelating agent was taken as an equimolar of Fe(III) ion in the feed phase. In this process, the membrane separated two electrolyte solutions: the feed solution, initially containing metal salts (Fe, Ti), or metal salts solution, containing a chelating agent, and the other side (receiver solution) being HCl solution. An external potential field is not applied. It was observed that the chelating agents affect the metal transport; the transport of Fe(III) is decreased and the transport of Ti(IV) is increased.The general diagram of ion transport from cation-exchange membrane.
Keywords: Donnan dialysis; Metal transport; Chelating agent; Cation-exchange membrane;

Stable thin films and hollow spheres composing chiral polyaniline composites by Linglu Yang; Zhaohui Yang; Weixiao Cao (503-508).
Chiral polyaniline composite (CPAC) thin films were fabricated by self-assembly using diazoresin (DR) and CPAC. The weak linkage between the DR and CPAC of the film will convert to covalent bonds under UV irradiation or heating, and the thin film becomes very stable toward polar solvents and electrolyte aqueous solutions. Core–shell particles with stable DR/CPAC shell and polystyrene (PS) core can be prepared by similar methods. After the PS core is removed by chemical etching, stable DR/CPAC hollow spheres were obtained. Circular dichroism spectra and cyclic voltammetry measurements show that the DR/CPAC thin films are chirally active and possess good electrochemical stability.Stable thin films and hollow spheres composed of chiral polyaniline composites and diazoresin are respectively fabricated in planar and spherical substrates by self-assembly and photo- or thermo-crosslinking technique.
Keywords: Chiral polyaniline; Self-assembly; Core–shell particles; Hollow spheres; Photocrosslinking;

Preparation and characterization of polyaniline-containing Na-AlMCM-41 as composite material with semiconductor behavior by Oscar A. Anunziata; Marcos B. Gómez Costa; Rodolfo D. Sánchez (509-516).
Composite material formed from a mesoporous aluminosilicate, Na-AlMCM-41, with conducting polyaniline (PANI) has been synthesized by an in situ polymerization technique. Studies of aniline adsorption over mesoporous Na-AlMCM-41 synthesized in our laboratory allowed us to find the modes in which aniline interacts with the active sites of Na-AlMCM-41. In order to obtain the best reaction conditions to polymerize aniline onto Na-AlMCM-41, aniline was first polymerized to produce pure PANI. Hence, the oxidative in situ polymerization was carried out by two procedures, differing in the polymerization time and in static or stirring conditions. Studies of infrared spectroscopy and UV–vis spectroscopy indicated that higher polymerization time and static conditions allowed us to obtain mainly polyaniline in emeraldine form on the host. The N2 isotherm of the polyaniline/Na-AlMCM-41 composite (PANI/MCM) indicated that the shape was similar to that of MCM, but the shift to saturation transition to lower partial pressure shows that the channels are occupied by PANI and they are now narrowed. The thermal properties of PANI, Na-AlMCM-41, and composite were investigated by TGA analyses and we found that the polymer shows higher thermal stability when it is forming the composite. Scanning electron microscopy indicated that PANI is not on the outer surface of the host. Conductivity studies show that PANI/Na-AlMCM-41 exhibits semiconductor behavior at room temperature and its conductivity was 7.0 × 10 −5  S / cm , smaller than that of pure polyaniline. PANI/Na-AlMCM-41 conductivity shows an increase as temperature increases. Magnetic measurements at room temperature confirmed that the composite has paramagnetic behavior; at lower temperatures the composite became diamagnetic.
Keywords: Composite; Aniline; PANI; M41S; Conductivity; Nanowire;

Capillarity–dissolution system for a two-dimensional geometry by Stéphane Clain; François Dupret (517-536).
We consider a system composed of two fluids in contact with a solid where one of these fluids dissolves the solid material. Both the dissolution process and the capillary phenomena play a role in the system evolution, which is analyzed on the basis of stability arguments for a two-dimensional geometry.
Keywords: Capillarity; Dissolution; Metastable curve;

Lead biosorption study with Rhizopus arrhizus using a metal-based titration technique by Ghinwa Naja; Christian Mustin; Jacques Berthelin; Bohumil Volesky (537-543).
Acid–base and metal-based potentiometric titration methods were used to analyze sorption mechanisms of lead by Rhizopus arrhizus fungal biomass. Biosorption was not considered globally but as the result of successive sorption reactions on various binding sites with different selectivities. Precipitation occurred rapidly when lead concentration increased. Lead was sorbed essentially by carboxylic groups and by phosphates and sulfonates (less abundant) of the organic matter. The lead affinity to carboxylic, sulfonate and phosphate binding sites depended on the association coefficient with proton or counter-ion and on the spatial distribution of the surface sites promoting the formation of mono- or bi-dentate complexes. Chemical bonds and binding sites were confirmed using microscopic and spectroscopic techniques (IR, MET-EDAX). It appeared that although the total organic acidity was reached, number of ionized and free carboxylic groups were not involved in lead sorption reactions. In spite of lead speciation in the solution, surface micro-precipitation was observed and the two processes, surface adsorption and micro-precipitation, are sequential and possibly overlapping. At low concentrations ( < 10 −6   M ) adsorption is the dominant phenomenon and beyond ( > 10 −5   M ) surface clusters appeared before the predicted solution precipitation phenomenon.
Keywords: Metal-based high resolution potentiometric titration; Acidic functional groups; Sorption capacity; Rhizopus arrhizus fungal biomass;

Effect of cosurfactant on the free-drainage regime of aqueous foams by Alfredo Cervantes-Martínez; Arnaud Saint-Jalmes; Amir Maldonado; Dominique Langevin (544-547).
We report results of drainage in aqueous foams of small bubble size D ( D = 180   μm ) prepared with SDS-dodecanol solutions. We have performed free-drainage experiments in which local drainage rates are measured by electrical conductivity and by light scattering techniques. We have investigated the role of the surfactant–cosurfactant mass ratio on the drainage regime. The results confirm that a drainage regime corresponding to a high surface mobility can indeed be found for such small bubbles, and show that an increase in the cosurfactant content can induce a transition to a low surface mobility drainage regime. We show that the transition is not linked to variations of the bulk properties, but rather to variations of the interfacial properties. However, the results show that the added amount of dodecanol to trigger the transition is quite high, evidencing that the relevant control parameter for drainage regimes includes both bubble size and interfacial contributions.
Keywords: Foams; Drainage; Cosurfactant; Sodium dodecyl sulfate; Surface viscosity;

The effect of copolymer concentration, temperature, and sodium halides (NaI, NaBr, NaCl, and NaF) on micellization and micellar properties of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic copolymer (Pluronic L64: EO13PO30EO13), was examined by different methods such as dye spectral change, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), small angle neutron scattering (SANS), dynamic light scattering (DLS), viscosity, and cloud point (CP). Temperature/polymer concentration/salt dependent aggregation behavior of L64 was observed. The data on critical micelle concentration (CMC), critical micelle temperature (CMT), (CP), micelle size, and shape are reported. The Fourier transform infrared (FTIR) showed temperature dependent changes in C–O–C stretching variation band towards higher wave numbers and broadening of band width during the micellization process; this was attributed to increase in proportion of the anhydrous methyl groups, while the proportion of the hydrated methyl groups was decreased. Differential scanning calorimetry (DSC) provides CMTs and CPs from the same experiment. CMC values derived from dye spectral change, decrease significantly with the addition of salt. The increases in salt/copolymer concentration lower the onset temperature of micellization (CMT). Halide anions influence both CMT and CP in the order of F > Cl > Br > I when total salt and copolymer concentration kept constant. SANS results show the increase of inter-micellar interaction due to the increase in temperature/salt concentration; this is supported by viscosity data.
Keywords: Pluronics; Cloud points; Inter-micellar;

The effects of hydrolysable Cu2+, Al3+ and Th4+ ions on the zeta potential and yield stress behaviour of silica dispersions were evaluated as a function of pH and metal ions concentration. Silica dispersion remained dispersed at its point of zero charge (pzc) of pH ∼2.0 (CR1). Adsorbed hydrolysis products of Cu2+ and Al3+ caused the dispersion to display two further points of charge reversal (CR2 and CR3) at moderate ions concentration. CR2 occurred near the pH for the formation of the first hydrolysis product. This pH is about 2.8 for Al3+ and 5.0 for Cu2+. For all three metal ions, CR3 approached the pzc of the metal hydroxides at complete surface coverage. At CR3, the dispersions displayed a maximum yield stress. As many as three type of attractive forces; bridging, charged patch and van der Waals, may account for the maximum yield stress at low surface coverage. At complete coverage, only the van der Waals force is in play—the adsorbed hydrolysis products must have increased significantly the effective Hamaker constant of silica. With Al3+ the yield stress was absent at CR2 because particle bridging and charged patch attraction are unimportant as the silica surface charge is near zero. Adsorption of strongly hydrolysed Th4+ ions at pH < 2.0 caused the dispersion to display only one pzc (CR3).
Keywords: Metal ions hydrolysis products; Yield stress; Zeta potential; Charged patch attraction; Bridging; Silica;

Transient streaming potential in a finite length microchannel by Ali Mansouri; Carl Scheuerman; Subir Bhattacharjee; Daniel Y. Kwok; Larry W. Kostiuk (567-580).
Pressure-driven flow of an electrolyte solution in a microchannel with charged solid surfaces induces a streaming potential across the microchannel. Such a flow also causes rejection of ions by the microchannel, leading to different concentrations in the feed and permeate reservoirs connecting the capillary, which forms the basis of membrane based separation of electrolytes. Modeling approaches traditionally employed to assess the streaming potential development and ion rejection by capillaries often present a confusing picture of the governing electrochemical transport processes. In this paper, a transient numerical simulation of electrochemical transport process leading to the development of a streaming potential across a finite length circular cylindrical microchannel connecting two infinite reservoirs is presented. The solution based on finite element analysis shows the transient development of ionic concentrations, electric fields, and the streaming potential over the length of the microchannel. The transient analysis presented here resolves several contradictions between the two types of modeling approaches employed in assessing streaming potential development and ion rejection. The simulation results show that the streaming potential across the channel is predominantly set up at the timescale of the developing convective transport, while the equilibrium ion concentrations are developed over a considerably longer duration.
Keywords: Electrokinetic transport phenomena; Streaming potential; Transient simulation; Microfluidics;

We have investigated the influences of the magnetic field strength, shear rate, and random forces on transport coefficients such as viscosity and diffusion coefficient, and also on the orientational distributions of rodlike particles of a dilute colloidal dispersion. This dispersion is composed of ferromagnetic spheroidal particles with a magnetic moment normal to the particle axis. In the present analysis, these spheroidal particles are assumed to conduct the rotational Brownian motion in a simple shear flow as well as an external magnetic field. The basic equation of the orientational distribution function has been derived from the balance of the torques and solved numerically. The results obtained here are summarized as follows. For a very strong magnetic field, the rodlike particle is significantly restricted in the field direction, so that the particle points to a direction normal to the flow direction (and also to the magnetic field direction). However, the present particle does not exhibit a strong directional characteristic, which is one of the typical properties for the previous particle with a magnetic moment parallel to the particle axis. That is, the particle can rotate around the axis of the magnetic moment, although the magnetic moment nearly points to the field direction. The viscosity significantly increases with the field strength, as in the previous particle model. The particle of a larger aspect ratio leads to the larger increase in the viscosity, since such elongated particles induce larger resistance in a flow field. The diffusion coefficient under circumstances of an applied magnetic field is in reasonable agreement between theoretical and experimental results.
Keywords: Ferromagnetic colloidal dispersion; Aggregation phenomena; Simple shear flow; Spheroidal particle; Orientational distribution function; Rheological properties; Viscosity; Diffusion coefficient;

Influence of glymes upon percolative phenomena in AOT-based microemulsions by J. Dasilva-Carbalhal; L. García-Río; D. Gómez-Díaz; J.C. Mejuto; M. Pérez-Lorenzo (591-594).
A study was carried out on the influence of different polyethylene glycol dimethyl ethers (glymes) on the conductance percolation of AOT/isooctane/water microemulsions. The glymes used were chosen on the basis of this chain length (the number of polymeric units). In all cases we observed a decrease in the percolation threshold on increasing the amount of a glyme added to the microemulsion. We observed a correlation between the effect exerted by the glyme and its chain length, which shows the importance of including them in the interface for the percolative phenomenon. Such inclusion modifies the properties of the AOT film, facilitating the exchange of matter between droplets. The influence of glymes on percolation phenomena in water in oil microemulsions is a consequence of their association to the interface and their ability to form complexes with Na+.Display Omitted
Keywords: Conductance conductivity; Percolation; Microemulsion; AOT; Glyme; Percolation temperature; Percolation threshold;

Discharging a high-energy spark underwater creates a shock wave that dissipates through an acoustic field. Colloidal acrylate polymers suspended in water containing dissolved calcium are agglomerated as a result. The degree of agglomeration increases with the number of sparks applied and with increasing calcium content. The calcium decreases the charge on the colloidal particles and thereby increases their propensity to be agglomerated by the acoustic wave. These observations are confirmed in full-scale trials in paper recycling mills where sparking improves the efficiency of centrifugal cleaners by increasing the particle size of the contaminants.Effect of sparking on colloidal contaminants in the accepts stream. The ordinate represents daily samples. The circles and triangles represent results for control and “sparker on” situations, respectively. The two bars represent averages of 0.45 (sparked) and 0.51 (control).
Keywords: Acoustic; Polymer; Spark; Electrohydraulic; Centrifugal cleaner; Recycle; PSA;

A novel method of flocculation resulting in both rapid sedimentation and low sediment moisture is described. It relies on changing the inter-particle forces from repulsive to attractive (aggregation and fast settling results) and then back to repulsive (densification of sediment then occurs). The change in inter-particle force is controlled by a stimulus such as pH or temperature. The technique is demonstrated without polymer using the isoelectric point and pH as the stimulus. The polyelectrolyte chitosan produces faster sedimentation and clearer supernatants as a pH sensitive flocculant. Methylcellulose is an effective temperature sensitive flocculant. The sediment bed volumes can be reduced by between 10 and 45% depending upon the conditions which, as yet, have not been fully optimized.Solid/liquid separation is improved using stimulant sensitive flocculants. Attraction only (pH 8) results in low density sediment; attraction followed by repulsion (pH 8 then pH 4.5) results in dense sediment.
Keywords: Flocculation; Smart polymers; Sedimentation; Consolidation; Chitosan; Methylcellulose;