Journal of Colloid And Interface Science (v.290, #1)

Heterogeneous Do–Do model of water adsorption on carbons by Sylwester Furmaniak; Piotr A. Gauden; Artur P. Terzyk; Gerhard Rychlicki; Radosław P. Wesołowski; Piotr Kowalczyk (1-13).
The model of water adsorption on carbons proposed five years ago by Do and Do is analyzed and improved. Following the experimental evidence that for activated carbons surface active groups differ in the value of the energy of interaction with water molecules, we propose to extend the original model to take this fundamental feature into account. For the original DD model, as well as proposed new heterogeneous one (HDDM), we develop also the corresponding isosteric enthalpy of adsorption formulas. The features of the HDDM are studied via simulations. It is shown that the new model predicts the shapes of adsorption isotherm as well as corresponding enthalpy observed for real experimental systems. Finally, the HDDM is successfully applied to description of arbitrarily chosen adsorption and enthalpy of adsorption data. Up to our knowledge, HDDM is the first model describing satisfactorily water adsorption isotherms and corresponding enthalpy data measured on different microporous activated carbons in the whole relative pressure range.
Keywords: Carbon; Water adsorption; Chemisorption; Microporosity; Hydrophilic centers; Primary adsorption sites; Heat of adsorption; Surface properties;

Surface complexation of organic arsenic on nanocrystalline titanium oxide by Chuanyong Jing; Xiaoguang Meng; Suqin Liu; Salem Baidas; Ravi Patraju; Christos Christodoulatos; George P. Korfiatis (14-21).
The adsorption mechanisms of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) on nanocrystalline titanium oxide (TiO2) were investigated with X-ray absorption spectroscopy (XAS), surface charge and zeta potential measurements, adsorption edge, and surface complexation modeling. XAS data demonstrated that MMA and DMA formed bidentate and monodentate inner sphere complexes with the TiO2 surface, respectively. The charge and zeta potential behaviors of TiO2 as a function of ionic strength suggested that the point of zero charge (PZC) and isoelectric point (IEP) of TiO2 were identical at pH 5.8. Adsorption of MMA and DMA on TiO2 shifted the IEP to pH 4.1 and 4.8, respectively, indicating the formation of negatively charged surface complexes. A satisfactory interpretation of the experimental data was provided by the charge distribution (CD) multi-site complexation (MUSIC) model with the triple plane option under the constraint of the XAS evidence.
Keywords: Organic arsenic; TiO2; EXAFS; Surface charge; Zeta potential; CD-MUSIC model;

Studies on manganese nodule leached residues by K.M. Parida; S. Mallick; S.S. Dash (22-27).
Adsorption of phosphate onto manganese nodule leached residues was investigated as a possible alternative to conventional methods of phosphate removal from industrial effluents. Adsorption behaviors were studied as a function of time, temperature, pH, and concentration level of adsorbate and adsorbent in acetic acid–sodium acetate buffer medium. The adsorption of phosphate follows the Langmuir adsorption isotherms. The magnitude of adsorption of phosphate in manganese nodule leached residues was compared with that in naturally occurring Mn nodule. Manganese nodule leached residues show better affinity toward phosphate adsorption.
Keywords: Manganese nodules; Manganese nodule leached residues; Adsorption; Surface area; Phosphates;

Competitive adsorption behavior of heavy metals on kaolinite by Prashant Srivastava; Balwant Singh; Michael Angove (28-38).
Polluted and contaminated soils can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a soil system will be affected by the presence of other metals. In this study we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto kaolinite in single- and multi-element systems as a function of pH and concentration, in a background solution of 0.01 M NaNO3. In adsorption edge experiments, the pH was varied from 3.5 to 10.0 with total metal concentration 133.3 μM in the single-element system and 33.3 μM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH50 (the pH at which 50% adsorption occurs) was found to follow the sequence Cu < Zn < Pb < Cd in single-element systems, but Pb < Cu < Zn < Cd in the multi-element system. Adsorption isotherms at pH 6.0 in the multi-element systems showed that there is competition among various metals for adsorption sites on kaolinite. The adsorption and potentiometric titrations data for various kaolinite–metal systems were modeled using an extended constant-capacitance surface complexation model that assumed an ion-exchange process below pH 7.0 and the formation of inner-sphere surface complexes at higher pH. Inner-sphere complexation was more dominant for the Cu(II) and Pb(II) systems.
Keywords: Heavy metals; Cadmium; Copper; Lead; Zinc; Kaolinite; Competitive adsorption; Surface complexation modeling; Extended constant-capacitance model;

Sorption and immobilization of cellulase on silicate clay minerals by Ali Akbar Safari Sinegani; Giti Emtiazi; Hossain Shariatmadari (39-44).
The interaction of organic molecules with mineral surfaces is a subject of interest in a variety of disciplines. Enzymes are able to be sorbed and immobilized by clay minerals and humic colloids in soil environment. The present study was done to elucidate some aspects of sorption and immobilization of cellulase on soil components by analysis of the sorption, and immobilization of cellulase on Avicel, a soil sample, illite, kaolinite, montmorillonite, and palygorskite. Palygorskite displayed the highest sorption capacity. Sorbents coated with hydroxyaluminum displayed significantly higher capacity than uncoated sorbents. The positive effects of Al(OH) x coating on sorption capacities of the different sorbents were not equal. The effect decreased in the order soil > palygorskite > kaolinite > Avicel > montmorillonite > illite. The amount of sorbed cellulase desorbed from external surfaces of soil was quite low (about 16%), especially in coated samples (about 6%). X-ray diffraction analysis of K-montmorillonite and Ca-montmorillonite showed that Al(OH) x was intercalated between the montmorillonite layers. Immobilization of cellulase on the sorbents did not result in expansion of their crystal structures. Therefore, it may be concluded that the amount of cellulase immobilized on internal surfaces of the sorbents was negligible.
Keywords: Silicate clay minerals; Cellulase; Sorption; Immobilization; X-ray diffraction;

Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides by Ramesh Chitrakar; Satoko Tezuka; Akinari Sonoda; Kohji Sakane; Kenta Ooi; Takahiro Hirotsu (45-51).
Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 °C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide (δ-MnO2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm3. The analyses of the uptakes of other constituents (Na+, K+, Ca2+, Cl, and SO2− 4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of log K F = 1.25 and 1 / n = 0.65 , indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO2− 4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.
Keywords: Calcined layered double hydroxides; Adsorption; Selectivity; Phosphate; Seawater;

Fixed-bed column studies were undertaken to evaluate the performance of iron oxide-coated cement (IOCC) in removing As(V), from aqueous environment, under varying operating conditions. Investigations revealed IOCC to be a very efficient media for the removal of As(V) from water. The Bohart and Adams sorption model was employed to determine characteristic parameters such as depth of exchange zone, time required for exchange zone to move its own height, adsorption rate, and adsorption capacity, useful for process design. The IOCC media effectively removed As(V) from a 2 mg/L solution with a maximum adsorption capacity of 505.3 mg/L. Predicted data points obtained using a Freundlich isotherm model were compared against experimental data points determined in the dynamic process. The effects of important design parameters such as flow rate and influent concentration on the As(V) breakthrough curves were also investigated. The bed depth service time (BDST) model was extended to the prediction of service times of columns operated at different flow rates and influent concentrations and these predicted values were compared with the experimental values. The columns were regenerated by eluting the bound As(V) with 10% NaOH after the adsorption studies.
Keywords: As(V); Iron oxide-coated cement; Adsorption; Column study; Breakthrough curve; BDST; Regeneration;

Removal of Cr(VI) from wastewater using rice bran by K.K. Singh; R. Rastogi; S.H. Hasan (61-68).
The novel biosorbent rice bran has been successfully utilized for the removal of Cr(VI) from wastewater. The maximum removal of Cr(VI) was found to be 99.4% at pH 2.0, initial Cr(VI) concentration of 200 mg l−1, and temperature 20 °C. The effect of different parameters such as contact time, adsorbate concentration, pH of the medium, and temperature was investigated. The adsorption kinetics was tested for first-order reversible, pseudo-first-order, and pseudo-second-order; reaction and the rate constants of kinetic models were calculated. Mass transfer of Cr(VI) from the bulk to the solid phase (rice bran) was studied at different temperatures. Different thermodynamic parameters, viz., changes in standard free energy, enthalpy, and entropy, have also been evaluated and it has been found that the reaction was spontaneous and endothermic in nature. The Langmuir and Freundlich equations for describing adsorption equilibrium were applied to data. The constants and correlation coefficients of these isotherm models were calculated and compared. Desorption studies was also carried out and found that complete desorption of Cr(VI) took place at pH of 9.5. The data were also subjected to multiple regression analysis and a model was developed to predict the removal of Cr(VI) from wastewater.
Keywords: Adsorption; Rice bran; Cr(VI); Endothermic; Pseudo-first-order; Monolayer;

Energetic heterogeneity has been investigated for Engelhard titanium silicate Na-ETS-4 adsorbent and its Sr-exchanged variant, Sr-ETS-4. Na-ETS-4 was nearly homogeneous, while Sr exchange seemed to induce some degree of energetic heterogeneity in the sample, which diminished upon dehydration at higher temperature. Analysis of the entropy change during adsorption showed that the adsorbate molecules at low as well as moderate loading possess entropy greater than that predicted by the 2-D mobile film model, the excess being attributed to vibrational freedom. The wavelength of this vibration decreased with increasing coverage, as expected. For oxygen, the observed entropy drops in Na-ETS-4 and in Sr-ETS-4 are comparable, whereas, for nitrogen and methane, Sr exchange resulted in a greater entropy drop than in Na-ETS-4, suggesting greater restriction to movement in the Sr-exchanged sample. This study presents a simplistic yet effective understanding of the energetic behavior of the adsorbed molecules in ETS-4 adsorbent. This is vital to a thorough energetic characterization and study of the adsorption phenomenon in these new, promising adsorbents.
Keywords: ETS-4; Energetic heterogeneity; Entropy;

The molecular and crystal structures of N-benzyl-N,N-dimethylalkylammonium bromides monohydrates with chain length n = 8 – 10 have been determined. The crystals are isostructural with the N-benzyl-N,N-dimethyldodecylammonium bromide monohydrate. The structures consist of alternated hydrophobic and hydrophilic layers perpendicular to [001]. The attraction between N+ of the cation head-groups and Br anions is achieved through weak C―H⋯Br interactions. The water molecules incorporated into ionic layers are donors for two O―H⋯Br hydrogen bonds and serve as the acceptors in two weak interactions of C―H⋯O type. The methylene chains, with the slightly curved general shape, have the extended all-trans conformation. The mutual packing of the chains in the hydrophobic layers is governed by weak C―H⋯π interactions.
Keywords: N-benzyl-N,N-dimethylalkylammonium bromides; X-ray analysis; Hydrophobic layers; Adsorption on Na-montmorillonite;

The mass transfer and effective intraparticle diffusion coefficients were determined in the adsorption process of 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chloroform, carbon tetrachloride, 1,1-dichloroethene, perchloroethene, and 1,1,2-trichloroethene from seven-component aqueous solution onto a thin layer of activated carbon. A modified constant-volume method was used in the studies. A correlation between similarity numbers in the form of Sh = 2 + 1.54 Re 0.66 Sc 0.33 was derived for a range of the Reynolds numbers ∈ ( 1 – 15 ) . Based on the Biot number, it was found that within the range of Reynolds numbers <14 the mass transport through a film decides the adsorption rate.
Keywords: Adsorption; Activated carbon; Diffusion; Kinetics; Chlorohydrocarbons;

Modes of conformational changes of proteins adsorbed on a planar hydrophobic polymer surface reflecting their adsorption behaviors by Ryo Ishiguro; Yasuhiro Yokoyama; Hirotaka Maeda; Aya Shimamura; Keiichi Kameyama; Koichi Hiramatsu (91-101).
Infrared spectra of hen egg white lysozyme and bovine serum albumin (BSA) adsorbed on a solid poly tris(trimethylsiloxy)silylstyrene (pTSS) surface in D2O solution were measured using attenuated total reflection (ATR) Fourier transform infrared spectroscopy. From the area and shape of the amide I′ band of each spectrum, the adsorption amount and the secondary structure were determined simultaneously, as a function of adsorption time. We could show that the average conformation for all the adsorbed lysozyme molecules was solely determined by the adsorption time, and independent of the bulk concentration, while the adsorption amount increased with the bulk concentration as well as the adsorption time. These results suggest that lysozyme molecules form discrete assemblies on the surface, and that the surface assemblies grow over several hours to have a definite architecture independent of the adsorption amount. As for BSA, the extent of the conformational change was solely determined by the adsorption amount, regardless of the bulk concentration and the adsorption time. These differences in the adsorption properties of lysozyme and BSA may reflect differences in their conformational stabilities.
Keywords: FTIR; ATR; Hen egg white lysozyme; Bovine serum albumin; Adsorption; Conformational change;

Silica nanotubes for lysozyme immobilization by Hao-Min Ding; Lei Shao; Run-Jing Liu; Qing-Gui Xiao; Jian-Feng Chen (102-106).
Silica nanotubes were synthesized and used as enzyme immobilization carriers. The immobilization profiles were described by the adsorption of lysozyme molecules from aqueous solution onto the hydrophilic silica surface. The driving force of the adsorption, structure changes in the immobilized lysozyme molecules, and enzymatic activities were investigated. A study of the zeta potentials of silica with and without the immobilized lysozyme showed that there was an increase in the isoelectric point with the increase in the loading amount of lysozyme. FTIR spectra indicated that protein secondary structure was maintained well in the immobilized molecules. It was observed that enzymatic activities first increased and then decreased with increasing surface coverage of silica nanotubes by lysozyme, which suggested that the overlap and aggregation of lysozyme molecules reduced enzymatic activities of the adsorbed lysozyme molecules at high surface coverage.
Keywords: Lysozyme immobilization; Silica nanotubes; Enzymatic activities; Surface coverage;

An algorithm for semi-empirical design of nucleation rate surface by Lyubov Anisimova; Michael Anisimov; George Semin; Peter Turner; Philip K. Hopke (107-116).
During the last half of century, Classical Nucleation Theory (CNT) has been developed and there have been advances in the molecular theory of nucleation. Most of these efforts have been directed towards small molecule system modeling using intermolecular potentials. Summarizing the nucleation theory, it can be concluded that the current theory is far from complete. Agreement is generally not obtained between experimental and theoretical results. In practical applications, parametric theories can be used for the systems of interest. However, experimental measurements are still the best source of information on nucleation. Experiments are labor intensive and costly, and thus, it is useful to extend the value of limited experimental measurements to a broader range of nucleation conditions. The available nucleation parameters represent only small regions of possible nucleation conditions over the range from the critical temperature to absolute zero. Thus, it is useful to develop better tools to use the data to estimate semi-empirical nucleation rate surfaces. Following our published approach, the nucleation rate surface for any system can be constructed over its phase diagram. This concept involves using the phase equilibrium diagram to establish lines of zero nucleation rates. Nucleation rate surfaces arise from equilibrium lines and their extensions that are representing unstable equilibria. Only limited experimental data is available for use in normalizing the slopes of the linearized nucleation rate surfaces. The nucleation rate surface is described in terms of steady-state nucleation rates. To design the surfaces of nucleation rates, several assumptions are presented. In the present study, an algorithm for the semi-empirical design of nucleation rate surfaces is introduced. The topology of the nucleation rate surface for a unary system using the example of water vapor nucleation is created semi-empirically. The nucleation of two concurrent (stable and unstable) phase states of critical embryos is considered in the context of multi-surface nucleation rates. Only one phase transition (melting) in the condensed state of water is considered for simplicity. The nucleation rate surface is constructed numerically using the available experimental results for vapor nucleation and phase diagram for water. The nucleation rate for water vapor is developed for the full temperature interval, i.e. from critical point to absolute zero. The results help to suggest a new direction for experimental nucleation research.
Keywords: Nucleation; Vapor; Spinodal; Critical point; Zero temperature;

Nanobimetallic particles consisting of Au–Pd, Au–Ag, and Au–Pt have been synthesized in a single step by a sol–gel process and stabilized in liquid and solid matrices. Organically modified silicates (Ormosils) that play a dual role of a matrix and of a stabilizer have been used to obtain very stable dispersions in the form of sols, gels, and monoliths. The simultaneous reduction of metal ions leads to either a surface enriched with one component or an alloy type of structure depending on the bimetal combination. The nanometallic dispersions are characterized by absorbance, TEM, XRD, IR, XPS, and CO adsorption studies. The stabilized nanoparticles are found to be good electrocatalysts and the preliminary results on the electrochemical reduction of oxygen are reported.
Keywords: Bimetallic nanoparticles; Sol–gel; Au; Ag; Pd; Pt; Aminosilane;

In this article we report the rapid preparation of uniform, large, spherical Ag particles through a simple wet-chemical route. The formation of Ag particles with about 750 nm in diameter occurs in a single process, carried out by direct mix of AgNO3 aqueous solution and ortho-phenylenediamine N-methyl-2-pyrrolidone solution at room temperature, producing a relatively low-polydispersity product. It is also found that raising the temperature results in larger particles. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectra have been used to characterize the resulting product.
Keywords: Colloids; Uniform; Large; Silver spheres;

The effect of polymer, plasticizer, and surfactant additives on stress development during drying of calcium carbonate particulate coatings was studied using a controlled-environment apparatus that simultaneously monitors drying stress, weight loss, and relative humidity. We found that the calcium carbonate coatings display a drying stress evolution typical of granular films, which is characterized by a sharp capillary-induced stress rise followed by a rapid stress relaxation. The addition of a soluble polymer to the CaCO3 suspension resulted in a two-stage stress evolution process. The initial stress rise stems from capillary-pressure-induced stresses within the film, while the second, larger stress rise occurs due to solidification and shrinkage of the polymeric species. Measurements on the corresponding pure polymer solutions established a clear correlation between the magnitude of residual stress in both the polymer and CaCO3–polymer films to the physical properties of the polymer phase, i.e. its glass transition temperature, T g , and Young's modulus. The addition of small organic molecules can reduce the residual stress observed in the CaCO3–polymer films; e.g., glycerol, which acts as a plasticizer, reduces the drying stress by lowering T g , while surfactant additions reduce the surface tension of the liquid phase, and, hence, the magnitude of the capillary pressure within the film.
Keywords: Drying; CaCO3; Coating; Suspension; Stress; Plasticizer; Polymer; Surfactant; CMC; PVA; EHEC;

Surface properties of various powdered hydroxyapatites by L. García Rodenas; J.M. Palacios; M.C. Apella; P.J. Morando; M.A. Blesa (145-154).
Electrophoretic mobilities of various synthetic and semisynthetic hydroxyapatites (Ca10(PO4)6(OH)2, HAP) suspended in aqueous solutions have been measured as a function of pH and calcium concentration. The studied powders differ in particle size, crystallinity degree and surface contamination (carbonate). When equilibrated in mineral acids or bases, a large plateau of negative mobility is observed in the pH range 5–8, with increasing negative values at higher pH. Only in the case of the sample composed of nanoparticles, positive mobility obtains at pH < 8.9. When Ca2+ is added, positive mobility values are observed for all samples, and a bell-shaped profile results as a function of pH. Two possible models are explored to describe the results: the Nernstian approach, which assumes solubility equilibrium and surface potentials determined by the three potential-determining ions (Ca2+, PO3− 4, and OH), and the surface complexation approach, based on the idea of negligible phase transfer of structural phosphate. The Nernstian model is inadequate, whereas a very simple surface complexation model based on the equations Ca5(PO4)+ 3 = Ca4(PO4) 3 + Ca2+, Ca4(PO4) 3 + H+ = Ca4(PO4)2(PO4H), Ca5(PO4)+ 3 + OH = Ca5(PO4)3(OH), coupled with a very simple electrical double layer, model suffices to reproduce the bell-shaped profile of the mobility as a function of pH in the presence of added calcium salts. The results also show that the sample composed of nanoparticles exchanges ions more easily with the solution, without reaching the solubility equilibrium in the explored timespans. In the presence of soluble phosphate salts, it is postulated that the same surface ensembles define the surface charge, with participation of phosphate as described by the equation 4 5 Ca5(PO4)+ 3 + 3 5 PO3− 4 = Ca4(PO4) 3. HAP is just one member of a family of calcium phosphates with different (Ca)/(P) ratios. Electrophoretic mobilities of another member, tricalcium diphosphate, Ca3(PO4)2, were also measured and shown to be described by the same basic model. Comparison with previous literature data shows that the negative plateau in the mobility is a general feature of many HAP samples at low Ca2+, again in agreement with the surface complexation model. FTIR data demonstrates that surface phosphate indeed undergoes protonation, as postulated in the model.
Keywords: Hydroxyapatite; Electrophoretic mobilities; Ca2+ adsorption; Nernstian model; Surface complexation approach;

Preferred orientation in filtercakes of kaolinite by Ana C. Perdigon-Aller; Mark Aston; Stuart M. Clarke (155-165).
The orientational order parameter of dense colloidal dispersions of plate-like particles as a function of volume fraction is measured using neutron diffraction. This non-invasive experimental approach directly provides the full particle orientation distribution from which the order parameters can be calculated. The orientation parameters are shown to be linked to the solids fractions of the cakes and the macroscopic permeability of the samples. However, this study suggests that, although orientation can be relevant for a given system, other factors can have a stronger influence, for example, the degree of dispersion or colloidal stability of the clay and may be the principle factor that controls permeability. In addition, we report enhanced ordering of these materials under the influence of an external cross-flow field.
Keywords: Orientational order; Neutron diffraction; Filtercakes; Kaolinite; Clay;

Tetrasulfonated copper phthalocyanine (CuTsPc)-capped TiO2 nanoparticle ultrathin films were fabricated by a layer-by-layer (LBL) self-assembly technique. Alternating bilayer structures were formed by consecutive adsorption of CuTsPc-capped TiO2 nanoparticles with poly(diallyldimethylammonium chloride). Optical and electrical measurements were carried out to characterize the CuTsPc-capped TiO2 nanoparticle ultrathin films. Optical measurements revealed uniform deposition. The surface morphology of such bilayer films showed a granular morphology similar to other classes of LBL films. Electrical measurements revealed an abnormal phenomenon under white light illumination. Electrochemical and photoelectrochemical measurements on such a bilayer system were carried out to elucidate the electron transport processes and the photovoltaic effect.
Keywords: Phthalocyanine; Titanium dioxide; Layer-by-layer; Electrochemistry; Photovoltaic;

Surface reactions of 4-aminothiophenol (4-ATP) with a series of heterogeneous crosslinkers containing both maleimide and succinimidyl ester groups were investigated with infrared reflection absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS). Two types of surface reactions exist: (1) for most crosslinkers, a dominant reaction of amine and succinimidyl ester gave homogeneous maleimide-pendant surfaces; (2) for other crosslinkers, a side reaction between amine and maleimide, accompanying the main reaction, yielded heterogeneous surfaces with two linking groups, maleimide and succinimidyl ester. A typical example for the second case is the reaction of surface amines with N-succinimidyl-6-maleimidylhexanoate (SMH). Finally, a peptide, H-Gly-Arg-Gly-Asp-Ser-Pro-Cys-OH (GRGDSPC), was immobilized on the SMH-derived surface as a bridging structure through two linkages, cysteine thioether and glycine amide.
Keywords: Surface reaction; Heterogeneous crosslinker; Biomolecular immobilization; IRRAS; XPS;

Kinetics of the reduction of water-soluble colloidal MnO2 by ascorbic acid by Zaheer Khan; Parveen Kumar; Kabir-ud-Din (184-189).
The kinetics of the reduction of colloidal MnO2 by ascorbic acid has been studied spectrophotometrically. Under pseudo-first-order conditions ([ascorbic acid] ≫ [(MnO2) n ]) the reaction was very fast. To obtain the rate constants as a function of [ascorbic acid], [(MnO2) n ], and temperature, second-order conditions were maintained in each kinetic run. The rate of the reduction increases and decreases with the increase in [ascorbic acid] and [(MnO2) n ], respectively. The reaction was catalyzed by perchloric acid. The addition of sodium pyrophosphate and sodium fluoride has inhibitory effect on the reaction rate. Externally added Mn(II) (a product of the reaction) has composite effect (inhibition and catalytic). The effect of gum arabic has also been studied. Activation parameters have been evaluated from the Arrhenius and Eyring equations. The kinetic evidence does not indicate the formation of an intermediate complex between colloidal MnO2 and ascorbic acid. A mechanism consistent with the observed kinetics has been proposed and discussed.
Keywords: Kinetics; Colloidal MnO2; Reduction; Ascorbic acid; Oxidation; Gum arabic;

Adsorption and electrosorption of thiocyanate (SCN) anions on active carbon felt electrodes were measured by UV spectroscopy and cyclic voltammetry to provide more knowledge of the application of electrosorption on high-area carbon material in industrial waste water purification. Positive polarization caused increased adsorption of SCN. SCN showed the highest electrosorption capacity at about pH 3. Reversible electrosorption of SCN to different extents was observed by changing the direction of polarization currents, which is possibly accompanied by the accessible surface area of C-felt being increased by positive polarization and electrochemical oxidation of SCN. The enhanced capacity for adsorption by positive polarization will improve reuse of active carbon felt.
Keywords: Active carbon felt; Electrosorption; Thiocyanate; Desorption; Electrical double layer (EDL);

Intercalation of ZnO quantum dots into two-dimensional (2D) laminated sodium lauryl sulfonate films in a colloidal solution was demonstrated. Without any substrates, hybrid films composed of a dispersed ZnO dots layer and organic films exhibit a high stability and regular 2D superlattice stacking after removal of cosurfactant molecules and water. The 2D superlattice films were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). UV–visible absorption and photoluminescence spectra were used to investigate the growth of ZnO QDs between organic films and study their collective optical characteristics.
Keywords: ZnO; 2D superlattice; Quantum dots; Morphologies; Semiconductor; Hybrid materials;

Template evaporation method for controlling anatase nanocrystal size in ordered macroporous TiO2 by Chiara Dionigi; Gianluca Calestani; Tiziano Ferraroni; Giampiero Ruani; Leonarda F. Liotta; Andrea Migliori; Petr Nozar; Dimitros Palles (201-207).
The importance of pure-phase titanium oxide materials as catalysts, sensors, and photonic band-gap materials has been growing steadily. Recently, more attention has been focused on nanostructured titanium oxide showing controlled and periodic porosity on a nanometric scale. The nanocrystal size control of porous nanostructured titanium oxide in an anatase form is a crucial step for the organic template method. Simple template removal by evaporation in an inert atmosphere is reported in this article and compared with the calcination technique usually reported in the literature. The proposed method allows the formation of a double-porous (macro and meso) anatase phase. We demonstrate that it highly preserves the macropore order into a titanium oxide material and induces narrowly dispersed mesopores by controlling the nano-crystal size that is kept around 6 nm. For the proposed method, polystyrene beads are particularly suitable as templates, being evaporated in the temperature range of anatase existence. The final high surface area makes the materials appealing for applications as photocatalysts or sensors.
Keywords: Template evaporation; Titanium oxide nanocrystals; Periodic porosity; Polystyrene beads;

Surface and porosity of nanocrystalline boehmite xerogels by Pierre Alphonse; Matthieu Courty (208-219).
Boehmite xerogels are prepared by hydrolysis of Al(OC4H9)3 followed by peptization with HNO3 (H+/Al = 0, 0.07, 0.2). XRD and TEM show that these gels are made of nanosized crystals (5–9 nm in width and 3 nm thick). According to the amount of acid, no significant differences are found in size and shape, but only in the spatial arrangement of the crystallites. Nitrogen adsorption–desorption isotherms of nonpeptized gels are of type IV, whereas isotherms of peptized gels are of type I. These isotherms are analyzed by the t-plot method. The majority of pore volume results from intercrystalline mesopores, but the peptized gels also contain intercrystalline micropores. The particle packing is very dense for the gel peptized with H+/Al = 0.2 (porosity = 0.26), but it is less dense in non-peptized gel (porosity = 0.44). Heating these gels under vacuum creates, from 250 °C onwards, an intracrystalline microporosity resulting from the conversion of boehmite into transition alumina. But heating also causes intercrystalline micropores collapsing. The specific surface area increases up to a limit temperature (300 °C for nonpeptized gels and 400 °C for peptized) beyond which sintering of the particles begins and the surface decreases. The PSD are calculated assuming a cylindrical pore geometry and using the corrected Kelvin equation proposed by Kruk et al. Peptized xerogels give a monomodal distribution with a maximum near 2 nm and no pores are larger than 6 nm. Nonpeptized gels have a bimodal distribution with a narrow peak near to 2 nm and a broad unsymmetrical peak with a maximum at 4 nm. Heating in air above 400 °C has a strong effect on the porosity. As the temperature increases, there is a broadening of the distribution and a marked decrease of small pores (below 3 nm). However, even after treatment at 800 °C, micropores are still present.
Keywords: Boehmite; Specific surface area; Porosity; PSD; Comparative plot;

Bénard–Marangoni instability, with coupled gravity and surface tension effects, in an evaporating liquid layer surmounted by its vapor and an inert gas is investigated theoretically. We show that this system can be described by a model that consists in the liquid layer equations plus the diffusion equation for the vapor in the gas (the so-called 1.5-sided model) and that this model is equivalent to a one-sided model when the vapor mass fraction field can be considered as quasi-stationary, provided that the equivalent Biot number is a nonlocal function of the interface temperature. A comparison of weakly nonlinear results for the 1.5-sided model with a previous one-sided model [M. Dondlinger, J. Margerit, P.C. Dauby, J. Colloid Interface Sci. 283 (2) (2005) 522–532] that considered a Biot number depending on the wavenumber evaluated at the threshold is performed. Very good agreement is found between both models. For this reason, the present analysis can also be considered as a detailed theoretical justification for the use of a one-sided model in the study of evaporative thermoconvection.
Keywords: Marangoni convection; Evaporation; Pattern formation; Amplitude equations;

Relativistic state equations were obtained for various interfaces and cases. The relativistic state equation was done for perfect gases as well.
Keywords: Interface; Surface; Surface tension; Relativistic thermodynamics; State equation;

Interfacial behavior of Cyanex 302 and kinetics of lanthanum extraction by Dongbei Wu; Ying Xiong; Deqian Li; Shulan Meng (235-240).
In this paper, interfacial tension of Cyanex 302 is measured by a Sigma-701 tensiometer and the adsorption parameters are calculated according to the Gibbs and Szyszkowski adsorption isotherms. The interfacial adsorbed behavior of Cyanex 302 is investigated. The results demonstrate that the dimer is the predominant species in the bulk organic phase; however, the monomer is adsorbed at the interface and more interfacially active. The effects of aqueous pH, ion strength, and temperature on the interfacial activity of Cyanex 302 in heptane are discussed and explained in detail. The lower interfacial activity of Cyanex 302 in aromatic hydrocarbon than in aliphatic hydrocarbon has also been determined. The values of interfacial excess at the saturated interface increase in the order n-heptane > cyclohexane > toluene > benzene, which is consistent with the order of extractability of lanthanum by Cyanex 302 in these diluents. The interfacial activity data are used to discuss the kinetic mechanism of lanthanum(III) extraction. It is shown that an interfacial mechanism is very probable, and the extraction limiting step is the reaction between the Cyanex 302 molecules in the organic phase sublayer and the adsorbed intermediate complex.
Keywords: Interfacial tension; Interfacial activity; Cyanex 302; Kinetics; Lanthanum extraction;

We examined the morphologies of two-phase emulsions in the ternary 2-butoxyethanol/n-decane/water system at various temperatures and water-to-oil ratios (WORs). The two-phase emulsion morphologies depended on temperature, WOR, and amphiphile concentration, and the results are presented in a temperature–amphiphile concentration coordinate system or a “fish” diagram. The observations made in this work contradict the predictions by the phase-inversion-temperature (PIT) concept. At WOR<1, a vertical inversion line was observed at T < T lc (lower critical endpoint temperature), dividing the two-phase region into the subregions of B/T (W/O) and T/B (O/W) emulsions. At T > T uc (upper critical endpoint temperature) and at low amphiphile concentrations, only B/T emulsions appeared, irrespective of temperature. At WOR > 1, the situation was reversed; T/B emulsions at T < T lc , T/B and B/T emulsions at T > T uc , and T/B emulsions at low amphiphile concentrations, irrespective of temperature. At WOR = 1, two horizontal inversion lines, one each at T < T lc and T > T uc , were observed. The morphologies of the two-phase emulsions were B/T or T/B emulsions at low amphiphile concentrations, and at higher amphiphile concentrations T/B at T < T lc and B/T at T > T uc . All these findings along with three-phase emulsion data result in complete emulsion morphology diagrams in the temperature–amphiphile concentration space or fish diagram.
Keywords: Two-phase emulsions; Emulsion morphology; Emulsion inversion; Water-to-oil ratio (WOR); “Fish” diagram; Phase inversion temperature (PIT);

The effect of the keratolytic drug salicylic acid (SA) on the thermotropic properties and fluidity of the mixed lipid membrane dipalmitoyl phosphatidylcholine (DPPC)–dipalmitoyl phosphatidylethanolamine (DPPE) had been studied using DSC, (1H and 31P) NMR, SAXS, and dynamic light scattering. The membrane was in multilamellar vesicular (MLV) and unilamellar vesicular (ULV) form with SA/(DPPC + DPPE) molar ratios, R m , in the range from 0 to 0.5. It was found that the mechanism of interaction of SA with the lipid mixture exhibited similar patterns in both ULV and MLV. Both the NMR and DSC studies indicated that the drug molecules were probably localized in the lipid–water interfacial region neighboring the lipid headgroups or the glycerol moiety. The presence of the drug increased the fluidity of the membrane and the acyl chain order. However, studies on MLV showed that the presence of the drug in high concentration ( R m ⩾ 0.2 ), caused destabilization of the DPPC–DPPE mixture, as indicated by the appearance of two endothermic transitions. DSC studies indicated that prolonged equilibration of the membrane led to reduced interaction between the lipid headgroups and the SA molecules. This reduced interaction could be due to the sequestering of the drug molecules into the lipid–water interfacial region, out of proximity to the polar headgroup or glycerol moiety. Effect of inclusion of cholesterol in the membrane systems was also studied.
Keywords: DPPC; DPPE; Differential scanning calorimetry; NMR; Salicylic acid; Unilamellar vesicles; Multilamellar vesicles; Model membranes; Chain melting transition;

The nonionic surfactant of sorbitan trioleate (Span 85) was modified with Cibacron Blue F-3GA (CB) as an affinity surfactant (CB–Span 85) to form affinity-based reversed micelles in n-hexane. The reversed micelles formed by the mixture of Span 85 and CB–Span 85 conjugate were extensively characterized in water content, hydrodynamic radius, and aggregation number. The results show that the water content and hydrodynamic radius of the reversed micelles were significantly increased by the introduction of CB ligands (CB–Span 85 conjugate), and the reversed micelles with CB–Span 85 conjugate had a wider aggregation number distribution than the Span 85 reversed micelles. Using lysozyme as a model protein, protein solubilization by the reversed micelles was investigated. Lysozyme solubilization increased significantly with the coupled CB concentration, indicating that the extraction was based upon the affinity interactions between lysozyme molecules and the CB ligand. High solubilization of lysozyme was obtained by the affinity-based reversed micelles of 62.7 mmol/L Span 85 with coupled CB higher than 0.25 mmol/L. Lysozyme recovery was carried out using a stripping solution of high ionic strength. The recovered lysozyme exhibited an activity equivalent to the native lysozyme and its secondary structure was also unchanged. The results indicate that the reversed micellar system would find potential application in protein separation.
Keywords: Affinity-based reversed micelles; Span 85; Cibacron blue F-3GA; Water content; Hydrodynamic radius; Solubilization; Lysozyme;

Catanionic surfactants formed by the pairing of two ionic amphiphilic chains of opposite charge are now recognized as an important class of amphiphiles. Many aspects of their phase behavior have yet to be explored. In this work, two homologous series of catanionic surfactants were synthesized, based on the cationic headgroups trimethylammonium and pyridinium. Within each series, the headgroup and chain length of the cationic counterpart remains constant while for the anionic counterpart the headgroup is varied, while its alkyl chain length is also kept constant. Thus, one can directly monitor the influence of headgroup chemistry on the thermal behavior of these compounds. Differential scanning calorimetry (DSC) and polarizing light microscopy show that these compounds bear a rich and often complex thermotropic behavior, with the headgroup chemistry in some instances having a rather dramatic influence on phase behavior. Several liquid crystalline phases appear between the solid crystalline phase and the isotropic liquid phase. A qualitative correlation between the observed thermotropic behavior and the chemical nature of headgroup is presented.
Keywords: Catanionic surfactants; Headgroups; Thermotropic; Asymmetric; Charge density; Liquid crystals;

The array and interfacial activity of sodium dodecyl benzene sulfonate and sodium oleate at the oil/water interface by Ying Li; Peng Zhang; Feng-Lan Dong; Xu-Long Cao; Xin-Wang Song; Xiao-Hong Cui (275-280).
There is a close correlation between the interfacial activity and the adsorption of the surfactant at the interface, but the detailed molecular standard information was scarce. The interfacial activity of two traditional anionic surfactants sodium dodecyl benzene sulfonate (SDBS) and sodium oleate (OAS) were studied by experimental and computer simulation methods. With the spinning drop method and the suspension drop method, the interfacial tension of oil/aqueous surfactant systems was measured, and the influence of surfactant concentration and salinity on the interfacial tension was investigated. The dissipative particle dynamics (DPD) method was used to simulate the adsorption of SDBS and OAS at the oil/water interface. It was shown that it is beneficial to decrease interfacial tension if the hydrophobic chains of the surfactant and the oil have similar structure. The accession of inorganic salts causes surfactant molecules to form more compact and ordered arrangements and helps to decrease the interfacial tension. There is an osculation relation between interfacial density and interfacial activity. The interfacial density calculated by molecular simulation is an effective parameter to exhibit the interfacial activity.
Keywords: Sodium dodecyl benzene sulfonate; Sodium oleate; Interfacial tension; Molecular simulation;

Interfacial forces and Marangoni flow on a nematic drop retracting in an isotropic fluid by Pengtao Yue; James J. Feng; Chun Liu; Jie Shen (281-288).
Nematic-isotropic interfaces exhibit novel dynamics due to anchoring of the liquid crystal molecules on the interface. The objective of this study is to demonstrate the consequences of such dynamics in the flow field created by an elongated nematic drop retracting in an isotropic matrix. This is accomplished by two-dimensional flow simulations using a diffuse-interface model. By exploring the coupling among bulk liquid crystal orientation, surface anchoring and the flow field, we show that the anchoring energy plays a fundamental role in the interfacial dynamics of nematic liquids. In particular, it gives rise to a dynamic interfacial tension that depends on the bulk orientation. Tangential gradient of the interfacial tension drives a Marangoni flow near the nematic-isotropic interface. Besides, the anchoring energy produces an additional normal force on the interface that, together with the interfacial tension, determines the movement of the interface. Consequently, a nematic drop with planar anchoring retracts more slowly than a Newtonian drop, while one with homeotropic anchoring retracts faster than a Newtonian drop. The numerical results are consistent with prior theories for interfacial rheology and experimental observations.
Keywords: Dynamic interfacial tension; Liquid crystals; Anchoring energy; Two-phase flow;

Transient response of compressed electrorheological fluid by Yu Tian; Minliang Zhang; Yonggang Meng; Shizhu Wen (289-297).
Transient behaviors of a compressed electrorheological (ER) fluid based on zeolite and silicone oil have been experimentally investigated. The ER fluid is purely compressed between two parallel plates. Compressive speed and voltage amplitude effects on the transient process and randomly applied on/off voltages have been studied. Through normalizing compressive stress of the ER fluid, the characteristic compressive strain and the response time constant corresponding to the rise of compressive stress have been fitted with exponential equations. Results show that the rising time of the transient compressive stress is greatly affected by the compressive speed and the compressive strain position applying voltages, while the amplitude of the applied voltage has little effect on the rising time. The obtained transient compressive strain for the compressive stress to rise to its stable value is much smaller than that working in the transient process of ER fluids under shearing. The decay time and decay strain of compressive stress are much less than for stress rising. The half decay compressive strain is as small as 0.0003 in the experiment. Results show that the response time of compressed ER fluids is quick enough for the usual working conditions of squeezing ER dampers.
Keywords: Electrorheological fluid; Parallel plates; Transient compressive stress; Characteristic compressive strain; Response time constant; Decay time; Electric field strength;

Fragmentation of wastewater sludge floc by planar ice front by T. Tao; X.F. Peng; D.J. Lee (298-301).
Floc size has substantial impact on sludge dewaterability, which might be increased or reduced after freezing and thawing. It is commonly assumed that floc size would be increased by low-speed freezing, with a planar ice front rejecting most flocs ahead of it to form large aggregates. We demonstrate in this work that an advancing planar ice front can not only engulf an activated sludge floc of size 3030 μm, but also fragment it. During floc freezing, when the ice engulfed a thin layer of floc, the latter would be pulled apart vertically by the action of the former. This particular portion of floc was then axially elongated and fixed in the frozen layer, with accumulated force pushing upward. In the present test the floc's vertical length was increased by over 92% and its width decreased by 37% over freezing. The force measurement and floc morphology tracking revealed that the force gradient that pulled apart the floc was 0.0027 N/m. The floc under investigation was fragmented at the point where the normal stress acting on the interior network exceeded 8 Pa.
Keywords: Freezing; Thawing; Floc; Interface; Force;

by Arthur Hubbard (302).