Journal of Colloid And Interface Science (v.349, #2)

Cover 1 (OFC).

Self-assembled templates for the generation of arrays of 1-dimensional nanostructures: From molecules to devices by Richard A. Farrell; Nikolay Petkov; Michael A. Morris; Justin D. Holmes (449-472).
The review article describes the use of self-assembled nanoscale porous architectures as hosts for templating one dimensional (1D) nano-entities for a wide range of electronic, photonic, magnetic and environmental applications. Special attention is given to the different ways of directing self-assembly with a focus on properties such as uni-directional alignment, precision placement and registry of the self-assembled structures to hierarchal or top-down architectures.Self-assembled nanoscale porous architectures, such as mesoporous silica (MPS) films, block copolymer films (BCP) and porous anodic aluminas (PAAs), are ideal hosts for templating one dimensional (1D) nano-entities for a wide range of electronic, photonic, magnetic and environmental applications. All three of these templates can provide scalable and tunable pore diameters below 20 nm . Recently, research has progressed towards controlling the pore direction, orientation and long-range order of these nanostructures through so-called directed self-assembly (DSA). Significantly, the introduction of a wide range of top-down chemically and physically pre-patterning substrates has facilitated the DSA of nanostructures into functional device arrays. The following review begins with an overview of the fundamental aspects of self-assembly and ordering processes during the formation of PAAs, BCPs and MPS films. Special attention is given to the different ways of directing self-assembly, concentrating on properties such as uni-directional alignment, precision placement and registry of the self-assembled structures to hierarchal or top-down architectures. Finally, to distinguish this review from other articles we focus on research where nanostructures have been utilised in part to fabricate arrays of functioning devices below the sub 50 nm threshold, by subtractive transfer and additive methods. Where possible, we attempt to compare and contrast the different templating approaches and highlight the strengths and/or limitations that will be important for their potential integration into downstream processes.
Keywords: Self-assembly; Nanostructures; Templates; Block copolymers; Mesoporous materials; Porous anodic alumina;

Synthesis of mesoporous silica by a surface charge reversal route by Wei-Min Zhang; Jia Liu; Zhong-Xi Sun; Bao-Qiang Fan; Zhen-Dong Yang; Wills Forsling (473-476).
This paper demonstrates that the surface charge reversal caused by adsorption of zinc ions could be an effective approach for synthesizing pore adjustable silica.Display Omitted► Using TEOS as a silica source. ► Adsorption of divalent metal ions at the surfaces of silica. ► Adding SDBS as a template. ► Formation of mesostructured silica. ► Obtaining the mesoporous silica after calcinations.Pore size adjustable mesoporous silica was synthesized by adsorption of varying amounts of sodium dodecyl benzenesulfonate at the surface of silica activated by zinc ion via a novel surface charge reversal route. The pore size and volume can be adjusted from 5.9 to 13.76 nm and 0.88 to 1.08 cm3 g−1, respectively, with increasing the SDBS concentration from 0.77 to 3.08 mmol L−1. Adsorption of Zn2+ as a function of pH and N2 adsorption/desorption isotherms demonstrated that the metal ions such as Zn2+ could be readily removed with dilute nitric acid without apparent collapse of the pore structure at the proper range of SDBS concentration.
Keywords: Mesoporous silica; Adsorption; Surface charge reversal;

Sulfur doped anatase TiO2 single crystals with a high percentage of {0 0 1} facets by Gang Liu; Chenghua Sun; Sean C. Smith; Lianzhou Wang; Gao Qing (Max) Lu; Hui-Ming Cheng (477-483).
Sulfur doped anatase TiO2 single crystal sheets with a high percentage of {0 0 1} facets show an additional visible light absorption band and corresponding visible-light photocatalytic activity.Extending the response range of wide-bandgap (3.2 eV) anatase TiO2 photocatalysts into the visible light range can play an important role in promoting the practical applications of photocatalysts. Here, we report a route to prepare sulfur doped anatase TiO2 single crystal sheets with a high percentage of {0 0 1} facets. The resultant TiO2 sheets were investigated by a combination of experimental characterizations and electronic structure calculations. The synthesized sulfur doped anatase samples show an additional visible light absorption band from 400 nm to ca. 550 nm and some visible-light photocatalytic activity in OH radical generation and photodecomposition of organic dyes. The Ti–S bond structure causes not only visible light absorption but also changes to an extent the surface structures of doped anatase TiO2 sheets. Theoretically, localized 3p states of S formed in the bandgap are implicated for the visible light absorption of the sulfur doped anatase TiO2.
Keywords: Anatase; TiO2; {0 0 1}; Sulfur doping;

Lanthanide-doped LaPO4 (monazite) spherical (<0.5 μm) phosphors of different colors have been synthesized at 120 °C by a homogeneous precipitation process from solutions containing La3+-citrate complexes and phosphate anions in ethylene glycol.A simple method for the synthesis of spherical LaPO4 (monazite) particles with narrow size distribution and tailored size in the 150–500 nm range is reported. The procedure is based on a homogeneous precipitation process at low temperature (120 °C) from solutions containing La3+, citrate and phosphate ions under a very restrictive set of experimental conditions, which involves the use of La nitrate, citric acid and phosphoric acid as precursors and ethylene glycol as solvent. The growth mechanism of the spheres was investigated aiming at explaining the differences in particle size and shape observed when varying the experimental conditions. The applicability of this method for the synthesis of spherical particles of other lanthanide (Ce, Tb, Eu) phosphates is also analyzed. Finally, it is shown that the developed procedure can be used to dope the lanthanum phosphate particles with lanthanide cations, which resulted in spherical phosphors as illustrated for the Eu-doped, Ce-doped and Ce, Tb codoped systems, whose luminescent properties are also evaluated.
Keywords: Spheres; LaPO4; Europium; Cerium; Terbium; Luminescence;

Forces measured between a silica sphere coated by a film of silicone oil of viscosity 60,000 cS, and a flat mica substrate, 1 – in water, 2 – in 1.7 mmol/L NaCl, 3 – in 17 mmol/L NaCl. Theoretical curve was fitted into the samples.An investigation has been made of the interactions between silicone oil and various solid substrates immersed in aqueous solutions. Measurements were made using an atomic force microscope (AFM) using the colloid-probe method. The silicone oil drop is simulated by coating a small silica sphere with the oil, and measuring the force as this coated sphere is brought close to contact with a flat solid surface. It is found that the silicone oil surface is negatively charged, which causes a double-layer repulsion between the oil drop and another negatively charged surface such as mica. With hydrophilic solids, this repulsion is strong enough to prevent attachment of the drop to the solid. However, with hydrophobic surfaces there is an additional attractive force which overcomes the double-layer repulsion, and the silicone oil drop attaches to the solid. There is circumstantial evidence that linear and nonlinear effect take part in force results from compression of the silicone oil film coated on the glass sphere.
Keywords: Silicon oil; Interface forces; Surface potential; AFM forces; PDMS interface forces;

The presence of a colloidal shell reduces transport rate when compared to an uncoated film but is independent of the dimensions of the particles composing the shell.Recent studies suggest that coating microcapsules by a shell composed of impenetrable colloidal particles (thereby forming ‘colloidosomes’) can be used to control surface porosity, and therefore, permeability. The voids between the particles in the coating define the size of the surface pores available for transport. However, to date, data demonstrating this selectivity has been largely qualitative. In this paper we examine, quantitatively, the effect of a surface coating (shell), composed of colloidal particles, on release from hydrogels. We find that the presence of a colloidal shell does indeed reduce the rate of transport of three model molecules: Aspirin, caffeine, and FITC-dextran with MW of ∼3000–5000. Contrary to expectation, however, we find that for all three molecules the reduction in transport rate is largely independent of the dimensions of the particles composing the shell, despite differences that range over three orders of magnitude. In the case of the small molecules, caffeine and aspirin, the colloidal shell reduces the effective diffusion coefficient by a factor of 3. In the case of dextran, the suppression in the release rate due to the colloidal shell was much larger. These results are explained using a simple diffusion model that accounts for the volume fraction and diameter of the colloidal particles in the shell, and the size of the diffusing molecules.
Keywords: Colloidosomes; Alginate hydrogels; Diffusion; Surface porosity; Colloidal coatings;

Improved photoluminescence properties of a novel europium(III) complex covalently grafted to organically modified silicates by Yinghui Wang; Bin Li; Liming Zhang; Qinghui Zuo; Lina Liu; Peng Li (505-511).
A novel Eu(III) complex has been covalently immobilized by ORMOSILs, and the luminescent intensity and emission quantum efficiency of the composite hybrid materials are improved considerably.A series of novel organic–inorganic hybrid materials with a Eu(III) complex [(C2H5)4N][Eu(DBM)3(DBM-OH)] (DBM = dibenzoylmethanate, DBM-OH =  p-hydroxydibenzoylmethanate) covalently bonded into vinyl-modified silica networks have been successfully assembled through a sol–gel process. DBM-OH was grafted to the coupling agent 3-(triethoxysilyl)propylisocyanate (TESPIC), and the as-obtained molecular precursor DBM-Si was used as a bridge molecule both coordinate to Eu3+ and forming an inorganic Si–O network with tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) after cohydrolysis and co-condensation processes. The luminescence properties of VTES/TEOS composite hybrid materials were systematically studied in comparison to those of TEOS-derived hybrid material and pure [(C2H5)4N][Eu(DBM)4], respectively. The results indicate that the luminescent quantum efficiencies of VTES/TEOS composite hybrid materials are greatly improved. And it is interesting to find that the luminescent intensity of VTES/TEOS composite hybrid material is enhanced by optimizing the molar ratio of VTES to TEOS (VTES:TEOS = 4:6) by 3.3 and 2.4 times compared with TEOS-derived hybrid material and pure [(C2H5)4N][Eu(DBM)4], respectively. In addition, the thermal stability of the emission was also improved considerably. The results presented in this paper indicate that the use of vinyl-modified silicates as a matrix opens the door to improving the photoluminescence properties of Eu(III) complexes.
Keywords: ORMOSILs; Covalently grafted; Europium(III) complex; Photoluminescence;

Smart responsive microcapsules capable of recognizing heavy metal ions by Shuo-Wei Pi; Xiao-Jie Ju; Han-Guang Wu; Rui Xie; Liang-Yin Chu (512-518).
A novel smart responsive microcapsule has been developed for sensing heavy metal ions. The microcapsule exhibits an isothermal and significant swelling by recognizing special heavy metal ions.Display Omitted► Smart responsive microcapsules are fabricated with poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) membranes. ► Microcapsules can selectively recognize heavy metal ions such as Pb2+ or Ba2+ by forming host-guest complexes. ► Microcapsules exhibit isothermal and significant swelling by recognizing Pb2+ or Ba2+.Smart responsive microcapsules capable of recognizing heavy metal ions are successfully prepared with oil-in-water-in-oil double emulsions as templates for polymerization in this study. The microcapsules are featured with thin poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (P(NIPAM-co-BCAm)) membranes, and they can selectively recognize special heavy metal ions such as barium(II) or lead(II) ions very well due to the “host–guest” complexation between the BCAm receptors and barium(II) or lead(II) ions. The stable BCAm/Ba2+ or BCAm/Pb2+ complexes in the P(NIPAM-co-BCAm) membrane cause a positive shift of the volume phase transition temperature of the crosslinked P(NIPAM-co-BCAm) hydrogel to a higher temperature, and the repulsion among the charged BCAm/Ba2+ or BCAm/Pb2+ complexes and the osmotic pressure within the P(NIPAM-co-BCAm) membranes result in the swelling of microcapsules. Induced by recognizing barium(II) or lead(II) ions, the prepared microcapsules with P(NIPAM-co-BCAm) membranes exhibit isothermal and significant swelling not only in outer and inner diameters but also in the membrane thickness. The proposed microcapsules in this study are highly attractive for developing smart sensors and/or carriers for detection and/or elimination of heavy metal ions.
Keywords: Microcapsules; Ion-recognition; Host–guest systems; Crown ether; Phase transitions;

Colloidal hematite nanoparticles with different morphologies, truncated rhombohedra, hexagon and pseudo-hexagon, were employed as building blocks to form complex structures by self-assembly.In this work, complex structures such as long chain, “semi-flexible” chain, “threefold junction” and network were formed by self-assembly of colloidal hematite nanoparticles. Morphology of these colloidal nanoparticles used as building blocks transformed from truncated rhombohedra, hexagon to pseudo-hexagon by altering reaction time and surfactants. By further observation using HRTEM, these nanoparticles were confirmed to grow along the c-axis. It was found that the molecular structures of surfactants make great influence on the transformation of bonding modes between carboxyl and iron atom on the surface. Then crystal growth rate was changed. It led to two opposite growth trends along the c-axis. More interestingly, the chains formed by these colloidal nanoparticles were also assembled along the c-axis. Meanwhile, configuration diversity seemed related to the morphological anisotropy along the c-axis. It was believed that two main forces between the nanoparticles were responsible for the various configurations, magnetic dipole–dipole and exchange-coupling interaction. The morphological anisotropy was considered to play a key role in the coordination of the two interactions which led to different complex structures by self-assembly. Discussion was taken to explain the formation of these interesting configurations.
Keywords: Hematite nanoparticles; Anisotropic morphology; Self-assembly; Magnetic dipolar interaction; Exchange coupling; Chain structure;

Colloidal thermoresponsive gel forming hybrids by Ruixue Liu; Nicola Tirelli; Francesco Cellesi; Brian R. Saunders (527-536).
Laponite and cationic thermoresponsive copolymers spontaneously form colloidal hybrids which themselves associate in water to give thermoresponsive gels and hybrid hydrogels.Colloidal hybrids comprise organic and inorganic components and are attracting considerable attention in the literature. Recently, we reported hybrid anisotropic microsheets that formed thermoresponsive gels in polymer solutions [Liu et al., Langmuir, 25, 490, 2009]. Here, we investigate the composition and properties of these hybrid colloids themselves in detail for the first time. Three different cationic PNIPAm (N-isopropylacrylamide) graft copolymers and two inorganic nanoparticle types (laponite and Ludox silica) were used to prepare a range of hybrids. Anisotropic microsheets only formed when laponite particles were added to the copolymer implying directed self-assembly. Aqueous dispersions of the microsheets spontaneously formed gels at room temperature and these gels were thermoresponsive. They represent a new class of gel forming colloid and are termed thermoresponsive gel forming hybrids. The compositions of the hybrids were determined from thermogravimetric analysis and those that gave gel forming behaviour identified. Variable-temperature rheology experiments showed that the elasticity of the gels increased linearly with temperature. The reversibility of the thermally-triggered changes in gel elasticity was investigated. The concentration dependence of the rheology data was well described by elastic percolation scaling theory and the data could be collapsed onto a master curve. The concentration exponent for the elastic modulus was 2.5. The strong attractive interactions that exist between the dispersed gel forming hybrids was demonstrated by the formation of stable thermoresponsive hybrid hydrogels through casting of hybrid dispersions.
Keywords: Isopropylacrylamide; Laponite; Particle gel; Rheology;

Interfacial displacement of nanoparticles by surfactant molecules in emulsions by Charu Vashisth; Catherine P. Whitby; Daniel Fornasiero; John Ralston (537-543).
Adding surfactant molecules which preferentially adsorb at the oil–water interface displaces nanoparticles from Pickering emulsions.The remarkable stability of nanoparticles attached to oil–water interfaces in macroemulsions hinders controlled detachment of these particles from emulsions. In this work it is shown that adding surfactant molecules which preferentially adsorb at the oil–water interface displaces nanoparticles from the interface. Surfactant adsorption at the oil–water interface is energetically favoured and readily occurs on mixing nanoparticle-stabilised oil-in-water emulsions with surfactant solutions. Depending on the surfactant concentration, there is a significant reduction in the interfacial tension. Hence there is substantial fragmentation of the oil droplets and foaming of the emulsion during mixing. Surfactant concentrations above the critical micelle concentration are required to achieve complete interfacial displacement and hence recovery of the nanoparticles from the emulsions. The effects of surfactant addition have important implications for tailoring the interfacial composition of emulsions.
Keywords: Particle-stabilised emulsions; Pickering emulsions;

The stability of high internal phase emulsions at low surfactant concentration studied by small angle neutron scattering by Philip A. Reynolds; Duncan J. McGillivray; Jitendra P. Mata; Peter N. Yaron; John W. White (544-553).
High internal phase emulsions become unstable when the micelle concentration in the continuous phase reaches a critical lower concentration perhaps no longer suppressing capillary wave instability.The changes in structure of high internal phase emulsions at low concentrations and at elevated temperature are reported for comparison with the same emulsions under conditions well away from instability. Small angle neutron scattering measurements on aqueous ammonium nitrate droplets dispersed in hexadecane and stabilized by very small quantities of a polyisobutylene-based surfactant (PIBSA) as well as related inverse micellar solutions in hexadecane, have been made as a function of temperature and surfactant concentration. Experimental conditions here favour larger and more deformable droplets than in previous studies. Besides the expected micelles and adsorbed surfactant, planar bilayers of micron lateral extent between touching droplets cover 20% of the droplet surface. Another difference from previous experiments is that the oil phase in the emulsions, and corresponding inverse micellar solutions are different in micellar radii and composition.The differences, and changes with surfactant concentration and temperature, are attributed to fractionation of the polydisperse PIBSA in the emulsions, but not the inverse micellar solutions. At low PIBSA concentration and high temperature the SANS shows emulsion decomposing into separate oil and aqueous phases. This occurs when the micelle concentration reaches a very small but measurable value. The inverse micelles may suppress by steric action long wavelength unstable capillary waves in the bilayers. Depletion repulsion forces here have a minor role in the emulsion stabilization.
Keywords: Small angle neutron scattering; Emulsion structure; Emulsion stability; High internal phase emulsions; PIBSA; Capillary waves;

Phase behavior of liquid–crystalline emulsion systems by Petra Kudla; Tobias Sokolowski; Bernhard Blümich; Klaus-Peter Wittern (554-559).
The phase behavior of a liquid crystalline emulsion system of N-(3-dimethylaminopropyl) octadecanamide, fatty alcohols and water was studied.The phase behavior of a mixture containing a surfactant, fatty alcohols and water has been analyzed. Depending on the amount of surfactant, i.e. N-(3-dimethylaminopropyl) octadecanamide, the emulsion-like system forms different microstructures. With increasing surfactant content the formulation evolves from a system with lyotropic lamellar phases to a system with crystal layer phases. 13C-CPMAS NMR studies carried out at varying surfactant levels showed significant differences in the behavior of the system. Using 2H and 13C-CPMAS NMR, X-ray scattering, DSC and polarization microscopy a phase diagram of this system could be derived. Additionally, ultrasonic velocity measurements showed that the ripening process of the emulsions can take up to 2 weeks and longer.
Keywords: Phase diagram; Surfactant; Lyotropic liquid crystals; Lamellar phases;

Self-assembly of a series of random copolymers bearing amphiphilic side chains by Xu Wu; Yingjie Qiao; Hui Yang; Jinben Wang (560-564).
Increase the number of carbon atoms in the alkyl group or polymer concentration can lead the association of side chains to occur more preferentially among different molecules.A novel series of comb-like random copolymers were prepared by polymerization of amphiphilic macromonomers, 2-(acrylamido)-octane sulfonic acid (AMC8S), 2-(acrylamido)-dodecane sulfonic acid (AMC12S), and 2-(acrylamido)-hexadecane sulfonic acid (AMC16S), with 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) respectively. The synthesis of the polymers with the same contents of amphiphilic units as side chains, but different chain length, enabled us to study the chain length dependence of their association in salt solution. Steady-state fluorescence measurements with pyrene as a polarity probe, quasielastic light scattering techniques (QELS) and transmission electron micrograph (TEM) were employed to investigate the associative properties of the system. The above investigations showed that all kinds of side chains begin to assemble at certain polymer concentrations and the critical aggregation concentration (CAC) decrease dramatically with the increase in the length and content of alkyl. An interesting phenomenon is that the assembly tends more favorably to occur among different molecules rather than within single molecule when the number of carbon atoms in the alkyl groups or the polymer concentration increases, leading to the formation of larger multimolecular micelle-like aggregate. The aim of the present work is to establish the fundamental preconditions of intramolecular and intermolecular association fashions for the polymers, which is useful for the exploitation of functional groups and contributes to the development of amphiphilic random polymers.
Keywords: Random copolymer; Amphiphilic side chain; Intramolecular; Intermolecular; Association;

The thermochromism of the E T(30) betaine in a micro-heterogeneous medium: A spectral and dynamics simulation study by Carolina Aliaga; Luis Briones; Marcos Caroli Rezende; Cristián Tirapegui (565-570).
The thermochromic behavior of the E T(30) dye in aqueous solutions of three different poloxamers was studied and interpreted with the aid of molecular dynamics simulations.A spectral investigation of the thermochromic behavior of Reichardt’s E T(30) betaine in aqueous solutions of block copolymers (“poloxamers”) P407, P237 and P105 was carried out as a function of temperature and concentration. The betaine microenvironment at various stages of the micellization process in these systems was mimicked with the aid of molecular dynamics simulations of model systems. These consisted of the E T(30) probe in boxes of water molecules, in the presence of an isolated block copolymer of formula (PEO)11–(PPO)16–(PEO)11, and of a micelle formed of 50 of these unimers.
Keywords: Thermochromism; Solvatochromism; Micelles; Poloxamers; Pluronics; Molecular dynamics simulation;

Preparation of microspherical α-zirconium phosphate catalysts for conversion of fatty acid methyl esters to monoethanolamides by Fazhi Zhang; Yaru Xie; Wei Lu; Xiaoying Wang; Sailong Xu; Xiaodong Lei (571-577).
α-Zirconium phosphate (α-ZrP) micropheres were fabricated by a two-step route involving separate nucleation and aging steps(SNAS) and spray-drying. After being calcined at 573 K, the α-ZrP micropheres exhibit better catalytic activity in acylation of amino derivatives than similar α-ZrP powder due to higher surface area and increased acidity.The performance of solid catalysts and catalyst supports is generally believed to be dependent on their morphology, surface area, and architecture. In order to fully exploit their attractive properties in actual practical applications, layered zirconium phosphate materials should be fabricated into macroscopic form. Here, we report the fabrication of microscopic spheres of α-zirconium phosphate (α-ZrP) by a spray-drying process. The layered α-ZrP nanoparticles were originally obtained using a synthesis route involving separate nucleation and aging steps (SNAS). The resulting products are composed of nanosize α-ZrP particles aggregated into solid microspheres with a diameter of 5–45 μm and a sphericity of 0.80. After calcination at 573 K, surface area of 43.8 m2/g could be obtained for α-ZrP microspheres, which is larger than that of the α-ZrP powder after similar thermal treatment (36.2 m2/g). Furthermore, the number of acidic sites of the α-ZrP microspheres is greater than for the α-ZrP powder due to its unique textual properties and higher surface area. The acylation reaction of fatty acid methyl esters (methyl stearate) with ethanolamine to form monoethanolamides was chosen as a probe reaction to evaluate the catalytic activity of the resulting microspherical α-ZrP materials, which showed high activity compared to the sample in the form of powders, with about 92.9% methyl stearate conversion at 393 K for 12 h. The enhanced performance in the reaction is determined by the large surface area and the increased number of acidic sites in the multiple-scales porosity of α-ZrP microspheres.
Keywords: Zirconium phosphates and phosphonates; Microspheres; Spray-drying; Fatty acid methyl esters; Solid acid catalysts;

This study investigated the sorption of tetracycline onto clays and marine sediment, and developed an empirical model that calculated the individual sorption coefficient (Kdn ) for each species of tetracycline.The sorption of tetracycline onto clays and marine sediment from seawater was investigated at different pH levels, salinities (ionic strength), and temperatures. The sorption isotherms for tetracycline onto kaolinite, montmorillonite, and sediment clay were found to fit well with the Freundlich model. It is found that the linear model was better for marine sediment. Generally the sorption decreased with increasing pH and salinity. The individual sorption coefficient, Kdn , calculated from an empirical model, showed that the sorption coefficient of positive species, Kd +, was higher than that of zwitterions, Kd 0, and negative species, Kd , for montmorillonite, sediment clay, and marine sediment. The sorption capacity of marine sediment was lower than that of sediment clay due to the organic matter covered on the sorption sites. The results of the thermodynamic function calculation showed that the sorption was a spontaneous and exothermic process which was accompanied with a decrease in the degree of freedom.
Keywords: Tetracycline; Sorption; Clay; Marine sediment; Sorption thermodynamics;

Removal of Cu(II) ions from aqueous streams using poly(acrylic acid-co-acrylamide) hydrogels by Eulogio Orozco-Guareño; Fernanda Santiago-Gutiérrez; José Luis Morán-Quiroz; Saira L. Hernandez-Olmos; Victor Soto; Wencel de la Cruz; Ricardo Manríquez; Sergio Gomez-Salazar (583-593).
Cu2+ ion removal from aqueous streams by poly(acrylic acid-co-acrylamide) hydrogels is discussed. The monomer ratio has a significant effect on Cu2+ removal. XPS and FTIR results suggest the formation of a tetradentate copper complex.The adsorption of Cu(II) ions from aqueous solutions onto poly(acrylic acid-co-acrylamide) hydrogels was investigated. The hydrogels were prepared via free-radical solution polymerization using Irgacure 754 as a photoinitiator and ethylene glycol dimethacrylate as a cross-linking agent. Loading of acrylamide/acrylic acid moieties on the surfaces of hydrogels and the amount of cross-linking agent were varied to determine the maximum metal uptake. Polymerization kinetics was investigated by 1H NMR. The physicochemical properties of hydrogels were investigated by nitrogen sorption measurements, elemental analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The 1H NMR results demonstrated that the polymerization reaction was carried out almost to completion and confirmed the absence of residual monomers. Swelling results indicated that, by appropriate selection of cross-linking agent amount and monomer ratio, hydrogels can be swollen up to 70,000%. Further characterization of the hydrogels showed rapid adsorption kinetics and equilibrium Cu(II) adsorption capacities of 121 mg g−1. Cu(II) adsorption kinetic data followed pseudo-first-order kinetics. Adsorption equilibrium data were better fitted by a Langmuir isotherm. FTIR and XPS results indicated the presence of a tetradentate copper complex on the surfaces of hydrogels. The copper uptake achieved suggests the potential use of hydrogels to extract toxic metals from industrial aqueous streams.
Keywords: Adsorption; Swelling; Hydrogels; XPS;

Effect of cell shape on mineral–microbe interaction energy and adhesion behavior (at pH 10.5).The adhesion behavior of Ferroplasma acidiphilum archaeon to pyrite mineral was investigated experimentally and theoretically. F. acidiphilum showed high affinity to adhere to pyrite surface at acidic regions, however low affinity was observed at neutral and alkaline regions. The microbe–mineral adhesion was assessed by the extended DLVO theory. Hamaker constants, electron donors, electron acceptors and surface charges for the microbe and the mineral were experimentally determined. The extended DLVO theory was used to explain the adhesion results. Significant changes to the pyrite surface properties after being treated with the microbial cells were observed. Pyrite lost its hydrophobic nature and became hydrophilic, the contact angle of untreated pyrite was 61° and this decreased to 36° after the treatment. As a consequence, the flotation experiment results showed that F. acidiphilum strain could act as a good depressant for pyrite in xanthat flotation; where in absence of F. acidiphilum cells, over 95% of pyrite can be recovered as a float. However, when the mineral was pretreated with F. acidiphilum cells, less than 20% can be recovered as a float.
Keywords: Adhesion; Biosurface modification; Extended DLVO theory; Flotation; Ferroplasma acidiphilum;

Adsorption of the complex ion Au ( CN ) 2 - onto sulfur-impregnated activated carbon in aqueous solutions by Kardia Ramírez-Muñiz; Shaoxian Song; Selene Berber-Mendoza; Shitang Tong (602-606).
The adsorption of Au ( CN ) 2 - on the sulfur-impregnated activated carbon, SIAC 8.0, in an aqueous solution was much stronger than on the conventional activated carbon, GRC-22. The maximum gold adsorption density on the SIAC 8.0 was 2.25× that on the GRC-22, which suggests that the SIAC 8.0 had a much higher adsorption capacity for Au ( CN ) 2 - than the GRC-22.The adsorption of the gold–cyanide complex ion (Au ( CN ) 2 - ) on sulfur-impregnated activated carbon in aqueous solution has been studied in order to find a better adsorbent for the gold cyanidation process for extracting gold from ores. This study was performed using sulfur-impregnated activated carbon (SIAC 8.0) made from high-sulfur petroleum coke and an artificial aqueous solution of Au ( CN ) 2 - . The experimental results have shown that Au ( CN ) 2 - strongly adsorbed onto the SIAC 8.0, leading the gold adsorption capacity of the SIAC 8.0 to be 2.25× that on conventional activated carbon. It has been also found that the adsorption fit the Langmuir isotherm well, and the adsorption density of Au ( CN ) 2 - on the SIAC 8.0 in aqueous solution increased with increasing temperature, suggesting chemical adsorption. The chemical adsorption might be attributed to the formation of S–Au–CN on SIAC 8.0 surfaces through the covalent bond between the gold atom of the ion and the sulfur in the molecular structure of the SIAC 8.0. In addition, the desorption test has demonstrated that the majority of the adsorption was irreversible, which depended on the density of the adsorption sites on the SIAC.
Keywords: Sulfur-impregnated activated carbon; Chemical adsorption; Gold–cyanide complex ion;

Selective removal of Pb(II), Cd(II), and Zn(II) ions by hydrous manganese oxide was compared to the performance of a macroporous cation exchanger, D-001 and an iminodiacetic acid chelating exchanger, Amberlite IRC 748.Selective removal of three toxic metal ions, Pb(II), Cd(II), and Zn(II), from aqueous solution by amorphous hydrous manganese dioxide (HMO) was evaluated. Two polymeric exchangers, a polystyrene–sulfonic cation exchanger, D-001, and an iminodiacetic acid chelating exchanger, Amberlite IRC 748, were involved for comparison. Hydrogen ion release is accompanied by metal uptake onto HMO, implying that metal sorption could be generally represented by an ion-exchange process. As compared to both exchangers, HMO exhibits preferable sorption toward the toxic metals in the presence of Ca(II) ions at greater levels. FT-IR of the HMO samples laden with different metals indicate that Ca(II) uptake onto HMO is mainly driven by outer-sphere complexation, while that of three toxic metals might be related to inner-sphere complex formation. In addition, uptake of heavy metals onto HMO approaches equilibrium quickly and the exhausted HMO particles can be regenerated readily for repeated use by HCl solution. The results reported strongly display the potential of HMO as an economic and selective sorbent for removal of toxic metals from contaminated waters.
Keywords: Hydrous manganese dioxide; Heavy metals; Selective removal; Cation-exchange resin; Chelating resin;

Hollow Pd–Fe nanospheres are fabricated using vesicle template, which are easier to handle and exhibit enhanced catalytic reactivity in aqueous C–C coupling reactions than their dense counterparts.Display Omitted► Hollow Pd–Fe nanospheres can be easily fabricated through a vesicle template. ► Hollow Pd–Fe nanospheres exhibit enhanced catalytic reactivity in aqueous C–C coupling reactions. ► Hollow Pd–Fe nanospheres are easily handled in liquid-phase reaction due to its lower density. ► Hollow Pd–Fe nanospheres can be easily recovery due to its magnetic property.Hollow Pd–Fe nanospheres were fabricated through a vesicle-assisted chemical reduction method. With the characterization of X-ray diffraction, selected area electron diffraction, X-ray photoelectron spectroscopy, scanning electron micrography, transmission electron micrography, and N2 physisorption experiment, the resulting Pd–Fe material was identified to be hollow spherical with mesoporous shell. During aqueous Sonogashira-, Heck-, and Ullmann-type coupling reactions of aryl halide, the as-prepared hollow Pd–Fe nanospheres exhibited much higher activity than the dense counterpart nanoparticles. The enhanced reactivity was attributed to both the hollow chamber structure and the promotional effect of Fe-dopants, which provided more Pd active sites for the reactants. Moreover, this hollow material displayed other advantages such as low-cost, recyclability and easy experimental handling.
Keywords: Pd–Fe; Hollow nanospheres; Vesicle template; Coupling reaction; Green chemistry;

Study of solvent adsorption on chemically bonded stationary phases by microcalorimetry and liquid chromatography by Bogusław Buszewski; Szymon Bocian; Gerhard Rychlicki; Péter Vajda; Attila Felinger (620-625).
The most significant decrease of the heat of adsorption is observed between naked silica to the stationary phase with a coverage density of 1.11 μmol/m2.A detailed, molecular-level description of the sorption mechanism in reversed-phase liquid chromatography is of great interest to analytical chemists. For this purpose, solvent adsorption in the octadecyl stationary bonded phase was investigated. Preferential adsorption of solvents from an acetonitrile–water and methanol–water mobile phase was measured on a series of non-end-capped octadecyl bonded phases with different coverage densities of bonded ligands using the minor disturbance method. For a comparison, a microcalorimetric study of organic solvent adsorption on the stationary phase was executed. The results from the excess isotherm measurement agree well with the experimental measurement of the heat of immersion of the bonded stationary phases by the test solvents. The microcalorimetric measurement is another method for determination of solvation processes of the stationary phases. Changes of the heat of immersion provide information about the surface accessibility for interaction with solvent molecules. The increase of the stationary phase coverage density reduces the free space between bonded chains and penetration of solvent between organic chains.
Keywords: Solvent adsorption; Stationary phase; Excess isotherm; Surface heterogeneity; Microcalorimetry; Heat of immersion;

A robust strategy for assembling and disassembling of highly luminescent blue emitting Zn x Cd1− x S/dodecylamine complexes via a facile water/chloroform interface.We present a robust strategy for assembling and disassembling of highly luminescent blue emitting Zn x Cd1− x S/dodecylamine (DDA) complexes via a facile water/chloroform interface. Firstly, thioglycolic acid (TGA)-stabilized ternary Zn x Cd1− x S nanocrystals (NCs) were synthesized in aqueous solution. And then, relying upon the facile water/chloroform interfacial platform, such NCs are assembled into the flake-like microstructures under the direction of DDA molecules when the pH of the water phase is adjusted into an optimal acidic range. Simultaneously, the NCs are transferred from the water into the chloroform phase due to the electrostatic interactions between carboxyl groups and amino of DDA molecules. Interestingly, by reversibly adjusting the pH of the water phase into an optimal basic range, the flake-like Zn x Cd1− x S/DDA complexes are disassembled into separate NCs and DDA, and these NCs are reversibly transferred back into the water phase. The photoluminescence (PL) quantum yield (QY) of Zn x Cd1− x S/DDA complexes after interfacial assembly is improved to 55% from 6%. Particularly, a QY of about 22% still retains for the Zn x Cd1− x S NCs even after the interfacial disassembly.
Keywords: Zn x Cd1− x S NCs; Dodecylamine; Quantum dots; Blue emitting; Interfacial assembly; Interfacial disassembly;

By tracing the time course of the interfacial tension of a water/nitrobenzene interface with a time-resolved quasi-elastic laser scattering method, it was experimentally revealed that the Marangoni convection induced by injection of a sodium alkylsulfate solution is accompanied by a heterogeneity of the interfacial tension.The interface of a biphasic system of water and nitrobenzene exhibits a rapid flip motion and a tangential flow, so-called Marangoni convection, accompanying a pulse-like change of interfacial electrical potential when an aqueous solution of sodium alkylsulfate is introduced to the interface through a capillary. Although it is conventionally known that the Marangoni convection is triggered by heterogeneity of the interfacial tension, the heterogeneity of the interfacial tension of this system has not been directly measured. Here, we employed a time-resolved quasi-elastic laser scattering method with a time resolution of 200 ms to trace the time course of the interfacial tension at the water/nitrobenzene interface, and we demonstrated the first experimental evidence for the heterogeneity of the interfacial tension. Moreover, we found that the homogeneity of interfacial tension was restored within 1 s and that, in the presence of an electrolyte in the water phase, the surfactant molecules were homogeneously adsorbed on the interface immediately after they were conveyed by the tangential flow at the interface, whereas in the absence of electrolyte, the surfactant molecules were distributed only in the bulk phases.
Keywords: Liquid/liquid interface; Chemical oscillation; Surfactant; Marangoni convection; Quasi-elastic laser scattering;

Lensless microscopy technique for static and dynamic colloidal systems by D.C. Alvarez-Palacio; J. Garcia-Sucerquia (637-640).
In this paper we use digital in-line holographic microscopy (DIHM), a simple microscopy method, for imaging colloidal systems. In the figure are shown the reconstructions of temporal observations of a dewetting wavefront on colloidal suspension observed with DIHM.We present the application of a lensless microscopy technique known as digital in-line holographic microscopy (DIHM) to image dynamic and static colloidal systems of microspheres. DIHM has been perfected up to the point that submicrometer lateral resolution with several hundreds of micrometers depth of field is achieved with visible light; it is shown that the lateral resolution of DIHM is enough to resolve self-assembled colloidal monolayers built up from polystyrene spheres with submicrometer diameters. The time resolution of DIHM is of the order of 4 frames/s at 2048 × 2048 pixels, which represents an overall improvement of 16 times the time resolution of confocal scanning microscopy. This feature is applied to the visualization of the migration of dewetting fronts in dynamic colloidal systems and the formation of front-like arrangements of particles.
Keywords: Digital in-line holographic microscopy; Colloidal systems; Dewetting; Colloidal crystals;

A soft particle in an external electric field.Display Omitted► The limiting electrophoretic mobility of a highly charged soft particle is obtained. ► A highly charged soft particle behaves as if it were a hard particle in the limit of high Donnan potentials. ► A solidification effect is observed for soft particles.It is known that the electrophoretic mobility of a spherical rigid particle in an electrolyte solution with large κa (where κ  = Debye–Hückel parameter and a  = particle radius) and large Dukhin number (Du ≫ 1) tends to a nonzero constant value in the limit of high zeta potentials. A highly charged liquid drop exhibits the same limiting mobility value. That is, a liquid drop behaves as if it were a rigid particle (the solidification effect). In the present paper we derive the corresponding mobility expression for a highly charged spherical soft particle (i.e., a polyelectrolyte-coated particle) consisting of the particle core of radius a covered with an ion-penetrable surface layer of thickness d in a symmetrical electrolyte solution of valence z. It is shown that for κa  ≫ and κd  ≫ 1, the magnitude of the scaled limiting mobility μ ( ) is given by |μ ( )| = 2εrεokT/3ηze  · (1 +  a 3/2b 3) · 2 ln 2, where εr is the relative permittivity of the electrolyte solution, εo is the permittivity of a vacuum, e is the elementary electric charge, and kT is the thermal energy. When a  ≈  b, the obtained limiting mobility expression tends to the result for a rigid sphere. That is, the solidification effect is observed also for a soft particle.
Keywords: Soft particle; Limiting electrophoretic mobility; Donnan potential; Solidification effect;

by Arthur Hubbard (645).