Journal of Colloid And Interface Science (v.361, #2)
Polyelectrolyte complexes: Bulk phases and colloidal systems
by Jasper van der Gucht; Evan Spruijt; Marc Lemmers; Martien A. Cohen Stuart (pp. 407-422).
Complex formation between oppositely charged polyelectrolytes and its application to making colloidal systems are reviewed.Display Omitted► Understanding polyelectrolyte complexes: the state of the art. ► Driving forces, cohesive energy and phase behavior. ► Dynamics of polyelectrolyte complexes. ► From phase behavior to controlled microphases: micelles and micellar networks. ► Polyelectrolyte complexes on surfaces: multilayers and brushes.When aqueous solutions of polycations and polyanions are mixed, polyelectrolyte complexes form. These are usually insoluble in water, so that they separate out as a new concentrated polymer phase, called a complex coacervate. The behavior of these complexes is reviewed, with emphasis on new measurements that shed light on their structural and mechanical properties, such as cohesive energy, interfacial tension, and viscoelasticity. It turns out that stoichiometric complexes can be considered in many respects as pseudo-neutral, weakly hydrophobic polymers, which are insoluble in water, but become progressively more soluble as salt is added. In fact, the solubility-enhancing effect of salt is quite analogous to that of temperature for polymers in apolar solvents.Since two-phase systems can be prepared in colloidal form, we also discuss several kinds of colloids or ‘microphases’ that can arise due to polyelectrolyte complexation, such as thin films, ‘zipper’ brushes, micelles, and micellar networks. A characteristic feature of these charge-driven two-phase systems is that two polymeric ingredients are needed, but that some deviation from strict stoichiometry is tolerated. This turns out to nicely explain how and when the layer-by-layer method works, how a ‘leverage rule’ applies to the density of the ‘zipper brush’, and why soluble complexes or micelles appear in a certain window of composition. As variations on the theme, we discuss micelles with metal ions in the core, due to incorporation of supramolecular coordination polyelectrolytes, and micellar networks, which form a new kind of physical gels with unusual properties.
Keywords: Polyelectrolyte complexation; Phase behavior; Layer-by-layer assembly; Polyelectrolyte multilayers; Complex coacervate core micellesAbbreviations; PDMAEMA; poly(2-(; N; ,; N; -dimethyl amino)-ethyl methacrylate; PTMAEMA; poly(2-(; N; ,; N; ,; N; -trimethyl amino)-ethyl methacrylate; PEO; poly(ethylene oxide); P2MVP; poly(; N; -methyl-2-vinyl pyridinium iodide); PAA; poly(acrylic acid); PVA; poly(vinyl alcohol); PAAm; poly(acryl amide); PNIPAM; poly(; N; -isopropyl acrylamide); PSPMA; poly(3-sulfopropyl methacrylate); PSS; poly(styrene sulfonate); PEI; poly(ethylene imine); PAH; poly(allyl amine) hydrochloride; PDADMAC; poly(diallyldimethylammonium chloride); PMA; poly(maleic acid); PMMA; poly(methyl methacrylate); PLL; poly(; l; -lysine)
Monodisperse red blood cell-like particles via consolidation of charged droplets
by Chul Ho Park; Nae-oh Chung; Jonghwi Lee (pp. 423-428).
Non-spherical or asymmetrical particles have garnered considerable attention due to their novel features. This study reports red blood cell-like particles with controllable torus structures. Understanding of the consolidation mechanism provides novel idea to engineer multi-functional structures as well as to create core/shell torus structures with using a coaxial nozzle system..Display Omitted► Torus structure was observed in jettingusing both THF and Py solvents at 25 °C. ► Jetting using DMF produced torus structures at surrounding temperatures above 35 °C. ► We showed the fabrication of core/shell torus structure using coaxial nozzles. ► Rheological properties play a critical role in the formation of torus structure.Recently, researchers have tried to produce non-spherical and anisotropic particles to be used in the next generation of multi-functional materials. Of key interest is the red blood cell-like particle. The torus structure was produced under the relatively fast consolidation of monodisperse droplets, and its parameters were found to be tunable by temperature as well as solvent type and concentration. The observation of consolidation demonstrated that the polymers were accumulated and solidified in the torus structure, naturally, whereas there was the critical droplet size to induce the asymmetry diffusivities. The torus structures could be simply tuned by the flow rate and concentration. The coaxial nozzle system produced the core/shell torus particles. These results state that the consolidation mechanism can hold important clues to enhance the range of tuning capabilities.
Keywords: Torus particle; Doughnut-like particle; Blood cell-like particle; Consolidation; Core/shell particle; Electrohydrodynamic jetting; Electrospray
Fabrication of large scale two-dimensional colloidal crystal of polystyrene particles by an interfacial self-ordering process
by Zhicheng Lu; Ming Zhou (pp. 429-435).
Large scale two-dimensional colloidal crystal of orderly-packed polystyrene particles was prepared through an interfacial self-ordering process with the assistance of Triton X 100.Display Omitted► An interfacial self-ordering method was used to prepare monolayer of PS spheres. ► An interfacial swelling method was used to detect the three-phase contact angle. ► TX 100 is an effective assistant reagent for the formation of the monolayer. ► Laser diffraction revealed the nearly uniform lattice orientation of the monolayer.Monolayer films of hexagonal close-packed polystyrene (PS) spheres were formed at the air–water interface through a self-ordering process without using Langmuir trough. The contact angle of PS particles on the surface of water was determined by an interfacial swelling method. It was found that the concentration and the nature of surfactant had an obvious influence on the arrangement of PS particles. PS suspension containing Triton X 100 (TX 100) of an appropriate concentration self-assembled into a closely packed monolayer on the surface of water. Sodium dodecyl sulfonate, an anionic surfactant, had a relative weak influence on the arrangement of pre-dried PS particles, in contrast, had an obvious effect on newly synthesized PS particles. Quantitative ultraviolet–visible (UV–vis) absorption spectrometry indicated that about 3% of the added TX 100 was adsorbed on the PS particle surface. Laser diffraction patterns on the monolayer film were used to investigate the lattice orientation. Ultraviolet–visible–near infrared (UV–vis–NIR) spectra of monolayer films of different sized PS particles displayed that the method presented here was universal for preparation of two-dimensional (2D) colloidal crystals.
Keywords: Polystyrene particle; 2D colloidal crystal; Self-ordering; Interface; Laser diffraction
Gallium ion-assisted room temperature synthesis of small-diameter ZnO nanorods
by Seungho Cho; Semi Kim; Kun-Hong Lee (pp. 436-442).
We report a method for synthesizing single crystalline small-diameter (∼9nm) pure ZnO nanorods at room temperature (20°C) and normal atmospheric pressure (1atm) by the addition of gallium salts to the reaction solution.Display Omitted► Single crystalline small-diameter ZnO nanorods were synthesized by gallium-assisted reaction. ► No gallium atoms were incorporated into the synthesized nanorods. ► Gallium ions were involved in suppressing the dissolution of ZnO. ► The UV–Vis absorption spectra of the ZnOs were blue-shifted relative to that of 230nm diameter ZnO.We report a method for synthesizing small-diameter ZnO nanorods at room temperature (20°C), under normal atmospheric pressure (1atm), and using a relatively short reaction time (1h) by adding gallium salts to the reaction solution. The ZnO nanorods were, on average, 92nm in length and 9nm in diameter and were single crystalline in nature. Quantitative analyses revealed that gallium atoms were not incorporated into the synthesized nanocrystals. On the basis of the experimental results, we propose a mechanism for the formation of small-diameter ZnO nanorods in the presence of gallium ions. The optical properties were probed by UV–Vis diffuse reflectance spectroscopy. The absorption band of the small-diameter ZnO nanorods was blue-shifted relative to the absorption band of the ∼230nm diameter ZnO nanorods (control samples). Control experiments demonstrated that the absence of metal ion-containing precipitants (except ZnO) at room temperature is essential, and that the ZnO nanorod diameter distributions were narrow for the stirred reaction solution and broad when prepared without stirring.
Keywords: Nanomaterials; Zinc oxide; Room temperature reaction; Crystal growth
Electrophoresis of concentrated colloidal dispersions in low-polar solvents
by Teun Vissers; Arnout Imhof; Félix Carrique; Ángel V. Delgado; Alfons van Blaaderen (pp. 443-455).
A method is presented to measure the electrophoretic mobility in concentrated colloidal dispersions in real space. Data are shown on the surface potential, charge, and self-diffusion as a function of volume fraction.Display Omitted► A new method is presented to measure the electrophoretic mobility in real space. ► The method is applied to a colloidal dispersion in a low-polar solvent. ► The electrophoretic mobility decreases as function of volume fraction. ► We find a decreasing charge and roughly constant surface potential with increasing volume fraction.We present a method to accurately measure the electrophoretic mobility of spherical colloids at high volume fractions in real space using confocal laser scanning microscopy (CLSM) and particle tracking. We show that for polymethylmethacrylate (PMMA) particles in a low-polar, density- and refractive-index-matched mixture of cyclohexylbromide and cis-decahydronaphthalene, the electrophoretic mobility decreases nonlinearly with increasing volume fraction. From the electrophoretic mobilities, we calculate the ζ-potential and the particle charge with and without correcting for volume fraction effects. For both cases, we find a decreasing particle charge as a function of volume fraction. This is in accordance with the fact that the charges originate from chemical equilibria that represent so-called weak association and/or dissociation reactions. Finally, as our methodology also provides data on particle self-diffusion in the presence of an electric field, we also analyze the diffusion at different volume fractions and identify a nonlinear decreasing trend for increasing volume fraction.
Keywords: Colloids; Electrophoresis; Low-polar; Real-space; Zeta-potential; Charge; Self-diffusion
Slightly surface-functionalized polystyrene microspheres prepared via Pickering emulsion polymerization using for electrophoretic displays
by Guannan Yin; Zheng Zheng; Haitao Wang; Qiangguo Du (pp. 456-464).
The surface structure of polymer microspheres is dramatically affected by the copolymerization of bifunctional molecules during Pickering emulsion polymerization.Display Omitted► Slightly surface-functionalized PS microspheres are prepared by photocatalytic Pickering emulsion polymerization. ► Sodium styrene sulfonate modified titania hydrosol is used as stabilizer. ► PS microspheres with small size, narrow distribution, and uniform surface chemistry are achieved. ► PS microspheres with slightly modified surface are expected to be suitable for the application of E-ink.Slightly surface-functionalized polystyrene (PS) microspheres are prepared by photocatalytic Pickering emulsion polymerization using sodium styrene sulfonate (SSS)-modified titania hydrosol as a stabilizer. Aqueous electrophoresis measurements indicate the adsorption of bifunctional SSS anions on the surface of titania nanoparticles via electrostatic interaction. SSS molecules participate in the copolymerization with the monomers before the nucleation and thus have a great effect on the morphology and surface structure of the obtained PS microspheres. Appropriate SSS concentration leads to PS microspheres with small size, narrow distribution, and uniform surface chemistry. This kind of polymer particles can be used as a good candidate for the electrophoretic displays because of their high colloidal stability and electrophoretic mobility in the apolar solvent.
Keywords: Colloidal stability; Emulsion polymerization; Functionalization of polymers; Nanocomposites; Polymer microspheres
Nanostructured functional co-polymers bioconjugate integrin inhibitors
by Aldo Laganà; Iole Venditti; Ilaria Fratoddi; Anna Laura Capriotti; Giuseppe Caruso; Chiara Battocchio; Giovanni Polzonetti; Filippo Acconcia; Maria Marino; Maria Vittoria Russo (pp. 465-471).
Bioconjugates based on functionalized polymeric nanoparticles and monoclonal anti-Integrin antibody were prepared. Bioconjugates loading was quantitatively assessed with LC/ESI-MS/MS investigations and their reduced migration potential was tested in HEK293 cells.Display Omitted► Polymeric and co-polymeric nanoparticles with different functionalities were obtained. ► Bioconjugates were obtained by loading anti-Integrin antibody. ► Bioconjugates qualitative and quantitative loading analyses were carried out. ► The biological efficacy of bioconjugates was tested with HEK293 cells.Synthesis and properties of bioconjugates based on functionalized polymeric nanoparticles (PNs) and monoclonal anti-Integrin αV CD51 (aI) antibody were investigated. Polymeric and co-polymeric colloidal nanoparticles with different functionalities, i.e., acid, amine, or thiol, namely poly(methylmethacrylate-co-acrylic acid) [P(MMA-co-AA)], poly(methylmethacrylate-co-dimethylpropargylamine) [P(MMA-co-DMPA)], poly(methylmethacrylate-co-allil mercaptane) [P(MMA-co-AM)], were obtained by tailoring emulsion synthesis and fully characterized by means of spectroscopic techniques and scanning electron microscopy (SEM). Bioconjugates (PN/aI) based on P(MMA) or P(MMA-co-AA) were obtained by loading the polymeric nanoparticles with the antibody anti-Integrin with a simple and straightforward immobilization strategy. Bioconjugates qualitative and quantitative loading analyses were carried out by means of polyacrylamide gel electrophoresis 1D-PAGE, MALDI-TOF, and LC/ESI–MS/MS investigations. The biological efficacy of bioconjugates was confirmed by the reduced migration potential of PN/aI-treated human kidney cells (HEK293). The easy immobilization procedure and high immobilization capacity of polymeric nanoparticles together with tuneable chemical functionalities and dimension of the polymeric nanoparticles open applicative perspectives for targeted delivery.
Keywords: Nanostructured polymers; Bioconjugates; Anti-Integrin antibody; Functional co-polymers; Nanoparticles; XPS; LC/ESI–MS/MS
Facile method to synthesize platelet SBA-15 silica with highly ordered large mesopores
by Liang Cao; Michal Kruk (pp. 472-476).
Highly ordered large-pore SBA-15 silica with platelet particle morphology was synthesized using a micelle expander 1,3,5-triisopropylbenzene by employing short initial stirring time followed by static aging at low temperature.Display Omitted► Highly ordered SBA-15 with large pore size (18nm) and short pore length was obtained. ► Plate-like morphology was achieved by employing short stirring time and static aging. ► Platelet SBA-15 had (100) interplanar spacing as large as 17nm. ► Platelet SBA-15 had high surface area (470m2g−1) and large pore volume (1.6cm3g−1).Highly ordered mesoporous SBA-15 silica with large pore diameter of 18nm (nominal BJH pore diameter ∼22nm) and short pore length (∼500nm) was synthesized using a micelle expander 1,3,5-triisopropylbenzene in the absence of ammonium fluoride by employing short initial stirring time at 17°C followed by static aging at low temperature. Scanning and transmission electron microscopies revealed that the material comprised of platelet particles in which large mesopores were nearly flawlessly arranged within uniform domains up to 3μm in size. The platelet SBA-15 had the (100) interplanar spacing of 17nm, high surface area (∼470m2g−1) and large pore volume (∼1.6cm3g−1). The hydrothermal treatment at 130°C for 2days was employed to eliminate constrictions from the pore channels. The control experiment showed that a sample prepared with prolonged stirring had very similar mesoporous properties, but the particle size was smaller and the domains were irregular, proving that the static conditions facilitate the formation of SBA-15 with platelet particle morphology. The absence of ammonium fluoride was also critical in attaining the platelet particle shape.
Keywords: Ordered mesoporous silica; Templated synthesis; SBA-15; Pore size tailoring; Platelet particles
Effect of structural isomerism and polymer end group on the pH-stability of hydrogen-bonded multilayers
by Irem Erel; Helmut Schlaad; A. Levent Demirel (pp. 477-482).
LbL films of a polyacid and PIPOX or PNIPAM, two structural isomers, showed difference in pH-stability. Addition of electrostatic interactions only at the chain end shifted the critical dissolution pH to higher values.Display Omitted► Structurally isomeric hydrogen accepting neutral polymers behaved differently within LbL films. ► Different arrangement of atoms in isomeric polymers resulted in different film thickness and pH-stability of multilayers. ► pH-stability of hydrogen-bonded films can be enhanced by functionalizing only the chain end of the hydrogen accepting polymer.Association of tannic acid (TA) with structurally isomeric poly( N-isopropylacrylamide) (PNIPAM) and poly(2-isopropyl-2-oxazoline) (PIPOX) has been examined at surfaces to understand the effect of different molecular arrangements in a polymer repeating unit of structural isomers on the construction and pH-stability of hydrogen-bonded multilayers. Films were fabricated using layer-by-layer (LbL) technique through hydrogen-bonding interactions primarily between carbonyl groups of neutral polymers and hydroxyl groups of TA molecules at pH 2. PIPOX and TA formed thinner and more stable films in the pH scale with a critical dissolution pH of 9 when compared to films of PNIPAM and TA with a critical pH of 8. The differences in the thickness and pH-stability were due to different conformational behavior of PNIPAM and PIPOX in water which affects the accessibility of carbonyl groups for participation in the hydrogen bonding and the number of binding sites between the polymer pairs. Addition of electrostatic interactions by introducing amino groups only at the PIPOX chain end shifted the critical dissolution pH to higher values and resulted in gradual dissolution of the films in a wide pH range of 9–12. Such films hold promise for use in biomedical field due to biocompatibility and lower critical solution temperature (LCST) behavior at near physiological temperature of PNIPAM and PIPOX together with the pH-response of the hydrogen-bonded films.
Keywords: Layer-by-layer technique; Hydrogen-bonding; Multilayers; Structural isomers; Polymer end-group; pH-responsive
Triazole-forming waterborne polyurethane composites fabricated with silane coupling agent functionalized nano-silica
by Daoxing Sun; Xiao Miao; Kejie Zhang; Hern Kim; Yongan Yuan (pp. 483-490).
DTG curves of pristine and functionalized nano-silica modified waterborne polyurethane using “click” chemistry.Display Omitted► Click chemistry was exploited to form the functional waterborne polyurethane. ► Fabricate waterborne polyurethane can effectively link nano-silica and silane coupling agent together by triazole ring. ► Nano-silica dispersed well in the functional waterborne polyurethane. ► The properties of the functional waterborne polyurethane were exhibited well with the modification of the functional nano-silica.In the research work, “click” chemistry was used to modify waterborne polyurethane (WPU) with silane coupling agent (SiCA) functionalized nano-silica. The modified WPU (CWPU) was characterized by FTIR, scanning electron microscope (SEM), thermogravimetric analysis (TGA) and contact angle measurement. The experiment results show that the modification can improve the thermal stability, hardness, and water or weather resistance of CWPU.
Keywords: Triazole; Click chemistry; Waterborne polyurethane; Nano-silica
Noninjection, one-pot synthesis of Cu-deficient CuInS2/ZnS core/shell quantum dots and their fluorescent properties
by Da-Eun Nam; Woo-Seuk Song; Heesun Yang (pp. 491-496).
Cu-deficient CuInS2 QDs exhibited a high quantum yield of 50% along with a progressive blue-shift in emission upon ZnS shell coating.Display Omitted► Cu-deficient CuInS2 QDs are synthesized by a noninjection approach. ► CuInS2/ZnS QDs exhibit an efficient yellow emission with a QY of ∼50%. ► An alternative radiative recombination in core/shell QDs is suggested.Non-toxic, environment-benign colloidal CuInS2 (CIS) quantum dots (QDs) were synthesized through a facile noninjection, one-pot approach by reacting Cu and In precursors with dodecanethiol dissolved in 1-octadecence at 220°C. The Cu:In precursor molar ratio was varied from 1:1 to 1:4 to intentionally generate Cu-deficient CIS QDs. Depending on the stoichiometry of the QDs, their emission peak wavelengths were tuned in red–deep red region. More Cu-deficient CIS QDs (Cu:In=1:4) were found to be more efficient than ones with Cu:In=1:1. After successive ZnS shell was overgrown on the surface of core QDs with Cu:In=1:4, the resulting core/shell QDs exhibited a highly efficient yellow emission with a quantum yield of ∼50%. A substantially blue-shifted emission from the core/shell QDs versus core ones was described by suggesting an alternative recombination pathway that may be induced by the ZnS shell coating.
Keywords: Non-toxic; CuInS; 2; /ZnS; Quantum dots; Cu-deficient; Yellow emission; Quantum yield; Recombination pathway
Adsorption–stress relationship in drying of silica/PVA suspensions
by Sunhyung Kim; Jun Hee Sung; Sangki Chun; Kyung Hyun Ahn; Seung Jong Lee (pp. 497-502).
For silica/PVA suspensions, both the polymer adsorption ( Γ) and stress of dry film (σ p) was scaled onto a single master curve as a function of mixing time (t m).Display Omitted► We study the stress development for silica/PVA suspensions. ► Scaled relationship between polymer adsorption and film stress is found. ► Film structure also has a similar trend with adsorption. ► These relations enable to control the film performance by polymer adsorption.In this study, we investigated drying process of silica/PVA suspensions. After measuring the amount of polymer adsorption and the stress evolution of a film during drying process, we could find a quantitative relationship between polymer adsorption and stress development, for silica/PVA suspensions of different pH and mixing time. For all the suspensions of different pH, both the amount of polymer adsorption ( Γ) and the plateau stress of dry film (σ p) could be scaled onto a single master curve as a function of mixing time (t m). The scaling of mixing time for both Γ andσ p could be performed by the same scale factor, which implies that there is a one to one correlation between adsorption and stress. This correlation implies that we can control the microstructure and performance of dry film by adjusting the amount of polymer adsorption. The origin of adsorption kinetics of silica/PVA suspension was also discussed in terms of saponification of acetate groups in PVA, which facilitates hydrogen bonding between silica and PVA.
Keywords: Particle/polymer suspension; Drying; Adsorption; Stress development; Saponification
Highly ordered macroporous carbon spheres and their catalytic application for methanol oxidation
by Jianming Zhang; Yuxiao Zhang; Suoyuan Lian; Yang Liu; Zhenhui Kang; Shuit-Tong Lee (pp. 503-508).
Fabrication of highly ordered macroporous carbon spheres, which can be used as a good catalyst support for methanol oxidation.Display Omitted► Three-dimensional macroporous carbon spheres (3DMPCS) were successfully prepared. ► The pore sizes of 3DMPCS can be easily controlled. ► 3DMPCS have large specific areas and the ordered interconnected channels. ► 3DMPCS can serve as ideal candidate for catalyst supports.Highly ordered three dimensionally macroporous carbon spheres (3DMPCS) were successfully prepared against removable colloidal silica crystal bead templates by carbonization of glucose. The unique structural characteristics of the well-developed three dimensionally interconnected macropores were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption. The 3DMPCS have uniform large pore structures with size about 250nm. Pt nanoparticles were supported on the macroporous carbon spheres by two aqueous impregnation methods, and it was found that the 3DMPCS supported Pt exhibited high electrocatalytic activity for methanol oxidation.
Keywords: Colloidal silica particles; Macroporous carbon spheres; Pt nanoparticles; Methanol oxidation
Organic–inorganic hybrid of chitosan/organoclay bionanocomposites for hexavalent chromium uptake
by Sadanand Pandey; Shivani B. Mishra (pp. 509-520).
The chitosan/clay hybrid was prepared by solvent casting method. Possible interaction mechanism of Cr(VI) with chitosan and organoclay was discussed.Display Omitted► Chitosan-clay nanocomposite prepared by solvent casting method. ► Chitosan -clay nanocomposite act as an efficient chromium(VI) removal. ► Possible interaction mechanism of Cr(VI) with chitosan and organoclay. ► Nanocomposite useful for the fabrication and design of wastewater treatment plant. ► Nanocomposite has higher adsorption capability, reusability, and stability.Organic–inorganic hybrid of chitosan and nanoclay (Cloisite 10A) was chosen to develop a nanomaterial with combine properties of hydrophilicity of an organic polycation and adsorption capacity of inorganic polyanion. The chitosan/clay nanocomposite (CCN) was prepared by solvent casting method. The material synthesis was found most efficient in adsorbent behavior was studied in detail taking Cr(VI) as representative ion. The chemical, structural and textural characteristics of the material were determined by FTIR, XRD, TEM, SEM and EDAX analysis. XRD and TEM results indicated that an exfoliated structure was formed with addition of small amounts of MMT–Na+(montmorillonite–Na+) to the chitosan matrix. These composite material were used for the removal of chromium(VI) from aqueous solution. The conditions for the adsorption by the composite have been optimized and kinetics and thermodynamic studies were performed. Though the adsorption takes place in wide pH range, pH 3 was found most suitable and at this pH the adsorption data were modeled using the Langmuir and Freundlich isotherms at 15°C and 35°C, where the data fitted satisfactorily to Langmuir isotherms, the R2 values being 0.998 and 0.999 respectively indicating unilayer adsorption. Based on Langmuir model,Q o was calculated to be 357.14mg/g. The adsorption showed pseudo second order kinetics with a rate constant of 8.0763×10−4gmg−1min−1 at 100ppm Cr(VI) concentration.
Keywords: Chitosan/clay nanocomposite; Layered silicate; Nanoclay; X-ray diffraction; Cr(VI) adsorption
Facile synthesis of hierarchical nanocrystalline ZSM-5 zeolite under mild conditions and its catalytic performance
by Youming Ni; Aiming Sun; Xiaoling Wu; Guoliang Hai; Jianglin Hu; Tao Li; Guangxing Li (pp. 521-526).
Hierarchical nanocrystalline ZSM-5 zeolite was prepared under mild conditions and exhibited a long lifetime and a low average coking rate in MTH reaction.Display Omitted► Hierarchical nanocrystalline ZSM-5 zeolite NZ5 was prepared under mild condition. ► Evaporation of solvent and addition of methylamine were vital to the preparation. ► NZ5 showed a long lifetime and a high anti-coking property in MTH reaction.Hierarchical nanocrystalline ZSM-5 zeolite (NZ5) was synthesized at 100°C under atmospheric pressure using methylamine as a mineralizing agent. The crystallization process of NZ5 was characterized by dynamic light scattering (DLS), X-ray diffraction (XRD), and infrared spectroscopy (FTIR). The results of contrastive experiments showed that evaporation of the solvent promoted the aggregation of primary particles, and the addition of methylamine accelerated the crystallization process. The NZ5 aggregate consisted of 20nm individual particles, as shown in scanning electron microscope (SEM). The lattice fringes in the transmission electron microscope (TEM) images and the XRD results indicated that individual particles of NZ5 were highly crystalline. N2 adsorption-desorption isotherms showed that NZ5 had high BET surface areas with mesopores having a mean diameter of about 9nm. NZ5 exhibited a long lifetime, a stable and high yield of liquid hydrocarbons, and a high anti-coking performance in methanol-to-hydrocarbons reaction. Catalytic testing and TGA results showed that the lifetime of NZ5 was about ten times longer than that of micro-sized ZSM-5 zeolite (MZ5), and the average coking rate with NZ5 was one fifth over that of MZ5.
Keywords: Hierarchical ZSM-5 zeolite; Nanocrystalline; Methylamine; Methanol-to-hydrocarbons; Anti-coking
Preparation of rattle-type magnetic mesoporous carbon spheres and their highly efficient adsorption and separation
by Yuyong Yin; Shuxue Zhou; Chen Min; Limin Wu (pp. 527-533).
Rattle-type magnetic mesoporous carbon spheres with high magnetism core and mesoporous shell were successfully prepared, and they showed highly efficient adsorption and separation properties.Display Omitted►Rattle-type magnetic mesoporous carbon spheres were prepared by a template method. ► They are composed of a magnetic core and a mesoporous carbon shell. ► They have high magnetization strength and high specific surface areas. ► They show a good performance for adsorption, separation of dye molecules.Novel rattle-type magnetic mesoporous carbon spheres are successfully prepared using composite spheres with Fe3O4 as core and mesoporous SiO2 as shell plus solid SiO2 as a middle layer as templates. These rattle-type spheres possess the magnetization strength of as high as 37.5emu/g, high and tunable specific surface areas (382–512.6m2/g) due to mesoporous carbon shells. This magnetic rattle-type structure and the readily accessible mesoporous shell are very favoring for the fast adsorption and release of guest objects triggered by external stimulus, for example, the spheres showed very good adsorptive property to dye.
Keywords: Rattle-type structure; Mesoporous carbon materials; Magnetic properties; Template synthesis; Adsorbent
Charged polystyrene nanoparticles: Role of ionic comonomers structures
by Dhamodaran Arunbabu; Tushar Jana (pp. 534-542).
The structural effects of ionic comonomers on the size, morphology, charge density, and the self-assembly of the monodispersed charged polystyrene particles have been investigated.Display Omitted► Synthesis of monodispersed charged polystyrene nanoparticles. ► Structural effects of ionic comonomers on particle properties. ► Self-assembled light diffracting polymer nanoparticles.Emulsion copolymerizations of styrene were carried out with four structurally different ionic comonomers namely acrylic acid (AAc), methacrylic acid (MAA), 2-hydroxyethyl methacrylate (HEMA), and sodium styrene sulfonate (NaSS) to study the effect of monomer structure on the copolymerization kinetics and size, morphology, charge density, and the self-assembly of the particles. The copolymerization kinetics was found to be highly dependent upon the ionic comonomer structure, and the nature of this dependence altered from homogeneous to micellar nucleation regime. The decrease in particle size (D) with increasing surfactant concentration (S) was observed in all the cases; however, the exponents of D vs. S were not similar for all the cases. In the homogeneous nucleation regime, exponents followed the order as AAc (0.446)>MAA (0.396)>NaSS (0.252)>HEMA (0.241), whereas the order was almost reversed in the micellar nucleation regime as NaSS (0.406)>HEMA (0.228)>AAc (0.206)>MAA (0.172). The hydrophobic/hydrophilic character and the steric factors were found to be the driving force for the variation in D vs. S exponents with ionic comonomer structure. The presence of charges on the particle surface contributed by the ionic comonomers triggered the self-assembly of the particles upon sedimentation and diffracted visible light obeying Bragg’s law.
Keywords: Polystyrene; Nanoparticles; Emulsion copolymerization; Self-assembly; Charged monodisperse particles
Monodisperse sub-10nm gold nanoparticles by reversing the order of addition in Turkevich method – The role of chloroauric acid
by Sankar Kalidas Sivaraman; Sanjeev Kumar; Venugopal Santhanam (pp. 543-547).
Display Omitted► Monodisperse 5–10nm size nanoparticles were prepared using sodium citrate as the reducing/stabilizing agent. ► Reversing the order of addition used in the Turkevich method results in monodisperse nanoparticles. ► Chloroauric acid reactivity plays a key role by controlling the rate of oxidation of citrate into acetone dicarboxylic acid. ► The system exhibits a ‘memory’ of the order of addition, even for conditions resulting in slow reduction.The Turkevich method for synthesizing gold nanoparticles, using sodium citrate as the reducing agent, is renowned for its ability to produce biocompatible colloids with mean size>10nm. Here we show that monodisperse gold nanoparticles in the 5–10nm size range can be synthesized by simply reversing the order of addition of reactants, i.e. adding chloroauric acid to citrate solution. Kinetic studies and electron microscopic characterization revealed that the reactivity of chloroauric acid, initial molar ratio of citrate to chloroauric acid (MR), and reaction mixture pH play an important role in producing monodisperse gold nanoparticles. Reversing the order of addition also enhanced the stabilization of nanoparticles at high MR values. Remarkably, the system exhibits a ‘memory’ of the order of addition, even when the timescale of mixing is much shorter than the timescale of synthesis.
Keywords: Citrate; Chloroauric acid speciation; Gold nanoparticles; Order of addition; Turkevich method
Self-assembly and supramolecular liquid crystals based on organic cation encapsulated polyoxometalate hybrid reverse micelles and pyridine derivatives
by Shengyan Yin; Hang Sun; Yi Yan; Hui Zhang; Wen Li; Lixin Wu (pp. 548-555).
Diverse liquid crystal structures with organic–inorganic hybrid reverse micelles can be achieved by introducing different hydrogen-bonding acceptors.Display Omitted► Fabrication of multi-component hybrid materials using supramolecular interactions. ► Study of combined response of reverse micelles to added hydrogen-bonding acceptors. ► Diverse liquid crystal structures of reverse micelles have been achieved. ► The liquid crystal structures of hybrid assemblies can be conveniently adjusted.The controlled self-assembly of multi-components in one system represents the capability integrating intermolecular interactions and functions of components and is believed the key procedure leading to multifunctional materials finally. In pursuing this goal, we used a double-chain cationic surfactant with a benzoic acid group at the end of one tail to encapsulate Keggin-type polyanion clusters via electrostatic interaction, obtaining uniform supramolecular hybrid reverse micelles, which served as hydrogen-bonding donors. Five pyridine derivatives containing conjugated and non-conjugated groups were chosen as hydrogen-bonding acceptors to bind with reverse micelles. Through mixing with these components according to chemical stoichiometry, the hybrid reverse micelle changed to a new self-assembly precursor through intermolecular hydrogen bonding. The as-prepared reverse micelles bearing conjugated pyridine groups exhibit supramolecular liquid crystal properties, which were characterized by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The length and number of the alky chain in the pyridine derivatives, as well as the charges of polyoxometalates were also studied with regard to the liquid crystal structure. The synergistic effect of among three components was analyzed, and the liquid crystal properties could be conveniently adjusted through the modification of the hydrogen-bonding acceptor components.
Keywords: Supramolecular liquid crystals; Hybrid reverse micelles; Hydrogen-bonding; Polyoxometalate
New dimeric cholesteryl-based A(LS)2 gelators with remarkable gelling abilities: Organogel formation at room temperature
by Min Xue; Di Gao; Xiangli Chen; Kaiqiang Liu; Yu Fang (pp. 556-564).
Three new dimeric cholesterol-based A(LS)2 compounds have been prepared. Very interestingly, 16 of 37 gel systems can gel spontaneously at room temperature (∼25°C). And these gels possess smart thixotropic properties.Display Omitted► Three new A(LS)2 compounds prepared can act as efficient gelators. ► A small difference in the structures is crucial to the gelation behaviors of gelators. ► Sixteen gel systems can form spontaneously at room temperature (∼25°C). ► The gels formed at room temperature possess smart thixotropic properties.Three new dimeric cholesterol-based compounds of A(LS)2 type, where A stands for aromatic component, S steroid moiety, and L a linker connecting the two units, have been designed and prepared. Gelation test in 30 solvents demonstrated that the compounds can gel some of the solvents and form 37 gels, of which 16 form spontaneously at room temperature (∼25°C). These gels possess smart thixotropic properties as revealed by rheological studies. FTIR and1H NMR measurements revealed that hydrogen bonding is an important driving force for the formation of the gel networks. XRD analysis demonstrated that unlike commonly found layered structures adopted by dimeric cholesterol-based low-molecular mass gelators (LMMGs), one of the gelators created in this study adopts a hexagonal packing structure in its benzene gel.
Keywords: Low-molecular-mass organic gelators; A(LS); 2; Thixotropic properties
Preparation of positively charged oil/water nano-emulsions with a sub-PIT method
by Zhen Mei; Shangying Liu; Lei Wang; Jingjing Jiang; Jian Xu; Dejun Sun (pp. 565-572).
Positively charged oil/water nano-emulsions were prepared in a mixed cationic-nonionic surfactant system using a low energy one-step sub-PIT method, where the PIT is reduced by addition of an inorganic salt.Display Omitted► Positively charged O/W nano-emulsions were prepared by a low energy sub-PIT method. ► The addition of NaBr can reduce the higher PIT of the systems caused by CTAB. ► Mechanism of the method is solubilization of oil into swollen micelles above the TCB. ► Mechanism of the method is solubilization of oil into swollen micelles above the TCB. ► The obtained O/W nano-emulsions have tunable zeta potential and long-term stability.The phase inversion temperature (PIT) method is generally used to prepare nonionic surfactant stabilized nano-emulsions because of its low energy and surfactant consumption. The emulsion droplets are usually negatively charged because of the selective adsorption of OH− onto the droplet surfaces. In this work, positively charged oil/water nano-emulsions were prepared by adding a cationic surfactant to the system. The cationic molecules change the spontaneous curvature of the surfactant layers and raise the PIT above 100°C. The PIT can be depressed by addition of NaBr, as shown by conductivity measurements and equilibrium phase behavior. Therefore, these nano-emulsions can be prepared by the PIT method. We found that the formation of the nano-emulsions did not require a cross-PIT cycle. The mechanism of the emulsification is the formation of mixed swollen micelles that can solubilize all the oil above a “clearing boundary”, followed by a stir-quench to a temperature where these droplets become metastable emulsions. The zeta potential of the emulsion droplets can be easily tuned by varying the cationic surfactant concentrations. Due to electrosteric stabilization, the resulting nano-emulsions are highly stable, thus could find significant applications in areas such as pharmaceuticals, cosmetics and food industries.
Keywords: Positively charged nano-emulsions; Phase inversion temperature; Spontaneous curvature; Clearing boundary; Zeta potential; Long-term stability
Investigation of interfacial and structural properties of CTAB at the oil/water interface using dissipative particle dynamics simulations
by Yiming Li; Yingyan Guo; Mutai Bao; Xueli Gao (pp. 573-580).
Interfacial thickness versus CTAB concentration for different oil/water ratios and its variation against oil/water ratio at different concentrations. The snapshot is for a CTAB concentration 0.086, and oil/water ratio 1.5.Display Omitted► DPD is used to study the interfacial properties of CTAB/oil/water systems. ► CTAB is more upright and the interface thickens with CTAB and oil/water ratio. ► The area compressibility modulus decreases with the oil/water ratio. ► 〈 h2〉1/2 and S show a weak dependence on oil/water ratio but an increase with CTAB.We have used dissipative particle dynamics (DPD) to simulate the system of cetyltrimethylammonium bromide (CTAB) monolayer at the oil/water interface. The interfacial properties (interfacial density, interfacial thickness, and interfacial tension), structural properties (area compressibility modulus, end to end distance, and order parameter), and their dependence on the oil/water ratio and the surfactant concentration were investigated. Three different microstructures, spherical oil in water (o/w), interfacial phase, and water in oil (w/o), can be clearly observed with the oil/water ratio increasing. Both the snapshots and the density profiles of the simulation show that a well defined interface exists between the oil and water phases. The interface thickens with CTAB concentration and oil/water ratio. The area compressibility modulus decreases with an increase in the oil/water ratio. The CTAB molecules are more highly packed at the interface and more upright with both concentration and oil/water ratio. The root mean square end-to-end distance and order parameter have a very weak dependence on the oil/water ratio. But both of them show an increase with CTAB concentration, indicating that the surfactant molecules at the interface become more stretched and more ordered at high concentration. As CTAB concentration increases further, the order parameter decreases instead because the bending of the interface. At the same time, it is shown that CTAB has a high interfacial efficiency at the oil/water interface.
Keywords: Spatial structure; Interfacial density; Interfacial thickness; Interfacial tension; Area compressibility modulus; End-to-end distance; Order parameter
Destabilization mechanisms in a triple emulsion with Janus drops
by Hida Hasinovic; Stig E. Friberg (pp. 581-586).
The lighter Janus drops cream (A–B), coalesce (B), a VO layer separates (B–C). Remaining drops are heavier, sediment (C) coalesce (D) and an aqueous layer separates (E).Display Omitted► A triple Janus emulsion of water and two oils. ► Its destabilization included creaming, coalescence, sedimentation and inversion. ► Initial creaming was followed by coalescence and inversion. ► Final stage sedimentation followed by coalescence and inversion.The destabilization mechanism was investigated of a triple Janus emulsion. The inner part of the emulsion consisted of Janus drops of a vegetable oil (VO) and a silicone oil (SO) in an aqueous (W) drop, (VO+SO)/W. This drop, in turn was dispersed in a VO drop forming a double emulsion (VO+SO)/W/VO. Finally, these complex drops generated a complex Janus (SO+VO)/W/VO/SO triple emulsion by being dispersed in a continuous SO phase. The observations were limited to the time dependence of the over-all creaming/sedimentation processes, to the separation of layers of the compounds and to optical microscopy of the drop configuration with time. In the destabilization process the rise of the complex drops, (SO+VO)/W/VO, caused crowding in the upper part of the emulsion, which in turn led to enhanced coalescence, inversion and separation of a dilute vegetable oil emulsion. As a consequence of the separation of VO in the process, the remaining drops contained a greater W fraction and greater density. This change, in turn, resulted in sedimentation of the complex drops to form several high internal ratio morphologies in an SO continuous emulsion in the lower part of the test tube, among them a W/VO/SO emulsion. Finally, an inversion took place into an SO/VO/W double emulsion forming a separate bottom layer.
Keywords: Janus emulsions; Triple emulsions; Double emulsions; Silicone emulsions; Vegetable oil emulsions
Design, synthesis and stimuli responsive gelation of novel stigmasterol–amino acid conjugates
by Hana Svobodová; Nonappa; Zdeněk Wimmer; Erkki Kolehmainen (pp. 587-593).
Acid–base triggered reversible sol–gel transition of stigmasterol-amino acid conjugates causing by introduction and neutralization of HCl gas or its solution.Display Omitted► Three stigmasterol-amino acid conjugates were prepared and fully characterized. ► Gelation properties of the compounds were tested in 22 organic solvents and water. ► The protonation of NH2 group of amino acid is crucial for the gel formation. ► Reversible sol–gel transitions can be induced with pH stimuli. ► The gelators, gels and xerogels were studied by solution and solid-state NMR, IR and SEM.An efficient synthesis of three novel stigmasterol-amino acid (glycine,l-leucine andl-phenylalanine) conjugates as stimuli responsive gelators is reported. The gelation properties of the prepared compounds were investigated in a variety of organic as well as aqueous solvents. The most striking finding of our investigation was that the hydrochloride salts of the prepared conjugates acted as gelators, whereas the neutral conjugates were either non-gelators or formed only a weak gel in anisole. The hydrochloride salts of stigmasteryl glycinate andl-leucinate form gels in n-alcohols ( n=4–10) and in ethane-1,2-diol, and that of stigmasteryll-phenylalaninate forms gels in aromatic solvents and in tetrachloromethane. These unique properties of the gelators were explored to prepare stimuli responsive, “acid–base” triggered reversible sol–gel transitions. The gelators and their gels were characterized by liquid and solid-state NMR as well as FT-IR. The morphology of their corresponding xerogels was investigated by SEM.
Keywords: Stigmasterol; Amino acid; LMOG; Organogel; pH responsive
Primary, secondary, and tertiary amines for CO2 capture: Designing for mesoporous CO2 adsorbents
by Young Gun Ko; Seung Su Shin; Ung Su Choi (pp. 594-602).
The adsorption amount and bonding-affinity of CO2 increased in the order of tertiary, secondary, and primary amino-adsorbents while CO2 was easily desorbed from the adsorbent in the reverse order.Display Omitted► Amino-functionalized (1o, 2o, and 3o amines) monolayers on SBA-15 surfaces for CO2 capture. ► Adsorption capacity, adsorption–desorption kinetics, and thermodynamics of CO2 adsorption on adsorbents. ► The maximum CO2 adsorption capacity and the bonding-affinity were in the order of primary (1o), secondary (2o), and tertiary (3o) amino-adsorbents. ► This work demonstrates apt amine types to catch CO2 and regenerate the adsorbent.CO2 emissions, from fossil-fuel-burning power plants, the breathing, etc., influence the global worming on large scale and the man’s work efficiency on small scale. The reversible capture of CO2 is a prominent feature of CO2 organic–inorganic hybrid adsorbent to sequester CO2. Herein, (3-aminopropyl) trimethoxysilane (APTMS), [3-(methylamino)propyl] trimethoxysilane (MAPTMS), and [3-(diethylamino) propyl] trimethoxysilane (DEAPTMS) are immobilized on highly ordered mesoporous silicas (SBA-15) to catch CO2 as primary, secondary, and tertiary aminosilica adsorbents. X-ray photoelectron spectroscopy was used to analyze the immobilized APTMS, MAPTMS, and DEAPTMS on the SBA-15. We report an interesting discovery that the CO2 adsorption and desorption on the adsorbent depend on the amine type of the aminosilica adsorbent. The adsorbed CO2 was easily desorbed from the adsorbent with the low energy consumption in the order of tertiary, secondary, and primary amino-adsorbents while the adsorption amount and the bonding-affinity increased in the reverse order. The effectiveness of amino-functionalized (1o, 2o, and 3o amines) SBA-15s as a CO2 capturing agent was investigated in terms of adsorption capacity, adsorption–desorption kinetics, and thermodynamics. This work demonstrates apt amine types to catch CO2 and regenerate the adsorbent, which may open new avenues to designing “CO2 basket”.
Keywords: CO; 2; adsorbent; Organic–inorganic hybrid; Amine type; SBA-15; Aminosilane
Extension of Langmuir kinetics in dilute solutions to include lateral interactions according to regular solution theory and the Kiselev association model
by Adam W. Marczewski (pp. 603-611).
Adsorption rate profiles in Langmuir and mRSK models are strongly affected by equilibrium uptake and adsorption coverage. Adsorption and desorption term-related lateral interactions exert dramatic influence on rate profiles.Display Omitted► Langmuir kinetics in dilute solutions has been extended to consider lateral interactions. ►Non-specific interactions are included in terms of the regular solution model. ► Specific interactions are included in terms of the Kiselev model. ► The kinetic model is extended to encompass Langmuir–Freundlich energetic heterogeneity. ► Kinetic and equilibrium adsorption data of 4-nitrobenzoic acid on carbon is analyzed in the framework of this model.The influence of lateral non-specific and specific interactions on the kinetics in dilute solutions is analyzed within the framework of the Langmuir model. Regular solution theory is used to derive kinetic equations for dilute solutions (RSK model). RSK equations are modified to include simple Kiselev associative interactions and deviations from the regular solution theory (mRSK model) and LF-type energetic heterogeneity (LF–mRSK). Derived models lead to significantly different kinetic behavior than the commonly used FG model or the SRT approach. The influence of the equilibrium uptakeu eq and coverageθ eq on the observed effects of lateral interactions is discussed. A new kind of kinetic plot for data analysis is also presented. The mixed LF–mRSK model is applied to analysis of solute adsorption on mesoporous carbon.
Keywords: Adsorption kinetics; Langmuir kinetics; Lateral interactions; Dilute solution; Regular solution model; Kiselev model; Langmuir–Freundlich kinetics; SRT
Adsorption of pyridine onto the metal organic framework MIL-101
by Mi Jin Kim; Se Min Park; Sun-Jung Song; Jiyeon Won; Jin Yong Lee; Minyoung Yoon; Kimoon Kim; Gon Seo (pp. 612-617).
Pyridine can be adsorbed on coordinative unsaturated sites of MIL-101 formed during dehydration with a high stabilization energy.Display Omitted► Quantitative examination of pyridine adsorption on MIL-101. ► Theoretical calculation of the stabilization energy for the pyridine adsorption. ► Discussion on the adsorption site and strength of pyridine on MIL-101.The adsorption of pyridine onto the metal organic framework MIL-101 was investigated by experimental and theoretical methods. The amount of pyridine adsorbed on MIL-101 was extraordinarily large at 20°C, corresponding to about 950mg/g of dried MIL-101 and approximately half of the voids being filled. Most of the pyridine that had filled the voids was rapidly removed by evacuation at room temperature, but some of the pyridine was so strongly adsorbed that it was retained even under evacuation at 150°C. Although IR spectra of the adsorbed pyridine indicated the adsorption of pyridine as pyridinium ions and coordinated pyridine at low temperatures, increasing the adsorption temperature induced partial cleavage of the pyridine rings. The high stabilization energy of pyridine on the coordinative unsaturated sites (CUS) of MIL-101, obtained by theoretical calculation, −103kJ/mol, supported the strong adsorption of pyridine on the CUS.
Keywords: MOF MIL-101; Pyridine; Adsorption; Theoretical calculation
Effect of dissolved organic matter from Guangzhou landfill leachate on sorption of phenanthrene by Montmorillonite
by Pingxiao Wu; Yini Tang; Wanmu Wang; Nengwu Zhu; Ping Li; Jinhua Wu; Zhi Dang; Xiangde Wang (pp. 618-627).
The objective of this work was to compare the difference between DOM–MMT complexes and the raw MMT on sorption behavior to phenanthrene using a combination of spectroscopic, microscopic adsorption techniques and molecular modeling.Display Omitted► MMT combined with DOM in leachate enhance the sorption of PHE. ► DOM was bound on the surfaces of MMT via H-bondings and cation bridges. ► DOM-MMT complex possessed higher Si/O atomic ratio on silica layers. ► The characteristic of PHE sorption isotherm is linear.To investigate the effect of dissolved organic matter (DOM) on the adsorption of phenanthrene (PHE) by montmorillonite (MMT), organic clay complex was prepared by associating montmorillonite with DOM extracted from landfill leachate. Both the raw MMT, DOM, and MMT complex (DOM–MMT) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photo-emission spectroscopy (XPS), and scanning electron microscope (SEM). Batch adsorption studies were carried out on the adsorption of PHE as a function of contact time, temperature, and adsorbent dose. The sorption of PHE on complex was rapid, and the kinetics could be described well by the Pseudo-first-order model ( R2>0.99), with an equilibrium time of 120min. The adsorption isotherm was in good agreement with the Henry equation and Freundlich equation. Also, thermodynamic studies showed that the adsorption process was exothermic and spontaneous in nature. Compared with MMT, the adsorption capacity of DOM–MMT complex for PHE was greatly enhanced. The effects of DOM on PHE sorption by MMT may be attributed to the changes in the surface structure, the specific surface area, the hydrophobic property, and the average pore size of MMT. A series of atomistic simulations were performed to capture the structural and functional qualities observed experimentally.
Keywords: Desorption; Kinetics; Surface properties; Complex; Clay liner; Model
Interfacial chemical bonding effect on the photocatalytic activity of TiO2–SiO2 nanocoupling systems
by Musashi Fujishima; Hiroaki Takatori; Hiroaki Tada (pp. 628-631).
The TiO2 nanoparticles combined on the surfaces of SiO2 microspheres exhibited the enhanced UV-light photocatalytic activity due to the lowering of the valence band edge with the interfacial Si–O–Ti bond formation.Display Omitted► TiO2 nanoparticles were deposited onto the surfaces of mesoporous SiO2. ► The TiO2 particles were anatase crystals firmly combined on the SiO2 surfaces. ► The bandgap of TiO2 was widened by the coupling with the SiO2. ► The coupling with the SiO2 enhanced the UV-light-activity of TiO2. ► DFT calculations suggested the lowering of the valence band edge of TiO2.TiO2 nanoparticles (NPs) were deposited on the surfaces of SiO2 microspheres with a mesoporous structure prepared by a hydrolysis-controlled sol–gel technique. The TiO2 NPs were firmly combined on the surfaces of SiO2 microspheres through the interfacial Si–O–Ti bonds. The coupling causes the bandgap widening up to 3.37eV, enhancing the photocatalytic activity for the decomposition of acetaldehyde under illumination of UV-light (330< λ<400nm). Density functional theory calculations for model clusters suggested that the observed results are derived from the lowering in the valence band edge energy with the interfacial bond formation.
Keywords: Titanium dioxide; Silica microsphere; Photocatalysis; Density functional theory calculation
Electrokinetic properties of wavellite and its floatability with cationic and anionic collectors
by Aline Pereira Leite Nunes; Antônio Eduardo Clark Peres; Armando Corrêa de Araujo; George Eduardo Sales Valadão (pp. 632-638).
The aluminum and phosphates species and the H+ e OH− ions will determine the wavellite-solution interface properties. Wavellite presents high floatability with amines in alkaline pH region..Display Omitted► Microelectrophoretic technique was used for electrokinetic measurements of wavellite. ► The isoelectric point was achieved at the pH 4.5. ► Wavellite-solution interfacial properties are mainly determined by Al and P species. ► Wavellite’s floatability was higher with amines. ► Corn starch was not efficient depressant for wavellite.The reverse apatite flotation with fatty acids has been widely used for the reduction of phosphorus content of magmatic origin iron ores. However, the occurrence of phosphorus intensely disseminated as secondary minerals such as wavellite renders the anionic reverse flotation a challenge. Zeta potential measurements and microflotation tests of wavellite with the use of anionic and cationic collectors were carried out in this work. The wavellite’s IEP value was achieved at pH 4.5. Below the IEP value, the surface positively charged sites are made up of aluminum ions. The speciesH+,Al(OH)2+,Al(OH)2+,Al3+,OH-,H2PO4-,HPO42-, andPO43- play a role in the protonation and deprotonation reactions that will determine the wavellite-solution interface properties. The highest values of wavellite’s floatability under basic pH conditions were achieved in the presence of cationic collectors (1×10−4molL−1). The formation of surface complexes and the precipitation of insoluble salt of aluminum onto wavellite surface seems to be the most likely hypothesis for the chemical nature interactions between amines and wavellite. The surface formation of aluminum oleate on the wavellite’s surface seems to be the most probable hypothesis for the adsorption mechanism and the resultant high floatability of wavellite between pH 7.5 and pH 10.0 in the presence of sodium oleate (1×10−4molL−1). The results showed that the cationic reverse flotation of secondary phosphates is a promising route to reduce the phosphorus content of iron ores from deposits that underwent a supergene enrichment process, since wavellite floatability in the alkaline pH range, using amine as collector, was not significantly affected by the presence of corn starch.
Keywords: Wavellite; Eletctrokinetic potential; Flotation; Collectors
Electroosmotic-capillary penetration in circular microchannels
by Rachid Chebbi (pp. 639-642).
Schematic of liquid penetrating into capillary tube.Display Omitted► Analytical solutions for the dynamics of electroosmotic penetration are provided. ► For horizontal microcapillaries the Lucas–Washburn equation is extended to include electroosmotic effects. ► A different analytical solution is obtained for the case where gravity effects come into play. ► The analysis can be extended to account for significant changes in the dynamic contact angle.Electroosmotic forces can be used to promote penetration of electrolytes in microcapillaries. Analytical solutions for the dynamics of penetration are provided. The investigation includes both the electroosmotic and Poiseuille flows. For horizontal microcapillaries, the expression extends the Lucas–Washburn equation to account for the presence of electroosmotic effects. An analytical solution is also obtained for the case where gravity effects come into play.
Keywords: Penetration; Analytical solution; Microfluidics; Electroosmotic; Capillary; Washburn equation; Filling; Microchannel
Capillary rise of superspreaders
by Jovana Radulovic; Khellil Sefiane; Martin E.R. Shanahan (pp. 643-648).
Superspreader solutions rise less than pure water in glass capillaries, and the dynamics are dictated by the underlying diffusion..Display Omitted► Aqueous trisiloxane solutions in thin glass capillaries. ► Lower rise than pure water. ► Exponential rising trends. ► Diffusion dictates the overall dynamics.Trisiloxane surfactants, known as ‘superspreaders’, are commonly employed in numerous applications where enhanced wetting is of the utmost importance. The underlying mechanisms of superspreader wetting have been a focus of scientific interest for ca. 2 decades, and a number of mechanisms have been proposed to explain the unique trisiloxane dynamics. We have studied trisiloxane behaviour in thin capillaries to get further insight into their interfacial activity. Additionally, our knowledge of the capillary rise of superspreaders is surprisingly limited, and the effect of this extraordinary group of surfactants on capillary phenomena has been largely overlooked. Diffusion was confirmed to be the limiting factor of trisiloxane behaviour. A tentative theoretical explanation for the phenomenon studied and an appropriate mathematical model are presented. It is concluded that the enhancement of wetting due to surfactant addition is also a function of geometry: the effect is clear for a sessile drop, but more complex and less beneficial in a capillary.
Keywords: Capillary; Surfactant; Diffusion; Trisiloxane
Particle synergy and aerosol performance in non-aqueous liquid of two combinations metered dose inhalation formulations: An AFM and Raman investigation
by Philippe G.A. Rogueda; Robert Price; Tim Smith; Paul M. Young; Daniela Traini (pp. 649-655).
The interactions in fluorinated liquids between micronised drug particles were studied by AFM and Raman spectroscopy. The interactions between budesonide and formoterol (cf Symbicort), were suggested to be of a different nature from those between salbutamol and fluticasone (cf Seretide). This was translated in different deposition patterns on Andeersen Cascade Impactor plates when aerosolised. The budesonide/formoterol deposited as discreet particles, while fluticasone/salbutamol tended to deposit as agglomerates. The difference in these patterns was attributed to differences in the nature of the interactionsDisplay Omitted► Particle interactions in pMDI combination products (Symbicort and Seretide) were studied by AFM and Raman microscopy. ► Drug components in Symbicort (budesonide and formoterol) deposit on ACI plates as individual particles. ► Salmeterol and fluticasone tend to form aggregates. ► This tendency is evidenced with AFM measurements, and suggest a chemical synergy between salmeterol and fluticasone not present between formoterol and budesonide.The drug–drug interaction of two pMDI (pressure metered dose inhaler) combination products budesonide–formoterol fumarate dihydrate and salmeterol xinafoate–fluticasone propionate were investigated using in situ atomic force microscopy (AFM), equipped with a liquid cell filled with model a propellant, and Raman spectroscopy. Electron microscopy images of the budesonide–formoterol formulation suggested discrete particulates while the salmeterol–fluticasone formulation appeared agglomerated. Based on the analysis of the AFM curves, it is proposed that interactions in the budesonide–formoterol system (cohesion and adhesion) are dominated by van der Waals forces while interactions between salmeterol and fluticasone are of a chemical nature. Such observations are further substantiated by analysis of the Raman maps produced from pMDI actuations deposited on Andersen cascade impactor plates. The relevance of such synergy between particulates of different chemical nature is discussed. In particular, it is anticipated that strong interactions between particles could lead to heteroflocculation, increase aerosol particle size and consequently reduction of the respirable fine particle fraction.
Keywords: pMDI; Suspension; Raman spectroscopy; AFM; Colloid probe microscopy; Inhalation medicine; Aerosol; Combination products; Symbicort; Seretide