Journal of Colloid And Interface Science (v.359, #1)

Cover 1 (OFC).

One-pot hydrothermal synthesis of uniform β-MnO2 nanorods for nitrite sensing by Jiu-Ju Feng; Pei-Pei Zhang; Ai-Jun Wang; Yan Zhang; Wen-Ju Dong; Jian-Rong Chen (1-8).
A simple hydrothermal method was developed to prepare mono-dispersed single-crystal β-MnO2 nanorods, which was tested successfully for the electrocatalytic determination of nitrite in aqueous solution.Display Omitted► Uniform single-crystal β-MnO2 nanorods were synthesized by one-pot hydrothermal method. ► The pH, temperature, and reactant molar ratios were essential to the morphologies of the final products. ► The β-MnO2 nanorods showed good electrocatalytic ability toward the electrooxidation of nitrite. The sensor showed a wide linear range, high sensitivity, low detection limit, and fast response.A simple hydrothermal method was developed for the synthesis of uniform single-crystal β-MnO2 nanorods only using potassium permanganate and sodium nitrite in acidic solution, without any seed or template. The as-prepared β-MnO2 nanorods have the average diameter of 300 ± 20 nm and a length up to 1.2 ± 0.2 μm. Moreover, the effects of pH, temperature, and reactant molar ratios on the morphology of the final product were studied in detail. In addition, the catalytic ability of the as-prepared β-MnO2 nanorods was tested for the electrooxidation of nitrite. The resulting sensor showed a wide linear range from 0.29 μM to 26.09 mM (R  = 0.9986), high sensitivity (1.21 μA mM−1, S/N  = 3), low detection limit (0.29 μM), and fast response (less than 5 s).
Keywords: Hydrothermal; Manganese dioxide; Nanorods; Nitrite; Sensor;

Display Omitted► A feasible control over engineering of adsorbents with cage cubic Im3m mesopores was achieved. ► The mesocage adsorbents can act as a powerful tool for adsorption/removal of organic dyes. ► The adsorbents are reversible and offering potential for multiple adsorption assays.Growing public awareness on the potential risk to humans of toxic chemicals in the environment has generated demand for new and improved methods for toxicity assessment and removal, rational means for health risk estimation. With the aim of controlling nanoscale adsorbents for functionality in molecular sieving of organic pollutants, we fabricated cubic Im3m mesocages with uniform entrance and large cavity pores of aluminosilicates as highly promising candidates for the colorimetric monitoring of organic dyes in an aqueous solution. However, a feasible control over engineering of three-dimensional (3D) mesopore cage structures with uniform entrance (∼5 nm) and large cavity (∼10 nm) allowed the development of nanoadsorbent membranes as a powerful tool for large-quantity and high-speed (in minutes) adsorption/removal of bulk molecules such as organic dyes. Incorporation of high aluminum contents (Si/Al = 1) into 3D cubic Im3m cage mesoporous silica monoliths resulted in small, easy-to-use optical adsorbent strips. In such adsorption systems, natural surfaces of active acid sites of aluminosilicate strips strongly induced both physical adsorption of chemically responsive dyes and intraparticle diffusion into cubic Im3m mesocage monoliths. Results likewise indicated that although aluminosilicate strips with low Si/Al ratios exhibit distortion in pore ordering and decrease in surface area and pore volume, enhancement of both molecular converges and intraparticle diffusion onto the network surfaces and into the pore architectures of adsorbent membranes was achieved. Moreover, 3D mesopore cage adsorbents are reversible, offering potential for multiple adsorption assays.
Keywords: Cage pores; Nanoadsorbents; Organic compounds; Dye adsorption; Colorimetric determination;

A novel practical and convenient method to prepare pure stable colloidal silver nanoparticles, which have high conductivity and will be useful in printed electronic circuits, is presented.Display Omitted► A practical method to prepare stable colloidal silver nanoparticles is presented. ► A dispersant and two reducing agents including 2-(dimethylamino) ethanol are used. ► The protective mechanism of polyvinylpyrrolidone and effect of amines are studied. ► Stable, pure nano-sized colloidal silver nanoparticles can be obtained easily. ► This method has many advantages, making it practically useful in various fields.This paper describes a practical and convenient method to prepare stable colloidal silver nanoparticles for use in printed electronic circuits. The method uses a dispersant and two kinds of reducing agents including 2-(dimethylamino) ethanol (DMAE), which play important roles in the reduction of silver ions in an aqueous medium. The effect of DMAE and dispersant, as well as the factors affecting particle size and morphology are investigated. In the formation of the silver nanoparticles, reduction occurs rapidly at room temperature and the silver particles can be separated easily from the mixture in a short time. In addition, organic solvents are not used. Pure, small and relatively uniform particles with a diameter less than 10 nm can be obtained that exhibit high electroconductivity. The silver nanoparticles are stable, and can be isolated as a dried powder that can be fully redispersed in deionized water. This method of producing colloidal silver nanoparticles will find practical use in electronics applications.
Keywords: Silver nanoparticle; Electronic circuit; Digital fabrication; Inkjet ink; Electroconductivity; Amine;

Removal of methylene blue from aqueous solution by graphene oxide by Sheng-Tao Yang; Sheng Chen; Yanli Chang; Aoneng Cao; Yuanfang Liu; Haifang Wang (24-29).
Graphene oxide is a highly effective absorbent of methylene blue (MB) with a huge absorption capacity.Display Omitted► Graphene oxide has a huge absorption capacity for methylene blue. ► Graphene oxide absorbs methylene blue effectively under various conditions. ► Methylene blue interacts with graphene oxide via electrostatic interactions.Graphene oxide (GO) is a highly effective absorbent of methylene blue (MB) and can be used to remove MB from aqueous solution. A huge absorption capacity of 714 mg/g is observed. At initial MB concentrations lower than 250 mg/L, the removal efficiency is higher than 99% and the solution can be decolorized to nearly colorless. The removal process is fast and more efficient at lower temperatures and higher pH values. The increase of ionic strength and the presence of dissolved organic matter would further enhance the removal process when MB concentration is high. The results indicate that GO can be applied in treating industrial effluent and contaminated natural water. The implications to graphene-based environmental technologies are discussed.
Keywords: Graphene oxide; Methylene blue; Absorption; Decontamination;

Characterization and dissolution properties of ruthenium oxides by Todd P. Luxton; Matthew J. Eick; Kirk G. Scheckel (30-39).
Hydrous ruthenium oxide undergoes reductive dissolution by both oxalic and ascorbic acid at pH 3 as evidenced by the decrease in binding energy for Ru 3p3/2 and Ru 3p1/2. However, the calculated dissolution rate is at least one order of magnitude less than common iron and manganese oxides.Display Omitted► Characterization and dissolution properties RuO2 and RuO2·1·1H2O. ► Materials insoluble in 1 M HCl and NaOH. ► Oxalate induced dissolution of RuO2 and RuO2·1·1H2O. ► Ascorbate induced dissolution of RuO2·1·1H2O. ► Ru oxides highly insoluble in the presence of organic acids.Ruthenium oxides (RuO2·1·10H2O and RuO2) have been synthesized by forced hydrolysis and oxidation of ruthenium chloride. The resulting materials were extensively characterized to determine the crystallinity, surface area, and ruthenium oxidation state. Surface charging experiments indicate a large quantity of reactive functional groups for both materials and a decrease in the acidity of the surface functional groups with crystallization of the hydrous oxide. Dissolution studies conducted in acidic and basic pH environments indicate Ru-oxides are insoluble in 0.1 M HCl and slightly soluble in 0.1 M NaOH. Oxalate and ascorbate (5 mM) promoted dissolution of RuO2·1·10H2O demonstrated an increase in dissolution rates with decreasing pH and increasing ligand surface coverage. XPS analysis of the RuO2·1·10H2O surface after ligand promoted dissolution revealed the reduction of Ru(IV) to Ru(III) indicating that both ascorbate and oxalate reductively dissolve RuO2·1·10H2O. Dissolution experiments with RuO2 resulted in dissolution only for 5 mM oxalate at pH 3. Dissolution rates calculated for RuO2·1·10H2O and RuO2 are compared with previously published dissolution rates for iron oxides, demonstrating an order of magnitude decrease in the oxalate and ascorbate promoted dissolution.
Keywords: Ruthenium oxide; Dissolution; Adsorption; X-ray photoelectron spectroscopy; XPS; Organic acid; Oxalate; Ascorbic acid;

Synthesis of confined Ag nanowires within mesoporous silica via double solvent technique and their catalytic properties by Xiubing Huang; Wenjun Dong; Ge Wang; Mu Yang; Li Tan; Yanhui Feng; Xinxin Zhang (40-46).
Ag nanowires with several micrometers length have been successfully synthesized within SBA-15 by a simple double solvent method. The morphology and loaded amount of Ag can be controlled by the concentrations of AgNO3.Display Omitted► Ag nanowires with several micrometers length have been successfully synthesized. ► The amount and morphology of Ag can be controlled by the concentrations of AgNO3. ► The mechanism of Ag formation through the double solvent technique is proposed.Ag nanowires within the channels of mesoporous silica have been successfully synthesized via a double solvent technique, in which n-hexane is used as a hydrophobic solvent to disperse mesoporous silica and an AgNO3 aqueous solution is used as a hydrophilic solvent to fill mesochannels. The morphology of the obtained Ag (nanowires, nanoparticles or nanorods) can be controlled by adjusting the concentration of AgNO3 solution and the template pore size. HRTEM images demonstrate extensive Ag nanowires with several to tens of hundreds nanometers in length are deposited along the long axis of mesochannels when the atomic AgNO3/Si ratio is 0.090. When the atomic AgNO3/Si ratio is 0.068 or 0.11, there is a combination of Ag nanoparticles and nanowires; nanoparticles are mainly formed when the atomic AgNO3/Si ratio is higher than 0.14. Further, the catalytic results of the oxidation of styrene show that styrene oxide and benzaldehyde are the main products of the reaction, and the morphology and diversity of Ag in Ag/mesoporous silica composites have an effect on the conversion of styrene and selectivity of styrene oxide.
Keywords: Mesoporous silica; Ag nanowires; Double solvent technique; Oxidation;

Solvent induced aggregation of protoporphyrin and octacarboxylphthalocyanine of zinc deposited on gold surface by Virginie Gadenne; Mabinty Bayo-Bangoura; Louis Porte; Lionel Patrone (47-55).
ZnPP and ZnPc(COOH)8 clustering in solution is tuned by ethanol proportion in ethanol/DMF solvent and determines the nanoscale morphology of the films self-assembled onto gold.Display Omitted► ZnPP & ZnPc(COOH)8 are highly soluble in DMF, and ZnPc(COOH)8 partly in ethanol. ► ZnPP & ZnPc(COOH)8 clustering in solution is increased along with ethanol content. ► Nanograin size in macrocycle films is controlled by clustering in solution. ► Aggregation is enhanced for ZnPc(COOH)8 compared to ZnPP in both solution and films. ► Thin films of ZnPc(COOH)8 grains exhibit Q absorption band splitting.In this paper, we studied the influence of solvent on the morphology of zinc protoporphyrin and zinc octacarboxylphthalocyanine films transferred onto gold surface by dipping. In these films, carboxylic acid groups borne in periphery of macrocycles allow anchoring to gold via ionic interaction. First, we followed by UV–Visible absorption spectroscopy the solvation state of these conjugated macrocycles in pure DMF, in pure ethanol and in various ethanol/DMF mixtures. We show that the increase in ethanol proportion promotes interactions between macrocycles. Second, molecular layers of macrocycles spontaneously adsorbed from these various solutions onto gold surface were analyzed by ellipsometry, water contact angle measurements, UV–Visible absorption spectroscopy and atomic force microscopy. Results evidenced the layers were mainly composed of grains whose size of a few nanometers was directly related to the solvation conditions of molecules. In addition, Q band splitting was observed in the absorption spectrum of zinc octacarboxylphthalocyanine grain films which indicates specific organization of those molecules. Therefore solvent is shown to have a profound influence on the nanostructuration of as-prepared macrocycle layers on gold surface by promoting pre-organization in solution, and its composition enables to better control the morphology of those films by tuning the solubilization of macrocycles.
Keywords: Zinc protoporphyrin; Zinc phthalocyanine; Solvent; Aggregation; Self-assembled monolayer; Gold surface;

Amorphous calcium carbonate (ACC) transforms into the crystalline vaterite polymorph as Ca(OH)2 is depleted during carbonation, with particle diameter increasing sharply from less than 10 to around 30 nm.Display Omitted► Residual Ca(OH)2 rather than CaCl2 stabilizes amorphous calcium carbonate (ACC). ► ACC transforms into vaterite rather than calcite once carbonation is completed. ► Understanding phase transformation enhances quality control of lubricant additives. ► Overbased nanodetergents in vaterite form of low viscosity obtained for the first time.The preparation and application of overbased nanodetergents with excess alkaline calcium carbonate is a good example of nanotechnology in practice. The phase transformation of calcium carbonate is of extensive concern since CaCO3 serves both as an important industrial filling material and as the most abundant biomineral in nature. Industrially valuable overbased nanodetergents have been prepared based on calcium salts of heavy alkylbenzene sulfonate by a one-step process under ambient pressure, the carbonation reaction has been monitored by the instantaneous temperature changes and total base number (TBN). A number of analytical techniques such as TGA, DLS, SLS, TEM, FTIR, and XRD have been utilized to explore the carbonation reaction process and phase transformation mechanism of calcium carbonate. An enhanced understanding on the phase transformation of calcium carbonate involved in calcium sulfonate nanodetergents has been achieved and it has been unambiguously demonstrated that amorphous calcium carbonate (ACC) transforms into the vaterite polymorph rather than calcite, which would be of crucial importance for the preparation and quality control of lubricant additives and greases. Our results also show that a certain amount of residual Ca(OH)2 prevents the phase transformation from ACC to crystalline polymorphs. Moreover, a vaterite nanodetergent has been prepared for the first time with low viscosity, high base number, and uniform particle size, nevertheless a notable improvement on its thermal stability is required for potential applications.
Keywords: Phase transformation; Amorphous calcium carbonate; Vaterite; Overbased nanodetergent; Calcium heavy alkylbenzene sulfonate;

Porous magnetic manganese oxide nanostructures: Synthesis and their application in water treatment by Hongmin Chen; Paul K. Chu; Junhui He; Tao Hu; Mingqing Yang (68-74).
Magnetic manganese oxide nanostructures used as absorbents with strong adsorption capability and large removal rates in wastewater treatment, which could be separated easily and efficiently under an external magnetic field, recovered by combustion and kept their adsorption capability.Display Omitted► Magnetic manganese oxide nanostructures are fabricated by mixing a KMnO4 solution and oleic acid capped Fe3O4 particles. ► Magnetic manganese oxide nanostructures used as absorbents with strong adsorption capability and large removal rates in wastewater treatment. ► Magnetic manganese oxide nanostructures could be separated easily and efficiently under an external magnetic field. ► Magnetic manganese oxide nanostructures could be recovered by combustion and kept their adsorption capability.Magnetic manganese oxide nanostructures are fabricated at room temperature by mixing a KMnO4 solution and oleic acid capped Fe3O4 particles. Oleic acid molecules capped Fe3O4 particles are oxidized by potassium permanganate (KMnO4) in an aqueous solution to produce porous magnetic manganese oxide nanostructures. The synthesis technique can be extended to other MnO x structures with composition of different nanocrystals, such as quantum dots, noble metal crystals which may have important applications as catalysts, adsorbents, electrodes and advanced materials in many scientific disciplines. Transmission electron microscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and nitrogen adsorption–desorption measurements are employed to characterize the structures. As an adsorbent in water treatment, the nanostructures possess a large adsorption capability and high organic pollutant removal rates due to the large surface area and pore volume. The nanostructures are recyclable as their adsorption capability can be recovered by combustion. Furthermore, the strong magnetism exhibited by the structures provides an easy and efficient separation means in wastewater treatment under an external magnetic field.
Keywords: Mesoporous materials; Magnetic manganese oxide nanostructures; Recyclability; Water treatment;

How does organic matter constrain the nature, size and availability of Fe nanoparticles for biological reduction? by Mathieu Pédrot; Ange Le Boudec; Mélanie Davranche; Aline Dia; Odile Henin (75-85).
Transmission electron microscopy micrographs of Fe nanoparticles: (a) and (b) correspond to pure Fe system; whereas (c) and (d) correspond to Fe–HA system.Display Omitted► New data demonstrating the impact of HS on the formation and reactivity of Fe oxides. ► Humic substances reduce the extent of the Fe oxidation-hydrolysis reaction. ► Humic substance directly impact the size and the nature of formed Fe oxides. ► A fraction of Fe does not contribute to the genesis of nanoparticles. ► Mixed Fe nanoparticles-organic colloids are much more bioavailable than Fe oxides.Few studies have so far examined the kinetics and extent of the formation of Fe-colloids in the presence of natural organic ligands. The present study used an experimental approach to investigate the rate and amount of colloidal Fe formed in presence of humic substances, by gradually oxidizing Fe(II) at pH 6.5 with or without humic substances (HS) (in this case, humic acid – HA and fulvic acid – FA). Without HS, micronic aggregates (0.1–1 μm diameter) of nano-lepidocrocite is obtained, whereas, in a humic-rich medium (HA and FA suspensions at 60 and 55 ppm of DOC respectively), nanometer-sized Fe particles are formed trapped in an organic matrix. A proportion of iron is not found to contribute to the formation of nanoparticles since iron is complexed to HS as Fe(II) or Fe(III). Humic substances tend to (i) decrease the Fe oxidation and hydrolysis, and (ii) promote nanometer-sized Fe oxide formation by both inhibiting the development of hydroxide nuclei and reducing the aggregation of Fe nanoparticles.Bioreduction experiments demonstrate that bacteria (Shewanella putrefaciens CIP 80.40 T) are able to use Fe nanoparticles associated with organic matter about eight times faster than in the case of nano-lepidocrocite. This increase in bioreduction rate appears to be related to the presence of humic acids that (i) indirectly control the size, shape and density of oxyhydroxides and (ii) directly enhance biological reduction of nanoparticles by electron shuttling and Fe complexation. These results suggest that, in wetlands but also elsewhere where mixed organic matter-Fe colloids occur, Fe nanoparticles closely associated with organic matter represent a bioavailable Fe source much more accessible for microfauna than do crystallized Fe oxyhydroxides.
Keywords: Colloids; Humic substances; Fe nanoparticles; Oxidation-hydrolysis reaction; Bioreduction; Shewanella putrefaciens;

Synthesis and solid-state NMR characterization of cubic mesoporous silica SBA-1 functionalized with sulfonic acid groups by Hui-Hsu Gavin Tsai; Po-Jui Chiu; Guang-Liang Jheng; Chun-Chiang Ting; Yu-Chi Pan; Hsien-Ming Kao (86-94).
29Si{1H} HETCOR NMR reveals that the protons in sulfonic acid groups are in close proximity to the Q3 species, but not close enough to form a hydrogen bond.Display Omitted► SBA-1 functionalized with –SO3H groups has been prepared and characterized. ► The status of the incorporated –SH groups was monitored by using 13C NMR technique. ► The transformation of –SH to –SO3H groups was achieved via oxidation with H2O2. ► 29Si{1H} HETCOR NMR revealed that the –SO3H groups are in close proximity to Q3.Well-ordered cubic mesoporous silicas SBA-1 functionalized with sulfonic acid groups have been synthesized through in situ oxidation of mercaptopropyl groups with H2O2 via co-condensation of tetraethoxysilane (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) templated by cetyltriethylammonium bromide (CTEABr) under strong acidic conditions. Various synthesis parameters such as the amounts of H2O2 and MPTMS on the structural ordering of the resultant materials were systematically investigated. The materials thus obtained were characterized by a variety of techniques including powder X-ray diffraction (XRD), multinuclear solid-state Nuclear Magnetic Resonance (NMR) spectroscopy, 29Si{1H} 2D HETCOR (heteronuclear correlation) NMR spectroscopy, thermogravimetric analysis (TGA), and nitrogen sorption measurements. By using 13C CPMAS NMR technique, the status of the incorporated thiol groups and their transformation to sulfonic acid groups can be monitored and, as an extension, to define the optimum conditions to be used for the oxidation reaction to be quantitative. In particular, 29Si{1H} 2D HETCOR NMR revealed that the protons in sulfonic acid groups are in close proximity to the silanol Q3 species, but not close enough to form a hydrogen bond.
Keywords: Mesoporous materials; Solid-state NMR; Sulfonic acid groups;

Particle interactions in kaolinite suspensions and corresponding aggregate structures by Vishal Gupta; Marc A. Hampton; Jason R. Stokes; Anh V. Nguyen; Jan D. Miller (95-103).
Interaction energies indicate that the face–face (silica face–alumina face) association for kaolinite particles is the dominant particle interaction Display Omitted► Silica face–alumina face interactions are dominant for kaolinite particle aggregation at low pH. ► Face-face and edge-face interactions explain the maximum shear yield stress for kaolinite at pH 5–5.5. ► Cryo-SEM of kaolinite aggregates confirms the face–face association.The surface charge densities of the silica face surface and the alumina face surface of kaolinite particles, recently determined from surface force measurements using atomic force microscopy, show a distinct dependence on the pH of the system. The silica face was found to be negatively charged at pH > 4, whereas the alumina face surface was found to be positively charged at pH < 6, and negatively charged at pH > 8. The surface charge densities of the silica face and the alumina face were utilized in this study to determine the interaction energies between different surfaces of kaolinite particles.Results indicate that the silica face–alumina face interaction is dominant for kaolinite particle aggregation at low pH. This face–face association increases the stacking of kaolinite layers, and thereby promotes the edge–face (edge–silica face and edge–alumina face) and face–face (silica face–alumina face) associations with increasing pH, and hence the maximum shear-yield stress at pH 5–5.5. With further increase in pH, the face–face and edge–face association decreases due to increasing surface charge density on the silica face and the edge surfaces, and decreasing surface charge density on the alumina face. At high pH, all kaolinite surfaces become negatively charged, kaolinite particles are dispersed, and the suspension is stabilized. The face–face association at low pH has been confirmed from cryo-SEM images of kaolinite aggregates taken from suspension which show that the particles are mostly organized in a face–face and edge–face manner. At higher pH conditions, the cryo-SEM images of the kaolinite aggregates reveal a lower degree of consolidation and the edge–edge association is evident.
Keywords: Kaolinite; Interaction energy; Rheology; Cryo-SEM;

Innovative synthesis of citrate-coated superparamagnetic Fe3O4 nanoparticles and its preliminary applications by S. Srivastava; Rishi Awasthi; Namdeo S. Gajbhiye; Vikas Agarwal; Amit Singh; Abhishek Yadav; Rakesh K. Gupta (104-111).
In this study, we describe the development of a facile and effective route for the synthesis of Fe3O4-based T 1 contrast agent, which can be useful for in vivo magnetic resonance (MR) imaging. Citrate-coated Fe3O4 nanoparticles (6 nm) with a narrow size distribution were synthesized by “one-pot green chemistry route” in diethylene glycol (DEG) solvent. At room temperature, nanoparticles exhibited superparamagnetic nature with high saturation magnetization. Contrast agent developed by this method showed a relatively higher longitudinal relaxivity (r 1) and the lowest relaxivity ratio (r 2/r 1  = 1.46) at 3T MR field. The in vitro studies showed both phagocytic and non-phagocytic uptake of these NPs. In vivo MR imaging of swine showed both T 1 and T 2 contrast effect.Display Omitted► An effective route for citrate coated Fe3O4-based MR contrast agent. ► A relatively higher longitudinal relaxivity (r 1) and lowest relaxivity ratio (r 2/r 1). ► In vitro studies show both phagocitic and non-phagocytic uptake of these nanoparticles. ► In vivo MR imaging of swine head and spine tissues show both T 1 and T 2 contrast effect.In this study, we describe the development of a facile and effective route for the synthesis of Fe3O4-based T 1 contrast agent, which can be useful for in vivo magnetic resonance (MR) imaging. Citrate-coated Fe3O4 nanoparticles (6 nm) with a narrow size distribution were synthesized by “one-pot green chemistry route” in diethylene glycol (DEG) solvent. The synthesized nanoparticles were characterized by different analytical techniques including XRD, TEM, HRTEM, and FTIR. At room temperature, nanoparticles exhibited superparamagnetic nature with high saturation magnetization. The longitudinal (r 1) and transverse (r 2) relaxivities were found to be 35.45 and 51.81 mM−1  s−1, respectively. Contrast agent developed by this method showed a relatively higher longitudinal relaxivity (r 1) and the lowest relaxivity ratio (r 2/r 1  = 1.46) at 3T MR field. The anionic nature of citric acid facilitated non-specific internalization without impairment of cell viability and functionality. The in vitro studies showed both phagocitic and non-phagocytic uptake of these NPs. In vivo MR imaging of swine showed both T 1 and T 2 contrast effect.
Keywords: Fe3O4 magnetic nanoparticles; Citric acid; Relaxivity; Contrast agent; MR imaging;

Effect of soluble polymer binder on particle distribution in a drying particulate coating by Felix Buss; Christine C. Roberts; Kathleen S. Crawford; Katharina Peters; Lorraine F. Francis (112-120).
Drying regime map demonstrating role of soluble polymer on particle distribution in a drying coating: E – evaporation, D – diffusion, and S – sedimentation.Display Omitted► A model predicts particle and polymer distribution in a drying coating. ► Results are summarized in maps showing regions of particle accumulation. ► Addition of binder slows particles, favors particle accumulation at the surface. ► Experimental results corroborate model predictions.Soluble polymer is frequently added to inorganic particle suspensions to provide mechanical strength and adhesiveness to particulate coatings. To engineer coating microstructure, it is essential to understand how drying conditions and dispersion composition influence particle and polymer distribution in a drying coating. Here, a 1D model revealing the transient concentration profiles of particles and soluble polymer in a drying suspension is proposed. Sedimentation, evaporation and diffusion govern particle movement with the presence of soluble polymer influencing the evaporation rate and solution viscosity. Results are summarized in drying regime maps that predict particle accumulation at the free surface or near the substrate as conditions vary. Calculations and experiments based on a model system of poly(vinyl alcohol) (PVA), silica particles and water reveal that the addition of PVA slows the sedimentation and diffusion of the particles during drying such that accumulation of particles at the free surface is more likely.
Keywords: Coatings; Particles; Drying; Sedimentation; Diffusion;

Preparation of counterion stabilized concentrated silver sols by Sylas LaPlante; Ionel Halaciuga; Dan V. Goia (121-125).
Stable concentrated silver sols were obtained by reducing silver salicylate with ascorbic acid. The salicylate counterion protonation and adsorption on particle surface causes the increase in the range of the electrostatic repulsive forces responsible for the stability at high metal concentrations.Display Omitted► Novel approach for obtaining dispersant-free stable concentrated silver sols. ► Colloid stability at high concentration achieved by using salicylate as counterion. ► Enhanced colloid stability given by the protonation of salicylate and its adsorption on silver.A strategy for obtaining stable concentrated silver dispersions without dedicated stabilizing agents is presented. This approach consists of rapidly mixing aqueous solutions of silver salicylate and ascorbic acid. By using salicylate as Ag+ counterion, it is possible to prepare stable sols with metal concentrations up to two orders of magnitude higher than with silver nitrate. The stabilizing effect of the counterion is the result of a decreased ionic strength due to salicylate protonation and its adsorption on the surface of silver. Both effects increase the range of the electrostatic repulsive forces by expanding the electrical double layer.
Keywords: Counterion; Salicylate; Silver sol; Electrostatic stabilization;

Inversion of particle-stabilized emulsions of partially miscible liquids by mild drying of modified silica particles by Kathryn A. White; Andrew B. Schofield; Philip Wormald; Joseph W. Tavacoli; Bernard P. Binks; Paul S. Clegg (126-135).
Confocal microscopy images of emulsions/bijels formed via phase separation by particles dried for increasing lengths of time at 170 °C (left to right 30, 130 min. and 10 hrs.). Scale bar = 100 μm; green = silica particles, red = lutidine-rich phase labeled with rhodamine B; sample composition: 28 wt% lutidine in water, 2 vol% particles; T = 40 °C.Display Omitted► For Pickering emulsions of water and lutidine mixtures with silica particles, the hydration of the particle surface causes a change in emulsion structure. ► For water and lutidine at critical composition, decreasing silica particle hydration inverts the emulsion. ► For silica particles with some amino surface groups, a bijel forms at inversion. ► The character of the silica surfaces can change during phase separation.Using a system of modified silica particles and mixtures of water and 2,6-lutidine to form particle-stabilized emulsions, we show that subtle alterations to the hydration of the particle surface can cause major shifts in emulsion structure. We use fluorescence confocal microscopy, solid state nuclear magnetic resonance (NMR) and thermo-gravimetric analysis (TGA) to explore this sensitivity, along with other shifts caused by modifications to the silica surface chemistry. The silica particles are prepared by a variant of the Stöber procedure and are modified by the inclusion of 3-(aminopropyl)triethoxysilane and the dye fluorescein isothiocyanate. Treatment prior to emulsification consists of gently drying the particles under carefully controlled conditions. In mixtures of water and 2,6-lutidine of critical composition, the particles stabilize droplet emulsions and bijels. Decreasing particle hydration yields an inversion of the emulsions from lutidine-in-water (L/W) to water-in-lutidine (W/L), with bijels forming around inversion. So dependent is the emulsion behavior on particle hydration that microscopic differences in drying within a particle sample can cause differences in the wetting behavior of that sample, which helps to stabilize multiple emulsions. The formation of bijels at emulsion inversion is also crucially dependent on the surface modification of the silica.
Keywords: Pickering emulsion; Transitional inversion; Bijel; Binary fluid; Drying; Hydration; Adsorption; Stöber silica; Colloidal particles; 2,6-Dimethylpyridine;

The effect of interlayer anion on the reactivity of Mg–Al layered double hydroxides: Improving and extending the customization capacity of anionic clays by Ricardo Rojas; Felipe Bruna; Carlos P. de Pauli; M. Ángeles Ulibarri; Carla E. Giacomelli (136-141).
Dodecylsulfate uptake allows modifying the surface properties (charge, hydrophilic/hydrophobic character, adsorptive capacity) of layered double hydroxides without changing the particles bulk composition.Display Omitted► LDHs interfacial properties and reactivity depend on the interlayer anion. ► Chloride produces positive, hydrophilic particles with anion-exchange properties. ► DDS generate negative, hydrophobic particles with cation exchange capacities. ► These changes can be produced without changing the particles bulk composition. ► The surface properties tailoring extend and improve LDHs applications.Layered double hydroxides (LDHs) reactivity and interfacial behavior are closely interconnected and control particle properties relevant to the wide range of these solids’ applications. Despite their importance, their relationship has been hardly described. In this work, chloride and dodecylsulfate (DDS) intercalated LDHs are studied combining experimental data (electrophoretic mobility and contact angle measurements, hydroxyl and organic compounds uptake) and a simple mathematical model that includes anion-binding and acid–base reactions. This approach evidences the anion effect on LDHs interfacial behavior, reflected in the opposite particle charge and the different surface hydrophobic/hydrophilic character. LDHs reactivity are also determined by the interlayer composition, as demonstrated by the cation uptake capability of the DDS intercalated sample. Consequently, the interlayer anion modifies the LDHs interfacial properties and reactivity, which in turn extends the customization capacity of these solids.
Keywords: Surface charge; Hydrophobic/hydrophilic character; Anion-binding; Acid–base reactions; Adsorption;

Scheme of growth of gold nanoparticles conjugated with thermoresponsive polymer by thermal stimuli.Display Omitted► Thermal stimuli, heating followed by cooling, induces growth of gold nanoparticles. ► Shrinkage of thermoresponsive polymers coating the nanoparticles causes the growth. ► No chemical depositions with gold ions are required for the growth.The growth of gold nanoparticles without chemical reduction of gold (III) ions was achieved by the disruption of thermoresponsive polymers conjugated with the gold nanoparticles through the phase transition of the polymers. When a solution of gold nanoparticles coated with thermoresponsive polymers was heated, chains of the thermoresponsive polymers were disrupted because of dehydration, resulting in the fusion of gold nanoparticles to form larger nanoparticles. The evolution of the extinction band around 550 nm evidenced the formation of these large (post-fusion) gold nanoparticles, which were characterized by transmission electron microscope (TEM) and dynamic light scattering (DLS). TEM images verified the formation of the large gold nanoparticles having particle sizes of 80–100 nm, whereas DLS indicated the existence of large nanoparticles with hydrodynamic diameters exceeding 200 nm. The deposition did not require the addition of reductants or trivalent gold ions for the formation of the large gold nanoparticles. Both the heating and the solution conditions were studied to elucidate the mechanism of the formation of large gold nanoparticles.
Keywords: Gold; Nanoparticles; Thermoresponsive polymer; Growth;

FRET can be used to measure the adsorption of oligonucleotides on quantum dots coated with mercaptopropionic acid and identify conditions that favor strong adsorption.Display Omitted► Oligonucleotides adsorb on quantum dots coated with mercaptopropionic acid (MPA). ► Adsorption driven by dipolar interactions between neutral MPA ligands and nucleobases. ► The extent of adsorption depends on oligonucleotide sequence composition and length. ► The extent of adsorption depends on the degree of ionization of the MPA ligands. ► Adsorption can be manipulated by adjusting pH and ionic strength.Semiconductor quantum dots (QDs) coated with thioalkyl acid ligands are often used as probes and reporters for nucleic acid sensing, or protein sensing using aptamers, and are also potential vectors for gene delivery. In such applications, the interactions that potentially lead to the adsorption of oligonucleotides onto the surface of colloidal QDs are an important consideration. To explore such interactions, fluorescence resonance energy transfer (FRET) between QDs and oligonucleotides labeled with a fluorescent dye was used to identify and characterize a set of conditions that favor strong adsorption on 3-mercaptopropionic acid (MPA)-coated CdSe/ZnS QDs. Adsorption curves and competitive binding experiments were used to determine that the order of affinity for nucleobase adsorption was dC > dA ⩾ dG ≫ dT. The length of the oligonucleotide sequence was also important, with an 80-mer sequence adsorbing more strongly than its 20-mer analog. Adsorption decreased with increasing pH and corresponded to the ionization of the carboxylic acid groups of the MPA ligands. Increased ionic strength partially offsets ligand ionization and increased the extent of adsorption. The interaction between QDs and oligonucleotides was labile, with increases in adsorption at lower concentrations of oligonucleotide and with an increasing number of oligonucleotides per QD. The results were consistent with a hydrogen-bonding model for adsorption, where neutral thioalkyl acid ligands interact favorably with nucleobases and ionized ligands resist adsorption.
Keywords: Adsorption; Fluorescence resonance energy transfer (FRET); Ionic strength; Nucleobase; pH; Oligonucleotides; Quantum dots;

In situ formed Mg(OH)2 nanoparticles as pH-switchable stabilizers for emulsions by Junjun Tan; Jun Wang; Liya Wang; Jian Xu; Dejun Sun (155-162).
In situ formed magnesium hydroxide nanoparticles could be used not only as a excellent emulsifier but also with excellent pH-switchability.Display Omitted► In situ formed magnesium hydroxide nanoparticles (MHp) could served as a excellent emulsion stabilizer. ► Owing to strong pH dependence during precipitation of MHp, MHp shows excellent pH-dependent and reversibility, which make it with pH-switchability for emulsion stability. ► The key rule for such phenomenon is a pH reversibility between ionic form and particle form, which may be applied to other metal hydroxide nanoparticles.Different from traditional methods for preparing pH-switchable Pickering emulsifiers, a simple and straightforward approach is established on the basis of a reversible process between in situ formation and dissolution of Mg(OH)2 nanoparticles (MHp). It was found that when pH value was above 9.5, emulsions of liquid paraffin-in-water can be stabilized by the resulting surface-active particles. Below this pH, emulsions demulsify, resulting in a reversible Pickering emulsifier. Based on the strongly pH-dependent precipitation of metal hydroxide nanoparticles, this procedure offers a new way to design pH-switchable emulsifiers without aid of any other organic matters.
Keywords: Pickering emulsion; pH-switchability; In situ formed nanoparticles; Magnesium hydroxide;

Dilution induced thickening in hydrotrope-rich rod-like micelles by Gunjan Verma; V.K. Aswal; Gerhard Fritz-Popovski; C.P. Shah; Manmohan Kumar; P.A. Hassan (163-170).
The zero-shear viscosity of a micellar solution that contains 8.5%w/w hydrotrope and 1.5%w/w surfactant (C total  = 10.0%w/w) increases by about four orders of magnitude upon dilution to 3.0%.Display Omitted► Dilution induces growth of hydrotrope-rich rod-like micelles. ► Viscosity of a surfactant–hydrotrope mixture increases with dilution. ► Desorption of hydrotropes from mixed micelles leads to a micelle–vesicle transition.Dilution induced changes in the microstructure and rheological behavior of micelles formed by a cationic surfactant–anionic hydrotrope mixture has been investigated in the hydrotrope-rich region. The surfactant used is cetyltrimethylammonium bromide (CTAB) and the hydrotropic salt is sodium 3-hydroxy naphthalene 2-carboxylate (SHNC). The concentration of the mixture is varied from 0.5% to 10.0% w/w (ϕ  = 0.005–0.100) at a fixed weight ratio of hydrotrope to surfactant (85:15). Rheological studies indicate Newtonian flow behavior at low and high volume fractions (0.005 and 0.100) while a shear thinning behavior is observed at intermediate volume fractions. The zero-shear viscosity η 0 also passes through a maximum upon changes in the concentration. The most striking feature in our study is that a low viscosity Newtonian fluid transforms to a viscoelastic fluid, upon dilution, and then again to a Newtonain fluid. Small angle neutron scattering studies of 10.0% micellar solution show the presence of rod-like aggregates. Upon dilution, the scattering intensity per unit concentration shows an increase in the low q-region. The nature of pair distance distribution function and subsequent model fitting indicates a transition from rod-like micelles to unilamellar vesicles upon dilution. This behavior is explained in terms of the volume fraction dependant solubilization of hydrotropes in the rod-like micelles and consequent changes in the composition of the mixed micelles.
Keywords: Worm-like micelle; Rheology; Hydrotrope; Sodium 3-hydroxy naphthalene 2-carboxylate;

Temperature induced formation of particle coated non-spherical droplets by Junjun Tan; Mei Zhang; Jun Wang; Jian Xu; Dejun Sun (171-178).
Aging temperature induces the formation of non-spherical emulsion droplets and the origins are attributed to the partial coalescence which is resulted from the particle size growth and the decrease of particle coverage on the droplet surface.Display Omitted► Non-spherical emulsion droplets could be obtained by aging spherical emulsion droplets stabilized by freshly precipitated magnesium hydroxide nanoparticles at certain temperature. ► Particle concentration, oil/water ratio, aging temperature and aging time remarkably influence the formation of non-spherical emulsion droplets. ► The decrease of particle coverage on the droplet surface is the origin of non-spherical emulsion droplet formation.Herein we offer a simple method to produce non-spherical emulsion droplets stabilized by freshly formed Mg(OH)2 nanoparticles (MPs). The non-spherical degree of droplets as a function of experiment conditions was investiged and the origins of the presence of non-spherical dropelts were discussed. The results of optical microscope images show that stable spherical droplets can be fused into non-spherical at given aging temperature. It is also recognized that particle concentration, oil/water ratio and aging time significantly affect droplet fusion and excess particles that are not adsorbed on the oil/water interface are helpful in restraining droplet fusion. Based on the TEM, XRD and Fluorescence confocal microscopy results, the origins of droplet fusion are inferred from the presence of vacant holes in the particle layer. Because of Oswald ripening, particles on droplet surfaces grow larger than the freshly precipitated ones under a given aging temperature. The growth of particles results in the reduction of total cover area of particle layer and thus creates vacant holes in the particle layer which would cause partial coalescence of droplets once they collide. Thus, these findings can offer a simple alternative to obtain a large amount of non-spherical emulsion droplets but also can help the preparation of non-spherical colloid particles.
Keywords: Pickering emulsion; Non-spherical droplets; Partial coalescence; Temperature; Mg(OH)2 nanoparticles;

Scattering techniques and rheological tests are able to highlight different structures formed by reverse Pluronic aqueous mixtures.Display Omitted► SANS applied to 25R4 reverse Pluronic shows different structuring in L1 aqueous phase. ► SAXS shows the influence of temperature and composition on D interlamellar distance. ► Rheology shows defects in the hexagonal phase and densely packed vesicles in D phase.The micro- and mesoscopic structure of reverse Pluronic 25R4 in aqueous mixtures has been studied by SANS, SAXS and shear rheology. These techniques have been able to give a deep insight into the complex structure of the system phase diagram, that includes an isotropic water-rich liquid phase L1, and liquid crystalline phases with hexagonal, E, or lamellar order, D.Particular attention has been paid to the isotropic water-rich phase L1, which has a large stability region in the temperature-composition phase diagram. This region is crossed by a large “cloudy zone”. Below it, namely at low temperature and composition, SANS data show the presence of polymer unimers in a gaussian coil conformation. Above the “cloudy zone”, at higher temperature and composition, the L1 phase is structured as a network of interconnected multimeric micelles. Rheology adds information about the structuring of the L1 phase showing its incipient hexagonal pre-structuring. This technique is also able to highlight the defective structure of the E phase itself.In the temperature and concentration ranges in which a lamellar phase D is present, SANS and SAXS results are in complete agreement, showing how interlamellar distance is influenced by both polymer composition and temperature according to an “ideal deswelling” or a “not ideal swelling” mechanism. In addition, in the D phase rheology suggests the presence of densely packed vesicles.
Keywords: Reverse pluronic; Lyotropic phases; Micellar aggregates; Defects; Packed vesicles;

Specific counterion effect on the adsorbed film of cationic surfactant mixtures at the air/water interface by H.H. Li; Y. Imai; M. Yamanaka; Y. Hayami; T. Takiue; H. Matsubara; M. Aratono (189-193).
The M ^ vs. X ^ 2 H curve (solid line) is shifted to the left hand side from the corresponding ideal mixing (dashed line) curve, which indicates a better miscibility of Br−1 and BF 4 - counterions in the adsorbed film.Display Omitted► BF 4 - ions were richer in the surface than in the bulk solution. ► The different size of counterions caused their better miscibility in adsorbed films. ► Composition of Br in the surface was higher than predictions based on ideal mixing. ► Dehydration free energy may be the principal factor governing the adsorption of ions. ► Specific forces and natures of counterions should be added to the Poisson–Boltzmann theory.To investigate the counterion effects, we employed dodecyltrimethylammonium bromide (DTABr)–dodecyltrimethylammonium tetrafluoroborate (DTABF4) mixed aqueous solutions and measured their surface tensions, then analyzed these data in a thermodynamic treatment. The tensiometry showed that DTABF4 was more effective in lowering the surface tension of water. The phase diagram of adsorption demonstrated that the surface was enriched with BF 4 - ions, but the composition of Br ions in the adsorbed film was slightly enhanced compared to the ideal mixing criteria. These were explained in terms of the size and polarizability of counterions. Moreover, the distribution of counterions of the DTABr–DTABF4 mixtures in the adsorbed film is greatly different from that of the 1-hexyl-3-methylimidazolium bromide (HMIMBr)–1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF4) mixtures, where a stronger hydrogen-bonding exists between BF 4 - and HMIM+ ions. These findings suggest that the adsorption of counterions in electric double layers is likely subject to two factors: the nature of counterion and their interactions with surfactant ions.
Keywords: Thermodynamics of adsorption; Miscibility of counterions; Surfactants; Specific ion effects;

Internal surface polarity of regenerated cellulose gel depends on the species used as coagulant by Noriyuki Isobe; Ung-Jin Kim; Satoshi Kimura; Masahisa Wada; Shigenori Kuga (194-201).
The cellulose gels generated using aqueous coagulants tend to form membrane-like structures with hydroxyl-rich surfaces, whereas those obtained by using organic coagulants tend to have fibrous structures with hydrophobic surfaces.Display Omitted► Regenerated cellulose gels can be prepared from aqueous solution by using various coagulants. ► Gels show different adsorptivity comparing an aromatic dye and iodine. ► X-ray diffraction and SEM images show corresponding structural differences. ► Internal gel surface is hydrophobic when coagulated by alcohols; but hydrophilic if water is used.Cellulose gels regenerated from aqueous alkali–urea solvent were found to have different surface polarity depending on coagulant species. Gels coagulated by alcohols adsorbed Congo red about twice as much as those coagulated by aqueous coagulants. The difference was also noted in the iodine reaction; the alcohol-coagulated gels showed blue coloration similar to that of iodine–starch reaction in contrast to those from aqueous coagulants, which gave light yellow colors similar to that of the original iodine solution. These phenomena can be ascribed to the influence of coagulant species on the surface nature of cellulose fibrils internal to the gels. X-ray diffractometry indicated that the hydrophobicity was likely to result from exposure of glucopyranoside ring planes on the surface of cellulose fibrils. Scanning electron microscopy showed characteristic differences in nanometer-scale morphologies between the two types of cellulose gel.
Keywords: Regenerated cellulose hydrogel; Hydrophobicity; Hydrophilicity; Surface property; Dye adsorption; Iodine color reaction;

Structural organization of plasma membrane lipids isolated from cells cultured as a monolayer and in tissue-like conditions by Galya Staneva; Teodora Lupanova; Claude Chachaty; Diana Petkova; Kamen Koumanov; Roumen Pankov; Albena Momchilova (202-209).
Liquid/liquid immiscibility of 2D plasma membrane lipid extracts at 20 °C (a) and liquid/liquid gel-like at 4 °C (b). Liquid/gel-like immiscibility was observed for 3D extracts (c (14 °C)) and (d (4 °C)). Lower order parameter and larger reorientation correlation time of the deoxy-16-stearic acid spin-probe in the 3D lipid extract were observed in the deep hydrophobic in the lipid bilayer compared to 2D extract.Display Omitted► Structural organization of plasma membrane lipids extracted from 2D and 3D fibroblasts. ► Influence of cell culture conditions on plasma membrane lipid composition. ► Different order in the hydrophobic and interfacial region of the 2D and 3D lipid bilayer. ► Different domain patterns of the membrane bilayer for 2D and 3D lipid extracts.Complementary biophysical approaches were used to study the structural organization of plasma membrane lipids obtained from fibroblasts cultured as two-dimensional (2D) monolayer and in tissue-like three-dimensional (3D) conditions. Fluorescence microscopy experiments demonstrated different domain patterns for 2D and 3D plasma membrane lipid extracts. ESR demonstrated that 3D lipid extract is characterized with lower order parameter than 2D in the deep hydrophobic core of the lipid bilayer. Higher cholesterol and sphingomyelin content in 3D extract, known to increase the order in the glycerophospholipid matrix, was not able to compensate higher fatty acid polyunsaturation of the phospholipids. The interfacial region of the bilayer was probed by the fluorescent probe Laurdan. A higher general polarization value for 3D extract was measured. It is assigned to the increased content of sphingomyelin, cholesterol, phosphatidylethanolamine and phosphatidylserine in the 3D membranes. These results demonstrate that cells cultured under different conditions exhibit compositional heterogeneity of the constituent lipids which determine different structural organization of the membranes.
Keywords: Plasma membrane lipids; Membrane domains; 3D matrix; Cholesterol; Sphingomyelin; Order parameter;

Display Omitted► A clinoptilolite-polypropylene composite for adsorption of lead has been prepared. ►The activation of clinoptilolite before mixing with polypropylene was essential. ► The mechanical strength of polypropylene was not affected by the activation process. ► The adsorption and desorption of lead from aqueous media have been successful. ►The composite can thus be used on a routine basis in water purification systems.A polymer composite of polypropylene (PP) and clinoptilolite (CLI) for the adsorption of lead has been prepared using the melt-mixing compounding technique in a rheomixer. Characterization of the composite was performed using scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), X-ray diffraction (XRD), Brunuer–Emmett–Teller (BET), and Fourier transform infrared spectroscopy (FTIR). The influence of contact time, pH, initial metal-ion concentration, temperature, and pretreatment on the adsorption of lead (Pb) by the PP–CLI composite was investigated. Optimum pH was found to be between pH 6 and pH 8 while the maximum sorption of lead at optimal pH was 95%. No difference was observed between the adsorption behavior of composites functionalized with 20% and 30% clinoptilolite, respectively, while the pretreatment with HCl and NaCl made a slight difference to the adsorption capacity of composites. The findings from this study on the lead adsorption behavior of CLI–PP composite may have potential applications in wastewater and water purification works.
Keywords: Polypropylene; Clinoptilolite; Composites; Lead; Adsorption;

The schematic profile depicting the energy band structure and occurrence of vectorial electron transfer in the TiO2/CdS heteroarchitectures.Display Omitted► The size and content of CdS nanoparticles grown on TiO2 nanofibers are tunable. ► TiO2/CdS nanofibers have higher photocatalytic activity by visible light. ► The electrospinning method combined with hydrothermal process is novel and valuable.Herein, we have demonstrated that the electrospun nanofibers of TiO2/CdS heteroarchitectures could be fabricated through combining electrospinning technique with hydrothermal process. The configuration, crystal structure, and element composition of the as-prepared TiO2/CdS heteroarchitectures were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), resonant Raman spectrometer, X-ray photoelectron spectroscopy (XPS). The results indicated that the high-density hexagonal wurtzite CdS crystalline particles of ca. 6–40 nm in diameter were uniformly and closely grown on anatase TiO2 nanofibers. Especially, the light-absorption properties as well as photocatalytic characteristics of pure TiO2 nanofibers and TiO2/CdS heteroarchitectures with different amount loading of CdS were also investigated. The absorption of TiO2/CdS heteroarchitectures was extended to the visible due to effective immobilization of sensitizing agent CdS on TiO2. In contrast with the pure TiO2 nanofibers, the TiO2/CdS heteroarchitectures showed excellent photocatalytic activity by using rhodamine B dye as a model organic substrate under visible-light irradiation. It was worth noting that the cooperative photocatalytic mechanism of the TiO2/CdS heteroarchitectures was also discussed.
Keywords: Cadmium sulfide; Titanium dioxide; Heteroarchical; Nanofibers; Photocatalytic;

Adsorbents based on carbon microfibers and carbon nanofibers for the removal of phenol and lead from water by Anindita Chakraborty; Dinesh Deva; Ashutosh Sharma; Nishith Verma (228-239).
The hierarchical web of activated carbon microfibers (ACF) and carbon nanofibers (ACF/CNF) displayed a greater adsorption capacity for Pb2+ than ACF. On the other hand, the adsorption capacity of ammonia (NH3) functionalized ACFs for phenol was larger than that of the multiscale ACF/CNF webs.Display Omitted► CNFs grown on ACFs can be directly used as adsorbents without requiring a post-synthesis step. ► Molecular size and structure of adsorbates and adsorbents determine adsorption capacity. ► ACF/CNF composites are efficient adsorbents for environmental remediation applications.This paper describes the production, characteristics, and efficacy of carbon microfibers and carbon nanofibers for the removal of phenol and Pb2+ from water by adsorption. The first adsorbent produced in the current investigation contained the ammonia (NH3) functionalized micron-sized activated carbon fibers (ACF). Alternatively, the second adsorbent consisted of a multiscale web of ACF/CNF, which was prepared by growing carbon nanofibers (CNFs) on activated ACFs via catalytic chemical vapor deposition (CVD) and sonication, which was conducted to remove catalytic particles from the CNF tips and open the pores of the CNFs. The two adsorbents prepared in the present study, ACF and ACF/CNF, were characterized by several analytical techniques, including SEM–EDX and FT-IR. Moreover, the chemical composition, BET surface area, and pore-size distribution of the materials were determined. The hierarchal web of carbon microfibers and nanofibers displayed a greater adsorption capacity for Pb2+ than ACF. Interestingly, the adsorption capacity of ammonia (NH3) functionalized ACFs for phenol was somewhat larger than that of the multiscale ACF/CNF web. Difference in the adsorption capacity of the adsorbents was attributed to differences in the size of the solutes and their reactivity towards ACF and ACF/CNF. The results indicated that ACF-based materials were efficient adsorbents for the removal of inorganic and organic solutes from wastewater.
Keywords: Activated carbon fiber (ACF); Carbon nanofiber (CNF); Phenol; Lead; Adsorption;

Usefulness of alkoxyltitanosiloxane for the preparation of mesoporous silica containing a large amount of isolated titanium by Kwang-Min Choi; Ryutaro Wakabayashi; Takashi Tatsumi; Toshiyuki Yokoi; Kazuyuki Kuroda (240-247).
Mesoporous carbon (CMK-3) can be used as a hard template to prepare Ti-containing mesoporous silica with a large amount of isolated Ti by pyrolysis of isopropoxytris(tris-tert-butoxysiloxy)titanium (TS3: ( i PrO)Ti[OSi(O t Bu)3]3).Display Omitted► Isopropoxytris(tris-tert-butoxysiloxy)titanium (TS3: ( i PrO)Ti[OSi(O t Bu)3]3 was synthesized. ► Ti-containing mesoporous silica was prepared by pyrolysis of TS3 through a hard template method. ► The method provides mesoporous silica with very high Si/Ti ratio.Mesoporous silica containing a large amount of isolated Ti was prepared from an alkoxytitanosiloxane precursor through a hard template method. Isopropoxytris(tris-tert-butoxysiloxy)titanium (( i PrO)Ti[OSi(O t Bu)3]3, TS3) was synthesized and TS3 was mixed with mesoporous carbon (CMK-3), a hard template. The mixture was pyrolyzed at 180 °C to form a composite consisting of titanosilica and the hard template. After calcination at 600 °C for the removal of the carbon template, the titanium species were not transformed to anatase TiO2, proved by DR-UV–Vis, FTIR, XPS, and XRD, while the ESR results indicated the presence of isolated Ti. The mesoporous structure was verified by SEM, TEM, and N2 adsorption. The Si/Ti ratio of the product was consistent with that of the precursor. All the results show that the material prepared from the precursor is ordered mesoporous silica containing a large amount of isolated Ti in the frameworks. The use of well-defined alkoxytitanosiloxane precursor leads to the formation of mesoporous silica with exactly controlled composition of titanium with neither loss of Ti nor transformation to anatase.
Keywords: Ti-containing mesoporous silica; Alkoxytitanosiloxane; Isolated titanium;

Laser-induced luminescence spectra of U(VI) sorbed on calcium silicate hydrates (C―S―H phases) at different loadings revealed the presence of a Ca–uranate precipitate and two sorbed species either bound to silanol groups on the surface or incorporated in the C―S―H interlayer.Display Omitted► Strong sorption of (UVI) by C―S―H phases illustrated by R d values up to 106  L kg−1. ► Identification of an U(VI) surface complex and an incorporated U(VI) species. ► Incorporation into the C―S―H structure is a slow process. ► The solid U(VI) speciation appears to be independent of the pH. ► At high U(VI) loadings (1.0 mol kg−1) a Ca–uranate precipitate was observed.Batch sorption experiments and time-resolved luminescence spectroscopy investigations were carried out to study the U(VI) speciation in calcium silicate hydrates for varying chemical conditions representing both fresh and altered cementitious environments. U(VI) uptake was found to be fast and sorption distribution ratios (R d values) were very high indicating strong uptake by the C―S―H phases. In addition a strong dependence of pH and solid composition (Ca:Si mol ratio) was observed. U(VI) luminescence spectroscopy investigations showed that the U(VI) solid speciation continuously changed over a period up to 6 months in contrast to the fast sorption kinetics observed in the batch sorption studies. Decay profile analysis combined with factor analysis of series of spectra of U(VI) – C―S―H suspensions, recorded with increasing delay times, revealed the presence of four luminescent U(VI) species in C―S―H suspensions, in agreement with the batch sorption data. Along with the aqueous UO 2 ( OH ) 4 2 - species and a Ca–uranate precipitate, two different sorbed species were identified which are either bound to silanol groups on the surface or incorporated in the interlayer of the C―S―H structure.
Keywords: Uranium(VI); C―S―H phases; Cementitious materials; Sorption; Uptake; Incorporation; Luminescence spectroscopy; TRLFS;

Bright-field HR-TEM micrographs of Pt–FTO/MWCNT composites with low and high magnification.Display Omitted► Pt-FTO composites supported on MWCNTs as new catalysts were synthesized. ► Pt-FTO/MWNT catalyst show higher catalytic activity for methanol electro-oxidation. ► This is due to the sufficient electrical conductivity of FTO/MWCNT composites.Fluorine tin oxide (FTO) and multi-walled carbon nanotube (MWCNT) composites synthesized by a sol–gel process followed by a hydrothermal treatment process have been explored as a support for Pt nanoparticles (Pt–FTO/MWCNTs). X-ray diffraction analysis and high resolution transmission electron microscopy show that the Pt and FTO nanoparticles with crystallite size of around 4–8 nm are highly dispersed on the surface of MWCNTs. Pt–FTO/MWCNT catalyst is evaluated in terms of the electrochemical catalytic activity for methanol electrooxidation using cyclic voltammetry, steady state polarization experiments, and electrochemical impedance spectroscopy technique in acidic medium. The Pt–FTO/MWCNT catalyst exhibits a higher intrinsic catalytic activity for methanol electrooxidation with high stability during potential cycling than Pt nanoparticles supported on tin dioxide/multi-walled carbon nanotube composites. The results suggest that FTO/MWCNT composites could be considered as an alternative support for Pt-based electrocatalysts in direct alcohol fuel cells.
Keywords: Platinum; Fluorine tin oxide; Anode catalyst; Methanol oxidation;

Arsenic (V) adsorption on Fe3O4 nanoparticle-coated boron nitride nanotubes by Rongzhi Chen; Chunyi Zhi; Huang Yang; Yoshio Bando; Zhenya Zhang; Norio Sugiur; Dmitri Golberg (261-268).
Mechanism of Fe coating was studied by first-principles calculation results for the energy of the metal-BNNT systems. We conclude that the most possible absorption site of the Fe3+ ion is the hollow of a B3N3 hexagonal ring. This absorption mode is very similar to the coordinated Fe ions in ferrocene.Display Omitted► The magnetic Fe3O4 nanoparticles were successfully loaded on boron nitride nanotube. ► The Fe3O4-functionalized BNNTs possess elevated the adsorption capacity for arsenic. ► Simple & rapid separation of magnetic metal-loaded adsorbent from water was achieved.Multiwalled boron nitride nanotubes (BNNTs) functionalized with Fe3O4 nanoparticles (NPs) were used for arsenic removal from water solutions. Sonication followed by a heating process was developed to in situ functionalize Fe3O4 NPs onto a tube surface. A batch of adsorption experiments conducted at neutral pH (6.9) and room temperature (25 °C) and using the developed nanocomposites revealed effective arsenic (V) removal. The Langmuir, Freundlich, and Dubinin-Radushkevich adsorption isotherms were measured for a range of As(V) initial concentrations from 1 to 40 mg/L under the same conditions. The equilibrium data well fitted all isotherms, indicating that the mechanism for As(V) adsorption was a combination of chemical complexation and physical electrostatic attraction with a slight preference for chemisorption. The magnetite NPs functionalized on BNNTs led to a simple and rapid separation of magnetic metal-loaded adsorbents from the treated water under an external magnetic field.
Keywords: Arsenic adsorption; Boron nitride nanotube; Functionalization; Nanoparticle; Nanostructure;

The surface segregation of the fluorinated moieties in end-capped poly(n-alkyl methacrylates) was greatly enhanced by the crystallinity of the nonfluorinated block.Display Omitted► Study on the surface segregation of poly(n-alkyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate. ► The extent of fluorine segregation increased with increasing of the length of side n-alkyl chain. ► The surface enrichment by fluorine was enhanced greatly by the crystallinity of the side chains. ► The film formed superhydrophobic surfaces with superior long-lasting barrier properties. ► The film formed superhydrophobic surfaces with superior long-lasting barrier properties.The effects of the alkyl group on the surface segregation of poly(n-alkyl methacrylate) end-capped with various numbers of units of 2-perfluorooctylethyl methacrylate (FMA) (PnAMA-ec-PFMA) were investigated by differential scanning calorimetry, angle-resolved XPS analysis, contact angle measurements, and X-ray diffraction (XRD). The results show that with similar numbers of FMA units at the polymer chain end the extent of fluorine segregation (Q) increased with increasing the number of carbon atoms in the side n-alkyl chains of poly(n-alkyl methacrylate). The surface fluorine content within 5 nm deep of the film of poly(n-octadecyl methacrylate) end-capped with one FMA unit (PODMA160-ec-PFMA1.0) was 208-fold higher than that of the bulk level. These observed differences in Q values were found due to the aggregate structure of the end-capped polymers in the solution, the flexibility, and the crystallinity of the n-alkyl side chains. When the nonfluorinated block was completely amorphous, the molecular aggregate structure of the end-capped polymers in the solution played an important role in the surface segregation of the fluorinated moieties on the resulting film. However, when the nonfluorinated block was crystalline, crystallinity would enhance greatly the segregation of the fluorinated moieties.
Keywords: Surface segregation; Fluorinated polymers; Comonomer structure; End-capped polyacrylates;

Interaction of the cationic peptide bactenecin with mixed phospholipid monolayers at the air–water interface by Ana B. López-Oyama; Pablo Taboada; María. G. Burboa; Ezequiel Rodríguez; Víctor Mosquera; Miguel A. Valdez (279-288).
AFM image of a DPPC:DMPG/bactenecin film on mica, obtained at 20 mN/m from the Langmuir Balance with pure water in the subphase. An aggregation process takes place, similar to the one suggested by the carpet model for the antimicrobial peptides–membrane interaction.Display Omitted► Interaction of bactenecin with phospholipids mixture at the air–water interface. ► Effect of NaCl in the subphase on the peptide adsorption at the DPPC:DMPG monolayer. ► Evidence of peptide–phospholipids aggregation to build a carpet-like structure. ► Critical peptide concentration to build holes as predicted by the carpet model.The initial mechanism by which antimicrobial peptides target microbes occurs via electrostatic interactions; however, the mechanism is not well understood. We investigate the interaction of the antimicrobial peptide bactenecin with a 50:50 w:w% 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (DMPG) phospholipid mixture at the air–water interface with different NaCl concentrations (0.01, 0.05, 0.1, 0.5 M) in the subphase. A larger shift of DPPC:DMPG isotherms was obtained for 0.1 M salt concentration at lower and higher pressures, demonstrating the influence of the negative charge of DMPG molecules and the screening of the electrostatic interaction by the salt concentration. Raman spectroscopy of monolayers demonstrated the presence of cysteine–cysteine bridges in bactenecin loops. The peptide adsorption in DPPC:DMPG monolayers observed by AFM images suggests a self-assembled aggregation process, starting with filament-like networks. Domains similar to carpets were formed and pore structures were obtained after a critical peptide concentration, according to the carpet model.
Keywords: Antimicrobial peptides; Isotherms; AFM; Raman spectroscopy; Carpet model; Bactenecin;

The role of conditioning film formation and surface chemical changes on Xylella fastidiosa adhesion and biofilm evolution by Gabriela S. Lorite; Carolina M. Rodrigues; Alessandra A. de Souza; Christine Kranz; Boris Mizaikoff; Mônica A. Cotta (289-295).
Conditioning film formed by culture medium affects the roughness, hydrophobicity, and chemical composition of the surface. Our results indicate that chemical surface changes are involved in facilitating biofilm growth.Display Omitted ► Periwinkle wilt (PW) culture medium forms conditioning film on different surfaces. ► This film changes the surface hydrophobicity, roughness, and chemical composition. ► Chemical surface changes are involved in facilitating biofilm growth. ► Results are correlated well with current models for Xylella fastidiosa cell adhesion.Biofilms are complex microbial communities with important biological functions including enhanced resistance against external factors like antimicrobial agents. The formation of a biofilm is known to be strongly dependent on substrate properties including hydrophobicity/hydrophilicity, structure, and roughness. The adsorption of (macro)molecules on the substrate, also known as conditioning film, changes the physicochemical properties of the surface and affects the bacterial adhesion. In this study, we investigate the physicochemical changes caused by Periwinkle wilt (PW) culture medium conditioning film formation on different surfaces (glass and silicon) and their effect on X. fastidiosa biofilm formation. Contact angle measurements have shown that the film formation decreases the surface hydrophilicity degree of both glass and silicon after few hours. Atomic force microscopy (AFM) images show the glass surface roughness is drastically reduced with conditioning film formation. First-layer X. fastidiosa biofilm on glass was observed in the AFM liquid cell after a period of time similar to that determined for the hydrophilicity changes. In addition, attenuation total reflection–Fourier transform infrared (ATR-FTIR) spectroscopy supports the AFM observation, since the PW absorption spectra increases with time showing a stronger contribution from the phosphate groups. Although hydrophobic and rough surfaces are commonly considered to increase bacteria cell attachment, our results suggest that these properties are not as important as the surface functional groups resulting from PW conditioning film formation for X. fastidiosa adhesion and biofilm development.
Keywords: Biofilm; Conditioning film; AFM; ATR-FTIR; Adhesion process; Xylella fastidiosa;

Superhydrophobic PMSQ surfaces with excellent solvent resistance and thermal stability were prepared. Modifying sponge with PMSQ not only endows ultra water repellency, but also enhances acoustic performance by 12%.Display Omitted► Superhydrophobic PMSQ surfaces were prepared by electrospinning at sol–gel transition. ► Superhydrophobic PMSQ surfaces show excellent resistance to solvents. ► Superhydrophobic PMSQ surfaces show thermal stability as high as 300 °C. ► Superior acoustical performance was obtained when the sponge decorated with PMSQ.Multifunctional superhydrophobic polymethylsilsesquioxane (PMSQ) surfaces with excellent solvent resistance, thermal stability and enhanced sound absorption property were manufactured by electrospinning. The surfaces with various hierarchical morphologies and hydrophobicity were obtained by electrospinning at the different stages of sol–gel transition of PMSQ prepolymer solution. At the stage with a proper viscosity the superhydrophobic PMSQ surface with a contact angle as high as 151° and a sliding angle as low as 8° was prepared. Due to the excellent thermal stability and solvent resistance properties of the cured PMSQ, the resultant surfaces remain superhydrophobicity after thermal treatment at 300 °C and immersion into many solvents. Additionally, an enhanced acoustical performance and ultra water repellency were obtained simultaneously when the traditional acoustical sponge was decorated with the electrospun PMSQ superhydrophobic surface. The robust superhydrophobic PMSQ surfaces may promise practical applications in many fields.
Keywords: Electrospinning; Polymethylsilsesquioxane; Sol–gel transition; Superhydrophobicity; Sound absorption;

For a hydrophilic surface, the contact angle of a nanodrop increases as the roughness increases. In contrast, the contact angle of a macroscopic drop decreases with increasing roughness.Display Omitted► The contact angle of a nanodrop on a hydrophilic surface increases with increasing roughness. ► In contrast, the contact angle of a macrodrop decreases as the roughness increases. ► A gradient of the pillar–fluid interactions generates asymmetrical drops in metastable states.A two-dimensional nanodrop on a hydrophilic solid surface decorated with nanopillars is examined using a nonlocal density functional theory. It is shown that, in contrast to the commonly used Wenzel formula, even an extremely small roughness can considerably increase the contact angle. The contact angle depends on the distance between pillars, their height and width, as well as their composition. It was found that for all selected pillar heights and compositions, the largest contact angle is obtained when the distance between pillars acquires a size at which the liquid molecules can no longer penetrate between them. The further decrease in the interpillar distance decreases the contact angle, in qualitative agreement with the Cassie–Baxter formula. Considering pillars of various compositions, the role of the gradient of the fluid–solid interaction potential is examined. The presence of such a gradient does not allow the formation of a stable nanodrop on the surface. However, asymmetrical metastable nanodrops can be formed.
Keywords: Rough surface; Nanodrops; Density functional theory; Contact angle;

Fast functionalization of multi-walled carbon nanotubes by an atmospheric pressure plasma jet by Daniel Kolacyak; Jörg Ihde; Christian Merten; Andreas Hartwig; Uwe Lommatzsch (311-317).
Functionalization of multi-walled carbon nanotubes with a novel atmospheric pressure plasma process incorporates about 6.6 at.% of oxygen and is proposed as an alternative to acidic treatment.Display Omitted► Atmospheric pressure plasma enhances dispersibility of multi-walled carbon nanotubes. ► Plasma treatment introduces hydroxylic and carboxylic functional groups. ► Functionalization occurs within less than 1 s of effective plasma treatment. ► CNT morphology is largely preserved in plasma treatment.The afterglow of an atmospheric pressure plasma has been used for the fast oxidative functionalization of multi-walled carbon nanotubes (MWCNTs). Scanning electron microscopy and Raman spectroscopy demonstrate that the MWCNT morphology is mostly preserved when the MWCNTs are dispersed in a solvent and injected as a spray into the plasma. Contact angle measurements show that this approach enhances the wettability of MWCNTs and reduces their sedimentation in an aqueous dispersion. X-ray photoelectron spectroscopy, IR spectroscopy, and electrokinetic measurements show that oxygen plasma incorporates about 6.6 at.% of oxygen and creates mainly hydroxyl and carboxyl functional groups on the MWCNT surface. The typical effective treatment time is estimated to be in the range of milliseconds. The approach is ideally suited for combination with the industrial gas phase CVD synthesis of MWCNTs.
Keywords: Atmospheric pressure plasma; Multi-walled carbon nanotubes; Morphology; Surface modification; Agglomeration; Dispersibility;

We tried a simple method for the direct conjugation of curcumin to hyaluronic acid by utilizing reactive functional groups in hyaluronic acid such as carboxylic acid. Hyaluronic acid–curcumin conjugates form nano sized micelle in aqueous solution through hydrophobic interactions which enhances poor aqueous solubility and stability of curcumin.Display Omitted► Polymer-drug conjugates have gained much attention largely to circumvent lower drug solubility and to enhance drug stability. ► Curcumin is widely known for its medicinal properties including its anticancer efficacy. One of the serious drawbacks of curcumin is its poor water solubility which leads to reduced bioavailability. ► We synthesized Hyaluronic acid–curcumin (HA–Cur) conjugate. ► The conjugates, interestingly found to assembles as micelles in aqueous phase. ► The formation of micelles seems to improve the stability of the drug in physiological pH.Polymer-drug conjugates have gained much attention largely to circumvent lower drug solubility and to enhance drug stability. Curcumin is widely known for its medicinal properties including its anticancer efficacy. One of the serious drawbacks of curcumin is its poor water solubility which leads to reduced bioavailability. With a view to address these issues, we synthesized hyaluronic acid–curcumin (HA–Cur) conjugate. The drug conjugate was characterized using FT-IR, NMR, Dynamic light scattering and TEM techniques. The conjugates, interestingly found to assembles as micelles in aqueous phase. The formation of micelles seems to improve the stability of the drug in phisiological pH. We also assessed cytotoxicty of the conjugate using L929 fibroblast cells and quantified by MTT assay.
Keywords: Curcumin; Hyaluronic acid; Polymer conjugates; Esterification; Cytotoxicity; Micelles; MTT assay; Solubility; Stability; Degradation;