Journal of Colloid And Interface Science (v.357, #1)
Cover 1 (OFC).
The imaging ammeter by Christopher L. Wirth; Paul J. Sides; Dennis C. Prieve (1-12).
The imaging ammeter employs colloidal particles (diameter ∼5.7 μm) as probes of local electrochemical current density. Measuring local current density is important to high throughput electrocatalysis and corrosion research. This work concerns the basic science of single particle motion as it applies to the development of the imaging ammeter.Display Omitted► Colloidal particles as probes of local electrochemical current. ► Probes distinguish between reversible and irreversible reaction with no species requirement. ► Local electrochemical activity inferred on patterned working electrodes.A method for measuring local current density, not requiring segmentation of the electrode or spatial scanning, is presented. The motion of colloidal particles in response to local current density, characterized by the intensity of the light they scatter, is the fundamental phenomenon of the technique. The scattering was produced and measured with the electrochemical total internal reflection microscope, a tool that places an electrochemical cell within a total internal reflection apparatus. The electrolysis of water and the oxidation of ferrocene monocarboxylic acid were used as test reactions. Light scattered by a probe particle produced an “image” of current density; scattered light was converted to local current density by a function derived herein. Numerical simulations supplemented experimental evidence that local current density controlled the probe particle’s vertical motion. The spatial resolution of the method was approximately the length scale of the probe particle, in this case 5.7 μm. The resolution of current density was better than 100 nA cm−2. The method might find use in high throughput screening of electrocatalysts.
Keywords: Local current density; Total internal reflection microscopy; High throughput screening; Electrocatalysts;
Laser fragmentation in liquid medium: A new way for the synthesis of PbTe nanoparticles by C. Chubilleau; B. Lenoir; S. Migot; A. Dauscher (13-17).
A laser fragmentation technique was used to prepare lead telluride nanoparticles. Various experimental parameters were investigated and their influence on particle size, size distribution and cristallographic structure is discussed.Display Omitted► Laser fragmentation an effective method to produce nanoparticles in water. ► Few seconds are enough to synthesize PbTe nanoparticles (6 nm). ► No change in the cristallographic structure after short irradiation duration.Synthesis of PbTe nanoparticles has been performed by pulsed laser fragmentation of PbTe micron-sized powders in distilled water with a Nd:YAG laser. The influence of various experimental parameters (wavelength, treatment duration, and output energy) on the yield of fragmentation, the size and the crystallographic structure of the nanoparticles produced has been investigated. Characterization of the nanopowders was performed by X-ray diffraction analyses and transmission electron microscopy observations. Thanks to a careful control of the synthesis parameters, PbTe nanoparticles with an average diameter close to 6 nm and exhibiting a sharp distribution in size have been produced.
Keywords: Lead telluride; Nanopowders; Laser ablation; Liquid;
The distribution of stresses in rigid fractal-like aggregates in a uniform flow field by Andrea Gastaldi; Marco Vanni (18-30).
Interfacial normal forces in a settling aggregate: the filamentous structure of the cluster accumulates internal stresses in the inner region of the cluster.Display Omitted► Internal stress is propagated and accumulated along the filaments of the structure. ► The most stressed bonds are located in the internal region of the aggregate. ► The structure of fractal aggregates enhances internal stress.The distribution of stresses in rigid fractal-like aggregates moving in a uniform flow field was investigated for particle–cluster and cluster–cluster aggregates with fractal dimensions ranging from 1.7 to 2.3. The method of reflections was used to calculate the drag force on each monomer, while the internal inter-monomer interactions were calculated by applying force and torque balances on each primary particle. The stress distribution was found to be very dissimilar from that of the applied external forces. Although the highest external forces act on the monomers located at the periphery of the aggregate where the drag is more intense, the most stressed inter-monomer bonds are always located in the internal part of the aggregate. This phenomenon is a consequence of the structure of the studied fractal aggregates, which are made mainly of filaments of monomers: the stress generated by the external forces is propagated and progressively accumulated by such filaments up to their roots, which are situated in the inner part of the cluster. Such a behaviour is different from that exhibited by highly connected structures, in which the loads are absorbed locally by the structure and the largest stresses are normally found in the proximity of the highest applied external forces.
Keywords: Colloidal aggregates; Stress distribution; Breakage; Dispersion;
Size tuned electrophoretic pyrazoline nanoparticles prepared through dispersion–polymerization by Sun Wha Oh; Chang Woo Kim; Se-Mo Son; Young Soo Kang (31-35).
Highly monodispersed pyrazoline nanoparticles of different sizes were prepared and encapsulated in methyl methacrylate and ethylene glycol dimethacrylate, which on adding charge controlling additive show size dependent high electrophoric mobility and image display behaviors.Display Omitted► We prepared highly monodispersed pyrazoline nanoparticles with different sizes. ► Pyrazoline nanoparticles were encapsulated through Dispersion-Polymerization. ► After adding charge controlling additive, they show size dependent high electrophoric mobility and image display behaviors.Highly monodispersed electrophoretic particles of size ranging from 550 to 160 nm could be prepared through dispersion–polymerization of methyl methacrylate and ethylene glycol dimethacrylate in presence of pyrazoline nanoparticles in a methanol–water mixture. The size of the fabricated electrophoretic particles could be controlled by adjusting the concentration of surfactant. Stearic acid, used as surfactant during the polymerization process also acts as charge controlling additive to control the electrophoric mobility of the particles. Maximum electrophoric mobility (−7.513 × 10−5 cm2/V s) was obtained for the 400 nm electrophoretic particles prepared with 1.5 wt.% of stearic acid surfactant. The electrophoric display cells prepared with our electrophoretic particles reveal good current voltage characteristics and color change under applied bias voltage.
Keywords: Electrophoretic particles; Pyrazoline nanoparticles; Dispersion–polymerization;
Flower-like porous hematite nanoarchitectures achieved by complexation–mediated oxidation–hydrolysis reaction by Xing Huang; Jianguo Guan; Zhidong Xiao; Guoxiu Tong; Fangzhi Mou; Xi’an Fan (36-45).
Taking advantage of the unique complexing ability of Tris(hydroxymethyl)aminomethane with Fe(II) ions, the iron oxide precursor composed of ultra-thin nanoflakes was prepared. Flower-like hematite (α-Fe2O3) nanoparticles with hierarchical porous structures were further obtained through annealing the iron oxide precursor.Display Omitted► Flower-like porous iron oxide nanostructures are prepared via a solution-based reaction utilizing the complexing ability of Tris with Fe(II) ions. ► The morphology of resultant nanostructures is controlled by a balance between the crystallization rate of γ-FeOOH with the dissociation rate of the Fe(II)–Tris complex. ► They exhibit excellent visible photocatalysis in treating DMSO industrial wastewater.Flower-like porous hematite (α-Fe2O3) nanoarchitectures composed of ultra-thin nanoflakes were prepared by annealing the iron oxide precursor formed via the oxidation-hydrolysis reaction between Fe(II) ions and Tris(hydroxymethyl)aminomethane (abbreviated as Tris). The microstructure of the prepared FeOOH and hematite samples were fully characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier-transforming infrared spectra, thermogravimetric analysis, and nitrogen adsorption–desorption isotherm. Based on the influences of reactant concentrations, reaction time and reaction temperature on the morphologies of the resultant samples, a formation mechanism of etching was proposed, Fe(II)–Tris complexes were self-assembled via hydrogen bonds into brick-like building blocks, which then aggregated into rudimentary nanoparticles, and the synergistic effect between the crystallization of FeOOH and dissociation of Fe(II)–Tris complexes make the rudimentary nanoparticles evolve into the flower-like products. The as-prepared flower-like α-Fe2O3 nanostructures possessed a Brunauer–Emmett–Teller specific surface area of 191.63 m2 g−1, hierarchical pore distribution ranging from micropores to macropores, and good crystallinity, and excellent visible photocatalysis in terms of removing chemical oxygen demand of dimethyl sulfoxide industrial wastewater. The current work provides a reliable approach for building functional hierarchical nanoarchitectures and the prepared iron oxide nanomaterials demonstrate an excellent ability to remove toxic pollutants in industrial wastewater.
Keywords: Flower-like; Hierarchical nanostructures; Porous; Hematite; Formation mechanism; Visible photocatalysis; Industrial wastewater;
Ionic liquid-assisted direct synthesis of PdO nanoparticles immobilized on boehmite nanoparticles by Sung Dae Cho; HoSeok Park (46-49).
The PdO nanoparticle immobilized on boehmite or γ-alumina nanoparticles were readily synthesized through an ionic liquid (IL)-assisted one-pot solution method by controlling chemical compositions.Display Omitted► PdO nanoparticles were immobilized on boehmite nanoparticles through an IL-assisted synthesis. ► The nanostructures of PdO and boehmite were co-constructed at a proper stoichiometry. ► The morphology of the as-obtained nanomaterials was characterized by TEM and STEM. ► The molecular structures of the as-obtained nanomaterials were analyzed by XRD and 27Al NMR.We demonstrated a simple route to simultaneously synthesize PdO and boehmite nanoparticles, and to directly immobilize the former on the latter using an ionic liquid (IL)-assisted one-pot solution method. PdO nanoparticles were directly immobilized on boehmite nanoparticles, and their amount and distribution were controlled by the stoichiometry of the mixture. In particular, γ-alumina nanofibers, which were topochemically transformed from boehmites, exhibited lengths of ca. 40–70 nm and diameters of ca. 1.5–3 nm, while PdO nanoparticles had diameters of ca. 2–4 nm. The nanocrystalline structures of the PdO nanoparticles immobilized on the boehmite nanoparticles were characterized by high-resolution transmission electron microscopy (HR–TEM), X–ray diffraction (XRD), and 27Al nuclear magnetic resonance (NMR). The one-step synthetic method described herein allows for the design and fabrication of host–guest systems of inorganic or metallic nanomaterials with hetero-nanostructures.
Keywords: Supramolecular assembly; Ionic liquids; Alumina; Nanoparticles; Nanocomposites;
Design of water-based ferrofluids as contrast agents for magnetic resonance imaging by Maria F. Casula; Anna Corrias; Paolo Arosio; Alessandro Lascialfari; Tapas Sen; Patrizia Floris; Ian J. Bruce (50-55).
Cost-effective, water-based surface modification approaches which can be easily scaled-up for the large scale synthesis of iron oxide ferrofluids have been investigated. Surface coating with silica and/or non-toxic commercial dispersants produces ferrofluids with potential for use as MRI negative contrast agents.Display Omitted► Surface modification of iron oxide lead to stable water-based ferrofluids. ► Coating of nanoparticles with silica and/or non-toxic dispersants was optimized. ► All the materials synthesized function as MRI negative contrast agents. ► Improved relaxometric properties are observed for silica-coated nanoparticles.We report the synthesis, characterization and relaxometric study of ferrofluids based on iron oxide, with potential for use as magnetic resonance imaging (MRI) contrast agents (CAs). The effect of different cost-effective, water-based surface modification approaches which can be easily scaled-up for the large scale synthesis of the ferrofluids has been investigated. Surface modification was achieved by silanization, and/or coating with non-toxic commercial dispersants (a lauric polysorbate and a block copolymer with pigment affinic groups, namely Tween 20 and Disperbyk 190) which were added after or during iron oxide nanoparticle synthesis. It was observed that all the materials synthesized functioned as negative contrast agents at physiological temperature and at frequencies covered by clinical imagers. The relaxometric properties of the magnetic nanoparticles were significantly improved after surface coating with stabilizers compared to the original iron oxide nanoparticles, with particular reference to the silica-coated magnetic nanoparticles. The results indicate that the optimization of the preparation of colloidal magnetic ferrofluids by surface modification is effective in the design of novel contrast agents for MRI by enabling better or more effective interaction between the coated iron oxide nanoparticles and protons present in their aqueous environment.
Keywords: Nanoparticles; Ferrofluids; Surface modification; Relaxometry;
Collagen containing microcapsules: Smart containers for disease controlled therapy by Laura Pastorino; Svetlana Erokhina; Federico Caneva Soumetz; Paolo Bianchini; Oleg Konovalov; Alberto Diaspro; Carmelina Ruggiero; Victor Erokhin (56-62).
Enzymatic degradation of collagen based drug micro-containers.Display Omitted► Planar nanostructured films of collagen type I. ► Collagen type I nanostructured microcapsules. ► Degradation of collagen planar layers by matrix metalloproteinase I. ► Degradation of collagen based microcapsules by matrix metalloproteinase I. ► Drug release dependent on the biochemistry of the pathological state.The protein collagen is the major component of connective tissue and it is involved in many biological functions. Its degradation is at the basis of different pathological processes. The up-regulated expression of matrix metalloproteinases and the down-regulated expression of their inhibitors are the causes for such degradation. The aim of this work was to evaluate the possibility to fabricate collagen based containers for drug encapsulation and release by cellular demand by the action of matrix metalloproteinases. In present work collagen type I based microcapsules were fabricated by means of the layer-by-layer assembly of oppositely charged collagen and poly (stirene sulfonate) onto colloidal particles, followed by removal of the cores to obtain hollow microcapsules. The process of shell growth on planar supports was monitored by quartz crystal microbalance. X-ray reflectivity measurements were carried out at the solid/water interface to study the interaction of matrix metalloproteinase 1 with LbL films of collagen. The morphology of hollow capsules was characterized by scanning electron microscopy, and compared to that of capsules exposed to the matrix metalloproteinase 1. Finally the matrix metalloproteinase 1 mediated permeability of capsules variation was studied by Confocal Laser Scanning Microscopy. The results demonstrated the possibility to fabricate a drug delivery system where the release of the drug is dependent on the biochemistry of the pathological state.
Keywords: Collagen; Matrix metalloproteinase; Layer-by-layer self assembly; Microcapsules; Disease-dependent release;
One pot synthesis of functionalized SBA-15 by using an 8-hydroxyquinoline-5-sulfonamide-modified organosilane as precursor by Alireza Badiei; Hassan Goldooz; Ghodsi Mohammadi Ziarani; Alireza Abbasi (63-69).
A novel AlQ3-functionalized SBA-15 mesoporous material was synthesized by using a modified organosilane as precursor and its emission spectra was studied.Display Omitted► Synthesis a modified precursor in which 8-HQ is attached to the APTES via a stable sulfonamide bond. ► Synthesis a new 8-HQ functionalized SBA-15 type material. ► Grafting of AlQ3 complex to this new 8-HQ functionalized SBA-15 type material. ► Grafted AlQ3 in prepared material displays blue shift in comparison with AlQ3 complex in solution. ► The emission of grafted AlQ3 can be tuned by using appropriate substitution on 8-HQ.A novel functionalized SBA-15 mesoporous material was prepared through co-condensation of tetraethylorthosilicate with an 8-hydroxyquinoline-5-sulfonamide-modified organosilane precursor in the presence of P123 as structure-directing agent. After removal of template, the obtained material was characterized by powder X-ray diffraction (XRD), nitrogen adsorption–desorption, Fourier transform infrared (FT-IR), thermal analysis (TGA–DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental analysis. Then, aluminum quinolate complex was attached covalently to this functionalized SBA-15 by using coordinating ability of grafted 8-HQ and its emission spectra showed a slightly blue shift in comparison with AlQ3 complex.
Keywords: Mesoporous silica; SBA-15; Direct synthesis; 8-Hydroxyquinoline; Sulfonamide; Emission spectra;
Bilayer heating in magnetite nanoparticle–liposome dispersions via fluorescence anisotropy by Geoffrey D. Bothun; Matthew R. Preiss (70-74).
Bilayer-based temperature measurements of magnetoliposomes (liposomes containing encapsulated magnetic nanoparticles) subjected to cycled electromagnetic field heating.Display Omitted► Anisotropy measures bilayer heating of magnetoliposomes in an electromagnetic RF field. ► Measurements aided by cholesterol, which broadens the phase transition window. ► Nanoscale heating not observed due to rapid heat dissipation from the nanoparticles into water.Temperature measurements have been made within magnetite (Fe3O4) nanoparticle–liposome dispersions subjected to electromagnetic field at radiofrequency (RF) heating based on the fluorescence anisotropy of diphenylhexatriene (DPH) embedded within the bilayer. Incorporating cholesterol within dipalmitoylphosphatidylcholine (DPPC) bilayers broadened the anisotropy window associated with lipid melting. Cryogenic transmission electron microscopy showed that the dispersions contained magnetoliposomes with nanoparticle aggregates at both low and high encapsulation densities. RF heating results demonstrated the ability to measure the temperature of the ML bilayer with on/off RF cycles using DPH anisotropy. These measurements reflected the temperature of the bulk aqueous phase, which is consistent with previous work showing rapid heat dissipation from a nanoparticle surface during RF heating and a negligible difference between surface and bulk temperature.
Keywords: Magnetoliposome; Magnetic nanoparticle; Electromagnetic heating; Hyperthermia; Lipid bilayer;
Optimizing the formation of biocompatible gold nanorods for cancer research: Functionalization, stabilization and purification by Nicolas Bogliotti; Birgit Oberleitner; Aurélie Di-Cicco; Frédéric Schmidt; Jean-Claude Florent; Vincent Semetey (75-81).
Functionalization of the surface of CTAB-stabilized gold nanorods with various PEG-thiols revealed an influence of PEG chain length, reaction conditions and purification method on the stability of the produced particles.Display Omitted► Only PEG-thiols above 2000 Da provide efficient steric GNR stabilization. ► GNR-S-PEGmX can be efficiently purified by size exclusion chromatography. ► GNR-S-PEGmX stability varies according to the purification technique used.We have investigated the most efficient way of preparing biocompatible gold nanorods (GNR) used as tool for cancer imaging and therapy. The surface of cetyltrimethylammonium bromide-stabilized gold nanorods (GNR-CTAB) was functionalized with various thio-polyethylene glycols of the general formula HS-PEGmX (m = 356–10,000; X = −OMe, −NH2). The influence of several parameters such as PEG chain length, reaction conditions and purification method on long-term stability, morphology and optical properties of the produced GNR-S-PEGmX was studied, demonstrating the existence of a threshold HS-PEGmX chain length (with molecular weight m ⩾ 2000) for efficient steric stabilization of GNR. Several purification techniques were compared: dialysis, centrifugation and a rarely used technique in this field, size exclusion chromatography. While a very weak efficiency of dialysis was evidenced, both centrifugation and size exclusion chromatography were found to provide pure GNRs, though the latter method yielded nanoparticles with a significantly higher stability. Finally, the long-term stability of the produced GNRs was investigated in various media: water, PBS buffer and serum.
Keywords: Gold nanorods; Polyethylene glycol; Surface functionalization; Stability; Purification;
Scattering of intersecting spherical particles in the Rayleigh-Gans approximation by Guillermo E. Eliçabe (82-87).
A Pickering particle consists of a large sphere with small spheres incrusted on its surface. This particle is a good example of many colloidal particles that can be thought of as intersecting spheres.Display Omitted► A new model for the scattering of intersecting spherical particles is presented. ► Many colloidal particles can be thought of as intersecting spheres. ► Some of them are Pickering emulsions, key–lock colloids, and Janus particles. ► Some features of these particles can be discerned from the scattering spectra.In this work a novel semianalytical procedure to calculate the exact scattering behavior of complex particles made of intersecting spheres in the Rayleigh-Gans approximation is presented. Pickering emulsions, Janus particles, and lock and key particle colloids are particular cases of particles built from intersecting spheres. The proposed methodology is based on the decomposition of the complex particle as a sum of simpler components whose scattering properties can be evaluated using a simple integral. The procedure is developed for any number of spheres that intersect in pairs but it can be directly extended to intersections that involve more than two spheres at the same time. Some examples are presented to illustrate the application of the model to: (i) the study of the sensitivity of scattering spectra to detect complex particles from approximated model particles; (ii) the detection of different degrees of penetration of one particle into the other; (iii) the identification of the location of the cavity in particles that intersect with a spherical surface of contact; and (iv) the follow up of the evolution of a complex particle from a mix of its components.
Keywords: Scattering; Colloids; Pickering emulsions; Lock and key colloids; Janus particles;
A tri-block copolymer templated synthesis of gold nanostructures by Ester Falletta; Francesca Ridi; Emiliano Fratini; Chiara Vannucci; Patrizia Canton; Sabrina Bianchi; Valter Castelvetro; Piero Baglioni (88-94).
A novel hydrophilic tri-block copolymer (BMB) has been used as a capping and stabilizing agent for in water Au nanoparticles synthesis. The BMB/Au ratio affects the particle size, shape and monodispersity.Display Omitted► Ultra-small gold nanoparticles were synthesized in water with a new capping agent. ► The capping agent is a hydrophilic tri-block copolymer (BMB). ► The BMB/Au ratios affect the particle size, shape and polydispersity allowing their control.Stable ultra-small gold nanoparticles have been synthesized in aqueous phase by using a tri-block copolymer (BMB) as a templating agent consisting of two PEG-methylacrylate chains (B blocks) anchored to a poly(methacrylic) moiety containing a trithiocarbonate unit (M block). The effect of the BMB/Au molar ratios on the final particle size, shape and monodispersity has been investigated. The synthesized nanosols have been characterized by means of Visible Absorption, Small Angle X-ray Scattering (SAXS), and Transmission Electron Microscopy (TEM). Results clearly indicate that the polymer plays a key role in determining the size and shape of gold particles, from fractal-like structures to monodisperse spherical particles with a mean diameter of about 3 nm. The aggregation behavior of these nanostructures has been characterized both in solution (SAXS) as well as on mica substrate (AFM) and has been proven to be driven by the polymer to gold concentration ratio.
Keywords: Gold nanoparticles; Block copolymer; Capping agent; SAXS; AFM; TEM;
Preparation, characterization and catalytic property of CuO nano/microspheres via thermal decomposition of cathode-plasma generating Cu2(OH)3NO3 nano/microspheres by Zhi-Kun Zhang; Deng-Zhu Guo; Geng-Min Zhang (95-100).
Cu2(OH)3NO3 nano/microspheres were generated in cathodic-plasma electrolysis, and they were thermally decomposed into CuO nano/microspheres, which exhibited excellent catalytic activity in the thermal decomposition of ammonium perchlorate.Display Omitted► Cu2(OH)3NO3 nano/microspheres are synthesized via cathodic-plasma electrolysis. ► The Cu2(OH)3NO3 nano/microspheres can be thermally transformed into CuO species. ► The CuO nano/microspheres show excellent catalytic activity in decomposition of AP. ► Several techniques are used for comprehensive characterization of the samples. ► The preparation method is simple, nontoxic and productive.CuO nano/microspheres with a wide diametric distribution were prepared by thermal decomposition of Cu2(OH)3NO3 nano/microspheres formed in a simple asymmetric-electrode based cathodic-plasma electrolysis. The morphological, componential, and structural information about the two kinds of spheres were characterized in detail by SEM, TEM, EDX, XPS and XRD, and the results revealed that the morphology of the spheres were well kept after the componential and structural transformation from Cu2(OH)3NO3 into CuO. The TGA/DSC study showed that the CuO nano/microspheres could be explored to be a promising additive for accelerating the thermal decomposition of ammonium perchlorate (AP). Combining with the current curve and emission spectrum measured in the plasma electrolysis, formation mechanism of the Cu2(OH)3NO3 spheres was also discussed.
Keywords: CuO; Cu2(OH)3NO3; Sphere; Plasma electrolysis; Ammonium perchlorate;
Novel cationic pH-responsive poly(N,N-dimethylaminoethyl methacrylate) microcapsules prepared by a microfluidic technique by Jie Wei; Xiao-Jie Ju; Rui Xie; Chuan-Lin Mou; Xi Lin; Liang-Yin Chu (101-108).
Novel cationic pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDM) microcapsules are successfully prepared using oil-in-water-in-oil double emulsions as templates using a microfluidic technique. The pH-responsive characteristics of these PDM microcapsules are significantly affected by the composition and pH of the monomer solutions.Display Omitted► Novel cationic pH-responsive microcapsules are prepared by a microfluidic technique. ► The microcapsules swell at low pH due to the protonation of ―N(CH3)2 groups. ► The pH-sensitivity of the microcapsules is affected by pH of the monomer solutions.Novel monodisperse cationic pH-responsive microcapsules are successfully prepared using oil-in-water-in-oil double emulsions as templates by a microfluidic technique in this study. With the use of a double photo-initiation system and the adjustment of pH value of the monomer solution, cross-linked poly(N,N-dimethylaminoethyl methacrylate) (PDM) microcapsules with good sphericity and monodispersity can be effectively fabricated. The obtained microcapsule membranes swell at low pH due to the protonation of ―N(CH3)2 groups in the cross-linked PDM networks. The effects of various preparation parameters, such as pH of the aqueous monomer fluid, concentration of cross-linker, concentration of monomer N,N-dimethylaminoethyl methacrylate (DM) and addition of copolymeric monomer acrylamide (AAm), on the pH-responsive swelling characteristics of PDM microcapsules are systematically studied. The results show that, when the PDM microcapsules are prepared at high pH and with low cross-linking density and low DM monomer concentration, they exhibit high pH-responsive swelling ratios. The addition of AAm in the preparation decreases the swelling ratios of PDM microcapsules. The external temperature has hardly any influence on the swelling ratios of PDM microcapsules when the external pH is less than 7.4. The prepared PDM microcapsules with both biocompatibility and cationic pH-responsive properties are of great potential as drug delivery carriers for tumor therapy. Moreover, the fabrication methodology and results in this study provide valuable guidance for preparation of core–shell microcapsules via free radical polymerization based on synergistic effects of interfacial initiation and initiation in a confined space.
Keywords: pH-responsive microcapsules; Cationic pH-responsive property; Microcapsule membranes; Poly(N,N-dimethylaminoethyl methacrylate) (PDM); Microfluidic technique;
Reversible buckling and diffusion properties of silica-coated hydrogel particles by Petra Haufová; Zdeněk Knejzlík; Jaroslav Hanuš; Aleš Zadražil; František Štěpánek (109-115).
Alginate particles coated by silica are able to reversibly buckle during drying and rehydration. The effect of coating on the diffusion rates water, vitamin B12 and lysozyme was investigated.Display Omitted► Silica-coated alginate particles were synthesised and characterised. ► The surface layer is flexible and capable of reversible buckling. ► Diffusion rate of water and vitamin B12 is not affected by coating. ► Uptake rate of lysozyme is strongly affected by the silica layer.The structure and diffusion properties of composite particles consisting of a calcium alginate hydrogel core and a thin SiO2 surface layer have been investigated. The composite particles were formed by depositing a silica layer onto calcium alginate cores using a sol–gel process starting from alkoxysilane precursors. The composite particles were found to have a remarkable ability to reversibly rehydrate and return to their original size and shape after partial drying. The organo-silica skin was able to sustain large local deformations (such as complete folding) without the formation of cracks or defects. Such mechanical properties are uncharacteristic of pure silica and they can be attributed to the specific microstructure of the alginate–silica composite. The structure and composition of the alginate–silica particles were characterised by SEM, X-ray micro-tomography, Laser Scanning Confocal Microscopy and Thermo-gravimetry. In order to quantify the effect of the organo-silica layer on the diffusional transport into and out of the alginate particles, the uptake and release rates of several test molecules with increasing molecular weight were measured for both un-coated and silica-coated particles. While the diffusion rate of small and medium-size molecules (water, vitamin B12) was essentially unaffected by the presence of the silica layer, the diffusion rate of a larger biomolecule (lysozyme) was found to be slowed down by the presence of the surface layer. The flexibility of the organo-silica layer combined with the ability of even large biomolecules to diffuse through it indicate that the silica layer is macroporous, formed by individual SiO2 nanoparticles dispersed and immobilised in the surface layer of the alginate hydrogel.
Keywords: Biomineralisation; Diffusion; Drying; Hydrogel; Core–shell particle;
Mesoporous rare earth fluoride nanocrystals and their photoluminescence properties by Chunye Wen; Lingling Sun; Jinghui Yan; Yang Liu; Jinzhuang Song; Yao Zhang; Hongzhou Lian; Zhenhui Kang (116-120).
Nanoparticles assembly construction for YF3 and YF3:Eu3+ mesoporous (pore size, 2–4 nm) hexagonal nanoplates and the significant enhancement in PL intensity.Display Omitted► YF3 and YF3:Eu3+ mesoporous nanocrystals were synthesized by an assembly route. ► YF3:Eu3+ mesoporous nanoplates show a significant PL intensity enhancement. ► This assembly strategy is a novel method for mesoporous materials preparation.YF3 and YF3:Eu3+ mesoporous hexagonal nanocrystals were successfully synthesized via a simple hydrothermal process based on the in situ assembly of the as-synthesized YF3 and YF3:Eu3+ nanoparticles. The well defined mesoporous nanostructures are formed by phenanthroline assisted assembly of ∼20 nm nanoparticles, and 2–4 nm pores are contained as indicated by N2 adsorption–desorption studies. The obtained YF3:Eu3+ mesoporous hexagonal nanoplates show a significant photoluminescence intensity enhancement compared with other shaped YF3:Eu3+ nanocrystals.
Keywords: Nanoparticles; Rare earth fluorides; Photoluminescence; Assembly; Mesopore design;
Kinetic and rheological measurements of the effects of inert 2-, 3- and 4-bromobenzoate ions on the cationic micellar-mediated rate of piperidinolysis of ionized phenyl salicylate by Nor Saadah M. Yusof; M. Niyaz Khan (121-128).
Kinetic observation of the effects of [3-BrBzNa] on the rate of piperidinolysis of ionized phenyl salicylate in the presence of CTABr micelles.Display Omitted► Determination of ion exchange constants, K X Br , for counterions of cationic micelles. ► New kinetic model for studying the effects of inert salts, MX, on reaction rates in CTABr micelles. ► Relationship between magnitudes of K X Br and formation of wormlike micelles. ► Kinetic demonstration of the occurrence of independent ion exchange processes on micelle. ► Maxima of the plots of shear viscosity vs. [MX] at 15 mM CTABr are indicative of wormlike micelles.The effects of the concentration of inert organic salts, [MX], (MX = 2-, 3- and 4-BrBzNa with BrBzNa = BrC6H4CO2Na) on the rate of piperidinolysis of ionized phenyl salicylate (PS−) have been rationalized in terms of pseudophase micellar (PM) coupled with an empirical equation. The appearance of induction concentration in the plots of k obs versus [MX] (where k obs is pseudo-first-order rate constants for the reaction of piperidine (Pip) with PS−) is attributed to the occurrence of two or more than two independent ion exchange processes between different counterions at the cationic micellar surface. The derived kinetic equation, in terms of PM model coupled with an empirical equation, gives empirical parameters F X/S and K X/S whose magnitudes lead to the calculation of usual ion exchange constant K X Br (=K X/K Br with K X and K Br representing cationic micellar binding constants of counterions X− and Br−, respectively). The value of F X/S measures the fraction of S− (=PS−) ions transferred from the cationic micellar pseudophase to the aqueous phase by the optimum value of [MX] due to ion exchange X−/S−. Similarly, the value of K X/S measures the ability of X− ions to expel S− ions from cationic micellar pseudophase to aqueous phase through ion exchange X−/S−. This rather new technique gives the respective values of K X Br as 8.8 ± 0.3, 71 ± 6 and 62 ± 5 for X− = 2-, 3- and 4-BrBz−. Rheological measurements reveal the shear thinning behavior of all the surfactant solutions at 15 mM CTABr (cetyltrimethylammonium bromide) indicating indirectly the presence of rodlike micelles. The plots of shear viscosity (η) at a constant shear rate (γ), i.e. ηγ , versus [MX] at 15 mM CTABr exhibit maxima for MX = 3-BrBzNa and 4-BrBzNa while for MX = 2-BrBzNa, the viscosity maximum appears to be missing. Such viscosity maxima are generally formed in surfactant solutions containing long stiff and flexible rodlike micelles with entangled and branched/multiconnected networks. Thus, 15 mM CTABr solutions at different [MX] contain long stiff and flexible rodlike micelles for MX = 3- and 4-BrBzNa and short rodlike micelles for MX = 2-BrBzNa.
Keywords: Kinetics of piperidinolysis of phenyl salicylate; Effects of organic salts and cationic micelles; Rheometric measurements; Counterionic ion exchange constants; K X Br ; X = sodium 2-, 3- and 4-bromobenzoates; Determination of K X Br ;
Synthesis and surface properties of semi-fluorinated gemini surfactants with two reactive bromo pendant groups by M.El Kateb; E. Taffin de Givenchy; A. Baklouti; F. Guittard (129-134).
Novel class of semi-fluorinated cationic gemini surfactants with two bromo anchorage groups.Display Omitted► Hybrid surfactants were synthesized in five steps from perfluoroethyl iodides. ► These gemini surfactants can be precursors of non leaching biocidal surfaces. ► They showed a singular behaviour as compare to hydrocarbon homologues. ► Increasing the hydrocarbon spacer length destabilize the micelle oleophobic core.This paper presents a series of semi-fluorinated gemini surfactants with two bromo pendant groups. It reviews the effect of the number of methylene units in the spacer group between the two hydrophilic quaternary ammonium heads. Critical micelle concentration (cmc) and free energy of micellization ( Δ G M 0 ) of the title surfactants, in aqueous solution, have been investigated as a function of the number n of carbon atoms in the hydrocarbon spacer. We have pointed out a different behaviour as compared to Gemini hydrocarbon homologues.In the present study, when the number of methylene units (n) in the spacer increases, the cmc first decreases and reaches an optimum for (n = 6), then it increases linearly from n ⩾ 6. Variations of cmc have been interpreted in terms of conformation changes of the surfactant ion and progressive penetration of the alkyl chain spacer in the micelle hydrophobic core. In this series, the increase of the hydrophobicity seems not to favour the micellisation process as expected, probably impacted by the mutual phobicity of the perfluorinated tails and the hydrocarbon spacer. A minimum is reached for a spacer with six methylene units which seems to be the optimal conformation. The free energy of micellization ( Δ G M 0 ) confirm this tendency.
Keywords: Gemini surfactants; Semi-fluorinated surfactants;
Acoustic sensing of the bacterium–substratum interface using QCM-D and the influence of extracellular polymeric substances by Adam L.J. Olsson; Henny C. van der Mei; Henk J. Busscher; Prashant K. Sharma (135-138).
Adsorbed mass at a liquid–solid interface can be accurately registered by QCM-D as a negative frequency shift. Often adhesion of colloids causes positive frequency shifts, indicating mass loss according to the Sauerbery equation. During bacterial adhesion, colloidal adhesion and molecular adsorption take place simultaneously. Point-contacts at a bacterium-sensor interface are here described as a spring with stiffness k, as per the coupled-oscillator theory while extracellular polymeric substances (EPS) behaves as an adsorbed mass. Accordingly, the amount of EPS involved in the adhesion of a single bacterium is estimated to correspond to only a few percent of the bacterial weight.Display Omitted► Bacterial adhesion and EPS adsorption is studied using quartz crystal microbalance (QCM). ► Bacteria adhere as coupled oscillator on QCM sensor surface giving rise to positive frequency shift. ► EPS adsorption gives negative frequency shifts as per the normal mass loading theory. ► Amount of EPS, as quantified by QCM, was few percent of bacterial cell mass.It is commonly assumed that bacterial presence on a QCM sensor-surface is associated with a negative frequency shift according to conventional mass-loading theory. Here, we demonstrate that bacteria adhering to QCM sensor-surface may yield positive frequency shifts up to 1.9 × 10−6 Hz per bacterium according to a coupled-oscillator theory. Furthermore, it is demonstrated that the excretion of extracellular polymeric substances (EPS) by adhering bacteria can change the frequency shift in the negative direction by 1.7 × 10−6 Hz per bacterium, according to conventional mass-loading theory. The difference in frequency shifts between an EPS-producing and a non-EPS producing staphylococcal strain correlated with the excretion of 3 × 10−14 g EPS per bacterium, representing only a few percent of the weight of a bacterium. Thus an adsorbed molecular mass as low as a few percent of the mass of an adhering bacterium significantly alters the QCM-signal. Since adhesion of many different bacterial strains is accompanied by molecular adsorption of EPS, with potentially opposite effects on the QCM-signal, a combination of the coupled-oscillator and normal mass-loading theory has to be applied for proper interpretation of QCM-frequency shifts in bacterial detection.
Keywords: EPS; Microbial adhesion; QCM; Positive frequency shift; Negative frequency shift; Staphylococcus epidermidis;
Tunable multicolor pattern and stop-band shift based on inverse opal hydrogel heterostructure by Jianying Wang; Yanchun Han (139-146).
Inverse opal hydrogel heterostructure (PAAm–PAA/PAAm IPN) forms a permanent two-color pattern, which shows various color display by controlling the mixed solvent ratio and crosslinking degree.Display Omitted► Inverse opal hydrogel heterostructure (PAAm–PAA/PAAm IPN) forms a permanent two-color pattern. ► Multi two-color patterns are obtained by controlling the solvent ratio and crosslinking degree. ► Two-color pattern becomes one-color pattern by reducing the PAAm infiltration degree in IPN part.The inverse opal hydrogel heterostructure (polyacrylamide (PAAm) (left side)–polyacrylic acid (PAA)/PAAm interpenetrating polymer network (IPN) (right side) is created by colloidal crystal templating. The two parts, PAAm and IPN, appear different structural colors due to the varied lattice constants and solvent response behaviors. The IPN part keeps red color and PAAm part shows different colors when the composition of the mixed solvent (ethanol and water) and crosslinking degree are changed. For example, as the ethanol content in the mixed solvents increases from 0% to 70%, the PAAm part color changes from red, yellow, green to blue when the PAAm crosslinking degree is 5 mol% or 1 mol%. Meanwhile, a large blue shift of about 200 nm can be realized covering almost the entire wavelength of visible light due to the decreased lattice spacing induced by the PAAm shrinkage. Thus, multi two-color patterns can be realized by changing the color of PAAm and the color of IPN remain red as background for contrast. Moreover, the IPN part can change from red to green by reducing the PAAm infiltration time in IPN part, which can realize the change from two-color pattern to one-color pattern at green region.
Keywords: Inverse opal hydrogel heterostructure; Colloidal crystal templating; Tunable multicolor pattern; Stop-band shift;
New dendronized polymers from acrylate Behera amine and their ability to produce visco-elastic structured fluids when mixed with CTAT worm-like micelles by Julio C. Cuggino; Marcelo Calderón; Cecilia I. Alvarez; Miriam C. Strumia; Karolaine N. Silva; Evis K. Penott-Chang; Alejandro J. Müller (147-156).
Rheological behavior of aqueous Solutions of PL1/CTAT mixtures in comparison of neat PL1 dendronized polymer and CTAT solutionsDisplay Omitted► Two new water soluble dendronized polymers (PLn) were successfully synthesized. ► Synergistic viscosity enhancements were found by adding dendronized polymers to CTAT. ► The new PL1/CTAT structured fluid displayed enhanced visco-elasticity and thixotropy.Two new water soluble dendronized polymers (PLn) from acrylate Behera amine monomer of different molecular weights were successfully synthesized. The polymers were characterized by FTIR, NMR, GPC and DLS. Both GPC and DLS results indicated that these PLn have a remarkable tendency to form aggregates in solution that lead to apparent molecular weights that are much higher than their theoretical values, as well as large diameters in solution. However, the addition of any PLn to water did not cause any increase in viscosity up to concentrations of 1000 ppm.The possible interactions of PLn with the cationic surfactant CTAT were explored by solution rheometry. A synergistic viscosity enhancement was found by adding small amounts of dendronized PLn polymers to a CTAT solution composed of entangled worm-like micelles. The highest association tendency with CTAT was found for PL1 at the maximum polymer concentration before phase separation (i.e., 100 ppm). The solution viscosity at low-shear rates could be increased by an order of magnitude upon addition of 100 ppm of PL1 to a 20 mM CTAT solution. For this mixture, the fluid obtained was highly structured and exhibited only shear thinning behavior from the smallest shear rates employed. These PL1/CTAT mixtures exhibited an improved elastic character (as determined by dynamic rheometry) that translated in a much longer value of the cross-over relaxation time and a pronounced thixotropic behavior which are indicative of a strong intermolecular interaction.In the case of the polymer with a higher theoretical molecular weight, PL2, its association with CTAT leads to an extraordinary doubling of solution viscosity with just 0.25 ppm polymer addition to a 20 mM CTAT solution. However, such synergistic viscosity enhancement saturated at rather low concentrations (25 ppm) indicating an apparent lower solubility as compared to PL1, a fact that may be related to its higher molecular weight.
Keywords: Dendrons; Dendronized polymers; Structured fluids; CTAT; Worm-like micelles;
KOH catalysed preparation of activated carbon aerogels for dye adsorption by Sie King Ling; H.Y. Tian; Shaobin Wang; Thomas Rufford; Z.H. Zhu; C.E. Buckley (157-162).
Activated carbon aerogels were synthesised using KOH catalyst and they exhibited high adsorption capacity for organic dyes.Display Omitted► A highly porous carbon aerogel was successfully synthesised at pH 9 with KOH catalyst. ► KOH as a catalyst prevents graphite crystallisation and improves the stability of carbonisation. ► Activated carbon aerogel exhibits higher dye adsorption than activated carbon.Organic carbon aerogels (CAs) were prepared by a sol–gel method from polymerisation of resorcinol, furfural, and hexamethylenetetramine catalysed by KOH at around pH 9 using ambient pressure drying. The effect of KOH in the sol–gel on CA synthesis was studied. It was found that addition of KOH prior to the sol–gel polymerisation process improved thermal stability of the gel, prevented the crystallinity of the gel to graphite, increased the microporosity of CA and promoted activation of CA. The CAs prepared using the KOH catalyst exhibited higher porosity than uncatalysed prepared samples. Activation in CO2 at higher temperature also enhanced the porosity of CAs. Adsorption tests indicated that the CAs were effective for both basic and acid dye adsorption and the adsorption increased with increasing surface area and pore volume. The kinetic adsorption of dyes was diffusion control and could be described by the second-order kinetic model. The equilibrium adsorption of dyes was higher than activated carbon.
Keywords: Carbon aerogel; KOH catalysis; Dye adsorption;
Quantitative characterization of hydroxyl radicals produced by various photocatalysts by Quanjun Xiang; Jiaguo Yu; Po Keung Wong (163-167).
The formation rates of hydroxyl radicals on various photocatalysts were quantitatively characterized by photoluminescence technique and a new concept “OH-index” was first proposed to compare relative activity of photocatalysts.Display Omitted► • OH produced on various photocatalysts was quantitatively characterized by PL method. ► The formation rate of • OH on the surface of P25 is higher than that on other semiconductors. ► The acidic solution and bi-phase structure of TiO2 can enhance the formation rate of • OH. ► A new concept “OH-index” was first proposed to compare relative activity of photocatalysts.Hydroxyl radicals ( • OH) have been deemed to be the major active species during the photocatalytic oxidation reaction. In this study, • OH produced on various semiconductor photocatalysts in aqueous solution under Xenon lamp irradiation was quantitatively investigated by the photoluminescence (PL) technique using coumarin (COU) as a probe molecule. The results indicated that the formation rate of • OH on the surface of irradiated commercial Degussa P25 (P25) was much higher than that of other semiconductor. The pH values of the solution and phase structure of TiO2 significantly influenced the production rate of • OH. The acidic pH environment of the solutions and bi-phase structure (anatase and rutile) of TiO2 were beneficial to enhancing the formation rate of • OH. In addition, the formation rate of • OH on anatase TiO2 and P25 was much faster than that of • OH on the other semiconductors (such as rutile TiO2, ZnO, WO3, CdS, Bi2WO4 and BiOCl, etc.). A new concept “OH-index” was first proposed to compare photocatalytic activity of photocatalysts, which would provide new insight into the investigation of semiconductor photocatalysts.
Keywords: Hydroxyl radicals; Semiconductor photocatalysts; Coumarin; Fluorescent probe; OH-index;
Enhancement of the photocatalytic activity of TiO2 by doping it with calcium ions by U.G. Akpan; B.H. Hameed (168-178).
A Ca-doped TiO2 photocatalyst that brought about a complete mineralization of acid red 1 dye by UV light irradiation was developed and characterized by XPS, FTIR, XRD, and SEM.Display Omitted► A photocatalyst that brings about a complete degradation of AR1 dye was developed. ► The developed catalyst (Ca–TiO2) is more effective than a commercial TiO2. ► The XPS analysis revealed the presence of Ca, Ti, O, and adventitious C. ► Ti4+ and Ca2+ were identified without interference, and so the Ca–TiO2 catalyst is stable.Titanium dioxide (TiO2) with an enhanced photocatalytic activity was developed by doping it with calcium ions through a sol–gel method. The developed photocatalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, N2 physisorption, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. Their surface morphologies were studied using surface scanning electron microscopy (SEM). The XPS analyses confirmed the presence of Ti, O, Ca, and C in the Ca-doped TiO2 sample. The activities of the catalysts were evaluated by photocatalytic degradation of an azo dye, acid red 1 (AR1), using UV light irradiation. The results of the investigations revealed that the samples calcined at 300 °C for 3.6 h in a cyclic (2 cycles) mode had the best performance. Lower percentage dopant, 0.3–1.0 wt.%, enhanced the photocatalytic activity of TiO2, with the best at 0.5 wt.% Ca–TiO2. The performance of 0.5 wt.% Ca–TiO2 in the degradation of AR1 was far superior to that of a commercial anatase TiO2 Sigma product CAS No. 1317-70-0. The effect of pH on the degradation of AR1 was studied, and the pH of the dye solution exerted a great influence on the degradation of the dye.
Keywords: Photocatalytic; Degradation; Cyclic heat treatment; Acid red 1; Doping; TiO2;
Visualization of an adsorption model for surfactant transport from micelle solutions to a clean air/water interface using fluorescence microscopy by Qing Song; Mingjun Yuan (179-188).
This work shows how to visualize a transport model for adsorption of surfactant from micellar solutions onto clean air/water interfaces.Display Omitted► There are two regimes for adsorption dynamics when surfactants absorb from very dilute micellar solution. ► Regime I is the case at lower aggregate concentration, in which micelle diffusion cannot keep up with the kinetic adsorption and micelle-free zone emerges from the surface and move back into the bulk. ► Regime II is the case at higher aggregate concentration, in which the micelle diffuse flux is commensurate with the kinetic adsorption and a micelle-free zone does not form. ► Fluorescence microscopy visualized these two regimes.This work pertains to visualizing a transport model for adsorption of surfactants from micelle solutions onto a clean air/water interface. Under the condition of surfactant adsorption from very dilute solutions, the time scale for diffusion of a surfactant monomer is much slower than the time scale for kinetic breakdown of the aggregates. A theoretical model predicts two regimes for the adsorption dynamics. We visualize these two regimes under the mechanism of solubilization using fluorescence microscopy, in which an insoluble fluorescent probe, NBD-HAD (4-(hexadecylamino)-7-nitrobenz-2-oxa-1,3-diazole), is used to illuminate the micelles. The dye fluoresces in the microenvironment of micelles but is quenched in the aqueous solution on laser excitation. The region containing micelles is illuminated, but the region which does not contain micelles appears dark. For surfactant solution of C14E6 at concentration just above the critical micelle concentration (CCMC ), CCMC = 4.4 mg/L, a dark region between the bright image of the air/water interface and the micelle-containing zone is observed. This dark region becomes smaller with time and finally disappears once equilibrium is reached. For a surfactant solution of C14E6 at the concentration of 4.74CCMC , which is higher than a critical total surfactant concentration ( C T c ) of 4.25CCMC , we observe bright images through surfactant solutions during the adsorption process. Fluorescence images validate the theoretical model.
Keywords: Surfactant; Kinetic adsorption; Critical micelle concentration (CCMC ); Transport mechanisms; Fluorescence microscopy; Visualization;
Raman spectroelectrochemical study of Meldola blue, adsorbed and electropolymerized at a gold electrode by Regina Mažeikienė; Gediminas Niaura; Olegas Eicher-Lorka; Albertas Malinauskas (189-197).
Thin layers of adsorbed and electropolymerized redox dye Meldola blue were prepared at a gold electrode, and features of its structure were studied by surface-enhanced Raman spectroelectrochemistry.Display Omitted► Electropolymerized layers of Meldola blue were prepared and studied by surface-enhanced Raman spectroscopy. ► Flat or slightly tilted orientation of aromatic rings of the dye with respect to electrode surface has been deduced from Raman spectra. ► Electrochemical redox processes of poly(Meldola blue) layers can be followed by characteristic Raman bands and their relative intensities.Surface-enhanced Raman spectroscopy (SERS) was used to probe the structure of adsorbed and electropolymerized Meldola blue (MB) films on roughened gold surfaces in solutions with pH 1.0 and 7.0 by using 785 nm excitation wavelength. Spectral bands were assigned based on density functional theory (DFT) calculations at B3LYP/6-311+G(2d, p) level. The most characteristic band of the oxidized MB form was found to be the breathing vibration of the central ring containing heteroatoms at 596 cm−1. Based on a red shift of bands assigned to vibrations of double C＝N(C2H6) bonds and adjacent ring C＝C bonds in surface spectra as compared with solution 1 it was suggested that polymerization and interaction with an electrode surface proceed through these moieties. The presence of out-of-plane bands in SERS spectra was attributed to “flat” or slightly “tilted” orientation of aromatic rings at the interface. Potential-dependent spectral changes were followed by SERS spectroscopy. Raman spectra of the reduced MB form were obtained in both pH 1.0 and pH 7.0 solutions by analysis of the potential-difference SERS spectra. Reduced MB form can be recognized by characteristic bands near 1620, 1574, 1374, and 1234 cm−1. By comparing the intensities of 1637 cm−1 (oxidized MB form) and 1374 cm−1 (reduced MB form) bands in experimental spectra of polymerized MB in pH 1.0 solution, a reduction-induced decrease by factor of 7 was estimated. A similar tendency in intensity changes showed calculations indicating that this effect is associated with reduction-induced changes in the molecular structure of the dye.
Keywords: Raman spectroscopy; Spectroelectrochemistry; Modified electrodes; Meldola blue; Electropolymerization;
New inorganic (an)ion exchangers based on Mg–Al hydrous oxides: (Alkoxide-free) sol–gel synthesis and characterisation by Natalia Chubar (198-209).
New inorganic ion exchange adsorbents based on double Mg–Al hydrous oxides showed higher affinity to arsenate as well as competitive removal capacity to arsenite, bromate, bromide, fluoride, selenate and borate.Display Omitted► Novel cost-effective (alkoxide-free) sol–gel synthesis method of double Mg–Al hydrous oxides is developed. ► Surface chemistry of the adsorptive materials is controlled by various ways of hydrogel treatments. ► Exceptionally higher affinity and adsorptive capacity towards arsenate is confirmed. ► Competitive removal ability of arsenite, fluoride, bromate, bromide, selenate and borate is shown.New inorganic ion exchangers based on double Mg–Al hydrous oxides were generated via the new non-traditional sol–gel synthesis method which avoids using metal alkoxides as raw materials. Surface chemical and adsorptive properties of the final products were controlled by several ways of hydrogels and xerogels treatments which produced the materials of the layered structure, mixed hydrous oxides or amorphous adsorbents. The final adsorptive materials obtained via thermal treatment of xerogels were the layered mesoporous materials with carbonate in the interlayer space, surface abundance with hydroxylic groups and maximum adsorptive capacity to arsenate. Higher affinity of Mg–Al hydrous oxides towards H 2 AsO 4 - is confirmed by steep adsorption isotherms having plateau (removal capacity) at 220 mg[As] g dw - 1 for the best sample at pH = 7, fast adsorption kinetics and little pH effect. Adsorption of arsenite, fluoride, bromate, bromide, selenate, borate by Mg–Al hydrous oxides was few times high either competitive (depending on the anion) as compare with the conventional inorganic ion exchange adsorbents.
Keywords: Inorganic ion exchange adsorbents; Mg–Al hydrous oxides; Alkoxide-free sol–gel; Arsenate; Arsenite; Fluoride; Bromate; Bromide; Selenate; Borate;
Adsorption of phenol on supercritically activated carbon fibres: Effect of texture and surface chemistry by J.L. Figueiredo; N. Mahata; M.F.R. Pereira; M.J. Sánchez Montero; J. Montero; F. Salvador (210-214).
The amount of chemisorbed phenol over activated carbon fibres decreases with an increase in surface oxygen concentration.Display Omitted► Activation of carbon fibre by H2O or CO2 results in samples with different texture. ► Amount of adsorbed phenol increases with increase in volume of small micropores. ► Adsorption capacity decreases when large amounts of oxygen groups are introduced. ► Most of the phenol is adsorbed physically and nearly independent of surface oxygen. ► Amount of chemisorbed phenol decreases with increase in surface oxygen.The influence of texture and surface chemistry on the phenol adsorption capacity of activated carbon fibres (ACFs) was studied. ACFs were prepared by carbonization of a phenolic textile fibre under nitrogen flow, followed by activation with H2O and CO2 (under atmospheric pressure and supercritical state). The materials were characterised by N2 and CO2 adsorption, and by temperature programmed desorption studies. A strong correlation between the amount of adsorbed phenol and the micropore volume has been observed. The relationship between surface oxygen concentration and amount of physisorbed and chemisorbed phenol was assessed, and it was shown that higher amounts of surface oxygen groups decreased the phenol chemisorption capacity of ACFs.
Keywords: Activated carbon fibres; Supercritical activation; Phenol adsorption; Texture; Surface chemistry;
Surface area and pore structure properties of urethane-based copolymers containing β-cyclodextrin by Lee D. Wilson; Mohamed H. Mohamed; John V. Headley (215-222).
Display Omitted► Copolymer containing β-CD possess tunable surface area and pore structure (textural) properties. ► Sorbents with variable co-monomer composition were studied using N2 and PNP adsorptives. ► Remarkable differences in solid-gas and solid-solution adsorption properties were observed. ► Solvent-induced swelling and morphological changes occurs are observed for such copolymers. ► Hydration phenomena affect the textural properties of “soft” carbohydrate-based materials.The surface area and pore structure characteristics were investigated for a series of aliphatic- and aromatic-based polyurethane (PU) copolymers containing a macromolecular porogen (β-cyclodextrin). The bi-functional diisocyanates used as crosslinker units were: 1,6-hexamethylene, 4,4′-dicyclohexylmethane, 4,4′-diphenylmethane, 1,4-phenylene, and 1,5-naphthalene diisocyanate, respectively. The macromolecular porogen content was controlled by fixing the composition of β-CD and varying the co-monomer mole ratio from unity to larger integer values. Nitrogen adsorption results reveal that copolymer materials with variable mole ratios (β-CD: crosslinker) from 1:1 to 1:3 displayed relatively low BET surface areas (SA ∼ 101 m2/g) and mesopore diameters (∼16–29 nm). In contrast, a dye adsorption method in aqueous solution with p-nitrophenol (PNP) at pH = 4.60 and 295 K provided estimates of the surface area (1.5–6.2 × 102 m2/g) for the corresponding copolymer materials. Variation of the copolymer SA was attributed to the type of diisocyanate crosslinker and its relative mole ratio. The differences in the estimated SA values from porosimetry and the UV–Vis dye adsorption method for these nanoporous copolymers were attributed to the role of solvent as evidenced by swelling of the copolymer framework in aqueous solution and the respective temperature conditions.
Keywords: Nitrogen adsorption; Surface area; Pore structure; Dye adsorption; Copolymer; Swelling; β-Cyclodextrin;
Photocatalytic hydrogen production over CuO-modified titania by Jiaguo Yu; Yang Hai; Mietek Jaroniec (223-228).
CuO-modified titania nanocomposite photocatalysts exhibited an enhanced photocatalytic H2-production activity under ultraviolet light emitting diodes (UV-LED) irradiation.Display Omitted► CuO-modified TiO2 showed an enhanced photocatalytic H2-production activity. ► The optimal CuO content in the photocatalyst was found to be 1.3 wt.%. ► Efficient hydrogen production and decomposition of glycerol were achieved. ► CuO clusters can substitute noble metals in photocatalysts for H2 production. ► Quantum size effect can enhance hydrogen production activity.Efficient hydrogen production and decomposition of glycerol were achieved on CuO-modified titania (CuO–TiO2) photocatalysts in glycerol aqueous solutions. CuO clusters were deposited on the titania surface by impregnation of Degussa P25 TiO2 powder (P25) with copper nitrate followed by calcination. The resulting CuO–TiO2 composite photocatalysts were characterized by X-ray diffraction (XRD), UV–visible spectrophotometry, X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption, transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The low-power ultraviolet light emitting diodes (UV-LED) were used as the light source for photocatalytic H2-production reaction. A detailed study of CuO effect on the photocatalytic H2-production rates showed that CuO clusters can act as an effective co-catalyst enhancing photocatalytic activity of TiO2. The optimal CuO content was found to be 1.3 wt.%, giving H2-production rate of 2061 μmol h−1 g−1 (corresponding to the apparent quantum efficiency (QE) of 13.4% at 365 nm), which exceeded the rate of pure TiO2 by more than 129 times. The quantum size effect of CuO clusters is deemed to alter its energy levels of the conduction and valence band edges in the CuO–TiO2 semiconductor systems, which favors the electron transfer and enhances the photocatalytic activity. This work shows not only the possibility of using CuO clusters as a substitute for noble metals in the photocatalytic H2-production but also demonstrates a new way for enhancing hydrogen production activity by quantum size effect.
Keywords: Photocatalytic hydrogen production; Pollutant decomposition; CuO; Titania;
Wettability, FTIR and dielectric studies of 1,4-dioxane and water system by V. Madhurima; Debarun Dhar Purkayastha; N.V.S Rao (229-233).
Studies of concentration dependent FTIR, dielectric and wetability of aqueous 1,4-dioxane show distinct regions of interactions. The formation of clathrates is verified through contact angle measurements over various substrates and FTIR spectra.Display Omitted► Concentration dependent wettability of aqueous 1,4-dioxane over different substrates. ► Distinct concentrations corresponding to different interaction mechanisms are seen. ► Formation of bifurcated hydrogen bonds is seen in the blue shift in IR spectra. ► Clathrate formation is verified through contact angles over all substrates studied.Wettability studies are of importance for electronic devices. Various methods are known to convert the hydrophobic substrates to hydrophilic substrates, but the studies on the relative dependence of wettability with varying concentrations of an aqueous system are meager. The wetting of different substrates with varying concentration of 1,4-dioxane in water is investigated and the results of concentration dependence of wetting are presented. The FTIR spectrum shows a blue shift of the OH peak – a feature typical of aqueous-1,4-dioxane systems. Concentration dependence of dielectric permittivity of this system also showed an anomaly.
Keywords: Contact angle; Wettability; Hydrophilic; Hydrophobic; Hydrogen bonding; FTIR; Permittivity;
Superhydrophilic and superhydrophobic nanostructured surfaces via plasma treatment by Juan P. Fernández-Blázquez; Daniela Fell; Elmar Bonaccurso; Aránzazu del Campo (234-238).
PET films have been nanostructured at different levels using oxidative plasma treatment and perfluorinated coatings. Stable superhydrophilic and superhydrophobic PET surface were obtained depending on the chemistry and topography at the surface.Display Omitted► A facile method to obtain superhydrophobic surfaces. ► Tunable wetting via etching ratio, i.e. nanopattern geometry. ► Quantification of pattern stability via drop-impact studies.Polyethylene terephthalate (PET) films have been structured with isolated nanofibrils and fibril bundles using oxidative plasma treatments with increasing etching ratios. The transition from fibrils to bundles was smooth and it was associated with a significant reduction in the overall top area fraction and with the development of a second organisation level at a larger length scale. This increased complexity was reflected in the surface properties. The surfaces with two-level substructures showed superhydrophilic and superhydrophobic properties depending on the surface chemistry. These properties were preserved during prolonged storage and resisted moderate mechanical stress. By combining different contact angle and drop impact measurements, the optimum surface design and plasma processing parameters for maximizing stability of the superhydrophobic or superhydrophilic properties of the PET films were identified.
Keywords: Plasma patterning; Nanostructures; Superhydrophobic; Nanofibrils;
Improved spreading rates for monolayers applied as emulsions to reduce water evaporation by M.A. Herzig; G.T. Barnes; I.R. Gentle (239-242).
Emulsion spreading can be used to spread evaporation retarding monolayers very quickly. With careful choice of emulsifier such monolayers maintain good evaporation resistance.Display Omitted► Using emulsions to apply monolayers can dramatically raise spreading rate over powder application. ► The choice of emulsifier is critical for effective evaporation resistance. ► This work enables the use of monolayer materials that otherwise spread too slowly.To be suitable for reducing water evaporation, monolayers need to be easy to apply and also spread quickly across the surface of water. However, the choice of monolayer often involves a compromise between spreading rate and evaporation resistance. Because emulsions of the monolayer material have been suggested as a way to improve spreading, emulsions were made with the long-chain alcohols hexadecanol, octadecanol and eicosanol using the non-ionic surfactants Brij 78 and Tween 60 as emulsifying agents. The emulsions of octadecanol and eicosanol spread faster than the corresponding powder. However there was no improvement in the spreading of hexadecanol emulsion due to a significant amount of the material dispersing into the bulk water instead of spreading at the interface. The choice of emulsifier to stabilise the emulsions is critical for effective evaporation resistance. Whereas the octadecanol emulsion made with Brij 78 showed improved evaporation resistance, the emulsion with Tween 60 had an appreciably lower evaporation resistance than powdered octadecanol. One limitation of the emulsion application method is the poor spreading on surfaces with an already high surface pressure.
Keywords: Water evaporation; Langmuir monolayers; Evaporation reduction; Emulsion application;
Continuous-flow production of polymeric micelles in microreactors: Experimental and computational analysis by Lorenzo Capretto; Dario Carugo; Wei Cheng; Martyn Hill; Xunli Zhang (243-251).
The efficient, fast and tuneable mixing provided by microfluidic reactors can be used to control the self-assembly of polymeric micelles. The fluid dynamics inside the microreactors is further analyzed by a CFD model in order to asses the implications for the mixing process and controlled self-assembly of polymeric micelles.Display Omitted► A continuous flow process was developed for the production of polymeric micelles. ► Smaller and homogeneous polymeric micelles can be produced by microfluidic approaches. ► Hydrodynamics within microreactors strongly affects the nanoprecipitation process. ► The process may be extended to produce other nanomaterials with controlled characteristics.We report the development of a microfluidic-based process for the production of polymeric micelles (PMs) in continuous-flow microreactors where Pluronic® tri-block copolymer is used as model polymeric biomaterial relating to drug delivery applications. A flow focusing configuration is used enabling a controllable, and fast mixing process to assist the formation of polymeric micelles through nanoprecipitation which is triggered by a solvent exchange process when organic solutions of the polymer mixed with a non-solvent. We experientially investigate the effect of polymer concentration, flow rate ratio and microreactor dimension on the PMs size characteristics. The mixing process within the microfluidic reactors is further analyzed by computational modeling in order to understand the hydrodynamic process and its implication for the polymeric micells formation process. The results obtained show that besides the effect of the flow rate ratio, the chemical environment in which the aggregation takes place plays an important role in determining the dimensional characteristics of the produced polymeric micelles. It is demonstrated that microfluidic reactors provide a useful platform for the continuous-flow production of polymeric micelles with improved controllability, reproducibility, and homogeneity of the size characteristics.
Keywords: Polymeric micelles; Microfluidic reactors; Nanoprecipitation; Pluronic, CFD;
Steric repulsion as a way to achieve the required stability for the preparation of ionic liquid-based ferrofluids by Laura Rodríguez-Arco; Modesto T. López-López; Fernando González-Caballero; Juan D.G. Durán (252-254).
Magnetite nanoparticles coated with a double layer of oleic acid dispersed in an ionic liquid ([EMIM][EtSO4]) give rise, by steric repulsion, to a true ferrofluid: with long-life colloidal stability.Display Omitted► Suspensions of magnetic nanoparticles in ionic liquids are prepared. ► Bare nanoparticles irreversibly aggregate when dispersed in the ionic liquid. ► Electrostatic repulsion in ionic liquids seems to be screened. ► Coverage with compatible surfactant layers is required to obtain a stable ferrofluid. ► Stability in these ferrofluids is achieved by a steric repulsion mechanism.With this work we would like to emphasize the necessity of steric repulsion to stabilize novel ionic liquid-based ferrofluids. For this purpose, we prepared a suspension of magnetite nanoparticles coated with a double layer of oleic acid, dispersed in 1-ethyl-3-methylimidazolium ethylsulphate ([EMIM][EtSO4]). For comparison, a suspension of bare magnetite nanoparticles in [EMIM][EtSO4] was also prepared. The stability of these suspensions was checked by magnetic sedimentation and centrifugation processes. Furthermore, their yield stress was measured as a function of the applied magnetic field, which gave additional information on their stability. The results of these experiments showed that the suspension of bare nanoparticles was rather unstable, whereas the suspension of double layer coated nanoparticles gave rise to a true (stable) ferrofluid.
Keywords: Magnetic materials; Ferrofluid; Ionic liquid; Nanoparticle; Viscoelasticity;