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Showing papers in "Langmuir in 2009"


Journal ArticleDOI
16 Jul 2009-Langmuir
TL;DR: The results clearly indicate that the metal-free g-C(3)N(4) has good performance in photodegradation of organic pollutant.
Abstract: The g-C3N4 photocatalyst was synthesized by directly heating the low-cost melamine. The methyl orange dye (MO) was selected as a photodegrading goal to evaluate the photocatalytic activity of as-prepared g-C3N4. The comparison experiments indicate that the photocatalytic activity of g-C3N4 can be largely improved by the Ag loading. The strong acid radical ion (SO42− or NO3−) can promote the degrading rate of MO for g-C3N4 photocatalysis system. The MO degradation over the g-C3N4 is mainly attributed to the photoreduction process induced by the photogenerated electrons. Our results clearly indicate that the metal-free g-C3N4 has good performance in photodegradation of organic pollutant.

2,362 citations


Journal ArticleDOI
02 Jul 2009-Langmuir
TL;DR: This perspective reviews recent developments in the synthesis, electrochemistry, and optical properties of gold nanoparticles, with emphasis on papers initiating the developments and with an eye to their consequences.
Abstract: This perspective reviews recent developments in the synthesis, electrochemistry, and optical properties of gold nanoparticles, with emphasis on papers initiating the developments and with an eye to their consequences. Key aspects of Au nanoparticle synthesis have included the two-phase synthesis of thiolated nanoparticles, the sequestration and reduction of Au salts within dendrimers, the controlled growth of larger particles of well-defined shapes via the seeded approach, and the assembling of a variety of nanoparticle networks and nanostructures. The electrochemistry of thiolated Au nanoparticles is systemized as regions of bulk-continuum voltammetry, voltammetry reflective of quantized double-layer charging, and molecule-like voltammetry reflective of molecular energy gaps. These features are principally determined by the nanoparticle core. Interesting multielectron Au nanoparticle voltammetry is observed when the thiolate ligand shell has been decorated with redox groupings. Another development is that Au nanoparticles were discovered to exhibit unanticipated properties as heterogeneous catalysts, starting with the low-temperature oxidation of CO. Substantial progress has also been made in understanding the surface plasmon spectroscopy of Au nanoparticles and nanorods. The need to investigate the optical properties of metal particles of a single, well-defined shape and size has motivated the development of a number of new techniques, leading to the study of electron transfer and redox catalysis on single nanoparticles.

940 citations


Journal ArticleDOI
09 Jul 2009-Langmuir
TL;DR: Graphene sheets produced through chemical exfoliation of natural graphite flake and hydrazine conversion are found to be hydrophilic and hydrophobic, and isolated graphene layers seem more difficult to wet in comparison to graphite, and low adhesion work was found in the graphene-liquid interface.
Abstract: Graphene sheets were produced through chemical exfoliation of natural graphite flake and hydrazine conversion. Subsequently, graphene sheets were assembled into a thin film, and microscale liquid droplets were placed onto the film surface for measurement of wettability and contact angle. It is found that a graphene oxide sheet is hydrophilic and a graphene sheet is hydrophobic. Isolated graphene layers seem more difficult to wet in comparison to graphite, and low adhesion work was found in the graphene-liquid interface. Approximation of solid-liquid interfacial energy with the equation of state theory was applied to determine the graphene surface energy. The results indicate that surface energy of graphene and graphene oxide is 46.7 and 62.1 mJ/m2, respectively, while natural graphite flake shows a surface free energy of 54.8 mJ/m2 at room temperature. These results will provide valuable guidance for the design and manufacturing of graphene-based biomaterials, medical instruments, structural composites, electronics, and renewable energy devices.

927 citations


Journal ArticleDOI
06 Mar 2009-Langmuir
TL;DR: This work shows that after creating certain dual scale roughness structures by femtosecond laser irradiation different metal alloys initially show superhydrophilic behavior with complete wetting of the structured surface, however, over time, these surfaces become nearly super Hydrophobic with contact angles in the vicinity of 150 degrees and superHydrophobicwith contact angles above 150 degrees.
Abstract: This work shows that after creating certain dual scale roughness structures by femtosecond laser irradiation different metal alloys initially show superhydrophilic behavior with complete wetting of the structured surface. However, over time, these surfaces become nearly superhydrophobic with contact angles in the vicinity of 150° and superhydrophobic with contact angles above 150°. The contact angle hysteresis was found to lie between 2 and 6°. The change in wetting behavior correlates with the amount of carbon on the structured surface. The explanation for the time dependency of the surface wettability lies in the combined effect of surface morphology and surface chemistry.

643 citations


Journal ArticleDOI
02 Apr 2009-Langmuir
TL;DR: The chemically reduced graphene oxide nanosheets were hardly distinguishable from their unreduced counterparts in the topographic AFM images, however, they could be readily discriminated through phase imaging in the attractive regime of tapping-mode AFM, probably because of differences in hydrophilicity arising from their distinct oxygen contents.
Abstract: Graphene nanosheets produced in the form of stable aqueous dispersions by chemical reduction of graphene oxide and deposited onto graphite substrates have been investigated by atomic force and scanning tunneling microscopy (AFM/STM). The chemically reduced graphene oxide nanosheets were hardly distinguishable from their unreduced counterparts in the topographic AFM images. However, they could be readily discriminated through phase imaging in the attractive regime of tapping-mode AFM, probably because of differences in hydrophilicity arising from their distinct oxygen contents. The chemically reduced nanosheets displayed a smoothly undulated, globular morphology on the nanometer scale, with typical vertical variations in the subnanometer range and lateral feature sizes of ∼5−10 nm. Such morphology was attributed to be the result of significant structural disorder in the carbon skeleton, which originates during the strong oxidation that leads to graphene oxide and remains after chemical reduction. Direct ev...

641 citations


Journal ArticleDOI
21 Sep 2009-Langmuir
TL;DR: Graphene sheets functionalized covalently with biocompatible poly-l-lysine (PLL) were first synthesized in an alkaline solution and played an important role as connectors to assemble these active amino groups of poly- Llysine, which provided a very biOCompatible environment for further functionalization, such as attaching bioactive molecules.
Abstract: Graphene sheets functionalized covalently with biocompatible poly-l-lysine (PLL) were first synthesized in an alkaline solution. PLL-functionalized graphene is water-soluble and biocompatible, which makes it a novel material promising for biological applications. Graphene sheets played an important role as connectors to assemble these active amino groups of poly-l-lysine, which provided a very biocompatible environment for further functionalization, such as attaching bioactive molecules. As an example, an amplified biosensor toward H2O2 based on linking peroxidase onto PLL-functionalized graphene was investigated.

620 citations


Journal ArticleDOI
05 Feb 2009-Langmuir
TL;DR: This work investigated the inter-relationship between ink-jet printability and physical fluid properties by monitoring droplet formation dynamics and determined the printability of the fluids was determined using the inverse of the Ohnesorge number which relates to the viscosity, surface tension, and density of the fluid.
Abstract: Ink-jet printing is a method for directly patterning and fabricating patterns without the need for masks. To achieve this, the fluids used as inks must have the capability of being stably and accurately printed by ink-jetting. We have investigated the inter-relationship between ink-jet printability and physical fluid properties by monitoring droplet formation dynamics. The printability of the fluids was determined using the inverse (Z) of the Ohnesorge number (Oh) which relates to the viscosity, surface tension, and density of the fluid. We have experimentally defined the printable range as 4 ≤ Z ≤ 14 by considering characteristics such as single droplet formability, positional accuracy, and maximum allowable jetting frequency.

617 citations


Journal ArticleDOI
19 May 2009-Langmuir
TL;DR: Anchoring of ZnO nanoparticles on 2-D carbon nanostructures provides a new way to design semiconductor-carbon nanocomposites for catalytic applications.
Abstract: Graphene oxide sheets suspended in ethanol interact with excited ZnO nanoparticles and undergo photocatalytic reduction. The luminescence quenching of the green emission of ZnO serves as a probe to monitor the electron transfer from excited ZnO to graphene oxide. Anchoring of ZnO nanoparticles on 2-D carbon nanostructures provides a new way to design semiconductor−carbon nanocomposites for catalytic applications.

588 citations


Journal ArticleDOI
Xiaowang Liu1, Qiyan Hu1, Zhen Fang1, Xiaojun Zhang1, Beibei Zhang1 
06 Jan 2009-Langmuir
TL;DR: Synthetic magnetic chitosan nanocomposites were used as a useful recyclable tool for heavy metal ion removal and provides a potential platform for developing a unique route for heavyMetal ion removal from wastewater.
Abstract: Magnetic chitosan nanocomposites have been synthesized on the basis of amine-functionalized magnetite nanoparticles. These nanocomposites can be removed conveniently from water with the help of an external magnet because of their exceptional properties. The nanocomposites were applied to remove heavy metal ions from water because chitosan that is inactive on the surface of the magnetic nanoparticles is coordinated with them. The interaction between chitosan and heavy metal ions is reversible, which means that those ions can be removed from chitosan in weak acidic deionized water with the assistance of ultrasound radiation. On the basis of the reasons referred to above, synthesized magnetic chitosan nanocomposites were used as a useful recyclable tool for heavy metal ion removal. This work provides a potential platform for developing a unique route for heavy metal ion removal from wastewater.

481 citations


Journal ArticleDOI
10 Jul 2009-Langmuir
TL;DR: The dynamics and structure of water at hydrophobic and hydrophilic diamond surfaces is examined via non-equilibrium Molecular Dynamics simulations and the effect of the Lennard-Jones cutoff length on the interfacial properties is discussed.
Abstract: The dynamics and structure of water at hydrophobic and hydrophilic diamond surfaces is examined via non-equilibrium Molecular Dynamics simulations. For hydrophobic surfaces under shearing conditions, the general hydrodynamic boundary condition involves a finite surface slip. The value of the slip length depends sensitively on the surface water interaction strength and the surface roughness; heuristic scaling relations between slip length, contact angle, and depletion layer thickness are proposed. Inert gas in the aqueous phase exhibits pronounced surface activity but only mildly increases the slip length. On polar hydrophilic surfaces, in contrast, slip is absent, but the water viscosity is found to be increased within a thin surface layer. The viscosity and the thickness of this surface layer depend on the density of polar surface groups. The dynamics of single water molecules in the surface layer exhibits a similar distinction: on hydrophobic surfaces the dynamics is purely diffusive, while close to a h...

448 citations


Journal ArticleDOI
10 Feb 2009-Langmuir
TL;DR: The hierarchical structured surface of the lotus leaf provides a model for the development of biomimetic self-cleaning surfaces and geometric scale effects were responsible for superior performance of nanostructured surfaces.
Abstract: The hierarchical structured surface of the lotus (Nelumbo nucifera, Gaertn.) leaf provides a model for the development of biomimetic self-cleaning surfaces. On these water-repellent surfaces, water droplets move easily at a low inclination of the leaf and collect dirt particles adhering to the leaf surface. Flat hydrophilic and hydrophobic, nanostructured, microstructured, and hierarchical structured superhydrophobic surfaces were fabricated, and a systematic study of wettability and adhesion properties was carried out. The influence of contact angle hysteresis on self-cleaning by water droplets was studied at different tilt angles (TA) of the specimen surfaces (3° for Lotus wax, 10° for n-hexatriacontane, as well as 45° for both types of surfaces). At 3° and 10° TA, no surfaces were cleaned by moving water applied onto the surfaces with nearly zero kinetic energy, but most particles were removed from hierarchical structured surfaces, and a certain amount of particles were captured between the asperities ...

Journal ArticleDOI
12 Jun 2009-Langmuir
TL;DR: It is shown here that the presence of this sublayer induces a significant delay in freezing, when depositing water on cold solids, and if the substrate is slightly tilted, these drops can thus be removed without freezing and without accumulating on the substrate, a property of obvious practical interest.
Abstract: Water drops on hydrophobic microtextured materials sit on a mixture of solid and air. In standard superhydrophobic situations, the drop contacts more air than solid, so that we can think of exploiting the insulating properties of this sublayer. We show here that its presence induces a significant delay in freezing, when depositing water on cold solids. If the substrate is slightly tilted, these drops can thus be removed without freezing and without accumulating on the substrate, a property of obvious practical interest.

Journal ArticleDOI
15 Jun 2009-Langmuir
TL;DR: The data presented offer additional support for the hypothesis that zeolite crystals alter polyamide thin film structure when they are present during the interfacial polymerization reaction.
Abstract: Zeolite-polyamide thin film nanocomposite membranes were coated onto polysulfone ultrafiltration membranes by interfacial polymerization of amine and acid chloride monomers in the presence of Linde type A zeolite nanocrystals. A matrix of three different interfacial polymerization chemistries and three different-sized zeolite crystals produced nanocomposite thin films with widely varying structure, morphology, charge, hydrophilicity, and separation performance (evaluated as reverse osmosis membranes). Pure polyamide film properties were tuned by changing polymerization chemistry, but addition of zeolite nanoparticles produced even greater changes in separation performance, surface chemistry, and film morphology. For fixed polymer chemistry, addition of zeolite nanoparticles formed more permeable, negatively charged, and thicker polyamide films. Smaller zeolites produced greater permeability enhancements, but larger zeolites produced more favorable surface properties; hence, nanoparticle size may be considered an additional "degree of freedom" in designing thin film nanocomposite reverse osmosis membranes. The data presented offer additional support for the hypothesis that zeolite crystals alter polyamide thin film structure when they are present during the interfacial polymerization reaction.

Journal ArticleDOI
28 Jul 2009-Langmuir
TL;DR: Underwater applications, the oleophobicity/philicity of an oil droplet in water was studied on the surfaces with different surface energies of various interfaces and contact angles of water and oil droplets in air and a model for predicting the contact angles was proposed.
Abstract: Biomimetics, mimicking nature for engineering solutions, provides a model for the development of superhydrophobic/superoleophobic and self-cleaning surfaces. A number of biomimetic superhydrophobic surfaces have been developed by using a hydrophobic coating, surface roughness, and the ability to form air pockets between solid and water. Oleophobic surfaces that have the potential for self-cleaning and antifouling from biological and organic contaminants in both air and water need to be studied. The surface tension of oil and organic liquids is lower than that of water, so to create a superoleophobic surface, the surface energy of the solid surface in air should be lower than that of oil. The wetting behavior of water and oil droplets for hydrophobic/philic and oleophobic/philic surfaces in three-phase interfaces was studied. In order to make the surface oleophobic at a solid-air-oil interface, a material with a surface energy lower than that of oil was used. In underwater applications, the oleophobicity/philicity of an oil droplet in water was studied on the surfaces with different surface energies of various interfaces and contact angles of water and oil droplets in air. A model for predicting the contact angles of water and oil droplets was proposed. To validate the model, the wetting behavior of flat and micropatterned surfaces with varying pitch values were studied. Furthermore, the wetting behavior of the nano- and hierarchical structures found in Lotus plant surfaces and the shark skin replica as an example of aquatic animal were also studied. On the basis of the experimental data and the model, the trends were explained.

Journal ArticleDOI
13 Feb 2009-Langmuir
TL;DR: HA adsorption showed that HA-coated nano-oxides could be more easily dispersed and suspended and more stable in solution than uncoated ones because of their enhanced electrostatic repulsion.
Abstract: Adsorption of natural organic matter (NOM) on nanoparticles (NPs) is important for evaluating their transport, transfer, and fate in the environment, which will also affect sorption of hydrophobic organic compounds (HOCs) by NPs and thereby potentially alter the toxicity of NPs and the fate, transport, and bioavailability of HOCs in the environment. Therefore, the adsorption behavior of humic acids (HA) by four types of nano-oxides (i.e., TiO2, SiO2, Al2O3, and ZnO) was examined in this study to explore their interaction mechanisms using techniques including Fourier transform infrared (FTIR) spectroscopy and elemental, ζ potential, and surface area analyses. Adsorption of HA was observed on nanosized TiO2, Al2O3, and ZnO but not on nano-SiO2. Furthermore, HA adsorption was pH-dependent. HA adsorption by nano-oxides was mainly induced by electrostatic attraction and ligand exchange between HA and nano-oxide surfaces. Surface hydrophilicity and negative charges of nano-oxides affected their adsorption of HA...

Journal ArticleDOI
18 Aug 2009-Langmuir
TL;DR: An entangled network of flexible fibrils forming a weak hydrogel dominates at high pH, while nongelling flat rigid ribbons form at intermediate pH values, which provides further understanding of the self-assembly mechanism of aromatic short peptide derivatives.
Abstract: We report the effect of pH on the self-assembly process of Fmoc-diphenylalanine (Fmoc-FF) into fibrils consisting of antiparallel β-sheets, and show that it results in two apparent pKa shifts of ∼6.4 and ∼2.2 pH units above the theoretical pKa (3.5). Using Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), wide angle X-ray scattering (WAXS), and oscillatory rheology, these two transitions were shown to coincide with significant structural changes. An entangled network of flexible fibrils forming a weak hydrogel dominates at high pH, while nongelling flat rigid ribbons form at intermediate pH values. Overall, this study provides further understanding of the self-assembly mechanism of aromatic short peptide derivatives.

Journal ArticleDOI
06 Apr 2009-Langmuir
TL;DR: The synthesis of cellulose nanocrystals grafted by polystyrene chains via surface-initiated ATRP is reported, able to produce cellulose nanoparticles with varying grafting densities and varying polymer brush length through polymerization control.
Abstract: This paper reports the synthesis of cellulose nanocrystals grafted by polystyrene chains via surface-initiated ATRP. Naturally occurring cellulose was first hydrolyzed to obtain cellulose nanocrystals. Their surface was then chemically modified using 2-bromoisobutyryl bromide to introduce initiating sites for ATRP. A varying extent of surface modification was achieved by changing reaction conditions. Further initiation of styrene polymerization from these modified nanocrystals with a CuBr/PMDETA (N,N,N′,N′,N′′-pentamethyldiethylenetriamine) catalytic system and in the presence of a sacrificial initiator produced polysaccharide nanocrystals grafted by polystyrene chains. A range of nanocrystals-g-polystyrene with different graft lengths (theoretical polymerization degree = 27−171) was synthesized through this method and characterized by elemental analysis, XPS, FT-IR, TEM, and contact angle measurements. We are thus able to produce cellulose nanoparticles with varying grafting densities (by altering extent...

Journal ArticleDOI
07 Jul 2009-Langmuir
TL;DR: This work measured the adhesion strength of artificially created glaze ice on rough fluoropolymer-based hydrophobic surfaces with different contact angle (CA) and wetting hysteresis to show a direct correlation between ice repellency and CA on superhydrophilic surfaces.
Abstract: In this work, we measured the adhesion strength of artificially created glaze ice (similar to accreted in nature) on rough fluoropolymer-based hydrophobic surfaces with different contact angle (CA) and wetting hysteresis. The previously reported direct correlation between ice repellency and CA on superhydrophobic surfaces is shown to be only valid for surfaces with low wetting hysteresis. Another correlation was found between wetting hysteresis and ice adhesion strength on rough surfaces with similar chemistry.

Journal ArticleDOI
24 Aug 2009-Langmuir
TL;DR: The central Fe3O4 cores are superparamagnetic at room temperature with strong magnetic response to externally applied magnetic field, thus providing a convenient means for separating the nanocomposite from solution.
Abstract: We report a new method to synthesize magnetically responsive Fe3O4@polyaniline@Au nanocomposites. The superparamagnetic Fe3O4@polyaniline with well-defined core/shell nanostructure has been synthesized via an ultrasound-assisted in situ surface polymerization method. The negatively charged Au nanoparticles with a diameter of about 4 nm have been effectively assembled onto the positively charged surface of the as-synthesized Fe3O4@polyaniline core/shell microspheres via electrostatic attraction. The morphology, phase composition, and crystallinity of the as-prepared nanocomposites have been characterized by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The central Fe3O4 cores are superparamagnetic at room temperature with strong magnetic response to externally applied magnetic field, thus providing a convenient means for separating the nanocomposite from solution. As-prepared inorganic/organic nanocomposite can be used as a magnetically recoverable nanocatalyst for the reduction of a selected substrate.

Journal ArticleDOI
06 Apr 2009-Langmuir
TL;DR: Small incidence angle X-ray diffraction revealed that the nanocrystal and MFC films exhibited a cellulose I crystal structure and that the films prepared from N-methylmorpholine-N-oxide, LiCl/DMAc solutions, using the Langmuir-Schaefer technique, possessed a cellulOSE II structure.
Abstract: A systematic study of the degree of molecular ordering and swelling of different nanocellulose model films has been conducted. Crystalline cellulose II surfaces were prepared by spin-coating of the precursor cellulose solutions onto oxidized silicon wafers before regeneration in water or by using the Langmuir−Schaefer (LS) technique. Amorphous cellulose films were also prepared by spin-coating of a precursor cellulose solution onto oxidized silicon wafers. Crystalline cellulose I surfaces were prepared by spin-coating wafers with aqueous suspensions of sulfate-stabilized cellulose I nanocrystals and low-charged microfibrillated cellulose (LC-MFC). In addition, a dispersion of high-charged MFC was used for the buildup of polyelectrolyte multilayers with polyetheyleneimine on silica with the aid of the layer-by-layer (LbL) technique. These preparation methods produced smooth thin films on the nanometer scale suitable for X-ray diffraction and swelling measurements. The surface morphology and thickness of th...

Journal ArticleDOI
23 Apr 2009-Langmuir
TL;DR: The strategy proposed is based on the freeze-drying of aqueous solutions containing the individual counterparts of DES and the preformed liposomes (also known as large unilamellar vesicles or LUV), which should make it suitable for the incorporation of different self-assembled structures in DES in its pure state.
Abstract: This work describes how the preparation of deep eutectic solvents (DES) in its pure state can be accomplished through a simple approach based on the freeze-drying of aqueous solutions of the individual counterparts of DES. DES in its pure state obtained via freeze-drying are studied by 1H NMR, which reveals the formation of halide ion−hydrogen-bond-donor supramolecular complexes (characteristic of DES), and by cryo-etch-SEM, which provides insight about the capability of aqueous solutions of DES to be segregated in DES and ice upon freezing. The paper also explores the suitability of the freeze-drying approach to incorporate organic self-assemblies (in particular, liposomes of ca. 200 nm) in DES with full preservation of their self-assembled structure. This is not a trivial issue given that amphiphilic molecules tend to be readily dissolved (hence, disassembled) in DES. The strategy proposed in this work is based on the freeze-drying of aqueous solutions containing the individual counterparts of DES and t...

Journal ArticleDOI
08 Sep 2009-Langmuir
TL;DR: It is proved that control of plasma nanotexture can be achieved by carefully choosing the reactor wall material and X-ray photoelectron spectroscopy is used to study the surface chemical modification in the plasma.
Abstract: Plasma processing is used to fabricate super hydrophilic or super hydrophobic polymeric surfaces by means of O-2 plasma etching of two organic polymers, namely, poly(methyl methacrylate) (PMMA) and poly(ether ether ketone) (PEEK); a C4F8 plasma deposition follows O-2 plasma etching, if surface hydrophobization is desired. We demonstrate high aspect ratio pillars with height ranging from 16 nm to several micrometers depending oil the processing time, and contact angle (CA) close to 0 degrees after O-2-Plasma treatment or CA of 153 degrees (with CA hysteresis lower than 5 degrees) after fluorocarbon deposition. Super hydrophobic surfaces are robust and stable in time; in addition, aging of super hydrophilic surfaces is significantly retarded because of the beneficial effect of the nanotextured topography. The mechanisms responsible for the plasma-induced PMMA and PEEK surface nanotexturing are unveiled through intelligent experiments involving intentional modification of the reactor wall material and X-ray photoelectron spectroscopy, which is also used to study the surface chemical modification in the plasma. We prove that control of plasma nanotexture call be achieved by carefully choosing the reactor wall material.

Journal ArticleDOI
29 Apr 2009-Langmuir
TL;DR: A robust and cost-effective coating method to fabricate long-term durable superhydrophobic and simultaneousantireflective surfaces by a double-layer coating comprising trimethylsiloxane surface-functionalized silica nanoparticles partially embedded into an organosilica binder matrix produced through a sol-gel process.
Abstract: We present a robust and cost-effective coating method to fabricate long-term durable superhydrophobic and—simultaneously—antireflective surfaces by a double-layer coating comprising trimethylsiloxane (TMS) surface-functionalized silica nanoparticles partially embedded into an organosilica binder matrix produced through a sol−gel process A dense and homogeneous organosilica gel layer was first coated onto a glass substrate, and then, a trimethylsilanized nanospheres-based superhydrophobic layer was deposited onto it After thermal curing, the two layers turned into a monolithic film, and the hydrophobic nanoparticles were permanently fixed to the glass substrate Such treated surfaces showed a tremendous water repellency (contact angle = 168°) and stable self-cleaning effect during 2000 h of outdoor exposure Besides this, nanotextured topology generated by the self-assembled nanoparticles-based top layer produced a fair antireflection effect consisting of more than a 3% increase in optical transmittance

Journal ArticleDOI
Jianchun Wang1, Ping Liu1, Xianzhi Fu1, Zhaohui Li1, Wei Han1, Xuxu Wang1 
20 Jan 2009-Langmuir
TL;DR: Photocatalytic activity measurements show that the sample with a higher amount of oxygen defects exhibits excellent activity toward the degradation of rhodamine B, and the oxygen defects are proposed to be the active sites of the ZnO photocatalyst.
Abstract: ZnO nanocrystals with different oxygen defects (type and concentration) are successfully prepared via the templating method in Nafion membranes. Photoluminescence and infrared characterizations reveal that the concentration of oxygen defects (oxygen vacancy and interstitial oxygen) is quite different for the samples prepared via different synthesis processes. Photocatalytic activity measurements show that the sample with a higher amount of oxygen defects exhibits excellent activity toward the degradation of rhodamine B. Compared with bulk ZnO, ZnO nanocrystals embedded in Nafion membranes have an antiphotocorrosion property. The possible photocatalytic mechanism is discussed in detail, and the oxygen defects are proposed to be the active sites of the ZnO photocatalyst.

Journal ArticleDOI
03 Sep 2009-Langmuir
TL;DR: The observed pH effects on adsorption indicate that the protonated neutral form of sulfonamide adsorbs much more strongly than the deprotonated anionic counterpart does.
Abstract: The presence of sulfonamide antibiotics in aquatic environments has been recognized as an issue warranting consideration. In this study, we evaluated multiwalled carbon nanotubes (MWNT) as a potential effective adsorbent for removal of two sulfonamide antibiotics, sulfapyridine and sulfamethoxazole, from aqueous solutions. Nonporous, functionality-free graphite was included as a comparative adsorbent. Despite the very low hydrophobicity, the two sulfonamides adsorbed strongly to MWNT and graphite, a fact attributed to π−π electron coupling with the graphene surface of the adsorbent. For both sulfonamide antibiotics, similar patterns of pH-dependent adsorption were observed between MWNT and graphite, implying the predominance of graphene structures for the adsorption to MWNT. Moreover, the observed pH effects on adsorption indicate that the protonated neutral form of sulfonamide adsorbs much more strongly than the deprotonated anionic counterpart does. The effects of ionic strength (NaCl and CaCl2) and the...

Journal ArticleDOI
03 Feb 2009-Langmuir
TL;DR: The mechanical properties of these monolayers, as measured by surface shear rheology, showed that the monolayer of ellipsoids exhibit a substantial surface modulus even at low surface coverage and can be used to create more elastic monol layers compared to aggregate networks of spheres of the same size and surface properties.
Abstract: Colloidal particles confined at liquid interfaces have important applications, for example in the stabilization of emulsions and foams. Also the self-assembly of particles at interfaces offers potential for novel applications and structured particle films. As the colloidal interactions of colloidal particles at interfaces differ from those in bulk, colloidal microstructures can be achieved at an interface which cannot be produced in bulk. In the present work the particle shape, surface charge, and wetting properties are varied, and the resulting self-assembly of particles at a fluid interface is studied. Model monodisperse micrometer-sized ellipsoidal particles were prepared by a mechanical stretching method. These particles were chosen to be well-suited for investigation by optical microscopy. When deposited at an interface between two fluids, shape-induced capillary interactions compete with the electrostatic repulsion. Changing the surface charge and the position at the interface can be used to manipulate the experimentally observed self-assembly process. The initial microstructure of charged ellipsoids at a decane-water interface consists of individual ellipsoids coexisting with linear chains of ellipsoids, connected at their tips. The aggregation behavior in these monolayers was investigated by optical microscopy combined with quantitative image analysis and a dominant tip-tip aggregation was observed. Microstructural information was quantified by calculating the pair-distribution and orientation-distribution functions, as a function of time. Compared to particles at an oil-water interface, particles of the same surface chemistry and charge at an air-water interface seem to have weaker electrostatic interactions, and they also have a different equilibrium position at the interface. The latter leads to differences in the capillary forces. The subsequent change in the balance between electrostatic and capillary forces gave rise to very dense networks having as a typical building block ellipsoids connected at their tips in triangular or flower-like configuration. These networks were very stable and did not evolve in time. The resulting monolayers responded elastically and buckled under compression. Furthermore, the mechanical properties of these monolayers, as measured by surface shear rheology, showed that the monolayer of ellipsoids exhibit a substantial surface modulus even at low surface coverage and can be used to create more elastic monolayers compared to aggregate networks of spheres of the same size and surface properties.

Journal ArticleDOI
22 Jan 2009-Langmuir
TL;DR: It proved to be essential to add the nanoparticle layer in achieving superoleophobicity, especially in terms of low roll-off angles for hexadecane, and was successfully obtained by incorporating perfluoroalkyl groups onto the surface of the modified cotton.
Abstract: Common cotton textiles are hydrophilic and oleophilic in nature. Superhydrophobic cotton textiles have the potential to be used as self-cleaning fabrics, but they typically are not super oil-repellent. Poor oil repellency may easily compromise the self-cleaning property of these fabrics. Here, we report on the preparation of superoleophobic cotton textiles based on a multilength-scale structure, as demonstrated by a high hexadecane contact angle (153° for 5 μL droplets) and low roll-off angle (9° for 20 μL droplets). The multilength-scale roughness was based on the woven structure, with additional two layers of silica particles (microparticles and nanoparticles, respectively) covalently bonded to the fiber. Superoleophobicity was successfully obtained by incorporating perfluoroalkyl groups onto the surface of the modified cotton. It proved to be essential to add the nanoparticle layer in achieving superoleophobicity, especially in terms of low roll-off angles for hexadecane.

Journal ArticleDOI
07 Jul 2009-Langmuir
TL;DR: It is demonstrated that the polyCBAA surfaces after antibody immobilization maintain undetectable protein adsorption from undiluted human blood serum, which is the first time that an effective nonfouling material suitable for applications in complex blood media has been demonstrated.
Abstract: Human blood serum and plasma pose significant challenges to blood-contacting devices and implanted materials because of their high nonspecific adsorption onto surfaces. In this work, we investigated nonspecific protein adsorption from single protein solutions and complex media such as undiluted human blood serum and plasma onto poly(carboxybetaine acrylamide) (polyCBAA)-grafted surfaces at different temperatures. The polyCBAA grafting was done via atom-transfer radical polymerization (ATRP) with varying film thicknesses. The objective is to create a surface that experiences “zero” protein adsorption from complex undiluted human blood serum and plasma. Results show that protein adsorption from undiluted human blood serum, plasma, and aged serum on the polyCBAA-grafted surface is undetectable at both 25 and 37 °C by a surface plasmon resonance (SPR) sensor. This was achieved with a film thickness of ∼21 nm. Furthermore, it is demonstrated that the polyCBAA surfaces after antibody immobilization maintain und...

Journal ArticleDOI
21 Jul 2009-Langmuir
TL;DR: The results suggest that the kinetics of the interfacial lithium ion transfer at graphite is influenced by the compositions of SEI films as well as the desolvation of lithium ion from solvent molecules.
Abstract: The kinetics of lithium ion transfer at an interface between graphite and liquid electrolyte was studied by ac impedance spectroscopy. Using highly oriented pyrolytic graphite (HOPG) as a model electrode, we evaluated the activation energies of the interfacial lithium ion transfer from the temperature dependences of the interfacial conductivities. When a binary electrolyte consisting of LiClO4 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by volume) was used, the activation energy of the interfacial lithium ion transfer was 58 kJ mol−1, while an electrolyte consisting of LiClO4 dissolved in DMC gave an activation energy of 40 kJ mol−1. A calculation with the density functional theory clarified that the solvation ability of EC is higher than that of DMC. Therefore, we concluded that the activation energies of the interfacial lithium ion transfer at graphite reflected the energies for the desolvation of lithium ion from the solvent molecule. Furthermore, the activation ...

Journal ArticleDOI
13 Mar 2009-Langmuir
TL;DR: The experimental results indicate that the trans-azobenzene units are bound strongly within the cavities of 2 whereas the cis-azabenzene is not bound at all.
Abstract: A deoxycholic acid-modified β-cyclodextrin derivative (2) and an azobenzene-branched poly(acrylic acid) copolymer (3) were prepared, and the association and dissociation of 2 with the trans/cis-azobenzene units in 3 were characterized by UV/vis spectroscopy, induced circular dichroism, and 1H NMR spectroscopy. The experimental results indicate that the trans-azobenzene units are bound strongly within the cavities of 2 whereas the cis-azobenzene is not bound at all. A supramolecular inclusion complex (1), formed by 2 and 3, is accompanied by the formation of a hydrogel. The light-responsive gel-to-sol and sol-to-gel phase transitions of the hydrogel, induced by trans-cis photoisomerization of the azobenzene units, were investigated. In the hydrogel system, the trans-azobenzene units in 3 are included inside the hydrophobic cavity of 2. Upon photoirradiation with UV light of 355 nm, the hydrogel is converted efficiently to the sol phase because the trans-azobenzene units are converted photochemically to the...