Showing papers in "Langmuir in 2013"
TL;DR: Results give rise to a verified structural assignment of PDA wherein dihydroxyindole and indoledione units with different degrees of (un)saturation are covalently linked by C-C bonds between their benzene rings.
Abstract: Polydopamine (PDA) formed by the oxidation of dopamine is an important polymer, in particular, for coating various surfaces. It is composed of dihydroxyindole, indoledione, and dopamine units, which are assumed to be covalently linked. Although PDA has been applied in a manifold way, its structure is still under discussion. Similarities have been observed in melanins/eumelanins as naturally occurring, deeply colored polymer pigments derived from l-DOPA. Recently, an alternative structure was proposed for PDA wherein dihydroxyindoline, indolinedione, and eventually dopamine units are not covalently linked to each other but are held together by hydrogen bonding between oxygen atoms or π stacking. In this study, we show that this structural proposal is very unlikely to occur taking into account unambiguous results obtained by different analytical methods, among them 13C CPPI MAS NMR (cross-polarization polarization–inversion magic angle spinning NMR), 1H MAS NMR (magic angle spinning NMR), and ES-HRMS (elect...
795 citations
TL;DR: Chemical and physical characterization of polydopamine films deposited on gold surfaces from stirred basic solutions at times ranging from 2 to 60 min are reported, with a focus on times ≤10 min.
Abstract: Current interest in melanin films derived from the autoxidation of dopamine stems from their use as a universal adhesion layer. Here we report chemical and physical characterization of polydopamine films deposited on gold surfaces from stirred basic solutions at times ranging from 2 to 60 min, with a focus on times ≤10 min. Data from Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical methods suggest the presence of starting (dopamine) and intermediate (C=N-containing tautomers of quinone and indole) species in the polydopamine films at all deposition times. A uniform overlayer analysis of the XPS data indicates that film thickness increased linearly at short deposition times of ≤10 min. At deposition times ≥10 min, the films appeared largely continuous with surface roughness ≈ ≤ 2 nm, as determined by atomic force microscopy (AFM). Pinhole-free films, as determined by anionic redox probe measurements, required deposition times of 60 min or greater.
702 citations
TL;DR: The INTERFACE force field operates as an extension of common harmonic force fields by employing the same functional form and combination rules to enable simulations of in organic-organic and inorganic-biomolecular interfaces and increases the transferability of the parameters by introducing thermodynamic consistency.
Abstract: The complexity of the molecular recognition and assembly of biotic–abiotic interfaces on a scale of 1 to 1000 nm can be understood more effectively using simulation tools along with laboratory instrumentation. We discuss the current capabilities and limitations of atomistic force fields and explain a strategy to obtain dependable parameters for inorganic compounds that has been developed and tested over the past decade. Parameter developments include several silicates, aluminates, metals, oxides, sulfates, and apatites that are summarized in what we call the INTERFACE force field. The INTERFACE force field operates as an extension of common harmonic force fields (PCFF, COMPASS, CHARMM, AMBER, GROMACS, and OPLS-AA) by employing the same functional form and combination rules to enable simulations of inorganic–organic and inorganic–biomolecular interfaces. The parametrization builds on an in-depth understanding of physical–chemical properties on the atomic scale to assign each parameter, especially atomic ch...
652 citations
TL;DR: The synergistic effect between graphene and ZnO1-x for high separation efficiency of photoinduced electron-hole pairs mainly resulting from the promotion of HOMO orbit of graphene and the Oi″ defect level of ZnNO 1-x in Zn o-x/graphene was attributed.
Abstract: ZnO1–x/graphene hybrid photocatalyst was prepared via a facile in-situ reduction of graphene oxide and ZnO1–x surface defect oxide. The hybrid photocatlayst showed enhanced photocatalytic activity for the photodegradation of methylene blue. The photocorrosion of ZnO1–x was successfully inhibited by graphene hybridation. ZnO1–x/graphene hybrid photocatalyst with 1.2 wt % graphene showed the optimized photocatalytic activity. The photocatalytic activity of ZnO1–x/graphene-1.2 wt % under visible and UV light was about 4.6 and 1.2 times that of ZnO1–x sample, respectively. The photocurrent intensity of ZnO1–x under visible and UV light irradiation can be enhanced by 2 and 3.5 times by graphene hybridization. The enhancement of photocatalytic activity and photocurrent intensity in ZnO1–x/graphene was attributed to the synergistic effect between graphene and ZnO1–x for high separation efficiency of photoinduced electron–hole pairs mainly resulting from the promotion of HOMO orbit of graphene and the Oi″ defect ...
451 citations
TL;DR: It is shown that a variation of the contact angle from 90° on graphite to 127° on graphene would imply that both of the first two carbon layers of graphite contribute approximately the same interaction energy with water, which is incompatible with the short-range nature of the interaction between water and this substrate.
Abstract: Although experimental and theoretical studies have addressed the question of the wetting properties of graphene, the actual value of the contact angle of water on an isolated graphene monolayer remains unknown. While recent experimental literature indicates that the contact angle of water on graphite is in the range 90–95°, it has been suggested that the contact angle on graphene may either be as high as 127° or moderately enhanced in comparison with graphite. With the support of classical molecular dynamics simulations using empirical force-fields, we develop an argumentation to show that the value of 127° is an unrealistic estimate and that a value of the order of 95–100° should be expected. Our study establishes a connection between the variation of the work of adhesion of water on graphene-based surfaces and the interaction potential between individual water molecules and these surfaces. We show that a variation of the contact angle from 90° on graphite to 127° on graphene would imply that both of the...
422 citations
TL;DR: The cross-linked substituted tobermorite model, CSTM, provides a more advanced description of the chemistry and structure of calcium-sodium aluminosilicate gel structures than that previously established in the literature.
Abstract: Structural models for the primary strength and durability-giving reaction product in modern cements, a calcium (alumino)silicate hydrate gel, have previously been based solely on non-cross-linked tobermorite structures. However, recent experimental studies of laboratory-synthesized and alkali-activated slag (AAS) binders have indicated that the calcium-sodium aluminosilicate hydrate [C-(N)-A-S-H] gel formed in these systems can be significantly cross-linked. Here, we propose a model that describes the C-(N)-A-S-H gel as a mixture of cross-linked and non-cross-linked tobermorite-based structures (the cross-linked substituted tobermorite model, CSTM), which can more appropriately describe the spectroscopic and density information available for this material. Analysis of the phase assemblage and Al coordination environments of AAS binders shows that it is not possible to fully account for the chemistry of AAS by use of the assumption that all of the tetrahedral Al is present in a tobermorite-type C-(N)-A-S-H gel, due to the structural constraints of the gel. Application of the CSTM can for the first time reconcile this information, indicating the presence of an additional activation product that contains highly connected four-coordinated silicate and aluminate species. The CSTM therefore provides a more advanced description of the chemistry and structure of calcium-sodium aluminosilicate gel structures than that previously established in the literature.
372 citations
TL;DR: A novel approach that combines experimental measurements and theoretical calculations was used to determine the aggregation kinetics of GO sheets in aqueous solutions under different chemistry conditions, suggesting that edge-to-edge and face- to-face interactions were the dominant modes of GO aggregation in the presence of divalent metal ions and H(+), respectively.
Abstract: Although graphene oxide (GO) has been used in many applications to improve human life quality, its environmental fate and behavior are still largely unknown. In this work, a novel approach that combines experimental measurements and theoretical calculations was used to determine the aggregation kinetics of GO sheets in aqueous solutions under different chemistry conditions (e.g., cation valence and pH). Experimental data showed that both cation valence and pH showed significant effect on the aggregation of GO sheets. The measured critical coagulation concentrations were in good agreement with the predictions of the extended Schulze–Hardy rule. Ca2+ and Mg2+ were more effective than Na+ in aggregating the GO sheets, which could be attributed to the cross-linking between GO sheets by the divalent cations through “bridging” the functional groups at the edges of the GO sheets. When solution pH increases, deprotonation of carboxylic groups was found to play a key role in increasing GO sheet stability and surfa...
365 citations
TL;DR: The structural characterizations confirmed the formation of Co-N bonds and the close electron coupling between Co-g-C3N4 and graphene sheets, and bodes well for a promising non-noble cathode catalyst for the application of direct methanol fuel cells.
Abstract: Graphitic carbon nitride (g-C3N4) polymer was doped with cobalt species and supported on a similar sp2 structure graphene, to form a novel nitrogen–metal macrocyclic catalyst for the oxygen reduction reaction (ORR) in alkaline fuel cells. The structural characterizations confirmed the formation of Co–N bonds and the close electron coupling between Co-g-C3N4 and graphene sheets. The electrocatalytic measurements demonstrated Co-g-C3N4-catalyzed reduction of oxygen mainly in a four electron pathway. The improvement of ORR activity is closely related to the abundant accessible Co–Nx active sites and fast charge transfer at the interfaces of Co-g-C3N4/graphene. Also, Co-g-C3N4@graphene exhibited comparable ORR activity, better durability, and methanol tolerance ability in comparison to Pt/C, and bodes well for a promising non-noble cathode catalyst for the application of direct methanol fuel cells. The chemical doping strategy in this work would be helpful to improve other present catalysts for fuel cell appl...
359 citations
TL;DR: Interestingly, polyguanidino oxanorbornenes stabilizes the silver nanoparticles better than PA as evident from the spectroscopic data.
Abstract: We report the facile one-pot single-phase syntheses of silver nanoparticles stabilized by norbornene type cationic polymers. Silver nanoparticles (AgNPs) stabilized by polyguanidino oxanorbornenes (PG) at 5 and 25 kDa and polyamino oxanorbornenes (PA) at 3 and 15 kDa have been synthesized by the reduction of silver ions with NaBH4 in aqueous solutions at ambient temperature. The four different silver nanoparticles have been characterized by UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and transmission electron microscopy (TEM) for their particle size distributions. Interestingly, PG stabilizes the silver nanoparticles better than PA as evident from our spectroscopic data. Furthermore, the AgNP-PG-5K (5K = 5 kDa) was found to serve as an effective catalyst for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4. The reduction has a pseudo-first-order rate constant of 5.50 × 10–3 s–1 and an activity parameter of 1375 s–1 g–1, which...
334 citations
TL;DR: By applying the electrochemical driving force sufficiently slowly it was possible to measure the electrodes at equilibrium conditions and verify by spectroscopy, microscopy, and diffractometry that these electrodes undergo fully reversible structural changes upon Mg-ion insertion/deinsertion cycling.
Abstract: Electrochemical, surface, and structural studies related to rechargeable Mg batteries were carried out with monolithic thin-film cathodes comprising layered V2O5 and MoO3. The reversible intercalation reactions of these electrodes with Mg ion in nonaqueous Mg salt solutions were explored using a variety of analytical tools. These included slow-scan rate cyclic voltammetry (SSCV), chrono-potentiometry (galvanostatic cycling), Raman and photoelectron spectroscopies, high-resolution microscopy, and XRD. The V2O5 electrodes exhibited reversible Mg-ion intercalation at capacities around 150-180 mAh g(-1) with 100% efficiency. A capacity of 220 mAh g(-1) at >95% efficiency was obtained with MoO3 electrodes. By applying the electrochemical driving force sufficiently slowly it was possible to measure the electrodes at equilibrium conditions and verify by spectroscopy, microscopy, and diffractometry that these electrodes undergo fully reversible structural changes upon Mg-ion insertion/deinsertion cycling.
333 citations
TL;DR: It is demonstrated that the process of freezing subcooled condensate and frost formation on such lubricant-impregnated surfaces is accompanied by the migration of the lubricant from the wetting ridge and from within the textured substrate to the surface of frozen droplets.
Abstract: Frost formation is a major problem affecting a variety of industries including transportation, power generation, construction, and agriculture. Currently used active chemical, thermal, and mechanical techniques of ice removal are time-consuming and costly. The use of nanotextured coatings infused with perfluorinated oil has recently been proposed as a simple passive antifrosting and anti-icing method. However, we demonstrate that the process of freezing subcooled condensate and frost formation on such lubricant-impregnated surfaces is accompanied by the migration of the lubricant from the wetting ridge and from within the textured substrate to the surface of frozen droplets. For practical applications, this mechanism can comprise the self-healing and frost-repelling characteristics of lubricant impregnated-surfaces, regardless of the underlying substrate’s topography. Thus, further research is necessary to develop liquid-texture pairs that will provide a sustainable frost suppression method.
TL;DR: Results indicated that a significant fraction of the amines of the chitosan were inserted between the GO layers and reacted with carboxyl and epoxy groups of GO, leading to its reduction and hence the destruction of the layered structure.
Abstract: In the current study, the functionalization of graphite oxide (GO) with magnetic chitosan (Chm) was investigated to prepare a nanocomposite material (GO-Chm) for the adsorption of a reactive dye (Reactive Black 5). The synthesis mechanism was investigated by various techniques (SEM/EDAX, FTIR spectroscopy, XRD, XPS, DTA, DTG, VSM). Characterization results indicated that a significant fraction of the amines of the chitosan (i) were inserted between the GO layers and (ii) reacted with carboxyl and epoxy groups of GO, leading to its reduction and hence the destruction of the layered structure. The concentrations of iron were found to be ∼25% for Chm and ∼12% for GO-Chm. A VSM plot presents the value of 9 emu/g for the saturation magnetization of GO-Chm. The adsorption behavior of the prepared composite was elucidated with a series of experiments. The tests of the effects of pH revealed that the adsorption mechanism dominated (between dye molecules and the GO-Chm matrix) and showed that acidic conditions were the optimum for the adsorption process (pH 3). Kinetic experiments presented the relatively "fast" adsorption phenomenon using pseudo-first-order, pseudo-second-order, and modified pseudo-second-order equations. The equilibrium data were fitted to the Langmuir, Freundlich, and Langmuir-Freundlich (L-F) models, calculating the maximum adsorption capacities at 25, 45, and 65 °C (391, 401, and 425 mg/g, respectively). Thermodynamic analysis was also performed to calculate the changes in free energy (ΔG(0)), enthalpy (ΔH(0)), and entropy (ΔS(0)).
TL;DR: The design rules developed in this work can be applied to select a mesh surface with optimal topography and wetting characteristics to harvest enhanced water fluxes over a wide range of natural convected fog environments.
Abstract: Fog represents a large untapped source of potable water, especially in arid climates. Numerous plants and animals use textural and chemical features on their surfaces to harvest this precious resource. In this work, we investigate the influence of the surface wettability characteristics, length scale, and weave density on the fog-harvesting capability of woven meshes. We develop a combined hydrodynamic and surface wettability model to predict the overall fog-collection efficiency of the meshes and cast the findings in the form of a design chart. Two limiting surface wettability constraints govern the re-entrainment of collected droplets and clogging of mesh openings. Appropriate tuning of the wetting characteristics of the surfaces, reducing the wire radii, and optimizing the wire spacing all lead to more efficient fog collection. We use a family of coated meshes with a directed stream of fog droplets to simulate a natural foggy environment and demonstrate a five-fold enhancement in the fog-collecting eff...
TL;DR: The results suggest that narrow graphene pores functionalized with hydroxyl groups remain effective at excluding Cl(-) ions even at moderate solution ionic strength, which could be useful for the design of water desalination membranes.
Abstract: Molecular dynamics simulations were employed to study the transport of water and ions through pores created on the basal plane of one graphene sheet (GS). Graphene pore diameters ranged from 7.5 to 14.5 A. Different pore functionalities were considered, obtained by tethering various functional groups to the terminal carbon atoms. The ease of ion and water translocation across the pores was monitored by calculating the potential of mean force along the direction perpendicular to the GS pore. The results indicate that effective ion exclusion can be achieved only using nonfunctionalized (pristine) pores of diameter ∼7.5 A, whereas the ions can easily penetrate pristine pores of diameters ∼10.5 and 14.5 A. Carboxyl functional groups can enhance ion exclusion for all pores considered, but the effect becomes less pronounced as both the ion concentration and the pore diameter increase. When compared to a carbon nanotube of similar pore diameter, our results suggest that GS pores functionalized with COO– groups a...
TL;DR: This is the first report on the synthesis of Zr-codoped Ag-ZnO and its use in the degradation of RR 120 dye under natural sunlight illuminatioin and this catalyst is found to be reusable.
Abstract: The different wt % of Zr-codoped Ag–ZnO catalysts were prepared by the simple precipitation–thermal decomposition method and used for degradation of anionic azo dye Reactive Red 120 (RR 120) under natural sunlight. Highly efficient 4 wt % of Zr-codoped Ag–ZnO was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM) images, field emission scanning electron microscope (FE-SEM) images, energy-dispersive spectra (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and BET surface area measurements. Metal codopants increase the absorbance of ZnO to the entire visible region. XRD and XPS reveal that Ag is in the form of Ag0 and Zr in the form of Zr4+. The photocatalytic activity of 4 wt % Zr-codoped Ag–ZnO was compared with other single-metal-doped, undoped, and commercial catalysts. The quantum yields of all processes were determined and analyzed. Zr–Ag–ZnO was found to be more e...
TL;DR: The results obtained here serve as a basis to select Au@Ag core-shell NPs of specific size and composition with maximum SERS efficiency at their respective excitation wavelengths for SERS-based analytical and bioimaging applications.
Abstract: We describe a simple and efficient methodology for the aqueous synthesis of stable, uniform, and size tunable Au@Ag core–shell nanoparticles (NPs) that are stabilized by citrate ions. The synthetic route is based on the stepwise Ag reduction on preformed Au NPs. The final size of the core–shell NPs and therefore their optical properties can be modulated at least from 30 to 110 nm by either tuning the Ag shell thickness or changing the size of the Au core. The optical properties of the Au@Ag core–shell NPs resemble those of pure Ag NPs of similar sizes, which was confirmed by means of Mie extinction calculations. We additionally evaluated the surface-enhanced raman scattering (SERS) enhancing properties of Au@Ag core–shell NP colloids with three different laser lines (532, 633, and 785 nm). Importantly, such core–shell NPs also exhibit a higher SERS efficiency than Ag NPs of similar size under near-infrared excitation. The results obtained here serve as a basis to select Au@Ag core–shell NPs of specific si...
TL;DR: Two types of metal-organic frameworks have been synthesized and evaluated in the separation of C2 and C3 olefins and paraffins and the zeolitic imidazolate framework ZIF-8 behaves in the opposite way and preferentially adsorbs the alkane.
Abstract: Two types of metal–organic frameworks (MOFs) have been synthesized and evaluated in the separation of C2 and C3 olefins and paraffins. Whereas Co2(dhtp) (=Co–CPO-27 = Co–MOF-74) and Mg2(dhtp) show an adsorption selectivity for the olefins ethene and propene over the paraffins ethane and propane, the zeolitic imidazolate framework ZIF-8 behaves in the opposite way and preferentially adsorbs the alkane. Consequently, in breakthrough experiments, the olefins or paraffins, respectively, can be separated.
TL;DR: Direct cryogenic SEM imaging of the fractured ice surface and the interface between ice and lubricant-impregnated textured surface reveal stress concentrators and crack initiation sites that can increase with texture density and result in lowering adhesion strength.
Abstract: Ice accretion is an important problem and passive approaches for reducing ice-adhesion are of great interest in various systems such as aircrafts, power lines, wind turbines, and oil platforms. Here, we study the ice-adhesion properties of lubricant-impregnated textured surfaces. Force measurements show ice adhesion strength on textured surfaces impregnated with thermodynamically stable lubricant films to be higher than that on surfaces with excess lubricant. Systematic ice-adhesion measurements indicate that the ice-adhesion strength is dependent on texture and decreases with increasing texture density. Direct cryogenic SEM imaging of the fractured ice surface and the interface between ice and lubricant-impregnated textured surface reveal stress concentrators and crack initiation sites that can increase with texture density and result in lowering adhesion strength. Thus, lubricant-impregnated surfaces have to be optimized to outperform state-of-the-art icephobic treatments.
TL;DR: This first demonstration of soft-lithography fabrication with liquid-phase GaIn alloy expands the space of allowable circuit geometries and eliminates the need for mold or mask fabrication.
Abstract: Liquid-phase electronic circuits are patterned on an elastomer substrate with a microcontact printer. The printer head dips into a pool of a liquid-phase gallium–indium alloy, e.g., eutectic gallium–indium (EGaIn) or gallium–indium–tin (Galinstan), and deposits a single drop on a silicone elastomer substrate. After patterned deposition, the liquid-phase circuit is sealed with an additional layer of silicone elastomer. We also demonstrate patterned deposition of the liquid-phase GaIn alloy with a molded polydimethylsiloxane stamp that is manually inked and pressed into an elastomer substrate. As with other liquid-phase electronics produced through needle injection or masked deposition, the circuit is elastically deformable and can be stretched to several times its natural length without losing electronic functionality. In contrast to existing fabrication techniques, microcontact printing and stamp lithography can be used to produce circuits with any planar geometric feature, including electrodes with large...
TL;DR: The enhanced activities of npg-C3N4 can be attributed to the larger number of surface active sites, improved separation of photogenerated electron-hole pairs, and higher efficiency of charge immigration.
Abstract: Nanoporous g-C3N4 (npg-C3N4) with high surface area was prepared by a bubble-templating method. A higher calcination heating rate and proportion of thiourea can result in a larger surface area and better adsorption and photodegradation activities of npg-C3N4. Compared with the bulk g-C3N4, the adsorption capacity for the target pollutants and photocatalytic degradation and photocurrent performances under visible light irradiation of npg-C3N4 were greatly improved. The optimal photodegradation activity of npg-C3N4 was 3.4 times as high as that of the bulk g-C3N4. The enhanced activities of npg-C3N4 can be attributed to the larger number of surface active sites, improved separation of photogenerated electron–hole pairs, and higher efficiency of charge immigration.
TL;DR: A general, simple, and low-cost methodology is suggested for the promising anti-icing applications in various engineering materials and different fields (e.g., power lines and aircrafts).
Abstract: It has been expected that superhydrophobic (SHP) surfaces could have potential anti-icing applications due to their excellent water-repellence properties. However, a thorough understanding on the anti-icing performance of such surfaces has never been reported; even systematic characterizations on icing behavior of various surfaces are still rare because of the lack of powerful instrumentations. In this study, we employed the electrochemical anodic oxidation and chemical etching methods to simplify the fabrication procedures for SHP surfaces on the aluminum alloy substrates, aiming at the anti-icing properties of SHP surfaces of various engineering materials. We found that the one-step chemical etching with FeCl3 and HCl as the etchants was the most effective for ideal SHP surfaces with a large contact angle (CA, 159.1°) and a small contact angle hysteresis (CAH, 4.0°). To systematically investigate the anti-icing behavior of the prepared SHP surfaces, we designed a robust apparatus with a real-time control system based on the two stage refrigerating method. This system can monitor the humidity, pressure, and temperature during the icing process on the surfaces. We demonstrated that the SHP surfaces exhibited excellent anti-icing properties, i.e., from the room temperature of 16.0 °C, the icing time on SHP surfaces can be postponed from 406s to 676s compared to the normal aluminum alloy surface if the surfaces were put horizontally, and the icing temperature can be decreased from -2.2 °C to -6.1 °C. If such surfaces were tilted, the sprayed water droplets on the normal surfaces iced up at the temperature of -3.9 °C, but bounced off the SHP surface even as the temperature reached as low as -8.0 °C. The present study therefore suggests a general, simple, and low-cost methodology for the promising anti-icing applications in various engineering materials and different fields (e.g., power lines and aircrafts).
TL;DR: Copper oxide formation on copper during standard antimicrobial testing was measured in situ by spectroscopic ellipsometry and CuO was found to significantly inhibit contact killing, compared to pure copper, meaning that antimicrobial objects will retain their antimicrobial properties even after oxide formation.
Abstract: The potential of metallic copper as an intrinsically antibacterial material is gaining increasing attention in the face of growing antibiotics resistance of bacteria. However, the mechanism of the so-called "contact killing" of bacteria by copper surfaces is poorly understood and requires further investigation. In particular, the influences of bacteria-metal interaction, media composition, and copper surface chemistry on contact killing are not fully understood. In this study, copper oxide formation on copper during standard antimicrobial testing was measured in situ by spectroscopic ellipsometry. In parallel, contact killing under these conditions was assessed with bacteria in phosphate buffered saline (PBS) or Tris-Cl. For comparison, defined Cu2O and CuO layers were thermally generated and characterized by grazing incidence X-ray diffraction. The antibacterial properties of these copper oxides were tested under the conditions used above. Finally, copper ion release was recorded for both buffer systems by inductively coupled plasma atomic absorption spectroscopy, and exposed copper samples were analyzed for topographical surface alterations. It was found that there was a fairly even growth of CuO under wet plating conditions, reaching 4-10 nm in 300 min, but no measurable Cu2O was formed during this time. CuO was found to significantly inhibit contact killing, compared to pure copper. In contrast, thermally generated Cu2O was essentially as effective in contact killing as pure copper. Copper ion release from the different surfaces roughly correlated with their antibacterial efficacy and was highest for pure copper, followed by Cu2O and CuO. Tris-Cl induced a 10-50-fold faster copper ion release compared to PBS. Since the Cu2O that primarily forms on copper under ambient conditions is as active in contact killing as pure copper, antimicrobial objects will retain their antimicrobial properties even after oxide formation.
TL;DR: A simple and highly effective solution process to fabricate indium-tin oxide (ITO) thin films with high uniformity, reproducibility, and scalability, and can meet the requirements for most practical applications.
Abstract: Deposition technology of transparent conducting oxide (TCO) thin films is critical for high performance of optoelectronic devices. Solution-based fabrication methods can result in substantial cost reduction and enable broad applicability of the TCO thin films. Here we report a simple and highly effective solution process to fabricate indium–tin oxide (ITO) thin films with high uniformity, reproducibility, and scalability. The ITO films are highly transparent (90.2%) and conductive (ρ = 7.2 × 10–4 Ω·cm) with the highest figure of merit (1.19 × 10–2 Ω–1) among all the solution-processed ITO films reported to date. The high transparency and figure of merit, low sheet resistance (30 Ω/sq), and roughness (1.14 nm) are comparable with the benchmark properties of dc sputtering and can meet the requirements for most practical applications.
TL;DR: This study used lipid NPs, the cationic lipid 3β-[N-(N',N'-dimethylaminoethane)-carbamoyl] (DC- Chol) and the zwitterionic lipid dioleoylphosphatidylethanolamine (DOPE), that are among the most promising nanocarriers both in vitro and in vivo to investigate the time evolution of DC-Chol-DOPE NPs upon exposure to HP.
Abstract: When nanoparticles (NPs) enter a biological fluid (e.g., human plasma (HP)), proteins and other biomolecules adsorb on the surface leading to formation of a rich protein shell, referred to as “protein corona”. This corona is dynamic in nature and its composition varies over time due to continuous protein association and dissociation events. Understanding the time evolution of the protein corona on the time-scales of a particle’s lifetime in blood is fundamental to predict its fate in vivo. In this study, we used lipid NPs, the cationic lipid 3β-[N-(N′,N′-dimethylaminoethane)-carbamoyl] (DC-Chol) and the zwitterionic lipid dioleoylphosphatidylethanolamine (DOPE), that are among the most promising nanocarriers both in vitro and in vivo. Here, we investigated the time evolution of DC-Chol–DOPE NPs upon exposure to HP. On time scales between 1 and 60 minutes, nanoliquid tandem mass spectrometry revealed that the protein corona of DC-Chol–DOPE NPs is mainly constituted of apolipoproteins (Apo A-I, Apo C–II, Ap...
TL;DR: Three drugs, ibuprofen, aspirin, and erythromycin, are encapsulated in spherical Pluronic F127 micelles and the mean hydrodynamic radii and polydispersities of the micells are found to increase with decrease in temperature and in the presence of drug molecules.
Abstract: Three drugs, ibuprofen, aspirin, and erythromycin, are encapsulated in spherical Pluronic F127 micelles. The shapes and the size distributions of the micelles in dilute, aqueous solutions, with and without drugs, are ascertained using cryo-scanning electron microscopy and dynamic light scattering (DLS) experiments, respectively. Uptake of drugs above a threshold concentration is seen to reduce the critical micellization temperature of the solution. The mean hydrodynamic radii and polydispersities of the micelles are found to increase with decrease in temperature and in the presence of drug molecules. The hydration of the micellar core at lower temperatures is verified using fluorescence measurements. Increasing solution pH leads to the ionization of the drugs incorporated in the micellar cores. This causes rupture of the micelles and release of the drugs into the solution at the highest solution pH value of 11.36 investigated here and is studied using DLS and fluorescence spectrocopy.
TL;DR: The ROS generation kinetics of uncoated silver, gold, nickel, and silicon NPs in aqueous suspension under UV irradiation is reported and the potential ROS photogeneration mechanisms as well as the associated antibacterial effects are analyzed.
Abstract: Oxidative stress induced by reactive oxygen species (ROS) is one of the major toxicity mechanisms of engineered nanoparticles (NPs). To advance our knowledge of the photogeneration of ROS on NPs, this Letter reports the ROS generation kinetics of uncoated silver (AgNPs), gold (AuNPs), nickel (NiNPs), and silicon (SiNPs) NPs in aqueous suspension under UV irradiation (365 nm) and analyzes the potential ROS photogeneration mechanisms as well as the associated antibacterial effects. The results showed that AgNPs generated superoxide and hydroxyl radicals, whereas AuNPs, NiNPs, and SiNPs generated only singlet oxygen. The electronic structure and redox potentials of SiNPs were shown to mediate ROS generation. By contrast, ROS generation on AuNPs, AgNPs, and NiNPs was primarily due to surface plasmon resonance. The antibacterial activities of these NPs toward E. coli cells under UV irradiation were AgNPs (strongest) > SiNPs > NiNPs > AuNPs. ROS generation and metal ion release significantly enhanced the NPs’ a...
TL;DR: The RGO/PAM displays adsorption capacities as high as 1000 and 1530 mg/g for Pb(II) and MB, respectively, indicating RGO-PAM is a good adsorbent for the adsorptive processes of the heavy metals and benzenoid compounds.
Abstract: Carboxyl groups at the periphery of reduced graphene oxide (RGO) sheets are converted to amine groups by reaction with N-hydroxysuccinimide and 1,3-diaminopropane, and a free-radical polymerization initiator is anchored to the RGO sheets. Poly(acrylamide) (PAM) polymer brushes on RGO sheets (RGO/PAM) are synthesized by in situ free-radical polymerization. The heavy metals, Pb(II), and the benzenoid compounds, methylene blue, (MB) were selected and adsorbed by RGO/PAM composites, and the adsorption capacity of RGO/PAM for Pb(II) and MB was measured. The experimental data of RGO/PAM isotherms for Pb(II) and MB followed the Langmuir isotherm model. The RGO/PAM displays adsorption capacities as high as 1000 and 1530 mg/g for Pb(II) and MB, respectively, indicating RGO/PAM is a good adsorbent for the adsorption of Pb(II) and MB. The adsorption kinetics of Pb(II) and MB onto RGO/PAM can be well fitted to the pseudo-second-order model. The adsorption processes of Pb(II) and MB onto RGO/PAM are spontaneous at 298...
TL;DR: Large anions such as iodide have a high hydrophobic surface affinity and increase the effective charge magnitude on negatively charged unpolar surfaces, which explains the well-known asymmetry between cations and anions.
Abstract: Using a two-step modeling approach, we address the full spectrum of direct, reversed, and altered ionic sequences as the charge of the ion, the charge of the surface, and the surface polarity are v...
TL;DR: A library of spherical and rod-shaped gold nanoparticles (GNPs) was used to evaluate the process of protein adsorption to their surfaces, and equilibrium binding constant determinations indicated that BSA has a comparable binding affinity to all of the GNPs tested, regardless of surface charge.
Abstract: Investigating the adsorption process of proteins on nanoparticle surfaces is essential to understand how to control the biological interactions of functionalized nanoparticles. In this work, a library of spherical and rod-shaped gold nanoparticles (GNPs) was used to evaluate the process of protein adsorption to their surfaces. The binding of a model protein (bovine serum albumin, BSA) to GNPs as a function of particle shape, size, and surface charge was investigated. Two independent comparative analytical methods were used to evaluate the adsorption process: steady-state fluorescence quenching titration and affinity capillary electrophoresis (ACE). Although under favorable electrostatic conditions kinetic analysis showed a faster adsorption of BSA to the surface of cationic GNPs, equilibrium binding constant determinations indicated that BSA has a comparable binding affinity to all of the GNPs tested, regardless of surface charge. BSA was even found to adsorb strongly to GNPs with a pegylated/neutral surf...
TL;DR: The comparatively detections showed that the antimicrobial activity of ZnO was correlated with its production of H2O2, and the t-ZnO treated in H2, which possessed the most V(O) in its crystal, produced the most H2 O2 and displayed the best antimacterial activity.
Abstract: The production of H2O2 has been taken for a crucial reason for antimicrobial activity of ZnO without light irradiation. However, how the H2O2 generates in ZnO suspension is not clear. In the presen...