Investigation of the dynamics of the interaction of metal particles with a Langmuir single layer upon an increase in the surface pressure

X-ray studies of dipalmitoylphosphatidylcholine (DPPC) single layers on the surface of a liquid provide detailed information on the interaction of metal particles with a single layer upon an increase in the surface pressure up to the collapse. Two complementary X-ray methods are used: grazing incidence diffraction and the X-ray standing waves method. The experimental results obtained for a single layer formed on a colloidal solution of magnetite nanoparticles reveal that the increase in the surface pressure is accompanied by an increase in the concentration of nanoparticles near the surface. In a series of experiments where metal particles of submicron size are sputtered onto a DPPC single layer, a sharp decrease in the intensity of the fluorescence yield from metal atoms is observed while the single layer is compressed. These data suggest that metal particles deposited onto the surface of a single layer were extruded into the aqueous subphase.     

Effects of Calcium Ions on Thermodynamic Properties of Mixed Bilirubin/Cholesterol Monolayers

通过?-A等温线研究了含钙离子浓度不同的水溶液亚相上胆红素/胆固醇混合单分子膜的性质．在此基础上,采用数学方法计算了不同亚相上单分子膜的平均单分子面积、崩溃压、表面压缩系数、超额单分子面积、混合自由能和超额自由能．结果表明,在钙离子溶液亚相上混合单分子膜的结构发生扩张,并且在界面上形成非理想混合单分子膜．与理想混合时相比,这种混合单分子膜在超额单分子面积上表现为明显的正偏差．在纯水亚相上,胆红素与胆固醇的摩尔比为3:2时混合单分子膜为热力学最稳定体系．但是在钙离子浓度逐渐增大的亚相中,这种摩尔比的混合单分子膜热力学稳定性被破坏,即混合单分子膜中的不同组分间自发混合能力下降,这是由于受到钙离子与胆红素和胆固醇之间配位作用的影响．此外,在钙离子溶液亚相中,在较低的表面压下制备出的混合膜具有更好的热力学稳定性．     

硬脂酸单分子膜上电沉积Ag膜的研究

通过电沉积方法 ,以气 /液界面上形成的硬脂酸单分子膜为模板诱导沉积金属银膜 .考察了镀液 pH值、单分子膜表面压及沉积电位对银膜形貌及结构的影响 .实验发现 ,酸性镀液的气 /液界面上形成的单分子膜不能诱导沉积银 ,而在中性和碱性镀液的气 /液界面上可以诱导银膜的生长 .当单分子膜处于液态或固态时 ,气 /液界面有银膜形成 ;液态单分子膜上的银膜生长速度较快 ,且银膜的结构一致 .随着电极电位的升高 ,银膜沉积的速度加快 ,呈环状向外生长的圆形银膜逐渐变得不规则 .将不同实验条件下的银膜转移出来 ,采用扫描电镜 (SEM )、透射电镜 (TEM )对银膜的结构与形貌进行了表征 .研究表明 ,银首先在单分子膜上异相成核 ,由八面体构型逐渐发展成星型 ,最终在气 /液界面形成具有松枝状微观结构的光亮银膜 .     

Enhanced microwave absorption performance of MOF-derived hollow Zn-Co/C anchored on reduced graphene oxide

Composite materials assembled by metal/carbon nanoparticles and 2D layered flakes can provide abundant interfaces, which are beneficial for high-performance microwave absorbers. Herein, Zn-Co/C/RGO composites, composed of Zn-Co metal-organic framework-derived Zn-Co/C nanoparticles and reduced graphene oxide (RGO), were obtained through a facile method. The multilayer structure was due to the introduction of hollow Zn-Co/C nanoparticles in the RGO sheets. Zn-Co/C nanoparticles provided abundant polarization and dipole centers on the RGO surface, which enhanced the microwave absorption abilities. Different concentrations of RGO were introduced to optimize impedance matching. The minimum reflection loss (R_L) of Zn-Co/C/RGO with a thickness of 1.5 mm reached -32.56 dB with the bandwidth corresponding to R_L at -10 dB, which can reach 3.92 GHz, while a minimum R_L of -47.15 dB at 11.2 GHz was also obtained at a thickness of 2.0 mm. The electromagnetic data demonstrate that Zn-Co/C/RGO presented excellent absorption performance and has potential for application in the microwave absorption field.     

Structure characterization and stability of mixed lipid/protein monolayer at the air/water interface

A mixed protein/lipid monolayer has been constructed by the protein adsorption from subphase into the spread phospholipid monolayer. A precisely controlled pump was used to exchange the protein solution with different pH values after the protein was ensured to reach the less condensed surface.

The domains formed in the coexistence region of D-dipalmitoylphosphatidylcholine (D-DPPC) have been recorded by Brewster angle microscopy (BAM) combined with the film balance before and after the penetration of the protein, human serum albumin (HSA). The subphase was exchanged by gradually increasing or decreasing pH value of the solution. Three isotherms of the mixed D-DPPC/HSA monolayer with the subphase of pH=4.2, pH=7.0 and pH=9.1, respectively, were obtained. It indicated that the area per lipid molecule with protein increased as the subphase pH value was lowed. Simultaneously, morphological dynamic changes caused by the gradual changing on subphase pH were observed. These variations can be ascribed to the conformation change of protein under the fluctuation of pH value. The hydrophobic and electrostatic interactions between the phospholipid and HSA were as considered for the interpretation of domain change based on the current experimental results     

Preparation of supramolecular assembled films of fullerene C60 on the aqueous solution of water-soluble azocalixarene

A convenient procedure was developed to prepare an ultra-thin film of supermolecules of a spherical fullerene C₆₀ and water-soluble azocalix[6]arene. The C₆₀ molecule is so hydrophobic that it easily forms a three-dimensional aggregate on the water surface. When C₆₀ molecules were spread on an aqueous solution of water-soluble azocalixarene that acts as a host for C₆₀, the hydrophobic C₆₀ was captured in the cavity of the host molecule at the boundary of two phases and formed amphiphilic supermolecules. The supermolecules assembled spontaneously into ultra-thin films over 1-cm wide. The monolayer-like film could be transferred onto a solid support by the Langmuir–Blodgett technique or the inverse Langmuir–Schaefer technique. The morphology and the transferability of the supramolecular assembled films were examined by changing the host molecules, the initial density of C₆₀ on the water surface, the subphase temperature and the metal ions in the subphase.     

Direct synthesis of graphene nanosheets support Pd nanodendrites for electrocatalytic formic acid oxidation

We report a solvothermal method preparation of dendritic Pd nanoparticles(DPNs) and spherical Pd nanoparticles(SPNs) supported on reduced graphene oxide(RGO). Drastically different morphologies of Pd NPs with nanodendritic structures or spherical structures were observed on graphene by controlling the reduction degree of graphene oxide(GO) under mild conditions. In addition to being a commonplace substrate, GO plays a more important role that relies on its surface groups, which serves as a shape-directing agent to direct the dendritic growth. As a result, the obtained DPNs/RGO catalyst exhibits a significantly enhanced electro-catalytic behavior for the oxidation of formic acid compared to the SPNs/RGO catalyst.     

X-ray standing wave studies of metal ions incorporation in Langmuir–Blodgett films

The molecular organization in Langmuir–Blodgett films of phospholipids and metallomesogen deposited on silicon has been studied by the X-ray standing-wave method at the synchrotron radiation source BESSY (Germany). Analysis of the experimental data obtained made it possible to determine the composition of the organic multilayer nanosystems and localize the position of metal ions incorporated in organic layers from the aqueous subphase during film deposition.     

Formation and Deposition of Langmuir-Blodgett Films with Thiol-Stabilized CdTe Nanoparticles

Incorporation of the thiol-stabilized CdTe nanoparticles into mono- and multilayer films produced by Langmuir-Blodgett (LB) technique was investigated using “pressure-area” isotherms, Quartz Crystal Microbalance, FTIR, UV/Vis absorption and photoluminescence spectroscopy. LB films were formed from cationic (octadecyltrinonylammonium iodide—ODTNA) and anionic (behenic acid) surfactants. Both noticeable increase of limiting surface area of behenic acid monolayer and simultaneous decrease of film strength have been established when the aqueous solution of CdTe nanoparticles was used as a subphase. LB films deposition on solid substrates depends on the type of stabilizing ligands (1-thioglycerol or 2-mercaptoethanol) for CdTe nanoparticles. Optical absorption and photoluminescence properties of the films obtained from behenic acid monolayers that has thioglycerol-stabilized CdTe nanoparticles incorporated into them acquire the same properties as the size-quantized CdTe nanoparticles. The bonding of the cadmium ions, that released as a result of a partial dissociation of ligand-stabilized CdTe nanoparticles with carboxylic group, is considered to be responsible for the incorporation in case of behenic acid surfactant, and in case of ODTNA the incorporation proceeds by means of a weak “nanoparticle-LB matrix” interaction.     

P–n junction characteristics of graphene oxide and reduced graphene oxide on n-type Si(111)

The semiconductor behavior of graphene oxide (GO) and reduced graphene oxide (RGO) synthesized by the Hummers method on n-type Si(111) were investigated. Graphene oxide is a product of the oxidation of graphite, during which numerous oxygen functional groups bond to the carbon plane during oxidation. RGO was prepared by adding excess hydrazine to the GO showing p-type semiconductor material behavior. In the C–O bond, the O atom tends to pull electrons from the C atom, leaving a hole in the carbon network. This results in p-type semiconductor behavior of GO, with the carrier concentration dependent upon the degree of oxidation. The RGO was obtained by removing most of the oxygen-containing functionalities from the GO using hydrazine. However, oxygen remaining on the carbon plane caused the RGO to exhibit p-type behavior. The I–V characteristics of GO and RGO deposited on n-type Si(111) forming p–n junctions exhibited different turn-on voltages and slope values.     

Physical and chemical properties of Co n?m Cu m nanoclusters with n?=?2–6 atoms via ab-initio calculations

The aim of this work is to investigate the influence of the preparation method on the surface charge and electrokinetic properties of poly-??-caprolactone-based particles using poloxamer 188 as stabilizing agent. To target such objective, two processes (the nanoprecipitation and the emulsification-diffusion) are used to prepare well-defined nanospheres ranging in hydrodynamic diameters from 100 to 200?nm. The effect of the materials used on the particle zeta potential is systematically studied to compare the two preparation methods. The polarity of the organic solvent directly affects the zeta potential of particles prepared via the emulsification-diffusion method. The results obtained suggest that the aqueous phase used for preparing particles affects the possible re-arrangement of polymers during the emulsification step. As the aqueous phase is saturated with the organic solvent, the polar and the non-polar moieties of the polymer chains might be re-conformed following organic solvent diffusion from the particle core to the continuous phase. Regarding the nanoprecipitation process, the electrokinetic properties of the particles were found to be organic solvent independent, but principally affected by the pH and the salinity of the aqueous phase used during the particle preparation.     

Flexible and transparent resistive switching devices using Au nanoparticles decorated reduced graphene oxide in polyvinyl alcohol matrix

We have investigated the resistive switching mechanism in solution processed Au-reduced graphene oxide-polyvinyl alcohol (PVA) nanocomposites on flexible substrates. Monodispersed gold nanoparticles (Au NPs) attached to reduced graphene oxide (RGO) in aqueous PVA solution have been synthesized using a novel one pot technique. The fabricated hybrid device showed high On/Off switching ratio more than 10³ with low operating voltages. The performance of hybrid device can be effectively enhanced over control RGO device. The switching mechanism occurs from the electrochemical reduction/oxidation process of partially reduced graphene oxide. The proposed devices reveal superior asymmetric bipolar resistive switching characteristics attractive for solution processable flexible and transparent non-volatile memory applications.     

Nanosized titania encapsulated silica particles using an aqueous TiCl4 solution

In this study, sub-micron sized silica particles were encapsulated with nanosized titania particles using an aqueous TiCl₄ solution. The particle size distribution of the synthesized titania particles in the coating layer was estimated to be 10 nm from X-ray powder diffraction and transmission electron microscopy. The thickness of the coating layer ranged from a few nm to about 30 nm from transmission electron microscopy analysis. Zeta potential analysis demonstrated the presence of a titania particle coating layer and the extent of its coverage on the surface of silica particles. X-ray photoelectron spectroscopy analysis also demonstrated that titania particles were successfully deposited on the surface of core silica particles from the chemical shift of binding energies of O 1s, Ti 2p and Si 2p.     

Synthesis and electrochemical performance of LiNi0.6Co0.2Mn0.2O2/reduced graphene oxide cathode materials for lithium-ion batteries

A LiNi_0.6Co_0.2Mn_0.2O₂/reduced graphene oxide (RGO) composite with RGO content of 1.2 % was prepared by a simple spray-drying method instead of high-energy ball milling method. The composite has been characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, energy dispersive spectroscopy, and charge/discharge test. The X-ray diffractometry result showed that composite possessed a typical hexagonal structure. The RGO sheets served as efficient electronically conductive frameworks benefitting from its 2D structure and outstanding electronic conductivity. The scanning electron microscope and transmission electron microscopy verified that LiNi_0.6Co_0.2Mn_0.2O₂ particles were wrapped with RGO sheets, which facilitated electronic conductivity between particles. The electrochemical results indicated that composite delivered a higher discharge capacity at various discharge rates. The cycling performance was also evaluated. The composite exhibited better cycling performance than pristine sample. Electrochemical impedance spectroscopy showed that the RGO can greatly reduce the charge transfer resistance. The results here gave clear evidence of RGO to improve electrochemical performance.     

Engineering and characterization of mesoporous silica-coated magnetic particles for mercury removal from industrial effluents

Mesoporous silica coatings were synthesized on dense liquid silica-coated magnetite particles using cetyl-trimethyl-ammonium chloride (CTAC) as molecular templates, followed by sol-gel process. A specific surface area of the synthesized particles as high as 150 m²/g was obtained. After functionalization with mercapto-propyl-trimethoxy-silane (MPTS) through silanation reaction, the particles exhibited high affinity of mercury in aqueous solutions. Atomic force microscopy (AFM), zeta potential measurement, thermal gravimetric analysis (TGA), analytical transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS) were used to characterize the synthesis processes, surface functionalization, and mercury adsorption on the synthesized magnetite particles. The loading capacity of the particles for mercury was determined to be as high as 14 mg/g at pH 2. A unique feature of strong magnetism of the synthesized nanocomposite particles makes the subsequent separation of the magnetic sorbents from complex multiphase suspensions convenient and effective.     

Study of photooxidation of styrene-butadiene copolymers by surface pressure measurements at the air-water interface

Block and random copolymers of butadiene and styrene as well as polybutadiene and polystyrene homopolymers have been investigated with respect to their monolayer properties and photooxidation behavior. Whereas polystyrene and block copolymers of styrene and butadiene form stable monolayers, polybutadienes and random copolymers do not interact with the aqueous subphase. The monolayer properties of block copolymers with different styrene content indicate that polybutadiene also contributes to the surface pressure. Photo-oxidation of random and block copolymers of styrene and butadiene leads to a significant enhancement in surface pressure of the monolayers due to the generation of groups which can effectively interact with the aqueous surface. FTIR spectral studies show the formation of carbonyl, hydroxyl, and hydroperoxyl groups in the polymers on photooxidation. A comparison of the pressure-area isotherms of random and block copolymers oxidized in solution indicates that there is an energy transfer from butadiene to styrene units in the case of random copolymers, resulting in a protective effect of butadiene units from oxidation. In addition, in the monolayers of oxidized block copolymers, a phase transition occurs which is attributed to the extrusion of polystyrene blocks from the monolayer. The surface pressure-area isotherms and the rates of photooxidation are strongly dependent on the microstructure of polybutadiene as well as on whether oxidation is performed in solution or at the oxygen-water interface.     

Complete coverage of reduced graphene oxide on silicon dioxide substrates

Reduced graphene oxide(RGO) has the advantage of an aqueous and industrial-scale production route. No other approaches can rival the RGO field effect transistor platform in terms of cost(相似文献   

Preparation and probe analysis of Langmuir–Blodgett films with metal-containing dendritic and cluster structures

We aim to reveal the influence of?pH values of the working solution on spatial arrangement of metal-containing inclusions in the monolayer coatings prepared by Langmuir?CBlodgett (LB) technology and transferred to solid substrates with consequent modification of surface electrical properties. Consequently, films with inclusions in the form of dendrites and cluster shapes have been obtained. Submicron and micron lead-containing formations in Langmuir?CBlodgett films have been characterized by using the atomic force microscopy, Kelvin probe microscopy, and scanning electron microscopy methods. The results show that increasing?pH value of the subphase has caused the significant changes in the shape and composition of the inclusions in Langmuir?CBlodgett films. The synthesized inclusions on the solid substrate surface resulted in formation of the regions with the local electric fields and, as consequence, to significant modification of the structure and electrical properties. The location and length of the regions with surface potential disturbance depend on the shape of inclusions, and consequently, on?pH value of the subphase used in LB technology.     

Synergetic Photocatalytic Nanostructures Based on Au/TiO2/Reduced Graphene Oxide for Efficient Degradation of Organic Pollutants

Recently, there is crucial interest in the design and fabrication of nanocatalysts for efficient decomposition of organic pollutants in wastewater using visible light. This work reports the assembling fabrication of synergetic photocatalytic Au/TiO₂/RGO nanostructures by utilizing the reduced graphene oxide (RGO) as substrate material and efficient separator for electrons and holes. The Au/TiO₂ nanostructures with a ≈7 nm TiO₂ particles size are dispersed uniformly on RGO nanosheets. UV–vis diffuse reflectance spectroscopy verifies that Au/TiO₂/RGO nanocomposites show strong absorption of visible light. The degradation efficiency after 1 h for hydroquinone under visible light and UV light is ≈77% and ≈90%, respectively. Under visible light, the calculated apparent rates (k ) of the Au/TiO₂/RGO nanocomposites are 0.0112 and 0.0174 min^?1 for decomposition of methylene blue and hydroquinone. That are five times greater than that of bare TiO₂. The high photocatalytic activity is mainly attributed to the synergy between RGO and Au/TiO₂ nanostructure. The strategy of composite nanostructures assembling on RGO is ensured to have a great practicable potential for the designing of high efficient multielement composite nanoparticles catalysts.