Substrates In Aqueous Solution Research Articles

Controlled Growth of Zinc Oxide Nanorods by Aqueous-Solution Method

The controlled growth of zinc oxide nanorods in aqueous-solution is reported. Zinc oxide (ZnO) micro- and nano-rods were successfully prepared on gold-seeded Si substrates in aqueous solution containing 1:1 ratio of varying concentrations of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) and hexamethylenetetramine (HMTA) (C6H12N4). The ZnO rods were characterized by scanning electron microscopy, X-ray diffraction and photoluminescence (PL) spectroscopy. A unique evolution of size and growth orientation is directly affected by the change in concentration of Zn2 + solution. The mechanism of growth governed by HMTA and chemical equations are suggested.

Morphology-tuned growth of ZnO microstructures

Morphology-tuned ZnO microcrystals can be prepared by oxidizing zinc metal substrates in aqueous solution using hydrothermal technique. Some typical ZnO growth morphologies such as nanorod superstructures, nanorod arrays, microspheres, hierarchical nanostructures, and split crystals have been chemically fabricated. These microscopic shapes can be finely controlled by selecting Zn(NO 3) 2 concentration and solvent. A conceptual model was proposed to explain the formation of the as-prepared ZnO structures by selecting proper kinetic environments. This one-step, wet-chemical approach is controllable and reproducible, which can be conveniently transferred to industrial applications.

Dye Adsorption Characteristics of Anatase TiO 2 Film Prepared in an Aqueous Solution

Anatase TiO 2 film was deposited on SnO 2: F substrate in aqueous solution. The film had an assembly of acicular TiO 2 nanocrystals on the surface. The crystals grew along the c-axis, i.e. perpendicular to the substrate. Dye adsorption increased with film thickness. Intensity of photoluminescence originating from the dye adsorbed on the nanostructured film after annealing was 3 times higher than that of thicker particulate film constructed of TiO 2 nanoparticles (P25). Additionally, dye adsorption property of the film without annealing was two times higher than the film with annealing. Consequently, the as-deposited film had high dye adsorption property which is about 6 times higher that that of thicker particulate film constructed of TiO 2 nanoparticles (P25). Assemblies of acicular crystals on the surface increased the surface area and amount of dye adsorption. The film may be useful for biomolecule sensors and dye-sensitized solar cells.

Controlled growth of well-aligned hierarchical ZnO arrays by a wet chemical method

A simple synthesis route to hierarchical ZnO arrays on zinc substrate in aqueous solution containing zinc nitrate and ammonia water was reported, without the assistance of any seeds, catalysts and surfactants. The as-prepared product consisted of very thin nanosheets attached onto the top of well-aligned nanorod arrays. A possible growth mechanism was proposed. The room-temperature photoluminescence spectrum showed UV emission around 398 nm and diverse visible emission peaks, indicating there might be a large concentration of oxygen defects in the sample. This method is both controllable and reproducible.

Nanostructured Iron Oxide Films Prepared by Electrochemical Method for Electrochemical Capacitors

Nanostructured iron oxides were electrodeposited anodically onto nickel substrate in aqueous solution at room temperature. Deposited films after annealing at 300°C are characterized as rhombohedral Fe 2 O 3 . The morphology of the porous film deposited at high current density shows nanosheets of 10-16 nm in thickness. A film deposited at low current density has aggregates of nanorods. Electrochemical impedance results show that the film of randomly distributed nanosheets has a higher percentage of large pores than the film of aggregated nanorods. Consequently, specific capacitance of the film with nanosheets is higher than that of the film with aggregated nanorods at galvanostatic charge/discharge.

Positioning multiple proteins at the nanoscale with electron beam cross-linked functional polymers.

Constructing multicomponent protein structures that match the complexity of those found in nature is essential for the next generation of medical materials. In this report, a versatile method for precisely arranging multicomponent protein nanopatterns in two-dimensional single-layer or three-dimensional multilayer formats using electron beam lithography is described. Eight-arm poly(ethylene glycol)s (PEGs) were modified at the chain ends with either biotin, maleimide, aminooxy, or nitrilotriacetic acid. Analysis by 1H NMR spectroscopy revealed that the reactions were efficient and that end-group conversions were 91-100%. The polymers were then cross-linked onto Si surfaces using electron beams to form micron-sized patterns of the functional groups. Proteins with biotin binding sites, a free cysteine, an N-terminal alpha-oxoamide, and a histidine tag, respectively, were then incubated with the substrate in aqueous solutions without the addition of any other reagents. By fluorescence microscopy experiments it was determined that proteins reacted site-specifically with the exposed functional groups to form micropatterns. Multicomponent nanoscale protein patterns were then fabricated. Different PEGs with orthogonal reactivities were sequentially patterned on the same chip. Simultaneous assembly of two different proteins from a mixture of the biomolecules formed the multicomponent two-dimensional patterns. Atomic force microscopy demonstrated that nanometer-sized polymer patterns were formed, and fluorescence microscopy demonstrated that side-by-side patterns of the different proteins were obtained. Moreover, multilayer PEG fabrication produced micron- and nanometer-sized patterns of one functional group on top of the other. Precise three-dimensional arrangements of different proteins were then realized.

A General Synthesis for PEDOT‐Coated Nonconductive Materials and PEDOT Hollow Particles by Aqueous Chemical Polymerization

A method for coating functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) on nonconductive substrates in aqueous solution allows the deposition of PEDOT thin layers on various substrates, including silica and polystyrene (PS) nanoparticles, siliceous mesocellular foam, and chitosan-alginate fibers. The surface property is tuned by controlling the monomer composition in the aqueous solutions. Using appropriate organic solvents to remove the PS cores of PEDOT-coated PS nanoparticles, hollow PEDOT particles with single holes and PEDOT capsules can be formed.

Acicular crystal-assembled TiO 2 thin films and their deposition mechanism

Acicular crystal-assembled TiO 2 thin films were prepared on fluorine-doped tin oxide (FTO) substrates in aqueous solutions. They consisted of anatase crystals grown along the c-axis, which caused high c-axis orientation in X-ray diffraction patterns and electron diffraction patterns. Morphologies of TiO 2 crystals were controlled by growth conditions to fabricate several types of TiO 2 thin films. Furthermore, deposition mechanism of acicular crystals was investigated by comparison of crystal morphologies deposited for different immersion periods using solution aging method.

Polyaniline nanofibers prepared by a facile electrochemical approach and their supercapacitor performance

Polyaniline (PANI) nanofibers were prepared electrochemically by a template-free method on different active substrates in aqueous solutions containing aniline and inorganic acid or organic acid. The influences of experimental parameters, such as polymerization potential, techniques of applied potential, electrolyte composition, and polymerization temperature, on the morphologies of the PANI nanofibers were systematically investigated. The PANI nanofibers obtained have promising applications in supercapacitors whose specific capacitance is as high as 1.21 × 103 F/g, which is the highest value possible using sulfuric acid (1.00 M H2SO4) as electrolyte. In addition, the formation mechanism of PANI nanofibers is discussed.

Conducting Polypyrrole Conical Nanocontainers: Formation Mechanism and Voltage Switchable Property

AbstractNanostructures with stimuli‐responsive properties are of great importance for the application of smart materials in nanotechnology. Unique hollow polypyrrole nanostructured arrays with a conical shape have been produced by a stepwise electropolymerization process. The polypyrrole conical nanocontainers exhibit a reversible switchable behavior between open and closed states, which is controlled by the movement of counter ions during electrically controlled reversible oxidation and reduction processes. The formation of conical nanocontainers is affected by the oleo‐wettability of the substrate. Conical nanocontainers can be formed on oleo‐phobic substrates in aqueous solution by using dopant‐stabilized pyrrole nanodroplets as the guiding template for the polymerization.magnified image

Assembly of Dithiocarbamate-Anchored Monolayers on Gold Surfaces in Aqueous Solutions

Dithiocarbamates (DTCs) can be formed by the in situ condensation of polar alkylamines with CS 2, and assembled into dithiocarbamate-anchored monolayers (DAMs) on Au substrates in aqueous solutions. Primary and secondary amines can both be used to prepare DTCs, but have significant differences in their reactivities and product stabilities. Ultraviolet absorption spectroscopy provides a convenient method for monitoring in situ DTC formation as well as the formation of potential byproducts. The kinetics of DAM assembly on Au substrates as measured by second harmonic generation (SHG) indicated first-order rate processes and saturation coverages similar to those of alkanethiols on Au. However, the rate of adsorption did not change with DTC concentration in a manner expected of Langmuir kinetics, and is attributed to the competitive adsorption of alkylammonium counterions to the freshly oxidized Au substrate. These analyses establish a practical range of conditions for preparing DAMs from polar amines using in situ DTC formation.

Hydrogen-Free Homogeneous Catalytic Reduction of Olefins in Aqueous Solutions

Herein we report a study involving the homogeneous catalytic reduction of unsaturated substrates in aqueous solutions or water-organic solvent mixtures. The reduction of olefins has been carried out in the presence of catalytic amounts of [Fe(CN)5NH3](3-) and excess of NH2OH, which under mild reaction conditions can be used to reduce carbon-carbon unsaturations without affecting carbonyl functionalities and aromatic rings. To explore the scope of the catalytic reduction, a wide variety of representative unsaturated substrates have been examined. The steric effects of the substituents on the carbon-carbon multiple bond as well as the regioselectivity and stereoselectivity of the catalyst have been studied. The deuterium kinetic isotope effect on the catalytic reduction of double bonds in olefins has been analyzed, and no significant kinetic isotope effect was found. Among the great advantages of this novel procedure for catalytic reduction are that hydrogen and high pressures are not needed, the catalyst is inexpensive and easily prepared, and water as well as water-organic solvent mixtures can be used as reaction media.

Surfaces Modified by Amphiphilic Copolymer: Preparation and Application

N-isopropylacrylamide (NIPAM)-ethylene oxide (EO) copolymer was grafted on filter paper surface to obtain paper-based adsorptive membrane. Protein adsorption on and release from the membrane was evaluated under various conditions using humanized monoclonal antibody as model protein. The results obtained indicated that amphiphilic copolymer modified filter paper could be used as a novel chromatographic membrane for protein separation/purification. Comb-block copolymers of NIPAM with N-vinylpyrrolidone (VP) were prepared through RAFT polymerization and macromonomer techniques. Surface modification of substrates, such as plastics and glass, was carried out by treatment of the substrates in aqueous solution of the amphiphilic comb-block copolymer (adsorptive coating, pre-adsorption). It was found that the adsorbed copolymer layer was stable in aqueous environment even when shear stress was applied. Protein adhesion on the material surfaces before and after the modification was investigated using lysozyme as model protein. The results obtained showed that the adsorptive coating layer on the material surfaces significantly reduced non-specific protein adhesion.

The Photo-Favorskii Reaction of p-Hydroxyphenacyl Compounds Is Initiated by Water-Assisted, Adiabatic Extrusion of a Triplet Biradical

The p-hydroxyphenacyl group 1 is an effective photoremovable protecting group, because it undergoes an unusual photo-Favorskii rearrangement concomitant with the fast release (<1 ns) of its substrates in aqueous solution. The reaction mechanism of the diethyl phosphate derivative 1a was studied by picosecond pump−probe spectroscopy, nanosecond laser flash photolysis, and step−scan FTIR techniques. The primary photoproduct is a triplet biradical, 33, with a lifetime of about 0.6 ns. The release of diethyl phosphate determines the lifetime of the triplet state T1(1a), τ(T1) = 60 ps in wholly aqueous solution. Formation of a new photoproduct, p-hydroxybenzyl alcohol (6), was observed at moderate water concentrations in acetonitrile. It is formed by CO elimination from the elusive spirodione intermediate (4), followed by hydration of the resulting p-quinone methide (5). Computational studies show that CO elimination from the spirodione is a very facile process.

Wet Etching of Pillar-Covered Silicon Surfaces: Formation of Crystallographically Defined Macropores

Silicon substrates exposed to laser ablation in a chemically reactive environment such as or HCl can experience spontaneous formation of conical pillars. We use these pillars as a template to define the dimensions and order of macropores produced by etching such substrates in aqueous solutions of KOH or tetramethylammonium hydroxide. The pillars anchor the sidewalls of the pores during etching, and the interpillar spacing controls the width of the pores. The macropores have crystallographically defined shapes for which we develop an explanation based on the kinetics of etching. Si(001) macropores can be etched such that they are rectangular with straight walls and an inverted pyramidal bottom. They have been etched as through holes, which is of interest for optical applications. On Si(111), there is a transition from hexagonal to triangular macropores that are all aligned in one direction. The Si(111) pores exhibit an optimum etch time before they begin to disappear. The behavior of the macropores is quite similar regardless of whether the pillars are produced by nanosecond or femtosecond lasers. Differences observed relate to the different initial structures (spacing and regularity) of these two different types of pillar-covered surfaces.

Seed-layer controlled synthesis of well-aligned ZnO nanowire arrays via a low temperature aqueous solution method

A simple and controllable method has been developed to synthesize well-aligned ZnO nanowire arrays on silicon and glass substrates in aqueous solution. A thin ZnO seed-layer coated with colloidal ZnO nanocrystals was introduced to control the density and orientation of ZnO nanowires. X-ray diffraction (XRD) and scanning electron microscopy (SEM) result show the high dense and well-aligned character of ZnO nanowires. The photoluminescence (PL) reveals the high crystal quality of the nanowires. It was found that the ZnO seed-layer can effect the size distribution, density and crystal structure of the nanowires. The growth mechanism of ZnO nanowires was also discussed.

Simultaneous measurement of structural and hydrodynamic forces between colloidal surfaces in complex fluids

An AFM study was performed to measure the effect of approach/retraction speed on the interaction force between a colloidal particle and a flat substrate in aqueous solutions containing silica nanospheres at concentrations of 4.5 and 6.5 vol.%. The total force consisted of contributions of electrostatic, depletion, structural and hydrodynamic forces. The hydrodynamic component of the force could be isolated by comparing the force profiles measured upon approach and retraction. It was found that when the hydrodynamic component was subtracted from the total force, the resulting force profiles measured at scan speeds of 80, 800, 2400, 4800 and 11,200 nm/s all overlaid, indicating that the surface forces (electrostatic, depletion and structural) were not affected by the scan speed. This result was further supported by an approximation of the rates of viscous and diffusive motion in the gap region. In addition, the variation of the hydrodynamic force with particle/plate separation distance agreed relatively well with a prediction made using the mobility correction factor developed for simple fluids, suggesting that the nanoparaticles do not alter the flow in the lubrication layer at these concentrations.

Manipulation of the Growth of Gold and Silver Nanomaterials on Glass by Seeding Approach

This paper describes the growth of gold and silver nanomaterials from their corresponding colloidal seeds on glass substrates. The glass substrates were treated with 3-mercaptopropyltrimethoxysilane (MPTMS) and then with gold or silver nanoparticle seeds (AuNPSs or AgNPSs) at different concentrations. After separately immersing the thus-prepared MPTMS-AuNPS and MPTMS-AgNPS glass substrates in aqueous solutions containing cetyltrimethylammonium bromide, ascorbic acid, and gold or silver ions, we obtained Au and Ag nanomaterials of different sizes and shapes, which we characterized through scanning electron microscopy (SEM) and dark-field microscopy (DFM). At 0.001x concentrations AuNPSs and AgNPSs (i.e., 1000-fold-diluted solutions of the as-prepared samples), Au and Ag nanomaterials having 1.36 and 5.21 mum lengths and aspect ratios of 11 and 24 were prepared in yields of 27% and 54%, respectively. Scattering spectra of the thus-prepared single AuNRs and AgNRs revealed that the uniformity in the shape of the AuNRs was greater than that of the AgNRs. In addition, we demonstrate the preparation (using a laboratory-made synthesis system) and characterization (through DFM measurements) of Au nanomaterials, including AuNRs, from five AuNPS solutions of different concentrations on a single glass substrate.

Magnetic properties of nanostructured Co xFe 3− xO 4 (0 < x < 0.2) thin films obtained by a low-temperature soft solution processing method

Single phase, highly crystalline and uniform cobalt ferrite thin films were deposited on glass and silicon substrates in aqueous solutions at 80 °C through the liquid phase deposition (LPD) method. Regardless of the chemical composition, the Co x Fe 2− x O 4 (0 < x < 1) thin films identified with a crystal structure as spinel-type are homogeneous, being constructed by spherical particles. The magnetic films present a hysteretic behavior at room temperature with saturation magnetization values close to the bulk material and coercivities depending on the cobalt content.

Tracking Single Molecular Diffusion on Glass Substrate Modified with Periodic Ag Nano-architecture

Diffusion of individual dye-labeled molecules in self-spreading lipid bilayer on glass substrate in aqueous solution was observed directly using total internal reflection fluorescence microscopy (TIRFM). The molecular diffusion was evaluated quantitatively by the mean square displacement (MSD) analysis for the trajectories of individual molecules. The mode of normal Brownian diffusion in lipid bilayer was changed in the presence of the periodic triangular Ag nanoparticles on the surface of the substrate. Suppressed diffusivity observed at the system with the triangular Ag nanoparticles was attributed to the confinement of the molecular motion in the micro-compartment surrounded by the Ag triangles.