Aqueous Colloidal Solution Research Articles

Preparation and optical properties of polyethyleneimine-stabilized colloidal CdSe and CdS x Se1–x quantum dots

Using unbranched polyethyleneimine as a stabilizer, we have obtained colloidal aqueous solutions of ultrasmall (1.8-1.9 nm) CdSe particles, characterized by a narrow size distribution and photoluminescence in the visible region of the spectrum with quantum yields up to 12% and decay constants in the range 10-1 to 102 ns. A similar approach was used to obtain colloids of nanoparticles of a CdS x Se1–x solid solution with a tailored composition.

Electrooptical effects in colloid systems subjected to short pulses of strong electricfield

Existing electrooptical experimental techniques applied to a colloid solution allow thedetermination of different particle parameters, such as rotary diffusion coefficient, size,polarizability anisotropy and others. If the solution is polydisperse, numerical methods canbe used to determine the distribution of particles in the solution on their parameters. Thesetechniques can be applied to systems that are prone to lengthy application of electric field.To study polydisperse systems that cannot stand lengthy application of electric field it isproposed to apply short pulses of strong sine-shaped electric field. It is shown that it is stillpossible to determine the main particle parameters from the experimental data obtained inthis technique. The limitations of this approach are studied. This technique wasexperimentally probed on aqueous colloid solutions of diamond, graphite andpalygorskite. It is shown that for these systems the relaxation of the electroopticaleffect after application of strong pulses of sine-shaped electric field is similar tothe relaxation of the electrooptical effect from the state of saturated orientationinduced by sine-shaped electric field, which is proven by the presented correlationcoefficients.

Deaggregation of Nanodiamond Powders Using Salt- and Sugar-Assisted Milling

Diamond particles of 5-10 nm in size can be produced in large quantities by denonating oxygen-lean explosives in a closed chamber. They have numerous useful properties and are used in applications ranging from lubricants to drug delivery. Aggregation of diamond nanoparticles is limiting wider use of this important carbon nanomaterial because most applications require single separated particles. We demonstrate that dry media assisted attrition milling is a simple, inexpensive, and efficient alternative to the current ways of deaggregating of nanodiamond. This technique uses water-soluble nontoxic and noncontaminating crystalline compounds, such as sodium chloride or sucrose. When milling is complete, the media can be easily removed from the product by water rinsing, which provides an advantage when compared to milling with ceramic microbeads. Using the dry media assisted milling with subsequent pH adjustment, it is possible to produce stable aqueous nanodiamond colloidal solutions with particles <10 nm in diameter, which corresponds to 1-2 primary nanodiamond particles. The study of milling kinetics and the characterization of the produced nanodiamond colloids led us to conclude that aggregates of less than 200 nm in diameter, observed at the tail of the pore size distribution of milled nanodiamond, are loosely bonded and rather dynamic in nature. Color change observed in ND colloids upon shifting their pH toward the basic end allowed us to demonstrate that the coloration comes from the light interaction with colloidal particles and not from an increase in nondiamond carbon content.

Forces within Single Pairs of Charged Colloids in Aqueous Solutions of Ionic Liquids as Studied by Optical Tweezers

Forces of interaction within single pairs of negatively charged microsized blank colloids in aqueous solutions of water miscible room temperature ionic liquids (RTILs) have been measured at varying concentrations and pH by using optical tweezers (OT). Three different water miscible RTILs (1-butyl-3-methylimidazolium tetrafluoroborate [BMIM-BF4], 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM-TfO], and 1-butyl-3-methylimidazolium chloride [BMIM-Cl]) having the same organic cation [BMIM]+ and different inorganic anions ([BF4]−, [TfO]−, and Cl−) are used and compared with the high temperature molten salt (KCl). The experimental data are well described by a size-corrected screened Coulomb interaction approach which originates from the linearized Poisson−Boltzmann (PB) equation. The effective surface charge density σ derived from the fitted force-separation data is found to be concentration and pH dependent.

The Preparation of Polymer/Silver Nanocomposites and Application as an Antibacterial Material

An elegant and facile route for the preparation of polymer/silver nanocomposites for polymers having solubility in organic solvents has been developed. Aqueous colloidal solution of nano-silver has been used as the source of nano-silver particles. Nano-silver particles were transferred to the poly(methyl acrylate) (PMA) solution in chloroform using phase transfer methodology. Separation of the aqueous phase gave solution of nano-silver/PMA in chloroform. The solution was coated onto glass substrate providing uniform film of antibacterial PMA/silver nanocomposite, thus exhibiting its potential application as a coating material. The same methodology has been successfully extended to prepare polyether sulphone/silver nanocomposites.

ChemInform Abstract: Intercalation and Photochromism of Spiropyrans on Clay Interlayers.

1′,3′,3′-Trimethylspiro[2H-1-benzopyran-2,2′-indoline](abbreviated to H–SP) and its derivatives, 6-nitro (NO2–SP) and 6-nitro-8-(pyridinium)methyl spiropyrans (Py+–SP), have been intercalated in the interlayers of Montmorillonite. The intercalation was highly dependent on the substituent groups on the SPs. Charged Py+–SP was quantitatively adsorbed on the clay as an equilibrium mixture with the corresponding merocyanine (Py+–MC) in aqueous colloidal solution, the ratio Py+–SP:Py+–MC being 35:65 and exhibiting reversed photochromism. In contrast, a preferential adsorption as Py+–SP was observed for the hydrophobic clay layers coadsorbing cetyltrimethylammonium bromide (CTAB), which displays normal photochromism. The thermal isomerization of Py+–SP intercalated in aqueous colloidal clay exhibited a linear combination of two components of the first-order reactions, while that of the Py+–SP–CTAB coadsorbed system satisfied a single first-order kinetics. The two-component kinetics are explicable in terms of the intervention of at least two different kinds of microscopic environment, e.g. non-polar and polar phases, in the clay interlayers. We also show that the photochemical decoloration of Py+–MC was significantly retarded by the intercalation. All of these results are discussed on the basis of the polarity of the intercalation.

Absorption of carbon dioxide in aqueous colloidal silica solution with NaOH

The absorption rate (R A ) of carbon dioxide was measured into an aqueous nanometer-sized colloidal silica solution of 0–31 wt% and NaOH of 0–2 kmol/m3 in a flat-stirred vessel for various sizes and speeds of 25 °C and 101.3 N/m2 to obtain the volumetric liquid-side mass transfer coefficient (k L a L ) of CO2. The film theory accompanied by chemical reaction between CO2 and NaOH was used to estimate the theoretical value of absorption rate of CO2. The empirical correlation formula containing the relationship between k L a L and rheological property of the aqueous colloidal silica solution was presented. The value of R A in the aqueous colloidal silica solution was decreased by the reduction of k L a L due to elasticity of the solution.

Hydrothermal synthesis of highly water-dispersible anatase nanocrystals from transparent aqueous sols of titanate colloids

Transparent colloidal aqueous solutions of anatase nanocrystals were hydrothermally synthesized from aqueous transparent sols with tetramethylammonium titanate colloids, the surfaces of which were modified with citric acid, by structural conversion of the titanate to anatase. This modification hindered coalescence of the titanate colloids during the hydrothermal synthesis. Although the amount of citric acid adsorbed on the colloids was reduced during hydrothermal treatment, a small amount of citric acid was adsorbed on the resulting anatase nanocrystals. Moreover, the use of the titanate colloids as a precursor was compared with the use of a citrato Ti complex, tetramethylammonium citratotitanate. The hydrothermal treatment of the transparent aqueous solutions of the Ti complex yielded opaque solutions with large anatase colloids, suggesting that the titanate colloids were useful for preparing transparent anatase colloidal solutions. Because the shape and size of resulting colloids may be dependent on the size and shape of starting colloids, the use of titanate colloids as a precursor may make it easy to control size and shape of anatase colloids.

Hydrogen Production by Selective Photo-dissociation of Water in Aqueous Colloidal Nano-particles of Doped Iron (III) Oxides Semiconductors

Homogenous and heterogeneous production of hydrogen via photo-dissociation of water has been achieved with visible range solar radiation without any external potential at room temperature. Potassium ferrocyanide as a solvated-electron supplier and electron exchanger in basic buffers was used as a homogenous media for hydrogen production. Aqueous colloidal solutions of p-type Fe2O3 doped with MgO (Fe1.8Mg0.2O3) or with ZnO (Fe1.9Zn0.1O3) suspensions in ferrocyanide solutions were used as heterogeneous media for hydrogen generation by reduction of ferricyanide. The effects of the hole-scavengers such as oxo-anions and solvated-electron- suppliers were investigated. Results showed that Fe2O3 doped with ZnO was more efficient than that doped with MgO. The studies also showed that the aqueous nano-systems we used retained their stability as indicated by the reproducibility of their photocatalytic activities. Solar radiated assemblies of doped Fe2O3/[Fe(CN)6]−4 sustained cyclic systems for continuous hydrogen production.

Synthesis of Composite Polystyrene/Silica Nanoparticles via Precipitation and Emulsion Polymerization Methods

Polystyrene/silica composite nanoparticles were synthesized via precipitation and emulsion polymerization methods, in the presence of a basic co-monomer (e.g., 4-VP and 1-VID), and a colloidal aqueous silica solution. The effects of key process parameters, that is, solvent type, monomer/co-monomer volume ratio and total monomers concentration for precipitation polymerization, and reaction temperature, pH value, initial silica-sol concentration and initial monomer/co-monomer molar ratio for emulsifier-free emulsion polymerization on the particle morphology, silica content, and particle size distribution of the composite nanoparticles were experimentally investigated. Stable, spherical, and uniform in size composite nanoparticles were synthesized by both techniques. The average particle diameter varied from 108 to 182 nm for the emulsifier-free emulsion polymerization and from 400 to 800 nm for the precipitation polymerization, while the silica content was as high as 38.3 wt.-% for the former method and up to 15.5 wt.-% for the later. The synthesized composite polymer/silica particles were then electrolytically co-deposited with zinc on steel plates to improve the corrosion resistance of the metal's surface.

Solution Phase Interactions Controlled Ordered Arrangement of Gold Nanoparticles in Dried State

Gold (Au) nanoparticles (NPs) were synthesized in the presence of water soluble biomolecules such as DNA, chitosan, phospholipids, and BSA by using seed-mediated approach at room temperature. All reactions produced mostly spherical geometries with comparable size (< or = 20 nm). The NPs were arranged in a typical pearl-necklace type arrangement except in the presence of BSA. Different measurements such as UV-visible, TEM, XRD, and XPS were used to characterize the Au NPs. Fluorescence spectroscopy was used to identify the interactions between biomolecules and blank (uncapped) Au NPs in aqueous colloidal solutions. It was concluded that the favorable interactions between Au NPs and biomolecules in aqueous phase, in fact, drive them into pearl-necklace type arrangement in the dried state.

Preparation of stable colloidal solution of cadmium sulfide CdS using ethylenediaminetetraacetic acid

By the method of chemical condensation a stable aqueous colloidal solution of nanoparticles of cadmium sulfide was obtained. The solution obtained in the daylight had a bright lemon-yellow color. For the temporary stabilization of the solution was used an organic complexone, disodium ethylenediaminetetraacetate (EDTA), that prevented coagulation of colloidal particles up to several months at 4°C. At room temperature, the solution remained stable during a month. The structure and properties of the disperse phase were studied by the X-ray diffraction, optical fluorescence, and electron microscopy. The solid particles size is about 3 nm, they have a disordered close-packed structure with the space group P6mm and possess the photoluminescence color from green to orange depending on the duration of keeping the solution. The size of coagulates was 10 nm, 100 nm, and 1 μm after keeping for 1, 2, and 4 months, respectively.

ENHANCEMENT OF ELECTROCHROMIC DURABILITY OF A FILM MADE OF SILICA-POLYANILINE CORE-SHELL NANOPARTICLES

Enhancing the operation life time or the electrochemical durability is one of the key issues in electrochromic material studies. It is generally accepted that the inorganic–organic hybrid structure is one of the effective ways to enhance the chemical stability of the material. In this study, an electrochromic film made of silica-polyaniline core-shell composite nanoparticles was tested. The composite particles were prepared through a chemical dispersion polymerization of aniline in an aqueous colloidal solution of silica. The synthesized particles were then dispersed into ethanol and the solution was deposited onto an Indium Tin Oxide (ITO)-coated glass substrate. The electrochromic characterization on the prepared films was performed using the cyclovoltammetry and the optical response to a switching potential. The results showed that the inorganic–organic core-shell hybrid nanoparticle could be a promising choice for the enhancement of electrochromic durability.

X-ray Photoelectron Spectroscopy of Fast-Frozen Hematite Colloids in Aqueous Solutions. 2. Tracing the Relationship between Surface Charge and Electrolyte Adsorption

Colloidal-sized hematite spheroids exposed to aqueous NaCl solutions were investigated by X-ray photoelectron spectroscopy using the fast-frozen technique. The O1s region provided evidence for (de)protonation reactions of surface (hydr)oxo groups of OH-enriched/O-depleted hematite surfaces. These results were also correlated to changes in sodium (Na 1s) and chloride (Cl 2p) contents with pH. Electrolyte ion surface loadings were successfully predicted using a classic thermodynamic adsorption model normalized for surface site density. These efforts pointed to ion-specific inner-Helmholtz plane capacitances.

Effects of Citrate Additive on Transparency and Photostability Properties of YVO4 : Bi3 + , Eu3 + Nanophosphor

nanoparticles were prepared by the wet chemical synthesis in various concentrations of sodium citrate, , where is the nominal molar percentage of citrate relative to the sum of metallic ions, , , and . Mean primary nanoparticle diameter and mean hydrodynamic size in the aqueous colloidal solution have minimum values, 21 and , respectively, for the sample prepared at . The transparency of the aqueous colloidal solution in the visible region increases with decreasing the mean hydrodynamic size, and the sample prepared at shows the highest transparency. nanoparticles show the characteristic photobleaching behavior and the photoreduction of to under the irradiation of near-UV light, where the fraction of photobleach becomes larger at large . These results suggest that the citrate ion works not only as an effective dispersion agent, but also as a reducing agent against of .

Reactivity in organised assemblies

This report reviews the 2009 literature on reactivity in organised assemblies, with virtually all examples taken from literature covering aqueous systems. The report is broadly organised along the lines that we set out last year,1 but with the addition of a “miscellaneous” section containing two papers that we did not want to leave out of this report. Nevertheless, as always, we cannot and will not claim that this report provides an exhaustive review. Several main themes covered by this report were reviewed in 2009; Prins and Scrimin reviewed covalent capture which they defined as relying on “the combined use of covalent and noncovalent synthesis by taking advantage of their complementarity”,2 Peyralans and Otto reviewed recent highlights in systems chemistry,3 metallomicellar catalysis was reviewed by Tecilla et al.4 and one of us reviewed kinetic medium effects on organic reactions in aqueous colloidal solutions.5

Spectroscopical properties of organic/metal nanohybrids

The aim of our work was to prepare stable nanohybrids of controlled size and shape consisting of a noble metal core decorated with polydiacetylenes (PDAs). Due to the combination of the outstanding linear and nonlinear optical properties of the polydiacetylenic chains with the electromagnetic field-enhancing capability of metal nanostructures, these novel composites can find potential application in different fields. In particular, the different colours exhibited by PDAs in relation to the chemical nature of the monomer and the polymerization procedure, as well as in response to environmental perturbations, make them excellent materials for the fabrication of sensing devices. On the basis of our previous work on PDA self-assembled monolayers on flat metal surfaces, the results of which are briefly reported, we prepared differently-shaped gold and silver nanocores (spheres, cages) coated with various diacetylenic monomers having end-groups able to firmly anchor to the metal surface. These nanohybrids exhibit in aqueous colloidal solution an enhanced photochemical polymerization monitored step by step with UV-Vis and SERS techniques. It is shown that in these stable assemblies an intra-particle polymerization takes place and that the dominant PDA form is conditioned by the core size and geometry. While the nanoparticles are SERS active in the visible, the nanocages should be excellent SERS substrates from the visible to the near infrared regions.

Preparation of Thin Films of TiO2-Nanoparticles Using Electrophoresis Deposition Method

TiO2-nanoparticles of anatase-type were synthesized and deposited using the electrophoresis depo-sition method. All of TiO2-nanoparticles were positively charged in colloidal aqueous solution and were attracted toward ITO glass as the negative electrode as same as nanoparticles (P25) whose diameter is larger than that of TiO2-nanoparticles. Many of the TiO2-nanoparticles were connected with each other and formed clusters, although single TiO2-nanoparticles were also observed. The cracks generated in the thin film with increasing the deposition time and thin film was flaked off from substrate. High optical transparency TiO2-nanoparticles-thin film without cracks was deposited when the deposition time was short. Moreover, the thickness of TiO2-thin film, which has high optical transparency and no cracks, could be increased using mixture of TiO2-nanoparticles and P25.

Synthesis and Aqueous Colloidal Solutions of RE2(OH)5NO3·nH2O (RE = Nd and La)

AbstractA new, simple route leading to layered rare‐earth hydroxy nitrates was developed. The pH‐independent procedure uses ethanol containing alkali‐metal hydroxide (KOH, RbOH, or CsOH) as a solvothermal medium. Two new, layered rare‐earth hydroxy nitrates (LRHs), Nd2(OH)5NO3·nH2O and La2(OH)5NO3·nH2O, were prepared by this nonaqueous solvothermal reaction. Because the RE = Nd and La members have not yet been synthesized in an aqueous system, the successful synthesis of these compounds implies the completion of the RE2(OH)5NO3·nH2O (RE = rare earths) series. The typical properties of a layered structure was demonstrated by ready ion‐exchange reactions between NO3– and some organic anions such as decanoate, decanesulfonate, and decyl sulfate. In particular, the as‐synthesized hydroxide from solvothermal reaction, where the alkali‐metal nitrates are partially intercalated in the interlayer gallery, form an aqueous colloidal solution under ultrasonic treatment. Hydration of the LRHs intercalated with alkali‐metal salts results in the formation of colloidal LRH suspensions in water. The colloidal character of the LRH solutions is supported by the Tyndall effect, TEM, and AFM images.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)

Fabrication of Copper Oxide Nanoboxes Containing a Platinum Nanocluster via an Optical and Galvanic Route

Copper oxide hollow nanoboxes containing a platinum nanocluster have been fabricated in mild conditions at room temperature by dropping a laser-irradiated aqueous platinum colloidal solution onto a copper substrate. The irradiation of laser pulses at 1064 nm induces the ejection of photoelectrons from platinum nanoclusters suspended in water. The aqueous colloidal solution containing photooxidized platinum nanoclusters was then dropped onto a bulk copper substrate to form hollow (CuO)0.75(Cu2O)0.25 nanoboxes having an average edge size of 195 nm and an average wall thickness of 26 nm, and the resulting platinum nanoclusters, produced by galvanic reduction, remained inside the newly formed copper oxide nanoboxes.