Stable Colloidal Solutions Research Articles

Facile and efficient one-pot solvothermal and microwave-assisted synthesis of stable colloidal solutions of MFe2O4 spinel magnetic nanoparticles

Well-defined synthesis conditions of high quality MFe2O4 (M = Mn, Fe, Co, Ni, Zn, and Cu) spinel ferrite magnetic nanoparticles, with diameters below 10 nm, have been described based on facile and efficient one-pot solvothermal or microwave-assisted heating procedures. Both methods are reproducible and scalable and allow forming concentrated stable colloidal solutions in polar solvents, but microwave-assisted heating allows reducing 15 times the required annealing time and leads to an enhanced monodispersity of the nanoparticles. Non-agglomerated nanoparticles dispersions have been achieved using a simple one-pot approach where a single compound, triethyleneglycol, behaves at the same time as solvent and capping ligand. A narrow nanoparticle size distribution and high quality crystallinity have been achieved through selected nucleation and growth conditions. High resolution transmission electron microscopy images and electron energy loss spectroscopy analysis confirm the expected structure and composition and show that similar crystal faceting has been formed in both synthetic approaches. The spinel nanoparticles behave as ferrimagnets with a high saturation magnetization and are superparamagnetic at room temperature. The influence of synthesis route on phase purity and unconventional magnetic properties is discussed in some particular cases such as CuFe2O4, CoFe2O4, and ZnFe2O4.

Preparation and characterization of polyethylene/silver nanocomposite films with antibacterial activity

AbstractIn this work, a novel method was proposed for the fabrication of antibacterial nanocomposite polymeric films, for use in food packaging. In the first step, a stable colloidal solution of silver nanoparticles was prepared by chemical reduction of silver salt using fructose as an environmental friendly reducing agent. In the second step, corona air plasma was used as a pretreatment of low density polyethylene (LDPE) films to increase the adhesion of silver nanoparticles on the film surface. In the third step, silver nanoparticles were coated on the LDPE surface by immersion of the treated films in the colloidal silver solutions. Surface morphology of the silver/LDPE nanocomposite was characterized by FE‐SEM and AFM analysis. The amounts of coated silver and silver ion release from the nanocomposite surface were determined. In addition, the antibacterial activity of the fabricated films was evaluated by agar well diffusion and dynamic shake flask methods. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Photochemical reduction of graphene oxide in colloidal solution

Stable aqueous colloidal solutions of graphene oxide stabilized with sodium polyphosphate were obtained. During irradiation of the colloids the oxygen-containing groups of the graphene oxide are eliminated, and the aromatic graphite-like regions in its composition are expanded. This is accompanied by decrease in the energy of the electronic transitions Ebg in such sp2-hybridized fragments. Photoreduction of the colloidal particles of graphene oxide leads to changes in their hydrodynamic size, resulting from 𝜋𝜋 interactions between the aromatic fragments in the particles. It was shown that the Ebg value can be varied purposefully in the range of 0.5-1.9 eV by varying the experimental conditions.

Micellar assemblies from amphiphilic polyurethanes for size-controlled synthesis of silver nanoparticles dispersible both in polar and nonpolar media

A size-controlled synthesis of silver nanoparticles (AgNPs) dispersible in polar and nonpolar media was carried out in micellar assemblies from amphiphilic invertible polyurethanes (AIPUs) based on poly(ethylene glycol) as a hydrophilic constituent and polytetrahydrofuran as a hydrophobic constituent. At a low concentration, AIPUs form micelles with a hydrophilic interior and a hydrophobic exterior. As concentration increases, individual micelles self-assemble into micellar assemblies with hydrophilic interior and hydrophobic exterior domains. It was shown that these domains can be applied simultaneously as nanoreactors and colloidal stabilizers to synthesize size-controlled batches of AgNPs in a nonpolar solvent. Size control and narrow particle size distribution can be facilitated by changes in the AIPU composition, macromolecular configuration, and polymer solution concentration. Depending on the length of polymer hydrophilic and hydrophobic fragments, and fragment distribution along the macromolecule, the size of fabricated AgNPs has been changed from 6 to 14 nm. Owing to the invertible properties of polyurethanes, the synthesized silver nanoparticles can be successfully dispersed in either polar or nonpolar media, where they form stable colloidal solutions.

Functionalization and Dispersion of Hexagonal Boron Nitride (h‐BN) Nanosheets Treated with Inorganic Reagents

A mixture of bulk hexagonal boron nitride (h-BN) with hydrazine, 30% H(2)O(2), HNO(3)/H(2)SO(4), or oleum was heated in an autoclave at 100 °C to produce functionalized h-BN. The product formed stable colloid solutions in water (0.26-0.32 g L(-1)) and N,N-dimethylformamide (0.34-0.52 g L(-1)) upon mild ultrasonication. The yield of "soluble" h-BN reached about 70 wt%. The dispersions contained few-layered h-BN nanosheets with lateral dimensions in the order of several hundred nanometers. The functionalized dispersible h-BN was characterized by IR spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV/Vis spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). It is shown that h-BN preserves its hexagonal structure throughout the functionalization procedure. Its exfoliation into thin platelets upon contact with solvents is probably owing to the attachment of hydrophilic functionalities.

Eggshell membrane: a natural biotemplate to synthesize fluorescent gold nanoparticles

In this article we report a simple, environmentally friendly, and naturally available protein based biotemplate, viz. the chicken eggshell membrane, truly one of nature's gifts, for preparing highly fluorescent gold nanoparticles in solution at ambient conditions in a single step. We propose this as a simple green method to prepare gold nanoparticles both in solution and on the membrane for various applications. A stable colloidal solution of fluorescent Au nanoparticles has been formed in situ during the reduction. The gold nanoparticles, consisting of sizes below 20 nm, were highly fluorescent and exhibited intense blue emission around 437 ± 5 nm. Red emission around 630 ± 5 nm was also observed for the solution. The novelty of this technique lies in the unique properties of this membrane, such as high resistance to pH, safety in handling, and abundant availability in nature. The most important feature of this method is the easy abundance of the source material, which enables cost-effective preparation of gold nanoparticles. In addition to preparing nanoparticles of metals for various applications, this could be used as a very simple method to recover precious metals from chemical and industrial waste.

Controllable Multicolor Upconversion Luminescence of Lanthanide Doped NaGdF4 Nanocrystals Through Single Laser Excitation at 980 nm

Room temperature multicolor Upconversion (UC) luminescence in Yb3+, Tm3+, Er3+ ions doped NaGdF4 nanocrystals have been successfully synthesized by a hydrothermal method. As-prepared nanocrystals are highly crystalline and well-dispersed in cyclohexane to form stable and clear colloidal solutions, which demonstrates strong emission properties with a single laser excitation at 980 nm. The multicolor light consists of blue, green, and red UC radiations that correspond to transitions 1G4 --> 3H6 of Tm3+, 2H(11/2)/4S(3/2) --> 4I(15/2), and 4F(9/2) --> 4I(15/2) of Er3+ ions, respectively. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses.

Synthesis and characterization of Mn doped ZnS d-dots with controllable dual-color emissions

High-quality Mn doped ZnS d-dots were successfully synthesized via an alternative route based on the solvothermal method using oleic acid as stabilizing agent. X-ray diffraction (XRD), transmission electron microscopy (TEM) as well as photoluminescence (PL) spectra were employed to characterize the obtained samples. The as-obtained d-dots are highly crystalline and uniform sized, and they can be well dispersed in hexane to form stable and clear colloidal solution. The optical properties of the d-dots with different Mn doped concentration are investigated in detail. The Mn doped ZnS d-dots have two emission bands, including surface state emission (blue) and Mn emission (orange), which are both sensitivity to the Mn doped concentration. By varying the Mn doped concentration, the relative PL intensities of dual-color emissions can be well manipulated, showing their application in tunable color output. Furthermore, a subsequent ligand exchange has been introduced to give the d-dots hydrophilic surfaces, which are favorable for biological applications.

Pyridylthiourea-grafted polyethylenimine offers an effective assistance to siRNA-mediated gene silencing in vitro and in vivo

Success of synthetic interfering nucleic acids (siRNAs)-based therapy relies almost exclusively on effective, safe and preferably nanometric delivery systems which can be easily prepared, even at high concentrations. We prepared by chemical synthesis various self-assembling polymers to entrap siRNAs into stable polyplexes outside cells but with a disassembly potential upon sensing endosomal acidity. Our results revealed that pyridylthiourea-grafted polyethylenimine (πPΕΙ) followed the above-mentioned principles. It led to above 90% siRNA-mediated gene silencing in vitro on U87 cells at 10nM siRNA concentration and did not have a hemolytic activity. Assembly of siRNA/πPΕΙ at high concentration was then studied and 4.5% glucose solution, pH 6.0, yielded stable colloidal solutions with sizes slightly below 100nm for several hours. A single injection of these concentrated siRNA polyplexes into luciferase-expressing human glioblastoma tumors, which were subcutaneously xenografted into nude mice, led to a significant 30% siRNA-mediated luciferase gene silencing 4days post-injection. Our results altogether substantiate the potential of self-assembling cationic polymers with a pH-sensitive disassembly switch for siRNA delivery in vitro and also in vivo experiments.

Alkyl sulfonated diphosphines-stabilized ruthenium nanoparticles as efficient nanocatalysts in hydrogenation reactions in biphasic media

The organometallic synthesis of ruthenium nanoparticles stabilized by water-soluble alkyl sulfonated diphosphines as ligands is described for the first time. After isolation, the so-obtained nanoparticles could be easily dispersed into water giving rise to stable aqueous colloidal solutions without precipitation over the course of several months. The catalytic behaviour of these aqueous colloidal solutions has been investigated in the hydrogenation of unsaturated substrates (tetradecene, styrene and acetophenone) in biphasic liquid–liquid conditions, showing interesting results in terms of reactivity. Interestingly, small structural differences in the backbone of the diphosphine ligands influence the catalytic activity of these nanocatalysts. In addition, preliminary tests of recycling showed promising results with neither loss of activity or significant precipitation.

Simulation of Asphaltene Aggregation and Related Properties Using an Equilibrium-Based Mathematical Model

Aggregation of asphaltenes was simulated using a mathematical model based on the following consecutive equilibrium: nA⇄K1An and mA+An⇄K2An+m, where A, An, An+m, K1, K2 represent asphaltenes, n aggregates, n + m aggregates, and equilibrium constants, respectively. A mass balance lead to a n + m polynomial in C (C0, n, m, K1, K2, M), where C is the concentration of free solute (monomer), M is the monomer molecular mass, and C0 is the total monomer concentration added to solution. Using numerical methods, this polynomial was solved in terms of C0, K1, and K2 for given values of n, m, and M. Selection of n = 3, m = 5, and M = 800 g L–1 was consistent with data in the literature, and determination of K1 and K2 was achieved by fitting to experimental data from ultrasound velocity, thermal diffusion [thermal lens and dual-beam photothermal reflection (DBPR)], and self-diffusion coefficient techniques. The good fittings found suggest that asphaltene aggregation is adequately described by the present model. A procedure based on the present model was employed to simulate the stepwise adsorption of asphaltenes at the toluene/glass interface. The above sequential equilibrium is discussed in terms of aggregation of the toluene-insoluble asphaltene fraction molecules (A1TM, first equilibrium), followed by incorporation into aggregates of toluene-soluble fraction molecules (A2TM, second equilibrium). This sequential scheme is proposed as a means to keep fraction A1 as nanoaggregates (first step), which, were it not by the presence of A2 (second step), would lead to phase separation. The formation of small aggregates at very low concentrations, predicted by the model, is consistent with the very low solubility of the A1 fraction. When the above mathematical model is combined with the Hansen solubility parameter (HSP) method, it is concluded that asphaltenes form stable colloid solutions in toluene and similar solvents where A1 is insoluble. In other words, for these colloidal solutions, interfacial tension would be zero.

Aberration-Corrected STEM Imaging and In Situ Heating Experiments on Stable Colloidal Solutions of FePt Nanoparticles

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Rare-Earth-Doped Bifunctional Alkaline-Earth Metal Fluoride Nanocrystals via a Facile Microwave-Assisted Process

Rare-earth-doped magnetic-optic bifunctional alkaline-earth metal fluoride nanocrystals have been successfully synthesized via a facile microwave-assisted process. The as-prepared nanocrystals were monodisperse and could form stable colloidal solutions in polar solvents, such as water and ethanol. They show bright-green fluorescence emisson. Furthermore, Gd(3+)-doped ones exhibit paramagnetic behavior at room temperature and superparamagnetic behavior at 2 K.

Adsorption Behavior of 4-Methoxypyridine on Gold Nanoparticles

We demonstrate a phase transfer method to create stable colloidal solutions of Au nanoparticles with 4-methoxypyridine ligands. We then investigate the adsorption behavior of 4-methoxypyridine onto gold surfaces by Raman spectroscopy, DFT calculations, and (1)H NMR. In contrast to unsubstituted pyridine and the frequently used (N,N-dimethylamino)pyridine (DMAP), a flat adsorption of 4-methoxypyridine on gold was found.

Chemical Solution Approaches to YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7−δ</SUB>-Au Nanocomposite Superconducting Thin Films

We explore the feasibility of preparing YBa2CU3O7-Au (YBCO-Au) nanocomposite thin films by chemical solution deposition (CSD). Two approaches were used: (i) A standard in-situ methodology where Au metallorganic salts are added into the precursor solution of YBCO trifluoroacetate (TFA) salts and (ii) a novel approach where stable colloidal solutions of preformed gold nanoparticles (5-15 nm) were homogeneously mixed with TFA-YBCO solutions. A detailed analysis of the microstructure of the films showed that in both cases, there is a strong tendency of gold nanoparticles to migrate to the film surface. However the kinetics of this migration evidences important differences and in the case of preformed nanoparticles their size remains unchanged (a few nanometers) whereas for the in-situ nanocomposites gold ripening leads to large particles (hundreds of nanometers). The grown YBCO-Au films showed good superconducting characteristics (J(c) 2 MA/cm2 at 77 K) but the absence of Au inclusions inside the YBCO matrix explains the fact that no enhancement of vortex pinning was observed.

Preparation and luminescence of water soluble poly (N-vinyl-2-pyrrolidone)/LaF3:Eu3+ nanocrystals

Lanthanide-doped luminescent nanocrystals have great potential as biological luminescent labels, but their use has been limited because of most of these nanocrystals are hydrophobic. In this work, water soluble LaF3:Eu3+ down-conversion nanocrystals were prepared by encapsulated individual nanocrystals with polyvinylpyrrolidone (PVP). Their morphology, surface structure and luminescence properties were explored in detail. The results indicate that these nanocrystals can be readily dispersed in water, forming a stable and transparent colloidal solution. The colloidal solution displayed unique red luminescence with high emission intensity under ultraviolet excitation. These results suggest that these nanocrystals have great potential as luminescent labeling materials for biological applications.

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.

Dual-mode luminescence from lanthanide tri-doped NaYF 4 nanocrystals

Silica-coated NaYF 4:Yb/Er(Tm)/Eu nanocrystals (NCs) with a mean size of 35 nm were prepared and characterized. Each of the core/shell NCs can be dispersed in ethanol and water to form stable colloidal solutions and emit bright visible light of two colors (blue and red, green and red) by up- and down-converting excitation modes. As we know, this is the first time to obtain the distinct dual-color photos of NaYF 4:Yb/Er(Tm)/Eu NCs which were dispersed in deionized water. In particular, the ability to optically manipulate luminescence color of NCs doped with RE ions opens the door to multiplexed detection for high precision in more complex biotic environment.

Deagglomeration and surface modification of thermally annealed nanoscale diamond

Thermally annealed nanodiamond has been functionalized by C–C coupling of the partially graphitized diamond surface using aryl diazonium salts. Depending on the terminal functional groups, the modified bucky diamond nanoparticles show good solubility (up to 0.63 mg mL −1) in different solvents. The agglomerate size of the originally strongly bound detonation diamond (>0.5 μm) is substantially reduced to ∼20–50 nm by this chemical procedure and without using mechanical techniques such as strong ultrasound or milling. Arylation with functionalized aryl diazonium salts carrying COOH, SO 3H, NO 2 or bromoethyl groups opens the way for further covalent grafting of organic structures. Arylation with Ar–COOH or Ar–SO 3H leads to the formation of stable colloidal solutions in water and physiological media (i.e. PBS buffer), an important prerequisite for biomedical applications.

Pore Fabrication in Various Silica-Based Nanoparticles by Controlled Etching

A novel method based on controlled etching was developed to fabricate nanopores on preformed silica nanoparticles (<100 nm in diameter). The obtained monodisperse nanoporous particles could form highly stable homogeneous colloidal solution. Fluorescent silica nanoparticles and magnetic silica-coated gamma-Fe(2)O(3) nanoparticles were investigated as examples to illustrate that this strategy could be generally applied to various silica-based functional nanoparticles. The results indicated that this method was effective for generating pores on these nanoparticles without altering their original functionalities. The obtained multifunctional nanoparticles would be useful for many biological and biomedical applications. These porous nanoparticles could also serve as building blocks to fabricate three-dimensionally periodic structures that have the potential to be used as photonic crystals.