Surface characterization of detonation nanodiamond particles

Specific features of formation of stable suspensions of detonation nanodiamond (DND) in media of different polarities were considered. A relation between the dispersity of DND particles and their surface activity was found. The surface activity of diamond nanoparticles (10–100 nm) is significantly (by a factor of 4) lower than that of submicron-sized particles, which indicates satisfactory environmental parameters of nanosized diamonds. An attempt to reduce the surface energy by grafting hydrophobic radicals led to appreciable increase in the dispersity of DND particles, thereby reducing the risk of harmful DND effect on the environment.     

Surface charge density on spherical silica particles in aqueous alkali chloride solutions

The results of a systematic investigation on the influence of different alkali ion species on the surface charge density, ₀, of spherical silica particles (AEROSIL 300) in the pH range between 4 and 8 and with electrolyte concentrations from 0.005 M to 0.3 M are presented. The accuracy of the data may be described by a residual deviation,s( ₀ ^m ), including at least four single measurements:s( ₀ ^m )>0.2C/cm². The alkali sequence found for the spherical particles is in agreement with data for porous silica published by other authors.     

Comprehensive study of electrosurface properties of detonation nanodiamond particle agglomerates in aqueous KCl solutions

The electrosurface properties of nanoporous agglomerates of detonation nanodiamond (DND) particles purified from acidic impurities by dialysis are comprehensively investigated. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry are employed to measure the adsorption isotherms $\Gamma _{H^ + } (pH)$ and $\Gamma _{OH^ - } (pH)$ of potential-determining ions, as well as the dependences of surface charge density ??₀, electrophoretic mobility u _e, and specific conductivity K _p of the agglomerates on the pH = 3.5?C10.5 of aqueous 0.0001?C0.1 M KCl solutions. The obtained adsorption isotherms indicate heterogeneity of the DND surface, i.e., the presence of different proton-donor and proton-acceptor surface functional groups. Computer simulation of the adsorption isotherms is carried out for a DND surface containing two types of functional groups, namely, acidic carboxyl (-COOH) and amphoteric hydroxyl (-COH) groups, the predominant content of which is confirmed by FTIR spectroscopy data. The optimal values are determined for the reaction constants of ionization of these groups. It is revealed that the effective conductivity of the porous agglomerates is one or two orders of magnitude higher than the conductivity of equilibrium solutions. Corresponding values of electrokinetic potential ?? are calculated as functions of pH and KCl concentration from the electrophoretic mobility of the agglomerates using different equations of electrophoresis theory. It is shown that use of the Miller formula, which takes into account the electromigration fluxes of ions and electroosmotic flows of solutions in pores of dispersed particles, yields more correct ?? potential values for DND agglomerates.     

Biotinylated nanodiamond: simple and efficient functionalization of detonation diamond

We have developed a simple and efficient method for the covalent functionalization of detonation nanodiamond. After homogenization of the surface by borane reduction, the surface was modified with (3-aminopropyl)trimethoxysilane. Subsequent grafting of biotin yielded covalently biotinylated nanodiamond, which was characterized by FTIR spectroscopy, X-ray powder diffractometry, thermogravimetry, and elemental analysis. The activity was tested with horseradish peroxidase-labeled streptavidin. The surface loading of biotin was found to be 1.45 mmol g-1. The new material opens the way to covalently bonded diamond bioconjugates for labeling, drug delivery, and other applications.     

Preparation of clear colloidal solutions of detonation nanodiamond in organic solvents

Highly transparent colloidal solutions of detonation nanodiamonds in organic solvents such as tetrahydrofuran (THF), methyl ethyl ketone (MEK) and acetone were attained in this investigation through an easy process, in which the detonation nanodiamond powder was oxidized at 420 °C for 1.5 h and then dispersed into solvents by beads-milling with the addition of the surfactant, oleylamine (OLA). The results of both Fourier transform infrared spectroscopy and zeta potential measurements confirm that a readily apparent number of Lewis acid sites composed of mainly carboxylic acid and cyclic acid anhydrides were derived on the surface of thermally oxidized nanodiamond (T-ND). This acid sites-derived T-ND is chemically active, favoring the formation of charge-transfer complexes with the amino-containing surfactants such as OLA and octadecylamine (ODA). After being dispersed with one of the surfactants, OLA or ODA, the T-ND shows good dispersion stability in organic solvents; however, the dispersion efficiency of the saturated ODA is not as good as that of the unsaturated OLA. By using the dispersant OLA, accompanied with de-agglomeration by beads-milling, a clear colloidal solution of T-ND in solvents of THF, MEK or acetone can be easily attained and stabilized for at least 3 months.     

Surface charge and adsorption properties of polyethylene in aqueous solutions of inorganic electrolytes

Summary The streaming potentials of several sorts of polyethylene were determined as a function of p_H and composition of aqueous solutions and the electrokinetic (zeta) potentials were calculated. The results were compared with the electrokinetic properties of glass and polystyrene. It has been found that H⁺ and OH^– ions are potential-determining on polyethylene. The surface of polyethylene is charged negatively above p_H 2.5, probably due to dissociation of carboxyl groups, contained on polyethylene as a result of its oxidation during its polymerization and/or further processing. The zeta potentials depend in a rather complicated way on the concentration of various 11 inorganic electrolytes. The probable interpretation of this dependence has been given and conclusion was derived about the absence of compact adhered layer of water molecules at the surface of polyethylene. The results of the present work may be of some importance for elucidating the adsorption properties of polyethylene.

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Zusammenfassung Die Strömungspotentiale verschiedener Arten von Polyäthylen wurden als Funktion des p_H-Wertes und der Zusammensetzung wäßriger Lösungen bestimmt und aus diesen die elektrokinetischen Potentiale (Zeta) berechnet. Die Ergebnisse wurden mit den elektrokinetischen Eigenschaften von Glas und Polystyrol verglichen. Es zeigt sich, daß H⁺- und OH^–-Ionen auf Polyäthylen potentialbestimmend sind. Die Oberfläche des Polyäthylen ist oberhalb p_H 2,5 negativ geladen, vermutlich entsprechend der Dissoziation von Carboxylgruppen, die als Ergebnis der Oxydation während der Polymerisation und/oder weiterer Verarbeitungsprozesse im Polyäthylen enthalten sind. Die Zeta-Potentiale hängen in ziemlich komplizierter Weise von der Konzentration verschiedener ein-einwertiger anorganischer Elektrolyte ab. Die wahrscheinlichste Interpretation dieser Abhängigkeit wurde gegeben und Schlüsse über die Abwesenheit kompakter adsorbierter Schichten von Wassermolekülen auf der Oberfläche des Polyäthylens gezogen.Die Ergebnisse der vorliegenden Arbeit mögen von einiger Bedeutung für die Erkenntnisse der Adsorptionseigenschaften von Polyäthylen sein.

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The authors are indebted to Dr.P. Skivan for helpful discussion of the streaming potential method and to Dr.J. Hradil for kindly supplying the polyethylene samples.     

Electrosurface properties of single-crystalline detonation nanodiamond particles obtained by air annealing of their agglomerates

A complex study of electrosurface properties has been performed for single-crystalline detonation nanodiamond particles with sizes of 4–5 nm obtained by air annealing of their agglomerates. FTIR spectroscopy and X-ray photoelectron spectroscopy data indicate that the investigated properties result from the presence of two types of ionogenic functional groups on the particle surface, i.e., acidic carboxyl and amphoteric hydroxyl groups. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry have been employed to measure the Γ_H⁺(pH) and Γ_OH^-(pH) adsorption isotherms of potential-determining ions, as well as the pH dependences (in a pH range of 3.5–10.5) of the surface charge density, electrophoretic mobility, and specific surface conductivity of detonation nanodiamond particles in aqueous 0.0001–0.01 M KCl solutions.     

Ion-exchange properties of microdispersed sintered detonation nanodiamond

The adsorption of transition metal cations and inorganic anions from aqueous solutions on microdispersed sintered detonation nanodiamond (MSDN) is systematically studied. The selectivity series Fe³⁺ > Al³⁺ > Cu²⁺ > Mn²⁺ > Zn²⁺ > Cd²⁺ > Co²⁺ > Ni²⁺ with maximum adsorption capacity between 2 and 5 µmol g^?1 is obtained. It is found that anions may significantly contribute to the adsorption of transition metal cations, so the adsorption of CH₃COO^?, Cl^?, B₄O₇ ^2?, ClO₄ ^?, I^?, SO₄ ^2?, C₂O₄ ^2?, PO₄ ^3? is also studied. For the first time, dominating adsorption of anions over cations is demonstrated for detonation nanodiamond. The maximum anion-exchange capacity of 50–150 µmol g^?1 is found for MSDN. Beside of electrostatic interactions, the formation of complexes with hydroxyl groups and interaction with metal impurities contribute to the adsorption of B₄O₇ ^2? and PO₄ ^3?, respectively. Therefore, anion exchange selectivity of MSDN is different from that observed for common anion exchange resins. In all cases, the adsorption on MSDN obeys Langmuir law. The pH effect on the adsorption of SO₄ ^2?, PO₄ ^3? and B₄O₇ ^2? is different from that observed for other anions due to specific interactions.     

Counterion condensation in hydrosols of single-crystalline detonation nanodiamond particles obtained by air annealing of their agglomerates

The pattern of previously recorded dependences of the specific surface charge and electrophoretic mobility of monodisperse detonation nanodiamond particles on pH of aqueous KCl solutions suggests that counterions are condensed on the particle surface. Counterion condensation is considered in terms of the Levin model, and the experimental ratios between the densities of the electrokinetic and surface charges of dispersed particles, as well as the fractions of condensed counterions, are calculated as depending on pH and KCl concentration in nanodiamond hydrosols. The obtained dependences lead to the conclusion that counterion condensation on the surface of detonation nanodiamond particles does indeed take place.     

The effect of simple electrolytes on coagulation of hydrosols of monodisperse negatively charged detonation nanodiamond

The influence of the concentration of potassium and barium chlorides on the aggregation stability of a hydrosol of monodisperse negatively charged detonation nanodiamond with particle sizes of 4?5 nm obtained by annealing of its agglomerates in air has been studied by turbidimetry. The experimental results have been discussed within the classical and generalized Derjaguin?Landau?Verwey?Overbeek theories. The analysis of the pair interaction potentials calculated for ultradispersed particles of detonation nanodiamond has led to the conclusion that the coagulation occurs by the barrier mechanism in the primary potential minimum. It has been assumed that the structural component of the interparticle interaction energy contributes to the total balance of the surface forces.     

Purification of detonation nanodiamond material using high-intensity processes

New procedures were developed for chemical treatment of detonation nanodiamonds and diamond-containing detonation blend to remove water-insoluble metal-containing impurities. The detonation nanodiamond material is treated with complexing agent solutions under cavitation conditions and at high temperature and pressure. Sodium 2,3-dimercaptopropanesulfonate (Unithiol), disodium dihydrogen ethylenediaminetetraacetate, thiourea, potassium thiocyanate, dicyandiamide, and hexamethylenetetramine are used as complexing agents. The complexing agent concentration in solution is 0.5–20 wt % at the nanodiamond material to complexing agent weight ratio higher than 0.2. The use of aqueous solutions of the complexing agents at high temperatures and pressures appeared to be the most efficient.     

Redispergation of TiO2 particles in aqueous solutions

The colloidal stability of TiO2 dispersions in aqueous solutions was studied. Aqueous solutions of ATLAS G-3300 (1.57 x 10(-3) mol/l), TRITON X-100 (5 x 10(-5) mol/l), and PMAA (4 x 10(-6) and 5.81 x 10(-3) mol/l) have been used as medium for redispergation of TiO2 particles. Stability of dispersions was investigated at different pH values by two different methods. By using analytical centrifuge the sedimentation velocity of TiO2 particles was directly measured and by means of light scattering the particle size of dispersed particles has been monitored. Combination of these two methods allowed determination of the aggregation degree of TiO2 particles as well as structure of the aggregates formed in aqueous phase. It has been found that redispergation process does not provide complete separation of virgin TiO2 particles. Even in the case of stable dispersions some aggregates were found, which consisted of 2-4 virgin TiO2 particles. With increasing colloidal stability of dispersions aggregates appear to be spherically shaped. In the system where TRITON X-100 was used, formation of secondary aggregates by fusion of primary ones was observed.     

Water and aqueous solutions: simple non-speculative model approach

Different ways of molecular modeling of water are analyzed and their similarities and differences identified. An up-to-date summary of achievements of a general approach to common rigid site-site interaction models of molecular fluids applied to water and aqueous solutions is then presented and discussed. The method is based on considering only a short-range part of a total realistic potential (such as SPC/E or TIPxP) which determines the structure of water (and fluids in general). A simplification of the interactions at short intermolecular separations leads then to simple models, called primitive models. Quite accurate results in an analytic form for the thermodynamic properties of the models are obtained using the thermodynamic perturbation theory. It is shown that the properly constructed primitive models reproduce, qualitatively, anomalies of pure water and basic characteristics of hydrophobic hydration. The concept of an extended excluded volume, based on pseudo-hard bodies, is introduced and exemplified by considering the partial molar volume of apolar solutes. Potential future development towards a theory of water based on the primitive models as a reference with the long-range contributions added as a perturbation is discussed.     

Gel permeation chromatography of simple anions in aqueous solutions

Semi-automatic liquid chromatographic apparatus is described for the separation of simple inorganic anions in aqueous solution, using dextran gels for the separation and differential conductivity for detection. The influence of different types of eluent on the degree and order of separation is discussed.     

Mechanism of formation of adsorption complexes amikacin–detonation nanodiamond

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Surface selective deposition of Mo(IV) on Ni/TiO2 particles in aqueous solutions

The selective depositions of MoS2 and MoO2 over Ni surfaces are demonstrated on Ni/TiO2 particles in a mild electroless deposition process. High-resolution transmission electron microscopy (HRTEM) images show the uniform distribution of 10-30 nm spherical and hemispherical Ni particles on TiO2 surface, and three to six layers of MoS2 on the surface of Ni particles. The as-prepared MoS2-Ni/TiO2 is used as a catalyst for the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT), and shows a significant increase over commercial catalysts in turnover frequencies as the result of unique distribution of active components in the binary catalyst. The selective material deposition is explained in the context of Ni catalyzed KBH4 decomposition, which produces strong reducing species responsible for the site selective deposition of Mo. The synthetic method can be potentially used to prepare bimetallic materials with similar nanostructures such as those of Mo-Co, Mo-Pd, and Mo-Rh.     

Substitutional nitrogen in nanodiamond and bucky-diamond particles

The inclusion of dopants (such as nitrogen) in diamond nanoparticles is expected to be important for use in future nanodevices, such as qubits for quantum computing. Although most commercial diamond nanoparticles contain a small fraction of nitrogen, it is still unclear whether it is located within the core or at the surface of the nanoparticle. Presented here are density functional tight binding simulations examining the configuration, potential energy surface, and electronic charge of substitutional nitrogen in nanodiamond and bucky-diamond particles. The results predict that nitrogen is likely to be positioned at the surface of both hydrogenated nanodiamond and (dehydrogenated) bucky-diamond, and that the coordination of the dopants within the particles is dependent upon the surface structure.