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.     

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 of detonation nanodiamond particles in aqueous solutions of simple 1 : 1 Electrolytes

Adsorption isotherms of potential-determining H⁺ and OH⁻ ions and the pH dependences of the specific surface charge of detonation nanodiamond (DND) particles are obtained in a pH range of 3–10 by the acid-base titration of their hydrosols containing 0.001–1 M LiCl, NaCl, KCl, NaNO₃, KNO₃, and NaClO₄ as background electrolytes. The data obtained attest to the chemical nonuniformity (heterogeneity) of a DND surface and different degrees of binding of background electrolyte cations and anions with ionized groups. It is revealed that the adsorption of OH-anions diminishes in the lyotropic series of cations Na⁺ > K⁺ > Li⁺ and increases with a decrease in the adsorbability of anions in the following series: NO₃⁻ ≊ ClO₄⁻ > Cl⁻. The adsorption of potential-determining H⁺ and OH⁻ ions on a DND surface containing two types of functional groups, i.e., acidic carboxyl and amphoteric hydroxyl groups, is simulated by the Protofit software package. The optimal surface densities and ionization constants that correspond to minimal deviations of model adsorption isotherms from the experimental curves are found for these groups.     

Stable colloidal dispersions of fullerenes in polar organic solvents.

Colloidal dispersions of C60 and C70 were prepared by simply mixing a fullerene solution in a good solvent with a poor polar organic solvent for fullerenes. The process was very easy and fast and the formation of particles with average diameter in the colloidal range was detected immediately after the components were mixed. The formation and the properties of the fullerene particles were studied mainly with dynamic light scattering and high-resolution transmission electron microscopy. The most interesting findings are the long-term colloid stability of the samples in the absence of any stabilizers, the relatively narrow size distribution, and the different average sizes of the particles formed by C60, C70, and their mixtures. The influence of various factors such as fullerene concentration, mixing procedure, solvent properties, and C60/C70 ratio was investigated. It is shown that the smaller particles are formed when the total fullerene concentration in the good solvent is decreased and that the fullerene particles have crystalline structure. The measured negative values for the electrophoretic mobility of the particles suggest that fullerene dispersions in polar organic solvents are stabilized by repulsive electrostatic interactions.     

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.     

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.     

Oxidation and reduction of nanodiamond particles in colloidal solutions by laser irradiation or radio-frequency plasma treatment

Functionalized nanodiamond particles (NDs) represent carbon nanomaterial with unique properties for various applications. Here we report on a new approach to surface modification of NDs by their exposure to radio frequency (RF) plasma or laser irradiation (LI) plasma directly in aqueous solution. By using grazing angle reflectance Fourier transform infrared spectroscopy and supporting analysis by X-ray photoelectron spectroscopy, zeta-potential, and Kelvin force microscopy we show that surface chemistry of NDs produced by detonation process (DNDs) or high-pressure high-temperature process (HPHT NDs) works in different way. Moieties on as-received NDs are dominated by COOH and COC groups due to wet chemical cleaning procedures. On DNDs, both RF and LA treatment lead to removal of sp² shell and additional oxidation of the surface to C OC groups. On HPHT NDs the RF treatment leads to reduction of COC groups that are transformed into COH and CH moieties. Thus at least partial hydrogenation of colloidal HPHT NDs seems feasible.     

Drying dissipative patterns of colloidal crystals of silica spheres in organic solvents

Drying dissipative structural patterns formed in the course of drying colloidal crystals of silica spheres (110 nm in diameter) in water, methyl alcohol, ethyl alcohol, 1-propyl alcohol, diethyl ether, and in the mixtures of ethyl alcohol with the other solvents above have been studied on a cover glass. The macroscopic broad rings were formed in the outside edges of the dried film for all the solvents examined. Furthermore, much distinct broad rings appeared in the inner area when the solvents were ethyl alcohol, methyl alcohol, and their mixtures. Profiles of the thickness of the dried films were sensitive to the organic solvents and explained well with changes in the surface tensions, boiling points, and viscosities of the solvents. The macroscopic and microscopic spoke-like crack patterns formed. The drying area (or the drying time) increased (or decreased) as the surface tension of the solvent decreased. However, the absolute values of these drying parameters are determined also by the boiling points of the solvents. Importance of the fundamental properties of the solvents is supported in addition to the characteristics of colloidal particles in the drying dissipative pattern formation.     

Formation of colloid crystals from polymer-modified monodisperse colloidal silica in organic solvents

The formation of colloid crystals from monodisperse and polymer-modified silica particles in organic solvents was investigated. Maleic anhydride–styrene copolymer-modified silica formed crystals in polar organic solvents, which dissolve the copolymer, while the original colloidal silica formed crystals in organic solvents which were miscible with water. The critical volume fraction in the crystal formation of the polymer-modified silica was lower than that from the unmodified silica in the same solvent. Polystyrene- and poly(methyl methacrylate)-modified silica particles also crystallized in organic solvents, but the features of the formation were different from those of poly(maleic anhydride-styrene)-modified particles. Received: 19 September 1998 Accepted in revised form: 1 January 1999     

Colloidal crystallization of colloidal silica modified with ferrocenyl group-contained polymers in organic solvents

Surface modification of colloidal silica with ferrocenyl-grafted polymer and colloidal crystallization of the particles in organic solvent were studied. Poly(methyl methacrylate-co-vinylferrocene)-grafted silica never formed colloidal crystals in polar solvent, such as acetone, acetonitrile, ethanol and N,N-dimethylformamide (DMF), while poly(methyl methacrylate-co-ferrocenyl acrylate)-grafted silica gave colloidal crystallization in DMF. The particles prepared by grafting of poly(N,N-dimethylacrylamide-co-vinylferrocene), with vinylferrocene (Vfc) mole fraction of 1/13 and 1/23, were observed to give the crystallization in ethanol and DMF over particle volume fraction of 0.058. Further, silica modified with copolymer of Vfc and N-vinyl-2-pyrrolidone, N-vinylcarbazole or N-isopropylacrylamide formed colloidal crystals in ethanol and DMF. Especially, poly(N-isopropylacrylamide-co-Vfc)-grafted silica, which was composed of the highest mole fraction of vinylferrocene, 1/3, afforded colloidal crystallization in ethanol over particle volume fraction of 0.053. Relatively high polar vinylferrocene copolymer grafting of silica resulted in colloidal polymerization in organic solvents.     

Preparation and properties of surfactant-bacillolysin ion-pair in organic solvents

The transesterification-active enzyme bacillolysin was extracted into organic solvents such as isooctane by enzyme-AOT (bis (2-ethylhexyl) sulfosuccinate) ion-pairing preserving its natural second structure and catalytic activity. Extraction efficiency was affected by the interaction mode of the two phases, ionic strength, and pH of aqueous phase, surfactant and enzyme concentration. Magnetic stirring with phase mixing was favorable for the enzyme extraction. Optimal ionic strength and pH were 8 mM CaCl₂ and 5.0, respectively. Critical number of AOT molecule for an enzyme molecule to be extracted into isooctane was 89. Optimal initial enzyme concentration in the aqueous phase was 7 mg mL⁻¹ while the initial AOT concentration in isooctane was 3 mM. Within CMC (critical micellar concentration) of AOT in isooctane, the increase of initial AOT concentration enhanced the extraction efficiency.     

Mechanism of formation of adsorption complexes amikacin–detonation nanodiamond

1. Download : Download high-res image (161KB)
2. Download : Download full-size image

     

Immobilization of enzyme on detonation nanodiamond for highly efficient proteolysis

Immobilization of enzyme on detonation nanodiamond (dND, 3-10 nm) and its application for efficient proteolysis have been demonstrated. By evaluation of the Michaelis constant (K_m) and maximum velocity (V_max) of immobilized enzyme, its activity was not impaired significantly by immobilization. And enzyme immobilized on dNDs exhibited much better thermal and chemical stabilities than its free counterpart and maintained high activity even after 10 times reuse. The efficient proteolysis by trypsin immobilized on dNDs (dND-trypsin) is demonstrated with the digestion of myoglobin (or other model protein) in a short time (5 min). Large numbers of identified peptides obtained by dNDs-trypsin enable a higher degree of sequence coverage and more positive identification of proteins than those obtained by in-solution digestion and the commercial immobilized trypsin beads, respectively. Moreover, immobilization of peptide-N-glycosidase F (PNGase F) on dNDs was realized and resulted in faster sequential glycosidase digestion of glycopeptides in less than 10 min.     

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 organomagnesium reagents in hydrocarbon solvents without organic bases

A detailed investigation of the formation of n-R₂Mg compounds in hydrocarbon solvents in the absence of organic base is reported, including information on the nature of the solutions formed and by-products, the effect of the alkyl halide, the hydrocarbon solvent and temperature of formation. The colorless product solutions had relatively high R₂Mg/MgX₂ ratios ranging from about 4 for preparations from alkyl iodides to almost 30 for those from alkyl chlorides. sec-Butyl bromide reacted only in the presence of a stoichiometric amount of diethyl ether in hexane to form solutions of [s-BuMgBr-Et₂O]_x. The reactions of the n-R₂Mg compounds in hydrocarbon solutions were also examined. Possible implications are discussed regarding the nature of these compounds.