Oleate Ions Research Articles

Facet control of ceria nanocrystals synthesized by an oleate-modified hydrothermal method

Ceria nanoparticles with controlled crystal orientations were fabricated via an oleate-modified hydrothermal method, which involved varying the molar ratio of oleate ions to cerium ions in the reaction solution ([Ole/Ce]) from 0 to 1. Quasicubic nanoparticles having primary {100} facets in addition to {110} edges were obtained for [Ole/Ce] values greater than 1/2. On the other hand, polyhedral nanoparticles surrounded by primary {111} facets appeared on nanoparticle surface at [Ole/Ce] smaller than 1/4. It was found that the bonding of the carboxyl terminals of the oleate ions with the cerium(IV) ions on the {100} surfaces balanced the electric charge of the stacked layers and that this is what resulted in the formation of cubic nanoparticles surrounded by {100} facets for [Ole/Ce] values larger than 1/2.

Comparison of microwave irradiation and oxidation roasting as pretreatment methods for modification of ilmenite physicochemical properties

The effect of microwave irradiation and oxidation roasting (as a conventional heating method) on ilmenite surface properties and its flotation behavior were compared. This comparison was performed by carrying out micro and laboratory scales flotation tests, XPS, XRD, FTIR, SEM and microprobe analyses, zeta potential and contact angle measurements. The micro scale flotation experiments indicated that the ilmenite flotation recovery improves from 73.5% to almost 94% and 91% after pretreatment by microwave irradiation and oxidation roasting, respectively. This is in good concordance with the results of XPS analysis showing the increase of Fe3+ content from 48.5% to 66% after pretreatment by microwave irradiation and 64.8% after oxidation roasting. As evidenced by FTIR analysis, zeta potential and contact angle measurements, the improvement in ilmenite floatability and hydrophobicity after pretreatment is due to the entrance of more oleate ions into the Helmholtz layer and the increase of the formation of ferric iron oleate which is more insoluble than the ferrous one. The surface properties and floatability of quartz does not change significantly after pretreatment by both methods.In ore flotation experiments, when the grinded ore was pretreated by microwave irradiation and oxidation roasting, without significant changes in the TiO2 grade of flotation concentrate, the recovery of TiO2 improves from 65.4 to 76.2% and 73.7%, respectively. In the case of non-grinded ore, the recovery of TiO2 increases up to 79.8% and 70.2% after microwave irradiation and oxidation roasting, respectively. The decrease of iron content in the gangue minerals increases the improvement of TiO2 grade and recovery after pretreatment by both methods. Using microwave irradiation as a pretreatment process, the improvement in the recovery of TiO2 and separation efficiency is more than those of oxidation roasting. In addition, microwave irradiation reduces the consumption of activation and depressant agents.

Selective Growth and Structural Analysis of Regular MnO Nanooctapods Bearing Multiple High-Index Surface Facets.

Although numerous morphologies of MnO nanostructures have been reported, an exact structural analysis and mechanistic study has been lacking. In the present study, the formation of regular MnO octapods was demonstrated in a simple procedure, comprising the thermal decomposition of manganese oleate. Because of their structural uniformity, an ideal three-dimensional model was successfully constructed. The eight arms protruded from the cubic center with tip angles of 38° and surface facets of {311} and {533} with rounded edges. The concentrations of oleate and chloride ions were the determining factors for the octapod formation. Selective coordination of the oleate ions to the {100} faces led to edge growth along the <111> direction, which was then limited by the chloride ions bound to the high-index surface facets. These structural and mechanistic analyses should be helpful for understanding the complex nanostructures and for tuning their structure-related properties.

Capreomycin oleate microparticles for intramuscular administration: Preparation, in vitro release and preliminary in vivo evaluation

Capreomycin sulfate (CS) is a second-line drug used for the treatment of multidrug-resistant tuberculosis (MDR-TB). The adverse effects profile and uncomfortable administration scheme of CS has led to the development of formulations based on liposomes and polymeric microparticles. However, as CS is a water-soluble peptide that does not encapsulate properly into hydrophobic particulate matrices, it was necessary to reduce its aqueous solubility by forming the pharmacologically active capreomycin oleate (CO) ion pair. The aim of this research was to develop a new formulation of CO for intramuscular injection, based on biodegradable microparticles that encapsulate CO in order to provide a controlled release of the drug with reduced local and systemic adverse effects.The CO-loaded microparticles prepared by spray drying or solvent emulsion-evaporation were characterized in their morphology, encapsulation efficiency, in vitro/in vivo kinetics and tissue tolerance. Through scanning electron microscopy it was confirmed that the microparticles were monodisperse and spherical, with an optimal size for intramuscular administration. The interaction between CO and the components of the microparticle matrix was confirmed on both formulations by X-ray powder diffraction and differential scanning calorimetry analyses. The encapsulation efficiencies for the spray-dried and emulsion-evaporation microparticles were 92% and 56%, respectively.The in vitro kinetics performed on both formulations demonstrated a controlled and continuous release of CO from the microparticles, which was successfully reproduced on an in vivo rodent model. The results of the histological analysis demonstrated that none of the formulations produced significant tissue damage on the site of injection. Therefore, the results suggest that injectable CO microparticles obtained by spray drying and solvent emulsion-evaporation could represent an interesting therapeutic alternative for the treatment of MDR-TB.

Stable Colloidal Suspension of Magnetic Nanoparticles for Applications in Life Sciences

Various utilizations of magnetitc nanoparticles (MNPs), highly biocompatible, in biomedicine and environmental sciences require not only fine granulated powder but also stable dispersion in fluid media. MNPs were synthesized by chemical co-precipitation route. MNP surface modification was carried out with oleate ions as coating shell able to ensure colloidal MNP stability and also allowing further adding of secondary organic shell for conferring hydrophylicity or possibility of grafting various biomolecules. Granularity of colloidal MNPs was analyzed using microscopy techniques, crystalline properties by X-ray diffraction while superparamagnetic properties by magnetometry were assessed. The influences of magnetic and non-magnetic stirring, used alternatively during the preparation steps - on the microstructural and magnetic features are discussed. The MNP suspensions response to electromagnetic fields was studied by measuring the components of magnetic susceptibility. The investigation results suggested the usefulness of the yielding technology based on non-magnetic mixing during both ferrophase preparation and surface modification.

Synthesis of Monodisperse SrTi1–xZrxO3 Nanocubes in Oleate by a Two‐Phase Solvothermal Method

AbstractNanocubes of mixed‐crystal perovskites SrTi1–xZrxO3 (x = 0.25–0.6) were obtained in a two‐phase oil/water solvothermal environment. In an optically transparent autoclave, the evolution of an alkali metal oleate phase at the oil/water interface was monitored; this phase is the environment for nucleation and growth of the nanocrystals. The typical synthesis yields monodisperse nanocubes with an edge length of 10 nm. The size and shape of the nanoparticles do not depend on the Zr content and, most remarkably, do not vary with reaction time. We propose a growth mechanism that depends on the accessibility of the metal hydroxyalkanoate monomers to the growing crystal: after the formation of {100} facets, they are densely capped by oleate ion surfactants, and monomers are no longer able to attach. Increasing the reaction time only increases the amount of nanoparticles formed. As determined by Raman spectroscopy and energy‐dispersive X‐ray spectroscopy, the nanoparticles have the cubic (Pm$\bar {3}$m) perovskite structure and have an excess of B‐site ions (Ti + Zr), which is explained by a terminating Ti/Zr + O surface layer of the nanocubes. The monodisperse particles self‐assemble to form monolayers on a support.

Influence of microwave irradiation on ilmenite surface properties

Abstract In this study, the effect of microwave irradiation on ilmenite surface properties and its flotation behavior was investigated. After microwave irradiation, Fe 2+ ions on the ilmenite surface are oxidized to Fe 3+ ions. XPS analysis indicated that the relative content of Fe 3+ increased from 48.5% to 66% after microwave irradiation for 2.5 min. This conversion decreased the ilmenite surface zeta potential in a wide pH range and resulted in the shift of PZC from a pH of 5.4 to a pH of 2.7. FTIR spectra and zeta potential measurements showed that the microwave irradiation enhances the adsorption of oleate ions on the ilmenite Helmholtz layer. The greater stability of chemisorbed ferric iron oleate than ferrous iron oleate resulted in the increase of contact angle and the decrease of surface zeta potential. Therefore, the microwave irradiation pretreatment improves the ilmenite hydrophobicity and floatability in a wide pH range. The maximum floatability of ilmenite occurring at a pH of 6.3 was 73.5% and 94% for non-irradiated and irradiated ilmenite, respectively.

Formulation design for target delivery of iron nanoparticles to TCE zones

Nanoparticles of zero-valent iron (NZVI) are effective reducing agents for some dense non-aqueous phase liquid (DNAPL) contaminants such as trichloroethylene (TCE). However, target delivery of iron nanoparticles to DNAPL zones in the aquifer remains an elusive feature for NZVI technologies. This work discusses three strategies to deliver iron nanoparticles to DNAPL zones. To this end, iron oxide nanoparticles coated with oleate (OL) ions were used as stable analogs for NZVI. The OL-coated iron oxide nanoparticles are rendered lipophilic via (a) the addition of CaCl2, (b) acidification, or (c) the addition of a cationic surfactant, benzethonium chloride (BC). Mixtures of OL and BC show promise as a target delivery strategy due to the high stability of the nanoparticles in water, and their preferential partition into TCE in batch experiments. Column tests show that while the OL-BC coated iron oxide nanoparticles remain largely mobile in TCE-free columns, a large fraction of these particles are retained in TCE-contaminated columns, confirming the effectiveness of this target delivery strategy.

Adsorption of phosphorylated chitosan on mineral surfaces

A chitosan sample was modified by phosphorylation reactions on the hydroxyl site. The chemical structure of the resulting grafted chitosan was studied by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The adsorption behaviors of the phosphorylated chitosan on two oxide minerals, copper carbonate (malachite) and manganese carbonate (rhodochrosite) were studied by flotation, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and XPS. It was observed that the phosphorylated chitosan adsorbed more strongly on rhodochrosite possibly through covalent bonds of both the PO group and the POH group with the rhodochrosite surface, but only the POH group was observed to bind with malachite surface possibly through hydrogen bonds. The different adsorption mechanisms led to the flotation of malachite and depression of rhodochrosite using sodium oleate as a collector. The oleate ions could replace the relatively weakly bound phosphorylated chitosan from malachite surfaces, making it floatable in the presence of the phosphorylated chitosan.

A green, low-cost, and highly effective strategy to enhance the performance of hybrid solar cells: Post-deposition ligand exchange by acetic acid

We utilize an adsorption/desorption process between the excess acetic acid in solution and the bound oleate ions on the surface of CdSe quantum dots to achieve ligand exchange process in the hybrid film of poly (3-hexylthione) (P3HT): CdSe quantum dots (QDs). By this post-deposition ligand exchange method, we achieved hybrid solar cells with power conversion efficiency of nearly 2% at low annealing temperature (120°C). Compared to the thiols that are widely used in hybrid solar cells, acetic acid shows its advantages of environmental friendliness, non-toxicity and mild odors. As such, our method is attractive for future hybrid solar cell applications.

Controllable synthesis of β-NaYF4:Yb,Er nanorods by potassium oleate as ligand

By using potassium oleate (KOL) as a part of ligand, nanorods of β-NaYF4:Yb,Er were synthesized. The aspect ratio of β-NaYF4:Yb,Er nanocrystals was tuned by changing the amount of KOL. We found that potassium from KOL is not only absorbed on the surface of nanocrystals, but also partially substitutes Na element in nanocrystals lattice. Different from the classical shape control mechanism that oleate ions are absorbed on different facets of nanocrystals, the anisotropic growth of β-NaYF4:Yb,Er in current work is caused by the doping of K+. The incorporation of K+ would not lead to obvious decrease of the upconversion fluorescence intensity. Meanwhile, oleate ions promote the phase transition of nanocrystals from cubic to hexagonal phase, resulting in the simultaneous controllability of the nanocrystals size.

Thermal decomposition synthesis of Al-doped ZnO nanoparticles: an in-depth study

Al-doped ZnO nanoparticles are synthesized by means of a heating up solution based thermal decomposition method. The synthesis involves a reaction of zinc acetylacetonate hydrate, aluminium acetylacetonate and 1,2-hexadecanediol in the presence of oleic acid and oleyl amine. A proposed reaction mechanism from reagents to monomers is corroborated by analysis of the evolving gases using headspace GC-MS analysis. The Al-doped ZnO nanoparticles synthesized are dynamically stabilized by adsorbed oleate ions, after deprotonation of oleic acid by oleyl amine, as was found by NOESY proton NMR and complementary FTIR spectroscopy. Precession electron diffraction shows a simultaneous increase in lattice parameters with Al concentration. This, together with HAADF-STEM and EDX maps, indicates the incorporation of Al into the ZnO nanoparticles. By the combination of complementary characterization methods during all stages of the synthesis, it is concluded that Al is incorporated into the ZnO wurtzite lattice as a dopant.

Growth Mechanisms and Kinetics of Gibbsite Crystallization: Experimental and Quantum Chemical Study

We present experimental and molecular modeling studies, which examine the influence of crystal growth modifiers (CGMs) on the crystallization mechanism and kinetics of gibbsite crystallization in supersaturated sodium aluminate solutions. Seeded, pure caustic sodium aluminate synthetic liquors and real industrial Bayer liquor containing significant amounts of organic and inorganic impurities, in the absence and presence of a CGM containing oleate ions, were investigated. Our results show massive growth of colloidal sized protrusions on the seed particle surfaces on addition of the CGM in the pure synthetic caustic aluminate liquors. Although the activation energies for both secondary nucleation and growth were found to be increased, the overall crystallization rate was surprisingly also increased by addition of CGM. This behavior is attributed to the increased pre-exponential factor possibly arising from higher probability of effective collisions due to more effective species orientation facilitating the crystallization process. The crystallization rate was significantly slower in the industrial Bayer liquor, most likely due to the presence of impurities; nevertheless, a greater degree of surface protrusions on crystal growth was noted on addition of the CGM. In conjunction with the experimental results, we use semiempirical quantum-chemical calculations to examine the underlying processes that result in the enhanced growth due to the presence of the CGM. Our quantum-chemical modeling results suggest that the increased crystallization rate may be due to a mechanism by which Al(III)-containing dimers are produced due to intervention by the oleate ion.

Interaction Between Y3+ and Oleate Ions for the Cubic-to-Hexagonal Phase Transformation of NaYF4 Nanocrystals

Understanding the phase transformation of NaYF4 nanocrystals from cubic to hexagonal is of great importance for both scientific interests and applications. Herein, based on the density functional theory, we found that the dominant difference between cubic and hexagonal phase NaYF4 is the location of Y3+, and oleate ions are particularly favorable to bonding with Y3+. The results indicated that oleate salts as ligand possibly induce the orderly arrangement of Y3+ and lower the energy barrier for the formation of hexagonal phase. The experiments of using different amount of oleate ions as ligand were designed to elucidate their influence on the phase transformation. We found that the approach with relatively high amount of sodium oleate results in dramatic shortening of reaction time (down to 5 min) on cubic-to-hexagonal phase transition for preparing ultrasmall (∼13 nm) hexagonal phase NaYF4 nanocrystals. To exclude the influence of Na+ increasing in using sodium oleate, potassium oleate was also used as l...

Size-Tunable, Bright, and Stable PbS Quantum Dots: A Surface Chemistry Study

PbS Qdots are synthesized using PbCl2 and elemental sulfur as precursors. The available size range is significantly expanded using tri-n-octylphosphine (TOP), enabling the synthesis of monodisperse suspensions of Qdots with a mean size varying between 3 and 10 nm. The ligand composition and dynamics are investigated with nuclear magnetic resonance (NMR) spectroscopy. We show that the Qdots are passivated solely by highly dynamic OlAm ligands, even when TOP is employed during synthesis. In this respect, TOP is a compound strongly modifying the Qdot synthesis, without affecting the final Qdot surface chemistry. Next, the OlAm ligands are exchanged for oleic acid (OlAc). NMR data show that the OlAc ligands are tightly bound to the Qdot surface, with a coverage of 3.0±0.4 nm(-2). In addition, we demonstrate that they are bound as oleate ions. Combining this with the inorganic Qdot composition, we observe that charge-neutral Qdots are obtained when taking into account the charge of the stoichiometric PbS Qdot core, the surface excess of Pb ions, the surface-adsorbed Cl ions and the oleate ligands. The Qdot suspensions are stable under atmospheric conditions, showing no changes in the NMR and absorbance spectra for several weeks. Finally, we determine the photoluminescence quantum yield (PL QY) for OlAc-capped PbS Qdots, synthesized either with or without TOP. In both cases, they are highly luminescent, with PL QY values varying between 20 and 90%, depending on the Qdot size.

Utilizing Self-Exchange To Address the Binding of Carboxylic Acid Ligands to CdSe Quantum Dots

We use solution NMR techniques to analyze the organic/inorganic interface of CdSe quantum dots (Q-CdSe) synthesized using oleic acid as a surfactant. It is shown that the resulting Q-CdSe are stabilized by tightly bound oleic acid species that only exchange upon addition of free oleic acid. The NMR analysis points toward a two-step exchange mechanism where free ligands are initially physisorbed within the ligand shell to end up as bound, chemisorbed ligands in a second step. Importantly, we find that every ligand is involved in this exchange process. By addition of oleic acid with a deuterated carboxyl headgroup, we demonstrate that the bound ligands are oleate ions and not oleic acid molecules. This explains why a dynamic adsorption/desorption equilibrium only occurs in the presence of excess free oleic acid, which donates the required proton. Comparing the number of oleate ligands to the excess cadmium per CdSe quantum dot, we find a ratio of 2:1. This completes the picture of Q-CdSe as organic/inorganic entities where the surface excess of Cd(2+) is balanced by a double amount of oleate ligands, yielding overall neutral nanoparticles.

Electrokinetic properties of hydroxyapatite under flotation conditions

The effect of calcite supernatant, calcium, and carbonate ions on the hydroxyapatite (HA) zeta potential without and in the presence of sodium oleate (1 × 10 −4 mol L −1) was examined within the pH range from 4 to 12. The interpretation of results was based on the HA surface and oleate solution chemistry, and on some floatability tests. HA, with different positive and negative surface sites formed depending on its solubility and pH, had a negative zeta potential over the whole pH range. This mineral is not naturally floatable (flotation recovery, 5% < R < 18%). The oleate ions (Ol −), present in a very low concentration in an acidic medium (pH from 4.8 to 6), chemisorb individually on HA surface centers Ca +, HPO 4Ca +, and OH 2 + , increasing the negative zeta potential of the mineral. Within the pH range from 7 to 9, the dominant oleate species Ol − ion and ion–molecule complex, H ( Ol ) 2 - , adsorbed on HA by head groups toward the solid and associated due to chain–chain interaction in hemimicelles, made the HA surface with zeta potential about −22/−23 mV, and more floatable ( R = 80–100%) than in 4 < pH < 7 ( R = 15–35%) or in pH > 9.3. The HA surface is less negatively charged in calcite supernatant than in water from pH 6.6 to 9.2 due to the adsorption on HA negative surface active centers ( HPO 4 - and PO 4 2 - ) of the Ca 2+, CaHCO 3 + , and CaOH + ions (present in the calcite supernatant), producing more surface sites HPO 4Ca +, PO 4Ca, HPO 4CaOH, and PO 4 - CaOH, and new centers HPO 4CaHCO 3 and PO 4 - CaHCO 3. In the presence of 1 × 10 −3 mol L −1 CaCl 2, the HA sample has positive zeta potential, the same as calcite from the same deposit, up to IEP at pH 11.25. Carbonate ions (1 × 10 −3 mol L −1 Na 2CO 3) do not affect the HA zeta potential. However, a possible process can be the ion-exchange reaction between bicarbonate (or carbonate) and some anion from the surface sites formed on HA. The obtained values of the HA zeta potential with the collector (1 × 10 −4 mol L −1 Na-oleate) added into hydroxyapatite/calcite supernatant suspensions corroborate the weak chemisorption of Ol − and H ( Ol ) 2 - . The likely processes in this system also are the ion-exchange reactions on HPO 4CaOH and PO 4 - CaOH, HPO 4CaHCO 3 and PO 4 - CaHCO 3 between oleate ion and surface hydroxyl and bicarbonate ions, surface and bulk precipitations of calcium oleate, Ca(Ol) 2, and the surface and bulk precipitations of Ca [ H ( Ol ) 2 - ] 2 over the pH range from 7 to 9. Calcite supernatant does not influence natural floatability of the mineral. However, calcite supernatant depresses the hydroxyapatite flotation in the presence of 1 × 10 −4 mol L −1 Na-oleate (pH 9, R ∼ 50%), a likely result of the weak chemisorption due to the steric effect of heterogeneous HA surface formed in calcite supernatant, Ca(Ol) 2 and Ca [ H ( Ol ) 2 - ] 2 surface and bulk precipitations.

Surface Modification of Exfoliated Layered Gadolinium Hydroxide for the Development of Multimodal Contrast Agents for MRI and Fluorescence Imaging

AbstractA novel method for modifying the surface of magnetic‐resonance‐contrasting layered gadolinium hydroxide (LGdH) is developed providing them with water‐ and bio‐compatibility and acid‐resistance, all of which are essential for medical applications. A stable colloid of exfoliated layers is synthesized by exchanging interlayer anions of LGdH with oleate ions. The delaminated layers are successively coated with phospholipids with poly(ethylene glycol) tail groups, and their effectiveness as a contrast agent for magnetic resonance imaging (MRI) is demonstrated. The adaptability of this surface modification approach for incorporating functional molecules and fabricating a fluorescent colloid of LGdH, which has the potential utility as a multimodal probe, is also demonstrated. This result provides a novel approach for expanding the applications of layered inorganic materials and developing a new class of MRI contrast agents.

Hydrothermal Growth of Fatty Acid Stabilized Iron Oxide Nanocrystals

Seed nanocrystals formed by the coprecipitation of ferric and ferrous ions with oleate modification, at the molar ratios of sodium oleate and Fe ion [SO]/[Fe] from 0.05 to 0.5, were subjected to a hydrothermal treatment at 100−230 °C to initiate the crystal growth. Fourier transform infrared spectroscopy revealed that these nanocrystals were stabilized by a surface oleate that formed a stable colloidal solution in various nonpolar solvents such as cyclohexane and benzene. An X-ray diffraction analysis showed that the higher hydrothermal temperatures and lower oleate concentration promoted the Ostwald ripening process to produce highly crystallized iron oxide nanocrystals based on a cation deficient magnetite polymorph. Transmission electron microscopy revealed that the oleate concentrations played an important role in controlling the nucleation and growth process; it was found that the lower oleate concentration was the preferable growth condition to produce uniformly sized and shaped nanoparticles with h...

On the Interaction of Doxorubicin with Oleate Ions: Fluorescence Spectroscopy and Liquid-Liquid Extraction Study

Increase of lipophilicity of cationic doxorubicin (DOX) by its association with a fatty acid ion is of interest for pharmaceutical formulations and could have an impact on the drug delivery into cancer cells. On the basis of spectroscopic analysis of intrinsic DOX fluorescence, this study provides an experimental evidence of DOX-oleate interactions as function of ion/drug molar ratio (R) and pH. An electrostatic attraction to oleates is dominant for the cationic form of DOX (pH 6.5) and a hydrophobic interaction is characteristic of the molecular form of DOX (pH 8.6). A high content of sodium oleate vesicles ([oleate]>/=0.2 mM, R>/=20) limits the electrostatic and hydrophobic interactions at pH 6.5 while favoring the hydrophobic interactions at pH 8.6. The influence of these interactions on the lipophilicity of the cationic form of DOX is analyzed by measuring the apparent partition coefficient (aqueous buffer pH 6.5/methylene chloride). The results show a lipophilicity gain for the cationic form of DOX in presence of 10 : 1 ion/drug molar ratio, while no lipophilicity increase is observed at 50 : 1 molar ratio.