Margarita Sanchez-Dominguez

Comparison and Functionalization Study of Microemulsion-Prepared Magnetic Iron Oxide Nanoparticles

Magnetic iron oxide nanoparticles (MION) for protein binding and separation were obtained from water-in-oil (w/o) and oil-in-water (o/w) microemulsions. Characterization of the prepared nanoparticles have been performed by TEM, XRD, SQUID magnetometry, and BET. Microemulsion-prepared magnetic iron oxide nanoparticles (ME-MION) with sizes ranging from 2 to 10 nm were obtained. Study on the magnetic properties at 300 K shows a large increase of the magnetization ~35 emu/g for w/o-ME-MION with superparamagnetic behavior and nanoscale dimensions in comparison with o/w-ME-MION (10 emu/g) due to larger particle size and anisotropic property. Moringa oleifera coagulation protein (MOCP) bound w/o- and o/w-ME-MION showed an enhanced performance in terms of coagulation activity. A significant interaction between the magnetic nanoparticles and the protein can be described by changes in fluorescence emission spectra. Adsorbed protein from MOCP is still retaining its functionality even after binding to the nanoparticles, thus implying the extension of this technique for various applications.

Microemulsions as reaction media for the synthesis of mixed oxide nanoparticles: relationships between microemulsion structure, reactivity, and nanoparticle characteristics.

Phase behavior, dynamics, and structure of W/O microemulsions of the system aqueous solution/Synperonic 13_6.5/1-hexanol/isooctane were studied, with the goal of determining their effect on Mn-Zn ferrite nanoparticle formation, kinetics and characteristics. Microemulsion structure and dynamics were studied systematically by conductivity, dynamic light scattering (DLS), differential scanning calorimetry (DSC), and small-angle neutron scattering (SANS). The main effect of cosurfactant 1-hexanol was a decrease in microemulsion regions as compared to the systems without cosurfactant; nevertheless, overlap of microemulsion regions in the systems with precursor salts (PS) and precipitating agent (PA) was achieved at lower S/O ratios, compared to the system without cosurfactant. At 50 °C, PA microemulsions are nonpercolated, while PS microemulsions are percolated. SANS indicates small prolate ellipsoidal micelles with the absence of free water up to 18 wt % PS solution; DSC studies confirm the absence of free water in this composition range. Kinetic studies show an increase in the reaction rate with increasing concentration of the aqueous solution; but the most significant effect in reaction kinetics was noted when cosurfactant was used, regardless of microemulsion dynamics and structure. On the other hand, the main difference regarding the characteristics of the obtained nanoparticles was observed when bicontinuous microemulsions were used as reaction media which resulted in 8 nm nanoparticles, versus a constant size of ~4 nm obtained with all other microemulsions regardless of aqueous solution content, dynamics, and presence or absence of cosurfactant. The latter effect of constant size is attributed to the fact that the water present is dominantly bound to the EO units of the surfactant.

Temperature induced conversion from surface to "bulk" sites in Eu3+- impregnated CeO2 nanocrystals

Evolution with calcination temperature of Eu3+ sites in CeO2 nanocrystals is investigated by time-resolved photoluminescence spectroscopy. In the as-synthesized Eu3+ impregnated CeO2, most of Eu3+ ions reside on surface (S) sites. The Eu3+emission in S sites is broad and short-lived (τ = 240 μs) being dominated by the electric dipole (ED) 5D0-7F2 emission with little evidence for clustering. After calcination (between 500 and 1300 °C), Eu3+ is distributed on surface, cubic and up to three additional crystalline sites. Surface type emission could be detected until 1100 °C. In cubic sites, Eu3 substitute for the lattice Ce4+ with Oh symmetry (O sites). The emission of Eu3+ in O sites is characterized by relative long-lived (τ = 1.8–2 ms) and ultra-narrow (FWHM = 7 cm−1) magnetic dipole (MD) 5D0-7F1 emission centered at ∼591 nm. Three more crystalline sites are attributed to the oxygen vacancy charge-compensated defects: trigonal with C3v symmetry (C1 sites) and C2 and C3 sites with C2v or lower symmetry. Eu...

Order and disorder effects in nano-ZrO2 investigated by micro-Raman and spectrally and temporarily resolved photoluminescence

Pure and europium (Eu(3+)) doped ZrO(2) synthesized by an oil-in-water microemulsion reaction method were investigated by in situ and ex situ X-ray diffraction (XRD), ex situ Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), steady state and time-resolved photoluminescence (PL) spectroscopies. Based on the Raman spectra excited at three different wavelengths i.e. 488, 514 and 633 nm and measured in the spectral range of 150-4000 cm(-1) the correlation between the phonon spectra of ZrO(2) and luminescence of europium is clearly evidenced. The PL investigations span a variety of steady-state and time resolved measurements recorded either after direct excitation of the Eu(3+) f-f transitions or indirect excitation into UV charge-transfer bands. After annealing at 500 °C, the overall Eu(3+) emission is dominated by Eu(3+) located in tetragonal symmetry lattice sites with a crystal-field splitting of the (5)D(0)-(7)F(1) emission of 20 cm(-1). Annealing of ZrO(2) at 1000 °C leads to a superposition of Eu(3+) emissions from tetragonal and monoclinic lattice sites with monoclinic crystal-field splitting of 200 cm(-1) for the (5)D(0)-(7)F(1) transition. At all temperatures, a non-negligible amorphous/disordered content is also measured and determined to be of monoclinic nature. It was found that the evolutions with calcination temperature of the average PL lifetimes corresponding to europium emission in the tetragonal and monoclinic sites and the monoclinic phase content of the Eu(3+) doped ZrO(2) samples follow a similar trend. By use of specific excitation conditions, the distribution of europium on the amorphous/disordered surface or ordered/crystalline sites can be identified and related to the phase content of zirconia. The role of zirconia host as a sensitizer for the europium PL is also discussed in both tetragonal and monoclinic phases.

Tuning High Aqueous Phase Uptake in Nonionic Water-in-Oil Microemulsions for the Synthesis of Mn–Zn Ferrite Nanoparticles: Phase Behavior, Characterization, and Nanoparticle Synthesis

In this work, the formation of water-in-oil (w/o) microemulsions with high aqueous phase uptake in a nonionic surfactant system is investigated as potential media for the synthesis of Mn-Zn ferrite nanoparticles. A comprehensive study based on the phase behavior of systems containing precursor salts, on one hand, and precipitating agent, on the other hand, was carried out to identify key regions on (a) pseudoternary phase diagrams at constant temperature (50 °C), and (b) pseudobinary phase diagrams at constant surfactant (S):oil(O) weight ratio (S:O) as a function of temperature. The internal structure and dynamics of microemulsions were studied systematically by conductivity and self-diffusion coefficient determinations (FT PGSE (1)H NMR). It was found that nonpercolated w/o microemulsions could be obtained by appropriate tuning of composition variables and temperature, with aqueous phase concentrations as high as 36 wt % for precursor salts and 25 wt % for precipitating agent systems. Three compositions with three different dynamic behaviors (nonpercolated and percolated w/o, as well as bicontinuous microemulsions) were selected for the synthesis of Mn-Zn ferrites, resulting in nanoparticles with different characteristics. Spinel structure and superparamagnetic behavior were obtained. This study sets firm basis for a systematic study of Mn-Zn ferrite nanoparticle synthesis via different scenarios of microemulsion dynamics, which will contribute to a better understanding on the relationship of the characteristics of the obtained materials with the properties of the reaction media.

Removal of Total Organic Carbon from Sewage Wastewater Using Poly(ethylenimine)-Functionalized Magnetic Nanoparticles

The increased levels of organic carbon in sewage wastewater during recent years impose a great challenge to the existing wastewater treatment process (WWTP). Technological innovations are therefore sought that can reduce the release of organic carbon into lakes and seas. In the present study, magnetic nanoparticles (NPs) were synthesized, functionalized with poly(ethylenimine) (PEI), and characterized using TEM (transmission electron microscopy), X-ray diffraction (XRD), FTIR (Fourier transform infrared spectroscopy), CCS (confocal correlation spectroscopy), SICS (scattering interference correlation spectroscopy), magnetism studies, and thermogravimetric analysis (TGA). The removal of total organic carbon (TOC) and other contaminants using PEI-coated magnetic nanoparticles (PEI-NPs) was tested in wastewater obtained from the Hammarby Sjöstadsverk sewage plant, Sweden. The synthesized NPs were about 12 nm in diameter and showed a homogeneous particle size distribution in dispersion by TEM and CCS analyses, respectively. The magnetization curve reveals superparamagnetic behavior, and the NPs do not reach saturation because of surface anisotropy effects. A 50% reduction in TOC was obtained in 60 min when using 20 mg/L PEI-NPs in 0.5 L of wastewater. Along with TOC, other contaminants such as turbidity (89%), color (86%), total nitrogen (24%), and microbial content (90%) were also removed without significant changes in the mineral ion composition of wastewater. We conclude that the application of PEI-NPs has the potential to reduce the processing time, complexity, sludge production, and use of additional chemicals in the WWTP.

Synthesis of Pt Nanoparticles in oil-in-water microemulsions : Phase Behavior and Effect of Formulation Parameters on Nanoparticle Characteristics

Pt nanoparticles were synthesized in oil-in-water (o/w) microemulsions, in contrast to the typically used water-in-oil microemulsion method. The new strategy implies the use of a Pt organometallic precursor (1,5-cyclooctadiene dimethyl platinum (II)), dissolved in nanometre-scale oil droplets, stabilized by surfactant, and dispersed in a continuous aqueous phase. Three different nonionic microemulsion systems were used. Characterization studies demonstrate that small, nanocrystalline Pt nanoparticles were obtained. The particle size and agglomeration was dependant on the microemulsion system used and its composition. The obtained results demonstrate the feasibility of this approach for the controlled synthesis of Pt nanoparticles with potential for catalytic purposes.

Spectrally and temporarily resolved luminescence study of short-range order in nanostructured amorphous ZrO2

The local structure amorphous ZrO(2) doped with europium (Eu(3+)) and its evolution during crystallization was investigated by using spectrally and temporally resolved luminescence of europium. A s ...

Synthesis of Mixed Cu/Ce Oxide Nanoparticles by the Oil-in-Water Microemulsion Reaction Method

Cerium oxide and mixed Cu/Ce oxide nanoparticles were prepared by the oil-in-water (O/W) microemulsion reaction method in mild conditions. The Cu/Ce molar ratio was varied between 0/100 and 50/50. According to X-ray diffraction (XRD), below 30/70 Cu/Ce molar ratio, the materials presented a single phase consistent with cubic fluorite CeO2. However, above Cu/Ce molar ratio 30/70, an excess monoclinic CuO phase in coexistence with the predominant Cu/Ce mixed oxide was detected by XRD and High-Resolution Transmission Electron Microscopy (HRTEM). Raman spectroscopy showed that oxygen vacancies increased significantly as the Cu content was increased. Band gap (Eg) was investigated as a function of the Cu/Ce molar ratio, resulting in values from 2.91 eV for CeO2 to 2.32 eV for the mixed oxide with 30/70 Cu/Ce molar ratio. These results indicate that below 30/70 Cu/Ce molar ratio, Cu2+ is at least partially incorporated into the ceria lattice and very well dispersed in general. In addition, the photodegradation of Indigo Carmine dye under visible light irradiation was explored for selected samples; it was shown that these materials can remove such contaminants, either by adsorption and/or photodegradation. The results obtained will encourage investigation into the optical and photocatalytic properties of these mixed oxides, for widening their potential applications.

New Trends on the Synthesis of Inorganic Nanoparticles Using Microemulsions as Confined Reaction Media

The development of nanotechnology depends strongly on the advances in nanoparticle preparation. Nowadays, there are a number of technologies available for nanoparticle synthesis, from the gas phase techniques such as laser evaporation (Gaertner & Lydtin, 1994), sputtering, laser pyrolisis, flame atomization and flame spray pyrolisis (Kruis et al. 1998), etc, to the liquid phase techniques such as coprecipitation from homogeneous solutions and sol-gel reactions (Qiao et al. 2011), solvothermal processes (Gautam et al. 2002), sonochemical and cavitation processing (Suslick et al. 1996), and surfactant and polymer-templated synthesis (Holmberg, 2004). Amongst the surfactant-based approaches, the microemulsion reaction method is one of the most used techniques for the preparation of very small and nearly monodispersed nanoparticles. This method offers a series of advantages with respect to other methods, namely, the use of simple equipment, the possibility to prepare a great variety of materials with a high degree of particle size and composition control, the formation of nanoparticles with often crystalline structure and high specific surface area, and the use of soft conditions of synthesis, near ambient temperature and pressure. The traditional method is based on water-in-oil microemulsions (W/O), and it has been used for the preparation of metallic and other inorganic nanoparticles since the beginning of the 1980’s (Boutonnet et al., 1982). The droplets of W/O microemulsions are conceived as tiny compartments or “nanoreactors”. The main strategy for the synthesis of nanoparticles in W/O microemulsions consists in mixing two microemulsions, one containing the metallic precursor and another one the precipitating agent. Upon mixing, both reactants will contact each other due to droplets collisions and coalescence, and they will react to form precipitates of nanometric size (Figure 1). This precipitate will be confined to the interior of microemulsion droplets. Numerous investigations have been published about the use of W/O microemulsions for the preparation of a variety of nanomaterials,