Oscar Perales-Perez

Synthesis of size-controlled cobalt ferrite particles with high coercivity and squareness ratio.

Cobalt ferrite particles with diameters ranging from a few micrometer to about 15 nm were synthesized using a modified oxidation process. The fine control of the particle size was achieved by introducing various concentrations of Fe(3+) ions at the beginning of the reaction. Among the particle sizes obtained by using this method, particles with a grain size of about 36 nm showed a magnetization (M(s)) of 64 emu/g and a maximum coercivity (H(c)) of 2020 Oe at room temperature. The corresponding squareness ratio was found to be 0.53.

Antimicrobial nanomaterials as water disinfectant: Applications, limitations and future perspectives

Nanotechnology and its application is one of the rapidly developing sciences. As demand of fresh drinking water is increasing, nanotechnology can contribute noticeable development and improvement to water treatment process. Disinfection process is the last and most important step in water and wastewater treatment process. Some nanomaterials can be used as disinfectants due to their antimicrobial properties and reduce the possibility of harmful disinfection by-products (DBPs) formation during traditional disinfection process. A significant number of research efforts is done or going on to understand the mechanisms and enhance the efficiency of nanomaterials as antimicrobial agents, although it will take more time to understand the full potential of nanomaterials in this field. This review paper focuses on inactivation pathways of benign nanomaterials, their possible and probable application and limitations as disinfectants and future opportunities for their application in water cleaning processes.

Growth dominant co-precipitation process to achieve high coercivity at room temperature in CoFe/sub 2/O/sub 4/ nanoparticles

Applications of CoFe/sub 2/O/sub 4/ are limited due to the lack of synthesis technique to produce monodispersed, single domain and high coercivity (H/sub c/) nanoparticles. Here, we describe the growth dominant co-precipitation process to achieve high H/sub c/, with moderate magnetization at room temperature (RT) in CoFe/sub 2/O/sub 4/ nanoparticles. It is well known that the particle size is closely related to the relative interdependence between the nucleation and growth steps, which in turn can strongly be affected by the solution chemistry and precipitation conditions. Based on this premise, the effect of 1) reaction temperature, 2) NaOH concentration, and 3) feeding rate of metal ions into the alkali solution were evaluated. The maximum H/sub c/ of 2.29 kOe (RT) was observed for the CoFe/sub 2/O/sub 4/ prepared at 98/spl deg/C, 1.13-mol NaOH, and the metal ion feeding rate of 0.00103 M/min. To improve the coercivity, single domain CoFe/sub 2/O/sub 4/ nanoparticles were produced by in situ growth of the CoFe/sub 2/O/sub 4/ seeds followed by size separation method. A coercivity of 4.3 kOe was achieved at RT for 40-nm single domain CoFe/sub 2/O/sub 4/ nanoparticles, which is close to the theoretical value of 5.3 kOe.

Tuning of magnetic properties in cobalt ferrite nanocrystals

Cobalt ferrite (CoFe2O4) possesses excellent chemical stability, good mechanical hardness, and a large positive first order crystalline anisotropy constant, making it a promising candidate for magneto-optical recording media. In addition to precise control of the composition and structure of CoFe2O4, its practical application will require the capability to control particle size at the nanoscale. The results of a synthesis approach in which size control is achieved by modifying the oversaturation conditions during ferrite formation in water through a modified coprecipitation approach are reported. X-ray diffraction, transmission electron microscopy (TEM) diffraction, and TEM energy-dispersive x-ray spectroscopy analyses confirmed the formation of the nanoscale cobalt ferrite. M-H measurements verified the strong influence of synthesis conditions on crystal size and hence, on the magnetic properties of ferrite nanocrystals. The room-temperature coercivity values increased from 460 up to 4626Oe under optimum...

Synthesis of high-coercivity cobalt ferrite nanocrystals

Cobalt ferrite (CoFe2O4) possesses excellent chemical stability, good mechanical hardness and a large positive first-order crystalline anisotropy constant, which made this ferrite a promising candidate for magneto-optical recording media. In addition to precise control on the composition and structure of CoFe2O4, the success of its practical application will depend on the capability of controlling particle size at the nanoscale. This size-controlled synthesis approach became possible by modifying the oversaturation conditions during ferrite formation in water. Optimum oversaturation was achieved by monitoring of the feeding flow-rate of reactant solutions. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) analyses confirmed the formation of the ferrite structure after a reaction time as short as 5min. M-H measurements verified the strong influence of synthesis conditions and crystal size on the magnetic properties of ferrite nanocrystals. The coercivity values increased from 210 up to 5840Oe under optimum synthesis conditions.

Sorption study of toluene and xylene in aqueous solutions by recycled tires crumb rubber

Sorption of toluene and xylene by tire crumb rubber (TCR) and its main components: carbon black (CB) and styrene-butadiene polymer (SBP) were evaluated. The 12 starting concentrations of adsorbates in aqueous solutions ranged from 0.05 mg/L to 100.0mg/L. The amounts of CB and SBP used in the sorption tests were determined considering their typical contents in tire crumb rubber (30% and 60% w/w, respectively). Freundlichs isotherms and Scatchard plot parameters suggested a two-step sorption process when TCR was used as the sorbent; whereas a single-step route was apparent when the sorption experiments were carried out with CB or SBP. Freundlichs n parameter was estimated at 0.65 for CB and 1.0 for both TCR and SBP. A removal of 60% of toluene and 81% of xylene from starting 50 ppm solutions was attained in the first 30 minutes of contact using 5 g/L of TCR.

Synthesis and magnetic behavior of nanostructured ferrites for spintronics

Zinc oxide based material systems are considered as promising candidate for spintronic devices if it could be coupled in heterostructure with a suitable ferromagnetic material. We synthesized Zn, Mn and Co substituted iron oxide powders and thin films using solution-based approaches. Structural properties of these materials were studied by X-ray diffraction, FT-IR and closed cycle SQUID for magnetic characterization. These studies indicates that Zn 1-x Co x Fe 2 O 4 , Mn 0.5 Zn 0.5 Fe 2 O 4 and CoFe 2 O 4 exhibited ferrimagnetic and superparamagnetic behavior, respectively, at room temperature. Superparamagnetic behavior in Mn 0.5 Zn 0.5 Fe 2 O 4 and CoFe 2 O 4 is attributed to the extremely small crystal size.

Effect of Dy-doping on the structural and magnetic properties of Co–Zn ferrite nanocrystals for magnetocaloric applications

Magnetic nanoparticles for magnetocaloric applications should combine small coercivity, low demagnetization temperature, and high pyromagnetic coefficients while keeping the magnetization as high as possible. The strong dependence of the magnetic properties of cobalt-zinc mixed ferrite with specific dopant species enables this material to be considered a promising candidate for magnetocaloric applications. On this basis, pure and Dy-doped Co0.7Zn0.3Fe2O4 cobalt-zinc ferrite nanocrystals have been synthesized by conventional and modified (i.e., flow rate controlled addition of reactants) coprecipitation routes. The modified approach allows the control of ferrite crystal growth at the nanoscale and hence tuning of the corresponding magnetic properties. The magnetic properties of the produced nanocrystals were determined as a function of their structure, nominal dopant concentration, and crystal size. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy analyses suggested both the actu...

MnxZn1-xFe2-yRyO4 (R=Gd, Eu) ferrite nanocrystals for magnetocaloric applications

We investigated the dependence of magnetic properties with composition in nanocrystalline Mn-Zn ferrites. Ferrite crystals were synthesized by a modified coprecipitation route where nucleation and crystal growth conditions were controlled during the reaction of 0.011M Fe(III) and 0.055M[Zn(II) + Mn(II)] solutions under alkaline conditions. When doping, suitable amounts of Gd(III) or Eu(III) salts were added to solutions. XRD, FT-IR and Raman spectroscopy analyses verified the formation of the ferrite structure. An average crystallite size varying from 8 to 12nm with composition was estimated by using Scherrers equation. SQUID analyses suggested that ferrite nanocrystals were superparamagnetic at room temperature. The maximum magnetization values were dependent on the composition of the Mn-Znferrite and varied from 15 emu/g up to 49.8 emu/g for x 0.0 and 0.8, respectively. The variation in magnetization with temperature for the ferrites was also investigated. A Tc of 79.4degC and a pyromagnetic coefficient of 8.9 A/m-degC were determined for an aqueous-based fluid bearing Mn0.7Zn0.3 Fe2O4 nanocrystals. The variation in both the Tc and the pyromagnetic coefficient were also measured for various concentrations of Gd(III) and Eu(III) species in the Mn-Zn ferrites.

Production of monodispersed particles by using effective size selection

In this article we report the results of two size selection methods that are based on interfacial interaction between nanosize particles, magnetite in this case, anionic surfactants, and nonpolar solvents. It is proposed that by selecting a suitable surfactant type and/or conditions to modify the particle–particle separation distance, only smaller particles can be stabilized against aggregation and settling making a size sensitive separation possible. Using this phenomenon, an effective size selection at the nanosize level has been achieved and the preliminary results are presented here. Depending on the conditions, stable suspensions of nearly monodispersed nanoparticles of magnetite (diameter less than 10 nm and standard deviation, σ, below 0.2) were obtained from polydispersed powders (less than 40 nm in diameter and σ around 0.6) synthesized from aqueous solutions at 25u200a°C. Magnetization measurements of the fractions confirmed the effectiveness of the developed size selection methods.