G.J. da Silva

Intercalation and Retention of Carbon Dioxide in a Smectite Clay promoted by Interlayer Cations

A good material for CO2 capture should possess some specific properties: (i) a large effective surface area with good adsorption capacity, (ii) selectivity for CO2, (iii) regeneration capacity with minimum energy input, allowing reutilization of the material for CO2 adsorption, and (iv) low cost and high environmental friendliness. Smectite clays are layered nanoporous materials that may be good candidates in this context. Here we report experiments which show that gaseous CO2 intercalates into the interlayer nano-space of smectite clay (synthetic fluorohectorite) at conditions close to ambient. The rate of intercalation, as well as the retention ability of CO2 was found to be strongly dependent on the type of the interlayer cation, which in the present case is Li+, Na+ or Ni2+. Interestingly, we observe that the smectite Li-fluorohectorite is able to retain CO2 up to a temperature of 35°C at ambient pressure, and that the captured CO2 can be released by heating above this temperature. Our estimates indicate that smectite clays, even with the standard cations analyzed here, can capture an amount of CO2 comparable to other materials studied in this context.

Electric Double Layered Magnetic Fluids (EDL-MF) based on spinel ferrite nanostructures [(M1-x+2Fex+3)]A [(Fe2-x+3 Mx+2)]BO4-2

This paper presents a review of Electric Double Layered Magnetic Fluids (EDL-MF) based on spinel ferrite type [(M1-x+2Fex+3)]A [(Fe2-x+3 Mx+2)]BO4-2, with M(II) = Mn, Co, Ni, Cu and Zn. The chemical synthesis of the nanoparticles using hydrothermal techniques and their complete peptization in an aqueous medium results in a ultra stable magnetic colloid, EDL-MF. The characterization of the particles was performed using X-ray diffraction and electronic microscopy techniques. The resulted sols were investigated by magnetic, magneto-optical measurements and magnetic resonance techniques.

Static magneto optical birefringence of new Electric Double Layered Magnetic Fluids

Magnetic birefringence measurements are performed under a static field on Electric Double Layered Magnetic Fluids based on copper and zinc ferrite nanostructures. The optical birefringence is related to a single-particle effect and well described by a Langevin model which includes a log- normal distribution of particles. By the field-induced birefringence level, these new magnetic fluids are comparable to usual ones, a result which could offer a new way for biological applications.

Gravitational and magnetic separation in self-assembled clay-ferrofluid nanocomposites

We report on experimental observations of self-assemblies in colloidal dispersions of clay nanoplatelets and magnetic nanoparticles. Visual observations have been combined with small angle X-ray scattering (SAXS) in the study of several composites at a fixed clay concentration in the dilute regime, and varying ferrofluid concentrations. Our visual observations which encompass macroscopic separation in gravitational- and magnetic field, indicate that all samples present a concentrated phase and a diluted one. SAXS data obtained from each phase are consistent with the interpretation that the scattering contribution from the clay nano-platelets in the samples can be neglected in comparison with the magnetic particle contribution. The analysis of the scattered intensity is performed combining two models, one based on the global scattering function and the other allowing the extraction of the structure factor of the mixtures. The parameters of the size distribution of magnetic nanoparticles determined by both methods are in good agreement. The structure factor of the mixtures shows that on a local scale, the mixtures behave like a gas of isolated magnetic nanoparticles. It also indicates the presence of interactions between magnetic nanoparticles mediated by the presence of Laponite platelets. Such interactions could be attributed with a progressive partial phase separation between spheres and discs rather than to the formation of dense aggregates.

Surface charge density determination in electric double layered magnetic fluids

We analyze potentiometric and conductimetric measurements, simultaneously performed in several complex systems (Bronsted acid-base-type). The results show an excellent agreement between reported and obtained values of the dissociation constants of the involved equilibria. A similar analysis is proposed to account, in electric double layered magnetic fluids (EDL-MF), for the charging of the particle surface based on a proton transfer proccess at the interface with the bulk dispersion. This model allows to relate the pH dependence of the phase diagram to the variations of the nanoparticle surface charge density, which leads to a useful method to monitor the colloidal stability of EDL-MF.

Small-angle X-ray and small-angle neutron scattering investigations of colloidal dispersions of magnetic nanoparticles and clay nanoplatelets

We investigated mixed colloidal dispersions of clay platelets and magnetic nanoparticles using small-angle X-ray and neutron scattering. Our results show that the contribution to the scattering is essentially due to the magnetic nanoparticles. The scattering intensities are proportional to the concentration of magnetic particles, indicating that from the scattering point of view the sample is a colloidal dispersion of non-interacting magnetic objects, although the laponite and magnetic particles clearly interact when the sample textures are observed in an optical microscope. The visually observed phase separation may be characterized as a liquid–gas transition.