Two-stage kinetics of field-induced aggregation of medium-sized magnetic nanoparticles

The present paper is focused on the theoretical and experimental study of the kinetics of field-induced aggregation of magnetic nanoparticles of a size range of 20-100 nm. Our results demonstrate that (a) in polydisperse suspensions, the largest particles could play a role of the centers of nucleation for smaller particles during the earliest heterogeneous nucleation stage; (b) an intermediate stage of the aggregate growth (due to diffusion and migration of individual nanoparticles towards the aggregates) is weakly influenced by the magnetic field strength, at least at high supersaturation; (c) the stage of direct coalescence of drop-like aggregates (occurring under magnetic attraction between them) plays a dominant role at the intermediate and late stages of the phase separation, with the time scale decreasing as a square of the aggregate magnetization

Correlation between Electrochemical Impedance Spectroscopy and Structural Properties of Amorphous Tunisian Metanacrite Synthetic Material

In the present work, we report the structural and electrochemical properties of metanacrite. Metanacrite is a synthetic material originated by heating (550°C) of a clay mineral (Tunisian nacrite) belonging to the kaolin group. The structure of the amorphous synthetic product was corroborated by X-ray diffraction (disappearing of nacrite peaks) and infrared spectroscopy (disappearing of Al–OH and water bands). The decomposition of the silicate framework was confirmed by transmission electron microscope (TEM). The obtained metanacrite synthetic material was also examined by electrochemical impedance spectroscopy (EIS). Accordingly, the electronic conduction is followed by the correlated barrier hopping (C.B.H.) model. Therefore, by combining ac and dc electrical conductivity, a semiconductor behavior is evidenced. The dependence of the dielectric constant (ε′) and dielectric loss (ε″) on both temperature and frequency is also discussed

Radial Electrical Resistivity Measurements of Rocks on Laboratory Core Samples Using an Electromagnetic Sensor: Macro and Micro Eddy Currents

Rocks subjected to weak alternating magnetic fields exhibit a magnetic hysteresis phenomenon due to the magnetic susceptibility and chemical composition of ferromagnetic or ferrimagnetic mineral grains. In order to characterize the physical properties of rocks, magnetic susceptibility and electrical resistivity measurements have been carried out. So a device has been developed in our laboratory as a highly sensitive sensor to measure the magnetic and electrical properties of rocks. This work deals with a nondestructive method to analyze these properties. A ballistic method has been considered by using a search coil in a sensitive alternating current bridge. Usually, the use of the complex ac magnetic susceptibility is convenient to reach the bulk magnetic susceptibility, where the imaginary component is often very weak and neglected. In this paper, we have considered this to determine the electrical resistivity of rocks

Geochemistry and P-T conditions of hydrothermal fluids associated with the Upper Miocene post-collisional magmatism at Wadi Belif (Northwestern Tunisia): Origin of metals and trace gold mineralization

International audienc

Organoclay hybrid materials as precursors of porous ZnO/silica-clay heterostructures for photocatalytic applications

In this study, ZnO/SiO2-clay heterostructures were successfully synthesized by a facile two-step process applied to two types of clays: montmorillonite layered silicate and sepiolite microfibrous clay mineral. In the first step, intermediate silica–organoclay hybrid heterostructures were prepared following a colloidal route based on the controlled hydrolysis of tetramethoxysilane in the presence of the starting organoclay. Later on, pre-formed ZnO nanoparticles (NP) dispersed in 2-propanol were incorporated under ultrasound irradiation to the silica–organoclay hybrid heterostructures dispersed in 2-propanol, and finally, the resulting solids were calcinated to eliminate the organic matter and to produce ZnO nanoparticles (NP) homogeneously assembled to the clay–SiO2 framework. In the case of montmorillonite the resulting materials were identified as delaminated clays of ZnO/SiO2-clay composition, whereas for sepiolite, the resulting heterostructure is constituted by the assembling of ZnO NP to the sepiolite–silica substrate only affecting the external surface of the clay. The structural and morphological features of the prepared heterostructures were characterized by diverse physico-chemical techniques (such as XRD, FTIR, TEM, FE-SEM). The efficiency of these new porous ZnO/SiO2-clay heterostructures as potential photocatalysts in the degradation of organic dyes and the removal of pharmaceutical drugs in water solution was tested using methylene blue and ibuprofen compounds, respectively, as model of pollutants.The authors thank the CSIC (i-COOP+ project COOPA20077) and the MINECO (project MAT2012-31759 and MAT2015-71117-R), Spain, and the EU (COST Action MP1202).Peer reviewe

Organoclay hybrid materials as precursors of porous ZnO/silica-clay heterostructures for photocatalytic applications

In this study, ZnO/SiO2-clay heterostructures were successfully synthesized by a facile two-step process applied to two types of clays: montmorillonite layered silicate and sepiolite microfibrous clay mineral. In the first step, intermediate silica–organoclay hybrid heterostructures were prepared following a colloidal route based on the controlled hydrolysis of tetramethoxysilane in the presence of the starting organoclay. Later on, pre-formed ZnO nanoparticles (NP) dispersed in 2-propanol were incorporated under ultrasound irradiation to the silica–organoclay hybrid heterostructures dispersed in 2-propanol, and finally, the resulting solids were calcinated to eliminate the organic matter and to produce ZnO nanoparticles (NP) homogeneously assembled to the clay–SiO2 framework. In the case of montmorillonite the resulting materials were identified as delaminated clays of ZnO/SiO2-clay composition, whereas for sepiolite, the resulting heterostructure is constituted by the assembling of ZnO NP to the sepiolite–silica substrate only affecting the external surface of the clay. The structural and morphological features of the prepared heterostructures were characterized by diverse physico-chemical techniques (such as XRD, FTIR, TEM, FE-SEM). The efficiency of these new porous ZnO/SiO2-clay heterostructures as potential photocatalysts in the degradation of organic dyes and the removal of pharmaceutical drugs in water solution was tested using methylene blue and ibuprofen compounds, respectively, as model of pollutants

Geochemistry and P-T conditions of hydrothermal fluids associated with the Upper Miocene post-collisional magmatism at Wadi Belif (Northwestern Tunisia): Origin of metals and trace gold mineralization

International audienc

ZnO/sepiolite heterostructured materials for photocatalytic degradation of emerging pollutants in wastewater

Oral presentation given at the XVI International Clay Conference, held in Granada (Spain) on July 17-21, 2017.The development of porous nanoarchitectures materials based on clays minerals is a topic of growing interest, being typically addressed to catalysis and adsorption applications [1,2]. Among clay minerals, sepiolite fibrous clay provides larger external surface area as well as the presence of external silanol groups in comparison to typical layered silicates (e.g., smectites), which favours the immobilization of diverse nanoparticles (NP). In this communication it will be introduced several porous ZnO-sepiolite nanostructured materials prepared using sepiolite or organosepiolite as intermediate to control the assembly and aggregation of the metal-oxide nanoparticles. On the one side, ZnO-sepiolite nanoarchitectures were prepared following a process based on the assembly of previously synthesized ZnO NP to sepiolite modified with hexadecyltrimethylammonium ions, both dispersed in 2-propanol medium, to produce an intermediate that after a thermal treatment consolidates the final ZnO/clay nanoarchitecture [3]. On the other side, the ZnO NP were incorporated to a sepiolite previously modified with SiO2 NP produced following a sol-gel methodology reported elsewhere [4]. In this case, it is intended to have a support of ZnO NP with a larger accessible surface area and also appropriate chemical reactivity of the clay surface. Finally, a novel heterostructure has been prepared using directly the sepiolite as substrate on which magnetite NP were in situ growth [5] and then ZnO NP were assembled as in the previously described materials. All types of samples have been characterized by diverse characterization techniques (XRD, FTIR, specific surface area and porosity determinations, TEM, FE-SEM-EDX, SQUID, etc.) and their activity in the photocatalytic degradation of emerging pollutants in water was tested. In this way, solutions of paracetamol, antypirine and ibuprofen drugs were exposed to a lamp that simulates solar light and the variation of their concentration with time of exposure was followed by HPLC. For instance, it has been observed that the ZnO/sepiolite heterostructure exhibits better photoactivity than ZnO/SiO2-sepiolite and ZnO/Fe3O4-sepiolite materials for the degradation of ibuprofen. However, the last material has an important advantage as it presents superparamagnetic afforded by the magnetite NP and it can be easily recovered from the reaction media by applying an external magnetic field, which makes very easy the reusability of the photocatalyst in consecutive cycles of treatment.MINECO (Spain, project MAT2015-71117-R) and CSIC (Spain, COOPA20077)