Adsorption of Organic Dyes on Magnetic Iron Oxide Nanoparticles. Part I: Mechanisms and Adsorption-Induced Nanoparticle Agglomeration.

This series of two papers is devoted to the effect of organic dye (methylene blue, MB; or methyl orange, MO) adsorption on the surface of either bare or citrate-coated magnetic iron oxide nanoparticles (IONPs) on their primary agglomeration (in the absence of an applied magnetic field) and secondary field-induced agglomeration. The present paper (Part I) is focused on physicochemical mechanisms of dye adsorption and adsorption-induced primary agglomeration of IONPs. Dye adsorption to oppositely charged IONPs is found to be mostly promoted by electrostatic interactions and is very sensitive to pH and ionic strength variations. The shape of adsorption isotherms is correctly reproduced by the Langmuir law. For the particular MB/citrated IONP pair, the maximum surface density of adsorbed MB seems to correspond to the packing density of an adsorbed monolayer rather than to the surface density of the available adsorption sites. MB is shown to form H-aggregates on the surface of citrate-coated IONPs. The effective electric charge on the IONP surface remains nearly constant in a broad range of surface coverages by MB due to the combined action of counterion exchange and counterion condensation. Primary agglomeration of IONPs (revealed by an exponential increase of hydrodynamic size with surface coverage by MB) probably comes from correlation attractions or π-stacking aromatic interactions between adsorbed MB molecules or H-aggregates. From the application perspective, the maximum adsorption capacity is 139 ± 4 mg/g for the MB/citrated IONP pair (pH = 4-11) and 257 ± 16 mg/g for the MO/bare IONP pair (pH ∼ 4). Citrated IONPs have shown a good potential for their reusability in water treatment, with the adsorption efficiency remaining about 99% after nine adsorption/desorption cycles.

Flexible magnetic membranes based on bacterial cellulose and its evaluation as electromagnetic interference shielding material.

Flexible magnetic membranes with high proportion of magnetite were successfully prepared by previous impregnation of the never dried bacterial cellulose pellicles with ferric chloride followed by reduction with sodium bisulfite and alkaline treatment for magnetite precipitation. Membranes were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), vibrating magnetometer, field emission scanning electron microscopy (FEG-SEM) and impedance spectroscopy. Microwave properties of these membranes were investigated in the X-band (8.2 to 12.4 GHz). FEG-SEM micrographs show an effective coverage of the BC nanofibers by Fe3O4 nanoparticles. Membranes with up to 75% in weight of particles have been prepared after 60 min of reaction. Magnetite nanoparticles in the form of aggregates well adhered to the BC fibers were observed by SEM. The average crystal sizes of the magnetic particles were in the range of 10±1 to 13±1 nm (estimated by XRD). The magnetic particles in the BC pellicles presented superparamagnetic behavior with a saturation magnetization in the range of 60 emu g(-1) and coercive force around 15 Oe. These magnetic pellicles also displayed high electrical permittivity and a potential application as microwave absorber materials.

Electrorheological and dielectric behavior of new ionic liquid/silica systems.

New phosphonium-based ionic liquids, denoted, 11-carboxyundecyltriphenylphosphonium bromide (IL1) and octadecyltriphenylphosphonium iodide (IL2), were employed on the sol-gel synthesis to prepare new silica-based matrices. The fastest gelation during the sol-gel process was observed in hydrolysis/condensation of tetraethoxysilane in the presence of IL1. The confinement of ionic liquids (especially IL1) inside the silica networks was suggested by thermogravimetric analysis and Fourier transform infrared spectroscopy. The resulting ionogels present higher permittivity than pure silica and were used as the solid component for the development of new electrorheological fluids, presenting good ER behavior, mainly those prepared with IL1.

New electrorheological fluid obtained from mercaptosilsesquioxane-modified silicate suspensions.

Ormosil based on mercaptosilsesquioxane-modified silicate (SiO2/SSQ-SH) particle was prepared by sol-gel process involving a co-condensation of the hydrolyzed 3-mercaptopropyl-trimethoxysilane (MPTMS) and tetraetoxysilane (TEOS). The resulting material was characterized by (29)Si solid nuclear magnetic resonance spectroscopy ((29)Si NMR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FEG-SEM) and small angle X-ray scattering (SAXS). The (SiO2/SSQ-SH) particle presents a hierarchical structure, extending from micro to nanoscale and consisting of three structural levels. This SiO2/SSQ-SH particle was used for the first time as the dispersed phase in silicone oil suspension to develop a new electro-rheological fluid with a very good response under the action of electrical field from 1 to 4 kV/mm, whose values are comparable to those exhibited by other conventional ER fluids, under the influence of electric field.