Self-assembled organic–inorganic magnetic hybrid adsorbent ferrite based on cyclodextrin nanoparticles

Abstract

SummaryOrganic–inorganic magnetic hybrid materials (MHMs) combine a nonmagnetic and a magnetic component by means of electrostatic interactions or covalent bonds, and notable features can be achieved. Herein, we describe an application of a self-assembled material based on ferrite associated with β-cyclodextrin (Fe-Ni/Zn/βCD) at the nanoscale level. This MHM and pure ferrite (Fe-Ni/Zn) were used as an adsorbent system for Cr3+ and Cr2O7 2− ions in aqueous solutions. Prior to the adsorption studies, both ferrites were characterized in order to determine the particle size distribution, morphology and available binding sites on the surface of the materials. Microscopy analysis demonstrated that both ferrites present two different size domains, at the micro- and nanoscale level, with the latter being able to self-assemble into larger particles. Fe-Ni/Zn/βCD presented smaller particles and a more homogeneous particle size distribution. Higher porosity for this MHM compared to Fe-Ni/Zn was observed by Brunauer–Emmett–Teller isotherms and positron-annihilation-lifetime spectroscopy. Based on the pKa values, potentiometric titrations demonstrated the presence of βCD in the inorganic matrix, indicating that the lamellar structures verified by transmission electronic microscopy can be associated with βCD assembled structures. Colloidal stability was inferred as a function of time at different pH values, indicating the sedimentation rate as a function of pH. Zeta potential measurements identified an amphoteric behavior for the Fe-Ni/Zn/βCD, suggesting its better capability to remove ions (cations and anions) from aqueous solutions compared to that of Fe-Ni/Zn.

Modulation of size and viscosity of Ni/Zn ferrites: Effect of doping with βCD and chemical treatment with HNO3 and NaOH

“…The obtained coefficients are much larger than those of perfectly spherical particles, suggesting the presence of non-symmetrical and poly-disperse agglomerates in suspension. In spite of the existence of spherical particles in the solid state, as observed by microscopy in our previous work [2], the presence of these aggregates must be resulting from strong particleeparticle interactions, which were also corroborated by the high values of K H coefficient.…”

“…Also, both compounds are completely ionized in solution and are extensively used in numerous technological processes involving slurries [30]. Moreover, they were used in our previous work for pH adjustment [2].…”

“…Recently we have reported the synthesis of an organiceinorganic ceramic material based on ferrite associated with bcyclodextrin (FeeNi/Zn/bCD) [2], where remarkable alterations were observed in morphological and structural properties due to the incorporation of b-cyclodextrin, which positively affected the nucleation process and further reduced the particle size. Cyclodextrins are cyclic oligosaccharides commonly formed by a(1 / 4) linked-D-glucopyranoside units (6, 7 or 8), so-called aCD, bCD and gCD, respectively.…”

“…These compounds have a rigid structure with a toroidal shape, in which a variety of guest molecules can be inserted into their cavities, resulting in the formation of inclusion complexes [15e17] and large aggregates [18,19]. It has been also demonstrated that these compounds are able to modulate the size of ferrite particles [2,20]. Irrespective of the use of precursors during the synthesis of ferrites in a wet chemical route, as co-precipitation or hydrothermal methods, hydroxyl groups are commonly and spontaneously retained in the samples, and they are held even after sintering at temperatures around 850 K [21e23].…”

“…Initially, FeeNi/Zn and FeeNi/Zn/bCD were synthesized according to the method previously described in the literature [2], and they were characterized in the solid state utilizing X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermal analysis (TG/DTA). Stoichiometries of ferrites were found through the combination of atomic emission spectroscopy (ICP) and elementary analysis (CHN).…”