Controlling Cation Distribution and Morphology in Colloidal Zinc Ferrite Nanocrystals

Abstract

This paper describes the first synthetic method to achieve independent control over both the cation distribution (quantified by the inversion parameter x) and size of colloidal ZnFe 2 O 4 nanocrystals. Use of a heterobimetallic triangular complex of formula ZnFe 2 (μ 3 -O)(μ 2 -O 2 CCF 3 ) 6 (H 2 O) 3 as a single-source precursor, solvothermal reaction conditions, absence of hydroxyl groups from the reaction solvent, and the presence of oleylamine are required to achieve well-defined, crystalline, and monodisperse ZnFe 2 O 4 nanoparticles. The size of the ZnFe 2 O 4 nanocrystals increases as the ratio of oleic acid and oleylamine ligands to precursor increases. The inversion parameter increases with increasing solubility of the precursor in the reaction solvent, with the presence of oleic acid in the reaction mixture, and with decreasing reaction temperature. These results are consistent with a mechanism in which ligand exchange between oleic acid and carboxylate ligands bound to the precursor complex influences the degree to which the reaction produces a kinetically trapped or thermodynamically stable cation distribution. Importantly, these results indicate that preservation of the triangular Zn−O−Fe 2 core structure of the precursor in the reactive monomer species is crucial to the production of a phase-pure ZnFe 2 O 4 product and to the ability to tune the cation distribution. Overall, these results demonstrate the advantages of using a single-source precursor and solvothermal reaction conditions to achieve synthetic control over the structure of ternary spinel ferrite nanocrystals.

MXene/Ferrite Magnetic Nanocomposites for Electrochemical Supercapacitor Applications

“…It is also noted that the particle size and shape influences the magnetic characteristics of the particle [ 71 , 72 , 73 , 74 ]. For the preparation of mixed ferrite, the divalent and trivalent metal ions can be introduced and adjusted for the complete phase formation with required cation distribution [ 75 , 76 ]. Similarly, other chemical methods such as the sonochemical process, solid state reaction, and auto-combustion method also could be adopted for the synthesis of various ferrite magnetic nanoparticles with the required shape and size [ 77 , 78 , 79 , 80 ].…”

Surface Adsorption and Photoinduced Degradation: A Study of Spinel Ferrite Nanomaterials for Removal of a Model Organic Pollutant from Water

“…Spinel ferrites are known to exhibit various distributions of the metal cations among the tetrahedral and octahedral crystal sites, and this cation distribution may also play a role in determining the surface charge. Notably, all of these variables can be tuned within the same spinel ferrite composition, i.e., same identity of M, by changing synthetic conditions, such as annealing temperature, , solvothermal reaction solvent and ligands, or applying postsynthetic surface chemical treatments with e.g. NaBH 4 . − Further work is needed to establish the extent to which these factors impact the pH pzc and, consequently, the surface charge at a given reaction pH.…”

The Chemistry of Spinel Ferrite Nanoparticle Nucleation, Crystallization, and Growth

“…The different divalent cations, M 2+ , are known to exhibit different affinities for the specific crystallographic sites resulting in formation of either normal spinel structures (all M 2+ occupying all tetrahedral 8 a Wyckoff sites), inverse spinel structures (all M 2+ occupying half the octahedral 16 d Wyckoff sites), or mixed spinels with a fraction, x , of the Fe 3+ ions (called the inversion degree) occupying the tetrahedral sites, [ M 2+ 1– x Fe 3+ x ] tet [ M x Fe 3+ 2– x ] oct O 4 . For larger/bulk crystallites, the thermodynamically stable cation distribution is normal ( x = 0) for ZnFe 2 O 4 , mixed for MnFe 2 O 4 , and inverse ( x = 1) for CoFe 2 O 4 and NiFe 2 O 4 , but nanosized crystallites have been reported to exhibit a variety of inversion degrees. − In their thermodynamically stable bulk forms and at room temperature, MnFe 2 O 4 and NiFe 2 O 4 are soft ferrimagnets, CoFe 2 O 4 is a hard ferrimagnet, and ZnFe 2 O 4 is paramagnetic, however, ultrafine nanocrystals of the compounds will exhibit superparamagnetic behavior below their blocking temperature. Thus, the magnetic properties and performance are governed both by the composition, cation distribution (inversion degree), and nanoparticle sizes, providing several flexible handles to tune the materials performance.…”