A comparative study about the effects of isomorphous substitution of transition metals (Ti, Cr, Mn, Co and Ni) on the UV/Fenton catalytic activity of magnetite

Physico-chemical properties of zinc partially substituted magnetite nanoparticles

“…Whereas a slight expansion in the interplanar spacing of (311) planes were found from 0.2519 to 0.2544 nm. These findings are attributed to a slight alteration in the spinel structural framework due to the difference in ionic radius between iron (Fe 2+ , 0.645 Å and Fe 3+ , 0.64Å) (12,6) and zinc (Zn 2+ , 0.74Å) (22, 27) cations. However, it is interesting that the crystallite size calculated according to Scherrer's equation shows that by increasing the zinc molar ratio, the crystallite size reduces by 30% (10.08 to 6.99 nm) for Fe 3-x Zn x O 4 nanoparticles.…”

“…The presence of surface hydroxyl groups were mainly derived from the dissociation of the water molecules adsorbed on the oxygen defect sites which can be correlated with the isomorphic partial substitution of zinc into the Fe 3 O 4 structure [10,13]. These surface hydroxyl groups can significantly influence the surface properties of materials [6,14] and adsorption of pollutants within the vicinity of the active sites during catalysis [15]. …”

“…Second, Fe 3 O 4 accommodates both Fe 2+ and Fe 3+ on the octahedral sites, allowing the Fe species to be reversibly oxidised and reduced while keeping the structure unchanged [4]. Third, the Fe cations in the Fe 3 O 4 structure can be isomorphically substituted with different types of transition metal cations which can significantly affect the microstructure, physicochemical properties and catalytic activity of the resulting materials [6,7].…”

“…To circumvent this issue, several transition metal cations have been isomorphically substituted into the Fe 3 O 4 structure in order to enhance and sustain its long term catalytic activity as well as its stability [4,6,9,10]. Recent studies have revealed that the isomorphic substitution of Fe 3 O 4 with Mn [6], Ti [10], Cr [9], and Co [4] have significantly enhanced its catalytic activity in various reactions. These enhancement were greatly dependent on the types of substituting metals, it's concentration as well as the occupancy of substitution sites which stimulates an effective generation of hydroxyl radicals (HO•) during catalysis.…”

Graphene oxide-iron oxide nanocomposites for dye contaminated wastewater remediation

“…Among these iron oxides and/ or iron hydroxides, the inverse spinel Fe3O4 has been found to work efficiently as a heterogeneous catalyst in the heterogeneous Fenton-like reaction, based on its high Fenton activity [46,53,54]. This is due to the fact that the Fe3O4 possesses several unique features [46,[55][56][57][58] on the octahedral sites allowing the iron species to be reversibly oxidised and reduced without structural change; and (iv) the iron ions in the spinel structure of Fe3O4 can be isomorphically substituted with several transition metals which have various redox properties altering the catalytic properties of the resulting materials. In addition, the Fe3O4 can be easily separated from the reaction medium using an external magnetic field due to its inherent magnetic properties [59][60][61].…”