The Correlation between Structure and Color of Iron Oxide‐type Solids, Sustainable Pigments with Gentle Hues

Abstract

Oxidic solids with hexaccordinate iron(III) appear as colored species only, if charge-transfer bands are present in the visible region, which originate from transitions, occurring between low-lying mainly oxygen-centered electronic states and antibonding, predominantly metal-3d states. Transitions within the 3d-shell are expected to be only very weak in intensity, because they are not only parity-but also spinforbidden, and hence don't usually contribute signifycantly to the coloration. It is shown by various examples, how one may steer the hue by the aimed manipulation of certain structural and chemical parameters, which effectively alter the location and, in particular, the band-width of the charge transfer transitions. The spectral properties are compared with those of the isoelectronic hexaoxo-coordinate manganese(II). The subsequent discussion of the color properties of 3d 6 -

Formulation of Iron Oxide and Oxy-hydroxide Nanoparticles from Ilmenite Sand through a Low-Temperature Process

“…The polymorphic nature of iron is known for a long time. Iron nanoparticles (INPs) are among the most interesting novel materials due to their unique physicochemical properties such as high catalytic activity, high magnetism, low toxicity, and ability of microwave absorption. − Iron nanoparticles can be classified into three major groups, namely (i) Iron oxide nanoparticles (IONs) (i.e., magnetite; Fe 3 O 4 , hematite: α-Fe 2 O 3 , maghemite; γ-Fe 2 O 3 ), (ii) Iron oxy-hydroxide (FeOOH) nanoparticles, and (iii) zero-valent iron (ZVI) nanoparticles.…”