  Iron oxide-based nanostructures receive significant attention as an efficient
adsorbent for organic dyes removal. The removal properties have strong
dependency on the stoichiometry, phases, reactive edges, defect states etc
present in the iron-oxides nanostructures. Herein, iron oxide/carbon composite
with well-defined heterophased grain boundaries is synthesized by simple
precipitation method and followed by calcination. The local structure, spin
dynamics and magnetic properties of heterophased iron oxides/carbon composite
are thoroughly investigated to explore its cationic and anionic dye removal
capability. To validate the effectivity of the presence of heterogeneous grain
boundaries, iron oxide/carbon nanocomposite with homogeneous grain boundaries
is also examined. It was found that the hetero-phased iron oxide/carbon showed
removal capacity of 35.45 mg g-1 and 45.84 mg g-1 for cationic (Crystal Violet)
and anionic (Congo Red) dyes, respectively as compared to that of
as-synthesised imidazole-capped superparamagnetic {\alpha}-Fe2O3 (25.11 mg g-1
and 40.44 mg g-1, respectively) and homophased iron oxide/carbon nanocomposite
(9.41 mg g-1 and 5.43 mg g-1, respectively). The plausible mechanism on the
local structural evolution of the heterophase in the course of calcination and
increase of the removal capacity is discussed. A detailed dye adsorption
investigation is presented including the adsorption kinetic study. The
pseudo-second order kinetic model is found to be an appropriate one and
suggests that the chemisorption is dominant factor leading to adsorption of
dyes. Whereas Weber-Morris model indicate the strong influence of boundary
layers of nanocomposite on the adsorption process.
