  The plasma deposition wall coated composite of ZnO and {\alpha}-Fe2O3 (ZF-W)
after exposure to ~ 2000 {\deg}C, mostly considered as waste-materials and
cleaned out from the deposition unit, was subjected to anneal at 300, 500 and
1000 {\deg}C to manipulate the structural properties. An evolution of defect
states along with the structural changes has been identified as annealing
temperature was varied. As a consequence, an unstable state of ZnFe2O4 was
found to be stabilized at 500 {\deg}C and migration of Zn from ZnO causes the
phase transformation from the {\alpha}-Fe2O3 to ZnFe2O4. While implemented for
methyl blue adsorption/degradation without the effect of any external sources,
the degradation for ZF-W annealed at 300 {\deg}C, 500 {\deg}C and 1000 {\deg}C
were 84%, 68% and 82%, respectively. Compared to annealed structures, pristine
ZF-W delivered the highest methyl blue adsorption efficiency of 86%. The
changes in adsorption/degradation properties have been correlated with the
simultaneous evolution of defects and structural properties of ZF-W as annealed
at different temperatures. The plausible mechanism on the interaction of methyl
blue with the composites on the adsorption/degradation is proposed. These
findings give a clear indication on the importance of defects presence in the
mixed metal oxide composite to obtain high-performance degradation/adsorption
properties for sustainable wastewater treatment.
