**4.4 Calcinations of green nanofibers**

To complete the formation of CuO/CeO2 nanofibers, the composite fibers prepared as above were left exposed to ambient moisture for 5 hr. to allow complete hydrolysis, then electrospun polyvinyl pyrrolidone (PVP) /cerium nitrate hexahydrate (CN)/copper acetate monohydrate (CA) fiber mats were removed from the aluminum foil. These composite fibers were placed on a ceramic crucible able to withstand high temperature and consequently calcined (500°C, 3 hr) in a muffle furnace in presence of air for eliminating the organic constituents and activating crystallization of Cu-Ce oxide.
