Facile synthesis of schwertmannite@akaganeite core/shell nanostructure from pickling waste liquor: Formation mechanism and potential application

An environmentally friendly and low-cost synthesis of schwertmannite@akaganeite (Sch@Aka) core/shell nanostructure was achieved from hydrochloric pickling waste liquor (HPWL). The Sch@Aka nanostructure had a pincushion-like shape composed of radially well-aligned nanorods with an average length of about 250 nm and a mean diameter of about 60 nm. Trace SO42− ions played a key role in the formation of the Sch@Aka nanostructure. In the presence of Fe3+, Cl− and trace SO42− ions, schwertmannite was preferentially nucleated and then served as a core for akaganeite growth. The novel Sch@Aka nanostructure not only exhibited a higher adsorption capacity (43.0 mg g−1) for heavy metal Cr(VI) ions, but also delivered a larger reversible storage capacity of 1245 mA h·g−1 with Coulombic efficiency of close to 82% as the anode material in Li-ion batteries, indicating its potential application value.