Fabrication of rod-shaped β-FeOOH: the roles of polyethylene glycol and chlorine anion

β-FeOOH nanorods of 40 nm wide and 450 nm long were fabricated through precisely regulating the hydrolysis kinetics of Fe3+ in polyethylene glycol and the concentration of Cl- as the structure-directing agent. Detailed structural and chemical analyses of the intermediates during the synthesis identified that the strong interaction between PEG and Fe3+ modulated the hydrolysis kinetics of Fe3+ and prevented the aggregation of β-FeOOH nanorods; while Cl- provided sufficient nucleation sites, stabilized the hollow channel of β-FeOOH, and more importantly induced the growth of the nanorods along [001] direction.