In their
study a two-layer semiconductor model, with the inner
layer a semiconductor with good (metallic) conductivity
(e.g., magnetite) and the outer one a semiconductor with
poorer-than-metallicconductivity (e.g., g-Fe2O3, maghemite),
was employed to tie all the experimental observations
together. Very recently, Huang and Zhang (2004)
further studied the effects of low pH (2–4.5) on nitrate
reduction by iron grains (approximately 0.5mm in
diameter with a BET surface area of 0.04m2 g1).