Figure 1. XRD patterns of the as-prepared products obtained by calcining the γ-MnOOH precursors under different conditions:(a) 350oC for 4h in air and then 200oC for 2h in H2 (b) 350oC for 4h in air, (c) at 600oC for 2h in air, (d) 600oC for 4h in argon.