Co 3 O 4 with high capacities and energy density has potential applications to be electrode materials for lithium ion batteries, one of the most important power sources. For improving the cycling stability, the Co 3 O 4 nanostructures are required. Herein, we report successful construction of Co 3 O 4 hexagonal nanorings and nanoplates/nanoparticles via treating Co-based metal organic frameworks (MOFs) with organic amine. The studies show that the release rate of Co(II) to the reaction system and the spatial hindrance of the organic linkers of MOFs determine the final morphology of Co 3 O 4 . As an anode for lithium ion batteries, Co 3 O 4 hexagonal nanorings with 1370 mA h g À1 specific capacity after 30 cycles displayed higher reversible capacity and better stability than commercial Co 3 O 4 particles with only 117 mA h g À1 specific capacity after 30 cycles. The improved performance of Co 3 O 4 hexagonal nanorings could be attributed to the shortened transfer path for Li + afforded by the special morphology.It is expected that plentiful metal oxide nanostructures could be constructed from MOFs due to the available versatile categories of MOFs.

a b s t r a c tThe question which type of signals can be determinately related to catastrophic rupture in heterogeneous brittle media still remains open. Here we report a specific precursor of catastrophic rupture, i.e. a power-law singularity of responses, based on rock experiments. Our experimental observations show that the singularity with power exponent À b, where b¼0.5170.10 (mean 7 s.d.), appears ahead of catastrophic rupture in some rocks, and the singularity does not appear at all for gradual failure. It is indicated that the power-law singularity can emerge well only close to catastrophic rupture and thus it could serve as a specific warning for catastrophic rupture. To address the potential forewarning of imminent catastrophic rupture, a fitting process based on the data before catastrophic rupture was developed to determine the two unknowns related to the occurrence, catastrophe point U F and the power exponent À b u . It is demonstrated that the power-law singularity appears only in the vicinity of catastrophe, and that the power-law singularity does not occur for gradual failure.