Porous ZnO/Co3O4/N-doped carbon nanocages synthesized via pyrolysis of complex metal-organic framework (MOF) hybrids as an advanced lithium-ion battery anode.

Metal oxides have a large storage capacity when employed as anode materials for lithium-ion batteries (LIBs). However, they often suffer from poor capacity retention due to their low electrical conductivity and huge volume variation during the charge-discharge process. To overcome these limitations, fabrication of metal oxides/carbon hybrids with hollow structures can be expected to further improve their electrochemical properties. Herein, ZnO-Co3O4 nanocomposites embedded in N-doped carbon (ZnO-Co3O4@N-C) nanocages with hollow dodecahedral shapes have been prepared successfully by the simple carbonizing and oxidizing of metal-organic frameworks (MOFs). Benefiting from the advantages of the structural features, i.e. the conductive N-doped carbon coating, the porous structure of the nanocages and the synergistic effects of different components, the as-prepared ZnO-Co3O4@N-C not only avoids particle aggregation and nanostructure cracking but also facilitates the transport of ions and electrons. As a result, the resultant ZnO-Co3O4@N-C shows a discharge capacity of 2373 mAh g-1 at the first cycle and exhibits a retention capacity of 1305 mAh g-1 even after 300 cycles at 0.1 A g-1. In addition, a reversible capacity of 948 mAh g-1 is obtained at a current density of 2 A g-1, which delivers an excellent high-rate cycle ability.

Construction of Ni-doped SnO2-SnS2 heterojunctions with synergistic effect for enhanced photodegradation activity.

Construction of heterostructures with proper band alignment and effective transport and separation of photogenerated charges is highly expected for photocatalysis. In this work, Ni-doped SnO2-SnS2 heterostructures (NiSnSO) are simply prepared by thermal oxidation of Ni-doped hierarchical SnS2 microspheres in the air. When applied for the photodegradation of organic contaminants, these NiSnSO exhibit excellent catalytic performance and stability due to the following advantages: (1) Ni doping leads to the enhancement of light harvesting of SnS2 in the visible light regions; (2) the formed heterojunctions promote the transport and separation of photogenerated electrons from SnS2 to SnO2; (3) Ni-SnO2 quantum dots facilitate the enrichment of reactants, provide more reactive centers and accelerate product diffusion in the reactive centers; (4) the SnS2 hierarchical microspheres constituted by nanoplates provide abundant active sites, high structural void porosity and accessible inner surface to faciliate the catalytic reactions. As a result, the optimized NiSnSO can photodegrade 92.7% methyl orange within 80 min under the irradiation of simulated sunlight, greatly higher than those of pure SnS2 (29.8%) and Ni-doped SnS2 (52.1%). These results reveal that the combination of heteroatom doping and heterostructure fabrication is a very promising strategy to deliver nanomaterials for effectively photocatalytic applications.