The careful design of nano-architectures and smart hybridization of expected active materials can lead to more advanced properties. Here we have engineered a novel hierarchical branching Cu/Cu₂O/CuO heteronanostructure by combining a facile hydrothermal method and subsequent controlled oxidation process. The fine structure and epitaxial relationship between the branches and backbone are investigated by high-resolution transmission electron microscopy. Moreover, the evolution of the branch growth has also been observed during the gradual oxidation of the Cu nanowire surface. The experimental results suggest that the surface oxidation needs to be performed via a two-step exposure process to varying humidity in order to achieve optimized formation of a core-shell structured branching architecture. Finally, a proof-of-concept of the function of such a hierarchical framework as the anode material in lithium-ion batteries is demonstrated. The branching core-shell heterostructure improves battery performance by several means: (i) The epitaxially grown branches provide a high surface area for enhanced electrolyte accessibility and high resistance to volume change induced by Li+ intercalation/extraction; (ii) the core-shell structure with its well-defined heterojunction increases the contact area which facilitates effective charge transport during lithiation; (iii) the copper core acts as a current collector as well as providing structural reinforcement.

Photodynamic therapy (PDT), which is a procedure that uses photosensitizing drug to apply therapy selectively to target sites, has been proven to be a safe treatment for cancers and conditions that may develop into cancers. Nano-sized TiO₂ has been regarded as potential photosensitizer for UV light driven PDT. In this study, four types of TiO₂ nanofibers were prepared from proton tri-titanate (H₂T₃O₇) nanofiber. The as-obtained nanofibers were demonstrated as efficient photosensitizers for PDT killing of HeLa cells. MTT assay and flow cytometry (FCM) were carried out to evaluate the biocompatibility, percentage of apoptotic cells, and cell viability. The non-cytotoxicity of the as-prepared TiO₂ nanofibers in the absence of UV irradiation has also been demonstrated. Under UV light irradiation, the TiO₂ nanofibers, particularly the mixed phase nanofibers, displayed much higher cell-killing efficiency than Pirarubicin (THP), which is a common drug to induce the apoptosis of HeLa cells. We ascribe the high cellkilling efficiency of the mixed phase nanofibers to the bandgap edge match and stable interface between TiO₂(B) and anatase phases in a single nanofiber, which can inhibit the recombination of the photogenerated electrons and holes. This promotes the charge separation and transfer processes and can produce more reactive oxygen species (ROS) that are responsible for the killing of HeLa cells.