Atmosphere-Controlled Synthesis of Hierarchical Cu/Cu ₂ O/CuO Microtube Architectures Decorated with High-Density CuO Nanowires from Recycled E-Waste

The design of hierarchical copper oxide microstructures with tailored nanomorphologies is essential for next-generation electrocatalytic, sensing, and nanoelectronic applications. Here, we report an atmosphere-controlled thermal oxidation route for the sustainable synthesis of hollow Cu/Cu₂O/CuO microtubes decorated with a dense array of vertically aligned CuO nanowires. The synthesis uses recycled copper microwires from electronic waste (e-waste) coated with a polyurethane (PU) polymer. Comparative analysis under ambient air and high-purity synthetic air reveals that the thermal degradation of the polymeric coating forms a carbon-rich layer, crucial for regulating asymmetric cation transport and inducing mass transport that drives void formation via the Kirkendall effect. This mechanism transforms the solid microwire into a concentric hollow microtube structure. Critically, oxidation under synthetic air promotes the extensive growth of long CuO nanowires (up to 20 μm), guided by anisotropic diffusion along twin boundaries and sustained by a strong chemical potential gradient. These findings establish atmosphere control as a powerful strategy to fine-tune the multiscale architecture of sustainable metal oxide nanostructures from e-waste precursors, opening pathways for the scalable production of multifunctional materials.