Solvent-controlled synthesis of bimetallic ZIF-coated tetra-needle ZnO whiskers toward hollow Co/C derivatives with enhanced microwave absorption

Aimed to address the poor impedance matching of pure tetra-needle ZnO (T-ZnO) as well as to optimise the structure of the wave-absorbing material, this research focused on constructing a bimetallic Zn/Co-ZIF-coated T-ZnO core–shell structure with T-ZnO as a self-sacrificial template. In this work, T-ZnO@Zn/Co-ZIF composites were synthesized by optimizing shell uniformity via modulating DMF/H 2 O solvent ratios (3:1 to 1:1 v/v) and reaction durations (6/24 h). By further pyrolysis, the formation of hollow structures of the derivatives was investigated and the electromagnetic wave absorption performance of the derived materials were evaluated. Optimal core–shell uniformity was achieved at DMF/H 2 O = 3:1 with 24 h reaction time (DH31-24). Pyrolysis at 800 °C (PDH31-24-800) produced hollow Co/C derivatives with complete ZnO volatilization. This material exhibited superior microwave absorption: minimum RL of − 16.40 dB at 14.00 GHz (3.00 mm thickness) and an effective bandwidth (RL ≤  − 10 dB) of 4.48 GHz (11.12–15.60 GHz).