Phenolic resin reinforcement: A new strategy for hollow NiCo@C microboxes against electromagnetic pollution

Metal-organic frameworks (MOFs) transformation is evolving into an attractive strategy for the synthesis of functional carbon-based materials in different fields. However, this method is usually inapplicable to hierarchical carbon-based composites, because high-temperature pyrolysis easily accounts for microstructure collapse. Herein, with NiCo Prussian blue analog (PBA) microcubes as the precursor, we successfully harvest hollow NiCo@C microboxes through alkaline etching and phenolic resin (PR) reinforcement. PR modification not only stabilizes the microstructure during high-temperature pyrolysis, but also realizes the regulation of chemical composition simultaneously. The stability of microstructure essentially benefits from the fact that PR-derived carbon layer suppresses the agglomeration of NiCo nanoparticles effectively. Electromagnetic (EM) analysis suggests that hollow microstructure is very helpful to enhance dielectric loss, stimulate multiple reflection and scattering of EM waves, and realize good impedance matching. When the thickness of PR layer is optimized, the resultant hollow NiCo@C microboxes will possess excellent microwave absorption property, whose minimum reflection loss value can be as strong as −68.4 dB at 13.4 GHz and qualified bandwidth can cover 14.1 GHz (3.9–18.0 GHz) by integrating the absorber thickness from 1.00 to 5.00 mm. Such a performance promises hollow NiCo@C microboxes a bright prospect as potential candidates against EM pollution.