Template-Free Gradient Selective Etching of Porous Carbon Nanospheres: Synergistic Dielectric Loss Optimization and Bifunctional Microwave Absorption-Corrosion Resistance Integration

The development of microwave-absorbing coatings for saline environments confronts dual challenges: dielectric loss optimization and porous carbon corrosion resistance. A solvent-mediated dynamic etching strategy achieving dual structural synergy is proposed. Acetone-regulated pore architecture enables template-free gradient etching, achieving tunable electromagnetic parameters and optimized absorption performance through pore size differentiation in nitrogen-doped 3D networks. In situ surface deoxygenation constructs hierarchical superhydrophobic micropores, decoupling pore topology from moisture adsorption. By bridging atomic-scale defect engineering and macroscopic interface optimization, a microstructure-mediated dielectric regulation paradigm is established. The optimized hollow porous carbon nanoparticles etched by 130 mL of acetone (HPCNs-130) demonstrate exceptional performance with −16.0 dB reflection loss at 2.78 mm thickness and 2.28 GHz bandwidth at 4.61 mm. Crucially, 48 h salt spray tests confirm superior corrosion resistance versus uncoated substrates. The coating significantly reduces the corrosion current from 25.44 to 0.53 µA cm⁻², achieving a corrosion inhibition efficiency of 97.9%. This work proposes a novel solvent-mediated dynamic etching strategy, enabling template-free and gradient-controlled pore architecture, overcoming template-dependent structural limitations. By bridging atomic-scale defect engineering and macroscopic interface optimization, a structure-function synergy paradigm is demonstrated that concurrently addresses electromagnetic attenuation and electrochemical degradation, providing transformative solutions for marine infrastructure protection.