Fabrication of Microwave-Responsive Confined NaCl in Polydopamine

Microwave-responsive nanoparticles hold promising applications in microwave thermal therapy and electromagnetic shielding; however, fabricating nanoparticles with high energy conversion efficiency remains challenging. This study leverages the catechol and amino groups in polydopamine (PDA) molecules to achieve simultaneous loading of Na+ and Cl– ions. Through potassium persulfate oxidation to protonate PDA's amino groups for Cl– adsorption, followed by Tris-base pH adjustment to facilitate Na+ binding with catechol groups, we successfully confined sodium chloride (NaCl) within PDA via layer-by-layer assembly, creating highly efficient NaCl@PDA microwave-responsive nanoparticles. Systematic investigation revealed that toluene and potassium persulfate dosage significantly influenced nanoparticle size, with 2 g of potassium persulfate yielding uniform spherical nanoparticles (≈149 nm diameter) with well-defined morphology. Through systematic optimization of the NaCl content, we found that a loading of 36.0 wt % endowed the nanoparticles with exceptional thermal conversion performance under ultralow-power microwave irradiation (2 W, 2450 MHz), achieving 53 °C within 600 s demonstrating 1.7-fold and 1.4-fold faster heating rates compared to physiological saline and pure PDA nanoparticles, respectively. The synthesized nanoparticles exhibit superior microwave responsiveness, showing great potential for applications in microwave thermal therapy and stealth coating technologies.