High-purity foam-like micron-sized gold cage material with tunable plasmon properties

Herein, by growing mono dispersed gold nanoparticles (MNPAu) on the surface of polystyrene (PS)/nanogold (Au) core-shell composites (PS@Au), we successfully synthesized a micron-sized gold cage (2.6-10.7 μm), referred to as PS@Au@MNPAu for the first time. The new micron-gold cage materials exhibit broadband absorption range from near-ultraviolet to near-infrared, which is unlike the conventional nanogold core-shell structure. The uniform growth of MNPAu on the surface forms a new photonic crystal spectrum. The strong coupling of the spectra causes anomalous absorption in the ultraviolet-near infrared band (400-900 nm). Furthermore, by removing the PS core, a nanogold cavity structure referred to as Au@MNPAu was prepared. This structure demonstrated a high purity (> 97 wt%), low density (9-223 mg/cm³), and high specific surface area (854 m²/g). As the purification process progressed, the MNPAu coupling on the surface of the micro-gold cage strengthened, resulting in the formation of peaks around 370 nm, plasma resonant peaks around 495 nm, and structural bands of photonic crystal peaks around 850 nm. The micron-sized gold cage provides hybridized and tunable plasmonic systems. The theoretical simulations indicate that this plasmon anomalous absorption phenomena can be understood as the novel form of the topological structural transitions near the percolation threshold, which is consistent experimental measurements.