Fig. 1: Gelation process of gold NPs triggered by NaBH4.

a Photographs of the fabrication process of the gold aerogel, where the wet gel was directly obtained from the HAuCl4 aqueous solution (5 mL) and further freeze-dried to yield the corresponding aerogel. Note for a clear demonstration, the aerogels shown in Fig. 1a were prepared from ~800 mL HAuCl4 solution. Time-lapse b in situ optical microscopy, c ex situ TEM, and d UV-vis absorption spectra monitoring the gelation process. e Ligament size evolution of the gold aggregates during the gelation process (error bars depict the standard deviation). f SEM image and TEM image (inset) of the resulting gold aerogel. The scale bars in b, c, f, and the inset in f are 20 μm, 200 nm, 10 μm, and 20 nm, respectively.