Cellulose nanofiber-mediated formation and catalytic behavior of silver Mille-Feuille balls

Cellulose nanofibers (CNFs), known for their high aspect ratio and abundant surface groups, have emerged as support materials for metal nanoparticles. Although numerous studies have reported the loading of spherical metal nanoparticles onto CNFs, achieving controlled loading of platelet-shaped metal nanoparticles remains a challenge. We developed a new method to achieve controlled loading of hexagonal silver nanoplates (h-AgNPs) onto CNFs. This process resulted in the formation of ball-like agglomerates with a diameter of ∼2 μm. These agglomerates, composed of Mille-Feuille-like sheets that intersect each other and form a spherical contour (silver Mille-Feuille ball (SMFB)), were prepared by adding CNFs into a colloidal solution of h-AgNPs. It was indicated that the self-assembly of the h-AgNPs was mediated by CNFs, leading to the formation of SMFBs. The high aspect ratio of the platelet shape and monodisperse size distribution of h-AgNPs contributed to the formation of SMFBs. Furthermore, the morphology of the agglomerates was successfully modified by varying the CNF-to-h-AgNP ratio. SMFBs exhibited superior catalytic activities as a rate constant of 0.901 min-1 for 4-nitrophenol reduction and an oxygen reduction reaction onset potential of 0.91V vs. RHE. These results highlight the potential of SMFBs for catalytic applications.