Fabrication of Electrically Conductive Cellulose Nanofiber Scaffolds with Ag Nanoparticles via Post-Reduction

Although a wide variety of functional materials based on cellulose nanofibers (CNFs) have been developed, fabricating CNF/nanoparticle hybrid materials remains challenging because nanoparticles readily aggregate into large clusters. In this study, we report the fabrication of CNF scaffolds decorated with Ag nanoparticles via a post-reduction strategy that suppresses nanoparticle aggregation during the reduction process. CNF gels were fabricated by combining freeze-casting and freeze-crosslinking of an aqueous CNF dispersion, resulting in networked structures whose morphology was controlled by the freezing conditions. Unidirectionally and radially aligned CNF-networked gels exhibited characteristic mechanical properties corresponding to their orientation. Ag+ cations were subsequently incorporated into the CNF networks, and freeze-drying yielded Ag+-loaded CNF scaffolds as precursors for electrically conductive porous materials. Thermal reduction of these precursors successfully produced electrically conductive CNF scaffolds with a well-dispersed state of Ag nanoparticles. In contrast, severe nanoparticle aggregation was observed when Ag+ cations were reduced with ascorbic acid under wet conditions prior to freeze-drying. This post-reduction strategy effectively suppressed Ag nanoparticle aggregation, leading to well-dispersed CNF/Ag networked structures and significantly improved electrical conductivity.