Growth of gold nanoparticles on cellulose nanofibers

The in-situ growth of gold nanoparticles (AuNPs) on cellulose nanofibers (CNFs) is a promising novel method to functionalize the CNFs. This work aims to study the synthesis mechanisms of the AuNP/CNF composites and develop the methods to control the particle size and surface coverage of AuNPs grown on CNFs. The growth process was monitored by the spectral analysis in real time, and the morphology of the AuNP/CNF composites was observed by using the electron microscopic techniques. The crystallography of AuNPs grown on CNFs was investigated by using a transmission electron microscopy (TEM). It has been found that the CNFs contribute to reducing the gold (Au) precursors, albeit at a much lower reduction rate than the citrate ions. The Au monomers have been found to strongly attach onto the CNFs to form the nucleation sites for the subsequent growth of AuNPs. The mechanisms underlying the formation of the AuNP/CNF composites have been proposed, with the emphasis on the effects of the CNFs on the growth of Au nanocrystals: the citrate ions play the dominant role in the reduction of Au precursors; the CNFs are able to offer the reduction sites for Au precursors and provide the nucleation sites for the formation of Au nanocrystals, and at the same time, having a prevention effect on the fusion of AuNPs formed on CNFs. Based on the proposed mechanisms, the methods of controlling the growth of AuNPs on CNFs have been developed: the size of AuNPs can be controlled by manipulating either the concentration of citrate ions or the initial pH value of the reaction suspension; the surface coverage of AuNPs on CNFs can be controlled by adjusting either the solid content of the CNFs or the initial pH value of the reaction suspension.