Comparison of methods for quantitative determination of silver content in cellulose nanowhisker/silver nanoparticle hybrids

Hybrid particles consisting of cotton-derived, carboxylated cellulose nanowhiskers (CCNWs) and silver nanoparticles (AgNPs) were prepared by exchanging the counterions of CCNW surface carboxyl groups for Ag+, followed by thermal or chemical reduction to form AgNPs. Hybrids were also prepared by mixing aqueous suspensions of CCNWs and AgNPs. Hybrids prepared by thermal reduction had more AgNP aggregates than those prepared by chemical reduction using NaBH4. Contact between CCNWs in the dry state during thermal reduction promoted aggregation, whereas effective isolation of CCNWs in a suspension during chemical reduction suppressed aggregation. The AgNP contents were determined by three different methods: combustion, Volhard titration, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). While these methods gave comparable AgNP contents, minor differences were observed owing to method-specific errors. The combustion results were closest to the theoretical values calculated from the Ag+ feeding ratio, followed by the titration results, and then the ICP-AES results.