Silver nanoparticle synthesis using lignin as reducing and capping agents: A kinetic and mechanistic study.

Silver nanoparticles (AgNPs) were robustly synthesized from aqueous AgNO3 with alkali lignin (low sulfonate) (ALls) severing as dual reducing and capping agent. The AgNP synthesis mechanisms were highly pH dependent. Under neutral and acidic conditions, polydispersed AgNPs were synthesized via the self-catalyzed reduction of Ag(+) on instantaneously formed Ag2O surfaces followed by the slower pseudo-first order reduction. The Ag2O nanoparticles functioned as the nucleating sites for the reduction of remaining silver cations to form AgNPs whose size and size distribution strongly dependent of lignin concentrations. AgNPs were optimally synthesized by reducing 2 mmol/L AgNO3 with 0.16 wt% ALls at pH 10 and 85°C in 30 min to near 100% yield in bimodal distributed sizes with 23% and 77% in feret diameters of 7.3 (± 2.2)nm and 14.3 (± 1.8)nm, respectively.