Synthesis, dissolution, and regeneration of silver nanoparticles stabilized by tannic acid in aqueous solution

Silver nanoparticles (AgNPs), especially with small size, are easy to release silver ion in aqueous solution owing to various reasons, which would significantly affect the stability, properties, and application of AgNPs. In this paper, monodisperse AgNPs with small size of ca. 10 nm were successfully prepared based on solid-state reactions. Ascorbic acid (AA) was used as reductant and tannic acid (TA) was used both as reductant and stabilizer in this environmentally friendly reaction. The dissolution and regeneration of the as-prepared TA-AgNPs in pure water were investigated by UV−vis spectra, TEM observations, and differential pulse anodic stripping voltammetry. The results indicated that the TA-AgNPs showed a little higher dissolution than conventional PVP-coated ones with similar size. However, the dissolved silver ion in the TA-AgNPs aqueous solution could be recovered just by adjusting the pH of the solution, which could be attributed to the reductant performance of TA at alkaline conditions. After regeneration, some smaller nanoparticles appeared in TA-AgNPs aqueous solution, indicating that new nucleation formed and the dissolved silver ions were actually recovered to Ag⁰.