*2.1. Chemicals and Reagents*

High-quality Acetone with a special purity 99.5% was used as a solvent for the production of metal nanoparticles via metal vapor synthesis (MVS) technique. Prior to the synthesis solvent, it was dried under molecular sieves (4 Å) and degassed in a vacuum pump under 10−<sup>1</sup> Pa by freezing and thawing cycles. The metal source was Cu foil (99.99 percent) with a surface pre-treated with concentrated HNO<sup>3</sup> and diluted H2O to remove oxide film.

In this work, two types of chitosan were used. Chitosan with a high molecular weight (ChitHMW) was purchased from ACROS Organics (Wheaton, IL, USA). Chitosan with a low molecular weight (ChitLMW) was bought from Wirud (Hamburg, Germany). Until impregnation, the chitosan powder was degassed at 40 ◦C for 12 h under a vacuum of 10−<sup>1</sup> Pa. Oxalic acid dihydrate was of analytical consistency.
