it was found that this reaction is very
slow because the Ag(S2O3)23 complexes immediately generated a
passive layer on the surface AgNPls. By adding Cu2+, the Cu2+ in the
0.1 M ammonia buffer at pH 11 forms the Cu(NH3)42+ complex and
the standard potential of Cu(NH3)42+/Cu2+ in the presence of S2O32
was increased (Eq. (2)).