Reduction mechanism
As the primary compound present in the LE is expected to be
protocatechuic acid type compound [39–41], two hydroxyl groups
present in the benzene ring may participate in the reduction
reaction. The probable reaction mechanism is presented in Scheme
1. The presence of Ag+ first oxidizes tannin and forms an
intermediate silver complex and then finally silver ion and
quinone. The silver ion then reduced to zero valance silver in
the presence of free electron or nascent/atomic hydrogen produced
in the process. Scheme 2 shows the possible capping mechanism of
polyphenolic compound. The interaction may be because of the
hydrogen atom of the phenolic compounds of LE with Ag
nanoparticles which are having negative z potential value in their
pure form.