The color of the solution of the samples NRL–
AgNP_0.2 % and NRL–AgNp_0.4 % became pale
yellow, suggesting that the NRL matrix liberated
AgNP (Fig. 4b, c). The plasmon absorption peak at
405 nm in the UV–Vis spectra of the collected
aliquots revealed that AgNp is present in water
(Fig. 4), confirming that the NRL membrane released
the nanoparticles in the water along time. The red shift
of the plasmon band from 390 to 405 nm is probably
associated with particle growth and/or agglomeration,
or it can be caused by the changes in the medium
surrounding the AgNPs. In the case of the pure
colloidal silver dispersion, the surrounding medium
consists of water molecules only; in the case of the
released AgNP, the medium may also contain molecules
released by the NRL