Fig. 5. (a). UV-visible spectra of Pt NPs synthesized by the bio-reduction of Pt ions using P. guajava extract. (b) UV-visible spectra of biosynthesized Pt NPs at various concentrations of P. guajavaextract. (c) UV-visible spectra of Pt NPs at various concentrations of the Pt salt solution. (d) UV-visible spectra of Pt NPs at different time intervals.