“Green” plant extract-based method will be used in the preparation of gold nanoparticles in this study. The bioreductant from the aqueous leaves extract of Dillenia philippinensis Rolfe. (Katmon) were found efficient in reducing the metallic gold from chloroauric acid. The synthesized AuNPs were optimized in terms of the volume ratio of Chloroauric Acid (HauCl4)/ plant extract, pH, reaction time and effect of addition. Approximately 800uL of 1mM HauCl4 and 1200uL of 1.5% Dillenia philippinensis Rolfe. (Katmon) plant extract were used in synthesizing AuNPs. The absorbance of the AuNPs was found to increase with time and it took 10 minutes for the AuNP to reach maximum absorption peak around 541nm. The effect of addition has no significant difference on the observed absorption peak. It was found that at lower pH, the AuNPs starts aggregating without any observable color change and at higher pH, the AuNPs changes from red wine to brownish color. Characterization of the gold nanoparticles with the use of UV-Vis spectrophotometer showed lambda peak at 541 nm, indicating presence of Surface Plasmon Resonance (SPR). Fourier Transform Infrared (FTIR) spectroscopy results showed positive for the presence of hydroxyl and amine, which were found to be effective in reducing and in capping gold ions. Dynamic Light Scattering – Particle Size Analysis (DLS-PSA) showed gold nanoparticles with a mean diameter of 57.6nm – 60.6nm (n=6). The polydispersity indexes (0.729 and 0.563 respectively) of the synthesized gold nanoparticles were found to be increasing as the diameter decreases. Zeta Potential Analyzer resulted -13.720 mV for the repulsion of the gold nanoparticles. The synthesized AuNPs was used for heavy metals in aqueous solution, and it was observed that as the volume of the aqueous metal sample increases, there is a hypochromic shift on the absorption peak of the metallic nanoparticles.  

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