Green-synthesized gold nanoparticles from Plumeria alba flower extract to augment catalytic degradation of organic dyes and inhibit bacterial growth

• Gold nanoparticles were successfully synthesized from Plumeria alba flower extract.
• The size of the gold nanoparticles could be controlled by varying concentrations of flower extract.
• Small size gold nanoparticles exhibited better antibacterial and catalytic activity.
• Mechanism of catalysis was explained.

Bio-inspired eco-friendly gold nanoparticles were synthesized by a green method using aqueous Plumeria alba flower extract (PAFE). The use of 1% and 5% concentrations of PAFE resulted in two different sizes of P. alba gold nanoparticles, PAGNPs1 and PAGNPs2, with surface plasmon resonance (SPR) peaks at 552 and 536 nm, respectively. Size-controlled formation of gold nanoparticles was indicated by the SPR shift observed with increasing concentration of PAFE. The accurate size and morphology of PAGNPs1 and PAGNPs2 were determined by transmission electron microscope (TEM) analysis is found to be 28 ± 5.6 and 15.6 ± 3.4 nm, respectively, and those are spherical in shape. The antibacterial activity of PAGNPs1 and PAGNPs2 was tested against Escherichia coli; the small-sized PAGNPs2 exhibited better antibacterial activity with a 16-mm zone of inhibition at a concentration of 400 μg/mL. Furthermore, the catalytic activity of PAGNPs1 and PAGNPs2 was analyzed on six hazardous dyes; PAGNPs2 exhibited more pronounced catalytic activity than PAGNPs1. Among all of the dyes, 4-nitrophenol was most rapidly degraded to 4-aminophenol by PAGNPs2 within 5 min. The mechanism of catalysis in the presence of PAGNPs1 and PAGNPs2 can be described as an electron transfer process from donor NaBH4 to an acceptor. The facile green synthesis of such eco-friendly nanoparticles in bulk suggests this method has potential industrial applications.

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