Title: Biosynthesis of silver nanoparticles using unriped Carica papaya fruit extract with different PH conditions

Authors: Hooi Chien Ng; Cheng Seong Khe; Azizan Aziz; Zulkifli Merican Aljunid Merican; Rajalingam Sokkalingam; Thiam Leng Chew; Chin Wei Lai

Addresses: School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia ' Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh Perak, Malaysia ' School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia ' Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh Perak, Malaysia ' Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh Perak, Malaysia ' Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh Perak, Malaysia ' Nanotechnology and Catalysis Research Centre (NANOCAT), Institute of Postgraduate Studies (IPS), University of Malaya, 3rd Floor, Block A, 50603 Kuala Lumpur, Malaysia

Abstract: Silver nanoparticles were successfully synthesised at room temperature from silver nitrate using unripe Carica papaya fruit extract as a reducing and capping agent. PH of the reaction solution was adjusted with the addition of sodium hydroxide from pH 5.6 (original pH of the broth) to pH 6.5, pH 7.5 and pH 8.5. Quasi spherical silver nanoparticles were obtained across the studied pH range. The average particle size obtained decreased from 34 nm to 15 nm as the pH of the solution increased from 5.6 to 8.5. From the observations and ultra violet-visible spectrophotometer analysis, the rate of reduction and formation of silver nanoparticles increased as the pH increased. The crystalline nature of the as-synthesised silver nanoparticles in a cubic structure was confirmed by the peaks in X-ray diffraction and selected area electron diffraction. From Fourier transform infrared spectra, it was found that proteins in unripe papaya fruit extract were strongly bounded to the surface of silver nanoparticles as a capping agent. The thin layer of protein coating also further confirmed under high resolution transmission electron microscope. A plausible formation mechanism has been briefly proposed.

Keywords: biosynthesis; silver nanoparticles; Carica papaya fruit extract; pH; twinning.

DOI: 10.1504/IJNP.2017.086127

International Journal of Nanoparticles, 2017 Vol.9 No.2, pp.55 - 70

Received: 09 Feb 2016
Accepted: 20 May 2016
Published online: 27 Aug 2017 *

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