Full Factorial Design Synthesis of Silver Nanoparticles Using Origanum vulgare

Abstract

Green synthesis of silver nanoparticles (AgNPs) involves a reduction reaction of a metal salt solution mixed with a plant extract. The reaction yield can be controlled using several independent factors, such as extract and metal concentration, temperature, and incubation time. AgNPs from Origanum vulgare (oregano) were synthesized in the past. However, no investigations were performed on the combined effects of independent factors that affect the synthesis. In this work, silver nitrate, oregano extract, and sodium hydroxide (NaOH) concentrations were chosen as the independent factors, and full factorial design under Response Surface Methodology was employed. UV–Vis absorbance spectroscopy, X-ray Powder Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) were used to characterize the nanoparticles. A Voigt function was fitted on the measured UV–Vis spectra. The fitting parameters of the Voigt function, peak wavelength, area, and Full Width at Half Maximum, were used as the responses. A quadratic model was fitted for the peak wavelength and area. The NaOH concentration proved to be the dominant factor in nanoparticle synthesis. UV–Vis absorbance showed a characteristic plasmon resonance of AgNPs at 409 nm. XRD verified the crystallinity of the nanoparticles and FTIR identified the ligands involved.

Green synthesis of silver nanoparticles using olive mill wastewater and olive stones extract and testing their antimicrobial activities against Escherichia coli and Staphylococcus epidermidis

“…The protocol for AgNPs synthesis was described in a previous work [19]. Silver nanoparticles using olive stone extract AgNP-OSE, or olive mill wastewater AgNP-OMW were formed.…”

“…Silver nitrate (0.25-5 mM), OSE (0%-50% v/v) or OMW (0.8%-20% v/v), and sodium hydroxide (0-20 mM) concentrations were investigated. A mixture of all three concentrations was incubated for 30 min [19]. The obtained NPs suspensions were centrifuged at 20,000 x g (Z 216 MK, Hermle Labortechnik) at 4 °C for 30 min and the derived pellets were stored at 4 °C in the dark for the subsequent experiments.…”

“…An aliquot from nanoparticle suspension prior to centrifugation was taken for UV-Vis spectroscopy measurements. Quartz cuvettes with 1 cm optical path length were used, employing the Perkin Elmer-Lamda 25 UV-vis spectrophotometer [19].…”

“…During green synthesis of nanoparticles (NPs) a reduction reaction occurs [18,19]. The factors that can influence the process of the synthesis are various and the valid assessment of this influence can only be extracted using statistical methods such as response surface methodology [20][21][22][23][24].…”

“…Recently, in another work, a quantitative method was proposed for correlating extract (Oregano), silver nitrate, and sodium hydroxide concentrations with AgNPs parameters [19]. This quantitative method was applied also here to elucidate on the influence these concentrations have on AgNPs synthesis by 'two factors at a time'.…”