Effects of synthesis conditions and storage on silver nanospheres chemically reduced by mulberry leaf extracts

Abstract

Silver (Ag) nanospheres were chemically reduced from 1 mM silver nitrate (AgNO₃) solutions using mulberry (Morus alba Linn.) leaf extracts. The increase of pH in the synthesis from 9 to 13 modified the surface plasmon resonance peak in UV-Vis spectra relating to the particle diameter around 20 nm. Smaller nanoparticles were obtained from the syntheses at pH 7.4-7.7 and their density was slightly increased with the increase in synthesis temperature from 25 °C to 90 °C. The particle size was increased with increasing AgNO₃ concentration from 0.1 to 0.5 M but the mixed phases were obtained from the 0.5 M AgNO₃ precursor. After storing for 10 months at room temperature, the nanosuspensions remained without Ag sediment but their colors had significantly changed due to particle agglomerations. The colors were characterized by the smartphone colorimetry according to the RGB, CIE space, as well as chroma and hue angle. Based on the chroma and CIE b* values, the effect of synthesis pH in the stored nanosuspensions was comparable to that before the storage. Although the temperature had only moderate effects, nanosuspensions synthesized at 25 °C, 80 °C, and 90 °C were clearly distinguished by the hue and CIE b* values.