Lichen biomass for green synthesis of silver nanocolloids

Lichen is one of the most abundant non-vascular biomasses, however, a
systematic study on application of the biomass in nanomaterial synthesis
is very limited. In this study, aqueous lichen extract was obtained from
Hypotrachyna cirrhata, one of the most abundant Himalayan Lichen biomass,
following a simple cold percolation method. The effect of extract to
silver nitrate mixing ratio, pH, and waiting time in growth and stability
of nanoparticle was systematically explored. The rate constant for
bio-reduction was found to be 5.3×10-3 min-1. Transmission electron
microscopy (TEM) showed a narrow particle size distribution with mean
particle size of 11.1±3.6 nm (n=200) The X-ray diffraction (XRD) and
selected area electron diffraction (SAED) techniques confirmed the
formation of cubic crystals. The synthesized colloidal solution showed
excellent response for Hg2+ and Cu2+ ions in spiked water samples. The
limit of detection and calibration sensitivity for Hg2+ and Cu2+ ions were
found to be 1 mg/L and 5 mg/L, and 2.9×10-3 units/ppm and 1.6×10-3
units/ppm; respectively. These findings suggested that green synthesis of
spherical silver nanoparticles having narrow size distribution is possible
using the aqueous lichen extract and the nanoparticles can be used for
detection of selected heavy metals.