Lichen biomass for green synthesis of silver nanocolloids

<p>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 <em>Hypotrachyna cirrhata, </em>one of the most abundant Himalayan Lichen biomass,<em> </em>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.</p>