LAUSR

Abstract This study demonstrates a green route for the preparation of high-concentration suspensions of silver nanoparticles (AgNPs), by incubating AgNO 3 with Laminaria japonica algal extract. The rate of AgNPs synthesis significantly increased within 2 min of initiating the incubation and elevating temperature from 90 °C to 120 °C. This method was also suitable for preparing AgNPs at ambient temperature but required 48–72 h for completion. A hydrothermal process (steam autoclave) resulted in accelerated temperature-controlled reduction of AgNO 3 in which AgNO 3 reduction to metallic AgNPs with robust control over optical and structural properties was successfully established using steam autoclaving at 100 kPa and 121 °C for 20 min. The process enabled a homogeneous reaction resulting in a narrow size distribution of AgNPs. Isotropic growth of AgNPs was evident under diverse synthetic conditions, designed considering various reaction factors including temperature, pH, extract concentration, and AgNO 3 ratios. Freeze-drying was used to increase yield and shelf-life of the nanoproduct and prevent aggregation. The AgNPs showed no significant effects on seed germination of either Triticum aestivum and Phaseolus mungo . However, they influenced lengths of shoots and roots in both plant species in a dose-dependent manner.