Unexpected formation of Ag2SO4 microparticles from Ag2S nanoparticles synthesised using poplar leaf extract

There are several methods for inorganic nanoparticle synthesis. However, these methods usually need high energy and generate toxic waste. Therefore, we explored biocrystallisation as a cheaper and safer method. We used poplar leaf extract to produce silver-based nanoparticles. Here, we studied nanoparticle crystallisation under various conditions such as light-dark cycles. Silver nanoparticles were analysed by transmission electron microscopy for particle morphology and size distribution, selected area electron diffraction for crystal structure and energy-dispersive X-ray for elemental analysis. Results show that individual Ag2S acanthite nanoparticles are formed after 3 days of dynamic cultivation in the dark. These particles have a typical spherical shape, which is found also in the form of aggregates with vermicular structure. These particles were unexpectedly transformed into Ag2SO4 micro-sized particles of good dispersity and high crystallinity upon application of light-dark cycles. Overall, our finding shows that poplar leaf extract is a good medium to catalyse the formation of silver-based nanoparticles.