Size-tunable silver nanoparticle synthesis in glycerol driven by a low-pressure nonthermal plasma

Abstract Silver nanoparticles are extensively used in electronic components, chemical sensors, and disinfection applications, in which many of their properties depend on particle size. However, control over silver nanoparticle size and morphology still remains a challenge for many synthesis techniques. In this work, we demonstrate the surfactant-free synthesis of silver nanoparticles using a low-pressure inductively coupled nonthermal argon plasma. Continuously forming droplets of silver nitrate (AgNO3) precursor dissolved in glycerol are exposed to the plasma, with the droplet residence time being determined by the precursor flow rate. Glycerol has rarely been studied in plasma-liquid interactions but shows favourable properties for controlled nanoparticle synthesis at low pressure. We show that the droplet residence time and plasma power have strong influence on nanoparticle properties, and that improved size control and particle monodispersity can be achieved by pulsed power operation. Silver nanoparticles had mean diameters of 20 nm with geometric standard deviations of 1.6 under continuous wave operation, which decreased to 6 nm mean and 1.3 geometric standard deviation for pulsed power operation at 100 Hz and 20% duty cycle. We propose that solvated electrons from the plasma and VUV radiation induced electrons produced in glycerol are the main reducing agents of Ag+, the precursor for nanoparticles, while no significant change of chemical composition of the glycerol solvent was detected.