Mechanism of silver nanoparicles production at the plasma-liquid interface

Summary form only given. Plasmas interacting with liquids have been used to produce metallic nanoparticles
¹
. Plasma acts as a reducing agent of metal ions in the solution and the formed neutral atoms subsequently agglomerate to form nanoparticles. The reduction of the plasma was suggested to be due to electrons injected by the plasma into the solution
¹
. The presence of solvated electrons at the plasma-liquid interface at concentrations of the order of 1 mM has been shown recently
²
. However solvated electrons have a very short lifetime and plasma produces many other reactive species such as OH, H and (V)UV photons at similar fluxes which could also play a significant role in reducing metal solutions. To unravel the mechanism we have studied silver nanoparticle formation by a RF driven plasma jet with argon and argon + H
₂
feed gases to vary the atomic hydrogen concentration. Both AgNO
₃
solutions with and without surfactant (fructose) have been used. These measurements have been complemented with a direct current pulsed plasma jet with the solution as one of the electrodes to assess the effect of electrons when changing the polarity of the solution. Absorption and transmission electron microscopy was used to assess the nanoparticles production. It was found that (V)UV photons played a significant role in initiating the liquid phase chemistry. Plasma induced conversion of fructose plays a dominant role in the presence of fructose. Nanoparticles are produced even when the plasma plume is not touching the liquid suggesting that species other than electrons play a role. Scavenger measurements suggest that atomic hydrogen plays an important role in production of silver nanoparticles in solution. Nonetheless distinct differences with and without the presence of electron injection have been observed. These differences could also be caused by significant differences in plasma-induced reactivity in water cathode and water anode case.