He/H_2 Pulsed-Discharge Plasma as a Tool for Synthesis of Surfactant-Free Colloidal Silver Nanoparticles in Water

摘要

In this study we investigated the interaction of atmospheric-pressure helium (He) and He/ H_2 pulsed-discharge plasma with different water solutions. We developed a synthetic path to obtain fairly uniform, small (~2 nm), surfactant-free silver (Ag) nanoparticles (NPs) with the treatment of an AgNO_3 solution with He/H_2 bipolar pulsed discharge. The colloidal solutions containing Ag NPs are stable for months and do not show any agglomeration (the measured zeta potential is -41 mV at pH ~8). The adsorption of negatively charged hydroxide (OH") ions on the surface of Ag NPs could be responsible for the electrostatic stabilization. The treatment of the air-saturated water by pure He plasma with a negative polarity leads to the creation of HNO_3 and hydrogen peroxide (H_2O_2) as stable species. Contrary to the acidification of the solution by He plasma treatment, He/H_2 discharge with negative and, in particular, with bipolar pulses produces only traces of HNO_3 and no H_2O_2. We demonstrate here that He/H_2 discharge with bipolar pulses is remarkably efficient in near-complete nitrate decomposition and slight alkalization of dilute HNO_3 and KNO_3 solutions.