Examination of the interactions occurring in the gas and liquid phases of atmospheric pressure glow discharge generated in contact with a liquid electrode leading to production of size-defined gold nanostructures

Very recently, we developed a simple, one-step, and environmental friendly method for synthesis of Au nanoparticles (AuNPs) in a continuous-flow reaction-discharge system based on atmospheric pressure glow discharge (APGD). In this system, APGD was generated between the surface of a flowing liquid electrode, acting as cathode, and an Ar nozzle jet, acting as anode. We have optimized this system to identify the conditions for production of the smallest sized AuNPs. To describe the processes and interactions occurring in the gas-liquid interface of the developed reaction-discharge system that lead to formation of size-defined AuNPs, identification of selected reactive nitrogen (RNS) and oxygen (ROS) species was performed. On the basis of optical emission spectrometry (OES) measurements it was suggested that several reactive species (OH, O, NO, NH, N2, N2+ and H) were produced in the gas phase of the discharge. These radicals could be responsible for generation of other active species in the liquid phase of the discharge that could be involved in reduction of Au(III) ions necessary for AuNPs formation. Then, the concentrations of NO2
^-
ions and H
₂
O
₂
molecules, as well as pH, were determined in the APGD-treated solutions.