Effect of voltage polarity and supply frequency on the properties of plasma contacting liquid electrodes and gold nanoparticle synthesis

Abstract

Plasma contacting with liquid provides many charged particles and reactive species into the liquid. The difficulty in controlling or selecting each specific species has significantly limited its applications in industry. Here, we present a study on using voltage polarity to regulate the type of charged particles absorbing from plasma into liquid. Detailed understanding of the processes at the plasma-liquid interface, electrolysis due to switching in voltage polarity was investigated via a visual pH observation, measuring the concentration of H2O2 and solvated electrons. The results indicated that changing in voltage polarity strongly affects the plasma properties, chemical properties, and electrolysis process in liquid, and further in the types of reducing species for gold nanoparticle synthesis. The results also showed using a suitable frequency could improve the efficiency of absorption of H2O2from plasma into the bulk liquid and the yield in the production of gold nanoparticles. The results provide a way to select desired species from plasma into the liquid for a distinct purpose and accompanying other properties in the system of plasma contacting with liquid.

Precise size-control and functionalization of gold nanoparticles synthesized by plasma–liquid interactions: using carboxylic, amino, and thiol ligands

“…When plasma irradiates the liquid, a large amount of reducing species (e aq and H 2 O 2 ) absorbed from the plasma concentrate in a liquid region close to the plasma-liquid interface, then diffuse to the surroundings at a low diffusion coefficient of about 10 À5 cm 2 s À1 . [22][23][24] These reducing species later reduce gold ions (AuCl 4 À ) into gold atoms (Au 0 ) at a high rate constant of up to 10 10 M À1 s À1 , followed by nucleation and aggregation into bigger particles. The generated Au 0 could condense in a tiny region due to combining the conditions of the small resident region of reducing species, reacting with gold ions at a high rate constant, and diffusing with a low coefficient.…”

“…PLIs produce a vast number of reducing species such as solvated electrons (e aq ) and H 2 O 2 in liquids. These species rapidly reduce gold ions in liquids into neutral gold atoms, which next aggregate and grow into a nanoscale [21][22][23][24] . The advantage of PLIs over other chemical methods is that the surface of synthesized GNPs is free of stabilized ligands.…”

“…However, all rapid processes involved in the generation of GNPs, including reduction, nucleation, and growth into final particles, are limited to a small region below the plasma-liquid interface, making it difficult to the size-control of GNPs. Some studies investigated the size-control of GNPs synthesized by PLIs via adjusting pH in the precursor medium 25,26 or modifying parameters generating PLIs 22,27 . Following these ways can adjust the reduction rate for gold ions and diffusion coefficient, possibly changing the speed of reduction-nucleation-growth into GNPs; consequently, the size of GNPs could be modified in certain ranges.…”

“…These species rapidly reduce gold ions in liquids into neutral gold atoms, which next aggregate and grow up to the nanoscale. [21][22][23][24] The advantage of PLIs over other chemical methods is that the surface of synthesized GNPs is free of stabilizing ligands. However, all rapid processes involved in the generation of GNPs, including reduction, nucleation, and growth into the nal particles, are limited to a small region below the plasmaliquid interface, making it difficult to control the size of GNPs.…”

“…Some studies investigated the size-control of GNPs synthesized by PLIs via adjusting the pH in the precursor medium 25,26 or modifying the parameters used to generate PLIs. 22,27 Following these methods can adjust the reduction rate for gold ions and the diffusion coefficient, possibly changing the speed of reduction-nucleation-growth into GNPs; consequently, the size of the GNPs could be modied in certain ranges. However, adjusting the parameters of PLIs is complex; even changing the pH values in the slightly alkaline range (pH 7-9) takes a prolonged time, making repetition of the size control difficult.…”