Effects of the gap distance on the characteristics of gold nanoparticles in nanofluids synthesized using solution plasma processing

In this study, gold nanoparticles for use in the production of nanofluids were synthesized with various gap distances of 1.0 mm to 16.0 mm between cathode and anode electrodes using Solution Plasma Processing (SPP). The size distribution and the shape of gold nanoparticles in the nanofluids were investigated using a UV-vis nir spectrophotometer and transmission electron microscope (TEM); the dispersion stability of the gold nanofluids was characterized using zeta-potential. The results demonstrate that the distances between electrodes have a strong effect on the formation of Au nanoparticles in nanofluids. The gap distance of 1.0 mm produced the smallest average particle size, 17.7 ± 6.0 nm in diameter, and the most uniform size distribution. In addition, the zeta-potential of the gold nanoparticles synthesized with a gap distance of 1.0 mm was measured at −45.4 ± 1.3 mV, which suggests excellent dispersion stability of nanoparticles in the nanofluids. Possible mechanisms for the formation of nanoparticles in SPP are suggested. The electrons provided from the solution plasma are believed to play a vital role in producing the Au nanoparticles. Also, increased electrical energy from the plasma is responsible not only for increasing the surface areas of the nanoparticles in the solution by making the nanoparticles even smaller in size, but also for facilitating good dispersion stability by negatively charging the nanoparticles.