Multiple approaches to control and assess the size of Pd nanoparticles synthesized via water-in-oil microemulsion

Abstract

Abstract Pd nanoparticles (NPs) were synthesized by a water-in-oil (w/o) microemulsion method using the water/AOT/isooctane system. N 2 H 4 and NaBH 4 were used as reducing agents and water-to-surfactant ratios (w 0 ) between 3 and 7 were considered. Multiple approaches, considering the physical operations and the synthesis conditions, were followed to assess and control the size of Pd NPs. Thus, the effect of the reduction time, the evaporation temperature and the purification with solvents in the formation of NPs was studied. Smaller NPs and narrower size distributions were obtained by TEM when the NPs were washed with methanol, indicating that a purification stage is needed to assess the influence of the synthesis conditions. Likewise, lower agglomeration and higher hydrophilicity of NPs was observed after washing with methanol. After a reduction time of 10 min, the evaporation of the microemulsion at 298 K led to larger NPs (7.1–9.7 nm) than at 368 K (6.2–7.7 nm). For a reduction time of 60 min, NPs with mean size between 9.1 and 11.7 nm were obtained, and the evaporation temperature only showed influence at high w 0 values. In general, smaller NPs and narrower size distributions were observed in the synthesis carried out with low w 0 values. The type of reducing agent also showed a relevant influence in Pd NPs size.