The development and extensive studies on cost-effective and eco-friendly nanofluids with efficacious thermophysical properties are essential regarding the ever-increasing concerns about environmental hazards. Thus, the present research intended to offer novel green nanofluids based on a two-step method for the dispersion of magnesium oxide (MgO) nanoparticles in two binary DESs and four ternary DESs. The binary DESs were composed of choline chloride (ChCl) and glycerol (Gly) in 1:2 and 1:5 M ratios, and the four ternary DESs consisted of ChCl, Gly, and water in 1:2:1 1:2:2, 1:5:1, and 1:5:2 M ratios. Dynamic light scattering analyzed the stability of samples for several days. Moreover, a comprehensive experimental analysis of thermophysical characteristics of DESs and DES-based nanofluids was executed by defining specific classifications, including type of base solvents, MgO mass concentration (1, 5, and 10 wt%), and temperature range (283.15 to 333.15 K). In addition, the isobaric thermal expansivities were calculated by empirical data. The experimental findings revealed that adding nanoparticles and water content in DES structure caused an augment in thermal conductivity. Around 4–21% increase in thermal conductivity was observed for nanofluids made up of binary DESs, and around 10% for those made up of ternary DESs. Furthermore, DES-based nanofluids showed an average 1.2% drop in density versus temperature, while around 3% enhancement was achieved for 5 wt% MgO suspended in 1ChCl:2Gly. Based on comparisons with the most relevant nanofluids reported in the previous studies, it was determined that the nanofluids presented in the current study were superior. Eventually, it was demonstrated that the nanofluid of 10 wt% MgO in binary 1ChCl:5Gly mixture achieved the highest thermal conductivity (0.304 W.m-1K−1) can be considered as a high-potential candidate for heat transfer purposes.
