This study investigates the potential of graphite, graphene, and graphene oxide nanofluids to enhance evaporation rates in solar distillation for brine desalination. Nanofluids were prepared at four concentrations (0.02mass%, 0.05mass%, 0.1mass%, and 0.2mass%) and evaluated across a salinity range of 100,000–140,000 µS \({cm}^{-1}\) . Stability in brine, which is an insufficiently studied factor, was assessed using four independent parameters: nanofluid concentration, salt concentration, pH, and time. These parameters were modeled and optimized via response surface methodology (RSM) based on a central composite rotatable design (CCRD), comprising 30 experiments (factorial, axial, and central points) for each nanofluid type. Results showed that all variables significantly influenced stability, with pH and time exerted the strongest effects. Stability tests were conducted within a pH range of 8–10. Optimal absorption occurred at 0.1mass% nanofluid concentration; however, stability was favored in the 0.025–0.075mass% range. Higher concentrations reduced light penetration due to particle aggregation. Among the tested materials, graphene exhibited superior performance, showing statistical significance (p value < 0.05) and minimal stability loss at residence times of 1–9h. In contrast, graphite showed notable instability under similar conditions. Nanofluids above 0.05mass% demonstrated high absorptivity with negligible reflection and transmission, making them suitable for solar collector applications. The solar evaporation performance of nanofluids at different nanoparticle concentrations was also evaluated. Results showed that higher concentrations improved light absorption, photothermal efficiency, and evaporation rate, with optimum performance at approximately 0.075mass%. Nanofluids above 0.05mass% exhibited excellent solar light-harvesting capability, demonstrating strong potential for solar steam generation and desalination applications.
