### Carbon Nanofluids in FSCs  
The use of carbon nanoparticles is of great interest, mainly due to their reduced weight, greater hardness, high TC, high heat absorption capacity and large surface area. The use of carbon nanoparticles has the additional benefit of having high TC, extreme durability and resistance to corrosion. CNTs made from sheets of graphene that have been rolled up can be found as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). [PERSON] et al. [15] carried out a study in which they dispersed graphene in the base fluid to increase the thermal efficiency of a solar collector. [PERSON] et al. [16] examined the thermophysical properties of nanofluids composed of carbon nanoparticles and metal oxides. The authors used different nanoparticles such as graphene, CNT, Al\({}_{2}\)O\({}_{3}\), and SiO\({}_{2}\). It was found that as more nanoparticles are added to the fluid, the viscosity of the fluid increases. It was observed that the addition of Al\({}_{2}\)O\({}_{3}\) and SiO\({}_{2}\) nanoparticles slightly increases the heat capacity of the nanofluids. The findings that the authors showed imply that the most successful nanoparticles for improving the TC of nanofluids are carbon nanotubes and graphene. While the addition of Al\({}_{2}\)O\({}_{3}\) and SiO\({}_{2}\) nanoparticles can increase the heat capacity, [PERSON] et al. [17] studied the influence of different types of nanoparticles on the efficiency of an FSC, where they used four types of nanoparticles, MWCNTs, CuO, Fe\({}_{3}\)O\({}_{4}\), and Al\({}_{2}\)O\({}_{3}\), to evaluate the thermophysical properties, such as their density, viscosity and TC, as well as the efficiency of a solar collector. The findings demonstrated that, compared to the base fluids, the MWCNT nanoparticles increased the efficiency of the solar collector. It was found that as the CuO concentration increased, the efficiency of the solar collector increased. It was found that the addition of Fe\({}_{3}\)O\({}_{4}\) increases the efficiency of the solar collector. Although the TC of Fe\({}_{3}\)O\({}_{4}\) is high, its low concentration in the nanofluids limited its effect on the efficiency of the solar collector. [PERSON] et al. [13] evaluated the thermal efficiency of FPSCs using CuO-MWCNT and MgO-MWCNT hybrid nanofluids with water. The efficiency of the FSCs with MgO hybrid nanofluids improved by 25.1% compared to the base fluid and by 16.28% with respect to the MgO/water nanofluid. To the extent that the literature review has been possible, Table 1 presents the simple and hybrid metal oxide and carbon nanofluids that have been used in FSCs until now. As can be seen in Table 1, the carbon nanoparticles that have been used until now in FSCs are those of graphene in its spherical form and in multi-walled and single-walled carbon nanotubes. However, it has been found that graphite has been used to improve the efficiency of evacuated tube, dish parabolic and linear parabolic solar collectors by [19; 20; 21], respectively. Likewise, it has been found that fullerene C60 has been used to improve the efficiency in flat photovoltaic/thermal and direct absorption solar collectors by [22; 23], respectively. As shown in this section, several studies have explored the use of simple and hybrid nanofluids in thermal solar collectors. However, there is a notable gap in the literature regarding the application of simple graphite and fullerene C\({}_{60}\) nanofluids, as well as hybrid