# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 3 Application of 2D Nanofluids
### Concentrated Solar Power
[92], 2D nanofluids were synthesized based on the inclusion of WS\({}_{2}\) nanosheets in a eutectic mixture of biphenyl and diphenyl oxide, which consisted of a typical heat transfer solution for CSP facilities to evaluate their viability to be employed in this technological field. The nanosheets of WS\({}_{2}\) were produced in situ in the heat transfer oil through liquid phase exfoliation where the inter-layer van der Waals forces of the bulk WS\({}_{2}\) were broken through ultrasonication in a fluid with the auxiliary action of the polyethylene glycol as the surfactant. The hydrogen bond interaction between the hydroxyl groups of the polyethylene glycol and the sulfur atoms of the WS\({}_{2}\) stabilizes thenanosheets within the fluid. The experimental results on stability revealed no appreciable alterations in the size of the nanosheets and zeta potential, which was confirmed by the low sedimentation levels observed. The enhancement of the polyethylene glycol fraction improved the stability of the 2D nanofluids and their viscosity was reported to be similar to that of the eutectic mixture base fluid, with only a slight increase reported at higher concentrations. The nanofluids provided a specific heat increase of 10%, whereas the TC showed an increase of 37.3% in compared with the base fluid itself. It was also confirmed that the HTC increased in all nanofluids by up to 22.1%, despite being synthesized with different amounts of polyethylene glycol and different ultrasonication times. The improved long-term stability of the nanofluids and heat transfer ameliorations were linked with the high surface area of the WS\({}_{2}\) nanosheets. The determined dynamic viscosity revealed that the developed nanofluids carry relevant features to be used in CSP plants, given that they would not entail the limitations associated with the piping obstruction and pressure drop in the involved systems. All findings suggested that these nanofluids would be a promising heat transfer medium in the CSP technological field. Aguilar et al. [143] considered GO 2D nanofluids as very promising for solar thermal applications given their high TC, simple exfoliation process of the filler, and intense black coloration. The researchers prepared a nanofluid composed of GO dispersed in the eutectic mixture of diphenyl oxide and biphenyl through liquid phase exfoliation. The nanofluids were synthesized by liquid phase exfoliation from the bulk GO with the aid of a Triton X-100, PEG-200, and other surfactants. It was observed that the most effective exfoliation was achieved with the Triton X-100 with the highest number of suspended nanostructures which were stable over time. The authors reported that 6.6%, 45.5%, and 29.7% enhancements for the specific heat, TC, and HTC, respectively, were observed in the Triton X-100-synthesized nanofluid. The determination of sunlight extinction and spatial distribution in the thermal fluid enabled the estimation of the dimensions of the direct solar absorbers using the Triton X-100 nanofluid. This nanofluid exhibited an almost complete sunlight attenuation between 3.5 mm and 20 mm depending on the weight fraction of the incorporated GO. The sunlight special distribution was revealed to be increasingly more intense near the input surface at greater amounts of GO. These findings allowed the researchers to arrive at the conclusion that the incorporating Triton-X surfactant nanofluids constitute a promising option to be used as customized sunlight absorbers to be employed in thermal solar collectors. In addition, these nanofluids were found to be strong-colored meaning they are suitable for the conceptualization and implementation of direct absorption solar collectors. Yan et al. [144] synthesized atomic-layer thick h-BN nanosheets and dispersed them into molten salt base fluid solar salt (NaNO\({}_{3}\)-KNO\({}_{3}\) with 60:40 of molar ratio).