# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 2 Types of 2D Nanofluids
### Titanium Carbide MXene  
MXene nanofluids possess great potential in solar thermal energy conversion and harvesting. Alongside enhanced heat transfer properties, MXene nanofluids present a high extinction coefficient, giving them an enhanced solar light absorption capability. Single-layer and thin-layer MXene nanofluids have a higher specific surface area and surface chemistry richness than their multilayer counterparts, which provides nanofluids of the MXene family with the highest stability and TC. Furthermore, a novel type of two-dimensional nanocrystalline carbide transition metal materials designated by MXene (Ti\({}_{3}\)C\({}_{2}\)) has already been synthesized [101]. Two-dimensional MXene is hydrophilic and can be etched selectively from its MAX-phase structure, where M represents an early transition metal such as titanium, A represents one of the A-group elements (e.g., aluminum), and X represents carbon or nitrogen. The employment of the environmentally benevolent MXene is common for different purposes in diverse research areas. Figure 9 schematically presents the acid etching and ultrasonication synthesis method for obtaining 2D MXene nanosheets dispersed in a base fluid. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Authors/Year** & **Concentration** & **Base Fluid** & **Main Findings** & **Remarks** \\ \hline \multirow{4}{*}{[98]} & \multirow{4}{*}{Shah et al., 2022} & MoS\({}_{2}\) at 0.005\%, & & & Approximately \\  & & 0.0075\%, and & & 11\% increase in & 14.7\% maximum \\  & & 0.01\% vol. & & the TC. & decrease in the \\  & & & & & viscosity at 50 \({}^{\circ}\)C \\  & & & & and at 0.005\% wt. \\ \hline \multirow{4}{*}{[99]} & \multirow{4}{*}{Arani and Sadripour, 2021} & MoS\({}_{2}\) at up to 4\% wt. & & The performance & Higher pressure \\  & & & & criterion of a solar & losses for the \\  & & & & collector at 3\% wt. & nanoplatelets than \\  & & & & and brick-shaped & for the \\  & & & & nanoparticles was & brick-shaped \\  & & & & of 1.269. & nanoparticles. \\ \hline \multirow{4}{*}{[100]} & \multirow{4}{*}{MoS\({}_{2}\)} & \multirow{4}{*}{MoS\({}_{2}\)} & 46\% increase in & & \\  & & & & the TC. & \\ \cline{1-1}  & & & & 4.7\% increase in & 21.3\% increase in \\ \cline{1-1}  & & & diphenyl oxide & the specific heat & the efficiency of \\ \cline{1-1}  & & & & capacity. & solar collectors. \\ \cline{1-1}  & & & & 3.2\% increase in & \\ \cline{1-1}  & & & & the viscosity. & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Recent studies on 2D MoS\({}_{2}\) nanofluids. Figure 9: Schematic diagram of the synthesis procedure of MXene nanosheets in a water-based nanofluid. Evaluations of the thermophysical characteristics of the MXene nanostructure have focused mainly on its solid phase, and only a few studies have investigated its corresponding nanofluid capability. Nevertheless, the study carried out by Rafieerad et al. [102] assessed the thermophysical properties of Ti\({}_{3}\)C\({}_{2}\)Tx MXene with non-covalent Gr nanoparticles and covalently functionalized COOH- and NH2-Gr nanoparticle nanofluids. The authors synthesized and studied the microstructure and thermophysical properties of different water-based nanofluids with 2D metal-carbide MXene and nanosheets of Gr. The obtained results confirmed the superior TC of MXene nanofluids compared with that of the Gr nanofluids. There were also observed increases in the TC and density at a concentration of nanosheets of 0.2 mg mL\({}^{-1}\), which were provided by the high surface area of these nanostructures. In addition, the authors used lamellar MXene membranes with an improved photothermal ability to demonstrate the heat-driven and light-induced ion transport in nanofluidic systems and their capabilities in osmotic energy system amelioration.