1. Introduction	3
2. Carbon-Based Nanofluids: Preparation and Stability	4
2.1. Carbon Nanomaterials	4
2.2. Preparation of Carbon-Based Nanofluids	6
2.3. Stability of Carbon-Based Nanofluids	6
2.3.1. Use Surface-Functionalized and Sonication Technique for Nanofluid Dispersion and Stability	7
2.3.2. Addition of Surfactants	8
3. Properties of Carbon-Based Nanofluids	9
3.1. Optical Properties	9
3.1.1. Theories for Modeling Optical Properties	9
3.1.2. Experiments on Optical Properties	13
3.1.3. Photothermal Conversion Performance	16
3.2. Thermal Conductivity	17
3.2.1. Thermal Conductivity of Graphene-Based Nanofluids	17
3.2.2. Thermal Conductivity of CNT-Based Nanofluids	20
3.3. Viscosity of Nanofluids Containing Carbon Structures	21
3.4. Solar Steam Generation of Nanofluids Containing Carbon Structures	22
3.5. Other Properties	25
4. Carbon-Based Nanofluids for Direct Solar Absorption	25
4.1. Carbon Nanotube-Based Nanofluids	25
4.2. Graphene-Based Nanofluids	27
4.3. Hybrid Carbon Nanomaterial-Based Nanofluids	28
4.4. Other Carbon Nanomaterial-Based Nanofluids	31
5. Challenges and Recommendations for Future Work	32
5.1. Challenges	32
5.1.1. Instability of Nanoparticles Dispersion	32
5.1.2. High Cost	32
5.1.3. Pump Power and Pressure Loss	32
5.1.4. Erosion of Components	32
5.2. Recommendations for Future Work	32
6. Conclusions	33
References	33