One of the most challenging problems that limit the practical application of carbon-based photothermal nanofluids is their poor dispersion stability and tendency to form aggregation. Herein, by using Fe3O4@graphene hybrid nanoparticles as a model system, we proposed a new method to prepare stably dispersed silicone oilbased solar-thermal nanofluids that can operate at high temperatures than water-based fluids. The introduction of Fe3O4 nanoparticles between graphene nanosheets not only physically increases the inter-plane distance of the graphene nanosheet but also provides numerous anchoring points for surface modification. Phosphate-terminated polydimethylsiloxane chains, which have high compatibility with the silicone oil base fluids and hightemperature stability, were synthesized and utilized to modify the Fe3 O4 nanoparticle surfaces. The attached chains create steric hindrance and effectively screen the strong inter-plane van der Waals attraction between graphene sheets. Dispersion stability of the nanofluids with different concentrations of surface-modified hybrid nanoparticles and heated under different temperatures was investigated. We have demonstrated that such fluids could maintain stable dispersion under a heating temperature up to 150 °C depending on the concentration of the hybrid nanoparticles. The resultant nanofluids maintained stable dispersion after repeated heating and were employed for consistent direct solar-thermal energy harvesting at 100 °C.
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