Self-assembled Au-CQDs nanofluids with excellent solar absorption and medium - high temperature stability for solar energy harvesting

Nanofluids-based direct absorption solar collectors are promising candidates for medium -high-temperature solar energy harvesting. However, nanofluids ' complicated preparation process and undesirable high -temperature stability have hindered their practical applications. Herein, we propose a facile method for synthesizing gold/ carbon quantum dots (Au-CQDs) nanofluids by directly carbonizing the base fluid and spontaneously assembling with Au nanoparticles (AuNPs) triggered by high temperatures. The results indicate that the self -assembled AuCQDs nanofluids can maintain high stability at 110 degrees C for 100 h without precipitation and keep excellent photothermal conversion performance under 10 sun irradiation. The concentration and particle size of AuNPs are crucial factors affecting the self -assembly process. By modulating the microscopic morphologies of the selfassembled nanoparticles, the extinction coefficient of the prepared nanofluids is up to 88.7 % at a low loading of 30 ppm. The nanofluids can reach an equilibrium temperature of 50 degrees C under 1 sun irradiation, 10.4 degrees C higher than the base fluid due to the enhanced plasmonic effects and stability resulting from the CQDs dotted AuNPs. This work offers a new strategy to fabricate highly stable nanofluids with excellent light absorption properties for efficient solar thermal applications.