Stability study of low-cost carbon quantum dots nanofluids with saline water and their application investigation for the performance improvement of solar still

Abstract

The poor stability of carbon nanofluids limits their application in solar desalination process, especially when nanoparticles need to contact with saline water directly. Herein, this study proposes a mild manufacturing route to prepare the highly stable carbon quantum dots (CQDs) nanofluids by microwave method coupling a simple dilution. The systematic stability evaluation was conducted and the results showed almost all of CQDs nanofluids could keep stable in saline water with a wide NaCl concentration range (from 0 to 50 g/L), different co-existing salt ions and organic matters. The high thermal stability of CQDs nanofluids also were proved and the variation of Turbiscan stability index (TSI) value was below 0.24 after five heating cycles. The optical properties were evaluated and nearly 100 % incoming solar energy was captured by 10 vol% CQDs nanofluids. The above results indicate the application potential of CQDs nanofluids in solar desalination process. Moreover, the performance of solar still with CQDs nanofluids was compared with the conventional solar still. The results show that the cumulative water productions are 521 mL in the conventional solar still and 823 mL in the solar still with CQDs nanofluids of an enhancement in the water productivity of 57.9 %. The average energy efficiency of solar still with or without CQDs nanofluids are 34.23 % and 21.52 %, respectively. In addition, the economic analysis was conducted and the results show water production cost is 0.013–0.015 $/L for solar still with CQDs nanofluids.