Recyclable Fe3O4@Polydopamine (PDA) nanofluids for highly efficient solar evaporation

Volumetric solar evaporations by using light-absorbing nanoparticles suspended in liquids (nanofluids) as solar absorbers have been widely regarded as one of the promising solutions for clean water production because of its high efficiency and low capital cost compared to traditional solar distillation systems. Nevertheless, previous solar evaporation systems usually required highly concentrated solar irradiation and high capital cost, limiting the practical application on a large scale. Herein, for the first time in this work, polydopamine (PDA)-capped nano Fe3O4 (Fe3O4@PDA) nanofluids were used as solar absorbers in a volumetric system for solar evaporation. The introduction of organic PDA to nano Fe3O4 highly contributed to the high light-absorbing capacity of over 85% in wide ranges of 200–2400 nm because of the existence of numerous carbon bonds and pi (π) bonds in PDA. As a result, high evaporation efficiency of 69.93% under low irradiation of 1.0 kW m−2 was achieved. Compared to other nanofluids, Fe3O4@PDA nanofluids also provided an advantage in high unit evaporation rates. Moreover, Fe3O4@PDA nanofluids showed excellent reusability and recyclability owing to the preassembled nano Fe3O4, which significantly reduced the material consumptions. These results demonstrated that the Fe3O4@PDA nanofluids held great promising application in highly efficient solar evaporation.