Nanonet trapping for effective removal of nanoplastics by iron coagulation

Nanoplastics (NPs) are emerging aqueous pollutants, posing risks to drinking water safety and human health. However, conventional coagulants, widely employed in water treatment plants globally, are ineffective at removing NPs. Here, we present an in-situ Fe(III) method based on the simultaneous use of Fe(II) coagulant and an oxidant to enhance conventional coagulation by altering the nanostructure of Fe-based precipitates in flocs for efficient NP removal. Unlike the nanospheres formed by conventional Fe(III) coagulation, which are weakly attached to the NP surface, nanosheets formed by our approach can fully encapsulate NPs, achieving efficient nanonet trapping with a flexible mesh structure. In-situ formed nanosheets exhibit faster agglomeration, higher removal rate, and stronger anti-interference ability. The practical viability of our approach was proven in different natural water samples, where the inhibition for NP removal by various constituents of natural organic matter was effectively reduced. Theoretical calculations demonstrate that crystal structure differences between such nanosheets and nanospheres change short-range forces, thereby enhancing NP removal. Overall, this concept of modifying the nanoscale crystal structure of flocs offers valuable insights into enhanced coagulation processes, with broad applications in water treatment and environmental systems, and provides a promising solution to the critical challenge of NP removal.