The following submission statement was provided by /u/filosoful:

Scientists developed iron oxide nanoparticles with water-resistant coatings. They showed that microplastics in water bind to the particles, which can then be removed with a magnet.

The paper is here.

Please reply to OP's comment here: https://old.reddit.com/r/Futurology/comments/yke9cq/removing_plastic_pollution_from_water_using/iusrl1q/