Sponge-based motor integrated with fluorescence signal for microplastics capture

Widespread use of plastic products had led to the prevalence of microplastics (MPs) in ecosystems and posed a great threat to the environment. Therefore, there was a pressing demand to quantify and remove MPs. This work presented two types of composite sponge-based motors with different driving mechanisms for the capture and fluorescence tracing of polyethylene (PE) MPs in water bodies. The first type of motor was driven by decomposing H₂O₂, and coated PDA on the surface of melamine sponge by in situ polymerization. Then TiO₂ and boron-doped carbon nanoparticles (BCNPs) were deposited to form BCNPs/TiO₂/PDA@MS with Janus structure. This material could move at a speed of 0.11 mm/s in H₂O₂ solution (0.29 wt%) and achieved rapid capture of PE MPs through van der Waals forces within 20 min. To enhance the adaptability of sponge-based motors, we synthesized magnetic drive sponge (BCNPs/PDA/Fe₃O₄@MS). The motion speed of BCNPs/PDA/Fe₃O₄@MS could reach 0.77 mm/s under the action of an external magnetic field. Because BCNPs excellent fluorescence properties and abundant surface groups, both two kinds of sponge base motors could be used as efficient fluorescent tags platform. They could be used as simple tools, which combined with capabilities of MPs capture and detection in aqueous solution. This experiment provided a new path for the monitoring and treatment of MPs.