The accidental release of radioactive waste, such as what occurred in the Chernobyl and Fukushima nuclear plant disasters, poses large threats to the environment, humans and wildlife. Scientists have developed materials to capture, separate, remove and recover radioactive uranium from water, but the materials have limitations. One of the most promising recent approaches is the use of metal-organic frameworks (MOFs) -- compounds that can trap specific substances, including radioactive uranium, within their porous structures. Martin Pumera and colleagues wanted to add a micromotor to a rod-shaped MOF called ZIF-8 to see if it could quickly clean up radioactive waste.

To make their self-propelled microrobots, the researchers designed ZIF-8 rods with diameters about 1/15 that of a human hair. The researchers added iron atoms and iron oxide nanoparticles to stabilize the structures and make them magnetic, respectively. Catalytic platinum nanoparticles placed at one end of each rod converted hydrogen peroxide "fuel" in the water into oxygen bubbles, which propelled the microrobots at a speed of about 60 times their own length per second. In simulated radioactive wastewater, the microrobots removed 96% of the uranium in an hour. The team collected the uranium-loaded rods with a magnet and stripped off the uranium, allowing the tiny robots to be recycled. The self-propelled microrobots could someday help in the management and remediation of radioactive waste, the researchers say.