European researchers have used tiny robots to clean water. 

The tiny, magnetic and temperature-sensitive nanorobots could be a solution to removing chemical pollution from water, according to experts from the Czech Republic. 

Engineers at the University of Chemistry and Technology Prague are developing long-lasting robots that can remove heavy metal ions and pesticides. The little machines disperse in cool water, but come together to trap pollutants like arsenic and atrazine, a common herbicide, in warmer water. 

The researchers say the bots can then be removed from the water using magnets, and when cooled they will unload the pollutants and be ready to re-use.

The nanorobots consist of a temperature sensitive polymer (pluronic triblock copolymer [PTBC]) that functions like miniature hands to ‘pick up’ and dispose of pollution, and iron oxide nanoparticles that make the robots magnetic.

The nanorobots have been shown to remove the heavy metal arsenic and atrazine (a common herbicide) from water. 

Their pollutant uptake/release is regulated by temperature - at 5°C, the nanorobots scattered in water but aggregated when the temperature was raised to 25°C, trapping the pollutants.  

When they are removed from water using magnets, cooling causes the nanorobots to separate and unload their pollutants, so the nanorobots could then be reused.

More details are accessible here.