Recent advances in nanotechnology have led to novel ways of dealing with environmental pollution, especially for water contaminated by heavy metals. Self-propelled, micro-scaled motors based on multifunctional materials promise better performances than more traditional filtering strategies. However, the environmental cost of these approaches is severely affected by the inability to reuse the same microbots for repeated cleaning cycles.
Now, Diana Vilela who is based at the Max Planck Institute for Intelligent Systems in Stuttgart and colleagues from Spain and Singapore have reported graphene-based, reusable microbots for the removal of heavy metal ions from water. The microbots have a three-layered tube structure of platinum, nickel and graphene oxide. The active graphene oxide outer layer adsorbs lead (II) ions, which crucially can then be removed in acidic solution, allowing the microbots to be reused without compromising their structure and adsorption efficiency.
Vilela and co-workers also demonstrated that lead adsorption is dramatically increased by allowing the microbots to swim in the liquid. The platinum-based inner layer catalyses the decomposition of hydrogen peroxide, forming oxygen bubbles, which propel the microbots forward. The nickel-based middle layer is ferromagnetic, allowing the removal of the microbots from the water following decontamination, and making it possible to guide their movement direction by external magnetic fields.