Magnetically Actuated Carbon Soot Nanoparticle-Based Catalytic CARBOts Coated with Ni/Pt Nanofilms for Water Detoxification and Oil-Spill Recovery

Abstract

Multifunctional chemically powered micromotors were fabricated from the airborne contaminant carbon soot (CS) for environmental remediation following two approaches: first, by physical deposition of catalytic platinum (Pt) and magnetic nickel (Ni) nanoscale films of ∼110 nm and ∼100 nm, respectively, on CS (CARBOts) and second, by the chemical deposition of magneto-catalytic iron nanoparticles (FeNPs) of ∼30 nm or less in size on the CS surface (iCARBOts). The chemical synthesis of magneto-catalytic iron nanoparticle (FeNPs)-based iCARBOts provides an economical alternative to the synthesis of CARBOts by a physical method. The hydrophobic soot contained agglomerates of high-density carbon nanospheres of ∼40 nm or less in size, generated from the incomplete combustion of a hydrocarbon source. The catalytic component (Pt nanofilm or FeNPs) on the nanostructures on the CS surface allowed the rapid catalytic decomposition of aqueous peroxide fuel (H2O2) to generate chemical propulsion. The issuance of O2 microbubbles from the motor surface imparted the required thrust for active bubble propulsion. Integration of a magnetic component (Ni nanofilm or FeNPs) facilitated remote magnetic control for micromotor navigation. These magneto-catalytic micromotors demonstrated the efficient catalytic degradation of methylene blue (MB) dye in the presence of 10% (v/v) H2O2 fuel under ambient conditions. The CARBOts completely decolorized the nonbiodegradable MB dye pollutant within 40 min of treatment. The magnetic sensitivity of motors facilitated the ease of retrieval and reusability after the execution of the remediation tasks, thereby increasing the feasibility of the water detoxification process. In addition, with the help of remote magnetic guidance, micromotors were employed for the removal of freely floating and surfactant-stabilized oil droplets in seawater without any further surface modification. The intrinsic superoleophilic nature of the micromotors owing to the presence of the nanostructured soot surface facilitated an enhanced oil–motor interaction, which led to efficient on-the-fly capturing of oil droplets with remote magnetic guidance.