Carbon nanotubes-ferrite-manganese dioxide micromotors for advanced oxidation processes in water treatment

Abstract

Multifunctional SW-Fe₂O₃/MnO₂ tubular micromotors are used for ‘on-the-fly’ advanced water oxidation of industrial organic pollutants. Catalytic decomposition of H₂O₂ as an oxidation agent results in the production of oxygen bubbles and hydroxyl radicals for complete mineralization of model pollutants into CO₂ and H₂O. The carbon backbone with Fe₂O₃ nanoparticles results in a rough catalytic layer for increased speed (16-fold acceleration as compared with smooth counterparts) and a higher radical production rate. The micromotors can propel autonomously in complex wastewater samples (400 μm s⁻¹, 2% H₂O₂) using a biocompatible surfactant and obviating the need for expensive Pt catalysts. Such self-propelled micromotors act as highly efficient dynamic oxidation platforms that offer significantly shorter and more efficient water treatment processes, reducing the use of chemical reagents. The effective operation of the SW-Fe₂O₃/MnO₂ micromotors is illustrated towards the oxidative degradation of mg L⁻¹ levels of Remazol Brilliant blue and 4-chlorophenol. Factors influencing the micromachine-enhanced oxidation protocol, such as the pH, navigation time and number of motors, have been investigated. High degradation rates of ∼80% are obtained for both pollutants following 60 min treatment of spiked wastewater samples at pH 4.0–5.0. The unique magnetic properties of the outer Fe₂O₃ layer allow the reusability of the micromotors and its convenient recovery and disposal after treatment. Such attractive performance holds considerable promise for its application in large scale water treatment systems and for a myriad of environmental, industrial and security defense fields.