Graphene-Based Microbots for Toxic Heavy Metal Removal and Recovery from Water

Diana Vilela,Samuel Sánchez,Yanli Zhao,Yongfei Zeng,Jemish Parmar

doi:10.1021/acs.nanolett.6b00768

Abstract

Heavy metal contamination in water is a serious risk to the public health and other life forms on earth. Current research in nanotechnology is developing new nanosystems and nanomaterials for the fast and efficient removal of pollutants and heavy metals from water. Here, we report graphene oxide-based microbots (GOx-microbots) as active self-propelled systems for the capture, transfer, and removal of a heavy metal (i.e., lead) and its subsequent recovery for recycling purposes. Microbots’ structure consists of nanosized multilayers of graphene oxide, nickel, and platinum, providing different functionalities. The outer layer of graphene oxide captures lead on the surface, and the inner layer of platinum functions as the engine decomposing hydrogen peroxide fuel for self-propulsion, while the middle layer of nickel enables external magnetic control of the microbots. Mobile GOx-microbots remove lead 10 times more efficiently than nonmotile GOx-microbots, cleaning water from 1000 ppb down to below 50 ppb in 60 min. Furthermore, after chemical detachment of lead from the surface of GOx-microbots, the microbots can be reused. Finally, we demonstrate the magnetic control of the GOx-microbots inside a microfluidic system as a proof-of-concept for automatic microbots-based system to remove and recover heavy metals.

Highlights

P ollution in water from heavy metals such as arsenic, mercury, cadmium, chromium, and lead, originates from various human industrial activities such as electroplating, mining, fabrication of batteries and microelectronics
The outer layer of graphene oxide captures lead on the surface, and the inner layer of platinum functions as the engine decomposing hydrogen peroxide fuel for self-propulsion, while the middle layer of nickel enables external magnetic control of the microbots
We demonstrate the magnetic control of the graphene oxide (GOx)-microbots inside a microfluidic system as a proof-of-concept for automatic microbots-based system to remove and recover heavy metals

Summary

Nano Letters

Between the Pb (II) ions and the abundant oxygen moieties on the GOx. due to the magnetic properties of these microbots, they can be removed from the water using a magnet after successful lead decontamination. The presence of oxygen moieties and delocalized π-electron systems in graphene oxide act as Lewis base and attach to the Pb(II) ions which act as Lewis acid This process is strongly dependent on the pH and temperature and independent of ionic strength.[37] We observed that the structure of the GOx-microbots was not damaged by the decontamination process maintaining its composition (Figure 4C, SEM image). We have demonstrated graphene oxide based microbots for very efficient removal of toxic heavy metal (Pb) from contaminated water through an adsorption process, the recovery of Pb(II) ions, and the subsequent reusability of GOxmicrobots.

■ ACKNOWLEDGMENTS

Findings

■ REFERENCES