(Invited) Sustainable Generator and in-Situ Monitor for Reactive Oxygen Species Using Photodynamic Effect of Single-Walled Carbon Nanotubes in Ionic Liquids

Abstract

Due to the demand of public health maintenance, disinfectant generator technologies that utilize green processes are becoming attractive. It has been confirmed that single-walled carbon nanotubes (SWCNTs) could generate reactive oxygen species (ROS) in water when illuminated with solar irradiation. However, low efficiency due to the competitive reactions between ROS and water in aqueous media and unclear kinetics hinder their potential practical applications. To overcome these limitations, here, the SWCNTs were studied in a nonaqueous ionic liquid (IL) to form a suspension system to generate superoxide (O2 -) under UV light. The as-obtained O2 - from SWCNTs was qualitatively confirmed by electron paramagnetic resonance and UV-visible spectroscopy. The sustainability of the new SWCNTs/IL system was confirmed by UV-visible spectroscopy and Fourier-transform infrared spectroscopy. The IL proved to be an ideal media that could extend the duration of O2 - from a few microseconds (commonly generated in the water) to at least 65 hours in the IL. The kinetics of photodynamic effect was investigated by electrochemical characterizations. A new method was established to in-situ monitor the O2 - level in the IL system. The O2 - level in the IL was quantitatively determined by combining cyclic voltammetry and chronoamperometry techniques. The SWCNTs/IL system generated 4.11 mM of O2 - in a mini-scale generator, which was excessive to germicidal levels for ROS. The sustainable, long duration and high-yield of the generator exhibited an excellent potential as a generator as well as an in-situ monitor for O2 -. This work could pave the way for O2 - generation using SWCNTs and promote its applications in air and water disinfection for public health, as well as O2 - sensitive chemical sensors for monitoring environmental quality.