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 increasing concerns regarding public health and climate change, disinfectant generator technologies that utilize green processes are becoming necessary. It has been confirmed that single-walled carbon nanotubes (SWCNTs) can generate reactive oxygen species (ROS) in aqueous media when illuminated with solar irradiation. However, low efficiency due to competitive reactions between ROS and water and unclear kinetics hinder their potential practical applications. To overcome these limitations, here, SWCNTs were studied in a non-aqueous ionic liquid (IL) to form a suspension system for generating superoxide (O2−) under UV light. The as-obtained O2− from SWCNTs was qualitatively confirmed by electron paramagnetic resonance and UV–vis spectroscopy. The sustainability of the new SWCNTs/IL system was confirmed by UV–vis and Fourier-transform infrared spectroscopy. The IL proved to be an ideal media that could extend the lifetime of O2− from a few microseconds (generated in water) to at least 65 h in the IL. The kinetics of photodynamic effect were 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 in excess of germicidal levels for ROS. The sustainable, long duration and high-yield of the generator exhibited 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 the environmental quality.