Unexpected Polymerization Pathway in the Carbocatalysts/Permanganate Processes for Water Decontamination

Permanganate (KMnO4) is widely used in water treatment but is often limited by its moderate oxidation potential for the deep decomposition of contaminants. Here, we found that multiple conductive carbocatalysts (e.g., carbon nanotube (CNT), ketjen black (KB), acetylene black (AB), graphite (GP), etc.) could enhance the oxidative removal of organic contaminant (i.e., sulfamethoxazole (SMX)) by KMnO4 under environmentally relevant conditions. Multiple lines of evidence, such as thermogravimetric analysis, mass spectroscopy, and gel permeation chromatography, revealed that a previously unidentified polymerization pathway significantly contributed to the enhanced SMX removal and total organic carbon (TOC) abatement in the carbocatalysts/KMnO4 processes. Taking the KB/KMnO4 process as the representative, the carbocatalyst serves a dual role. It acts not only as an activator, employing surface reducing groups to generate colloidal MnO2, but also as an electron mediator, whereby the structural defects and delocalized π-electrons facilitate electron transfer from SMX to KMnO4. The colloidal MnO2 produced via both pathways subsequently drives the degradation and polymerization of SMX. This study not only uncovers the unexpected polymerization pathway in the classic conductive carbon-catalyzed KMnO4 processes but also offers a new strategy to enhance TOC removal performance in the mild oxidant-mediated decontamination systems.