Regulating Phenolic Pollutant Polymerization from Oligomers to Multimers via Carbon Nanotubes in Permanganate Systems

Polymerization-based oxidation processes have emerged as a low-carbon-water purification technology for removing organic pollutants. Permanganate (Mn(VII)) can oxidize phenolic pollutants through polymerization; however, this process is currently challenged by the generation of soluble oligomers, resulting in low total organic carbon (TOC) removal and undesired byproducts in effluents. Herein, we demonstrated that incorporating carbon nanotubes (CNTs) into the Mn(VII) system effectively regulated phenol polymerization from soluble oligomers to insoluble multimers, remarkably enhancing TOC removal from 0.5% to 82.0% within 30 min. This remarkable enhancement originated from a synergetic mechanism involving interfacial enrichment and accelerated electron transfer, which promoted the generation of phenoxy radicals and their collisions with phenol and oligomers, thereby driving the polymer chain growth. These synergistic effects overcame the kinetic and steric limitations of the homogeneous Mn(VII) system during phenol oxidation. Quantitative structure-activity relationship analysis revealed the defect-rich and hydrophobic CNTs maximized the above-mentioned synergistic effect, while excessive carboxy contents suppressed phenol polymerization by increasing surface polarity and electrostatic repulsion. Overall, this work provided a simple yet facile strategy for regulating the polymerization products of phenolic pollutants in the Mn(VII) oxidation system, offering fundamental insights for the development of low-carbon and sustainable water treatment technology.