Nonradical degradation of phosphonates to orthophosphate via surface-activated peroxides on carbon nanotubes

The cleavage of the C-P bonds is essential for the removal and recovery of phosphorus from phosphonate-contaminated wastewaters. This study investigates the feasibility of utilizing carbon nanotubes (CNTs) to activate peroxides (e.g., peroxymonosulfate (PMS)) for degradation of phosphonates. With the exception of aminomethylphosphonic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid, the investigated phosphonates are effectively degraded to orthophosphate ( ortho -P), achieving conversion efficiencies ranging from 48.5% to 78.1% at a molar ratio of PMS to C-P bonds of 4:1. Taking aminotris(methylenephosphonic acid) (ATMP) as a model substrate, we deduce that the surface-activated PMS (CNTs-PMS*) serves as the primary reactive species, leading to C-P bonds cleavage predominantly through effective collision rather than the electron transfer process. Furthermore, the CNTs/PMS system maintains high performance over a wide pH range from 3.0 to 9.0 and in the presence of diverse inorganic ions, though its activity is reduced by natural organic matters. The practicality of the CNTs/PMS system in real water environments is also verified. The insights gained from this study are expected to significantly advance wastewater decontamination from phosphonates and enhance our cognition regarding the nonradical mechanism of peroxide activation by carbon-based materials.