Phenols and anilines degradation by permanganate in the absence/presence of carbon nanotubes: Oxidation and dehalogenation

Synergistic enhancement of phenols and anilines removal was investigated in permanganate oxidation in the presence of multi-walled carbon nanotubes (CNTs). Then the attendant dehalogenation was explored for bromophenols and bromoanilines from the perspective of dehalogenation number (DN). Permanganate decay and total manganese concentration decrease in the presence of CNTs indicates considerable formation of manganese dioxide (MnO₂) on carbon surface. The CNTs-enhanced phenol degradation is more favorable under lower pH, confirming that the generation of MnO₂ induced by the reaction between permanganate and CNTs enhances the phenol oxidation by permanganate. The first order rate constants of respective bromophenols and bromoanilines suggest the synergistic enhancement of CNTs and permanganate in removing these micropollutants. Bromide release experiments clearly demonstrate that the subsequent dehalogenation accompanying the oxidation of bromophenols and bromoanilines is significant for permanganate oxidation in the absence/presence of CNTs. Dehalogenation by permanganate follows the order of 4-bromophenol > 2-bromophenol > 3-bromophenol and 4-bromoaniline > 2-bromoaniline > 3-bromoaniline, respectively. Higher DN values in the presence of CNTs indicate a reduced dehalogenation. In real water application, permanganate in the presence of CNTs could effectively remove 4-bromoaniline with a maximum removal efficiency of ∼95% and a bromide release of 2 μM.