Non-photochemical production of singlet oxygen via activation of persulfate by carbon nanotubes

The reaction between persulfate (PS) and carbon nanotubes (CNTs) for the degradation of 2,4dichlorophenol (2,4-DCP) was investigated. It was demonstrated that CNTs could efficiently activate PS for the degradation of 2,4-DCP. Results suggested that the neither hydroxyl radical (center dot OH) nor sulfate radical (center dot SO4-) was produced therein. For the first time, the generation of singlet oxygen (O-1(2)) was proved by several methods including electron paramagnetic resonance spectrometry (EPR) and liquid chromatography mass spectrometry measurements. Moreover, the generation of the superoxide radical as a precursor of the singlet oxygen was also confirmed by using certain scavengers and EPR measurement, in which the presence of molecular oxygen was not required as a precursor of O-1(2). The efficient generation of O-1(2) using the PS/CNT5 system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral conditions with the mineralization and toxicity evaluated. A kinetic model was developed to theoretically evaluate the adsorption and oxidation of 2,4-DCP on the CNT5. Accordingly, a catalytic mechanism was proposed involving the formation of a dioxirane intermediate between PS and CNTs, and the subsequent decomposition of this intermediate into O-1(2). (C) 2017 Elsevier Ltd. All rights reserved.