Highly efficient degradation of rhodamine B by carbon nanotubes-activated persulfate

Recently, sulfate radical SO4 center dot-(E-0 = 2.60 V) generated by the activation of persulfate (PS) has been reported to be effective in destructing recalcitrant organic contaminants. However, conventional PS activation methods (e.g., via heat, UV or carbon-base materials) need high energy input or may cause secondary contamination (due to the use of transition metals). In the present study, a novel system with PS activated by metal-free carbon-nanotubes (CNTs) was developed. Results indicate that CNTs could efficiently activate PS for degradation of RhB (e.g., 100% removal with 150 min) with low concentrations of PS at the initial pH range of 3-9. The removal efficiency of RhB increased with an increase in CNTs dosage and PS concentration. The coexistence of natural organic matter (NOM) in the natural environment significantly promoted the degradation of RhB. Both radical and non-radical pathway could activate PS by CNTs, but non-radical pathway was dominated. PS can be activated by the oxygen-containing groups on the surface of CNTs to generate hydroxyl radical (OH center dot) and sulfate radical(SO4 center dot-). Meanwhile, the electron transfer process among PS, RhB and CNTs was confirmed by PS decomposition and linear sweep voltammetry (LSV) experiments. Furthermore, the possible degradation pathway of RhB was proposed according to the analytical results. These findings provides a new strategy for high efficiency treatment of RhB wastewater without using high energy input or introducing any secondary contamination associated with metal pollution.