Fig. 5: Application of the CNT_d–S2/free chlorine system for water purification.

a Time course of TOC removal in the reaction system. b Amperometric i–T curves of CNT_d–S2 in a three–electrode electrochemical system. Free chlorine and 10 mg L⁻¹ 2,4–DCP were added to the electrolyte at run times of approximately 100 s and 200 s, respectively. c Degradation pathway of 2,4–DCP in the CNT_d–S2/free chlorine system and its corresponding Gibbs free energy. The inset shows the activation energy of the transition state (TS). d Schematic illustration of the contact angle between CNT_d or CNT_d–S2 after contact with a solution of free chlorine alone, and a mixed solution of free chlorine and 2,4–DCP. The dark color indicates the contact angle from the catalyst in contact with the free chlorine solution. The light color means the contact angle from the catalyst in contact with the mixed solution of free chlorine and 2,4–DCP. e Schematic illustration of the practical application scenario of our continuous–flow system. The SEM image of the CNT_d–S2 membrane as an inset shows a rough 200 μM height of the membrane. f Evaluation of the long–term operation of this continuous–flow system for the removal of 2,4–DCP, 4–chlorophenol and methylene blue. The inset displays a digital photo of the continuous–flow system where the polluted water body of methylene blue was treated and decolorized by this apparatus. The effluent was colorless. Reaction conditions: 45 mg L⁻¹ free chlorine, 10 mg L⁻¹ organic contaminants, and a 4 mL min⁻¹ flow rate.