Facile synthesis of carbon nitride nanotube confined nano Fe0 for boosting activation of peroxymonosulfate towards tetracycline removal

Abstract

The nano-sized zero-valent iron (Fe⁰) exhibits excellent activity for organic contaminant remediation by activating peroxymonosulfate (PMS). Its catalytic performance, however, was restricted due to its susceptibility towards oxidation and agglomeration. Thus, carbon nitride nanotube embedded nano Fe⁰ catalysts (Fe⁰@NC) with various Fe contents were synthesized to simultaneously overcome the drawbacks. Fe⁰@NC-10 showed high specific surface area (S_BET, 118.87 m²·g⁻¹), stable crystal structure, plentiful Fe- and N-containing active sites. Under the optimal conditions (0.05 g·L⁻¹ Fe⁰@NC-10 and 0.15 g·L⁻¹ PMS), over 86 % tetracycline (TC) could be removed after 5 min, possessing a rate constant (K_obs) value as high as 1.81 min⁻¹. The constructed Fe⁰@NC-10/PMS system also showed prominent performance even at different solution pH values or with coexisting ions. Moreover, Fe⁰@NC-10 exhibited outstanding performance in the continuous degradation experiment. It was Fe⁰, Fe–N_x and graphitic nitrogen in Fe⁰@NC-10 that activated PMS to produce ferryl Fe-oxo species (Fe^IV=O) and ¹O₂, which collectively resulted in the removal of TC. Sixteen intermediate products were detected during TC degradation, which showed lower toxicity. This study provides a simple strategy for synthesizing an active and stable Fe⁰ nano-catalyst for TC removal by activating PMS.