Ru doped graphitic carbon nitride mediated peroxymonosulfate activation for diclofenac degradation via singlet oxygen

Metals doped carbon nitride (CN) is considered as a class of promising efficient catalysts for peroxymonosulfate (PMS) activation in water purification. Herein, ruthenium doped carbon nitride (CNRu) was synthesized via a facile one-pot method, and CNRu was in form of Ru–N2 that could efficiently activate PMS for DCF degradation and detoxification via nonradical pathway. DCF was completely removed within 10 min under the optimized condition in a wide working pH range of 3.00–9.00, while other traditional transition metals (e.g. Fe, Co, Ni, Cu) doped CN showed negligible removal of DCF due to adsorption rather than activation of PMS, which was demonstrated by DFT calculations. CNRu showed high stability and reusability after seven cycles and very few Ru leaching was detected in DCF degradation process. Ru was highly dispersed in form of Ru–N bond via coordinating to pyridine nitrogen, and the electron defect transfer between Ru and coordinated N, rather than redox cycle of Ru, mediated superoxide radicals (O2•−) evolution, which was further hydrolyzed into singlet oxygen (1O2) and responsible for DCF removal. Thus, the CNRu/PMS system showed high tolerance to inorganic anions. Much lower toxic intermediates/products than DCF were obtained via the strong electrophilic attack reaction between 1O2 and DCF in CNRu/PMS system. This study displayed a new practical application prospect of ruthenium-based materials for high-efficient removal and detoxification of DCF from wastewater.