Sulfidation of Ni-Fe-LDH for enhanced Fenton-like catalysis: Experimental validation and theoretical calculation

In this study, peroxymonosulfate (PMS) activation of Ni-Fe layered double hydroxide (Ni-Fe-LDH) toward to Tetracycline hydrochloride (TC) degradation was enhanced by sulfidation. When compared to the catalytic performance of Ni-Fe-LDH, the kinetic rate constant of the S-Ni-Fe-LDH/PMS system was 6.3 times higher than that of the Ni-Fe-LDH/PMS system. The degradation process in the S-Ni-Fe-LDH/PMS system was successfully achieved through the combined efforts of both radical and nonradical pathways, with singlet oxygen playing a key role in the process. The boosted performance brought by sulfidation was lie in: (i) the superior electrical conductivity; (ii) the low redox potential of S2- that facilitate metal redox in LDH; (iii) the production of 1O2 has been found to be increased in S-Ni-Fe-LDH compared to Ni-Fe-LDH, due to the higher energy desorption exhibited by S-Ni-Fe-LDH towards radical species; (iv) noteworthily, a new generation of high-valent metal-oxo species in S-Ni-Fe-LDH/PMS system. Consequently, the S-Ni-Fe-LDH/PMS system displayed satisfactory degradation efficiency in a broad pH range of 3–11 and even under the presence of inorganic ions and humic acid, as well as continuous-flow catalytic process. Based on the identification of transformation intermediates using HPLC-MS, three potential pathways for TC decomposition were deduced. The analysis conducted using ECOSAR demonstrated that the toxic effects decreased for the majority of transformation products during TC degradation. This work introduces new opportunities for designing highly efficient LDH-based catalysts for the decomposition of organic pollutants in water solutions.