Enhanced catalytic degradation of tetracycline hydrochloride by a NZVI@MOF-545 composite with peroxydisulfate: Performance and mechanism

Four different porphyrinic zirconium-based metal–organic frameworks (Zr-MOFs) were comparative studied to activate peroxydisulfate (PDS) for tetracycline hydrochloride (TCH) degradation. Results indicated NZVI@MOF-545 was the optimal catalyst and the NZVI@MOF-545/PDS system exhibited a high TCH (initial concentration of 100 mg/L) removal efficiency of 95.9 %. The catalytic reaction conditions of NZVI@MOF-545/PDS were optimized using response surface methodology (RSM) and results showed that the TCH (initial concentration of 800 mg/L) degradation rate of 90.34 ± 0.66 % was obtained under optimal conditions of 1.03 g/L PDS, 0.84 g/L NZVI@MOF-545 with the initial pH of 9.80, temperature of 45 ℃, and rotation speed of 265 rpm. The high degradation rate was attributed to the reactive species generated by the carbon-containing functional groups and metal sites of NZVI@MOF-545, and the relative contribution was 1O2 > SO4-•>HO•>O2–•. Moreover, the LC-MS results suggested that TCH could be degraded into 15 intermediates through three potential degradation pathways. Toxicity evaluation demonstrated an alleviation in median lethal concentration at 96 h (LC50-96 h), low bioaccumulation, significant reductions in developmental toxicity and mutagenicity for most intermediates. In brief, NZVI@MOF-545 possessed remarkable catalytic ability and acceptable reusability to active PDS for TCH degradation, and the toxicity of TCH could be significantly reduced after the degradation.