Fluorine-free MXene activate peroxymonosulfate to remove tetracyclic antibiotics

The most typical synthesis method for MXene is to etch the Al layer from its MAX phase using an acidic solution containing fluorine. However, etching with fluorine-containing reagents can lead to environmental contamination and experimental safety issues. Herein, fluorine-free Ti3C2Tx (Ff-Ti3C2Tx) was successfully prepared by using a safer and more environmentally friendly tetramethylammonium hydroxide solution (TMAOH) at a controlled temperature of 40 °C and reacting continuously for one week. Based on the characterization results, we demonstrated that the prepared Ff-Ti3C2Tx exhibits outstanding hydrophilicity and exposes more active sites on the surface, which is beneficial towards activating peroxymonosulfate (PMS). The catalyst exhibited superior degradation of tetracycline hydrochloride (TC) than Fluorine-Ti3C2Tx (F-Ti3C2Tx). The effects of catalyst dosage, optimum concentration of PMS, initial pH, common coexisting ions (Cl−, SO42−, HCO3− and humic acid) and different real water environments on TC degradation were systematically investigated in the Ff-Ti3C2Tx/PMS system. Meanwhile, the degradation effects of both Doxycycline (DC) and Oxytetracycline (OTC) reached more than 89.7%. In addition, Ff-Ti3C2Tx exhibited excellent reusability with a mineralization efficiency of 49.7%. Based on the electron paramagnetic resonance (EPR) test, quenching experience, radical probe experiments, electrochemical measurements and XPS characterization, a possible activation mechanism was proposed. The contribution of reactive oxygen species (ROS) was calculated, 1O2 (45.3%) and ·O2− (30.2%) play a major role in the degradation of TC. Furthermore, a possible degradation pathway was proposed by liquid chromatography-mass spectrometry (LC-MS) with a decreasing trend in the toxicity of TC intermediates. This work not only demonstrates a novel strategy for preparing fluorine-free MXene via simple TMAOH etching, but it also provides new insight into the use of MXene as a catalyst directly in the activation of PMS.