Fluorine-free MXene activate peroxymonosulfate to remove tetracyclic antibiotics

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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.