Improving the removal of tetracycline via carbonate-mediated triplet-excited state by the Cu-containing zeolites activated percarbonate

The removal of tetracycline (TC) via various advanced oxidation processes (AOPs) under visible light has been widely investigated. However, the photosensitive effect of TC on its removal has been mostly neglected. In this work, the photosensitization of TC is explored by a novel catalytic system, Cu-containing zeolite (Cu/ZSM5) activation on sodium percarbonate (SPC) under visible light irradiation. Experimental results indicated that the Cu/ZSM5/vis/SPC process could achieve 100 % removal of TC within 40 min (kobs = 0.099 min−1), while only removal of 58.1 % was achieved under dark conditions (kobs = 0.016 min−1). It was confirmed for the first time by phosphorescence spectroscopy that carbonate ions (CO32–) could induce TC to be excited into triplet states (3TC*) under visible light, synergistically forming the carbonate radicals (•CO3−). Besides, the CO32– reacted with hydroxyl radical (•OH) derived from the heterogeneous Fenton-like pathway by Cu/ZSM5, leading to the generation of multiple kinds of reactive oxygen species (•OH, •CO3−, •O2−, and 1O2), which further together contribute to the TC removal. This study does not only present a novel strategy via Cu-containing zeolite with SPC to remove TC but also found that TC acts as both a sensitizer and oxidized substrate.