Photodegradation of naproxen using CuZnAl-layered double hydroxides as photocatalysts†
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Qingzhu
Li,
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Abstract
Naproxen (NPX), as a typical pharmaceutical and personal care product (PPCP), is frequently detected in water and is difficult to remove effectively by conventional methods. Layered double hydroxides, as highly efficient photocatalysts, have not been used in photocatalysis of PPCP. In this study, CuZnAl-layered double hydroxide (CuZnAl-LDH) was prepared and its performance in the photocatalytic degradation of NPX under UV light illumination was investigated. The results indicated that the NPX photodegradation is considerably enhanced by CuZnAl-LDH with an efficiency of 98.25% in the optimal conditions, which was obviously more than that under pure light condition (efficiency less than 30%). In addition, the CuZnAl-LDH photocatalyst exhibited superior photocatalytic stability confirmed by the analyses of the catalyst structure, morphology, and cycle experiments. Moreover, by the comparison of optical properties of ZnAl-LDH and CuZnAl-LDH, it was found that Cu2+ can broaden light absorption and facilitate the separation of photogenerated charges electrons (e−) and holes (h+), and in the CuZnAl-LDH system, the formation mechanism of active species complies with the mechanisms of the ligand-to-metal charge transfer (LMCT) from the 2p orbital of oxygen to the 3d orbital of M2+ and of the d–d transition of Cu2+ ions of the CuO6 unit. Besides, ESR and scavenging tests revealed that the photocatalytic process was enhanced by the synergistic effect of h+, ˙O2−, and ˙OH, which displayed the sequence of h+ > ˙O2− > ˙OH. Finally, the intermediate products were identified by LCMS-IT-TOF, and no intermediates with greater toxicity than NPX were produced. The possible degradation pathway of NPX was proposed involving the decarboxylation, demethylation, and hydroxylation reactions and ring-opening based on intermediates. These results are expected to provide new data on the photodegradation of naproxen.
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