Novel 3D Cu2O/N-CQD/ZIF-8 composite photocatalyst with Z-scheme heterojunction for the efficient photocatalytic reduction of Cr(Ⅵ)

Abstract

ZIF-8 exhibits poor visible light response and rapid electron-hole recombination. To address these problems, we constructed an N-CQD/ZIF-8 framework by in-situ synthesis method, then prepared a novel Z-scheme heterostructure photocatalyst (Cu2O/N-CQD/ZIF-8) by reduction precipitation method for the efficient photocatalytic reduction of Cr(Ⅵ). Cu2O/N-CQD/ZIF-8 (with a 10% Cu2O loading) had a unique heterostructure and exhibited significantly improved performance for Cr(Ⅵ) photoreduction. This photocatalyst successfully reduced 98.99% of the Cr(Ⅵ) in a pH = 3 solution system, which was 6 times higher than that of ZIF-8. Meantime, due to its stable interfacial adhesion, the reduction efficiency of Cr(Ⅵ) by Cu2O/N-CQD/ZIF-8 still reached 97.13% after five cycles. Therefore, Cu2O/N-CQD/ZIF-8 exhibited superior photocatalytic activity and recyclability compared with unmodified ZIF-8. The charge transfer path of this Z-scheme heterojunction was verified by free radical trapping experiments and X-ray photoelectron spectroscopy. Moreover, a possible charge transfer mechanism was proposed. N-CQD provided a potential driving force for the construction of the internal Z-scheme charge transfer system. Moreover, the synergistic effect between Cu2O and ZIF-8 inhibited the rapid recombination of photogenerated electron-hole pairs. This work provides potential insights for the innovative design of high-performance photocatalysts based on metal-organic frameworks for the restoration of Cr(Ⅵ)-containing wastewater.