Core-shell structured Cu2O@HKUST-1 heterojunction photocatalyst with robust stability for highly efficient tetracycline hydrochloride degradation under visible light

Constructing heterojunction has been widely applied in optimizing photocatalysts for organic pollutant removal. However, incompact contact interface and inappropriate band alignment in the heterointerface of two materials increase interfacial recombination, lowering the degradation efficiency. Herein, a facile strategy without any other surfactants or modification pretreatment was employed to encapsulate cubic Cu2O using metal-organic frameworks (MOFs) to construct heterojunction photocatalysts. The oriented growth of Cu-MOFs (HKUST-1) around cubic Cu2O (Cu2O@HKUST-1) with desired feedstock ratio for enhanced photocatalytic degradation performance was achieved. Compared with the individual components, the optimized Cu2O@HKUST-1 heterostructures exhibited enhanced tetracycline hydrochloride (TC-HCl) removal rate of 93.40% within 60 min under visible light irradiation. Obviously, mechanism exploration revealed that the combined effect between the coreshell structure with compact interfacial contact and an ideal type-II band alignment in Cu2O@HKUST-1 increased the carrier density and accelerated interfacial charge separation and transfer. Meanwhile, HKUST-1 shell protected Cu2O core from the photocorrosion well, assuring the robust stability of photocatalyst during the photocatalytic process. After the fourth cycle, the photocatalytic TC-HCl degradation efficiency and total organic carbon (TOC) removal rate by Cu2O@HKUST-1 remained at 90.02% and 49.64%, respectively. The radical trapping results and electron spin resonance (ESR) identified the h+ and center dot O2xe213; were main active species in this photocatalytic degradation system. Besides, the TC-HCl degradation pathway was investigated by threedimensional excitation-emission matrix fluorescence spectra and liquid chromatography-mass spectrometry technology. This work provides a facile method towards creating efficient and stable photocatalyst for organic pollutant removal.