The facile fabrication of 2D/3D Z-scheme g-C3N4/UiO-66 heterojunction with enhanced photocatalytic Cr(VI) reduction performance under white light

Z-scheme g-C3N4/UiO-66 (BGxUy) heterojunctions constructed from 3D UiO-66 and 2D g-C3N4 sheets were facilely fabricated using ball-milling method, which were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption measurement (BET), thermogravimetric analysis (TGA), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS), electron spin resonance (ESR) and density functional theory (DFT) calculations. The photocatalytic activities of Cr(VI) reduction over the BGxUy heterojunctions were tested upon the irradiation of white light. The influence factors on photocatalytic performances of BG60U40 like different organics, pH and different co-existing foreign ions (ions in lake water, tap water, simulated sea water, and simulated leather tanning water) were clarified. The experiment results demonstrated that the optimal BG60U40 exhibited superior Cr(VI) reduction efficiency than pristine UiO-66 and g-C3N4 due to the declined recombination of photo-induced charge carriers. As well, the heterojunction displayed good reusability and stability in the cyclic experiment. The corresponding Z-scheme mechanism of photocatalytic Cr(VI) reduction was proposed and verified by electrochemical analysis, ESR measurement and DFT calculations.