The photoelectrocatalytic performance of ZnIn₂S₄ nanosheets and microspheres grown on flexible graphite felt

The fabrication of ternary ZnIn₂S₄ on flexible graphite felt (GF) by the one-step hydrothermal method was intensively investigated regarding the photoelectrochemical and photoelectrocatalytic degradation performance. The scanning electron microscopy (SEM) showed that the fabrication of ZnIn₂S₄ started from the formation of net-like nanosheet film on GF substrate and then followed with the growth of microspheres on the nanosheet layer. The transient photocurrent response, cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were adopted to evaluate the photoelectrochemical performance. The 5 mm GF electrode with one layer of ZnIn₂S₄ coating exhibited the best photoelectrochemical properties. More ZnIn₂S₄ layers in turn led to a compact blocked structure and further deteriorated the photoelectrochemical properties. The effect of applied anodic and cathodic bias potential under both direct (DC) and alternating (AC) current on the photoelectrocatalytic (PEC) degradation of tetracycline was comparatively studied. Comparing the DC at a potential of −0.6 V, AC shifting wave plus a below offset of −0.6 V increased the photoelectrocatalytic efficiency. At the same time, shifting wave plus an above offset of 0.9 V remarkably reduced the efficiency compared to anodic DC of 0.9 V. The best 64% photoelectrocatalytic mineralisation of tetracycline was achieved by the DC mode at anodic bias of 0.9 V after 3 h PEC process.