(a) Steady-state photoluminescence spectra. (b) Time-resolved photoluminescence decay. (d) Periodic on/off photocurrent responses of ZnIn2S4 and Co9S8@ZnIn2S4. (c) Electrochemical impedance spectra Nyquist plots of ZnIn2S4, Co9S8@ZnIn2S4, and Co9S8@ZnIn2S4 under illumination. (e, f) optimized structural model (top view and side view) of the Co9S8@ZnIn2S4. (g, h) The charge density distribution of Co9S8@ZnIn2S4. (i) transfer process of the photogenerated electrons and holes in the Co9S8@ZnIn2S4 heterostructure.