It implies that the CdS/Cu2O composites have lower recombination of photogenerated electrons and holes than that of CdS NWs. In other words, CdS/Cu2O composites can provide more active electrons and holes, which promote the photocatalytic degradation. This is consistent with above photocatalytic experiments. The effective separation of photogenerated electrons and holes in CdS/Cu2O composites is due to their matched band structure of heterojunctions. The band structures of Cu2O and CdS are shown in Fig. 6b.