[en] Highlights: • Co_3O_4 rods were grown on plasma treated Ti foil. • Cu_2O QDs were uniformly distributed on the surface of nanorods. • Ti/Co_3O_4/Cu_2O exhibited visible light photocatalytic activity with KHSO_5. • Degradation mechanism was supported by ESR technique and radical scavenger tests. • The heterojunction was highly stable even after recycling many times. - Abstract: A heterogeneous nanocomposite catalyst constructed by the Co_3O_4 nanorods decorated with the Cu_2O quantum dots (QDs) were successfully synthesized via a simple hydrothermal method followed by an oxidation-reduction processing. The fabricated Cu_2O/Co_3O_4 nanocomposite was characterized by the SEM, TEM, XPS, XRD, UV–vis and PL, and the (2 2 0) and (3 1 1) facets of the Co_3O_4 were exposed. Compared with the original Co_3O_4 nanorods with an average diameter of 350 nm, a substantial decrease in the band gap was observed after doping the nanorods with the Cu_2O QDs (average diameter of 5 nm). Such a dramatic decrease in the band gap indicated a significant enhancement of the photocatalytic activities under visible light. The methylene blue (MB) dye and the phenol were used as model organic pollutants, and the Cu_2O/Co_3O_4 nanocomposite catalyst exhibited both high catalytic activity and good recycling stability. The catalytic activities of the Cu_2O/Co_3O_4/potassium monopersulfate triple salt (PMS) system for cleaving the MB and the phenol were dependent on the dosages of the Cu_2O QDs, and the calculated degradation rates achieved by 7.0 wt% Cu_2O/Co_3O_4 nanocomposite catalyst were about 11.3 and 1.8 times than that of the pristine Co_3O_4 nanorod catalyst for the MB and the phenol, respectively. The reactive species of ·O_2"− and the holes were determined to be the main active species for the phenol photocatalytic degradation by the 7 wt% Cu_2O/Co_3O_4/PMS system and the 7 wt% Cu_2O/Co_3O_4/H_2O_2 system, respectively.