It was widely accepted that pristine CdS showed weak photocatalytic activity for reduction of 4-nitroaniline (4-NA) to p-phenylenediamine (PPD) because of its poor photogenerated carriers separation and transfer efficiency. Yet the influence of conduction band (CB) and valence band (VB) redox potentials on its photocatalytic reduction reaction efficiency was often neglected, especially the VB potential. Considering the above facts, in this work, we design a highly efficient carbon quantum dots (CQDs)/Zn2+ ions doped-CdS nanowires (ZnCdS NWs) composite photocatalysts, where CQDs were acted as metal-free co-catalysts to promote the separation and transfer of photogenerated carriers and Zn2+ ions doping was used to adjust the redox of CdS NWs. As a result, under visible light irradiation, 4-NA could be completely converted to PPD with near 100% selectivity over the as-synthesized CQDs/ZnCdS NWs within 6 min in the presence of ammonium formate. It was found that Zn2+ ions doping increased VB potential of CdS rather than lowering its CB potential, which was responsible for its enhanced photocatalytic activity. The present strategy on the combination of co-catalyst and energy band engineering could open a new avenue to develop highly efficient visible-light-driven photocatalysts for green organic synthesis. (C) 2018 Elsevier B.V. All rights reserved.