Herein, 3D hollow-sphere structure graphitic carbon nitride (g-C3N4) with large specific surface area and high porosity is synthesized through a mild, heat polymerization, template-free route. The as-prepared hollow-sphere structure can be used as a substrate material for uniformly dispersing Pd nanoparticles to enhance the absorption of visible light and expose more active sites. Pd nanoparticles as electron acceptor are implanted into g-C3N4, which increases the trapping capability of capturing transition electrons to gain more photogenerated carriers participating in surface reactions. Therefore, the estimated charge separation lifetime of Pd/SCN (10 h) investigated by transient absorption spectroscopy was 1.4 ns +/- 338.0 ps, which is only half of SCN. Benefiting from the unique structure and the excellent optical performance, the obtained Pd/SCN composites exhibited prominent photocatalytic hydrogen evolution performance under visible light irradiation. Especially, the photocatalytic hydrogen rate of Pd/SCN (10 h) reached 267.9 mu mol/h, almost 10 times higher than the Pd/2D g-C3N4. Simultaneously, a possible mechanism for photocatalytic H-2 reaction was proposed based on the characterization results. (C) 2019 Elsevier Inc. All rights reserved.