Silver (Ag) nanoparticles are successfully modified onto mesoporous graphitic carbon nitride (mg-C3N4) by photo-assisted reduction. Modifying mg-C3N4 with Ag significantly increases the photoelectric conversion performance. The promotion mechanism is studied through electrochemical methods for the first time. Modifying mg-C3N4 with Ag also increases the conductivity and lowers the energy barrier of the interface reactions. A heterojunction electric field, forms on the interface between the modified Ag and mg-C3N4, enhances the separation efficiency of photogenerated electron-hole pairs. The enhanced separation efficiency thus prolongs the lifetime of the photogenerated electrons and significantly improves the photoelectric conversion performance of mg-C3N4. Furthermore, Modifying mg-C3N4 with Ag significantly improves the adsorption capacity and photocatalytic degradation efficiency. Smaller Ag nanoparticles are much more effective than larger ones in improving photoelectric conversion performance. (C) 2013 Elsevier B.V. All rights reserved.