An all-solid-state Z-scheme heterojunction-structured photocatalyst, 3,4-dihydroxybenzaldehyde-functionalized Ga2O3/graphitic carbon nitride (Ga2O3-DBDig-C3N4), was synthesized using a facile post-grafting strategy via Schiff base chemistry. It was proposed for the first time that aromatic rings served as electron mediators in the Z-scheme photocatalytic system. In addition, the aromatic rings were conducive to the formation of a well-developed combined interface between Ga2O3-DBD and g-C3N4, greatly improving the separation of electrons and holes. The Ga2O3-DBD/g-C3N4 exhibited a wide absorption range, high charge-separation efficiency and high redox potential, thus enhancing its activity and stability for visible-light photocatalytic nitrogen fixation. The reaction mechanism was demonstrated to be that O-2 was first reduced to H2O2, which was further oxidized to (OH)-O-center dot; then, (OH)-O-center dot reacted with methanol to form (CO2-)-C-center dot, which facilitated the reduction of N-2 to NH3. This study demonstrates a simple and cost-effective approach to synthesize all-solid-state Z-scheme photocatalytic system using the aromatic rings, and this system exhibits great potential for practical applications of visible-light photocatalytic nitrogen fixation. (C) 2017 Elsevier B.V. All rights reserved.