▎ 摘　　要

Photochemical synthesis under visible light irradiation is a novel approach in the field of green chemistry, and composites with abundant active centers for electrochemical detection are highly attractive. Herein, a meso-tetra(4-sulfonatophenyl)porphyrin silver/Ag nanoparticles/graphene phase C3N4 nanosheets (Ag2TPPS4/AgNPs/ng-C3N4) material with a sandwich-like structure was synthesized using a two-step photocatalytic reaction at room temperature (25 degrees C). In the first visible light irradiation step and in the presence of a hole capture agent, Ag+ ions were photocatalytically reduced onto the surface of ng-C3N4 that was used as a photocatalyst. Then, the protons (H+) in the core of H2TPPS4 were substituted in situ by photo-oxidized Ag+ during the second visible light irradiation step and in the presence of an electron capture agent. The electrochemical response of Ag2TPPS4 and ng-C3N4 to ractopamine (RAC) results in the unique double-faced active centers of Ag2TPPS4/AgNPs/ng-C3N4, and the cores (AgNPs) are beneficial as bridges for the connection between Ag2TPPS4 and ng-C3N4 and for high-efficiency electron transfer. Hence, as-synthesized Ag2TPPS4/AgNPs/ng-C3N4 exhibits high sensitivity (a low detection limit of 5.1 x 10(-8) M, S/N = 3.0), a wide linear range (1 x 10(-7) to 1.2 x 10(-5) M), and long-term stability. Based on the experimental verification of the electrochemical dynamics and electrostatic attraction at the interface between the dual-active-center surface and RAC, the electrochemical mechanism has been clarified. Specifically, in the multi-cycle oxidation of RAC, the blue shift of specific UV-vis peaks also confirms the electrocatalytic oxidation of the two terminal hydroxyl groups of RAC. In brief, Ag2TPPS4/AgNPs/ng-C3N4 with a sandwich-like structure and double-faced active centers enhances the detection sensitivity and electrocatalytic efficiency towards RAC.