2-D Heterometallic Pb-Iodoargentate Framework [PbAg2I6]n with a Diskoid [Pb(18-crown-6)]2+ Linker and Cocatalyst for Synergistically Enhanced Photocatalytic Properties via g-C3N4 Doping.

Abstract

The heterometallic Pb-iodoargentate hybrid [Pb(18-crown-6)(PbAg2I6)]n (1; 18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane) was prepared via self-assembly of the tetrahedal AgI4 and octahedral PbI6 primary units using crown ether 18-crown-6 as an organic ligand in DMF solvent. The hybrid heterocomposite cocatalyst based on 1 and graphitic carbon nitride (g-C3N4) was prepared by a facile solvothermal method. In 1, the dimeric units Ag2I6 and Pb2I10 are joined via face sharing, leading to a ternary heterometallic 1-D [PbAg2I62-]n chain containing novel Ag2Pb2I4 cubes. The 1-D chains are joined by the discoid [Pb(18-crown-6)]2+ complex cations, forming the 2-D [Pb(18-crown-6)(PbAg2I6)]n hybrid with the skeleton of [Pb2Ag2I6]n. Compound 1 shows photocatalytic activity in the degradation of MB at room temperature under visible-light irradiation. The photoelectric response measurement showed that the photocurrent of 1 increased from 1.41 to 2.43 μA/cm-2 when g-C3N4 was loaded, indicating that the introduction of a certain amount of g-C3N4 on the surface of 1 improves the separation and migration rate of photoinduced electrons and holes. The 1/g-C3N4 composite showed much higher photocatalytic efficiency in comparison to pristine 1 and g-C3N4 for MB degradation, which suggests the synergistic effect between 1 and g-C3N4 toward visible-light-driven photocatalytic performance. Meanwhile, the 1/g-C3N4 composite exhibited good reusability and stability in the photocatalytic reaction. Free radical quenching experiments showed that the •O2- radical is the main reactive substance over catalyst 1, while h+, •OH, and •O2- species have synergistic effects over the 1/g-C3N4 composite catalyst in the process of photodegradation.