Tetrasulfonate substituted phthalocyaninatozinc (II) (ZnTSPc) modification on the two dimensional surface of ZnO: On-surface synthesis, interface characteristics, and its selective photodegradation under visible irradiation

The photo-degradative selectivity for a photocatalyst is strongly dependent to the specific interaction between the photocatalyst and substrate. Here, a hydrophilic functional molecule, tetrasulfonate substituted phthalo-cyaninatozinc (II) (ZnTSPc) was modified on the two dimensional (2D) surface of ZnO via an on-surface synthesis. In the synthetic process, the dangling bonds of zinc ions on the high active facet ((001) and (100)) of dumbbell-like ZnO (ZnO ZDs) were used as a template of cyclotetramerization reaction for ZnTSPc by an onsurface process, where 4-(potassium sulfonate) phthalonitrile was used as a precursor. Compared with pure ZnTSPc, a significant fluorescence quenching (96.3 %) for ZnTSPc/ZnO happened. The photogenerated electronhole pairs were effectively separated by photoexcited electrons injecting from ZnTSPc into ZnO ZDs conduction band with a rapid charge transfer rate (6.1 x 10(7) s(-1)). Under visible light irradiation, ZnTSPc/ZnO as a photo-catalyst illustrates higher catalytic degradation rate for both phenol (PL) and methylene blue (MB) than those by using ZnO ZDs. Due to the hydmphilicity of sulfo groups on the peripheral substituted ZnTSPc, MB as a hydrophilic dye had strong attraction towards super-hydrophilic ZnTSPc/ZnO via pi-pi conjugation, but PL with hydrophobicity. The relative degradation rate of MB by using ZnTSPc/ZnO is 4.19 times faster than that of PL, illustrating ZnTSPc/ZnO with distinct photocatalytic selectivity under visible irradiation. The energy-band feature and mechanism for photoexcited electrons transition are illustrated based on electrochemical analysis.