Synergistic Effect in Zinc Phthalocyanine—Nanoporous Gold Hybrid Materials for Enhanced Photocatalytic Oxidations

Nanoporous gold (npAu) supports were prepared as disks and powders by corrosion of Au-Ag alloys. The npAu materials have pore sizes in the range of 40 nm as shown by scanning electron microscopy (SEM). The surface was modified by a self-assembled monolayer (SAM) with an azidohexylthioate and then functionalized by a zinc (II) phthalocyanine (ZnPc) derivative using “click chemistry”. By atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectrometry (ICP-MS) the content of zinc was determined and the amount of immobilized ZnPc on npAu was calculated. Energy-dispersive X-ray (EDX) spectroscopy gave information about the spatial distribution of the ZnPc throughout the whole porous structure. NpAu and ZnPc are both absorbing light in the visible region, therefore, the heterogeneous hybrid systems were studied as photocatalysts for photooxidations using molecular oxygen. By irradiation of the hybrid system, singlet oxygen is formed, which was quantified using the photooxidation of 1,3-diphenylisobenzofuran (DPBF) as a selective singlet oxygen quencher. The illuminated surface area of the npAu-ZnPc hybrid system and the coverage of the ZnPc were optimized. The synergistic effect between the plasmon resonance of npAu and the photosensitizer ZnPc was shown by selective irradiation and excitation of only the phthalocyanine, the plasmon resonance of the npAu support and both absorption bands simultaneously, resulting in an enhanced photooxidation activity by nearly an order of magnitude.