Photocatalytic Recovery of Noble Metals by Covalent Silyl Polyoxophosphotungstate–Porphyrin Copolymers

The photocatalytic recovery of noble metals on photosensitive semiconductors such as TiO2 is well-established for forming M/TiO2 but has notable drawbacks. TiO2 suffers from low conversion efficiency due to significant recombination of photogenerated electron–hole pairs. Its wide energy band gap (3.2 eV) also restricts excitation to high-energy UV light, limiting its use with solar energy. This study proposes an efficient alternative using hybrid polyoxometalate (POM)–porphyrin copolymers for the photocatalytic recovery of Ag and Pt under visible light. Copolymeric films composed of hybrid polyoxometalates and porphyrins have been obtained by the electrooxidation of 5,15-(di-p-tolyl)porphyrin (H2T2P) or 2,3,7,8,12,13,17,18-octaethylporphine zinc(II) (ZnOEP) together with Keggin or Wells–Dawson-type organosilyl polyoxophosphotungstate ([PW11Si2O40C26H16N2]TBA3 or [P2W17Si2O62C26H16N2]TBA6). In these films, porphyrin subunits can be excited under visible illumination, acting as photosensitizers that transfer electrons to the polyoxometalate catalysts. Notably, POM–porphyrin films demonstrated high efficiency in Pt(IV) photoreduction over repeated cycles without catalyst degradation.