Ag₃PO₄ colloidal nanocrystal clusters with controllable shape and superior photocatalytic activity

Cluster-like Ag₃PO₄ nanostructures including nanoparticles, trisoctahedrons, tetrahedrons and tetrapods have been prepared by the synergetic reaction of Ag nanocrystals, phosphate anions and hydrogen peroxide. The acidity and alkalinity of the reaction solution are tuned to adjust the oxidizing ability of H₂O₂, and thus control the final morphology. Ag nanocrystals function as a sacrificial precursor, leading to the generation of cluster-like nanostructures. Through a kinetic study, the formation of Ag₃PO₄ nanocrystal clusters can be understood as the conversion from Ag to Ag₃PO₄ nanocrystals assisted by H₂O₂, followed by the oriented attachment of nanocrystals into cluster-like colloids with specific shapes. The as-prepared Ag₃PO₄ nanostructures have higher photocatalytic activity than commercial TiO₂ and some reported Ag₃PO₄ microcrystals in the degradation of dyes. The catalytic activity decreases in the order nanoparticles > trisoctahedrons > tetrahedrons > tetrapods, while the stability increases in the order nanoparticles < tetrahedrons < trisoctahedrons < tetrapods, which can be explained by the extent of absorption of visible light and structural factors, including size and exposed crystal facets.