Photoresponsive Nanosheets of Polyoxometalates Formed by Controlled Self-Assembly Pathways

Anionic Keggin polyoxometalates (POMs) and ether linkage-enriched ammonium ions spontaneously self-assemble into rectangular ultrathin nanosheets in aqueous media. The structural flexibility of the cation is essential to form oriented nanosheets; as demonstrated by single-crystal X-ray diffraction measurements. The difference in initial conditions exerts significant influence on selecting for self-assembly pathways in the energy landscape. Photoillumination of the POM sheets in pure water causes dissolution of reduced POMs, which allowed site-specific etching of nanosheets using laser scanning microscopy. By contrast, photoetching was suppressed in aqueous AgNO₃ and site-selective deposition of silver nanoparticles occurred as a consequence of electron transfer from the photoreduced POMs to Ag⁺ ions on the nanosheet surface.