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.
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