Thermal Synthesis of Silver Nanoplates Revisited: A Modified Photochemical Process

The well-known photochemical and thermal methods for silver nanoplate synthesis have been generally regarded as two parallel processes without strong connections. Here we report a surprising finding that both visible light and ambient O-2, which are critically important in the photochemical process, also play determining roles in the thermal synthesis. By designing a series of control experiments, we reveal that the typical thermal synthesis is essentially a modified photochemical synthesis coupled with the unique redox properties of H2O2. Light irradiation and dissolved O-2 are found to be essential for initiating the formation of nanoplates, but the continued growth of nanoplates is supported by the oxidative etching and subsequent reduction of Ag due to H2O2. O-2 resulting from the catalytic decomposition of H2O2 etches small nanoparticles to produce Ag+ ions, which are then reduced back to Ag-0 by anions of H2O2 to support the growth of nanoplate seeds. The involvement of H2O2 in the reaction significantly speeds up the nanoplate formation process. These findings not only greatly improve our understanding of the unique functions of H2O2 in the thermal synthesis, but also bridge the two well established synthesis processes with a unified mechanism, and significantly enhance the reproducibility of the thermal synthesis of Ag nanoplates by identifying the critical importance of ambient light and O-2.