Intermittent microwave heating-promoted rapid fabrication of sheet-like Ag assemblies and small-sized Ag particles and their use as co-catalyst of ZnO for enhanced photocatalysis

An easy and rapid intermittent microwave heating (IMH) method was developed for the synthesis of Ag nanostructures with high yields within the short time of 2 minutes. A Ag-DT (dodecanethiol) complex with sheet-like structure was used as precursor. After an IMH treatment of the solid Ag-DT, Ag nanoparticles (NPs) with a small size below 5 nm were obtained. Time-dependent experiments and a series of tests indicated that the Ag NPs were formed and grown in the sheet-like Ag-DT precursor. Specifically, the fewer IMH cycles (less than 3 times) would result in the formation of the sheet-like assemblies of Ag NPs linked by the Ag-DT. The sheet-like assemblies of Ag NPs were rarely observed in previous reports. The Ag NPs with small size below 5 nm would emerge as major products with increasing the number of IMH cycles to 5 times. With further increase of IMH cycles, Ag NPs with a large size of 20 nm were observed. Notably, due to the presence of DT groups on the surface of Ag NCs, the small-sized Ag NPs could directly combine with an oxide (ZnO here) to form Ag-oxide composites with no need for additional modification. The Ag-ZnO composites exhibited enhanced performance for the photocatalytic degradation of dye pollutants over unmodified ZnO and P25 TiO2, demonstrating the large application potential of composites in advanced areas. The IMH strategy developed here will be important for the practical application of Ag-based materials due to the fast synthesis process, high yields benefiting from the solid-based reaction, high stability, as well as the ability of the as-prepared Ag NCs to easily combine with oxide materials to form functional nanocomposites (ZnO here).