An Ag@AgBr nanoparticle-decorated K4Nb6O17 (Ag@AgBr/K4Nb6O17) photocatalyst was prepared via the oil-in-water self-assembly method. The Ag@AgBr nanoparticles, with average diameters of 20 nm, were uniformly deposited on the K4Nb6O17 surface. The as-prepared Ag@AgBr/K4Nb6O17 composites exhibited high visible light absorption, high photocurrent intensity, and high charge transfer efficiency, thus enhancing the photocatalytic performance for methyl-blue (MB) dye degradation. The Ag@AgBr (20 wt%)/K4Nb6O17 composite displayed the highest photocatalytic activity, degrading 96% of the MB solution under visible light irradiation for 60 min, which was 2.3-times and 8.5-times that of the bulk Ag@AgBr and K4Nb6O17, respectively. The excellent photocatalytic activity of the Ag@AgBr/K4Nb6O17 composites is due to the synergistic effect between Ag@AgBr and K4Nb6O17, where the Ag@AgBr nanoparticles not only enhanced visible light absorption efficiency due to the Ag nanoparticles' SPR, but also greatly accelerated the separation of the photogenerated electron-hole pairs. From the UV-vis spectra, the Ag@AgBr nanoparticles greatly extend the composites' visible light absorption. The data collected from photoluminescence (PL), photocurrent and electrochemical impedance spectra (EIS) were consistent and confirmed the rapid separation of charge carriers. Moreover, the composite exhibited a larger specific surface area, which was also beneficial for the photocatalytic activity. In addition, the roles of the radical species were investigated, and the holes and ·O2 - radicals were hypothesized to dominate the photocatalytic process. Based on the characterization analysis and experimental results, a possible photocatalytic mechanism for the enhancement of photocatalytic activity is proposed.
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