Freeze-dried PVP-Ag+ precursors to novel AgBr/AgCl-Ag hybrid nanocrystals for visible-light-driven photodegradation of organic pollutants

AgBr/AgCl-Ag nanocrystals with various molar Br-to-Ag ratios (RBr/Ag = 0, 1/3, 1/2, 2/3, 1) and different photoreduction times (0-20 min) were synthesized via stepwise liquid-solid reactions using the freeze-dried PVP-Ag+ hybrid as the Ag source, followed by a photoreduction reaction. The AgBr/AgCl-Ag7.5(1:2) nanocrystals obtained take on a spherical morphology with a particle-size range of 58 ± 15 nm. The photocatalytic performance of AgBr/AgCl-Ag nanocrystals was evaluated by photodegrading organic dyes, 4-chlorophenol and isopropanol under artificial visible light (λ⩾420 nm, 100 mW cm−2). For the decomposition of rhodamine B, the AgBr/AgCl-Ag7.5(1:2) nanocrystals has a photodegradation rate of ∼0.87 min−1, ∼159 times higher than that (∼0.0054 min−1) of TiO2 (P25), whereas the AgCl-Ag and AgBr-Ag nanocrystals have photodegradation rates of 0.35 min−1 and 0.45 min−1, respectively. The efficient separation of photogenerated electron-hole pairs in the ternary system consisting of AgBr, AgCl and Ag species plays a key role in the enhancement of photocatalytic performance.