Large-scale synthesis and enhanced visible-light-driven photocatalytic performance of hierarchical Ag/AgCl nanocrystals derived from freeze-dried PVP-Ag~+ hybrid precursors with porosity

摘要

To achieve high-performance, hierarchical plasmonic Ag/AgCl photocatalysts, a freeze-drying route was developed to form porous PVP-Ag~+ hybrid compounds, which were then transformed to hierarchical Ag/AgCl nanocrystals through a liquid-solid precipitation reaction followed by a partially photoreduction under ambient conditions. The PVP-Ag~+ hybrid precursors and their final Ag/AgCl nanocrystals obtained were characterized by various techniques. The hierarchical Ag/AgCl nanocrystals obtained had an appar-ent size range of 156 ± 50 nm, and the surfaces of the large particles were covered with small nanocrystals with sizes of 33 ± 12 nm. The photocatalytic performance of the hierarchical Ag/AgCl nanocrystals was estimated by degradating organic dyes (i.e., RhB, MO, and MB) and alcohols (i.e., methanol and iso-propanol) under visible light (A. > 420 nm) and sunlight. The results indicated that the hierarchical Ag/AgCl nanocrystals obtained were efficient visible-light-driven photocatalysts in decomposing organic dyes, and their RhB photodegradation rates (~0.97 mm~(-1)) was ~54 times higher than that (~0.018 min~(-1)) of TiO2 (P25) nanocrystals under the same visible-light conditions. The photodegradation efficiency of methanol and isopropanol reached ~45% and 35%, respectively, after visible-light irradiation for 60 min according to the COD data. The enhancement in visible-light-driven photodegradation performance results from the high absorbance through 350-800 nm due to the SPR effect of metal Ag species embedded in the hierarchical AgCl host nanocrystals. The influencing factors and possible growth mechanism of the Ag/AgCl nanocrystals were investigated, and the PVP molecules and the freeze-drying process were highly influenced the size and morphology of Ag/AgCl nanocrystals. The outstanding advantage of the freeze-drying assisted route is its ability in large-scale synthesis of hierarchical Ag/AgCl nanocrystals.