In this paper, we constructed a novel Pt/Bi12O17Cl2 composite through loading tiny amount of Pt quantum dots on the surface of Bi12O17Cl2 by using photoreduction method at room temperature. The phase structures, morphologies, optical properties and elemental contents of the obtained samples were studied by XRD, EDS, ICP-OES, SEM, HRTEM, BET, UV-vis DRS and XPS technologies. The photocatalytic activity of novel Pt/Bi12O17Cl2 was evaluated by degrading methyl orange (MO) and phenol under visible light (lambda > 400 nm). It shows that Pt/Bi12O17Cl2 exhibited largely enhanced activity in comparison with the pure Bi12O17Cl2, among which 15% Pt/Bi12O17Cl2 sample displayed the fastest degrading rate for MO (k(app) = 1.13 h(-1)) and phenol (k(app) = 0.18 h(-1)). The excellent photocatalytic activity of Pt/Bi12O17Cl2 resulted from the enhanced separation efficiency of photocharges, which is exactly ensured by the transient photocurrent and surface photovoltage investigation. Thesurface loaded Pt quantum dots acted as trappers to efficiently capture the photoinduced electrons originating from the Bi12O17Cl2 substrate under visible light, which intensively avoids the recombination of electrons and holes. This study provides a potential way to boost the activity of bismuth oxyhalide with non stoichiometric ratios via utilizing the intense electron trapping effect of noble metal quantum dots. (C) 2016 Elsevier B.V. All rights reserved.