A one-pot synthetic approach to prepare self-assembled BiOI/BiOCl microflowers by a template-free coprecipitation method at room temperature has been developed. The physicochemical structure of BiOI/BiOCl microflowers were characterized using transmission electron microscopy (TEM), high resolution TEM (HRTEM), scanning electron microscopy (SEM). The composition information and bonding energy structure of the BiOI/BiOCl microflowers were studied by X-ray diffraction (XRD) and high resolution X-ray photoelectron spectra (XPS), Fourier Transform Infrared Spectroscopy (FTIR), UV-vis diffuse reflectance spectroscopy (DRS) analysis and photoluminescence (PL) spectra. The photocatalytic performance of as-prepared BiOI/BiOCl microflowers was tested through photocatalytic oxidation of gas phase mercury, as a useful catalyst (or additive) in wet electrostatistic precipitator (WESP) to capture heavy metals including mercury. The results show that the prepared BiOI/BiOCl samples demonstrate higher photocatalytic efficiency than pure BiOI or BiOCl. By optimizing the component ratio of the BiOI and BiOCl, up to 72.2% oxidation efficiency can be achieved in BiOI/BiOCl microflowers. Finally, the photocatalytic influence of BiOI/BiOCl microflowers on gas-phase mercury oxidation had been proposed. (C) 2019 Elsevier Inc. All rights reserved.