Synthesis of Bi4O5I2/Bi5O7I heterojunction at weak acidic solution with preferentially growing facets and high photocatalytic activity

Bismuth-rich oxyiodides are promising photocatalysts owing to their unique layered structures, tunable band potentials and excellent redox ability. It is significant to explore a facile and energy-saving method to prepare BixOyIz-based heterojunction photocatalysts with enhanced photocatalytic performance. In this work, Bi4O5I2/ Bi5O7I heterojunction was prepared at room temperature in the existence of thiourea (TU). The addition of TU not only reduced pH value to 6 for the generation of Bi4O5I2/Bi5O7I heterojunction from pH 11 in water, but also improved the photocatalytic performance. The as-prepared Bi4O5I2/Bi5O7I (pH 6) heterojunction exhibited su-perior photocatalytic activity for the degradation of tetracycline (TC) and malachite green (MG) with degra-dation efficiency of 89.8% and 98.2% within 120 min of visible light illumination, respectively. And the photocatalytic performance was better than those of Bi4O5I2/BiOI heterojunction obtained in the absence of NaOH (79.2%; 85.8%), pure BiOI synthesized without the addition of TU (pH 6) (81%; 81.4%), and Bi4O5I2/ Bi5O7I heterojunction produced at pH 11 in water (38.7%; 85.4%). The enhanced photocatalytic activity of Bi4O5I2/Bi5O7I (pH 6) heterojunction could be attributed to smaller particles with higher specific surface area and high exposure ratio of (001) facet of Bi5O7I and (402) facet of Bi4O5I2.