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.

Automated summary

Bismuth-rich oxyiodides with a layered structure and tunable band potentials have great potential as photocatalysts. This study successfully prepared Bi4O5I2/Bi5O7I heterojunction photocatalysts with enhanced photocatalytic performance using thiourea as an additive. The addition of thiourea not only reduced the pH value, promoting the formation of the heterojunction, but also improved the photocatalytic activity. The as-prepared Bi4O5I2/Bi5O7I (pH 6) heterojunction exhibited superior photocatalytic activity for the degradation of organic dyes and antibiotics.