In situ low-temperature pyrolysis fabrication type II BiOIO3/Bi4O5I2 heterostructures with enhanced visible-light-driven photooxidation activity

Novel visible-light-driven heterostructure semiconductors are considered as promising photocatalysts for the elimination of environmental organic pollutants. Herein, a solvent-assisted low-temperature in situ calcination strategy was developed to fabricate type II BiOIO3/Bi4O5I2 heterojunction by using BiOIO3 as self-sacrificed template. The phase transition temperature of BiOIO3 was reduced under solvent-assisted operating conditions. By controlling the elevated temperature from 200 to 300 °C, an in situ stepwise pyrolysis reaction occurred during the calcination process, which was described as BiOIO3 → BiOIO3/Bi4O5I2 → Bi4O5I2. The light absorption edge of different samples significantly red shifted from 385 to 632 nm with the increase of calcination temperature. Meanwhile, two interlocked interface lattice fringes were identified in high resolution transmission electron microscope (HRTEM) of BiOIO3/Bi4O5I2-250 composites, confirming the formation of BiOIO3/Bi4O5I2 heterojunction. The as-obtained BiOIO3/Bi4O5I2 heterojunction demonstrated the optimal photodegradation performance, which brought about 99.4% of bisphenol A (BPA) degraded within 30 min visible light (λ > 420 nm) illumination. Besides, after 5 repeated cycles, the photoactivity of BiOIO3/Bi4O5I2 heterojunction still maintained 91.5%, unfolding its high photostability. The superior photoreactivity of BiOIO3/Bi4O5I2 nanosheets was assigned to the formation of well-matched type II heterojunction, which significantly enhanced the separation and migration of photoinduced charge carriers. Superoxide radical (O2-) and hole (h+) are dominant reactive species in this photodegradation system. Based on active species quenching experiments and electron paramagnetic resonance (ESR) measurements, a possible type II heterojunction mechanism for enhanced photodegradation performance of BiOIO3/Bi4O5I2 heterostructure was proposed. This work affords an innovative method for design and construction of type II composites toward sustainable water purification.