A critical review describes wastewater photocatalytic detoxification over Bi5O7I-based heterojunction photocatalysts: characterizations, mechanism insight, and DFT calculations

Bi5O7I-based photocatalysts have been extensively employed for wastewater photocatalysis thanks to their desirable catalytic properties. This review sums up the latest progress in Bi5O7I-based heterojunctions and provides crucial information about three main areas: synthesis approaches, characterizations, and their applications in wastewater photocatalysis. Special attention is given to the synthetic strategies, like co-precipitation, hydrothermal, solvothermal, sonication, and ionic liquid self-combustion, to obtain Bi5O7I-based heterojunctions with appropriate morphology, structure, physical, chemical, and optical characteristics. Deeply, it was detected that the structure of Bi5O7I inclines to build a 3D crystal structure by stacking the [Bi5O7]+ slices with I− ions. Beyond that, the Bi5O7I nanomaterials exhibited different morphologies, like nanoparticles, nanorods, nanosheets, and flower-like microspheres, manifesting excellent support structures to immobilize incorporated co-catalysts. Our review also highlights the major modification approaches, like doping, type II, p-n, Z-type, and S-type heterojunctions, that address the catalytic limitations of pristine Bi5O7I. Impressively, the density functional theory (DFT) calculations played a crucial role in simulating and characterizing the crystalline structure, band structure, work function, and charge transfer profile of these Bi5O7I-based heterojunctions. In more detail, doping with plasmonic nanoparticles could broaden the visible-light sensitivity of newly created Bi5O7I-based heterojunctions. Even though type II and p-n Bi5O7I-based heterojunctions allowed for excellent charge separation mechanisms, their redox potentials were insufficient to produce both •OH and •O2− radicals. On the other hand, Bi5O7I-based S-type and Z-type systems offered advantages for obstructing the charge reintegration rate, accelerating the photocarrier migration, expanding the photon absorption, and upgrading the redox potential. The applications of Bi5O7I-based heterojunctions in terms of the purification of pollutants are also reviewed, supported by a huge number of impactful experimental studies and DFT theoretical calculations. The Bi5O7I-based heterojunctions displayed superior catalytic performance against various environmental pollutants, like phenolic compounds, organic dyes, pharmaceuticals, microorganisms, Hg0, Cr(VI), and so on. The DFT calculations reflected an assistance role in proposing the degradation pathways of treated organic pollutants via Bi5O7I-based heterojunctions. Ultimately, this review may have a significant influence on the development of sustainable Bi5O7I-based photocatalysts with perfect photocatalytic properties.