Advanced Two-Dimensional Heterojunction Photocatalysts of Stoichiometric and Non-Stoichiometric Bismuth Oxyhalides with Graphitic Carbon Nitride for Sustainable Energy and Environmental Applications

Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and BixOyXz where X = Cl, Br, and I) are a relatively new class of semiconductors that have attracted considerable interest for photocatalysis applications due to attributes, viz., high stability, suitable band structure, modifiable energy bandgap and two-dimensional layered structure capable of generating an internal electric field. Recently, the construction of heterojunction photocatalysts, especially 2D/2D systems, has convincingly drawn momentous attention practicably owing to the productive influence of having two dissimilar layered semiconductors in face-to-face contact with each other. This review has systematically summarized the recent progress on the 2D/2D heterojunction constructed between BiOX/BixOyXz with graphitic carbon nitride (g-C3N4). The band structure of individual components, various fabrication methods, different strategies developed for improving the photocatalytic performance and their applications in the degradation of various organic contaminants, hydrogen (H2) evolution, carbon dioxide (CO2) reduction, nitrogen (N2) fixation and the organic synthesis of clean chemicals are summarized. The perspectives and plausible opportunities for developing high performance BiOX/BixOyXz-g-C3N4 heterojunction photocatalysts are also discussed.

Annealing effects on structural and photovoltaic properties of the dip-SILAR-prepared bismuth oxyhalides (BiOI, Bi7O9I3, Bi5O7I) films

Bismuth oxyhalides are becoming a promising contender for photovoltaic applications due to its non-toxic nature and decent optical properties. This study mainly deals with clarifying the effects of phase transformations on the structure, optical, and electrical properties of BiOI thin film prepared via dip-successive ionic layer adsorption and reaction (SILAR) method at different annealing temperatures ranging from 100 to 400 °C. Therefore, significant phase transformations (i.e., the existence of Bi7O9I3 and Bi5O7I have been confirmed at 300 °C and 400 °C, respectively) appeared in the produced films, which were mainly due to the change of annealing temperatures. The experimental results confirmed that produced films achieved the maximum current density and efficiency and minimum current density and efficiency at 100 °C and 400 °C, respectively. Experimental results were also showed that with increasing the annealing temperature from 100 to 400 °C, the indirect bandgap risen from 1.77 to 2.96 eV while the crystallite size decreased from 17.62 to 12.99 nm. The energy band diagram with electrolyte explained the observed poor electrical properties during the phase transformation. Hence, this result will add positive impacts on the new information on findings for the dip-SILAR-prepared BiOI photovoltaic cells.