Novel sphere-like g-C₃N₄/BiOI composite photocatalysts were prepared by a one-pot EG-assisted solvothermal process in the presence of reactable ionic liquid 1-butyl-3-methylimidazolium iodine ([Bmim]I). The nanostructured heterojunction was formed with g-C₃N₄ covering the surface of BiOI microspheres uniformly. Multiple techniques were applied to investigate the structure, morphology and photocatalytic properties of as-prepared samples. During the reactive process, the ionic liquid acted as solvent, reactant, template and dispersing agent at the same time, leading to g-C₃N₄ being uniformly dispersed on the sphere-like BiOI surface. Three different types of dyes rhodamine B (RhB), methylene blue (MB), methyl orange (MO) were chosen as model pollutants to evaluate the photocatalytic activity of g-C₃N₄/BiOI composite. The as-prepared g-C₃N₄/BiOI composite exhibited much higher photocatalytic activity than the pure BiOI. At the same time, colourless endocrine disrupting chemical bisphenol A (BPA) and phenols 4-chlorophenol (4-CP) were chosen to further evaluate the photocatalytic activity of g-C₃N₄/BiOI composite. The g-C₃N₄/BiOI composite also exhibited much higher photocatalytic activity than the pure BiOI, which showed a broad spectrum of photocatalytic degradation activities. The results indicated that the formed heterojunction of g-C₃N₄ covers the BiOI microspheres contributed to improved electron–hole separation and enhancement in photocatalytic activity. A photocatalytic mechanism of g-C₃N₄/BiOI composites is also proposed.

The design of efficient and stable photocatalysts for robust CO₂ reduction without sacrifice reagent or extra photosensitizer is still challenging. Herein, a single-atom catalyst of isolated single atom cobalt incorporated into Bi₃O₄Br atomic layers is successfully prepared. The cobalt single atoms in the Bi₃O₄Br favors the charge transition, carrier separation, CO₂ adsorption and activation. It can lower the CO₂ activation energy barrier through stabilizing the COOH* intermediates and tune the rate-limiting step from the formation of adsorbed intermediate COOH* to be CO* desorption. Taking advantage of cobalt single atoms and two-dimensional ultrathin Bi₃O₄Br atomic layers, the optimized catalyst can perform light-driven CO₂ reduction with a selective CO formation rate of 107.1 µmol g⁻¹ h⁻¹, roughly 4 and 32 times higher than that of atomic layer Bi₃O₄Br and bulk Bi₃O₄Br, respectively.