Bismuth oxyhalides (BiOX, where X = F, Cl, Br, I) are interesting materials due to their layered structure, which can be useful for different applications. In this work, we present the synthesis of the complete BiOX family in the thin film form. The tetragonal phase Bi2O3 film deposited onto a glass substrate was transformed into BiOF, BiOCl or BiOBr by a simple immersion at ambient temperature in a halide (X = F, Cl, Br) containing solution. For these films, a residual phase from the oxide was present and for BiOF another phase (tentatively identified as Bi7O5F11) was present too. For the BiOI film synthesis, an iodine and bismuth containing solution was sprayed onto the glass substrate heated at 275 °C and a pure phase was obtained. Microstructural and morphological characterization was performed by X-ray diffraction and scanning electron microscopy, while the chemical environment was studied by X-ray photoelectron spectroscopy. Optical and photocatalytic properties were also obtained. The physical and chemical characteristics of the BiOX films follow a correlation with the atomic radius of the halogen atom incorporated into the corresponding lattice. All the BiOX films showed a photocatalytic response for the photodiscoloration of indigo carmine dye under simulated sunlight irradiation in an alkaline medium. The photocatalytic reactions occurred via 2 proton-electron transfer from the oxide or oxyhalide to the adsorbed IC dye, favoring its reduction to the corresponding leuco IC form.

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In this work, we synthesized and characterized carbon nitride (CN) nanoparticles obtained by the thermal treatment (550 °C) of urea, melamine, dicyandiamine, and dicyandiamine-barbituric acid in an open reactor and evaluated the effect of different precursors on the photocatalytic performance. CNs obtained from melamine, dicyandiamine, and dicyandiamine-barbituric acid were 3D melon-type structures. On the other hand, CN obtained from urea was a 2D microporous, amorphous structure whose melon or graphitic arrangement could not be determined. The presence of structural defective states (mainly C radicals) was corroborated by EPR studies of the solids. The photocatalytic activity of CN powders for methyl orange (MO) discoloration was investigated using 350 nm and simulated solar light (SSL) irradiation. MO removal efficiencies were correlated with the particle’s energy gap, specific surface area, degree of crystallinity, and C radical defects produced upon irradiation. Moreover, the obtained conduction and valence band potentials in the range of −0.60 and + 2.14 V vs NHE (pH = 7), respectively, evidence CN capacity to oxidize water to hydroxyl radicals (HO•) and reduce O2 to superoxide radical anions (O2 •–). The formation of both radicals upon SSL irradiation of CN suspensions was confirmed by EPR experiments. The largest specific surface area, the highest charge carrier density, and the amount of C radical defects observed for CN obtained from urea (CNu) account for their highest photocatalytic performance. However, the estimated CNu photonic efficiency of ca. 8% still indicates a deficient separation/migration efficiency of photoinduced charge carriers. Despite CNu performance being higher than those of other CNs obtained from the thermal treatment of simple precursors, further environmentally friendly strategies are still needed to overcome the intrinsic disadvantages of CN before it may be employed in technological applications. A discussion on probable CN mechanisms forming reactive species and leading to MO decolorization is given.