UVA- and visible-light-driven photocatalytic activity of three-layer perovskite Dion-Jacobson phase CsBa2M3O10 (M = Ta, Nb) and oxynitride crystals in the removal of caffeine from model wastewater

• Oxide and oxynitride crystals showed absorption edges in the UV and visible region.
• Oxide and oxynitride crystals exhibited photocatalytic activity in the removal of CAF.
• Photodegradation of CAF and its derivatives followed pseudo-first order kinetics.
• Treatment of CAF wastewater by visible light irradiation did not reveal toxicity.

The presence of caffeine in treated wastewaters indicates its low removal efficiency during conventional wastewater treatment processes. A great efficiency has been achieved by photocatalytic processes in the removal of resistant organic pollutants from aquatic systems. In this study, the application of three-layer perovskite Dion-Jacobson phase CsBa2M3O10 (M = Ta, Nb) and oxynitride crystals in the removal of caffeine was tested by photocatalysis under UVA and visible light irradiation. The as-grown oxide and oxynitride crystals have pure phase, different crystal shapes, and optical band gap energies (1.8–3.5 eV). The highest efficiency in the removal of caffeine under UVA light was observed for LaTiO2N (80% caffeine removal and 55% TOC removal), whereas the lowest efficiency in the removal of caffeine was noted for CsBa2Ta3O10 and CaTaO2N (60–65% caffeine removal). Compared with UVA, the photodegradation process of caffeine over the crystals under visible light proceeded differently. The pseudo-first order kinetic model was applied to evaluate the rate of caffeine removal by the studied crystals. The highest k1 values were obtained for the LaTiO2N and SrTaO2N crystals at 365 nm and 550 nm, respectively. The possible photodegradation mechanisms of caffeine over the studied crystals are also demonstrated. The photocatalytic treatment of model wastewaters containing caffeine using the crystals under visible light did not reveal toxicity to Vibrio fischeri and Lepidium sativum, except CaTaO2N crystals for V. fischeri under UVA light.

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