Visible-light-driven photocatalysis of carbon dioxide and organic pollutants by MFeO2 (M = Li, Na, or K)

In recent years, lithium-containing ceramic materials have attracted considerable research attention as high-temperature adsorbents of carbon dioxide. The recycling of electrode materials from spent lithium-ion batteries for use as photocatalysts in recovering CO2 and degrading organic pollutants is worthy of exploration. Solid, magnetic ferrite-containing photocatalysts are easily separated from reaction solutions by using magnetic devices. Solid catalysts (e.g., LiFeO2, LiFe5O8, NaFeO2, and K2Fe2O4) were prepared through the calcination of Fe2O3 and M2CO3. CO2 was photoreduced and crystal violet (CV) and 2-hydroxybenzoic acid (2-HBA) were photodegraded under visible light irradiation. The optimized K2Fe2O4 photocatalyst increased the rate of photocatalytic conversion from CO2 to methane at 20.9 µmol g−1 h−1. The catalytic efficiency indicated that the optimized reaction rate constants of CV with LiFeO2, NaFeO2, and K2Fe2O4 were 2.98 × 10−1, 5.32 × 10−1, and 4.36 × 10−1 h−1, respectively. The quenching effect achieved through the use of various scavengers and the electron paramagnetic resonance in CV degradation revealed the substantial contribution of the reactive superoxide anion radical O2− and the minor roles of h+ and the OH radical. Its usefulness in the synthesis of solid-base catalyst MFeO2 is promising for environmental control and relevant applications, particularly in solar energy manufacturing.