Recyclable g-C3N4 and K-doped g-C3N4 pellets for the photocatalytic production of H2O2 under direct sunlight

Abstract

Hydrogen peroxide (H₂O₂) is an environmentally friendly oxidant, producing only water as a by-product upon decomposition. Given the energy-intensive nature of the conventional anthraquinone process for commercial H₂O₂ production, photocatalytic production of H₂O₂ using graphitic carbon nitride (g-C₃N₄) emerges as a viable alternative. Among the other alternatives for improving the efficiency of g-C₃N₄, potassium ion doping in g-C₃N₄ is one of the efficient methods that can further increases the yield of H₂O₂ production, as the K⁺ doping enhances the photogenerated charge carriers’ separation, intensity and range of visible light absorption, etc. However, traditional methods of catalyst dispersion are inefficient due to the challenges of retrieving the catalyst. Immobilization, while addressing the retrieval issues, adversely affects mass transfer and lowers photocatalyst efficiency. Hence, in this study, we explore an innovative approach to catalyst recycling by forming the catalyst into pellets that avoid immobilization, centrifugation, or any other tedious energy intensive separation process. Pellets of undoped g-C₃N₄ and 10 wt% K-doped g-C₃N₄ are tested for the photocatalytic production of H₂O₂ under direct sunlight and recycled for three times. These materials, i.e., undoped g-C₃N₄ and 10 wt% K-doped g-C₃N₄ pellets are able to produce ~ 407 µM g⁻¹ h⁻¹ and ~ 853 µM g⁻¹ h⁻¹ of H₂O₂, respectively, after three recycles. Such a novel approach of recycling the catalysts in the form of pellets can be extended for the large-scale production of H₂O₂ by loading the pellets to fixed bed column and operating it in continuous flow manner.