Photocatalytic removal of 2-chlorophenol from water by using waste eggshell-derived calcium ferrite

A new approach to recycling low-value eggshell food waste was to produce a CaFe₂O₄ semiconductor with a narrow band gap (E_g = 2.81 eV) via hydrothermal treatments of powdered eggshell suspended in aqueous ferric salt (Fe³⁺) solutions at varying Fe loadings. It was possible to obtain a single phase of CaFe₂O₄ without any Ca(OH)₂ and CaO impurities using an optimal Fe loading (30 wt% of Fe³⁺ by eggshell weight). The CaFe₂O₄ material was used as a photocatalyst for the breakdown of 2-chlorophenol (2-CP, a herbicide model chemical) as a pollutant in water. The CaFe₂O₄ with a Fe loading of 7.1 wt% exhibited a high 2-CP removal efficiency of 86.1% after 180 min of UV-visible light irradiation. Additionally, the eggshell-derived CaFe₂O₄ photocatalyst can be effectively reused, giving a high removal efficiency of 70.5% after the third cycle, without the requirement of regeneration processes (washing or re-calcination). Although radical trapping experiments confirmed that hydroxyl radicals were generated in the photocatalytic reactions, photogenerated holes play a significant role in the high 2-CP degradation efficiencies. The performance of the bioderived CaFe₂O₄ photocatalysts in the removal of pesticides from water demonstrated the benefits of resource recycling in the area of materials science and in environmental remediation and protection.