Synthesis of cerium dioxide–calcium oxide composite antibacterial materials and their use for water treatment and dye degradation

Bacterial infections have become a major challenge to global public health security. In this study, based on the concept of green synthesis, three cerium dioxide (CeO₂)-calcium oxide (CaO) composites (CS-CeO₂@CaO, CT-CeO₂@CaO, and CTD-CeO₂@CaO) were developed using chemical hydrothermal (CS), chrysanthemum tea impregnation (CT), and residue impregnation (CTD). Eggshell-derived calcium oxide was used as the carrier, in combination with the functional components of chrysanthemum tea and its residue extract. The antibacterial efficacy of these materials against Escherichia coli exceeded 90% at a concentration of 50 µg/mL, and their bactericidal performance in water remained stable after six treatment cycles. Structural characterization experiments revealed that CT and CTD composites exhibited larger specific surface areas and hierarchical pores, which enhanced bacterial adsorption via π-π* interactions. X-ray photoelectron spectroscopy analysis indicated that Ca²⁺ released from the eggshell-derived CaO caused ionic interference, while Ce³⁺/Ce⁴⁺ redox pairs generated reactive oxygen species, together establishing a synergistic adsorption-ion-oxidation antimicrobial mechanism. Additionally, the composites exhibited dual water treatment functions: an 80% degradation of methylene blue within 40 min and efficient biofilm removal. By valorizing waste resources (eggshells and tea residues), this work offers a sustainable approach to develop cost-effective multifunctional materials for addressing drug-resistant bacterial infections and remediating dye-contaminated wastewater.