This study showed the synthesis of a covalent-frameworked 2D crown ether, named C₂O, consisting of carbon and oxygen in a 2:1 mol ratio, using solvent-free synthesis for the first time. The synthesized C₂O is distinguished by its structure, which includes numerous phenol groups akin to phlorotannins, conferring high antibacterial property through contact-based mechanisms and biocompatibility. The inherent crown ether structure of C₂O facilitates efficient metal adsorption, allowing for the easy facile preparation of C₂O containing Cu atom (Cu@C₂O). Cu@C₂O exhibits enhanced antibacterial property at much lower concentrations compared to the native C₂O. For practical application, polylactic acid (PLA) nanocomposite films were prepared using C₂O as a filler, achieving 99.99% of antibacterial property at just 0.1wt% concentration. When the PLA nanocomposite films were prepared using Cu@C₂O as the filler, the required concentration was further reduced to 0.03wt%, while still demonstrating 99.99 % of antibacterial property. Additionally, the excellent copper ion adsorption capacity of Cu@C₂O ensures minimal leaching, thus mitigating cytotoxicity concerns. Given their high and long-term antibacterial properties, biocompatibility, these materials represent promising candidates for various biomedical, packaging and antifouling paint applications, demonstrating significant potential across diverse domains.