Fabrication of hollow covalent-organic framework microspheres via emulsion-interfacial strategy to enhance laccase immobilization for tetracycline degradation

Abstract

• Hollow microspheres H-COF-OMe were prepared by emulsion interfacial polymerization. • Interfacial-defects in H-COF-OMe were formed by confined growth on emulsion droplets. • Lac@H-COF-OMe showed both high laccase loading and activity recovery. • Lac@H-COF-OMe displayed excellent structure stability and recyclability. • Lac@H-COF-OMe exhibited better adsorption uptake and faster degradation rate for tetracycline. Hollow covalent organic framework microsphere (H-COF-OMe) using TAPB and DMTP with enriched interfacial defects was fabricated via emulsion interfacial polymerization and in turn applied as a novel host for high laccase loading and tetracycline (TC) degradation. Benefited from the space-confined growth in the multiphase solvent interface, H-COF-OMe exhibited hollow spherical microstructure, high surface area and unique defects-rich interface. Attributed to these intriguing aspects, H-COF-OMe achieved maximum loading capacity of 567 mg/g and activity recovery of 85% for laccase. H-COF-OMe efficiently stabilized the active conformation of laccase from structural distortion via multiple binding sites, which endowed Lac@H-COF-OMe significantly higher pH, thermal, and storage stabilities, and reusability than free laccase and Lac@COF-OMe. Interestingly, the hollow morphology and defective interface of Lac@H-COF-OMe accelerated the diffusion of TC and shortened the reaction pathway, which endowed it with markedly enhanced TC degradation and recycling performance than many state-of-the-art catalysts. Significantly, Lac@H-COF-OMe (20 mg) could achieve 99% degradation of 50 mg/L tetracycline (50 mL) within 100 min. Monitoring of the intermediate products indicated that Lac@H-COF-OMe showed outstanding detoxification performance of the degradation products. This work suggested a novel COF synthesis strategy as laccase immobilization supporters for high TC degradation, which makes it as a promising candidate for degradation of organic pollutants.