Porous Ca-doped Al₂O₃ with abundant basic sites for enhanced hydrolysis of fermentative antibiotics

Efficient elimination of antibiotics from wastewater is crucial for the stability of biological treatment systems and the safety of effluent. This study presents a heterogeneous catalytic hydrolysis system using porous calcium-doped alumina (P-Ca-Al), synthesized with ammonium chloride as a green gas template. Characterization reveals that calcium species are highly dispersed in the tetrahedral sites of alumina, forming Ca-O-Al bonds. The coexistence of surface basic sites and Lewis acid sites on P-Ca-Al was confirmed by CO₂ temperature-programmed desorption spectrum and pyridine adsorption infrared spectroscopy. These sites are responsible for the highly efficient hydrolysis of Erythromycin-A (Ery-A), achieving an 18-fold increase in efficiency compared to conventional NaOH aqueous solutions, with no degradation observed on solid CaO under identical conditions. The selective hydrolysis of the antibacterial functional groups of Ery-A reduces antimicrobial activity with low energy and reagent consumption. The degradation mechanism is confirmed through solvent kinetic isotope effect (KIE) investigation and identification of hydrolysis intermediates. The macrolide ring and glycosidic bond in Ery-A are hydrolyzed by proton subtraction from surface basic sites, preventing resistance gene formation as confirmed by metagenomic analysis. This work provides a possible way to selectively remove antibiotics from complex industrial wastewater.