Quaternized chitosan-coordinated metal-azolate framework: Core-bridge-shell composite for electrostatic flocculation and long-term Microcystis aeruginosa inhibition

Harmful algal blooms dominated by Microcystis aeruginosa ( M. aeruginosa ) threaten aquatic ecosystems and public health. Traditional treatment methods had limitations of temporary effects or slow response. To address these issues, this study designed a multifunctional CTA-CS/M composite with flocculation and long-term algal inhibition, which constructed "metal-azolate frameworks (M) core - chitosan (CS) bridge - 3-chloro-2-hydroxypropyl trimethylammonium chloride (CTA) shell" hierarchical structure constructed via CS/M coordination and covalent grafting of CTA onto CS. CTA-CS/M was systematically characterized by zeta potential, XRD, FTIR, XPS, SEM and other techniques. Flocculation experiments showed that CTA-CS/M exhibited superior aggregation of M. aeruginosa , at a dosage of ≥ 10 mg L −1 , complete sedimentation was achieved within 30 min, outperforming the commercial flocculant polyaluminium chloride (PAC) and similar flocculants reported. The composite maintained clear supernatants for 60 days, demonstrating long-term inhibition of algal regeneration. At a concentration of ≥ 10 mg L −1 , it showed strong adaptability to pH (7.0–10.0) and algal concentrations (0.8–5.5 ×10 8 cells L −1 ), and could be combined with low-cost cotton towel filtration for efficient floc separation. Mechanistic studies revealed that the adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm, with -N(CH 3 ) 3 + groups on CTA-CS/M as the key functional groups, driving single-layer chemical adsorption through electrostatic attraction with negatively charged groups on M. aeruginosa . This work upgrades flocculation into a comprehensive long-term strategy for cyanobacterial bloom control.