Sustainable synthesis of NaA zeolite-modified MnFe<sub>2</sub>O<sub>4</sub> for synergistic removal of NH<sub>4</sub><sup>+</sup> and tetracycline

<p>A sustainable hydrothermal strategy converts coal fly ash, an industrial byproduct, into MnFe₂O₄/NaA composite molecular sieves. Despite the promise of molecular sieve-based composites in water remediation, existing materials often lack sufficient recyclability, long-term stability, and a clear understanding of their regeneration mechanisms. This approach addresses these knowledge gaps and waste management while creating a material capable of simultaneously removing NH₄⁺-N and photo-catalytically degrading tetracycline (TC). The composite demonstrates synergistic pollutant removal via integrated adsorption-photocatalysis. Comprehensive characterization confirmed the successful integration of MnFe₂O₄ nanoparticles within the NaA framework. The optimized 8% MnFe₂O₄/NaA composite achieved exceptional performance, with 66% NH₄⁺-N removal and 89% TC degradation under optimal conditions. The processes followed pseudo-second-order kinetics, and radical trapping identified •OH as the dominant reactive species. Remarkably, the composite maintained high efficiency across multiple regeneration cycles, demonstrating robust stability and reusability. This work presents a novel, waste-derived material that aligns with circular economy principles by transforming fly ash into a high-value adsorbent/catalyst for wastewater treatment.</p>