Green-synthesized chitosan/AuNPs@calcium alginate microspheres for efficient and reusable catalytic reduction of 4-nitrophenol

Gold nanoparticles (AuNPs) exhibit excellent catalytic activity but face significant practical constraints, such as insufficient stability and difficult recovery. This study employed a quercetin-mediated green reduction method with chitosan as a stabilizer to synthesize Chitosan/AuNPs (Chit/AuNPs) capable of maintaining long-term dispersion stability (960 h). It was clearly demonstrated that the chitosan dosage is critical for controlling the size of AuNPs, with 0.8 mL of chitosan yielding smaller AuNPs with an average particle size of about 16.8 nm. Subsequently, Chit/AuNPs were immobilized within a calcium alginate network via electrostatic attraction and Ca 2+ cross-linking, successfully fabricating reusable Chitosan/AuNPs@Calcium Alginate (Chit/AuNPs@CaA) composite microspheres. The catalyst exhibited high activity at room temperature, achieving a 4-NP conversion rate of 97.0% within 25 min with an apparent rate constant (k) of 0.168 min −1 . Notably, after five consecutive uses, the conversion rate remained at 96.9% within 25 min, confirming its reliability as a reusable catalyst. Furthermore, in real water samples, the catalyst maintained over 96.1% conversion rate, demonstrating strong environmental tolerance. This research contributes to the development of novel catalytic materials with high activity, remarkable stability, and practical application potential.