Dialdehyde pineapple starch as a reactive carbohydrate platform for pyridyl–acylhydrazone crosslinked networks in Au and Pd recovery

The development of sustainable adsorbents for noble-metal recovery is essential for circular resource utilization. Here, a nitrogen-rich carbohydrate adsorbent was prepared by upcycling pineapple-stem starch via oxidation to dialdehyde starch, followed by crosslinking with pyridine-2,6-dicarbohydrazide (PCH) to form an acylhydrazone ligand network (DAS–PCH). FTIR, solid-state NMR, CHNS, and TGA confirmed successful oxidation and network formation with improved thermal stability. Nitrogen content increased with PCH loading across the series. Among the series, DAS–PCH5 delivered strong noble-metal uptake, reaching capacities of 194 mg g⁻¹ for Pd(II) and > 250 mg g⁻¹ for Au(III) under the tested conditions. Notably, a real-sample demonstration using an acidic gold-leaf leachate afforded quantitative Au, corresponding to an adsorption capacity of 631.51 mg g⁻¹. Kinetic studies revealed rapid Au(III) uptake (equilibrium within 30 min), whereas Pd(II) adsorption was slower. Adsorption was strongly pH dependent and favored acidic media. XPS, PXRD, and TEM analyses are consistent with ligand-assisted adsorption and partial reduction followed by immobilization of the adsorbed noble-metal species, with Au(III) undergoing more extensive reduction to Au(0) nanoparticles than Pd(II). The adsorbent showed high selectivity for Au and Pd and retained excellent performance over repeated adsorption–desorption cycles. Overall, biomass-derived starch offers a sustainable platform for high-performance noble-metal recovery.