Adsorption and recovery of palladium from aqueous solution by silica gel incorporated chitosan-based composite nanofibers

The efficient adsorption of precious palladium metal ions from industrial wastewater is crucial for both reducing environmental pollution and recycling valuable palladium resources. In this research, a combination of electrospinning and annealing treatment was employed to fabricate low-cost and stable silica gel incorporated chitosan composite nanofibers, which were served as an efficient adsorbent for adsorbing Pd²⁺ ions from aqueous solution. The fiber morphology was analyzed by scanning electron microscopy (SEM). Brunauer–Emmett–Teller (BET) analysis and positron annihilation lifetime spectroscopy (PALS) were employed to analyze the microstructure. The surface area of composite nanofibers reaches the maximum of 81.46 m²/g with 23.1% loading of silica gel. These fiber adsorbents were used to adsorb the Pd²⁺ ions in aqueous solution and the related factors of silica gel content, the annealing temperature and the adsorption parameters (e.g. adsorption time, solution pH, and initial Pd²⁺ concentration) were investigated and optimized. The adsorption results demonstrate that the unique fibrous structure and the incorporation of silica gel significantly enhance the adsorption efficiency for Pd²⁺ ions with a maximum adsorption capacity of ~ 113 mg/g. The adsorption mechanism analysis reveals the involvement of chelation and electrostatic interaction between the amino groups in chitosan and Pd²⁺ ions. Thermodynamic analysis indicates that the adsorption process is endothermic and spontaneous with ΔH⁰ and ΔS⁰ values of − 26.59 kJ/mol and 96.02 J/mol K, respectively. Moreover, the fibrous adsorbent exhibits outstanding recyclability, retaining 85.2% of its initial adsorption capacity after five successive reuse cycles. In conclusion, this low-cost and high-performance fibrous adsorbent holds great potential for the efficient separation and recovery of precious Pd²⁺ ions from industrial wastewater.