Fabrication of Kaolin Loaded Chitosan Hybrid Nanofibers for Recovery of Precious Palladium Cations from Aqueous Solution

Palladium plays an important role in modern industry, agriculture and medicine. The direct discharge of palladium results in serious environmental pollution and loses of precious palladium metal. Herein, kaolin/chitosan hybrid nanofibers were successfully prepared to recover Pd²⁺ cations from aqueous solution. Chitosan and kaolin mixture was first electrospun into nanofibers with citric acid as the in situ crosslinking agent and poly(ethylene oxide) as the co-spinning polymer. Then, the chitosan molecules in these hybrid nanofibers were in situ crosslinked by critic acid at elevated temperatures to endow these nanofibers with excellent solvent resistance. Their structure characterization was conducted by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and positron annihilation lifetime spectroscopy (PLAS). The adsorption performances of these fibrous adsorbents were carefully investigated and optimized (e.g. kaolin content, temperature, pH of solution and initial Pd²⁺ concentration). The adsorption results demonstrated that incorporation of kaolin powders into the nanofibers could enhance the adsorption capacity from 31 mg/g to 64 mg/g. Thermodynamic parameters studies revealed the endothermic and spontaneous natures of the adsorption process of Pd²⁺ cations on these hybrid nanofibers. The Pd²⁺ adsorption behavior of this fibrous adsorbent fitted well with the second-order kinetic model, suggesting the chemical adsorption behavior of Pd²⁺ cations on this fibrous adsorbent. Moreover, this fibrous adsorbent can be easily regenerated and reused at least three times without significant loss of initial adsorption capacities. These results clearly indicate that this fibrous chitosan/kaolin hybrid absorbent holds great potential in the recovery of precious palladium cations from aqueous solution.