Selective capture of palladium(II) from highly acidic solution by proline-valinol amide functionalized silica nanoparticles

With the rapid development of the automobile industry and increasingly strict regulations on automobile exhaust emissions around the world, the production of waste purification catalysts for automobile exhaust will increase, leading to an increasing demand for palladium. Recycling waste three-way catalysts (TWCs) is an important way to obtain palladium resources. However, it is still a challenge to obtain highly selective adsorbents for palladium. Herein, we successfully fabricated two different kinds of Pd²⁺ selective composite adsorbents (PVA@MSNs and PVA@MONs) through covalent attachment of a proline-valinol amide (PVA) as the ligand on silica nanoparticles. The as-prepared adsorbents were characterized by TEM, SEM, elemental analysis, ²⁹Si and ¹³C CP MAS NMR, N₂-adsorption-desorption isotherm analysis, DLS, zeta-potential, p-XRD and FT-IR, revealing their high loading rate, and the mesoporous structure in the case of PVA@MSNs. In order to evaluate the ability of these two sorbents to selectively capture palladium(II), a series of sequential adsorption experiments were performed. The results showed that 56.35 mg and 67.74 mg of Pd²⁺ could be captured per gram by PVA@MSNs and PVA@MONs, respectively. Furthermore, they had a stronger selectivity towards Pd²⁺ than other cations (i.e. Co²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Fe²⁺,) present in the simulated sample. Both sorbents were able to remain stable and show consistent performance in cyclic adsorption-desorption runs. Interestingly, the adsorbents realized for the first time the enrichment and recovery of palladium from organic solvents, offering a potential application in palladium catalyst-loaded industrial waste liquid processes.