Polyethylenimine modified ultrafine palladium nanocrystals on reduced graphene oxide for hexavalent chromium reduction

Highlights: • Highly-quality PE@Pd-RGO hybrids are synthesized by a simple adsorption-reduction strategy. • PE molecules effectively serve as complex-forming, linker and functional reagents. • PE@Pd-RGO hybrids show prominent catalytic activity for Cr^VI reduction. • The activity enhancement originates from small particle size of Pd nanocrystals and PE functionalization. Palladium-catalytic hydrogenation is an efficient method for remediating inorganic/organic contaminants. Herein, a very simple adsorption-reduction strategy is applied to synthesize the polyethylenimine (PE) modified ultrafine palladium nanocrystals on reduced graphene oxide (RGO) hybrids (PE@Pd-RGO). The surface composition, structure, and morphology of PE@Pd-RGO hybrids are minutely characterized by various physical characterization techniques and the formation mechanism of PE@Pd-RGO hybrids is defined according to experimental observation. Physical characterizations demonstrate that palladium nanocrystals with only 2.91 nm size uniformly anchor at RGO surface and PE modification endows PE@Pd-RGO hybrids with eminent water-solubility. When applied as catalyst for hexavalent chromium reduction, PE@Pd-RGO hybrids reveal excellent catalytic activity (rate constant: 0.0785 min⁻¹, turnover frequency: 1.166 mol_Cr mol_Pd⁻¹ min⁻¹) and stability due to the small particle size of palladium nanocrystals, excellent colloidal stability, and distinctive electrostatic attraction between PE with –NH₃⁺ and Cr₂O₇^2- ion.