▎ 摘　　要

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 watersolubility. 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 molCr molPd- 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 Cr2O72- ion.