An atomic layer deposition (ALD) method has been employed to synthesize Fe₃O₄/graphene and Ni/graphene composites. The structure and microwave absorbing properties of the as-prepared composites are investigated. The surfaces of graphene are densely covered by Fe₃O₄ or Ni nanoparticles with a narrow size distribution, and the magnetic nanoparticles are well distributed on each graphene sheet without significant conglomeration or large vacancies. The coated graphene materials exhibit remarkably improved electromagnetic (EM) absorption properties compared to the pristine graphene. The optimal reflection loss (RL) reaches −46.4 dB at 15.6 GHz with a thickness of only 1.4 mm for the Fe₃O₄/graphene composites obtained by applying 100 cycles of Fe₂O₃ deposition followed by a hydrogen reduction. The enhanced absorption ability arises from the effective impedance matching, multiple interfacial polarization and increased magnetic loss from the added magnetic constituents. Moreover, compared with other recently reported materials, the composites have a lower filling ratio and smaller coating thickness resulting in significantly increased EM absorption properties. This demonstrates that nanoscale surface modification of magnetic particles on graphene by ALD is a very promising way to design lightweight and high-efficiency microwave absorbers.

Ni-coated ZnO was fabricated by atomic layer deposition and exhibited remarkably improved microwave absorption properties compared to ZnO.

The synergistic nature of bicomponent catalysts remains a challenging issue, due to the difficulty in constructing well-defined catalytic systems. Here we study the origin of synergistic effects in CoO_x-Pt catalysts for selective hydrogenation by designing a series of closely contacted CoO_xPt/TiO₂ and spatially separated CoO_x/TiO₂/Pt catalysts by atomic layer deposition (ALD). For CoO_x/TiO₂/Pt, CoO_x and platinum are separated by the walls of titania nanotubes, and the CoO_x-Pt intimacy can be precisely tuned. Like CoO_xPt/TiO₂, the CoO_x/TiO₂/Pt shows higher selectivity to cinnamyl alcohol than monometallic TiO₂/Pt, indicating that the CoO_x-Pt nanoscale intimacy almost has no influence on the selectivity. The enhanced selectivity is ascribed to the increased oxygen vacancy resulting from the promoted hydrogen spillover. Moreover, platinum-oxygen vacancy interfacial sites are identified as the active sites by selectively covering CoO_x or platinum by ALD. Our study provides a guide for the understanding of synergistic nature in bicomponent and bifunctional catalysts.