We report self-assembly of charge-stabilized gold and silver nanoparticles at water–air and water–oil interfaces, via manipulation of the interactions between the interfaces and the adsorbing nanoparticles. Nanoparticle adsorption from bulk colloids to an interface is an energy-favored, but finite sorption barrier-restrained (kinetics-controlled) process. Consequently, to successfully mediate self-assembly of nanoparticles, the finite sorption barrier should be decreased. That can be accomplished by manipulating its three controlling forces: the repulsive electrostatic force, the repulsive van der Waals force, and the attractive hydrophobic force between the interface and the adsorbing nanoparticles. It was found that hydrophobic coatings change nanoparticle hydrophobicity and greatly increase the attractive hydrophobic force. Surface active organic solvents (methanol, ethanol, isopropanol, and acetone) decrease the attractive hydrophobic force to some extent. However, they decrease the repulsive electrostatic force to a larger extent, via a “charge dilution” mechanism, due to their positive adsorption at the charged water–air and water–oil interfaces. Hydrophobic coatings and organic solvents consequently decrease the sorption barrier, facilitate nanoparticles overcoming the sorption barrier, and mediate the self-assembly of nanoparticles.

Ultrathin PtPdBi tri-metallic nanowires (NWs, diameters ranged from 3 nm to 5 nm) were prepared in a one-pot polyol process in which the molar ratios of the three metals could be tuned depending on the amount of initial precursors. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and elemental mapping revealed that these NWs were alloys with a face-centered cubic crystal structure similar to PtPd alloy. p-Nitrophenol was used as a probe to assess the catalytic activities of the as-prepared PtPdBi NWs. The results indicated that the existence of a small amount of Bi in the PtPdBi alloy efficiently improved its catalytic capability towards the reduction of p-nitrophenol. At the specified Pt : Pd : Bi ratio of 55 : 38 : 7, PtPdBi nanowires showed the best catalytic activity of all the nanomaterials tested (Pt, Pd and PdPd spherical nanoparticles; PtBi and PdBi nanowires) a feature that was attributed to the optimal synergistic effect of the three metallic elements.

Three-dimensional (3D) cubic superstructures of PtPd nanocubes were achieved by spontaneous adjustment of Pt^IV reduction kinetics, and exhibited enhanced catalytic activity and long-term durability towards methanol oxidation compared with the state-of-the-art Pt/C. This work demonstrates the first example of designing 3D shaped architectures of PtPd nanocubes for methanol electrooxidation.