No abstract

No abstract

We report on a novel template-free method for the fabrication of crack-free colloidal crystals by using a modified vertical deposition method. In this method, a colloidal suspension of silica spheres containing a silica precursor (an acidic tetraethyl orthosilicate (TEOS) solution) was used in the vertical deposition fabrication process. Hydrolysis of the silica precursor produced silica species, which filled up the voids between the self-assembled silica spheres to avoid the formation of cracks upon drying of the colloidal crystal film. The silica in the interstices of the silica beads can be easily removed using hydrofluoric acid vapor, leaving behind a crack-free colloidal crystal film. The amount of the silica precursor solution needed to fabricate crack-free film increased with the increasing number of layers of silica spheres. When an excessive amount of the silica precursor solution was added in the vertical deposition process of producing silica sphere bilayer, the resultant colloidal crystal film curled and peeled off from the substrate and a large-area nanobowl array was left on the substrate.

We describe the use of a horizontal deposition method to prepare large-area binary colloidal crystals (bCCs). Two different sets of binary polystyrene spheres were employed to demonstrate the validity of this method. By varying the number ratios of small spheres with respect to large spheres, the stoichiometric configuration of the bCCs can be altered. Stable corresponding replica structures of the bCCs were also prepared, and the cross-sectional images of the binary inverse opals were obtained. Optical characterization demonstrated the presence of pseudostop bands, which were in agreement with the compositions of the material. The formation of the bCC by such a simple self-assembly method was attributed to the cooperative effect of interparticle electrostatic interactions and geometrical constrictions. This facile fabrication method further enhances the application potential of the bCCs and their inverse porous replicas with a binary pore system in the fields of photonics, solar cells, separations, catalysis, and biosensing.

This work reports a novel approach for the synthesis of FeCo alloy nanoparticles (NPs) embedded in the N,P-codoped carbon coated nitrogen-doped carbon nanotubes (NPC/FeCo@NCNTs). Specifically, the synthesis of NCNT is achieved by the calcination of graphene oxide-coated polystyrene spheres with Fe 3+ , Co 2+ and melamine adsorbed, during which graphene oxide is transformed into carbon nanotubes and simultaneously nitrogen is doped into the graphitic structure. The NPC/FeCo@NCNT is demonstrated to be an efficient and durable bifunctional catalyst for oxygen evolution (OER) and oxygen reduction reaction (ORR). It only needs an overpotential of 339.5 mV to deliver 10 mA cm −2 for OER and an onset potential of 0.92 V to drive ORR. Its bifunctional catalytic activities outperform those of the composite catalyst Pt/C + RuO 2 and most bifunctional catalysts reported. The experimental results and density functional theory calculations have demonstrated that the interplay between FeCo NPs and NCNT and the presence of N,P-codoped carbon structure play important roles in increasing the catalytic activities of the NPC/FeCo@NCNT. More impressively, the NPC/FeCo@NCNT can be used as the air-electrode catalyst, improving the performance of rechargeable liquid and flexible all-solid-state zinc-air batteries.