Carbon Nanotubes Decorated with Platinum Nanoparticles for Field-Emission Application.

In this work, a simple and scalable method was presented to decorate carbon nanotubes (CNTs) with platinum nanoparticles (Pt NPs) by atomic layer deposition (ALD) for field emission (FE) application. The size and distribution of NPs were precisely controlled by adjusting the number of ALD cycles. It was discovered that a higher cycle number of ALD resulted in continuously increased conductivity of the CNTs@Pt nanocomposite. It could be explained by not only the increased loading of Pt NPs but also by the gradually decreased presence of the PtO compound in NPs. As a result, a significant improvement in the FE characteristics of the cold cathode was observed because of the decoration of CNTs with metal NPs. The higher number of ALD cycles resulted in the gradual lowering of the turn-on electric field which reached a minimum value of ∼0.43 V/µm after 100 cycles of ALD.

Fabrication of TiO2 on porous g-C3N4 by ALD for improved solar-driven hydrogen evolution.

Porous graphitic carbon nitride (P-g-C3N4) thin sheets were fabricated by a one-step calcination of a mixture of urea, melamine, and ammonia chloride at 550 °C. P-g-C3N4 showed 48% higher photocatalytic H2 production from methanol aqueous solution than conventional urea-derived graphitic carbon nitride (g-C3N4) because the existence of numerous pores reduces the recombination rate of charge carriers. In order to further enhance the photocatalytic activity, TiO2 was uniformly deposited on P-g-C3N4 by 60-300 cycles of atomic layer deposition (ALD) to form the TiO2@P-g-C3N4 composite. They exhibited much higher photocatalytic hydrogen production rates than both TiO2 and P-g-C3N4. Among all composites, the sample deposited with 180 ALD cycles of TiO2 showed the highest H2 production because of optimal diffusion length for electrons and holes. It also performed better than the sample of g-C3N4 deposited with 180 cycles of TiO2.

Direct growth of ultra-long platinum nanolawns on a semiconductor photocatalyst.

A template- and surfactant-free process, thermally assisted photoreduction, is developed to prepare vertically grown ultra-long Pt nanowires (NWs) (about 30-40 nm in diameter, 5-6 µm in length, and up to 80 NWs/100 µm2 in the wire density) on TiO2 coated substrates, including Si wafers and carbon fibers, with the assistance of the photocatalytic ability and semiconductor characteristics of TiO2. A remarkable aspect ratio of up to 200 can be achieved. TEM analytical results suggest that the Pt NWs are single-crystalline with a preferred 〈111〉 growth direction. The precursor adopted and the heat treatment conditions are crucial for the yield of NWs. The photoelectrons supplied by TiO2 gives rise to the formation of nano-sized Pt nuclei from salt melt or solution. The subsequent growth of NWs is supported by the thermal electrons which also generated from TiO2 during the post thermal treatment. The interactions between the ions and the electrons in the Pt/TiO2 junction are discussed in this study.