ABSTRACT
Achieving high photocatalytic activity with the lowest possible platinum (Pt) consumption is crucial for reducing the cost of Pt-based cocatalysts and enabling large-scale applications. Bimetallic Ni-Pt cocatalysts exhibit excellent photocatalytic performance and are considered one of the most promising photocatalysts capable of replacing pure Pt for hydrogen evolution reaction (HER). However, the synergistic photocatalytic mechanism between bimetallic Ni-Pt cocatalysts needs to be further investigated. Herein, we deposit highly dispersed Ni-Pt bimetallic cocatalysts on the surface of TiO2 by radiolytic reduction. We study the dynamics of photogenerated charge carriers of the Ni-Pt-comodified TiO2 and propose their underlying electron transfer mechanisms, in which Pt acts as an electron trap, whereas Ni serves as an electron supplier. The synergistic effect is Ni/Pt ratio-dependent and can confer bimetallic Ni-Pt to pure Pt-like photocatalytic activity in HER. The Ni2-Pt1-comodified TiO2 is optimized to be the most cost-effective photocatalyst with robust stability, which exhibits about 40-fold higher performance than bare TiO2.
ABSTRACT
Core-shell structured TiO2@carbon nanowire (TiO2@C NW) hybrids with different carbon shell thicknesses were synthesized by a combination of a hydrothermal reaction and the chemical vapor deposition (CVD) method. Pristine TiO2 NWs with a high aspect ratio were obtained by a hydrothermal reaction and the as-synthesized TiO2 NWs were subsequently employed as the template for carbon shell deposition during the CVD procedure. The obtained TiO2@C NW hybrids have a uniform carbon shell and the thickness of the carbon shell could be precisely designed from 4 nm to 40 nm by controlling the deposition time. With the help of solution and melt blending methods, the TiO2@C NW hybrids were subsequently incorporated into the PVDF matrix to fabricate TiO2@C NWs/PVDF nanocomposites, which exhibit a similar percolative dielectric behavior to that reported in other percolative nanocomposites. Moreover, the dielectric properties of the TiO2@C NWs/PVDF nanocomposites could be accurately adjusted by tuning the carbon shell thickness of the TiO2@C NW hybrids. The highest dielectric constant (2171) of the TiO2@C NWs/PVDF nanocomposites is 80 times larger than those of the pristine TiO2-filled ones at the same filler loading, and 241 times higher than that of the pure PVDF matrix. The enhanced dielectric performance could be attributed to the improved interfacial polarizations of TiO2/C and C/PVDF interfaces. This approach provides an interesting alternative to fabricate high-performance dielectric nanocomposites for practical applications in the electronic industry.
ABSTRACT
A quantitative study of the interphase and interface of graphene nanoplatelets (GNPs)/epoxy and graphene oxide (GO)/epoxy was carried out by combining scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). The interphase regions between GNPs and epoxy matrix were clearly identified by the discrepancy of the plasmon peak positions in the low energy-loss spectra due to different valence electron densities. The spectrum acquisitions were carried out along lines across the interface. An interphase thickness of 13 and 12.5 nm was measured for GNPs/epoxy and GO/epoxy, respectively. The density of the GNPs/epoxy interphase was 2.89% higher than that of the epoxy matrix. However, the density of the GO/epoxy interphase was 1.37% lower than that of the epoxy matrix. The interphase layer thickness measured in this work is in good agreement with the transition layer theory, which proposed an area with modulus linearly varying across a finite width. The results provide an insight into the interphase for carbon-based polymer composites that can help to design the functionalization of nanofillers to improve the composite properties.
ABSTRACT
A rich variety of single crystalline BaTiO3 (BT) nanostructures have been synthesized by two different routes using titanate nanorods and nanotubes as precursors. Free standing, mixed or agglomerated nanotori, solid or hollow nanospheres and nanocubes were obtained. A careful analysis of the shape evolution of the resulting BT nano-objects obtained with both types of precursors and different parameters (precursor composition and shape, temperature, Ba/Ti molar ratio) allowed an improved understanding of the nanostructure formation. The morphogenesis models at play such as Ostwald ripening and the Kirkendall effect have been identified. Other mechanisms hereafter called the self and merging rebuilding processes and a tentative Turing-reaction-diffusion-model are proposed to explain the formation of these obtained nanoparticles.
