We present the design of a concentric tube (CT) reactor for roll-to-roll chemical vapor deposition (CVD) on flexible substrates, and its application to continuous production of graphene on copper foil. In the CTCVD reactor, the thin foil substrate is helically wrapped around the inner tube, and translates through the gap between the concentric tubes. We use a bench-scale prototype machine to synthesize graphene on copper substrates at translation speeds varying from 25 mm/min to 500 mm/min, and investigate the influence of process parameters on the uniformity and coverage of graphene on a continuously moving foil. At lower speeds, high-quality monolayer graphene is formed; at higher speeds, rapid nucleation of small graphene domains is observed, yet coalescence is prevented by the limited residence time in the CTCVD system. We show that a smooth isothermal transition between the reducing and carbon-containing atmospheres, enabled by injection of the carbon feedstock via radial holes in the inner tube, is essential to high-quality roll-to-roll graphene CVD. We discuss how the foil quality and microstructure limit the uniformity of graphene over macroscopic dimensions. We conclude by discussing means of scaling and reconfiguring the CTCVD design based on general requirements for 2-D materials manufacturing.

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We used polyisoprene-block-ethyleneoxide copolymers as structure-directing agents to synthesise well-ordered and highly-crystalline mesoporous WO 3 architectures that possess improved photocatalytic properties due to enhanced dye-adsorption in absence of diffusion limitation.As a green technology, semiconductor photocatalysis has attracted increasing interest driven by the search for new energy sources during the past few decades.1 The performance of the photocatalysts strongly depends on their crystal structure and morphology.1,2 It is widely recognized that high crystallinity and a continuous network architecture with controlled pore sizes that facilitate molecular access to high surface areas are highly desired for maximizing their photocatalytic performance. 3,4 This has recently stimulated intensive research in designing mesoporous metal oxides, such as TiO 2 , Nb 2 O 5 , and ZrO 2 . 5 The major drawback of these attempts is that the oxide structures often contain a significant amount of undesired amorphous content, which facilitates the recombination of electrons and holes, thereby limiting the catalytic efficiency.2 The crystallinity can be improved by annealing at high temperatures, upon which, however, the ordered structure typically collapses. Hence, synthesising well-ordered mesoporous structures with high crystallinity still remains a major challenge. 6 Recently, we used polyisoprene-block-ethyleneoxide (PI-b-PEO) copolymers as structure-directing agents to synthesise TiO 2 with controlled mesoporous structures. 7,8 The large interaction parameter between the PI and PEO blocks and the high degree of polymerization allows the rapid formation of structures with long-range order. In addition, the PI-b-PEO morphology has relatively large pore sizes, which facilitate the effective infiltration of functional materials. The resulting TiO 2 exhibited excellent performance in dye-sensitized solar cells. Although TiO 2 is currently the most studied semiconductor photocatalyst, its wide band gap (3.2 eV) limits TiO 2 to a small ultraviolet fraction of solar energy. 9 In contrast, tungsten trioxide (WO 3 ) has a narrower band gap (2.4-2.8 eV) that enables harvesting visible light.10 Only a few studies have so far been devoted to the synthesis of porous WO 3 , i.e. using PMMA spheres 11 and by anodization of tungsten foil. 12 Despite yielding only macroporous and weakly-ordered structures these studies still demonstrated enhanced photocatalytic properties compared with their dense counterparts. It is therefore likely that improving the pore structure and crystallinity will maximise the photocatalytic performance of WO 3 . Herein, we demonstrate the synthesis of highly-crystalline mesoporous WO 3 with well-ordered pore architectures using a sol-gel process and PI-b-PEO copolymers as structure-directing agents. We investigated the effect of polymer-to-WO 3 weight ratio on the morphology and tested the photocatalytic performance for the degradation of methylene blue under visible light.In a typical synthesis, 45 mg ...

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SummaryThe catalytic chemical vapour deposition (c-CVD) technique was applied in the synthesis of vertically aligned arrays of nitrogen-doped carbon nanotubes (N-CNTs). A mixture of toluene (main carbon source), pyrazine (1,4-diazine, nitrogen source) and ferrocene (catalyst precursor) was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N-CNT arrays, we investigated the influence of key parameters, i.e., growth temperature (660, 760 and 860 °C), composition of the feedstock and time of growth, on morphology and properties of N-CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N-CNTs down to about one twentieth compared to the growth rate of multi-wall CNTs (MWCNTs). As revealed by electron microscopy studies (SEM, TEM), the individual N-CNTs (half as thick as MWCNTs) grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e., 5 × 108 nanotubes per mm2 (100 times more than for MWCNTs grown in the absence of nitrogen precursor). In turn, the internal crystallographic order of the N-CNTs was found to be of a ‘bamboo’-like or ‘membrane’-like (multi-compartmental structure) morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt %, was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT-IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp2-hybridisation of graphene C-atoms. As studied by XRD, the temperature and the [pyrazine]/[ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N-CNTs into a ‘mixed base-and-tip’ (primarily of the base-type) type as compared to the purely ‘base’-type for undoped MWCNTs.