Stable colloidal Co–Pd nanocatalysts for carbon nanotube growth

Abstract

The standard preparation method for catalysts for surfacebound growth of carbon nanotubes (CNT) is to sputter or evaporate the metal catalyst (Fe, Co, and Ni) onto the surface. A lower cost method for large areas is to use liquid delivery. Colloids have the advantage of containing the catalyst in nanocluster form. Our previously developed colloidal catalysts were successful for growth but had limited shelf-life due to oxidation and coagulation. Here, we develop an air-stable colloidal catalyst with long shelf-life of many months to years.

Confined palladium colloids in mesoporous frameworks for carbon nanotube growth

“…3 clearly show excellent coverage of the surface of the thin film, there being no significant surface defects or cracks, after the CNT growth step, with a CNT forest present at the surface of the composite material after PECVD treatment. In comparison to our previous results, obtained using pure Pd nanoparticles to grow CNT forests in the absence of a mesoporous thin film [25][26][27][28], the CNTs grown herein show a smaller average diameter (20.6 ± 6.8 nm in [25] versus 10.7 ± 5.7 nm presently). This is a clear indication that the porous network of the titania film is not only able to efficiently adsorb the Pd nanoparticles, but that it also prevents their agglomeration at high temperature during the CNT growth process.…”

Co-Catalytic Solid-State Reduction Applied to Carbon Nanotube Growth

“…The use of cocatalysts and multielemental catalyst composition to tune reactivity and selectivity is an approach well-known in heterogeneous catalysis. − Rational catalyst design, however, requires a detailed understanding of what causes the advantageous effect, and to date many of the actual mechanisms remain unknown. For the catalytic chemical vapor deposition (CVD) of carbon nanotubes (CNTs), single-element Fe, Co, and Ni remain the most commonly used catalyst materials, but a number of bimetallic cocatalyst systems have been reported to enhance chiral selectivity, to narrow the diameter distribution, and to enhance yield and allow lower growth temperatures (e.g., CoMo, − FeRu, NiFe, , CoMn, , CoCr, FeCu, CoW, , CoPd, CoTi, CoMn, and FeMo − ). However, the suggested cocatalytic interactions and mechansims are highly speculative and often rather contradictory in current literature.…”

Switchable Surfactant-Assisted Carbon Nanotube Coatings: Innovation through pH Shift

“…Concerning the controlled preparation of CNT films or coatings on conventional devices, there are many examples in the literature using macroscopic or even patterned substrates. The two main techniques, which have hitherto been used are chemical vapor deposition (CVD) along with its variant plasmaenhanced chemical vapor deposition (PECVD) (Franklin and Dai, 2000;Berenguer-Murcia et al, 2009;Kumar and Ando, 2010) and electrophoretic deposition (EPD) (Gao et al, 2001;Boccaccini et al, 2006;Padmarj et al, 2009). While CVD would in principle be best suited for its adaptation in microdevices, there are several drawbacks that should be considered: (i) concerning the distribution of the catalytically active phase, achieving a homogenous distribution may not be straightforward in geometries more complex than flat (patterned or unpatterned) surfaces, which in turn raises the issue of how CNTs will grow in complex architectures due to inhomogeneous temperature and/or flow distribution and (ii) the range of temperatures used in the CNT preparation (in the range between 350 and 800°C) may affect the integrity of the reactor material, making it unsuitable for polymeric materials.…”