Despite three decades of intense research efforts, the most fundamental question “why do carbon nanotubes grow?” remains unanswered. In fact, carbon nanotubes (CNTs) should not grow since the encapsulation of a catalyst with graphitic carbon is energetically more favorable than CNT growth in every aspect. Here, we answer this question using a theoretical model based on extensive first-principles and molecular dynamics calculations. We reveal a historically overlooked yet fundamental aspect of the CNT-catalyst interface, viz., that the interfacial energy of the CNT–catalyst edge is contact angle-dependent. The contact angle increases via graphitic cap lift-off, drastically decreasing the interfacial formation energy by up to 6–9 eV/nm, overcoming van der Waals cap-catalyst adhesion, and driving CNT growth. Mapping this remarkable and simple interplay allows us to understand, for the first time, why CNTs grow.

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The controlled growth of metallic single-wall carbon nanotubes (m-SWCNTs) is very important for the fabrication of high-performance interconnecting wires, transparent conductive electrodes, light and conductive fibers, etc. However, it has been extremely difficult to synthesize m-SWCNTs due to their lower abundance and higher chemical reactivity than semiconducting SWCNTs (s-SWCNTs). Here, we report the kinetically controlled growth of m-SWCNTs by manipulating their binding energy with the catalyst and promoting their growth rate. We prepared CoRe 4 nanoparticles with a hexagonal close-packed structure and an average size of ∼2.3 nm, which have a lower binding energy with m-SWCNTs than with s-SWCNTs. The selective growth of m-SWCNTs from the CoRe 4 catalyst was achieved by using a low concentration of carbon source feed at a relative low temperature of 760 °C. The m-SWCNTs had a narrow diameter distribution of 1.1 ± 0.3 nm, and their content was over 80%.

The conversion of solar power to hydrogen (H 2 ) energy efficiently encounters some obstacles due to the lack of superior catalysts and efficient catalytic approaches. Herein, three-dimensional/ two-dimensional (3D/2D) CuS/g-C 3 N 4 photothermal catalysts were obtained via an easy, one-step hydrothermal method after pyrolysis. The favorable heterojunction interface for H 2 production was constructed by snowflake-like CuS embedded in the graphite carbon nitride (g-C 3 N 4 ) nanosheets, leading to the acceleration of charge transfer and separation, decrease of charge transfer distance, and perfect realization of photothermal effects (PTEs) induced by nearinfrared (NIR) light. The 3D/2D CuS/g-C 3 N 4 catalyst presents a topmost H 2 -production rate (1422 μmol h −1 g −1 ) under dual wavelength (420 + 850 nm) and a moderate H 2 -production rate under 420 nm, which are 12-fold and 9-fold higher than pure g-C 3 N 4 , respectively, owing to a strong action from PTEs induced by NIR. The feasible NIR-enhanced photothermal catalysis is expected to apply in multifarious heat-assisted photocatalysis processes by designing multifunctional composites with super PTE and photocatalytic capacity.

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