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[Display omitted] • The single-walled carbon nanotubes and multi-walled carbon nanotubes were grown on the same ZrO 2 /Fe catalyst by adjusting the carbon sources. • A combination of experimental data and density functional theory simulations was able to reveal the underlying activity competition mechanism between hyperactive catalysts and hypoactive supports. Activity competition commonly exist when using multiple catalyst particles for growing carbon nanotubes (CNTs), and the diverse catalysts can compete with the carbon source and affect the growth kinetics and morphology of the nanotubes. However, the existed problem is that whether the support materials themselves also can engage in activity competition with the catalysts, and how this may impact the growth of CNTs. Here, we investigated the influence of hypoactive ZrO 2 support material and hyperactive ZrO 2 /Fe catalysts on the growth of CNTs, and the activity competition relationship between the support and the catalysts. ZrO 2 /Fe catalysts were prepared via a facile hydrothermal method, and employed both CH 4 and C 2 H 5 OH as carbon sources for growing CNTs. It is interesting that single-walled carbon nanotubes (SWCNTs) were grown by utilizing CH 4 as carbon source, and multi-walled carbon nanotubes (MWCNTs) were synthesized for the use of C 2 H 5 OH as carbon source. A combination of experimental data and density functional theory simulations was able to reveal the underlying activity competition mechanism between hyperactive catalysts and hypoactive supports. It would provide new insight into the growth mechanisms of CNTs, and provide new ideas for the rational design and controlled growth of CNTs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porous Fe/FeO/Fe 2 O 3 nanorods anchored on RGO form crosslinked FFORGO composite. • Coupling high loss and impedance match by adjusting dielectric and magnetic components. • Achieving multiple absorption mechanism and good EM wave absorption property. Electromagnetic wave absorbers composed of reduced graphene oxide (RGO) and magnetic nanoparticles integrates dielectric and magnetic loss features, which is extremely desirable for enhancing electromagnetic wave absorption ability. Here, porous Fe/FeO/Fe 2 O 3 nanorods/RGO composites (FFORGO) are synthesized via anchoring FeO(OH) nanorods on graphene oxide (GO) through dopamine polymerization followed by thermal reduction treatment. The porous Fe/FeO/Fe 2 O 3 nanorods are anchored on RGO, and crosslinked structure formed in FFORGO composites when the GO addition is higher than 5 mg‧ml−1. The abundant active sites (e.g., functional groups, dangling bonds, and lattice defects), the numerous heterointerfaces (among Fe, FeO, Fe 2 O 3 and RGO) and crosslinked structure trigger multiple dipole polarization, interface polarization and enhanced conductive loss. The EM wave absorption property is optimized by tuning the GO addition. FORGO4 with filler loading of 30 wt% achieves the maximal reflection loss of −24.1 dB at a thickness of 1.9 mm and the effective bandwidth below −10 dB of 3.01 GHz with a thickness of 2.2 mm, owing to the proper ratio of Fe/FeO/Fe 2 O 3 nanorods/RGO and synergistic effect between dielectric loss (dipole polarization, interface polarization, conductive loss) and magnetic loss (eddy current loss and exchange resonance). With the filler loading of 35 wt%, the maximal reflection loss of FFORGO4 is −50.7 dB at a thickness of 1.7 mm and the effective bandwidth reaches to 3.74 GHz at a thickness of 1.8 mm. [ABSTRACT FROM AUTHOR]