In‐Situ Growth of Ultrathin Films of NiFe‐LDHs: Towards a Hierarchical Synthesis of Bamboo‐Like Carbon Nanotubes

Abstract

The synthesis of ultrathin films (UTFs) of NiFe‐LDHs has been achieved by means of an in situ hydrothermal approach, leading to a flat disposition of the LDH crystallites on the substrate, in clear contrast to the most common perpendicular orientation reported to date. Experimental factors like time of synthesis or the nature of the substrate, seem to play a crucial role during the growing process. The 2D morphology of the NiFe‐LDH crystallites was kept after a calcination procedure, leading to a topotactic transformation into mixed‐metal oxide platelets. Hereby, in order to study the catalytic behavior of our samples, a chemical vapor deposition process is explored upon the as‐synthesized films. In presence of a carbon source (ethylene), these films catalyze a preferential low‐temperature (550 °C) growth of bamboo‐like carbon nanotubes, in stark contrast to the different mixture of carbon nanoforms obtained from the bulk samples. This work opens the door for the development of UTFs based on LDHs, which may be of utmost importance in a wide range of potential applications ranging from magnetic storage, catalysis or biomedical applications, to electrochemical batteries, anti‐corrosion and superhydrophobic coatings.

CVD synthesis of carbon spheres using NiFe-LDHs as catalytic precursors: structural, electrochemical and magnetoresistive properties

“…The common broadness of the peaks in the carbon sphere spectra indicates a low range in the structural order. 10,28 According to Bragg's equation, the interlayer spacing d 002 of our CS is 0.356 nm, which agrees with the literature, 30,31 with a low deviation for the ideal d 002 space (0.343 nm) in a graphitic structure (JCPDS-ICDD Card No. ).…”

“…26,28 Moreover, we have demonstrated that the calcinated NiFe-LDH preserves the structural integrity, with the in situ formed FeNi 3 nanoparticles being the main catalytic seeds. 27 Herein, control experiments consisting of the calcination of NiFe-LDHs at 900 1C, supplying H 2 but in the absence of a carbon source, gave rise to a mixture of NiFe 2 O 4 , NiO and FeNi 3 phases as revealed by XRPD (see SI 2.1, ESI †).…”

“…Indeed, a low-temperature CVD process at 550 1C with bulk samples leads to a mixture of carbon nanoforms formed by few-layer graphene, carbon fibers and multi-wall carbon nanotubes (see ref. 28 for further information). According to Li and co-workers, these graphitic structures could evolve towards the formation of carbon spheres for larger times of feeding.…”

“…26 The NiFe-LDH materials have demonstrated their utility as catalysts in the lowtemperature synthesis of several carbon nanoforms, including carbon nano-onions, 27 bamboo-like carbon nanotubes 28 or even graphene -when they are used as precursors for the preparation of hybrid FeNi 3 -graphene nanocomposites. [28][29][30] We have thoroughly characterized the as-obtained spheres by means of XRD, Raman, FT-IR, TG, FESEM, FIB-SEM, HRTEM, DLS, N 2 isotherms, XPS and Electrochemistry. Furthermore, their magneto-transport properties revealed a semiconducting behaviour with an intrinsic large MR of ca.…”

Alkoxide-intercalated NiFe-layered double hydroxides magnetic nanosheets as efficient water oxidation electrocatalysts

“…The processability of LDH into thin films is one of the most rapidly growing areas in this field, as the large-scale correct disposition of the LDH platelets would facilitate their application in energy storage and conversion devices. 20,37 Along this front, we checked the formation of continuous thin films by physical deposition. The first attempts with the water suspensions were unsatisfactory due to an inhomogeneous coverage even after using O 2 -plasma cleaning for the activation of the substrates (Fig.…”