Abstract
Functional 3D materials can be developed from graphene-based hybrids by introducing other nanomaterials, with multi-walled carbon nanotubes (CNTs) being the most studied additive. For large-scale applications, few-layer graphene (FLG)-CNT hybrids are produced by catalytic chemical vapor deposition (c-CVD) starting from a mixture of catalysts (one for FLG and one for CNTs) in the required proportions. Due to the difference in growth kinetics between CNTs and FLG, the composition of such hybrids is not well controlled. In this study, we report the single-step preparation of FLG-CNT hybrid materials by a fixed-bed c-CVD process using a single catalyst with the formula AlxCo1−xFe2O4 (x = 0.025–0.10). Different catalysts (with varying x) were prepared by the citrate–nitrate gel combustion method. Then, c-CVD synthesis was carried out at 650 °C in a horizontal fixed-bed reactor using ethylene as the carbon source. Only FLG was obtained when using CoFe2O4. However, the introduction of small amounts of Al (x < 0.05) induced the simultaneous production of CNTs, leading to the formation of uniform FLG-CNT hybrids. For catalysts with higher Al content (e.g., AlCoFeO4), CNTs were selectively produced. Thus, we observed the existence of a narrow Al-doping window, where CNTs and FLG can be obtained simultaneously. Our results can pave the way to developing high-yield single catalyst-based CVD synthesis of FLG-CNT hybrid materials.
Highlights
Graphene is an extremely versatile 2D material for nanotechnology applications due to its excellent physical, chemical, and mechanical properties [1,2,3]
We show that doping cobalt ferrite with 0.025 mol of Al leads to the formation of a uniform few-layer graphene (FLG)-carbon nanotubes (CNTs) hybrid
Our previous work on FLG growth from ferrite catalysts has shown that the thickness of the graphene obtained depends critically on the grain size of the ferrite [25], and in the case of the hybrid, it is well known that the diameter and number of walls in CNTs are intimately related to the grain size of the catalyst
Summary
Graphene is an extremely versatile 2D material for nanotechnology applications due to its excellent physical, chemical, and mechanical properties [1,2,3]. Due to their chemical similarity, there is a strong interaction between CNTs and graphene. Such interaction is highly favorable for synergy in applications, it means that properties of the hybrid depend significantly on the preparation method, including the assembling technique used. For large-scale applications, the development of one-step production methods to achieve large volumes of hybrid material with controlled morphology and structure is highly desirable. A precise control of the hybrid composition in large-scale production of these materials is still far from being optimized
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