Researchers introduced a novel single-step method for synthesizing nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) decorated with iron (Fe) and copper (Cu) nanoparticles directly on copper foil substrates.
Using aerosol-assisted chemical vapor deposition (AACVD), they produced hybrid nanomaterials that combine the properties of carbon nanotubes (CNTs) with the advantages of metal nanoparticles.
A recent study published in the journal Nanotechnology detailed the synthesis and characterization of these materials, highlighting their structural and electrochemical properties and potential applications in electronics and energy storage.
The Role of Carbon Nanomaterials
Carbon nanomaterials, primarily CNTs, have gained significant attention due to their excellent electrical, mechanical, and thermal properties. These features make them useful in electronics, energy storage, and composite materials.
Incorporating nitrogen into the CNT structure further enhances their electrochemical performance, resulting in nitrogen-doped CNTs (N-CNTs) that perform even better in devices like supercapacitors and batteries. However, optimizing synthesis conditions remains a key challenge for achieving high-quality N-CNTs with desirable structural and functional characteristics.
Synthesis of Nitrogen-Doped Carbon Nanotubes
Researchers focused on synthesizing N-MWCNTs on copper foil substrates using a single-step AACVD method with a precursor mixture of benzylamine (C7H9N) and ferrocene (C10H10Fe). The experimental setup included a quartz tube reactor heated by a horizontal tubular furnace, with 40 cm-long copper foils serving as substrates.
The synthesis was conducted at five temperatures (750°C, 800°C, 850°C, 900°C, and 950°C) for 80 minutes under a controlled argon-hydrogen gas flow (1 L/min). This variation allowed the study of how heat affected the morphology and properties of the N-MWCNTs.
After synthesis, the samples were characterized using techniques like scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and energy-dispersive spectroscopy (EDS). Additionally, ImageJ software was used to analyze nanoparticle sizes, while electrochemical impedance spectroscopy (EIS) was used to evaluate capacitive behavior.
Structural and Compositional Outcomes
Temperature significantly influenced the morphology, composition, and electrochemical behavior of the N-MWCNTs grown on copper foils. At 750 °C, the material mainly consisted of multilayer graphene islands and Fe- and Cu-based nanoparticles encapsulated in graphitic carbon, with a few CNTs also present, detached from the copper substrate.
SEM images showed thin tubular structures with an average CNT diameter of approximately 8 nm and NP sizes of around 14 nm. EDS analysis indicated atomic concentrations of carbon (C, 83.82%), Fe (10.94%), Cu (0.92%), and oxygen (O, 4.32%).
At 800 °C, the growth shifted toward bamboo-shaped N-MWCNT bundles, with diameters ranging from 5 nm to 40 nm and a high density of Fe and Cu nanoparticles. EDS showed optimal elemental composition with C (92.08%), Fe (5.59%), Cu (0.20%), and O (2.13%), suggesting efficient benzylamine decomposition and enhanced nitrogen incorporation. TEM confirmed that two distinct types of CNTs were produced: thicker bamboo-shaped N-MWCNTs decorated with Fe nanoparticles and thinner CNTs likely catalyzed by Cu nanoparticles.
At 850-950 °C synthesis temperatures, larger tubular-defective fiber-type carbonaceous aggregates (~500 nm) were produced with fewer CNTs. EDS indicated fluctuating elemental concentrations, with sample 950 exhibiting the highest Cu content (5.74%) and the lowest Fe content (2.88%).
Raman spectroscopy confirmed the graphitic nature of the synthesized materials, showing clear D, G, and 2D bands. The ID/IG ratio ranged from 0.79 to 0.88, indicating moderate structural disorder, while the G-band downshift suggested improved graphitization.
EIS indicated that N-MWCNTs synthesized at 800 °C exhibited promising capacitive behavior, with a charge transfer resistance (Rct) of 1884 Ω and a double-layer capacitance (Cdl) of 1.07×10-1 Fcm-2, making them suitable for energy storage applications.
By contrast, samples synthesized at 850 °C and 950 °C showed diffusion limitations and significantly lower capacitance values, showing that 800 °C provided the most favorable balance of structural order and electrochemical performance.
Applications of N-Doped Carbon Nanotubes
The synthesized hybrid materials have significant potential for use in energy storage devices, primarily supercapacitors. The N-MWCNTs synthesized at 800 °C demonstrated low charge-transfer resistance and high double-layer capacitance, indicating excellent charge storage ability. Their nitrogen doping and decoration with metal nanoparticles improved electrochemical performance, making them suitable for flexible electronics.
A key advantage of this method is the direct growth of N-MWCNTs on copper substrates, which eliminates the need for binders or current collectors and reduces interfacial resistance. This simplification could enable the creation of lightweight, efficient, and stable energy devices.
Beyond supercapacitors, these N-MWCNTs could also enhance lithium-ion batteries and other fast charge–discharge systems. Their ability to fine-tune their structure and metal nanoparticle content provides opportunities for catalysis and sensing applications.
Conclusion and Future Directions
This research successfully demonstrated the single-step AACVD synthesis of N-MWCNTs on copper substrates, highlighting the strong influence of synthesis temperature on the morphology, composition, and electrochemical properties of the resulting nanomaterials. The optimal temperature of 800 °C produced bamboo-shaped N-MWCNTs decorated with Fe and Cu nanoparticles, showing high carbon content and excellent capacitive behavior.
Future work should focus not only on fine-tuning synthesis parameters and exploring alternative precursor combinations but also on testing different substrate materials and deposition conditions, which could yield a wider variety of hybrid nanomaterials with tailored properties.
Investigating substrate modifications and hybrid material designs may develop electrodes with improved electrochemical behavior and applications beyond energy storage, such as sensing and catalysis.
Overall, this study offers key insights into the controlled growth of hybrid carbon nanomaterials and paves the way for innovative applications in a broader field.
Journal Reference
Padilla-Teniente, B, V., & et al. (2025). Copper foils as substrates for growing nitrogen-doped carbon nanotubes. Nanotechnology, 36, 365601. DOI: 10.1088/1361-6528/ae0042, https://iopscience.iop.org/article/10.1088/1361-6528/ae0042
