Chemical Reviews | A Comprehensive Review on the Synthesis, Properties, and Applications of Filled Carbon Nanotubes

This article systematically summarizes recent advances in carbon nanotube filling technologies, covering various fill materials and application directions, providing comprehensive guidance for the design of novel functionalized nanocomposites.

 

Literature Overview

The article, 'A Comprehensive Review on Filled Carbon Nanotubes: Synthesis, Properties and Applications,' published in the journal Chemical Reviews, reviews and summarizes the synthesis strategies, physicochemical property modulation, and applications in multiple cutting-edge fields of carbon nanotubes (CNTs) as nanoscale containers filled with different materials. The paper systematically categorizes encapsulated materials, including inorganic substances, organic molecules, liquids, and gases, and thoroughly explores how nanoconfinement effects influence the structure and properties of these fillers. Furthermore, the authors highlight the potential applications of filled carbon nanotubes in biomedicine, catalysis, energy storage, gas separation, sensing, and nanoelectronics. This comprehensive review not only critically evaluates existing technologies but also identifies future research directions and challenges in the field.

Background Knowledge

Carbon nanotubes have long been regarded as ideal nanoreactors or carriers due to their unique hollow tubular structure and excellent electrical and mechanical properties. In recent years, encapsulating functional materials inside carbon nanotubes to form 'filled' composites has become a key strategy for tuning material properties. Such confined environments can significantly alter the crystal structure, electronic states, and chemical reactivity of the fillers, enabling novel quantum phenomena and catalytic activities unattainable in bulk materials. Current research focuses on precisely controlling the filling process, improving filling efficiency, and understanding the nature of confinement effects. Although various filling methods—such as in situ growth, capillary action, and electrochemical deposition—have been developed, efficiently encapsulating organic and biomolecules remains challenging, particularly in preserving their structural integrity and functional activity. Moreover, limitations in characterization techniques hinder atomic-level analysis of filled structures. Therefore, developing more efficient filling strategies and advanced characterization methods is crucial for advancing this field. This review comprehensively integrates recent research achievements, providing a theoretical foundation and practical guidelines for the future design of functional materials.

 

 

Research Methods and Experiments

This paper employs a literature review methodology to systematically summarize recent advances in filled carbon nanotube research. The authors first introduce the basic structure of carbon nanotubes and filling mechanisms, including two main strategies—in situ and ex situ filling—and provide a detailed comparison of the scope, advantages, and limitations of different methods. Subsequently, the article categorically discusses various filler materials, such as metals, alloys, salts, oxides, carbon allotropes (e.g., fullerenes), organic molecules, polymers, drugs, biomolecules, liquids, and gases, integrating experimental findings with theoretical simulations to reveal how confinement effects modulate the structure and properties of these materials. Theoretical methods such as density functional theory (DFT), quantum Monte Carlo (QMC), molecular dynamics (MD), and finite element method (FEM) are also systematically reviewed to explain energy changes and interaction mechanisms during the filling process.

Key Conclusions and Perspectives

• The hollow structure of carbon nanotubes enables them to serve as nanoscale containers, effectively encapsulating various functional materials and endowing composite systems with novel optical, electronic, catalytic, and mechanical properties
• Confinement effects significantly alter the physicochemical properties of fillers, including band structure, magnetism, phase stability, and chemical reaction pathways, even inducing quantum phenomena absent in bulk materials
• Filling methods can be categorized into in situ and ex situ approaches: the former achieves filling during synthesis, while the latter relies on capillary action, vapor diffusion, solution diffusion, or electrochemical deposition
• Theoretical simulation tools such as DFT and MD play a crucial role in understanding filling mechanisms, predicting stable structures and electronic properties, and guiding experimental design
• Filled carbon nanotubes show broad application prospects in biomedicine (e.g., cancer therapy, bioimaging), energy storage (lithium/sodium/potassium-ion batteries, supercapacitors), gas storage and separation (hydrogen, methane, CO₂), catalysis (thermal, electro-, photo-, and magneto-catalysis), sensors, and nanoelectronics
• Despite significant progress, challenges remain in achieving uniform filling, high filling ratios, selective encapsulation, and long-term stability

Research Significance and Prospects

This review provides researchers with a systematic knowledge framework on filled carbon nanotubes, summarizing existing achievements and identifying future research directions, such as developing more efficient filling strategies, achieving multi-component cooperative encapsulation, and exploring dynamically responsive filling systems. Additionally, combining in situ characterization techniques with multiscale simulations will deepen the understanding of confined chemistry.

Looking ahead, filled carbon nanotubes are expected to become an ideal platform for constructing intelligent responsive materials, single-molecule devices, and high-efficiency catalysts. In biomedicine, encapsulating drugs or contrast agents could enable targeted therapy and theranostic integration. In the energy sector, their high specific surface area and confinement effects could significantly enhance ion diffusion kinetics and cycling stability of electrode materials.

 

 

Conclusion

This article comprehensively reviews the synthesis methods, physicochemical property modulation, and applications of filled carbon nanotubes in various high-tech fields. Carbon nanotubes, serving as nanoscale confined spaces, can significantly alter the structure and electronic characteristics of fillers, generating novel functionalities. Through in situ or ex situ methods, numerous inorganic, organic, and biomolecules have been successfully encapsulated, showing great potential in catalysis, energy, sensing, and biomedicine. Advances in theoretical simulations and advanced characterization techniques have further deepened the understanding of confinement effects. However, achieving high-efficiency, high-selectivity, and stable filling remains a current challenge. Future research should focus on developing controllable filling strategies, exploring multifunctional composite systems, and promoting their integration into practical devices. This review provides an important reference for designing next-generation functional nanomaterials, offering broad scientific value and application prospects.

 

Stefania Sandoval, Gil Gonçalves, Jorge Pérez Barrio, Marianna V Kharlamova, and Gerard Tobías-Rossell. A Comprehensive Review on Filled Carbon Nanotubes: Synthesis, Properties and Applications. Chemical Reviews.