Carbon Nanomaterials for Advanced Technology

Carbon nanomaterials are composed of extended networks of bonded carbon atoms. The hybridization of bonded carbon (spⁿ, n = 1, 2, or 3) modulates their properties and structure. As a result, carbon allotropes exist across multiple dimensions, ranging from zero-dimensional fullerenes to one-dimensional carbon nanotubes and nanofibers, two-dimensional graphene, and three-dimensional diamond. Additionally, carbon forms stable bonds with a large and diverse array of elements, enabling the functionalization of carbon nanomaterials and the fabrication of composite materials with tailored physicochemical properties for application.

Carbon nanomaterials possess exceptional mechanical, thermal, and optoelectronic properties, attracting widespread scientific attention aimed at controlling and exploiting these properties [1,2,3]. There has been tremendous research effort and significant advances towards understanding how and why carbon nanomaterials are formed [4,5] and how they may be applied in advanced technologies, with both experimental and theoretical approaches being instrumental in this endeavor [6]. These technologies include (but are not limited to) nanoelectronics, sensing, biomedicine, catalysis, surface coatings, and energy storage [7,8,9,10,11,12].

Carbon nanomaterials have been at the forefront of materials science for decades, remaining an influential field of research. However, key challenges persist in upscaling the production of carbon nanomaterials and in controlling their structure and properties [13,14]. With rapidly developing technological and methodological advances in experimental and theoretical approaches [15,16,17,18], opportunities to tackle long-standing challenges are emerging [19,20,21,22,23]. As a result, unique applications of carbon nanomaterials have been demonstrated, and our fundamental understanding of these remarkable materials continues to expand.

This Special Issue of Inorganics showcases a collection of research articles and reviews highlighting recent advances in the understanding of carbon nanomaterials and their behavior and function in the advanced technological materials field. The studies focus on carbon nanomaterials spanning fullerenes, nanotubes, nanofibers, graphene, and unique composite materials.

Due to their outstanding electronic properties, carbon nanotubes (CNTs) demonstrate potential to be applied in supercapacitors and high-energy-density batteries as part of composite electrodes. Choi et al. conducted an insightful review of how the performance of these energy storage and harvesting devices is influenced by the stability of CNT dispersion within the electrode matrix [24].

Hu et al. conducted a review on the properties of graphene oxide (GO) and chitosan (CS) in the context of biomedical applications. Hydrophilic GO/CS composite material is a promising drug delivery agent due to its large surface area, the favorable physicochemical interactions of GO with target molecules, and CS’s biocompatibility. Their combined properties also afford opportunities in biomedical imaging and tissue engineering [25].

The high mechanical strength of GO has led to its use in ultra-high-performance concrete (UHPC), though it is an expensive material, limiting its widespread use. Lv et al. employed machine learning (ML) via an artificial neural network to develop a predictive model of UHPC’s compressive strength and fluidity, and they used a genetic algorithm to determine optimal UHPC mix ratios to reduce costs [26].

Samoei et al. used graphene as part of a graphene/polyvinylidene fluoride (PVDF) composite film for pressure-sensing applications. They reported a highly sensitive and flexible piezoresistive sensor. The strength of the interaction between graphene and PVDF directly influenced the electrical conductivity, mechanical strength, and thermal stability of the composite film [27].

The properties of graphene composites depend strongly on the alignment of the combined materials. Bident et al. reported that applying a hot rolling treatment to a graphene/copper composite improved its hardness and alignment in the rolling direction, confirmed by Raman spectroscopy and scanning electron microscopy (SEM) [28].

The atomistic molecular dynamics (MD) simulations conducted by Markopoulou et al. provide comprehensive insights into the aqueous self-assembly of diphenylalanine dipeptides in the presence of graphene-based nanosheets. Understanding the interactions of graphene-based nanosheets with biomolecules is crucial for biomedical applications. The authors report findings consistent with experimental results, where peptides rapidly form a more stable layer on pristine graphene, with the functionalized graphene surface being more solvent-accessible [29].

The density functional theory (DFT) calculations carried out by Slanina et al. demonstrate the CO₂ encapsulation capacity of C₈₄ fullerenes, exhibiting similar encapsulation energies (CO₂@C₈₄) to the experimentally realized CO@CO₆₀. This demonstrates the potential for encapsulation and/or sensing applications for a broad range of fullerenes [30].

Han et al. used the high mechanical strength of carbon nanotubes to reinforce and repair delamination areas in carbon fiber-reinforced polymer (CFRP) films. They reported that a pre-coating acetone-based solution with only a 1 m/m% CNT composition, injected via a small drilled hole in the film, is significantly more effective than a solution without CNTs, achieving 77% flexural strength restoration for internal delamination and 100% restoration for edge delamination [31].

Li et al. demonstrated that carbon nanofibers (CNFs) derived from the carbonization of cellulose aerogels exhibit superior microwave adsorption performance when cellulose is emulsified with cyclohexane prior to freeze drying and aerogel formation. The authors found an ultralight, more porous network of CNFs as the cyclohexane disrupted the hydrogen bonding network of the cellulose, with the electromagnetic parameters being tunable with the volume of cyclohexane used [32].

Kim et al. reported an in-situ polymerization technique for homogenously incorporating co-catalysts into the boronated polyacrylonitrile (B-PAN) matrix. The authors presented a novel approach of synthesizing highly graphitized carbon-based nanomaterials integrating aluminum triflate (Al(OTf)₃) and zirconocene dichloride (C₅H₅)₂ZrCl₂ into B-PAN, which lead to a highly ordered and mechanically stable structure [33].

De Luca et al. functionalized carbon nanotubes with carboxylic functional groups and saw improved purification of water contaminated with benzoic acid. However, they reported that this reduced the efficacy of purifying water contaminated with diesel, highlighting the importance of selective functionalization for optimal performance [34].

This Special Issue exemplifies the versatility of carbon nanomaterials and their potential applications in advanced technologies across a broad spectrum of industries. These studies highlight opportunities for future research as the carbon nanomaterials community continues to tackle key challenges in modern science and engineering.

As Guest Editors of this Special Issue, we thank all the authors and peer reviewers who contributed to this unique collection. We also thank Inorganics for providing a platform for this research and to the editorial team at Inorganics.