The era of carbon allotropes

Exploring Approaches for the Synthesis of Few-Layered Graphdiyne

Graphdiyne (GDY) is an emerging carbon allotrope in the graphyne (GY) family, demonstrating extensive potential applications in the fields of electronic devices, catalysis, electrochemical energy storage, and nonlinear optics. Synthesis of few-layered GDY is especially important for both electronic applications and structural characterization. This work critically summarizes the state-of-art of GDY and focuses on exploring approaches for few-layered GDY synthesis. The obstacles and challenges of GDY synthesis are also analyzed in detail. Recently developed synthetic methods are discussed such as i) the copper substrate-based method, ii) the chemical vapor deposition (CVD) method, iii) the interfacial construction method, and iv) the graphene-templated method. Throughout the discussion, the superiorities and limitations of different methods are analyzed comprehensively. These synthetic methods have provided considerable inspiration approaching synthesis of few-layered or single-layered GDY film. The work concludes with a perspective on promising research directions and remaining barriers for layer-controlled and morphology-controlled synthesis of GDY with higher crystalline quality.

On-Surface Activation of Trimethylsilyl-Terminated Alkynes on Coinage Metal Surfaces

The controlled attachment of protecting groups combined with the ability to selectively abstract them is central to organic synthesis. The trimethylsilyl (TMS) functional group is a popular protecting group in solution. However, insights on its activation behavior under ultra-high vacuum (UHV) and surface-confined conditions are scarce. Here we investigate a series of TMS-protected alkyne precursors via scanning tunneling microscopy (STM) regarding their compatibility with organic molecular beam epitaxy (OMBE) and their potential deprotection on various coinage metal surfaces. After in-situ evaporation on the substrates held in UHV at room temperature, we find that all molecules arrived and adsorbed as intact units forming ordered supramolecular aggregates stabilized by non-covalent interactions. Thus, TMS-functionalized alkyne precursors with weights up to 1100 atomic mass units are stable against OMBE evaporation in UHV. Furthermore, the TMS activation through thermal annealing is investigated with STM and X-ray photoelectron spectroscopy (XPS). We observe that deprotection starts to occur between 400 K and 500 K on the copper and gold surfaces, respectively. In contrast, on silver surfaces, the TMS-alkyne bond remains stable up to temperatures where molecular desorption sets in (≈600 K). Hence, TMS functional groups can be utilized as leaving groups on copper and gold surfaces while they serve as protecting groups on silver surfaces.

The Consequences of Twisting Nanocarbons: Lessons from Tethered Twisted Acenes

The properties of polycyclic aromatic hydrocarbons are determined by their size, shape, and functional groups. Equally important is their curvature, since deviation from planarity can affect their optical, electronic, and magnetic properties and also induce chirality. Acenes, which can be viewed as one-dimensional nanocarbons, are often twisted out of planarity. Although twisting is expected to affect the above-mentioned properties, it is often overlooked. This Account focuses on helically locked twistacenes (twisted acenes) having different twist angles and the effect of twisting on their electronic and optical properties. Various synthetic approaches to inducing backbone twist in acenes are discussed, with a focus on the introduction of a diagonal tether across the core, as this minimizes confounding substituent effects. Using such tethered acenes as our model, we then discuss the effects of twisting the aromatic core on twistacene properties. Electronic properties. Increasing the degree of twist only slightly affects the HOMO and LUMO energy levels. Twisting leads to a small increase in the HOMO level and a decrease in the LUMO level, which produces an overall decrease in the HOMO-LUMO gap. Optical properties. As the degree of twist increases, a slight bathochromic shift is observed in the absorption spectra, in accordance with the decrease in the HOMO-LUMO gap. The fluorescence quantum efficiency and the fluorescence lifetime also decrease. This is likely to be related to an increasing rate of intersystem crossing, which arises from increased spin-orbit coupling. In addition, computational studies indicate that the S⁰-T¹ energy gap decreases with increasing twist. Chiroptical properties. Increased twisting results in a larger Cotton effect and anisotropy factor, with the anisotropy factors of Ant-Cn being higher than those of longer helicenes. The parallel orientation of electric and magnetic transition dipole moments in twistacenes underlies this behavior and renders them as excellent chiroptical materials. The same trend is observed for the radical cations of twistacenes, which absorb in the NIR spectral region. Conjugation and delocalization. Twisting the anthracene radical cation up to 40° (13° per benzene ring) does not significantly affect spin delocalization, with the EPR spectra of twistacene radical cations showing that only slight localization occurs. This is in line with computational studies, which show only a small decrease in π-overlap for large acene twist. Overall, modifying the length of the tether in diagonally tethered acenes allows chemists to control core twist and to induce chirality. Twisting affects key optical, electronic, and chiroptical properties of acenes. Consequently, controlling the twist angle can improve the future design of nanocarbons with desired properties.

Chemically Cross-Linked Carbon Nanotube Films Engineered to Control Neuronal Signaling

In recent years, the use of free-standing carbon nanotube (CNT) films for neural tissue engineering has attracted tremendous attention. CNT films show large surface area and high electrical conductivity that combined with flexibility and biocompatibility may promote neuron growth and differentiation while stimulating neural activity. In addition, adhesion, survival, and growth of neurons can be modulated through chemical modification of CNTs. Axonal and synaptic signaling can also be positively tuned by these materials. Here we describe the ability of free-standing CNT films to influence neuronal activity. We demonstrate that the degree of cross-linking between the CNTs has a strong impact on the electrical conductivity of the substrate, which, in turn, regulates neural circuit outputs.

Physical properties of RIr3 (R = Gd, Tb, Ho) compounds with coexisting polymorphic phases

The binary compounds GdIr₃, TbIr₃ and HoIr₃ are synthesized successfully and found to form with macroscopic co-existence of two polymorphic phases: AuBe₅ (C15b) and AuCu₃-type. The dc magnetization and heat capacity studies confirm that the C15b phase orders ferromagnetically, whereas the AuCu₃ phase remains paramagnetic down to 2 K. The frequency dependent ac-susceptibility data, time dependent magnetic relaxation behavior and magnetic memory effect studies suggest that TbIr₃ and HoIr₃ are cannonical spin-glass systems, but no glassy feature could be found in GdIr₃. The critical behavior of all three compounds has been investigated using the magnetization and heat capacity measurements around the transition temperature (T_C). The critical exponents α, β, γ and δ have been estimated using different techniques such as the Arrott-Noakes plot, Kouvel-Fisher plot and critical isotherm as well as analysis of specific heat data and study of magnetocaloric effect. The critical analysis study identifies the type of universal magnetic class in which the three compounds belong.

Synthesis of radiaannulene oligomers to model the elusive carbon allotrope 6,6,12-graphyne

Graphyne allotropes of carbon are fascinating materials, and their electronic properties are predicted to rival those of the “wonder material” graphene. One allotrope of graphyne, having rectangular symmetry rather than hexagonal, stands out as particularly attractive, namely 6,6,12-graphyne. It is currently an insurmountable challenge, however, to design and execute a synthesis of this material. Herein, we present synthesis and electronic properties of molecules that serve as model compounds. These oligomers, so-called radiaannulenes, are prepared by iterative acetylenic coupling reactions. Systematic optical and redox studies indicate the effective conjugation length of the radiaannulene oligomers is nearly met by the length of the trimer. The HOMO-LUMO gap suggested by the series of oligomers is still, however, higher than that expected for 6,6,12-graphyne from theory, which predicts two nonequivalent distorted Dirac cones (no band gap). Thus, the radiaannulene oligomers present a suitable length in one dimension of a sheet, but should be expanded in the second dimension to provide a unique representation of 6,6,12-graphyne.

6,6,12-graphyne is an intriguing synthetic allotrope of carbon that is predicted to have unique electronic properties but has not been successfully synthesized. Here, the authors prepare a series of radiaannulene oligomers that can be regarded as large segments of this elusive graphyne allotrope.

Oxidation stability of confined linear carbon chains, carbon nanotubes, and graphene nanoribbons as 1D nanocarbons

Three typical one-dimensional (1D)/quasi-1D nanocarbons, linear carbon chains, carbon nanotubes, and graphene nanoribbons have been proved to grow inside single-walled carbon nanotubes. This gives rise to three types of hybrid materials whose behaviour and properties compared among each other are far from being understood. After proving the successful synthesis of these nanostructured materials in recently published work, we have now been able to study their oxidation stability systematically by using resonance Raman spectroscopy. Surprisingly, the linear carbon chains, which have been theoretically predicted to be very unstable, are actually thermally stable up to 500 °C, assisted by the protection of the carbon nanotube hosts. Besides, longer linear carbon chains inside narrower CNTs are more stable than the shorter ones inside larger tubes, suggesting that the thermal stability not only depends on the length of linear carbon chains alone, but it is correlated with the confinement of the host tubes in a more complicated manner. In addition, graphene nanoribbons overall appear to be the most stable confined structures. On the other hand, peculiarities like the higher stability of the (6,5) CNT compared to that of its (6,4) counterpart allow this study to provide a solid platform for further studies on the application of these 1D nanocarbons (including true 1D linear carbon chains) under ambient conditions.

Bidirectional charge-transfer behavior in carbon-based hybrid nanomaterials

In recent years there has been a growing interest in finding materials revealing bidirectional charge-transfer characteristics, that is, materials behaving as an electron donor or an acceptor in the presence of redox and photoactive addends, for optoelectronic applications. In this respect, carbon-based nanostructures, such as graphene and carbon nanotubes, have emerged as promising nanomaterials for the development of hybrid systems for bidirectional charge transfer, whose behaviour can be switched from donor-type to acceptor-type by simply changing the electroactive counterpart to which they are anchored. In this review we provide an overview of the main advances that have been made over the past few years in carbon-based hybrid architectures involving different types of carbon nanostructures and photosensitizers. In particular, carbon nanotube and graphene-based hybrid systems will be highlighted.

Single-walled carbon nanotubes in tetrahydrofuran solution: microsolvation from first-principles calculations

The molecular interactions between the commonly used solvent tetrahydrofuran (THF) and single-walled carbon nanotubes (SWCNT) are studied using density functional theory calculations and Car-Parrinello molecular dynamics simulations. The competitive interplay between THF-THF and THF-SWCNT interactions via C-H⋯O and C-H⋯π hydrogen bonds is analyzed in detail. The binding energies for different global and local energy minima configurations of THF monomers, dimers, trimers, and tetramers on SWCNT(10,0) were determined. The adsorbed species are analyzed in terms of their coordination to the surface via weak hydrogen bonds of the C-H⋯π type and in terms of their ability to form intermolecular C-H⋯O hydrogen bonds, which are responsible for the self-aggregation of THF molecules and a possible dimerization or tetramerization process. A special focus is put on the pseudorotation of the THF molecules at finite temperatures and on the formation of blue-shifting hydrogen bonds.

Three-Dimensional Crystalline Modification of Graphene in all-sp2 Hexagonal Lattices with or without Topological Nodal Lines

The discovery of fullerenes, nanotubes, and graphene has ignited tremendous interest in exploring additional all-sp² carbon networks with novel properties. Here we identify by ab initio calculations a new series of three-dimensional crystalline modification of carbon in all-sp² bonding networks that comprise trigonal polycyclic benzenoid nanoflakes in a 2 n² ( n ≥ 4) atom hexagonal cell. The resulting 32-, 50-, 72-, and 98-atom structures (termed as tr32, tr50, tr72, and tr98) in trigonal ( P3̅ m1) symmetry are characterized as the crystalline modification of ( n × n × 1)-graphene in AA stacking, which are energetically more stable than or comparable to the solid fcc-C₆₀ and (5,5) carbon nanotube. Electronic band structure calculations show that tr72 without 2 d (1/3, 2/3, z) symmetric carbon atoms is a semiconductor, while tr32, tr50, and tr98 with 2 d carbon atoms are topological nodal-line semimetals comprising nodal lines on the H-K-H' edge in the hexagonal Brillouin zone, as a three-dimensional extension of the Dirac point at the K-point in two-dimensional graphene. The present findings establish an additional crystalline modification of graphene in the all-sp² carbon allotrope family and offer insights into its outstanding structural and electronic properties.

Disposition of fullerene C60 in rats following intratracheal or intravenous administration

Fullerene C60 is used in a variety of industrial and consumer capacities. As part of a comprehensive evaluation of the toxicity of fullerene C60 by the National Toxicology Program, the disposition following intratracheal (IT) instillation and intravenous (IV) administration of 1 or 5 mg/kg b.wt. fullerene C60 was investigated in male Fischer 344 rats. Following IT instillation, fullerene C60 was detected in the lung as early as 0.5 h post-exposure with minimal clearance over the 168 h period; the concentration increased ≥20-fold with a 5-fold increase in the dose. Fullerene C60 was not detected in extrapulmonary tissues. Following IV administration, fullerene C60 was rapidly eliminated from the blood and was undetectable after 0.5 h post-administration. The highest tissue concentrations of fullerene C60 occurred in the liver, followed by the spleen, lung and kidney. Fullerene C60 was cleared slowly from the kidney and the lung with estimated half-lives of 24 and 139 h, respectively. The liver concentration of fullerene C60 did not change much with time; over 90% of the fullerene C60 remained there over the study duration up to 168 h. Fullerene C60 was also not detected in urine or feces. These data support the hypothesis that fullerene C60 accumulates in the body and therefore has the potential to induce detrimental health effects following exposure.

Cellular Toxicity and Immunological Effects of Carbon-based Nanomaterials

BACKGROUND

Carbon nanomaterials are a growing family of materials featuring unique physicochemical properties, and their widespread application is accompanied by increasing human exposure.

MAIN BODY

Considerable efforts have been made to characterize the potential toxicity of carbon nanomaterials in vitro and in vivo. Many studies have reported various toxicology profiles of carbon nanomaterials. The different results of the cytotoxicity of the carbon-based materials might be related to the differences in the physicochemical properties or structures of carbon nanomaterials, types of target cells and methods of particle dispersion, etc. The reported cytotoxicity effects mainly included reactive oxygen species generation, DNA damage, lysosomal damage, mitochondrial dysfunction and eventual cell death via apoptosis or necrosis. Despite the cellular toxicity, the immunological effects of the carbon-based nanomaterials, such as the pulmonary macrophage activation and inflammation induced by carbon nanomaterials, have been thoroughly studied. The roles of carbon nanomaterials in activating different immune cells or inducing immunosuppression have also been addressed.

CONCLUSION

Here, we provide a review of the latest research findings on the toxicological profiles of carbon-based nanomaterials, highlighting both the cellular toxicities and immunological effects of carbon nanomaterials. This review provides information on the overall status, trends, and research needs for toxicological studies of carbon nanomaterials.

Kerr Nonlinearity in 2D Graphdiyne for Passive Photonic Diodes

Graphdiyne is a new carbon allotrope comprising sp- and sp² -hybridized carbon atoms arranged in a 2D layered structure. In this contribution, 2D graphdiyne is demonstrated to exhibit a strong light-matter interaction with high stability to achieve a broadband Kerr nonlinear optical response, which is useful for nonreciprocal light propagation in passive photonic diodes. Furthermore, advantage of the unique Kerr nonlinearity of 2D graphdiyne is taken and a nonreciprocal light propagation device is proposed based on the novel similarity comparison method. Graphdiyne has demonstrated a large nonlinear refractive index in the order of ≈10^-5 cm² W^-1 , comparing favorably to that of graphene. Based on the strong Kerr nonlinearity of 2D graphdiyne, a nonlinear photonic diode that breaks time-reversal symmetry is demonstrated to realize the unidirectional excitation of Kerr nonlinearity, which can be regarded as a significant demonstration of a graphdiyne-based prototypical application in nonlinear photonics and might suggest an important step toward versatile graphdiyne-based advanced passive photonics devices in the future.

A Perspective on Recent Advances in Phosphorene Functionalization and Its Applications in Devices

Phosphorene, the 2D material derived from black phosphorus, has recently attracted a lot of interest for its properties, suitable for applications in materials science. The physical features and the prominent chemical reactivity on its surface render this nanolayered substrate particularly promising for electrical and optoelectronic applications. In addition, being a new potential ligand for metals, it opens the way for a new role of the inorganic chemistry in the 2D world, with special reference to the field of catalysis. The aim of this review is to summarize the state of the art in this subject and to present our most recent results in the preparation, functionalization, and use of phosphorene and its decorated derivatives. We discuss several key points, which are currently under investigation: the synthesis, the characterization by theoretical calculations, the high pressure behavior of black phosphorus, as well as its decoration with nanoparticles and encapsulation in polymers. Finally, device fabrication and electrical transport measurements are overviewed on the basis of recent literature and the new results collected in our laboratories.

Exploring T-carbon for energy applications

Seeking for next-generation energy sources that are economic, sustainable (renewable), clean (environment-friendly), and earth-abundant, is crucial when facing the challenges of the energy crisis. There have been numerous studies exploring the possibility of carbon-based materials to be utilized in future energy applications. In this paper, we introduce T-carbon, which is a theoretically predicted but also a recently experimentally synthesized carbon allotrope, as a promising material for next-generation energy applications. It is shown that T-carbon can be potentially used in thermoelectrics, hydrogen storage, lithium ion batteries, etc. The challenges, opportunities, and possible directions for future studies of energy applications of T-carbon are also addressed. With the development of more environment-friendly technologies, the promising applications of T-carbon in energy fields would not only produce scientifically significant impact in related fields, but also lead to a number of industrial and technical applications.

Application of carbon nanotubes in cancer vaccines: Achievements, challenges and chances

Tumour-specific, immuno-based therapeutic interventions can be considered as safe and effective approaches for cancer therapy. Exploitation of nano-vaccinology to intensify the cancer vaccine potency may overcome the need for administration of high vaccine doses or additional adjuvants and therefore could be a more efficient approach. Carbon nanotube (CNT) can be described as carbon sheet(s) rolled up into a cylinder that is nanometers wide and nanometers to micrometers long. Stemming from the observed capacities of CNTs to enter various types of cells via diversified mechanisms utilising energy-dependent and/or passive routes of cell uptake, the use of CNTs for the delivery of therapeutic agents has drawn increasing interests over the last decade. Here we review the previous studies that demonstrated the possible benefits of these cylindrical nano-vectors as cancer vaccine delivery systems as well as the obstacles their clinical application is facing.

Generation of a large compressive strain wave in graphite by ultrashort-pulse laser irradiation

We have studied strain wave generation in graphite induced by an intense ultrashort laser pulse. The study was performed in the intensity regime above the ablation threshold of graphite. The aim was to maximize the strain and, thus, also the internal pressure (stress). Laser pulses with a 1 ps temporal duration melt the surface of graphite resulting in a molten material which initially exists at the solid density. As the molten material expands, a compressive strain wave starts propagating into the crystal below the molten layer. The strain pulse was studied with time-resolved X-ray diffraction. At a temporal delay of 100 ps after laser excitation, we observed >10% compressive strain, which corresponds to a pressure of 7.2 GPa. This strain could be reproduced by hydrodynamic simulations, which also provided a temperature map as a function of time and depth.

All-Carbon Pressure Sensors with High Performance and Excellent Chemical Resistance

An all-carbon pressure sensor is designed and fabricated based on reduced graphene oxide (rGO) nanomaterials. By sandwiching one layer of superelastic rGO aerogel between two freestanding high-conductive rGO thin papers, the sensor works based on the contact resistance at the aerogel-paper interfaces, getting rid of the alien materials such as polymers and metals adopted in traditional sensors. Without the limitation of alien materials, the all-carbon sensors demonstrate an ultrawide detecting range (0.72 Pa-130 kPa), low energy consumption (≈0.58 µW), ultrahigh sensitivity (349-253 kPa^-1 ) at low-pressure regime (<1.4 Pa), fast response time (8 ms at 1 kPa), high stability (10 000 unloading-loading cycles between 0 and 1 kPa), light weight (<10 mg), easily scalable fabrication process, and excellent chemical stability. These merits enable them to detect real-time human physiological signals and monitor the weights of various droplets of not only water but also hazardous chemical reagents including strong acid, strong alkali, and organic solvents. This shows their great potential applications in real-time health monitoring, sport performance detecting, harsh environment-related robotics and industry, and so forth.

Science and applications of wafer-scale crystalline carbon nanotube films prepared through controlled vacuum filtration

Carbon nanotubes (CNTs) make an ideal one-dimensional (1D) material platform for the exploration of novel physical phenomena under extremely strong quantum confinement. The 1D character of electrons, phonons and excitons in individual CNTs features extraordinary electronic, thermal and optical properties. Since their discovery in 1991, they have been continuing to attract interest in various disciplines, including chemistry, materials science, physics and engineering. However, the macroscopic manifestation of 1D properties is still limited, despite significant efforts for decades. Recently, a controlled vacuum filtration method has been developed for the preparation of wafer-scale films of crystalline chirality-enriched CNTs, and such films have enabled exciting new fundamental studies and applications. In this review, we will first discuss the controlled vacuum filtration technique, and then summarize recent discoveries in optical spectroscopy studies and optoelectronic device applications using films prepared by this technique.

Structure modulated charge transfer in carbon atomic wires

sp-Hybridized carbon atomic wires are appealing systems with large property tunability. In particular, their electronic properties are intimately related to length, structure, and type of functional end-groups as well as to other effects such as the intermolecular charge transfer with metal nanoparticles. Here, by a combined Raman, Surface Enhanced Raman Scattering (SERS) investigation and first principles calculations of different N,N-dimethylanilino-terminated polyynes, we suggest that, upon charge transfer interaction with silver nanoparticles, the function of sp-carbon atomic wire can change from electron donor to electron acceptor by increasing the wire length. In addition, the insertion into the wire of a strong electrophilic group (1,1,4,4-tetracyanobuta-1,3-diene-2,3-diyl) changes the electron-accepting molecular regions involved in this intermolecular charge transfer. Our results indicate that carbon atomic wires could display a tunable charge transfer between the sp-wire and the metal, and hold promise as active materials in organic optoelectronics and photovoltaics.

Review of the Electronic, Optical, and Magnetic Properties of Graphdiyne: From Theories to Experiments

Graphdiyne (GDY), a two-dimensional artificial-synthesis carbon material, has aroused tremendous interest because of its unique physical properties. The very high activity affords the possibility to chemically dope GDY with metal atoms or lightweight elements such as hydrogen and halogen and so on. Chemical doping has been confirmed to be an effective method to lead to various GDY derivatives with useful physical properties. Thus, this review is intended to provide an overview of the electronic, optical, and magnetic properties of pristine GDY and its derivatives reported from theories to experiments. Because of the importance of pristine GDY and its derivatives in real applications, we also summarize the main physical applications of GDY and its derivatives reported in recent years in this review. We believe that the review will be valuable to all those interested in GDY.

Function-driven engineering of 1D carbon nanotubes and 0D carbon dots: mechanism, properties and applications

Metal-free carbonaceous nanomaterials have witnessed a renaissance of interest due to the surge in the realm of nanotechnology. Among myriads of carbon-based nanostructures with versatile dimensionality, one-dimensional (1D) carbon nanotubes (CNTs) and zero-dimensional (0D) carbon dots (CDs) have grown into a research frontier in the past few decades. With extraordinary mechanical, thermal, electrical and optical properties, CNTs are utilized in transparent displays, quantum wires, field emission transistors, aerospace materials, etc. Although CNTs possess diverse characteristics, their most attractive property is their unique photoluminescence. On the other hand, another growing family of carbonaceous nanomaterials, which is CDs, has drawn much research attention due to its cost-effectiveness, low toxicity, environmental friendliness, fluorescence, luminescence and simplicity to be synthesized and functionalized with surface passivation. Benefiting from these unprecedented properties, CDs have been widely employed in biosensing, bioimaging, nanomedicine, and catalysis. Herein, we have systematically presented the fascinating properties, preparation methods and multitudinous applications of CNTs and CDs (including graphene quantum dots). We will discuss how CNTs and CDs have emerged as auspicious nanomaterials for potential applications, especially in electronics, sensors, bioimaging, wearable devices, batteries, supercapacitors, catalysis and light-emitting diodes (LEDs). Last but not least, this review is concluded with a summary, outlook and invigorating perspectives for future research horizons in this emerging platform of carbonaceous nanomaterials.

Graphyne and Its Family: Recent Theoretical Advances

Graphyne and its family are new carbon allotropes in 2D form with both sp and sp² hybridization. Recently, the graphyne with different structures have attracted great attentions from both experimental and theoretical communities, especially because the first successful synthesis of graphdiyne, which is a typical member of the graphyne family. In this review, recent theoretical progresses in the research of the graphyne family are summarized. More specifically, we systematically introduce the structural, mechanical, band, electronic transport, and thermal properties of graphyne and its family, as well as their possible applications, such as gas separation, water desalination and purification, anode material for ion battery, H₂ storage, and catalysis application. Several related theoretical methods are also reviewed. The coexistence of sp and sp² hybridization and the unique atom arrangement of the graphyne family members bring many novel properties and make them promising materials for many potential applications.

Fingerprints of sp¹ Hybridized C in the Near-Edge X-ray Absorption Spectra of Surface-Grown Materials

Carbon structures comprising sp 1 chains (e.g., polyynes or cumulenes) can be synthesized by exploiting on-surface chemistry and molecular self-assembly of organic precursors, opening to the use of the full experimental and theoretical surface-science toolbox for their characterization. In particular, polarized near-edge X-ray absorption fine structure (NEXAFS) can be used to determine molecular adsorption angles and is here also suggested as a probe to discriminate sp 1 /sp 2 character in the structures. We present an ab initio study of the polarized NEXAFS spectrum of model and real sp 1 /sp 2 materials. Calculations are performed within density functional theory with plane waves and pseudopotentials, and spectra are computed by core-excited C potentials. We evaluate the dichroism in the spectrum for ideal carbynes and highlight the main differences relative to typical sp 2 systems. We then consider a mixed polymer alternating sp 1 C 4 units with sp 2 biphenyl groups, recently synthesized on Au(111), as well as other linear structures and two-dimensional networks, pointing out a spectral line shape specifically due to the the presence of linear C chains. Our study suggests that the measurements of polarized NEXAFS spectra could be used to distinctly fingerprint the presence of sp 1 hybridization in surface-grown C structures.

The Mechanical Properties of Defective Graphyne

Graphyne is a two-dimensional carbon allotrope with superior one-dimensional electronic properties to the “wonder material” graphene. In this study, via molecular dynamics simulations, we investigated the mechanical properties of α-, β-, δ-, and γ-graphynes with various type of point defects and cracks with regard to their promising applications in carbon-based electronic devices. The Young’s modulus and the tensile strength of the four kinds of graphyne were remarkably high, though still lower than graphene. Their Young’s moduli were insensitive to various types of point defects, in contrast to the tensile strength. When a crack slit was present, both the Young’s modulus and tensile strength dropped significantly. Furthermore, the Young’s modulus was hardly affected by the strain rate, indicating potential applications in some contexts where the strain rate is unstable, such as the installation of membranes.

Self-Assembled Monolayers as Templates for Linearly Nanopatterned Covalent Chemical Functionalization of Graphite and Graphene Surfaces

An approach for nanoscale covalent functionalization of graphite surfaces employing self-assembled molecular monolayers of n-alkanes as templating masks is presented. Linearly aligned aryl groups with a lateral periodicity of 5 or 7 nm are demonstrated utilizing molecular templates of different lengths. The key feature of this approach is the use of a phase separated solution double layer consisting of a thin organic layer containing template molecules topped by an aqueous layer containing aryldiazonium molecules capable of electrochemical reduction to generate aryl radicals which bring about surface grafting. Upon sweeping of the potential, lateral displacement dynamics at the n-alkane terminal edges acts in conjunction with electrochemical diffusion to result in templated covalent bond formation in a linear fashion. This protocol was demonstrated to be applicable to linear grafting of graphene. The present processing described herein is useful for the realization of rationally designed nanoscale materials.

Langmuir-Blodgett self-assembly of ultrathin graphene quantum dot films with modulated optical properties

Multiple-color-emissive graphene quantum dots (GQDs) have great potential in diverse applications such as bioimaging, light emission, and photocatalysis. Growing interest in GQDs is largely focused on their macro-scale aggregations that could inherit the unique properties of individual dots. However, the lack of advanced fabrication methods limits the practical applications of GQDs. Here, we employed a Langmuir-Blodgett (LB) technique to fabricate ultrathin, high-quality GQD aggregated films with well-modulated optical properties in a wide range of wavelengths. Through the combination of a bottom-up synthesis of GQDs and the LB assembly method, uniform, closely packed, and ultra-thin GQD films can be self-assembled with a well-controlled thickness on different substrates. The photoluminescence (PL) spectra of ultra-thin GQD films have an obvious red-shift compared with isolated GQD solution. We then elucidate remarkably strong energy transfer in self-assembled GQDs. Furthermore, the ultra-thin GQD films exhibit a clear excitation-dependent PL that could almost cover the entire visible light. This convenient self-assembly method and systematic optical and physical studies of ultra-thin GQD films may provide a new direction for developing low-cost, GQD film-based light-emitting devices.

Comparisons between Graphene Oxide and Graphdiyne Oxide in Physicochemistry Biology and Cytotoxicity

Graphdiyne (GDY) and graphene are regarded as two promising two-dimensional carbon-based materials, which have unique planar structure and novel electronic properties. Differences between the two carbon allotropes in their physicochemistry biology and cytotoxicity have never been explored. Here, we chemically functionalized the surface of the two carbon allotropes using similar oxidation processes and compared their physicochemistry, biology, and mutagenesis. Graphene oxide (GO) and GDY oxide (GDYO) showed similarities in their size, morphology, and physical spectral characteristics, excepting the differences in sp- and sp²-hybridizations and Fourier transform infrared spectroscopy. GDYO was well soluble in various media. In contrast, GO was only soluble in H₂O, but kinetically aggregated in 0.9% NaCl, phosphate buffered saline, and cell media within 24 h incubation when its concentrations increased. GO nanoparticles adhered and aggregated to the surface of a human hepatocyte membrane, resulting in cell membrane ruffle, methuosis, and apoptosis. Adhesion of GO to cells caused cell stress and induced reactive oxygen species. In contrast, GDYO did not adhere to the cell membrane to produce the related consequences. Both GDYO and GO showed in vivo mutagenesis potential but no erythrocyte-killing effect, and both were antioxidant and bioequivalent at binding to single-stranded DNA and doxorubicin, thus causing fluorescence quenching. The present study significantly enriches our existing knowledge of GO/alkene and GDYO/alkyne chemistry.

Advances in Nanomaterials for Brain Microscopy

Microscopic imaging of the brain continues to reveal details of its structure, connectivity, and function. To further improve our understanding of the emergent properties and functions of neural circuits, new methods are necessary to directly visualize the relationship between brain structure, neuron activity, and neurochemistry. Advances in engineering the chemical and optical properties of nanomaterials concurrent with developments in deep-tissue microscopy hold tremendous promise for overcoming the current challenges associated with in vivo brain imaging, particularly for imaging the brain through optically-dense brain tissue, skull, and scalp. To this end, developments in nanomaterials offer much promise toward implementing tunable chemical functionality for neurochemical targeting and sensing, and fluorescence stability for long-term imaging. In this review, we summarize current brain microscopy methods and describe the diverse classes of nanomaterials recently leveraged as contrast agents and functional probes for microscopic optical imaging of the brain.

A Review on the Use of Hydroxyapatite-Carbonaceous Structure Composites in Bone Replacement Materials for Strengthening Purposes

Biomedical materials constitute a vast scientific research field, which is devoted to producing medical devices which aid in enhancing human life. In this field, there is an enormous demand for long-lasting implants and bone substitutes that avoid rejection issues whilst providing favourable bioactivity, osteoconductivity and robust mechanical properties. Hydroxyapatite (HAp)-based biomaterials possess a close chemical resemblance to the mineral phase of bone, which give rise to their excellent biocompatibility, so allowing for them to serve the purpose of a bone-substituting and osteoconductive scaffold. The biodegradability of HAp is low (Ksp ≈ 6.62 × 10-126) as compared to other calcium phosphates materials, however they are known for their ability to develop bone-like apatite coatings on their surface for enhanced bone bonding. Despite its favourable bone regeneration properties, restrictions on the use of pure HAp ceramics in high load-bearing applications exist due to its inherently low mechanical properties (including low strength and fracture toughness, and poor wear resistance). Recent innovations in the field of bio-composites and nanoscience have reignited the investigation of utilising different carbonaceous materials for enhancing the mechanical properties of composites, including HAp-based bio-composites. Researchers have preferred carbonaceous materials with hydroxyapatite due to their inherent biocompatibility and good structural properties. It has been demonstrated that different structures of carbonaceous material can be used to improve the fracture toughness of HAp, as they can easily serve the purpose of being a second phase reinforcement, with the resulting composite still being a biocompatible material. Nanostructured carbonaceous structures, especially those in the form of fibres and sheets, were found to be very effective in increasing the fracture toughness values of HAp. Minor addition of CNTs (3 wt.%) has resulted in a more than 200% increase in fracture toughness of hydroxyapatite-nanorods/CNTs made using spark plasma sintering. This paper presents a current review of the research field of using different carbonaceous materials composited with hydroxyapatite with the intent being to produce high performance biomedically targeted materials.

D-carbon: Ab initio study of a novel carbon allotrope

By means of ab initio computations and the global minimum structure search method, we have investigated structural, mechanical, and electronic properties of D-carbon, a crystalline orthorhombic sp³ carbon allotrope (space group Pmma [ D2h5 ] with 6 atoms per cell). Total-energy calculations demonstrate that D-carbon is energetically more favorable than the previously proposed T₆ structure (with 6 atoms per cell) as well as many others. This novel phase is dynamically, mechanically, and thermally stable at zero pressure and more stable than graphite beyond 63.7 GPa. D-carbon is a semiconductor with a bandgap of 4.33 eV, less than diamond's gap (5.47 eV). The simulated X-ray diffraction pattern is in satisfactory agreement with previous experimental data in chimney or detonation soot, suggesting its possible presence in the specimen.

Fullerene Building Blocks with Tailor-Made Solubility and New Insights into Their Hierarchical Self-Assembly

Herein, the synthesis of fullerene derivatives with adjustable polarities and lyotropic aggregation properties is reported. The polarity range spans from superhydrophobic to hydrophilic, while simultaneously providing a further reactive position with a view to graft them onto other materials. The synthetic strategy relies on a selective protection with an isoxazoline moiety. The remaining octahedral positions were further functionalized with the desired groups to tune their solubility, yielding mixed [5:1] hexakisadducts. The subsequent deprotection by clean photolytic reaction led to fullerene pentakisadducts with an incomplete octahedral addition pattern, which are useful forerunners for the synthesis of building blocks. Their hydrophobic/hydrophilic behavior has been characterized both in solution and surface through octanol/water partition coefficients (log P) and contact angle measurements. Furthermore, these derivatives can form supramolecular constructions which have been studied by dynamic light scattering (DLS) and cryo‐TEM.

Closed trail distance in a biconnected graph

Graphs describe and represent many complex structures in the field of social networks, biological, chemical, industrial and transport systems, and others. These graphs are not only connected but often also k-connected (or at least part of them). Different metrics are used to determine the distance between two nodes in the graph. In this article, we propose a novel metric that takes into account the higher degree of connectivity on the part of the graph (for example, biconnected fullerene graphs and fulleroids). Designed metric reflects the cyclical interdependencies among the nodes of the graph. Moreover, a new component model is derived, and the examples of various types of graphs are presented.

Carbon Nanomaterials for Targeted Cancer Therapy Drugs: A Critical Review

Cancer represents one of the main causes of human death in developed countries. Most current therapies, unfortunately, carry a number of side effects, such as toxicity and damage to healthy cells, as well as the risk of resistance and recurrence. Therefore, cancer research is trying to develop therapeutic procedures with minimal negative consequences. The use of nanomaterial-based systems appears to be one of them. In recent years, great progress has been made in the field using nanomaterials with high potential in biomedical applications. Carbon nanomaterials, thanks to their unique physicochemical properties, are gaining more and more popularity in cancer therapy. They are valued especially for their ability to deliver drugs or small therapeutic molecules to these cells. Through surface functionalization, they can specifically target tumor tissues, increasing the therapeutic potential and significantly reducing the adverse effects of therapy. Their potential future use could, therefore, be as vehicles for drug delivery. This review presents the latest findings of research studies using carbon nanomaterials in the treatment of various types of cancer. To carry out this study, different databases such as Web of Science, PubMed, MEDLINE and Google Scholar were employed. The findings of research studies chosen from more than 2000 viewed scientific publications from the last 15 years were compared.

Ionic liquids plus microwave irradiation: a general methodology for the retro-functionalization of single-walled carbon nanotubes

One of the most important objectives nowadays in the field of chemical modification of carbon nanotubes (CNTs) is to control the degree of functionalization, since excessive modification can disrupt the π-conjugated system and adversely affect their useful properties. Covalent functionalization is one of the most common methods for the modification of single-walled carbon nanotubes (SWCNTs). However, only a few examples have appeared in the last few years regarding the control of the functionalization degree and the reversibility of the reaction. We present here an approach for the retro-functionalization of SWCNTs which could be applied to different types of covalent functionalizations, allowing the restoration of the π-conjugated structure. The process is performed through the combination of ionic liquids plus microwave irradiation and it is applicable to the retro-arylation and retro-cycloaddition reactions on SWCNTs. The successful retro-functionalization is monitored by Raman spectroscopy, thermogravimetric analysis and UV-Vis-NIR spectroscopy.