Bottom-Up Synthesis of Discrete Conical Nanocarbons

Functionalized carbon nanocones performance in water harvesting

In this work, we investigate the water capture process for functionalized carbon nanocones (CNCs) through molecular dynamic simulations in the following three scenarios: a single CNC in contact with a reservoir containing liquid water, a single CNC in contact with a water vapor reservoir, and a combination of more than one CNC in contact with vapor. We found that water flows through the nanocones when in contact with the liquid reservoir if the nanocone tip presents hydrophilic functionalization. In contact with steam, we observed the formation of droplets at the base of the nanocone only when hydrophilic functionalization is present. Then, water flows through in a linear manner, a process that is more efficient than that in the liquid reservoir regime. The scalability of the process is tested by analyzing the water flow through more than one nanocone. The results suggest that the distance between the nanocones is a fundamental ingredient for the efficiency of water harvesting.

Atmospheric water harvesting using functionalized carbon nanocones

In this work, we propose a method to harvest liquid water from water vapor using carbon nanocones. The condensation occurs due to the presence of hydrophilic sites at the nanocone entrance. The functionalization, together with the high mobility of water inside nanostructures, leads to a fast water flow through the nanostructure. We show using molecular dynamics simulations that this device is able to collect water if the surface functionalization is properly selected.

Stereo- and Regioselectivity of Hydrogenation of a Recently Synthesized Carboncone and Its Predictive Models

Since its atomically precise synthesis in recent experiments, the carboncone molecule presents a novel example of discrete nanocarbons with promising applications, but little is known yet about its chemical properties. In this work, we present a comprehensive computational study on the hydrogenation of carboncone with a varying number of added H atoms (from 1 to 12). Unlike planar benzenoid hydrocarbons, carboncone prefers that all H atoms be added to its external, convex surface. The previous topology-based model for hydrogenated fullerenes and benzenoid hydrocarbons is shown to be no longer valid for carboncone. We here propose an extended model capable of predicting the hydrogenation regioselectivity for carboncone, which is largely governed by π delocalization. Yet the H···H repulsion at rim sites also plays an important role in adduct stability. Interestingly, some preferred addition patterns can be understood by counting the size of intact π rings upon H addition. These findings may provide insightful guidance to the functionalization of carboncones and related nanocarbons.

DFT calculations of plutonium-doped conical nanocarbons: Exploring structural and electronic features

By the importance of performing investigations on developing characteristic features of nano-based materials for assigning their further applications, this work was done to recognize such features for plutonium (Pu)-doped conical nanocarbons materials. Density functional theory (DFT) calculations were performed for providing information of this work. Three models of conical nanocarbons with disclination angles of 120, 180, and 240 degrees were investigated, in which the Pu atom was doped at the apex of conical structure yielding the models of PuNC120, PuNC180, and PuNC240. Accordingly, formations of four, three, and two PU–C chemical bonds were examined by considering such models systems. The results indicated the PuNC120 with four Pu–C bonds was the distinguished model of this work showing remarkable electronic and conductivity features. As a consequence, the models systems were recognized based on the structural and electronic features to be designated for further applications.

Synthetic chiral molecular nanographenes: the key figure of the racemization barrier

Chirality is one of the most intriguing concepts of chemistry, involving living systems and, more recently, materials science. In particular, the bottom-up synthesis of molecular nanographenes endowed with one or several chiral elements is a current challenge for the chemical community. The wilful introduction of defects in the sp² honeycomb lattice of molecular nanographenes allows the preparation of chiral molecules with tuned band-gaps and chiroptical properties. There are two requirements that a system must fulfill to be chiral: (i) lack of inversion elements (planes or inversion centres) and (ii) to be configurationally stable. The first condition is inherently established by the symmetry group of the structure, however, the limit between conformational and configurational isomers is not totally clear. In this feature article, the chirality and dynamics of synthetic molecular nanographenes, with special emphasis on their racemization barriers and, therefore, the stability of their chiroptical properties are discussed. The general features of nanographenes and their bottom-up synthesis, including the main defects inducing chirality in molecular nanographenes are firstly discussed. In this regard, the most common topological defects of molecular NGs as well as the main techniques used for determining their energy barriers are presented. Then, the manuscript is structured according to the dynamics of molecular nanographenes, classifying them in four main groups, depending on their respective isomerization barriers, as flexible, detectable, isolable and rigid nanographenes. In these sections, the different strategies used to increase the isomerization barrier of chiral molecular nanographenes that lead to configurationally stable nanographenes with defined chiroptical properties are discussed.

Extension and Quantification of the Fries Rule and Its Connection to Aromaticity: Large-Scale Validation by Wave-Function-Based Resonance Analysis

The Fries rule is a simple, intuitive tool to predict the most dominant Kekulé structures of polycyclic aromatic hydrocarbons (PAHs), which is valuable for understanding the structure, stability, reactivity, and aromaticity of these conjugated compounds. However, it still remains an empirical hypothesis, with limited qualitative applications. Herein, we verify, generalize, and quantify the Fries rule based on the recently developed resonance analysis of the DFT wave functions of over 1500 PAH and fullerene molecules with over a billion Kekulé structures. The extended rules, counting the numbers of electrons within all rings (not just sextets), are able to rank the relative importance of all Kekulé structures for all considered systems. The statistically meaningful quantification also opens a way to evaluate ring aromaticity based on the resonance theory, which generally agrees well with conventional aromaticity descriptors. Furthermore, we propose a purely graph-based aromaticity indicator nicely applicable to PAHs and fullerenes, with no need of any quantum chemistry calculations, so that it can make valuable predictions for molecular properties that are related to local aromaticity.

The Synthesis of Conical Carbon

Conical carbon, specifically multi-walled carbon nanocones (CNCs) and single-walled carboncones, is a new class of sp² -hybridized carbon allotrope, in addition to fullerene, carbon nanotubes (CNTs), and graphene. Characterized by a conical and delocalized aromatic configuration, the conical carbon structure is considered the intermediate structure between planar graphene and open-cage fullerene. CNCs can be stiffer than CNTs and exhibit intriguing physical and chemical properties owing to their unique hollow conical structure, which make these materials promising for application as field emission sources and scanning probes. The research on conical carbon structures is in its nascent stage, mainly because of the limitations in the synthesis and purification of conical carbons. This review summarizes the significant progress in the synthesis of CNCs and carboncones. Particularly, the synthetic methods, which can be divided into traditional physical-chemical synthesis methods for multi-walled CNCs and emerging bottom-up organic synthesis methods for single-walled carboncones, are comprehensively discussed. In addition, the advantages and disadvantages of the various synthetic methods as well as the possible formation and growth mechanisms of CNCs and carboncones are discussed. Finally, some outlooks on the potential solutions to the synthesis of single-walled carboncones with uniform apex angles are presented.

Gas-Phase Transformation of Fluorinated Benzoporphyrins to Porphyrin-Embedded Conical Nanocarbons

Geodesic nitrogen-containing graphene fragments are interesting candidates for various material applications, but the available synthetic protocols, which need to overcome intrinsic strain energy during the formation of the bowl-shaped skeletons, are often incompatible with heteroatom-embedded structures. Through this mass spectrometry-based gas-phase study, we show by means of collision-induced dissociation experiments and supported by density functional theory calculations, the first evidence for the formation of a porphyrin-embedded conical nanocarbon. The influences of metalation and functionalization of the used tetrabenzoporphyrins have been investigated, which revealed different cyclization efficiencies, different ionization possibilities, and a variation of the dissociation pathway. Our results suggest a stepwise process for HF elimination from the fjord region, which supports a selective pathway towards bent nitrogen-containing graphene fragments.