State, synthesis, perspective applications, and challenges of Graphdiyne and its analogues: A review of recent research

Carbon materials technology provides the possibility of synthesizing low-cost, outstanding performance replacements to noble-metal catalysts for long-term use. Graphdiyne (GDY) is a carbon allotrope with an extremely thin atomic thickness. It consists of carbon elements, that are hybridized with both sp. and sp2, resulting in a multilayered two-dimensional (2D) configuration. Several functional models suggest, that GDY contains spontaneously existing band structure with Dirac poles. This is due to the non-uniform interaction among carbon atoms, which results from various fusions and overlapping of the 2pz subshell. Unlike other carbon allotropes, GDY has Dirac cone arrangements, that in turn give it inimitable physiochemical characteristics. These properties include an adjustable intrinsic energy gap, high speeds charging transport modulation efficiency, and exceptional conductance. Many scientists are interested in such novel, linear, stacked materials, including GDY. As a result, organized synthesis of GDY has been pursued, making it one of the first synthesized GDY materials. There are several methods to manipulate the band structure of GDY, including applying stresses, introducing boron/nitrogen loading, utilizing nanowires, and hydrogenations. The flexibility of GDY can be effectively demonstrated through the formation of nano walls, nanostructures, nanotube patterns, nanorods, or structured striped clusters. GDY, being a carbon material, has a wide range of applications owing to its remarkable structural and electrical characteristics. According to subsequent research, the GDY can be utilized in numerous energy generation processes, such as electrochemical water splitting (ECWS), photoelectrochemical water splitting (PEC WS), nitrogen reduction reaction (NRR), overall water splitting (OWS), oxygen reduction reaction (ORR), energy storage materials, lithium-Ion batteries (LiBs) and solar cell applications. These studies suggested that the use of GDY holds significant potential for the development and implementation of efficient, multimodal, and intelligent catalysts with realistic applications. However, the limitation of GDY and GDY-based composites for forthcoming studies are similarly acknowledged. The objective of these studies is to deliver a comprehensive knowledge of GDY and inspire further advancement and utilization of these unique carbon materials.

Two-Dimensional Carbon Graphdiyne: Advances in Fundamental and Application Research

Graphdiyne (GDY), a rising star of carbon allotropes, features a two-dimensional all-carbon network with the cohybridization of sp and sp² carbon atoms and represents a trend and research direction in the development of carbon materials. The sp/sp²-hybridized structure of GDY endows it with numerous advantages and advancements in controlled growth, assembly, and performance tuning, and many studies have shown that GDY has been a key material for innovation and development in the fields of catalysis, energy, photoelectric conversion, mode conversion and transformation of electronic devices, detectors, life sciences, etc. In the past ten years, the fundamental scientific issues related to GDY have been understood, showing differences from traditional carbon materials in controlled growth, chemical and physical properties and mechanisms, and attracting extensive attention from many scientists. GDY has gradually developed into one of the frontiers of chemistry and materials science, and has entered the rapid development period, producing large numbers of fundamental and applied research achievements in the fundamental and applied research of carbon materials. For the exploration of frontier scientific concepts and phenomena in carbon science research, there is great potential to promote progress in the fields of energy, catalysis, intelligent information, optoelectronics, and life sciences. In this review, the growth, self-assembly method, aggregation structure, chemical modification, and doping of GDY are shown, and the theoretical calculation and simulation and fundamental properties of GDY are also fully introduced. In particular, the applications of GDY and its formed aggregates in catalysis, energy storage, photoelectronic, biomedicine, environmental science, life science, detectors, and material separation are introduced.

Facile Synthesis of Hydrogen-Substituted Graphdiyne Powder via Dehalogenative Homocoupling Reaction

Graphdiyne and its analogs are a series of artificial two-dimensional nanomaterials with sp hybridized carbon atoms, which can be viewed as the insertion of two acetylenic units between adjacent aromatic rings, evenly expanded on a flat surface. Although developed in recent years, new synthetic strategies for graphdiyne analogs are still required. This work proposed a new method to prepare hydrogen-substituted graphdiyne powder via a dehalogenative homocoupling reaction. The polymerization was unanticipated while the initial goal was to synthesize a γ-graphyne analog via Sonogashira cross-coupling reaction. Compared with previous synthetic strategies, the reaction time was conspicuously shortened and the Pd catalyst was inessential. The powder obtained exhibited a porous structure and high electrocatalytic activity in the hydrogen/oxygen evolution reaction, which has the potential for application in electrochemical catalysis. The reported methodology provides an efficient synthetic strategy for large-scale preparation.

Construction of Nitrogen-abundant Graphyne Scaffolds via Mechanochemistry-Promoted Cross-Linking of Aromatic Nitriles with Carbide Toward Enhanced Energy Storage

The 2D graphyne-related scaffolds linked by carbon-carbon triple bonds have demonstrated promising applications in the field of catalysis and energy storage due to their unique features including high conductivity, permanent porosity, and electron-rich properties. However, the construction of related scaffolds is still mainly limited to the cross-linking of CaC₂ with multiple substituted aromatic halogens and there is still a lack of efficient methodology capable of introducing high-concentration heteroatoms within the architectures. The development of alternative and facile synthesis procedures to afford nitrogen-abundant graphyne materials is highly desirable yet challenging in the field of energy storage, particularly via the facile mechanochemical procedure under neat and ambient conditions. Herein, graphyne materials with abundant nitrogen-containing species (nitrogen content of 6.9-29.3 wt.%), tunable surface areas (43-865 m²  g^-1 ), and hierarchical porosity are produced via the mechanochemistry-driven pathway by deploying highly electron-deficient multiple substituted aromatic nitriles as the precursors, which can undergo cross-linking reaction with CaC₂ to afford the desired nitrogen-doped graphyne scaffolds efficiently. Unique structural features of the as-synthesized materials contributed to promising performance in supercapacitor-related applications, delivering high capacitance of 254.5 F g^-1 at 5 mV s^-1 , attractive rate performance, and good long-term stability.

Graphdiyne Electrochemistry: Progress and Perspectives

Graphdiyne, a carbon allotrope, was synthesized in 2010 for the first time. It consists of two acetylene bonds between adjacent benzene rings. Graphdiyne and its composites thus exhibit ultrahigh intrinsic electrochemical activities. As "star" electrode materials, they have been utilized for various electrochemical applications. With the aim of giving a full screen of graphdiyne electrochemistry, this review starts from the history of graphdiyne materials, followed by their structural and electrochemical features. Recent progress and achievements in the synthesis of graphdiyne materials and their composites are overviewed. Subsequently, various electrochemical applications of graphdiyne materials and their composites are summarized, covering those in the fields of electrochemical energy conversion, electrochemical energy storage, and electrochemical sensing. The perspectives of graphdiyne electrochemistry are also discussed and outlined.

Water-soluble pillar[5]arene-modified graphdiyne functional material and its application towards ultrasensitive and robust electrochemical methylamphetamine determination

Schematic illustration of the application of the novel material WP5–GDY/GCE for the electrochemical sensing of methylamphetamine (MA).

Developments in Synthesis and Potential Electronic and Magnetic Applications of Pristine and Doped Graphynes

Doping and its consequences on the electronic features, optoelectronic features, and magnetism of graphynes (GYs) are reviewed in this work. First, synthetic strategies that consider numerous chemically and dimensionally different structures are discussed. Simultaneous or subsequent doping with heteroatoms, controlling dimensions, applying strain, and applying external electric fields can serve as effective ways to modulate the band structure of these new sp2/sp allotropes of carbon. The fundamental band gap is crucially dependent on morphology, with low dimensional GYs displaying a broader band gap than their bulk counterparts. Accurately chosen precursors and synthesis conditions ensure complete control of the morphological, electronic, and physicochemical properties of resulting GY sheets as well as the distribution of dopants deposited on GY surfaces. The uniform and quantitative inclusion of non-metallic (B, Cl, N, O, or P) and metallic (Fe, Co, or Ni) elements into graphyne derivatives were theoretically and experimentally studied, which improved their electronic and magnetic properties as row systems or in heterojunction. The effect of heteroatoms associated with metallic impurities on the magnetic properties of GYs was investigated. Finally, the flexibility of doped GYs' electronic and magnetic features recommends them for new electronic and optoelectronic applications.

Synthesis of hydrogen-substituted graphdiynes via dehalogenative homocoupling reactions

A new method is introduced to prepare hydrogen-substituted graphdiynes (HsGDYs) via the dehalogenative homocoupling of terminal alkynyl bromides. Compared with previous synthetic strategies, the reaction conditions are moderate and the time is shortened. HsGDYs exhibit porous structures and hydrogen/oxygen evolution reaction (HER/OER) catalytic activity, endowing applications in electrochemical catalysis.

Large-Area Assembly of Metal-Organic Layered Ultrathin Films at the Liquid/Liquid Interface

Two-dimensional functional metal-organic frameworks and coordination polymers have attracted much attention and have been successfully prepared in solutions and at interfaces through the coordination of ligands to metal ions. However, the preparation of large-area ultrathin ordered films is still a challenge. Here, a modified liquid/liquid interfacial epitaxial growth method has been developed. A planar liquid/liquid interface between a chloroform solution of bipyridine derivatives and pure water was constructed first, and then an aqueous solution of Eu³⁺ or Cu²⁺ ions was added dropwise into the water phase. A layered ultrathin film with the size of several hundreds of square micrometers appeared at the liquid/liquid interface after a certain time. The monitoring results showed that the formation of ultrathin films was a result of continuous epitaxial growth of the adsorbed species due to the synergistic effects of hydrophobic effects of the alkyl chains, coordination bonds between the ligands and metal ions, π-π interactions between the ligands, and the restriction of the interface on the vertical growth. This offers a way to fabricate more large-area thin films of amphiphilic molecules.

Ultrahigh hydrogen storage capacity of holey graphyne

Holey graphyne (HGY), a novel two-dimensional (2D) single-crystalline carbon allotrope, was recently synthesized by Castro-Stephens coupling reaction. The naturally existing uniform periodic holes in the 2D carbon-carbon network demonstrate its promising potential in energy storage. Herein, we conduct density functional theory (DFT) calculation and ab initio molecular dynamics simulations (AIMD) to predict the H storage properties of a single-layer HGY sheet modified by Li metal atoms. The DFT calculations demonstrate that Li atoms can bind strongly to the HGY sheet without forming clusters, and each Li atom can anchor four H2 molecules with an average adsorption energy of about -0.22 eV/H2. The largest H storage capacity of the doped HGY sheet can reach as high as 12.8 wt%, showing that the Li/HGY complex is an ideal H storage material at ambient conditions. In addition, we investigate the polarization mechanism of the storage media and find that the polarization originates from the electric field induced by both the ionic Li atoms and the weak polarized H2 molecules. Finally, the desorption mechanism of the adsorbed H2 molecules is thoroughly investigated using a kinetic AIMD method.

Toward the synthesis, fluorination and application of N-graphyne

The discovery of properties and applications of unknown materials is one of the hottest research areas in materials science. In this work, we navigate a route towards these goals by the development of a new type of graphyne nanostructure. It is synthesised by a Sonogashira cross-coupling reaction of 1,3,5-triethynylbenzene with cyanuric chloride resulting in an extended carbon-based material called TCC. Also, we modify the obtained TCC via fluorination using XeF2 at various concentrations to investigate the effect of fluorination on the triple bonds and the conjugated structure of graphyne. In this study, we put special emphasis on the determination of the impact of the fluorine content and the type of CF functionalities on the morphology, chemical and electronic structure, biocompatibility, electrical conductivity and possible applicability as anode materials for Li-ion batteries. The obtained results indicate that the character of C-F bonds influences the final properties of fluorinated materials. The polar C-F bonds are preferable for cell proliferation while CF2 groups are most suitable for battery devices, however, the appearance of PTFE-like units may have a negative impact on battery specific capacitance as well as on cell viability.

Graphdiyne bearing pillar[5]arene-reduced Au nanoparticles for enhanced catalytic performance towards the reduction of 4-nitrophenol and methylene blue

Graphdiyne (GD), a novel two dimensional (2D) carbon material, has earned a lot of attention in recent years. Constructing a novel hybrid nanomaterial based on GD, macrocyclic host and Au nanoparticles is an effective strategy for heterogeneous catalysis applications. While tremendous advancements in the preparation of two dimensional (2D) materials anchoring Au nanoparticles have been made, it is an urgent requirement to explore a green, efficient and facile approach for obtaining small-sized Au nanoparticles. The use of the 2D material graphdiyne (GD) presents more-promising candidates for constructing excellent sites for loading metal nanoparticles. In this study, a novel 2D heterogeneous hybrid nanomaterial (P5A-Au-GD) based on GD and pillar[5]arene (P5A)-reduced Au nanoparticles (P5A-Au) was successfully prepared. In this strategy, the P5A can reduce HAuCl4 with the aid of NaOH in the dispersion of GD. Accordingly, the generated P5A-Au can immediately interact with GD to form the P5A-Au-GD hybrid nanomaterial without any harsh reduced materials or other energies. The Au nanoparticles with average diameter of 2-3 nm are homogeneously dispersed on the surface of GD. The heterogeneous 2D catalyst of P5A-Au-GD shows high catalytic performances in the reduction of 4-nitrophenol and methylene blue by comparing commercial Pd/C catalyst. Meanwhile, the unique 2D heterogeneous hybrid material P5A-Au-GD exhibits durable recyclability and stability during the catalytic reaction. Considering the outstanding merits of the heterogeneous 2D catalyst of P5A-Au-GD as well as the simple and green preparation, this study might not only present enormous opportunities for the stabilized, high-performance and sustainable catalysts but also be applied in other frontier studies of sustainable functionalized nanocomposites and advanced materials.

Graphdiyne-Based Materials: Preparation and Application for Electrochemical Energy Storage

Graphdiyne (GDY) has drawn much attention for its 2D chemical structure, extraordinary intrinsic properties, and wide application potential in a variety of research fields. In particular, some structural features and basic physical properties including expanded in-plane pores, regular nanostructuring, and good transporting properties make GDY a promising candidate for an electrode material in energy-storage devices, including batteries and supercapacitors. The chemical structure, synthetic strategy, basic chemical-physical properties of GDY, and related theoretical analysis on its energy-storage mechanism are summarized here. Moreover, through a view of the mutual promotion between the structure modification of GDY and the corresponding electrochemical performance improvement, research progress on the application of GDY for electrochemical energy storage is systematically explored and discussed. Furthermore, the development trends of GDY in energy-storage devices are also comprehensively assessed. GDY-based materials represent a bright future in the field of electrochemical energy storage.

Top-down strategy synthesis of fluorinated graphdiyne for lithium ion battery

Fluorine doped graphdiyne was synthesized by exposure to XeF₂ under mild temperature. Owing to the enhanced conductivity and enhanced mechanical properties, the electrochemical performances are significantly improved.