Electron beam method enables high-yield graphdiyne synthesis in seconds under ambient conditions, offering a fast route to carbon-based catalytic materials.
(Nanowerk Spotlight) The promise of graphdiyne—a carbon-based material with a porous framework and extended electronic structure—has remained largely unrealized, not because its properties are in doubt, but because it is exceptionally difficult to produce. Like graphene, which consists of a single layer of hexagonally arranged carbon atoms, graphdiyne belongs to the family of two-dimensional carbon allotropes.
But it differs in a key way: its structure includes regularly spaced carbon–carbon triple bonds embedded between benzene rings. This configuration creates uniformly distributed pores, a tunable band gap, and a highly conjugated π-electron system that together make graphdiyne promising for applications where graphene falls short—including selective molecular transport, semiconducting electronics, and electrocatalysis.
Graphene has been widely explored due to its strength and conductivity, yet its zero band gap limits its use in logic devices and certain catalytic systems. Graphdiyne, in contrast, offers structural and electronic diversity while still being lightweight and robust. But despite these advantages, graphdiyne has remained largely confined to the lab bench. The problem lies in its synthesis: no method has been able to produce it quickly, under ambient conditions, and in sufficient yield for practical use.
The challenge stems from the need to couple reactive molecular building blocks, such as hexaethynylbenzene (HEB), into an extended network. HEB is unstable in air, so researchers typically use a protected version, HEB-TMS, which requires an additional chemical step to remove the protective trimethylsilyl groups before coupling can occur. Most existing methods rely on hours of heating, toxic solvents, and inert environments to carry out these steps, severely limiting scalability. Attempts to simplify the process using microwave heating or interface coupling have made incremental progress but haven’t overcome the central tradeoff between molecular stability and reactivity.
Meanwhile, electron beam chemistry has quietly matured into a reliable tool for constructing complex frameworks under mild conditions. Used in areas such as polymer crosslinking and metal-organic framework fabrication, high-energy electrons can directly excite molecules, generate radicals, and initiate reactions without thermal input. These traits suggest a route to bypass the bottlenecks that have held back graphdiyne production.
A research team at Xiamen University has now applied this idea directly, using electron beam irradiation to convert HEB-TMS into graphdiyne within seconds. The process requires no inert atmosphere, no heating, and no pre-activation. It represents a shift not only in how graphdiyne can be synthesized, but also in how ambient-condition chemistry might unlock previously inaccessible carbon materials.
Schematic diagram of graphdiyne synthesis. a) Classical synthesis; b) Deprotection-free method; c) Electron beam irradiation synthesis. (Image: Reprinted with permission by Wiley-VCH Verlag)
To carry out the synthesis, the team prepared a solution of HEB-TMS, copper acetate, and the solvent dimethylformamide (DMF), then exposed it to a focused electron beam. Within five seconds, the solution darkened as the graphdiyne network began to form. With an absorbed radiation dose of 50 kilograys—reached in under a minute—the system produced a black precipitate in high yield. After purifying the product to remove residual copper oxide, the researchers obtained graphdiyne with a nearly complete conversion.
The mechanism behind this rapid transformation relies on the interplay between the electron beam and copper species in solution. The beam’s high-energy particles reduce copper ions (Cu²⁺) to Cu⁺, which then remove the TMS protective groups from HEB-TMS. This generates copper acetylide intermediates—compounds in which the carbon–carbon triple bonds are coordinated with copper. Under continued irradiation, these intermediates undergo bond cleavage to form alkynyl radicals. These radicals are highly reactive and couple with one another to form the extended graphdiyne framework.
Each part of the process was validated using spectroscopy, mass spectrometry, and quantum mechanical simulations. Electron trapping experiments showed that when radical scavengers were introduced, graphdiyne formation was almost entirely suppressed. Control reactions without either copper or irradiation produced no product, demonstrating that both are essential.
Simulations revealed that copper species lower the energy barriers for both precursor activation and bond formation, and that electron irradiation promotes the radical pathway needed to link the building blocks together.
Characterization of the resulting material confirmed the successful formation of the graphdiyne network. Raman spectroscopy showed disappearance of signals from unreacted monoalkynes and the appearance of bands characteristic of diacetylene linkages. Solid-state nuclear magnetic resonance and X-ray photoelectron spectroscopy confirmed the expected mix of sp- and sp²-hybridized carbon atoms. Electron microscopy revealed the material’s layered morphology, consistent with stacked graphdiyne sheets.
The irradiation process also led to the spontaneous formation of copper(I) oxide (Cu₂O) nanoparticles, which formed in situ on the surface of the growing graphdiyne. These particles were around 3 nanometers in size, well-dispersed, and strongly anchored to the carbon structure. The result was a nanocomposite—Cu₂O/graphdiyne—with both electronic conductivity and catalytic functionality.
To explore the catalytic potential of this composite, the researchers tested it in the electrochemical reduction of nitrate (NO₃⁻) to ammonia (NH₃). This reaction is of interest as a lower-energy, decentralized alternative to industrial ammonia synthesis, as well as a means of removing nitrate pollution from water.
The Cu₂O/graphdiyne material achieved a Faradaic efficiency of 94 percent and an ammonia production rate of 26,997 micrograms per hour per milligram of catalyst at an applied voltage of –1.7 volts. These values place it among the most effective nitrate reduction catalysts reported to date.
Further experiments showed that the catalytic activity depended strongly on the copper loading and irradiation dose during synthesis. Optimal performance was achieved when using 30 milligrams of copper acetate and a radiation dose of 50 kilograys. Stability tests over multiple reaction cycles showed no significant degradation in activity, suggesting the composite is durable and resistant to fouling.
Control tests with copper oxide alone, or supported on other materials like graphitic carbon nitride or carbon black, produced lower yields and lower efficiencies. The improved performance of the Cu₂O/graphdiyne system was attributed to the strong interaction between the copper oxide and the carbon framework, which stabilized the active Cu⁺ species and promoted selective nitrate reduction.
In situ spectroscopy and computational modeling supported this interpretation. Density functional theory calculations showed that the interface between Cu₂O and graphdiyne lowered the energy required for key reaction steps, particularly nitrate adsorption and intermediate hydrogenation.
These findings demonstrate how the structure of the support can directly influence catalytic behavior, not just by providing surface area but by modulating electronic states and facilitating charge transfer. The graphdiyne framework plays an active role in stabilizing the catalytic sites and guiding the reaction pathway.
Beyond this specific application, the study presents a more general approach to synthesizing carbon materials under mild conditions. By using electron beams to activate protected precursors directly, the researchers have sidestepped long-standing tradeoffs between chemical stability and reactivity. The method uses low-cost reagents, no external heating, and avoids environmentally hazardous solvents or byproducts.
The resulting graphdiyne can be produced in seconds, with near-quantitative yield and structural fidelity. This opens the possibility of manufacturing not just graphdiyne, but other complex carbon architectures that were previously too difficult or costly to scale. By uniting fast, clean synthesis with in situ catalyst formation, the approach could support broader efforts to develop high-performance materials for energy, sensing, and environmental remediation.
Graphene’s discovery helped launch the field of two-dimensional materials, but its limitations spurred interest in alternatives. Graphdiyne has stood out among them—offering structural tunability and electronic properties that graphene lacks—but has been hampered by its synthetic inaccessibility. This work brings it closer to practical use and suggests that tools from electron beam science may help unlock other materials still trapped behind synthetic barriers.
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