Abstract
Abstract
Hydrogen-substituted graphdiyne(HsGDY) is a two-dimensional material composed of an sp-sp2 carbon skeleton, which has attracted much attention recently because of its structure with larger pores and band gap than other nanocarbon materials such as graphene[1]. HsGDY is expected to be applied as a new battery electrode[2,3] due to its high ion diffusivity resulting from its porous structure, and as a carbon framework catalyst[4] without precious metals such as Pt because of its band gap.
In recent years, research has concentrated on synthesizing HsGDY by a simple drop method using copper as a catalyst/substrate[3]. However, this method requires the use of toxic pyridine, and the deposition process takes several days. A method for synthesizing HsGDY by surface reaction on a substrate[5], i.e., homo-coupling reaction on the Au(111) surface, has been proposed as a solution for these problems. This method is expensive because synthesis is carried out in an ultra-high vacuum(UHV), and the UHV chamber limits the synthesizable specimen size, preventing its practical application.
In this study, we aim to develop a synthesis method for HsGDY by the drop method in air, in order to promote the practical use of HsGDY. To achieve this target, we modified previous studies[5,6] and devised a method in which the precursor is dissolved in an organic solvent and dropped onto a substrate.
1,3,5-tris(bromoethynyl)benzene(tBEP), the precursor of HsGDY, was synthesized at room temperature in the air with 1,3,5-triethynylbenzene(TEB) as a raw material, N-Bromosuccinimide(NBS) as a bromine source, and silver nitrate as a catalyst. As a substrate for HsGDY synthesis, the Au(111) surface was prepared by depositing gold on mica and annealing it with a burner. HsGDY was synthesized by dropping the organic solvent solution of tBEP onto this substrate and annealing at 150°C for 5 minutes.
HsGDY synthesized on the Au(111) surface was observed by scanning tunneling microscopy(STM). Fig. 1 shows an STM image of part of the HsGDY structure in the process of homo-coupling reaction, i.e., there is a gold atom between the precursors. The distances between three and neighbor six-membered rings consisting of 6 precursors are around 6 and 3.5 nm, respectively, which corresponds well to the center distances of the three circular structures observed in Fig. 1.
From the above, we have successfully synthesized a portion of HsGDY on Au(111) using the drop method in air. However, the homo-coupling reaction is not completed, and the synthesis conditions need to be optimized. In the future, we will achieve a large area (on the order of µm) of the two-dimensional structure for applications such as catalysts. In order to improve the synthesis method for a large-area structure, it is necessary to search for optimal synthesis conditions by changing parameters such as synthesis reaction time, the temperature at which the substrate is heated, and organic solvents in which the precursor is dissolved.
Our work provides a new and low-cost way to obtain amazing materials.
References
[1] H. Pan et al., App. Surf. Sci. 513, 145694 (2020).
[2] S. Kong et al., Nanoscale 13, 3817-3826 (2021).
[3] J. He et al., Nat. Comm. 8, 1172 (2017).
[4] Z. Zuo et al., Adv. Mat. 31, 1803762 (2019).
[5] Q. Sun et al., ACS Nano 10, 7023-7030 (2016).
[6] A. Okada et al., Surf. Sci. 702, 121718 (2020).
