# Single-crystal 2D covalent organic frameworks for high-capacity methane storage

## TL;DR

Researchers created single-crystal 2D covalent organic frameworks with high methane storage capacity, comparable to 3D materials.

## Contribution

A substituent strategy was used to produce single-crystal 2D COFs with atom-resolution structures and high gas storage performance.

## Key findings

- A single-crystal 2D COF (GZU-1) achieved a surface area of ~2100 m² g⁻¹ and pore volume of 1.40 cm³ g⁻¹.
- The COF showed a methane uptake of 240 cm³ (STP) cm⁻³, the highest among 2D COFs.
- This performance is comparable to excellent 3D metal-organic frameworks (MOFs).

## Abstract

2D covalent organic frameworks (COFs) usually possess a polycrystalline nature as well as lower porosity and surface area than 3D counterparts, restraining their exploration over gas storage applications. Herein, a substituent strategy has been proposed and employed to generate three robust single-crystal 2D COFs isomers with atom-resolution structures determined by 3D electron diffraction. Among three isomers, a precise engineering of their interlayer distance affords the highest Brunauer−Emmett−Teller surface area of ~2100 m2 g−1 and the largest pore volume of 1.40 cm3 g−1 for the desolvated GZU-1. This COF shows the highest total volumetric methane uptake of 240 cm3 (STP) cm−3 at 273 K and 100 bar among 2D COFs, even comparable with those for excellent 3D MOFs. This work not only delivers unique insight into the design of 2D single-crystal COFs by interlayer stacking regulation, but also promotes the application of highly porous 2D COFs in gas storage.

2D covalent organic frameworks usually possess a polycrystalline nature as well as lower porosity and surface area than 3D counterparts, limiting their gas storage application. Here, the authors report the formation of single-crystal 2D covalent organic frameworks isomers with atom-resolution structures for methane storage.