The supply-demand imbalance of clean water results in global sustainability crisis. The United Nations World Water Developments Report 2023 reveals that 2-3 billion populations are suffering from water shortage.

Seawater desalination via membrane separation to clean water offers a promising approach. However, most membranes are restricted by the low water flux because membrane quality is challenged by harsh conditions and/or complex processes in preparation, leading to low water productivity, energy efficiency and membrane usage. Thus, it is essential to develop desalination membranes with high flux.

Recently, a research group led by Prof. ZENG Gaofeng at Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences, in collaboration with Prof. SHI Guosheng at Shanghai University, has developed graphdiyne composite membranes and achieved nearly complete salt rejections and ultrahigh water flux in seawater desalination.

The results were published in Nature Water on Sept. 4.

The researchers fabricated nanopore-structured graphdiyne membranes with thickness of submicron on porous Cu hollow fibers directly from monomer of hexaethynylbenzene via Glaser-Hay cross-coupling reaction under mild solvothermal conditions.

The graphdiyne membranes exhibited over 99.9% rejections to small ions of seawater and 1-3 orders of magnitude higher water fluxes than commercial membranes, such as zeolite membranes, metal-organic frameworks membranes and graphene-based membranes. They also exhibited reliable stability in the long-term tests with hypersaline water, real seawater and pollutant-containing waters.

Theoretical calculations suggested that interfaces of saline-water/graphdiyne and saline-water/vapor contained 1-3 molecular layers of pure water without salt, which contributed to complete salt rejections on graphdiyne membrane. Through a two-layered graphdiyne channel model, ultrahigh water fluxes were achieved, which is in line with experimental observations.

These findings not only provide an adaptive method for preparing graphdiyne membranes but also indicate the potential of obtaining other alkadiyne containing membranes under similar methodology, which may be used for membrane separation, ions transfer and energy conversion.