The increasing demand for freshwater as drinking water and for agriculture makes it necessary to develop improved methods for water desalination and purification. Nanofiltration using membranes based on graphene oxide (GO) is one promising approach. However, finding a balance between water permeability and separation efficiency is challenging, and existing membranes are not stable in aqueous solutions over the long term.

Wencai Ren, Shenyang National Laboratory for Materials Science, Chinese Academy of Sciences, and colleagues have developed reduced graphene oxide (rGO)-based nanofiltration membranes with high water permeability, separation efficiency, and stability. The team prepared GO sheets by exfoliation of graphite oxide and used either tannic acid (TA) or theanine (TH) as a reducing agent and cross-linker.

The TA or TH molecules increase the interlayer distance between the rGO sheets, which improves water permeability. The crosslinkers also help to block solutes from passing through the membrane, which leads to a high separation efficiency. In contrast to GO membranes, which disintegrate in water after only five days, the synthesized membranes are stable in aqueous solutions for over a month and can even withstand acidic and basic conditions.

• Highly stable graphene-oxide-based membranes with superior permeability,
  Khalid Hussain Thebo, Xitang Qian, Qing Zhang, Long Chen, Hui-Ming Cheng, Wencai Ren,
  Nat. Commun. 2018.
  https://doi.org/10.1038/s41467-018-03919-0