Membranes made from nanomaterials such as graphene oxide (GO) are useful in different applications. Researchers have made GO membranes with well-defined nanochannels to facilitate proton exchange. However, the lack of proton donor groups on the surface of the GO sheets, along with weak interlamellar interactions, result in low proton conductivities and insufficient stability in water for many membranes.

Zhongyi Jiang, Hong Wu, Tianjin University, China, and colleagues have incorporated sulfonated graphene quantum dots (SGQDs) into GO membranes to improve their proton conductivity and stability. The team aimed to control the edge electrostatic and in-plane π–π interactions between the SGQDs and GO sheets. To do this, the researchers used three different electron-withdrawing groups to modulate these interactions and increase the resistance to water swelling. The graphene-containing nanostructures were synthesized using a modified Hummers’ methods and the SGQD-GO membranes were prepared using wet chemical and ultrasonic methods.

The quantum dots, which have an abundance of proton donor groups, were found to assemble on the sp² domains of the GO sheet via in-plane π−π interactions. There, they provide low-energy-barrier proton channels. The SGQD-GO membranes were found to have an enhanced proton conductivity of 324 mS cm^–1 and a high resistance to water over long time periods.

• Control of Edge/in-Plane Interactions toward Robust, Highly Proton Conductive Graphene Oxide Membranes,
  Benbing Shi, Hong Wu, Jianliang Shen, Li Cao, Xueyi He, Yu Ma, Yan Li, Jinzhao Li, Mingzhao Xu, Xunli Mao, Ming Qiu, Haobo Geng, Pengfei Yang, Zhongyi Jiang,
  ACS Nano 2019.
  https://doi.org/10.1021/acsnano.9b04156