Interaction between Water Molecules and Oxygen-containing Groups of Reduced Graphene Oxide Membranes

Jan Sebastian Dominic Rodriguez¹, Zong-Jhe Hsieh¹, Takuji Ohigashi², Chueh-Cheng Yang³, Chia-Hsin Wang³, Cheng-Hao Chuang^1*

¹Department of Physics, Tamkang University, New Taipei City, Taiwan
²Photon Factory, High Energy Accelerator Research Organization, Tsukuba, Japan
³National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Cheng-Hao Chuang, email:chasehao@gmail.com

While the applications of graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) have been extensively studied, a comprehensive understanding of their surface interactions with water molecules, particularly the complex behaviors of hydrogen bonding, van der Waals forces, and electrostatic interactions, has received less attention in the scientific community. Advancing water filtration in the liquid phase and selective gas filtration in the gas phase are of practical importance for membrane synthesis with multi-functionality, driven by the global demand for efficient and cost-effective solutions. There are conflicting results regarding how the oxidation degree and the types of functional groups influence the orientation of water structuring at the nanochannel stacking structure, as well as absorption, adsorption, and transport dynamics within the nanoscale interaction field. Our idea is to utilize electrochemical and thermal reduction treatments to modify the residual surface oxidation and control the interlayer spacing of multi-stacking in GO materials. Through tunable interlayer spacing and surface functional groups, we will investigate the optimization of permeability and selectivity in in-situ environments using X-ray operando techniques. Key findings reveal the degree of de-oxidation influence on rGO membranes, as determined by X-ray absorption spectra from scanning transmission X-ray microscopy (STXM) and surface potential capability of Kelvin probe force microscopy. The element-resolved chemical structure, along with the in-situ thermal desorption process, has been measured using ambient pressure X-ray photoelectron spectroscopy, leading to the resolvable and individual bondings (C=C, C-OH, C-O-C, C=O, COOH). The evolution of water molecules and the effect on the surface work function of the rGO membrane, regardless of surface morphology, suggests the recycling of surface chemical bonds and the active absorption/adsorption of water molecules. At the nanoscale, STXM offers a crucial perspective on a specific area, where chemical evolution is driven by lattice structure and surface contributions. By studying the properties of the rGO membrane, we can evaluate various water-induced interactions to gain insights into water transport and ion rejection, which are essential for membrane design and future energy applications.

Keywords: Reduced graphene oxide, Membrane, Water molecules, Scanning transmission X-ray microscopy (STXM) , Ambient pressure X-ray photoelectron spectroscopy (APXPS)