Cross-Linking With Diamine Monomers to Prepare Graphene Oxide Composite Membranes With Varying D-Spacing for Enhanced Desalination Properties.

Hong Ju,Jinzhuo Duan,Weihui Xu,Haitong Lu

doi:10.3389/fchem.2021.779304

Hong Ju, Jinzhuo Duan + Show 2 more

Open Access

https://doi.org/10.3389/fchem.2021.779304

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Abstract

As a new type of membrane material, graphene oxide (GO) can easily form sub-nanometer interlayer channels, which can effectively screen salt ions. The composite membrane and structure with a high water flux and good ion rejection rate were compared by the cross-linking of GO with three different diamine monomers: ethylenediamine (EDA), urea (UR), and p-phenylenediamine (PPD). X-ray photoelectron spectroscopy (XPS) results showed that unmodified GO mainly comprises π-π interactions and hydrogen bonds, but after crosslinking with diamine, both GO and mixed cellulose (MCE) membranes are chemically bonded to the diamine. The GO-UR/MCE membrane achieved a water flux similar to the original GO membrane, while the water flux of GO-PPD/MCE and GO-EDA/MCE dropped. X-ray diffraction results demonstrated that the covalent bond between GO and diamine can effectively inhibit the extension of d-spacing during the transition between dry and wet states. The separation performance of the GO-UR/MCE membrane was the best. GO-PPD/MCE had the largest contact angle and the worst hydrophilicity, but its water flux was still greater than GO-EDA/MCE. This result indicated that the introduction of different functional groups during the diamine monomer cross-linking of GO caused some changes in the performance structure of the membrane.

Highlights

The shortage of water resources has become a global problem
A Graphene oxide (GO) sheet contains a large number of oxygen-containing groups: carboxyl groups and hydroxyl groups are located around the edges, while carbonyl and epoxy groups are located at the center (Lerf et al, 1998; Suk et al, 2010), which can be cross-linked with diamine monomers to prepare GO composite films with varying d-spacing
According to the contact angles (CAs) measurement results, it was expected that the hydrophilicity of the PPD membrane decreased the most, yet it showed a higher water flux than the EDA membrane. The reason for this result was that the d-spacing was larger in the wet state, and water molecules passed more. These results indicated that the changes in the salt rejection rate and water flux of the GO composite membrane were related multiple other factors, and the result of the interaction between the interlayer distance and the groups in the membrane

Summary

INTRODUCTION

The shortage of water resources has become a global problem. To solve the growing freshwater crisis, sewage treatment (Shannon et al, 2008; Ren et al, 2020) and seawater desalination technology (Wu et al, 2007; Logan Elimelech, 2012; Shao et al, 2017; Zhao et al, 2017) have been rapidly developed. A GO sheet contains a large number of oxygen-containing groups: carboxyl groups and hydroxyl groups are located around the edges, while carbonyl and epoxy groups are located at the center (Lerf et al, 1998; Suk et al, 2010), which can be cross-linked with diamine monomers to prepare GO composite films with varying d-spacing The presence of these hydrophilic oxygen-containing groups gives the graphene oxide good hydrophilic properties, and the unique nanostructures form an sp nanocapillary network to achieve ultra-fast water molecule transmembrane transport (Eda and Chhowalla, 2010; Loh et al, 2010; Nair et al, 2012; Yu et al, 2020). Where R is the salt rejection rate; and C1 and C2 represent the original ion concentration of the salt solution and the ion concentration after filtration, respectively

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT