In this study, functionalized graphene oxide was prepared by surface grafting of ethylenediaminetetraacetic acid (EDTA) to graphene oxide (GO) surface using ethylenediamine as linking agent and was introduced into polyethersulfone membrane matrix. Grafting of ethylenediaminetetraacetic acid to graphene oxide was confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis and X-ray diffraction. The characteristics of prepared nanocomposite membranes were investigated using FESEM and contact angle measurements. The performance of the nanocomposite membranes was investigated in detail for water permeability, salt rejection and protein antifouling test. Also, the performance of membranes in the elimination of several heavy metals and dyes was investigated. The results confirm the significant improvement of hydrophilicity in the modified membranes and a remarkable increase in the salt, heavy metal and dye rejection was achieved.

Keywords: nanocomposite membranes, functionalized graphene oxide, antifouling, surface modification

Membrane technology is a fast growing research area with several applications like desalination and water purification.^1,2 Among the used polymers in membrane fabrication technology, polyethersulfone (PES) has proper film formation property, chemical and mechanical resistant, and miscibility with hydrophilic additives; which made it an appropriate option for many membrane based applications.³ However, fouling phenomenon under separation condition for the polyethersulfone membranes is caused due to intrinsic hydrophobic property of this polymer.⁴ In order to reduce the fouling phenomenon, researchers have investigated several approaches such as surface modification and hydrophilic polymer blending.⁵
Introducing hydrophilic nanoparticles into PES matrix through common blending method has been aroused as one of the most effective strategies to enhance the hydrophilicity of PES membranes.^6,7
As a new nanostructured material, GO recently has attracted much attention as an additive to enhance the properties of polymer membranes.^8-10 GO can be prepared by the oxidation of graphite. It has a layered structure with oxygen functional groups on its basal planes and edges which makes the GO as a nano material with an ultra-high specific surface area, hydrophilic surface, and negative charged surface.¹¹ Therefore, many studies show that GO as an additive has a great effect on membrane properties like antifouling and hydrophilicity.^9-12
However, graphene sheets have some disadvantages for application in membranes. Limited dispersion due to their strong tendency to aggregation causes a decline in permeability and antifouling performances of graphene-incorporated membranes.¹³ The entrance of graphene derivatives in mem-branes may also reduce mechanical strength of membranes, due to weak interaction between graphene and polymer matrix.¹⁴ Therefore, application of modified graphene derivatives with more functional groups and surface charge on the sheets^15-17 can improve the performance of membranes. Additionally, interaction between membrane and foulant can be affected by functionalization. However, there are very few reports on using functionalized GO (FGO) nanostructures on PES membrane properties.¹⁸
Surface functionalization of GO can be performed by physical wrapping9 or covalent grafting of species with numerous functional groups.¹⁴
In this paper, fabrication of a novel nanocomposite membrane by incorporating FGO has been reported. It has been tried to synthesis novel FGO by grafting of EDTA to the surface of GO (GO-EDTA). The existence of hydrophilic moiety on GO surface can enhance surface hydrophilicity, surface charge properties, and as a consequence, membrane antifouling could be improved. To the best of our knowledge, GOEDTA has not been used to fabricate nanocomposite membranes. Here, the synthesized FGO nanomaterial was blended in the PES matrix dope solution and the phase inversion method was used to fabricate the membrane nanocomposite. The effect of FGO amounts on membranes morphology, hydrophilicity, flux, and antifouling performance were investigated too. FTIR, FESEM and water contact angle analysis were used to investigate the structural properties of prepared membranes. The fouling resistance of the membranes was also analyzed using bovine serum albumin (BSA). The prepared nanocomposite membranes were used for separation of soluble heavy metals (Zn, Cu, Ni and Cd) and dyes like methylene blue (MB) and methyl orange (MO) from water.