# Fabrication and Characterization of Modified Graphene Oxide/PAN Hybrid Nanofiber Membrane
## 2 Materials and Methods
### Synthesis of Graphene Oxide (GO) and Modified GO by PolydiallyIdimethylammonium (PDDA) (GP)  
GO was synthesized from graphite using a time-saving improved Hummer's method. Briefly, graphite flake (2 g), NaNO\({}_{3}\) (1.52 g), and sulfuric acid (68 mL) were mixed and stirred for 10 min, and then 9 g of KMnO\({}_{4}\) was slowly added into the mixture. The mixture was then allowed to heat to 60 \({}^{\circ}\)C and stirred for 40 min. One hundred milliliters of distilled water (DI water) was added to the solution, followed by mixing for 1 h at 90 \({}^{\circ}\)C [30]. The temperature of the mixture was decreased to 50 \({}^{\circ}\)C, followed by the addition of 100 mL DI water again. The mixture was then fully dispersed by sonication for 3 h and then the mixture was filtered using a filter paper (No. 2, Advantec, Dublin, CA, USA). In order to remove the unreacted residue in the filtrate, DI water (180 mL), H\({}_{2}\)O\({}_{2}\) (6 mL), and sulfuric acid (1 mL) were added, respectively, and then the mixed filtrate was centrifuged at 4000 rpm for 30 min [31]. The filtrate was washed several times with DI water and ethanol, then thoroughly dried in a vacuum oven for 24 h to obtain the GO product. Dried GO (0.5 g) was fully dispersed in water (100 mL) for 1 h by sonication and centrifuged for 30 min. Then, the final GO was obtained by filtering the GO solution and dried in a vacuum oven. The fully dried GO (0.05 g) was dispersed in DI water (99.95 g) to prepare GO suspension for modification with the help of sonication. PDDA (0.033 g) was added to the GO suspension and stirred for 24 h. Finally, the GO + PDDA (GP) was obtained by filtering and vacuum drying. Fabrication of Polyacrylonitrile (PAN) and Graphene Oxide Modified by Polydiallyldimethylammonium Chloride/Polyacrylonitrile (GP/PAN) Hybrid Nanofiber Membranes via Electrospinning  
The PAN nanofiber membranes incorporated with varying amounts of GP were fabricated via the electrospinning method. A homogenous precursor solution of PAN and GP listed in Table 1 was prepared and a series of GP (0-1.0 wt.%) was initially dispersed in DMF by sonication for 1 h. PAN powder was then added to the above solution and fully dissolved by stirring for 24 h at 50 \({}^{\circ}\)C. Then, the prepared solutions were filled into a 5 mL syringe with a 23-gauge needle. The syringe was positioned vertically for 30 min or more to remove the air bubbles. Subsequently, the syringe was installed in an automated syringe pump (KDS100, KD Scientific Korea Inc., Seoul, Korea) to control the ejection speed of the solution, and the voltage supply equipment used was a CPS 60K02 VIT (CHUNGPA EMT co., Ltd., Seoul, Korea). Prepared spinning solutions were electrospun on to aluminum foil under an electrical field with optimized voltage (15 kV), flow rate (0.8 mL/h), distance between the needle tip and the collector (15 cm), relative humidity (20-40%) and room temperature. Characterization of Synthesized Graphene Oxide GO and Graphene Oxide Modified by Polydiallyldimethylammonium Chloride/Polyacrylonitrile (GP/P) Hybrid Nanofiber Membranes  
The morphological analysis of the GO was carried out by FESEM (Field Emission Scanning Electron Microscope, Hitachi Korea, S-4200, Seoul, Korea). An AFM (Atomic Force Microscope, NanoSurf Korea, Seoul, Korea) was used to analyze the surface morphology of GO. FT-IR (JASCO, FT/IR-620, Tokyo, Japan) was used to observe the various functional groups of synthesized GO. The Raman test was performed on Thermo DXR Raman Spectroscopy (Thermo Fisher Scientific Korea, Seoul, Korea) with a 532 nm laser and 1-5 mW power. The optical image of nanofibers was taken with a Pentax K-S2 DSLR Camera and the structural features of nanofibers were examined by scanning electron microscope (SEM, JSM5410, Tokyo, Japan) after coating with a gold target.