Fabrication and characterization of Polyethersulfone/Aliquat 336/Graphene Oxide Ultrafiltration Membrane for Humic Acid Removal

Humic acid (HA) is one of the natural organic matter (NOM) that naturally exists in water and soil. However, uncontrollable usage of HA can cause an increase in the concentration of HA in water which causes adverse effects on the environment and living things. Ultrafiltration (UF) is one of the methods commonly applied in water treatment due to its effectiveness. However, membrane filtration has encountered difficulties in removing humic acid because of fouling activities. To overcome this problem, mixed matrix membranes (MMM) incorporating ionic liquid, namely Aliquat 336 and Graphene Oxide (GO) were fabricated. Polyethersulfone (PES) was used as polymer, while dimethylacetamide (DMAC) was the solvent. First, a pure PES membrane (B0) was produced. Then, the membranes with different percentages of Aliquat 336 (5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.%), which were labeled with B1, B2, B3, and B4, and mixed matrix membranes with varying percentages of GO (0.5 wt.%, 1.0 wt.%, 1.5 wt.%, and 2.0 wt.%), which labelled with C1, C2, C3, and C4 were fabricated respectively. After that, the membranes were characterized using Fourier transform infrared spectroscopy (FTIR) for functional groups, thermogravimetric analysis (TGA) for thermal stability, contact angle (CA) for hydrophilicity, and scanning electron microscopy (SEM) for membrane morphology. Then, the performance of membranes was analyzed in terms of water flux permeation, humic acid (HA) rejection, and adsorption capacity. For fouling evaluation, reversible flux ratio (RFR) and flux recovery ratio (FRR) were also studied. HA with a concentration of 20 mg/L and the pressure used for UF in this study was 2 bar, which was constant for all membranes. Based on experimental results, the different composition of Aliquat 336 and GO has different effects on the membrane. The functional group of Aliquat 336 membranes has peaks that represent -CH3 (2923 cm-1) meanwhile the quaternary ammonium group was found at 1460 cm-1 and 1380 cm-1. For mixed matrix membranes, 2925 cm-1 was found which corresponds to CH3, the carboxylic group of GO. Next, the boiling point of B4 was 276 oC and improved to 445 oC for C4. The lowest CA of the fabricated membranes was B4 (52o) and C1 (51o). SEM analysis shows that pores become more visible as the Aliquat 336 content increase, meanwhile lowest GO concentration (C1) illustrates the most visible pores compared to all membranes. Mixed matrix membrane, C1 which was incorporated with both ionic liquid (20 wt.%) and GO (0.5 wt.%) has successfully achieved 99.93% rejection towards HA. It also shows good antifouling properties where it managed to achieve RFR (30%) and FRR (83%). This proves that the incorporation of ionic liquid and GO as mixed matrix membranes are compatible and efficient in removing HA due to the enhanced membrane physicochemical, performance, and antifouling properties.