Razi University

The shortage of freshwater resources and the increasing demand for water have highlighted the need for efficient wastewater treatment and water reuse. In this regard, industrial wastewater containing dyes requires effective treatment methods due to the presence of various dye compounds and other pollutants. Membrane processes, particularly nanofiltration, are considered promising options owing to their suitable separation performance, relatively low energy consumption, and lower environmental impact. However, challenges such as membrane fouling, flux decline, and the need to achieve both high separation efficiency and stable performance limit the application of conventional polymeric membranes. In the present study, a pristine polyethersulfone (PES) control membrane and mixed-matrix nanofiltration membranes containing graphene oxide (GO) and a silver-based metal–organic framework/graphene oxide nanocomposite (Ag-MOF@GO) were fabricated to improve membrane performance and enhance antifouling properties. First, mixed-matrix membranes containing 0.03, 0.05, 0.07, and 0.09 wt.% GO were fabricated, and their performance was evaluated in terms of water flux, fouling behavior, and dye rejection. Based on the results, the membrane containing 0.05 wt.% GO was selected as the optimal membrane at this stage. Subsequently, to investigate the effect of incorporating a silver-based metal–organic framework into graphene oxide, Ag-MOF@GO nanocomposites were synthesized using three ligand-to-silver mass ratios (1:0.5, 1:1, and 1:1.5). Mixed-matrix membranes containing 0.05 wt.% of each synthesized nanocomposite were then fabricated. The performance of the prepared membranes was evaluated in terms of pure-water flux, rejection of synthetic dyes, treatment of real wastewater, and fouling properties. Evaluation of the modified membranes revealed that the membrane containing 0.05 wt.% Ag-MOF@GO nanocomposite with a silver-to-ligand mass ratio of 1:1 exhibited better performance than the control membrane and the other nanocomposite-containing membranes and was therefore selected as the optimal membrane. The optimal membrane exhibited a lower water contact angle (54.2°) than the control membrane (77°), indicating enhanced surface hydrophilicity. Furthermore, pure-water flux increased from 18 to 50.1 kg m?² h?¹. The flux recovery ratio following fouling with bovine serum albumin (BSA) increased from 68.1% for the control membrane to 95.9% for the optimal membrane. The irreversible fouling resistance decreased from 31.8% for the control membrane to 4% for the optimal membrane. In addition, Congo red rejection increased from 97% to 99.3%, while methylene blue rejection increased from 91% to 97% for the control and optimal membranes, respectively. Finally, the performance of the selected membrane was evaluated using real industrial wastewater. The results showed that the optimal membrane achieved COD removal and color removal efficiencies of greater than 95% and 99.8%, respectively, and reduced turbidity to 2 NTU, compared with 52% COD removal, 96.7% color removal, and a turbidity of 7 NTU for the control membrane.    Keywords: Nanofiltration, polyethersulfone, graphene oxide, silver-based metal–organic framework, Ag-MOF@GO nanocomposite, membrane fouling, dye rejection, industrial wastewater.