Fabrication and characterization of novel polyacrylonitrile/α-Fe2O3 ultrafiltration mixed-matrix membranes for nitrate removal from aqueous solutions

Abstract

In this study, novel ultrafiltration mixed-matrix membranes (MMMs), consisting of polyacrylonitrile (PAN) and hematite (α-Fe2O3) nanoparticles (NPs), were developed for the removal of nitrate (NO3−) from aqueous solutions. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, Brunauer-Emmett-Teller (BET) analysis, Fourier-transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were performed to characterize the physiochemical and morphological properties of α-Fe2O3 NPs and MMMs. The effects of α-Fe2O3 NP loading on the membrane pure water flux, contact angle, porosity, and NO3− adsorption capacity were also investigated. Based on the results, addition of α-Fe2O3 NPs (up to 1 wt%) reduced the contact angle (higher hydrophilicity), while increasing the pure water flux and porosity. The batch adsorption experiments indicated that the maximum adsorption capacity of the optimized membrane (M-1) was 47.7 mg/g in a pH range of 3–4 and equilibrium time of 120 min. As indicated by the experimental data, the adsorption isotherms and kinetics very well fitted the Langmuir and pseudo-second order models, respectively. Besides, the dead-end UF experiments showed that the M-1 membrane could potentially remove NO3− from aqueous solutions at 50 mg/L by producing a permeate (<11.3 mg/L) within 150 min. The regeneration tests of the optimized membrane showed that the breakthrough time of NO3− removal in real sample reduced from 72 h to 30 and 15 h after the second and third cycles, respectively. The M-1 membrane could also produce NO3−-free water in about 3 days (72 h) at 15.1 L/m2/h under acidic pH and at 22.3 L/m2/h under neutral pH conditions.