Synthesis of a Novel Hybrid Nanofiltration Membrane by Incorporating Functionalized Multiwall Carbon Nanotubes Doped with Silver and Nacl–Polyethersulfone for Efficient Volatile Fatty Acids Recovery

Abstract

In this study we aim to develop and characterize new nanofiltration (NF) membranes that are specifically used for recovery volatile fatty acids (VFAs). The NF membranes were developed through a precise method involving the integration of multi-walled carbon nanotubes (MWCNTs) with silver (Ag), and then incorporation into a polyethersulfone (PES) matrix. MWCNTs have a high surface area and excellent adsorption capacity, while Ag materials have antimicrobial properties, which reduce bacterial fouling during VFA recovery. Additionally, the inclusion of NaCl, the pore-forming agent, created a network of interconnected pores within the membrane structure. We characterized these membranes with Fourier Transform Infrared (FT-IR), Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX), Atomic Force Microscopy (AFM), contact angles and Zeta potential analyzer. Among the prepared membranes of different MWCNTs/Ag/NaCl contents (3.75/0.25/5 wt.%, 5.75/0.25/10 wt.% and 7.75/0.25/15 wt.%), with an initial concentration of 500ppm of the VFAs, the membrane with the highest content (7.75/0.25/15 wt.%) had a remarkable water permeability of 60.10 L·m-2·h-1·bar-1, and an impressive maximum VFA rejection of 67.32 ±1.5% for acetate, 75.80±1.5% for propionate, 81.06±1.5% for butyrate, and 92.30±1.5% for the three mixtures. The analyses of membrane surface morphology, functional groups and discharges suggest that the enhanced separation of VFA molecules was ascribed to pore size exclusion and electrostatic repulsion. This work presents a first-of-its-kind study to investigate how MWCNTs-Ag/NaCl contents affect the PES membrane properties. The optimized composite NF membrane displays exceptional water permeability and VFA rejection capabilities, making it a promising candidate for applications in water treatment and VFA recovery.

Keywords: Nanofiltration, membrane, polyethersulfone, multiwalled carbon nanotubes, Silver