Highly permeable nanofibrous polyamide membranes for multi-component wastewater treatment: Exploration of multiple separation mechanism

Multi-component wastewater containing a variety of organic toxins, e.g., dyes and inorganic particulates induces serious environmental concerns, which must be addressed by innovative approaches instead of conventional chemical and physical processes, which are limited by purification efficiency, secondary pollution, and cost-effectiveness. Therefore, it is important to find new avenues of purification methods that are both sustainable and effective. Ultra-fine nanofibrous microfiltration membranes were fabricated by multi-nozzle electrospinning of polyamide-66 (PA-66) and were employed to remove 0.2-μm-nanoparticles and dyes simultaneously from wastewater through filtration and dynamic adsorption performance, in an attempt to discover a one-step filtration system for both dyes and nanoparticles. The fiber diameter and surface morphology of the nanofibrous membranes varied with the concentrations of polyamide solutions, where the ultra-fine nanofibrous membrane exhibited optimum mechanical properties at a specific concentration of PA-66 (11 wt%). The nanofibrous membranes had adsorption capabilities of 133.3 and 204.5 mg/g, respectively, against both anionic dyes (e.g., metanil yellow) and cationic dyes (e.g., chrysoidine), respectively. The membrane also selectively filtrated fine nanoparticles with a nearly 100% rejection ratio. A multiple separation mechanism, including adsorption based on electrostatic interaction, hydrogen bonding interaction, and hydrophobic interaction, as well as depth filtration, was proposed. As an applicable demonstration, the spiral wound cartridge fabricated by PA-66 nanofibrous membrane was used for a simulated multi-component wastewater treatment that contained dyes and nanoparticles of different concentrations. During the multicomponent test at flow rate 1 mL/min, a rejection rate of 97% and greater than 99% were achieved against dyes and nanoparticles, respectively.